2018 Revision to: 

Technical Guidance for Assessing the 

Effects of Anthropogenic Sound on 

Marine Mammal Hearing (Version 2.0) 

Underwater Thresholds for Onset of Permanent 

and Temporary Threshold Shifts 

Office of Protected Resources 

National Marine Fisheries Service 

Silver Spring, MD 20910 

U.S. Department of Commerce 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

NOAA Technical Memorandum NMFS-OPR-59 

April 2018 
 

 

 

 

 

2018 Revisions to: 

Technical Guidance for Assessing the Effects of 

Anthropogenic Sound on Marine Mammal Hearing 

(Version 2.0) 

Underwater Thresholds for Onset of Permanent and Temporary 

Threshold Shifts 

NOAA Technical Memorandum NMFS-OPR-59 

April 2018 

U.S. Department of Commerce 

Wilbur Ross, Secretary 

National Oceanic and Atmospheric Administration 

Tim Gallaudet, Ph.D., USN Ret., Acting Administrator 

National Marine Fisheries Service 

Chris Oliver, Assistant Administrator for Fisheries 
 

 

 

 

 

Recommended citation: 

National Marine Fisheries Service. 2018. 2018 Revisions to: Technical Guidance for Assessing 

the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0): Underwater 

Thresholds for Onset of Permanent and Temporary Threshold Shifts. U.S. Dept. of Commer., 

NOAA. NOAA Technical Memorandum NMFS-OPR-59, 167 p. 

Copies of this report may be obtained from: 

Office of Protected Resources 

National Oceanic and Atmospheric Administration 

1315 East-West Highway, F/PR2 

Silver Spring, MD 20910 

Or online at: 

NOAA Fisheries Publication web site 

Photo Credits: 

Bearded seal (Erignathus barbatus), Phocid pinniped Photo: John Jansen (NOAA) 

North Atlantic right whales (Eubalaena glacialis), Low-frequency cetacean Photo: NOAA 

Bottlenose dolphin (Tursiops truncatus), Mid-frequency cetacean Photo: Allison Henry (NOAA) 

Dall’s porpoise (Phocoenoides dalli), High-frequency cetacean Photo: Kate Stafford (NOAA) 

California sea lion (Zalophus californianus), Otariid pinniped Photo: Sharon Melin (NOAA) 

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TABLE OF CONTENTS TABLE OF CONTENTS 

LIST OF TABLES ............................................................................................................................V 

LIST OF FIGURES .........................................................................................................................VI 

ABBREVIATIONS, ACRONYMS, AND SYMBOLS ....................................................................VIII 

EXECUTIVE SUMMARY .................................................................................................................1 

I. INTRODUCTION.................................................................................................................6 

1.1. THRESHOLDS WITHIN THE CONTEXT OF AN EFFECTS ANALYSIS ...........................................7 

1.2 ADDRESSING UNCERTAINTY AND DATA LIMITATIONS ...........................................................7 

1.2.1 Assessment Framework ............................................................................................. 7 

1.2.2 Data Standards ........................................................................................................... 8 

II. NMFS’ THRESHOLDS FOR ONSET OF PERMANENT THRESHOLD SHIFTS IN MARINE 

MAMMALS .........................................................................................................................8 

2.1 MARINE MAMMAL HEARING GROUPS..................................................................................8 

2.1.1 Application of Marine Mammal Hearing Groups.......................................................10 

2.2 MARINE MAMMAL AUDITORY WEIGHTING FUNCTIONS .......................................................11 

2.2.1 Use of Auditory Weighting Functions in Assessing Susceptibility to Noise-Induced Hearing 

Loss...........................................................................................................................11 

2.2.2 Marine Mammal Auditory Weighting Functions ........................................................12 

2.2.3 Derivation of Function Parameters ...........................................................................15 

2.2.4 Application of Marine Mammal Auditory Weighting Functions for PTS Onset Thresholds 

..................................................................................................................................18 

2.3 PTS ONSET THRESHOLDS...............................................................................................19 

2.3.1 Impulsive and Non-Impulsive Source Thresholds ....................................................20 

2.3.2 Metrics.......................................................................................................................22 

2.3.3 Development of PTS Onset Thresholds ...................................................................24 

III. UPDATING OF ACOUSTIC TECHNICAL GUIDANCE AND THRESHOLDS ................29 

3.1 PROCEDURE AND TIMELINE FOR UPDATING THE TECHNICAL GUIDANCE .............................29 

3.1.1 Consideration for New Scientific Publication ............................................................29 

APPENDIX A: FINNERAN TECHNICAL REPORT............................................................32 

ADMINISTRATIVEINFORMATION ...............................................................................................34 

EXECUTIVE SUMMARY ...............................................................................................................35 

I. INTRODUCTION...............................................................................................................39 

1.1 OVERVIEW......................................................................................................................39 

1.2 IMPULSE VS. NON-IMPULSIVE NOISE..................................................................................39 

1.3 NOISE-INDUCED THRESHOLD SHIFTS ................................................................................39 

1.4 AUDITORY WEIGHTING FUNCTIONS ...................................................................................40 

1.5 TAP PHASE 3 WEIGHTING FUNCTIONS AND TTS/PTS THRESHOLDS...................................40 

II. WEIGHTING FUNCTIONS AND EXPOSURE FUNCTIONS ...........................................42 

III. METHODOLOGY TO DERIVE FUNCTION PARAMETERS...........................................47 

IV. MARINE MAMMAL SPECIES GROUPS .........................................................................49 

4.1 LOW-FREQUENCY (LF) CETACEANS..................................................................................49 

4.2 MID-FREQUENCY (MF) CETACEANS..................................................................................49 

4.3 HIGH-FREQUENCY (HF) CETACEANS ................................................................................49 

4.4 SIRENIANS ......................................................................................................................49 

4.5 PHOCIDS ........................................................................................................................50 

4.6 OTARIIDS AND OTHER NON-PHOCID MARINE CARNIVORES ..................................................50 

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V. COMPOSITE AUDIOGRAMS ..........................................................................................52 

VI. EQUAL LOUDNESS DATA..............................................................................................60 

VII. EQUAL LATENCY DATA.................................................................................................61 

VIII. TTS DATA ........................................................................................................................62 

8.1 NON-IMPULSIVE (STEADY-STATE) EXPOSURES – TTS........................................................62 

8.2 NON-IMPULSIVE (STEADY-STATE) EXPOSURES – PTS........................................................64 

8.3 IMPULSIVE EXPOSURES....................................................................................................65 

IX. TTS EXPOSURE FUNCTIONS FOR SONARS ...............................................................74 

9.1 LOW- AND HIGH-FREQUENCY EXPONENTS (a, b)................................................................74 

9.2 FREQUENCY CUTOFFS (ʄ1, ʄ2) ...........................................................................................74 

9.3 GAIN PARAMETERS K AND C ............................................................................................76 

X. PTS EXPOSURE FUNCTIONS FOR SONARS...............................................................83 

XI. TTS/PTS EXPOSURE FUNCTIONS FOR EXPLOSIVES................................................84 

XII. SUMMARY........................................................................................................................87 

APPENDIX A1. ESTIMATING A LOW-FREQUENCY CETACEAN AUDIOGRAM ............92 

A1.1. BACKGROUND.....................................................................................................................92 

A1.2. AUDIOGRAM FUNCTIONAL FORM AND REQUIRED PARAMETERS ...............................................93 

A1.3. ESTIMATING AUDIOGRAM PARAMETERS ................................................................................95 

XIII. REFERENCES..................................................................................................................98 

APPENDIX B: RESEARCH RECOMMENDATIONS FOR IMPROVED THRESHOLDS.....108 

I. SUMMARY OF RESEARCH RECOMMENDATIONS ...................................................108 

1.1 LOW-FREQUENCY CETACEAN HEARING..........................................................................108 

1.2 HEARING DIVERSITY AMONG SPECIES AND AUDITORY PATHWAYS...................................109 

1.3 REPRESENTATIVENESS OF CAPTIVE INDIVIDUALS............................................................109 

1.3.1 Impacts of Age on Hearing .....................................................................................109 

1.4 ADDITIONAL TTS MEASUREMENTS WITH MORE SPECIES AND/OR INDIVIDUALS .................110 

1.5 SOUND EXPOSURE TO MORE REALISTIC SCENARIOS ......................................................111 

1.5.1 Frequency and Duration of Exposure .....................................................................111 

1.5.2 Multiple Sources .....................................................................................................111 

* Frequency-dependent hearing loss and overall hearing ability within a hearing group is taken into 

account, quantitatively, with auditory weighting functions. .....................................112 

1.5.3 Possible Protective Mechanisms ............................................................................112 

1.5.4 Long-Term Consequences of Exposure.................................................................113 

1.6 IMPACTS OF NOISE-INDUCED THRESHOLD SHIFTS ON FITNESS........................................113 

1.7 BEHAVIOR OF MARINE MAMMALS UNDER EXPOSURE CONDITIONS WITH THE POTENTIAL TO CAUSE 

HEARING IMPACTS........................................................................................................114 

1.8 CHARACTERISTICS OF SOUND ASSOCIATED WITH NIHL AND IMPACTS OF PROPAGATION ..115 

1.9 NOISE-INDUCED THRESHOLD SHIFT GROWTH RATES AND RECOVERY .............................115 

1.10 METRICS AND TERMINOLOGY.........................................................................................115 

1.11 EFFECTIVE QUIET .........................................................................................................116 

1.12 TRANSLATING BIOLOGICAL COMPLEXITY INTO PRACTICAL APPLICATION...........................117 

APPENDIX C: TECHNICAL GUIDANCE REVIEW PROCESSES: PEER REVIEW, PUBLIC 

COMMENT, AND REVIEW UNDER EXECUTIVE ORDER 13795................................118 

I. PEER REVIEW PROCESS ............................................................................................118 

1.1 2013 INITIAL PEER REVIEW (ASSOCIATED WITH 2013 DRAFT GUIDANCE)........................119 

1.2 2015 SECOND PEER REVIEW (REVIEW OF THE FINNERAN TECHNICAL REPORT)...............119 

1.2.1 2016 Follow-Up to Second Peer Review ................................................................120 

1.3 2015 THIRD PEER REVIEW (REVIEW OF TRANSITION RANGE METHODOLOGY) .................120 

1.4 CONFLICT OF INTEREST DISCLOSURE.............................................................................121 

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LIST OF TABLES 

II. PUBLIC COMMENT PERIODS......................................................................................121 

2.1 2013/2014 INITIAL PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2013 DRAFT TECHNICAL 

GUIDANCE) ..................................................................................................................122 

2.1.1 Summary of Public Comments Received ...............................................................122 

2.2 2015 SECOND PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2015 DRAFT TECHNICAL GUIDANCE) 

...................................................................................................................................123 

2.2.1 Summary of Public Comments Received ...............................................................123 

2.3 2016 THIRD PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2016 PROPOSED CHANGES FROM DRAFT 

TECHNICAL GUIDANCE).................................................................................................123 

2.3.1 Summary of Public Comments Received ...............................................................124 

III. REVIEW UNDER EXECUTIVE ORDER 13795..............................................................125 

3.1 REVIEW OF 2016 TECHNICAL GUIDANCE UNDER EO 13795 ...........................................125 

3.1.1 2017 Public Comment Period .................................................................................125 

3.1.2 2017 Federal Interagency Consultation..................................................................126 

3.2 REVISIONS TO THE 2016 TECHNICAL GUIDANCE AS A RESULT OF REVIEW UNDER EO 13795127 

APPENDIX D: ALTERNATIVE METHODOLOGY ...........................................................129 

I. INTRODUCTION.............................................................................................................129 

II. WEIGHTING FACTOR ADJUSTMENT ASSOCIATED WITH SELCUM THRESHOLDS129 

2.1 APPLICATION FOR NARROWBAND SOUNDS .....................................................................129 

132 

2.2 APPLICATION FOR BROADBAND SOUNDS ........................................................................132 

2.2.1 Special Considerations for Broadband Source.......................................................133 

2.3 OVERRIDING THE WEIGHTING FACTOR ADJUSTMENT ......................................................134 

III. MODELING CUMULATIVE SOUND EXPOSURE LEVELS..........................................135 

3.1 MORE SOPHISTICATED MODELS ....................................................................................135 

3.2 LESS SOPHISTICATED MODELS ......................................................................................136 

3.2.1 Mobile Sources .......................................................................................................136 

3.2.2 Stationary Sources..................................................................................................140 

APPENDIX E: GLOSSARY ..............................................................................................141 

LITERATURE CITED...................................................................................................................149 

LIST OF TABLES 

Table ES1: Marine mammal hearing groups. ........................................................................................ 3 

Table ES2: Summary of auditory weighting and exposure function parameters...................................3 

Table ES3: Summary of PTS onset thresholds. .................................................................................... 4 

Table 1: Marine mammal hearing groups. ..............................................................................................10 

Table 2: Summary of data available for deriving composite audiograms............................................16 

Table 3: Summary of auditory weighting and exposure function parameters.........................................18 

Table 4: Summary of PTS onset thresholds. ..........................................................................................21 

Table 5: Available underwater marine mammal threshold shift studies. .............................................26 

Table 6: TTS onset thresholds for non-impulsive sounds. ..................................................................27 

Table AE-1. Summary of weighting function parameters and TTS/PTS thresholds.............................36 

Table A1. Species group designations for Navy Phase 3 auditory weighting functions. .......................51 

Table A2. References, species, and individual subjects used to derive the composite audiograms.....54 

Table A3. Composite audiogram parameters values for use in Eq. (A9)...............................................55 

Table A4. Normalized composite audiogram parameters values for use in Eq. (A9). ...........................55 

Table A5. Frequency of best hearing and the magnitude of the low-frequency slope derived from 

composite audiograms and equal latency contours...........................................................................59 

Table A6. Summary of marine mammal TTS growth data and onset exposure levels..........................71 

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LIST OF FIGURES 

Table A7. Differences between composite threshold values and TTS onset values at the frequency of 

best hearing for the in-water marine mammal species groups. .........................................................77 

Table A8. Weighting function and TTS exposure function parameters for steady-state exposures......78 

Table A9. TTS and PTS thresholds for explosives and other impulsive sources ..................................86 

Table A10. Summary of weighting function parameters and TTS/PTS thresholds. ................................88 

Table B1: Summary of currently available marine mammal data. .......................................................108 

Table B2: Additional factors for consideration (frequency and duration of exposure) in association with 

PTS onset thresholds. ......................................................................................................................112 

Table C1: Initial peer review panel. ......................................................................................................119 

Table C2: Second peer review panel. ..................................................................................................120 

Table C3: Third peer review panel. ......................................................................................................121 

Table C4: Summary of commenters.....................................................................................................126 

Table C5: Ten Federal agency attendees ............................................................................................127 

Table D1: Applicability of weighting factor adjustments for frequencies associated with broadband 

sounds .............................................................................................................................................134 

Table D2: Comparison of adjustment associated with incorporating entire broadband spectrum vs. 

default, single frequency WFA for a seismic array...........................................................................135 

LIST OF FIGURES 

Figure ES1: Auditory weighting functions for low-frequency, mid-frequency, and high-frequency 

cetaceans. ............................................................................................................................................ 5 

Figure ES2: Underwater auditory weighting functions for otariid and phocid pinnipeds.........................5 

Figure 1: Auditory weighting functions for low-frequency, mid-frequency, and high-frequency 

cetaceans. ..........................................................................................................................................12 

Figure 2: Underwater auditory weighting functions for otariid and phocid pinnipeds. .........................13 

Figure 3: Illustration of function parameter in both auditory weighting functions and exposure 

functions .............................................................................................................................................14 

Figure 4: Resulting normalized composite audiograms for low-frequency, mid-frequency, and highfrequency cetaceans and phocid (PW) and otariid (OW) pinnipeds ..................................................15 

Figure AE-1. Navy Phase 3 weighting functions for all species groups.................................................36 

Figure AE-2. TTS and PTS exposure functions for sonars and other (non-impulsive) active acoustic 

sources . .........................................................................................................................................37 

Figure AE-3. TTS and PTS exposure functions for explosives, impact pile driving, air guns, and other 

impulsive sources ...............................................................................................................................38 

Figure A1. Examples of weighting function and exposure function........................................................43 

Figure A2. Influence of parameter values on the resulting shapes of the weighting functions and 

exposure functions .............................................................................................................................44 

Figure A3. Navy Phase 2 weighting function for the mid-frequency cetacean group. ...........................45 

Figure A4. Comparison of Otariid, Mustelid, and Odobenid psychophysical hearing thresholds 

measured underwater.. ......................................................................................................................50 

Figure A5. Thresholds and composite audiograms for the six species groups......................................56 

Figure A6. Normalized thresholds and composite audiograms for the six species groups....................57 

Figure A7. Composite audiograms for the various species groups, derived with the original data and 

normalized data..................................................................................................................................58 

Figure A8. Underwater marine mammal equal latency contours are available for Phocoena phocoena 

and Tursiops truncatus.......................................................................................................................61 

Figure A9. TTS measured using behavioral and AEP methods do not necessarily agree, with marine 

mammal studies reporting larger TTS obtained using AEP methods. ...............................................63 

Figure A10. TTS growth data for mid-frequency cetaceans obtained using behavioral methods........67 

Figure A11. TTS growth data for mid-frequency cetaceans obtained using AEP methods. ................68 

Figure A12. TTS growth data for high-frequency cetaceans obtained using behavioral and AEP 

methods. ..........................................................................................................................................69 

Figure A13. TTS growth data for pinnipeds obtained using behavioral methods.................................70 

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Figure A14. The cutoff frequencies ......................................................................................................75 

Figure A15. Effect of ΔT adjustment on the TTS exposure functions for the mid-frequency cetaceans 

Figure A16. Relationship between ΔT and the resulting mean-squared error between the exposure 

and high-frequency cetaceans ...........................................................................................................75 

functions and onset TTS data. ...........................................................................................................76 

Figure A17. Exposure functions with the parameters specified in Table A7. .......................................79 

Figure A18. Mid-frequency cetacean exposure function, composite audiogram, and Phase 2 exposure 

functions compared to mid-frequency cetacean TTS data.................................................................80 

Figure A20. Phocid (underwater) exposure function, composite audiogram, and Phase 2 exposure 

Figure A21. Navy Phase 3 weighting functions for marine mammal species groups exposed to 

Figure A22. TTS and PTS exposure functions for sonars and other (non-impulsive) active acoustic 

Figure A23. TTS and PTS exposure functions for explosives, impact pile driving, air guns, and other 

Figure D1: Example illustrating concept of weighting factor adjustment at 1 kHz (red line) with cetacean 

Figure A19. High-frequency cetacean TTS exposure function, composite audiogram, and Phase 2 

exposure functions compared to high-frequency cetacean TTS data................................................81 

functions compared to phocid TTS data. ...........................................................................................82 

underwater sound. Parameters required to generate the functions are provided in Table A10. .......87 

sources. . .........................................................................................................................................90 

impulsive sources...............................................................................................................................91 

FIGURE A1.1. Relationship between estimated threshold, T(f), low-frequency term, L(f), and highfrequency term....................................................................................................................................95 

FIGURE A1.2. Comparison of proposed LF cetacean thresholds to those predicted by anatomical and 

finite-element models. ........................................................................................................................97 

(top) and pinniped (bottom) auditory weighting functions. ...............................................................131 

Figure D2: Simple example illustrating concept of weighting factor adjustment on isopleths for LF 

and MF cetaceans using hypothetical 1 kHz narrowband, intermittent source represented by the red 

dot (RMS source level of 200 dB; 1-second ping every 2 minutes).................................................132 

Figure D3: Example auditory weighting function illustrating where the use of weighting factor 

adjustments are and are not appropriate for broadband sources....................................................133 

Figure D4: Maximum one-third octave band source level in the horizontal plane for a generic 8000 in3 

Figure D5: Illustration of the concept for mobile sources, with each red dot representing the source 

seismic array ....................................................................................................................................134 

traveling over time. ...........................................................................................................................137 

Figure E1. Example audiogram. ...........................................................................................................141 

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ABBREVIAT ABBREVIATIONS, IONS, AACRONYMS, CRONYMS, AND SYMBOLS AND SY BOLS 

a Low-frequency exponent MMC Marine Mammal Commission 

ABR Auditory Brainstem MMPA Marine Mammal Protection 

Response Act 

AEP Auditory Evoked Potentials MSA Magnuson-Stevens Fishery 

AM Amplitude Modulated Conservation and 

ANSI American National Standards Management Act 

b 

Institute 

High-frequency exponent 

MSE 

m 

Mean-squared error 

meter 

BOEM Bureau of Ocean Energy msec Milliseconds 

C 

Management 

Weighting function gain (dB) 

NAZ 

NIHL 

Narrow Azimuth 

Noise-induced Hearing Loss 

CT 

D 

dB 

Computerized Tomography 

Duty Cycle 

Decibel 

NMFS 

NMSA 

National Marine Fisheries 

Service 

National Marine Sanctuaries 

PK Peak sound level Act 

DPOAE 

Eaud(ƒ) 

E0 

EEH 

EO 

Distortion product 

otoacoustic emission 

Auditory exposure function 

Exposure Threshold 

Equal Energy Hypothesis 

Executive Order 

NOAA 

NOS 

NRC 

NS2 

NSF 

National Oceanic and 

Atmospheric Administration 

National Ocean Service 

National Research Council 

National Standard 2 

National Science Foundation 

EQL 

ES 

ESA 

ƒ0

ƒ1

ƒ2 

G&G 

h 

Equal Loudness 

Executive Summary 

Endangered Species Act 

Best hearing (kHz) 

Low-frequency cutoff (kHz) 

High-frequency cutoff (kHz) 

Geological and Geophysical 

hour 

OMB 

ONMS 

OPR 

OSHA 

Office of Management and 

Budget 

Office of National Marine 

Sanctuaries 

Office of Protected 

Resources 

Occupational Safety and 

Health Administration 

HF 

HISA 

Hz 

High-frequency 

Highly Influential Scientific 

Assessment 

Hertz 

OW 

p0 

Pa 

π

Otariids in water 

Sound Pressure Level 

Pascals 

pi 

in3 Cubic inches PK peak sound pressure level 

ISI Influential Scientific PTS Permanent Threshold Shift 

ISO 

Information 

International Organization for 

Standardization 

PW 

R 

R0 

Phocids in water 

Range 

“Safe Distance” 

IQG 

K 

kHz 

LDEO 

Information Quality 

Guidelines 

Exposure function gain (dB) 

Kilohertz 

Lamont-Doherty Earth 

Observatory 

R2 

RMS 

S 

SE 

s 

Goodness of fit 

Root-Mean-Square sound 

pressure level 

Source Factor 

Energy Source Factor 

Seconds 

LF 

L0-pk 

L0-pk,flat 

LE,24h 

Low-frequency 

Peak sound pressure level 

Peak sound pressure level 

(unweighted) 

Sound exposure level, 

cumulative 24h 

s 

s0 

SEL 

SELcum 

SIO 

Distance from source 

Slope 

Sound exposure level 

Cumulative sound exposure 

level 

Scripps Institution of 

MF 

min 

Mid-frequency 

Minutes SL 

Oceanography 

Source Level 

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SLE Energy Source Level 

s0 Slope (dB/decade) 

SPL Sound Pressure Level 

SSC-PAC SPAWAR Systems Center 

Pacific 

τ 1/repetition rate 

TAP U.S. Navy’s Tactical Training 

Theater Assessment and 

Planning Program 

TS Threshold Shift 

TTS Temporary Threshold Shift 

μPa Micropascal 

μPa2-s Micropascal squared second 

USFWS U.S. Fish and Wildlife 

Service 

vv Velocity (transit speed) 

Waud(ƒ) Auditory weighting function 

WAZ Wide Azimuth 

WFA Weighting factor adjustments 

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EXECUTIVE SUMMARY EXECUTIVE SU ARY 

This document provides voluntary technical guidance for assessing the effects of underwater 

anthropogenic (human-made) sound on the hearing of marine mammal species under the 

jurisdiction of the National Marine Fisheries Service (NMFS) and was completed in collaboration 

with the National Ocean Service (NOS), Office of National Marine Sanctuaries. Specifically, it 

identifies the received levels, or thresholds, at which individual marine mammals are predicted to 

experience changes in their hearing sensitivity (either temporary or permanent) for acute, 

incidental exposure to underwater anthropogenic sound sources. This Technical Guidance may 

be used by NMFS analysts/managers and other relevant action proponents/stakeholders, 

including other federal agencies, when seeking to determine whether and how their activities are 

expected to result in potential impacts to marine mammal hearing via acoustic exposure. Please 

note that action proponents have discretion as to whether to use the Technical Guidance; other 

scientifically rigorous methods are acceptable. This document outlines the development of NMFS’ 

thresholds and describes how they will be updated in the future. 

NMFS has compiled, interpreted, and synthesized the scientific literature, including a Technical 

Report by Dr. James Finneran (U.S. Navy-SPAWAR Systems Center Pacific (SSC-PAC)) 

(Finneran 2016; Appendix A of this Technical Guidance), to produce thresholds for onset of 

temporary (TTS) and permanent threshold shifts (PTS) (Table ES2). This document includes a 

protocol for estimating PTS onset thresholds for impulsive (e.g., airguns, impact pile drivers) and 

non-impulsive (e.g., tactical sonar, vibratory pile drivers) sound sources, the formation of marine 

mammal hearing groups (low- (LF), mid- (MF), and high- (HF) frequency cetaceans, and otariid 

(OW) and phocid (PW) pinnipeds; Table ES1), and the incorporation of marine mammal auditory 

weighting functions (Figures ES1 and ES2) into the derivation of PTS onset thresholds. These 

thresholds are presented using dual metrics of weighted cumulative sound exposure level 

(SELcum) and peak sound level (PK) for impulsive sounds and weighted SELcum for non-impulsive 

sounds. 

While the Technical Guidance’s thresholds are more complex than those used to date in most 

cases by NMFS, they reflect the current state of scientific knowledge regarding the characteristics 

of sound that have the potential to impact marine mammal hearing sensitivity. NMFS recognizes 

that the implementation of marine mammal weighting functions and the weighted SELcum metric 

represent new factors for consideration, which may extend beyond the capabilities of some action 

proponents. Thus, NMFS has developed alternative tools for those who cannot fully incorporate 

these factors (See Appendix D, Technical Guidance’s companion User Spreadsheet tool1, and 

recently developed User Spreadsheet Manual (NMFS 2018)1). 

These thresholds do not represent the entirety of a comprehensive analysis of the effects of a 

proposed action, but rather serve as one tool (along with, e.g., behavioral impact thresholds, 

auditory masking assessments, evaluations to help understand the ultimate effects of any 

particular type of impact on an individual’s fitness, population assessments, etc.) to help evaluate 

the effects of a proposed action and make the relevant findings required by NOAA’s various 

statutes. The Technical Guidance may inform decisions related to mitigation and monitoring 

requirements, but it does not mandate any specific mitigation be required. The Technical 

Guidance does not address or change NMFS’ application of these thresholds in the regulatory 

context, under applicable statutes and does not create or confer any rights for or on any person, 

or operate to bind the public. It only updates NMFS’ thresholds based on the most recent science. 

This Technical Guidance is classified as a Highly Influential Scientific Assessment (HISA) by the 

President’s Office of Management and Budget (OMB). As such, independent peer review was 

required prior to broad public dissemination by the Federal Government. Details of the three peer 

reviews, associated with the Technical Guidance, are within this document (Appendix C). 

1 Link to Technical Guidance web page. 

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REVISIONS TO 2016 TECHNICAL GUIDANCE 

Presidential Executive Order (EO) 13795, Implementing an America-First Offshore Energy 

Strategy (82 FR 20815; April 28, 2017), states in section 2 that “It shall be the policy of the United 

States to encourage energy exploration and production, including on the Outer Continental Shelf, 

in order to maintain the Nation’s position as a global energy leader and foster energy security and 

resilience for the benefit of the American people, while ensuring that any such activity is safe and 

environmentally responsible.” Section 10 of the E.O. called for a review of the 2016 Technical 

Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing 

(Technical Guidance; NMFS 2016a) as follows: “The Secretary of Commerce shall review 

[Technical Guidance] for consistency with the policy set forth in Section 2 of this order and, after 

consultation with the appropriate Federal agencies, take all steps permitted by law to rescind or 

revise that guidance, if appropriate.” 

To assist the Secretary in carrying out the directive under EO 13795, NMFS held a 45-day public 

comment period (82 FR 24950; May 31, 2017) and a Federal Interagency Consultation 

(September 25, 2017) to solicit comments on the Technical Guidance for consistency with the 

EO’s policy. 

Many of the comments NMFS received, including those from Federal agencies, were supportive 

of the Technical Guidance, including the science used in its derivation and the robust process 

that NMFS followed, including four independent peer reviews. The majority of commenters 

recommended that the Technical Guidance remain unchanged. The Federal agencies, Members 

of Congress, and subject matter experts expressed support for the Technical Guidance as 

reflecting the best available science. NMFS received no recommendations to rescind the 2016 

Technical Guidance. The majority of comments pertained to recommendations to improve 

implementation of the Technical Guidance, rather than the Technical Guidance itself, or were 

beyond the scope of the Technical Guidance and/or its review under section 10 of EO 13795. 

NMFS’ evaluation of comments received during this process affirmed that the Technical 

Guidance is based on upon the best available science. However, to facilitate its use and 

implementation, NMFS revised the 2016 Technical Guidance (NMFS 2016a), per approval of the 

Secretary of Commerce, to provide improvements and clarification on implementation of the 

document (i.e., 2018 Revised Technical Guidance, Version 2.0). 

SUMMARY OF TECHNICAL ASPECTS 

This document is organized so that the most pertinent information can be found easily in the main 

body. Additional details are provided in the appendices. Section I introduces the document. 

NMFS’ thresholds for onset of PTS for marine mammals exposed to underwater sound are 

presented in Section II. NMFS’ plan for periodically updating thresholds is presented in Section 

III. More details on the development of thresholds, the peer review and public comment process, 

research recommendations, alternative methodology, and a glossary of acoustic terms are found 

in the appendices. 

The following Tables and Figures summarize the three main aspects of the Technical Guidance: 

1) Marine mammal hearing groups (Table ES1); 2) Marine mammal auditory weighting functions 

(Figures ES1 and ES2; Table ES2); and PTS onset thresholds (Table ES3). 

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(J I t,Y" } 2 ' 

Table ES1: Marine mammal hearing groups. 

Hearing Group Generalized Hearing 

Range* 

Low-frequency (LF) cetaceans 

(baleen whales) 7 Hz to 35 kHz 

Mid-frequency (MF) cetaceans 

(dolphins, toothed whales, beaked whales, bottlenose whales) 150 Hz to 160 kHz 

High-frequency (HF) cetaceans 

(true porpoises, Kogia, river dolphins, cephalorhynchid, 

Lagenorhynchus cruciger & L. australis) 

275 Hz to 160 kHz 

Phocid pinnipeds (PW) (underwater) 

(true seals) 50 Hz to 86 kHz 

Otariid pinnipeds (OW) (underwater) 

(sea lions and fur seals) 60 Hz to 39 kHz 

* Represents the generalized hearing range for the entire group as a composite (i.e., all species within the group), 

where individual species’ hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65 

dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall et 

al. 2007) and PW pinniped (approximation). 

Table ES2: Summary of auditory weighting and exposure function parameters.* 

Hearing Group a b ƒ1 

(kHz) 

ƒ2 

(kHz) 

C 

(dB) 

K 

(dB) 

Low-frequency (LF) cetaceans 1.0 2 0.2 19 0.13 179 

Mid-frequency (MF) cetaceans 1.6 2 8.8 110 1.20 177 

High-frequency (HF) cetaceans 1.8 2 12 140 1.36 152 

Phocid pinnipeds (PW) (underwater) 1.0 2 1.9 30 0.75 180 

Otariid pinnipeds (OW) (underwater) 2.0 2 0.94 25 0.64 198 

* Equations associated with Technical Guidance’s auditory weighting (Waud(f)) and exposure functions (Eaud(f)): 

dB 

dB 

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Table ES3: Summary of PTS onset thresholds. 

PTS Onset Thresholds* 

(Received Level) 

Hearing Group Impulsive Non-impulsive 

Low-Frequency (LF) 

Cetaceans 

Cell 1 

Lp,0-pk,flat: 219 dB 

LE,p, LF,24h: 183 dB 

Cell 2 

LE,p, LF,24h: 199 dB 

Mid-Frequency (MF) 

Cetaceans 

Cell 3 

Lp,0-pk,flat: 230 dB 

LE,p, MF,24h: 185 dB 

Cell 4 

LE,p, MF,24h: 198 dB 

High-Frequency (HF) 

Cetaceans 

Cell 5 

Lp,0-pk,flat: 202 dB 

LE,p,HF,24h: 155 dB 

Cell 6 

LE,p, HF,24h: 173 dB 

Phocid Pinnipeds (PW) 

(Underwater) 

Cell 7 

Lp,0-pk.flat: 218 dB 

LE,p,PW,24h: 185 dB 

Cell 8 

LE,p,PW,24h: 201 dB 

Otariid Pinnipeds (OW) 

(Underwater) 

Cell 9 

Lp,0-pk,flat: 232 dB 

LE,p,OW,24h: 203 dB 

Cell 10 

LE,p,OW,24h: 219 dB 

* Dual metric thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a 

non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive 

sounds, these thresholds are recommended for consideration. 

Note: Peak sound pressure level (Lp,0-pk) has a reference value of 1 μPa, and weighted cumulative sound exposure level 

(LE,p) has a reference value of 1μPa2

s. In this Table, thresholds are abbreviated to be more reflective of International 

Organization for Standardization standards (ISO 2017). The subscript “flat” is being included to indicate peak sound 

pressure are flat weighted or unweighted within the generalized hearing range of marine mammals (i.e., 7 Hz to 160 kHz). 

The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal 

auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended 

accumulation period is 24 hours. The weighted cumulative sound exposure level thresholds could be exceeded in a 

multitude of ways (i.e., varying exposure levels and durations, duty cycle). When possible, it is valuable for action 

proponents to indicate the conditions under which these thresholds will be exceeded. 

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Figure ES1: Auditory weighting functions for low-frequency (LF; dashed line), midfrequency (MF; solid line), and high-frequency (HF; dotted line) cetaceans. 

Figure ES2: Underwater auditory weighting functions for otariid (OW; solid line) and 

phocid (PW; dotted line) pinnipeds. 

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REVISION TO: TECHNICAL GUIDANCE FOR ASSESSING THE EFFECTS OF 

ANTHROPOGENIC SOUND ON ARI E AMMAL HEARING (VERSION 2.0) 

UNDERWATER THRESHOLDS FOR ONSET OF PERMANENT AND 

TEMPORARY THRESHOLD SHIFTS 

I. INTRODUCTION 

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ANTHROPOGENIC SOUND ON MARINE MAMMAL HEARING (VERSION 2.0) 

UNDERWATER THRESHOLDS FOR ONSET OF PERMANENT AND 

TEMPORARY THRESHOLD SHIFTS 

I. INTRODUCTION

This document provides technical guidance2 for assessing the effects of anthropogenic (humanmade) sound on the hearing of marine mammal species under the jurisdiction3 of the National 

Marine Fisheries Service (NMFS) and was completed in collaboration with the National Ocean 

Service (NOS), Office of National Marine Sanctuaries. Specifically, it identifies the received 

levels, or thresholds, at which individual marine mammals are predicted to experience changes in 

their hearing sensitivity for acute, incidental exposure to all underwater anthropogenic sound 

sources. This Technical Guidance is intended for use by NMFS analysts/ managers and other 

relevant action proponents/stakeholders, including other federal agencies, when seeking to 

determine whether and how their activities are expected to result in impacts to marine mammal 

hearing via acoustic exposure. This document outlines NMFS’ thresholds, describing in detail 

threshold development (via Appendix A), and how they will be revised and updated in the future. 

The thresholds presented in this document do not represent the entirety of an effects analysis, 

but rather serve as one tool among others (e.g., behavioral impact thresholds, auditory masking 

assessments, evaluations to help understand the effects of any particular type of impact on an 

individual’s fitness, population assessments, etc.), to help evaluate the effects of a proposed 

action and make findings required by NOAA’s various statutes. The Technical Guidance may 

inform decisions related to mitigation and monitoring requirements, but it does not mandate any 

specific mitigation be required4. The Technical Guidance does not address or change NMFS’ 

application of these thresholds in the regulatory context, under applicable statutes and does not 

create or confer any rights for or on any person, or operate to bind the public. It only updates 

NMFS’ thresholds based on the most recent science. 

2 The use of the Technical Guidance is not mandatory; it does not create or confer any rights for or on any person, or 

operate to bind the public. An alternative approach that has undergone independent peer review may be proposed (by 

federal agencies or prospective action proponents) and used if case-specific information/data indicate that the alternative 

approach is likely to produce a more accurate estimate of auditory impact for the project being evaluated; and if NMFS 

determines the approach satisfies the requirements of the applicable statutes and regulations. 

3 Link to marine mammals under NMFS' jurisdiction. This document does not pertain to marine mammal species under the 

U.S. Fish and Wildlife Service’s (USFWS) jurisdiction (e.g., walrus, polar bears, West Indian manatees, sea otters). 

However, since marine mammal audiogram data are limited, a decision was made to include all available datasets from 

in-water groups, including sirenian datasets (Gerstein et al. 1999; Mann et al. 2009), to derive composite audiogram 

parameters and threshold of best hearing for LF cetaceans (see Appendix A1). Additionally, audiogram data from a single 

Pacific walrus (Kastelein et al. 2002) and a single sea otter (Ghoul and Reichmuth 2014) were included in the derivation of 

the composite audiogram for OW pinnipeds. 

4 Mitigation and monitoring requirements associated with a Marine Mammal Protection Act (MMPA) authorization or an 

Endangered Species Act (ESA) consultation or permit are independent management decisions made in the context of the 

proposed activity and comprehensive effects analysis, and are beyond the scope of the Technical Guidance. NMFS 

acknowledges exclusion zones and monitoring zones often correspond to thresholds but that is not a legal requirement, 

and the thresholds may make such a simple correlation more challenging. The Technical Guidance can be used to inform 

the development of mitigation or monitoring. NMFS is currently developing a separate document further describing how 

the Technical Guidance is used in the MMPA authorization process to inform mitigation decisions. This document, when 

available, can be found at: NMFS Incidental Take Authorization web page. 

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Note: This document does not set forth requirements to conduct sound source verification 

studies. 

1.1. THRESHOLDS WITHIN THE CONTEXT OF AN EFFECTS ANALYSIS 

The Technical Guidance’s thresholds do not represent the entirety of an effects analysis, but 

rather serve as one tool to help evaluate the effects of sound produced during a proposed action 

on marine mammals and make findings required by NOAA’s various statutes. In a regulatory 

context, NMFS uses thresholds to help assess and quantify “take” and to conduct more 

comprehensive effects analyses under several statutes. NMFS is currently developing a separate 

document5 further describing how the Technical Guidance is used in the MMPA authorization 

process to estimate “take.” 

Specifically, the Technical Guidance will be used in conjunction with sound source 

characteristics, environmental factors that influence sound propagation, anticipated marine 

mammal occurrence and behavior near the activity, as well as other available activity-specific 

factors, to estimate the number and types of takes of marine mammals. This document only 

addresses thresholds for auditory impact (i.e., does not address or make recommendations 

associated with sound propagation or marine mammal occurrence or density). 

1.2 ADDRESSING UNCERTAINTY AND DATA LIMITATIONS 

Inherent data limitations occur in many instances when assessing acoustic effects on marine 

mammal hearing. Data limitations, which make it difficult to account for uncertainty and variability, 

are not unique to assessing the effects of anthropogenic sound on marine mammals and are 

commonly encountered by resource managers (Ludwig et al. 1993; Francis and Shotton 1997; 

Harwood and Stokes 2003; Punt and Donovan 2007). Southall et al. (2007) and Finneran (2016) 

acknowledged the inherent data limitations when making recommendations for criteria to assess 

the effects of noise on marine mammals, including data available from a limited number of 

species, a limited number of individuals within a species, and/or limited number of sound sources. 

Both Finneran (2016) and Southall et al. (2007) applied certain extrapolation procedures to 

estimate effects that had not been directly measured but that could be reasonably approximated 

using existing information and reasoned logic. The Technical Guidance articulates where NMFS 

has faced such uncertainty and variability in the development of its thresholds. 

1.2.1 Assessment Framework 

NMFS’ approach applies a set of assumptions to address uncertainty in predicting potential 

auditory effects of sound on individual marine mammals. One of these assumptions includes the 

use of “representative” or surrogate individuals/species for establishing PTS onset thresholds for 

species where little to no data exists. The use of representative individuals/species is done as a 

matter of practicality (i.e., it is unlikely that adequate data will exist for the all marine mammal 

species found worldwide or that we will be able to account for all sources of variability at an 

individual level) but is also scientifically based (i.e., taxonomy, hearing group). As new data 

become available for more species, this approach can be reevaluated. NMFS recognizes that 

additional applicable data may become available to better address many of these issues (e.g., 

uncertainty, surrogate species, etc.).6 As these new data become available, NMFS has an 

approach for updating this document (see Section III). 

5 Document, when available, can be found at: NMFS Incidental Take Authorization web page. 

6 NMFS is aware that the authors of Southall et al. (2007) are in the process of updating their original publication and 

recognizes that when this updated publication becomes available, it may suggest alternative means for predicting an 

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II. NMFS' THRESHOLDS FOR ONSET OF PERMANENT THRESHOLD 

SHIFTS IN ARINE A ALS 

1.2.2 Data Standards 

In assessing potential acoustic effects on marine mammals, as with any such issue facing the 

agency, standards for determining applicable data need to be articulated. Specifically, NOAA has 

Information Quality Guidelines7 (IQG) for “ensuring and maximizing the quality, objectivity, utility, 

and integrity of information disseminated by the agency” (with each of these terms defined within 

the IQG). Further, the IQG stipulate that “To the degree that the agency action is based on 

science, NMFS will use (a) the best available science and supporting studies (including peerreviewed science and supporting studies when available), conducted in accordance with sound 

and objective scientific practices, and (b) data collected by accepted methods or best available 

methods.” 

The National Research Council (NRC 2004) provided basic guidelines for National Standard 2 

(NS2) in section 301 of the Magnuson-Stevens Fishery Conservation and Management Act, 

which states that “Conservation and management measures shall be based upon the best 

scientific information available” (NOAA 2013). They recommended that data underlying the 

decision-making and/or policy-setting process be: 1) relevant, 2) inclusive, 3) objective, 4) 

transparent and open, 5) timely, 6) verified and validated, and 7) peer reviewed.8 Although NRC’s 

guidelines (NRC 2004) were not written specifically for marine mammals and this particular issue, 

they do provide a means of articulating minimum data standards. NMFS considered this in 

assessing acoustic effects on marine mammals. Use of the NRC Guidelines does not preclude 

development of acoustic-specific data standards in the future. 

II. NMFS’ THRESHOLDS FOR ONSET OF PERMANENT THRESHOLD 

SHIFTS IN MARINE MAMMALS 

The Technical Guidance advances NMFS’ assessment ability based upon the compilation, 

interpretation, and synthesis of the scientific literature. This document provides thresholds for the 

onset of PTS based on characteristics defined at the acoustic source. No direct measurements of 

marine mammal PTS have been published; PTS onset thresholds have been extrapolated from 

marine mammal TTS measurements (i.e., using growth rates from terrestrial and marine mammal 

data). PTS onset thresholds, for all sound sources are divided into two broad categories: 1) 

impulsive and 2) non-impulsive. Thresholds are also presented as dual metric thresholds using 

weighted cumulative sound exposure level (SELcum,) and peak sound pressure (PK) metrics for 

impulsive sounds. As dual metrics, NMFS considers onset of PTS to have occurred when either 

one of the two metrics is exceeded. For non-impulsive sounds, thresholds are provided using the 

weighted SELcum metric. Additionally, to account for the fact that different species groups use and 

hear sound differently, marine mammals are sub-divided into five broad hearing groups (i.e., LF, 

MF, HF, PW, and OW) and thresholds in the weighted SELcum metric incorporate auditory 

weighting functions. 

2.1 MARINE MAMMAL HEARING GROUPS 

Current data (via direct behavioral and electrophysiological measurements) and predictions 

(based on inner ear morphology, modeling, behavior, vocalizations, or taxonomy) indicate that not 

auditory weighting function and thresholds for LF cetaceans. Accordingly, NMFS may re-evaluate our methodology for LF 

cetaceans when this updated Southall et al. publication becomes available. 

7 NMFS National Standards 2 web page. 

8 NMFS also requires Peer Review Plans for Highly Influential Scientific Assessments (HISA) and Influential Scientific 

Information (ISI). 

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all marine mammal species have equal hearing capabilities, in terms of absolute hearing 

sensitivity and the frequency band of hearing (Richardson et al. 1995; Wartzok and Ketten 1999; 

Southall et al. 2007; Au and Hastings 2008). Hearing has been directly measured in some 

odontocete and pinniped species9 (see reviews in Southall et al. 2007; Erbe et al. 2016; Finneran 

2016). Direct measurements of mysticete hearing are lacking.10 Thus, hearing predictions for 

mysticetes are based on other methods including: anatomical studies and modeling (Houser et al. 

2001; Parks et al. 2007; Tubelli et al. 2012; Cranford and Krysl 201511); vocalizations12 (see 

reviews in Richardson et al. 1995; Wartzok and Ketten 1999; Au and Hastings 2008); taxonomy; 

and behavioral responses to sound (Dahlheim and Ljungblad 1990; see review in Reichmuth 

2007). 

To better reflect marine mammal hearing capabilities, Southall et al. (2007) recommended that 

marine mammals be divided into hearing groups (Table 1). NMFS made the following 

modifications to the hearing groups proposed in Southall et al. (2007)13: 

• Division of pinnipeds into PW and OW hearing groups: NMFS subdivided pinnipeds into 

their two families: Phocidae and Otariidae. Based on a review of the literature, phocid 

species have consistently demonstrated an extended frequency range of hearing 

compared to otariids, especially in the higher frequency range (Hemilä et al. 2006; 

Kastelein et al. 2009a; Reichmuth et al. 2013). Phocid ears are anatomically distinct from 

otariid ears in that phocids have larger, more dense middle ear ossicles, inflated auditory 

bulla, and larger sections of the inner ear (i.e., tympanic membrane, oval window, and 

round window), which make them more adapted for underwater hearing (Terhune and 

Ronald 1975; Schusterman and Moore 1978; Kastak and Schusterman 1998; Hemilä et 

al. 2006; Mulsow et al. 2011; Reichmuth et al. 2013). 

• Recategorization of hourglass (Lagenorhynchus cruciger) and Peale’s (L. australis) 

dolphins from MF cetacean to HF cetacean hearing group: Echolocation data (Kyhn et al. 

2009; Kyhn et al. 2010; Tougaard and Kyhn. 2010) indicate that the hourglass and 

Peale’s dolphin produce sounds (i.e., higher mean peak frequency) similar to other 

narrow band high-frequency cetaceans, such as porpoises, Kogia, and Cephalorhynchus, 

and are distinctly different from other Lagenorhynchus species. Genetic data also 

suggest these two species are more closely related to Cephalorhynchus species (MayCollado and Agnarsson 2006). Thus, based on this information, NMFS has decided to 

move these two species from MF cetaceans to HF cetaceans. 

9 Hearing measurements both in air and underwater have been collected for pinniped species. 

10 There was an unsuccessful attempt to directly measure hearing in a stranded gray whale calf by Ridgway and Carder 

2001. 

11 Note: The modeling of Cranford and Krsyl (2015) predicts that the primary mechanism for hearing in LF cetaceans is 

bone conduction. Additionally, this predictive model was based on the skull geometry of a newborn fin whale. 

12 Studies in other species indicate that perception of frequencies may be broader than frequencies produced (e.g., Luther 

and Wiley 2009). 

13 NMFS considered dividing LF cetaceans into two separate groups (i.e., some species may have better low frequency 

hearing than others, like blue and fin whales; Clark and Ellison 2004), but decided there was not enough data to support 

such a division at this time. NMFS also considered separating sperm whales from other MF cetaceans, but there are not 

enough data are available to stipulate exactly how to do this. Sperm whale placement within MF cetaceans is considered 

appropriate based on Ketten (2000), which classified sperm whales as having Type I cochlea, similar to other MF 

cetaceans. 

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Table 1: Marine mammal hearing groups. 

Hearing Group Generalized Hearing 

Range* 

Low-frequency (LF) cetaceans 

(baleen whales) 7 Hz to 35 kHz 

Mid-frequency (MF) cetaceans 

(dolphins, toothed whales, beaked whales, bottlenose whales) 150 Hz to 160 kHz 

High-frequency (HF) cetaceans 

(true porpoises, Kogia, river dolphins, cephalorhynchid, 

Lagenorhynchus cruciger & L. australis) 

275 Hz to 160 kHz 

Phocid pinnipeds (PW) (underwater) 

(true seals) 50 Hz to 86 kHz 

Otariid pinnipeds (OW) (underwater) 

(sea lions and fur seals) 60 Hz to 39 kHz 

* Represents the generalized hearing range for the entire group as a composite (i.e., all species within the group), where 

individual species’ hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65 dB 

threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall et al. 2007) 

and PW pinniped (approximation). 

NMFS’ modification results in marine mammal hearing groups being defined in this Technical 

Guidance as depicted in Table 1. Table 1 defines a generalized hearing range each hearing 

group. This generalized hearing range was determined based on the ~65 dB14 threshold from the 

normalized composite audiograms (Figure 4). For LF cetaceans and PW pinnipeds, the ~65 dB 

threshold resulted in a lower bound that was considered too low to be biologically plausible for 

these two groups. Instead, for LF cetaceans the lower frequency limit from Southall et al. 2007 

was used, while for PW pinnipeds 50 Hz was chosen as a reasonable approximation for the lower 

frequency limit (relative to otariid pinnipeds)15. 

2.1.1 Application of Marine Mammal Hearing Groups 

The application of marine mammal hearing groups occurs throughout the Technical Guidance in 

two ways. First, thresholds are divided by hearing group to acknowledge that not all marine 

mammal species have identical hearing or susceptibility to noise-induced hearing loss (NIHL). 

Outside the generalized hearing range, the risk of auditory impacts from sounds is considered 

highly unlikely or very low16 (the exception would be if a sound above/below this range has the 

potential to cause physical injury, i.e., lung or gastrointestinal tract injury from underwater 

explosives). 

Second, marine mammal hearing groups are used in the establishment of marine mammal 

auditory weighting functions discussed next. 

14 In humans, functional hearing range is typically defined as 60 dB above the hearing threshold at greatest hearing 

sensitivity. To account for uncertainty associated with marine mammal hearing, NMFS based the Technical Guidance’s 

generalized hearing range on 65 dB. 

15 Understanding of low-frequency pinniped hearing is limited (i.e., few studies have direct measurements of hearing 

below 100 Hz). 

16 Animals are able to detect sounds beyond their generalized hearing range by non-auditory mechanisms. However, 

typically, these sounds have to be extremely loud and would be considered uncomfortable (Wartzok and Ketten 1999). If a 

sound is on the edge of a hearing group’s generalized hearing range and there is the potential for exposure to high sound 

pressure levels, then consider the potential for detection beyond normal auditory pathways. 

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2.2 MARINE MAMMAL AUDITORY WEIGHTING FUNCTIONS 

The ability to hear sounds varies across a species’ hearing range. Most mammal audiograms 

have a typical “U-shape,” with frequencies at the bottom of the “U” being those to which the 

animal is more sensitive, in terms of hearing (i.e. the animal’s best hearing range; for example 

audiogram, see Glossary, Figure F1). Auditory weighting functions best reflect an animal’s ability 

to hear a sound (and do not necessarily reflect how an animal will perceive and behaviorally react 

to that sound). To reflect higher hearing sensitivity at particular frequencies, sounds are often 

weighted. For example, A-weighting for humans deemphasize frequencies below 1 kHz and 

above 6 kHz based on the inverse of the idealized (smoothed) 40-phon equal loudness hearing 

function across frequencies, standardized to 0 dB at 1 kHz (e.g., Harris 1998). Other types of 

weighting functions for humans (e.g., B, C, D) deemphasize different frequencies to different 

extremes (e.g., flattens equal-loudness perception across wider frequencies with increasing 

received level; for example, C-weighting is uniform from 50 Hz to 5 kHz; ANSI 2011). 

Auditory weighting functions have been proposed for marine mammals, specifically associated 

with PTS onset thresholds expressed in the weighted SELcum 17 metric, which take into account 

what is known about marine mammal hearing (Southall et al. 2007; Erbe et al. 2016). The 

Finneran Technical Report (Finneran 2016) developed marine mammal auditory weighting 

functions that reflect new data on: 

• Marine mammal hearing (e.g., Sills et al. 2014; Sills et al. 2015; Cranford and Krysl, 

2015; Kastelein et al. 2015c) 

• Marine mammal equal latency contours (e.g., Reichmuth 2013; Wensveen et al. 2014; 

Mulsow et al. 2015 

• Effects of noise on marine mammal hearing (e.g., Kastelein et al. 2012a; Kastelein et al. 

2012b; Finneran and Schlundt 2013; Kastelein et al. 2013a; Kastelein et al. 2013b; 

Popov et al. 2013; Kastelein et al. 2014a; Kastelein et al. 2014b; Popov et al. 2014; 

Finneran et al. 2015; Kastelein et al., 2015a; Kastelein et al. 2015b; Popov et al. 2015). 

This reflects a transition from auditory weighting functions that have previously been more similar 

to human dB(C) functions (i.e., M-weighting from Southall et al. 2007) to that more similar to 

human dB(A) functions. These marine mammal auditory weighting functions also provide a more 

consistent approach/methodology for all hearing groups. 

Upon evaluation, NMFS determined that the proposed methodology in Finneran 2016 reflects the 

scientific literature and incorporated it directly into this Technical Guidance (Appendix A) following 

an independent peer review (see Appendix C for details on peer review and link to Peer Review 

Report). 

2.2.1 Use of Auditory Weighting Functions in Assessing Susceptibility to Noise-Induced 

Hearing Loss 

Auditory weighting functions are used for human noise standards to assess the overall hazard of 

noise on hearing. Specifically, human auditory weighting functions provide a “rating that indicates 

the injurious effects of noise on human hearing” (OSHA 2013). Thus, while these functions are 

based on regions of equal loudness and best hearing, in the context of human risk assessments, 

as well as their use in the Technical Guidance, they are meant to reflect the susceptibility of the 

ear to noise-induced threshold shifts (TSs). Regions of enhanced susceptibility to noise may not 

17 Auditory weighting functions are not to be applied to PTS or TTS onset thresholds expressed as the PK metric (i.e., PK 

thresholds are flat or unweighted within the generalized hearing range). For more information, please see Section 2.3.2.2. 

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, ,,.-... 

~ 

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perfectly mirror a species’ region of best hearing (e.g., TTS measurements from bottlenose 

dolphin, belugas, and Yangtze finless porpoise support this). Thus, within the Technical 

Guidance, auditory weighting functions are meant to assess risk of NIHL and do not necessarily 

encompass the entire range of best hearing for every species within the hearing group. 

2.2.2 Marine Mammal Auditory Weighting Functions 

Frequency-dependent marine mammal auditory weighting functions were derived using data on 

hearing ability (composite audiograms), effects of noise on hearing, and data on equal latency 

(Finneran 201618). Separate functions were derived for each marine mammal hearing group 

(Figures 1 and 2). 

Figure 1: Auditory weighting functions for low-frequency (LF; dashed line), midfrequency (MF; solid line), and high-frequency (HF; dotted line) cetaceans. 

18 Wright 2015 provides a critique of this methodology. For NMFS’ response associated with this critique, see the Federal 

Register Notice associated with 2016 Technical Guidance (81 FR 51694; August 4, 2016), specifically the section 

responding to public comments. 

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-- 0 i:o 

"O 

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:l 

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s -20 

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C 

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-60 

0.01 

i-

. 

. . . . . • 

0.1 

-. • 

1 10 

Frequency (kHz) 

I 

r 

100 

- otariid 

• • • Phocid 

Figure 2: Underwater auditory weighting functions for otariid (OW; solid line) and 

phocid (PW; dotted line) pinnipeds. 

The overall shape of the auditory weighting functions is based on a generic band-pass filter 

described by Equation 1: 

dB Equation 1 

where Waud(ƒ) is the auditory weighting function amplitude in decibels (dB) at a particular 

frequency (ƒ) in kilohertz (kHz). The function shape is determined by the following auditory 

weighting function parameters: 

• Low-frequency exponent (a): This parameter determines the rate at which the weighting 

function amplitude declines with frequency at the lower frequencies. As the frequency 

decreases, the change in amplitude becomes linear with the logarithm of frequency with 

a slope of 20a dB/decade. 

• High-frequency exponent (b): Rate at which the weighting function amplitude declines 

with frequency at the upper frequencies. As the frequency increases, the change in 

amplitude becomes linear with the logarithm of frequency with a slope of 20b dB/decade. 

• Low-frequency cutoff (ƒ1): This parameter defines the lower limit of the band-pass filter 

(i.e., the lower frequency where weighting function amplitude begins to roll off or decline 

from the flat, central portion of the function). This parameter is directly dependent on the 

value of the low-frequency exponent (a). 

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E (J) = K -10102 { (J I J;)l" 

~ud -10 [l+(J I 1,/ [l+(J I f:f1 

Q.) 

"C 

::::I 

:t:::: 

a. 

E 

ro 

Eq. (1) - weighting function 

cf 

-20b 

Eq. (2) - exposure function 

20b 

frequency 

• High-frequency cutoff (ƒ2): This parameter defines the upper limit the band-pass filter (i.e., 

the upper frequency where weighting function amplitude begins to roll off or decline from 

the flat, central portion of the function). This parameter is directly dependent on the value 

of the high-frequency exponent (b). 

• Weighting function gain (C): This parameter determines the vertical position of the 

function and is adjusted to set the maximum amplitude of the auditory weighting function 

to 0 dB. 

Finneran (2016) illustrates the influence of each parameter value on the shape of the auditory 

weighting function (Appendix A, Figure A2). 

In association with auditory weighting functions are exposure functions that illustrate how auditory 

weighting functions relate to auditory thresholds. Auditory exposure functions (Equation 2) are the 

inversion of Equation 1: 

dB 

Equation 2 

where Eaud(ƒ) is the acoustic exposure as a function of frequency (ƒ) and the gain parameter 

constant (K), which is adjusted to set the minimum value of the curve to the weighted PTS/TTS 

onset auditory threshold. All other parameters are the same as those in Equation 1. Figure 3 

illustrates how the various weighting parameters relate to one another in both the auditory 

weighting and exposure functions. 

Figure 3: Illustration of function parameter in both auditory weighting functions and 

exposure functions (from Finneran 2016). Reference to Equations 1 and 2 

match those in the Technical Guidance. 

Finneran (2016) (Appendix A, Figures A-22 and A-23) provides a comparison of these auditory 

weighting functions with previously derived weighting functions (Finneran and Jenkins 2012 used 

in Navy Phase 2 Analysis). 

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0 

60 

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Cl) 

~ -20 

..c 0.01 0.1 10 100 0.1 10 100 0.1 10 100 

"O -

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N 

ro 60 

E 

..... 

0 40 

C 

20 

0 ow -20 

0.1 10 100 0.1 10 100 

frequency (kHz) 

8 

2.2.3 Derivation of Function Parameters 

Numeric values associated with auditory weighting function parameters were derived from 

available data from audiograms (measured and predicted), equal latency contours, and marine 

mammal TTS data using the following steps from Finneran (2016): 

1. Derivation of marine mammal composite audiograms (original and normalized) for each 

hearing group (Resulting normalized composite audiogram: Figure 4; Data sources: 

Table 2). 

Figure 4: Resulting normalized composite audiograms for low-frequency (LF), midfrequency (MF), and high-frequency (HF) cetaceans and phocid (PW) and 

otariid (OW) pinnipeds (from Finneran 2016). For resulting original 

composite audiogram, see Appendix A, Figure A5. 

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Table 2: Summary of data available for deriving composite audiograms.

† 

Hearing Group Species (number of 

individuals) References 

Mid-Frequency (MF) 

Cetaceans 

Beluga (9) White et al. 1978; Awbrey et al. 1988; Johnson et al. 

1989; Ridgway et al. 2001; Finneran et al. 2005b 

Bottlenose dolphin 

(6) 

Johnson 1967; Ljungblad et al. 1982; Lemonds 1999; 

Brill et al. 2001;Schlundt et al. 2008; Finneran et al. 

2010a 

False killer whale (1) Thomas et al. 1988 

Killer whale (8) Szymanski et al. 1999; Branstetter et al. 2017+ 

Risso’s dolphin (1) Nachtigall et al. 1995 

Pacific white-sided 

dolphin (1) Tremel et al. 1996 

Striped dolphin (1) Kastelein et al. 2003 

Tucuxi (1) Sauerland and Dehnhardt 1998 

High-Frequency (HF) 

Cetaceans 

Amazon River 

dolphin (1) Jacobs and Hall 1972 

Harbor porpoise (5) Kastelein et al. 2010; Kastelein et al. 2015c; Kastelein 

et al. 2017a+ 

Phocid Pinnipeds 

(PW) Underwater 

Harbor seal (4) Terhune 1988; Kastelein et al. 2009b; Reichmuth et al. 

2013 

Northern elephant 

seal (1) Kastak and Schusterman 1999 

Ringed seal (1) Sills et al. 2015 

Spotted seal (2) Sills et al. 2014 

Otariid Pinnipeds* 

(OW) Underwater 

California sea lion 

(4) 

Mulsow et al. 2012; Reichmuth and Southall 2012; 

Reichmuth et al. 2013 

Northern fur seal (3) Moore and Schusterman 1987; Babushina et al. 1991 

Steller sea lion (2) Kastelein et al. 2005a 

† More details on individual subjects are available in Appendix A (Table A2). Some datasets were excluded due to 

subjects having high-frequency hearing loss or aberrant audiograms. These included subjects from: Møhl 1968; Andersen 

1970; Hall and Johnson 1972; Terhune and Ronald 1972; Terhune and Ronald 1975; Thomas et al. 1990; Wang et al. 

1992; Babushina 1997; Kastak et al. 2002; Finneran et al. 2005 (Turner); Yuen et al. 2005; Finneran et al. 2007a; Sills et 

al. 2015 (Natchek). Decisions to exclude data were based on comparison of the individual published audiograms and 

ambient noise characteristics to those for other individuals of the same or closely related species. The most common 

reasons for excluding an individual’s data were abnormal audiograms featuring high-frequency hearing loss (typically 

seen in older animals) or “notches” in the audiogram, or data collected in the presence of relatively high ambient noise 

that resulted in elevated thresholds. Excluding these data ensured that the composite audiograms were not artificially 

elevated, which could result in unrealistically high thresholds. 

+Two publications with behavioral audiograms became available after the Technical Guidance’s finalization in 2016. 

However, upon consideration of these two studies during EO 13795 review of the Technical Guidance, including 

recommendations from other Federal agencies, NMFS determined it is not practical from an implementation standpoint to 

add these studies at this time. NMFS will include these studies in the next revision of this document (i.e., Version 3.0). For 

more detail on these studies, see Section III. 

* The otariid pinniped (underwater) hearing group’s composite audiogram contains data from a single Pacific walrus 

(Odobenus rosmarus) from Kastelein et al. 2002 and a single sea otter (Enhydra lutris nereis) from Ghoul and Reichmuth 

2014, which are species under the jurisdiction of the USFWS. However, since marine mammal audiogram data are 

limited, a decision was made to include all available datasets from in-water groups to derive composite audiograms for 

this hearing group. For frequencies below 30 kHz, the difference in the composite audiogram with and without these data 

are < 2 dB. For comparison, see Appendix A, Figure A4. 

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In deriving marine mammal composite audiograms, NMFS established an informal data 

hierarchy in terms of assessing these types of data. Specifically, audiograms obtained via 

behavioral methodologies were determined to provide the most representative (sensitive) 

presentation of hearing ability (Finneran et al. 2007a), followed by auditory evoked 

potential (AEP) data,19 and lastly by mathematical/anatomical models for species where 

no data are available (i.e., LF cetaceans). Thus, the highest quality data available for a 

specific hearing group were used.20 

For LF cetaceans, only two studies were available for consideration (i.e., predicted 

audiogram for a humpback whale from Houser et al. 2001 and fin whale from Cranford 

and Krysl 2015), which alone was not enough to derive a predicted audiogram for this 

entire hearing group. Thus, an alternative approach was used to derive a composite 

audiogram21 and associated auditory weighting function for LF cetaceans (i.e., composite 

audiogram parameters had to be predicted; For specifics, on this process, see Appendix 

A1). 

2. The low-frequency exponent (a) was defined using the smaller of the low-frequency slope 

from either the composite audiogram or the lower-frequency slope of the equal latency 

contours (if available) and then divided by twenty (s0/20 ). This results in the slope 

matching the shallower slope of the audiogram. 

3. The high-frequency exponent (b) was set equal to two to match the previously derived 

marine mammal auditory weighting functions from Finneran and Jenkins (2012), since no 

new TTS measurements were available at higher frequencies and equal latency data at 

these frequencies are considered highly variable. 

4. Low- (ƒ1) and high-frequency cutoffs (ƒ2) were defined as the frequencies below and 

above the frequency of best hearing (ƒ0) from original data, where the threshold values 

were ΔT above the threshold at ƒ0 . These two parameters reflect the hearing group’s 

most susceptible frequency range. 

5. To determine ΔT, the auditory exposure function amplitude was calculated for MF and HF 

cetaceans examining ΔT values ranging from zero to 20 dB. Then, the K gain parameter 

was adjusted to minimize the mean-squared error (MSE) between the function amplitude 

(original and normalized composite audiograms) and MF and HF cetacean TTS data. The 

value of ΔT resulting the lowest MSE was eleven for both the normalized and original 

data. This value was used for other hearing groups. 

6. Hearing groups where TTS data are available (i.e., MF and HF cetaceans and PW and 

OW pinniped) were used to define K (Step 4 above). For LF cetaceans, where data were 

19 Despite not directly including AEP audiograms in the development of a hearing groups’ composite audiogram, these 

date were evaluated to ensure species were placed within the appropriate hearing group and to ensure a species where 

only AEP data are available were within the bounds of the composite audiogram for that hearing group. Furthermore, AEP 

TTS data are presented within the Technical Guidance for comparative purposes alongside TTS data collected by 

behavioral methods illustrating that the AEP TTS data are within the bounds (the majority of the time above) of those 

collected by behavioral methods. 

20 Behavioral techniques for obtaining audiograms measure perception of sound by a receiver, while AEP methods 

measure only neural activity (Jewett and Williston 1971) (i.e., two methodologies are not necessarily equivalent). As a 

result, behavioral techniques consistently produce lower thresholds than those obtained by AEPs (e.g., Szymanski et al. 

1999; Yuen et al. 2005; Houser and Finneran 2006). Currently, there are no means established for “correcting” AEP data 

so that it may be more comparable to those obtained via behavioral methods (Heffner and Heffner 2003; Finneran 2015; 

Sisneros et al. 2016; Erbe et al. 2016). 

21 During the third public comment period on the Technical Guidance in March 2016, ambient noise levels from Clark and 

Ellison 2004 were offered by a group of subject matter experts as additional scientific support to NMFS’ LF cetacean 

weighting function (for direct comparison to NOAA’s 2016 LF cetacean weighting function see: Public comment made via 

Regulations.gov). 

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not available, TTS onset was estimated by assuming the numeric difference between 

auditory threshold (Figure 4, original data) and TTS onset at the frequency of best 

hearing (ƒ0) would be similar across hearing groups. For LF cetaceans auditory threshold 

had to be predicted, since no data exist (For specifics on methodology, see Appendix A, 

Table A7). 

7. The weighting function parameter (C) was determined by substituting parameters a, b, ƒ1, 

and ƒ2 in Equation 1 and setting the peak amplitude of the function to zero. 

For each hearing group, the resulting numeric values associated with these parameters and 

resulting weighted TTS onset threshold for non-impulsive sources (weighted SELcum metric) are 

listed in Table 3 and resulting auditory weighting functions are depicted in Figures 1 and 2. 

Table 3: Summary of auditory weighting and exposure function parameters. 

Hearing Group a b ƒ1 

(kHz) 

ƒ2 

(kHz) 

C 

(dB) 

K 

(dB) 

Weighted TTS onset 

threshold* (SELcum) 

Low-frequency (LF) 

cetaceans 1.0 2 0.2 19 0.13 179 179 dB 

Mid-frequency (MF) 

cetaceans 1.6 2 8.8 110 1.20 177 178 dB 

High-frequency (HF) 

cetaceans 1.8 2 12 140 1.36 152 153 dB 

Phocid pinnipeds (PW) 

(underwater) 1.0 2 1.9 30 0.75 180 181 dB 

Otariid pinnipeds (OW) 

(underwater) 2.0 2 0.94 25 0.64 198 199 dB 

* Determined from minimum value of auditory exposure function and the weighting function at its peak (i.e., 

mathematically equivalent to K + C). 

Note: Appendix A, Figure A17 illustrates that the resulting auditory exposure functions (and 

subsequent weighting functions) are broader than the composite audiograms or audiogram from 

an individual species. This is important to note because the auditory weighting/exposure functions 

are derived not just from data associated with the composite audiogram but also account for 

available TTS onset data. 

2.2.4 Application of Marine Mammal Auditory Weighting Functions for PTS Onset 

Thresholds 

The application of marine mammal auditory weighting functions emphasizes the importance of 

making measurements and characterizing sound sources in terms of their overlap with 

biologically-important frequencies (e.g., frequencies used for environmental awareness, 

communication or the detection of predators or prey), and not only the frequencies of interest or 

concern for the completion of the sound-producing activity (i.e., context of sound source). 

If the frequencies produced by a sound source are outside a hearing group’s most susceptible 

hearing range (where the auditory weighting function amplitude is 0), sounds at those frequencies 

are required to have a higher sound pressure level to produce a similar threshold shift (i.e., PTS 

onset) as sounds with frequencies in the hearing group’s most susceptible hearing range. 

Because auditory weighting functions take into account a hearing group’s differing susceptibility 

to frequencies, the implementation of these functions typically results in smaller isopleths22 for 

22 Note: Thresholds associated with a hearing group do not change depending on how much a sound may overlap a 

group’s most susceptible frequency range. Instead, weighting functions affect exposure modeling/analysis via the 

resulting size of the isopleth (area) associated with the threshold based on how susceptible that particular hearing group 

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frequencies where the group is less susceptible. Additionally, if the sound source produces 

frequencies completely outside the generalized hearing range of a given hearing group (i.e., has 

no harmonics/subharmonics that are capable of producing sound within the hearing range of a 

hearing group), then the likelihood of the sound causing hearing loss is considered low.23 

Marine mammal auditory weighting functions are used in conjunction with corresponding 

weighted SELcum PTS onset thresholds. If the use of the full auditory weighting function is not 

possible by an action proponent (i.e., consider auditory weighting function over multiple 

frequencies for broadband source), NMFS has provided an alternative tool based on a simpler 

auditory weighting function (See Appendix D). 

Tougaard et al. (2015) reviewed the impacts of using auditory weighting functions and various 

considerations when applying them during the data evaluation and implementation stages (e.g., 

consequences of using too broad or too narrow of a filter) and suggested some modifications 

(correction factors) to account for these considerations. However, there are no data to support 

doing so (i.e., selection would be arbitrary). Moreover, various conservative factors have been 

accounted for in the development of auditory weighting functions and thresholds: A 6 dB 

threshold shift was used to represent TTS onset; the methodology does not incorporate 

exposures where TTS did not occur; and the potential for recovery is not accounted for. 

Additionally, the means by which NMFS is applying auditory weighting functions is supported and 

consistent with what has been done for humans (i.e., A-weighted thresholds used in conjunction 

with A-weighting during implementation). 

2.2.4.1 Measuring and Maintaining Full Spectrum for Future Analysis 

It is recommended marine mammal auditory weighting functions be applied after sound field 

measurements24 have been obtained (i.e., post-processing; it is recommended that auditory 

weighting functions not be applied beforehand), with the total spectrum of sound preserved for 

later analysis (i.e., if auditory weighting functions are updated or if there is interest in additional 

species, then data can still be used). Additionally, it is important to consider measurements that 

encompass the entire frequency band that a sound source may be capable of producing (i.e., 

sources often produce sounds, like harmonics/subharmonics, beyond the frequency/band of 

interest; e.g., Deng et al. 2014; Hastie et al. 2014). 

2.3 PTS ONSET THRESHOLDS 

Available data from humans and other terrestrial mammals indicate that a 40 dB threshold shift 

approximates PTS onset (see Ward et al. 1958; Ward et al. 1959; Ward 1960; Kryter et al. 1966; 

Miller 1974; Ahroon et al. 1996; Henderson et al. 2008). Southall et al. (2007) also recommended 

this definition of PTS onset. 

PTS onset thresholds for marine mammals have not been directly measured and are extrapolated 

from available TTS onset measurements. Thus, based on cetacean measurements from TTS 

is to the sound being modeled. For example, a hearing group could have different size isopleths associated with the same 

threshold, if one sound was within its most susceptible frequency range and the other was not (i.e., sound in most 

susceptible hearing range will result in larger isopleth compared to sound outside the most susceptible hearing range). 

23 The potential for sound to damage beyond the level the ear can perceive exists (Akay 1978), which is why the 

thresholds also include the PK metric, which are flat or unweighted within the generalized hearing range of a hearing 

group. 

24 Note: Sound field measurements refers to actual field measurements, which are not a requirement of this Technical 

Guidance, and not to exposure modeling analyses, where it may be impractical due to data storage and cataloging 

restraints. 

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studies (see Southall et al. 2007; Finneran 2015; Finneran 2016 found in Appendix A of this 

Technical Guidance) a threshold shift of 6 dB is considered the minimum threshold shift clearly 

larger than any day-to-day or session-to-session variation25 in a subject’s normal hearing ability 

and is typically the minimum amount of threshold shift that can be differentiated in most 

experimental conditions (Finneran et al. 2000; Schlundt et al. 2000; Finneran et al. 2002). Thus, 

NMFS has set the onset of TTS at the lowest level that exceeds recorded variation (i.e., 6 dB). 

There are different mechanisms (e.g., anatomical, neurophysiological) associated with TTS vs. 

PTS onset, making the relationship between these types of TSs not completely direct. 

Nevertheless, the only data available for marine mammals, currently and likely in the future, will 

be from TTS studies (i.e., unlike for terrestrial mammals where direct measurements of PTS 

exist). Thus, TTS represents the best information available from which PTS onset can be 

estimated. 

The thresholds presented in Table 4 consist of both an acoustic threshold and auditory weighting 

function for the SELcum metric (auditory weighting functions are considered not appropriate for PK 

metric). 

NMFS recognizes that the implementation of marine mammal auditory weighting functions 

represents a new factor for consideration that may exceed the capabilities of some action 

proponents. Thus, NMFS has developed alternative tools for those who cannot fully apply 

auditory weighting functions associated with the weighted SELcum metric (See Appendix D). 

2.3.1 Impulsive and Non-Impulsive Source Thresholds 

This Technical Guidance divides sources into impulsive and non-impulsive based on physical 

characteristics at the source, with impulsive sound having physical characteristics making them 

more injurious26 (e.g., high peak sound pressures and rapid rise times) than non-impulsive sound 

sources (terrestrial mammal data: Buck et al. 1984; Dunn et al. 1991; Hamernik et al. 1993; 

Clifford and Rogers 2009; marine mammal data: reviewed in Southall et al. 2007 and Finneran 

2016 that appears as Appendix A of this Technical Guidance). 

The characteristics of the sound at a receiver, rather than at the source, are the relevant 

consideration for determining potential impacts. However, understanding these physical 

characteristics in a dynamic system with receivers moving over space and time is difficult. 

Nevertheless, it is known that as sound propagates from the source the characteristics of 

impulsive sounds that make them more injurious start to dissipate due to effects of propagation 

(e.g., time dispersion/time spreading; Urick 1983; Sertlek et al. 2014). 

25 Similarly, for humans, NIOSH (1998) regards the range of audiometric testing variability to be approximately 5 dB. 

26 Exposure to impulsive sounds more often lead to mechanical damage of the inner ear, as well as more complex 

patterns of hearing recovery (e.g., Henderson and Hamernik 1986; Hamernik and Hsueh 1991). 

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Table 4: Summary of PTS onset thresholds. 

PTS Onset Thresholds* 

(Received Level) 

Hearing Group Impulsive Non-impulsive 

Low-Frequency (LF) 

Cetaceans 

Cell 1 

Lpk,flat: 219 dB 

LE,LF,24h: 183 dB 

Cell 2 

LE,LF,24h: 199 dB 

Mid-Frequency (MF) 

Cetaceans 

Cell 3 

Lpk,flat: 230 dB 

LE,MF,24h: 185 dB 

Cell 4 

LE,MF,24h: 198 dB 

High-Frequency (HF) 

Cetaceans 

Cell 5 

Lpk,flat: 202 dB 

LE,HF,24h: 155 dB 

Cell 6 

LE,HF,24h: 173 dB 

Phocid Pinnipeds (PW) 

(Underwater) 

Cell 7 

Lpk,flat: 218 dB 

LE,PW,24h: 185 dB 

Cell 8 

LE,PW,24h: 201 dB 

Otariid Pinnipeds (OW) 

(Underwater) 

Cell 9 

Lpk,flat: 232 dB 

LE,OW,24h: 203 dB 

Cell 10 

LE,OW,24h: 219 dB 

* Dual metric thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a 

non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive 

sounds, these thresholds are recommended for consideration. 

Note: Peak sound pressure level (Lp,0-pk) has a reference value of 1 μPa, and weighted cumulative sound exposure level 

(LE,p) has a reference value of 1μPa2

s. In this Table, thresholds are abbreviated to be more reflective of International 

Organization for Standardization standards (ISO 2017). The subscript “flat” is being included to indicate peak sound 

pressure are flat weighted or unweighted within the generalized hearing range of marine mammals (i.e., 7 Hz to 160 kHz). 

The subscript associated with weighted cumulative sound exposure level thresholds indicates the designated marine 

mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended 

accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude of 

ways (i.e., varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to 

indicate the conditions under which these thresholds will be exceeded. 

For the purposes of this Technical Guidance,27 sources are divided and defined as the following: 

• Impulsive: produce sounds that are typically transient, brief (less than 1 second), 

broadband, and consist of high peak sound pressure with rapid rise time and rapid decay 

(ANSI 1986; NIOSH 1998; ANSI 2005). 

• Non-impulsive: produce sounds that can be broadband, narrowband or tonal, brief or 

prolonged, continuous or intermittent) and typically do not have a high peak sound 

pressure with rapid rise/decay time that impulsive sounds do (ANSI 1995; NIOSH 1998). 

Note: The term “impulsive” in this document relates specifically to NIHL and specifies the physical 

characteristics of an impulsive sound source, which likely gives them a higher potential to cause 

auditory TTS/PTS. This definition captures how these sound types may be more likely to affect 

auditory physiology and is not meant to reflect categorizations associated with behavioral 

disturbance. 

27 If there is unclear, consider the most applicable definition and consult with NMFS. 

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2.3.2 Metrics 

2.3.2.1 Weighted Cumulative Sound Exposure Level (SELcum) Metric 

The weighted SELcum metric takes into account both received level and duration of exposure 

(ANSI 2013), both factors that contribute to NIHL. Often this metric is normalized to a single 

sound exposure of one second. NMFS intends for the weighted SELcum metric to account for the 

accumulated exposure (i.e., weighted SELcum cumulative exposure over the duration of the 

activity within a 24-h period). 

The recommended application of the weighted SELcum metric is for individual activities/sources. It 

is not intended for accumulating sound exposure from multiple activities occurring within the 

same area or over the same time or to estimate the impacts of those exposures to an animal 

occurring over various spatial or temporal scales. Current data available for deriving thresholds 

using this metric are based on exposure to only a single source and may not be appropriate for 

situations where exposure to multiple sources is occurring. As more data become available, the 

use of this metric can be re-evaluated, in terms of appropriateness, for application of exposure 

from multiple activities occurring in space and time. 

Equal Energy Hypothesis 

One assumption made when applying the weighted SELcum metric is the equal energy hypothesis 

(EEH), where it is assumed that sounds of equal SELcum produce an equal risk for hearing loss 

(i.e., if the weighted SELcum of two sources are similar, a sound from a lower level source with a 

longer exposure duration may have similar risks to a shorter duration exposure from a higher 

level source). As has been shown to be the case with humans and terrestrial mammals 

(Henderson et al. 1991), the EEH does not always accurately describe all exposure situations for 

marine mammals due the inherent complexity of predicting TSs (e.g., Kastak et al. 2007; Mooney 

et al. 2009a; Mooney et al. 2009b; Finneran et al. 2010a; Finneran et al. 2010b; Finneran and 

Schlundt 2010; Kastelein et al. 2012b; Kastelein et al. 2013b; Kastelein et al. 2014a; Popov et al. 

2014). 

Factors like sound level (e.g., overall level, sensation level, or level above background), duration, 

duty cycle (intermittent versus continuous exposure; potential recovery between intermittent 

periods), number of transient components (short duration and high amplitude), and/or frequency 

(especially in relation to hearing sensitivity) often are also important factors associated with TSs 

(e.g., Buck et al. 1984; Clark et al. 1987; Ward 1991; Lataye and Campo 1996). This is especially 

the case for exposure to impulsive sound sources (Danielson et al. 1991; Henderson et al. 1991; 

Hamernik et al. 2003), which is why thresholds in this Technical Guidance are also expressed as 

a PK metric (see next section). However, in many cases the EEH approach functions reasonably 

well as a first-order approximation, especially for higher-level, short-duration sound exposures 

such as those that are most likely to result in TTS in marine mammals28 (Finneran 2015). 

Additionally, no currently supported alternative method to accumulate exposure is available. If 

alternative methods become available, they can be evaluated and considered when the Technical 

Guidance is updated. 

Recommended Accumulation Period 

To apply the weighted SELcum metric, a specified accumulation period is needed. Generally, it is 

predicted that most receivers will minimize the amount of time they remain in the closest ranges 

to a sound source/activity. Exposures at the closest point of approach are the primary exposures 

contributing to a receiver’s accumulated level (Gedamke et al. 2011). Additionally, several 

28 When possible, it is valuable for action proponents to indicate the exposure conditions under which these thresholds are 

likely to be exceeded. 

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important factors determine the likelihood and duration a receiver is expected to be in close 

proximity to a sound source (i.e., overlap in space and time between the source and receiver). 

For example, accumulation time for fast moving (relative to the receiver) mobile sources is driven 

primarily by the characteristics of source (i.e., speed, duty cycle). Conversely, for stationary 

sources, accumulation time is driven primarily by the characteristics of the receiver (i.e., swim 

speed and whether transient or resident to the area where the activity is occurring). NMFS 

recommends a maximum baseline accumulation period of 24 hours, but acknowledges that there 

may be specific exposure situations where this accumulation period requires adjustment (e.g., if 

activity lasts less than 24 hours or for situations where receivers are predicted to experience 

unusually long exposure durations29). 

After sound exposure ceases or between successive sound exposures, the potential for recovery 

from hearing loss exists, with PTS resulting in incomplete recovery and TTS resulting in complete 

recovery. Predicting recovery from sound exposure can be quite complicated. Currently, recovery 

in wild marine mammals cannot be accurately quantified. However, Finneran et al. (2010a) and 

Finneran and Schlundt (2013) proposed a model that approximates recovery in bottlenose 

dolphins and whose applicability to other species and other exposure conditions has yet to be 

determined. In the development of the Technical Guidance’s thresholds, NMFS assumes for 

intermittent, repeated exposure that there is no recovery between subsequent exposures, 

although it has been demonstrated in terrestrial mammals (Clark et al. 1987; Ward 1991) and 

more recently in a marine mammal studies (Finneran et al. 2010b; Kastelein et al. 2014a; 

Kastelein et al. 2015b), that there is a reduction in damage and hearing loss with intermittent 

exposures. 

Existing NMFS thresholds have only accounted for proximity of the sound source to the receiver, 

but thresholds in this Technical Guidance (i.e., expressed as weighted SELcum) now take into 

account the duration, as well as level of exposure. NMFS recognizes that accounting for duration 

of exposure, although supported by the scientific literature, adds a new factor, as far as 

application of this metric to real-world activities and that not all action proponents may have the 

ability to easily apply this additional component. 

NMFS does not provide specifications necessary to perform exposure modeling and relies on the 

action proponent to determine the model that best represents their activity. However, NMFS 

acknowledges that different action proponents may have different capabilities and levels of 

modeling sophistication. NMFS has provided a simple means of approximating exposure for 

action proponents that are unable to apply various factors into their model (See Appendix D). 

NMFS will convene a working group to investigate means for deriving more realistic accumulation 

periods, especially for stationary sources (anticipated in 2018). 

2.3.2.2 Peak Sound Pressure Level (PK) Metric30 

Sound exposure containing transient components (e.g., short duration and high amplitude; 

impulsive sounds) can create a greater risk of causing direct mechanical fatigue to the inner ear 

(as opposed to strictly metabolic) compared to sounds that are strictly non-impulsive (Henderson 

and Hamernik 1986; Levine et al. 1998; Henderson et al. 2008). Often the risk of damage from 

these transients does not depend on the duration of exposure. This is the concept of “critical 

level,” where damage switches from being primarily metabolic to more mechanical and short 

29 For example, where a resident population could be found in a small and/or confined area (Ferguson et al. 2015) and/or 

exposed to a long-duration activity with a large sound source, or where a continuous stationery activity is nearby an area 

where marine mammals congregate, like a pinniped pupping beach. 

30 Note: Do not confuse peak sound pressure level with maximum root mean square sound pressure level. 

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duration of impulse can be less than the ear’s integration time, leading to the potential to damage 

beyond the level the ear can perceive (Akay 1978). 

Human noise standards recognize and provide separate thresholds for impulsive sound sources 

using the PK metric (Occupational Safety and Health Administration (OSHA) 29 CFR 1910.95; 

Starck et al. 2003). Thus, weighted SELcum is not an appropriate metric to capture all the effects 

of impulsive sounds (i.e., often violates EEH; NIOSH 1998), which is why instantaneous PK level 

has also been chosen as part of NMFS’ dual metric thresholds for impulsive sounds.31 Auditory 

weighting is not considered appropriate with the PK metric, as direct mechanical damage 

associated with sounds having high peak sound pressures typically does not strictly reflect the 

frequencies an individual species hears best (Ward 1962; Saunders et al. 1985; ANSI 1986; DOD 

2004; OSHA 29 CFR 1910.95). Thus, this Technical Guidance recommends that the PK 

thresholds be considered unweighted/flat-weighted within the generalized hearing range of 

marine mammals (i.e., 7 Hz to 160 kHz). 

2.3.2.3 Comparison Among Metrics 

NMFS’ existing thresholds were expressed as root-mean-square sound pressure level (RMS 

SPL), which is a different metric from the PK and weighted SELcum that are being recommended 

for the PTS onset thresholds in this Technical Guidance. Thus, NMFS recommends caution when 

comparing prior thresholds to those presented in this document (i.e., metrics are not directly 

comparable). For example, a RMS SPL threshold of 180 dB is not equal to a PK threshold of 180 

dB. Further, the weighted SELcum metric incorporates exposure duration and is an energy level 

with a different reference value (re: 1μPa2-s). Thus, it is not directly comparable to other metrics 

that describe sound pressure levels (re: 1 μPa)32. 

2.3.3 Development of PTS Onset Thresholds 

The development of the PTS onset thresholds consisted of the following procedure described in 

Finneran 2016 (Appendix A33): 

1. Identification of available data on marine mammal hearing and noise-induced hearing 

loss (e.g., Southall et al. 2007; Finneran 2015; Finneran 2016 references listed in 

available reports/publications). 

2. Methodology to derive marine mammal auditory weighting functions (described in more 

detail in Section 2.2.3 and Appendix A). 

3. Evaluation and summary of currently available published data (32 studies found in Table 

5) on hearing loss associated with sound exposure in marine mammals. 

• Because no published measurements exist on PTS in marine mammals, TTS 

onset measurements and associated thresholds were evaluated and summarized 

to extrapolate to PTS onset thresholds. 

31 For non-impulsive sounds, the weighted SELcum threshold will likely to result in the largest isopleth, compared to the PK 

threshold. Thus, for the majority of non-impulsive sounds, the consideration of the PK threshold is unnecessary. However, 

if a non-impulsive sound has the potential of exceeding the PK threshold associated with impulsive sounds, NMFS 

recommends these thresholds be considered (i.e., dual metrics). 

Publications on how to estimate PK from SEL for seismic airguns and offshore impact pile drivers may be useful to action 

proponents (Galindo-Romero et al. 2015; Lippert et al. 2015). 

32 For more information and illustrations on metrics, see: Discovery of Sound in the Sea. 

33 Wright 2015 provides a critique of this methodology. For NMFS’ response to this critique, see the Federal Register 

notice associated with the finalized Technical Guidance, specifically the section responding to public comments. 

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• Studies divided into the following categories: 

o Temporal Characteristics: Impulsive and Non-impulsive 

o Marine Mammal Hearing Groups: LF Cetaceans, MF Cetaceans, HF 

Cetaceans, PW Pinnipeds, and OW Pinniped 

4. Determination of TTS onset threshold by individual (RLs, in both PK and SELcum metrics) 

based on methodology from Finneran 2016 for impulsive and non-impulsive sounds (Full 

detail in Appendix A). 

• Non-impulsive sounds: 

o Only TTS data from behavioral studies were used, since studies using 

AEP methodology typically result in larger thresholds shifts (e.g., up to 

10 dB difference, Finneran et al. 2007a) and are considered to be nonrepresentative (as illustrated in Appendix A, Figure A9) 

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Table 5: Available underwater marine mammal threshold shift studies. 

References in 

Chronologic Order+ 

Sound Source 

(Sound Source Category) 

Species (number of 

individuals^) 

Kastak et al. 1999 Octave-band noise (non-impulsive) California sea lion (1); northern 

elephant seal (1); harbor seal (1) 

Finneran et al. 2000 Explosion simulator (impulsive)* Bottlenose dolphin (2); beluga (1) 

Schlundt et al. 2000 Tones (non-impulsive) Bottlenose dolphin (5); beluga (2) 

Finneran et al. 2002 Seismic watergun (impulsive) Bottlenose dolphin (1); beluga (1) 

Finneran et al. 2003 Arc-gap transducer (impulsive)* California sea lion (2) 

Nachtigall et al. 2003 Octave-band noise (non-impulsive) Bottlenose dolphin (1) 

Nachtigall et al. 2004 Octave-band noise (non-impulsive) Bottlenose dolphin (1) 

Finneran et al. 2005a Tones (non-impulsive) Bottlenose dolphin (2) 

Kastak et al. 2005 Octave-band noise (non-impulsive) California sea lion (1); northern 

elephant seal (1); harbor seal (1) 

Finneran et al. 2007a Tones (non-impulsive) Bottlenose dolphin (1) 

Lucke et al. 2009 Single airgun (impulsive) Harbor porpoise (1) 

Mooney et al. 2009a Octave-band noise (non-impulsive) Bottlenose dolphin (1) 

Mooney et al. 2009b Mid-frequency sonar (non-impulsive) Bottlenose dolphin (1) 

Finneran et al. 2010a Tones (non-impulsive) Bottlenose dolphin (2) 

Finneran et al. 2010b Tones (non-impulsive) Bottlenose dolphin (1) 

Finneran and Schlundt 

2010 Tones (non-impulsive) Bottlenose dolphin (1) 

Popov et al. 2011a 1⁄2 octave band noise (non-impulsive) Yangtze finless porpoise (2) 

Popov et al. 2011b 1⁄2 octave band noise (non-impulsive) Beluga (1) 

Kastelein et al. 2012a Octave-band noise (non-impulsive) Harbor seal (2) 

Kastelein et al. 2012b Octave-band noise (non-impulsive) Harbor porpoise (1) 

Finneran and Schlundt 

2013 Tones (non-impulsive) Bottlenose dolphin (2) 

Popov et al. 2013 1⁄2 -octave band noise (non-impulsive) Beluga (2) 

Kastelein et al. 2013a Octave-band noise (non-impulsive) Harbor seal (1) 

Kastelein et al. 2013b Tone (non-impulsive) Harbor porpoise (1) 

Popov et al. 2014 1⁄2 octave band noise (non-impulsive) Beluga (2) 

Kastelein et al. 2014a 1-2 kHz sonar (non-impulsive) Harbor porpoise (1) 

Kastelein et al. 2014b 6.5 kHz tone (non-impulsive) Harbor porpoise (1) 

Kastelein et al. 2015a Impact pile driving (impulsive) Harbor porpoise (1) 

Kastelein et al. 2015b 6-7 kHz sweeps (non-impulsive) Harbor porpoise (1) 

Finneran et al. 2015 Single airgun producing multiple shots 

(impulsive)* Bottlenose dolphin (3) 

Popov et al. 2015 1⁄2 octave band noise (non-impulsive) Beluga (1) 

Kastelein et al. 2016 Impact pile driving (impulsive)* Harbor porpoise (2) 

Reichmuth et al. 2016 Single airgun (impulsive) * Ringed seals (2); Spotted seals (2) 

Popov et al. 2017 1⁄2 octave band noise (non-impulsive) Beluga (1) 

Kastelein et al. 2017b Simultaneous airguns producing 

multiple shots (impulsive) Harbor porpoise (1) 

Kastelein et al. 2017c 3.5-4.1 kHz sonar (non-impulsive) Harbor porpoise (2) 

^Note: Some individuals have been used in multiple studies. 

*No incidents of temporary threshold shift were recorded in study. 

o TTS onset derived on a per individual basis by combining available data 

to create single TTS growth curve (e.g., dB TTS/dB noise) by frequency 

as a function of SELcum. 

o TTS onset was defined as the SEL cum value from the growth curve 

interpolated at a value of TTS = 6 dB. Only datasets where data were 

available with a threshold shift (TS) above and below 6 dB were used to 

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define TTS onset (i.e., extrapolation was not performed on datasets not 

meeting this criterion). 

o Interpolation was used to estimate SEL cum necessary to induce 6 dB of 

TTS by hearing group (Appendix A, Figures A10-A13). Note: Appendix 

A, Figures A18-A20 illustrate available marine mammal TTS data in 

relation to the composite audiogram and auditory exposure function. 

o Finally, weighted thresholds for TTS onset were determined by the 

minimum value of the auditory exposure function (Equation 2), which is 

mathematically equivalent to K + C (Table 6). 

Table 6: TTS onset thresholds for non-impulsive sounds. 

Hearing Group K 

(dB) 

C 

(dB) 

Weighted TTS 

onset acoustic 

threshold 

(SEL cum) 

Low-frequency (LF) cetaceans 179 0.13 179 dB 

Mid-frequency (MF) cetaceans 177 1.20 178 dB 

High-frequency (HF) cetaceans 152 1.36 153 dB 

Phocid pinnipeds (underwater) 180 0.75 181 dB 

Otariid pinnipeds (underwater) 198 0.64 199 dB 

• Impulsive sounds: 

o Available TTS data for impulsive sources were weighted based on 

auditory weighting functions for the appropriate hearing group (MF and 

HF cetaceans only from two studies: Finneran et al. 2002; Lucke et al. 

2009). 

o For hearing groups, where impulsive TTS onset data did not exist (LF 

cetaceans and PW and OW pinnipeds), Finneran (2015) derived 

impulsive TTS onset thresholds using the relationship between nonimpulsive TTS onset thresholds and impulsive TTS onset thresholds for 

MF and HF cetaceans (i.e., similar to what was presented in Southall et 

al. 2007). Using the mean/median of these data resulted in an 11 dB 

relationship, which was used as a surrogate for the other hearing groups 

(i.e., non-impulsive TTS threshold was 11 dB higher than impulsive TTS 

threshold). 

o A similar approach was investigated for the PK threshold, resulting in a 

45 dB relationship, which was considered unrealistic (approaching 

cavitation level of water; Southall et al. 2007). Upon further 

consideration, the auditory system’s dynamic range was determined a 

more appropriate methodology for estimating PK sound pressure 

thresholds.34 

The dynamic range methodology assumes that the PK TTS onset 

acoustic threshold for MF and HF cetaceans defines the upper end of 

34 Dynamic range is used in human noise standards to define the PK acoustic threshold for impulsive sounds (e.g., 140 

dB from OSHA 29 CFR 1910.95). For the purposes of this Technical Guidance, the intent is to relate the threshold of 

audibility and TTS onset level, not the threshold of pain, as dynamic range is typically defined (Yost 2007). 

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those hearing groups’ dynamic range (i.e., PK threshold: 224 dB for MF 

cetaceans and PK threshold: 196 dB for HF cetaceans), with the 

threshold of audibility derived from the frequency of best hearing (ƒ0) from 

the composite audiogram (i.e., 54 dB for MF cetaceans and 48 dB for HF 

cetaceans) defining the lower end of the groups’ dynamic range. 

This results in a dynamic range of 170 dB for MF cetaceans and 148 dB 

for HF cetaceans. The median/mean dynamic range from these two 

hearing groups (i.e., 159 dB) is used as the surrogate dynamic range for 

LF cetaceans (best hearing at ƒ0= 54 dB; Resulting in a PK TTS 

threshold of 213 dB); PW pinnipeds (best hearing at ƒ0=53 dB; Resulting 

in a PK TTS threshold of 212 dB); and OW pinnipeds (best hearing at ƒ0 

=67 dB; Resulting in a PK TTS threshold of 226 dB). 

5. Extrapolation for PTS onset threshold (in both PK and SEL metrics) based on data from 

humans and terrestrial mammals, with the assumption that the mechanisms associated 

with noise-induced TS in marine mammals is similar, if not identical, to that recorded in 

terrestrial mammals. 

• Non-impulsive sounds: 

o PTS onset thresholds were estimated using TTS growth rates based on 

those marine mammal studies where 20 dB or more of a TS was 

induced. This was done to estimate more accurately PTS onset, since 

using growth rates based on smaller TSs are often shallower than 

compared to those inducing greater TSs (See Appendix A, Figures A10-

A13). 

o PTS onset was derived using the same methodology as TTS onset, with 

PTS onset defined as the SELcum value from the fitted curve at a TTS of 

40 dB. 

o Offset between TTS and PTS onset thresholds were examined and 

ranged from 13 to 37 dB (mean/median: 25/25 dB for cetacean data). 

Thus, based on these data, a conservative 20 dB offset was chosen to 

estimate PTS onset thresholds from TTS onset thresholds for nonimpulsive sources (i.e., 20 dB was added to K to determine PTS onset, 

assuming the shape of the PTS auditory exposure function is identical to 

the TTS auditory exposure function for that hearing group). 

• Impulsive sounds: Based on limited available marine mammal impulsive data, the 

relationships previously derived in Southall et al. (2007), which relied upon 

terrestrial mammal growth rates (Henderson and Hamernik 1982; Henderson and 

Hamernik 1986; Price and Wansack 1989; Levine et al. 1998; Henderson et al. 

2008), was used to predict PTS onset: 

o Resulting in an approximate 15 dB difference between TTS and PTS 

onset thresholds in the SELcum metric. 

o Southall et al. (2007) recommended a 6 dB of TTS/dB of noise growth 

rate for PK thresholds. This recommendation was based on several 

factors, including ensuring that the PK acoustic threshold did not 

unrealistically exceed the cavitation threshold of water. Resulting in an 

approximate 6 dB difference between TTS and PTS onset thresholds in 

the PK metric. 

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Ill. UPDATING OF ACOUSTIC TECHNICAL GUIDANCE AND 

THRESHOLDS 

III. UPDATING OF ACOUSTIC TECHNICAL GUIDANCE AND 

THRESHOLDS 

Research on the effects of anthropogenic sound on marine mammals has increased dramatically 

in the last decade and will likely continue to increase in the future. As such, the Technical 

Guidance will be reviewed periodically and updated as appropriate to reflect the compilation, 

interpretation, and synthesis of the scientific literature. 

NMFS’ initial approach for updating current thresholds for protected marine species consisted of 

providing thresholds for underwater PTS onset for marine mammals via this document. As more 

data become available, thresholds may be established for additional protected marine species, 

such as sea turtles and marine fishes. As with this document, public review and outside peer 

review will be integral to the process. 

3.1 PROCEDURE AND TIMELINE FOR UPDATING THE TECHNICAL GUIDANCE 

NMFS will continue to monitor and evaluate new data as they become available and periodically 

convene staff from our various offices, regions, and science centers to update the Technical 

Guidance as appropriate (anticipating updates to occur on a three to five year cycle). In addition 

to evaluating new, relevant scientific studies, NMFS will also periodically re-examine basic 

concepts and definitions (e.g., hearing groups, PTS, TTS, auditory weighting functions), 

appropriate metrics, temporal and spatial considerations, and other relevant topics. Updates will 

be posted at Link to Technical Guidance web page. 

Since the methodology for deriving composite audiograms and associated marine mammal 

auditory weighting functions, as well as TTS thresholds is data driven, any new information that 

becomes available has the potential to cause some amount of change for that specific hearing 

group but also other hearing groups, if they rely on surrogate data. It may not be feasible to make 

changes every time a new data point becomes available. Instead, NMFS will periodically examine 

new data to date and consider the impacts of those studies on the Technical Guidance to 

determine what revisions/updates may be appropriate. At the same time, there may be special 

circumstances that merit evaluation of data on a more accelerated timeline (e.g., LF cetacean 

data that could result in significant changes to the current Technical Guidance). 

3.1.1 Consideration for New Scientific Publication 

During the Technical Guidance’s recent review under EO 13795 (i.e., public comment period; 82 

FR 24950; May 31, 2017), several commenters provided information on newly published scientific 

literature (i.e., 12 publications) for consideration and inclusion in a revised version of the 

Technical Guidance. NMFS reviewed all literature suggested by commenters. The majority of 

suggested papers were either already considered within the 2016 Technical Guidance or were 

not applicable for incorporation (i.e., many newly available marine mammal audiograms were 

collected via auditory evoked potential (AEP), which cannot be directly incorporated in the current 

methodology). Of the studies suggested, only the Branstetter et al. 2017 publication, which 

provides behavioral audiograms for six individual killer whales, was appropriate for consideration 

within the Technical Guidance. Since the close of the public comment period, a paper providing 

two new additional behavioral audiograms for harbor porpoise (Kastelein et al. 2017a), a paper 

examining TTS in harbor porpoise exposed to multiple airgun shots (Kastelein et al. 2017b), and 

a paper examining TTS in harbor porpoise exposed to mid-frequency sonar playbacks (Kastelein 

et al. 2017c) were published. These three additional papers are also appropriate for consideration 

within the Technical Guidance. 

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The Technical Guidance’s methodology (Appendix A) is data driven, meaning every new 

publication has the potential to result in some change to either the thresholds and/or auditory 

weighting functions for a single or multiple hearing groups (i.e., those groups whose data are 

used as surrogates for other hearing groups), and with every change comes a necessary 

transition period to allow action proponents to adapt to these changes. Thus, there are scientific, 

as well as practical implications that need consideration before making even a minor a change to 

the Technical Guidance. One commenter said it best by “The value of a revision of any sciencebased advice hinges on the balance between the availability of new scientific evidence and the 

need for a period of stability. The greater the complexity of the advice the greater the need for a 

long stable period to assimilate that advice before it is updated35.” The Marine Mammal 

Commission (MMC) and U.S. Navy offered similar cautions about the practicality of revising the 

Technical Guidance every time a new study becomes available. 

Upon consideration of these most recent studies during our review under EO 13795 and 

considering recommendations from other Federal agencies and public commenters, NMFS 

determined it is not practical from an implementation standpoint to add these studies at this time. 

NMFS will include these studies in the next revision of this document (i.e., Version 3.0) and 

adhere to our stipulated 3 to 5 year update schedule, where we can evaluate all new relevant 

publications and make changes in a more predictable manner. 

3.1.1.1 Preliminary Analysis of Branstetter et al. 2017, Kastelein et al. 2017a, Kastelein et 

al. 2017b, and Kastelein et al. 2017c 

NMFS conducted a preliminary analysis examining the new data provided in Branstetter et al. 

2017, Kastelein et al. 2017a, Kastelein et al. 2017b, and Kastelein et al. 2017c in the context of 

the Technical Guidance’s current MF and HF cetacean composite audiograms (Branstetter et al. 

2017; Kastelein et al. 2017a) and HF cetacean TTS/PTS onset thresholds (Kastelein et al. 2017b; 

Kastelein et al. 2017c). 

Branstetter et al. 2017 

The Technical Guidance’s composite audiogram for MF cetaceans does incorporate behavioral 

audiograms from two individual killer whales (i.e., Vigga and Yakka from Szymanski et al. 1999). 

In Figure 3 from the Branstetter et al. 2017 publication, they plot Vigga and Yakka’s audiogram 

data as a comparison to the audiograms obtained to in their study. From this figure and 

corresponding threshold table (Table 1 in Branstetter et al. 2017), in the killer whale’s most 

sensitive hearing range, the data already included in the Technical Guidance align with 

Branstetter et al.’s new audiograms, and for most frequencies, Vigga and Yakka have lower 

thresholds. 

Kastelein et al. 2017a 

The Technical Guidance’s composite audiogram for HF cetaceans does incorporate behavioral 

audiograms for three harbor porpoises (i.e., PpSH047 and Jerry from Kastelein et al. 2010; ID 

No. 04 from Kastelein et al. 2015c). In Figure 1 from Kastelein et al. 2017a, they plot their 

previously published audiograms from these three individuals as a comparison to the two new 

individual audiograms obtained in this study. Kastelein et al. (2017) concluded from this most 

recent study “The basic audiograms of the young female and male harbor porpoises in the 

present study were similar to those of the three previously tested young male harbor porpoises 

(Fig 1).” 

35 Link to public comment made on Regulations.gov. 

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Kastelein et al. 2017b 

In this study, a harbor porpoise was exposed to either 10 or 20 consecutive shots from two 

airings simultaneously. A mean threshold shift of 4.4 dB occurred after exposure to a weighted 

cumulative level of 140.3 dB. The Technical Guidance’s TTS onset threshold (weighted SELcum) 

for HF cetaceans and impulsive sources is 140 dB, which is consistent with the results from this 

most recent study. This paper also concludes, “the initial results indicate that the frequencyweighting function proposed by NOAA (NMFS, 2016) provides a reasonably robust measure of 

low levels of TTS occurring over a range of spectra of impulsive sound sources.” 

Kastelein et al. 2017c 

This study exposed two harbor porpoises to mid-frequency sonar (3.5 to 4.1 kHz) and reported 

that to induce a 6 dB threshold shift in harbor porpoises an unweighted cumulative level between 

175 and 180 dB would be needed. If these data were weighted using the Technical Guidance’s 

auditory weighting function, the values would be ~157.7 and ~162.7 dB SELcum 36. The Technical 

Guidance’s TTS onset threshold (weighted SELcum) for HF cetaceans and non-impulsive sources 

is 153 dB, which is consistent with the results from this most recent study (i.e., the thresholds 

from Kastelein et al. 2017c are likely slightly higher than the Technical Guidance because it was 

an intermittent source allowing for a greater potential for recovery between pauses of the various 

signal components). 

Preliminary Conclusions 

Thus, from this preliminary analysis, NMFS concludes that the Branstetter el. 2017 and Kastelein 

et al. 2017a audiograms are consistent with data already included in the Technical Guidance for 

these two species (i.e., the data from these two recent studies align with previous data collected 

and incorporated within the current version of the Technical Guidance). Additionally, the HF 

cetacean TTS data presented in Kastelein et al. 2017b and Kastelein et al. 2017c are consistent 

with the HF cetacean thresholds presented in the Technical Guidance. 

36 NMFS contacted the authors of this paper to confirm weighted levels. 

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APPENDIX A: APPENDIX A: FINNERAN Fl NERA TECHNICAL REPORT TECHNICAL REPORT 

The entire Finneran Technical Report (Finneran 2016), regarding methodology for deriving 

auditory weighting functions and thresholds for marine mammal species under NMFS’ jurisdiction, 

is included for reference in Appendix A. Its contents have not been modified by NMFS, other than 

adding “A” before figures and tables to denote Appendix A and be consistent with the other 

appendices in the Technical Guidance. 

Notes: 

a. Literature cited in this section are included at the end of this Appendix (i.e., not all 

references found in this Appendix are included in the Literature Cited for the Technical 

Guidance). Additionally, terminology, symbols, and abbreviations used in this appendix 

may not match those used elsewhere in the Technical Guidance. 

b. The derivation of the Technical Guidance's thresholds and auditory weighting functions 

are from two primary sets of data: 1) Audiogram data (used to derive composite 

audiograms for each hearing group) and 2) TTS onset data (used to derive auditory 

weighting functions and TTS onset thresholds by hearing group). For each of these two 

primary data sets, either data points were derived directly from the published study or if 

data were originally reported in terms of sound pressure level and duration, they 

converted to sound exposure level via standard relationships. 

c. Since the final Finneran Technical Report was received, an additional TTS study became 

available (Kastelein et al. 2016). Information regarding this study is added as a footnote 

by NMFS. 

d. After the Technical Guidance’s finalization, an additional two TTS studies became 

available (Kastelein et al. 2017b; Kastelein et al. 2017c). In the Kastelein et al. 2017b 

study, a harbor porpoise was exposed to either 10 or 20 consecutive shots from two 

airguns simultaneously. Kastelein et al. 2017c exposed two harbor porpoises to midfrequency sonar (3.5 to 4.1 kHz). The HF cetacean TTS data (i.e., TTS onset levels) 

presented in these two most recent studies are consistent with the HF cetacean 

thresholds presented in the Technical Guidance. 

e. Additionally, two behavioral audiogram publications became available after the Technical 

Guidance’s finalization in 2016 (Branstetter et al. 2017; Kastelein et al. 2017a). However, 

upon consideration of these two studies during EO 13795 review of the Technical 

Guidance, including recommendations from other Federal agencies (e.g. Navy), NMFS 

determined it is not practical from an implementation standpoint to add these studies at 

this time (i.e., Version 2.0). NMFS will include these studies in the next revision of this 

document (i.e., Version 3.0). From this preliminary analysis, NMFS concludes that the 

Branstetter el. 2017 and Kastelein et al. 2017a audiograms are consistent with data 

already included in the Technical Guidance for these two species (i.e., the data from 

these two recent studies align with previous data collected and incorporated within the 

current version of the Technical Guidance). 

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TECHNICAL REPORT 3026 

December 2016 

Auditory Weighting Functions and 

TTS/PTS Exposure Functions for Marine 

Mammals Exposed to Underwater Noise 

J. J. Finneran 

Approved for public release. 

SSC Pacific 

San Diego, CA 92152-5001 

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. V .. Fllynn CAPT, US I 

Oomrnanding Officer 

SSC SAN DIEGO 

San Diego, California 92152~5001 

C . .A. Keeney 

IE:xeoutive Direct,or 

ADMINISTRATIVEINFORMATION 

This work described in this report was prepared for Commander, U.S. Fleet Forces 

Command, Norfolk, VA, by the Marine Mammal Scientific & Vet Support Branch (Code 

71510) of the Biosciences Division (Code 71500), Space and Naval Warfare Systems 

Center Pacific (SSC Pacific), San Diego, CA. 

Released under authority of 

M. J. Xitco, Head 

Biosciences Division 

This is a work of the United States Government and therefore is not copyrighted. This 

work may be copied and disseminated without restriction. Many SSC San Diego public 

release documents are available in electronic format at SPAWAR publication web site. 

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EXECUTIVE SUMMARY EXECUTIVE SU MARY 

The US Navy’s Tactical Training Theater Assessment and Planning (TAP) Program 

addresses environmental challenges that affect Navy training ranges and operating areas. 

As part of the TAP process, acoustic effects analyses are conducted to estimate the 

potential effects of Navy activities that introduce high-levels of sound or explosive 

energy into the marine environment. Acoustic effects analyses begin with mathematical 

modeling to predict the sound transmission patterns from Navy sources. These data are 

then coupled with marine species distribution and abundance data to determine the sound 

levels likely to be received by various marine species. Finally, criteria and thresholds are 

applied to estimate the specific effects that animals exposed to Navy-generated sound 

may experience. 

This document describes the rationale and steps used to define proposed numeric 

thresholds for predicting auditory effects on marine mammals exposed to active sonars, 

other (non-impulsive) active acoustic sources, explosives, pile driving, and air guns for 

Phase 3 of the TAP Program. Since the derivation of TAP Phase 2 acoustic criteria and 

thresholds, important new data have been obtained related to the effects of noise on 

marine mammal hearing. Therefore, for Phase 3, new criteria and thresholds for the onset 

of temporary and permanent hearing loss have been developed, following a consistent 

approach for all species of interest and utilizing all relevant, available data. The effects of 

noise frequency on hearing loss are incorporated by using auditory weighting functions to 

emphasize noise at frequencies where a species is more sensitive to noise and deemphasize noise at frequencies where susceptibility is low. 

Marine mammals were divided into six groups for analysis: low-frequency cetaceans 

(group LF: mysticetes), mid-frequency cetaceans (group MF: delphinids, beaked whales, 

sperm whales), high-frequency cetaceans (group HF: porpoises, river dolphins), sirenians 

(group SI: manatees), phocids in water (group PW: true seals), and otariids and other 

non-phocid marine carnivores in water (group OW: sea lions, walruses, otters, polar 

bears). 

For each group, a frequency-dependent weighting function and numeric thresholds for the 

onset of temporary threshold shift (TTS) and permanent threshold shift (PTS) were 

derived from available data describing hearing abilities of and effects of noise on marine 

mammals. The resulting weighting function amplitudes are illustrated in Figure AE-1; 

Table AE-1 summarizes the parameters necessary to calculate the weighting function 

amplitudes. For Navy Phase 3 analyses, the onset of TTS is defined as a TTS of 6 dB 

measured approximately 4 min after exposure. PTS is assumed to occur from exposures 

resulting in 40 dB or more of TTS measured approximately 4 min after exposure. 

Exposures just sufficient to cause TTS or PTS are denoted as “TTS onset” or “PTS 

onset” exposures. 

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-ca LF , "O , 

- , Q) -20 , 

"O PW :J 

~ 

0.. -40 E , ow 

C1l 

-60 

0.01 0.1 10 100 0.1 10 100 

frequency (kHz) 

W(J) ~ C+ IOk,g l (/if,)" l ID [1+(11 .1;)'J[1+(f/ .1SJ 

Figure AE-1. Navy Phase 3 weighting functions for all species groups. Parameters required to 

generate the functions are provided in Table AE-1. 

Table AE-1. Summary of weighting function parameters and TTS/PTS thresholds. SEL 

thresholds are in dB re 1 μPa2

s and peak SPL thresholds are in dB re 1 μPa.

Non-impulsive Impulse 

TTS 

threshold 

PTS 

threshold 

TTS 

threshold 

PTS 

threshold 

Group a b f1 

(kHz) 

f2 

(kHz) 

C 

(dB) 

SEL 

(weighted) 

SEL 

(weighted) 

SEL 

(weighted) 

peak SPL 

(unweighted) 

SEL 

(weighted) 

peak SPL 

(unweighted) 

LF 1 2 0.20 19 0.13 179 199 168 213 183 219 

MF 1.6 2 8.8 110 1.20 178 198 170 224 185 230 

HF 1.8 2 12 140 1.36 153 173 140 196 155 202 

SI 1.8 2 4.3 25 2.62 186 206 175 220 190 226 

OW 2 2 0.94 25 0.64 199 219 188 226 203 232 

PW 1 2 1.9 30 0.75 181 201 170 212 185 218 

To compare the Phase 3 weighting functions and TTS/PTS thresholds to those used in 

TAP Phase 2 analyses, both the weighting function shape and the weighted threshold 

values must be taken into account; the weighted thresholds by themselves only indicate 

the TTS/PTS threshold at the most susceptible frequency (based on the relevant 

weighting function). In contrast, the TTS/PTS exposure functions incorporate both the 

shape of the weighting function and the weighted threshold value, they provide the best 

means of comparing the frequency-dependent TTS/PTS thresholds for Phase 2 and 3. 

Figures AE-2 and AE-3 compare the TTS/PTS exposure functions for non-impulsive 

sounds (e.g., sonars) and impulsive sounds (e.g., explosions), respectively, used in TAP 

Phase 2 and Phase 3. 

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·•, .. '.',,_ ... .... ......... . 

200 ' ~-"' 

VJ 

180 

"' ctl 

'3_ 160 

LF 

Q) 

L. 140 co 0.01 0.1 10 ~ 

_J V,/ LU 

Cl) 220 

200 

-- ------- -- 180 SI 

0.1 10 100 

MF 

10 100 

\ 

\ 

' ' 

ow 

0.1 10 100 

frequency (kHz) 

10 100 

,

\ 

~/2 . - _.· 

' \ 

PW 

0.1 10 100 

- - Phase 2 - TTS faposure function 

· · · · · · Phase 2 - PTS Exposure function 

- - Phase 3 - TTS faposure function 

- Phase 3 - PTS Exposure function 

Figure AE-2. TTS and PTS exposure functions for sonars and other (non-impulsive) active 

acoustic sources. Heavy solid lines — Navy Phase 3 TTS exposure functions (Table 

AE-1). Thin solid lines — Navy Phase 3 PTS exposure functions (Table AE-1). 

Dashed lines — Navy Phase 2 TTS exposure functions. Short dashed lines — Navy 

Phase 2 PTS exposure functions. 

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:·"'~ ............. / /, 

' ' -~ ·-.... y ,1, 180 - ' 

.... -- ... 

en" 160 N 

ro 

a.. 

:i. 140 LF .... 

Q) 

L.. 0.01 0.1 10 

en 220 ~ 

....J 

llJ 

(f) 

200 

180 ' 

SI 

160 

0.1 10 100 

10 100 

ow 

0.1 1 10 100 

frequency (kHz) 

10 100 

0.1 10 100 

- - Phase 2 - TTS E,posure function 

· · · · · · Phase 2 - PTS Exposure function 

- Phase 3 - TTS E,posure function 

- Phase 3 - PTS Exposure function 

Figure AE-3. TTS and PTS exposure functions for explosives, impact pile driving, air guns, and 

other impulsive sources. Heavy solid lines — Navy Phase 3 TTS exposure functions 

(Table AE-1). Thin solid lines — Navy Phase 3 PTS exposure functions (Table AE1). Dashed lines — Navy Phase 2 TTS exposure functions. Short dashed lines — 

Navy Phase 2 PTS exposure functions. 

The most significant differences between the Phase 2 and Phase 3 functions include: (1) 

Thresholds at low frequencies are generally higher for Phase 3 compared to Phase 2. This 

is because the Phase 2 weighting functions utilized the “M-weighting” functions at lower 

frequencies, where no TTS existed at that time. Since derivation of the Phase 2 weighting 

functions, additional data have been collected to support the use of new functions more 

similar to human auditory weighting functions. (2) Impulsive TTS/PTS thresholds near 

the region of best hearing sensitivity are lower for Phase 3 compared to Phase 2. 

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I. I. INTRODUCTION INTRODUCTION 

1.1 OVERVIEW 

The US Navy’s Tactical Training Theater Assessment and Planning (TAP) Program 

addresses environmental challenges that affect Navy training ranges and operating areas. 

As part of the TAP process, acoustic effects analyses are conducted to estimate the 

potential effects of Navy training and testing activities that introduce high-levels of sound 

or explosive energy into the marine environment. Acoustic effects analyses begin with 

mathematical modeling to predict the sound transmission patterns from Navy sources. 

These data are then coupled with marine species distribution and abundance data to 

determine sound levels likely to be received by various marine species. Finally, criteria 

and thresholds are applied to estimate the specific effects that animals exposed to Navygenerated sound may experience. 

This document describes the rationale and steps used to define proposed numeric 

thresholds for predicting auditory effects on marine mammals exposed to underwater 

sound from active sonars, other (non-impulsive) active acoustic sources, explosives, pile 

driving, and air guns for Phase 3 of the TAP Program. The weighted threshold values and 

auditory weighting function shapes are summarized in Section 12. 

1.2 IMPULSE VS. NON-IMPULSIVE NOISE 

When analyzing the auditory effects of noise exposure, it is often helpful to broadly 

categorize noise as either impulse noise — noise with high peak sound pressure, short 

duration, fast rise-time, and broad frequency content — or non-impulsive (i.e., steadystate) noise. When considering auditory effects, sonars, other coherent active sources, and 

vibratory pile driving are considered to be non-impulsive sources, while explosives, 

impact pile driving, and air guns are treated as impulsive sources. Note that the terms 

non-impulsive or steady-state do not necessarily imply long duration signals, only that 

the acoustic signal has sufficient duration to overcome starting transients and reach a 

steady-state condition. For harmonic signals, sounds with duration greater than 

approximately 5 to 10 cycles are generally considered to be steady-state. 

1.3 NOISE-INDUCED THRESHOLD SHIFTS 

Exposure to sound with sufficient duration and sound pressure level (SPL) may result in 

an elevated hearing threshold (i.e., a loss of hearing sensitivity), called a noise-induced 

threshold shift (NITS). If the hearing threshold eventually returns to normal, the NITS is 

called a temporary threshold shift (TTS); otherwise, if thresholds remain elevated after 

some extended period of time, the remaining NITS is called a permanent threshold shift 

(PTS). TTS and PTS data have been used to guide the development of safe exposure 

guidelines for people working in noisy environments. Similarly, TTS and PTS criteria 

and thresholds form the cornerstone of Navy analyses to predict auditory effects in 

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marine mammals incidentally exposed to intense underwater sound during naval 

activities. 

1.4 AUDITORY WEIGHTING FUNCTIONS 

Animals are not equally sensitive to noise at all frequencies. To capture the frequencydependent nature of the effects of noise, auditory weighting functions are used. Auditory 

weighting functions are mathematical functions used to emphasize frequencies where 

animals are more susceptible to noise exposure and de-emphasize frequencies where 

animals are less susceptible. The functions may be thought of as frequency-dependent 

filters that are applied to a noise exposure before a single, weighted SPL or sound 

exposure level (SEL) is calculated. The filter shapes are normally “band-pass” in nature; 

i.e., the function amplitude resembles an inverted “U” when plotted versus frequency. 

The weighting function amplitude is approximately flat within a limited range of 

frequencies, called the “pass-band,” and declines at frequencies below and above the 

pass-band. 

Auditory weighting functions for humans were based on equal loudness contours — 

curves that show the combinations of SPL and frequency that result in a sensation of 

equal loudness in a human listener. Equal loudness contours are in turn created from data 

collected during loudness comparison tasks. Analogous tasks are difficult to perform with 

non-verbal animals; as a result, equal loudness contours are available for only a single 

marine mammal (a dolphin) across a limited range of frequencies (2.5 to 113 kHz) 

(Finneran and Schlundt, 2011). In lieu of performing loudness comparison tests, reaction 

times to tones can be measured, under the assumption that reaction time is correlated with 

subjective loudness (Stebbins, 1966; Pfingst et al., 1975). From the reaction time vs. SPL 

data, curves of equal response latency can be created and used as proxies for equal 

loudness contours. 

Just as human damage risk criteria use auditory weighting functions to capture the 

frequency-dependent aspects of noise, US Navy acoustic impact analyses use weighting 

functions to capture the frequency-dependency of TTS and PTS in marine mammals. 

1.5 TAP PHASE 3 WEIGHTING FUNCTIONS AND TTS/PTS THRESHOLDS 

Navy weighting functions for TAP Phase 2 (Finneran and Jenkins, 2012) were based on 

the “M-weighting” curves defined by Southall et al. (2007), with additional highfrequency emphasis for cetaceans based on equal loudness contours for a bottlenose 

dolphin (Finneran and Schlundt, 2011). Phase 2 TTS/PTS thresholds also relied heavily 

on the recommendations of Southall et al. (2007), with modifications based on 

preliminary data for the effects of exposure frequency on dolphin TTS (Finneran, 2010; 

Finneran and Schlundt, 2010) and limited TTS data for harbor porpoises (Lucke et al., 

2009; Kastelein et al., 2011). 

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Since the derivation of TAP Phase 2 acoustic criteria and thresholds, new data have been 

obtained regarding marine mammal hearing (e.g., Dow Piniak et al., 2012; Martin et al., 

2012; Ghoul and Reichmuth, 2014; Sills et al., 2014; Sills et al., 2015), marine mammal 

equal latency contours (e.g., Reichmuth, 2013; Wensveen et al., 2014; Mulsow et al., 

2015), and the effects of noise on marine mammal hearing (e.g., Kastelein et al., 2012b; 

Kastelein et al., 2012a; Finneran and Schlundt, 2013; Kastelein et al., 2013a; Kastelein et 

al., 2013b; Popov et al., 2013; Kastelein et al., 2014b; Kastelein et al., 2014a; Popov et 

al., 2014; Finneran et al., 2015; Kastelein et al., 2015c; Kastelein et al., 2015b; Popov et 

al., 2015). As a result, new weighting functions and TTS/PTS thresholds have been 

developed for Phase 3. The new criteria and thresholds are based on all relevant data and 

feature a consistent approach for all species of interest. 

Marine mammals were divided into six groups for analysis. For each group, a frequencydependent weighting function and numeric thresholds for the onset of TTS and PTS were 

derived from available data describing hearing abilities and effects of noise on marine 

mammals. Measured or predicted auditory threshold data, as well as measured equal 

latency contours, were used to influence the weighting function shape for each group. For 

species groups for which TTS data are available, the weighting function parameters were 

adjusted to provide the best fit to the experimental data. The same methods were then 

applied to other groups for which TTS data did not exist. 

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I. WEIGHTING FUNCTIONS AND EXPOSURE FU CTIO S 

W(f) = C + IO log 1 ! (f / J.)2a I 10 [1+(! / 1irJ[1+(f ! 1irr 

II. WEIGHTING FUNCTIONS AND EXPOSURE FUNCTIONS 

The shapes of the Phase 3 auditory weighting functions are based on a generic band-pass 

filter described by 

, (A1) 

where W( f ) is the weighting function amplitude (in dB) at the frequency f (in kHz). The 

shape of the filter is defined by the parameters C, f1, f2, a, and b (Figs. A1 and A2, left 

panels): 

C weighting function gain (dB). The value of C defines the vertical position of 

the curve. Changing the value of C shifts the function up/down. The value of 

C is often chosen to set the maximum amplitude of W to 0 dB (i.e., the value 

of C does not necessarily equal the peak amplitude of the curve). 

f1 low-frequency cutoff (kHz). The value of f1 defines the lower limit of the filter 

pass-band; i.e., the lower frequency at which the weighting function amplitude 

begins to decline or “roll-off” from the flat, central portion of the curve. The 

specific amplitude at f1 depends on the value of a. Decreasing f1 will enlarge 

the pass-band of the function (the flat, central portion of the curve). 

f2 high-frequency cutoff (kHz). The value of f2 defines the upper limit of the 

filter pass-band; i.e., the upper frequency at which the weighting function 

amplitude begins to roll-off from the flat, central portion of the curve. The 

amplitude at f2 depends on the value of b. Increasing f2 will enlarge the passband of the function. 

a low-frequency exponent (dimensionless). The value of a defines the rate at 

which the weighting function amplitude declines with frequency at the lower 

frequencies. As frequency decreases, the change in weighting function 

amplitude becomes linear with the logarithm of frequency, with a slope of 20a 

dB/decade. Larger values of a result in lower amplitudes at f1 and steeper 

rolloffs at frequencies below f1. 

b high-frequency exponent (dimensionless). The value of b defines the rate at 

which the weighting function amplitude declines with frequency at the upper 

frequencies. As frequency increases, the change in weighting function 

amplitude becomes linear with the logarithm of frequency, with a slope of -

20b dB/decade. Larger values of b result in lower amplitudes at f2 and steeper 

rolloffs at frequencies above f2. 

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(1) - weighting function Eq. (2) - exposure function 

cf 

20b 

-20b 

K 

frequency 

If a = 2 and b = 2, Eq. (A1) is equivalent to the functions used to define Navy Phase 2 

Type I and EQL weighting functions, M-weighting functions, and the human Cweighting function (American National Standards Institute (ANSI), 2001; Southall et al., 

2007; Finneran and Jenkins, 2012). The change from fixed to variable exponents for 

Phase 3 was done to allow the low- and high-frequency rolloffs to match available 

experimental data. During implementation, the weighting function defined by Eq. (A1) is 

used in conjunction with a weighted threshold for TTS or PTS expressed in units of SEL. 

Figure A1. Examples of (left) weighting function amplitude described by Eq. (A1) and (right) 

exposure function described by Eq. (A2). The parameters f1 and f2 specify the extent 

of the filter pass-band, while the exponents a and b control the rate of amplitude 

change below f1 and above f2, respectively. As the frequency decreases below f1 or 

above f2, the amplitude approaches linear-log behavior with a slope magnitude of 

20a or 20b dB/decade, respectively. The constants C and K determine the vertical 

positions of the curves. 

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(1) - weighting function Eq. (2) - exposure function 

frequency 

Figure A2. Influence of parameter values on the resulting shapes of the weighting functions 

(left) and exposure functions (right). The arrows indicate the direction of change 

when the designated parameter is increased. 

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E(j) = K -10 lo~ l ( f I J°J2a ) 0 [1+(111.rJ[1+(1 / 1irJ 

0 

i -20 

::l 

~ 

a. 

~ -40 

weighting function -Cl) 

N 

ro 220 a.. 

:::t 

..... 

~ 

co 200 

:3, 

..... 

Q) 

Cl) 

§ 180 

CJ) 

-60 L.L..a. ...................................................................... __._ ........... wL......o ~ 

0.01 0.1 10 100 0.01 

frequency (kHz) 

exposure function 

0.1 10 100 

For developing and visualizing the effects of the various weighting functions, it is helpful 

to invert Eq. (A1), yielding 

, (A2) 

where E( f ) is the acoustic exposure as a function of frequency f, the parameters f1, f2, a, 

and b are identical to those in Eq. (A1), and K is a constant. The function described by 

Eq. (A2) has a “U-shape” similar to an audiogram or equal loudness/latency contour 

(Figs. A1 and A2, right panels). If K is adjusted to set the minimum value of E( f ) to 

match the weighted threshold for the onset of TTS or PTS, Eq. (A2) reveals the manner 

in which the exposure necessary to cause TTS or PTS varies with frequency. Equation 

(A2) therefore allows the frequency-weighted threshold values to be directly compared to 

TTS data. The function defined by Eq. (A2) is referred to as an exposure function, since 

the curve defines the acoustic exposure that equates to TTS or PTS as a function of 

frequency. To illustrate the relationship between weighting and exposure functions, Fig. 

A3 shows the Navy Phase 2 weighting function [Eq. (A1), left panel] and TTS exposure 

function [Eq. (A2), right panel] for mid-frequency cetaceans exposed to sonars. 

Figure A3. (left panel) Navy Phase 2 weighting function for the mid-frequency cetacean group. 

This function was used in conjunction with a weighted TTS threshold of 178 dB re 1 

μPa2

s. For narrowband signals, the effective, weighted TTS threshold at a 

particular frequency is calculated by adding the weighting function amplitude at 

that frequency to the weighted TTS threshold (178 dB re 1 μPa2

s). To visualize the 

frequency-dependent nature of the TTS threshold, the weighting function is 

inverted and the minimum value set equal to the weighted TTS threshold. This is 

illustrated in the right panel, which shows the SEL required for TTS onset as a 

function of frequency. The advantage of this representation is that it may be directly 

compared to TTS onset data at different exposure frequencies. 

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X(f) = IO log l (f I J;)2a ) 

io [I+(// 1;)2J[ I+(// _t;)2r 

W(f) = C + X(f) 

E(f)=K-X(f) 

W(f )=O=C+X(f) p p 

T =C+K wgt 

The relationships between Eqs. (A1) and (A2) may be highlighted by defining the 

function X( f ) as 

. (A3) 

The peak value of X( f ) depends on the specific values of f1, f2, a, and b and will not 

necessarily equal zero. Substituting Eq. (A3) into Eqs. (A1) and (A2) results in 

(A4) 

and 

, (A5) 

respectively. The maximum of the weighting function and the minimum of the exposure 

function occur at the same frequency, denoted fp. The constant C is defined so the 

weighting function maximum value is 0 dB; i.e., W( fp ) = 0, so 

. (A6) 

The constant K is defined so that the minimum of the exposure function [i.e., the value of 

E( f ) when f = fp ] equals the weighted TTS or PTS threshold, Twgt, so 

. (A7) 

Adding Eqs. (A6) and (A7) results in 

. (A8) 

The constants C, K, and the weighted threshold are therefore not independent and any one 

of these parameters can be calculated if the other two are known. 

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III. METHODOLOGY TO DERI Ill. METHODOLOGY TO DERIVE VE FUNCTION PARAMETE FUNCTION PARA ETERS RS 

Weighting and exposure functions are defined by selecting appropriate values for the 

parameters C, K, f1, f2, a, and b in Eqs. (A1) and (A2). Ideally, these parameters would be 

based on experimental data describing the manner in which the onset of TTS or PTS 

varied as a function of exposure frequency. In other words, a weighting function for TTS 

should ideally be based on TTS data obtained using a range of exposure frequencies, 

species, and individual subjects within each species group. However, at present, there are 

only limited data for the frequency-dependency of TTS in marine mammals. Therefore, 

weighting and exposure function derivations relied upon auditory threshold 

measurements (audiograms), equal latency contours, anatomical data, and TTS data when 

available. 

Although the weighting function shapes are heavily influenced by the shape of the 

auditory sensitivity curve, the two are not identical. Essentially, the auditory sensitivity 

curves are adjusted to match the existing TTS data in the frequency region near best 

sensitivity (step 4 below). This results in “compression” of the auditory sensitivity curve 

in the region near best sensitivity to allow the weighting function shape to match the TTS 

data, which show less change with frequency compared to hearing sensitivity curves in 

the frequency region near best sensitivity. 

Weighting and exposure function derivation consisted of the following steps: 

1. Marine mammals were divided into six groups based on auditory, 

ecological, and phylogenetic relationships among species. 

2. For each species group, a representative, composite audiogram (a graph 

of hearing threshold vs. frequency) was estimated. 

3. The exponent a was defined using the smaller of the low-frequency 

slope from the composite audiogram or the low-frequency slope of equal 

latency contours. The exponent b was set equal to two. 

4. The frequencies f1 and f2 were defined as the frequencies at which the 

composite threshold values are ∆T-dB above the lowest threshold value. 

The value of ∆T was chosen to minimize the mean-squared error between 

Eq. (2) and the non-impulsive TTS data for the mid- and high-frequency 

cetacean groups. 

5. For species groups for which TTS onset data exist, K was adjusted to 

minimize the squared error between Eq. (A2) and the steady-state (nonimpulsive) TTS onset data. For other species, K was defined to provide the 

best estimate for TTS onset at a representative frequency. The minimum 

value of the TTS exposure function (which is not necessarily equal to K) 

was then defined as the weighted TTS threshold. 

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6. The constant C was defined to set the peak amplitude of the function 

defined by Eq. (A1) to zero. This is mathematically equivalent to setting C 

equal to the difference between the weighted threshold and K [see Eq. 

(A8)]. 

7. The weighted threshold for PTS was derived for each group by adding a 

constant value (20 dB) to the weighted TTS thresholds. The constant was 

based on estimates of the difference in exposure levels between TTS onset 

and PTS onset (i.e., 40 dB of TTS) obtained from the marine mammal 

TTS growth curves. 

8. For the mid- and high-frequency cetaceans, weighted TTS and PTS 

thresholds for explosives and other impulsive sources were obtained from 

the available impulse TTS data. For other groups, the weighted SEL 

thresholds were estimated using the relationship between the steady-state 

TTS weighted threshold and the impulse TTS weighted threshold for the 

mid- and high-frequency cetaceans. Peak SPL thresholds were estimated 

using the relationship between hearing thresholds and the impulse TTS 

peak SPL thresholds for the mid- and high-frequency cetaceans. 

The remainder of this document addresses these steps in detail. 

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IV. IV. MARINE MAMMAL MARINE AM AL SPECIES GROUPS SPECIES GROUPS 

Marine mammals were divided into six groups (Table A1), with the same weighting 

function and TTS/PTS thresholds used for all species within a group. Species were 

grouped by considering their known or suspected audible frequency range, auditory 

sensitivity, ear anatomy, and acoustic ecology (i.e., how they use sound), as has been 

done previously (e.g., Ketten, 2000; Southall et al., 2007; Finneran and Jenkins, 2012). 

4.1 LOW-FREQUENCY (LF) CETACEANS 

The LF cetacean group contains all of the mysticetes (baleen whales). Although there 

have been no direct measurements of hearing sensitivity in any mysticete, an audible 

frequency range of approximately 10 Hz to 30 kHz has been estimated from observed 

vocalization frequencies, observed reactions to playback of sounds, and anatomical 

analyses of the auditory system. A natural division may exist within the mysticetes, with 

some species (e.g., blue, fin) having better low-frequency sensitivity and others (e.g., 

humpback, minke) having better sensitivity to higher frequencies; however, at present 

there is insufficient knowledge to justify separating species into multiple groups. 

Therefore, a single species group is used for all mysticetes. 

4.2 MID-FREQUENCY (MF) CETACEANS 

The MF cetacean group contains most delphinid species (e.g., bottlenose dolphin, 

common dolphin, killer whale, pilot whale), beaked whales, and sperm whales (but not 

pygmy and dwarf sperm whales of the genus Kogia, which are treated as high-frequency 

species). Hearing sensitivity has been directly measured for a number of species within 

this group using psychophysical (behavioral) or auditory evoked potential (AEP) 

measurements. 

4.3 HIGH-FREQUENCY (HF) CETACEANS 

The HF cetacean group contains the porpoises, river dolphins, pygmy/dwarf sperm 

whales, Cephalorhynchus species, and some Lagenorhynchus species. Hearing sensitivity 

has been measured for several species within this group using behavioral or AEP 

measurements. High-frequency cetaceans generally possess a higher upper-frequency 

limit and better sensitivity at high frequencies compared to the mid-frequency cetacean 

species. 

4.4 SIRENIANS 

The sirenian group contains manatees and dugongs. Behavioral and AEP threshold 

measurements for manatees have revealed lower upper cutoff frequencies and 

sensitivities compared to the mid-frequency cetaceans. 

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140 

0.. 

::i. 

..- 120 

~ 

!g 100 

---0 

O 80 

.c. 

(/) 

Q) 

..c 60 

- ········ Odobenid 

--Otariid 

0.1 1 10 100 

frequency (kHz) 

4.5 PHOCIDS 

This group contains all earless seals or “true seals,” including all Arctic and Antarctic ice 

seals, harbor or common seals, gray seals and inland seals, elephant seals, and monk 

seals. Underwater hearing thresholds exist for some Northern Hemisphere species in this 

group. 

4.6 OTARIIDS AND OTHER NON-PHOCID MARINE CARNIVORES 

This group contains all eared seals (fur seals and sea lions), walruses, sea otters, and polar 

bears. The division of marine carnivores by placing phocids in one group and all others 

into a second group was made after considering auditory anatomy and measured 

audiograms for the various species and noting the similarities between the non-phocid 

audiograms (Fig. A4). Underwater hearing thresholds exist for some Northern 

Hemisphere species in this group. 

Figure A4. Comparison of Otariid, Mustelid, and Odobenid psychophysical hearing thresholds 

measured underwater. The thick, solid line is the composite audiogram based on 

data for all species. The thick, dashed line is the composite audiogram based on the 

otariids only. 

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Table A1. Species group designations for Navy Phase 3 auditory weighting functions. 

Code Name Members 

LF Low-frequency 

cetaceans 

Family Balaenidae (right and bowhead whales) 

Family Balaenopteridae (rorquals) 

Family Eschrichtiidae (gray whale) 

Family Neobalaenidae (pygmy right whale) 

MF Mid-frequency 

cetaceans 

Family Ziphiidae (beaked whales) 

Family Physeteridae (Sperm whale) 

Family Monodontidae (Irrawaddy dolphin, beluga, narwhal) 

Subfamily Delphininae (white-beaked/white-sided/ 

Risso’s/bottlenose/spotted/spinner/striped/common dolphins) 

Subfamily Orcininae (melon-headed whales, false/pygmy killer whale, killer 

whale, pilot whales) 

Subfamily Stenoninae (rough-toothed/humpback dolphins) 

Genus Lissodelphis (right whale dolphins) 

Lagenorhynchus albirostris (white-beaked dolphin) 

Lagenorhynchus acutus (Atlantic white-sided dolphin) 

Lagenorhynchus obliquidens (Pacific white-sided dolphin) 

Lagenorhynchus obscurus (dusky dolphin) 

HF High-frequency 

cetaceans 

Family Phocoenidae (porpoises) 

Family Platanistidae (Indus/Ganges river dolphins) 

Family Iniidae (Amazon river dolphins) 

Family Pontoporiidae (Baiji/ La Plata river dolphins) 

Family Kogiidae (Pygmy/dwarf sperm whales) 

Genus Cephalorhynchus (Commersen’s, Chilean, Heaviside’s, Hector’s dolphins) 

Lagenorhynchus australis (Peale’s or black-chinned dolphin) 

Lagenorhynchus cruciger (hourglass dolphin) 

SI Sirenians Family Trichechidae (manatees) 

Family Dugongidae (dugongs) 

OW Otariids and other 

non-phocid marine 

carnivores (water) 

Family Otariidae (eared seals and sea lions) 

Family Odobenidae (walrus) 

Enhydra lutris (sea otter) 

Ursus maritimus (polar bear) 

PW Phocids (water) Family Phocidae (true seals) 

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V. V. COMPOSITE AUDIOGRAMS CO POSITE AUDIOGRAMS 

Composite audiograms for each species group were determined by first searching the 

available literature for threshold data for the species of interest. For each group, all 

available AEP and psychophysical (behavioral) threshold data were initially examined. 

To derive the composite audiograms, the following rules were applied: 

1. For species groups with three or more behavioral audiograms (all 

groups except LF cetaceans), only behavioral (no AEP) data were used. 

Mammalian AEP thresholds are typically elevated from behavioral 

thresholds in a frequency-dependent manner, with increasing discrepancy 

between AEP and behavioral thresholds at the lower frequencies where 

there is a loss of phase synchrony in the neurological responses and a 

concomitant increase in measured AEP thresholds. The frequencydependent relationship between the AEP and behavioral data is 

problematic for defining the audiogram slope at low frequencies, since the 

AEP data will systematically over-estimate thresholds and therefore overestimate the low-frequency slope of the audiogram. As a result of this rule, 

behavioral data were used for all marine mammal groups. 

For the low-frequency cetaceans, for which no behavioral or AEP 

threshold data exist, hearing thresholds were estimated by synthesizing 

information from anatomical measurements, mathematical models of 

hearing, and animal vocalization frequencies (see Appendix A1). 

2. Data from an individual animal were included only once at a particular 

frequency. If data from the same individual were available from multiple 

studies, data at overlapping frequencies were averaged. 

3. Individuals with obvious high-frequency hearing loss for their species 

or aberrant audiograms (e.g., obvious notches or thresholds known to be 

elevated for that species due to masking or hearing loss) were excluded. 

4. Linear interpolation was performed within the threshold data for each 

individual to estimate a threshold value at each unique frequency present 

in any of the data for that species group. This was necessary to calculate 

descriptive statistics at each frequency without excluding data from any 

individual subject. 

5. Composite audiograms were determined using both the original 

threshold values from each individual (in dB re 1 μPa) and normalized 

thresholds obtained by subtracting the lowest threshold value for that 

subject. 

Table A2 lists the individual references for the data ultimately used to construct the 

composite audiograms (for all species groups except the LF cetaceans). From these data, 

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the median (50th percentile) threshold value was calculated at each frequency and fit by 

the function 

, (A9) 

where T( f ) is the threshold at frequency f, and T0, F1, F2, A, and B are fitting parameters. 

The median value was used to reduce the influence of outliers. The particular form of Eq. 

(A9) was chosen to provide linear-log rolloff with variable slope at low frequencies and a 

steep rise at high frequencies. The form is similar to that used by Popov et al. (2007) to 

describe dolphin audiograms; the primary difference between the two is the inclusion of 

two frequency parameters in Eq. (A9), which allows a more shallow slope in the region 

of best sensitivity. Equation (A9) was fit to the median threshold data using nonlinear 

regression (National Instruments LabVIEW 2015). The resulting fitting parameters and 

goodness of fit values (R2

) are provided in Tables 3 and 4 for the original and normalized 

data, respectively. Equation (A9) was also used to describe the shape of the estimated 

audiogram for the LF cetaceans, with the parameter values chosen to provide reasonable 

thresholds based on the limited available data regarding mysticete hearing (see Appendix 

A1 for details). 

Figures A5 and A6 show the original and normalized threshold data, respectively, as well 

as the composite audiograms based on the fitted curve. The composite audiograms for 

each species group are compared in Fig. A6. To allow comparison with other audiograms 

based on the original threshold data, the lowest threshold for the low-frequency cetaceans 

was estimated to be 54 dB re 1 μPa, based on the median of the thresholds for the other 

in-water species groups (MF, HF, SI, OW, PW). From the composite audiograms, the 

frequency of lowest threshold, f0, and the slope at the lower frequencies, s0, were 

calculated (Table A5). For the species with composite audiograms based on experimental 

data (i.e., all except LF cetaceans), audiogram slopes were calculated across a frequency 

range of one decade beginning with the lowest frequency present for each group. The 

low-frequency slope for LF cetaceans was not based on a curve-fit but explicitly defined 

during audiogram derivation (see Appendix A1). 

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Table A2. References, species, and individual subjects used to derive the composite 

audiograms. 

Group Reference Species Subjects 

MF (Finneran et al., 2005b) Delphinapterus leucas Beethoven 

(Szymanski et al., 1999) Orcinus orca Yaka, Vigga 

(Nachtigall et al., 1995) Grampus griseus N/a 

(Kastelein et al., 2003) Stenella coeruleoalba Meyen 

(Lemonds, 1999) Tursiops truncatus Itsi Bitsy 

(Brill et al., 2001) Tursiops truncatus CAS 

(Ljungblad et al., 1982) Tursiops truncatus 12-y male 

(Johnson, 1967) Tursiops truncatus Salty 

(Sauerland and Dehnhardt, 1998) Sotalia fluviatilis Paco 

(Johnson et al., 1989) Delphinapterus leucas 2-y female 

(White et al., 1978) Delphinapterus leucas Edwina, Kojak 

(Awbrey et al., 1988) Delphinapterus leucas Kojak, female, male 

(Thomas et al., 1988) Pseudorca crassidens I'a nui hahai 

(Finneran et al., 2010b) Tursiops truncatus TYH 

(Schlundt et al., 2008) Tursiops truncatus WEN 

(Ridgway et al., 2001) Delphinapterus leucas MUK, NOC 

(Tremel et al., 1998) Lagenorhynchus obliquidens female 

HF (Jacobs and Hall, 1972) Inia geoffrensis male 

(Kastelein et al., 2002a)** Phocoena PpSH047 

(Kastelein et al., 2010) Phocoena Jerry 

(Kastelein et al., 2015a) Phocoena ID No. 04 

SI (Gaspard et al., 2012) 

(Gerstein et al., 1999) 

Trichechus manatus 

Trichechus manatus 

Buffet, Hugh 

Stormy, Dundee 

OW (Moore and Schusterman, 1987) Callorhinus ursinus Lori, Tobe 

(Babushina et al., 1991) Callorhinus ursinus N/a 

(Kastelein et al., 2002b) Odobenus rosmarus Igor 

(Mulsow et al., 2012) Zalophus californianus JFN 

(Reichmuth and Southall, 2012) Zalophus californianus Rio, Sam 

(Reichmuth et al., 2013) Zalophus californianus Ronan 

(Kastelein et al., 2005) Eumetopias jubatus EjZH021, EjZH022 

(Ghoul and Reichmuth, 2014) Enhydra lutris nereis Charlie 

PW (Kastak and Schusterman, 1999) Mirounga angustirostris Burnyce 

(Terhune, 1988) Phoca vitulina N/a 

(Reichmuth et al., 2013) Phoca vitulina Sprouts 

(Kastelein et al., 2009) Phoca vitulina 01, 02 

(Sills et al., 2014) Phoca largha Amak, Tunu 

(Sills et al., 2015) Pusa hispida Nayak 

** Corrected thresholds from Kastelein et al. (2010) were used. 

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Table A3. Composite audiogram parameters values for use in Eq. (A9). For all groups except 

LF cetaceans, values represent the best-fit parameters from fitting Eq. (A9) to 

experimental threshold data. For the low-frequency cetaceans, parameter values for 

Eq. (A9) were estimated as described in Appendix A1. 

Group T0 (dB) F1 (kHz) F2 (kHz) A B R2 

LF 53.19 0.412 9.4 20 3.2 – 

MF 46.2 25.9 47.8 35.5 3.56 0.977 

HF 46.4 7.57 126 42.3 17.1 0.968 

SI -40.4 3990 3.8 37.3 1.7 0.982 

OW 63.1 3.06 11.8 30.1 3.23 0.939 

PW 43.7 10.2 3.97 20.1 1.41 0.907 

Table A4. Normalized composite audiogram parameters values for use in Eq. (A9). For all 

groups except LF cetaceans, values represent the best-fit parameters after fitting 

Eq. (A9) to normalized threshold data. For the low-frequency cetaceans, parameter 

values for Eq. (A9) were estimated as described in Appendix A1. 

Group T0 (dB) F1 (kHz) F2 (kHz) A B R2 

LF -0.81 0.412 9.4 20 3.2 – 

MF 3.61 12.7 64.4 31.8 4.5 0.960 

HF 2.48 9.68 126 40.1 17 0.969 

SI -109 5590 2.62 38.1 1.53 0.963 

OW 2.36 0.366 12.8 73.5 3.4 0.958 

PW -39.6 368 2.21 20.5 1.23 0.907 

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120 

,....._ 100 

co 

a.. 80 ::1. 

T""" 60 

Q) 

I.... 40 LF HF co 

..._... 

"'O 20 

0.1 1 10 100 0.1 1 10 100 0.1 10 100 "'O 

_g 140 

en 

~ 120 

...c:: 

+-' 

100 

80 

60 SI ow 

40 

0.1 1 10 100 0.1 1 10 100 0.1 1 10 100 

frequency (kHz) 

Figure A5. Thresholds and composite audiograms for the six species groups. Thin lines 

represent the threshold data from individual animals. Thick lines represent either 

the predicted threshold curve (LF cetaceans) or the best fit of Eq. (A9) to 

experimental data (all other groups). Derivation of the LF cetacean curve is 

described in Appendix A1. The minimum threshold for the LF cetaceans was 

estimated to be 54 dB re 1 μPa, based on the median of the lowest thresholds for the

other groups. 

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60 

-

c:c 

,:, 40 

--- ,:, 

0 20 

..c: 

(/) 0 Q) LF HF L.. 

..c: 

_, -20 

,:, 0.01 0.1 1 10 100 0.1 1 10 100 0.1 1 10 100 

Q) 

N 80 

cu 

E 

L.. 60 

0 

C 40 

20 

0 SI ow PW 

-20 

0.1 1 10 100 0.1 1 10 100 0.1 1 10 100 

frequency (kHz) 

Figure A6. Normalized thresholds and composite audiograms for the six species groups. Thin 

lines represent the threshold data from individual animals. Thick lines represent 

either the predicted threshold curve (LF cetaceans) or the best fit of Eq. (A9) to 

experimental data (all other groups). Thresholds were normalized by subtracting 

the lowest value for each individual data set (i.e., within-subject). Composite 

audiograms were then derived from the individually normalized thresholds (i.e., the 

composite audiograms were not normalized and may have a minimum value ≠ 0).

Derivation of the LF cetacean curve is described in Appendix A1. 

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original PW ...-.... 

co I 

a.. 120 ~ ; 

T""" 

Q) 100 '-

(l'.) 

"C 

- 80 

"C LF 

0 

..c 60 

en 

Q) 

'- HF ..c 

...., 40 

20 

0.1 1 10 100 

80 normalized 

PW 

...-.... 

(l'.) 60 I 

"C I ; 

- I 

"C 40 0 

..c 

en .. . ·' Q) 20 ·~ '- LF ·,. ..c ~-, . ...., 

0 

-20 

0.1 1 10 100 

frequency (kHz) 

Figure A7. Composite audiograms for the various species groups, derived with the original data 

(upper) and normalized data (lower). The gray lines in the upper left panel 

represent ambient noise spectral density levels (referenced to the left ordinate, in dB 

re 1 μPa2

/Hz) corresponding to the limits of prevailing noise and various sea-state 

conditions, from 0.5 to 6 (National Research Council (NRC), 2003). 

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Table A5. Frequency of best hearing (f0) and the magnitude of the low-frequency slope (s0) 

derived from composite audiograms and equal latency contours. For the species 

with composite audiograms based on experimental data (i.e., all except LF 

cetaceans), audiogram slopes were calculated across a frequency range of one 

decade beginning with the lowest frequency present for each group. The lowfrequency slope for LF cetaceans was not based on a curve-fit but explicitly defined 

during audiogram derivation (see Appendix A1). Equal latency slopes were 

calculated from the available equal latency contours (Fig. A8). 

Group 

Original data 

composite audiogram 

Normalized data 

composite audiogram 

Equal latency 

curves 

f0 

(kHz) 

s0 

(dB/decade) 

f0 

(kHz) 

s0 

(dB/decade) 

s0 

(dB/decade) 

LF 5.6 20 5.6 20 — 

MF 55 35 58 31 31 

HF 105 37 105 36 50 

SI 16 36 12 37 — 

OW 12 27 10 39 — 

PW 8.6 19 13 20 — 

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VI. VI. EQUAL LOUDNESS DATA EQUAL LOUDNESS DATA 

Finneran and Schlundt (2011) conducted a subjective loudness comparison task with a 

bottlenose dolphin and used the resulting data to derive equal loudness contours and 

auditory weighting functions. The weighting functions agreed closely with dolphin TTS 

data over the frequency range 3 to 56 kHz (Finneran and Schlundt, 2013); however, the 

loudness data only exist for frequencies between 2.5 kHz and 113 kHz and cannot be 

used to estimate the shapes of loudness contours and weighting functions at lower 

frequencies. 

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VII. EQUAL LATENCY DATA 

200 

Tursiops truncatus 

180 

,......, 

cu 160 a.. 

::i 

,..... 140 

Q) 

.... 

co 120 

-0 

-...J 100 

a.. 

Cl) 80 '•.,.' threshold 

60 threshold 

40 

0.1 10 100 0.1 1 

frequency (kHz) 

10 

' ' 

, .. 

" " " :,, 

'" "' 

100 

VII. EQUAL LATENCY DATA 

Reaction times to acoustic tones have been measured in several marine mammal species 

and used to derive equal latency contours and weighting functions (Fig. A8, Wensveen et 

al., 2014; Mulsow et al., 2015). Unlike the dolphin equal loudness data, the latency data 

extend to frequencies below 1 kHz and may be used to estimate the slopes of auditory 

weighting functions at lower frequencies. 

Figure A8. Underwater marine mammal equal latency contours are available for Phocoena phocoena 

(Wensveen et al., 2014) and Tursiops truncatus (Mulsow et al., 2015). The slopes for 

the contours at low frequencies were obtained from the literature (Phocoena 

phocoena) or calculated from the best linear-log fits to the lower frequency data. 

The slope of the contour passing through an SPL approximately 40 dB above the 

threshold at f0 was selected as the most appropriate based on: (1) human Aweighting, (2) observations that the relationship between equal latency and loudness 

can break down at higher sensation levels, and (3) for many data sets the slopes 

increase at higher SPLs rather than decrease as expected. The resulting slopes are 

listed in Table A5. 

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VIII. VIII. TTS DATA TTS DATA 

8.1 NON-IMPULSIVE (STEADY-STATE) EXPOSURES – TTS 

For weighting function derivation, the most critical data required are TTS onset exposure 

levels as a function of exposure frequency. These values can be estimated from published 

literature by examining TTS as a function of SEL for various frequencies. 

To estimate TTS onset values, only TTS data from psychophysical (behavioral) hearing 

tests were used. Studies have shown differences between the amount of TTS from 

behavioral threshold measurements and that determined using AEP thresholds (Fig. A9). 

TTS determined from AEP thresholds is typically larger than that determined behaviorally, 

and AEP-measured TTS of up to ~ 10 dB has been observed with no corresponding change 

in behavioral thresholds (e.g., Finneran et al., 2007). Although these data suggest that AEP 

amplitudes and thresholds provide more sensitive indicators (than behavioral thresholds) of 

the auditory effects of noise, Navy acoustic impact analyses use TTS both as an indicator of 

the disruption of behavioral patterns that are mediated by the sense of hearing and to predict 

when the onset of PTS is likely to occur. Navy analyses assume that exposures resulting in a 

NITS > 40 dB measured a few minutes after exposure will result in some amount of residual 

PTS. This is based on relationships observed in early human TTS studies utilizing 

psychophysical threshold measurements. To date, there have been no reports of PTS in a 

marine mammal whose initial behavioral threshold shift was 40 dB or less; however, 

behavioral shifts of 35 to 40 dB have required multiple days to recover, suggesting that these 

exposures are near those capable of resulting in PTS. In contrast, studies utilizing AEP 

measurements in marine mammals have reported TTSs of 45 dB that recovered in 40 min 

and 60 dB that recovered in < 24 h, suggesting that these exposures were not near those 

capable of resulting in PTS (Popov et al., 2013). 

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Cl) 30 

II- 20 

10 

AEP 

behavioral 

(a) AEP (b) 

0 ~~~-~~-~~~~~- ~~~-~~~~~~~~~ 

1 10 100 1000 10000 10 100 1000 10000 

time post-exposure (min) 

Figure A9. TTS measured using behavioral and AEP methods do not necessarily agree, with marine 

mammal studies reporting larger TTS obtained using AEP methods. For the data 

above, thresholds were determined using both techniques before and after the same 

noise exposure. Hearing thresholds were measured at 30 kHz. Behavioral thresholds 

utilized FM tones with 10% bandwidth. AEP thresholds were based on AM tones 

with a modulation frequency of 1.05 kHz. Noise exposures consisted of (a) a single, 

20-kHz tone with duration of 64 s and SPL of 185 dB re 1 μPa (SEL = 203 dB re 1

μPa2

s) and (b) three 16-s tones at 20 kHz, with mean SPL = 193 dB re 1 μPa

(cumulative SEL = 210 dB re 1 μPa2

s). Data from Finneran et al. (2007). 

To determine TTS onset for each subject, the amount of TTS observed after exposures 

with different SPLs and durations were combined to create a single TTS growth curve as 

a function of SEL. The use of (cumulative) SEL is a simplifying assumption to 

accommodate sounds of various SPLs, durations, and duty cycles. This is referred to as 

an “equal energy” approach, since SEL is related to the energy of the sound and this 

approach assumes exposures with equal SEL result in equal effects, regardless of the 

duration or duty cycle of the sound. It is well-known that the equal energy rule will overestimate the effects of intermittent noise, since the quiet periods between noise exposures 

will allow some recovery of hearing compared to noise that is continuously present with 

the same total SEL (Ward, 1997). For continuous exposures with the same SEL but 

different durations, the exposure with the longer duration will also tend to produce more 

TTS (e.g., Kastak et al., 2007; Mooney et al., 2009; Finneran et al., 2010b). Despite these 

limitations, however, the equal energy rule is still a useful concept, since it includes the 

effects of both noise amplitude and duration when predicting auditory effects. SEL is a 

simple metric, allows the effects of multiple noise sources to be combined in a 

meaningful way, has physical significance, and is correlated with most TTS growth data 

reasonably well — in some cases even across relatively large ranges of exposure duration 

(see Finneran, 2015). The use of cumulative SEL for Navy sources will always overestimate the effects of intermittent or interrupted sources, and the majority of Navy 

sources feature durations shorter than the exposure durations typically utilized in marine 

mammal TTS studies, therefore the use of (cumulative) SEL will tend to over-estimate 

the effects of many Navy sound sources. 

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Marine mammal studies have shown that the amount of TTS increases with SEL in an 

accelerating fashion: At low exposure SELs, the amount of TTS is small and the growth 

curves have shallow slopes. At higher SELs, the growth curves become steeper and 

approach linear relationships with the noise SEL. Accordingly, TTS growth data were fit 

with the function 

, (A10) 

where t is the amount of TTS, L is the SEL, and m1 and m2 are fitting parameters. This 

particular function has an increasing slope when L < m2 and approaches a linear 

relationship for L > m2 (Maslen, 1981). The linear portion of the curve has a slope of 

m1/10 and an x-intercept of m2. After fitting Eq. (10) to the TTS growth data, 

interpolation was used to estimate the SEL necessary to induce 6 dB of TTS — defined 

as the “onset of TTS” for Navy acoustic impact analyses. The value of 6 dB has been 

historically used to distinguish non-trivial amounts of TTS from fluctuations in threshold 

measurements that typically occur across test sessions. Extrapolation was not performed 

when estimating TTS onset; this means only data sets with exposures producing TTS both 

above and below 6 dB were used. 

Figures A10 to A13 show all behavioral and AEP TTS data to which growth curves 

defined by Eq. (A10) could be fit. The TTS onset exposure values, growth rates, and 

references to these data are provided in Table A6. 

8.2 NON-IMPULSIVE (STEADY-STATE) EXPOSURES – PTS 

Since no studies have been designed to intentionally induce PTS in marine mammals (but 

see Kastak et al., 2008), onset-PTS levels for marine mammals must be estimated. 

Differences in auditory structures and sound propagation and interaction with tissues 

prevent direct application of numerical thresholds for PTS in terrestrial mammals to 

marine mammals; however, the inner ears of marine and terrestrial mammals are 

analogous and certain relationships are expected to hold for both groups. Experiments 

with marine mammals have revealed similarities between marine and terrestrial mammals 

with respect to features such as TTS, age-related hearing loss, ototoxic drug-induced 

hearing loss, masking, and frequency selectivity (e.g., Nachtigall et al., 2000; Finneran et 

al., 2005b). For this reason, relationships between TTS and PTS from marine and 

terrestrial mammals can be used, along with TTS onset values for marine mammals, to 

estimate exposures likely to produce PTS in marine mammals (Southall et al., 2007). 

A variety of terrestrial and marine mammal data sources (e.g., Ward et al., 1958; Ward et 

al., 1959; Ward, 1960; Miller et al., 1963; Kryter et al., 1966) indicate that threshold 

shifts up to 40 to 50 dB may be induced without PTS, and that 40 dB is a conservative 

upper limit for threshold shift to prevent PTS; i.e., for impact analysis, 40 dB of NITS is 

an upper limit for reversibility and that any additional exposure will result in some PTS. 

This means that 40 dB of TTS, measured a few minutes after exposure, can be used as a 

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conservative estimate for the onset of PTS. An exposure causing 40 dB of TTS is 

therefore considered equivalent to PTS onset. 

To estimate PTS onset, TTS growth curves based on more than 20 dB of measured TTS 

were extrapolated to determine the SEL required for a TTS of 40 dB. The SEL difference 

between TTS onset and PTS onset was then calculated. The requirement that the 

maximum amount of TTS must be at least 20 dB was made to avoid over-estimating PTS 

onset by using growth curves based on small amounts of TTS, where the growth rates are 

shallower than at higher amounts of TTS. 

8.3 IMPULSIVE EXPOSURES 

Marine mammal TTS data from impulsive sources are limited to two studies with 

measured TTS of 6 dB or more: Finneran et al. (2002) reported behaviorally-measured 

TTSs of 6 and 7 dB in a beluga exposed to single impulses from a seismic water gun 

(unweighted SEL = 186 dB re 1 μPa2

s, peak SPL = 224 dB re 1 μPa) and Lucke et al. 

(2009) reported AEP-measured TTS of 7 to 20 dB in a harbor porpoise exposed to single 

impulses from a seismic air gun [Fig. A12(f), TTS onset = unweighted SEL of 162 dB re 

1 μPa2s or peak SPL of 195 dB re 1 μPa]. The small reported amounts of TTS and/or the

limited distribution of exposures prevent these data from being used to estimate PTS 

onset. 

In addition to these data, Kastelein et al. (2015c)37 reported behaviorally-measured mean 

TTS of 4 dB at 8 kHz and 2 dB at 4 kHz after a harbor porpoise was exposed to a series 

of impulsive sounds produced by broadcasting underwater recordings of impact pile 

driving strikes through underwater sound projectors. The exposure contained 2760 

individual impulses presented at an interval of 1.3 s (total exposure time was 1 h). The 

average single-strike, unweighted SEL was approximately 146 dB re 1 μPa2s and the 

cumulative (unweighted) SEL was approximately 180 dB re 1 μPa2

s. The pressure 

waveforms for the simulated pile strikes exhibited significant “ringing” not present in the 

original recordings and most of the energy in the broadcasts was between 500 and 800 

Hz, near the resonance of the underwater sound projector used to broadcast the signal. As 

a result, some questions exist regarding whether the fatiguing signals were representative 

of underwater pressure signatures from impact pile driving. 

Several impulsive noise exposure studies have also been conducted without measurable 

(behavioral) TTS. Finneran et al. (2000) exposed dolphins and belugas to single impulses 

from an “explosion simulator” (maximum unweighted SEL = 179 dB re 1 μPa2

s, peak 

SPL = 217 dB re 1 μPa) and Finneran et al. (2015) exposed three dolphins to sequences 

of 10 impulses from a seismic air gun (maximum unweighted cumulative SEL = 193 to 

195 dB re 1 μPa2s, peak SPL =196 to 210 dB re 1 μPa) without measurable TTS. 

Finneran et al. (2003) exposed two sea lions to single impulses from an arc-gap 

37 Footnote added by NMFS: Since the NMFS received this version of the Finneran Technical Report, another TTS study 

became available (Kastelein et al. 2016). In this study, two harbor porpoises were exposed to playbacks of impact pile 

driving strikes. Neither individual had a TTS of 6 dB after exposure. Kastelein et al. 2016 estimated TTS onset to occur at 

SELcum 175 dB (unweighted). 

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transducer with no measurable TTS (maximum unweighted SEL = 163 dB re 1 μPa2s, 

peak SPL = 203 dB re 1 μPa). Reichmuth et al. (2016) exposed two spotted seals (Phoca 

largha) and two ringed seals (Pusa hispida) to single impulses from a 10 in3 sleeve air 

gun with no measurable TTS (maximum unweighted SEL = 181 dB re 1 μPa2

s, peak SPL 

~ 203 dB re 1 μPa).

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0 (a) (b) (c) 

30 

20 

10 3 kHz 

0 • • 

• 

40 (d) (e) (f) 

-

CO 30 ~ 

-- • Cl) 20 3 kHz • 

I- .. 

I- 10 

. ,, 

0 

40 

(g) I (h) (i) I 

I 

30 I 

14.1kHz, I 

I 

0 56.6 kHz , 

I 

20 9' I 

I 

10 ,e 10 kHz 

0 

120 140 160 180 200 220 140 160 180 200 220 140 160 180 200 220 

SEL (dB re 1 μPa2s) 

4 

Figure A10. TTS growth data for mid-frequency cetaceans obtained using behavioral methods. 

Growth curves were obtained by fitting Eq. (A10) to the TTS data as a function of 

SEL. Onset TTS was defined as the SEL value from the fitted curve at a TTS = 6 

dB, for only those datasets that bracketed 6 dB of TTS. Onset PTS was defined as 

the SEL value from the fitted curve at a TTS = 40 dB, for only those datasets with 

maximum TTS > 20 dB. Frequency values within the panels indicate the exposure 

frequencies. Solid lines are fit to the filled symbols; dashed lines are fit to the open 

symbols. See Table A6 for explanation of the datasets in each panel. Frequencies 

listed in each panel denote the exposure frequency. 

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(b) o' (c) I 

50 22.5 kHz ' 

I 

40 I 

I.) ., 

30 

,.._20 

en ; 

~ 10 ; 

-

Cl) 0 II- 60 (d) ; 

; 

22.5 kHz ,, 50 ., (M) ., ; 

40 §"" • ; ., o,, 

30 ; 

0 ~.,~. 22.5 kHz 20 _§- "o j (F) ., ; ., 

I I • 10 ., ., ., ., ., 

0 

160 170 180 190 200 210 170 180 190 200 210 170 180 190 200 210 

SEL (dB re 1 μPa2s) 

Figure A11. TTS growth data for mid-frequency cetaceans obtained using AEP methods. 

Growth curves were obtained by fitting Eq. (A10) to the TTS data as a function of 

SEL. Onset TTS was defined as the SEL value from the fitted curve at a TTS = 6 

dB, for only those datasets that bracketed 6 dB of TTS. Onset PTS was defined as 

the SEL value from the fitted curve at a TTS = 40 dB, for only those datasets with 

maximum TTS > 20 dB. Frequency values within the panels indicate the exposure 

frequencies. Solid lines are fit to the filled symbols; dashed lines are fit to the open 

symbols. See Table A6 for explanation of the datasets in each panel. 

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40 (a) (b) (c) I 

I 

I 

30 I 

4 kHz 6.5 kHz 

20 

1-2 kHz 

10 

0 

I 

(d) (e) 0 (f) 40 I 

--- co 

""O 30 

-(/) 20 II- I 

10 

~ 

0 

140 160 180 200 140 160 180 200 

40 (g) SEL (dB re 1 μPa2s) 

30 

20 .) 10 

impulsive 

0 

• 

140 160 180 200 

SEL (dB re 1 μPa2s) 

Figure A12. TTS growth data for high-frequency cetaceans obtained using behavioral and AEP 

methods. Growth curves were obtained by fitting Eq. (A10) to the TTS data as a 

function of SEL. Onset TTS was defined as the SEL value from the fitted curve at a 

TTS = 6 dB, for only those datasets that bracketed 6 dB of TTS. Onset PTS was 

defined as the SEL value from the fitted curve at a TTS = 40 dB, for only those 

datasets with maximum TTS > 20 dB. The exposure frequency is specified in normal 

font; italics indicate the hearing test frequency. Percentages in panels (b), (d) 

indicate exposure duty cycle (duty cycle was 100% for all others). Solid lines are fit 

to the filled symbols; dashed lines are fit to the open symbols. See Table A6 for 

explanation of the datasets in each panel. 

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~ 

(a) (b) (c) 

02 

2.5 kHz 4 kHz T 

10 ~ 

2~ 

Pv --yf Ma 

0 ~ 

160 180 200 160 180 200 160 180 200 

2 SEL (dB re 1 μPa s) 

20 

Figure A13. TTS growth data for pinnipeds obtained using behavioral methods. Growth curves 

were obtained by fitting Eq. (A10) to the TTS data as a function of SEL. Onset TTS 

was defined as the SEL value from the fitted curve at a TTS = 6 dB, for only those 

datasets that bracketed 6 dB of TTS. Frequency values within the panels indicate 

the exposure frequencies. Numeric values in panel (c) indicate subjects 01 and 02. 

Solid lines are fit to the filled symbols; dashed lines are fit to the open symbols. See 

Table A6 for explanation of the datasets in each panel. 

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Table A6. Summary of marine mammal TTS growth data and onset exposure levels. Only those data from which growth curves could be 

generated are included. TTS onset values are expressed in SEL, in dB re 1 μPa2

s. Tests featured continuous exposure to steady-state 

noise and behavioral threshold measurements unless otherwise indicated. 

Group Species Subject Freq. 

(kHz) 

Min 

TTS 

(dB) 

Max 

TTS 

(dB) 

TTS 

Onset 

(dB 

SEL) 

TTS 

growth 

rate 

(dB/dB) 

PTS 

Onset 

(dB 

SEL) 

TTSPTS 

offset 

(dB) 

Notes Reference Figure 

MF Tursiops 

truncatus 

BEN 3 0 7 211* 0.21 — — 

TTS onset higher 

than subsequent 

test 

(Finneran et al., 2005a) 10(a) 

MF Tursiops 

truncatus 

NAY 3 0 5 — 0.13 — — (Finneran et al., 2005a) 10(b) 

MF Tursiops 

truncatus 

BLU 3 4 11 207* 1.5 — — intermittent (Finneran et al., 2010a) 10(c) 

MF Tursiops 

truncatus 

BLU 3 0 23 206* 1.0 240 34 

TTS onset higher 

than subsequent 

tests 

(Finneran et al., 2010b) 10(d) 

MF Tursiops 

truncatus 

TYH 3 0 9 194 0.35 — — (Finneran et al., 2010b) 10(e) 

MF Tursiops 

truncatus 

BLU 

3 

7.1 

10 

14.1 

20 

28.3 

0 

0 

1 

0 

0 

0 

13 

7 

13 

22 

25 

30 

190 

184 

179 

176 

181 

177 

0.28 

0.21 

0.48 

0.95 

1.2 

4.5 

— 

— 

— 

213 

212 

190 

— 

— 

— 

37 

31 

13 

(Finneran and Schlundt, 

2013) 

10(f) 

10(f) 

10(g) 

10(g) 

10(h) 

10(h) 

MF Tursiops 

truncatus 

TYH 40 

56.6 

0 

0 

11 

12 

182 

181 

0.46 

1.1 

— 

— 

— 

— 

(Finneran and Schlundt, 

2013) 

10(i) 

10(i) 

MF Delphinapterus 

leucas N/a 32 20 40 — 1.4 195 — AEP (Popov et al., 2011b) 11(a) 

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Group Species Subject Freq. 

(kHz) 

Min 

TTS 

(dB) 

Max 

TTS 

(dB) 

TTS 

Onset 

(dB 

SEL) 

TTS 

growth 

rate 

(dB/dB) 

PTS 

Onset 

(dB 

SEL) 

TTSPTS 

offset 

(dB) 

Notes Reference Figure 

MF Delphinapterus 

leucas female 

11.2 

22.5 

45 

90 

25 

38 

9 

21 

50 

63 

51 

31 

— 

— 

— 

— 

2.8 

2.5 

3.0 

0.8 

190 

183 

193 

208 

— 

— 

— 

— 

AEP (Popov et al., 2013) 

11(b) 

11(b) 

11(c) 

11(c) 

MF Delphinapterus 

leucas male 

11.2 

22.5 

45 

90 

15 

28 

13 

8 

48 

55 

42 

24 

— 

— 

— 

— 

2.5 

1.7 

2.7 

1.5 

195 

188 

198 

210 

— 

— 

— 

— 

AEP (Popov et al., 2013) 

11(d) 

11(d) 

11(e) 

11(e) 

MF Delphinapterus 

leucas female 22.5 0 40 184* 1.7 206 22 AEP (Popov et al., 2014) 11(f) 

MF Delphinapterus 

leucas male 22.5 12 40 — 1.2 197 — AEP (Popov et al., 2014) 11(f) 

HF Phocoena 

phocoena 02 4 2 15 165 0.3 — — (Kastelein et al., 2012a) 12(a) 

HF Phocoena 

phocoena 02 ~1.5 

~1.5 

0 

0 

32 

7 

191 

197* 

2.8 

0.4 

207 

— 

16 

— 

100% duty cycle 

10% duty cycle (Kastelein et al., 2014b) 12(b) 

12(b) 

HF Phocoena 

phocoena 02 6.5 

6.5 

1 

0 

13 

22 

161 

176* 

0.3 

1.3 

— 

204 

— 

28 

6.5 kHz test freq. 

9.2 kHz test freq. (Kastelein et al., 2014a) 12(c) 

12(c) 

HF Phocoena 

phocoena 02 ~6.5 

~6.5 

2 

2 

21 

13 

180* 

182* 

2.7 

1.3 

197 

— 

17 

— 

100% duty cycle 

10% duty cycle (Kastelein et al., 2015b) 12(d) 

12(d) 

HF Neophocaena 

phocaenoides male 22 

32 

28 

25 

35 

45 

— 

— 

0.7 

1.0 

186 

177 

— 

— AEP (Popov et al., 2011a) 12(e) 

HF Neophocaena 

phocaenoides female 45 

90 

23 

18 

30 

25 

— 

— 

0.36 

0.48 

213 

213 

— 

— AEP (Popov et al., 2011a) 12(f) 

HF Phocoena 

phocoena Eigil impulse 0 20 162 ** — — AEP (Lucke et al., 2009) 12(g) 

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Group Species Subject Freq. 

(kHz) 

Min 

TTS 

(dB) 

Max 

TTS 

(dB) 

TTS 

Onset 

(dB 

SEL) 

TTS 

growth 

rate 

(dB/dB) 

PTS 

Onset 

(dB 

SEL) 

TTSPTS 

offset 

(dB) 

Notes Reference Figure 

OW Zalophus 

californianus Rio 2.5 5 9 199 0.17 — — (Kastak et al., 2005) 13(a) 

PW Phoca vitulina Sprouts 2.5 3 12 183 6.4 — — (Kastak et al., 2005) 13(b) 

PW Mirounga 

angustirostris Burnyce 2.5 3 5 — — — — (Kastak et al., 2005) 13(b) 

PW Phoca vitulina 01 4 0 10 180 0.33 — — (Kastelein et al., 2012b) 13(c) 

PW Phoca vitulina 02 4 0 11 183* 0.68 — — TTS16 (Kastelein et al., 2012b) 13(c) 

* SELs not used in subsequent analyses to optimize ∆T or define K for TTS or PTS exposure functions. Reasons for exclusion include: (i) another data set resulted in a lower 

onset TTS at the same frequency, (ii) the data set featured a duty cycle less than 100%, (iii) TTS values were measured at times significantly larger than 4 min, (iv) data 

were obtained from AEP testing, or (v) a lower TTS onset was found at a different hearing test frequency (also see Notes). 

** Distribution of data did not support an accurate estimate for growth rate (the standard error was four orders of magnitude larger than the slope estimate) 

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IX. IX. TTS EXPOSURE FUNCTIO TTS EXPOSURE FUNCTIONS NS FOR SONARS FOR SONARS 

Derivation of the weighting function parameters utilized the exposure function form 

described by Eq. (A2), so that the shapes of the functions could be directly compared to 

the TTS onset data (Table A6) when available. The function shapes were first determined 

via the parameters a, b, f1, and f2, then the gain constant K was determined for each group 

to provide the best fit to the TTS data or estimated TTS onset value at a particular 

frequency. 

9.1 LOW- AND HIGH-FREQUENCY EXPONENTS (a, b) 

The high-frequency exponent, b, was fixed at b = 2. This was done to match the previous 

value used in the Phase 2 functions, since no new TTS data are available at the higher 

frequencies and the equal latency data are highly variable at the higher frequencies. 

The low-frequency exponent, a, was defined as a = s0/20, where s0 is the lower of the 

slope of the audiogram or equal latency curves (in dB/decade) at low frequencies (Table 

A5). This causes the weighting function slope to match the shallower slope of the 

audiogram or equal latency contours at low frequencies. In practice, the audiogram slopes 

were lower than the equal latency slopes for all groups except the mid-frequency 

cetaceans (group MF). 

9.2 FREQUENCY CUTOFFS (ʄ1, ʄ2) 

The frequency cutoffs f1 and f2 were defined as the frequencies below and above the 

frequency of best hearing (f0, Table A5) where the composite audiogram thresholds 

values were ∆T-dB above the threshold at f0 (Fig. A14). If ∆T = 0, the weighting function 

shape would match the shape of the inverse audiogram. Values of ∆T > 0 progressively 

“compress” the weighting function, compared to the audiogram, near the frequency 

region of best sensitivity. This compression process is included to match the marine 

mammal TTS data, which show less change in TTS onset with frequency than would be 

predicted by the audiogram in the region near best sensitivity. 

To determine ∆T, the exposure function amplitude defined by Eq. (A2) was calculated for 

the mid- and high-frequency cetaceans using ∆T values that varied from 0 to 20 dB. For 

each ∆T value, the constant K was adjusted to minimize the mean-squared error between 

the function amplitude and the TTS data (Fig. A15). This process was performed using 

composite audiograms based on both the original and normalized threshold data. Fits 

were performed using only TTS data resulting from continuous exposures (100% duty 

cycle). If hearing was tested at multiple frequencies after exposure, the lowest TTS onset 

value was used. 

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0 -en N 

cu 

a.. 

::1. 

..-

0> 200 ,._ 

en 

"'O 

.._,,, 

-

Q) 

~ 180 

0 

en 

II1 

--100 co 

"'O 

-

"'O 

0 80 ..c 

(/) 

~ ..c 

..... 

• 

10 

frequency 

MF 200 

180 

160 

• 140 

120 

100 1 10 100 

frequency (kHz) 

Figure A14. The cutoff frequencies f1 and f2 were defined as the frequencies below and above f0 

at which the composite audiogram values were ΔT-dB above the threshold at f0 (the 

lowest threshold). 

Figure A15. Effect of ΔT adjustment on the TTS exposure functions for the mid-frequency 

cetaceans (left) and high-frequency cetaceans (right). To calculate the exposure 

functions, a and b were defined as a = s0/20 and b = 2. ΔT was then varied from 0 to 

20. At each value of ΔT, K was adjusted to minimize the squared error between the 

exposure function and the onset TTS data (symbols). As ΔT increases, f1 decreases 

and f2 increases, causing the pass-band of the function to increase and the function 

to “flatten”. 

For the original and normalized data, the errors between the best-fit exposure functions and 

the TTS data for the MF and HF cetaceans were squared, summed, and divided by the total 

number of TTS data points (12). This provided an overall mean-squared error (MSE) for the 

original and normalized data as a function of ∆T (Fig. A16). The conditions (∆T value and 

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I... 

e 22 I... 

Q) 20 

-c 

~ 18 

cu 

5-16 

<{' 14 

C 

ffi 12 

E 10 

8 

0 

• I 

·\

0

\ I l ~ riginal / / 0 

\ \ I I 

• 'o, Nj.(o,// 

\ o"O·J' o 

., ✓ 

normalized •'•-•·•/ 

t 

5 10 15 20 

~T (dB) 

original/normalized threshold audiograms) resulting in the lowest MSE indicated the best 

fit of the exposure functions to the TTS data. For the MF and HF cetacean data, the 

lowest MSE occurred with the normalized threshold data with ∆T = 9 dB. Therefore, f1 

and f2 for the remaining species groups were defined using composite audiograms 

based on normalized thresholds with ∆T = 9 dB. 

Figure A16. Relationship between ΔT and the resulting mean-squared error (MSE) between the 

exposure functions and onset TTS data. The MSE was calculated by adding the 

squared errors between the exposure functions and TTS data for the MF and HF 

cetacean groups, then dividing by the total number of TTS data points. This process 

was performed using the composite audiograms based on original and normalized 

threshold data and ΔT values from 0 to 20. The lowest MSE value was obtained 

using the audiograms based on normalized thresholds with ΔT = 9 dB (arrow). 

9.3 GAIN PARAMETERS K AND C 

The gain parameter K was defined to minimize the squared error between the exposure 

function and the TTS data for each species group. Note that K is not necessarily equal to 

the minimum value of the exposure function. 

For the low-frequency cetaceans and sirenians, for which no TTS data exist, TTS onset at 

the frequency of best hearing (f0) was estimated by assuming that, at the frequency of best 

hearing, the numeric difference between the auditory threshold (in dB SPL) and the onset 

of TTS (in dB SEL) would be similar to that observed in the other species groups. Table 

A7 summarizes the onset TTS and composite threshold data for the MF, HF, OW, and 

PW groups. For these groups, the median difference between the TTS onset and 

composite audiogram threshold at f0 was 126 dB. In the absence of data, the hearing 

threshold at f0 for the LF group was set equal to the median threshold at f0 for the other 

groups (MF, HF, SI, OW, PW, median = 54 dB re 1 μPa). The TTS onset value at f0 is 

therefore 180 dB re 1 μPa2s for the low-frequency cetaceans (Table A7). For the 

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sirenians, the lowest threshold was 61 dB re 1 μPa, making the onset TTS estimate 187 

dB re 1 μPa2s (Table A7). 

Table A7. Differences between composite threshold values (Fig. A5) and TTS onset values at 

the frequency of best hearing (f0) for the in-water marine mammal species groups. 

The values for the low-frequency cetaceans and sirenians were estimated using the 

median difference (126) from the MF, HF, OW, and PW groups. 

Group f0 

(kHz) 

Threshold 

at f0 

(dB re 1 μPa)

TTS onset 

at f0 

(dB re 1 μPa2s) 

Difference Estimated 

difference 

Estimated 

TTS onset at f0 

(dB re 1 μPa2s) 

LF 5.6 54 126 180 

MF 55 54 179 125 

HF 105 48 156 108 

SI 16 61 126 187 

OW 12 67 199 132 

PW 8.6 53 181 128 

Once K was determined, the weighted threshold for onset TTS was determined from the 

minimum value of the exposure function. Finally, the constant C was determined by 

substituting parameters a, b, f1, and f2 into Eq. (A1), then adjusting C so the maximum 

amplitude of the weighting function was 0 dB; this is equivalent to the difference 

between the weighted TTS threshold and K [see Eqs. (A3)–(A8)]. 

Table A8 summarizes the various function parameters, the weighted TTS thresholds, and 

the goodness of fit values between the TTS exposure functions and the onset TTS data. 

The various TTS exposure functions are presented in Figs. A17–A20. 

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Table A8. Weighting function and TTS exposure function parameters for use in Eqs. (A1) and 

(A2) for steady-state exposures. R2 values represent goodness of fit between 

exposure function and TTS onset data (Table A6). 

Group a b f1 

(kHz) 

f2 

(kHz) 

K 

(dB) 

C 

(dB) 

Weighted TTS 

threshold 

(dB SEL) 

R2 

LF 1 2 0.20 19 179 0.13 179 — 

MF 1.6 2 8.8 110 177 1.20 178 0.825 

HF 1.8 2 12 140 152 1.36 153 0.864 

SI 1.8 2 4.3 25 183 2.62 186 — 

OW 2 2 0.94 25 198 0.64 199 — 

PW 1 2 1.9 30 180 0.75 181 0.557 

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200 

---(/) 

N(U 180 

a_ 

::i. 

T""" 160 

Q) 

~ 

' ' ' 

LF 

' 

···' "·-···._ 

' 

MF HF 

a:l 140 ...... __._ .............................. .._ ...................................................... ..__ ................. .._ ................ ...._ ................................ ..__ ................. .._ ................ ..._ ......... 

~ 0.01 

+-' 

Q) 

(/) 

C 220 

0 

Cf) 

II- 200 

180 SI 

0.1 

0.1 1 10 

' • • . ......... .. . ······ ·· 

1 10 100 

10 100 

ow 

0.1 10 100 

frequency (kHz) 

10 100 

PW 

0.1 10 100 

--Exposure fun ction [Eq. (2)1 

- - Composite audiogram 

· ··· ·· Phase 2 exposure function 

• TTS onset data 

0 Estimated TTS onset 

Figure A17. Exposure functions (solid lines) generated from Eq. (A2) with the parameters 

specified in Table A7. Dashed lines — (normalized) composite audiograms used for 

definition of parameters a, f1, and f2. A constant value was added to each audiogram 

to equate the minimum audiogram value with the exposure function minimum. 

Short dashed line — Navy Phase 2 exposure functions for TTS onset for each group. 

Filled symbols — onset TTS exposure data (in dB SEL) used to define exposure 

function shape and vertical position. Open symbols — estimated TTS onset for 

species for which no TTS data exist. 

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7'1 T11 

210 

' ~ I 

--(/) I N .. I Schlund! 2000 

ro T Nachtigall 2003 

0.. 200 I 

~4.311  Nachtigall 2004 ::i () Finneran 2005 T""" I  Finneran 2007 (behav) 

Q) [>o,3, 

~ Finneran 2007 (AEP) L. I Mooney 2009a m 190 " Mooney 2009b '"O 

-- !I Finneran 201 Oa ..... Finneran 201 Ob Q) 

(/) <1 Popov 2011a 

c:: 180 • Finneran 2013 

0 I> Popov 2013 

Cf) 0 Popov 2014 (F) 

I- * Popov 2014 (M) 

I- 0 Popov 2015 170 - Exposure function 

• • • • Phase 2 function 

- - Composite audiogram 

160 

1 10 100 

frequency (kHz) 

Figure A18. Mid-frequency cetacean exposure function, (normalized) composite audiogram, and 

Phase 2 exposure functions compared to mid-frequency cetacean TTS data. Large 

symbols with no numeric values indicate onset TTS exposures. Smaller symbols 

represent specific amounts of TTS observed, with numeric values giving the amount 

(or range) or measured TTS. Filled and half-filled symbols — behavioral data. 

Open symbols — AEP data. 

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190 

-Cl') N 

C'Cl 

a.. 

::i 180 ..... 

Q) 

'--

en 

"O 

--...... 

Q) 

Cl') 

C: 

0 

Cf) 

~ 

........... 

170 

160 

150 

140 

0.5 

() 

..................... 

1 

i d sd o 

" 

ci35 cJ5 

030037<:Js 

cJ8 

... ... 

10 

frequency (kHz) 

cJ3 

cJ5 

0 Popov (2011) 

cJ5  Kastelein (2012a) 

* Kastelein (2013b) 

cJ3 T Kastelein (2014a) - 6.5 kHz 

i Kastelein (2014a) - 9.2 kHz 

<:JO Kastelein (2014b) . 100% 

() Kastelein (2014b) - 10% 

0 18 I [I Kastelein (2015a) - 100% 

<> Kastelein (2015a) - 10% 

-Exposure function 

• • • • Phase 2 function 

- - Composite aud iogram 

100 

Figure A19. High-frequency cetacean TTS exposure function, (normalized) composite 

audiogram, and Phase 2 exposure functions compared to high-frequency cetacean 

TTS data. Large symbols with no numeric values indicate onset TTS exposures. 

Smaller symbols represent specific amounts of TTS observed, with numeric values 

giving the amount (or range) or measured TTS. Filled and half-filled symbols — 

behavioral data. Open symbols — AEP data. 

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210 

en N 

ro 

a.. 

:::i.. 

T""" 

ID 200 I... 

ID 190 en 

C 

' 

0 •. 

Cl) 

II- 180 

170 

0.1 

' ' ' ' ' ' ' ' ' ' ' ' ' ' ' 

T SO+ 

.A 44 

1 10 

frequency (kHz) 

I 

I 

 Kastak 2005 

• Kaslele in 2012 (seal 01 ) 

I ? Kastele in 2012 (seal 02) 

I Kastele in 2013 

I ... Kastak 2008 

I 

I -Exposure function 

• • • • Phase 2 func tion 

- - Composite audiogram 

, , , , 

Figure A20. Phocid (underwater) exposure function, (normalized) composite audiogram, and 

Phase 2 exposure functions compared to phocid TTS data. Large symbols with no 

numeric values indicate onset TTS exposures. Smaller symbols represent specific 

amounts of TTS observed, with numeric values giving the amount (or range) or 

measured TTS. 

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X. PTS EXPOSURE FUNCTIO PTS EXPOSURE FUNCTIONS NS FOR SONARS FOR SONARS 

As in previous acoustic effects analyses (Southall et al., 2007; Finneran and Jenkins, 

2012), the shape of the PTS exposure function for each species group is assumed to be 

identical to the TTS exposure function for that group. Thus, definition of the PTS 

function only requires the value for the constant K to be determined. This equates to 

identifying the increase in noise exposure between the onset of TTS and the onset of PTS. 

For Phase 2, Navy used a 20-dB difference between TTS onset and PTS onset for 

cetaceans and a 14-dB difference for phocids, otariids, odobenids, mustelids, ursids, and 

sirenians (Finneran and Jenkins, 2012). The 20-dB value was based on human data (Ward 

et al., 1958) and the available marine mammal data, essentially following the 

extrapolation process proposed by Southall et al. (2007). The 14-dB value was based on a 

2.5 dB/dB growth rate reported by Kastak et al. (2007) for a California sea lion tested in 

air. 

For Phase 3, a difference of 20 dB between TTS onset and PTS onset is used for all 

species groups. This is based on estimates of exposure levels actually required for PTS 

(i.e., 40 dB of TTS) from the marine mammal TTS growth curves (Table 6), which show 

differences of 13 to 37 dB (mean = 24, median = 22, n = 9) between TTS onset and PTS 

onset in marine mammals. These data show most differences between TTS onset and PTS 

onset are larger than 20 dB and all but one value are larger than 14 dB. 

The value of K for each PTS exposure function and the weighted PTS threshold are 

therefore determined by adding 20 dB to the K-value for the TTS exposure function or 

the TTS weighted threshold, respectively (see Table A10). 

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XI. XI. TTS/PTS EXPOSURE FUN TTS/PTS EXPOSURE FUNCTIONS CTIONS FOR EXPLOSIVE FOR EXPLOSIVES S 

The shapes of the TTS and PTS exposure functions for explosives and other impulsive 

sources are identical to those used for sonars and other active acoustic sources (i.e., 

steady-state or non-impulsive noise sources). Thus, defining the TTS and PTS functions 

only requires the values for the constant K to be determined. 

Phase 3 analyses for TTS and PTS from underwater detonations and other impulsive 

sources follow the approach proposed by Southall et al. (2007) and used in Phase 2 

analyses (Finneran and Jenkins, 2012), where a weighted SEL threshold is used in 

conjunction with an unweighted peak SPL threshold. The threshold producing the greater 

range for effect is used for estimating the effects of the noise exposure. 

Peak SPL and SEL thresholds for TTS were based on TTS data from impulsive sound 

exposures that produced 6 dB or more TTS for the mid- and high-frequency cetaceans 

(the only groups for which data are available). The peak SPL thresholds were taken 

directly from the literature: 224 and 196 dB re 1 μPa, for the mid- and high-frequency 

cetaceans, respectively (Table A9). The SEL-based thresholds were determined by 

applying the Phase 3 weighting functions for the appropriate species groups to the 

exposure waveforms that produced TTS, then calculating the resulting weighted SELs. 

When this method is applied to the exposure data from Finneran et al. (2002) and Lucke 

et al. (2009), the SEL-based weighted TTS thresholds are 170 and 140 dB re 1 μPa2

s for 

the mid- and high-frequency cetaceans, respectively (Table A9). Note that the data from 

Lucke et al. (2009) are based on AEP measurements and may thus under-estimate TTS 

onset; however, they are used here because of the very limited nature of the impulse TTS 

data for marine mammals and the likelihood that the high-frequency cetaceans are more 

susceptible than the mid-frequency cetaceans (i.e., use of the mid-frequency cetacean 

value is not appropriate). Based on the limited available data, it is reasonable to assume 

that the exposures described by Lucke et al. (2009), which produced AEP-measured TTS 

of up to 20 dB, would have resulted in a behavioral TTS of at least 6 dB. 

The harbor porpoise data from Kastelein et al. (2015c) were not used to derive the highfrequency cetacean TTS threshold, since the largest observed TTS was only 4 dB. 

However, these data provide an opportunity to check the TTS onset proposed for the 

high-frequency cetacean group. Kastelein et al. (2015c) provide a representative 

frequency spectrum for a single, simulated pile driving strike at a specific measurement 

location. When the high-frequency cetacean weighting function is applied to this 

spectrum and the 1/3-octave SELs combined across frequency, the total weighted SEL 

for a single strike is found to be 114 dB re 1 μPa2

s. For 2760 impulses, the cumulative, 

weighted SEL would then be 148 dB re 1 μPa2s. The average SEL in the pool was 

reported to be 9 dB lower than the SEL at the measurement position, thus the average, 

cumulative weighted SEL would be approximately 139 dB re 1 μPa2s, which compares 

favorably to the high-frequency cetacean TTS threshold of 140 dB re 1 μPa2

s derived 

from the Lucke et al. (2009) air gun data. 

For species groups for which no impulse TTS data exist, the weighted SEL thresholds 

were estimated using the relationship between the steady-state TTS weighted threshold 

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C 

and the impulse TTS weighted threshold for the groups for which data exist (the mid- and 

high-frequency cetaceans): 

, (A11) 

where G indicates thresholds for a species group for which impulse TTS data are not 

available, indicates the median threshold for the groups for which data exist, the 

subscript s indicates a steady-state threshold, and the subscript i indicates an impulse 

threshold (note that since data are only available for the mid- and high-frequency 

cetaceans the median and mean are identical). Equation (A11) is equivalent to the 

relationship used by Southall et al. (2007), who expressed the relationship as 

. For the mid- and high-frequency cetaceans, the steady-state TTS 

thresholds are 178 and 153 dB re 1 μPa2s, respectively, and the impulse TTS thresholds 

are 170 and 140 dB re 1 μPa2s, respectively, making = 11 dB. Therefore, for each 

of the remaining groups the SEL-based impulse TTS threshold is 11 dB below the steadystate TTS threshold (Table A9). 

To estimate peak SPL-based thresholds, Southall et al. (2007) used Eq. (A11) with peakSPL values for the impulse thresholds and SEL-based values for the steady-state 

thresholds. For the mid- and high-frequency cetaceans, the steady-state (SEL) TTS 

thresholds are 178 and 153 dB re 1 μPa2s, respectively, and the peak SPL, impulse TTS 

thresholds are 224 and 196 dB re 1 μPa, respectively, making = -44 dB. Based on 

this relationship, the peak SPL-based impulse TTS threshold (in dB re 1 μPa) would be

44 dB above the steady-state TTS threshold (in dB re 1 μPa2s), making the peak SPL 

thresholds vary from 222 to 243 dB re 1 μPa. Given the limited nature of the underlying

data, and the relatively high values for some of these predictions, for Phase 3 analyses 

impulsive peak SPL thresholds are estimated using a “dynamic range” estimate based on 

the difference (in dB) between the impulsive noise, peak SPL TTS onset (in dB re 1 μPa)

and the hearing threshold at f0 (in dB re 1 μPa) for the groups for which data are available

(the mid- and high-frequency cetaceans). For the mid-frequency cetaceans, the hearing 

threshold at f0 is 54 dB re 1 μPa and the peak SPL TTS threshold is 224 dB re 1 μPa, 

resulting in a dynamic range of 170 dB. For the high-frequency cetaceans, the hearing 

threshold at f0 is 48 dB re 1 μPa and the peak SPL-based TTS threshold is 196 dB re 1 

μPa, resulting in a dynamic range of 148 dB. The median dynamic range for the mid- and 

high-frequency cetaceans is therefore 159 dB (since there are only two values, the mean 

and median are equal). For the remaining species groups, the impulsive peak SPL-based 

TTS thresholds are estimated by adding 159 dB to the hearing threshold at f0 (Table A9). 

Since marine mammal PTS data from impulsive noise exposures do not exist, onset-PTS 

levels for impulsive exposures were estimated by adding 15 dB to the SEL-based TTS 

threshold and adding 6 dB to the peak pressure based thresholds. These relationships 

were derived by Southall et al. (2007) from impulse noise TTS growth rates in 

chinchillas. The appropriate frequency weighting function for each functional hearing 

group is applied only when using the SEL-based thresholds to predict PTS. 

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Table A9. TTS and PTS thresholds for explosives and other impulsive sources. SEL thresholds 

are in dB re 1 μPa2

s and peak SPL thresholds are in dB re 1 μPa.

Group Hearing 

threshold at f0 

TTS 

threshold 

PTS 

threshold 

SPL 

(dB SPL) 

SEL (weighted) 

(dB SEL) 

peak SPL 

(dB SPL) 

SEL (weighted) 

(dB SEL) 

peak SPL 

(dB SPL) 

LF 54 168 213 183 219 

MF 54 170 224 185 230 

HF 48 140 196 155 202 

SI 61 175 220 190 226 

OW 67 188 226 203 232 

PW 53 170 212 185 218 

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XII. SUM ARY 

0 ,, .,, ...--.. 

co LF I. 

"O 

..__ 

Q) -20 

"O 

:::J 

-+-' 

Q. -40 E 

co 

-60 

0.01 0.1 1 10 100 0.1 1 10 100 

frequency (kHz) 

XII. SUMMARY 

Figure A21 illustrates the shapes of the various Phase 3 auditory weighting functions. 

Table A10 summarizes the parameters necessary to calculate the weighting function 

amplitudes using Eq. (A1). 

Figure A21. Navy Phase 3 weighting functions for marine mammal species groups exposed to 

underwater sound. Parameters required to generate the functions are provided in 

Table A10. 

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{ (/! J.)'° 

W(/) = C+IOlog,o [1+(/! 1.)'J[1+(/ 

Table A10. Summary of weighting function parameters and TTS/PTS thresholds. SEL 

thresholds are in dB re 1 μPa2

s and peak SPL thresholds are in dB re 1 μPa.

Non-impulsive Impulse 

TTS 

threshold 

PTS 

threshold 

TTS 

threshold 

PTS 

threshold 

Grou 

p 

a b f1 

(kHz) 

f2 

(kHz) 

C 

(dB) 

SEL 

(weighted) 

SEL 

(weighted) 

SEL 

(weighted) 

peak SPL 

(unweight 

ed) 

SEL 

(weighted 

) 

peak SPL 

(unweight 

ed) 

LF 1 2 0.20 19 0.13 179 199 168 213 183 219 

MF 1.6 2 8.8 110 1.20 178 198 170 224 185 230 

HF 1.8 2 12 140 1.36 153 173 140 196 155 202 

SI 1.8 2 4.3 25 2.62 186 206 175 220 190 226 

OW 2 2 0.94 25 0.64 199 219 188 226 203 232 

PW 1 2 1.9 30 0.75 181 201 170 212 185 218 

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To properly compare the TTS/PTS criteria and thresholds used by Navy for Phase 2 and 

Phase 3, both the weighting function shape and weighted threshold values must be taken 

into account; the weighted thresholds by themselves only indicate the TTS/PTS threshold 

at the most susceptible frequency (based on the relevant weighting function). Since the 

exposure functions incorporate both the shape of the weighting function and the weighted 

threshold value, they provide the best means of comparing the frequency-dependent 

TTS/PTS thresholds for Phase 2 and 3 (Figs A22 and A23). 

The most significant differences between the Phase 2 and Phase 3 functions include the 

following: 

(1) Thresholds at low frequencies are generally higher for Phase 3 compared to Phase 2. 

This is because the Phase 2 weighting functions utilized the “M-weighting” functions 

(Southall et al., 2007) at lower frequencies, where no TTS existed at that time. Since 

derivation of the Phase 2 thresholds, additional data have been collected (e.g., Kastelein 

et al., 2012a; Kastelein et al., 2013b; Kastelein et al., 2014b) to support the use of 

exposure functions that continue to increase at frequencies below the region of best 

sensitivity, similar to the behavior of mammalian audiograms and human auditory 

weighting functions. 

(2) In the frequency region near best hearing sensitivity, the Phase 3 underwater 

thresholds for otariids and other marine carnivores (group OW) are lower than those used 

in Phase 2. In Phase 2, the TTS onset for the otariids was taken directly from the 

published literature (Kastak et al., 2005); for Phase 3, the actual TTS data from Kastak et 

al. (2005) were fit by a TTS growth curve using identical methods as those used with the 

other species groups. 

(3) Impulsive TTS/PTS thresholds near the region of best hearing sensitivity are lower 

for Phase 3 compared to Phase 2. 

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180 

(/) 

N 

co 

'3_ 160 

LF 

Q) 

,._ 

CD 140 

,:, 0.01 

--_J 

w 

en 220 

200 

0.1 

' , -- - - -- - - - - 180 SI 

0.1 10 

10 

100 

·· ·· ·· ·~ . .: 

\ ~ 

MF 

1 10 100 

ow 

0.1 1 10 100 

frequency (kHz) 

1 10 100 

' 

PW 

0.1 10 100 

- - Phase 2 - TTS Exposure function 

· · · · · · Phase 2 - PTS Exposure function 

- Phase 3 - TTS Exposure function 

- Phase 3 - PTS Exposure function 

--

Figure A22. TTS and PTS exposure functions for sonars and other (non-impulsive) active 

acoustic sources. Heavy solid lines — Navy Phase 3 TTS exposure functions (Table 

A10). Thin solid lines — Navy Phase 3 PTS exposure functions for TTS (Table A10). 

Dashed lines — Navy Phase 2 TTS exposure functions. Short dashed lines — Navy 

Phase 2 PTS exposure functions. 

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180 

·· ·•······........ .//, ' ... ~ ,'/ ' I I ' -- , 

en 160 N 

ro 

a.. 

:::t 140 LF MF ~ 

Q} 

,_ 0.01 0.1 10 1 10 100 10 100 

co 220 -0 

--_J 

w 

en 

····· \ ·······•······· ···1 I 

', ·:·~ ,,/ 

200 

180 

SI ow 

160,__ ............... uL.-.................. -""L ...................... ___..~~ ............................... ..__ ............. c........ .................................................................................................... ..._ .... 

0.1 1 10 100 0. 1 1 10 100 

frequency (kHz) 

0.1 1 10 100 

- - Phase 2 - TTS Exposure function 

· · · · · · Phase 2 - PTS Exposure function 

- Phase 3 - TTS Exposure function 

- Phase 3 - PTS Exposure function 

Figure A23. TTS and PTS exposure functions for explosives, impact pile driving, air guns, and 

other impulsive sources. Heavy solid lines — Navy Phase 3 TTS exposure functions 

(Table A10). Thin solid lines — Navy Phase 3 PTS exposure functions for TTS 

(Table A10). Dashed lines — Navy Phase 2 TTS exposure functions. Short dashed 

lines — Navy Phase 2 PTS exposure functions. 

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APPENDIX A1. ESTIMATING A LOW-FREQUENCY CETACEAN 

AUDIOGRA 

APPENDIX A1. ESTIMATING A LOW-FREQUENCY CETACEAN 

AUDIOGRAM 

A1.1. BACKGROUND 

Psychophysical and/or electrophysiological auditory threshold data exist for at least one 

species within each hearing group, except for the low-frequency (LF) cetacean (i.e., 

mysticete) group, for which no direct measures of auditory threshold have been made. 

For this reason, an alternative approach was necessary to estimate the composite 

audiogram for the LF cetacean group. 

The published data sources available for use in estimating mysticete hearing thresholds 

consist of: cochlear frequency-place maps created from anatomical measurements of 

basilar membrane dimensions (e.g., Ketten, 1994; Parks et al., 2007); scaling 

relationships between inter-aural time differences and upper-frequency limits of hearing 

(see Ketten, 2000); finite element models of head-related and middle-ear transfer 

functions (Tubelli et al., 2012; Cranford and Krysl, 2015); a relative hearing sensitivity 

curve derived by integrating cat and human threshold data with a frequency-place map 

for the humpback whale (Houser et al., 2001); and measurements of the source levels and 

frequency content of mysticete vocalizations (see review by Tyack and Clark, 2000). 

These available data sources are applied here to estimate a mysticete composite 

audiogram. Given that these data are limited in several regards and are quite different 

from the type of data supporting composite audiograms in other species, additional 

sources of information, such as audiograms from other marine mammals, are also 

considered and applied to make conservative extrapolations at certain decision points. 

Mathematical models based on anatomical data have been used to predict hearing curves 

for several mysticete species (e.g., Ketten and Mountain, 2009; Cranford and Krysl, 

2015). However, these predictions are not directly used to derive the composite 

audiogram for LF cetaceans for two primary reasons: 

(1) There are no peer-reviewed publications that provide a complete description 

of the mathematical process by which frequency-place maps based on anatomical 

measurements were integrated with models of middle-ear transfer functions 

and/or other information to derive the predicted audiograms presented in several 

settings by Ketten/Mountain (e.g., Ketten and Mountain, 2009). As a result, the 

validity of the resulting predicted audiograms cannot be independently evaluated, 

and these data cannot be used in the present effort. 

(2) Exclusion of the Ketten/Mountain predicted audiograms leaves only the 

Cranford/Krysl predicted fin whale hearing curve (Cranford and Krysl, 2015). 

However, this curve cannot be used by itself to predict hearing thresholds for all 

mysticetes because: 

(a) The Cranford/Krysl model is based on sound transmission through the head 

to the ear of the fin whale, but does not include the sensory receptors of the 

cochlea. There is therefore no way to properly predict the upper cutoff of 

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( F 1 ( f 18 

T(f)=T +Alog ll+__1_j +l-J 

o rn f F2 

T(f) = T0 + L(f)+ H(f) 

hearing and the shape of the audiogram at frequencies above the region of best 

predicted sensitivity. 

(b) The audiogram does not possess the typical shape one would expect for an 

individual with normal hearing based on measurements from other mammals. 

Specifically, the “hump” in the low-frequency region and the shallow roll-off 

at high frequencies do not match patterns typically seen in audiometric data 

from other mammals with normal hearing. Given these considerations, the 

proposed audiogram cannot be considered representative of all mysticetes 

without other supporting evidence. Although the specific numeric thresholds 

from Cranford and Krysl (2015) are not directly used in the revised approach 

explained here, the predicted thresholds are still used to inform the LF 

cetacean composite audiogram derivation. 

Vocalization data also cannot be used to directly estimate auditory sensitivity and audible 

range, since there are many examples of mammals that vocalize below the frequency 

range where they have best hearing sensitivity, and well below their upper hearing limit. 

However, it is generally expected that animals have at least some degree of overlap 

between the auditory sensitivity curve and the predominant frequencies present in 

conspecific communication signals. Therefore vocalization data can be used to evaluate, 

at least at a general level, whether the composite audiogram is reasonable; i.e., to ensure 

that the predicted thresholds make sense given what we know about animal vocalization 

frequencies, source levels, and communication range. 

The realities of the currently available data leave only a limited amount of anatomical 

data and finite element modeling results to guide the derivation of the LF cetacean 

composite audiogram, supplemented with extrapolations from the other marine mammal 

species groups where necessary and a broad evaluation of the resulting audiogram in the 

context of whale bioacoustics. 

A1.2. AUDIOGRAM FUNCTIONAL FORM AND REQUIRED PARAMETERS 

Navy Phase 3 composite audiograms are defined by the equation 

, (A1.1) 

where T( f ) is the threshold at frequency f, and T0, F1, F2, A, and B are constants. To 

understand the physical significance and influence of the parameters T0, F1, F2, A, and B, 

Eq. (A1.1) may be viewed as the sum of three individual terms: 

, (A1.2) 

where 

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( Fl 

L(f)=Alog10 l 1+ j) 

(Fl 

L(f)=Alog10 l j) 

L(f) = Alog10 f; - Alog10 f 

, (A1.3) 

and 

. (A1.4) 

The first term, T0, controls the vertical position of the curve; i.e., T0 shifts the audiogram 

up and down. 

The second term, L(f ), controls the low-frequency behavior of the audiogram. At low 

frequencies, when f < F1, Eq. (A1.3) approaches 

, (A1.5) 

which can also be written as 

. (A1.6) 

Equation (A.6) has the form of y(x) = b - Ax, where x = log10f; i.e., Eq. (A.6) describes a 

linear function of the logarithm of frequency. This means that, as frequency gets smaller 

and smaller, Eq. (A.3) — the low-frequency portion of the audiogram function — 

approaches a linear function with the logarithm of frequency, and has a slope of ‐A 

dB/decade. As frequency increases towards F1, L(f ) asymptotically approaches zero. 

The third term, H(f ), controls the high-frequency behavior of the audiogram. At low 

frequencies, when f << F2, Eq. (A1.4) has a value of zero. As f increases, H(f ) 

exponentially grows. The parameter F2 defines the frequency at which the thresholds 

begin to exponentially increase, while the factor B controls the rate at which thresholds 

increase. Increasing F2 will move the upper cutoff frequency to the right (to higher 

frequencies). Increasing B will increase the “sharpness” of the high-frequency increase. 

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70 

60 

in 50 

H(f) 

"C 

"C -- 40 

0 

..c 30 en I 

(1) 

L.. I 

..c 20 +-' I 

10 I 

I ,, 0 ------------ -10 

0.01 0.1 1 10 

frequency (kHz) 

FIGURE A1.1. Relationship between estimated threshold, T(f), (thick, gray line), lowfrequency term, L(f), (solid line), and high-frequency term, H(f), (dashed 

line). 

A1.3. ESTIMATING AUDIOGRAM PARAMETERS 

To derive a composite mysticete audiogram using Eq. (A1.1), the values of T0, F1, F2, A, 

and B must be defined. The value for T0 is determined by either adjusting T0 to place the 

lowest threshold value to zero (to obtain a normalized audiogram), or to place the lowest 

expected threshold at a specific SPL (in dB re 1 μPa). For Navy Phase 3 analyses, the

lowest LF cetacean threshold is defined to match the median threshold of the in-water 

marine mammal species groups (MF cetaceans, HF cetaceans, sirenians, otariids and 

other marine carnivores in water, and phocids in water; median = 54 dB re 1 μPa). The

choices for the other parameters are informed by the published information regarding 

mysticete hearing. 

The constant A is defined by assuming a value for the low-frequency slope of the 

audiogram, in dB/decade. Most mammals for which thresholds have been measured have 

low-frequency slopes ~30 to 40 dB/decade. However, finite element models of middle 

ear function in fin whales (Cranford and Krysl, 2015) and minke whales (Tubelli et al., 

2012) suggest lower slopes, of ~25 or 20 dB/decade, respectively. We therefore 

conservatively assume that A = 20 dB/decade. 

To define F1, we first define the variable T′ as the maximum threshold tolerance within 

the frequency region of best sensitivity (i.e., within the frequency range of best 

sensitivity, thresholds are within T′ dB of the lowest threshold). Further, let f ′ be the

lower frequency bound of the region of best sensitivity. When f = f ′, L(f ) = T′, and Eq. 

(A1.3) can then be solved for F1 as a function of f ′, T′, and A: 

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~ = r(10T'/A_1) . (A1.7) 

Anatomically-based models of mysticete hearing have resulted in various estimates for 

audible frequency ranges and frequencies of best sensitivity. Houser et al. (2001) 

estimated best sensitivity in humpback whales to occur in the range of 2 to 6 kHz, with 

thresholds within 3 dB of best sensitivity from ~1.4 to 7.8 kHz. For right whales, Parks et 

al. (2007) estimated the audible frequency range to be 10 Hz to 22 kHz. For minke 

whales, Tubelli et al. (2012) estimated the most sensitive hearing range, defined as the 

region with thresholds within 40 dB of best sensitivity, to extend from 30 to 100 Hz up to 

7.5 to 25 kHz, depending on the specific model used. Cranford and Krysl (2015) 

predicted best sensitivity in fin whales to occur at 1.2 kHz, with thresholds within 3-dB 

of best sensitivity from ~1 to 1.5 kHz. Together, these model results broadly suggest best 

sensitivity (thresholds within ~3 dB of the lowest threshold) from ~1 to 8 kHz, and 

thresholds within ~40 dB of best sensitivity as low as ~30 Hz and up to ~25 kHz. 

Based on this information, we assume LF cetacean thresholds are within 3 dB of the 

lowest threshold over a frequency range of 1 to 8 kHz, therefore T′ = 3 dB and f ′= 1 

kHz, resulting in F1 = 0.41 kHz [Eq. (A1.7)]. In other words, we define F1 so that 

thresholds are ≤ 3 dB relative to the lowest threshold when the frequency is within the

region of best sensitivity (1 to 8 kHz). 

To define the high-frequency portion of the audiogram, the values of B and F2 must be 

estimated. To estimate B for LF cetaceans, we take the median of the B values from the 

composite audiograms for the other in-water marine mammal species groups (MF 

cetaceans, HF cetaceans, sirenians, otariids and other marine carnivores in water, and 

phocids in water). This results in B = 3.2 for the LF cetaceans. Once B is defined, F2 is 

adjusted to achieve a threshold value at 30 kHz of 40 dB relative to the lowest threshold. 

This results in F2 = 9.4 kHz. Finally, T0 is adjusted to set the lowest threshold value 

to 0 dB for the normalized curve, or 54 dB re 1 μPa for the non-normalized curve; 

this results in T0 = -0.81 and 53.19 for the normalized and non-normalized curves, 

respectively. 

The resulting composite audiogram is shown in Fig. A1.2. For comparison, predicted 

audiograms for the fin whale (Cranford and Krysl, 2015), and humpback whale (Houser 

et al., 2001) are included. The LF cetacean composite audiogram has lowest threshold at 

5.6 kHz, but the audiogram is fairly shallow in the region of best sensitivity, and 

thresholds are within 1 dB of the lowest threshold from ~1.8 to 11 kHz, and within 3 dB 

of the lowest threshold from ~0.75 to 14 kHz. Low-frequency (< ~500 Hz) thresholds 

are considerably lower than those predicted by Cranford and Krysl (2015). Highfrequency thresholds are also substantially lower than those predicted for the fin whale, 

with thresholds at 30 kHz only 40 dB above best hearing thresholds, and those at 40 

kHz approximately 90 dB above best threshold. The resulting LF composite audiogram 

appears reasonable in a general sense relative the predominant frequencies present in 

mysticete conspecific vocal communication signals. While some species (e.g., blue 

whales) produce some extremely low (e.g., 10 Hz) frequency call components, the 

majority of mysticete social calls occur in the few tens of Hz to few kHz range, 

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70 

60 

---

~ 50 --- . i:::::, . 0 40 

..c 

Cl) 

Q.) 

~ 30 

..c 

....... 

20 

10 

0 

0.01 

. 

. 

. . . 

proposed LF cetacean 

- - - - Cranford (2015)- fin 

- - Houser (2001 ) - humpback 

' --, , 

,. 

, 

' ' 

. 

. . . 

' ' 

' ' 

' ' ' ' ' ' 

, --.. , . 

I 

' 

0.1 1 

frequency (kHz) 

, 

' 

, ' 

' 

,·, 

I 

I 

I 

I 

' ,' I 

I 

I 

I 

I 

I 

I 

10 

overlapping reasonably well with the predicted auditory sensitivity shown in the 

composite audiogram (within ~0 to 30 dB of predicted best sensitivity). A general 

pattern of some social calls containing energy shifted below the region of best hearing 

sensitivity is well-documented in other low-frequency species including many phocid 

seals (see Wartzok and Ketten, 1999) and some terrestrial mammals, notably the Indian 

elephant (Heffner and Heffner, 1982). 

FIGURE A1.2. Comparison of proposed LF cetacean thresholds to those predicted by 

anatomical and finite-element models. 

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Tyack, P.L. and Clark, C.W. (2000). “Communication and acoustic behavior of dolphins and whales,” 

in Hearing by Whales and Dolphins, edited by W.W.L. Au, A.N. Popper, and R.R. Fay 

(Springer, New York), pp. 156-224. 

Ward, W.D. (1960). “Recovery from high values of temporary threshold shift,” J. Acoust. Soc. Am. 32, 

497-500. 

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Crocker (Wiley, New York, NY), pp. 1497-1507. 

Ward, W.D., Glorig, A., and Sklar, D.L. (1958). “Dependence of temporary threshold shift at 4 kc on 

intensity and time,” J. Acoust. Soc. Am. 30, 944-954. 

Ward, W.D., Glorig, A., and Sklar, D.L. (1959). “Temporary Threshold Shift from Octave-Band Noise: 

Applications to Damage-Risk Criteria,” J. Acoust. Soc. Am. 31, 522-528. 

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Mammals, edited by J.E. Reynolds and S.A. Rommel (Smithsonian Institution Press, 

Washington, DC). 

Wensveen, P.J., Huijser, L.A.E., Hoek, L., and Kastelein, R.A. (2014). “Equal latency contours and 

auditory weighting functions for the harbour porpoise (Phocoena phocoena),” J. Exp. Biol. 

217, 359-369. 

White, M.J., Norris, J., Ljungblad, D.K., Baron, K., and di Sciara, G.N. (1978). “Auditory thresholds of 

two beluga whales (Delphinapterus leucas),” (Hubbs Sea World Research Institute, San 

Diego). 

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APPENDIX B: RESEARCH RECOM ENDATIONS FOR I PROVED 

THRESHOLDS 

I. SUMMARY OF RESEARCH RECOMMENDATIONS 

APPENDIX B: RESEARCH RECOMMENDATIONS FOR IMPROVED 

THRESHOLDS 

In compiling, interpreting, and synthesizing the scientific literature to produce thresholds for this 

Technical Guidance, it is evident that additional data would be useful for future iterations of this 

document, since many data gaps still exist (Table B1). The need for the Technical Guidance to 

identify critical data gaps was also recommended during the initial peer review and public 

comment period. 

Table B1: Summary of currently available marine mammal data. 

Hearing Group 

Audiogram 

Data/Number of 

Species 

TTS 

Data/Number of 

Species 

Sound Sources for TTS Studies 

LF Cetaceans 

Predictive 

modeling/2 

species 

None/0 species None 

MF Cetaceans Behavioral/8 

species 

Behavioral/2 

species 

Octave-band noise; Tones; Midfrequency sonar; Explosion 

simulator; Watergun; Airgun 

HF Cetaceans Behavioral/2 

species 

Behavioral/1 

species 

Tones, Mid-frequency sonar; 

Impact pile driver; Airgun* 

PW Pinnipeds Behavioral/5 

species 

Behavioral/2 

species 

Octave-band noise; Impact pile 

driver 

OW Pinnipeds Behavioral/3 

species 

Behavioral/1 

species 

Octave-band noise; Arc-gap 

transducer 

* Data collected using AEP methodology (directly incorporated in Technical Guidance, since only data set available). 

Below is a list of research recommendations that NMFS believes would help address current data 

gaps. Some of these areas of recommended research have been previously identified in other 

publications/reports (e.g., NRC 1994; NRC 2000; Southall et al. 2007; Southall et al. 2009; 

Hawkins et al. 2014;38 Houser and Moore 2014; Lucke et al. 2014; Popper et al. 2014;39 Williams 

et al. 2014; Erbe et al. 2016; Lucke et al. 2016). Note: Just because there may not be enough 

information to allow for quantifiable modifications to thresholds associated with many of these 

recommendations, does not mean these recommendations cannot be incorporated as qualitative 

considerations within the comprehensive effects analysis. 

I. SUMMARY OF RESEARCH RECOMMENDATIONS 

1.1 LOW-FREQUENCY CETACEAN HEARING 

As previously stated, direct measurements of LF cetacean hearing are lacking. Therefore, 

hearing predictions for these species are based on other methods (e.g., anatomical studies, 

predictive models, vocalizations, taxonomy, and behavioral responses to sound). Thus, additional 

38 Although, Hawkins et al. 2014 identifies research gaps for fishes and invertebrates, many of the research 

recommendations can also be considered for other species, like marine mammals. 

39 Although, Popper et al. 2014 identifies research gaps for fishes and sea turtles, many of the research recommendations 

can also be considered for other species, like marine mammals. 

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data40 collected would be extremely valuable to furthering the understanding of hearing ability 

within this hearing group and validating other methods for approximating hearing ability. For 

example, data collected on either stranded or animals associated with subsistence hunts would 

be extremely useful in confirming current predictions of LF cetacean hearing ability and would 

allow for the development of more accurate auditory weighting functions (e.g., Do species that 

vocalize at ultra-low frequencies, like blue and fin whales, have dramatically different hearing 

abilities than other mysticete species?). Until direct measurements can be made, predictive 

models based on anatomical data will be the primary means of approximating hearing abilities, 

with validation remaining a critical component of any modeling exercise (e.g., Cranford and Krysl 

2014). 

1.2 HEARING DIVERSITY AMONG SPECIES AND AUDITORY PATHWAYS 

A better understanding of hearing diversity among species within a hearing group is also needed 

(e.g., Mooney et al. 2014) to comprehend how representative certain species (e.g., bottlenose 

dolphins, harbor porpoise, harbor seals) are of their hearing group as a whole. For example, are 

there certain species more susceptible to hearing loss from sound (i.e., all members of HF 

cetaceans), or are there additional delineations needed among the current hearing groups (e.g., 

deep diving species, etc.)? Having more data from species within a hearing group would also 

help identify if additional hearing groups are needed. This is especially the case for HF cetaceans 

where data are only available from four individuals of two species and those individuals have a 

lower hearing threshold compared to all other hearing groups. 

Additionally, having a more complete understanding of how sound enters the heads/bodies of 

marine mammals and its implication on hearing and impacts of noise among various species is 

another area of importance (e.g., bone conduction mechanism in mysticetes: Cranford and Krysl 

2015; previously undescribed acoustic pathways in odontocetes: Cranford et al. 2008; Cranford et 

al. 2010; filtering/amplification of transmission pathway: Cranford and Krysl 2012; directional 

hearing: Renaud and Popper 1975; Au and Moore 1984; Kastelein et al. 2005b). 

1.3 REPRESENTATIVENESS OF CAPTIVE INDIVIDUALS 

Data from Castellote et al. (2014), from free-ranging belugas in Alaska, indicate that of the seven 

healthy individuals tested (3 females/4 males; 1 subadult/6 adults), all had hearing abilities 

“similar to those of belugas measured in zoological settings.” Similarly, data from Ruser et al. 

(2017) reported that harbor porpoise live-stranded (15 individuals both males and females; 

subadults and adults) and wild individuals incidentally caught in pound nets (12 both males and 

females; subadult and adults) had “the shape of the hearing curve is generally similar to 

previously published results from behavioral trials.” Thus, from these studies, it appears that for 

baseline hearing measurements, captive individuals may be appropriate surrogates for freeranging animals. Additionally, Mulsow et al. (2011) measured aerial hearing abilities of seven 

stranded California sea lions and found a high degree of intersubject variability but that highfrequency hearing limits were consistent with previously tested captive individuals. However, 

these are currently the only studies of their kind,41 and more research is needed to examine if this 

trend is applicable to other species (Lucke et al. 2016). 

1.3.1 Impacts of Age on Hearing 

40 Data should be collected under appropriate permits or authorizations. 

41 NMFS is aware that additional baseline hearing measurements have been recorded for additional free-ranging belugas 

by Castellote et al. with the analysis still in process. Furthermore, NMFS is aware that audiogram (AEP) data are often 

obtained during marine mammal stranding events exists, but these have yet to be published. 

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Hearing loss can result from a variety of factors beyond anthropogenic noise, including exposure 

to ototoxic compounds (chemicals poisonous to auditory structures), disease and infection, and 

heredity, as well as a natural part of aging (Corso 1959; Kearns 1977; WGSUA 1988; Yost 2007). 

High-frequency hearing loss, presumably a normal process of aging that occurs in humans and 

other terrestrial mammals, has also been demonstrated in captive cetaceans (Ridgway and 

Carder 1997; Yuen et al. 2005; Finneran et al. 2005b; Houser and Finneran 2006; Finneran et al. 

2007b; Schlundt et al. 2011) and in stranded individuals (Mann et al. 2010). Thus, the potential 

impacts of age on hearing can be a concern when extrapolating from older to younger individuals. 

Few studies have examined this phenomenon in marine mammals, particularly in terms of the 

potential impact of aging on hearing ability and TSs: 

• Houser and Finneran (2006) conducted a comprehensive study of the hearing sensitivity 

of the U.S. Navy bottlenose dolphin population (i.e., tested 42 individuals from age four to 

47 years; 28 males/14 females). They found that high-frequency hearing loss typically 

began between the ages of 20 and 30 years. However, the frequencies where this 

species is most susceptible to noise-induced hearing loss (i.e., 10 to 30 kHz) are the 

frequencies where the lowest variability exists in mean thresholds between individuals of 

different ages. 

• Houser et al. (2008) measured hearing abilities of 13 Pacific bottlenose dolphins, ranging 

in age from 1.5 to 18 years. The authors’ reported that “Variability in the range of hearing 

and age-related reductions in hearing sensitivity and range of hearing were consistent 

with those observed in Atlantic bottlenose dolphins.” 

• Mulsow et al. (2014) examined aerial hearing thresholds for 16 captive sea lions, from 

age one to 26 years, and found that only the two 26-year old individuals had hearing 

classified as “aberrant” compared to other individuals (i.e., high-frequency hearing loss), 

which were deemed to have similar hearing abilities to previously measured individuals. 

• Additionally, for harbor seals, similar exposure levels associated with TTS onset were 

found in Kastelein et al. 2012a for individuals of four to five years of age compared to that 

used in Kastak et al. 2005, which was 14 years old and for belugas in Popov et al. 2014 

for an individual of 2 years of age compared to those used in Schlundt et al. 2000, which 

were 20 to 22 years old or 29 to 31 years old. 

From these limited data, it appears that age may not be a significant complicating factor, in terms 

of assessing TSs for animals of different ages. Nevertheless, additional data are needed to 

confirm if these data are representative for all species (Lucke et al. 2016). 

1.4 ADDITIONAL TTS MEASUREMENTS WITH MORE SPECIES AND/OR INDIVIDUALS 

Currently, TTS measurements only exist for four species of cetaceans (bottlenose dolphins, 

belugas, harbor porpoises, and Yangtze finless porpoise) and three species of pinnipeds 

(Northern elephant seal, harbor seal, and California sea lion). Additionally, the existing marine 

mammal TTS measurements are from a limited number of individuals within these species. 

Having more data from a broader range of species and individuals would be useful to confirm 

how representative current individuals are of their species and/or entire hearing groups (Lucke et 

al. 2016). For example, TTS onset thresholds for harbor porpoise (HF cetacean) are much lower 

compared to other odontocetes (MF cetaceans), and it would be useful to know if all HF 

cetaceans share these lower TTS onset thresholds or if harbor porpoises are the exception. 

Measured underwater hearing of two captive spotted seals (Sills et al. 2014) and two captive 

ringed seals (Sills et al. 2015) found these species’ hearing abilities are comparable to harbor 

seals. Thus, harbor seals, where TTS data are available, are an appropriate surrogate for ice seal 

species. As more data become available, this assumption will be re-evaluated. 

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Finally, cetaceans are often used as surrogates for pinnipeds when no direct data exist. Having 

more information on the appropriateness of using cetaceans as surrogates for pinnipeds would 

be useful (i.e., Is there another mammalian group more appropriate?). 

1.5 SOUND EXPOSURE TO MORE REALISTIC SCENARIOS 

Most marine mammal TTS measurements are for individuals exposed to a limited number of 

sound sources (i.e., mostly tones and octave-band noise42) in laboratory settings. Measurements 

from exposure to actual sound sources (opposed to tones or octave-band noise) under more 

realistic exposure conditions (e.g., more realistic exposure durations and/or scenarios, including 

multiple pulses/pile strikes and at frequencies below 1 kHz where most anthropogenic noise 

occurs) are needed. 

1.5.1 Frequency and Duration of Exposure 

In addition to received level, NMFS recognizes that other factors, such as frequency and duration 

of exposure, are also important to consider within the context of PTS onset thresholds (Table B2). 

However, there are not enough data to establish numerical thresholds based on these added 

factors (beyond what has already been included in this document, in terms of marine mammal 

auditory weighting functions and SELcum thresholds). When more data become available, it may 

be possible to incorporate these factors into quantitative assessments. 

Further, it has been demonstrated that exposure to lower-frequency broadband sounds has the 

potential to cause TSs at higher frequencies (e.g., Lucke et al. 2009; Kastelein et al. 2015a; 

Kastelein et al. 2016). The consideration of duty cycle (i.e., energy per unit time) is another 

important consideration in the context of exposure duration (e.g., Kastelein et al. 2015b). Having 

a better understanding of these phenomena would be helpful. 

1.5.2 Multiple Sources 

Further, a better understanding of the effects of multiple sources and multiple activities on TS, as 

well as impacts from long-term exposure is needed. Studies on terrestrial mammals indicate that 

exposure scenarios from complex exposures (i.e., those involving multiple types of sound 

sources) result in more complicated patterns of NIHL (e.g., Ahroon et al. 1993). 

42 More recent studies (e.g., Lucke et al. 2009; Mooney et al. 2009b; Kastelein et al. 2014a; Kastelein et al. 2014b; 

Kastelein et al. 2015a; Kastelein et al. 2015b; Finneran et al. 2015; Kastelein et al. 2016; Kastelein et al. 2017b; Kastelein 

et al. 2017c) have used exposures from more realistic sources, like airguns, impact pile drivers, or tactical sonar. 

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Table B2: Additional factors for consideration (frequency and duration of exposure) 

in association with PTS onset thresholds. 

I. Frequency*: 

General Trend Identified: 

1) Growth of TS: Growth rates of TS (dB of TTS/dB noise) are higher for frequencies 

where hearing is more sensitive (e.g., Finneran and Schlundt 2010; Finneran and 

Schlundt 2013; Kastelein et al. 2014a; Kastelein et al. 2015b) 

II. Duration: 

General Trends Identified: 

1) Violation of EEH: Non-impulsive, intermittent exposures require higher SELcum to 

induce a TS compared to continuous exposures of the same duration (e.g., Mooney et 

al. 2009a; Finneran et al. 2010b; Kastelein et al. 2014a) 

2) Violation of EEH: Exposures of longer duration and lower levels induce a TTS at a 

lower level than those exposures of higher level (below the critical level) and shorter 

duration with the same SELcum (e.g., Kastak et al. 2005; Kastak et al. 2007; Mooney et 

al. 2009b; Finneran et al. 2010a; Kastelein et al. 2012a; Kastelein et al. 2012b) 

3) Recovery from a TS: With the same SELcum, longer exposures require longer durations 

to recover (e.g., Mooney et al. 2009b; Finneran et al. 2010a) 

4) Recovery from a TS: Intermittent exposures recover faster compared to continuous 

exposures of the same duration (e.g., Finneran et al. 2010b; Kastelein et al. 2014a; 

Kastelein et al. 2015b) 

III. Cumulative Exposure: 

General Trend Identified: 

1) Animals may be exposed to multiple sound sources and stressors, beyond acoustics, 

during an activity, with the possibility of the possibility of additive or synergistic effects 

(e.g., Sih et al. 2004; Rohr et al. 2006; Chen et al. 2007; Lucke et al. 2016; NRC 2016) 

* Frequency-dependent hearing loss and overall hearing ability within a hearing group is taken into account, 

quantitatively, with auditory weighting functions. 

1.5.3 Possible Protective Mechanisms 

Nachtigall and Supin (2013) reported that a false killer whale was able to reduce its hearing 

sensitivity (i.e., conditioned dampening of hearing) when a loud sound was preceded by a 

warning signal. Nachtigall and Supin (2014) reported a similar finding in a bottlenose dolphin, a 

beluga (Nachtigall et al. 2016a), and in harbor porpoises (Nacthigall et al. 2016b). Further studies 

showed that conditioning is associated with the frequency of the warning signal (Nachtigall and 

Supin 2015), as well as if an animal is able to anticipate when a loud sound is expected to occur 

after a warning signal (Nachtigall et al. 2016c). 

Additionally, Finneran et al. (2015) observed two of the three dolphins in their study displayed 

“anticipatory” behavior (e.g., head movement) during an exposure sequence to multiple airgun 

shots. It is unknown if this behavior resulted in some mitigating effects of the exposure. Popov et 

al. (2016) investigated the impact of prolonged sound stimuli (i.e., 1500 s continuous pip 

successions vs. 500-msec pip trains) on the beluga auditory system and found that auditory 

adaptation occurred during exposure (i.e., decrease in amplitude of rate following response 

associated with evoked potentials) at levels below which TTS onset would likely be induced. The 

amount of amplitude reduction depended on stimulus duration, with higher reductions occurring 

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during prolonged stimulation. The authors also caution that adaptation will vary with sound 

parameters. Finneran (2018) confirmed that bottlenose dolphins can “self mitigate” when warned 

of an upcoming exposure and that mechanism for this mitigation occurs in the cochlea or auditory 

nerve. 

In the wild, potential protective mechanisms have been observed, with synchronous surfacing 

associated with exposure to playbacks of tactical sonar recorded in long-finned pilot whales 

(Miller et al. 2012). However, it is unclear how effective this behavior is in reducing received 

levels (Wensveen et al. 2015). 

Thus, marine mammals may have multiple means of reducing or ameliorating the effects noise 

exposure. However, at this point, directly incorporating them into a comprehensive effects 

analysis that anticipates the likelihood of exposure ahead of an activity is difficult. More 

information on these mechanisms, especially associated with real-world exposure scenarios, 

would be useful. 

1.5.4 Long-Term Consequences of Exposure 

Kujawa and Liberman (2009) found that with large, but recoverable noise-induced thresholds 

shifts (maximum 40 dB TS measured by auditory brainstem response (ABR)), sound could cause 

delayed cochlear nerve degeneration in mice. Further, Lin et al. (2011) reported a similar pattern 

of neural degeneration in mice after large but recoverable noise-induced TSs (maximum ~50 dB 

TS measured by ABR), which suggests a common phenomenon in all mammals. The long-term 

consequences of this degeneration remain unclear. 

Another study reported impaired auditory cortex function (i.e., behavioral and neural 

discrimination of sound in the temporal domain (discriminate between pulse trains of various 

repetition rates)) after sound exposure in rats that displayed no impairment in hearing (Zhou and 

Merzenich 2012). Zheng (2012) found reorganization of the neural networks in the primary 

auditory cortex (i.e., tonotopic map) of adult rats exposed to low-level noise, which suggests an 

adaptation to living in a noisy environment (e.g., noise exposed rats performed tasks better in 

noisy environment compared to control rats). Heeringa and van Dijk (2014) reported firing rates in 

the inferior colliculus of guinea pigs had a different recovery pattern compared to ABR thresholds. 

Thus, it is recommended that there be additional studies to look at these potential effects in 

marine mammals (Tougaard et al. 2015). 

Finally, it is also important to understand how repeated exposures resulting in TTS could 

potentially lead to PTS (e.g., Kastak et al. 2008; Reichmuth 2009). For example, occupational 

noise standards, such as those from the Occupational Safety & Health Administration (OSHA), 

consider the impact of noise exposure over a lifetime of exposure (e.g., 29 CFR Part 1926 over 

40 years). Similar, longer-term considerations are needed for marine mammals. 

1.6 IMPACTS OF NOISE-INDUCED THRESHOLD SHIFTS ON FITNESS 

When considering noise-induced thresholds shifts, it is important to understand that hearing is 

more than merely the mechanical process of the ear and neural coding of sound (detection). It 

also involves higher processing and integration with other stimuli (perception) (Yost 2007; Alain 

and Berstein 2008). Currently, more is known about the aspects of neural coding of sounds 

compared to the higher-level processing that occurs on an individual level. 

Typically, effects of noise exposure resulting in energetic (Williams et al. 2006; Barber et al. 2010) 

and fitness consequences (increased mortality or decreased reproductive success) are deemed 

to have the potential to affect a population/stock (NRC 2005; Southall et al. 2007; SMRU Marine 

2014) or as put by Gill et al. 2001 “From a conservation perspective, human disturbance of 

wildlife is important only if it affects survival or fecundity and hence causes a population to 

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decline.” The number of individuals exposed and the location and duration of exposure are 

important factors, as well. To determine whether a TS will result in a fitness consequence 

requires one to consider several factors. 

First, one has to consider the likelihood an individual would be exposed for a long enough 

duration or to a high enough level to induce a TS (e.g., realistic exposure scenarios). Richardson 

et al. (1995) hypothesized that “Disturbance effects are likely to cause most marine mammals to 

avoid any ‘zone of discomfort or nonauditory effects’ that may exist” and that “The greatest risk of 

immediate hearing damage might be if a powerful source were turned on suddenly at full power 

while a mammal was nearby.” It is uncertain how frequently individuals in the wild are 

experiencing situations where TSs are likely from individual sources (Richardson et al.1995; Erbe 

and Farmer 2000; Erbe 2002; Holt 2008; Mooney et al. 2009b). 

In determining the severity of a TS, it is important to consider the magnitude of the TS, time to 

recovery (seconds to minutes or hours to days), the frequency range of the exposure, the 

frequency range of hearing and vocalization for the particular species (i.e., how animal uses 

sound in the frequency range of anthropogenic noise exposure; e.g., Kastelein et al. 2014b), and 

their overlap (e.g., spatial, temporal, and spectral). Richardson et al. (1995) noted, “To evaluate 

the importance of this temporary impairment, it would be necessary to consider the ways in which 

marine mammals use sound, and the consequences if access to this information were impaired.” 

Thus, exposure to an anthropogenic sound source, may affect individuals and species differently 

(Sutherland 1996). 

Finally, different degrees of hearing loss exist: ranging from slight/mild to moderate and from 

severe to profound (Clark 1981), with profound loss being synonymous with deafness (CDC 

2004; WHO 2015). For hearing loss in humans, Miller (1974) summarized “any injury to the ear or 

any change in hearing threshold level that places it outside the normal range constitutes a 

hearing impairment. Whether a particular impairment constitutes a hearing handicap or a hearing 

disability can only be judged in relation to an individual’s life pattern or occupation.” This 

statement can translate to considering effects of hearing loss in marine mammals, as well (i.e., 

substituting “occupation” for “fitness”). 

Simply because a hearing impairment may be possible does not necessarily mean an individual 

will experience a disability in terms of overall fitness consequence. However, there needs to be a 

better understanding of the impacts of repeated exposures. As Kight and Swaddle (2011) indicate 

“Perhaps the most important unanswered question in anthropogenic noise research – and in 

anthropogenic disturbance research, in general – is how repeated exposure over a lifetime 

cumulatively impacts an individual, both over the short- (e.g. condition, survival) and long- (e.g., 

reproductive success) term.” Thus, more research is needed to understand the true 

consequences of noise-induced TSs (acute and chronic) to overall fitness. 

1.7 BEHAVIOR OF MARINE MAMMALS UNDER EXPOSURE CONDITIONS WITH THE POTENTIAL TO 

CAUSE HEARING IMPACTS 

Although assessing the behavioral response of marine mammals to sound is outside the scope of 

this document, understanding these reactions, especially in terms of exposure conditions having 

the potential to cause NIHL is critical to be able to predict exposure better. Understanding marine 

mammal responses to anthropogenic sound exposure presents a set of unique challenges, which 

arise from the inherent complexity of behavioral reactions. Responses can depend on numerous 

factors, including intrinsic, natural extrinsic (e.g., ice cover, prey distribution), or anthropogenic, as 

well as the interplay among factors (Archer et al. 2010). Behavioral reactions can vary not only 

among individuals but also within an individual, depending on previous experience with a sound 

source, hearing sensitivity, sex, age, reproductive status, geographic location, season, health, 

social behavior, or context. 

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Severity of behavioral responses can also vary depending on characteristics associated with the 

sound source (e.g., whether it is moving or stationary, number of sound sources, distance from 

the source) or the potential for the source and individuals to co-occur temporally and spatially 

(e.g., persistence or recurrence of the sound in specific areas; how close to shore, region where 

animals may be unable to avoid exposure, propagation characteristics that are either enhancing 

or reducing exposure) (Richardson et al. 1995; NRC 2003; Wartzok et al. 2004; NRC 2005; 

Southall et al. 2007; Bejder et al. 2009). 

Further, not all species or individuals react identically to anthropogenic sound exposure. There 

may be certain species-specific behaviors (e.g., fight or flight responses; particularly behaviorally 

sensitive species) that make a species or individuals of that species more or less likely to react to 

anthropogenic sound. Having this information would be useful in improving the recommended 

accumulations period (i.e., 24 h) and understanding situations where individuals are more likely to 

be exposed to noise over longer durations and are more at risk for NIHL, either temporary or 

permanent. 

1.8 CHARACTERISTICS OF SOUND ASSOCIATED WITH NIHL AND IMPACTS OF PROPAGATION 

It is known as sound propagates through the environment various physical characteristics change 

(e.g., frequency content with lower frequencies typically propagating further than higher 

frequencies; pulse length due to reverberation or multipath propagation in shallow and deep 

water). Having a better understanding of the characteristics of a sound that makes it injurious 

(e.g., peak pressure amplitude, rise time, pulse duration, etc.; Henderson and Hamernik 1986; 

NIOSH 1998) and how those characteristics change under various propagation conditions would 

be extremely helpful in the application of appropriate thresholds and be useful in supporting a 

better understanding as to how sounds could possess less injurious characteristics further from 

the source (e.g., transition range). 

Further, validation and/or comparison of various propagation and exposure models for a variety of 

sources would be useful to regulators, who with thresholds that are more complex will be faced 

with evaluating the results from a multitude of models. This would also allow for a more complete 

comparison to the methodologies provided in this Technical Guidance. This would allow for a 

determination of how precautionary these methodologies are under various scenarios and allow 

for potential refinement. 

1.9 NOISE-INDUCED THRESHOLD SHIFT GROWTH RATES AND RECOVERY 

TS growth rate data for marine mammals are limited, with higher growth rates for frequencies 

where hearing is more sensitive (Finneran and Schlundt 2010; Finneran and Schlundt 2013; 

Kastelein et al. 2015b). Understanding how these trends vary with exposure to more complex 

sound sources (e.g., broadband impulsive sources) and among various species would be 

valuable. 

Understanding recovery after sound exposure is also an important consideration. Currently, there 

is a lack of recovery data for marine mammals, especially for exposure to durations and levels 

expected under real-world scenarios. Thus, additional marine mammal noise-induced recovery 

data would be useful. A better understanding of likely exposure scenarios, including the potential 

for recovery, including how long after noise exposure recovery is likely to occur, could also 

improve the recommended baseline accumulation period. 

1.10 METRICS AND TERMINOLOGY 

Sound can be described using a variety of metrics, with some being more appropriate for certain 

sound types or effects compared with others (e.g., Coles et al. 1968; Hamernik et al. 2003; 

Madsen 2005; Davis et al. 2009; Zhu et al. 2009). A better understanding of the most appropriate 

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metrics for establishing thresholds and predicting impacts to hearing would be useful in 

confirming the value of providing dual metric thresholds using the PK and weighted SELcum 

metrics for impulsive sources. As science advances, additional or more appropriate metrics may 

be identified and further incorporated by NMFS. However, caution is recommended when 

comparing sound descriptions in different metrics (i.e., they are not directly comparable). 

Additionally, the practicality of measuring and applying metrics is another important consideration. 

Further, the Technical Guidance’s thresholds are based on the EEH, which is known to be 

inaccurate in some situations. Popov et al. 2014 suggested that RMS SPL multiplied by log 

duration better described their data than the EEH. Thus, better means of describing the 

interaction between SPL and duration of exposure would be valuable. 

Finally, in trying to define metrics and certain terms (e.g., impulsive and non-impulsive) within the 

context of the Technical Guidance, NMFS often found difficulties due to lack of universally 

accepted standards and common terminology. Within the Technical Guidance, NMFS has tried to 

adopt terminology, definitions, symbols, and abbreviations that reflect those of the American 

National Standards Institute (ANSI) or more appropriately the more recent International 

Organization for Standardization (ISO)43. Thus, NMFS encourages the further development of 

appropriate standards for marine application. 

1.11 EFFECTIVE QUIET 

“Effective quiet” is defined as the maximum sound pressure level that will fail to produce any 

significant TS in hearing despite duration of exposure and amount of accumulation (Ward et al. 

1976; Ward 1991). Effective quiet can essentially be thought of as a “safe exposure level” (i.e., 

risks for TS are extremely low or nonexistent) in terms of hearing loss44 (Mills 1982; NRC 1993) 

and is frequency dependent (Ward et al. 1976; Mills 1982). Effective quiet is an important 

consideration for the onset TTS and PTS thresholds expressed by the weighted SELcum metric 

because if not taken into consideration unrealistically low levels of exposure with long enough 

exposure durations could accumulate to exceed current weighted SELcum thresholds, when the 

likelihood of an actual TS is extremely low (e.g., humans exposed to continuous levels of normal 

speech levels throughout the day are not typically subjected to TTS from this type of exposure). 

Currently, defining effective quiet for marine mammals is not possible due to lack of data. 

However, a study by Popov et al. 2014 on belugas exposed to half-octave noise centered at 22.5 

kHz indicates that effective quiet for this exposure scenario and species might be around 154 dB. 

In Finneran’s (2015) review of NIHL in marine mammals, effective quiet is predicted to vary by 

species (e.g., below 150 to 160 dB for bottlenose dolphins and belugas; below 140 dB for 

Yangtze finless porpoise; 124 dB for harbor porpoise; and 174 dB for California sea lions). 

As more data become available, they would be useful in contributing to the better understanding 

of appropriate accumulations periods for the weighted SELcum metric and NIHL, as well as the 

potential of low-level (e.g., Coping et al. 2014; Schuster et al. 2015), continuously operating 

sources (e.g., alternative energy tidal, wave, or wind turbines) to induce noise-induced hearing 

loss. 

43 This version (2.0) of Technical Guidance is more reflective of ISO 18405 (ISO 2017). ISO 18405 is the preferred 

standard because it was developed specifically for underwater acoustics, compared with standards developed for airborne 

acoustics that use different conventions. 

44 Note: “Effective quiet” only applies to hearing loss and not to behavioral response (i.e., levels below “effective quiet” 

could result in behavioral responses). It also is separate consideration from defining “quiet” areas (NMFS 2009). 

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1.12 TRANSLATING BIOLOGICAL COMPLEXITY INTO PRACTICAL APPLICATION 

Although, not a specific research recommendation, practical application of science is an important 

consideration. As more is learned about the potential effects of sound on marine mammals, the 

more complex future thresholds are likely to become. For example, before the 2016 Technical 

Guidance, NMFS primarily relied on two generic thresholds for assessing auditory impacts, with 

one for cetaceans (SPL RMS 180 dB) and one for pinnipeds (SPL RMS 190 dB). In this 

document, these two simple thresholds have now been replaced by ten PTS onset thresholds 

(with dual metrics for impulsive sounds), including the addition of auditory weighting functions. 

Although, these thresholds better represent the current state of knowledge, they have created 

additional challenges for implementation. Practical application always needs to be weighed 

against making thresholds overly complicated (cost vs. benefit considerations). The creation of 

tools to help ensure action proponents, as well as managers apply complex thresholds correctly, 

is a critical need. 

Additionally, there is always a need for basic, practical acoustic training opportunities for action 

proponents and managers (most acoustic classes available are for students within an academic 

setting and not necessarily those who deal with acoustics in a more applied manner). Having the 

background tools and knowledge to be able to implement the Technical Guidance is critical to this 

document being a useful and effective tool in assessing the effects of noise on marine mammal 

hearing. 

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APPENDIX C: TECHNICAL GUIDANCE REVIEW PROCESSES: PEER 

REVIEW, PUBLIC CO ME T, AND REVIEW U DER 

EXECUTIVE ORDER 13795 

I. PEER REVIEW PROCESS 

APPENDIX C: TECHNICAL GUIDANCE REVIEW PROCESSES: PEER 

REVIEW, PUBLIC COMMENT, AND REVIEW UNDER 

EXECUTIVE ORDER 13795 

The Technical Guidance (NMFS 2016a) before its finalization in 2016 went through several 

stages of peer review and public comment. Additionally, this document underwent further review 

under E0 13795. 

I. PEER REVIEW PROCESS 

The President’s Office Management and Budget (OMB 2005) states, “Peer review is one of the 

important procedures used to ensure that the quality of published information meets the 

standards of the scientific and technical community. It is a form of deliberation involving an 

exchange of judgments about the appropriateness of methods and the strength of the author’s 

inferences. Peer review involves the review of a draft product for quality by specialists in the field 

who were not involved in producing the draft.” 

The peer review of this document was conducted in accordance with NOAA’s Information Quality 

Guidelines45 (IQG), which were designed for “ensuring and maximizing the quality, objectivity, 

utility, and integrity of information disseminated by the agency” (with each of these terms defined 

within the IQG). Further, the IQG stipulate that “To the degree that the agency action is based on 

science, NOAA will use (a) the best available science and supporting studies (including peerreviewed science and supporting studies when available), conducted in accordance with sound 

and objective scientific practices, and (b) data collected by accepted methods or best available 

methods.” Under the IQG and in consistent with OMB’s Final Information Quality Bulletin for Peer 

Review (OMB Peer Review Bulletin (OMB 2005), the Technical Guidance was considered a 

Highly Influential Scientific Assessments (HISA),46 and peer review was required before it could 

be disseminated by the Federal Government. OMB (2005) notes “Peer review should not be 

confused with public comment and other stakeholder processes. The selection of participants in a 

peer review is based on expertise, with due consideration of independence and conflict of 

interest.” 

The peer review of the Technical Guidance (NMFS 2016a) consisted of three independent 

reviews covering various aspects of the document: 1) There was an initial peer review of the 

entire draft Guidance in 2013, 2) a second peer review in March/April 2015 that focused on 

newly available science from the Finneran Technical Report (Finneran 2016; See Appendix A), 

and 3) a third peer review in April 2015 in response to public comments received during the initial 

public comment period, which focused on a particular technical section relating to the proposed 

application of impulsive and non-impulsive PTS onset thresholds based on physical 

characteristics at the source and how those characteristics change with range.47 Upon completion 

of the three peer reviews, NMFS was required to post and respond to all peer reviewer comments 

received via three separate Peer Review Reports. 

45 NOAA's Information Quality Guidelines. 

46 “Its dissemination could have a potential impact of more than $500 million in any one year on either the public or private 

sector; or that the dissemination is novel, controversial, or precedent-setting; or that it has significant interagency interest” 

(OMB 2005). The Technical Guidance is not a regulatory action subject to a cost-benefit analysis under Executive 

Orders12866 and 13563. The Technical Guidance was classified as a HISA because it was novel and precedent setting, 

not due to the potential financial implications. 

47 Note: Upon evaluation of public comment received during the Technical Guidance’s second public comment period 

(July 2015), NMFS decided to postpone implementing this methodology until more data were available to support its use. 

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1.1 2013 INITIAL PEER REVIEW (ASSOCIATED WITH 2013 DRAFT GUIDANCE) 

For the initial peer review of this document (July to September 2013), potential qualified peer 

reviewers were nominated by a steering committee put together by the MMC. The steering 

committee consisted of MMC Commissioners and members of the Committee of Scientific 

Advisors (Dr. Daryl Boness, Dr. Douglas Wartzok, and Dr. Sue Moore). 

Nominated peer reviewers were those with expertise marine mammalogy, acoustics/bioacoustics, 

and/or acoustics in the marine environment. Of the ten nominated reviewers, four volunteered, 

had no conflicts of interest, had the appropriate area of expertise,48 and were available to 

complete an individual review (Table C1). The focus of the peer review was on the 

scientific/technical studies that have been applied and the manner that they have been applied in 

this document. 

Table C1: Initial peer review panel. 

Name Affiliation 

Dr. Paul Nachtigall University of Hawaii 

Dr. Doug Nowacek Duke University 

Dr. Klaus Lucke* Wageningen University and Research (The Netherlands) 

Dr. Aaron Thode Scripps Institution of Oceanography 

* Present affiliation: Curtin University (Australia). 

Peer reviewers’ comments and NMFS’ responses to the comments, from this initial peer review, 

can be found at: Link to Technical Guidance's Peer Review Plan. 

1.2 2015 SECOND PEER REVIEW (REVIEW OF THE FINNERAN TECHNICAL REPORT) 

For their Phase 3 Acoustic Effects Analysis, the U.S. Navy provided NMFS with a technical 

report, by Dr. James Finneran, describing their proposed methodology for updating auditory 

weighting functions and subsequent numeric thresholds for predicting auditory effects (TTS/PTS 

thresholds) on marine animals exposed to active sonars, other (non-impulsive) active acoustic 

sources, explosives, pile driving, and air guns utilized during Navy training and testing activities. 

Upon evaluation, NMFS preliminarily determined that the proposed methodology, within the 

Finneran Technical Report (Finneran 2016), reflected the scientific literature and decided to 

incorporate it into the Technical Guidance. Before doing so, we commissioned an independent 

peer review of the Finneran Technical Report (i.e. second peer review). Note: Reviewers were 

not asked to review the entire Technical Guidance document. 

For the second peer review (March to April 2015), NMFS again requested the assistance of the 

MMC to nominate peer reviewers. As with the initial peer review, potential qualified peer 

reviewers were nominated by a steering committee put together by the MMC, which consisted of 

MMC Commissioners and members of the Committee of Scientific Advisors (Dr. Daryl Boness, 

Dr. Douglas Wartzok, and Dr. Sue Moore). 

Nominated peer reviewers were those with expertise49 specifically in marine mammal hearing 

(i.e., behavior and/or AEP) and/or noise-induced hearing loss. Of the twelve nominated 

48 Reviewer credentials are posted at: Link to Technical Guidance's Peer Review Plan. 

49 Reviewer credentials are posted at: Link to Technical Guidance's Peer Review Plan. 

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reviewers, four volunteered, had not conflicts of interest, had the appropriate area of expertise, 

and were available to complete an individual review of the Finneran Technical Report (Table C2). 

Table C2: Second peer review panel. 

Name Affiliation 

Dr. Whitlow Au University of Hawaii 

Dr. Colleen Le Prell University of Florida* 

Dr. Klaus Lucke Curtin University (Australia) 

Dr. Jack Terhune University of New Brunswick (Canada) 

*Affiliation during initial review (Affiliation during follow-up peer review: The University of Texas at Dallas. 

Peer reviewers’ comments and NMFS’ responses to the comments, from the second peer review, 

can be found at: Link to Technical Guidance's Peer Review Plan. 

1.2.1 2016 Follow-Up to Second Peer Review 

Concurrent with the Technical Guidance’s third public comment period (see Section 2.3 of this 

appendix), a follow-up peer review was conducted. The focus of this peer review was whether the 

2016 Proposed Changes to the Technical Guidance, associated with the third public comment 

period, would substantially change any of the peer reviewers’ comments provided during their 

original review (i.e., peer reviewers were not asked to re-review the Finneran Technical Report). 

Additionally, peer reviewers were not asked to comment on any potential policy or legal 

implications of the application of the Technical Guidance, or on the amount of uncertainty that is 

acceptable or the amount of precaution that should be embedded in any regulatory analysis of 

impacts. 

All four previous peer reviewers were available to perform the follow-up peer review. Peer 

reviewers’ comments and NMFS’ responses to the comments, from this follow-up peer review, 

can be found at: Link to Technical Guidance's Peer Review Plan. 

1.3 2015 THIRD PEER REVIEW (REVIEW OF TRANSITION RANGE METHODOLOGY) 

During the Technical Guidance’s initial public comment period, NMFS received numerous 

comments relating to how the Technical Guidance classifies acoustic sources based on 

characteristics at the source (i.e., non-impulsive vs. impulsive). Many expressed concern that as 

sound propagates through the environment and eventually reaches a receiver (i.e., marine 

mammal) that physical characteristics of the sound may change and that NMFS’ categorization 

may not be fully reflective of real-world scenarios. Thus, NMFS re-evaluated its methodology for 

categorizing sound sources to reflect these concerns. Thus, a third peer review focused on 

particular technical section relating to the Technical Guidance's proposed application of impulsive 

and non-impulsive PTS onset thresholds based on physical characteristics at the source and how 

those characteristics change with range (i.e., transition range). Note: Reviewers were not asked 

to review the entire Technical Guidance document. 

Since the focus of the third peer review was focused on the physical changes a sound 

experiences as it propagates through the environment, the Acoustical Society of America’s 

Underwater Technical Council was asked to nominate peer reviewers with expertise in 

underwater sound propagation and physical characteristics of impulsive sources, especially high 

explosives, seismic airguns, and/or impact pile drivers. Of the six nominated reviewers, two 

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II. PUBLIC CO MENT PERIODS 

volunteered, were available, had no conflicts of interest, and had the appropriate area of 

expertise50 to complete an individual review of the technical section (Table C3). 

Additionally, NMFS wanted peer reviewers with expertise in marine and terrestrial mammal noiseinduced hearing loss to review this technical section and ensure the proposed methodology was 

ground-truthed in current biological knowledge. Thus, NMFS re-evaluated peer reviewer 

nominees previously made by the MMC for the first and second peer reviews. From this list, two 

reviewers volunteered, were available, had no conflicts of interest, and had the appropriate area 

of expertise to serve as peer reviewers (Table C3). 

Table C3: Third peer review panel. 

Name Affiliation 

Dr. Robert Burkard University at Buffalo 

Dr. Peter Dahl* University of Washington 

Dr. Colleen Reichmuth+ University of California Santa Cruz 

Dr. Kevin Williams* University of Washington 

* Peer reviewers with expertise in underwater acoustic propagation. 

+ Dr. Reichmuth was an alternate on the MMC original peer reviewer nomination list. 

Peer reviewers’ comments and NMFS’ responses to the comments, from the third peer review, 

can be found at: Link to Technical Guidance's Peer Review Plan. 

Note: In response to public comments made during the second public comment period, NMFS 

decided to withdraw its proposed transition range methodology until more data can be collected 

to better support this concept (i.e., see Appendix B: Research Recommendations). 

1.4 CONFLICT OF INTEREST DISCLOSURE 

Each peer reviewer (i.e., initial, second, and third peer review) completed a conflict of interest 

disclosure form. It is essential that peer reviewers of NMFS influential scientific information (ISI) 

or HISA not be compromised by any significant conflict of interest. For this purpose, the term 

“conflict of interest” means any financial or other interest which conflicts with the service of the 

individual because it (1) could significantly impair the individual's objectivity or (2) could create an 

unfair competitive advantage for any person or organization. No individual can be appointed to 

review information subject to the OMB Peer Review Bulletin if the individual has a conflict of 

interest that is relevant to the functions to be performed. 

The following website contains information on the peer review process including: the charge to 

peer reviewers, peer reviewers’ names, peer reviewers’ individual reports, and NMFS’ response 

to peer reviewer reports. 

II. PUBLIC COMMENT PERIODS 

In addition to the peer review process, NMFS recognizes the importance of feedback from action 

proponents/stakeholders and other members of the public. The focus of the public comment 

process was on both the technical aspects of the document, as well as the implementation of the 

science in NMFS’ policy decisions under the various applicable statutes. The first two public 

50 Reviewer Credentials. 

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comment periods were held after the peer review to ensure the public received the most 

scientifically sound product for review and comment. A third public focused comment period was 

held after incorporation of recommendations made by NMFS and Navy scientists (SSC-PAC) 

during further evaluation of the Finneran Technical Report after the second public comment 

period. During this third public comment period, there was a concurrent follow-up peer review. 

See section 1.2.1 above. 

2.1 2013/2014 INITIAL PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2013 DRAFT TECHNICAL 

GUIDANCE) 

A public meeting/webinar was held to inform interested parties and solicit comments on the first 

publicly available version of the Draft Technical Guidance. The meeting/webinar was held on 

January 14, 2014, in the NOAA Science Center in Silver Spring, Maryland. The presentation and 

transcript from this meeting is available electronically. 

This public comment period was advertised via the Federal Register and originally lasted 30 

days, opening on December 27, 2013 (NMFS 2013). During this 30-day period, multiple groups 

requested that the public comment period be extended beyond 30 days. Thus, the public 

comment period was extended an additional 45 days and closed on March 13, 2014 (NMFS 

2014). 

2.1.1 Summary of Public Comments Received 

A total of 12951 comments were received from individuals, groups, organizations, and affiliations. 

Twenty-eight of these were in the form of a letter, spreadsheet, or individual comment submitted 

by representatives of a group/organization/affiliation (some submitted on behalf of an organization 

and/or as an individual). Those commenting included: 11 members of Congress; eight 

state/federal/international government agencies; two Alaskan native groups; seven industry 

groups; five individual subject matter experts; a scientific professional organization; 12 nongovernmental organizations; an environmental consulting firm; and a regulatory watchdog group. 

Each provided substantive comments addressing technical aspects or issues relating to the 

implementation of thresholds, which were addressed in the Final Technical Guidance or related 

Federal Register Notice.52 

Of those not mentioned above, an additional 101 comments were submitted in the form of a letter 

or individual comment. Twelve of these comments specifically requested an extension of the 

original 30-day public comment period (a 45-day extension to original public comment period was 

granted). The remaining 89 comments were not directly applicable to the Technical Guidance 

(e.g., general concern over impacts of noise on marine mammals from various industry or military 

activities) and were not further addressed. Specific comments can be viewed on Regulations.gov. 

NMFS’ responses to substantive comments made during the initial public comment period were 

published in the Federal Register located on the following web site in conjunction with the Final 

Technical Guidance. 

51 Of this number, one comment was directed to the Federal Communications Commission (i.e., not meant for the 

Technical Guidance) and one commenter submitted their comments twice. In addition, one comment was not included in 

this total, nor posted because it contained threatening language. 

52 With the updates made to the Technical Guidance as a result of the second and third peer reviews, some of the 

comments made during the initial public comment period were no longer relevant and as such were not addressed. 

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2.2 2015 SECOND PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2015 DRAFT TECHNICAL 

GUIDANCE) 

Because of the significant changes made to the Draft Technical Guidance from the two additional 

peer reviews, NMFS proposed a second 45-day public comment, which occurred in the summer 

of 2015. Notice of this public comment period was published in the Federal Register on July 31, 

2015, and closed September 14, 2015 (NMFS 2015). 

2.2.1 Summary of Public Comments Received 

A total of 20 comments were received from individuals, groups, organizations, and affiliations in 

the form of a letter or individual comment submitted by representatives of a 

group/organization/affiliation (some submitted on behalf of an organization and/or as an 

individual). Those commenting included: two federal agencies; four industry groups; seven 

subject matter experts; a scientific professional organization; seven non-governmental 

organizations; two Alaskan native groups; an environmental consulting firm; and a regulatory 

watchdog group. Each provided substantive comments addressing technical aspects and/or 

issues relating to the implementation of thresholds, which were addressed in the Final Technical 

Guidance or related Federal Register Notice. 

Of those not mentioned above, an additional four comments were submitted in the form of a letter 

or individual comment. One of these comments specifically requested an extension of the 45-day 

public comment period, while the remaining three comments were not directly applicable to the 

Technical Guidance (e.g., general concern over impacts of noise on marine mammals from 

various industry or military activities) and were not further addressed. Specific comments can be 

viewed on Regulations.gov. 

NMFS responses to substantive comments made during the second public comment period were 

published in the Federal Register located on the following web site in conjunction with the Final 

Technical Guidance: Link to Technical Guidance web page. 

2.3 2016 THIRD PUBLIC COMMENT PERIOD (ASSOCIATED WITH 2016 PROPOSED CHANGES FROM 

DRAFT TECHNICAL GUIDANCE)53 

While NMFS was working to address public comments and finalize the Technical Guidance, after 

the second public comment period, the Finneran Technical Report was further evaluated 

internally by NMFS, as well as externally by Navy scientists (SSC-PAC). As a result, several 

recommendations/modifications were suggested. 

The recommendations included: 

• Modification of methodology to establish predicted the composite audiogram and 

weighting/exposure functions for LF cetaceans 

• Modification of the methodology used to establish thresholds for LF cetaceans 

• Movement of the white-beaked dolphin (Lagenorhynchus albirostris) from MF to HF 

cetaceans54 

53 Concurrent with this third public comment period, NMFS requested that the peer reviewers of the Finneran Technical 

Report review the Draft Technical Guidance’s proposed changes and indicate if the revisions would significantly alter any 

of the comments made during their original review (i.e., follow-up to second peer review). 

54 Upon re-evaluation and considering comments made during the third public comment period, it was decided this move 

was not fully supported (i.e., move not supported to the level of that of the other two species in this family). Thus, this 

species remains a MF cetacean. 

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• Inclusion of a newly published harbor porpoise audiogram (HF cetacean) from Kastelein 

et al. 2015c 

• The exclusion of multiple data sets, based on expert evaluation, from the phocid pinniped 

auditory weighting function 

• Removal of PK thresholds for non-impulsive sounds 

• Use of dynamic range to predict PK thresholds for hearing groups where impulsive data 

did not exist. 

After consideration of these recommendations, NMFS proposed to update the Draft Technical 

Guidance to reflect these suggested changes and solicited public comment on the revised 

sections of the document via a focused 14-day public comment period. This public comment 

period was advertised via the Federal Register and opened on March 16, 2016, and closed 

March 30, 2016 (NMFS 2016b). 

2.3.1 Summary of Public Comments Received 

A total of 2055 comments were received from individuals, groups, organizations, and affiliations in 

the form of a letter or individual comment submitted by representatives of a 

group/organization/affiliation (some submitted on behalf of an organization and/or as an 

individual). Those commenting included: two federal agencies; seven industry groups; three 

subject matter experts; a scientific professional organization; and nine non-governmental 

organizations. Each provided substantive comments addressing technical aspects and/or issues 

relating to the implementation of thresholds, which were addressed in the Final Technical 

Guidance or related Federal Register Notice. 

Of those not mentioned above, an additional comment was submitted from a member of the 

public in the form of an individual comment. Three of these comments specifically requested an 

extension56 of the 14-day public comment period. Specific comments can be viewed on 

Regulations.gov. 

NMFS responses to substantive comments made during the third public comment period were 

published in the Federal Register located on the following web site in conjunction with the Final 

Technical Guidance. 

2.4 CHANGES TO TECHNICAL GUIDANCE AS A RESULT OF PUBLIC COMMENTS 

Public comment provided NMFS with valuable input during the development of the Technical 

Guidance. As a result of public comments, numerous changes were incorporated in the Final 

Technical Guidance, with the most significant being: 

• Re-examination and consideration of LF auditory weighting function and thresholds 

throughout the public comment process 

55 One group of commenters had trouble in submitting their public comments via regulations.gov. As a result, their 

duplicate comments were submitted three times and were counted toward this total of 20 public comments. 

56 The majority of the 20 comments received requested an extension of the public comment period. Three comments were 

from industry groups that only requested an extension and never provided additional comments (i.e., others in additional 

to requesting an extension provided substantive comments). 

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Ill. REVIEW UNDER EXECUTIVE ORDER 13795 

• Updated methodology (dynamic range) for approximating PK thresholds for species 

where TTS data from impulsive sources were not available 

• Removal of PK thresholds for non-impulsive sources 

• Addition of an appendix providing research recommendations 

• Adoption of a consistent accumulation period (24-h) 

• More consistent means of defining generalized hearing range for each marine mammal 

hearing group based on ~65 dB threshold from the normalized composite audiogram. 

• Modification to reflect ANSI standard symbols and abbreviations. 

• Withdraw of the proposed transition range methodology (July 2015 Draft) until more data 

can be collected to better support this concept. Instead, this concept has been moved to 

Research Recommendations (Appendix B). 

• Replacement of alternative thresholds with weighting factor adjustments (WFAs) that 

more accurately allow those incapable of fully implementing the auditory weighting 

functions to implement this concept (Technical Guidance; Appendix D). 

III. REVIEW UNDER EXECUTIVE ORDER 13795 

Presidential Executive Order (EO) 13795, Implementing an America-First Offshore Energy 

Strategy (82 FR 20815; April 28, 2017), stated in section 2 that “It shall be the policy of the United 

States to encourage energy exploration and production, including on the Outer Continental Shelf, 

in order to maintain the Nation’s position as a global energy leader and foster energy security and 

resilience for the benefit of the American people, while ensuring that any such activity is safe and 

environmentally responsible.” Section 10 of the EO called for a review of the 2016 Technical 

Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing 

(Technical Guidance; NMFS 2016a) as follows: “The Secretary of Commerce shall review 

[Technical Guidance] for consistency with the policy set forth in Section 2 of this order and, after 

consultation with the appropriate Federal agencies, take all steps permitted by law to rescind or 

revise that guidance, if appropriate.” 

3.1 REVIEW OF 2016 TECHNICAL GUIDANCE UNDER EO 13795 

3.1.1 2017 Public Comment Period 

To assist the Secretary in carrying out that directive under EO 13795, NMFS held a 45-day public 

comment period (82 FR 24950; May 31, 2017) to solicit comments on the Technical Guidance 

(NMFS 2016a) for consistency with the EO’s policy. 

3.1.1.1 Summary of Comments Received 

NMFS received 62 comments directly related to the 2016 Technical Guidance.57 Comments were 

submitted by Federal agencies (Bureau of Ocean Energy Management (BOEM), U.S. Navy, 

57 NMFS received an additional 137 comments during the Technical Guidance’s public comment period relating to an 

overlapping public comment period for “Takes of Marine Mammals Incidental to Specified Activities; Taking Marine 

Mammals Incidental to Geophysical Surveys in the Atlantic Ocean” (82 FR 26244). Thus, the majority (approximately 

70%) of public comments NMFS received during the Technical Guidance’s public comment period related to the proposed 

action of oil and gas activity in the Atlantic. 

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MMC), oil and gas industry representatives, Members of Congress, subject matter experts, nongovernmental organizations, a foreign statutory advisory group, a regulatory advocacy group, and 

members of the public (Table C4). 

Table C4: Summary of commenters 

Commenter 

Category Specific Commenter 

U.S. Federal 

agencies 

Bureau of Ocean Energy Management; Marine Mammal Commission; 

U.S. Navy 

Members of 

Congress* 22 members 

Oil & gas industry 

representatives 

American Petroleum Institute/International Association of Geophysical 

Contractors/Alaska Oil and Gas Association/National Ocean Industries 

Association 

Non-Governmental 

Organization 

Natural Resources Defense Council/The Human Society of the 

US/Whale and Dolphin Conservation; Ocean Conservation Research 

Regulatory advocacy 

group Center for Regulatory Effectiveness 

Foreign statutory 

advisor Group Joint Nature Conservation Committee 

Subject matter 

experts (SME) Marine scientist/mammologist; Geophysicist/Geochemist; Acoustician 

General public 47 members 

; indicates separate comments, while / indicates comments submitted together. 

* Letter sent directly to Secretary Ross (i.e., not submitted to Regulations.gov). 

Most of the comments (85%) recommended no changes to the Technical Guidance, and no 

public commenter suggested rescinding the Technical Guidance. The U.S. Navy, Marine Mammal 

Commission, Members of Congress, and subject matter experts expressed support for the 

Technical Guidance’s thresholds and weighting functions as reflecting the best available science. 

The remaining comments (15%) focused on additional scientific publications for consideration or 

recommended revisions to improve implementation of the Technical Guidance. All public 

comments received during this review can be found at: Regulations.gov. 

3.1.2 2017 Federal Interagency Consultation 

Further, to assist the Secretary in carrying out the directive under EO 13795, NMFS invited, via 

letter, 15 Federal agencies to participate in an in-person meeting (i.e., Interagency Consultation) 

on September 25, 2017, at NMFS Headquarters in Silver Spring, Maryland, to serve as a formal 

forum to discuss this document and provide additional comments. Ten of the eleven58 expected 

Federal agencies participated in this meeting (Table C5). 

58 The U.S Fish & Wildlife Service, U.S. Coast Guard, and The U.S. Environmental Protection Agency declined NMFS’ 

invitation to participate. U.S. Department of Energy did not reply. 

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Table C5: Ten Federal agency attendees* 

Bureau of Ocean Energy Management National Science Foundation 

Department of State U.S. Air Force 

Federal Highway Administration U.S. Army Corps of Engineers 

Marine Mammal Commission U.S. Geological Survey+ 

National Park Service U.S. Navy 

*Bureau of Safety and Environmental Enforcement did not attend. 

+USGS participated via webinar/teleconference. 

3.1.2.1 Summary of Interagency Comments 

At the Federal Interagency Consultation, none of the Federal agencies recommended rescinding 

the Technical Guidance. Federal agencies were supportive of the Technical Guidance’s 

thresholds and auditory weighting functions and the science behind their derivation and were 

appreciative of the opportunity to provide input. Comments received at the meeting focused on 

improvements to implementation of the Technical Guidance and recommendations for future 

working group discussions to address implementation of the Technical Guidance based on any 

new scientific information as it becomes available. 

3.2 REVISIONS TO THE 2016 TECHNICAL GUIDANCE AS A RESULT OF REVIEW UNDER EO 13795 

NMFS acknowledges the importance of supporting sustainable ocean use, such as energy 

exploration and production on the Outer Continental Shelf, provided activities are conducted in a 

safe and environmentally responsible manner. Our development and implementation of the 

Technical Guidance are consistent with allowing activities vital to our nation’s security and 

economy to proceed, including those mentioned in EO 13795, and allows for decisions to be 

made based upon the best available information. 

The EO 13795 review process provided NMFS the opportunity to acquire valuable feedback from 

the public/stakeholders and Federal agencies on the 2016 Technical Guidance and its 

implementation, since its finalization. During both NMFS’ public comment period and Federal 

Interagency Consultation, neither the public/stakeholders nor Federal agencies recommended the 

2016 Technical Guidance (NMFS 2016a) be rescinded. Most comments were supportive of the 

thresholds and auditory weighting functions within 2016 Technical Guidance. Of those providing 

comments, most offered recommendations for improving the clarity of the document and 

facilitating implementation. 

During both the public comment period and the Federal Interagency Consultation, three key topic 

areas were raised: (1) the limited scientific data on the impacts of sound on LF cetacean hearing; 

(2) the need to determine the accumulation period for all species of marine mammals; and (3) the 

need to improve the 2016 Technical Guidance’s optional User Spreadsheet tool. Commenters 

also encouraged the agency to establish working groups to address these data gaps and future 

needs. 

NMFS’ evaluation of comments received during this process affirms that the Technical Guidance 

is based on the best available science. Nevertheless, based on consideration of comments 

received and per the approval of the Secretary of Commerce, NMFS made the following revisions 

to the 2016 Technical Guidance and/or companion User Spreadsheet tool to improve 

implementation and facilitate its use by action proponents, thereby further advancing the policy in 

section 2 of EO. 13795 (as reflected in this 2018 Technical Guidance, Version 2.0): 

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• To promote a more realistic assessment of the potential impacts of sound on marine 

mammal hearing, using the Technical Guidance, NMFS will re-evaluate implementation 

of the default 24-h accumulation period and plans to convene a working group later in 

2018 to investigate means for deriving more realistic accumulation periods. 

• To understand further the impacts of sound on hearing of LF cetaceans, a marine 

mammal group where no direct data on hearing exists, NMFS plans to convene a 

working group later in 2018 to explore this topic. NMFS will incorporate any changes that 

may result from the working group’s efforts in future updates to the Technical Guidance. 

• NMFS created a new User Manual for NMFS’ User Spreadsheet tool that provides 

detailed instructions and examples on how to use this optional tool. This new User 

Manual (NMFS 2018) is available at: Link to Technical Guidance web page. NMFS plans 

to submit the User Manual for public comment later in 2018 to gain input from 

stakeholders and inform future versions of the User Manual. 

• NMFS issued an updated optional User Spreadsheet tool to provide PTS onset isopleths 

associated with the Technical Guidance’s PK thresholds associated with impulsive 

sources, so action proponents will not have to perform this calculation separately. The 

modified version (Version 2.0) of the optional User Spreadsheet tool is available at: Link 

to Technical Guidance web page. 

• NMFS issued an updated optional User Spreadsheet tool to include a custom sheet for 

vibratory pile driving activities to facilitate the ease of assessing PTS onset for this 

commonly used sound source. Custom tabs for multiple and single 

explosives/detonations were also added to the updated optional User Spreadsheet tool. 

These custom tabs, within the optional User Spreadsheet tool (Version 2.0), are available 

at: Link to Technical Guidance web page. 

• NMFS summarized and conducted a preliminary analysis of the relevant scientific 

literature published since the 2016 Technical Guidance’s finalization (Section 3.1.1). 

• NMFS modified the Technical Guidance threshold’s symbols and glossary to be more 

reflective of the International Organization for Standardization (ISO) 2017 Underwater 

Acoustics – Terminology standard (ISO 18405), which was specifically developed for 

underwater acoustics. 

• Appendix A has been updated to include the Navy’s finalized version (Technical Report 

3026, December 2016) of their Technical Report that NMFS used to derive the Technical 

Guidance’s thresholds and auditory weighting functions. 

• To increase understanding of how regulatory programs use and recommend the use of 

the Technical Guidance, which would facilitate implementation and thereby further 

advance the Policy in section 2 of EO 13795, NMFS is developing a separate document 

describing how the Technical Guidance is used in the MMPA incidental take authorization 

process to estimate “take” and inform mitigation decisions.. This document, once 

available, will be found at: Link to Incidental Take Authorization web page. 

Note: Several comments received during both the public comment period and Federal 

Interagency Consultation were beyond the scope of the Technical Guidance and/or its review 

under section 10 of EO 13795. However, NMFS is evaluating these recommendations and 

determining the best way to address them via other means outside this review. 

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APPENDIX D: ALTERNATIVE ETHODOLOGY 

I. INTRODUCTION 

II. WEIGHTI G FACTOR ADJUSTMENT ASSOCIATED WITH SELcu THRESHOLDS 

APPENDIX D: ALTERNATIVE METHODOLOGY 

I. INTRODUCTION 

This Appendix is provided to assist action proponents in the application of thresholds presented in 

this Technical Guidance. Since the adoption of NMFS’ original thresholds for assessing auditory 

impacts (i.e., RMS SPL: 180 dB for cetaceans; 190 dB for pinnipeds), the understanding of the 

effects of noise on marine mammal hearing has greatly advanced (e.g., Southall et al. 2007; 

Finneran 2015; Finneran 2016) making it necessary to re-examine the current state of science 

and our thresholds. However, NMFS recognizes in updating our thresholds to reflect the scientific 

literature, they have become more complex. 

This Appendix provides a set of alternative tools, examples, and weighting factor adjustments 

(WFAs) to allow action proponents with different levels of exposure modeling capabilities to be 

able to apply NMFS’ thresholds for the onset of PTS for all sound sources. These tools are 

incorporated in NMFS’ optional User Spreadsheet tool, with examples provided in the recently 

developed User Spreadsheet Manual (NMFS 2018)59. 

There is no obligation to use the optional User Spreadsheet tool, and the use of more 

sophisticated exposure modeling or consideration of additional action- or location-specific factors, 

if possible, is encouraged. 

II. WEIGHTING FACTOR ADJUSTMENT ASSOCIATED WITH SELCUM THRESHOLDS 

Numerical criteria presented in the Technical Guidance consist of both an acoustic threshold and 

auditory weighting function associated with the SELcum metric. NMFS recognizes that the 

implementation of marine mammal auditory weighting functions represents a new factor for 

consideration, which may extend beyond the capabilities of some action proponents. Thus, NMFS 

has developed simple weighting factor adjustments (WFA) for those who cannot fully apply 

auditory weighting functions associated with the SELcum metric. 

WFAs consider marine mammal auditory weighting functions by focusing on a single frequency. 

This will typically result in similar, if not identical, predicted exposures for narrowband sounds or 

higher predicted exposures for broadband sounds, since only one frequency is being considered, 

compared to exposures associated with the ability to fully incorporate the Technical Guidance’s 

auditory weighting functions. 

WFAs use the same thresholds contained in the Technical Guidance and allow adjustments to be 

made for each hearing group based on source-specific information. 

NMFS has provided a companion User Spreadsheet tool and User Manual for the User 

Spreadsheet tool to help action proponents incorporate WFAs to determine isopleths for PTS 

onset associated with their activity: Link to Technical Guidance web page. 

2.1 APPLICATION FOR NARROWBAND SOUNDS 

For narrowband sources, the selection of the appropriate frequency for consideration associated 

with WFAs is straightforward. WFAs for a narrowband sound would take the auditory weighting 

59 The most recent version of the optional User Spreadsheet tool and companion User Manual (NMFS 2018) is available 

at: Link to Technical Guidance web page. 

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function amplitude, for each hearing group, associated with the particular frequency of interest 

and use it to make an adjustment to reflect the hearing’s group susceptibility to that narrowband 

sound. 

As an example, a 1 kHz narrowband sound would result in the following WFAs: 

• LF cetaceans: -0.06 dB 

• MF cetaceans: -29.11 dB 

• HF cetaceans: -37.55 dB 

• Phocid pinnipeds: -5.90 dB 

• Otariid pinnipeds: -4.87 dB 

As this example illustrates, WFAs always result in zero or a negative dB amplitude. Additionally, 

the more a sound’s frequency is outside a hearing group’s most susceptible range (most 

susceptible range is where the weighting function amplitude equal zero), the more negative WFA 

that results (i.e., in example above 1 kHz is outside the most susceptible range for MF and HF 

cetaceans but in the most susceptible range for LF cetaceans; Figure D1). Further, the more 

negative WFA that results will lead to a smaller effect distance (isopleth) compared to a less 

negative or zero WFA. In other words, considering an identical weighted SELcum acoustic 

threshold, a more negative WFA (i.e., source outside most susceptible frequency range) will 

result in a smaller effect distance (isopleth) compared to one that is less negative or closer to 

zero (i.e., source inside most susceptible frequency range; Figure D2). 

Note: NMFS reminds action proponents to be aware and consider that sources may not always 

adhere to manufacturer specifications and only produce sound within the specified frequency 

(i.e., often sources are capable of producing sounds, like harmonics and subharmonics, outside 

their specified bands; Deng et al. 2014; Hastie et al. 2014). If it is unclear whether a source is 

narrowband or not, please consult with NMFS. 

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0 

,__ 

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ti 

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0/J -SO 

~ 

-10 

-20 

-30 

-40 . 

. 

-50 

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. 

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. 

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. . 

. 

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. . . . . . . . . . 

WiFA 

WFA 

10 

Frequency (kHz) 

100 

- LF 

- MF 

• • • HF 

- otariid 

• • • Ph ocid 

Figure D1: Example illustrating concept of weighting factor adjustment at 1 kHz (solid 

red line) with cetacean (top) and pinniped (bottom) auditory weighting 

functions. 

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' 

I \ 

I - } \ / ' -... 

MF cetacean isopleth : 1.2 m 

LF cetacean isopleth: 30 m 

Figure D2: Simple example illustrating concept of weighting factor adjustment on 

isopleths for LF and MF cetaceans using hypothetical 1 kHz narrowband, 

intermittent source represented by the red dot (RMS source level of 200 dB; 

1-second ping every 2 minutes). For a non-impulsive source, the PTS 

onset weighted SELcum threshold for LF cetaceans is 199 dB, while for MF 

cetaceans is 198 dB. Despite LF cetaceans having a higher PTS onset 

threshold than MF cetaceans, the isopleth associated with LF cetaceans 

(30 m solid purple circle) is larger than that for MF cetaceans (1.2 m dashed 

green circle) based on 1 kHz being within LF cetacean’s most susceptible 

frequency range vs. outside the most susceptible frequency range for MF 

cetaceans (isopleths not to scale). 

2.2 APPLICATION FOR BROADBAND SOUNDS 

For broadband sources, the selection of the appropriate frequency for consideration associated 

with WFAs is more complicated. The selection of WFAs associated with broadband sources is 

similar to the concept used for to determine the 90% total cumulative energy window (5 to 95%) 

for consideration of duration associated with the RMS metric and impulsive sounds (Madsen 

2005) but considered in the frequency domain, rather than the time domain. This is typically 

referred to as the 95% frequency contour percentile (Upper frequency below which 95% of total 

cumulative energy is contained; Charif et al. 2010). 

NMFS recognizes the consideration of WFAs may be new for action proponents and have 

provided representative “default” values for various broadband sources (see associated User 

Spreadsheet tool and User Manual for User Spreadsheet tool). 

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10 100 

2.2.1 Special Considerations for Broadband Source 

Since the intent of WFAs is to broadly account for auditory weighting functions below the 95% 

frequency contour percentile, it is important that only frequencies on the “left side” of the auditory 

weighting function be used to make adjustments (i.e., frequencies below those where the auditory 

weighting function amplitude is zero60 or below where the function is essentially flat; resulting in 

every frequency below the WFA always having a more negative amplitude than the chosen WFA) 

(Figure D3). It is inappropriate to use WFAs for frequencies on the “right side” of the auditory 

weighting function (i.e., frequencies above those where the auditory weighting function amplitude 

is zero). For a frequency on the “right side” of the auditory weighting function (Table D1), any 

adjustment is inappropriate and WFAs cannot be used (i.e., an action proponent would be 

advised to not use auditory weighting functions and evaluate its source as essentially 

unweighted; see “Use” frequencies in Table D1, which will result in a auditory weighting function 

amplitude of 0 dB). 

Figure D3: Example auditory weighting function illustrating where the use of 

weighting factor adjustments are (Green: “left side”) and are not (Red: 

“right side”) appropriate for broadband sources. 

60 A criteria of a -0.4 dB weighting function amplitude from the Technical Guidance’s auditory weighting function was used 

to determine the demarcation between appropriate and inappropriate frequencies to use the WFAs. 

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Table D1: Applicability of weighting factor adjustments for frequencies associated 

with broadband sounds 

Hearing Group Applicable Frequencies Non-Applicable Frequencies* 

Low-Frequency Cetaceans (LF) 4.8 kHz and lower Above 4.8 kHz (Use: 1.7 kHz) 

Mid-Frequency Cetaceans (MF) 43 kHz and lower Above 43 kHz (Use: 28 kHz) 

High-Frequency Cetaceans (HF) 59 kHz and lower Above 59 kHz (Use: 42 kHz) 

Phocid Pinnipeds (PW) 11 kHz and lower Above 11 kHz (Use: 6.2 kHz) 

Otariid Pinnipeds (OW) 8.5 kHz and lower Above 8.5 kHz (Use: 4.9 kHz) 

* With non-applicable frequencies, users input the “use” frequency in the User Spreadsheet tool, which will result in an 

auditory weighting function amplitude of 0 dB (i.e., unweighted). 

2.3 OVERRIDING THE WEIGHTING FACTOR ADJUSTMENT 

An action proponent is not obligated to use WFAs. If an action proponent has data or 

measurements depicting the spectrum of their sound source, they may use these data to override 

the User Spreadsheet WFA output. By including a source’s entire spectrum, this will allow an 

action proponent to incorporate the Technical Guidance’s marine mammal auditory weighting 

functions over the entire broadband frequency range of the source, rather than just for one 

frequency via the WFA. As a result, overriding the optional User Spreadsheet’s WFA with a 

sound sources’ spectrum will result in more realistic (i.e., likely smaller) isopleths. NMFS is 

currently evaluating whether surrogate spectrum are available and applicable for particular sound 

sources, if an applicant does not have data of their own to use. 

As an example, Figure 118 in Appendix D of the Final Environmental Impact Statement for Gulf of 

Mexico OCS Proposed Geological and Geophysical Activities (BOEM 2017) provides a generic 

spectrum for an 8000 in3 airgun array (Figure D4). 

Figure D4: Maximum one-third octave band source level in the horizontal plane for a 

generic 8000 in3 seismic array (BOEM 2017) 

Table D2 provides a comparison of the dB adjustment between using the BOEM 2017 spectrum 

used to override the optional User Spreadsheet tool’s default WFA and the direct use of the 

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Ill. MODELING CUMULATIVE SOUND EXPOSURE LEVELS 

default WFA. As NMFS has stated previously, the more factors an action proponent can 

incorporate in their modeling, the more realistic results expected. 

Table D2: Comparison of adjustment (dB) associated with incorporating entire 

broadband spectrum vs. default, single frequency WFA for a seismic array. 

Weighting LF 

cetacean 

MF 

cetacean 

HF 

cetacean 

PW 

pinniped 

OW 

pinniped 

Default WFA 

(1 kHz) -0.06 dB -29.11 dB -37.55 dB -5.90 dB -4.87 dB 

Seismic array spectrum 

(BOEM 2017)* -12.7 dB -57.4 dB -65.7 dB -28.7 dB -33.6 dB 

* BOEM 2017 spectrum digitized using WebPlotDigitizer: Link to WebPlotDigitizer web page. 

III. MODELING CUMULATIVE SOUND EXPOSURE LEVELS 

To apply the PTS onset thresholds expressed as the weighted SELcum metric, a specified 

accumulation period is necessary. Generally, it is predicted that most receivers will minimize their 

time in the closest ranges to a sound source/activity and that exposures at the closest point of 

approach are the primary exposures contributing to a receiver’s accumulated level (Gedamke et 

al. 2011). Additionally, several important factors determine the likelihood and duration of time a 

receiver is expected to be in close proximity to a sound source (i.e., overlap in space and time 

between the source and receiver). For example, accumulation time for fast moving (relative to the 

receiver), mobile source, is driven primarily by the characteristics of source (i.e., transit speed, 

duty cycle). Conversely, for stationary sources, accumulation time is driven primarily by the 

characteristics of the receiver (i.e., swim speed and whether species is transient or resident to the 

area where the activity is occurring). For all sources, NMFS recommends a baseline 

accumulation period of 24-h, but acknowledges that there may be specific exposure situations 

where this accumulation period requires an adjustment (e.g., if activity lasts less than 24 hours or 

for situations where receivers are predicted to experience unusually long exposure durations61). 

Previous NMFS thresholds only accounted for the proximity of the sound source to the receiver, 

but thresholds in the Technical Guidance (i.e., expressed as weighted SELcum) now take into 

account the duration of exposure. NMFS recognizes that accounting for duration of exposure, 

although supported by the science literature, adds a new factor, as far as the application of this 

metric to real-world activities and that all action proponents may not have the ability to easily 

incorporate this additional component. NMFS does not provide specifications necessary to 

perform exposure modeling and relies on the action proponent to determine the model that best 

represents their activity. 

3.1 MORE SOPHISTICATED MODELS 

Because of the time component associated with the weighted SELcum metric, the use of different 

types of models to predict sound exposure may necessitate different approaches in evaluating 

likely effects in the context of the PTS onset thresholds. All marine mammals and some sources 

move in space and time, however, not all models are able to simulate relative source and receiver 

movement. Additionally, some models are able to predict the received level of sound at each 

modeled animal (often called animats) and accumulate sound at these receivers while 

incorporating the changing model environment. 

61 For example, where a resident population could be found in a small and/or confined area (Ferguson et al. 2015) and/or 

exposed to a long-duration activity with a large sound source, or there could be a continuous stationery activity nearby an 

area where marine mammals congregate, like a pinniped pupping beach. 

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Models that are more sophisticated may allow for the inclusion of added details to achieve more 

realistic results based on the accumulation of sound (e.g. information on residence time of 

individuals, swim speeds for transient species, or specific times when activity temporarily 

ceases). Alternatively, there may be case-specific circumstances where the accumulation time 

needs to be modified to account for situations where animals are expected to be in closer 

proximity to the source over a significantly longer amount of time, based on activity, site, and 

species-specific information (e.g., where a resident population could be found in a small and/or 

confined area (Ferguson et al. 2015) and a long-duration activity with a large sound source, or a 

continuous stationery activity nearby a pinniped pupping beach). 

3.2 LESS SOPHISTICATED MODELS 

For action proponents unable to incorporate animal and/or source movement, it may not be 

realistic to assume that animals will remain at a constant distance from the source accumulating 

acoustic energy for 24 hours. Thus, alternative methods are needed, which can provide a 

distance from the source where exposure exceeding a threshold is expected to occur and can be 

used in the same manner as distance has been used to calculate exposures above previous 

NMFS thresholds. NMFS proposes two alternative methods: one for mobile sources and one for 

stationary sources. 

3.2.1 Mobile Sources62 

3.2.1.1 Linear Equivalents Used in Appendix 

In underwater acoustics, equations/derivations are typically expressed in terms of logarithmic terms 

(i.e., levels). These equations can be further simplified by introducing linear equivalents of the levels 

(i.e., factors) related by multiplication instead of by addition. For example, source level63 (SL) is 

replaced by the “source factor” 10SL/(10 dB) (Ainslie 2010). In this appendix, the following linear 

equivalents are used: 

• Sound exposure (E) = 10SEL/(10 dB) μPa2s 

• Mean-square sound pressure (pp��2�) = 10SPL/(10 dB) μPa2 

• Source factor (S) = 10SL/(10 dB) μPa2m2 

• Energy source factor64 (SE) = 10SLEE/(10 dB)

μPa2 m2s 

Both source level and energy source level (and their corresponding factors) are evaluated and 

reported in the direction producing the maximum SL. 

62 The methodology for mobile sources presented in this Appendix underwent peer review via the publication process 

(Sivle et al. 2014) but did not undergo a separate peer review. It is an optional tool for the application of the thresholds 

presented in the Technical Guidance. 

63 For definition of SL, see Ainslie 2010. SL ≡ 10log10 [p(s)2

s2 /(1 μPa2 m2)] dB (Ainslie writes this as SL ≡ 10log10 p2s2 dB 

re 1 μPa2

s m2.) For a point source, s is a small distance from the source, where distortions due to absorption, refraction, 

reflection, or diffraction are negligible and p(s) is the RMS sound pressure at that distance. For a large (i.e., finite) source, 

p is the hypothetical sound pressure that would exist at distance s from a point source with the same far-field radiant 

intensity as the true source. For further clarification, see ISO 2017, entry 3.3.2.1 “source level.” 

64 For definition of SLE, see Ainslie 2010. SLE ≡ 10log10 [E(s)s2 /(1 μPa2 m2 s)] dB (Ainslie writes this as SLE ≡10 log10 E 

(s)s2 dB 1 μPa2 m2

s). For a point source, s is a small distance from the source, where distortions due to absorption, 

refraction, reflection, or diffraction are negligible and E(s) is the unweighted sound exposure at that distance. For a large 

(i.e., finite) source, E is the hypothetical sound exposure that would exist at distance s from a point source with the same 

duration and far-field radiant intensity as the true source. For further clarification, see ISO 2017, entry 3.3.2.2 “energy 

source level.” 

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3.2.1.2 “Safe Distance” Methodology 

Cumulative sound exposure can be computed using a simple equation, assuming a constant 

received sound pressure level (SPL) that does not change over space and time65 (Equation D1.; 

e.g., Urick 1983; ANSI 1986; Madsen 2005): 

SELcum = SPL + 10 log10 (duration of exposure, expressed in seconds) dB 

Equation D1 

However, if one assumes a stationary receiver and a source moving at a constant speed in a 

constant direction, then exposure changes over space and time (i.e., greatest rate of 

accumulation at closest point of approach). 

An alternative approach for modeling moving sources is the concept of a “safe distance” (R0), 

which is defined by Sivle et al. (2014) as “the distance from the source beyond which a 

threshold66 for that metric (SPL0 or SEL0) is not exceeded.” This concept allows one to determine 

at what distance from a source a receiver would have to remain in order not to exceed a 

predetermined exposure threshold (i.e., EE0 which equals the weighted SELcum PTS onset 

threshold in this Technical Guidance) and is further illustrated in Figure D5. 

Figure D5: Illustration of the concept for mobile sources, with each red dot 

representing the source traveling over time. As the source travels further 

from the receiver, the source-receiver separation increases (i.e., 

hypotenuse gets longer). 

This methodology accounts for several factors, including source level, duty cycle, and transit 

speed of the source and is independent of exposure duration (Equations D2a67,b). 

65 Equation D1 assumes a constant source-receiver separation distance. 

66 The threshold considered by Sivle et al. 2014 was associated with behavioral reactions. 67 This equation matches Equation 3 from Sivle et al. (2014), but is written in a simpler manner. 

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a 

RR0 = EE

π

0vv

SSSS

Equations D2a,b 

For impulsive sources, SD is replaced with SE/τ: 

b π SSEE RR0 = EE0vv ττ

where: 

S = source factor (10SL/(10 dB) μPa2m2)

D =duty cycle (pulse duration x repetition rate)

vv= transit speed 

E0 =exposure threshold (10SEL0/(10 dB)) μPa2s)

SE = energy source factor (10SLEE/(10 dB)μPa2m2s) 

τ = 1/repetition rate 

R0 represents the exposure isopleth calculated using NMFS’ thresholds. Thus, area calculations 

and exposure calculations would be performed in the same manner68 action proponents have 

previously used (e.g., determine area covered over a 24-h period multiplied by the density of a 

marine mammal species). 

This approach considers four factors: 

1. Source level (direct relationship: as source level increases, so does R0; higher source 

level results is a greater accumulation of energy). 

2. Duty cycle (direct relationship: as duty cycle increases, so does R0; higher duty cycle 

results in more energy within a unit of time and leads a greater accumulation of energy). 

3. Source transit speed (inverse relationship: as transit speed decreases, R0 increases or 

vice versa; a faster transit speed results in less energy within a unit of time and leads to a 

lower accumulation of energy, while a slower transit speed will result in a greater 

accumulation of energy). 

4. Exposure threshold (inverse relationship: as the exposure threshold decreases, R0 

increases or vice versa; a higher exposure threshold result in needing more energy to 

exceed it compared to a lower threshold). 

The action proponent is responsible for providing information on factors one through three above, 

while factor four is the PTS onset acoustic threshold (expressed as weighted SELcum metric) 

provided within the Technical Guidance. 

For this approach to be applicable to a broad range of activities, the following assumptions69 are 

made: 

68 Note: “Take” calculations are typically based on speed expressed in kilometers per hour, duration of an exposure 

expressed in hours (i.e., 24 hours), isopleths expressed in kilometers, and animal density expresses as animals per 

square kilometers. Thus, units would need to be converted to use Equations D2a,b. 

69 If any of these assumptions are violated and there is concern that the isopleth produced is potentially underestimated, it 

is recommended action proponents contact NMFS to see if any there are any appropriate adjustments that can be made 

(e.g., addition of a buffer, etc.). If not, the action proponent is advised to pursue other methodology capable of more 

accurately modeling exposure. 

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• Action proponents that are unable to apply full auditory weighting functions will rely on 

WFAs. This will create larger isopleths, for broadband sources, compared to action 

proponents capable of fully applying auditory weighting functions. Note: Action 

proponents can override the WFA if spectral data for their sound source is available (See 

Section 2.3 of this Appendix). 

• The movement of the source is simple (i.e., source moves at a constant speed and in a 

constant direction). Caution is recommended if the source has the potential to move in a 

manner where the same group of receivers could be exposed to multiple passes from the 

source. 

• Minimal assumptions are made about the receivers. They are considered stationary and 

assumed to not move up or down within the water column. There is no avoidance and the 

receiver accumulates sound via one pass of the source (i.e., receiver is not exposed to 

multiple passes from the source). Because this methodology only examines one pass of 

the source relative to receiver, this method is essentially time-independent (i.e., action 

proponent does not need to specify how long an activity occurs within a 24-h period). 

o These assumptions are appropriate for sources that are expected to move much 

faster than the receiver does. Further, assuming receivers do not avoid the 

source or change position vertically or horizontally in the water column will result 

in more exposures exceeding the thresholds compared to those receivers that 

would avoid or naturally change positions in the water column over time. Caution 

is recommended if the receiver has the potential to follow or move with the sound 

source. 

• Distance (i.e., velocity x change over time) between “pulses” for intermittent sources is 

small compared with R0, and the distance between “pulses” for intermittent sources is 

consistent. This assumption is appropriate for intermittent sources with a predictable duty 

cycle. If the duty cycle decreases,R0 will become larger, while if the duty cycle increases, 

it will become smaller. Further, for intermittent sources, it is assumed there is no recovery 

in hearing threshold between pulses. 

• Sound propagation is simple (i.e., approach uses spherical spreading70: 20 log R, with no 

absorption). NMFS recognizes that this might not be appropriate for all activities, 

especially those occurring in shallow water (i.e., sound could propagate further than 

predicted by this model)71. Thus, modifications to theR0 predicted may be necessary in 

these situations. 

Despite these assumptions, this approach offers a better approximation of the source-receiver 

distance over space and time for various mobile sources than choosing a set accumulation period 

for all sources, which assumes a fixed source-receiver distance over that time. 

70 Assuming spherical spreading allows for Equations D2a,b to remain simplified (i.e., assuming another spreading model 

results in more complicated equations that are no longer user-friendly nor as easy to implement). 

71 Note: Many moving sources, like seismic airguns or sonar, can be highly-directional (i.e., most of time sound source is 

directed to the ocean floor, with less sound propagating horizontally, compared to the vertical direction), which is not 

accounted for with this methodology. Additionally, many higher-frequency sounds, like sonar, are also attenuated by 

absorption, which is also taken into account in this model. These, among other factors, are recommended for 

consideration when evaluating whether spherical spreading is potentially resulting in an underestimation of exposure. 

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Ainslie and Von Benda-Beckmann (2013) investigated the effect various factors had on the 

derivation of R0 and found exposures were highest for stationary receivers in the path of a source, 

compared to mobile receivers swimming away from the source. However, the authors did 

acknowledge, if the receivers actively swam toward the source, cumulative exposure would 

increase. Uncertainty associated with R0 was found to be primarily driven by the exposure 

threshold (i.e., Technical Guidance’s thresholds). Increasing duty cycle of the source or reducing 

speed (either source or receiver) will result in an increased R0 (Sivle et al. 2014) 

NMFS has provided a companion User Spreadsheet tool and User Manual for the User 

Spreadsheet tool to help action proponents use this methodology to determine isopleths for PTS 

onset associated with their activity (Link to Technical Guidance web page). 

3.2.2 Stationary Sources 

If there is enough information to accurately predict the travel speed of a receiver past a stationary 

sound source (including the assumption that the receiver swims on a straight trajectory past the 

source), then the mobile source approach can be modified for stationary sources (i.e., transit 

speed of the source is replaced by speed of the receiver). However, NMFS acknowledges that 

characteristics of the receiver are less predictable compared to those of the source (i.e., velocity 

and travel path), which is why the mobile source approach may not be appropriate for stationary 

sources and an alternate method is provided below. 

An alternative approach is to calculate the accumulated isopleth associated with a stationary 

sound source within a 24-h period. For example, if vibratory pile driving was expected to occur 

over ten hours within a 24-h period, then the isopleth would be calculated by adding area with 

each second the source is producing sound. This is a highly conservative means of calculating an 

isopleth because it assumes that animals on the edge of the isopleth (in order to exceed a 

threshold) will remain there for the entire time of the activity. 

For stationary, impulsive sources with high source levels (i.e., impulsive pile driving associated 

with large piles, stationary airguns associated with vertical seismic profiling (VSPs), and large 

explosives) accumulating over a 24-h period, depending on how many strikes or shots occur, 

could lead to unrealistically large isopleths associated with PTS onset. For these situations, 

action proponents are advised to contact NMFS for possible applicable alternative methods. 

NMFS has provided a companion User Spreadsheet tool and User Manual (NMFS 2018) for the 

User Spreadsheet tool to help action proponents wanting to use this methodology to determine 

isopleths for PTS onset associated with their activity (Link to Technical Guidance web page). 

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APPE DX E: GLOSSARY 

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Low -------------------------------------------------------------------• High 

Frequency (kHz) 

APPENDIX E: GLOSSARY 

95% Frequency contour percentile: Upper frequency below which 95% of total cumulative 

energy is contained (Charif et al. 2010). 

Accumulation period: The amount of time a sound accumulates for the SELcum metric. 

Acoustic threshold: An acoustic threshold in this document identifies the level of sound, after 

which exceeded, NMFS anticipates a change in auditory sensitivity (temporary or permanent 

threshold shift). 

Ambient noise: All-encompassing sound at a given place, usually a composite of sound from 

many sources near and far (ANSI 1994). 

Animat: A simulated marine mammal. 

Anthropogenic: Originating (caused or produced by) from human activity. 

Audible: Heard or capable of being heard. Audibility of sounds depends on level, frequency 

content, and can be reduced in the presence of other sounds (Morfey 2001) 

Audiogram: A graph depicting hearing threshold as a function of frequency (ANSI 1995; Yost 

2007) (Figure E1). 

Figure E1. Example audiogram. 

Auditory adaptation: Temporary decrease in hearing sensitivity occurring during the 

presentation of an acoustic stimulus (opposed to auditory fatigue which occurs post-stimulation) 

(ANSI 1995). 

Auditory bulla: The ear bone in odontocetes that houses the middle ear structure (Perrin et al. 

2009). 

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Auditory weighting function: Auditory weighting functions take into account what is known 

about marine mammal hearing sensitivity and susceptibility to noise-induced hearing loss and can 

be applied to a sound-level measurement to account for frequency-dependent hearing (i.e.,. an 

expression of relative loudness as perceived by the ear)(Southall et al. 2007; Finneran 2016). 

Specifically, this function represents a specified frequency-dependent characteristic of hearing 

sensitivity in a particular animal, by which an acoustic quantity is adjusted to reflect the 

importance of that frequency dependence to that animal (ISO 2017). Similar to OSHA (2013), 

marine mammal auditory weighting functions in this document are used to reflect the risk of noise 

exposure on hearing and not necessarily capture the most sensitive hearing range of every 

member of the hearing group. 

Background noise: Total of all sources of interference in a system used for the production, 

detection, measurement, or recording of a signal, independent of the presence of the signal 

(ANSI 2013). 

Band-pass filter: A filter that passes frequencies within a defined range without reducing 

amplitude and attenuates frequencies outside that defined range (Yost 2007). 

Bandwidth: Bandwidth (Hz or kHz) is the range of frequencies over which a sound occurs or 

upper and lower limits of frequency band (ANSI 2005). Broadband refers to a source that 

produces sound over a broad range of frequencies (for example, seismic airguns), while 

narrowband or tonal sources produce sounds over a more narrow frequency range, typically with 

a spectrum having a localized a peak in amplitude (for example, sonar) (ANSI 1986; ANSI 2005). 

Bone conduction: Transmission of sound to the inner ear primarily by means of mechanical 

vibration of the cranial bones (ANSI 1995). 

Broadband: See “bandwidth”. 

Cetacean: Any number of the order Cetacea of aquatic, mostly marine mammals that includes 

whales, dolphins, porpoises, and related forms; among other attributes they have a long tail that 

ends in two transverse flukes (Perrin et al. 2009). 

Cochlea: Spirally coiled, tapered cavity within the temporal bone, which contains the receptor 

organs essential to hearing (ANSI 1995). For cetaceans, based on cochlear measurements two 

cochlea types have been described for echolocating odontocetes (type I and II) and one cochlea 

type for mysticetes (type M). Cochlea type I is found in species like the harbor porpoise and 

Amazon river dolphin, which produce high-frequency echolocation signals. Cochlea type II is 

found in species producing lower frequency echolocation signals (Ketten 1992). 

Continuous sound: A sound whose sound pressure level remains above ambient sound during 

the observation period (ANSI 2005). 

Critical level: The level at which damage switches from being primarily metabolic to more 

mechanical; e.g., short duration of impulse can be less than the ear’s integration time, leading for 

the potential to damage beyond level the ear can perceive (Akay 1978). 

Cumulative sound exposure level (SELcum; re: 1μPa2s): Level of acoustic energy accumulated 

over a given period of time or event (EPA 1982) or specifically, ten times the logarithm to the 

base ten of the ratio of a given time integral of squared instantaneous frequency-weighted sound 

pressure over a stated time interval or event to the reference sound exposure (ANSI 1995; ANSI 

2013). Within the Technical Guidance, this metric is weighted based on the document’s marine 

mammal auditory weighting functions. 

Deafness: A condition caused by a hearing loss that results in the inability to use auditory 

information effectively for communication or other daily activities (ANSI 1995). 

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Decibel (dB): One-tenth of a bel. Unit of level when the base of the logarithm is the tenth root of 

ten, and the quantities concerned are proportional to power (ANSI 2013). 

dB/decade: This unit is typically used to describe roll-off, where a decade is a 10-times increase 

in frequency (roll-off can also be described as decibels per octave, where an octave is 2-times 

increase in frequency) 

Duty cycle: On/off cycle time or proportion of time signal is active (calculated by: pulse length x 

repetition rate). A continuous sound has a duty cycle of 1 or 100%. 

Dynamic range of auditory system: Reflects the range of the auditory system from the ability 

to detect a sound to the amount of sound tolerated before damage occurs (i.e., the threshold of 

pain minus the threshold of audibility) (Yost 2007). For the purposes of this document, the intent 

is relating the threshold of audibility and TTS onset levels, not the threshold of pain. 

Effective quiet: The maximum sound pressure level that will fail to produce any significant 

threshold shift in hearing despite duration of exposure and amount of accumulation (Ward et al. 

1976; Ward 1991). 

Endangered Species Act (ESA): The Endangered Species Act of 1973 (16. U.S.C 1531 et. 

seq.) provides for the conservation of species that are endangered or threatened throughout all or 

a significant portion of their range, and the conservation of the ecosystems on which they 

depend. 

NOAA’s National Marine Fisheries Service and the U.S. Fish and Wildlife Service (USFWS) share 

responsibility for implementing the ESA. 

Energy Source Level (SLE): The time-integrated squared signal sound pressure level measured 

in a given radian direction, corrected for absorption, and scaled to a reference distance (1 m) 

(adapted from Morfey 2001). 

Equal Energy Hypothesis (EEH): Assumption that sounds of equal energy produce the equal 

risk for hearing loss (i.e., if the cumulative energy of two sources are similar, a sound from a 

lower level source with a longer exposure duration may have similar risks to a shorter duration 

exposure from a higher level source) (Henderson et al. 1991). 

Equal latency: A curve that describe the frequency-dependent relationships between sound 

pressure level and reaction time and are similar in shape to equal loudness contours in humans 

(loudness perception can be studied under the assumption that sounds of equal loudness elicit 

equal reaction times; e.g., Liebold and Werner 2002). 

Equal-loudness contour: A curve or curves that show, as a function of frequency, the sound 

pressure level required to cause a given loudness for a listener having normal hearing, listening 

to a specified kind of sound in a specified manner (ANSI 2013). 

Far-field: The acoustic field sufficiently distant from a distributed source that the sound 

pressure decreases linearly with increasing distance (neglecting reflections, refraction, and 

absorption) (ANSI 2013). 

Fitness: Survival and lifetime reproductive success of an individual. 

Frequency: The number of periods occurring over a unit of time (unless otherwise stated, cycles 

per second or hertz) (Yost 2007). 

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Functional hearing range: There is no standard definition of functional hearing arrange currently 

available. “Functional” refers to the range of frequencies a group hears without incorporating nonacoustic mechanisms (Wartzok and Ketten 1999). Southall et al. 2007 defined upper and lower 

limits of the functional hearing range as ~60-70 dB above the hearing threshold at greatest 

hearing sensitivity (based on human and mammalian definition of 60 dB72). 

Fundamental frequency: Frequency of the sinusoid that has the same period as the periodic 

quantity (Yost 2007; ANSI 2013). First harmonic of a periodic signal (Morfey 2001). 

Harmonic: A sinusoidal quantity that has a frequency which is an integral multiple of the 

fundamental frequency of the periodic quantity to which it is related (Yost 2007; ANSI 2013). 

Hearing loss growth rates: The rate of threshold shift increase (or growth) as decibel level or 

exposure duration increase (expressed in dB of temporary threshold shift/dB of noise).Growth 

rates of threshold shifts are higher for frequencies where hearing is more sensitive (Finneran and 

Schlundt 2010). Typically in terrestrial mammals, the magnitude of a threshold shift increases 

with increasing duration or level of exposure, until it becomes asymptotic (growth rate begins to 

level or the upper limit of TTS; Mills et al. 1979; Clark et al. 1987; Laroche et al. 1989; Yost 2007). 

Hertz (Hz): Unit of frequency corresponding to the number of cycles per second. One hertz 

corresponds to one cycle per second. 

Impulsive sound: Sound sources that produce sounds that are typically transient, brief (less 

than 1 second), broadband, and consist of high peak sound pressure with rapid rise time and 

rapid decay (ANSI 1986; NIOSH 1998; ANSI 2005). They can occur in repetition or as a single 

event. Examples of impulsive sound sources include: explosives, seismic airguns, and impact pile 

drivers. 

Information Quality Guidelines (IQG): Section 515 of the Treasury and General Government 

Appropriations Act for Fiscal Year 2001 (Public Law 106-554), directs the Office of Management 

and Budget (OMB) to issue government-wide guidelines that “provide policy and procedural 

guidance to federal agencies for ensuring and maximizing the quality, objectivity, utility, and 

integrity of information (including statistical information) disseminated by federal agencies.” OMB 

issued guidelines directing each federal agency to issue its own guidelines. Link to NOAA's 

Information Quality Guidelines 

Integration time (of the ear): For a signal to be detected by the ear, it must have some critical 

amount of energy. The process of summing the power to generate the required energy is 

completed over a particular integration time. If the duration of a signal is less than the integration 

time required for detection, the power of the signal must be increased for it to be detected by the 

ear (Yost 2007). 

Intermittent sound: Interrupted levels of low or no sound (NIOSH 1998) or bursts of sounds 

separated by silent periods (Richardson and Malme 1993). Typically, intermittent sounds have a 

more regular (predictable) pattern of bursts of sounds and silent periods (i.e., duty cycle). 

Isopleth: A line drawn through all points having the same numerical value. In the case of sound, 

the line has equal sound pressure or exposure levels. 

Kurtosis: Statistical quantity that represents the impulsiveness (“peakedness”) of the event; 

specifically the ratio of fourth- order central moment to the squared second-order central moment 

(Hamernik et al. 2003; Davis et al. 2009). 

72 In humans, functional hearing is typically defined as frequencies at a threshold of 60 to 70 dB and below (Masterson et 

al. 1969; Wartzok and Ketten 1999), with normal hearing in the most sensitive hearing range considered 0 dB (i.e., 60 to 

70 dB above best hearing sensitivity). 

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Linear interpolation: A method of constructing new data points within the range of a discrete 

set of known data points, with linear interpolation being a straight line between two points. 

Marine Mammal Protection Act (MMPA): The Marine Mammal Protection Act (16. U.S.C. 1361 

et. seq.)was enacted on October 21, 1972 and MMPA prohibits, with certain exceptions, the 

“take” of marine mammals in U.S. waters and by U.S. citizens on the high seas, and the 

importation of marine mammals and marine mammal products into the United States. NOAA’s 

National Marine Fisheries Service and the U.S. Fish and Wildlife Service (USFWS) share 

responsibility for implementing the MMPA. 

Masking: Obscuring of sounds of interest by interfering sounds, generally of the similar 

frequencies (Richardson et al. 1995). 

Mean-squared error (MSE): In statistics, this measures the average of the squares of the 

“errors,” that is, the difference between the estimator and what is estimated. 

Mean-square sound pressure: Integral over a specified time interval of squared sound 

pressure, divided by the duration of the time interval for a specified frequency range (ISO 2017). 

Multipath propagation: This phenomenon occurs whenever there is more than one propagation 

path between the source and receiver (i.e., direct path and paths from reflections off the surface 

and bottom or reflections within a surface or deep-ocean duct; Urick 1983). 

Mysticete: The toothless or baleen (whalebone) whales, including the rorquals, gray whale, and 

right whale; the suborder of whales that includes those that bulk feed and cannot echolocate 

(Perrin et al. 2009). 

Narrowband: See “bandwidth”. 

National Marine Sanctuaries Act (NMSA): The National Marine Sanctuaries Act (16 U.S.C. 

1431 et. seq.) authorizes the Secretary of Commerce to designate and protect areas of the 

marine environment with special national significance due to their conservation, recreational, 

ecological, historical, scientific, cultural, archeological, educational, or esthetic qualities as 

national marine sanctuaries. Day-to-day management of national marine sanctuaries has been 

delegated by the Secretary of Commerce to NOAA’s Office of National Marine Sanctuaries. 

National Standard 2 (NS2): The Magnuson-Stevens Fishery Conservation and Management Act 

(MSA) (16 U.S.C. 1801 et. seq.) is the principal law governing marine fisheries in the U.S. and 

includes ten National Standards to guide fishery conservation and management. One of these 

standards, referred to as National Standard 2 (NS2), guides scientific integrity and states 

“(fishery) conservation and management measures shall be based upon the best scientific 

information available. 

Non-impulsive sound: Sound sources that produce sounds that can be broadband, narrowband 

or tonal, brief or prolonged, continuous or intermittent) and typically do not have a high peak 

sound pressure with rapid rise time that impulsive sounds do. Examples of non-impulsive sound 

sources include: marine vessels, machinery operations/construction (e.g., drilling), certain active 

sonar (e.g. tactical), and vibratory pile drivers. 

Octave: The interval between two sounds having a basic frequency ratio of two (Yost 2007). For 

example, one octave above 400 Hz is 800 Hz. One octave below 400 Hz is 200 Hz. 

Odontocete: The toothed whales, including sperm and killer whales, belugas, narwhals, dolphins 

and porpoises; the suborder of whales including those able to echolocate (Perrin et al. 2009). 

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Omnidirectional: Receiving or transmitting signals in all directions (i.e., variation with direction is 

designed to be as small as possible). 

One-third octave (base 10): The frequency ratio corresponding to a decidecade or one tenth of 

a decade (ISO 2017). 

Otariid: The eared seals (sea lions and fur seals), which use their foreflippers for propulsion 

(Perrin et al. 2009). 

Peak sound pressure level (PK; re: 1 μPa): The greatest magnitude of the sound pressure, 

which can arise from a positive or negative sound pressure, during a specified time, for a specific 

frequency range (ISO 2017). 

Perception: Perception is the translation of environmental signals to neuronal representations 

(Dukas 2004). 

Permanent threshold shift (PTS): A permanent, irreversible increase in the threshold of 

audibility at a specified frequency or portion of an individual’s hearing range above a previously 

established reference level. The amount of permanent threshold shift is customarily expressed in 

decibels (ANSI 1995; Yost 2007). Available data from humans and other terrestrial mammals 

indicate that a 40 dB threshold shift approximates PTS onset (see Ward et al. 1958, 1959; Ward 

1960; Kryter et al. 1966; Miller 1974; Ahroon et al. 1996; Henderson et al. 2008). 

Phocid: A family group within the pinnipeds that includes all of the “true” seals (i.e. the “earless” 

species). Generally used to refer to all recent pinnipeds that are more closely related to Phoca 

than to otariids or the walrus (Perrin et al. 2009). 

Pinniped: Seals, sea lions and fur seals (Perrin et al. 2009). 

Pulse duration: For impulsive sources, window that makes up 90% of total cumulative energy 

(5%-95%) (Madsen 2005) 

Propagation loss: Reduction in magnitude of some characteristic of a signal between two stated 

points in a transmission system (for example the reduction in the magnitude of a signal between a 

source and a receiver) (ANSI 2013). 

Received level: The level of sound measured at the receiver. 

Reference pressure: See sound pressure level. 

Repetition rate: Number of pulses of a repeating signal in a specific time unit, normally 

measured in pulses per second. 

Rise time: The time interval a signal takes to rise from 10% to 90% of its highest peak (ANSI 

1986; ANSI 2013). 

Roll-off: Change in weighting function amplitude (-dB) with changing frequency. 

Root-mean-square sound pressure level (RMS SPL; re: 1 μPa): Ten times the logarithm to the 

base 10 of the ratio of the mean-square sound pressure to the specified reference value in 

decibels (ISO 2017). 

Sensation level (dB): The pressure level of a sound above the hearing threshold for an 

individual or group of individuals (ANSI 1995; Yost 2007). 

Sound: An alteration in pressure propagated by the action of elastic stresses in an elastic 

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medium and that involves local compression and expansion of the medium (ISO 2017). 

Sound Exposure Level (SELcum; re: 1μPa2s): A measure of sound level that takes into account 

the duration of the signal. Ten times the logarithm to the base 10 of the ration of a given time 

integral of squared instantaneous frequency-weighted sound pressure over a stated time interval 

or event to the product of the squared reference sound pressure and reference duration of one 

second (ANSI 2013). 

Sound Pressure Level (SPL): A measure of sound level that represents only the pressure 

component of sound. Ten times the logarithm to the base 10 of the ratio of time-mean-square 

pressure of a sound in a stated frequency band to the square of the reference pressure (1 μPa in 

water) (ANSI 2013). 

Source Level (SL): Sound pressure level measured in a given radian direction, corrected for 

absorption, and scaled to a reference distance (Morfey 2001). For underwater sources, the sound 

pressure level of is measured in the far-field and scaled to a standard reference distance (1 

meter) away from the source (Richardson et al. 1995; ANSI 2013). 

Spatial: Of or relating to space or area. 

Spectral/spectrum: Of or relating to frequency component(s) of sound. The spectrum of a 

function of time is a description of its resolution into components (frequency, amplitude, etc.). The 

spectrum level of a signal at a particular frequency is the level of that part of the signal contained 

within a band of unit width and centered at a particular frequency (Yost 2007). 

Spectral density levels: Level of the limit, as the width of the frequency band approaches zero, 

of the quotient of a specified power-like quantity distributed within a frequency band, by the width 

of the band (ANSI 2013). 

Subharmonic: Sinusoidal quantity having a frequency that is an integral submultiple of the 

fundamental frequency of a periodic quantity to which it is related (ANSI 2013). 

Temporal: Of or relating to time. 

Temporary threshold shift (TTS): A temporary, reversible increase in the threshold of audibility 

at a specified frequency or portion of an individual’s hearing range above a previously established 

reference level. The amount of temporary threshold shift is customarily expressed in decibels 

(ANSI 1995, Yost 2007). Based on data from cetacean TTS measurements (see Southall et al. 

2007 for a review), a TTS of 6 dB is considered the minimum threshold shift clearly larger than 

any day-to-day or session-to-session variation in a subject’s normal hearing ability (Schlundt et al. 

2000; Finneran et al. 2000; Finneran et al. 2002). 

Threshold (of audibility): The threshold of audibility (auditory threshold) for a specified signal is 

the minimum effective sound pressure level of the signal that is capable of evoking an auditory 

sensation in a specified fraction of trials (either physiological or behavioral) (Yost 2007). It 

recommended that this threshold be defined as the lowest sound pressure level at which 

responses occur in at least 50% of ascending trials. (ANSI 2009). 

Threshold shift: A change, usually an increase, in the threshold of audibility at a specified 

frequency or portion of an individual’s hearing range above a previously established reference 

level. The amount of threshold shift is customarily expressed in decibels (ANSI 1995, Yost 2007). 

Tone: A sound wave capable of exciting an auditory sensation having pitch. A pure tone is a 

sound sensation characterized by a single pitch (one frequency). A complex tone is a sound 

sensation characterized by more than one pitch (more than one frequency) (ANSI 2013). 

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Uncertainty: Lack of knowledge about a parameter’s true value (Bogen and Spears 1987; Cohen 

et al. 1996). 

Variability: Differences between members of the populations that affects the magnitude of risk to 

an individual (Bogen and Spears 1987; Cohen et al. 1996; Gedamke et al. 2011). 

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