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Table of contents :
Preface 1. Introduction 2. Mitigation Measures 3. Sources of Anthropogenic Noise 4. Training 5. Offshore Life 6. MMO Theory and Practice 7. PAM Theory 8. Marine Mammal Vocalisations 9. PAM Practice 10. Report Writing Glossary Index
Marine Mammal Observer and Passive Acoustic Monitoring Handbook
Marine Mammal Observer and Passive Acoustic Monitoring Handbook Victoria L.G. Todd, Ian B. Todd, Jane C. Gardiner and Erica C.N. Morrin
Pelagic Publishing | www.pelagicpublishing.com
Published by Pelagic Publishing www.pelagicpublishing.com PO Box 725, Exeter EX1 9QU, UK Marine Mammal Observer and Passive Acoustic Monitoring Handbook ISBN 978-1-907807-66-4 (Pbk) ISBN 978-1-907807-67-1 (Hbk) ISBN 978-1-907807-68-8 (ePub) ISBN 978-1-907807-69-5 (Mobi) ISBN 978-1-907807-70-1 (PDF) Copyright © 2015 Ocean Science Consulting Ltd This book should be quoted as Todd, V.L.G, Todd, I.B., Gardiner, J.C. and Morrin, C.N. (2015) Marine Mammal Observer and Passive Acoustic Monitoring Handbook. Exeter: Pelagic Publishing. All rights reserved. No part of this document may be produced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior permission from the publisher. While every effort has been made in the preparation of this book to ensure the accuracy of the information presented, the information contained in this book is sold without warranty, either express or implied. Neither the authors, nor Pelagic Publishing, its agents and distributors will be held liable for any damage or loss caused or alleged to be caused directly or indirectly by this book. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Cover images © OSC 2015, except courtesy of the following: humpback whale, NOAA Fisheries; polar bear, Kostya Shvebs; windfarm, Tony Moran; vessel, Polarcus; and, hydrophone array, Seiche Measurements.
It is not the events in your life that determine your path, but your reaction to them. Anonymous
For Señor Niels Torgau for the first chance, Hanneke van den Berge for believing, and Petra Todd for her enduring and uplifting spirit.
About the Authors Foreword
List of Acronyms, Units, Prefixes and Symbols
1.1 General Overview
1.2 Marine Mammal Classification 1.2.1 Cetaceans 1.2.2 Pinnipeds 1.2.3 Sirenians 1.2.4 Marine mustelids 1.2.5 Polar bear
2 3 3 4 4 5
1.3 Marine Mammal Distribution
1.4 Effects of Anthropogenic Sound on Marine Mammals 1.4.1 Temporary Threshold Shift and Permanent Threshold Shift 1.4.2 Behavioural alterations 1.4.3 Stress 1.4.4 Masking 1.4.5 Strandings 1.4.6 Indirect effects
17 17 18 19 19 20 21
1.5 Marine Mammal Hearing 1.5.1 Audiograms 1.5.2 Hearing ranges 1.5.3 Sound exposure criteria
21 21 23 29
2.2 Protective Legislation
2.3 Marine Protected Areas
2.4 Project Planning
2.5 Control of Operational Procedures
2.6 Noise Reduction Methods
2.7 Acoustic Mitigation Devices
2.8 Active SONAR
2.9 Visual and Acoustic Watches
2.10 MMO and PAM Operator Requirements
2.11 Species for which Mitigation Applies
2.12 Exclusion Zones
2.15 Sound Source Testing
2.16 Operation Issues and Breaks in Sound Production
2.17 Delays and Shut-Downs
2.18 Night-Time and Low Visibility Working
2.19 Report Writing
Sources of Anthropogenic Noise
3.3 Offshore Wind Farms
3.4 Tidal Turbines
3.6 Drilling and Production
3.7 Floating Production Storage Offloading
3.8 Acoustic Mitigation Devices
3.10 Pile Driving
3.12 Whale Finders
4.2 Background Reading and Scientific Organisations
4.3 Becoming a Certified MMO or PAM Operator 4.3.1 MMO training
4.3.2 PAM Operator
4.4 Courses 4.4.1 UK and Ireland 4.4.2 USA (GoM) 4.4.3 Greenland 4.4.4 New Zealand 4.4.5 Offshore sea survival 22.214.171.124 BOSIET 126.96.36.199 Minimum Industry Safety Training 188.8.131.52 Safe Gulf safety training 4.4.6 Offshore medicals 184.108.40.206 Netherlands, Norway and UK 220.127.116.11 Seafarers’ medicals
66 66 66 66 67 67 68 68 69 69 70 70
4.6 Curriculum Vitae
4.7 Gaining Offshore Experience
5.2 Contract Award
5.5 Vantage Cards
5.7 Personal Protective Equipment
5.8 Pre-Project Research
5.13 Offshore Personnel
5.14 Personal Conduct
5.15 Phone and Internet
5.16 Drugs and Alcohol
5.17 Safety Management Systems
5.18 T-Card System
5.19 Safety Drills
5.21 Vessels 5.21.1 Kick-off meeting 5.21.2 Dealing with seasickness
88 88 88
5.21.3 Baseline surveys 5.21.4 Dredging 5.21.5 Hydrographical surveys 5.21.6 Seismic surveys 5.21.7 Piling 5.21.8 Military SONAR 5.22 Offshore Installations 5.22.1 Arrival 5.22.2 Layout 5.22.3 Kick-off, shift, and rotation meetings 5.22.4 Personnel 5.22.5 Operational activities 5.22.6 Weather 5.22.7 General hazards 5.22.8 Rig tow 5.22.9 Drilling rig and production platform complexes 5.22.10 VSP 5.22.11 Conductor hammering
MMO Theory and Practice
89 90 91 92 97 98 99 99 99 101 101 102 104 104 105 106 107 107 109
6.2 Equipment 6.2.1 Fold-over clipboard 6.2.2 Stationery 6.2.3 Digital watch 6.2.4 Marine radio 6.2.5 Binoculars 6.2.6 GPS 6.2.7 Cameras 6.2.8 Lenses 6.2.9 Plumb-bob 6.2.10 Field guides
110 110 111 111 111 111 112 112 115 116 116
6.3 Conducting an MMO Watch
6.4 Observation Platform
6.5 Recording Position 6.5.1 Ranging software
6.6 Recording Vessel Movements
6.7 Marine Mammal Identification 6.7.1 Cetacean identification 6.7.2 Pinniped identification
120 121 122
6.8 Range Estimation
6.9 Bearing Estimation
6.10 Photographing Marine Mammals
6.11 Data Collection 6.11.1 Cover page
6.11.2 Effort 6.11.3 Operations data 6.11.4 Sightings
129 132 132
6.12 MMO at Night
6.13 Distance Sampling
7.2 Basics of Sound 7.2.1 Frequency 7.2.2 Amplitude 7.2.3 Sound energy, intensity, and power 7.2.4 Sound Pressure Level and the decibel scale 7.2.5 Source Level 7.2.6 Sound propagation and transmission loss 7.2.7 Received Level 7.2.8 SONAR equation 7.2.9 Sound Exposure Level 7.2.10 Duty cycle
140 141 142 143 143 146 147 150 150 151 151
7.3 Displays of Sound 7.3.1 Spectrogram 7.3.2 Power spectrum and Power Spectral Density 7.3.3 Sound pressure density spectrum 7.3.4 Frequency bands 7.3.5 Percentile levels 7.3.6 Equivalent Continuous Sound Pressure Level 7.3.7 Waveform
151 151 152 153 154 155 156 156
Marine Mammal Vocalisations
8.2 Marine Mammal Sounds 8.2.1 Echolocation and clicks 8.2.2 Pulsed sounds 8.2.3 Tonal sounds 8.2.4 Song
158 159 159 160 161
8.3 Functions of Sound 8.3.1 Hunting and navigation 8.3.2 Individual and group recognition 8.3.3 Social cohesion and behaviour coordination 8.3.4 Mate finding 8.3.5 Agonistic and aggressive behaviour
161 161 162 163 164 165
8.4 Likelihood of a PAM Detection
8.5 Species Identification 8.5.1 Physeteridae 18.104.22.168 Sperm whale
167 190 190
8.5.2 Kogiidae 22.214.171.124 Pygmy sperm whale 8.5.3 Ziphiidae 126.96.36.199 Cuvier’s beaked whale 188.8.131.52 Arnoux’s beaked whale 184.108.40.206 Baird’s beaked whale 220.127.116.11 Longman’s beaked whale 18.104.22.168 Northern bottlenose whale 22.214.171.124 Gervais’ beaked whale 126.96.36.199 Sowerby’s beaked whale 188.8.131.52 Hubb’s beaked whale 184.108.40.206 Stejneger’s beaked whale 220.127.116.11 Blainville’s beaked whale 18.104.22.168 Deraniyagala’s beaked whale 8.5.4 Pontoporiidae 22.214.171.124 Franciscana/La Plata dolphin 8.5.5 Monodontidae 126.96.36.199 Narwhal 188.8.131.52 Beluga 8.5.6 Delphinidae 184.108.40.206 Commerson’s or Kerguelen Islands dolphin 220.127.116.11 Chilean dolphin 18.104.22.168 Heaviside’s dolphin 22.214.171.124 South Island or Maui’s dolphin/North Island Hector’s dolphin 126.96.36.199 Rough-toothed dolphin 188.8.131.52 Atlantic humpback dolphin 184.108.40.206 Pacific humpback dolphin 220.127.116.11 Guiana dolphin 18.104.22.168 Common or Black Sea bottlenose dolphin 22.214.171.124 Indo-Pacific bottlenose dolphin 126.96.36.199 Offshore or coastal pantropical spotted dolphin 188.8.131.52 Atlantic spotted dolphin 184.108.40.206 Gray’s, eastern, Central American or dwarf spinner dolphin 220.127.116.11 Clymene dolphin 18.104.22.168 Striped dolphin 22.214.171.124 Short-beaked or Black Sea common dolphin 126.96.36.199 Long-beaked or Indo-Pacific common dolphin 188.8.131.52 Fraser’s dolphin 184.108.40.206 White-beaked dolphin 220.127.116.11 Atlantic white-sided dolphin 18.104.22.168 Pacific white-sided dolphin 22.214.171.124 African, Fitzroy’s, Peruvian/Chilean or New Zealand dusky dolphin 126.96.36.199 Peale’s dolphin 188.8.131.52 Hourglass dolphin 184.108.40.206 Northern right whale dolphin 220.127.116.11 Risso’s dolphin 18.104.22.168 Melon-headed whale 22.214.171.124 Pygmy killer whale
191 191 191 191 191 192 192 192 193 193 193 194 194 195 195 195 195 195 196 197 197 198 198 198 198 199 199 199 200 201 201 202 203 203 204 204 205 205 206 206 207 207 208 208 208 208 210 210
126.96.36.199 False killer whale 188.8.131.52 Resident or transient killer whale/orca 184.108.40.206 North Atlantic, southern or North Pacific long-finned pilot whale 220.127.116.11 Short-finned pilot whale 18.104.22.168 Irrawaddy dolphin 22.214.171.124 Australian snubfin dolphin 8.5.7 Phocoenidae 126.96.36.199 Indo-Pacific finless porpoise 188.8.131.52 East Asian narrow-ridged finless porpoise 184.108.40.206 Atlantic, eastern Pacific, Black Sea or western Pacific harbour/common porpoise 220.127.116.11 Vaquita 18.104.22.168 Dalli-type or Truei-type Dall’s porpoise
210 211 212 213 213 214 214 214 214 214 215 216 217
9.2 Existing PAM Technologies
9.3 PAM Equipment 9.3.1 Tow cable 9.3.2 Hydrophones 9.3.3 Depth sensor 9.3.4 Deck cable 9.3.5 Data Acquisition Unit 9.3.6 Sound cards 9.3.7 Computers 9.3.8 Filters and gain 9.3.9 GPS 9.3.10 Serial-to-USB converter 9.3.11 Gender changer 9.3.12 Headphones 9.3.13 Connectors 9.3.14 Oscilloscope 9.3.15 Tool kit 9.3.16 Tape
219 219 220 221 222 223 224 225 225 226 226 226 227 227 228 229 229
9.4 PAM Mobilisation 9.4.1 Unpacking
9.5 Deck Cable Run
9.6 PAM Monitoring Station Configuration 9.6.1 Data Acquisition Unit 9.6.2 DAU connectors 9.6.3 Sound cards 9.6.4 Computers 9.6.5 GPS or NMEA feed 9.6.6 Headphones
234 235 236 237 239 240 241
9.7 PAMGuard 9.7.1 Starting PAMGuard
9.7.2 Configuring PAMGuard: Part I 22.214.171.124 Maps and mapping 126.96.36.199 Sound processing 188.8.131.52 Displays 184.108.40.206 Detectors 220.127.116.11 Utilities 9.7.3 Hydrophone specifications and sampling rate 18.104.22.168 Hydrophone frequency range 22.214.171.124 Hydrophone sensitivity 126.96.36.199 Sampling rate 9.7.4 Configuring PAMGuard: Part II 188.8.131.52 Maps and mapping 184.108.40.206 Sound processing 220.127.116.11 Display 18.104.22.168 Detectors 22.214.171.124 Utilities 126.96.36.199 Hydrophone settings 188.8.131.52 Filters 9.7.5 PAMGuard troubleshooting 184.108.40.206 Freezing and/or restarting 220.127.116.11 Position fix error 18.104.22.168 Erratic cursor 22.214.171.124 Spectrogram
242 244 244 245 246 246 248 248 248 248 250 250 251 254 255 256 256 258 260 261 261 263 264
9.8 Tap (Noise) Test
9.10 Depth Sensor Calibration
9.11 Tow Cable Deployment 9.11.1 General deployment 9.11.2 Seismic survey vessels 9.11.3 Offshore support vessels 9.11.4 Vertical deployment
268 269 273 276 276
9.12 PAM Monitoring 9.12.1 Shifts 9.12.2 Monitoring methods 9.12.3 Data collection 9.12.4 Detection metrics 9.12.5 Sound playback
277 277 278 279 280 281
9.13 PAM Detections During Industrial Operations 9.13.1 Localising animals 9.13.2 Zero marine mammal detections: possible explanations 9.13.3 Non-target noise
281 282 284 286
9.14 Equipment Responsibilities: Routine Housekeeping 9.14.1 Retrieval in bad weather 9.14.2 Loss of propulsion 9.14.3 Wiring, soldering and potting
289 290 290 290
9.15 PAM Demobilisation
9.15.1 Handover notes 9.15.2 Tow cable 9.15.3 Connectors, hydrophones and depth sensors 9.15.4 Deck cable removal 9.15.5 Cable reels and drums 9.15.6 PAM monitoring station 9.15.7 Pallet preparation 9.15.8 Documentation
Chapter 10 Report Writing
291 291 292 294 294 295 295 296 297
10.6 Results 10.6.1 Sightings 10.6.2 Delays or shut-downs 10.6.3 Weather
300 301 301 301
10.7 Discussion and Conclusion
10.9 Acknowledgements, References and Data Submission
Glossary of Terms
About the Authors
Dr Victoria Todd is a founding Managing Director and Marine Science Consultant at Ocean Science Consulting (OSC), a Director at Ocean Science Consulting NZ (Asia-Pacific) (OSC-NZ), and is a Visiting Scientist at Institute of Sound and Vibration Research (ISVR, Southampton University, UK). She undertook a post doc in commercial aquaculture at Scottish Association for Marine Science (SAMS, UK), planning and directing a comprehensive series of acoustic trials on seal scarers. She holds degrees in the ecology and acoustics of bats (PhD, Leeds University, UK), Oceanography (MSc, scholarship-funded by Woods Hole Oceanographic Institution, WHOI, US, and National Oceanography Centre, UK), and Marine Biology (BSc Hons, Liverpool University, UK). Dr Todd is also a Fellow of the Linnean Society of London. She is experienced in Galápagos fish taxonomy, marine mammal acoustics and marine mammal visual and acoustic surveys worldwide for scientific, commercial and defence contracts. Research interests include bioacoustics, the North Sea rigs-to-reefs concept, harbour porpoise foraging ecology around offshore oil and gas installations, and the effects of anthropogenic noise on marine life, all of which are core research topics at OSC. Dr Todd’s current scientific duties include training, survey design and project management, fieldwork, data analysis, reports, literature reviews, advice documents, Marine Mammal Mitigation Plans or Protocols (MMMPs), and publishing. As the Chief Scientist, she also coordinates most research. Ian Todd is a founding Managing Director and Marine Science Consultant at OSC, a Director at OSC-NZ, and is undertaking part-time postgraduate research in harbour porpoise (and other marine mammal) interactions with offshore installations and the environment at ISVR (PhD, Southampton University, UK). He holds degrees in Marine Resource, Development & Protection (NERC-funded MSc scholarship, Heriot-Watt University, UK) and Business & Economics (BCom with Honours, Edinburgh University, UK), various diplomas including Marine Engineering (HND, Glasgow College of Nautical Studies, UK), and a Marine Engineering Officer Certificate of Dual Competency (Class IV Steam and Motor Plants, Maritime & Coastguard Agency, UK). As a former Third Engineer Officer (including Health and Safety Officer) in the Merchant Navy, Mr Todd served deep-sea and worldwide with P&O Nedlloyd, then the world’s largest container-shipping company. He organises and supervises visual and acoustic surveys of marine mammals worldwide for scientific, commercial and defence contracts. Mr Todd’s research interests are as per OSC’s core research topics, but include distance sampling, and his current scientific duties are similar to Dr Victoria Todd, but include recruitment, procurement, logistics, finance, brand development, environmental risk assessments, and Health and Safety (H&S).
About the Authors
Jane Gardiner is a Research Assistant at OSC. She holds degrees in Applied Marine Science (MSc) and Marine Biology (BSc with Honours), both from University of Plymouth. Ms Gardiner is involved with peer-reviewed research publications, and has served Lead (field position) for visual and acoustic surveys of marine mammals worldwide for scientific and commercial contracts. Ms Gardiner’s research interests are as per OSC’s core research topics and her current scientific duties include fieldwork, literature reviews, social media, and H&S. Erica Morrin is a Marine Science Consultant at OSC and a Director at OSC-NZ. She holds degrees in Marine Mammal Science (MRes, University of St Andrews, UK) and Biology (BSc with Honours, Queen’s University, Canada). Ms Morrin is involved with commercial consultancy, and has served Lead (field position) for visual and acoustic surveys of marine mammals worldwide for scientific and commercial contracts. Ms Morrin’s research interests are as per OSC’s core research topics and her current scientific duties are similar to Ms Gardiner, but include data analysis, and personnel supervision.
In 1953, Jacques Cousteau wrote a best-selling book about the ocean and entitled it The Silent World. Which does make one wonder whether the man who could arguably be called the ‘father’ of marine conservation had spent rather too much time being oxygendeprived on long dives. For the ocean is anything but silent. Ever since 1819, when the steamship Savannah subjected a small space in the North Atlantic to the noise of an engine for the first time, the oceans of the world have been filled with human-generated sound. Today, thousands of large ships regularly ply the sea routes of the world, and the noise that many of these vessels generate is – perhaps sometimes literally – deafening. At very low frequencies – those within the hearing range of some baleen whales – a supertanker or large bulk carrier can be heard tens of km away. Seismic surveys for oil and gas exploration not only generate noise that can be heard literally halfway across an ocean basin, but do so with great frequency, so that some areas are subjected to a continual barrage of industrial noise. Elsewhere, naval active SONARs have been shown to cause lethal mass strandings, especially among deep-diving beaked whales. In many places, a host of more ‘minor’ activities such as pile driving or oil rig operations generate additional noise to pollute the waters. This is all of concern because marine mammals such as whales and dolphins live by sound. In a world in which visibility is always limited and often poor, these animals use hearing as their primary sense to communicate and to navigate, to find food and avoid predation. We know remarkably little about the short- or long-term effects of noise pollution on these animals, but it cannot be easy to exist and thrive in an environment which is often so saturated with human noise that the calls on which marine mammals rely for communication are masked or severely constrained in their range. Effects may include anything from disruption of important behaviors to exclusion from habitats, and perhaps even (in extreme cases) physical damage to the animals’ hearing apparatus. Given the potential for such impacts, there has been a growing awareness of the need to conduct monitoring – visual and/or acoustic – in association with human activities that generate noise, and to use such monitoring as a key element of mitigation plans. This can be as simple as placing visual observers on a vessel to search for marine mammals within a potential impact zone; or it can involve sophisticated acoustic monitoring to detect vocalizing animals, a technique which usually increases – often considerably – the range at which the presence of marine mammals can be confirmed. The book you have in your hands – okay, so you may be reading this online, don’t be pedantic – aims to provide a comprehensive guide that will familiarize lay
and specialist readers alike with every aspect of this monitoring. Remarkably, it covers and includes just about everything in this realm: identifying marine mammals, a primer on sound, description of commonly used monitoring and mitigation measures, what’s involved with training and data collection, how to write reports… and even what to expect when you, the brave new observer, go into the field and have to live in a confined space in often rough or otherwise distinctly uncomfortable conditions with other human beings for an extended period. I have known the first author of Marine Mammal Observer and Passive Acoustic Monitoring Handbook – seriously, Victoria, couldn’t you have come up with a shorter title? – for longer than either of us care to admit. We began our friendship years ago by way of a serious internet discussion of, well, something to do with whales; but said conversation quickly morphed into an often hilarious exchange about everything from classical music to pet rooks (Victoria claims to speak several dialects of crow, though as yet I have been unable to verify this). The laughter has continued ever since. Beyond a questionable sense of humor and appreciation of the absurd, we had in common a much-admired colleague, Bill Watkins of Woods Hole Oceanographic Institution. Watkins was one of the pioneers of marine mammal sound recording, a remarkable scientist who essentially invented tape recorders before there were any, and whose incisive analytical abilities and prodigious knowledge of marine mammals remained sharp until his death in 2004. Bill served as something of a mentor to both Victoria and I, and was always willing to share his knowledge and to patiently answer sometimes idiotic questions from individuals whose feckless youth and inexperience were barely compensated for by their enthusiasm for marine mammal biology. The mitigation of noise is important these days, and this issue is often overlooked as a problem for the animals who inhabit an environment that is ‘silent’ only to those who regard it from the deceptively serene perspective of the ocean surface. The Handbook is an indispensable How To guide to the growing and increasingly important occupation of marine mammal monitoring, written with clarity and humor by scientists who have extensive experience in this field. Phil Clapham, director of the Cetacean Assessment and Ecology Program at the National Marine Mammal Laboratory in Seattle.
Thanks to Dr Max Ruffert, and Dr John Todd for comprehensive and invaluable peerreviews. Credit also to Dr Dave Lundquist for valuable comments in relation to New Zealand guidelines, Dr Douglas Gillespie for reviewing the ‘really hard bits’ of Chapter 7, and to Professor Paul White for peer-reviewing Chapter 7, to make sure the other ‘not so hard’ bits were OK too. Thanks to Edward Lavallin (OSC) for valuable contributions to table content and diagrams, and to Nicola MacPherson (OSC) for inputs to tables and Chapter 5. Credit to Dr Manolo Castellote, Roy Wyatt and Dr Peter Chapman for further helpful comments, and to Professor Rodney Coates for his educational contributions in the field of underwater acoustics, who sadly passed away on 29 December 2013 and will be missed sorely. Finally, the authors believe that everything in life has the capacity for improvement, so any constructive feedback for the next edition would be received gratefully, for which readers are requested to use the following email address: [email protected] All images are © OSC 2015 unless otherwise stated.
List of Acronyms, Units, Prefixes and Symbols List of Acronyms Acronym
Auditory Brainstem Response
Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area
Adjustable Diversity Acoustic Telemetry System
Analogue to Digital Converter
Acoustic Doppler Current Profiler
Acoustic Deterrent Device
Auditory Evoked Potential
Acoustic Harassment Device
Automatic Information System
Acoustic Mitigation Devices
Australian Maritime Safety Authority
Acoustical Society of America
American Standard Code for Information Interchange
Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas
Anti-Submarine Detection Investigation Committee
Apparent Source Level
List of Acronyms, Units, Prefixes and Symbols
Auditory Steady State Response
Acoustic Thermometry of Ocean Climate
Autonomous Underwater Vehicles
Broadband Acoustic Spectrum Recorder
Best Available Technique
Bottom Hole Assembly
Body Mass Index
Bureau of Minerals and Petroleum
Bureau of Ocean Energy Management
Blow Out Preventer
Basic Offshore Safety Induction and Emergency Training
Blows Per Minute
Behavioural Response Function
Bureau of Safety and Environmental Enforcement
Convention on the Conservation of Antarctic Marine Living Resources
Consultative Committee on International Radio
Concrete Island Drilling Structure
Choke & Kill Hoses
Choke & Kill Lines
Code of Conduct
Communication. Used for COM port, not to be confused with COM (common) label on National Instrument sound card
Control of Substances Hazardous to Health
Central Processing Unit
Compact System Camera
Cutter Suction Dredger
List of Acronyms, Units, Prefixes and Symbols
Controlled Source Electromagnetic
Conductivity, Temperature, Depth
Digital Acoustic Telemetry System
Data Acquisition Unit
Danish Centre for Environment and Energy
Derrick Drilling Machine
Department of the Environment, Water, Heritage and the Arts
Department of Fisheries and Oceans
Receiver Directivity Index
Department of Conservation
Digital Storage Oscilloscope
Digital Versatile Disc
Emergency Breathing Systems
European Cetacean Society
Exclusive Economic Zone
Environment Protection and Biodiversity Conservation Act 1999
End Of Line
Endangered Species Act
European Seabirds At Sea
Estimated Time of Arrival
External Upset End
Floating, Drilling, Production (or Processing), Storage and Offloading
Fast Fourier Transform
List of Acronyms, Units, Prefixes and Symbols
Forward-Looking Infrared Sensors
Further Offshore Emergency Training
Field Of View
Floating, Production, Storage, and Offloading
Fast Rescue Craft
Floating, Storage and Offloading
Greenwich Mean Time
Gulf of México
Gallon Per Minute
Global Positioning System
High Frequency Acoustic Recording Package
High Definition Multimedia Interface
High Frequency Marine Mammal Monitoring SONAR
Helicopter Landing Officer
Head of Mining Installation
Health and Safety
Hydro Sound Dampers
Health and Safety Executive
Helicopter Underwater Escape Training
International Association of Geophysical Contractors
Brazilian Institute of the Environment and Natural Renewable Resources
International Council for the Exploration of the Sea
Infinite Impulse Response Filter
Integrated Marine Mammal Monitoring and Protection System
Institute of Acoustics
Infrared Search and Track
International Standards Organisation
List of Acronyms, Units, Prefixes and Symbols
International Union for the Conservation of Nature
Journal of the Acoustical Society of America
Joint Nature Conservation Committee
Joint Photographic Experts Group (file extension for image files)
Job Safety Analysis
Lost Circulation Material
Low Frequency Active SONAR
Low Specific Activity
Medium Wavelength Advanced Thermal Imaging system
Maritime and Coastguard Agency
Marine Ecology Progress Series
Middle Ear Transfer Function
Mid-Frequency Active SONAR
Marine Fauna Observer
Minimum Industry Safety Training
Marine Mammal Commission
Marine Mammal Impact Assessment
Marine Mammal Mitigation Plan
Marine Mammal Observer
Marine Mammal Observer Association
Marine Mammal Protection Act 1978
Marine Mammal Risk Mitigation program
Marine Mammal and Seabird Observer
MPEG 2 audio layer III
Marine Protected Area
Marine Renewable Energy Devices
Measurement While Drilling
Medium Wave Infrared Radiation
List of Acronyms, Units, Prefixes and Symbols
My Structured Query Language
North Atlantic Treaty Organisation
Narrow Band High Frequency
National Environmental Research Institute
National Marine Conservation Area
Norwegian Maritime Directive
Non-Magnetic Drill Collar
National Marine Electronics Association
National Marine Fisheries Service
National Marine Sanctuary
National Oceanographic Atmospheric Administration
National Parks and Wildlife Service
New South Wales
National Television System Committee
NATO Undersea Research Centre
Ocean Acoustic Waveguide Remote Sensing
Ocean Bottom Cable
Octave Band Noise
Ocean Bottom Seismic
Offshore Construction Manager
Offshore Installation Manager
Norwegian Oil Industry Association
Offshore Petroleum Industry Training Organization
Ocean Science Consulting Ltd
Passive Acoustic Monitoring
Passive Acoustic Monitoring Guardianship
List of Acronyms, Units, Prefixes and Symbols |
Pressure Build Up
Peak Equivalent Sound Pressure Level
Pre-Job Safety Meeting
Public Library of Science
Person On Board
Pull Out Of Hole
Personal Protective Equipment
parts per thousand
Power Spectral Density
Protected Species Observer
Permanent Threshold Shift
Pick Up Weight
Research and Development
Returned Goods Relief
Run In Hole
Rotary Kelly Bushing
Root Mean Square
Republic of Ireland
Remotely Operated Vehicle
Special Areas of Conservation
List of Acronyms, Units, Prefixes and Symbols
Static Acoustic Monitoring System
Species At Risk Act
Single Beam SONAR
Surface Controlled Sub-Surface Safety Valve
Self-Contained Underwater Breathing Apparatus
Sound Exposure Level
International System of Units (Système International)
Shut In Drill Pipe Pressure
Single Lens Reflex
Society for Marine Mammalogy
SOund Fixing And Ranging
Start Of Line
Sound Navigation And Ranging
Slag Off Weight
Shot Point Interval
Sound Pressure Level
Safety Training Observation Program
Surveillance Towed Array Sensor System
Sound Velocity Profile
Tropical Basic Offshore Safety Induction and Emergency Training
Tool Box Talk
Time Differences Of Arrival
Time to First Shot Point
Trailing Suction Hopper Dredger
Temporary Threshold Shift
List of Acronyms, Units, Prefixes and Symbols |
User Datagram Protocol
Ultra High Frequency
UK Continental Shelf
United Nations Environment Programme
Universal Serial Bus
US Fish and Wildlife Service
Universal Time Coordinated (i.e. Zulu or Greenwich Mean Time)
Visual and Acoustic Detection and Ranging [software]
Value Added Tax
Very High Frequency
Vertical Seismic Profiling
WAVeform audio file format (computer sound files)
Wait On Cement
List of Units Quantity name
List of Acronyms, Units, Prefixes and Symbols
List of Unit Prefixes Prefix
List of Symbols Symbol
This Handbook concerns potential interferences of man-made (anthropogenic) noise sources with the acoustic spectra exploited by marine mammals, the mitigation steps taken by industry, regulatory authorities and ultimately Marine Mammal Observers (MMOs), Protected Species Observers (PSOs), Marine Fauna Observers (MFOs), and Passive Acoustic Monitoring (PAM) Operators. For brevity, MMOs, PSOs, MFOs and all other visual observers are referred to collectively as MMOs throughout the Handbook. The purpose of this Handbook is to provide an all-in-one, comprehensive yet concise and simple user manual on the topic of marine mammal mitigation during industrial activities for all stakeholders, regardless of their experience. The Handbook aims to increase MMO and PAM standards universally, by bringing together all aspects of this discipline into one easily accessible resource. The manual serves as a platform to offer sound advice and dispel myths on what is achievable currently on marine mammal mitigation, considering physics of sound propagation, limitations of visual observation, and current industrial PAM technologies. If used correctly, the Handbook should edify the reader on how to understand sensible and practical mitigation techniques and to recognise substandard mitigation procedures and equipment in use currently throughout industry. Moreover, an MMO or PAM Operator armed with this book should be able to implement mitigation measures and respond knowledgeably to questions on the job, during general client liaison and project kick-off meetings, or when writing MMO and PAM reports. The Handbook has focused on visual and acoustic mitigation from vessels, and installations. For brevity, marine mammal aerial surveys are not discussed, as they are seldom used for mitigation in industry, and are more applicable to scientific research. Detecting marine mammals in the field is always challenging; for example, visual watches are constrained typically by weather, whilst PAM relies firstly on animals vocalising in sufficient proximity to an underwater microphone (hydrophone), and in some cases, animals vocalising towards a hydrophone. Consequently, the use of MMO and PAM is not 100 per cent (%) effective, but with adequate training and knowledge, MMO and PAM Operators armed with a well-engineered, installed, optimised and properly configured PAM system, can offer the most effective mitigation solution available. Intended readership: • trainees and existing MMOs, PAM Operators, and fisheries observers; • marine science and other discipline graduates considering entering the field;
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non-graduates (school-leavers) with no prior MMO or PAM experience; MMO/PAM trainers and course providers worldwide; PAM equipment manufacturers, suppliers, owners and distributors; environmental consultancies supplying MMO/PAM services; intermediary consultancies and recruitment agencies supplying MMO/PAM services; client and contractor representatives with job titles such as Health, Safety, Environment (HSE) and Quality Manager, Health and Safety (H&S) Advisor, Marine or Offshore Environment Manager, Environmental Development Manager, Environmental or Scientific Advisor, Environmental Policy Manager, Director of Environment, Environmental Coordinator, Regulatory Compliance and Environmental Manager, Environmental or Project and Consents Manager, Environmental Policy Analyst, Environmental Supervisor or Manager, Environmental and Community Relations Manager, Environmental Survey Manager, Operations or Project Manager, Marine or Offshore Project Officer or Manager, Technical Manager, Technical Superintendent, Technical Director, Permitting or Project Engineer, Permitting or Legal Advisor, Business or Product Development Manager, Sourcing or Procurement Manager, Commercial or Supply Chain Manager, Operations or Project Coordinator, Subcontractor Coordinator or Manager, Contracts Manager, Operations Manager, Vessel Manager or Superintendent, Dredging Supervisor or Superintendent, Hydrographic Party Chief or Manager, Chief Surveyor, Hydrographic Surveyor, Survey Engineer, Geophysicist, Geotechnical or Geophysical Engineer, Processing Geophysicist, Seismic Party Chief or Manager, Deputy Party Chief or Manager, Seismic Observer, Seismic Navigator, Air-Gun Mechanic, Navigation Officer (including vessel Master or Captain or Skipper or Coxswain), Offshore Installation Manager (OIM), Head of Mining Installation (HMI), Drilling Rig Manager, Head Drilling Engineer or Manager, Well Intervention Supervisor, Marine or Offshore Supervisor, Offshore Construction Manager (OCM), Military Exercise or Operations Manager, Research and Development (R&D) Manager, Fisheries Liaison Manager, and Reports Coordinator; governmental organisations such as Joint Nature Conservation Committee (JNCC) in the UK, National Parks and Wildlife Service (NPWS) in Ireland, Bureau of Minerals and Petroleum (BMP) in Greenland, National Environmental Research Institute (NERI) in Denmark, Bureau of Ocean Energy Management (BOEM) and Bureau of Safety and Environmental Enforcement (BSEE) in the USA, Department of Fisheries and Oceans (DFO) in Canada, Department of the Environment, Water, Heritage and the Arts (DEWHA) in Australia and, most recently, Department of Conservation (DOC) in New Zealand; non-governmental organisations (NGOs) such as whale, dolphin and porpoise charities; scientists, research assistants, and universities; members of the public, e.g. amateur professionals; media, e.g. television, press and radio; tourism industry representatives such as wildlife-watching cruise operators; and, commercial charter vessel operators.
Chapter 1 familiarises the reader with different types and species of marine mammal, including a comprehensive table of worldwide distributions. The table permits the reader to identify quickly which species are likely to occur in the work area of interest.
Potential effects of sound on marine mammals are discussed, as are their hearing abilities. Where known, hearing ranges are summarised in a table. Chapter 2 details mitigation techniques employed currently by offshore industries to minimise impact of noise on marine mammals, concluding with a table summarising current worldwide MMO and PAM guidelines. Chapter 3 focuses on various sources of anthropogenic noise such as vessel engines, seismic surveys, piling and sound navigation and ranging (SONAR). Following a general introduction to each activity, typical noise levels and frequencies are reviewed, with reference to published noise measurements. Potential and known effects of each activity on marine mammals are addressed briefly, but the reader is directed to further reading. Chapter 4 clarifies training and qualifications required to work as an MMO or PAM Operator worldwide. Prerequisites are listed, as are expected course contents, and details of offshore survival courses and medicals. The chapter concludes with writing Curricula Vitae (CV), and gaining offshore experience. Chapter 5 prepares the reader for life offshore. All aspects such as packing, etiquette, mobilisation and demobilisation are discussed in relation to vessels and installations; operations, such as dredging, drilling or seismic, are reviewed separately. Chapter 6 guides the reader through an MMO working shift, explaining equipment requirements, skills involved, data collection methods and marine mammal identification. Chapter 7 outlines the physical basics of sound and units and highlights various ways sound is reported, and displayed visually. Chapter 8 introduces types of marine mammal sounds, reviews potential functions, and presents vocalisation characteristics of all marine mammal species and subspecies (excluding freshwater marine mammals) in a comprehensive table. To assist in-field PAM species identification, literature for Odontocetes is expanded on in depth in the text. Chapter 9 presents a brief review of PAM systems in use today, focusing on the use of towed PAM for industrial mitigation purposes. The chapter details PAM equipment set-up, deployment, operation and care from mobilisation to demobilisation. A detailed section on configuration, use and troubleshooting in Passive Acoustic Monitoring Guardianship (PAMGuard) software is presented. The reality of the chances of detecting a vocalising marine mammal in an industrial situation is also discussed. Chapter 10 describes how to compose and structure simple and effective MMO and PAM reports. This Handbook contains a number of abbreviations and technical terms listed in the acronyms and glossary respectively. Abbreviations are written in full on first mention, and then acronyms used throughout. Likewise, terminologies in the glossary are in bold on first mention, but not thereafter. Units follow the International System of Units (SI) and those referred to in text are included in the units list, and explained in detail in Chapter 7. Used throughout the Handbook, the term ‘offshore’ refers to any marine environment activities, including those in coastal areas. This Handbook is organised into sections that facilitate quick and easy access to relevant information concerning any particular aspect of marine mammal mitigation. Sections provide the reader with topical background, knowledge and examples to assist with a fast and effective response to mitigation situations arising in the field. A competent PAM Operator requires moderate comprehension of the physics of sound propagation (and complete understanding of units used), but the Handbook does not
swamp the reader with equations, nor does it cover the wider field of anthropogenic sounds (and modelling), sound-related behaviour, or sound production and hearing capabilities of marine mammals. These topics are dealt with effectively in a plethora of scientific reviews, papers, reports and books, many of which are cited as further reading where applicable, and listed in the bibliography. Scientific names of all marine mammal species are included in Tables 1.1 and 1.2, but for brevity, species are referred to using British common names throughout; subspecies are not discussed in text, but distributions, hearing and vocalisation ranges are addressed separately in Tables 1.2, 1.4 and 8.3 respectively.
Light in the ocean is limited. At low latitudes, and under the right transmission conditions, light can be detected at 1,000 metres (m) depth, but penetrates rarely beyond 200 m. In temperate seas, coastal areas and estuaries, these distances are often reduced to tens of metres. Under favourable propagation conditions, however, underwater sound can be both generated and heard by ocean users and marine life thousands of kilometres (km) from the source. Given that sight is of limited use underwater, many marine animals (including nocturnal and crepuscular species) rely on both passive and active acoustics for survival. In a sense, some marine animals use sound in a similar way as many terrestrial species use sight or smell to explore their environment. In particular, cetaceans (whales, dolphins and porpoises) use different sound frequency bands for communication, foraging, navigation, threat detection/avoidance and a range of activities within the wider social group such as cohesive actions, warnings and maternal relationships. In most cases, the hearing range of marine mammals is less well understood, but it is assumed generally that animals hear over similar frequency ranges to the sounds they produce, with the exception of some porpoise species. In essence, the ocean is a noisy environment, which provides marine mammals with the ultimate ‘acoustic map’ of their surroundings. Underwater sound (and vibration) originates from a wide variety of both natural and anthropogenic sources. Both naturally occurring physical and biological processes generate noise. Physical processes include precipitation, wind, breaking waves, lightning strikes, ice movement, seismic and volcanic activity, interactions of water with substrata, and, at the molecular level, thermal noise. Biological noise sources include marine wildlife vocalisations and general behavioural activities such as noise produced by snapping shrimp. Incidental (non-deliberate) and intentional (deliberate) anthropogenic noise sources in continental shelf and offshore waters may be both static or mobile, and in the long term we expect production of such sound sources in the marine environment to increase. Some studies have suggested that anthropogenic noise increases at a fixed rate per decade. Chapman and Price (2011) stated that ambient noise in the Northeast Pacific increased at a rate of 3 decibels (dB) a decade, or 0.55 dB a year up to the 1980s, when it reduced to 0.2 dB a year. Examples of incidental sounds include shipping traffic (from ocean-going vessels to jet skis), hydrocarbon exploration (drilling), production and decommissioning (oil and gas platforms), marine aggregate dredging, mining, explosions (e.g. construction
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and well-head decommissioning), pile driving and Marine Renewable Energy Devices, MREDs (e.g. wind tidal and wave turbines). Intentional anthropogenic sound sources exploit the ocean as a signal transmission medium. Examples include hydrocarbon exploration (e.g. seismic), acoustic navigation aids (e.g. shipping, SONAR and high frequency echosounders), through-water data communication networks for scientific exploration (e.g. Autonomous Underwater Vehicles, AUVs, Remotely Operated Vehicles, ROVs), low frequency tomographic SONAR systems (e.g. Acoustic Thermometry of Ocean Climate, ATOC), seabed imaging (e.g. multi-beam and side-scan SONAR), military SONARs (e.g. Low Frequency Active SONAR, LFA), and marine mammal Acoustic Deterrent Devices (ADDs) for commercial aquaculture, static and trawl fisheries (e.g. pingers and seal scarers). Underwater acoustic telemetry systems (e.g. Adjustable Diversity Acoustic Telemetry System, ADATS, Digital Acoustic Telemetry System, DATS), linking numerous sampling stations into wide area monitoring networks, are also being developed currently. Scientists have conducted a substantial amount of research into effects of anthropogenic noise on marine mammals but results are varied, conflicting, and often inconclusive. Impacts are dependent evidently on a vast number of factors including the characteristics of the sound source, background noise levels, sound propagation paths, water depth and the hearing sensitivities of receivers, which for the purpose of this book are marine mammals. Effects of noise on other marine life is outside the scope of this Handbook, but potential impacts on, for example, fish is of great concern, and hence the subject of substantial research. Temporary or permanent changes in hearing thresholds of marine mammals, known as Temporary Threshold Shift (TTS) or Permanent Threshold Shift (PTS), can occur because of exposure to high intensity sounds, whilst mass stranding events of deep diving species have been correlated with military SONAR activities. Other studies have noted changes in behaviour, avoidance of habitats and alterations to vocalisations. Masking could also reduce communication distances. Concern and uncertainty surrounding potential effects of anthropogenic noise on marine mammals has compelled governments, regulatory bodies, and offshore industries to produce and enforce mitigation measures, which help to minimise potential impacts. In 1998, the JNCC published Guidelines for Minimising Acoustic Disturbance to Marine Mammals from Seismic Surveys (JNCC, 1998) for United Kingdom (UK) territorial waters. Since then, the JNCC has published revised versions and separate guidelines for pile driving and underwater explosions, and other countries have produced their own guidelines. Common to all current guidelines are the use of MMOs and PAM Operator specialists, as the Best Available Technique (BAT) to confirm visually or acoustically the absence of marine mammals in a designated exclusion zone prior to activating any anthropogenic noise source. Within this chapter, marine mammal classification and distribution are discussed, followed by an introduction to documented effects of anthropogenic noise on marine mammals. The chapter concludes with a description of audiograms, and a summary of marine mammal hearing ranges.
Marine Mammal Classification
In the simplest of terms, marine mammals are a diverse group of animals, which rely,
at least in part, on the ocean to survive. Classified broadly into five groups within three orders (Cetacea, Sirenia, and Carnivora), marine mammals comprise cetaceans (whales, dolphins and porpoises), pinnipeds (seals, sea lions, and the walrus), sirenians (manatees and dugongs), marine mustelids (otters) and the polar bear. Returning to an aquatic lifestyle at various evolutionary stages, all marine mammals have mammalian traits, although some have retained more terrestrial features than others and characteristics vary extensively (Uhen, 2007). All marine mammal species, therefore, need to be considered separately when discussing any potential effects of anthropogenic noise. More detailed reading on marine mammal classification can be found in Hoelzel (2002), Uhen (2007), and Reeves et al. (2008).
Included within the order Cetacea are all 88 or so species of whales, dolphins and porpoises. All cetaceans are descended from mesonychid condylarths, which were cat-like, carnivorous land-based ungulates that became amphibious in the Eocene, probably to exploit food-rich near-shore waters (Thewissen, 1998). In the intervening 50 to 60 million years, these condylarths transformed gradually from hoofed waders into fully fledged, flippered whales (Ketten, 2000) and every portion of their anatomy was reshaped physically and functionally to accommodate life in the water (Cranford, 2000). Recent research into fossil dinoflagellates in the Southern Ocean has indicated that a major shift in the plankton ecosystem occurred during the first major glaciation. It was suggested that phytoplankton–zooplankton shift could have contributed to the evolution of baleen whales, which evolved feeding mechanisms which allowed them to take advantage of the seasonal increase in krill (order Euphausiacea), which feed on dinoflagellates (Houben et al., 2013). Cetaceans are divided into two suborders, the Odontoceti (74 species) and the Mysticeti (14 species), toothed and baleen (or toothless) whales respectively. With the exception of the sperm whale, all of the great whales are mysticetes, and all, except the minke whale, are larger than the toothed whales. Cetaceans range in size from the largest animal to inhabit earth, the blue whale, to the tiny vaquita. The absence of functional teeth in mysticetes means that feeding strategies of the two suborders differ substantially. Despite their large size, mysticetes prey mainly on small marine organisms, including small crustaceans such as krill. The smaller odontocetes target larger fish and cephalopods; others such as some killer whales (and potentially false killer whales), target mammalian prey. The presence of the paired blowhole in the Mysticeti also distinguishes the two suborders. More detailed reading about cetaceans in general, can be found in Thewissen (1998), Bannister (2002), and Berta et al. (2006).
Encompassed within the pinnipeds are all seals, sea lions and the walrus. The word pinniped means fin-footed, and refers to marine mammals that have front and hind flippers, as opposed to flukes or tails. Pinnipeds are not related closely to cetaceans or to sirenians. Like cetaceans, millions of years ago, the ancestors of pinnipeds lived on land and were probably otter or bear-like animals that spent increasing periods in the water, eventually adapting to the marine environment. All pinnipeds must give birth on terra firma or ice.
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There are 34 living species of pinnipeds, distributed mainly in polar, sub-polar and temperate waters. Divided into three families, pinnipeds include Phocidae (true seals), Otariidae (eared seals) – which include fur seals and sea lions – and Odobenidae (the walrus). Otariidae differ from Phocidae in several ways, notably in that they have external ear flaps, walk generally on both their hind and fore flippers, and propel themselves through the water by their fore flippers with a flapping motion. Phocids, on the other hand, do not have visible earflaps, haul themselves along land by their fore flippers or by a ‘caterpillar motion’ of their bodies, and use their hind flippers to propel themselves through the water, their fore flippers being used for steering. The walrus possesses an interesting mixture of both phocid and otariid characteristics. More detailed reading about pinnipeds can be found in Higdon et al. (2007) and Berta and Churchill (2012).
Like cetaceans, the earliest sirenians were amphibious, four-limbed animals, which lived during the Eocene (Hoelzel, 2002). Now aquatic, modern-day sirenians have robust streamlined bodies with little hair, no dorsal fin and paddle-like forelimbs. Sirenians form part of the ungulate clade Tethytheria, which includes hoofed mammals in the order Proboscidea (elephants), and the extinct Desmostylia (Uhen, 2007). Today, the order Sirenia includes four species in two families, the Trichechidae (manatees) and the Dugongidae (dugongs). Identifiable by their tail flukes, manatees have a powerful paddle-like tail distinct from the V-shaped tail of the dugong. Sirenians are herbivorous marine mammals that reside in tropical and subtropical waters where sea grass and aquatic vegetation are plentiful. Dugongs are fully marine, and are found in the western Pacific and Indian oceans, whereas, manatees reside in coastal waters, estuaries and rivers and are primarily tropical. More detailed reading about sirenians can be found in Domning (1982), Marsh and Lefebvre (1994) and Marsh et al. (2011).
Within the order Carnivora, mustelids are mostly terrestrial or semi-aquatic animals. Only two species extant today can be classed as marine mammals, the sea otter and marine otter (Reeves et al., 2002). To better adapt them to the marine environment, sea otters and marine otters vary from other mustelids in several ways. For example, their higher fur density ensures air is trapped more efficiently when they dive, thus keeping them warmer (Liwanag et al., 2012). The majority of mustelids have to give birth on land; sea otters, which give birth in coastal waters, are the only exception. Additional differences between sea and marine otters include distribution, diet and consequently tooth shape. Sea otters, with their blunt rounded teeth, feed mainly on invertebrates, but the sharp pointed teeth of marine otters are better suited to their fish diet (Medina-Vogel et al., 2004). Sea otter distribution is broader, covering the North Pacific and southern Bering Sea, whilst marine otters are restricted to the Pacific coast of South America. More detailed reading about marine mustelids can be found in Riedman and Estes (1990), Anderson et al. (1996) and Valqui (2012).
Like marine mustelids and pinnipeds, the polar bear is part of the order Carnivora. One species exists currently. Distinct from other bear species, the polar bear resides only in the northern hemisphere in areas where sea ice coverage is extensive for the majority of the year (Amstrup, 2003). Branching off in the Pleistocene from the brown bear (Ursus arctos), they share a common ancestor, although significant morphological changes have occurred in the polar bear over the past 20,000–40,000 years (Amstrup, 2003; Derocher and Lynch, 2012). Reaching a length of 2.5 m (Evans and Raga, 2001), and feeding predominantly on seals, the polar bear is the largest and most predatory of the bears alive today (Amstrup, 2003). Adapted to its environment, the polar bear lacks a shoulder hump and is more streamlined than other members of the family Ursidae (Evans and Raga, 2001). It is also covered almost entirely in thick, pigment-free fur, which appears white (Amstrup, 2003) and provides the primary means of insulation (Liwanag et al., 2012). Using its forelimbs to swim, the polar bear relies on ice, land and sea to survive; the sea ice providing a platform for hunting and a place for females to give birth (Durner et al., 2003). More detailed reading about polar bears can be found in Amstrup (2003).
Marine Mammal Distribution
Marine mammals as a whole are widespread and found in all oceans of the world, but individual species distributions vary substantially. The killer whale, for example, has a vast range that spans the majority of marine environments (see review by Forney and Wade, 2006), whilst other species are confined to small areas such as a subspecies of Hector’s dolphin known as Maui’s dolphin, which is endemic to North Island, New Zealand (Ferreira and Roberts, 2003). Distributions of all marine mammals are displayed in Table 1.1; subspecies have been addressed separately in Table 1.2. Species follows the taxonomic list of marine mammals published by the Committee on Taxonomy (2014), but, considering the marine focus of this book, those species and subspecies deemed to have solely freshwater distributions have been excluded, but are addressed in freshwater regions tables available online (www.osc.co.uk). Division of regions refers to the main oceans, enclosed and semi-enclosed seas and inter connected sub seas. For a full regional breakdown of boundaries, see Figure 1.1. Where marine mammal ranges did not fit succinctly with our divisions, we have specified further by classifying species as vagrant, visitor or endemic. As per Reeves and Notarbartolo di Sciara (2006), ‘vagrant’ applies to species with any verified presence in regions beyond their usual range, whilst ‘visitor’ species are observed more commonly in regions beyond their usual range, but are not considered native to these external regions. Endemism refers to geographical constraint and range limitation of a species to a localised region (e.g. if a species is found throughout the entire North Pacific, it is not considered to be endemic to the North Pacific). More information on marine mammal ranges is sourced easily online. Useful resources include Culik (2010) and the IUCN red list (www.iucnredlist.org).
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Figure 1.1 World map of regional boundaries used to compose distributions of marine mammals (Tables 1.1 and 1.2).
Regions in Figure 1.1 are divided up as follows: • Antarctic: Amundsen Sea, Bellingshausen Sea, Drake Passage, Ross Sea, Scotia Sea and Weddell Sea. • Arctic: Baffin Bay, Barents Sea, Beaufort Sea, Chukchi Sea, Davis Strait, East Siberian Sea, Greenland Sea, Hudson Bay, Hudson Strait Kara Sea, Labrador Sea, Laptev Sea, North-western Passages, Norwegian Sea and White Sea. • Baltic: Gulf of Bothnia, Gulf of Finland and Gulf of Riga. • Black Sea: Sea of Azov. • Caspian Sea: Not Applicable (N/A). • Indo-Pacific: Andaman Sea, Arabian Sea, Arafura Sea, Banda Sea, Bay of Bengal, Bismarck Sea, Coral Sea, Great Australian Bight, Gulf of Aden, Gulf of Oman, Gulf of Thailand, Java Sea, Laccadive Sea, Mozambique Channel, Solomon Sea, Tasman Sea and Timor Sea. • Mediterranean Sea: Adriatic Sea, Aegean, Alboran Sea, Balearic Sea, Garabogözkal Basin, Ionian Sea, Ligurian Sea, Sea of Marmara and Tyrrhenian Sea. • North Atlantic: Bay of Biscay, Bristol Channel, Caribbean Sea, Celtic Sea, English Channel, Firth of Clyde, Gulf of Guinea, Gulf of México (GoM), Gulf of St Lawrence, Irish Sea, Kattegat, North Sea, Sargasso Sea, Skagerrak and St George’s Channel. • North Pacific: Bearing Sea, Celebes Sea, East China Sea, Gulf of Alaska, Gulf of California, Sea of Japan, Sea of Okhotsk, South China Sea, and Sulu Sea. • South Atlantic: Bahía Grande, Estrecho de Magallanes, Golfo San Jorge, Golfo Nuevo, Rio de La Plata and San Matías. • South Pacific: N/A.
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Effects of Anthropogenic Sound on Marine Mammals
The ocean is a very noisy environment, with both natural and anthropogenic sources contributing significantly to background noise levels. Interference with detection of natural sounds has the ability to impact upon marine mammals to some degree. If noise levels are sufficiently elevated at an animal’s most sensitive hearing frequencies, sounds can result in TTS or PTS (Section 1.4.1). Lower intensity sounds, unlikely to cause physical damage, could evoke behavioural reactions including avoidance or vocalisation alterations. Masking is also a concern, and can reduce the ranges at which marine mammals communicate. In some cases, characteristics of sound can affect behavioural responses of marine mammals. In worst cases, military SONAR has been correlated with mass stranding events of deep diving cetaceans. Within this section, we review briefly, existing literature and discuss potential effects of anthropogenic noise on marine mammals. There are a number of specialised books and review papers on the topic of sound and marine mammals and the reader is encouraged to consult reviews by Richardson et al. (1995), Ketten (2000), NRC (2003), Hildebrand (2005), and Popper and Hawkins (2012) for further information.
Temporary Threshold Shift and Permanent Threshold Shift
A TTS is a temporary increase in hearing threshold following exposure to loud noise. Given its transitory nature, effects on marine mammals should be minimal and shortlived, but awareness is important, as TTS onset and growth rates can be used to estimate levels of PTS onset (Gedamke et al., 2011). These levels can then be used in industry to define safe levels of exposure. The majority of TTS research on marine mammals to date has focused on odontocetes and pinnipeds. Studying TTS levels in mysticetes is more complicated and based currently on estimations using odontocete species. Common to all studies is the conclusion that level of threshold shift is dependent on a number of variables, including duration, frequency, and intensity of the sound source. More detailed information on TTS, PTS, and industry or naval exposure criteria can be found in Southall et al. (2007) and Finneran and Jenkins (2012). Threshold shift in bottlenose dolphins has been studied extensively (Schlundt et al., 2000; Nachtigall et al., 2003; Finneran et al., 2005b, 2010; Mooney et al., 2009b; Finneran and Schlundt, 2013). Most recently, Finneran and Schlundt (2013) tested TTS levels of two bottlenose dolphins exposed to 16 second (s) fatiguing tones between 3 and 80 kilohertz (kHz); the likelihood of TTS was found to increase for frequencies of 10–30 kHz. Highest TTS levels, recorded 4 minutes (min) post-exposure, were between 20 and 30 dB. Fatiguing noises used in the two trials that produced these levels were c. 14 kHz and c. 28 kHz, with a Sound Pressure Level (SPL) range of 132–182 dB referenced to 1 micropascal (re 1 µPa) and 133–173 dB re 1 µPa respectively. In comparison, 80 kHz noise with SPLs of 113–173 dB re 1 µPa produced TTS levels measured 4 min post-exposure of 4 dB. A number of TTS studies have also been undertaken on the beluga whale (Erbe and Farmer, 1998; Finneran et al., 2000; Erbe, 2008; Popov and Supin, 2010; Popov et al., 2011a). A TTS level of 40 dB was recorded after a 30 min exposure to half Octave Band Noise (OBN; Section 7.3.4), with a central frequency of 32 kHz and intensity of 160 dB re 1 µPa. This decreased to 20 dB TTS at exposures of 1–3 min (Popov et al., 2011a).
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The TTS studies on porpoises have been conducted on the Yangtze finless porpoise (Popov et al., 2011b), but most research has focused on the harbour porpoise (Lucke et al., 2009; Kastelein et al., 2012b). Kastelein et al. (2012b) measured TTS levels and recovery in a harbour porpoise exposed to 4 kHz OBN of varying SPL and duration. Results indicated the importance of exposure time and intensity. Using a mean received SPL of 124 dB re 1 µPa, increasing the exposure time from 7.5 to 240 min revealed an increase in TTS from 2.5 up to 9 dB. Altering SPL had the same effect, demonstrated by an increase in TTS from 9 to 10 dB, as SPL increased from 124 to 136 dB re 1 µPa. Hearing recovery occurred within 48 min and 48–96 min for SPLs of 124 and 136 dB re 1 µPa respectively. Kastelein et al. (2013b) exposed a harbour porpoise to a 1.5 kHz tone with no harmonics, and a received SPL of 154 dB re 1 µPa for 60 min. The TTS was tested at various frequencies between 1.5 and 125 kHz, 1–4 min post-exposure. No TTS was apparent at 125 kHz, but TTS of 14 and 11 dB was recorded at 1.5 and 2 kHz respectively. In both cases, recovery occurred within 96 min. Pinniped threshold shift studies have focused mainly on the California sea lion, harbour seal and northern elephant seal (Kastak et al., 1999, 2005). Kastelein et al. (2012a) exposed two harbour seals to 4 kHz OBN of varying SPL and durations. Highest TTS levels occurred 1–4 min after exposures to noise with SPLs of 148 dB re 1 µPa for 120 and 240 min. Hearing thresholds returned to normal after 60 min. One example of severe TTS in a harbour seal is reported by Kastelein et al. (2013a). Following a 60 min exposure to 4 kHz OBN, at a mean received SPL of 163 dB re 1 µPa, TTS of 44 dB was reported 12–16 min post-exposure. After three days, TTS had reduced to 4 dB, and hearing was back to normal by day four.
Anthropogenic noise has evoked a number of behavioural responses in marine mammals. Reactions are situation-specific, and results of studies are sometimes inconclusive or contradictory; some report little or no reaction. When exposed to seismic noise, course alterations and localised avoidance reactions have been observed in short-finned pilot whales (Weir, 2008) and humpback whales (McCauley et al., 2000a). Short-term avoidance has also been observed in harbour porpoises, but effects were short lived as individuals returned to the survey area within hours of sound source ceasing (Thompson et al., 2013). Minimal reactions were reported by Harris et al. (2001) for bearded, ringed and spotted seals. At most, individuals swam away from the immediate zone, but remained within the general area. Prolonged noise from vessels and industrial activities including dredging and drilling over a small spatial scale has been correlated with changes to distribution of beluga whales (Hoffman, 2010), bowhead whales (Richardson et al., 1987, 1990) and gray whales (Bryant et al., 1984). Bowhead whale Surface–Respiration–Dive (SRD) cycles vary naturally with reproductive status, activity, and season. Robertson et al. (2013) stated that seismic activity also affects SRD cycles, but the extent to which varies with situation. For example, whales (excluding calves) reacted more to seismic noise in autumn than in summer, and when travelling compared with feeding or social behaviours. Typical reactions included shorter surfacing intervals, and dive times and a decline in number of blows per surfacing. Whilst studying sperm whales exposed to seismic noise, Jochens and Biggs (2003) found that animals spent greater proportions of time at the surface, where noise levels are likely to be reduced. It was hypothesised that, because sperm whales feed at depth, this change in surfacing patterns could ultimately affect their feeding patterns; more
time spent at the surface is less time spent foraging (Jochens and Biggs, 2003). This contradicts earlier studies completed by Madsen and Møhl (2000) and Madsen et al. (2002a), which stated no observed changes in vocalisations or behaviour of sperm whales in the presence of detonator and seismic noise respectively. Vocalisations are central to communication for all marine mammal species. Unsurprisingly, mammals have been found to alter or cease calling patterns in the presence of elevated background noise. North Atlantic right whales (Parks et al., 2011) and killer whales (Holt et al., 2011) have both been observed increasing the amplitude, and subsequently communication distance, of their calls in the presence of noise. Reactions in humpback whales are varied, with Miller et al. (2000) reporting increased song lengths in the presence of LFA SONAR, and Risch et al. (2012) stating animals were less likely to vocalise in the presence of low frequency pulses produced by Ocean Acoustic Waveguide Remote Sensing (OAWRS). Blue whales are also less likely to vocalise in the presence of Mid-Frequency Active (MFA) SONAR (Melcón et al., 2012a). Fin whales have been recorded reducing call frequency and changing temporal structure of their vocalisations in the presence of shipping and seismic noise. The low frequency nature of altered calls means they have potential to travel longer distances; calling energy costs may be also increased and changing temporal characteristics could affect call functionality (Castellote et al., 2010, 2012). Considering that fin whale vocalisations have been correlated potentially with reproduction, Castellote et al. (2010) hypothesised that shipping noise, in the long term, could impact upon the reproductive capabilities of fin whales.
Prolonged exposure to anthropogenic noise has the potential to induce stress responses in marine mammals (Wright et al., 2007). Romano et al. (2004) tested the immune response of a bottlenose dolphin and a beluga whale before and after exposure to seismic airgun and pinger sounds. Results showed that levels of stress-related hormones (catecholamines, and lymphocyte subsets) increased following exposure. Similarly, Rolland et al. (2012) compared stress-related faecal hormones of North Atlantic right whales in the Bay of Fundy, Canada during busy and quiet shipping periods, noting that levels were higher during periods of increased noise.
Sounds which coincide with hearing ranges of marine mammals have the potential to mask important signals and reduce the distance over which individuals can communicate (Clark et al., 2009; Jensen et al., 2009a). Failure to detect signals of conspecifics, predators, or prey could impact significantly upon activities vital for survival, such as mate finding or predator avoidance. In order to assess the effects vessel traffic have on the communication range of fin, humpback and North Atlantic right whales, Clark et al. (2009) produced a model based on the SONAR equations (see Section 7.2.8). Factors considered within the model were sound source characteristics, sound propagation, and received Sound Exposure Levels (SEL). Data collected on the Stellwagen Bank National Marine Sanctuary were used to assess how communication spaces varied for each species when a vessel transited through the area. Communication space was defined as ‘the distance over which calls could be detected by conspecifics’. When approaching the communication space of
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the North Atlantic right whale, a 6% decrease in communication space was recorded, increasing to 97% as the vessel came within the communication space. Although masking was still an issue for fin and humpback whales, the effect was smaller. Long-range communication may not be as important to higher frequency odontocetes, but masking is still a concern. Jensen et al. (2009b) reported that in shallow water at a range of 50 m, a small vessel moving at 9.3 kilometres per hour (km h–1) can reduce communication range of bottlenose dolphins by 26%. This figure increased to 58% for short-finned pilot whales in deep water habitats. More recently, a study by Gervaise et al. (2012) noted that boat traffic in the Saguenay St Lawrence Marine Park, eastern Canada, had the potential to reduce the communication range of beluga whales by 85%.
Of all the cetaceans, beaked whales are unusual in their apparent vulnerability to injury or death associated with high intensity mid-frequency naval SONAR (Baird et al., 2008). Several aspects of beaked whale diving behaviour are considered potential factors related to susceptibility to anthropogenic noise. Due to limited oxygen supplies at the end of a long dive, an animal may have limited abilities to display any ‘normal’ avoidance behaviour (MacLeod and D’Amico, 2006). Deep-foraging dives are known to exceed 1 h in duration, with slower ascents than descents, and evidence suggests that these deep dives are followed by a period of progressively shallower ‘bounce’ dives (Tyack et al., 2006). Bounce dives may serve as recompression dives to reduce the likelihood of gas embolisms (Cox et al., 2006). Mass stranding events of Cuvier’s beaked whales are thought to coincide spatially and temporally with naval exercises (Frantzis, 1998; Balcomb, 2001; Jepson et al., 2003; Fernández et al., 2005, 2012; McCarthy, 2007). An atypical mass stranding of 12 Cuvier’s beaked whales was reported along the coast of Greece on 12–13 May 1996 (Frantzis, 1998). The stranding of these whales coincided with the North Atlantic Treaty Organisation (NATO) acoustic trials, which took place on 11–15 May 1996. It was hypothesised that the stranding was the result of exposure to LFA SONAR (Section 3.11); but as no gross or histological abnormalities were found in the beached whales, the cause could not be confirmed; however, these stranded beaked whales showed other characteristics unlike those that have occurred elsewhere, suggesting that the cause of stranding had a large synchronous spatial extent and a sudden onset (Frantzis, 1998). In March 2000, following nearby naval MFA SONAR operations, a mass multi-species stranding event occurred in the Bahamas. The majority of animals were beaked whales from the family Ziphiidae, but two minke whales and one spotted dolphin also stranded. Some animals were returned to the sea, but many that live-stranded died, and the survival rate of those rescued is unknown. Post-mortem examinations showed signs of haemorrhaging in the inner ears and cranial spaces of beaked whales. Other injuries such as renal capsular haemorrhage, larynx bruising and heart lesions were also recorded for one well-preserved beaked whale. All injuries were consistent with impulse trauma, which most likely resulted from SONAR operations (Balcomb, 2001). Investigations were carried out on stranded beaked whales in the Canary Islands with acute and chronic tissue damage as a result of the formation of in vivo gas bubbles (Jepson et al., 2003; Fernández et al., 2005). Fourteen beaked whales stranded close to the site of a naval exercise within four hours after commencement of MFA SONAR (Section 3.11) activity. Necropsies were carried out on some stranded animals and intravascular
bubbles were found in several organs. The lesions found in stranded animals were said to be consistent with acute trauma. The formation of these bubbles could be in response to SONAR exposure, with a change in behaviour of normal dive patterns, for example, accelerated ascent rate, which as a result causes excessive nitrogen super-saturation in the tissues, as occurs in decompression sickness (Jepson et al., 2003). The whales became stranded and died due to cardiovascular collapse during beaching (Fernández et al., 2005). A subsequent stranding of four Cuvier’s beaked whales occurred in the Canary Islands in July 2004, just a few days after a naval exercise had been carried out in the area. Data collected from the animals suggested that it was an atypical stranding, possibly related to the naval exercise. Post-mortem analysis showed evidence of fat emboli in all three animals examined (Fernández et al., 2012). It is important to note that, it is not just Source Level (SL) and frequency that provokes reactions, but also the type of noise. For example, along with actual and simulated SONAR sounds, Tyack et al. (2011) played simulated killer whale calls to Blainville’s beaked whales. Reactions, which included cessation of clicking, slower ascent rates, disruption of foraging and avoidance, occurred at lower SLs and for prolonged periods when killer whale sounds were played.
Noise and industrial activity has the potential to impact marine mammals indirectly by affecting their prey species. Many species of marine fish utilise low frequency sound, usually around 0.05–0.4 kHz (Popper et al., 2003) for communication and to sense the environment around them for predators, prey and potential mates (Scholik and Yan, 2002). Noise, which overlaps with these frequencies and thus masks signals, therefore has the potential to reduce chances of survival or reproductive success. Threshold shift has been reported for the fathead minnow (Pimephales promelas) after exposure to varying durations of white noise of 0.3–4 kHz, and SPLs of 142 dB re 1 µPa. Following a 24 h exposure, recovery to baseline levels had still not occurred for 1.5 and 2 kHz after 14 days (Scholik and Yan, 2001). Low frequency noise can also affect the swim bladders of fish physically (Erbe and Farmer, 2000), or damage sensory hair cells of cephalopods (Packard et al., 1990; Andre et al., 2011).
Marine Mammal Hearing
Knowledge on hearing abilities is crucial to understanding how noise could potentially affect marine mammals. Hearing is discussed comprehensively within the following section, but more detailed reading can be found in Richardson et al. (1995), Au (2000), Ketten (2000), Nachtigall et al. (2000, 2007a), Erbe (2002), Nachtigall (2004) and Mooney et al. (2012).
In all studies of vertebrate species, an animal’s sensitivity to sound varies as a function of frequency. Most species show low sensitivity at very low frequencies and at very high frequencies (the meaning of very high and very low is different for different species). An audiogram is a graph of the minimum detectable sound intensity as a function of frequency (Nachtigall et al., 2000), and usually takes the form of a U-shaped curve (Figure 1.2).
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Figure 1.2 Example of audiograms for five species of marine mammal.
Principally, an audiogram is obtained by testing the response of an individual to sounds of differing frequencies and intensities (loudness). As trials progress, intensity of a single frequency sound is reduced until no response is observed. This level is considered the threshold (i.e. the lowest intensity at which the subject can detect a sound of that frequency). In humans, conducting audiograms is as straightforward as asking an individual to press a button when a sound is heard, but in marine mammals the process is a little more complicated. Two methods, behavioural or electrophysiological, are used commonly. Behavioural methods are time consuming and require subjects to be highly trained, and consequently have been produced for a small number of marine mammal species only. Subjects are trained to respond in a specific way depending on if a sound has been heard; usually this involves a go/no go response or a choice between two stations. Prior to start, subjects are positioned at a listening station. The initial sound played is above the known threshold for the subject at a chosen frequency. Intensity is decreased in small, often 2 dB, steps, until the signal goes undetected. Electrophysiological methods, referred to commonly as Auditory Evoked Potential (AEP) or Auditory Brainstem Response (ABR) methods, assess the relative sensitivity of the auditory system to different frequencies. AEP methods are invasive, and involve connecting electrodes to the auditory end organ inside the head of the subject. ABR methods are less intrusive, as electrodes are attached externally to the head to record far-field measurements of the brainstem auditory nuclei. When sounds are played, a waveform response is evoked, which is picked up by electrodes. Again, intensity is reduced until no response can be measured. AEP and ABR methods are useful when subjects cannot be kept in captivity, or trained easily. Audiograms have been produced for odontocetes, pinnipeds and the polar bear. Obtaining audiograms for mysticetes is particularly difficult because of their size and unsuitableness for retention in captivity, which has led to the use of predictive methods. Research on terrestrial mammals has shown that anatomy and properties of the ear, in particular the basilar membrane, can be used to predict frequencies at which
the auditory system will be sensitive (Greenwood, 1990). Given that the mysticete ear is essentially a conventional mammalian ear (Ketten, 1997), it is possible to apply this theory to marine mammals, and thus estimate hearing sensitivity using a model based on analysis of the middle ear. Audiograms applying variations of these methods have been produced for humpback whale (Houser et al., 2001), minke whale (Tubelli et al., 2010, 2012) and North Atlantic right whale (Parks et al., 2007). Ideally, audiograms would span the entire dynamic hearing range of the test species, where below and above frequencies tested, sounds become infrasonic or ultrasonic. For technical reasons, obtaining audiometric data for marine mammals is, at best, challenging, and in some cases impossible, due to sound propagation physics. For example, the following back-of-the-envelope calculation can be used to determine the size of aquarium that would be required to test whether a harbour porpoise could detect a 1 Hz signal, typical of some drilling rig frequencies (Todd et al., 2009a):
Where λ is wavelength, ʋ is velocity, and ƒ is frequency. Given the speed of sound (ʋ) in water is roughly 1,500 metres per second (m s–1), a simple rearrangement of this equation would mean that the aquarium would need to be 1,500 m deep, and 1,500 m wide in order for the complete 1 Hz signal to be transmitted (and have a hope of being detected) by the porpoise. This is complicated further by the fact that sound reflects off water surface, and tank boundaries, producing a complex sound field. Measuring sound levels is almost impossible, and thus levels must be measured at the exact point in which an animal detects a sound to be accurate. This problem has been at the centre of a number of conferences recently, so inferences on low frequency hearing capabilities of species are generally limited to the lowest frequency of sounds played to these animals in aquaria. Another drawback of audiograms is small sample sizes; hearing has been tested on just a small number of any one species. The situation is further complicated by the occurrence of naturally deaf or hard of hearing individuals (Ridgeway and Carder, 1997). Human hearing changes with age and sex, and ability to detect sounds, or communicate in noisy environments diminishes over time. The same is thought to be true of marine mammals, but the extent to which it occurs is unknown. As a result, to date, there are insufficient sample sizes of audiogram data for a single marine mammal species to have captured this variation in hearing sensitivity between individuals. Where audiometric data are not available, closely related species have been used as a proxy, or alternatively the frequencies of vocalisations have been used to estimate hearing ranges. For example, whales producing signals in the range below 1 kHz are expected to have a higher hearing sensitivity in the low frequency range than whales producing sounds in the range above 100 kHz (NATO, 2004), but in some species it should be noted that hearing ranges can extend beyond vocalisation ranges.
At present, audiograms exist for 38 marine mammal species: 3 mysticetes, 22 odontocetes, 10 pinnipeds, 1 sirenian, 1 mustelid, and the polar bear. In air and underwater hearing ranges for all 38 species have been listed in Tables 1.3 and 1.4.
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Table 1.4 Marine mammal subspecies hearing ranges. Only species with audiograms or estimated audiograms are included, and for brevity, scientific names are excluded but are included in Table 1.2. Data are only included when subspecies scientific or common names are specified within the publication. To overcome discrepancies in accepted subspecies, this table follows the taxonomic list of marine mammals composed by the Committee on Taxonomy (2014). Freshwater species are excluded.
Sound exposure criteria
Species are sensitive differentially to sound at different frequencies. In humans, it has been shown that this differential sensitivity is related to an individual’s perception of the loudness of a sound (the sensation of loudness is expressed in phons). To account for differential sensitivity in humans, measures of sound may be normalised or weighted by applying a filter that matches these plots of perceived loudness. Weightings are applied numerically by adding or subtracting particular values on the decibel scale. The weighting applied commonly for humans, called A-weighting, is based on perceptions of loudness for rather quiet signals (40 phons). Other weighting curves have been developed that better predict human perception of other types and levels of noise. For example, D-weighting was developed to predict perception of intense sounds such as those from loud low-flying aircraft. If weightings are to be used, those based on higher sound levels might be more appropriate in any assessment of a sound’s ability to induce hearing damage; however, in spite of strong criticism from acousticians, A-weighting has been used in interpretation of a sound’s ability to induce hearing damage in humans. This is largely for the sake of simplicity, and because the A-weighting is available widely on sound level meters. A species weighting approach, which is essentially an A-weighting type scheme for many different species, has been produced and is known as the dBht (Nedwell, 2007; Nedwell et al., 2007b). In essence, it is sound level in dB stated relative to the hearing threshold (ht) of a species, hence dBht (species); see Terhune (2013) for an example of the weighting applied to harbour porpoises. By applying filters based on audiograms for different species, dBht aims to predict at what level a sound will cause auditory damage and/or elicit a behavioural response. It provides a weighted measure of the total acoustic power of a sound, which can be used to produce simple exposure criteria. For
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example, if sound emitted 90 dB above a species’ hearing threshold is thought to cause strong avoidance reactions, criteria can be put in place during planning operations, which states that noise cannot exceed 90 dBht for the species in question. The dB(ht) is based on a number of assumptions, and is reliant on accurate audiograms, which are largely confined to smaller species that are practical to keep in captivity. Even audiograms, which are available, tend to rely on measurements taken from a small number of individuals, so generalisations about their accuracy for a species must be made with caution. For species without audiograms, closely related species need to be used as a proxy. Whilst the dBht metric can, and is, used for multiple taxa, including fish, Southall et al. (2007) devised a matrix which focuses specifically on the effect of sound on cetaceans and pinnipeds. The frequency weighting applied is known as M-weighting and resembles the C-weighting used in humans for high amplitude sounds. Unlike the dBht metric, which considers all species separately, the noise exposure criteria created by Southall et al. (2007) groups marine mammals based on their functional hearing ability (Table 1.5); five groups are defined, with all species in that group considered to be equally receptive to noise. Table 1.5 Functional marine mammal hearing groups defined by Southall et al. (2007) for application of M-weighting. Source: Southall et al. (2007). Functional hearing group
Estimated auditory bandwidth
Low frequency cetaceans
7 Hz–22 kHz
Mid frequency cetaceans
150 Hz–160 kHz
High frequency cetaceans
200 Hz–180 kHz
Pinnipeds in air
75 Hz–75 kHz
Pinnipeds in water
75 Hz–30 kHz
Considering reactions are not consistent for all types of sound, the exposure criteria address single pulse, multiple pulse and non-pulsed sounds separately. Using calculated TTS onset levels, and TTS growth rates, estimated from terrestrial mammals, PTS onset levels were estimated for each functional hearing group, and used as an indication of hearing damage. Results are expressed as both SPL and M-weighted SEL. Combining all components results in a matrix of 15 cells, for each functional hearing group the SPLs, and SELs thought to cause PTS onset are included for the three types of noise. Criteria also include a behavioural matrix, based on literature reviews of observed effects of different types of noise on marine mammal species. The noise exposure criteria are considered precautionary, as the M-weighting functions are almost flat between upper and lower cut-off frequencies, meaning the same level of effect is considered to occur for the upper, lower and middle part of the hearing range. Similar limitations exist, as for the dBht, in that the criteria are based on audiograms of a few species. For example, low, mid and high frequency cetacean data are based on TTS onset levels of the beluga whale and bottlenose dolphin, whilst pinniped criteria are based on the harbour seal, northern elephant seal and Californian sea lion. Focusing on the effects of naval activities, Finneran and Jenkins (2012) produced criteria
similar to the noise exposure criteria devised by Southall et al. (2007), but all marine mammals have been included and divided into seven functional hearing groups (Table 1.6). Table 1.6 Functional marine mammal hearing groups as defined by Finneran and Jenkins (2012) for application of EQL (EQual Loudness) weighting. Source: Finneran and Jenkins (2012). Functional hearing group
Estimated auditory bandwidth
Low frequency cetaceans
7 Hz–22 kHz
Mid frequency cetaceans
150 Hz–160 kHz
High frequency cetaceans
200 Hz–180 kHz
Phocids in air
75 Hz–30 kHz
Phocids and sirenians in water
75 Hz–75 kHz
Otariids, odobenids, ursids and mustelids in air
100 Hz–35 kHz
Otariids, odobenids, ursids and mustelids in water
100 Hz–50 kHz
The weighting function used varies slightly from M-weighting, as it takes into account new data not available when M-weighting was developed. Weighting functions for humans are based on equal loudness contours, which for the most part are not available for marine mammals. Finneran and Schlundt (2011) calculated EQual Loudness (EQL) contours for the bottlenose dolphin from subjective loudness measurements; these were then used to compose a new weighting function, the EQL weighting. One advantage is that it better accounts for increased susceptibility to noise of certain frequencies. Subjective loudness measurements exist only for bottlenose dolphin, so the EQL weighting is restricted in its use, but can be extrapolated to closely related species, such as high and low frequency cetaceans. For this reason, two types of weighting function are used, Type I, which is similar to M-weighting, and is based on estimated hearing ranges, and Type II, which is a modified version of M-weighting, and which incorporates EQL weighting; it is used on cetaceans only. Physiological and behavioural exposure criteria have been calculated for explosive and non-explosive sources. Physiological criteria have been estimated using similar methods to Southall et al. (2007), but behavioural criteria are based on a Behavioural Response Function (BRF) which assesses the likelihood of a behavioural reaction to received SPL. The BRF assumes that the risk a sound poses to marine mammals is negligible if the SPL is below a certain value; low frequency marine mammals are assessed separately to other functional hearing groups. In the case of explosions, the risk of mortality or blast injury is also considered. The result is two exposure matrices; one for SONAR and other sound sources, with 30 cells, and one for blasts with 48 cells. The development of TTS, and the risk of hearing damage or PTS, is a function of received acoustic energy, which accumulates throughout the period of an activity. Over time, animals in the vicinity are expected to move away from the noise. To assess risk of hearing damage and determine required performance and efficacy of mitigation measures, a cumulative exposure model can be applied, which incorporates animal movement and propagation loss with range as well as the source characteristics and duty cycles of the sound sources. The fleeing animal model devised by Lepper et al. (2010) is one example. A summary of the different sound exposure criteria is provided in Table 1.7.
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Table 1.7 Sound exposure criteria. Weighting
Measures sensitivity of human hearing for quiet signals (40 phons)
Measures sensitivity of human hearing in high noise level conditions
Measures sensitivity of human hearing for intense sounds such as those from loud low-flying aircraft
Generalisation of A-weighting used to assess the hearing sensitivity of a wide range of species
Cetaceans and pinnipeds
Based on C-weighting, but weighting reflects hearing ranges of five functional hearing groups (Table 1.5)
All marine mammals Frequency weighting based on equal loudness contours for the bottlenose dolphin obtained from subjective loudness measurements
Mitigation Measures 2.1
Mitigation measures have been developed to minimise acoustic and physical disturbance to marine mammals and other protected species during certain industrial activities and ensure compliance with relevant legislation. Since 1998, when the JNCC produced guidelines concerning acoustic mitigation measures for marine mammals during seismic surveys (JNCC, 1998), advisory and regulatory bodies worldwide have adopted similar standards, which now exist for a number of regions and for a range of industrial activities. Guidelines may appear to lack statute, but regulatory authorities often ensure guidelines are legally binding via their licensing agreements for industrial activities. Data collected by MMOs or PAM Operators under guidelines also function to increase existing knowledge of species distribution, ecology, behaviour, or responses to offshore operations. In order to maximise protection, guidelines are specific to survey region and local species. For example, long dive times are considered when deciding pre-watch lengths for deep diving species, such as sperm whales; similarly, PSOs are employed in areas where other potentially sensitive species exist, such as turtles. Guidelines also vary for industrial activity and may be stricter for certain activities considered more harmful to marine life. Forexample, JNCC guidelines state a default exclusion zone with a radius of 1 km for explosives, which is twice the default for seismic and piling operations. In New Zealand and Australia, seismic guidelines vary depending on sound levels produced. For example, New Zealand specify three types of seismic survey, level one is largest (>427 inch cubed (in3)), followed by level two (151–426 in3), and level three (1.5 km.
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Soft-starts, which are conducted each time the sound source is activated, can be defined as a gradual increase in power output over a set period. They are undertaken whenever possible, to allow any animals within the vicinity to leave the operations area prior to full power being reached. If applicable to operations, guidelines specify the duration and method of soft-start, which must be carried out. For example, a single, low-powered airgun is activated first, and fired a set number of times. Gradually, higher powered airguns are added, until all airguns are firing at maximum capacity required (i.e. the source is working at full power). The length of time a soft-start takes is considered carefully during planning stages, to minimise noise exposure and amount of disturbance to marine mammals. Given that soft-starts increase the amount of noise exposure, lower and upper time limits are usually defined; typically, soft-starts have to be between 20 and 40 min. In Ireland, the NPWS guidelines for SONAR operations state that, if a softstart is not possible, the sound source should be switched on and off over a 20 min period.
Sound Source Testing
Prior to testing sound sources, seismic survey guidelines state a general requirement for a full start-up procedure including pre-watch and soft-start to the necessary test power. Not all sound source tests emit noise, for example a drop test of seismic airguns (Section 5.21.6), so mitigation is not required in all cases.
Operation Issues and Breaks in Sound Production
Unintentional breaks in sound production can, and do occur, due to operational issues. Guidelines define limits to which the sound source can be inactive before a full start-up procedure is needed. Limits range from 5 min in Brazil or Greenland, up to 30 min for piling or dredging activities in Ireland. Line changes for seismic surveys are also discussed within guidelines. Instead of imposing a full shut-down, guidelines may state a maximum time limit for shooting between lines at full power, and if exceeded, noise source power will need to be reduced, or switched off, until start of the next line. In the UK, Brazil, and Greenland, the limit is 20 min, but it is 60 min in Ireland.
Delays and Shut-Downs
Delays to start-up can occur if marine mammals or other protected species are sighted within the exclusion zone during pre-watch. Length of shut-down varies between 30 and 60 min after the last sighting. Once soft-start has begun, UK guidelines state operations can continue regardless, while in Ireland, operations can be halted until full power has been reached. In some regions, such as the GoM, Australia, and New Zealand, a shutdown can occur at any time.
Night-Time and Low Visibility Working
Visual observations, for the most part, are limited to daylight hours, good visibility, and preferable weather conditions. If circumstances are not conducive to visual watches, PAM is sometimes required, and other times strongly recommended. In the case of seismic work, operations may be able to continue, but not necessarily start without visual watches, whilst explosions are only permitted in daylight when visual watches are possible.
Guidelines specify general requirements for MMO and PAM reports (see Chapter 10).
Sources of Anthropogenic Noise 3.1
Natural and anthropogenic sources contribute substantially to ocean noise levels. Natural noise can be physical, for example ice deformation, earthquakes, lightning, and volcanic eruptions, or biological, for example snapping shrimp. SLs and frequencies of some are listed in Section 7.2.5, but the focus here is on anthropogenic noise sources. When discussing noise, it is important to note the difference between ambient and background noise. These terms are used interchangeably, but in reality, this should not occur. Ambient noise is the background noise, excluding self-noise generated by receiving hydrophone and any source that can be identified individually (e.g. a passing ship) (Cato, 2008). There are cases where an identifiable noise may be considered as ambient because it is ‘always’ present, for example, shipping traffic in a busy port, or a large group of marine mammals making continuous vocalisations. While the general source of these noises can be identified, individual ships or animals cannot be distinguished. Background noise is everything (i.e. ambient noise plus other individually identifiable noises). Noise pollution from anthropogenic sound sources can be intermittent, impulsive, continuous, high or low intensity, or combinations of these simultaneously. Increased use of the marine environment for a range of activities, such as geophysical exploration (for oil and gas), wind farm construction, military exercises, and commercial shipping, has resulted in noise levels that are estimated to be ten times higher today than a few decades ago. Spectral characteristics, including frequency and SL, are specific to each activity, as are the effects on marine mammals. The requirement for MMOs and PAM Operators thus encompasses many types of commercial activity, so it is important to understand each noise source individually. This chapter presents an overview of each sound source, including comprehensive descriptions of acoustic properties. More detailed reading about sources of anthropogenic noise can be found in Richardson et al. (1995), Hatch and Wright (2007), and Hildebrand (2009). A very brief summary of potential effects of noise sources on marine mammals is presented for each category, but the interested reader is directed to sources of further reading; documented effects of anthropogenic sound in general are discussed in detail in Section 1.4. For a full explanation of sound units and terms mentioned within this chapter, refer to Chapter 7.
Sources of Anthropogenic Noise
Vessels are one of the main sources of anthropogenic noise in the ocean today, and commercial shipping is one of the biggest contributors. Levels are increasing continually, as not only the number of vessels increases, but also their size and propulsion power. Shipping noise is not distributed uniformly throughout the ocean, but is instead concentrated in specific areas, such as shipping lanes and in busy ports and harbours. Shipping activity is greatest in the northern hemisphere. The majority of broadband sound emanating from vessels is created by bubble cavitation as propellers rotate, but additional noise sources include mechanical parts and movement of water around the hull. Noise from vessels is predominantly low frequency, but SLs will vary depending upon a number of factors, including vessel type, size, hull shape, propulsion system, and speed. Given the low frequency nature of noise, sound from a single vessel can travel great distances, and will likely combine with, and become indistinguishable from, noise emanating from other vessels, thus increasing ambient noise levels further. Consequently, to understand noise levels created by shipping in a single area, the number and size of vessels operating, and local propagation conditions all need to be considered. Noise from smaller vessels, utilised for recreational purposes or, for example, whale watching, is often localised in coastal areas. This means they are of less concern when discussing the effects of shipping over wide ranges, but localised noise can dominate a single area. SLs remain around 160–175 dB re 1 µPa @ 1 m and noise is still predominantly low frequency, but perhaps less so than large commercial ships, with a greater proportion of noise above 1 kHz. Jensen et al. (2009b) measured the noise levels of two vessels, representative of whale watching, recreational, and small research vessels at two speeds, 9.7 km h–1 and 18.5 km h–1, in Koombana Bay, Tenerife. Estimated broadband SLs for a vessel with a two stroke 135 horsepower outboard engine were 139 and 149 dB re 1 µPa rms at @ 1 m and 149 dB re 1 µPa rms @ 1 m, for the two speeds respectively, and frequencies were 0.2–40 kHz (see Section 7.2.4 for an explanation of Root Mean Square, RMS or rms). Similarly, estimated broadband SLs of a four stroke 80 horsepower outboard engine were 138 and 152 dB re 1 µPa rms @ 1 m, for frequencies of 0.2–40 kHz. Noise levels were found to be higher when hydrophones were located to the side of the vessel compared to the front. In terms of commercial vessels, there are many different types, such as passenger and cargo transport, tankers, fishing, dredging, offshore supply, research/survey, icebreakers, and military vessels. Each vessel has its own unique acoustic signature. McKenna et al. (2012) measured noise levels of seven types of commercial vessel operating in the Santa Barbara Channel. A High Frequency Acoustic Recording Package (HARP) was deployed to record the sound levels of ships, and results were then combined with ship traffic information collected by an on-board Automatic Identification System (AIS). Received Levels (RLs) were recorded at the closest point of approach to the HARP, which ranged between 2.6 and 3.5 km for all vessels recorded: six container ships, four vehicle carriers, five bulk carriers, four open hull cargo ships, four chemical product tankers, three crude oil tankers and three product tankers. RLs varied from 106 to 118.9 dB re 1 µPa2, with the lowest recorded for the chemical products tanker, and the highest for the container ship; frequencies ranged between 0.02 and 1 kHz. To make results more comparable, SLs were estimated, and ranged from 182.1 dB re 1 µPa2 @ 1m for the crude oil tanker to 188.1 dB re 1 µPa2 @ 1 m for the container ship. Again, frequencies ranged 0.02–1 kHz.
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Using RLs, Allen et al. (2012) estimated the SLs of four vessel types in the Bar Harbour, Maine (USA). Peak frequencies of the four cruise ships measured varied from 40 to 48 Hz, whilst estimated SLs ranged from 196 to 219 dB re 1 µPa @ 1 m. In comparison, the one high speed craft measured had a peak frequency of 44 Hz and SL of 210 dB re 1 µPa @ 1 m, whilst the three catamarans ranged from 44 to 46 Hz in frequency and had a SL 189–201 dB re 1 µPa @ 1 m. Fishing vessels had the highest sample number of 16, and the lowest SL, which ranged from 95 to 133 dB re 1 µPa @ 1 m, with peak frequencies 43–51 Hz. Low frequency noise produced by commercial vessels, and the potential for longrange propagation, are the highest risk for marine mammals. In particular, low frequency mysticetes will be at increased risk of masking. Where shipping lanes coincide with key areas, collisions can occur, and avoidance of harbours and busy ports is a possibility. For more information on effects of vessels on marine mammals, see papers such as Laist et al. (2001), Jensen and Silber (2003), Buckstaff (2004), Southall (2005), Aguilar Soto et al. (2006), Vanderlaan and Taggart (2007), Y. Simard et al. (2008), Jensen et al. (2009b), Lusseau et al. (2009), Gervaise et al. (2012), Allen et al. (2012), Noren et al. (2012), Pirotta et al. (2012), Reeve (2012), Rolland et al. (2012) and Tripovich et al. (2012).
Offshore Wind Farms
Offshore wind farm construction uses a combination of operations, such as pile driving, drilling, or dredging, which are addressed elsewhere within this chapter. This section discusses routine and regular operational noises from an offshore wind farm. For a comprehensive review of wind farm-related noise see Nedwell and Howell (2004). Operational noise emanates from multiple sources, such as rotating turbine blades, structural vibrations caused by mechanical parts, the movement of air over the turbine, and impact from waves (Nedwell et al., 2003). Sounds from the movement of air over turbine blades is primarily air-borne, but mechanical noise is transmitted into the ocean through foundations of various designs, such as monopod or monopole, gravity base, space frame (tripod or quadropod), semi-submersible, and spar. Used in shallow water, monopoles are single steel tubes, whilst gravity base structures are composed of a precast concrete shell filled with sand, gravel or stones. Utilised in deeper water, space frame foundations are composed of four cylindrical steel tubes that extend outwards from a central pile. Semi-submersible and spar are examples of floating foundations. Semi-submersible foundations consist of a buoyant platform anchored to the seabed via cables. Spar foundations are more complex, and are composed of a cylindrical buoy, weighted by ballast in the lower portions. The upper portions are empty, to increase buoyancy. In general, noise emitted from offshore wind farms is considered to be low in comparison to other sources, but unlike most others which are transient in nature, wind farm noise could be considered a permanent feature in the environment. Noise measurements were taken by Nedwell et al. (2007a) both inside and outside the vicinity of three wind farms. Average RLs, for a broadband frequency range of 1 Hz–120 kHz, inside North Hoyle (UK), Kentish Flats (UK) and Scroby Sands (UK), were 128, 114, and 130 dB re 1 µPa respectively. Underwater noise measurements of three operational wind farms were also taken by Tougaard et al. (2009). Noise was only audible above background noise levels for frequencies less than 315–500 Hz on all occasions. The highest received SPL of 126 dB re 1 µPa rms was recorded at 25 Hz, 14 m from Vindeby wind farm (Denmark). Received
Sources of Anthropogenic Noise
SPLs of 110 and 106 dB re 1 µPa rms were recorded for Bockstigen-Valar (Sweden) and Middelgrunden (Denmark) wind farms at 160 and 25 Hz respectively; both measurements were taken at a distance of 20 m. Noise from wind farms has generally lower SLs than other operations, and according to Nedwell et al. (2007), noise exceeds ambient levels only within the immediate vicinity of a farm, but any effects will be prolonged. In some cases, positive effects can result from the construction of offshore wind farms, as they form artificial reefs, and thus attract fish and foraging marine mammals. See Koschinski et al. (2003), Madsen et al. (2006b), Thomsen et al. (2006), Tougaard et al. (2008, 2009), Edren et al. (2010), Scheidat et al. (2011), and Teilmann and Carstensen (2012) for further information.
Tidal turbines convert the energy of tides into electricity. Unlike other renewable energy sources, such as wind or solar, tides can be used to generate predictable power. Tidal turbines are still at the R&D stage, but as the technology improves, so will the quantity and efficiency of electricity production. Noise from tidal turbines will vary substantially, depending on blade design, water depth, water velocity, and local bathymetry, but available data are limited, and noise measurements scarce. Noise from tidal turbines has been discussed by Wang et al. (2007), who estimated a SL of 131 dB re 1 µPa @ 1 m at 20 Hz. A review by OSPAR (2009) also briefly addresses tidal turbines, stating that SLs will vary between 165–175 dB re 1 µPa @ 1 m. Noise will have a broadband frequency range of 10–50 kHz. Like noise measurements, environmental impacts are relatively unknown, but collision is one of the threats posed to marine mammals. Others could include masking, avoidance reactions, and disturbance of prey species. For further reading see Wilson et al. (2007), Boehlert and Gill (2010), Simmonds and Brown (2010), and Wilson and Carter (2012).
Marine dredging is an excavation activity carried out predominantly in shallow seas with the purpose of physically removing substratum from the seabed and disposing of it at a different location. Applications can include deepening or widening of shipping channels and harbours, extraction of aggregates or minerals for construction projects, land reclamation, creation of artificial islands, replenishment of coastally eroded materials on public beaches and removal of materials prior to construction (foundations) or removal of contaminated sediments from the environment. Dredging is also used for fishing activities, although dredging in that context is not discussed here. The four main types of dredger used are Cutter Suction Dredgers (CSDs), Trailing Suction Hopper Dredgers (TSHDs), grab dredgers, and backhoe dredgers. Mechanisms used by the different dredgers vary substantially; consequently, so does the spectral content of noise produced (Figure 3.1). The type of dredger used depends on a number of factors including the extraction material, purpose and size of dredging operation, and marine environmental factors.
MMO and PAM Handbook
Figure 3.1 Common examples of dredgers and possible sound sources (a) Cutter Suction Dredger; (b) Trailing Suction Hopper Dredgers; (c) Grab; (d) Backhoe (adapted from CEDA, 2011).
Both CSDs and TSHDs use suction to remove material from the seabed, whilst grab and backhoe dredgers use a range of buckets to scoop material off the seabed. When dredging hard sediments, CSDs are a viable option, as a rotating cutter head is lowered into the water to break up material. A suction tube is then used to transfer sediment onto a barge or through pipelines to land. The drag head or suction tubes of TSHDs are towed along the seabed as the vessel moves, which can be used in conjunction with CSDs to collect loose sediment once it has been broken up. Backhoe and grab dredgers are moored when operational, and require the use of transportation barges. When operating from a grab dredger, a crane is used to lower a clamshell bucket into the water, which scrapes material off the seabed. Once closed, the bucket is brought to the surface, and sediment deposited onto a separate barge. Backhoe dredgers are similar, but a hydraulic arm operates a bucket from the rear of the vessel, which scoops material off the seabed, again depositing it onto a barge. Dredging produces continuous, broadband, low frequency sound, below 1 kHz, with SPLs between 168–186 dB re 1 μPa @ 1 m. One of the earliest dredging noise studies was carried out by Greene (1987). Two CSDs and three TSHDs were tested in various locations and in general, TSHDs were louder. RLs of 133 and 140 dB re 1 µPa were recorded 0.19 and 0.2 km from operating CSDs respectively. Frequency ranged between 20 Hz–1 kHz. Noise produced by TSHDs has been measured on a number of occasions, and is generally louder than that produced by CSDs. At a range of 0.93 km, for frequencies between 20 Hz and 1 kHz, Greene (1987) reported RLs of 142 dB re 1 µPa for a TSHD whilst loading. In comparison, Clarke et al. (2002) measured SPLs of 140 dB re 1 µPa for frequencies between 70 Hz and 1 kHz, whilst Parvin et al. (2008) estimated SLs of 186 dB re 1 µPa @ 1 m. More recently, Robinson et al. (2011) measured noise levels of six TSHDs, stating that operating dredgers are similar in noise level to that of merchant vessels, and that the primary source of noise is produced as material passes through the drag head, suction pipe and pump. Dredging gravel produces more noise than dredging sand. Noise produced by grab dredgers varies substantially with stage. Dickerson et al. (2001) measured SPLs at 0.15 km from a grab dredger throughout the entire process. The
Sources of Anthropogenic Noise
loudest SPLs of 124 dB re 1 µPa @ 1 m were recorded at peak frequencies of 0.16 kHz, when the bucket made impact with the sea floor; Clarke et al. (2002) also found this to be loudest stage. The low SLs produced whilst dredging suggest physical injury to auditory systems of marine mammals is unlikely; more probable are masking and behavioural effects. Collisions are possible, but unlikely due to the slow speed of dredgers. Sedimentation and increases in turbidity are unlikely to affect marine mammals that use echolocation, but could potentially impact those that rely more on sight. Indirect effects such as the destruction of habitats and changes in prey abundance and distribution should also be noted. For more detailed information on dredging and marine mammals see Richardson et al. (1990), IWC (2001), Gerstein et al. (2006), Thomsen et al. (2009), Tillin et al. (2011), Pirotta et al. (2013) and Todd et al. (2014).
Drilling and Production
Offshore drilling refers to a mechanical process in which a wellbore is drilled into the seabed, usually with a rotating drill bit. Drilling is used in construction and for location and extraction of hydrocarbon deposits. Multiple, specialised installations, such as drilling rigs, drilling ships, and artificial islands are used to conduct operations, but choice depends upon a number of factors such as depth, seabed conditions, and purpose. Mobile installations are used most commonly for exploratory work (e.g. jackup rigs; Figure 3.2), but permanent structures can be created if work is expected to continue over prolonged periods, for example, if reserves are found, and more wells need to be drilled.
Figure 3.2 Jack-up drilling rig showing possible sound sources.
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Drilling rigs and platforms are known collectively as offshore installations. Rigs explore for oil or gas, and platforms produce oil or gas. Both installations sit upon or are fixed to the seabed via legs or cable tensioners, or are floating semi-submersibles (discussed in Chapter 5), or a combination (e.g. semi-submersibles tensioned to the seabed). Considerable variation exists in offshore drilling installations. Jack-ups are mobile and have extendable legs, which are lowered to the seabed, raising the rig out of the water so the barge (main body of the rig) floats on the water once on site. Submersible rigs also require contact with the seabed, and like jack-ups, are limited to shallow water, unlike semi-submersible rigs, which can also be operated in deep water. The principle for submersibles and semi-submersibles is similar, in that the lower of two hulls is filled or emptied of air to alter buoyancy. When on site, air is discharged, causing the rig to sink. Submersibles sit on the sea floor, but semi-submersibles are only partly submerged, and kept in place by large anchors. Built to withstand extreme weather conditions, permanent platforms are heavy-duty structures. In shallow water, steel or concrete legs are attached to the seabed with piles, but other methods need to be applied in deeper water. Drill ships, which are used typically in deep water, are specialised vessels equipped with drilling apparatus; the drill is operated through a hole in the ship’s hull, known as a moon pool. To maintain position over a well, drill ships have mooring equipment and dynamic positioning, which is a computer-controlled system to maintain a vessel’s position and heading automatically by using its own propellers and thrusters. The ability to move between wells without the aid of other ships is advantageous, but drill ships are susceptible to sea conditions. In areas such as the Arctic, where drifting ice can pose problems for fixed platforms, artificial islands can be created from rock and gravel, from where drilling is then conducted. Noise emanating from fixed metal-legged rigs is considered generally to be relatively low level and at very low frequencies, approaching 5 Hz (DOI, 2004). Gales (1982) performed five field trips to 18 oil and gas installations engaged in drilling and/or production operations. These included semi-submersible drilling platforms, multilegged drilling rigs and production platforms, and a man-made production island. From bottom-founded platforms, Gales (1982) concluded that platform noise was minimal, and in Beaufort sea states >3 only just detectable over background noise, even when measured close to the platform. Measurements were all near-field, so source levels could not be calculated, but RLs were 119–127 dB re 1 µPa at a distance of 30 m, with the strongest tones around 5 Hz (Gales, 1982; Richardson et al., 1995a). Frequencies up to 1.2 kHz were recorded. Underwater noise from installations standing on metal legs would be expected to be relatively weak, because of the small surface area in contact with the water and the placement of machinery on decks well above the water (Richardson et al., 1995; Swift and Thompson, 2000). Acoustic measurements were taken by Todd et al. (2007) from a jack-up drilling rig in the North Sea during routine drilling activities. Sound levels generated by the rig were similar to previous measurements from metal-legged and bottom-founded platforms, both in level (120 dB re 1 µPa) and in the frequency range of dominant tonals (0.02–1.4 kHz). Sound levels were highly variable over short periods and generally varied by 15–20 dB between quietest (holding) and loudest (drilling) operations. The rig was significantly quieter than its associated support vessels at low frequency, although radiated noise levels were louder above 2 kHz. High frequency sound levels generated by the rig dropped rapidly above 8 kHz. Drill ships produce noise with tonal elements up to 0.6 kHz (Greene, 1987; Richard-
Sources of Anthropogenic Noise
son et al., 1995) and show higher noise levels than other types of installation, due to improved acoustic coupling through the drill ship hull (DOI, 2004). Most underwater noise from drill ships is still at low frequencies of primarily 0.02–1 kHz, where rotating machinery causes strong tones (Greene, 1987). Greene (1987) undertook sound measurements from a drill ship in the Beaufort Sea in waters 17 m deep at 0.7 km from the drilling source; sound levels of 122–125 dB re 1 µPa were recorded for frequencies between 0.02 and 1 kHz. On a separate occasion, sound measurements were taken 0.2 km from a drill ship in water 27 m deep, at this range, sound levels of 134 dB re 1 µPa were recorded for frequencies between 0.02 and 1 kHz (Greene, 1987). Richardson et al. (1990) found that RLs of industrial noise 4 and 10 km from a drill ship were, respectively, c. 118 and 109 dB re 1 µPa in the 0.02–1 kHz band. More recently, Kyhn et al. (2011) took underwater noise measurements of drilling and maintenance activities from Stena Forth, a double-hulled drill ship, in Greenland. In general, RLs were higher during maintenance works than during drilling. Assuming spherical spreading, and using RLs taken at 500 m and 1 km from the drill ship, SLs of 190 dB re 1 µPa rms were estimated for maintenance work and 184 dB re 1 µPa rms for drilling. At a range of 0.5 km from the drill ship, noise in the range of 0.1–>10 kHz was detectable during drilling activity, but by 2 km, noise levels were focused below 4 kHz. For maintenance activities, noise in the full range of 0.1–>10 kHz was detectable 38 km away. Underwater sounds produced by a Concrete Island Drilling Structure (CIDS) located in the Camden Bay region of the Alaskan sector of the Beaufort Sea were measured by Hall and Francine (1991). During idle and drilling operations, wideband SPL above 20 Hz at a range of 1,370 m was 89.7 dB re 1 µPa. With the high pass filter (see Section 9.7.4) set to 0.2 Hz, this increased to 111.9 dB re 1 µPa. Blackwell et al. (2004) made recordings of sounds underwater, in air, and of iceborne vibrations at Northstar Island, an artificial gravel island in the Beaufort Sea near Prudhoe Bay (Alaska). Measurements of four different scenarios (no drilling with no production, no drilling with production, drilling but no production, and drilling with production) were made during winter, when the island was surrounded by shore-fast ice. Drilling produced the highest underwater broadband (0.01–10 kHz) noise, but did not increase broadband levels in air or ice, relative to levels during other island activities. In all media, broadband levels decreased by 20 dB per tenfold change in distance. Noise did not exceed background levels at a distance of 9.4 km during drilling, and 3–4 km without. In the air and ice, background levels were not exceeded by 5–10 and 2–10 km, respectively, depending on wind, but irrespective of drilling. Like dredging, low SLs produced during drilling operations suggest that physical damage to the auditory system of marine mammals is unlikely. Masking is a distinct possibility for baleen whales, which utilise sound in the same frequency range, and the low frequency nature of sound sources means that in deeper waters, sound could travel substantial distances. Behavioural alterations and avoidance of habitats are also a possibility for baleen whales. Drilling noise is less of a concern for odontocetes, which vocalise and detect mid–high frequency sound, so although they may hear the noise, it is unlikely to cause any disturbance. To date, for harbour porpoises, no discernible effects of drilling noise on vocalisation behaviour have been documented (Todd et al., 2009b). For more information on potential effects of drilling and production on marine mammals see Richardson et al. (1990), Thomas et al. (1990a), Moulton et al. (2003) and Todd et al. (2009b).
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Floating Production Storage Offloading
Floating, Production, Storage, and Offloading (FPSO) installations are used by the oil and gas industry for the processing and storage of hydrocarbons extracted from nearby reserve wells by production platforms or subsea facilities. Hydrocarbons are piped to the FPSO via flexible risers, until the cargo is offloaded onto a tanker or, less frequently, transported via more permanent pipeline infrastructure. There are variations of floating installations, some of which include derricks for drilling exploration, such as Floating, Drilling, Production (or Processing), Storage, and Offloading (FDPSO) installations, while others, such as Floating, Storage, and Offloading (FSO) installations, are used exclusively for storage. Similarly, some of these floating installations are equipped with propulsion plants, while others are merely barges that need to be towed onto location. Floating installations are used preferentially in frontier-offshore locations (e.g. remote, deep water, and variable underwater topography), as they eliminate the need for seabed pipelines and associated infrastructure, and can be brought online quickly; consequently, they can offer a more economically attractive solution for hydrocarbon extraction from small and short-lived hydrocarbon reserves. Few noise measurements exist for FPSOs, but noise levels vary; FPSOs that utilise dynamic positioning produce considerably more noise than those that are moored. Mean monopole SLs recorded by Erbe et al. (2013) of six operational FPSOs ranged between 174 and 183 dB re 1 µPa @ 1 m for frequencies 0.02–2.5 kHz. The low frequencies produced by FPSOs mean mysticetes will be most susceptible to noise. Masking is a possibility, as are avoidance reactions, but in the absence of dynamic positioning, and whilst moored, noise levels should be relatively low in comparison to large commercial ships, but they will increase during transit. Minimal information on impacts of FPSOs on marine mammals is apparent in the literature.
Acoustic Mitigation Devices
AMDs, introduced briefly in Section 2.7, are used predominantly by the aquaculture industry to discourage seals from predating on fish, by the fishing industry to minimise the chance of marine mammal by-catch, or by a range of industries to warn off approaching marine mammals prior to commencing noisy activities. By producing loud acoustic signals, which cause annoyance or discomfort, AMDs aim to provoke avoidance reactions in marine mammals, thus excluding them from the vicinity of commercial activities. Traditionally, AMDs were separated generally into two types, low intensity ADDs and ‘pingers’ or high intensity AHDs, although nowadays the division is not so clearcut. To be effective, AMDs must produce noise within the hearing range of the target species, so AMDs designed to deter seals should have different spectral properties to those focused on dolphins or porpoises, although this is not always the case. Pulsed, irregular sounds are considered more effective at deterring marine mammals on a longterm basis, as habituation can occur. Much of what we know about the sound levels of AMDs comes from manufacturers, but research has shown that levels can vary substantially from those quoted (Kastelein et al., 2010b), and RLs also depend strongly on propagation conditions. To gain accurate insight into how AMDs could affect marine mammals in the field, trials need to be completed. Lepper et al. (2004) measured noise levels of three operating AMDs around a Scottish
Sources of Anthropogenic Noise
fish farm, the Airmar dB plus II, Ace Aquatec silent scrammer and the Terecos; spectral content differed substantially. The Airmar dB plus II signal, which is composed of pulsed tonal bursts, had a SL of 192 dB re 1 μPa @ 1 m, and a peak frequency of 10.3 kHz. In comparison, the Ace Aquatec produces random sequences of sounds composed of a mix of 28 different pulses. Maximum SLs of 193 dB re 1 μPa @ 1 m were recorded at a frequency of 10 kHz. The Terecos signal is highly randomised, with four different programs. For program one, a maximum SL of 177 dB re 1 μPa @ 1 m was observed at 6.6 kHz, but fundamental frequencies ranged from 1.8 to 3.8 kHz. Measurements of four AMDs were taken by Nedwell et al. (2010) in a flooded quarry in the UK. Three of the devices, the Ace Aquatec, Lofitech, and Marconi were designed to deter seals, but the Aquatec AquaMark 100 was intended specifically to deter harbour porpoises from gillnets. Mean peak-to-peak (p-p) RLs of 202 and 176 dB re 1 µPa were recorded at ranges of 1 and 80 m from the Ace Aquatec respectively. Frequencies ranged from 4 to 60 kHz but the majority of energy was focused between 10 and 30 kHz. Similarly, mean RLs of 200 and 174 dB re 1 µPa p-p were recorded at 1 and 80 m from the Lofitech, which had a peak frequency of 15 kHz, and harmonics up to 90 kHz. The Marconi was similar again, with mean RLs of 193 and 172 dB re 1 µPa p-p at 1 and 80 m respectively. The Aquatec AquaMark 100 was comparatively quieter, with mean RLs of 142 dB re 1 µPa p-p recorded at 1 m and 117 dB re 1 µPa p-p at 80 m. Frequency was also higher, with a range of 10–100 kHz, and peak at 45 kHz. Given their purpose, AMDs should cause some level of disturbance to marine mammals, and avoidance reactions are to be expected, but of concern are the effects AMDs have on non-target species. In areas where multiple AMDs are active, for example around fish farms, cetaceans could be displaced from key areas of their habitat. For more detail see Taylor et al. (1997), Jacobs and Terhune (2002), Johnston (2002), Morton and Symonds (2002), Olesiuk et al. (2002), Leeney et al. (2007), López and Mariño (2011), Berg Soto et al. (2013), Brandt et al. (2013), Götz and Janik (2013), Schakner and Blumstein (2013), and Waples et al. (2013).
Seismic exploration surveys are carried out in order to obtain information on the structure and stratigraphy of the seabed, which in turn, can be used to locate deposits of natural gas, crude oil, minerals, or water deposits. Acquiring a detailed image of the geological structure prior to excavation works optimises the success of exploration drilling activities. Specifics vary depending on survey requirements, but all seismic operations have a high-energy sound source and a receiver. A wave of energy, directed downwards, penetrates subsurface layers of the seabed (Figure 3.3). Reflections vary depending upon the acoustic properties of the sediment formations. Once received by pressure detectors known as hydrophones, or ground motion detectors, known as geophones, the signal is recorded digitally and analysed. Altering type, geometry, number of receivers, and density of the measurements ensures the survey is set for purpose.
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Figure 3.3 Example of a towed streamer seismic survey.
Suitable seismic sources produce short, discontinuous pulses with a good frequency response within the seismic bandwidth. Explosives, shockers, sparkers, and water guns have all been used in the past, but airguns are now used most commonly. Seismic airguns generate sound impulses by instantly expelling large volumes of high pressure air into the water. This produces an air-filled cavity that expands vigorously, then contracts and re-expands, producing loud sound with each oscillation. Although a single airgun can be used, most are towed on an array at depths of 4–8 m behind a vessel. Alternatively, vibration can be used as a seismic source. Vibroseis in the marine environment is used most commonly on shore-fast ice, where towed arrays are impractical. Vibration is produced by activating a line of hydraulic or electrically driven pads mounted to the underside of trucks. Signals are not impulsive, but instead have a duration 5–20 s, and have frequencies 10–70 Hz, but harmonics can extend well past this range (Richardson et al., 1995). Receivers are contained within a cable known as a streamer, and towed behind the vessel or placed on the seabed. Towed receivers are typically hydrophones, which detect pressure fluctuations of the sound wave as it returns; also contained in the streamer are electronic modules that transmit data to the vessel, an electrical transmission system, which provides the streamer with power, and stress members, which provide the strength required to tow the streamer. Streamer lengths vary depending on the size of area to be surveyed. Receivers placed on the seabed are often contained within cables, although ROVs can be used to deploy sensor nodes on the seabed. Sensors include hydrophones and geophones. Hydrophones measure Pressure waves (P waves), whilst geophones placed on the seabed detect ground motion, and the direction
Sources of Anthropogenic Noise
from which P and Shear waves (S waves) come from, giving a more detailed data set, which if three component geophones are used, can be multidirectional (IAGC, 2011). Most seismic exploration sounds are separated by quiet periods, though vibroseis is an exception (Richardson et al., 1995). SL varies with size and number of airguns used. Greene and Richardson (1988) measured seismic noise from multiple surveys in the Beaufort Sea. At a range of 1.9 km from a 1,708 in3 airgun array, Received Level (RL) was recorded as 179 dB re 1 µPa, with frequencies 0.032–0.2 kHz. At 11.1 km, RL was recorded as 150 dB re 1 µPa, with frequencies 0.19–0.32 kHz. Comparatively, at a range of 5 km from a single 40 in3 airgun, RL was recorded as 129 dB re 1 µPa with frequencies 0.05–0.1 kHz. Madsen et al. (2006a) measured RLs of seismic airguns using Dtags attached to sperm whales. M-weighted RLs were 131–167 dB re 1 µPa for ranges 1.4–12.6 km. When close to the surface, frequencies were predominantly between 0.3 and 3 kHz. Results showed that for each fire of the airgun array, whales were exposed to multiple pulses, all with differing temporal and spatial properties. For one whale, M-weighted SEL levels amounted to 150 dB re 1 µPa2 s. The 30 airgun array had 28 airguns in use during trials, with a firing pressure of 14 megapascal (MPa) and volume of 2,590 in3. Seismic surveys conducted in the Moray Firth, Scotland, with a 470 in3 airgun array, produced received SPLs of 165–172 dB re 1 µPa, 5–10 km from the seismic vessel (Thompson et al., 2013). High energy, low frequency noise produced by the bubble oscillations is of most concern to marine mammals, and is capable of travelling great distances in the water column. Consequently, airgun noise has the potential to mask low frequency baleen whale detections at great distances from the seismic survey site. Surveys that are conducted along transect lines (Section 5.21.6) can run for weeks at a time, leading to potentially elevated and cumulative noise levels over prolonged periods. A wealth of information can be sourced on line but some suggestions for further reading are Goold (1996), Richardson et al. (1999), McCauley et al. (2000a), Harris et al. (2001), Gordon et al. (2003), Nieukirk et al. (2004), Stone and Tasker (2006), Yazvenko et al. (2007), Lucke et al. (2009), Di Iorio and Clark (2010), Gedamke et al. (2011), Heide-Jørgensen et al. (2013), Robertson et al. (2013), and Thompson et al. (2013).
Pile driving (and conductor hammering) refers to the hammering of piles into the seabed. Usually this is carried out using hydraulic hammers, but vibration piling involves the use of hydraulically powered vibrating probes, known as vibroflots. Used commonly within the construction industry, piling is used to secure structures to the seabed. Choice of pile depends upon type, size, and weight of structure to be supported, and depth and physical properties of the seabed. Piling is a source of high amplitude, low frequency, impulsive sound (Robinson et al., 2012). To measure acoustic impact fully, noise in water, in air, and in the seabed, needs to be considered, along with seabed surface vibrations (Robinson et al., 2012). Piling occurs predominantly in shallow coastal waters, where local propagation conditions have a substantial impact upon how sound travels (Robinson et al., 2012). Noise levels produced depend upon pile size, hammer strike energy, and nature of the seabed. McHugh (2005) undertook underwater measurements close to sea floor piling operations in the North Sea during the summer of 2004, as part of the British Petroleum (BP) North Sea ‘Hot Tap’ installation. Two hydrophones recorded data at depths of 20
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and 65 m in a total water depth of c. 95 m. Through combining recorded acoustic data with underwater modelling, peak SLs of 210 dB re 1 µPa @ 1 m were estimated for the percussive pile-hammering signatures. Robinson et al. (2007) measured underwater radiated noise from a marine piling operation. To mitigate environmental effects of noise, the piling sequence in their study often began with a soft-start. Measurements included a full characterisation of the softstart period at the beginning of the piling sequence, where the hammer energy was increased gradually from 10% to 100% of the final energy level. Detailed measurements of underwater noise levels were then undertaken throughout the entire piling sequence (a little over 4 h) at two locations corresponding to ranges of 57 and 1,850 m. The soft-start sequence lasted for c. 68 min, during which time hammer energy was increased incrementally from 80 kilojoules (kJ) to 800 kJ. A steady increase in acoustic amplitudes during the soft-start period was observed, with p-p pressure levels showing an increase of about 12 dB from beginning to end of the soft-start, the rms pressure levels increasing by c. 13 dB, and the energy flux density level in the pulses increasing by c. 8 dB. Pulse periodicity was around 2 s during the main piling sequence, with pulse durations generally between 0.15 and 0.2 s. Pressure amplitude levels for the main piling sequence at a hammer power setting of 800 kJ were fairly stable, with mean p-p pressure levels of 211 and 191 dB re 1 μPa observed at ranges of 57 and 1,850 m respectively. Corresponding energy flux density levels of 178 and 164 dB re 1 μPa2 s were observed at both ranges respectively. More recently, measurements were taken by Robinson et al. (2012) around a 5 m diameter pile in water 15–20 m deep. Hydraulic hammers with typical strike energies of 1,000 kJ were used, for which the majority of noise was 60 dB above background at 380 m from the pile, reducing to hydrostatic mud pressure, then BOP closes; SIDPP is pressure observed at drill pipe gauge at surface
Slag Off Weight
When drill string is lowered, weight is gauged as an indicator of friction (like PUW)
Wait On Cement
Waiting on cement slurries to go hard
5.22.6 Weather Weather offshore is always challenging, particularly on installations, where it is not possible to seek shelter in the lee of land or turn into the weather. North Sea installations can be battered year-round by strong winds and relentless high waves. Most oil and gas fields in the petroleum-rich fields of Canada reach full capacity during bitterly cold winter months. In the USA, particularly in the unforgiving summer climate of the Southwest, temperatures exceed 37 °C regularly and installations along the US coastline in the GoM are placed on alert during hurricane season (1 June to 30 November).
5.22.7 General hazards Prior to undertaking any work or non-work-related activities, read and understand the installation operator’s safety policy (or operational standards) handbook or similar document(s) containing relevant safety information, which is available in electronic or hardcopy format, for which personal copies are often located in cabins on arrival (e.g. Figure 5.8). These documents cover topics such as leadership and commitment to HSE (corporate safety policies, etc.), communications (drills, hazard signs, etc.), hazard control (TBTs, job safety analysis, etc.), incident reporting, safe systems and operational control (permits to work, all equipment operations, etc.), emergency preparedness (installation evacuation, man overboard, etc.), PPE and safety equipment, occupational health control (medical fitness to work, personal hygiene, housekeeping, etc.), environmental protection (spills, emissions, etc.) and details of audits and inspection.
Figure 5.8 Examples of safety policy handbooks.
Aboard offshore installations, workers are on constant alert for countless hazards. For example, hydrocarbon reserves are under extreme pressure and may also contain toxic gases, such as hydrogen sulphide. Cranes lift and move supplies, heavy equipment, large sections of pipe, and forklifts may also be in use. Gas cutting operations create heat and sparks, and, additionally, electrical welding operations create high energy visible light that can damage unprotected eyes. Helicopters arrive and depart periodically. Many operations generate high noise levels, for which protection is required. Under no circumstances, leave the accommodation block without wearing full PPE and always use designated walkways. Generally, avoid the operational decks if possible; otherwise, look up when leaving any doorway and never walk under an active crane. Notify relevant crew members if deploying PAM equipment overboard. Clean any spills immediately inside (e.g. coffee) or outside (e.g. oil). Large vats of detergent, often known as ‘rig wash’, are available, along with copious amounts of rags, brushes and mops. Follow recycling rules, for which bins and skips are labelled clearly, e.g. ‘oily rags’, ‘general waste’, ‘metal’, ‘plastic’, ‘paper’, ‘glass’, ‘batteries’. In hot countries, the waters around installations appear cool, clear and inviting; however, never climb down installation legs, or hang a hammock between legs (yes, it has been done, with near-fatal consequences), or attempt to go swimming. Aside from being strictly forbidden, currents between installation legs can be extremely powerful and a swimmer will likely be swept away. Moreover, large sharks take advantage of the rigs-to-reefs effect, and regularly patrol the waters around rigs (including the North Sea, according to HMI and diver accounts, and ROV footage the authors have observed). If female, do not sunbathe topless on the helideck (yes, unbelievably, this has also been done by a particularly buxom Teutonic lady to the delight of onlooker radio officers), or sunbathe on the helideck under any circumstances, regardless of gender. Helicopters arrive and depart at all times, and aside from distracting crew, helidecks do not have any railings. If using the sauna, respect male and female sauna times. If laundry is undertaken by male stewards, it is sometimes appropriate for female MMO and PAM Operators to wash certain laundry separately, as underwear (in particular lingerie) has the occasional tendency to ‘go walkies’ on offshore installations, particularly rigs.
5.22.8 Rig tow An MMO is sometimes required to join a rig immediately prior to or during a tow from one location to another. PAM Operator requirements during a tow are unlikely. If boarding pre-tow, this is one of the most interesting experiences offshore. There are a multitude of specialists involved specifically for the departure, tow and arrival, who will
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leave with the first helicopter on arrival at the final location, so use this brief opportunity to learn about what they are doing and how they do it. In the case of a jack-up, the rig is jacked-down so the barge (main body of the rig) floats on the water. This involves the barge engineer lowering each leg individually, whilst various personnel lubricate the legs with thick grease, which inevitably ends up on rig decks, so stay clear of legs. Rig hulls/legs/barges are not streamlined, and are often top-heavy on account of derricks, cranes, and accommodation blocks, so tows are undertaken at minimal speeds by tugs (Figure 5.9) and in suitable weather conditions only.
Figure 5.9 Tug towing a jack-up rig in the North Sea. Helideck to the left.
Watching for marine mammals on tow can be extremely interesting, as there is evidence that some marine mammals (such as porpoises) follow rigs, which are effectively moving artificial reefs (Todd, 2013). Tows occur only in 0.5–1 m wave height, typically Beaufort sea state 2 and below, so viewing conditions are usually optimal for marine mammal detection.
5.22.9 Drilling rig and production platform complexes Drilling rigs attach to production platforms to drill new wells, and if further reserves are discovered, these are ‘produced’ via platforms’ existing infrastructure (Figure 5.10).
Figure 5.10 Four-legged jack-up rig (left) attached to a gas production platform (right) in the North Sea.
When a rig attaches to a platform, the rules change, as each has different operational procedures. The former are relatively dirtier and noisier environments with larger crews to cater for, which can be reflected in the standard of food. Platforms are virtually spotless and much quieter, and occasionally with ex cordon bleu chefs running the galley (they are paid better offshore, and have relatively fewer mouths to feed aboard platforms compared with restaurants). When joined, the two installations likely originate from different companies with different safety management systems. Given that all personnel are accounted for at all times (even when sneaking from the rig over to the platform for mussels in white wine sauce and profiteroles), the T-card system (Section 5.18) is adhered to at all times. Located usually at the walkway between the rig and platform, names of all installation personnel are printed on cards; the card is lifted from the ‘rig’ to the ‘platform’ slot and vice versa. The radio room also requires transfer confirmation, just in case there is an emergency evacuation, or a safety drill.
5.22.10 VSP On VSP surveys, geophones are lowered into a borehole. In a zero offset VSP, the seismic source is deployed from the rig or platform, whereas offset and walkway VSPs deploy the source from a vessel. For an offset VSP, the source vessel is at a fixed position, whereas, for a walkaway VSP, the source vessel traverses one or more lines away from the geophones. The seismic source used for VSP surveys is often much smaller than traditional seismic surveys, and may comprise three or fewer airguns. A VSP survey is generally very short, and may take only a matter of hours or days, for which MMO (sometimes complimented with PAM) watches are standard practice.
5.22.11 Conductor hammering Shepherd et al. (2006) and Thomsen et al. (2006) describe the typical process of pile driving during construction of offshore wind farms. This involves first locating a jackup, or DP or anchored crane vessel or barge, which secures the pile and hammer in position. Once the pile has been located, checked for vertical alignment, and allowed to settle, piling commences with a period of lower energy hammer blows to enable alignment to be monitored and adjusted. Hammering the pile to the appropriate depth involves blows being delivered at a rate of approximately 30–60 per min, and may continue over several hours (Thomsen et al., 2006; Robinson et al., 2007). There is an occasional requirement for MMO and PAM during initial phases of exploration drilling. In preparation for drilling, conductor sections are hammered into the seabed (Figure 5.11). Typical sizes are 10 m × 0.762 m, but conductor width is measured imperially in the drilling industry, so this corresponds to ‘30 inch’. Initial conductor sections are lowered to the seafloor to penetrate under their own weight. After self-penetration (typically c. 3–5 m in soft sediments, depending on conductor size), a hammer is lowered onto the uppermost conductor section to allow additional weight to assist with self-penetration. Once downwards movement has ceased, successive conductor sections are subject to blows, which vary according to hammer weight. Typical values for a 13 tonne hammer range from c. 10 to 93 kilonewton metre (kN m) with a variable blow rate. Hammering takes place on the drill floor and it is extremely noisy, so earplugs are worn at all times, and communication is hindered. In sensitive areas, prior to conductor hammering, a pinger (see Section 2.7) is usually deployed, the acoustic parameters of which are required for the MMO and PAM report.
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Figure 5.11 Conductor hammer on a drilling rig.
MMO and PAM watches are conducted the same way as for other routine types of marine operations, but for reporting purposes, conductor hammering operations are recorded and included each time the sound source commences and ceases. Figure 5.12 shows an MMO logging conductor hammering. MMOs might be required to work closely with the PAM Operators and any acousticians, if real-time noise measurements and sound propagation modelling is also being undertaken. Tight communication is required, especially if initial hammer blows are to be recorded. MMOs are responsible for informing the PAM Operators and Acousticians when the first strike is about to commence.
Figure 5.12 MMO logging conductor-hammering activity aboard a jack-up drilling rig.
MMO Theory and Practice 6.1
MMOs (Figure 6.1) are an essential part of all mitigation guidelines, and in many cases the only real-time mitigation method used. Visual monitoring is not without constraints; the ability to sight animals declines rapidly in rough seas, and although new technologies are emerging, detecting marine mammals at night is challenging, and affected severely by sea conditions. Nevertheless, a well-trained and knowledgeable MMO is an invaluable mitigation solution. In addition to patience and a willingness to watch, and concentrate on, the ocean for long periods, a number of skills, such as range estimation and marine mammal identification, are essential.
Figure 6.1 MMO standing on a laminated compass rose, alongside a range stick, operating from a jack-up drilling rig.
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This chapter details equipment requirements, explains essential skills, and guides the reader through an MMO working shift, from finding an observation platform to delaying operations due to sightings. For those with a scientific background, distancesampling methods are also discussed.
All MMOs are suitably equipped with the following (Figure 6.2):
Figure 6.2 Example of MMO equipment.
• • • • • • • • • •
industrial standard PPE (Section 5.7); plastic-coated fold-over clipboard; pencil, eraser, sharpener, paper; digital watch (set to UTC); marine radio; waterproof binoculars (with reticles); handheld GPS receiver; camera – digital SLR if possible; plumb-bob; and, field guide(s).
These are all regarded as personal items and, excluding the marine radio in some cases, are usually purchased, owned, and supplied by individual personnel.
A plastic-coated fold-over clipboard protects paper contents from spray, rain, and wind. The clipboard contains data forms, a copy of the guidelines, Beaufort sea state table, sunset and sunrise times for the region, range estimation table (Section 6.8) calculated for personal eye-height for each observation platform (e.g. bridge), and an angle board. With the exception of forms, laminate as much as possible. Pencils are attached inside the clipboard with string.
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When recording data in the field, pencil is preferable to pen; it does not smudge, and mistakes are erased easily. It is vital that all data are recorded, so a pencil sharpener, or extra lead if using a mechanical pencil, is important. A notepad is useful for writing notes quickly, and crucial in areas where data are recorded electronically, for example, New Zealand (Section 6.11.2). In the event of a sighting, it is not possible to sit at laptops recording information.
A waterproof and robust digital watch attached permanently inside the clipboard for easy access, and set to UTC time (Section 6.11), is very useful. When gloves and heavy clothing are worn as standard PPE or in cold conditions, it can cost valuable seconds to access a wrist-mounted watch. Aim to minimise recording effort when tracking animals visually.
When possible, carry a fully charged Very High Frequency/Ultra High Frequency (VHF/UHF) radio at all times, even when not on duty. On some offshore installations, such as gas production platforms, personal radios and other electrical equipment are not permitted, unless they are ‘explosion proof’, due to the risks of igniting flammable gases. In these situations, radios are ideal, but if in doubt, ask the employer/contractor/ client prior to mobilisation. In potentially sensitive operations (e.g. military contracts), alternative forms of short-range communication equipment such as ‘walkie talkies’ may be more appropriate for security reasons. These do not broadcast information to the wider maritime community.
Binoculars suited to marine use are heavy and unwieldy, so try various brands prior to purchasing. Ideally, they are nitrogen-filled (fogproof), waterproof, rubberised, sturdy, and contain a reticle (also known as ‘reticule’ or ‘graticule’), which is a scale of fine lines visible on one lens that can be used for range estimation (see Section 6.8). Binoculars require a magnification of 7–10 and an exit diameter of 40–50 mm. The magnification of 7–10 is the ratio of the focal lengths for the eyepiece lens to the front (objective) lens; the 40–50 mm is width of the objective lens. Most MMOs favour 7 × 50 binoculars. Binoculars may have an inbuilt compass that is viewed through the lens, but compasses will not measure accurately when any ferrous or electrical sources are nearby, so compasses are typically ignored when observing from steel platforms or near instrumentation. Additionally, power lines and even geological formations can influence a compass. When observing from a static metal structure, such as a construction vessel, platform, or rig, it is advisable to laminate a large compass rose, which can be orientated according to the installations’ heading. Alternatively, a GPS compass uses satellite signals and is therefore independent of local magnetic influences. The internet is a good place to review binoculars; in particular, the Marine Mammal Observer Association (MMOA) has a wealth of information on their website, www.mmo-
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association.org. Some examples of 7 × 50 binoculars with compass and reticles used currently by MMOs are listed in Table 6.1. Table 6.1 Examples of 7 × 50 (magnification × exit diameter) binoculars with compass and reticles. Manufacturer
Battalion fog/water/shockproof, with reticle and compass
Marine fog/water/shockproof, with reticle and compass
Marine fog/water/shockproof, with reticle and compass
Searanger II fog/water/shockproof, with reticle and compass
Oceana WP fog/water/shockproof, with range reticle and compass
Tornado marine fog/water/shockproof, with range reticle and compass
Lsf marine fog/water/shockproof, with reticle and compass
Marine fog/water/shockproof, with reticle and compass
Marine fog/water/shockproof, with reticle and compass
Marine fog/water/shockproof, with reticle and compass
A hand-held GPS is ergonomic, and shower- and shockproof. A GPS is searching for satellite signals constantly, which consumes power, so it is advisable to carry spare batteries when on duty. Compared with conventional batteries, rechargeable batteries are more environmentally friendly and cost-effective, and minimise baggage weight. When selecting a GPS, useful features include a compass and the ability to record sighting-waypoints to view tracks retrospectively, as MMOs should minimise distractions and concentrate on watching animals. In some regions, such as New Zealand and Greenland, tracks have to be downloaded on to a computer on a daily basis, so ensure this is possible if working in these regions. Additional mapping software may be required. Available features depend upon brand and model of GPS, but configured optimally, a single screen can display position, heading, time and speed simultaneously, which are all variables required in standard data recording forms.
Digital photography is highly advantageous, as images can be easily enlarged retrospectively for positive identification, and as evidence of sightings. Nowadays, film photography is used rarely, so all cameras discussed herein refer to digital technology, although much of the advice is applicable equally to film. An SLR camera is ideal for subjects and conditions in the marine environment, but compact and other cameras can provide images of sufficient quality also. Nikon, Olympus, Canon, and Sony are commonly used brands, but others include Fuji, Panasonic, and Pentax. Different brands and models have their own pros and cons, but personal preferences vary.
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An SLR uses a mirror and prism system, which directs light from the lens to the viewfinder, allowing the user to view a scene exactly as it will appear in the photograph. Typically, SLRs are faster to activate and respond and may be equipped with continuous shooting modes, which is crucial when photographing fast subjects. An SLR allows complete control over settings, performs better generally than a compact in low light situations, and detachable lenses are designed for specific tasks. Other than the escalating cost, the downsides of using an SLR include increased size, maintenance, and cleaning – detachable lenses mean cameras are prone to dust or moisture ingress. An SLR and associated peripherals (e.g. additional lenses, spare batteries, and charger) can account for considerable volume and weight of the already limited offshore baggage allowance, so it is advisable to avoid protective cases altogether, and instead place cameras inside a plastic bag (to exclude dust, fluff, possible leaking fluids, etc. from baggage contents), then wrap cameras in personal clothing, and position in the most protected baggage location. Compact cameras utilise a different technology from SLRs, are cheaper, smaller, and easier to operate. Some compacts may include SLR-type shooting modes, allowing optimal settings according to light conditions and speed of subject. Bridge cameras offer a compromise. Like compacts, they lack SLR technology and interchangeable lenses, but they include some of the manual settings on SLRs, and the zoom function is more advanced typically compared with compacts. Compact System Cameras (CSC) offer another compromise. They similarly lack SLR technology, but include interchangeable lenses and some of the manual settings on SLRs. Lens options may be limited, as CSCs are a relatively new development. The number of megapixels is an important consideration for any camera. For example, a 14-megapixel SLR with a powerful lens may produce reasonable images of a cetacean at a range of 500 m, whereas a 14-megapixel compact will produce a softer and unusable image. Often animals will be a considerable distance away, and an image containing a small subject will need to be cropped and enlarged, which further reduces the number of pixels, information, definition and sharpness. Some SLR camera manufacturers are producing models with megapixels in excess of 40–50, and there are rumours that Canon is in the process of field-testing an SLR camera that packs a whopping 75+ megapixels. Shutter speed is another critical consideration for fast-moving subjects. Some marine species surface quickly and offer a brief glimpse only, so increasing frames per second increases chances of capturing a subject before it submerges. Other useful features include autofocus, which helps to ensure images are sharp and not blurry, zoom to enlarge subjects, and a weather and shock-proof camera body, as the offshore environment can be harsh and unforgiving. Additionally, when reviewing camera type, consider whether images would be preferable in raw or JPEG format. Raw files retain more detail, but a greater level of editing is required, and the file size is considerably larger. Note only some compact cameras can take photographs in raw image format, which applies no compression and no image processing. Raw formats can be proprietary file format, such as (.orf) for Olympus models, but various programmes such as Adobe software (Photoshop®, Bridge®) can read these formats. The SLR bodies can have a lifespan of c. 350,000 shutter releases/clicks, but maintained properly, lenses last a lifetime. Magnification is required to capture details accurately, so a smaller proportion of a restricted budget should be spent on the body. Cheaper or older bodies should not be excluded from a shortlist; however, always check
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shutter counts for second-hand bodies. For popular brands of SLR, such as Nikon and Canon, cheaper brands of lenses are available. Some SLR bodies are intended for the beginner, so guides and hints are included. Numerous websites review and compare cameras (e.g. www.dpreview.com). Table 6.2 lists some SLR cameras available, including manufacturer, model, megapixels, and maximum shutter speed. Similar lists are provided separately for compact (Table 6.3), bridge (Table 6.4), and CSC (Table 6.5) cameras. Table 6.2 Examples of Single Lense Reflex (SLR) cameras.
Maximum shutter speed (seconds)
Table 6.3 Examples of compact cameras.
Maximum shutter speed (seconds)
PowerShot SX270 HS 20×
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Table 6.4 Examples of bridge cameras.
Maximum shutter speed (seconds)
PowerShot SX30 IS
Table 6.5 Examples of Compact System Cameras (CSCs).
Maximum shutter speed (seconds)
PEN Lite E-PL5
An additional consideration is memory cards. Capacity determines number of images that can be stored, which also depends on the format (e.g. raw images require more memory, cf. JPEG), and class determines speed rating and number of megabytes (MB) transferred to the memory card per second. Currently, there are five classes; the fastest, 10, transfers up to 10 MB per second.
Separate lenses are required for both SLR and CSC cameras, where choice depends upon systems selected. On the one hand, it can be argued that the high shutter speeds
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involved with marine-wildlife photography negate any requirement for image stabilisation, but on the other hand it can be argued that, in addition to the subject’s movement, operator movement and that of the vessel can affect images. Image stabilisation technology is contained within the body of some cameras, in which case it may be a less important consideration for a lens. Choice of lens depends upon system chosen, but zoom is essential and 200–300 mm focal lengths are ideal, so consider 70–200 or 300 mm telephoto lenses, which are popular with marine-wildlife photographers. Budget and model permitting, larger focal lengths (500+ mm) are available for more distant subjects or projects involving fin identification to individual animal level, where high resolution is crucial. These lenses have a shallow depth of field, which allows the subject to be isolated from its surrounding. They are also more expensive and a stand is advisable to bear the substantial weight, but given that, MMOs carry other equipment and should not be focusing on photography exclusively in most situations; larger lenses can be overkill. Professional wildlife photographers typically recommend 150–500 mm telephoto zoom lens, so it is worth noting that for common brands, cheaper, high quality lenses may be available, for example, Sigma lenses are an excellent alternative to Nikon, Olympus, Canon, and Sony. If large telephoto lenses are beyond budget, teleconverters, which are placed between camera and lens, magnify focal length and are a good way to expand capabilities of lenses. Filters are another consideration, which can be added to lenses to improve the photo quality. For example, polarising and UV filters are both useful when shooting in bright sunlight. Finally, no matter how good the tool, it is ultimately the user that determines whether the shot is good or not. Practice makes perfect. Read the manual.
A plumb-bob is a weight suspended from a piece of string, which can be used to determine vertical height of an observation platform above sea level. Observers then add personal eye-height when wearing appropriate steel-toe capped safety boots, and this total height is used for range estimation (Section 6.8).
6.2.10 Field guides A comprehensive field guide is essential. It not only aids in identification of marine mammals, but also helps to educate interested crew members. When choosing a field guide, firstly consider content. Some contain details on all marine mammals, whilst others focus specifically on cetaceans, and thus do not include pinnipeds. If working in Greenland, where birds are surveyed, a second bird Identification (ID) guide is essential, but if packing restrictions allow, they are a worthwhile addition to any survey, for personal, and crew interest, as well as identification practice. Secondly, consider area; does it need to cover worldwide, or can it concentrate on a smaller area? Worldwide field guides which address all species are large, so may be unrealistic if strict packing restrictions apply. Single-page laminated field guides are available with illustrations showing only relative size and shape of local species, which should be second nature for knowledgeable MMOs, but these are useful references to educate, interest, inspire, and involve crew. Single-page laminated field guides are available from various wildlife charities free of charge or at the cost of a nominal donation.
MMO Theory and Practice
Conducting an MMO Watch
MMOs are available throughout daylight hours, which in good conditions is around 30 min before sunrise, until around 30 min after sunset. Continuous watches are required in some locations. Some MMOs conduct watches during start-ups only, to the extent that if a survey is continuous (e.g. airguns continue to fire on turns) and MMOs go unchecked, they can, in theory, undertake relaxation and recreational activities instead of professional duties for the entire duration of the trip (e.g. watching DVDs and using the gym facilities). Needless to say, under these circumstances, any respect from crew members wanes quickly, individuals are remembered, and if clients make an effort to monitor these personnel and ensure this behaviour does not persist, a painfully short career can ensue. MMOs absent from their post when required by crew are usually reported and may, in serious cases, be awarded a STOP card (where applicable, see Section 5.17) or reported by a vessel representative to their employer. Nevertheless, MMO work is not an endurance test, so personnel should take regular breaks outside pre-watch and other crucial periods. If working with others, shifts are organised to ensure all MMOs receive regular breaks, as this helps to avoid fatigue and loss of concentration. Distractions are kept to a minimum at all times. Staying in contact with crew is important; radios are often the best option. When communicating over radio, speak clearly, slowly, and professionally and be aware that other marine users may be listening. To begin a conversation, state whom you wish to speak to, followed by MMO/PAM; for example, when contacting Seismic Observers, say ‘Observers, MMO’, or ‘instrument room, MMO’. A likely response is ‘MMO, Observers – go ahead’. Then proceed with the conversation. At minimum, communications with relevant crew occur before pre-watch and prior to activation of the sound source. Do not rely on crew for regular updates, pay attention to activities, and be in the right place at the right time.
When boarding a vessel or installation, MMOs must select an appropriate vantage point. There are various options usually, although some locations, such as the drilling floor and helipads, have restricted access, so always ask permission in advance from the appropriate member(s) of management, confirm restricted areas, and follow all PPE requirements. Confirm if a permit-to-work is required, and if so, ensure it is completed and signed by an appropriate crew member prior to venturing outdoors (Section 5.17). If the bridge is the only available observation platform, an MMO must not restrict the navigation crew’s view or access ways. Only observe from inside the bridge as a last resort, such as in the case of heavy rain and/or wind, extreme temperatures, or the crew’s preference for H&S reasons. There are too many visual distractions on a bridge, such as obstructed window views (frames, blinds, tinted glass, sun glare, reflections, water droplets, crystallised salt, dirt, etc.), flashing lights, instrumentation and controls, pictures and signs, drinks and snacks (especially fresh Belgian waffles and cream), and personnel movements. There are also too many acoustic distractions, such as radio communications, music, and crew conversations, which inevitably involve MMOs. Nonserious MMOs are always easy to identify on vessels, because they repeatedly spend most of their time sitting in the bridge’s pilot chair, gossiping to crew, drinking tea or coffee, eating cream cakes, listening to music, and even, astonishingly, reading. These MMOs persist in industry at the employment-expense of genuine incumbents, so clients
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who are serious about complying with environmental credentials have a duty of care to ensure such behaviour is not tolerated. Ideally, observation should occur outdoors, for which experienced personnel are equipped with appropriate clothing. This can on occasion afford the ideal 360° view. However, an unobstructed view is rarely possible, in which case MMOs should focus on the most relevant view according to operations. For example, on seismic vessels typically, prior to and during start-up of the airguns, MMOs ensure they have a minimum 180° view aft, which encompasses the exclusion zone (Section 2.12), whereas, once the airguns have reached full power and the vessel is underway, MMOs similarly ensure they have a minimum 180° view ahead. When ensuring unrestricted views of exclusion zones, note they are around the centre of the sound source, not the vessel or installation. Once in position, observe the whole zone and alternate between binocular and nakedeye scans. When scanning lookout for visual cues, such as: • • • • • •
blows; sighting of backs or fins; underwater shapes or patches; splashes (which are often the initial indication for smaller cetaceans); feeding seabird flocks (often associated with feeding cetaceans); oily slicks at the surface (often indicative of animal’s post-surfacing ‘footprints’ on calm water or oil from processing prey); and, • location of fronts and other oceanographic features (where marine fauna often congregate). It should be noted that chances of sighting smaller species, such as the harbour porpoise, increase substantially if using binoculars; animals will go unseen if conducting watches using only naked eye scans.
Recording vessel or sighting position accurately is essential. To achieve this, an understanding of latitude and longitude is required. Latitude, as defined by Bartlett (2003), is the ‘distance from the equator, expressed as an angle, measured in degrees, from the centre of the earth’. Essentially, lines of latitude comprise a series of horizontal lines that run parallel with the equator, known as parallels of latitude, which are measured 0–90°, either north or south of the equator. Vertical lines, drawn metaphorically between the poles, are referred to as meridians, and in concert with latitudes, separate the Earth into segments. The prime meridian, which acts as a reference point for all measurements, as the equator does for latitudes, was arbitrarily agreed to be one of the telescopes at the UK’s Greenwich Observatory. On this basis, longitude, as defined by Bartlett (2003), is ‘the angle between the plane of the prime meridian and the meridian of the place’, and is measured horizontally from 0° to 180°, either east or west of the prime meridian. Combined, latitude and longitude are used to specify position anywhere in the world. They can be expressed in degrees, minutes, and seconds; degrees and decimal minutes; or as decimal degrees. An example of the same latitude and longitude, expressed in these three different ways is shown in Table 6.6. Degree units are expressed as the symbol °, minutes as ´, and seconds as ´´.
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Table 6.6 Examples of how to record latitude and longitude. Latitude
Degrees, minutes, seconds
56° 6´ 4´´ N
2° 21´ 53´´ W
Degrees, decimal minutes
56° 6.07 N
2° 21.89 W
There are a few points to note. Firstly, regardless of format, latitude is written first, and direction specified (i.e. north or south of the equator, and east or west or the prime meridian). This is usually done with an ‘N’ or ‘S’ after the latitude and ‘E’ or ‘W’ after the longitude (Table 6.6), but in some cases, it is done with positive and negative numbers. Positive usually indicates north or east, and negative south or west, although in some locations west is positive, so it is advisable to check. Secondly, it is good to have an understanding of what the units actually mean. One degree is equivalent to over 100 km in distance on the Earth’s surface. Recording degrees only does not give an accurate indication of position, so degrees are divided into minutes, and, for further accuracy, seconds. Comparable to time, 1 degree equals 60 minutes, and 1 minute equals 60 seconds. Finally, it is useful to understand how to convert between the three formats. Formats are usually specified on data forms, generally degrees and decimal minutes. Data sources available, such as bridge navigation displays, may express latitude and longitude differently, but there are websites and software available that convert between the three formats, which can also be achieved by hand. To convert degrees, minutes, and seconds, to degrees and decimal minutes, remember there are 60 seconds in a minute, so divide the number of seconds by 60 and add the answer to the number of minutes, as follows:
For example, to convert 56° 6´ 4´´ N to degrees, decimal minutes, use the following equation:
To further convert this to decimal degrees, again remember there are 60 minutes in a degree, thus divide the number of minutes by 60 and add to the number of degrees:
To convert backwards from decimal degrees to either degrees and decimal minutes, or degrees, minutes, and seconds, subtract the figures after the decimal point, as opposed to add, and multiply by 60, as opposed to divide.
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In some regions such as Australia and New Zealand, some MMOs use computerised systems for tracking and monitoring marine life from land or vessels. One such example is Cyclops (now termed Visual and Acoustic Detection and Ranging, VADAR), a computer-based marine mammal positioning system developed by Dr Eric Kniest from the University of Newcastle, New South Wales, Australia (www.cyclops-tracker.com). The program is designed specifically to locate and record marine mammal position from a known location, either on land or aboard a vessel, relative to an acoustic source, and is able to track animal position accurately in real-time. Additional information such as weather variables, MMO sightings, animal behaviour and group composition can also be added in real-time. Ever more sophisticated software systems are being produced or are at the R&D stage, some of which incorporate gyro-based compasses that account for local magnetic variations in the Earth’s field; however, non-MMO form-based systems that involve real-time inputting of visual observation data into a computer, take considerable handling time and distract the MMO from undertaking empirical observations. Ideally, there should be a dedicated MMO for data entry only, and a visual observer, but this is rarely the case on commercial projects.
Recording Vessel Movements
Guidelines require varying levels of detail concerning vessel movements. Most stipulate vessel speed, in knots (kn), but some, such as New Zealand, also need the ship’s true course for sightings, and track records recorded on a GPS. True vessel speed or bottom speed is the speed at which the vessel is moving over ground, as measured by the GPS; it accounts for currents, and is the speed required on data forms. This is not to be confused with water speed, which does not account for currents. For example, a vessel travelling against a current has a slower bottom speed than water speed; bottom speed equals water speed minus current speed. Travelling with the current, bottom speed equals water speed plus current speed. Concerning vessel direction, course is the vessel’s intended direction of travel, and is expressed in degrees. True course is course referenced to true north, i.e. degrees from true north (0°). Heading, on the other hand, is the direction in which the vessel is facing at any given time. Course and heading are rarely exactly the same. Handheld GPS can be set to collect location data automatically at a set interval, for example every 30 s. Left on, the tracking function continually records, and logs vessel movements. Downloaded tracks can be viewed in mapping software, copied into reports, or compared with project boundaries or sightings. All handheld GPS work in different ways, so refer to instructions for how to log, and download tracks.
Marine Mammal Identification
Spotting and identifying marine mammals in the field can be challenging, and sometimes impossible. A single glimpse is often the only event in a long and tiring day, week, or even month. In order to take advantage of any sighting opportunity, always carry binoculars and camera for immediate detection, and an identification guide to confirm. Prior research of species present typically in any region narrows down identification
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options. Marine wildlife have many distinguishing features, but avoid identifying animals based on one feature alone, as significant variations can exist within a species. Take note of as many characteristics as possible, and use them in combination. Photographs are always useful and are increasingly becoming a verification requirement in more sensitive areas. There are a number of excellent field guides to marine mammals that expand extensively on the features listed herein (Section 6.2.10), so this section should be used as an introduction only, not as a replacement for a more detailed field guide.
One of the first detection cues of larger cetaceans is the blow, distinguishable by height, shape, and angle. Some mysticetes have V-shaped blows that, in good weather conditions, are visible as two distinct columns. Others have one column, which can be tall and narrow or short and bushy. Most are directed upwards, but in a sperm whale, for example, because of the position of the blowhole, the blow is directed forwards and to the animal’s left (Figure 6.3). Appearance depends on viewing angle, so for example if a sperm whale is facing towards you, the blow appears directed to the right. On a windy day, blows can dissipate and lose their shape quickly, so a visible absence of two columns does not necessarily confirm the presence of one column only.
Figure 6.3 Sperm whale blow, directed forwards and to the left.
Not all cetaceans have dorsal fins, so presence or absence is a good identification starting point. If a dorsal fin is present, observe the shape, size, position, and coloration. Dorsal fin size can range from small humps or ridges to, in the case of a male orca, 1.8 m tall. Shape can vary substantially, from triangular, rounded, falcate, straight, or even canted forward. If possible, also observe fin position on the back, as some species such as beaked whales, have dorsal fins set far back on the body. Cetaceans range in size from 1 to 30 m, so size can be a good indicator of species, but it can be hard to gauge scale at sea. This is especially true if trying to distinguish between two similar species, such as the fin or sei whale. Head shape of some mysticetes such as right or bowhead whales is very distinctive, and is characterised by a strongly arched mouth line. Head shape of rorquals can be pointed or rounded and flat with varying
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numbers of longitudinal ridges. Presence or absence of a beak is an identifying feature of odontocetes, as is head shape, which in some species is rounded or blunt. Cetacean body shape is described generally as being slender or robust. Humpback whales are distinguishable by their pectoral fins, which are particularly long and narrow. If seen in other species, note the size and shape, and whether they are slender, blunt, pointed, paddle shaped, or with an elbow. The majority of species have a central notch in their tail fluke, but not all, so if possible, note the presence or absence of a notch, and whether the fluke clears the water as an animal ‘sounds’ (dives). If visible, coloration can be useful for identification, such as the obvious black and white markings of the orca. Location, colour, and shape of any patterns vary substantially, and sometimes appear on one side only, such as the white lower right side of the fin whale’s jaw. Skin can be mottled, wrinkled, or covered in tubercles or callosities. Markings can accumulate over time through interactions with other species (such as predator scars), or from conspecific interactions, such as the multiple scratches often present on Risso’s dolphin. Quiet surface behaviour – where only the back and dorsal break the surface – is distinctive of some species, whilst others are more active typically. Many dolphin species may come towards vessels and bow ride, or if resting, animals can appear motionless at the surface, an activity known as logging. Mysticetes can travel in small pods, but many are solitary, whereas odontocetes can form large superpods with hundreds or even thousands of individuals. Mixed species assemblages are observed together comprising different odontocetes, or different mysticetes, or indeed odontocetes and mysticetes.
In the water, often only the head of the seal or sea lion is visible, leaving little for identification, although family is deciphered based upon the presence or absence of ear pinnae. Phocids do not have external pinnae, but otariids do, and they vary in size, while some protrude more than others. In some species, the muzzle is long and pointed, and in others, short, broad, or flattened; vibrissae (whiskers) may be present over the whole muzzle or just at the sides. Nostrils can also be distinctive, facing downwards, upwards, or parallel and straight ahead. Colour and size can be used for identification, but bear in mind that substantial variations exist between males and females of the same species and colours are distorted in water. If hauled-out, and body is visible, size, coloration, and the amount and location of hair are all distinguishable features. Movement of hind flippers can be used to distinguish between phocids and otariids.
In order to determine if a marine mammal is within the predetermined exclusion or ‘mitigation’ zone (which varies between industrial activities, authorities, jurisdiction, and clients), MMOs must be able to estimate range with a reasonable degree of accuracy. It is inadvisable, and in most cases inexcusable, to rely upon naked-eye judgement alone, regardless of MMO experience. Sometimes, at great expense to the client, and at considerable wasted effort of the crew, MMOs underestimate range and advise that operations should be shut-down or delayed when animals are vastly beyond exclusion zones. MMOs are not always the most popular personnel on industrial projects for obvious reasons, but MMOs would
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be wise to remember that they stand to lose the crew’s respect and further employment if they blatantly misjudge ranges. The reverse is also true, where MMOs overestimate ranges and fail to advise that operations should be delayed or shut-down when animals are considerably inside exclusion zones, which completely nullifies the point of MMOs. The authors have worked alongside MMOs who have made all sorts of ridiculous claims in the field, such as, ‘The horizon is 10,000 km away’, and ‘harbour porpoises can only be sighted within 50 m [of the observation platform]’, and the offenders quoted held Master’s degrees in marine mammal science. Range estimation has a golden rule: everyone must practise regularly. Consequently, prior to mobilising for any project, practising range-estimation skills is recommended. Firstly, find a vantage point at least several metres above sea level, which offers unobstructed views of objects on the water’s surface, such as buoys, vessels, and rocks. Ideally, these targets should be located at various ranges, at say, 250 m, 500 m, 1,000 m, 2,000 m and 3,000 m, which is about as far as animals can be sighted typically (although the authors have sighted animals at 6,000 m in ideal observation conditions, confirmed by the location of tail buoys on the end of seismic streamers). Secondly, write down naked-eye visual estimates of ranges to each of these targets. If there is more than one MMO involved, do not disclose personal estimates until everyone has completed this exercise, when it will become clear how estimates vary considerably, and why naked eye estimates are unreliable. Thirdly, accurate measurements of ranges to targets are required, which is achieved most easily with a laser range-finder. Laser range-finders are simple to operate: aim the device at the target, depress the measurement button, and read the distance. Note that laser range-finders should not be considered as a substitute for range estimation in the field, as reasonable-sized and slow-moving or stationary targets are required for a return signal (i.e. a reflected laser beam). To reap the full benefits of this exercise, an independent arbitrator should operate the laser range-finder and not disclose actual ranges to targets at this stage. Fourthly, estimated ranges to targets are required, for which there are two popular methods: binocular reticles and range-finding sticks. For either method, eye height above sea level must be measured whilst wearing work boots, for which observation platform height above sea level must be measurable. In order to make a range stick, outstretched arm-length-to-eye also needs to be measured. The authors favour binocular reticles, as practised MMOs can quickly and easily estimate ranges to exclusion zone boundaries with a reasonable degree of accuracy. Importantly, MMOs are already equipped with binoculars, so introducing yet another tool for range estimation involves removing eyes from binoculars, further distractions, and increases the probability of losing track of sighted animals. Furthermore, Section 6.2 has already introduced numerous items of equipment that MMOs are expected to carry and use at the same time as recording details. To estimate range with binocular reticles, a comprehensive explanation follows, but binoculars are accompanied usually with basic instructions. When an animal or other target of interest is sighted, as per the example shown in Figure 6.4, align the uppermost crosshair of the vertical reticle scale with the horizon (i.e. range estimation is impossible when the horizon is obscured) and count down the number of increments to the base of the target. Do not count down the number of increments to the uppermost extremity of the target, such as in the case of a breaching whale or the funnel of a passing vessel of interest, as this overestimates range. Each reticle is usually equivalent to 5 mils, so for the example shown in Figure 6.4, the sighting at c. 10 reticles equates to 50 mils (10 × 5),
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which will be used in an example calculation. Again, if several MMOs are involved in this exercise, do not compare personal counts of reticle increments.
Figure 6.4 An example of range estimation using reticle binoculars.
Note that the height of the observation platform can vary substantially from the specification drawings that may be available aboard vessels and installations, because of changes in ballast, cargo, and jack-up rigs, which alter their height between, and often during, projects. For example, in bad weather, jack-ups often jack-down, which may occur at night, unknown to MMOs. Consequently, it is prudent to carry a plumbbob (Section 6.2.9) with 100 m line to measure observation platform height, otherwise unknown changes translate to incorrect range estimations. The following equation is used to calculate ranges derived from binocular reticles:
Continuing with the 50 mils derived from the example sighting shown in Figure 6.4, where the observer’s personal eye height = 1.6 m and observation platform height above sea level = 40 m, range equals:
Range estimation is not accurate to within a few metres, so the observer rounds up or down to get an estimated range, in this case from 832 to 830 m. To avoid calculations altogether, enter the equation into an Excel® spreadsheet to create a conversion table, such as the example shown in Table 6.7, which was actually used for the sighting example shown in Figure 6.4 – check the corresponding range for 10 reticles. Alternatively, download a conversion table online (www.osc.co.uk) and update values to reflect observer height above sea level. Range tables laminated and attached to clipboards ensure that sightings are readily translated into ranges with minimal task
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loading. Alternatively, enter the number of reticle increments into data collection forms and convert into ranges when convenient. This is only practical however if distances are not required for real-time mitigation purposes. Table 6.7 An example of a range estimation table used in conjunction with binocular reticles. No. of reticles
Fifthly, and finally, use three-headed columns to compare naked-eye range estimates with binocular-reticle range estimates and laser range-finder measurements. The greater number of candidates involved with this exercise, the greater the variations in estimations, which serves to help MMOs understand why regular practice is required. Some candidates possess better range estimations than others, but experience also shows that this exercise is easier in general when terrestrial visual cues with familiar dimensions are present (such as harbour walls and other coastal features). Offshore, it is harder to estimate ranges to a target, when the horizon is the only comparable feature. Additionally, if this exercise is performed from a considerable height of, say, 30–50 m, when observing from a production platform or drilling rig, the mind is disorientated further, as naked-eye range estimations are markedly different from binocular-reticle range estimates and laser range-finder measurements. Irrespective of whether reticle increments are converted immediately or later, this method is less labour intensive than creating range sticks for each observation platform; however, similar measurable inputs are required to make a range stick, which requires either a small wooden stick or a paper-covered ruler. On the stick or ruler, increments are drawn that correspond to ranges. To determine increment positions, a computer program
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called ‘Range Stick’ (Heinemann, 1981) is available. Alternatively, an Excel® file with a range stick program can be downloaded from the Internet (www.osc.co.uk). Once eye height above sea level, along with arm length, have been entered into the equation, the program creates a table that specifies where range increments should be drawn on the stick or ruler, as per Figure 6.5, which continues with the previous sighting example. When a target is sighted, hold the range stick exactly vertical, perpendicular to the outstretched arm, with the top of the stick aligned with the horizon. Range is then read off the increment that aligns with the target.
Figure 6.5 An example of a range stick.
An alternative range-finding technique is the sextant, which MMOs are permitted to use optionally (binocular reticles and range sticks are equally accepted) in the New Zealand Government’s Code of Conduct (CoC); sextants are not used elsewhere generally. To an untrained eye, a sextant appears complex and difficult to use, but in the simplest of terms, it estimates range by measuring the angle between two objects, more specifically, the angle between the horizon and a target. The angle can then be used to estimate range, and as with reticles, a table can be created that provides corresponding ranges. The sextant, which was used traditionally in marine navigation, has a graduated 60° arc, a pivoted movable arm, and a series of mirrors. Firstly, looking through the viewfinder, the sextant sights are aligned with the horizon. The pivoted arm is then moved until the target comes into alignment with, or is effectively superimposed on, the horizon. The angle is then read off the scale, and entered into a calculation or checked against a table for a corresponding range. Sextants are relatively costly, but suggested models include the Davis Mark 15 or alloy Astra IIIB. To aid in range estimation once offshore, if applicable, find out distances to towed equipment, such as the sound source, or seismic doors (Section 5.21.6). Alternatively, although not in real time, the PAMGuard video range finder module
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estimates range from photographs or videos. See Section 9.7.2 for how to add modules to a configuration. Once calibrated with observation platform information, and camera and lens specifications, points on the horizon and waterline of objects (marine mammals, vessels, etc.) are selected, and range estimated. More information on using this module is contained within PAMGuard help files.
When an animal is sighted, the bearing is estimated, usually from dead ahead or astern in the case of moving or static operations, or sometimes from ‘true’ north, particularly where static operations are concerned. For simplicity, and given the issues associated with compasses, this is best achieved with an angle board, using the basic design shown in Figure 6.6. Angle boards are simple to produce, but can also be downloaded from the Internet (www.osc.co.uk). Angles to port (or the left, in the case of static operations) are often distinguished (from angles to starboard, or the right) with a negative sign. It is advisable to laminate an angle board and attach it permanently to the outside of the clipboard. More elaborate designs can assist accuracy by including, for example, a rotating dial fixed to the origin, and two alignment sights (e.g. pins) located at the origin and at zero.
Figure 6.6 A basic angle board design for measuring the bearing to a sighting (STBD = starboard).
When measuring bearings, it is important to understand that there are two norths, true and magnetic. True north, or geographical north, is the location of the North Pole, and is displayed on maps by a longitudinal line, or meridian (see Section 6.5). It is this north that is used for sightings. Magnetic north, on the other hand, refers to the location of the magnetic North Pole, which changes constantly. The difference between these two norths is known as the magnetic variation. To estimate bearings from true north, record the heading of the ship or installation, align the angle board’s 0° line with the heading of the ship, then rotate the pointer (or pencil) around the angle board until it aligns with the target and record the angle to port or starboard. These details are then converted retrospectively at a convenient time, as an MMO should not get distracted with mental arithmetic during a sighting; however, for sightings to starboard, the angle board bearing should be added to the ship or installation’s heading, and for sightings to port, subtracted. It is possible to end up with minus numbers, or numbers greater than 360°, in which case, add or subtract 360° to get the correct bearing. Alternatively, find out the heading of the ship/installation, and align the angle board bearings to match, rather than to 0°, then move the pointer/pencil round to the target and read off the bearing. Other angle board variations exist, and com-
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plete compass roses may also be used, particularly aboard static installations, that offer unobstructed 360° views.
Photographing Marine Mammals
Even with top of the range equipment, getting decent photographs of marine mammals is challenging. The Internet is replete with photography forums, advice and tips for taking high quality photographs of wildlife, but a few tips are listed below to help get started. Whether using an SLR or simple point-and-shoot: • • • •
be ready, anticipate where an animal will surface next, and focus on that spot; once sighted, keep your eyes on the target, and hold the camera to your eye; monitor light levels in relation to the target, if possible keep light behind you; and, keep your lens clean.
If taking photographs with a camera that has changeable settings, consider using outdoor sports or action modes, rather than auto. If taking photographs with an SLR in manual mode, consider the following: • know your camera, and learn how to change settings quickly; • use continuous shooting/burst mode; • use Aperture mode (manually select f-stop, but shutter speed is selected automatically); • use an f-stop of 8 or 9; • set International Standards Organisation (ISO) to at least 400, but increase in low light; • if setting manually, set shutter speed to c. 1,000–1,250; and, • manually alter white balance to reflect light conditions. Once taken, observe the histogram, which shows whether the photograph is under-exposed (histogram to the left) or over-exposed (histogram to the right), then alter settings accordingly before taking the next photograph. In bright sunlight, UV or polarising filters can be useful, and improve the quality of a photograph. Naturally, all these steps take time, so the most important consideration is that the animal is actually photographed. Spending precious minutes fiddling with camera settings to get the ‘perfect artistic shot’ at the expense of identification evidence is unacceptable, especially in sensitive areas.
The majority of data are collected in UTC, also termed ‘Greenwich Mean Time (GMT)’ or ‘Zulu’ time, which is the primary standard by which the world regulates clocks and time; however, if working in locations where the time difference is substantial, check guideline requirements, as data may be collected in local time. There are generally four types of information required: survey, operations, effort, and sightings. In some locations, such as New Zealand, data are collected around the clock, 24 hours per day, but effort data are only required whilst on-effort in, for example, UK, Ireland, and Europe generally. Complete records of operations are required at all times.
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Countries, including Australia, Brazil, Ireland, New Zealand, and the UK all provide data forms, which are downloadable from relevant websites. Greenland, on the other hand stipulates use of JNCC forms. GoM guidelines also suggest this, but give MMOs the option to create their own. If doing so, ensure all data required are collected, and compiled in a logical manner, which is easy for others to follow. Exact requirements are outlined in guidelines. The JNCC provides two versions of its forms. ‘Deck forms’ are printed out, and completed by hand whilst on-effort and data are transcribed onto electronic versions post-watch. Other regions do not supply separate, printer-friendly versions of their forms, but it is advisable to print, and fill out hard copies if possible. New Zealand and Australian data forms are electronic, automated and involved, so laptops are essential. When performing observations in these two countries, it is advisable to print, laminate and attach to the clipboard a list of essential sightings parameters required for the electronic data forms, and a notebook to record these into during sightings. This is because in the ‘heat’ of a sighting, memory should not be relied upon to record parameters simultaneously.
6.11.1 Cover page The first form is referred to as the ‘cover page’, and need only be completed once by an MMO. All survey specifics are required, such as location and details about the sound source. Further requirements might include observation platform heights, personal details, distance estimation methods, and PAM.
6.11.2 Effort Effort is a log of MMO activity. Data are entered each time the MMO situation changes, for example, at the start and end of watch, or when the number of MMOs changes. Data are also recorded when sound source activity or weather changes, and thus observation conditions. Some guidelines require more detail than others do; GoM guidelines state start and end times and positions must be recorded and average weather conditions noted. Other forms are considerably more detailed. Usually there is one effort form, to be completed only when on-effort, but an exception is New Zealand, where there are two, on-survey and off-survey. Completion of either form depends upon location. If within boundaries of the project area, regardless of if the sound source is active, use the on-survey effort form. If not on-effort, the appropriate effort form still needs to be completed, but activity altered to indicate off-effort. Personnel taking a break during shifts are evidently not ‘on-effort’. For example, personnel who stop watches briefly (irrespective of how briefly) to visit the galley for steak (or lobster and steak if it is Friday night aboard a Petroleum Geo-Services (PGS) vessel) without entering ‘off-effort’ into data forms, can end up submitting forms with >12 h straight monitoring, which might appear impressive superficially, but knowledgeable employers/contractors/clients can identify such culprits. This behaviour does occur, so to highlight this point further, if engrossed in coffee and cream cakes (by now the reader will have gathered that cream cakes feature a lot in the Handbook) and/or conversation on the bridge (which may be perfectly acceptable during non-essential periods), enter ‘off-effort’. Otherwise, data are skewed and unreliable (which may incorrectly influence regulators’ future environmental management
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plans), the monitoring efforts are a waste of the clients’ money, and this substandard practice reflects badly on the MMO profession generally. Moreover, where such ‘superhuman’ MMO effort is recorded, clients have been known to employ independent scientists to review third-party data, and in some cases, narrow it down to individual ‘offenders’. This is especially true when undertaking data analysis for baseline or research purposes, where it is necessary to compare pre-existing and longer-term data sets inter-annually and seasonally, and estimation of typical detection rates is needed, especially if industrial permit applications are required. For example, if MMO A watches for a total of 8 h, detects eight whales, and truthfully enters 8 h of effort, and MMO B watches for a total of 8 h, detects eight whales, yet enters 16 h on-effort, the estimated detection rate is one whale per hour for MMO A, but only 0.5 whale per hour for MMO B. Therefore, MMO B’s data indicate half the actual detection rates for that survey, region, and time of year. This is known as ‘observer bias’ and is sometimes very clear between rotations for the same region. Golden rule: Do not lie about effort. Weather data include sea state, wind speed and direction, swell height, glare, and precipitation. Wind speed and direction are obtained from bridge instruments, but swell height, glare, precipitation, and sea state are estimated typically by MMOs. Swell height, measured from crest to trough of the wave, is usually divided into brackets, and glare and precipitation into categories, such as light, medium, or heavy rain. Sea state is estimated most commonly using the Beaufort scale (Table 6.8), but in the UK for example, JNCC sea state is divided into only four categories: glassy, slight, choppy, and rough. It is important to distinguish between Beaufort wind state and Beaufort sea state scales. Beaufort sea state is estimated by examining sea surface conditions visually and comparing with those described in the final column of Table 6.8, while Beaufort wind state is obtained from reading instruments. It might seem logical to assume that wind speed could be determined from the row of Table 6.8 associated with a visual estimate of sea state and, indeed, this is done as a last resort when wind speed instruments are not available; however, sea state does not always reflect wind speed accurately. For example, wind speed instrument measurements may not be completely accurate, due to suboptimal weather vane location and height. Similarly, with sea state, water may appear smoother in the lee of a vessel or in a bay surrounded by low-lying islands that create shelter. It is also important to note that wind speed, obtained from instruments on the bridge, can be recorded in two ways. True wind speed, the actual speed and direction of the wind, is calculated by subtracting the wind created during vessel movement (speed and direction), whereas apparent wind speed is a combination of true wind speed and wind created during vessel movement. If a vessel is travelling with the wind, it appears less windy than it actually is, and true wind speed equals apparent wind speed plus vessel speed. If a vessel is travelling into the wind, it appears windier that it actually is, and true wind speed equals apparent wind speed minus vessel speed. True wind speed is required for forms, so ensure the correct measurement is taken.
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Table 6.8 Beaufort sea state table. Beaufort
Glassy – sea like a mirror
Ripples, but without foam crests
Small wavelets, still short, but more pronounced; crests have a glassy appearance and do not break; no white caps
Large wavelets; crests begin to break; foam of glassy appearance; occasional white caps
Small waves, becoming larger; fairly frequent white caps
Moderate waves, taking a more pronounced long form; many white caps are formed; chance of some spray
Large waves begin to form; white foam crests are more extensive everywhere; probably some spray
Sea heaps up; foam begins to flow in streaks
Waves increase visibly, moderate to high; foam in dense streaks, blown in direction of wind
Waves increase visibly; foam blown in dense streaks, crests of waves start to roll over, visibility could be affected by spray
High waves with overhanging crests, great foam patches, blown in dense streaks, sea looks white, visibility reduced
High waves, small to medium ships hidden in troughs, air full of spray, sea covered in long white patches of foam, visibility reduced
Air filled with foam and spray; sea white with driving spray, visibility reduced severely
Beaufort sea state affects marine mammal sightings substantially. Below sea state 2, the chances of sighting a marine mammal is often high, regardless of species; however, above this, the possibility declines, and rapidly for some species. In particular, the likelihood of detecting smaller cetaceans such as harbour porpoises decreases (Palka, 1996; Evans and Hammond, 2004), and it is unlikely they will be seen in sea states 3 or above. This does not apply solely to smaller cetaceans, as Mobley (2005) stated that the chances of sighting humpback whale declined above sea state 2, and Barlow et al. (2006) found that the chances of sighting beaked whale reduced substantially between sea state 1 and
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sea state 5. As a rule, unless stipulated otherwise in guidelines, there is little point in conducting watches in sea state >6.
6.11.3 Operations data Operations data refer to the activity of the sound source. Details required depend upon guidelines, but at minimum, start and end times are recorded. To ensure soft-start protocol is followed, most records require soft-start times. It can be difficult to keep track of operational times, but crew always keep a full record, which can be obtained upon request.
6.11.4 Sightings All sightings, whether on- or off-shift, are recorded. If third-party personnel report sightings, obtain as much information as possible for the records, including the name(s) of the third-party personnel. Only record definite sightings, as false sightings introduce data inaccuracies. For example, do not record marine mammal sightings unless 100% certain that fins are not suspicious-looking waves, or indeed other animals altogether, such as sunfish (Mola mola) or sharks (except where these animals are also specified as species of interest by the regulator or client, etc.). Similarly, where there is any doubt whatsoever about identification, sightings are recorded as ‘unidentified’ and as much detail as possible is included on sightings forms. It is generally acceptable to assign sightings to basic categories, such as ‘unidentified whale’, ‘unidentified dolphin’, ‘unidentified cetacean’, ‘unidentified pinniped’, ‘unidentified seal’, ‘unidentified sea lion’, and ‘unidentified mustelid’, but only record sightings down to species level when there is no doubt. Another golden rule: one either identifies a species or one does not. A ‘possible species’ is meaningless and misleading. Data fields are indicated on forms and most likely include the following: • • • • • • • • • • • •
start and end time of the sighting; MMO name and any PAM; location; depth; species; bearing; distance from the sound source; sound source activity; number of animals; direction of travel (compass and in relation to vessel); behaviour; and, any delays or shutdowns.
Waypoints, taken using a handheld GPS, are useful for sightings, as they log location. Once a marine mammal is sighted, use a GPS to mark a waypoint; refer to instruction manuals for how to do this. The waypoint itself will reflect vessel location, but to map sighting position, use bearing and distance from the animal to project the waypoint. Again, refer to instruction manuals for method. In New Zealand, waypoints and projected waypoints are named in a particular way, so consult guidelines to ensure data are recorded correctly. If waypoints are taken, and projected, every time an animal surfaces, a track of its move-
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ments is recorded. This saves time, and allows concentration to be focused on the sighting itself, as well as providing a visual representation, which can be compared with the vessel, and sound source. Once uploaded, different symbols, or colours portray different species, or new sightings, allowing direct comparisons to be made. Animal behaviour is not always obvious, but if possible, note apparent changes in activity. This is important as some guidelines (e.g. New Zealand) distinguish between initial and subsequent behaviour. Some behaviours observed commonly are described in Table 6.9. Table 6.9 Marine mammal behaviour. Behaviour
Bow riding/wake riding
[Cetaceans] Social behaviour where, typically delphinid species, swim in the bow waves of vessels
[Cetaceans] Energetic behaviour where an animal launches itself out of the water and creates a splash
Feeding or foraging
Associated commonly with birds, fish, or krill patches; may comprise large numbers; animals may remain in one area for long periods; behaviour varies with species
[Cetaceans] Often seen in deep diving species; tail flukes raised out of the water prior to diving
[Pinnipeds] Refers to when seals are on land
Lobtailing or flipper slapping
[Cetaceans] Forceful slapping of tail flukes (lobtailing) or flippers (flipper slapping) on the surface of the water
[Cetaceans] Whales lie almost motionless at or close to the surface of the water; deep diving species often log together for long periods
[Cetaceans] Remain in one location for a prolonged period, direction of travel is variable
Fast swimming motion of dolphins or pinnipeds, where regular leaps are alternated with swimming close to the surface
[Cetaceans] Whale faces vertically downwards in the water column, only the tail fluke remains motionless at the surface
[Cetaceans] An individual raises its head vertically out the water
[Cetaceans] Energetic behaviours displayed at the surface, will include breaching, lob tailing, flipper slapping etc.
Continual movement in a single direction, can be fast (i.e. porpoising) or slow, but animals do not remain in one area for any length of time
If a marine mammal is sighted in the exclusion zone during pre-watch, inform appropriate crew members immediately, who may then be able to minimise production loss by slowing or altering the course of the vessel prior to reaching SOL. It is important to understand when mitigation action is required. For example, based on UK JNCC guidelines, if a
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marine mammal is sighted once 5 min into a 30 min pre-watch, delays need not occur, as start-up is allowed 20 min after last sighting; crew are, however, still notified. Alternatively, if a marine mammal is sighted 20 min into pre-watch, sound source activation is delayed by a minimum of 10 min, unless it is observed leaving the exclusion zone. In all cases, sightings are discussed in the daily, weekly, monthly and final reports (Chapter 10), but some guidelines have further reporting procedures. For example, in the GoM, whales sighted in the exclusion zone, resulting in shut-downs, must be reported to the BOEM/BSEE within 24 h. In New Zealand, guidelines stipulate that, if higher numbers of marine mammals (in particular species of concern) are sighted than outlined in the MMIA, DOC must be contacted immediately.
MMO at Night
The majority of guidelines for marine mammal and other species stipulate daylight observation hours only; however, in more sensitive areas (or where governments are more environmentally minded, such as in Germany), there may be requirements (often experimentally) for observation during darkness also. Conventional night-vision binoculars operate in near darkness by intensifying existing visible (or near-visible) external radiation (from moonlight, starlight, sky-glow, etc.). Night-vision binoculars are most common, and operate very well if there is sufficient external illumination, but they cease to operate altogether in absolute darkness or in deep shadows (Baldacci et al., 2005). Furthermore, night-vision binoculars do not work in seaspray, smoke, dust, haze, etc. and are consequently useless at sea in anything other than the calmest conditions. The electromagnetic spectrum comprises radio waves, microwaves, infrared light, visible light, UV light, X-rays, and gamma rays. The only type of light the human eye can detect is visible light. Although infrared energy is not detectable by the human eye (because its wavelength is too long), it forms part of the electromagnetic spectrum we perceive as heat, which is detectable using infrared sensors. At different temperatures, both biological and non-biological objects emit energy at different wavelengths, and of varying intensities; however, as long as objects are above –273 °Celsius (°C) or 0 kelvin (absolute zero), they all emit infrared radiation. Even very cold objects, like ice, emit infrared. The higher the object’s temperature, the greater the infrared radiation emitted. Infrared radiation spans three orders of magnitude and has wavelengths between approximately 750 nanometres (nm) and 1 mm. Infrared systems work by detecting subtle changes in temperature from living matter or from reflected and scattered thermal energy (such as clouds). Infrared binoculars perform much the same function as an infrared video camera, which has a sensor that is sensitive to the infrared fraction of the electromagnetic spectrum. This ‘natural blackbody radiation’ can be described by various forms of the Planck radiation law, which governs the intensity of radiation emitted by a unit surface area into a fixed direction (solid angle) from the blackbody, as a function of wavelength for a fixed temperature. A host of chemical compounds found in the atmosphere attenuate infrared energy, but there are numerous windows in the spectrum where absorption is reduced, and signals can be detected. The most common bands of interest are 3–5 and 8–14 micrometre (µm), also termed Long-Wave Infrared (LWIR). These two bands have the least atmospheric absorption (e.g. by humidity, clouds, fog, sea spray, or smoke and other atmospheric obscurants) and are the bands covered by HgCdTe and microbolometers,
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used as detectors in thermal binoculars or thermal cameras. Microbolometers comprise a grid of, for example, vanadium oxide or amorphous silicon heat sensors superimposed upon a corresponding grid of silicon. Infrared radiation from a defined range of wavelengths strikes the vanadium oxide, changing its electrical resistance. This resistance change is measured and processed into temperatures, which can be represented graphically. Infrared thermography sensors thus produce images of infrared ‘heat’ radiation so they can detect warm objects against a cold background when it is completely dark (such as on a cloudy, moonless night). At night, the absence of solar radiation presents an exacting challenge for infrared systems. This is because blubber-coated marine mammals have extremely effective thermal insulation and there is only a small temperature difference between the animal’s skin and the surrounding water (Baldacci et al., 2005). Even if animals break the surface, they are still coated by a thin layer of water, often masking the temperature of the body (Cuyler et al., 1992). Furthermore, the apparent radiation temperature from whales is dependent strongly on sea conditions, signal angle, and atmospheric interference; detection thus depends upon weather (Cuyler et al., 1992). During darkness, MMOs equipped with infrared binoculars (in conjunction with PAM) represent a science in its infancy. Most systems have been trialled during the day, with little use at night; however, the Marine Mammal Risk Mitigation (MMRM) program at the NATO Undersea Research Centre (NURC) has been investigating, among others, non-traditional observation methods of marine mammals, especially for use during night-time military SONAR experiments (Baldacci et al., 2005). Infrared light does not penetrate the first few micrometres of the water surface, so marine mammals can only be detected when they break the surface, usually for short bursts of time when resting, foraging, travelling, or socialising. The main body trunk of the marine mammal is normally not a heat window, this function being reserved for the appendages such as the fins, the blow hole, and the blow (Cuyler et al., 1992). Previous experience using radar to follow the blows of sperm whales in the Mediterranean (V. Todd, personal observation) revealed this somewhat similar technique to be successful in calm weather. Certainly, the blow and blowhole provide a consistent positive signal with apparent temperature differences to the surroundings ranging from 0.2–4.1 °C (Cuyler et al., 1992). Thermal imagers are also sensitive to scattered solar energy, and during the day are reflected off disturbed water and the animal itself, providing more detection opportunities, particularly in the Medium Wave Infrared Radiation (MWIR) band, where the solar irradiance is at its maximum (Baldacci et al., 2005). There has been very little research on the use of infrared systems to detect marine mammals at night. Results of a short experiment carried out by Baldacci et al. (2005) were of mixed success, but they list the reasons why this might have been the case; mostly a lack of night-time testing opportunities. These authors are planning future tests of these systems at night to try to improve their results. Graber (2011) tested the use of infrared cameras for detection of orcas in light and in darkness. Detections were made during the day and at night at ranges of 42–162 m, showing that infrared cameras are capable of detecting marine mammals at night, but it was acknowledged that they were restricted by weather conditions, and like any camera, detection ranges depended upon specifications of the camera. In this study, night detections were not made in real-time, but instead recordings were reviewed the following day, so real-time monitoring applications are unclear. Numerous high specification Forward-Looking Infrared (FLIR) sensor systems use digital image processing to improve image quality. FLIR sensor arrays often have
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inconsistent responses from pixel to pixel and to rectify this problem, the response of each pixel is measured at the manufacturers, and a mostly linear transformation process maps the levels of measured brightness. FLIR sensor arrays are characterised in terms of FOV, frame rate, and number of pixels (Baldacci et al., 2005). The standard FLIR system has a relatively small FOV and a high resolution. Wider FOV FLIRs are available, but are characterised by a lower resolution. A typical FOV is 8° (horizontal) by 6° (vertical). A classic FLIR system is designed to produce real-time display for human observers, so it has high frame rates to avoid image flicker. There are two rates used most commonly in Europe (25 Hz, Consultative Committee on International Radio, CCIR, standard) and North America (30 Hz, National Television System Committee, NTSC, RS-170 standard). The small FOV of FLIRs results in relatively small numbers of pixels compared to, for example, Infrared Search and Track (IRST) systems. Image dimensions rarely exceed 1,024 × 1,024 pixels, but dimensions of 640 × 480 or smaller are usual. One such hand-held binocular-type system (semi-appropriate for marine observation) is a Medium Wavelength Advanced Thermal Imaging system (MATIS) manufactured by Sagem Défense Sécurité. The Sagem MATIS needs to be mounted onto a tripod for stability, as it weighs 2.5 kg (without the battery) and is realistically too heavy to be held for any length of time by an MMO. The system comprises a one-piece, fully autonomous camera that integrates a binocular display, controls, and a battery pack. At a cost of around £45,000, this is not a product affordable to MMOs without royal connections. Moreover, the Sagem MATIS is currently classified by the French authorities as ‘sensitive’ and is subject to export approval from the French administration, so it can take three months to get security clearance, a fact worth bearing in mind when advising a client with deep pockets and all the time in the world (i.e. forget it).
Occasionally, MMOs are required to undertake distance sampling surveys, which enable the density and abundance of biological populations to be estimated. Typically, this involves a line-transect methodology for data collection, using a vessel platform, from which MMOs conduct standardised and consistent surveys along predefined track-lines. Several parameters are measured for each sighting, including radial distance from vessel to animal(s) and sighting angle, which are subsequently transformed for analysis (Figure 6.7).
Figure 6.7 Distance of detections from survey track-lines are collected for distance sampling analysis. Source: adapted from Buckland et al. (1993).
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Accuracy of the line-transect method is dependent on some founding assumptions, including that all animals along the track-line are detected. This criterion is difficult to meet for marine mammals, as they become harder to detect with increasing distance from the line, resulting in proportionately fewer detections. The key to distance sampling is to fit a ‘detection function’ to the observed distances and use this to estimate the proportion of animals missed by the survey (Buckland et al., 2001). By measuring the distances of observed animals from the track-line, the probability of observing any animal along the survey line can be estimated. Distance sampling therefore relaxes the assumption that all animals along a survey line are counted. A computer program called ‘Distance’ (Thomas et al., 2006) is available to design and analyse distance sampling surveys. A comprehensive list of fundamental assumptions for line-transect surveys should include the following as a minimum (Buckland et al., 1993, 2005): • Objects (e.g. individual animals or animal groups) on the centre line must be observed with probability = 1.0 (i.e. every object on the line must be detected); however, as previously stated, distance sampling methods relax this assumption, by incorporating estimations to allow for some error; • Line transects are placed randomly, or at least objectively, with respect to the population being studied; • Objects do not move toward or away from the line-transect in response to the observation platform (vessel) prior to measuring distances; • Distances from the line transect to each object are measured accurately; • Line transect segments are straight; • The size of the object (or, if objects occur in groups, the size of the group) does not affect the probability of observation (otherwise it is necessary to employ analysis methods that account for size-bias); and, • Objects encountered are independent (i.e. observing an object does not affect the probability of observing any other object). Additionally, sample sizes (number of objects observed) must be sufficient to provide robust estimates of the detection function and its variance. If sample sizes are too small, results can be accurate in theory, but unreliable in practice. In reality, it is difficult to comply with all these assumptions and obtain reasonably large sample sizes under field conditions. Weather and sea conditions greatly affect the ability to detect marine mammals, but there is a trade-off between delaying surveys and the limited window of opportunity (in terms of time allocation, costs involved, and the logistical complexity of such projects to spiral out of control), so data should only be included in analyses when the following conditions are met: • sea state is Beaufort 5 or below (maximum of Beaufort 4 during seismic shooting); • swell is below 2 m (5 km during seismic shooting). Line transect surveys are more rigorous and structured in their design than standard seismic observations and require strict protocols to be followed. As with all field surveys, results are only as good as the data collected, so it is important to ensure that all data are collected with maximum consistency and precision.
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Equipment and skills required for distance sampling are similar to those required for other survey types (Section 6.2). Binoculars with range-finding reticles, GPS, bearing estimation tools, and a clipboard with data sheets are all essential. Ensure weather conditions are recorded correctly, and range estimated accurately, as incorrect data will most likely impact upon analysis. In order to collect high-quality data and achieve an even survey coverage over the entire area, observations are carried out from the highest possible vantage point, and in good sighting conditions. Consistency is vital to distance sampling methods, so ensure the same observation platform is used throughout the survey. Line transect methods are based on periods of ‘on-effort’ surveying, when observation and data collection are carried out in a standardised and replicable manner. On-effort is defined as periods when an MMO is scanning usually a 180° search area (e.g. 90° to port and 90° to starboard). During this time, binoculars are employed for the purposes of confirming species ID, assisting estimates of group size, and supporting ranges that are estimated with suitable methods of range estimation. During on-effort observations, MMOs are not assisted by other crew members. Sightings by others are recorded, but the on-effort MMO is not notified until after the animal has passed. The reason for this is to maintain consistent MMO effort of recorded sightings throughout the survey, to ensure final data are used to provide accurate estimates. Similar to other survey types, effort data are entered by MMOs throughout, but given that all line-transect methods require very accurate assessments of sea state and swell conditions, greater attention must be paid to weather, and all changes in environmental conditions are noted on effort forms immediately. Sightings also need to be recorded with the upmost accuracy, and all sightings of marine mammals, whether on-effort or off-effort, are recorded, and when possible, photographs taken. When a sighting occurs, recording latitude and longitude, distance to animal, sighting angle, vessel heading, and the direction of the animal’s travel is top priority; other fields, such as species, group size, and behaviour are lower priority, but complete all fields if possible.
PAM Theory 7.1
The field of acoustics is mathematical. The famous, witty, internationally leading researcher in this field, Dr Doug Gillespie (a.k.a. ‘the Brain’ to us lesser mortals) once said of PAM Operators, ‘If you don’t understand the SONAR equation, you are in the wrong job’. The SONAR equation excepted, this book avoids equations wherever possible, endeavouring to use written explanations of acoustic phenomena and terms. This chapter serves only as a basic introduction to acoustics, and is written with PAM Operators and MMOs in mind, not acousticians. Thus, we hope our more specialist readers understand that explaining these terms without the use of equations, and in a way that is understandable to non-acousticians, is a serious challenge. We tried our best, and while suggestions are welcome, please try not to be too hard on us. Anybody interested in ‘those beautiful methods of reckoning which are generally called by the terrifying names of differential calculus and integral calculus’ (Thompson, 1914) are best served by consulting Urick (1983) and Zimmer (2011). Nonetheless, a good understanding of the concept of underwater sound is essential for PAM Operators; however, MMOs must also have a firm grip on how sound behaves, and its potential impacts on marine mammals, otherwise they can neither understand potential impacts nor offer informed advice to clients. The direct impact a sound might have on a marine mammal is related to five main factors: (1) audibility; (2) received energy; (3) received intensity; (4) sound frequencies; and, (5) species’ sensitivities. Other factors play a role, including age and sound exposure history, such as habituation/attraction/association with danger or food. Without exception, all MMOs and PAM Operators must be able to report industrial sound in a marine mammal mitigation context accurately, including correct units and a full understanding of unit definitions and comparability. This chapter outlines the basics of sound and units, and highlights various ways sound is displayed visually. This chapter is an introduction only, the full extent of acoustics is beyond the scope of this book. Physical characteristics and descriptors of marine mammal vocalisations and noise are presented in Chapter 8. For a more detailed overview of acoustics related to the study of marine mammals, see Au and Hastings (2008) and Zimmer (2011). There are a plethora of textbooks and online sources that specialise in acoustics, audio/sound engineering, physics of sound, and signal processing that are available for those interested in a deeper understanding.
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Basics of Sound
Sound as defined by Morfey (2001) is ‘a disturbance in pressure that propagates through a compressible medium. More generally, sound can refer to any type of mechanical wave motion, in a solid or fluid medium, that propagates via the action of elastic stresses and that involves local compression and expansion of the medium’. The passage of a sound wave causes particles (small volumes of the medium) to oscillate around a fixed point. Sound cannot travel through a vacuum. In a fluid, sound propogates as a longitudinal pressure wave, in which particles move parallel to the direction the wave is travelling (Figure 7.1a). When sound travels through a medium, it is locally compressed and expanded at various points along the transmission path, processes termed compression and rarefaction respectively. Compression points are regions of pressure higher than the surrounding ambient pressure and rarefaction points are regions of relatively low pressure. The overall pressure, the ambient pressure plus the pressure caused by the acoustic wave, is always a positive value. These changes in pressure are received by ear structures or by fabricated receptors such as hydrophones. Pressure is a force per unit area. Acoustic or sound pressure is measured in Pa, and expressed often in µPa (Section 7.2.4). Properties of sound can be illustrated by considering a sinusoidal acoustic wave, as shown in Figure 7.1b. Maxima are points of high acoustic pressure where the medium is compressed as a result of the sound wave, and minima are points of low acoustic pressure (rarefaction).
Figure 7.1 (a) Compression and rarefaction as sound moves through a medium, and (b) graphical representation of pressure variations in a sound (sine) wave.
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A wavelength (λ) is the spatial distance over which a wave repeats itself and is often measured between a peak and a trough (Figure 7.2). Wave period is the smallest increment of time in which a wave repeats itself (s), and is measured as the interval between corresponding points on consecutive points on the wave, typically between maxima or minima. Thus wavelength is a measure of distance and period is a measure of time. For a sine wave, sound frequency (ƒ) is the number of periods per second, which is the rate of oscillation or vibration. The unit of frequency is the Hz, where one Hz corresponds to one cycle per second.
Figure 7.2 Sine wave showing how amplitude and wavelength can be measured.
The discernment of pitch by mammals is related directly to frequency. A low frequency sound (low pitch) has a small number of oscillations or vibrations per second, whereas a high frequency sound (high pitch) has a large number of oscillations or vibrations per second. Increasing frequency in equal steps, e.g. 1,000 Hz, 1,100 Hz, 2,000 Hz, 3,000 Hz, 4,000 Hz, leads to perceived increases in pitch that seem to grow smaller with each step. Understanding how humans hear is a complex subject involving the fields of physiology, psychology and acoustics, which is outside the scope of this Handbook. In short, young, healthy humans can hear in a range between c. 20 Hz–20 kHz (20,000 Hz); this band can vary with age, sex and exposure history. Low frequency sound below human hearing is categorised as infrasonic (0–18 Hz), and high frequency sound above human hearing is considered to be ultrasonic (>20 kHz). Other animals have different frequency sensitivities. For example, dolphins, bats, and dogs perceive certain ultrasonic sounds, whilst elephants, pigeons, and some baleen whales are able to detect some infrasonic sounds. Bandwidth is expressed as width of range or ‘band’ of frequencies, in terms of difference, in Hz, between the highest and lowest frequency signal components, and as such is measured in Hz. For example, in telecommunications, a typical system designed to carry speech signals has a bandwidth of c. 3 kHz, while an analogue television (TV) broadcast video signal has a bandwidth of 6 MHz, c. 2,000 times as wide as the telecommunications system. Band-
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width refers to a signal or a system (e.g. a hydrophone). For example, hearing bandwidth of an animal is defined as the range between minimum and maximum audible frequencies, e.g. for humans, using the values above, the hearing bandwidth would be 19,980 Hz. Similarly, the range of frequencies a hydrophone is sensitive to is referred to as its bandwidth. Sounds produced within a narrow range of frequencies are known as narrow bandwidth, while sounds covering a wide range of frequencies are known as broadband. Peak frequency is the frequency of maximum power (or maximum energy), and it corresponds to the frequency where the most energy lies. Peak frequency is also known as dominant frequency or frequency near maximum energy. Centroid frequency, or spectral centroid frequency, indicates location of ‘centre of mass/gravity’ for a spectrum, i.e. the frequency that divides spectrum energy into two equal parts. The average frequency is the sum of the product of the frequencies and amplitudes, divided by the sum of the amplitudes. Harmonics are a signal or wave, whose frequency is an integral (whole number) multiple of the frequency of a reference signal or wave. The reference is known as the fundamental frequency. Harmonics are thus 2×, 3×, 4×, etc. the fundamental frequency (Figure 7.3). In the power spectrum (Section 7.3.2), the fundamental frequency is the lowest common denominator of harmonic peaks and therefore relates to the periodicity of the sound (i.e. the interval in Hz which separates each harmonic). For example, if 100 Hz separates each harmonic, the fundamental frequency is 100 Hz. See Watkins (1967) for more details on the harmonic interval. Components, fundamental frequency, and harmonics are produced at the same time.
Figure 7.3 Sine curves illustrating harmonics expressed as higher frequencies in the form of integral multiples of a fundamental frequency.
Amplitude describes how much pressure is created by a sound wave, and is defined as the vertical distance (height) between maxima or minima of the sine curve and equilibrium value (Figure 7.2). Differences in amplitude and frequency are visualised easily by comparing sine waves (Figure 7.4). High amplitude waves carry a larger amount of energy than low amplitude waves. In human ears, amplitude is related to loudness; an increase is perceived as a sound getting louder, akin to turning up the volume on a TV and vice versa when volume is reduced; however, two sounds with identical amplitude, but differing frequencies are not perceived as having the same loudness. Humans, and other animals, have a range of frequency hearing sensitivities, meaning that frequencies on the periphery of best hearing range appear quieter. See Section 1.5.2 for more details on marine mammal hearing ranges.
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Figure 7.4 Sine waves with different amplitudes and frequencies.
Sound energy, intensity, and power
Energy of a sound wave is associated with the motion of matter and is referred to as acoustic energy, measured in joules (J). Intensity of a wave is the average amount of energy passing through a unit area per unit time in a specific direction. An increase in amplitude results in an increase in intensity (and loudness) and vice versa, with a decrease in amplitude. The amount of acoustic energy radiated per unit time is called power. Intensity of a sound wave is therefore the amount of power transmitted through a specified area in the direction in which the sound is travelling. Power is measured in watts (W), and intensity in watts per square metre (W/m2).
Sound Pressure Level and the decibel scale
In acoustics, the decibel (1/10 bel = 1 dB) is preferred because the highly sensitive human ear can detect changes in intensity as little as 1/10 of a bel. Magnitude of sound is often measured using SPL, the unit of which is the decibel (dB), which is a relative quantity defined as the ratio between received sound pressure or measured pressure, p, and a fixed reference pressure, p0, using the following equation:
Received pressure and reference pressure are measured in pascals (Pa). For underwater sound, a reference pressure of 1 μPa is the standard value chosen. Underwater sound is detectable at a wide range of pressures, thus a logarithmic scale is convenient to obtain numbers in a relatively compact range. Using a logarithmic scale means that doubling sound pressure does not double dB value. The concept of dB is extremely important for
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an MMO and PAM operator to understand. The SPL equation can be used to compare two sound pressures, where: log10 is the base 10 logarithm:
p1 and p2 are the pressures to compare (pressure in µPa). Doubling sound pressure adds c. 6 dB. For example, where sound pressure doubles from 2 to 4 µPa:
A 10-fold increase in pressure gives a 20 dB increase:
A 100-fold increase in pressure gives a 40 dB increase:
Insertion of any number of values into the above equations demonstrates how dB changes with increasing sound pressure and illustrates how doubling pressure does not double dB value; this can also be carried out using various online calculators, such as http://easycalculation.com. The dB on its own is a dimensionless unit and must therefore include a fixed reference pressure that depends on which medium sound is travelling through. Consequently, reference pressures used to compute sound levels in water or air are different. The SPL of sound in water is reported as dB re 1 µPa, where re denotes reference. In air, the agreed reference pressure is 20 μPa, because a 1 kHz sound in air with a pressure of 20 μPa is just about audible to the majority of humans. The different references for water and air render generated sound level comparisons between the two media meaningless. When two sound sources of equal intensity are compared, the pressure is 35.5 dB greater underwater than in air. When reporting sound levels as an MMO or PAM Operator, it is important to give sound levels in dB with reference level and sound frequency. This tenet is essential when considering units for MMO and PAM reports, and is addressed in Chapter 10. In older literature, SPL is reported as dB re 1 µbar, dB re 1 dyne/cm2, or dB re 0.0002 dyne/cm2. One µbar (1 dyne/cm2) was the standard unit for underwater acoustics and 0.0002 µbar for airborne acoustics and early research on underwater acoustics. To convert SPL in dB re 1 µbar to dB re 1 µPa, add 100 dB, and to convert from dB re 0.0002 µbar, add 26 dB. The dB scale is used also for sound intensity, which like sound pressure, is defined as the ratio between two intensities (I1 and I2). Sound intensity is proportional to the square of sound pressure and the dB equation for sound intensity is:
A sound that is 10 times more intense gives a 10 dB increase. A sound that is 100 (10 × 10) times more intense gives a 20 dB increase, and a sound 1,000 (10 × 10 × 10) times more intense gives a 30 dB increase. For example:
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Understanding differences in how sound pressure and SPLs are calculated and reported in publications is vital, as they are not comparable directly. Various methods of calculating SPL are illustrated in Figure 7.5. Peak pressure refers to maximum absolute amplitude over a specified period. Absolute indicates that a non-negative number is always reported, meaning peak pressure can be measured from zero pressure to either maxima or minima, and can be stated as 0-to-peak pressure. Peak-to-peak (p-p or pk-pk) pressure is measured from minima to maxima. An example of how peak-to-peak, measured 1 m from the source, can be reported in the literature is as follows: dB re 1 µPa @ 1 m p-p.
Figure 7.5 Methods of calculating sound pressure. rms = Root Mean Square.
The calculation of Root Mean Square (rms) pressure is more complicated than other methods, and involves taking instantaneous sound pressures (positive or negative), squaring the values, then averaging the squares and finally taking the square root of that average. Bioacousticians often use rms pressure, because it relates directly to sound intensity, and therefore reflects better how mammals hear sound. In general, taking rms is useful for sine waves, because squaring values eliminates the problem of having both positive and negative numbers (i.e. if an average of a sine wave is taken, it is always zero, regardless of amplitude, because positive and negative values cancel each other out). Root Mean Square pressure is also useful for continuous non-repeating signals, such as ambient noise. Root Mean Square relies on a selected window size to take average instantaneous sound pressures, so two rms pressures from the same sound wave change, if different windows are chosen. Consequently, rms pressure is not appropriate for impulsive signals, as rms pressure decreases as time window increases. There is no standardised time window for calculating rms pressure. Unless stated otherwise, pressure is inferred to indicate rms (Au and Hastings, 2008). Examples of rms pressure units taken 1 m from the source are as follows: dB re 1 µPa rms @ 1 m, dB re 1 µPa rms @ 1 m, or dB re 1 µPa @ 1 m rms.
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SL refers to acoustic intensity of a sound at its emission point (source). Commonly, it is reported as the intensity of a sound 1 m away from source location. For distributed sources (e.g. large vessels or source arrays), it is possible that SL measurements at 1 m are overestimated. Incorporating the acoustic intensity of a reference wave (in water, a plane wave of rms pressure 1 µPa), the full unit of measurement in water is expressed as dB re 1 µPa @ 1 m, dB re 1 µPa at 1 m, or dB re 1 µPa-m. In practice, SL is measured rarely 1 m from the source, so is most often estimated by measuring SPL at a known distance. Predicted attenuation effects are then subtracted from measured value to estimate SL. In older literature, SL reference distance is given as 1 yard; this is converted to levels at 1 m by subtracting 0.8 dB. Maximum SL is measured in line with the sound transmission path (i.e. on-axis). When SL is measured away from this path (i.e. off-axis) sound intensity is less. Apparent Source Level (ASL) comprises SL and the reduction of sound intensity as a function of off-axis angle, although it is often adopted when reporting SL from a signal with an unknown orientation. The function of off-axis attenuation will depend on multiple variables (e.g. bandwidth (Section 7.2.1), medium, etc.). A list of typical SLs in the marine environment are listed in Table 7.1. A simplified representation of frequencies vs. SLs is illustrated in Figure 7.6. SL is reported as dB re 1 µPa @ 1 m for consistency with Chapter 3 and Chapter 8. Values are not definitive, as variations exist within all sources (i.e. animals create loud and quiet vocalisations, and earthquake magnitude varies). Ambient noise (which is not a localised sound source) such as wind, waves, and rain, has not been included, as it is reported as sound pressure density spectrum levels (Section 7.3.3) (e.g. Wenz, 1962; Ross, 1976; Richardson et al., 1995; NRC, 2003). Table 7.1 Various Source Levels of anthropogenic, biological, and natural noises. Source: OSC, with values from www.dosits.org and www.fas.org, 2014. Source
Broadband SL (dB re 1 µPa @ 1 m)
Seafloor volcanic eruption
Sperm whale clicks
Humpback whale fluke and flipper slap
Blue whale moans
Fin whale moans
Offshore drilling rig
Humpback whale song
Bottlenose dolphin whistles
Open ocean ambient noise
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Figure 7.6 Underwater simplified frequency vs. Source Level (SL) of some anthropogenic (dark gray), underwater biological (light gray), and natural (checked) noise. AMD = Acoustic Mitigation Device. IMPAS = Integrated Marine Mammal Monitoring and Protection System. p-p = peak-topeak. rms = Root Mean Square.
Sound propagation and transmission loss
The method of sound travel through a medium is referred to as sound propagation. In water, it is dependent on a wide range of variables, such as salinity, temperature, depth (pressure), bottom (seabed) conditions, frequency, and source depth. Zone of influence (i.e. distance at which animals are affected by a noise source) varies daily, seasonally and regionally, to a large degree on account of interplay between factors affecting signal propagation. Understanding how sound propagates is essential for reliable assessment of potential sound impacts on marine mammals. Transmission Loss (TL) is the accumulated decrease in acoustic intensity (energy) as a sound pressure wave propagates outwards from a source. Signal intensity is reduced with increasing range from source due to spreading loss and attenuation. TL is expressed in dB, and denotes a ratio of sound intensity at two distances from the source (intensity at a distance of 1 m/intensity at a distance R). The TL value increases with increasing distance from the source. Spreading loss does not represent a loss of energy, but refers to the fact that propagation of the acoustic pulse is such that energy is spread over a progressively larger surface area, thus reducing its density. Spreading loss is not frequency dependent. In its simplest form, a point source in a uniform medium spreads outward as spherical waves (i.e. it spreads uniformly in every direction), and is referred to as spherical spreading (Figure 7.7). Spherical Spreading Law applies when sound energy spreads outwards with no refraction or reflection from boundaries (e.g. the sea floor or surface). With spherical spreading, when distance is doubled, sound levels lessen by 6 dB, and when distance increases by a factor of 10, levels lessen by 20 dB. When a medium is not uniform (i.e. density discontinuities or boundaries exist),
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cylindrical spreading takes place. In general, sound energy spreads outwards spherically from the source, then spreads cylindrically once it has reached a set of boundaries. For example, in shallow water, sound is reflected off the surface and seabed, which generate cylindrical spreading (Figure 7.7). With cylindrical spreading, when distance is doubled, sound levels lessen by 3 dB, and when distance increases by a factor of 10, levels lessen by 10 dB. True spreading is often somewhere between spherical and cylindrical predictions.
Figure 7.7 Simplified representation of spherical and cylindrical spreading.
Sound undergoes absorption and scattering losses as it propagates through a medium. Absorption losses arise because some acoustic energy is absorbed (attenuated) by the medium or at absorbing boundaries. During absorption, sound energy is converted into heat. Absorption loss depends strongly on frequency, and loss increases linearly with distance travelled. Sound is absorbed by water at a rate that is related to the square of frequency, so higher frequencies suffer greater attenuation. A lower frequency sound has a low absorption coefficient, allowing it to propagate long distances. In terms of marine mammals, this explains why large baleen whales that produce low frequency sounds are heard at greater distances than, for example, harbour porpoises, which produce higher frequency sounds. Scattering losses arise when a sound wave is diverted from its straight path, for example, when it encounters sea surface, seabed, suspended particles, living organisms, and bubbles. Scattering losses also increase with distance linearly. When scattering occurs, multiple sound wave paths can arise, causing small differences in arrival times or amplitude at a receiver. As sound travels it can also change direction due to changes in its velocity. Changes in temperature, pressure, and density (salinity) alter the speed of sound in water. This change in direction, or bending of a sound wave, is referred to as refraction. Refraction is governed by Snell’s law, which relates angles of incidence with changes in direction (Urick, 1983). A good introduction to oceanography is given in the UK’s Open University book series (e.g. Brown et al., 1995a,b). To appreciate underwater sound propagation, it is important to realise that as temperature, salinity, and pressure (depth) increase, sound speed increases, albeit at different rates for each variable. Changes in temperature are considered to have the most important influence on sound speed, followed by salinity, then pressure (depth). Sound speed increases by 4.6 m s–1 per °C, 1.3 m s–1 per ppt (parts per thousand, used to measure salinity), and 0.016 m s–1 per m depth respectively (Urick, 1983). The scale of oceanographical factors varies temporally and spatially throughout the world’s oceans. In general, salinity has minimal effect on sound speed in the open
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ocean, where changes are relatively small; however, in coastal or estuarine regions, salinity is more variable because of riverine freshwater inputs, so sound speed is influenced to a greater extent. Worldwide sound speed, temperature, and salinity profiles are available for free on the web in various downloadable forms, e.g. www.nodc.noaa.gov, but are more appropriate for acousticians undertaking noise measurements than PAM Operators. At any one location, in order to determine sound speed variability with depth, empirical measurements are made. This is best achieved with the oceanographer’s favourite tool, the Conductivity, Temperature, Depth (CTD) meter. Results are presented as a sound speed profile or Sound Velocity Profile (SVP) (Figure 7.8).
Figure 7.8 General sound speed profile.
In a general ocean SVP, not accounting for season or geographical location, the temperature of the uppermost surface layer varies over a 24 h period as the sun rises and sets. Below that, sound speed increases slightly with increasing depth through the isothermal layer, because of increase in pressure with depth. Sound speed through the thermocline decreases with depth, because of decreasing temperature with increasing depth. Water temperature continues to decrease until it reaches maximum, or peak, density at c. 4°C. At some point, sound speed reaches a minimum point, known as the sound channel axis or SOund Fixing And Ranging (SOFAR) axis or channel. Here, special temperature and pressure conditions allow sound waves to travel with minimal scattering. At the channel axis, higher temperatures towards the surface of the ocean and higher pressures towards the bottom results in a minimum sound speed. In this channel, it is thought that large whales can communicate across oceans (e.g. Tyack and Clarke, 2000). Beyond the sound channel axis, water temperature tends to reach a nearly constant value throughout the deep ocean. Increasing pressure at this stage has the most influence on the speed of sound, which increases with depth. Numerous sophisticated ray/beam noise propagation models have been developed that incorporate oceanographic and bathymetric variables into modelling applications for a wide range of novel, complex, and difficult acoustic sources. Underwater acousticians run real-time models to determine how sound from an industrial operation is likely to travel in order to predict consequences for marine mammals, often in the form of zones of acoustic impact. MMOs and PAM Operators sometimes work alongside
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acousticians during industrial operations (especially in North America), so it is important to gain an understanding of model results, implications for marine mammals, and what the various terms in acousticians’ reports mean. Noise reports discuss SLs, SELs related to marine mammal hearing (Sections 1.5.3 and 7.2.9), and zones of influence. A full explanation of acoustic noise propagation methods is outside the scope of this Handbook, but there are a wide variety of books and online resources available. For example, de Jong et al. (2011) give a good overview into measuring and monitoring underwater sound.
RLs refer to ‘loudness’ (acoustic pressure) of a sound at some distance away from source. Sound looses acoustic pressure as it travels through a medium (Section 7.2.6), therefore RL is lower than SL. The 500 m exclusion zone used in the UK’s JNCC guidelines is based on RLs likely being less than 180 dB re 1 µPa at 500 m from a seismic airgun with a SL of 237 dB re 1 µPa @ 1 m. In MMMPs, RLs from noise propagation models for a given anthropogenic noise source in a particular region of interest, are used to calculate different exclusion zones. The reception of sound by a marine mammal depends on a variety of factors (e.g. SL, sound spreading and absorption, ambient noise, and receiver characteristics). One important factor is the Signal-to-Noise Ratio (SNR), which determines whether a signal is heard over background noise. For example, a person speaking at a normal level in a library is heard and understood considerably better (in other words has a higher SNR value), than if they speak at the same level in the front row of a rock concert. The same applies to marine mammals using acoustic signals for communication, orientation, and foraging in the ocean. If background noise is elevated, resulting in a poor SNR, a transmitted signal is not received. The same principle applies for PAM Operators trying to detect vocalising animals during anthropogenic noise activities such as seismic exploration. SNR, often expressed in dB, can be estimated using the SONAR equation.
It is important that PAM Operators understand the reality of the chances of detecting a vocalising marine mammal in an industrial situation, and the SONAR equation (covered cursorily here, out of deference to ‘the Brain’) is central to this tenet. For a more technical explanation of the SONAR equation and how to calculate each component see Zimmer (2011). SONAR is either active or passive. Echolocating marine mammals use active SONAR while a PAM Operator using a hydrophone system uses passive SONAR. This Handbook covers only the passive SONAR equation. Received sound intensity for a passive SONAR system is less than source intensity because of TL as it travels from source (e.g. vocalising marine mammal) to receiver (e.g. hydrophone). Received signal intensity is therefore source intensity minus TL, in units of dB.
The SNR incorporates loss in intensity due to TL, along with Noise Level (NL) at the receiver.
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NL at the receiver is important because an animal producing a loud sound may not be detected if the noise at the receiver is substantial. Similarly, a person may not hear another person calling to them from the other side of a room, if surrounded by nearby noise. This is often the case when towing PAM arrays from seismic survey vessels. Hydrophone deployment distance is often restricted because of the presence of other towed equipment, meaning marine mammal vocalisations can be masked by industrial noise (e.g. seismic air guns, engines, thrusters, machinery vibration, propeller cavitation, etc.). Weather conditions, such as wind, rain and waves, and biological noise, such as snapping shrimp also affect NLs. A hydrophone’s directivity also influences SNR; this term is referred to as the Receiver Directivity Index (DIr).
A directional hydrophone increases sensitivity in one bearing by filtering out background noise that is not emanating from the target direction it is concentrating on. This is akin to a person cupping their ear against a door to block out noise on their side of the door, enabling them to hear sound on the other side. Additional components of the SONAR equation are off-axis attenuation, and array and processing gain of the receiver, which are explained by Zimmer (2011).
Sound Exposure Level
SEL, often expressed as dB re 1 μPa2 s, measures energy instead of pressure or power. Energy is proportional to the time integral of pressure squared. So, the amount of total energy is not given directly by instantaneous pressure levels. SEL is used commonly to measure airborne impulsive sounds, with A-weighting implied, but is observed in reports on transient underwater-pulsed sounds, without Aweights, such as those from airguns during a seismic survey. This measurement is used sometimes in underwater acoustics, but is used rarely in studies of underwater noise and marine mammals because applied A-weighting is not appropriate. See Section 1.5.3 for details on A-weighting.
7.2.10 Duty cycle The duty cycle of a sound is the fraction of time the sound source is ‘on’ (i.e. making sound). For example, if piling occurs for a total of 6 h over a 24 h period, the duty cycle is 6/24 = 0.25 = 25%.
Displays of Sound
Sound can be represented visually in a spectrogram, where horizontal dimension (x-axis) corresponds to time and vertical (y-axis) to frequency; amplitude in dB is indicated by colour or shade (Figure 7.9). A Fourier transform computes frequency content of a signal to create a
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spectrogram. In-depth detail of the Fourier transform and other signal processing techniques are outside the scope of this Handbook.
Figure 7.9 Modified (labelled axes) screen shot of a smooth scrolling spectrogram of false killer whale (Pseudorca crassidens) vocalisations, as viewed in PAMGuard. The vertical line (slightly before 4.0 s) scrolls with time.
Power spectrum and Power Spectral Density
The easiest way to describe power spectrum is to consult what bioacousticians affectionately call ‘the green bible’ (Richardson et al., 1995), which defines it as ‘the distribution of power in a signal versus frequency, where tones are the important components. Correct units are W, but the usual units in acoustics are µPa2; power is proportional to pressure squared and pressure is the measured quantity’. Power spectra are used often to examine frequency distribution of marine mammal clicks during real time mitigation. An example of a power spectrum, as displayed in RainbowClick, is shown in Figure 7.10. The authors note that this is not an ideal example, given the lack of specified units and axes in PAMGuard displays generally, but feel that its inclusion is important, as it shows PAM Operators what a power spectrum looks like when working with PAMGuard in the field.
Figure 7.10 Power spectrum (power vs. frequency) from a generalised beaked whale click viewed in RainbowClick (now a part of PAMGuard).
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To quote Richardson et al., 1995 again, Power Density Spectrum is defined as the ‘distribution of power in a signal versus frequency, where continuously distributed sound (not tones) is the important component. Correct units are W/Hz but the usual units in acoustics are µPa2/Hz; power is proportional to the mean square pressure and pressure is the measured quantity’. Explaining how to calculate Power Spectral Density (PSD) is complex, requires use of an FFT, and an understanding of Parseval’s theorem, and thus is not a topic we shall endeavour to explain here; however, the authors wish readers with a deeply mathematical bent the best of luck in their further reading, if terms like ‘Lebesgue measure’ and ‘Euclidean space’ tickle their fancy.
Sound pressure density spectrum
Sound pressure density spectrum (Figure 7.11) is the ‘distribution of sound pressure versus frequency, appropriate for signals with a continuous distribution of energy within the frequency range under consideration; pressure at any frequency is infinitesimal, but integration over a frequency band results in a nonzero quantity. Dimensions are pressure squared per unit frequency (e.g. µPa2/Hz)’ (Richardson et al., 1995). Units can also be expressed as dB re 1 µPa/√Hz which are the same as dB re 1 µPa2/Hz. Sound pressure density levels are reported for ambient underwater noise, notably Wenz Curves (Wenz, 1962).
Figure 7.11 Sound pressure density spectrum measured from jack-up drilling rig during routine operational activities. RL = Received Level.
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When performing analysis of a sound source, it is often impractical or time consuming to examine each and every frequency, especially if only a section is of interest. Full frequency range can therefore be divided into groups known as ‘frequency bands’. This is useful when measuring multiple sources that appear to create noise at the same frequency (i.e. signals overlap). Division into bands clarifies frequency ranges of the various sources. This is beneficial in a noise mitigation context, when applying noise reduction measures, because it details frequencies that need to be reduced. Octave (1-octave) and third octave (⅓ octave) bands are used most commonly in bioacoustics. In a 1-octave band, the upper limit is 2½ (c. 1.414) times the centre frequency, and the lower limit is the centre frequency divided by 2½ or multiplied by 2-½ (c. 0.707). The upper limit, in Hz, is twice the lower limit. For example, a 4 kHz 1-octave band stretches from c. 2.83 kHz (4 kHz ÷ 2½) to 5.66 kHz (4 kHz × 2½), and 2.83 kHz (lower limit) × 2 = 5.66 kHz (upper limit). Bandwidth (Section 7.2.1) is proportional to (i.e. is a constant percentage of) centre frequency. The bandwidth of an octave band is always 70.7% of the centre frequency. Calculations are summarised in Table 7.2. There are often set centre frequencies when dividing a signal into bands, and the lower and upper limits are rounded to give nice convenient numbers. As the name implies, the width of a ⅓ octave is ⅓ of a 1-octave band. Three adjacent ⅓ octave bands, therefore cover one octave. In a ⅓ octave band, the upper limit is 2⅙ (c. 1.22) times the centre frequency, and the lower limit is the centre frequency divided by 2⅙, or multiplied by 2-⅙ (c. 0.891). The upper limit of ⅓ octave band in Hz is 2⅓ (c. 1.260) times the lower limit. The bandwidth of a ⅓ octave band is 23% of the centre frequency. One-third octave bands are sometimes used to interpret noise effects on marine mammals because the standard bandwidth of the mammalian hearing system is a third octave. Noise measurement reports also use ⅓ octave bands to show average SPLs. For example, Figure 7.12 shows average rms SPL (over 5 s) of a source at different depths within ⅓ octave bands. Table 7.2. Calculating lower, upper, and bandwidth of octave and ⅓ octave bands, where ƒ0 is a centre frequency and ƒ1 is lower limit frequency. Octave band
1/3 octave band
ƒ0/2½ ≈ ƒ0/1.414 ƒ0(2-½) ≈ ƒ0(0.707)
ƒ0/2⅙ ≈ ƒ0/1.22 ƒ0(2-⅙) ≈ ƒ0(0.891)
ƒ0(2½) ≈ ƒ0(1.414)
ƒ0(2⅙) ≈ ƒ0(1.22)
ƒ1(2⅓) ≈ ƒ1(1.260)
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Figure 7.12 Averaged rms Sound Pressure Levels in ⅓ octave bands of a pile driving event. rms = Root Mean Square.
Noise can also be reported as percentile levels, which specify noise level (in dB) exceeded for n% of measured time (reported as Ln or L%). Percentile levels are often used when sound changes over time. A high percentile represents residual background noise, whereas a low percentile gives an indication of maximum noise levels. For example, a 90th percentile (reported as L90) indicates noise level that is exceeded for 90% of measurement duration (Figure 7.13). The value of L10 is noise level exceeded for 10% of the time. L10 minus L90 is used as a quantitative measure for range of amplitudes covered by the sound.
Figure 7.13 Noise percentile levels (L10, L50, and L90).
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Equivalent Continuous Sound Pressure Level
Equivalent continuous sound pressure level (Leq), is another method used to describe sound levels that vary over time, resulting in a single decibel value that takes into account total sound energy over the period of interest. Leq is not a simple arithmetic average of the logarithmic dB values. Decibel values have to first be converted to absolute values, then summed up, then divided by the number of samples, and finally converted back to equivalent dB levels. It is common practice to measure noise levels using the A-weighting method, in which case the term is properly known as LAeq and results are expressed, for example, in LAeq = 73 dB or Leq = 73 dBA (Figure 7.14). See Section 1.5.3 for frequency weightings.
Figure 7.14 A-weighted equivalent continuous sound pressure level (Leq).
Leq has origins as an in-air cumulative exposure value for humans but has also been used in underwater exposure MMMP provisions for operators obliged not to exceed noise thresholds within a specified exclusion zone. Leq is a viable measurement of broadband energy, not dissimilar to SEL, and most modern criteria include this type of broadband metric, and correspondingly some degree of frequency weighting.
A waveform display is a graph of pressure, amplitude, displacement, velocity, or voltage of a signal or noise, versus time (Figure 7.15). The sine waves used in this chapter to show different characteristics of a sound are examples of waveforms. A waveform may also be used to show characteristics of an echolocation click.
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Figure 7.15 Generalised beaked whale click waveform (pressure vs. time) viewed in RainbowClick (now part of PAMGuard).
Marine Mammal Vocalisations 8.1
Marine mammals vary in their degree of auditory and vocal level of specialisation, ranging from minor complexity in amphibious littoral species, such as otters and sea lions, medium in the pelagic great whales, and extreme in many of the odontocetes. Consequently, marine mammals produce sound in different frequency bands for a number of activities discussed in this chapter. Composition of each sound is often highly specialised and varies between species, activity and temporal-spatially. There are a number of mechanisms driving the underlying evolution of vocalisations within and between species and populations. For a review of the evolution of communication in odontocetes, see Morisaka and Connor (2007) or Morisaka (2012) and for a phylogenetic review of tonal sound production in whales in relation to sociality see May-Collado et al. (2007), and references therein. In the field, a PAM Operator must be able to use unique characteristics of each vocalisation to identify animals, especially in areas where exclusion zones are speciesdependent. Acoustic identification to species level is not always possible, but at minimum, a PAM Operator should be able to determine whether the detection is biological in origin, a mysticete or an odontocete, and the likelihood that action is required in terms of mitigation. Within this chapter, vocalisations are discussed in terms of physical properties, and potential functions. While not exhaustive, this review gives the reader an excellent background into the subject and, importantly, gives examples of recent research on the individual subjects. For a good overview of all topics relating to marine mammals and noise, see Richardson et al. (1995) and Au and Hastings (2008), but marine mammal passive acoustical detection and classification is an active field, so regular updated literature searches are advised.
Marine Mammal Sounds
Marine mammal sounds are divided broadly into echolocation ‘clicks’, tonal or pulsed sounds, and ‘song’. Further reading on physiology of sound production in cetaceans is covered by Au (1993), Tyack and Miller (2002), Cranford and Amundin (2004), Cazau et al. (2013), and Madsen et al. (2013). Echolocation is reviewed by Thomas et al. (2004).
Marine Mammal Vocalisations
Echolocation and clicks
Echolocation is one of the most well-documented vocalisation types and is produced only by odontocetes (all species studied so far). Clicks are generated pneumatically in nasal passages, and projected forward through the forehead. Functioning in a similar way to SONAR, the basic principle of echolocation is that an animal emits a click ‘pulse’ in a constrained forward-facing beam. New pulses are emitted only when returning ‘echoes’ have been received, allowing the individual time to process varied and detailed information encompassed within the received pulse. Clicks are emitted as a click ‘train’, which is a series of successive clicks. Pulses are short, discrete clicks that, in any one instant, cover a range of frequencies (10–150 kHz), and durations (50–200 µs). Despite considerable research, little is known about how odontocetes modify characteristics of echolocation pulses, such as SL and the time between each individual click (known as the Inter-Click Interval, ICI), with varying range to a target. Repetition rates are lower than for pulsed calls (Section 8.2.2), with a range of c. 6 clicks per second (s–1) up to about 250 clicks s–1 for feeding buzzes. Clicks have been noted in some mysticete species, such as minke (Beamish and Mitchell, 1973; Winn and Perkins, 1976; Mellinger et al., 2000), gray (Fish et al., 1974), and humpback (Stimpert et al., 2007) whales. Clicks have a SL of c. 145–151 dB re 1 µPa @ 1 m, and energy up to 12 kHz. The idea that clicks are utilised for echolocation in mysticetes has not been concluded with any certainty in the literature, and general opinion is that mysticetes do not echolocate. Much debate has occurred about whether pinnipeds echolocate, and research by Renouf et al. (1980) stated that harbour seals produce faint clicks of 7–16 kHz, which could serve a similar purpose to echolocation clicks in odontocetes. Clicks were also recorded by Schevill et al. (1963), but functionality was questioned as the faintness and low frequency nature does not lend itself to echolocation. Nowadays, the consensus is that pinnipeds do not echolocate (Richardson et al., 1995; Schusterman et al., 2000, 2004). It is agreed generally that sirenians, marine mustelids, and the polar bear do not echolocate.
Pulsed sounds span a range of frequencies in one instant. Duration of a pulse is measured as pulse length and is usually given in units of seconds or microseconds (µs), and calculated as the interval between the time the pulse reaches a specified percentage of peak amplitude for the first and last time. Pulsing the signal results in production of harmonic intervals, physical generation of which is described by Watkins (1967). Odontocete burst pulse sounds are perceived audibly by the human ear as continuous sounds, but are actually composed of high repetition rate pulses. Calls have SLs of 108–292 dB re 1 µPa @ 1 m, and are broadband, with substantial ultrasonic energy. Frequencies up to, and beyond 100 kHz are recorded commonly. Duration is 0.05–10 s and repetition rate is 250–5,000 clicks s–1. In the literature, odontocete burst pulse sounds are referred to as ‘squeals’, ‘barks’, ‘groans’, ‘screams’, ‘moans’, ‘cracks’, ‘pops’, and ‘squawks’. Names are usually onomatopoeic and relate to how the sound is perceived by the listener (Au, 2000). Production varies substantially with behaviour. Mysticete pulsed sounds have a SL of c. 120–203 dB re 1 µPa @ 1 m, and frequency of