1992 Federal Register / Vol. 87, No. 8 / Wednesday, January 12, 2022 / Notices 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric 

Administration 

[RTID 0648–XB628] 

Takes of Marine Mammals Incidental to 

Specified Activities; Taking Marine 

Mammals Incidental to Geophysical 

Surveys of the Guerrero Gap in the 

Eastern Tropical Pacific 

AGENCY: National Marine Fisheries 

Service (NMFS), National Oceanic and 

Atmospheric Administration (NOAA), 

Commerce. 

ACTION: Notice; proposed incidental 

harassment authorization; request for 

comments on proposed authorization 

and possible Renewal. 

SUMMARY: NMFS has received a request 

from the Lamont-Doherty Earth 

Observatory (L–DEO) for authorization 

to take marine mammals incidental to 

geophysical surveys of the Guerrero Gap 

off the coast of Mexico in the Eastern 

Tropical Pacific. Pursuant to the Marine 

Mammal Protection Act (MMPA), NMFS 

is requesting comments on its proposal 

to issue an incidental harassment 

authorization (IHA) to incidentally take 

marine mammals during the specified 

activities. NMFS is also requesting 

comments on a possible one-time, oneyear renewal that could be issued under 

certain circumstances and if all 

requirements are met, as described in 

Request for Public Comments at the end 

of this notice. NMFS will consider 

public comments prior to making any 

final decision on the issuance of the 

requested MMPA authorization and 

agency responses will be summarized in 

the final notice of our decision. 

DATES: Comments and information must 

be received no later than February 11, 

2022. 

ADDRESSES: Comments should be 

addressed to Jolie Harrison, Chief, 

Permits and Conservation Division, 

Office of Protected Resources, National 

Marine Fisheries Service submitted via 

email to ITP.Fowler@noaa.gov. 

Instructions: NMFS is not responsible 

for comments sent by any other method, 

to any other address or individual, or 

received after the end of the comment 

period. Comments, including all 

attachments, must not exceed a 25- 

megabyte file size. All comments 

received are a part of the public record 

and will generally be posted online at 

www.fisheries.noaa.gov/permit/ 

incidental-take-authorizations-undermarine-mammal-protection-act without 

change. All personal identifying 

information (e.g., name, address) 

voluntarily submitted by the commenter 

may be publicly accessible. Do not 

submit confidential business 

information or otherwise sensitive or 

protected information. 

FOR FURTHER INFORMATION CONTACT: 

Amy Fowler, Office of Protected 

Resources, NMFS, (301) 427–8401. 

Electronic copies of the application and 

supporting documents, as well as a list 

of the references cited in this document, 

may be obtained online at: https://

www.fisheries.noaa.gov/permit/ 

incidental-take-authorizations-undermarine-mammal-protection-act. In case 

of problems accessing these documents, 

please call the contact listed above. 

SUPPLEMENTARY INFORMATION: 

Background 

The MMPA prohibits the ‘‘take’’ of 

marine mammals, with certain 

exceptions. Sections 101(a)(5)(A) and 

(D) of the MMPA (16 U.S.C. 1361 et 

seq.) direct the Secretary of Commerce 

(as delegated to NMFS) to allow, upon 

request, the incidental, but not 

intentional, taking of small numbers of 

marine mammals by U.S. citizens who 

engage in a specified activity (other than 

commercial fishing) within a specified 

geographical region if certain findings 

are made and either regulations are 

proposed or, if the taking is limited to 

harassment, a notice of a proposed 

incidental harassment authorization is 

provided to the public for review. 

Authorization for incidental takings 

shall be granted if NMFS finds that the 

taking will have a negligible impact on 

the species or stock(s) and will not have 

an unmitigable adverse impact on the 

availability of the species or stock(s) for 

taking for subsistence uses (where 

relevant). Further, NMFS must prescribe 

the permissible methods of taking and 

other ‘‘means of effecting the least 

practicable adverse impact’’ on the 

affected species or stocks and their 

habitat, paying particular attention to 

rookeries, mating grounds, and areas of 

similar significance, and on the 

availability of the species or stocks for 

taking for certain subsistence uses 

(referred to in shorthand as 

‘‘mitigation’’); and requirements 

pertaining to the mitigation, monitoring 

and reporting of the takings are set forth. 

The definitions of all applicable MMPA 

statutory terms cited above are included 

in the relevant sections below. 

National Environmental Policy Act 

To comply with the National 

Environmental Policy Act of 1969 

(NEPA; 42 U.S.C. 4321 et seq.) and 

NOAA Administrative Order (NAO) 

216–6A, NMFS must review our 

proposed action (i.e., the issuance of an 

IHA) with respect to potential impacts 

on the human environment. 

Accordingly, NMFS plans to adopt 

the National Science Foundation’s 

(NSF’s) Environmental Assessment 

(EA), provided our independent 

evaluation of the document finds that it 

includes adequate information 

analyzing the effects on the human 

environment of issuing the IHA. The 

NSF’s EA is available at https://

www.fisheries.noaa.gov/permit/ 

incidental-take-authorizations-undermarine-mammal-protection-act. 

We will review all comments 

submitted in response to this notice 

prior to concluding our NEPA process 

or making a final decision on the IHA 

request. 

Summary of Request 

On August 21, 2021, NMFS received 

a request from L–DEO for an IHA to take 

marine mammals incidental to 

geophysical surveys of the Guerrero Gap 

off the coast of Mexico in the Eastern 

Tropical Pacific (ETP). The application 

was deemed adequate and complete on 

December 14, 2021. L–DEO’s request is 

for take of a small number of 30 species 

of marine mammals by Level B 

harassment and, for two of those 

species, by Level A harassment. Neither 

L–DEO nor NMFS expects serious injury 

or mortality to result from this activity 

and, therefore, an IHA is appropriate. 

Description of Proposed Activity 

Overview 

Researchers from L–DEO, University 

of Texas Institute of Geophysics (UTIG), 

and Northern Arizona University 

(NAU), with funding from the NSF, and 

in collaboration with researchers from 

the National Autonomous University of 

Mexico (Universidad Nacional 

Autonoma de Mexico or UNAM) and 

Kyoto University, propose to conduct 

high-energy seismic surveys from the 

research vessel (R/V) Marcus G. 

Langseth (Langseth) in and around the 

Guerrero Gap off western Mexico, in the 

ETP. The proposed study would use 

two-dimensional (2–D) seismic 

surveying to quantify incoming plate 

hydration and examine the role of fluids 

on megathrust slip behavior in and 

around the Guerrero Gap of the Middle 

America Trench. This is one of the bestknown examples in the world of alongstrike variations in slip behavior of the 

plate boundary. L–DEO proposes to 

conduct two different methods of 

seismic acquisition, multi-channel 

seismic (MCS) using a hydrophone 

streamer and refraction surveys using 

ocean bottom seismometers (OBSs). The 


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Federal Register / Vol. 87, No. 8 / Wednesday, January 12, 2022 / Notices 1993 

surveys would use a 36-airgun towed 

array with a total discharge volume of 

∼6600 cubic inches (in3) as an acoustic 

source, acquiring return signals using 

both a towed streamer as well as OBSs. 

The majority of the proposed 2–D 

seismic surveys would occur within the 

Exclusive Economic Zone (EEZ) of 

Mexico, including territorial seas, and a 

small portion would occur in 

International Waters. 

Dates and Duration 

The proposed research cruise would 

be expected to last for 48 days, 

including approximately 20 days of 

seismic survey operations, 3 days of 

transit to and from the survey area, 19 

days for equipment deployment/ 

recovery, and 6 days of contingency 

time for poor weather, etc. The R/V 

Langseth would likely leave out of and 

return to port in Manzanillo, Mexico, 

during spring 2022. The proposed IHA 

would be valid from March 1, 2022 

through February 28, 2023. 

Specific Geographic Region 

The proposed surveys would occur 

within the area of approximately 14– 

18.5°N and approximately 99–105°W. 

Representative survey tracklines are 

shown in Figure 1. Some deviation in 

actual track lines, including the order of 

survey operations, could be necessary 

for reasons such as science drivers, poor 

data quality, inclement weather, or 

mechanical issues with the research 

vessel and/or equipment. The majority 

of the proposed surveys would occur 

within the EEZ of Mexico, including 

territorial seas, and a small portion 

would occur in International Waters. 

The surveys would occur in waters up 

to 5,560 meters (m) deep. Most of the 

survey effort (94 percent) would occur 

in deep water (≤1000 m), and 6 percent 

would occur in intermediate water 

(100–1000 m deep); no effort would 

occur in shallow water (<100 m deep). 

A total of 3,600 kilometers (km) of 

transect lines would be surveyed (2,230 

km of 2–D MCS reflection data and 

1,370 km of OBS refraction data). 

Approximately 6 percent of the total 

survey effort would occur in Mexican 

territorial waters. Note that the MMPA 

does not apply in Mexican territorial 

waters. L–DEO is subject only to 

Mexican law in conducting that portion 

of the survey. However, NMFS has 

calculated the expected level of 

incidental take in the entire activity area 

(including Mexican territorial waters) as 

part of the analysis supporting our 

determination under the MMPA that the 

activity will have a negligible impact on 

the affected species (see Estimated Take 

and Negligible Impact Analysis and 

Determination). 

BILLING CODE 3510–22–P 


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• OBS Receiver Location 

--Seismic Lines 

- • Exclusive Economic Zone (EEZ) 

Territorial Sea (12 Nautical Miles) 

nctuary 

msar Wetland of International Importance 

nservation Areas 

Figure 1. Location of the Proposed Seismic Surveys and OBS Deployments in the 

Eastern Tropical Pacific Ocean 
1994 Federal Register / Vol. 87, No. 8 / Wednesday, January 12, 2022 / Notices 

BILLING CODE 3510–22–C 

Detailed Description of Specific Activity 

The procedures to be used for the 

proposed marine geophysical surveys 

would be similar to those used during 

previous surveys by L–DEO that 

received incidental take authorizations 

from NMFS (e.g., 85 FR 55645; 

September 9, 2020, 84 FR 35073; July 

22, 2019) and would use conventional 

seismic methodology. The survey would 

involve one source vessel, R/V 

Langseth, which would tow a 36-airgun 

array with a discharge volume of ∼6600 

in3 at a depth of 12 m. The array 

consists of 36 elements, including 20 

Bolt 1500LL airguns with volumes of 

180 to 360 in3 and 16 Bolt 1900LLX 

airguns with volumes of 40 to 120 in3. 

The airgun array configuration is 

illustrated in Figure 2–11 of NSF and 

the U.S. Geological Survey’s (USGS’s) 

Programmatic Environmental Impact 

Statement (PEIS; NSF–USGS, 2011). 

(The PEIS is available online at: 

www.nsf.gov/geo/oce/envcomp/usgsnsf-marine-seismic-research/nsf-usgsfinal-eis-oeis-with-appendices.pdf). 

The proposed surveys consist of eight 

MCS lines, of which six are coincident 

OBS refraction lines that are located 

perpendicular to the margin; these six 

lines would therefore be acquired twice. 

Approximately 62 percent of the total 

survey effort would be MCS surveys, 

with the remaining 38 percent using 

OBSs. There could be additional seismic 

survey operations associated with turns, 

airgun testing, and repeat coverage of 

any areas where initial data quality is 

sub-standard, and 25 percent has been 

added to the assumed survey line-kms 

to account for this potential. NMFS 

considers this a conservative approach 

to estimating potential acoustic 

exposures. 

The vessel speed during seismic 

survey operations would be ∼4.1 knots 

(∼7.6 km/hour) during MCS reflection 

surveys and 5 knots (∼9.3 km/hour) 

during OBS refraction surveys. The 

airguns would fire at a shot interval of 

50 m (approximately 24 seconds) during 

MCS surveys with the hydrophone 

streamer and at a 400-m (155 seconds) 

interval during refraction surveys to 

OBSs. The receiving system would 

consist of a 15-km long hydrophone 

streamer and short-period OBSs. As the 

airgun arrays are towed along the survey 

lines, the OBSs would receive and store 

the returning acoustic signals internally 

for later analysis, and the hydrophone 

streamer would transfer the data to the 

on-board processing system. 

The seismometers would consist of 33 

OBSs, which would be deployed at a 

total of 124 sites. The instruments 

would be deployed by R/V Langseth and 

spaced 10 or 12 km apart. Following 

refraction shooting of one line, shortperiod instruments on that line would 

be recovered, serviced, and redeployed 

on a subsequent refraction line while 

MCS data are acquired. The OBSs have 

a height and diameter of approximately 

1 m and an anchor weighing roughly 80 

kilograms (kg). OBS sample rate would 

be set at 200 hertz (Hz). All OBSs would 

be recovered by the end of the survey. 

To retrieve OBSs, an acoustic release 

transponder (pinger) is used to 

interrogate the instrument at a 

frequency of 8–11 kilohertz (kHz), and 

a response is received at a frequency of 

11.5–13 kHz. The burn-wire release 

assembly is then activated, and the 

instrument is released to float to the 

surface from the anchor which is not 

retrieved. Take of marine mammals is 

not expected to occur incidental to L– 

DEO’s use of OBSs. 

In addition to the operations of the 

airgun array, a multibeam echosounder 

(MBES), a sub-bottom profiler (SBP), 

and an Acoustic Doppler Current 

Profiler (ADCP) would be operated from 

R/V Langseth continuously during the 

seismic surveys, but not during transit 

to and from the survey area. Take of 

marine mammals is not expected to 

occur incidental to use of the MBES, 

SBP, or ADCP as, due to these sources’ 

characteristics (e.g., narrow downwarddirected beam), marine mammals would 

experience no more than one or two 

brief ping exposures from them, if any 

exposure were to occur. Accordingly, 

the use of MBES, SBP, and ADCP are 

not analyzed further in this document. 

Proposed mitigation, monitoring, and 

reporting measures are described in 

detail later in this document (please see 

Proposed Mitigation and Proposed 

Monitoring and Reporting). 

Description of Marine Mammals in the 

Area of Specified Activities 

Sections 3 and 4 of the application 

summarize available information 

regarding status and trends, distribution 

and habitat preferences, and behavior 

and life history, of the potentially 

affected species. Brief discussions of 

some species and stocks is presented 

below. For all other species, we refer the 

reader to the descriptions in L–DEO’s 

IHA application, incorporated here by 

reference, instead of reprinting the 

information. Additional information 

regarding population trends and threats 

may be found in NMFS’s Stock 

Assessment Reports (SARs; https://

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/marinemammal-stock-assessments) and more 

general information about these species 

(e.g., physical and behavioral 

descriptions) may be found on NMFS’s 

website (https://www.fisheries.

noaa.gov/find-species). 

Table 1 lists all species or stocks for 

which take is expected and proposed to 

be authorized for this action, and 

summarizes information related to the 

population or stock, including 

regulatory status under the MMPA and 

Endangered Species Act (ESA) and 

potential biological removal (PBR), 

where known. For taxonomy, we follow 

Committee on Taxonomy (2021). PBR is 

defined by the MMPA as the maximum 

number of animals, not including 

natural mortalities, that may be removed 

from a marine mammal stock while 

allowing that stock to reach or maintain 

its optimum sustainable population (as 

described in NMFS’s SARs). While no 

serious injury or mortality is anticipated 

or proposed for authorization here, PBR 

and annual serious injury and mortality 

from anthropogenic sources are 

included here as gross indicators of the 

status of the species and other threats. 

Marine mammal abundance estimates 

presented in this document represent 

the total number of individuals that 

make up a given stock or the total 

number estimated within a particular 

study or survey area. NMFS’s stock 

abundance estimates for most species 

represent the total estimate of 

individuals within the geographic area, 

if known, that comprises that stock. For 

some species, this geographic area may 

extend beyond U.S. waters. All managed 

stocks in this region are assessed in 

NMFS’s U.S. Pacific SARs. All values 

presented in Table 1 are the most recent 

available at the time of publication and 

are available in the 2020 SARs (Carretta 

et al., 2021) and draft 2021 SARs 

(available online at: https://

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/draftmarine-mammal-stock-assessmentreports). Where available, abundance 

and status information is also presented 

for marine mammals in the Pacific 

waters of Mexico and/or the greater ETP 

region. Table 1 denotes the status of 

species and stocks under the U.S. 

MMPA and ESA. We note also that the 

Guadalupe fur seal is classified as ‘‘En 

peligro de extincio ́n’’ (in danger of 

extinction) under the Norma Oficial 

Mexicana NOM–059–SEMARNAT–2010 

and all other marine mammal species 

listed in Table 1, with the exception of 

Longman’s beaked whales and 

Deraniyagala’s beaked whales, are listed 

as ‘‘Sujetas a proteccio ́n especial’’ 

(subject to special protection). 


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Federal Register / Vol. 87, No. 8 / Wednesday, January 12, 2022 / Notices 1995 

TABLE 1—MARINE MAMMALS THAT COULD OCCUR IN THE SURVEY AREA

Common name Scientific name Stock 

ESA/MMPA 

status; 

strategic (Y/N) 1

Stock abundance 

(CV, Nmin, most 

recent abundance 

survey) 2

PBR Annual M/SI3 ETP 

abundance 4

Mexico Pacific 

abundance 5

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales) 

Family Balaenopteridae (rorquals) 

Humpback Whale Megaptera 

novaeangliae.

Central N 

Pacific 

-, -, Y ................... 10,103 (0.3, 

7,890, 2006).

83 ........................ 26 2,566 ........................

Minke whale .......... Balaenoptera 

acutorostrata.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 115 ........................

Bryde’s whale ....... Balaenoptera 

edeni.

Eastern 

Tropical 

Pacific 

-, -, N .................. Unknown (Unknown, Unknown, N/A).Undetermined ..... Unknown 10,411 649 

Sei whale .............. Balaenoptera borealis.Eastern 

N Pacific 

E, D, Y ................ 519 (0.4, 374, 

2014).

0.75 ..................... ≥0.2 0 ........................

Fin whale .............. Balaenoptera 

physalus.

N/A E, D, Y ................ N/A ...................... N/A ...................... N/A 574 145 

Blue whale ............ Balaenoptera 

musculus.

Eastern 

N Pacific 

E, D, Y ................ 1,898 (0.085, 

1,767, 2018).

4.1 ....................... ≥19.4 1,415 773 

Superfamily Odontoceti (toothed whales, dolphins, and porpoises) 

Family Physeteridae 

Sperm whale ......... Physeter 

macrocephalus.

N/A E, D, Y ................ N/A ...................... N/A ...................... N/A 4,145 2810 

Family Kogiidae 

Dwarf Sperm 

Whale.

Kogia sima .......... N/A N/A ...................... N/A ...................... N/A ...................... N/A 6 11,200 ........................

Family Ziphiidae (beaked whales) 

Cuvier’s Beaked 

Whale.

Ziphius cavirostris N/A -, -, N .................. N/A ...................... N/A ...................... N/A 7 20,000 8 68,828 

Longman’s beaked 

whale.

Indopacetus 

pacificus.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 1,007 ........................

Blainville’s beaked 

whale.

Mesoplodon 

densirostris.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 9 25,300 8 68,828 

Ginkgo-toothed 

beaked whale.

M. ginkgodens .... N/A -, -, N .................. N/A ...................... N/A ...................... N/A 9 25,300 8 68,828 

Deraniyagala’s 

beaked whale.

M. hotaula ........... N/A -, -, N .................. N/A ...................... N/A ...................... N/A 9 25,300 8 68,828 

Pygmy beaked 

whale.

M. peruvianus ..... N/A -, -, N .................. N/A ...................... N/A ...................... N/A 9 25,300 8 68,828 

Family Delphinidae 

Risso’s dolphin ..... Grampus griseus N/A -, -, N .................. N/A ...................... N/A ...................... N/A 110,457 24,084 

Rough-toothed dolphin.Steno 

bredanensis.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 107,663 37,511 

Common 

bottlenose dolphin.

Tursiops 

truncatus.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 335,834 61,536 

Pantropical spotted 

dolphin.

Stenella attenuata N/A10 -, D, N ................. N/A ...................... N/A ...................... N/A 11 1,297,091 146,296 

Spinner dolphin ..... Stenella 

longirostris.

N/A10 -, D, N ................. N/A ...................... N/A ...................... N/A 11 2,075,871 186,906 

Striped dolphin ...... Stenella 

coeruleoalba.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 964,362 128,867 

Short-beaked common dolphin.Delphinus delphis N/A -, -, N .................. N/A ...................... N/A ...................... N/A 3,127,203 283196 

Fraser’s dolphin .... Lagenodelphis 

hosei.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 7 289,300 ........................

Short-finned pilot 

whale.

Globicephala 

macrorhynchus.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 12 589,315 3,348 

Killer whale ........... Orcinus orca ....... N/A -, -, N .................. N/A ...................... N/A ...................... N/A 7 8,500 852 

False killer whale .. Pseudorca 

crassidens.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 7 39,800 

Pygmy killer whale Feresa attenuata N/A -, -, N .................. N/A ...................... N/A ...................... N/A 7 38,900 ........................

Melon-headed 

whale.

Peponocephala 

electra.

N/A -, -, N .................. N/A ...................... N/A ...................... N/A 7 45,400 ........................

Order Carnivora—Superfamily Pinnipedia 

Family Otariidae (eared seals and sea lions) 

Guadalupe fur seal Arctocephalus 

townsendi.

Mexico T, D, Y ................ 34,187 (N/A, 

31,019, 2013).

1062 .................... ≥3.8 ........................ ........................


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1996 Federal Register / Vol. 87, No. 8 / Wednesday, January 12, 2022 / Notices 

TABLE 1—MARINE MAMMALS THAT COULD OCCUR IN THE SURVEY AREA—Continued 

Common name Scientific name Stock 

ESA/MMPA 

status; 

strategic (Y/N) 1

Stock abundance 

(CV, Nmin, most 

recent abundance 

survey) 2

PBR Annual M/SI3 ETP 

abundance 4

Mexico Pacific 

abundance 5

California sea lion Zalophus 

californianus.

U.S. -, -, N .................. 257,606 (N/ 

A,233,515, 

2014).

14011 .................. >320 105,000 ........................

1Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the 

ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or 

which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically 

designated under the MMPA as depleted and as a strategic stock. 2 NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports . CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable. 3These values, found in NMFS’s SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g., commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated 

mortality due to commercial fisheries is presented in some cases. 4From NMFS (2015b) unless otherwise noted. 

5Pacific Mexico excluding the Gulf of California (from Gerrodette and Palacios (1996) unless otherwise noted). 

6Estimate for ETP is mostly for K. sima but may also include some K. breviceps (Wade and Gerrodette 1993). 7Wade and Gerrodette 1993. 

8Abundance for all ziphiids. 

9This estimate for the ETP includes all species of the genus Mesoplodon. 10Several stocks of these species, while not classified as such in the U.S. SARs, are considered depleted due to historical interactions with tuna fisheries in the 

area. Please see below for a discussion of these stocks. 11 Includes abundance of several stocks added together. 12Based on surveys in 2000 (Gerrodette and Forcada 2002). 

As indicated above, all 30 species 

(with six managed stocks) in Table 1 

temporally and spatially co-occur with 

the activity to the degree that take is 

reasonably likely to occur, and we have 

proposed authorizing it. As the planned 

survey lines are outside of the U.S. EEZ, 

they do not directly overlap with the 

defined ranges for most U.S. managed 

stocks (Carretta et al., 2021). For some 

species (e.g., Bryde’s whale, Guadalupe 

fur seal; see Table 1), animals 

encountered during the surveys could 

be from a defined stock under the 

MMPA but most marine mammals in 

the survey area do not belong to any 

defined stock. Species that could 

potentially occur in the proposed 

research area but are not likely to be 

encountered due to the rarity of their 

occurrence (i.e., are considered 

extralimital or rare visitors to the coastal 

waters of Mexico in the Eastern Tropical 

Pacific) are described briefly but 

omitted from further analysis. These 

generally include species that do not 

normally occur in the area but for which 

there are one or more occurrence 

records that are considered beyond the 

normal range of the species. These 

species include the gray whale 

(Eschrichtius robustus), Hubbs’ beaked 

whale (Mesoplodon carlhubbsi), 

Stejneger’s beaked whale (M. stejnegeri), 

Perrin’s beaked whale (M. perrini), 

Baird’s beaked whale (Berardius 

bairdii), pygmy sperm whale (Kogia 

breviceps), long-finned pilot whale 

(Globicephala melas), Dall’s porpoise 

(Phocoenoides dalli), Pacific whitesided dolphin (Lagenorhynchus 

obliquidens), and northern right whale 

dolphin (Lissodelphis borealis), which 

all generally occur well north of the 

proposed survey area (e.g, north of the 

Baja peninsula). Five additional 

pinniped species are known to occur in 

the ETP but are considered extralimital 

in the proposed survey area: The 

Gala ́pagos sea lion (Zalophus 

wollebaeki), Gala ́pagos fur seal 

(Arctocephalus galapagoensis), South 

American fur seal (A. australis), and the 

South American sea lion (Otaria 

flavescens), which all occur south of the 

survey area, and the northern elephant 

seal (Mirounga angustirostris) which is 

found north of the survey area. 

Prior to 2016, humpback whales were 

listed under the ESA as an endangered 

species worldwide. Following a 2015 

global status review (Bettridge et al., 

2015), NMFS delineated 14 distinct 

population segments (DPSs) with 

different listing statuses (81 FR 62259; 

September 8, 2016) pursuant to the ESA. 

The DPSs that occur in U.S. waters do 

not necessarily equate to the existing 

stocks designated under the MMPA and 

shown in Table 1. The threatened 

Mexico DPS and endangered Central 

America DPS may occur within the 

proposed survey area. However, due to 

the expected timing of the proposed 

survey (spring), most humpbacks from 

the Mexico DPS will have begun their 

migration north toward the feeding 

grounds off of the U.S. west coast and 

are likely to be outside of the survey 

area. Humpbacks from the Central 

America DPS will likely be migrating 

northward through the survey area at 

the time of the proposed survey. 

Therefore, we assume that most 

humpback whales taken by the 

proposed survey activities will be from 

the Central America DPS. 

The pantropical spotted dolphin is 

one of the most abundant cetaceans and 

is distributed worldwide in tropical and 

some subtropical waters, between ∼40°N 

and 40°S (Jefferson et al., 2015). In the 

ETP, this species ranges from 25° N off 

the Baja California Peninsula to 17° S, 

off southern Peru (Perrin and Hohn, 

1994). There are two forms of 

pantropical spotted dolphin (Perrin 

2018a): Coastal (Stenella attenuata 

graffmani) and offshore (S. a. 

attenuata), both of which could occur 

within the proposed survey area. Along 

the coast of Latin America, the coastal 

form typically occurs within 20 km from 

shore (Urba ́n 2008 in Heckel et al., 

2020). There are currently three 

recognized stocks of spotted dolphins in 

the ETP: The coastal stock and two 

offshore stocks—the northeast and the 

west/south stocks (Wade and Gerrodette 

1993; Leslie et al., 2019). Much of what 

is known about the pantropical spotted 

dolphin in the ETP is related to the 

historical tuna purse-seine fishery in 

that area (Perrin and Hohn 1994). There 

was an overall stock decline of spotted 

dolphins from 1960–1980 because of the 

fishery (Allen 1985). In 1979, the 

population size of spotted dolphins in 

the ETP was estimated at 2.9–3.3 

million (Allen 1985). For 1986–1990, 

Wade and Gerrodette (1993) reported an 

estimate of 2.1 million. Gerrodette and 

Forcada (2005) noted that the 

population of offshore northeastern 

spotted dolphins had not yet recovered 

from the earlier population declines; 

possible reasons for the lack of growth 

were attributed to unreported bycatch, 

effects of fishing activity on survival 

and reproduction, and long-term 

changes in the ecosystem. The 

abundance estimate for 2006 was 

∼857,884 northeastern offshore spotted 


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dolphins, and 439,208 western-southern 

offshore spotted dolphins; the coastal 

subspecies was estimated at 278,155 

and was less affected by fishing 

activities (Gerrodette et al., 2008). In 

2004, the mortality rate in the tuna 

fishery was estimated at 0.03 percent 

(Bayliff 2004). Perrin (2018a) noted that 

for the last few years, hundreds of 

spotted dolphins have been taken in the 

fishery. Currently, there are ∼640,000 

northeastern offshore spotted dolphins 

inhabiting the ETP (Perrin 2018a). This 

stock is still considered depleted and 

may be slow to recover due to continued 

chase and encirclement by the tuna 

fishery, which may in turn affect 

reproductive rates (Cramer et al., 2008; 

Kellar et al., 2013). The northeastern 

offshore and coastal stocks of 

pantropical spotted dolphins are likely 

to be encountered during the proposed 

surveys. 

The spinner dolphin is pantropical in 

distribution, including oceanic tropical 

and sub-tropical waters between 40° N 

and 40° S (Jefferson et al., 2015). It is 

generally considered a pelagic species, 

but it can also be found in coastal 

waters (Perrin 2018b). In the ETP, three 

types of spinner dolphins have been 

identified and two of those are 

recognized as subspecies: The eastern 

spinner dolphin (Stenella longirostris 

orientalis), considered an offshore 

species, the Central American spinner 

(S.l. centroamericana; also known as the 

Costa Rican spinner), considered a 

coastal species occurring from southern 

Mexico to Costa Rica (Perrin 1990; 

Dizon et al., 1991), and the ‘whitebelly’ 

spinner which is thought to be a hybrid 

of the eastern spinner and Gray’s 

spinner (S.l. longirostris). Gray’s spinner 

dolphin is not expected to occur within 

the proposed study area. Although there 

is a great deal of overlap between the 

ranges of eastern and whitebelly spinner 

dolphins, the eastern form generally 

occurs in the northeastern portion of the 

ETP, whereas the whitebelly spinner 

occurs in the southern portion of the 

ETP, ranging farther offshore (Wade and 

Gerrodette 1993; Reilly and Fiedler 

1994). Reilly and Fiedler (1994) noted 

that eastern spinners are associated with 

waters that have high surface 

temperatures and chlorophyll and 

shallow thermoclines, whereas 

whitebelly spinners are associated with 

cooler surface temperatures, lower 

chlorophyll levels, and deeper 

thermoclines. The eastern spinner 

dolphins are the most likely to occur in 

the proposed survey area (see Ferguson 

and Barlow 2001; Heckel et al., 2020), 

as this subspecies occurs in the ETP, 

east of 145° W, between 24° N off the 

Baja California Peninsula and 10° S off 

Peru (Perrin 1990). Wade and Gerrodette 

(1993) reported an abundance estimate 

of 1.7 million, and Gerrodette et al. 

(2005) estimated the abundance at 1.1 

million for 2003. Gerrodette and 

Forcada (2005) noted that the 

population of eastern spinner dolphins 

had not yet recovered from the earlier 

population declines due to the tuna 

fishery. The population estimate for 

eastern spinner dolphins in 2003 was 

612,662 (Gerrodette et al., 2005). In 

2000, the whitebelly dolphin was 

estimated to number 801,000 in the ETP 

(Gerrodette et al., 2005). Bayliff (2004) 

noted a spinner dolphin mortality rate 

in the tuna fishery of 0.03 percent for 

2004. Possible reasons why the 

population has not recovered include 

under-reported bycatch, effects of 

fishing activity on survival and 

reproduction, and long-term changes in 

the ecosystem (Gerrodette and Forcada, 

2005). The continued chase and 

encirclement by the tuna fishery may be 

affecting the reproductive rates of the 

eastern spinner dolphin (Cramer et al., 

2008). 

The common dolphin is found in 

oceanic and nearshore waters of tropical 

and warm temperate oceans around the 

world, ranging from ∼60° N to ∼50° S 

(Jefferson et al., 2015). There are two 

subspecies of common dolphins that 

occur in the eastern Pacific Ocean, the 

short-beaked form (Delphinus delphis 

delphis) and the long-beaked form (D. 

delphis bairdii). The long-beaked form 

generally prefers shallower water 

(Perrin 2018c), typically occurring 

within 180 km from shore (Jefferson et 

al., 2015). The short-beaked form occurs 

along the entire coast of Mexico and has 

been sighted near the proposed survey 

area off Nayarit, Michoaca ́n, and 

Guerrero; the long-beaked form occurs 

off the Baja California Peninsula and the 

Gulf of California (Heckel et al., 2020). 

The southern limit of the long-beaked 

form appears to be 22° N (Urba ́n 2008), 

and no sightings in Mexican waters 

have been made to the south of that. 

Thus, only the short-beaked form is 

expected to occur within the study area. 

Unusual Mortality Events (UME) 

A UME is defined under the MMPA 

as ‘‘a stranding that is unexpected; 

involves a significant die-off of any 

marine mammal population; and 

demands immediate response.’’ For 

more information on UMEs, please visit: 

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/marinemammal-unusual-mortality-events. 

Increased strandings of Guadalupe fur 

seals have occurred along the entire 

coast of California. Guadalupe fur seal 

strandings began in January 2015 and 

were eight times higher than the 

historical average. Strandings have 

continued since 2015 and have 

remained well above average through 

2019. Strandings are seasonal and 

generally peak in April through June of 

each year. Strandings in Oregon and 

Washington became elevated starting in 

2019 and have continued to present. 

Strandings in these two states in 2019 

are five times higher than the historical 

average. As of December 2021, a total of 

724 Guadalupe fur seals have stranded 

and are considered part of the UME (542 

in California and 182 in Oregon and 

Washington). Stranded Guadalupe fur 

seals are mostly weaned pups and 

juveniles (1–2 years old). The majority 

of stranded animals showed signs of 

malnutrition with secondary bacterial 

and parasitic infections. For more 

information, please visit https://

www.fisheries.noaa.gov/national/ 

marine-life-distress/2015-2021- 

guadalupe-fur-seal-unusual-mortalityevent-california. 

Marine Mammal Hearing 

Hearing is the most important sensory 

modality for marine mammals 

underwater, and exposure to 

anthropogenic sound can have 

deleterious effects. To appropriately 

assess the potential effects of exposure 

to sound, it is necessary to understand 

the frequency ranges marine mammals 

are able to hear. Current data indicate 

that not all marine mammal species 

have equal hearing capabilities (e.g., 

Richardson et al., 1995; Wartzok and 

Ketten, 1999; Au and Hastings, 2008). 

To reflect this, Southall et al. (2007) 

recommended that marine mammals be 

divided into functional hearing groups 

based on directly measured or estimated 

hearing ranges on the basis of available 

behavioral response data, audiograms 

derived using auditory evoked potential 

techniques, anatomical modeling, and 

other data. Note that no direct 

measurements of hearing ability have 

been successfully completed for 

mysticetes (i.e., low-frequency 

cetaceans). Subsequently, NMFS (2018) 

described generalized hearing ranges for 

these marine mammal hearing groups. 

Generalized hearing ranges were chosen 

based on the approximately 65 decibel 

(dB) threshold from the normalized 

composite audiograms, with the 

exception for lower limits for lowfrequency cetaceans where the lower 

bound was deemed to be biologically 

implausible and the lower bound from 

Southall et al. (2007) retained. Marine 

mammal hearing groups and their 

associated hearing ranges are provided 

in Table 2. 


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TABLE 2—MARINE MAMMAL HEARING GROUPS

[NMFS, 2018] 

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). 

The pinniped functional hearing 

group was modified from Southall et al. 

(2007) on the basis of data indicating 

that phocid species have consistently 

demonstrated an extended frequency 

range of hearing compared to otariids, 

especially in the higher frequency range 

(Hemila ̈ et al., 2006; Kastelein et al., 

2009; Reichmuth and Holt, 2013). 

For more detail concerning these 

groups and associated frequency ranges, 

please see NMFS (2018) for a review of 

available information. 30 marine 

mammal species (28 cetacean and two 

pinniped (both otariid) species) have the 

reasonable potential to co-occur with 

the proposed survey activities. Please 

refer to Table 1. Of the cetacean species 

that may be present, six are classified as 

low-frequency cetaceans (i.e., all 

mysticete species), 20 are classified as 

mid-frequency cetaceans (i.e., all 

delphinid and ziphiid species and the 

sperm whale), and two are classified as 

high-frequency cetaceans (i.e., harbor 

porpoise and Kogia spp.). 

Potential Effects of Specified Activities 

on Marine Mammals and Their Habitat 

This section includes a summary and 

discussion of the ways that components 

of the specified activity may impact 

marine mammals and their habitat. The 

Estimated Take section later in this 

document includes a quantitative 

analysis of the number of individuals 

that are expected to be taken by this 

activity. The Negligible Impact Analysis 

and Determination section considers the 

content of this section, the Estimated 

Take section, and the Proposed 

Mitigation section, to draw conclusions 

regarding the likely impacts of these 

activities on the reproductive success or 

survivorship of individuals and how 

those impacts on individuals are likely 

to impact marine mammal species or 

stocks. 

Description of Active Acoustic Sound 

Sources 

This section contains a brief technical 

background on sound, the 

characteristics of certain sound types, 

and on metrics used in this proposal 

inasmuch as the information is relevant 

to the specified activity and to a 

discussion of the potential effects of the 

specified activity on marine mammals 

found later in this document. 

Sound travels in waves, the basic 

components of which are frequency, 

wavelength, velocity, and amplitude. 

Frequency is the number of pressure 

waves that pass by a reference point per 

unit of time and is measured in hertz 

(Hz) or cycles per second. Wavelength is 

the distance between two peaks or 

corresponding points of a sound wave 

(length of one cycle). Higher frequency 

sounds have shorter wavelengths than 

lower frequency sounds, and typically 

attenuate (decrease) more rapidly, 

except in certain cases in shallower 

water. Amplitude is the height of the 

sound pressure wave or the ‘‘loudness’’ 

of a sound and is typically described 

using the relative unit of the dB. A 

sound pressure level (SPL) in dB is 

described as the ratio between a 

measured pressure and a reference 

pressure (for underwater sound, this is 

1 microPascal (mPa)) and is a 

logarithmic unit that accounts for large 

variations in amplitude; therefore, a 

relatively small change in dB 

corresponds to large changes in sound 

pressure. The source level (SL) 

represents the SPL referenced at a 

distance of 1 m from the source 

(referenced to 1 mPa) while the received 

level is the SPL at the listener’s position 

(referenced to 1 mPa). 

Root mean square (rms) is the 

quadratic mean sound pressure over the 

duration of an impulse. Root mean 

square is calculated by squaring all of 

the sound amplitudes, averaging the 

squares, and then taking the square root 

of the average (Urick, 1983). Root mean 

square accounts for both positive and 

negative values; squaring the pressures 

makes all values positive so that they 

may be accounted for in the summation 

of pressure levels (Hastings and Popper, 

2005). This measurement is often used 

in the context of discussing behavioral 

effects, in part because behavioral 

effects, which often result from auditory 

cues, may be better expressed through 

averaged units than by peak pressures. 

Sound exposure level (SEL; 

represented as dB re 1 mPa2¥s) 

represents the total energy contained 

within a pulse and considers both 

intensity and duration of exposure. Peak 

sound pressure (also referred to as zeroto-peak sound pressure or 0-p) is the 

maximum instantaneous sound pressure 

measurable in the water at a specified 

distance from the source and is 

represented in the same units as the rms 

sound pressure. Another common 

metric is peak-to-peak sound pressure 

(pk-pk), which is the algebraic 

difference between the peak positive 

and peak negative sound pressures. 

Peak-to-peak pressure is typically 

approximately 6 dB higher than peak 

pressure (Southall et al., 2007). 

When underwater objects vibrate or 

activity occurs, sound-pressure waves 

are created. These waves alternately 

compress and decompress the water as 

the sound wave travels. Underwater 

sound waves radiate in a manner similar 

to ripples on the surface of a pond and 

may be either directed in a beam or 

beams or may radiate in all directions 

(omnidirectional sources), as is the case 

for pulses produced by the airgun arrays 

considered here. The compressions and 

decompressions associated with sound 

waves are detected as changes in 

pressure by aquatic life and man-made 

sound receptors such as hydrophones. 

Even in the absence of sound from the 

specified activity, the underwater 

environment is typically loud due to 

ambient sound. Ambient sound is 

defined as environmental background 

sound levels lacking a single source or 

point (Richardson et al., 1995), and the 

sound level of a region is defined by the 

total acoustical energy being generated 

by known and unknown sources. These 

sources may include physical (e.g., 

wind and waves, earthquakes, ice, 

atmospheric sound), biological (e.g., 


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sounds produced by marine mammals, 

fish, and invertebrates), and 

anthropogenic (e.g., vessels, dredging, 

construction) sound. A number of 

sources contribute to ambient sound, 

including the following (Richardson et 

al., 1995): 

• Wind and waves: The complex 

interactions between wind and water 

surface, including processes such as 

breaking waves and wave-induced 

bubble oscillations and cavitation, are a 

main source of naturally occurring 

ambient sound for frequencies between 

200 Hz and 50 kHz (Mitson, 1995). In 

general, ambient sound levels tend to 

increase with increasing wind speed 

and wave height. Surf sound becomes 

important near shore, with 

measurements collected at a distance of 

8.5 km from shore showing an increase 

of 10 dB in the 100 to 700 Hz band 

during heavy surf conditions; 

• Precipitation: Sound from rain and 

hail impacting the water surface can 

become an important component of total 

sound at frequencies above 500 Hz, and 

possibly down to 100 Hz during quiet 

times; 

• Biological: Marine mammals can 

contribute significantly to ambient 

sound levels, as can some fish and 

snapping shrimp. The frequency band 

for biological contributions is from 

approximately 12 Hz to over 100 kHz; 

and 

• Anthropogenic: Sources of ambient 

sound related to human activity include 

transportation (surface vessels), 

dredging and construction, oil and gas 

drilling and production, seismic 

surveys, sonar, explosions, and ocean 

acoustic studies. Vessel noise typically 

dominates the total ambient sound for 

frequencies between 20 and 300 Hz. In 

general, the frequencies of 

anthropogenic sounds are below 1 kHz 

and, if higher frequency sound levels 

are created, they attenuate rapidly. 

Sound from identifiable anthropogenic 

sources other than the activity of 

interest (e.g., a passing vessel) is 

sometimes termed background sound, as 

opposed to ambient sound. 

The sum of the various natural and 

anthropogenic sound sources at any 

given location and time—which 

comprise ‘‘ambient’’ or ‘‘background’’ 

sound—depends not only on the source 

levels (as determined by current 

weather conditions and levels of 

biological and human activity) but also 

on the ability of sound to propagate 

through the environment. In turn, sound 

propagation is dependent on the 

spatially and temporally varying 

properties of the water column and sea 

floor, and is frequency-dependent. As a 

result of the dependence on a large 

number of varying factors, ambient 

sound levels can be expected to vary 

widely over both coarse and fine spatial 

and temporal scales. Sound levels at a 

given frequency and location can vary 

by 10–20 dB from day to day 

(Richardson et al., 1995). The result is 

that, depending on the source type and 

its intensity, sound from a given activity 

may be a negligible addition to the local 

environment or could form a distinctive 

signal that may affect marine mammals. 

Details of source types are described in 

the following text. 

Sounds are often considered to fall 

into one of two general types: Pulsed 

and non-pulsed (defined in the 

following). The distinction between 

these two sound types is important 

because they have differing potential to 

cause physical effects, particularly with 

regard to hearing (e.g., Ward, 1997 in 

Southall et al., 2007). Please see 

Southall et al. (2007) for an in-depth 

discussion of these concepts. 

Pulsed sound sources (e.g., airguns, 

explosions, gunshots, sonic booms, 

impact pile driving) produce signals 

that are brief (typically considered to be 

less than one second), broadband, atonal 

transients (ANSI, 1986, 2005; Harris, 

1998; NIOSH, 1998; ISO, 2003) and 

occur either as isolated events or 

repeated in some succession. Pulsed 

sounds are all characterized by a 

relatively rapid rise from ambient 

pressure to a maximal pressure value 

followed by a rapid decay period that 

may include a period of diminishing, 

oscillating maximal and minimal 

pressures, and generally have an 

increased capacity to induce physical 

injury as compared with sounds that 

lack these features. 

Non-pulsed sounds can be tonal, 

narrowband, or broadband, brief or 

prolonged, and may be either 

continuous or non-continuous (ANSI, 

1995; NIOSH, 1998). Some of these nonpulsed sounds can be transient signals 

of short duration but without the 

essential properties of pulses (e.g., rapid 

rise time). Examples of non-pulsed 

sounds include those produced by 

vessels, aircraft, machinery operations 

such as drilling or dredging, vibratory 

pile driving, and active sonar systems 

(such as those used by the U.S. Navy). 

The duration of such sounds, as 

received at a distance, can be greatly 

extended in a highly reverberant 

environment. 

Airgun arrays produce pulsed signals 

with energy in a frequency range from 

about 10–2,000 Hz, with most energy 

radiated at frequencies below 200 Hz. 

The amplitude of the acoustic wave 

emitted from the source is equal in all 

directions (i.e., omnidirectional), but 

airgun arrays do possess some 

directionality due to different phase 

delays between guns in different 

directions. Airgun arrays are typically 

tuned to maximize functionality for data 

acquisition purposes, meaning that 

sound transmitted in horizontal 

directions and at higher frequencies is 

minimized to the extent possible. 

Acoustic Effects 

Here, we discuss the effects of active 

acoustic sources on marine mammals. 

Potential Effects of Underwater 

Sound—Please refer to the information 

given previously (‘‘Description of Active 

Acoustic Sound Sources’’) regarding 

sound, characteristics of sound types, 

and metrics used in this document. Note 

that, in the following discussion, we 

refer in many cases to a review article 

concerning studies of noise-induced 

hearing loss conducted from 1996–2015 

(i.e., Finneran, 2015). For study-specific 

citations, please see that work. 

Anthropogenic sounds cover a broad 

range of frequencies and sound levels 

and can have a range of highly variable 

impacts on marine life, from none or 

minor to potentially severe responses, 

depending on received levels, duration 

of exposure, behavioral context, and 

various other factors. The potential 

effects of underwater sound from active 

acoustic sources can potentially result 

in one or more of the following: 

Temporary or permanent hearing 

impairment, non-auditory physical or 

physiological effects, behavioral 

disturbance, stress, and masking 

(Richardson et al., 1995; Gordon et al., 

2004; Nowacek et al., 2007; Southall et 

al., 2007; Go ̈tz et al., 2009). The degree 

of effect is intrinsically related to the 

signal characteristics, received level, 

distance from the source, and duration 

of the sound exposure. In general, 

sudden, high level sounds can cause 

hearing loss, as can longer exposures to 

lower level sounds. Temporary or 

permanent loss of hearing will occur 

almost exclusively for noise within an 

animal’s hearing range. We first describe 

specific manifestations of acoustic 

effects before providing discussion 

specific to the use of airgun arrays. 

Richardson et al. (1995) described 

zones of increasing intensity of effect 

that might be expected to occur, in 

relation to distance from a source and 

assuming that the signal is within an 

animal’s hearing range. First is the area 

within which the acoustic signal would 

be audible (potentially perceived) to the 

animal, but not strong enough to elicit 

any overt behavioral or physiological 

response. The next zone corresponds 

with the area where the signal is audible 

to the animal and of sufficient intensity 


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to elicit behavioral or physiological 

responsiveness. Third is a zone within 

which, for signals of high intensity, the 

received level is sufficient to potentially 

cause discomfort or tissue damage to 

auditory or other systems. Overlaying 

these zones to a certain extent is the 

area within which masking (i.e., when a 

sound interferes with or masks the 

ability of an animal to detect a signal of 

interest that is above the absolute 

hearing threshold) may occur; the 

masking zone may be highly variable in 

size. 

We describe the more severe effects of 

certain non-auditory physical or 

physiological effects only briefly as we 

do not expect that use of airgun arrays 

are reasonably likely to result in such 

effects (see below for further 

discussion). Potential effects from 

impulsive sound sources can range in 

severity from effects such as behavioral 

disturbance or tactile perception to 

physical discomfort, slight injury of the 

internal organs and the auditory system, 

or mortality (Yelverton et al., 1973). 

Non-auditory physiological effects or 

injuries that theoretically might occur in 

marine mammals exposed to high level 

underwater sound or as a secondary 

effect of extreme behavioral reactions 

(e.g., change in dive profile as a result 

of an avoidance reaction) caused by 

exposure to sound include neurological 

effects, bubble formation, resonance 

effects, and other types of organ or 

tissue damage (Cox et al., 2006; Southall 

et al., 2007; Zimmer and Tyack, 2007; 

Tal et al., 2015). The survey activities 

considered here do not involve the use 

of devices such as explosives or midfrequency tactical sonar that are 

associated with these types of effects. 

Threshold Shift—Marine mammals 

exposed to high-intensity sound, or to 

lower-intensity sound for prolonged 

periods, can experience hearing 

threshold shift (TS), which is the loss of 

hearing sensitivity at certain frequency 

ranges (Finneran, 2015). TS can be 

permanent (PTS), in which case the loss 

of hearing sensitivity is not fully 

recoverable, or temporary (TTS), in 

which case the animal’s hearing 

threshold would recover over time 

(Southall et al., 2007). Repeated sound 

exposure that leads to TTS could cause 

PTS. In severe cases of PTS, there can 

be total or partial deafness, while in 

most cases the animal has an impaired 

ability to hear sounds in specific 

frequency ranges (Kryter, 1985). 

When PTS occurs, there is physical 

damage to the sound receptors in the ear 

(i.e., tissue damage), whereas TTS 

represents primarily tissue fatigue and 

is reversible (Southall et al., 2007). In 

addition, other investigators have 

suggested that TTS is within the normal 

bounds of physiological variability and 

tolerance and does not represent 

physical injury (e.g., Ward, 1997). 

Therefore, NMFS does not consider TTS 

to constitute auditory injury. 

Relationships between TTS and PTS 

thresholds have not been studied in 

marine mammals, and there is no PTS 

data for cetaceans but such relationships 

are assumed to be similar to those in 

humans and other terrestrial mammals. 

PTS typically occurs at exposure levels 

at least several dBs above (a 40-dB 

threshold shift approximates PTS onset; 

e.g., Kryter et al., 1966; Miller, 1974) 

that inducing mild TTS (a 6-dB 

threshold shift approximates TTS onset; 

e.g., Southall et al. 2007). Based on data 

from terrestrial mammals, a 

precautionary assumption is that the 

PTS thresholds for impulse sounds 

(such as airgun pulses as received close 

to the source) are at least 6 dB higher 

than the TTS threshold on a peakpressure basis and PTS cumulative 

sound exposure level thresholds are 15 

to 20 dB higher than TTS cumulative 

sound exposure level thresholds 

(Southall et al., 2007). Given the higher 

level of sound or longer exposure 

duration necessary to cause PTS as 

compared with TTS, it is considerably 

less likely that PTS could occur. 

For mid-frequency cetaceans in 

particular, potential protective 

mechanisms may help limit onset of 

TTS or prevent onset of PTS. Such 

mechanisms include dampening of 

hearing, auditory adaptation, or 

behavioral amelioration (e.g., Nachtigall 

and Supin, 2013; Miller et al., 2012; 

Finneran et al., 2015; Popov et al., 

2016). 

TTS is the mildest form of hearing 

impairment that can occur during 

exposure to sound (Kryter, 1985). While 

experiencing TTS, the hearing threshold 

rises, and a sound must be at a higher 

level in order to be heard. In terrestrial 

and marine mammals, TTS can last from 

minutes or hours to days (in cases of 

strong TTS). In many cases, hearing 

sensitivity recovers rapidly after 

exposure to the sound ends. Few data 

on sound levels and durations necessary 

to elicit mild TTS have been obtained 

for marine mammals. 

Marine mammal hearing plays a 

critical role in communication with 

conspecifics, and interpretation of 

environmental cues for purposes such 

as predator avoidance and prey capture. 

Depending on the degree (elevation of 

threshold in dB), duration (i.e., recovery 

time), and frequency range of TTS, and 

the context in which it is experienced, 

TTS can have effects on marine 

mammals ranging from discountable to 

serious. For example, a marine mammal 

may be able to readily compensate for 

a brief, relatively small amount of TTS 

in a non-critical frequency range that 

occurs during a time where ambient 

noise is lower and there are not as many 

competing sounds present. 

Alternatively, a larger amount and 

longer duration of TTS sustained during 

time when communication is critical for 

successful mother/calf interactions 

could have more serious impacts. 

Finneran et al. (2015) measured 

hearing thresholds in three captive 

bottlenose dolphins before and after 

exposure to ten pulses produced by a 

seismic airgun in order to study TTS 

induced after exposure to multiple 

pulses. Exposures began at relatively 

low levels and gradually increased over 

a period of several months, with the 

highest exposures at peak SPLs from 

196 to 210 dB and cumulative 

(unweighted) SELs from 193–195 dB. 

No substantial TTS was observed. In 

addition, behavioral reactions were 

observed that indicated that animals can 

learn behaviors that effectively mitigate 

noise exposures (although exposure 

patterns must be learned, which is less 

likely in wild animals than for the 

captive animals considered in this 

study). The authors note that the failure 

to induce more significant auditory 

effects likely due to the intermittent 

nature of exposure, the relatively low 

peak pressure produced by the acoustic 

source, and the low-frequency energy in 

airgun pulses as compared with the 

frequency range of best sensitivity for 

dolphins and other mid-frequency 

cetaceans. 

Currently, TTS data only exist for four 

species of cetaceans (bottlenose 

dolphin, beluga whale (Delphinapterus 

leucas), harbor porpoise (Phocoena 

phocoena), and Yangtze finless porpoise 

(Neophocaena asiaeorientalis)) exposed 

to a limited number of sound sources 

(i.e., mostly tones and octave-band 

noise) in laboratory settings (Finneran, 

2015). In general, harbor porpoises have 

a lower TTS onset than other measured 

cetacean species (Finneran, 2015). 

Additionally, the existing marine 

mammal TTS data come from a limited 

number of individuals within these 

species. There are no data available on 

noise-induced hearing loss for 

mysticetes. 

Critical questions remain regarding 

the rate of TTS growth and recovery 

after exposure to intermittent noise and 

the effects of single and multiple pulses. 

Data at present are also insufficient to 

construct generalized models for 

recovery and determine the time 

necessary to treat subsequent exposures 

as independent events. More 


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information is needed on the 

relationship between auditory evoked 

potential and behavioral measures of 

TTS for various stimuli. For summaries 

of data on TTS in marine mammals or 

for further discussion of TTS onset 

thresholds, please see Southall et al. 

(2007, 2019), Finneran and Jenkins 

(2012), Finneran (2015), and NMFS 

(2018). 

Behavioral Effects—Behavioral 

disturbance may include a variety of 

effects, including subtle changes in 

behavior (e.g., minor or brief avoidance 

of an area or changes in vocalizations), 

more conspicuous changes in similar 

behavioral activities, and more 

sustained and/or potentially severe 

reactions, such as displacement from or 

abandonment of high-quality habitat. 

Behavioral responses to sound are 

highly variable and context-specific and 

any reactions depend on numerous 

intrinsic and extrinsic factors (e.g., 

species, state of maturity, experience, 

current activity, reproductive state, 

auditory sensitivity, time of day), as 

well as the interplay between factors 

(e.g., Richardson et al., 1995; Wartzok et 

al., 2003; Southall et al., 2007, 2019; 

Weilgart, 2007; 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, 

context, and numerous other factors 

(Ellison et al., 2012), and can vary 

depending on characteristics associated 

with the sound source (e.g., whether it 

is moving or stationary, number of 

sources, distance from the source). 

Please see Appendices B–C of Southall 

et al. (2007) for a review of studies 

involving marine mammal behavioral 

responses to sound. 

Habituation can occur when an 

animal’s response to a stimulus wanes 

with repeated exposure, usually in the 

absence of unpleasant associated events 

(Wartzok et al., 2003). Animals are most 

likely to habituate to sounds that are 

predictable and unvarying. It is 

important to note that habituation is 

appropriately considered as a 

‘‘progressive reduction in response to 

stimuli that are perceived as neither 

aversive nor beneficial,’’ rather than as, 

more generally, moderation in response 

to human disturbance (Bejder et al., 

2009). The opposite process is 

sensitization, when an unpleasant 

experience leads to subsequent 

responses, often in the form of 

avoidance, at a lower level of exposure. 

As noted, behavioral state may affect the 

type of response. For example, animals 

that are resting may show greater 

behavioral change in response to 

disturbing sound levels than animals 

that are highly motivated to remain in 

an area for feeding (Richardson et al., 

1995; NRC, 2003; Wartzok et al., 2003). 

Controlled experiments with captive 

marine mammals have showed 

pronounced behavioral reactions, 

including avoidance of loud sound 

sources (Ridgway et al., 1997). Observed 

responses of wild marine mammals to 

loud pulsed sound sources (typically 

seismic airguns or acoustic harassment 

devices) have been varied but often 

consist of avoidance behavior or other 

behavioral changes suggesting 

discomfort (Morton and Symonds, 2002; 

see also Richardson et al., 1995; 

Nowacek et al., 2007). However, many 

delphinids approach acoustic source 

vessels with no apparent discomfort or 

obvious behavioral change (e.g., 

Barkaszi et al., 2012; Barkaszi and Kelly, 

2018). 

Available studies show wide variation 

in response to underwater sound; 

therefore, it is difficult to predict 

specifically how any given sound in a 

particular instance might affect marine 

mammals perceiving the signal. If a 

marine mammal does react briefly to an 

underwater sound by changing its 

behavior or moving a small distance, the 

impacts of the change are unlikely to be 

significant to the individual, let alone 

the stock or population. However, if a 

sound source displaces marine 

mammals from an important feeding or 

breeding area for a prolonged period, 

impacts on individuals and populations 

could be significant (e.g., Lusseau and 

Bejder, 2007; Weilgart, 2007; NRC, 

2005). However, there are broad 

categories of potential response, which 

we describe in greater detail here, that 

include alteration of dive behavior, 

alteration of foraging behavior, effects to 

breathing, interference with or alteration 

of vocalization, avoidance, and flight. 

Changes in dive behavior can vary 

widely, and may consist of increased or 

decreased dive times and surface 

intervals as well as changes in the rates 

of ascent and descent during a dive (e.g., 

Frankel and Clark, 2000; Ng and Leung, 

2003; Nowacek et al., 2004; Goldbogen 

et al., 2013a, b). Variations in dive 

behavior may reflect interruptions in 

biologically significant activities (e.g., 

foraging) or they may be of little 

biological significance. The impact of an 

alteration to dive behavior resulting 

from an acoustic exposure depends on 

what the animal is doing at the time of 

the exposure and the type and 

magnitude of the response. 

Disruption of feeding behavior can be 

difficult to correlate with anthropogenic 

sound exposure, so it is usually inferred 

by observed displacement from known 

foraging areas, the appearance of 

secondary indicators (e.g., bubble nets 

or sediment plumes), or changes in dive 

behavior. As for other types of 

behavioral response, the frequency, 

duration, and temporal pattern of signal 

presentation, as well as differences in 

species sensitivity, are likely 

contributing factors to differences in 

response in any given circumstance 

(e.g., Croll et al., 2001; Nowacek et al.; 

2004; Madsen et al., 2006; Yazvenko et 

al., 2007). A determination of whether 

foraging disruptions incur fitness 

consequences would require 

information on or estimates of the 

energetic requirements of the affected 

individuals and the relationship 

between prey availability, foraging effort 

and success, and the life history stage of 

the animal. 

Of note for one of the species that 

occur in the survey area, visual tracking, 

passive acoustic monitoring, and 

movement recording tags were used to 

quantify sperm whale behavior prior to, 

during, and following exposure to 

airgun arrays at received levels in the 

range 140–160 dB at distances of 7–13 

km, following a phase-in of sound 

intensity and full array exposures at 1– 

13 km (Madsen et al., 2006; Miller et al., 

2009). Sperm whales did not exhibit 

horizontal avoidance behavior at the 

surface. However, foraging behavior 

may have been affected. The sperm 

whales exhibited 19 percent less vocal 

(buzz) rate during full exposure relative 

to post exposure, and the whale that 

was approached most closely had an 

extended resting period and did not 

resume foraging until the airguns had 

ceased firing. The remaining whales 

continued to execute foraging dives 

throughout exposure; however, 

swimming movements during foraging 

dives were 6 percent lower during 

exposure than control periods (Miller et 

al., 2009). These data raise concerns that 

seismic surveys may impact foraging 

behavior in sperm whales, although 

more data are required to understand 

whether the differences were due to 

exposure or natural variation in sperm 

whale behavior (Miller et al., 2009). 

Variations in respiration naturally 

vary with different behaviors and 

alterations to breathing rate as a 

function of acoustic exposure can be 

expected to co-occur with other 

behavioral reactions, such as a flight 

response or an alteration in diving. 

However, respiration rates in and of 

themselves may be representative of 

annoyance or an acute stress response. 

Various studies have shown that 

respiration rates may either be 

unaffected or could increase, depending 

on the species and signal characteristics, 

again highlighting the importance in 


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understanding species differences in the 

tolerance of underwater noise when 

determining the potential for impacts 

resulting from anthropogenic sound 

exposure (e.g., Kastelein et al., 2001, 

2005, 2006; Gailey et al., 2007, 2016). 

Marine mammals vocalize for 

different purposes and across multiple 

modes, such as whistling, echolocation 

click production, calling, and singing. 

Changes in vocalization behavior in 

response to anthropogenic noise can 

occur for any of these modes and may 

result from a need to compete with an 

increase in background noise or may 

reflect increased vigilance or a startle 

response. For example, in the presence 

of potentially masking signals, 

humpback whales and killer whales 

have been observed to increase the 

length of their songs or amplitude of 

calls (Miller et al., 2000; Fristrup et al., 

2003; Foote et al., 2004; Holt et al., 

2012), while right whales have been 

observed to shift the frequency content 

of their calls upward while reducing the 

rate of calling in areas of increased 

anthropogenic noise (Parks et al., 2007). 

In some cases, animals may cease sound 

production during production of 

aversive signals (Bowles et al., 1994). 

Cerchio et al. (2014) used passive 

acoustic monitoring to document the 

presence of singing humpback whales 

off the coast of northern Angola and to 

opportunistically test for the effect of 

seismic survey activity on the number of 

singing whales. Two recording units 

were deployed between March and 

December 2008 in the offshore 

environment; numbers of singers were 

counted every hour. Generalized 

Additive Mixed Models were used to 

assess the effect of survey day 

(seasonality), hour (diel variation), 

moon phase, and received levels of 

noise (measured from a single pulse 

during each 10 minute sampled period) 

on singer number. The number of 

singers significantly decreased with 

increasing received level of noise, 

suggesting that humpback whale 

breeding activity was disrupted to some 

extent by the survey activity. 

Castellote et al. (2012) reported 

acoustic and behavioral changes by fin 

whales in response to shipping and 

airgun noise. Acoustic features of fin 

whale song notes recorded in the 

Mediterranean Sea and northeast 

Atlantic Ocean were compared for areas 

with different shipping noise levels and 

traffic intensities and during a seismic 

airgun survey. During the first 72 hours 

of the survey, a steady decrease in song 

received levels and bearings to singers 

indicated that whales moved away from 

the acoustic source and out of the study 

area. This displacement persisted for a 

time period well beyond the 10-day 

duration of seismic airgun activity, 

providing evidence that fin whales may 

avoid an area for an extended period in 

the presence of increased noise. The 

authors hypothesize that fin whale 

acoustic communication is modified to 

compensate for increased background 

noise and that a sensitization process 

may play a role in the observed 

temporary displacement. 

Seismic pulses at average received 

levels of 131 dB re 1 mPa2-s caused blue 

whales to increase call production (Di 

Iorio and Clark, 2010). In contrast, 

McDonald et al. (1995) tracked a blue 

whale with seafloor seismometers and 

reported that it stopped vocalizing and 

changed its travel direction at a range of 

10 km from the acoustic source vessel 

(estimated received level 143 dB pk-pk). 

Blackwell et al. (2013) found that 

bowhead whale call rates dropped 

significantly at onset of airgun use at 

sites with a median distance of 41–45 

km from the survey. Blackwell et al. 

(2015) expanded this analysis to show 

that whales actually increased calling 

rates as soon as airgun signals were 

detectable before ultimately decreasing 

calling rates at higher received levels 

(i.e., 10-minute SELcum of ∼127 dB). 

Overall, these results suggest that 

bowhead whales may adjust their vocal 

output in an effort to compensate for 

noise before ceasing vocalization effort 

and ultimately deflecting from the 

acoustic source (Blackwell et al., 2013, 

2015). These studies demonstrate that 

even low levels of noise received far 

from the source can induce changes in 

vocalization and/or behavior for 

mysticetes. 

Avoidance is the displacement of an 

individual from an area or migration 

path as a result of the presence of a 

sound or other stressors, and is one of 

the most obvious manifestations of 

disturbance in marine mammals 

(Richardson et al., 1995). For example, 

gray whales are known to change 

direction—deflecting from customary 

migratory paths—in order to avoid noise 

from seismic surveys (Malme et al., 

1984). Humpback whales showed 

avoidance behavior in the presence of 

an active seismic array during 

observational studies and controlled 

exposure experiments in western 

Australia (McCauley et al., 2000). 

Avoidance may be short-term, with 

animals returning to the area once the 

noise has ceased (e.g., Bowles et al., 

1994; Goold, 1996; Stone et al., 2000; 

Morton and Symonds, 2002; Gailey et 

al., 2007). Longer-term displacement is 

possible, however, which may lead to 

changes in abundance or distribution 

patterns of the affected species in the 

affected region if habituation to the 

presence of the sound does not occur 

(e.g., Bejder et al., 2006; Teilmann et al., 

2006). 

Forney et al. (2017) detail the 

potential effects of noise on marine 

mammal populations with high site 

fidelity, including displacement and 

auditory masking, noting that a lack of 

observed response does not imply 

absence of fitness costs and that 

apparent tolerance of disturbance may 

have population-level impacts that are 

less obvious and difficult to document. 

Forney et al. (2017) state that, for these 

animals, remaining in a disturbed area 

may reflect a lack of alternatives rather 

than a lack of effects. The authors 

discuss several case studies, including 

western Pacific gray whales, which are 

a small population of mysticetes 

believed to be adversely affected by oil 

and gas development off Sakhalin 

Island, Russia (Weller et al., 2002; 

Reeves et al., 2005). Western gray 

whales display a high degree of 

interannual site fidelity to the area for 

foraging purposes, and observations in 

the area during airgun surveys has 

shown the potential for harm caused by 

displacement from such an important 

area (Weller et al., 2006; Johnson et al., 

2007). Forney et al. (2017) also discuss 

beaked whales, noting that 

anthropogenic effects in areas where 

they are resident could cause severe 

biological consequences, in part because 

displacement may adversely affect 

foraging rates, reproduction, or health, 

while an overriding instinct to remain 

could lead to more severe acute effects. 

A flight response is a dramatic change 

in normal movement to a directed and 

rapid movement away from the 

perceived location of a sound source. 

The flight response differs from other 

avoidance responses in the intensity of 

the response (e.g., directed movement, 

rate of travel). Relatively little 

information on flight responses of 

marine mammals to anthropogenic 

signals exist, although observations of 

flight responses to the presence of 

predators have occurred (Connor and 

Heithaus, 1996). The result of a flight 

response could range from brief, 

temporary exertion and displacement 

from the area where the signal provokes 

flight to, in extreme cases, marine 

mammal strandings (Evans and 

England, 2001). However, it should be 

noted that response to a perceived 

predator does not necessarily invoke 

flight (Ford and Reeves, 2008), and 

whether individuals are solitary or in 

groups may influence the response. 

Behavioral disturbance can also 

impact marine mammals in more subtle 

ways. Increased vigilance may result in 


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costs related to diversion of focus and 

attention (i.e., when a response consists 

of increased vigilance, it may come at 

the cost of decreased attention to other 

critical behaviors such as foraging or 

resting). These effects have generally not 

been demonstrated for marine 

mammals, but studies involving fish 

and terrestrial animals have shown that 

increased vigilance may substantially 

reduce feeding rates (e.g., Beauchamp 

and Livoreil, 1997; Fritz et al., 2002; 

Purser and Radford, 2011). In addition, 

chronic disturbance can cause 

population declines through reduction 

of fitness (e.g., decline in body 

condition) and subsequent reduction in 

reproductive success, survival, or both 

(e.g., Harrington and Veitch, 1992; Daan 

et al., 1996; Bradshaw et al., 1998). 

However, Ridgway et al. (2006) reported 

that increased vigilance in bottlenose 

dolphins exposed to sound over a fiveday period did not cause any sleep 

deprivation or stress effects. 

Many animals perform vital functions, 

such as feeding, resting, traveling, and 

socializing, on a diel cycle (24-hour 

cycle). Disruption of such functions 

resulting from reactions to stressors 

such as sound exposure are more likely 

to be significant if they last more than 

one diel cycle or recur on subsequent 

days (Southall et al., 2007). 

Consequently, a behavioral response 

lasting less than one day and not 

recurring on subsequent days is not 

considered particularly severe unless it 

could directly affect reproduction or 

survival (Southall et al., 2007). Note that 

there is a difference between multi-day 

substantive behavioral reactions and 

multi-day anthropogenic activities. For 

example, just because an activity lasts 

for multiple days does not necessarily 

mean that individual animals are either 

exposed to activity-related stressors for 

multiple days or, further, exposed in a 

manner resulting in sustained multi-day 

substantive behavioral responses. 

Stone (2015) reported data from at-sea 

observations during 1,196 seismic 

surveys from 1994 to 2010. When large 

arrays of airguns (considered to be 500 

in3 or more) were firing, lateral 

displacement, more localized 

avoidance, or other changes in behavior 

were evident for most odontocetes. 

However, significant responses to large 

arrays were found only for the minke 

whale and fin whale. Behavioral 

responses observed included changes in 

swimming or surfacing behavior, with 

indications that cetaceans remained 

near the water surface at these times. 

Cetaceans were recorded as feeding less 

often when large arrays were active. 

Behavioral observations of gray whales 

during a seismic survey monitored 

whale movements and respirations 

pre-, during, and post-seismic survey 

(Gailey et al., 2016). Behavioral state 

and water depth were the best ‘natural’ 

predictors of whale movements and 

respiration and, after considering 

natural variation, none of the response 

variables were significantly associated 

with seismic survey or vessel sounds. 

Stress Responses—An animal’s 

perception of a threat may be sufficient 

to trigger stress responses consisting of 

some combination of behavioral 

responses, autonomic nervous system 

responses, neuroendocrine responses, or 

immune responses (e.g., Seyle, 1950; 

Moberg, 2000). In many cases, an 

animal’s first and sometimes most 

economical (in terms of energetic costs) 

response is behavioral avoidance of the 

potential stressor. Autonomic nervous 

system responses to stress typically 

involve changes in heart rate, blood 

pressure, and gastrointestinal activity. 

These responses have a relatively short 

duration and may or may not have a 

significant long-term effect on an 

animal’s fitness. 

Neuroendocrine stress responses often 

involve the hypothalamus-pituitaryadrenal system. Virtually all 

neuroendocrine functions that are 

affected by stress—including immune 

competence, reproduction, metabolism, 

and behavior—are regulated by pituitary 

hormones. Stress-induced changes in 

the secretion of pituitary hormones have 

been implicated in failed reproduction, 

altered metabolism, reduced immune 

competence, and behavioral disturbance 

(e.g., Moberg, 1987; Blecha, 2000). 

Increases in the circulation of 

glucocorticoids are also equated with 

stress (Romano et al., 2004). 

The primary distinction between 

stress (which is adaptive and does not 

normally place an animal at risk) and 

‘‘distress’’ is the cost of the response. 

During a stress response, an animal uses 

glycogen stores that can be quickly 

replenished once the stress is alleviated. 

In such circumstances, the cost of the 

stress response would not pose serious 

fitness consequences. However, when 

an animal does not have sufficient 

energy reserves to satisfy the energetic 

costs of a stress response, energy 

resources must be diverted from other 

functions. This state of distress will last 

until the animal replenishes its 

energetic reserves sufficiently to restore 

normal function. 

Relationships between these 

physiological mechanisms, animal 

behavior, and the costs of stress 

responses are well-studied through 

controlled experiments and for both 

laboratory and free-ranging animals 

(e.g., Holberton et al., 1996; Hood et al., 

1998; Jessop et al., 2003; Krausman et 

al., 2004; Lankford et al., 2005). Stress 

responses due to exposure to 

anthropogenic sounds or other stressors 

and their effects on marine mammals 

have also been reviewed (Fair and 

Becker, 2000; Romano et al., 2002b) 

and, more rarely, studied in wild 

populations (e.g., Romano et al., 2002a). 

For example, Rolland et al. (2012) found 

that noise reduction from reduced ship 

traffic in the Bay of Fundy was 

associated with decreased stress in 

North Atlantic right whales. These and 

other studies lead to a reasonable 

expectation that some marine mammals 

will experience physiological stress 

responses upon exposure to acoustic 

stressors and that it is possible that 

some of these would be classified as 

‘‘distress.’’ In addition, any animal 

experiencing TTS would likely also 

experience stress responses (NRC, 

2003). 

Auditory Masking—Sound can 

disrupt behavior through masking, or 

interfering with, an animal’s ability to 

detect, recognize, or discriminate 

between acoustic signals of interest (e.g., 

those used for intraspecific 

communication and social interactions, 

prey detection, predator avoidance, 

navigation) (Richardson et al., 1995; 

Erbe et al., 2016). Masking occurs when 

the receipt of a sound is interfered with 

by another coincident sound at similar 

frequencies and at similar or higher 

intensity, and may occur whether the 

sound is natural (e.g., snapping shrimp, 

wind, waves, precipitation) or 

anthropogenic (e.g., shipping, sonar, 

seismic exploration) in origin. The 

ability of a noise source to mask 

biologically important sounds depends 

on the characteristics of both the noise 

source and the signal of interest (e.g., 

signal-to-noise ratio, temporal 

variability, direction), in relation to each 

other and to an animal’s hearing 

abilities (e.g., sensitivity, frequency 

range, critical ratios, frequency 

discrimination, directional 

discrimination, age or TTS hearing loss), 

and existing ambient noise and 

propagation conditions. 

Under certain circumstances, marine 

mammals experiencing significant 

masking could also be impaired from 

maximizing their performance fitness in 

survival and reproduction. Therefore, 

when the coincident (masking) sound is 

man-made, it may be considered 

harassment when disrupting or altering 

critical behaviors. It is important to 

distinguish TTS and PTS, which persist 

after the sound exposure, from masking, 

which occurs during the sound 

exposure. Because masking (without 

resulting in TS) is not associated with 


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abnormal physiological function, it is 

not considered a physiological effect, 

but rather a potential behavioral effect. 

The frequency range of the potentially 

masking sound is important in 

determining any potential behavioral 

impacts. For example, low-frequency 

signals may have less effect on highfrequency echolocation sounds 

produced by odontocetes but are more 

likely to affect detection of mysticete 

communication calls and other 

potentially important natural sounds 

such as those produced by surf and 

some prey species. The masking of 

communication signals by 

anthropogenic noise may be considered 

as a reduction in the communication 

space of animals (e.g., Clark et al., 2009) 

and may result in energetic or other 

costs as animals change their 

vocalization behavior (e.g., Miller et al., 

2000; Foote et al., 2004; Parks et al., 

2007; Di Iorio and Clark, 2009; Holt et 

al., 2009). Masking can be reduced in 

situations where the signal and noise 

come from different directions 

(Richardson et al., 1995), through 

amplitude modulation of the signal, or 

through other compensatory behaviors 

(Houser and Moore, 2014). Masking can 

be tested directly in captive species 

(e.g., Erbe, 2008), but in wild 

populations it must be either modeled 

or inferred from evidence of masking 

compensation. There are few studies 

addressing real-world masking sounds 

likely to be experienced by marine 

mammals in the wild (e.g., Branstetter et 

al., 2013). 

Masking affects both senders and 

receivers of acoustic signals and can 

potentially have long-term chronic 

effects on marine mammals at the 

population level as well as at the 

individual level. Low-frequency 

ambient sound levels have increased by 

as much as 20 dB (more than three times 

in terms of SPL) in the world’s ocean 

from pre-industrial periods, with most 

of the increase from distant commercial 

shipping (Hildebrand, 2009). All 

anthropogenic sound sources, but 

especially chronic and lower-frequency 

signals (e.g., from vessel traffic), 

contribute to elevated ambient sound 

levels, thus intensifying masking. 

Masking effects of pulsed sounds 

(even from large arrays of airguns) on 

marine mammal calls and other natural 

sounds are expected to be limited, 

although there are few specific data on 

this. Because of the intermittent nature 

and low duty cycle of seismic pulses, 

animals can emit and receive sounds in 

the relatively quiet intervals between 

pulses. However, in exceptional 

situations, reverberation occurs for 

much or all of the interval between 

pulses (e.g., Simard et al. 2005; Clark 

and Gagnon 2006), which could mask 

calls. Situations with prolonged strong 

reverberation are infrequent. However, 

it is common for reverberation to cause 

some lesser degree of elevation of the 

background level between airgun pulses 

(e.g., Gedamke 2011; Guerra et al. 2011, 

2016; Klinck et al. 2012; Guan et al. 

2015), and this weaker reverberation 

presumably reduces the detection range 

of calls and other natural sounds to 

some degree. Guerra et al. (2016) 

reported that ambient noise levels 

between seismic pulses were elevated as 

a result of reverberation at ranges of 50 

km from the seismic source. Based on 

measurements in deep water of the 

Southern Ocean, Gedamke (2011) 

estimated that the slight elevation of 

background levels during intervals 

between pulses reduced blue and fin 

whale communication space by as much 

as 36–51 percent when a seismic survey 

was operating 450–2,800 km away. 

Based on preliminary modeling, 

Wittekind et al. (2016) reported that 

airgun sounds could reduce the 

communication range of blue and fin 

whales 2000 km from the seismic 

source. Nieukirk et al. (2012) and 

Blackwell et al. (2013) noted the 

potential for masking effects from 

seismic surveys on large whales. 

Some baleen and toothed whales are 

known to continue calling in the 

presence of seismic pulses, and their 

calls usually can be heard between the 

pulses (e.g., Nieukirk et al. 2012; Thode 

et al. 2012; Bro ̈ker et al. 2013; Sciacca 

et al. 2016). As noted above, Cerchio et 

al. (2014) suggested that the breeding 

display of humpback whales off Angola 

could be disrupted by seismic sounds, 

as singing activity declined with 

increasing received levels. In addition, 

some cetaceans are known to change 

their calling rates, shift their peak 

frequencies, or otherwise modify their 

vocal behavior in response to airgun 

sounds (e.g., Di Iorio and Clark 2010; 

Castellote et al. 2012; Blackwell et al. 

2013, 2015). The hearing systems of 

baleen whales are undoubtedly more 

sensitive to low-frequency sounds than 

are the ears of the small odontocetes 

that have been studied directly (e.g., 

MacGillivray et al. 2014). The sounds 

important to small odontocetes are 

predominantly at much higher 

frequencies than are the dominant 

components of airgun sounds, thus 

limiting the potential for masking. In 

general, masking effects of seismic 

pulses are expected to be minor, given 

the normally intermittent nature of 

seismic pulses. 

Vessel Noise 

Vessel noise from the Langseth could 

affect marine animals in the proposed 

survey areas. Houghton et al. (2015) 

proposed that vessel speed is the most 

important predictor of received noise 

levels, and Putland et al. (2017) also 

reported reduced sound levels with 

decreased vessel speed. Sounds 

produced by large vessels generally 

dominate ambient noise at frequencies 

from 20 to 300 Hz (Richardson et al. 

1995). However, some energy is also 

produced at higher frequencies 

(Hermannsen et al. 2014); low levels of 

high-frequency sound from vessels has 

been shown to elicit responses in harbor 

porpoise (Dyndo et al. 2015). Increased 

levels of ship noise have been shown to 

affect foraging by porpoise (Teilmann et 

al. 2015; Wisniewska et al. 2018); 

Wisniewska et al. (2018) suggest that a 

decrease in foraging success could have 

long-term fitness consequences. 

Ship noise, through masking, can 

reduce the effective communication 

distance of a marine mammal if the 

frequency of the sound source is close 

to that used by the animal, and if the 

sound is present for a significant 

fraction of time (e.g., Richardson et al. 

1995; Clark et al. 2009; Jensen et al. 

2009; Gervaise et al. 2012; Hatch et al. 

2012; Rice et al. 2014; Dunlop 2015; 

Erbe et al. 2015; Jones et al. 2017; 

Putland et al. 2017). In addition to the 

frequency and duration of the masking 

sound, the strength, temporal pattern, 

and location of the introduced sound 

also play a role in the extent of the 

masking (Branstetter et al. 2013, 2016; 

Finneran and Branstetter 2013; Sills et 

al. 2017). Branstetter et al. (2013) 

reported that time-domain metrics are 

also important in describing and 

predicting masking. In order to 

compensate for increased ambient noise, 

some cetaceans are known to increase 

the source levels of their calls in the 

presence of elevated noise levels from 

shipping, shift their peak frequencies, or 

otherwise change their vocal behavior 

(e.g., Parks et al. 2016a,b; Bittencourt et 

al. 2016; Dahlheim and Castellote 2016; 

Gospic ́ and Picciulin 2016; Gridley et al. 

2016; Heiler et al. 2016; Martins et al. 

2016; O’Brien et al. 2016; Tenessen and 

Parks 2016). Holt et al. (2015) reported 

that changes in vocal modifications can 

have increased energetic costs for 

individual marine mammals. A negative 

correlation between the presence of 

some cetacean species and the number 

of vessels in an area has been 

demonstrated by several studies (e.g., 

Campana et al. 2015; Culloch et al. 

2016). 


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Baleen whales are thought to be more 

sensitive to sound at these low 

frequencies than are toothed whales 

(e.g., MacGillivray et al. 2014), possibly 

causing localized avoidance of the 

proposed survey area during seismic 

operations. Reactions of gray and 

humpback whales to vessels have been 

studied, and there is limited 

information available about the 

reactions of right whales and rorquals 

(e.g., fin, blue, minke, humpback, sei, 

and Bryde’s whales). Reactions of 

humpback whales to boats are variable, 

ranging from approach to avoidance 

(Payne 1978; Salden 1993). Baker et al. 

(1982, 1983) and Baker and Herman 

(1989) found humpbacks often move 

away when vessels are within several 

kilometers. Humpbacks seem less likely 

to react overtly when actively feeding 

than when resting or engaged in other 

activities (Krieger and Wing 1984, 

1986). Increased levels of ship noise 

have been shown to affect foraging by 

humpback whales (Blair et al. 2016). Fin 

whale sightings in the western 

Mediterranean were negatively 

correlated with the number of vessels in 

the area (Campana et al. 2015). Minke 

whales have shown slight displacement 

in response to construction-related 

vessel traffic (Anderwald et al. 2013). 

Many odontocetes show considerable 

tolerance of vessel traffic, although they 

sometimes react at long distances if 

confined by ice or shallow water, if 

previously harassed by vessels, or have 

had little or no recent exposure to ships 

(Richardson et al. 1995). Dolphins of 

many species tolerate and sometimes 

approach vessels (e.g., Anderwald et al. 

2013). Some dolphin species approach 

moving vessels to ride the bow or stern 

waves (Williams et al. 1992). Pirotta et 

al. (2015) noted that the physical 

presence of vessels, not just ship noise, 

disturbed the foraging activity of 

bottlenose dolphins. Sightings of striped 

dolphin, Risso’s dolphin, sperm whale, 

and Cuvier’s beaked whale in the 

western Mediterranean were negatively 

correlated with the number of vessels in 

the area (Campana et al. 2015). 

There are few data on the behavioral 

reactions of beaked whales to vessel 

noise, though they seem to avoid 

approaching vessels (e.g., Wu ̈rsig et al. 

1998) or dive for an extended period 

when approached by a vessel (e.g., 

Kasuya 1986). Based on a single 

observation, Aguilar Soto et al. (2006) 

suggest foraging efficiency of Cuvier’s 

beaked whales may be reduced by close 

approach of vessels. 

Sounds emitted by the Langseth are 

low frequency and continuous, but 

would be widely dispersed in both 

space and time. Vessel traffic associated 

with the proposed survey is of low 

density compared to traffic associated 

with commercial shipping, industry 

support vessels, or commercial fishing 

vessels, and would therefore be 

expected to represent an insignificant 

incremental increase in the total amount 

of anthropogenic sound input to the 

marine environment, and the effects of 

vessel noise described above are not 

expected to occur as a result of this 

survey. In summary, project vessel 

sounds would not be at levels expected 

to cause anything more than possible 

localized and temporary behavioral 

changes in marine mammals, and would 

not be expected to result in significant 

negative effects on individuals or at the 

population level. In addition, in all 

oceans of the world, large vessel traffic 

is currently so prevalent that it is 

commonly considered a usual source of 

ambient sound (NSF–USGS 2011). 

Ship Strike 

Vessel collisions with marine 

mammals, or ship strikes, can result in 

death or serious injury of the animal. 

Wounds resulting from ship strike may 

include massive trauma, hemorrhaging, 

broken bones, or propeller lacerations 

(Knowlton and Kraus, 2001). An animal 

at the surface may be struck directly by 

a vessel, a surfacing animal may hit the 

bottom of a vessel, or an animal just 

below the surface may be cut by a 

vessel’s propeller. Superficial strikes 

may not kill or result in the death of the 

animal. These interactions are typically 

associated with large whales (e.g., fin 

whales), which are occasionally found 

draped across the bulbous bow of large 

commercial ships upon arrival in port. 

Although smaller cetaceans are more 

maneuverable in relation to large vessels 

than are large whales, they may also be 

susceptible to strike. The severity of 

injuries typically depends on the size 

and speed of the vessel, with the 

probability of death or serious injury 

increasing as vessel speed increases 

(Knowlton and Kraus, 2001; Laist et al., 

2001; Vanderlaan and Taggart, 2007; 

Conn and Silber, 2013). Impact forces 

increase with speed, as does the 

probability of a strike at a given distance 

(Silber et al., 2010; Gende et al., 2011). 

Pace and Silber (2005) also found that 

the probability of death or serious injury 

increased rapidly with increasing vessel 

speed. Specifically, the predicted 

probability of serious injury or death 

resulting from a strike increased from 45 

to 75 percent as vessel speed increased 

from 10 to 14 knots, and exceeded 90 

percent at 17 knots. Higher speeds 

during collisions result in greater force 

of impact, but higher speeds also appear 

to increase the chance of severe injuries 

or death through increased likelihood of 

collision by pulling whales toward the 

vessel (Clyne, 1999; Knowlton et al., 

1995). In a separate study, Vanderlaan 

and Taggart (2007) analyzed the 

probability of lethal mortality of large 

whales at a given speed, showing that 

the greatest rate of change in the 

probability of a lethal injury to a large 

whale as a function of vessel speed 

occurs between 8.6 and 15 knots. The 

chances of a lethal injury decline from 

approximately 80 percent at 15 knots to 

approximately 20 percent at 8.6 knots. 

At speeds below 11.8 knots, the chances 

of lethal injury drop below 50 percent, 

while the probability asymptotically 

increases toward 100 percent above 15 

knots. 

The vessel speed during seismic 

survey operations would be 

approximately 4.1 knots (7.6 km/h) 

during MCS reflection surveys and 5 

knots (9.3 km/h) during OBS refraction 

surveys. At this speed, both the 

possibility of striking a marine mammal 

and the possibility of a strike resulting 

in serious injury or mortality are so low 

as to be discountable. At average transit 

speed, the probability of serious injury 

or mortality resulting from a strike is 

less than 50 percent. However, the 

likelihood of a strike actually happening 

is again low. Ship strikes, as analyzed 

in the studies cited above, generally 

involve commercial shipping, which is 

much more common in both space and 

time than is geophysical survey activity. 

Commercial shipping vessels are also 

generally much larger than typical 

geophysical survey vessels (e.g., up to 

360 m long cargo vessels compared to 

the 71-m R/V Langseth). Jensen and 

Silber (2004) summarized ship strikes of 

large whales worldwide from 1975– 

2003 and found that most collisions 

occurred in the open ocean and 

involved large vessels (e.g., commercial 

shipping vessels). No such incidents 

were reported for geophysical survey 

vessels during that time period. 

It is possible for ship strikes to occur 

while traveling at slow speeds. For 

example, a hydrographic survey vessel 

traveling at low speed (5.5 knots) while 

conducting mapping surveys off the 

central California coast struck and killed 

a blue whale in 2009. The State of 

California determined that the whale 

had suddenly and unexpectedly 

surfaced beneath the hull, with the 

result that the propeller severed the 

whale’s vertebrae, and that this was an 

unavoidable event. This strike 

represents the only such incident in 

approximately 540,000 hours of similar 

coastal mapping activity (p = 1.9 × 10¥6; 

95 percent CI = 0–5.5 × 10¥6; NMFS, 

2013b). In addition, a research vessel 


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reported a fatal strike in 2011 of a 

dolphin in the Atlantic, demonstrating 

that it is possible for strikes involving 

smaller cetaceans to occur. In that case, 

the incident report indicated that an 

animal apparently was struck by the 

vessel’s propeller as it was intentionally 

swimming near the vessel. While 

indicative of the type of unusual events 

that cannot be ruled out, neither of these 

instances represents a circumstance that 

would be considered reasonably 

foreseeable or that would be considered 

preventable. 

Although the likelihood of the vessel 

striking a marine mammal is low, we 

require a robust ship strike avoidance 

protocol (see Proposed Mitigation), 

which we believe eliminates any 

foreseeable risk of ship strike during 

transit. We anticipate that vessel 

collisions involving a seismic data 

acquisition vessel towing gear, while 

not impossible, represent unlikely, 

unpredictable events for which there are 

no preventive measures. Given the 

required mitigation measures, the 

relatively slow speed of the vessel 

towing gear, the presence of bridge crew 

watching for obstacles at all times 

(including marine mammals), and the 

presence of marine mammal observers, 

we believe that the possibility of ship 

strike is discountable and, further, that 

were a strike of a large whale to occur, 

it would be unlikely to result in serious 

injury or mortality. No incidental take 

resulting from ship strike is anticipated, 

and this potential effect of the specified 

activity will not be discussed further in 

the following analysis. 

Stranding—When a living or dead 

marine mammal swims or floats onto 

shore and becomes ‘‘beached’’ or 

incapable of returning to sea, the event 

is a ‘‘stranding’’ (Geraci et al., 1999; 

Perrin and Geraci, 2002; Geraci and 

Lounsbury, 2005; NMFS, 2007). The 

legal definition for a stranding under the 

MMPA is that ‘‘(A) a marine mammal is 

dead and is (i) on a beach or shore of 

the United States; or (ii) in waters under 

the jurisdiction of the United States 

(including any navigable waters); or (B) 

a marine mammal is alive and is (i) on 

a beach or shore of the United States 

and is unable to return to the water; (ii) 

on a beach or shore of the United States 

and, although able to return to the 

water, is in need of apparent medical 

attention; or (iii) in the waters under the 

jurisdiction of the United States 

(including any navigable waters), but is 

unable to return to its natural habitat 

under its own power or without 

assistance.’’ 

Marine mammals strand for a variety 

of reasons, such as infectious agents, 

biotoxicosis, starvation, fishery 

interaction, ship strike, unusual 

oceanographic or weather events, sound 

exposure, or combinations of these 

stressors sustained concurrently or in 

series. However, the cause or causes of 

most strandings are unknown (Geraci et 

al., 1976; Eaton, 1979; Odell et al., 1980; 

Best, 1982). Numerous studies suggest 

that the physiology, behavior, habitat 

relationships, age, or condition of 

cetaceans may cause them to strand or 

might pre-dispose them to strand when 

exposed to another phenomenon. These 

suggestions are consistent with the 

conclusions of numerous other studies 

that have demonstrated that 

combinations of dissimilar stressors 

commonly combine to kill an animal or 

dramatically reduce its fitness, even 

though one exposure without the other 

does not produce the same result 

(Chroussos, 2000; Creel, 2005; DeVries 

et al., 2003; Fair and Becker, 2000; Foley 

et al., 2001; Moberg, 2000; Relyea, 

2005a; 2005b, Romero, 2004; Sih et al., 

2004). 

There is no conclusive evidence that 

exposure to airgun noise results in 

behaviorally-mediated forms of injury. 

Behaviorally-mediated injury (i.e., mass 

stranding events) has been primarily 

associated with beaked whales exposed 

to mid-frequency active (MFA) naval 

sonar. Tactical sonar and the alerting 

stimulus used in Nowacek et al. (2004) 

are very different from the noise 

produced by airguns. One should 

therefore not expect the same reaction to 

airgun noise as to these other sources. 

As explained below, military MFA 

sonar is very different from airguns, and 

one should not assume that airguns will 

cause the same effects as MFA sonar 

(including strandings). 

To understand why Navy MFA sonar 

affects beaked whales differently than 

airguns do, it is important to note the 

distinction between behavioral 

sensitivity and susceptibility to auditory 

injury. To understand the potential for 

auditory injury in a particular marine 

mammal species in relation to a given 

acoustic signal, the frequency range the 

species is able to hear is critical, as well 

as the species’ auditory sensitivity to 

frequencies within that range. Current 

data indicate that not all marine 

mammal species have equal hearing 

capabilities across all frequencies and, 

therefore, species are grouped into 

hearing groups with generalized hearing 

ranges assigned on the basis of available 

data (Southall et al., 2007, 2019). 

Hearing ranges as well as auditory 

sensitivity/susceptibility to frequencies 

within those ranges vary across the 

different groups. For example, in terms 

of hearing range, the high-frequency 

cetaceans (e.g., Kogia spp.) have a 

generalized hearing range of frequencies 

between 275 Hz and 160 kHz, while 

mid-frequency cetaceans—such as 

dolphins and beaked whales—have a 

generalized hearing range between 150 

Hz to 160 kHz. Regarding auditory 

susceptibility within the hearing range, 

while mid-frequency cetaceans and 

high-frequency cetaceans have roughly 

similar hearing ranges, the highfrequency group is much more 

susceptible to noise-induced hearing 

loss during sound exposure, i.e., these 

species have lower thresholds for these 

effects than other hearing groups 

(NMFS, 2018). Referring to a species as 

behaviorally sensitive to noise simply 

means that an animal of that species is 

more likely to respond to lower received 

levels of sound than an animal of 

another species that is considered less 

behaviorally sensitive. So, while 

dolphin species and beaked whale 

species—both in the mid-frequency 

cetacean hearing group—are assumed to 

(generally) hear the same sounds 

equally well and be equally susceptible 

to noise-induced hearing loss (auditory 

injury), the best available information 

indicates that a beaked whale is more 

likely to behaviorally respond to that 

sound at a lower received level 

compared to an animal from other midfrequency cetacean species that are less 

behaviorally sensitive. This distinction 

is important because, while beaked 

whales are more likely to respond 

behaviorally to sounds than are many 

other species (even at lower levels), they 

cannot hear the predominant, lower 

frequency sounds from seismic airguns 

as well as sounds that have more energy 

at frequencies that beaked whales can 

hear better (such as military MFA 

sonar). 

Navy MFA sonar affects beaked 

whales differently than airguns do 

because it produces energy at different 

frequencies than airguns. Mid-frequency 

cetacean hearing is generically thought 

to be best between 8.8 to 110 kHz, i.e., 

these cutoff values define the range 

above and below which a species in the 

group is assumed to have declining 

auditory sensitivity, until reaching 

frequencies that cannot be heard 

(NMFS, 2018). However, beaked whale 

hearing is likely best within a higher, 

narrower range (20–80 kHz, with best 

sensitivity around 40 kHz), based on a 

few measurements of hearing in 

stranded beaked whales (Cook et al., 

2006; Finneran et al., 2009; Pacini et al., 

2011) and several studies of acoustic 

signals produced by beaked whales (e.g., 

Frantzis et al., 2002; Johnson et al., 

2004, 2006; Zimmer et al., 2005). While 

precaution requires that the full range of 


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audibility be considered when assessing 

risks associated with noise exposure 

(Southall et al., 2007, 2019), animals 

typically produce sound at frequencies 

where they hear best. More recently, 

Southall et al. (2019) suggested that 

certain species amongst the historical 

mid-frequency hearing group (beaked 

whales, sperm whales, and killer 

whales) are likely more sensitive to 

lower frequencies within the group’s 

generalized hearing range than are other 

species within the group and state that 

the data for beaked whales suggest 

sensitivity to approximately 5 kHz. 

However, this information is consistent 

with the general conclusion that beaked 

whales (and other mid-frequency 

cetaceans) are relatively insensitive to 

the frequencies where most energy of an 

airgun signal is found. Military MFA 

sonar is typically considered to operate 

in the frequency range of approximately 

3–14 kHz (D’Amico et al., 2009), i.e., 

outside the range of likely best hearing 

for beaked whales but within or close to 

the lower bounds, whereas most energy 

in an airgun signal is radiated at much 

lower frequencies, below 500 Hz 

(Dragoset, 1990). 

It is important to distinguish between 

energy (loudness, measured in dB) and 

frequency (pitch, measured in Hz). In 

considering the potential impacts of 

mid-frequency components of airgun 

noise (1–10 kHz, where beaked whales 

can be expected to hear) on marine 

mammal hearing, one needs to account 

for the energy associated with these 

higher frequencies and determine what 

energy is truly ‘‘significant.’’ Although 

there is mid-frequency energy 

associated with airgun noise (as 

expected from a broadband source), 

airgun sound is predominantly below 1 

kHz (Breitzke et al., 2008; 

Tashmukhambetov et al., 2008; Tolstoy 

et al., 2009). As stated by Richardson et 

al. (1995), ‘‘[. . .] most emitted [seismic 

airgun] energy is at 10–120 Hz, but the 

pulses contain some energy up to 500– 

1,000 Hz.’’ Tolstoy et al. (2009) 

conducted empirical measurements, 

demonstrating that sound energy levels 

associated with airguns were at least 20 

dB lower at 1 kHz (considered ‘‘midfrequency’’) compared to higher energy 

levels associated with lower frequencies 

(below 300 Hz) (‘‘all but a small fraction 

of the total energy being concentrated in 

the 10–300 Hz range’’ [Tolstoy et al., 

2009]), and at higher frequencies (e.g., 

2.6–4 kHz), power might be less than 10 

percent of the peak power at 10 Hz 

(Yoder, 2002). Energy levels measured 

by Tolstoy et al. (2009) were even lower 

at frequencies above 1 kHz. In addition, 

as sound propagates away from the 

source, it tends to lose higher-frequency 

components faster than low-frequency 

components (i.e., low-frequency sounds 

typically propagate longer distances 

than high-frequency sounds) (Diebold et 

al., 2010). Although higher-frequency 

components of airgun signals have been 

recorded, it is typically in surfaceducting conditions (e.g., DeRuiter et al., 

2006; Madsen et al., 2006) or in shallow 

water, where there are advantageous 

propagation conditions for the higher 

frequency (but low-energy) components 

of the airgun signal (Hermannsen et al., 

2015). This should not be of concern 

because the likely behavioral reactions 

of beaked whales that can result in acute 

physical injury would result from noise 

exposure at depth (because of the 

potentially greater consequences of 

severe behavioral reactions). In 

summary, the frequency content of 

airgun signals is such that beaked 

whales will not be able to hear the 

signals well (compared to MFA sonar), 

especially at depth where we expect the 

consequences of noise exposure could 

be more severe. 

Aside from frequency content, there 

are other significant differences between 

MFA sonar signals and the sounds 

produced by airguns that minimize the 

risk of severe behavioral reactions that 

could lead to strandings or deaths at sea, 

e.g., significantly longer signal duration, 

horizontal sound direction, typical fast 

and unpredictable source movement. 

All of these characteristics of MFA 

sonar tend towards greater potential to 

cause severe behavioral or physiological 

reactions in exposed beaked whales that 

may contribute to stranding. Although 

both sources are powerful, MFA sonar 

contains significantly greater energy in 

the mid-frequency range, where beaked 

whales hear better. Short-duration, high 

energy pulses—such as those produced 

by airguns—have greater potential to 

cause damage to auditory structures 

(though this is unlikely for midfrequency cetaceans, as explained later 

in this document), but it is longer 

duration signals that have been 

implicated in the vast majority of 

beaked whale strandings. Faster, less 

predictable movements in combination 

with multiple source vessels are more 

likely to elicit a severe, potentially antipredator response. Of additional interest 

in assessing the divergent characteristics 

of MFA sonar and airgun signals and 

their relative potential to cause 

stranding events or deaths at sea is the 

similarity between the MFA sonar 

signals and stereotyped calls of beaked 

whales’ primary predator: The killer 

whale (Zimmer and Tyack, 2007). 

Although generic disturbance stimuli— 

as airgun noise may be considered in 

this case for beaked whales—may also 

trigger antipredator responses, stronger 

responses should generally be expected 

when perceived risk is greater, as when 

the stimulus is confused for a known 

predator (Frid and Dill, 2002). In 

addition, because the source of the 

perceived predator (i.e., what is actually 

a MFA sonar signal) will likely be closer 

to the whales (because attenuation 

limits the range of detection of midfrequencies) and moving faster (because 

it will be on faster-moving vessels), any 

antipredator response would be more 

likely to be severe (with greater 

perceived predation risk, an animal is 

more likely to disregard the cost of the 

response; Frid and Dill, 2002). Indeed, 

when analyzing movements of a beaked 

whale exposed to playback of killer 

whale predation calls, Allen et al. (2014) 

found that the whale engaged in a 

prolonged, directed avoidance response, 

suggesting a behavioral reaction that 

could pose a risk factor for stranding. 

Overall, these significant differences 

between sound from MFA sonar and the 

mid-frequency sound component from 

airguns and the likelihood that MFA 

sonar signals will be interpreted in error 

as a predator are critical to 

understanding the likely risk of 

behaviorally-mediated injury due to 

seismic surveys. 

The available scientific literature also 

provides a useful contrast between 

airgun noise and MFA sonar regarding 

the likely risk of behaviorally-mediated 

injury. There is strong evidence for the 

association of beaked whale stranding 

events with MFA sonar use, and 

particularly detailed accounting of 

several events is available (e.g., a 2000 

Bahamas stranding event for which 

investigators concluded that MFA sonar 

use was responsible; Evans and 

England, 2001). D’Amico et al. (2009) 

reviewed 126 beaked whale mass 

stranding events over the period from 

1950 (i.e., from the development of 

modern MFA sonar systems) through 

2004. Of these, there were two events 

where detailed information was 

available on both the timing and 

location of the stranding and the 

concurrent nearby naval activity, 

including verification of active MFA 

sonar usage, with no evidence for an 

alternative cause of stranding. An 

additional ten events were at minimum 

spatially and temporally coincident 

with naval activity likely to have 

included MFA sonar use and, despite 

incomplete knowledge of timing and 

location of the stranding or the naval 

activity in some cases, there was no 

evidence for an alternative cause of 


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stranding. The U.S. Navy has publicly 

stated agreement that five such events 

since 1996 were associated in time and 

space with MFA sonar use, either by the 

U.S. Navy alone or in joint training 

exercises with the North Atlantic Treaty 

Organization. The U.S. Navy 

additionally noted that, as of 2017, a 

2014 beaked whale stranding event in 

Crete coincident with naval exercises 

was under review and had not yet been 

determined to be linked to sonar 

activities (U.S. Navy, 2017). Separately, 

the International Council for the 

Exploration of the Sea reported in 2005 

that, worldwide, there have been about 

50 known strandings, consisting mostly 

of beaked whales, with a potential 

causal link to MFA sonar (ICES, 2005). 

In contrast, very few such associations 

have been made to seismic surveys, 

despite widespread use of airguns as a 

geophysical sound source in numerous 

locations around the world. 

A more recent review of possible 

stranding associations with seismic 

surveys (Castellote and Llorens, 2016) 

states plainly that, ‘‘[s]peculation 

concerning possible links between 

seismic survey noise and cetacean 

strandings is available for a dozen 

events but without convincing causal 

evidence.’’ The authors’ ‘‘exhaustive’’ 

search of available information found 10 

events worth further investigation via a 

ranking system representing a rough 

metric of the relative level of confidence 

offered by the data for inferences about 

the possible role of the seismic survey 

in a given stranding event. Only three of 

these events involved beaked whales. 

Whereas D’Amico et al. (2009) used a 1– 

5 ranking system, in which ‘‘1’’ 

represented the most robust evidence 

connecting the event to MFA sonar use, 

Castellote and Llorens (2016) used a 1– 

6 ranking system, in which ‘‘6’’ 

represented the most robust evidence 

connecting the event to the seismic 

survey. As described above, D’Amico et 

al. (2009) found that two events were 

ranked ‘‘1’’ and ten events were ranked 

‘‘2’’ (i.e., 12 beaked whale stranding 

events were found to be associated with 

MFA sonar use). In contrast, Castellote 

and Llorens (2016) found that none of 

the three beaked whale stranding events 

achieved their highest ranks of 5 or 6. 

Of the 10 total events, none achieved 

the highest rank of 6. Two events were 

ranked as 5: One stranding in Peru 

involving dolphins and porpoises and a 

2008 stranding in Madagascar. This 

latter ranking can only broadly be 

associated with the survey itself, as 

opposed to use of seismic airguns. An 

exhaustive investigation of this 

stranding event, which did not involve 

beaked whales, concluded that use of a 

high-frequency mapping system (12-kHz 

multibeam echosounder) was the most 

plausible and likely initial behavioral 

trigger of the event, which was likely 

exacerbated by several site- and 

situation-specific secondary factors. The 

review panel found that seismic airguns 

were used after the initial strandings 

and animals entering a lagoon system, 

that airgun use clearly had no role as an 

initial trigger, and that there was no 

evidence that airgun use dissuaded 

animals from leaving (Southall et al., 

2013). 

However, one of these stranding 

events, involving two Cuvier’s beaked 

whales, was contemporaneous with and 

reasonably associated spatially with a 

2002 seismic survey in the Gulf of 

California conducted by L–DEO, as was 

the case for the 2007 Gulf of Cadiz 

seismic survey discussed by Castellote 

and Llorens (also involving two Cuvier’s 

beaked whales). However, neither event 

was considered a ‘‘true atypical mass 

stranding’’ (according to Frantzis [1998]) 

as used in the analysis of Castellote and 

Llorens (2016). While we agree with the 

authors that this lack of evidence should 

not be considered conclusive, it is clear 

that there is very little evidence that 

seismic surveys should be considered as 

posing a significant risk of acute harm 

to beaked whales or other midfrequency cetaceans. We have 

considered the potential for the 

proposed surveys to result in marine 

mammal stranding and have concluded 

that, based on the best available 

information, stranding is not expected 

to occur. 

Entanglement—Entanglements occur 

when marine mammals become 

wrapped around cables, lines, nets, or 

other objects suspended in the water 

column. During seismic survey 

operations, numerous cables, lines, and 

other objects primarily associated with 

the airgun array and hydrophone 

streamers will be towed behind the 

Langseth near the water‘s surface. 

However, we are not aware of any cases 

of entanglement of mysticetes in seismic 

survey equipment. No incidents of 

entanglement of marine mammals with 

seismic survey gear have been 

documented in over 54,000 nmi 

(100,000 km) of previous NSF-funded 

seismic surveys when observers were 

aboard (e.g., Smultea and Holst 2003; 

Haley and Koski 2004; Holst 2004; 

Smultea et al., 2004; Holst et al., 2005; 

Haley and Ireland 2006; SIO and NSF 

2006; Hauser et al., 2008; Holst and 

Smultea 2008). Although entanglement 

with the streamer is theoretically 

possible, it has not been documented 

during tens of thousands of miles of 

NSF-sponsored seismic cruises or, to 

our knowledge, during hundreds of 

thousands of miles of industrial seismic 

cruises. Entanglement in OBSs and 

ocean bottom nodes (OBNs) is also not 

expected to occur. There are a relative 

few deployed devices, and no 

interaction between marine mammals 

and any such device has been recorded 

during prior NSF surveys using the 

devices. There are no meaningful 

entanglement risks posed by the 

proposed survey, and entanglement 

risks are not discussed further in this 

document. 

Anticipated Effects on Marine Mammal 

Habitat 

Physical Disturbance—Sources of 

seafloor disturbance related to 

geophysical surveys that may impact 

marine mammal habitat include 

placement of anchors, nodes, cables, 

sensors, or other equipment on or in the 

seafloor for various activities. 

Equipment deployed on the seafloor has 

the potential to cause direct physical 

damage and could affect bottomassociated fish resources. 

Placement of OBSs on the seafloor 

could damage areas of hard bottom 

where direct contact with the seafloor 

occurs and could crush epifauna 

(organisms that live on the seafloor or 

surface of other organisms). Damage to 

unknown or unseen hard bottom could 

occur, but because of the small area 

covered by most bottom-founded 

equipment and the patchy distribution 

of hard bottom habitat, contact with 

unknown hard bottom is expected to be 

rare and impacts minor. Seafloor 

disturbance in areas of soft bottom can 

cause loss of small patches of epifauna 

and infauna due to burial or crushing, 

and bottom-feeding fishes could be 

temporarily displaced from feeding 

areas. Overall, any effects of physical 

damage to habitat are expected to be 

minor and temporary. 

Effects to Prey—Marine mammal prey 

varies by species, season, and location 

and, for some, is not well documented. 

Fish react to sounds which are 

especially strong and/or intermittent 

low-frequency sounds, and behavioral 

responses such as flight or avoidance 

are the most likely effects. However, the 

reaction of fish to airguns depends on 

the physiological state of the fish, past 

exposures, motivation (e.g., feeding, 

spawning, migration), and other 

environmental factors. Several studies 

have demonstrated that airgun sounds 

might affect the distribution and 

behavior of some fishes, potentially 

impacting foraging opportunities or 

increasing energetic costs (e.g., Fewtrell 

and McCauley, 2012; Pearson et al., 


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1992; Skalski et al., 1992; Santulli et al., 

1999; Paxton et al., 2017), though the 

bulk of studies indicate no or slight 

reaction to noise (e.g., Miller and 

Cripps, 2013; Dalen and Knutsen, 1987; 

Pena et al., 2013; Chapman and 

Hawkins, 1969; Wardle et al., 2001; Sara 

et al., 2007; Jorgenson and Gyselman, 

2009; Blaxter et al., 1981; Cott et al., 

2012; Boeger et al., 2006), and that, most 

commonly, while there are likely to be 

impacts to fish as a result of noise from 

nearby airguns, such effects will be 

temporary. For example, investigators 

reported significant, short-term declines 

in commercial fishing catch rate of 

gadid fishes during and for up to 5 days 

after seismic survey operations, but the 

catch rate subsequently returned to 

normal (Engas et al., 1996; Engas and 

Lokkeborg, 2002). Other studies have 

reported similar findings (Hassel et al., 

2004). Skalski et al. (1992) also found a 

reduction in catch rates—for rockfish 

(Sebastes spp.) in response to controlled 

airgun exposure—but suggested that the 

mechanism underlying the decline was 

not dispersal but rather decreased 

responsiveness to baited hooks 

associated with an alarm behavioral 

response. A companion study showed 

that alarm and startle responses were 

not sustained following the removal of 

the sound source (Pearson et al., 1992). 

Therefore, Skalski et al. (1992) 

suggested that the effects on fish 

abundance may be transitory, primarily 

occurring during the sound exposure 

itself. In some cases, effects on catch 

rates are variable within a study, which 

may be more broadly representative of 

temporary displacement of fish in 

response to airgun noise (i.e., catch rates 

may increase in some locations and 

decrease in others) than any long-term 

damage to the fish themselves (Streever 

et al., 2016). 

SPLs of sufficient strength have been 

known to cause injury to fish and fish 

mortality and, in some studies, fish 

auditory systems have been damaged by 

airgun noise (McCauley et al., 2003; 

Popper et al., 2005; Song et al., 2008). 

However, in most fish species, hair cells 

in the ear continuously regenerate and 

loss of auditory function likely is 

restored when damaged cells are 

replaced with new cells. Halvorsen et al. 

(2012b. (2012) showed that a TTS of 4– 

6 dB was recoverable within 24 hours 

for one species. Impacts would be most 

severe when the individual fish is close 

to the source and when the duration of 

exposure is long—both of which are 

conditions unlikely to occur for this 

survey that is necessarily transient in 

any given location and likely result in 

brief, infrequent noise exposure to prey 

species in any given area. For this 

survey, the sound source is constantly 

moving, and most fish would likely 

avoid the sound source prior to 

receiving sound of sufficient intensity to 

cause physiological or anatomical 

damage. In addition, ramp-up may 

allow certain fish species the 

opportunity to move further away from 

the sound source. 

A recent comprehensive review 

(Carroll et al., 2017) found that results 

are mixed as to the effects of airgun 

noise on the prey of marine mammals. 

While some studies suggest a change in 

prey distribution and/or a reduction in 

prey abundance following the use of 

seismic airguns, others suggest no 

effects or even positive effects in prey 

abundance. As one specific example, 

Paxton et al. (2017), which describes 

findings related to the effects of a 2014 

seismic survey on a reef off of North 

Carolina, showed a 78 percent decrease 

in observed nighttime abundance for 

certain species. It is important to note 

that the evening hours during which the 

decline in fish habitat use was recorded 

(via video recording) occurred on the 

same day that the seismic survey 

passed, and no subsequent data is 

presented to support an inference that 

the response was long-lasting. 

Additionally, given that the finding is 

based on video images, the lack of 

recorded fish presence does not support 

a conclusion that the fish actually 

moved away from the site or suffered 

any serious impairment. In summary, 

this particular study corroborates prior 

studies indicating that a startle response 

or short-term displacement should be 

expected. 

Available data suggest that 

cephalopods are capable of sensing the 

particle motion of sounds and detect 

low frequencies up to 1–1.5 kHz, 

depending on the species, and so are 

likely to detect airgun noise (Kaifu et al., 

2008; Hu et al., 2009; Mooney et al., 

2010; Samson et al., 2014). Auditory 

injuries (lesions occurring on the 

statocyst sensory hair cells) have been 

reported upon controlled exposure to 

low-frequency sounds, suggesting that 

cephalopods are particularly sensitive to 

low-frequency sound (Andre et al., 

2011; Sole et al., 2013). Behavioral 

responses, such as inking and jetting, 

have also been reported upon exposure 

to low-frequency sound (McCauley et 

al., 2000b; Samson et al., 2014). Similar 

to fish, however, the transient nature of 

the survey leads to an expectation that 

effects will be largely limited to 

behavioral reactions and would occur as 

a result of brief, infrequent exposures. 

With regard to potential impacts on 

zooplankton, McCauley et al. (2017) 

found that exposure to airgun noise 

resulted in significant depletion for 

more than half the taxa present and that 

there were two to three times more dead 

zooplankton after airgun exposure 

compared with controls for all taxa, 

within 1 km of the airguns. However, 

the authors also stated that in order to 

have significant impacts on r-selected 

species (i.e., those with high growth 

rates and that produce many offspring) 

such as plankton, the spatial or 

temporal scale of impact must be large 

in comparison with the ecosystem 

concerned, and it is possible that the 

findings reflect avoidance by 

zooplankton rather than mortality 

(McCauley et al., 2017). In addition, the 

results of this study are inconsistent 

with a large body of research that 

generally finds limited spatial and 

temporal impacts to zooplankton as a 

result of exposure to airgun noise (e.g., 

Dalen and Knutsen, 1987; Payne, 2004; 

Stanley et al., 2011). Most prior research 

on this topic, which has focused on 

relatively small spatial scales, has 

showed minimal effects (e.g., 

Kostyuchenko, 1973; Booman et al., 

1996; S#tre and Ona, 1996; Pearson et 

al., 1994; Bolle et al., 2012). 

A modeling exercise was conducted 

as a follow-up to the McCauley et al. 

(2017) study (as recommended by 

McCauley et al.), in order to assess the 

potential for impacts on ocean 

ecosystem dynamics and zooplankton 

population dynamics (Richardson et al., 

2017). Richardson et al. (2017) found 

that for copepods with a short life cycle 

in a high-energy environment, a fullscale airgun survey would impact 

copepod abundance up to three days 

following the end of the survey, 

suggesting that effects such as those 

found by McCauley et al. (2017) would 

not be expected to be detectable 

downstream of the survey areas, either 

spatially or temporally. 

Notably, a more recent study 

produced results inconsistent with 

those of McCauley et al. (2017). 

Researchers conducted a field and 

laboratory study to assess if exposure to 

airgun noise affects mortality, predator 

escape response, or gene expression of 

the copepod Calanus finmarchicus 

(Fields et al., 2019). Immediate 

mortality of copepods was significantly 

higher, relative to controls, at distances 

of 5 m or less from the airguns. 

Mortality one week after the airgun blast 

was significantly higher in the copepods 

placed 10 m from the airgun but was not 

significantly different from the controls 

at a distance of 20 m from the airgun. 

The increase in mortality, relative to 

controls, did not exceed 30 percent at 

any distance from the airgun. Moreover, 


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the authors caution that even this higher 

mortality in the immediate vicinity of 

the airguns may be more pronounced 

than what would be observed in freeswimming animals due to increased 

flow speed of fluid inside bags 

containing the experimental animals. 

There were no sublethal effects on the 

escape performance or the sensory 

threshold needed to initiate an escape 

response at any of the distances from 

the airgun that were tested. Whereas 

McCauley et al. (2017) reported an SEL 

of 156 dB at a range of 509–658 m, with 

zooplankton mortality observed at that 

range, Fields et al. (2019) reported an 

SEL of 186 dB at a range of 25 m, with 

no reported mortality at that distance. 

Regardless, if we assume a worst-case 

likelihood of severe impacts to 

zooplankton within approximately 1 km 

of the acoustic source, the brief time to 

regeneration of the potentially affected 

zooplankton populations does not lead 

us to expect any meaningful follow-on 

effects to the prey base for marine 

mammals. 

A 2017 review article concluded that, 

while laboratory results provide 

scientific evidence for high-intensity 

and low-frequency sound-induced 

physical trauma and other negative 

effects on some fish and invertebrates, 

the sound exposure scenarios in some 

cases are not realistic to those 

encountered by marine organisms 

during routine seismic survey 

operations (Carroll et al., 2017). The 

review finds that there has been no 

evidence of reduced catch or abundance 

following seismic activities for 

invertebrates, and that there is 

conflicting evidence for fish with catch 

observed to increase, decrease, or 

remain the same. Further, where there is 

evidence for decreased catch rates in 

response to airgun noise, these findings 

provide no information about the 

underlying biological cause of catch rate 

reduction (Carroll et al., 2017). 

In summary, impacts of the specified 

activity on marine mammal prey species 

will likely be limited to behavioral 

responses, the majority of prey species 

will be capable of moving out of the area 

during the survey, a rapid return to 

normal recruitment, distribution, and 

behavior for prey species is anticipated, 

and, overall, impacts to prey species 

will be minor and temporary. Prey 

species exposed to sound might move 

away from the sound source, experience 

TTS, experience masking of biologically 

relevant sounds, or show no obvious 

direct effects. Mortality from 

decompression injuries is possible in 

close proximity to a sound, but only 

limited data on mortality in response to 

airgun noise exposure are available 

(Hawkins et al., 2014). The most likely 

impacts for most prey species in the 

survey area would be temporary 

avoidance of the area. The proposed 

survey would move through an area 

relatively quickly, limiting exposure to 

multiple impulsive sounds. In all cases, 

sound levels would return to ambient 

once the survey moves out of the area 

or ends and the noise source is shut 

down and, when exposure to sound 

ends, behavioral and/or physiological 

responses are expected to end relatively 

quickly (McCauley et al., 2000b). The 

duration of fish avoidance of a given 

area after survey effort stops is 

unknown, but a rapid return to normal 

recruitment, distribution, and behavior 

is anticipated. While the potential for 

disruption of spawning aggregations or 

schools of important prey species can be 

meaningful on a local scale, the mobile 

and temporary nature of this survey and 

the likelihood of temporary avoidance 

behavior suggest that impacts would be 

minor. 

Acoustic Habitat—Acoustic habitat is 

the soundscape—which encompasses 

all of the sound present in a particular 

location and time, as a whole—when 

considered from the perspective of the 

animals experiencing it. Animals 

produce sound for, or listen for sounds 

produced by, conspecifics 

(communication during feeding, mating, 

and other social activities), other 

animals (finding prey or avoiding 

predators), and the physical 

environment (finding suitable habitats, 

navigating). Together, sounds made by 

animals and the geophysical 

environment (e.g., produced by 

earthquakes, lightning, wind, rain, 

waves) make up the natural 

contributions to the total acoustics of a 

place. These acoustic conditions, 

termed acoustic habitat, are one 

attribute of an animal’s total habitat. 

Soundscapes are also defined by, and 

acoustic habitat influenced by, the total 

contribution of anthropogenic sound. 

This may include incidental emissions 

from sources such as vessel traffic, or 

may be intentionally introduced to the 

marine environment for data acquisition 

purposes (as in the use of airgun arrays). 

Anthropogenic noise varies widely in its 

frequency content, duration, and 

loudness and these characteristics 

greatly influence the potential habitatmediated effects to marine mammals 

(please see also the previous discussion 

on masking under ‘‘Acoustic Effects’’), 

which may range from local effects for 

brief periods of time to chronic effects 

over large areas and for long durations. 

Depending on the extent of effects to 

habitat, animals may alter their 

communications signals (thereby 

potentially expending additional 

energy) or miss acoustic cues (either 

conspecific or adventitious). For more 

detail on these concepts see, e.g., Barber 

et al., 2010; Pijanowski et al., 2011; 

Francis and Barber, 2013; Lillis et al., 

2014. 

Problems arising from a failure to 

detect cues are more likely to occur 

when noise stimuli are chronic and 

overlap with biologically relevant cues 

used for communication, orientation, 

and predator/prey detection (Francis 

and Barber, 2013). Although the signals 

emitted by seismic airgun arrays are 

generally low frequency, they would 

also likely be of short duration and 

transient in any given area due to the 

nature of these surveys. As described 

previously, exploratory surveys such as 

these cover a large area but would be 

transient rather than focused in a given 

location over time and therefore would 

not be considered chronic in any given 

location. 

Based on the information discussed 

herein, we conclude that impacts of the 

specified activity are not likely to have 

more than short-term adverse effects on 

any prey habitat or populations of prey 

species. Further, any impacts to marine 

mammal habitat are not expected to 

result in significant or long-term 

consequences for individual marine 

mammals, or to contribute to adverse 

impacts on their populations. 

Estimated Take 

This section provides an estimate of 

the number of incidental takes proposed 

for authorization through this IHA, 

which will inform both NMFS’ 

consideration of ‘‘small numbers’’ and 

the negligible impact analysis and 

determination. 

Harassment is the only type of take 

expected to result from these activities. 

Except with respect to certain activities 

not pertinent here, section 3(18) of the 

MMPA defines ‘‘harassment’’ as any act 

of pursuit, torment, or annoyance, 

which (i) has the potential to injure a 

marine mammal or marine mammal 

stock in the wild (Level A harassment); 

or (ii) has the potential to disturb a 

marine mammal or marine mammal 

stock in the wild by causing disruption 

of behavioral patterns, including, but 

not limited to, migration, breathing, 

nursing, breeding, feeding, or sheltering 

(Level B harassment). 

Authorized takes would primarily be 

by Level B harassment, as use of seismic 

airguns has the potential to result in 

disruption of behavioral patterns for 

individual marine mammals. There is 

also some potential for auditory injury 

(Level A harassment) for mysticetes and 

high frequency cetaceans (i.e., 


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porpoises, Kogia spp.). The proposed 

mitigation and monitoring measures are 

expected to minimize the severity of 

such taking to the extent practicable. 

As noted previously, no serious injury 

or mortality is anticipated or proposed 

to be authorized for this activity. Below 

we describe how the take is estimated. 

Generally speaking, we estimate take 

by considering: (1) Acoustic thresholds 

above which NMFS believes the best 

available science indicates marine 

mammals will be behaviorally harassed 

or incur some degree of permanent 

hearing impairment; (2) the area or 

volume of water that will be ensonified 

above these levels in a day; (3) the 

density or occurrence of marine 

mammals within these ensonified areas; 

and, (4) the number of days of activities. 

We note that while these basic factors 

can contribute to a basic calculation to 

provide an initial prediction of takes, 

additional information that can 

qualitatively inform take estimates is 

also sometimes available (e.g., previous 

monitoring results or average group 

size). Below, we describe the factors 

considered here in more detail and 

present the proposed take estimate. 

Acoustic Thresholds 

NMFS recommends the use of 

acoustic thresholds that identify the 

received level of underwater sound 

above which exposed marine mammals 

would be reasonably expected to be 

behaviorally harassed (equated to Level 

B harassment) or to incur PTS of some 

degree (equated to Level A harassment). 

Level B Harassment for non-explosive 

sources—Though significantly driven by 

received level, the onset of behavioral 

disturbance from anthropogenic noise 

exposure is also informed to varying 

degrees by other factors related to the 

source (e.g., frequency, predictability, 

duty cycle), the environment (e.g., 

bathymetry), and the receiving animals 

(hearing, motivation, experience, 

demography, behavioral context) and 

can be difficult to predict (Southall et 

al., 2007, Ellison et al., 2012). Based on 

what the available science indicates and 

the practical need to use a threshold 

based on a factor that is both predictable 

and measurable for most activities, 

NMFS uses a generalized acoustic 

threshold based on received level to 

estimate the onset of behavioral 

harassment. NMFS predicts that marine 

mammals are likely to be behaviorally 

harassed in a manner we consider Level 

B harassment when exposed to 

underwater anthropogenic noise above 

received levels of 120 dB re 1 mPa (rms) 

for continuous (e.g., vibratory piledriving, drilling) and above 160 dB re 1 

mPa (rms) for non-explosive impulsive 

(e.g., seismic airguns) or intermittent 

(e.g., scientific sonar) sources. L–DEO’s 

proposed activity includes the use of 

impulsive seismic sources. Therefore, 

the 160 dB re 1 mPa (rms) threshold is 

applicable for analysis of Level B 

harassment. 

Level A harassment for non-explosive 

sources—NMFS’ Technical Guidance 

for Assessing the Effects of 

Anthropogenic Sound on Marine 

Mammal Hearing (Version 2.0) 

(Technical Guidance, 2018) identifies 

dual criteria to assess auditory injury 

(Level A harassment) to five different 

marine mammal groups (based on 

hearing sensitivity) as a result of 

exposure to noise from two different 

types of sources (impulsive or nonimpulsive). L–DEO’s proposed seismic 

survey includes the use of impulsive 

(seismic airguns) sources. 

These thresholds are provided in the 

table below. The references, analysis, 

and methodology used in the 

development of the thresholds are 

described in NMFS 2018 Technical 

Guidance, which may be accessed at 

https://www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

marine-mammal-acoustic-technicalguidance. 

TABLE 3—THRESHOLDS IDENTIFYING THE ONSET OF PERMANENT THRESHOLD SHIFT

Hearing group 

PTS onset acoustic thresholds * 

(received level) 

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 acoustic 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 should 

also be considered. 

Note: Peak sound pressure (Lpk) has a reference value of 1 μPa, and cumulative sound exposure level (LE) has a reference value of 1μPa2s. 

In this Table, thresholds are abbreviated to reflect American National Standards Institute standards (ANSI 2013). However, peak sound pressure 

is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript ‘‘flat’’ is being 

included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. 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 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 acoustic thresholds will be exceeded. 

Ensonified Area 

Here, we describe operational and 

environmental parameters of the activity 

that will feed into identifying the area 

ensonified above the acoustic 

thresholds, which include source levels 

and transmission loss coefficient. 

The proposed 2–D survey would 

acquire data using the 36-airgun array 

with a total discharge of 6,600 in3 at a 

maximum tow depth of 12 m. L–DEO 

model results are used to determine the 

160-dBrms radius for the 36-airgun 

array in deep water (>1,000 m) down to 

a maximum water depth of 2,000 m. 

Received sound levels were predicted 

by L–DEO’s model (Diebold et al., 2010) 

which uses ray tracing for the direct 

wave traveling from the array to the 

receiver and its associated source ghost 

(reflection at the air-water interface in 

the vicinity of the array), in a constantvelocity half-space (infinite 

homogeneous ocean layer, unbounded 

by a seafloor). In addition, propagation 

measurements of pulses from the 36- 

airgun array at a tow depth of 6 m have 

been reported in deep water 

(approximately 1,600 m), intermediate 

water depth on the slope (approximately 

600–1,100 m), and shallow water 

(approximately 50 m) in the Gulf of 

Mexico in 2007–2008 (Tolstoy et al. 

2009; Diebold et al. 2010). 


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For deep and intermediate-water 

cases, the field measurements cannot be 

used readily to derive Level A and Level 

B harassment isopleths, as at those sites 

the calibration hydrophone was located 

at a roughly constant depth of 350– 

500 m, which may not intersect all the 

SPL isopleths at their widest point from 

the sea surface down to the maximum 

relevant water depth for marine 

mammals of ∼2,000 m. At short ranges, 

where the direct arrivals dominate and 

the effects of seafloor interactions are 

minimal, the data recorded at the deep 

and slope sites are suitable for 

comparison with modeled levels at the 

depth of the calibration hydrophone. At 

longer ranges, the comparison with the 

model—constructed from the maximum 

SPL through the entire water column at 

varying distances from the airgun 

array—is the most relevant. 

In deep and intermediate-water 

depths, comparisons at short ranges 

between sound levels for direct arrivals 

recorded by the calibration hydrophone 

and model results for the same array 

tow depth are in good agreement (Fig. 

12 and 14 in Appendix H of NSF–USGS, 

2011). Consequently, isopleths falling 

within this domain can be predicted 

reliably by the L–DEO model, although 

they may be imperfectly sampled by 

measurements recorded at a single 

depth. At greater distances, the 

calibration data show that seafloorreflected and sub-seafloor-refracted 

arrivals dominate, whereas the direct 

arrivals become weak and/or 

incoherent. Aside from local topography 

effects, the region around the critical 

distance is where the observed levels 

rise closest to the model curve. 

However, the observed sound levels are 

found to fall almost entirely below the 

model curve. Thus, analysis of the Gulf 

of Mexico calibration measurements 

demonstrates that although simple, the 

L–DEO model is a robust tool for 

conservatively estimating isopleths. 

For deep water (>1,000 m), L–DEO 

used the deep-water radii obtained from 

model results down to a maximum 

water depth of 2,000 m. The radii for 

intermediate water depths (100– 

1,000 m) were derived from the deepwater ones by applying a correction 

factor (multiplication) of 1.5, such that 

observed levels at very near offsets fall 

below the corrected mitigation curve 

(See Fig. 16 in Appendix H of NSF– 

USGS, 2011). 

L–DEO’s modeling methodology is 

described in greater detail in their IHA 

application. The estimated distances to 

the Level B harassment isopleths for the 

array are shown in Table 4. Please note 

that no survey effort will occur in 

waters <100 m deep. The estimated 

isopleth distance specific to shallow 

water depths are provided for reference 

only. 

TABLE 4—PREDICTED RADIAL DISTANCES TO ISOPLETHS CORRESPONDING TO LEVEL B HARASSMENT THRESHOLD

Source and volume Tow depth 

(m) 

Water depth 

(m) 

Level B 

harassment 

zone 

(m) 

36 airgun array; 6,600 in3 ............................................................................................................ 12 >1,000 

100–1,000 3 <100 

1 6,733 2 10,100 

4 25,494 

1 Distance based on L–DEO model results. 

2 Distance is based on L–DEO model results with a 1.5 × correction factor between deep and intermediate water depths. 3 No survey effort will occur in waters <100 m deep. 

4 Distance is based on empirically derived measurements in the Gulf of Mexico (GoM) with scaling applied to account for differences in tow 

depth. 

Predicted distances to Level A 

harassment isopleths, which vary based 

on marine mammal hearing groups, 

were calculated based on modeling 

performed by L–DEO using the 

NUCLEUS source modeling software 

program and the NMFS User 

Spreadsheet, described below. The 

acoustic thresholds for impulsive 

sounds (e.g., airguns) contained in the 

Technical Guidance were presented as 

dual metric acoustic thresholds using 

both SELcum and peak sound pressure 

metrics (NMFS 2018). As dual metrics, 

NMFS considers onset of PTS (Level A 

harassment) to have occurred when 

either one of the two metrics is 

exceeded (i.e., metric resulting in the 

largest isopleth). The SELcum metric 

considers both level and duration of 

exposure, as well as auditory weighting 

functions by marine mammal hearing 

group. In recognition of the fact that the 

requirement to calculate Level A 

harassment ensonified areas could be 

more technically challenging to predict 

due to the duration component and the 

use of weighting functions in the new 

SELcum thresholds, NMFS developed an 

optional User Spreadsheet that includes 

tools to help predict a simple isopleth 

that can be used in conjunction with 

marine mammal density or occurrence 

to facilitate the estimation of take 

numbers. 

The values for SELcum and peak SPL 

for the Langseth airgun arrays were 

derived from calculating the modified 

far-field signature. The far-field 

signature is often used as a theoretical 

representation of the source level. To 

compute the far-field signature, the 

source level is estimated at a large 

distance below the array (e.g., 9 km), 

and this level is back projected 

mathematically to a notional distance of 

1 m from the array’s geometrical center. 

However, when the source is an array of 

multiple airguns separated in space, the 

source level from the theoretical farfield signature is not necessarily the best 

measurement of the source level that is 

physically achieved at the source 

(Tolstoy et al., 2009). Near the source (at 

short ranges, distances <1 km), the 

pulses of sound pressure from each 

individual airgun in the source array do 

not stack constructively, as they do for 

the theoretical far-field signature. The 

pulses from the different airguns spread 

out in time such that the source levels 

observed or modeled are the result of 

the summation of pulses from a few 

airguns, not the full array (Tolstoy et al., 

2009). At larger distances, away from 

the source array center, sound pressure 

of all the airguns in the array stack 

coherently, but not within one time 

sample, resulting in smaller source 

levels (a few dB) than the source level 

derived from the far-field signature. 

Because the far-field signature does not 

take into account the large array effect 

near the source and is calculated as a 

point source, the modified far-field 

signature is a more appropriate measure 

of the sound source level for distributed 

sound sources, such as airgun arrays. L– 

DEO used the acoustic modeling 

methodology as used for estimating 

Level B harassment distances with a 

small grid step of 1 m in both the inline 

and depth directions. The propagation 

modeling takes into account all airgun 


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interactions at short distances from the 

source, including interactions between 

subarrays, which are modeled using the 

NUCLEUS software to estimate the 

notional signature and MATLAB 

software to calculate the pressure signal 

at each mesh point of a grid. 

In order to more realistically 

incorporate the Technical Guidance’s 

weighting functions over the seismic 

array’s full acoustic band, unweighted 

spectrum data for the Langseth’s airgun 

array (modeled in 1 Hz bands) was used 

to make adjustments (dB) to the 

unweighted spectrum levels, by 

frequency, according to the weighting 

functions for each relevant marine 

mammal hearing group. These adjusted/ 

weighted spectrum levels were then 

converted to pressures (mPa) in order to 

integrate them over the entire 

broadband spectrum, resulting in 

broadband weighted source levels by 

hearing group that could be directly 

incorporated within the User 

Spreadsheet (i.e., to override the 

Spreadsheet’s more simple weighting 

factor adjustment). Using the User 

Spreadsheet’s ‘‘safe distance’’ 

methodology for mobile sources 

(described by Sivle et al., 2014) with the 

hearing group-specific weighted source 

levels, and inputs assuming spherical 

spreading propagation and information 

specific to the planned survey (i.e., the 

2.2 m/s source velocity and (worst-case) 

50-m shot interval, equivalent to a 

repetition rate of 23.1 seconds), 

potential radial distances to auditory 

injury zones were then calculated for 

SELcum thresholds. 

Inputs to the User Spreadsheets in the 

form of estimated source levels are 

shown in Appendix A of L–DEO’s 

application. User Spreadsheets used by 

L–DEO to estimate distances to Level A 

harassment isopleths for the airgun 

arrays are also provided in Appendix A 

of the application. Outputs from the 

User Spreadsheets in the form of 

estimated distances to Level A 

harassment isopleths for the survey are 

shown in Table 5. As described above, 

NMFS considers onset of PTS (Level A 

harassment) to have occurred when 

either one of the dual metrics (SELcum

and Peak SPLflat) is exceeded (i.e., 

metric resulting in the largest isopleth). 

L–DEO proposes to conduct two 

different methods of seismic 

acquisition, MCS using a hydrophone 

streamer (approximately 62 percent of 

the total survey effort) and refraction 

surveys using OBSs (approximately 38 

percent of the total survey effort). The 

airguns would fire at a shot interval of 

50 m (repetition rate of 23 seconds) 

during MCS surveys and at a 400-m 

interval (repetition rate of 155 seconds) 

during refraction surveys to OBSs. The 

distances presented in Table 5 were 

calculated using the MCS survey inputs 

as using the 50-m shot interval provides 

more conservative distances than the 

400-m shot interval. 

TABLE 5—MODELED RADIAL DISTANCES (m) TO ISOPLETHS CORRESPONDING TO LEVEL A HARASSMENT THRESHOLDS

Source 

(volume) Threshold 

Level A harassment zone 

(m) 

LF cetaceans MF cetaceans HF cetaceans Otariids 

36-airgun array (6,600 in3) .................................................. SELcum ........... 320.2 0 1.0 0 

Peak ............... 8.9 13.9 268.3 10.6 

Note that because of some of the 

assumptions included in the methods 

used (e.g., stationary receiver with no 

vertical or horizontal movement in 

response to the acoustic source), 

isopleths produced may be 

overestimates to some degree, which 

will ultimately result in some degree of 

overestimation of Level A harassment. 

However, these tools offer the best way 

to predict appropriate isopleths when 

more sophisticated modeling methods 

are not available, and NMFS continues 

to develop ways to quantitatively refine 

these tools and will qualitatively 

address the output where appropriate. 

For mobile sources, such as the 

proposed seismic survey, the User 

Spreadsheet predicts the closest 

distance at which a stationary animal 

would not incur PTS if the sound source 

traveled by the animal in a straight line 

at a constant speed. 

Auditory injury is unlikely to occur 

for mid-frequency cetaceans and otariid 

pinnipeds, given very small modeled 

zones of injury for those species (all 

estimated zones less than 15 m for midfrequency cetaceans and otariid 

pinnipeds), in context of distributed 

source dynamics. The source level of 

the array is a theoretical definition 

assuming a point source and 

measurement in the far-field of the 

source (MacGillivray, 2006). As 

described by Caldwell and Dragoset 

(2000), an array is not a point source, 

but one that spans a small area. In the 

far-field, individual elements in arrays 

will effectively work as one source 

because individual pressure peaks will 

have coalesced into one relatively broad 

pulse. The array can then be considered 

a ‘‘point source.’’ For distances within 

the near-field, i.e., approximately 2–3 

times the array dimensions, pressure 

peaks from individual elements do not 

arrive simultaneously because the 

observation point is not equidistant 

from each element. The effect is 

destructive interference of the outputs 

of each element, so that peak pressures 

in the near-field will be significantly 

lower than the output of the largest 

individual element. Here, the relevant 

peak isopleth distances would in all 

cases be expected to be within the nearfield of the array where the definition of 

source level breaks down. Therefore, 

actual locations within this distance of 

the array center where the sound level 

exceeds the relevant peak SPL 

thresholds would not necessarily exist. 

In general, Caldwell and Dragoset (2000) 

suggest that the near-field for airgun 

arrays is considered to extend out to 

approximately 250 m. 

In order to provide quantitative 

support for this theoretical argument, 

we calculated expected maximum 

distances at which the near-field would 

transition to the far-field (Table 5). For 

a specific array one can estimate the 

distance at which the near-field 

transitions to the far-field by: 

with the condition that D >> l, and where 

D is the distance, L is the longest dimension 

of the array, and l is the wavelength of the 

signal (Lurton, 2002). 

Given that l can be defined by: 

where f is the frequency of the sound signal 

and v is the speed of the sound in the 

medium of interest, one can rewrite the 

equation for D as: 

and calculate D directly given a 

particular frequency and known speed 


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L2 

D=-

4,:i. 

fL2 

D=-

4v 
2014 Federal Register / Vol. 87, No. 8 / Wednesday, January 12, 2022 / Notices 

of sound (here assumed to be 1,500 

meters per second in water, although 

this varies with environmental 

conditions). 

To determine the closest distance to 

the arrays at which the source level 

predictions in Table 5 are valid (i.e., 

maximum extent of the near-field), we 

calculated D based on an assumed 

frequency of 1 kHz. A frequency of 1 

kHz is commonly used in near-field/farfield calculations for airgun arrays 

(Zykov and Carr, 2014; MacGillivray, 

2006; NSF and USGS, 2011), and based 

on representative airgun spectrum data 

and field measurements of an airgun 

array used on the Langseth, nearly all 

(greater than 95 percent) of the energy 

from airgun arrays is below 1 kHz 

(Tolstoy et al., 2009). Thus, using 1 kHz 

as the upper cut-off for calculating the 

maximum extent of the near-field 

should reasonably represent the nearfield extent in field conditions. 

If the largest distance to the peak 

sound pressure level threshold was 

equal to or less than the longest 

dimension of the array (i.e., under the 

array), or within the near-field, then 

received levels that meet or exceed the 

threshold in most cases are not expected 

to occur. This is because within the 

near-field and within the dimensions of 

the array, the source levels specified in 

Appendix A of L–DEO’s application are 

overestimated and not applicable. In 

fact, until one reaches a distance of 

approximately three or four times the 

near-field distance the average intensity 

of sound at any given distance from the 

array is still less than that based on 

calculations that assume a directional 

point source (Lurton, 2002). The 6,600- 

in3 airgun array planned for use during 

the proposed survey has an approximate 

diagonal of 28.8 m, resulting in a nearfield distance of 138.7 m at 1 kHz (NSF 

and USGS, 2011). Field measurements 

of this array indicate that the source 

behaves like multiple discrete sources, 

rather than a directional point source, 

beginning at approximately 400 m (deep 

site) to 1 km (shallow site) from the 

center of the array (Tolstoy et al., 2009), 

distances that are actually greater than 

four times the calculated 140-m nearfield distance. Within these distances, 

the recorded received levels were 

always lower than would be predicted 

based on calculations that assume a 

directional point source, and 

increasingly so as one moves closer 

towards the array (Tolstoy et al., 2009). 

Given this, relying on the calculated 

distance (138.7 m) as the distance at 

which we expect to be in the near-field 

is a conservative approach since even 

beyond this distance the acoustic 

modeling still overestimates the actual 

received level. Within the near-field, in 

order to explicitly evaluate the 

likelihood of exceeding any particular 

acoustic threshold, one would need to 

consider the exact position of the 

animal, its relationship to individual 

array elements, and how the individual 

acoustic sources propagate and their 

acoustic fields interact. Given that 

within the near-field and dimensions of 

the array source levels would be below 

those assumed here, we believe 

exceedance of the peak pressure 

threshold would only be possible under 

highly unlikely circumstances. 

In consideration of the received sound 

levels in the near-field as described 

above, we expect the potential for Level 

A harassment of mid-frequency 

cetaceans, otariid pinnipeds, and 

phocid pinnipeds to be de minimis, 

even before the likely moderating effects 

of aversion and/or other compensatory 

behaviors (e.g., Nachtigall et al., 2018) 

are considered. We do not believe that 

Level A harassment is a likely outcome 

for any mid-frequency cetacean, otariid 

pinniped, or phocid pinniped and do 

not propose to authorize any Level A 

harassment for these species. 

Marine Mammal Occurrence 

In this section we provide the 

information about the presence, density, 

or group dynamics of marine mammals 

that will inform the take calculations. 

L–DEO used habitat-based stratified 

marine mammal densities for summer 

for the ETP when available (Barlow et 

al., 2009), and densities for the ETP 

from NMFS (2015b) for all other species 

(Table 6). Barlow et al. (2009) used data 

from 16 NMFS Southwest Fisheries 

Science Center (SWFSC) ship-based 

cetacean and ecosystem assessment 

surveys between 1986 and 2006 to 

develop habitat models to predict 

density for 15 cetacean species in the 

ETP. Model predictions were then used 

in standard line-transect formulae to 

estimate density for each transect 

segment for each survey year. Predicted 

densities for each year were smoothed 

with geospatial methods to obtain a 

continuous grid of density estimates for 

the surveyed area in the ETP. These 

annual grids were then averaged to 

obtain a composite grid that represents 

our best estimates of cetacean density 

over the past 20 years in the ETP. The 

models developed by Barlow et al. 

(2009) have been incorporated into a 

web-based GIS software system 

developed by Duke University’s 

Strategic Environmental Research and 

Development Program. The habitatbased density models consist of 100 km 

× 100 km grid cells. Densities in the grid 

cells that overlapped the survey area 

were averaged for each of the three 

water depth categories (shallow, 

intermediate, deep). 

The NMFS SWFSC also developed 

density estimates for species in the ETP 

that may be affected by their own 

fisheries research activities (NMFS 

2015b). These estimates were derived 

from abundance estimates using shipbased surveys of marine mammals in 

the ETP, as reported by Gerrodette et al. 

(2008). While the SWFSC developed 

volumetric density estimates (animals/ 

km3) to account for typical dive depth 

of each species (0–200 m and >200 m), 

L–DEO used the area density (animals/ 

km2) to represent expected density 

across all water depth strata. 

For the sei whale, for which NMFS 

(2015b) reported a density of zero, L– 

DEO used the spring density for Baja 

from U.S. Navy (2017b). No regional 

density estimates are available for 

Guadalupe fur seals in the ETP; 

therefore, NMFS (2015b) used the 

density of Guadalupe fur seals in the 

California Current Ecosystem (CCE) as a 

proxy. However, as the survey area is 

south of the typical range of Guadalupe 

fur seals (Ortiz et al., 2019), the density 

from the CCE is likely an overestimate. 

In the survey area, Guadalupe fur seals 

are extremely unlikely to occur in 

waters over the continental shelf under 

2,000 m (T. Norris, pers. comm.). NMFS 

has therefore assumed that the density 

of Guadalupe fur seals in water depths 

under 2,000 m is zero animals per 

square km, and have retained the CCE 

density estimate for waters over 2,000 m 

deep (Table 6). 


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TABLE 6—ESTIMATED DENSITIES OF MARINE MAMMALS IN THE PROPOSED SURVEY AREA

Species 

Density (#/km2) in survey area 

Shallow water 

(<100 m) 

Intermediate 

water 

(100–1,000 m) 

Deep water 

(>1,000 m) 

Humpback whale ......................................................................................................................... 1 0.00013 1 0.00013 1 0.00013 

Minke whale ................................................................................................................................. 1 0.00001 1 0.00001 1 0.00001 

Bryde’s whale .............................................................................................................................. 2 0.000486 2 0.000489 2 0.000451 

Fin whale ..................................................................................................................................... 1 0.00003 1 0.00003 1 0.00003 

Sei whale ..................................................................................................................................... 3 0.00005 3 0.00005 3 0.00005 

Blue whale ................................................................................................................................... 2 0.00010 2 0.00009 2 0.00008 

Sperm whale ................................................................................................................................ 1 0.00019 1 0.00019 1 0.00019 

Cuvier’s beaked whale ................................................................................................................ 2 0.00105 2 0.00106 2 0.00107 

Longman’s beaked whale ............................................................................................................ 1 0.00004 1 0.00004 1 0.00004 

Mesoplodon spp 4 ........................................................................................................................ 2 0.00032 2 0.00033 2 0.00036 

Risso’s dolphin ............................................................................................................................. 1 0.00517 1 0.00517 1 0.00517 

Rough-toothed dolphin ................................................................................................................ 2 0.00880 2 0.00891 2 0.00945 

Common bottlenose dolphin ........................................................................................................ 2 0.04809 2 0.04502 2 0.03557 

Pantropical spotted dolphin ......................................................................................................... 1 0.12263 1 0.12263 1 0.12263 

Spinner dolphin (whitebelly) ........................................................................................................ 2 0.00148 2 0.00155 2 0.00193 

Spinner dolphin (eastern) ............................................................................................................ 2 0.13182 2 0.12989 2 0.12791 

Striped dolphin ............................................................................................................................. 2 0.02800 2 0.02890 2 0.03516 

Short-beaked common dolphin .................................................................................................... 2 0.04934 2 0.04881 2 0.04435 

Fraser’s dolphin ........................................................................................................................... 1 0.01355 1 0.01355 1 0.01355 

Short-finned pilot whale 5 ............................................................................................................. 2 0.00346 2 0.00344 2 0.00382 

Killer whale .................................................................................................................................. 1 0.0004 1 0.0004 1 0.0004 

False killer whale ......................................................................................................................... 1 0.00186 1 0.00186 1 0.00186 

Pygmy killer whale ....................................................................................................................... 1 0.00183 1 0.00183 1 0.00183 

Melon-headed whale ................................................................................................................... 1 0.00213 1 0.00213 1 0.00213 

Kogia spp ..................................................................................................................................... 1 0.00053 1 0.00053 1 0.00053 

Guadalupe fur seal ...................................................................................................................... 0 1 6 0.00741 1 0.00741 

California sea lion ........................................................................................................................ 1 0.16262 1 0.16262 7 0 

1 Density in greater ETP (NMFS 2015b). 

2 Density in proposed survey area (Barlow et al., 2009). 3 Density for Baja (U.S. Navy 2017b). 

4 Density for Mesoplodon species guild (Blainville’s beaked whale, Gingko-toothed beaked whale, Deraniyagala’s beaked whale, and pygmy 

beaked whale). 5 Density for Globicephala species guild. 6 Density is assumed to be zero in waters <2,000 m. 

7 Density is assumed to be zero in deep water (>1,000 m). 

Take Calculation and Estimation 

Here we describe how the information 

provided above is brought together to 

produce a quantitative take estimate. 

In order to estimate the number of 

marine mammals predicted to be 

exposed to sound levels that would 

result in Level A or Level B harassment, 

radial distances from the airgun array to 

predicted isopleths corresponding to the 

Level A harassment and Level B 

harassment thresholds are calculated, as 

described above. Those radial distances 

are then used to calculate the area(s) 

around the airgun array predicted to be 

ensonified to sound levels that exceed 

the Level A and Level B harassment 

thresholds. L–DEO identified specific 

seismic survey trackline(s) that could be 

surveyed on one day of research; in this 

case, a representative 182-km MCS line 

and a 222-km long OBS line were 

chosen. The distances to the 160-dB 

Level B harassment threshold and PTS 

(Level A harassment) thresholds (based 

on L–DEO model results) were used to 

draw a buffer around every transect line 

in GIS to determine the daily ensonified 

area in each depth category. The 

ensonified areas were then multiplied 

by the number of survey days (7 days for 

OBS survey effort; 13 days for MCS 

survey effort) increased by 25 percent. 

As noted previously, L–DEO has added 

25 percent in the form of operational 

days, which is equivalent to adding 25 

percent to the proposed line kilometers 

to be surveyed. This accounts for the 

possibility that additional operational 

days are required, but likely results in 

an overestimate of actual exposures. For 

additional details regarding calculations 

of ensonified area, please see Appendix 

D of L–DEO’s application. L–DEO’s 

estimated incidents of exposure above 

Level A and Level B harassment criteria 

are presented in Table 7. 

As previously noted, NMFS does not 

have authority under the MMPA within 

the territorial seas of foreign nations 

(from 0–12 nmi (22.2 km) from shore), as 

the MMPA does not apply in those 

waters, and therefore does not authorize 

incidental take that may occur as a 

result of activities occurring within 

territorial waters. However, NMFS has 

still calculated the estimated level of 

incidental take in the entire activity area 

(including Mexican territorial waters) as 

part of the analysis supporting our 

determination under the MMPA that the 

activity will have a negligible impact on 

the affected species. The total estimated 

take in U.S. and Mexican waters is 

presented in Table 8 (see Negligible 

Impact Analysis and Determination). 

L–DEO generally assumed that their 

estimates of marine mammal exposures 

above harassment thresholds to equate 

to take and requested authorization of 

those takes. Those estimates in turn 

form the basis for our proposed take 

authorization numbers. For the species 

for which NMFS does not expect there 

to be a reasonable potential for take by 

Level A harassment to occur, i.e., midfrequency cetaceans and all pinnipeds, 

we have added L–DEO’s estimated 

exposures above Level A harassment 

thresholds (and requests for take by 

Level A harassment) to their estimated 

exposures above the Level B harassment 

threshold to produce a total number of 

incidents of take by Level B harassment 


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that is proposed for authorization. 

Estimated exposures and proposed take 

numbers for authorization are shown in 

Table 7. 

TABLE 7—ESTIMATED AND PROPOSED TAKE BY LEVEL A AND LEVEL B HARASSMENT, AND PERCENTAGE OF POPULATION

Species 

Estimated 

takes by 

Level B 

harassment 

Estimated 

takes by 

Level A 

harassment 

Proposed 

takes by 

Level B 

harassment 

Proposed 

takes by 

Level A 

harassment 

Total 

proposed take 

Regional 

population 

size 

Percent of 

population 

Humpback whale ......... 8 0 8 0 8 a 2,566 0.31 

Minke whale ................. 1 0 b 2 0 b 2 115 1.74 

Bryde’s whale ............... 27 1 27 1 28 a 649 4.31 

Fin whale ...................... 2 0 2 0 2 a 145 1.38 

Sei whale ..................... 3 0 3 0 3 c 29,600 0.01 

Blue whale ................... 5 0 5 0 5 773 0.65 

Sperm whale ................ 12 0 12 0 12 2,810 0.43 

Cuvier’s beaked whale 69 0 69 0 69 c 20,000 0.35 

Longman’s beaked 

whale ........................ 3 0 3 0 3 c 1,007 0.30 

Mesoplodon spp ........... 23 0 23 0 23 c 25,300 0.09 

Risso’s dolphin ............. 327 1 328 0 328 a 24,084 1.36 

Rough-toothed dolphin 596 1 597 0 597 a 37,511 1.59 

Common bottlenose 

dolphin ...................... 2,268 6 2274 0 2274 a 61,536 3.70 

Pantropical spotted dolphin ........................... 7,973 15 7988 0 7988 a 146,296 5.46 

Spinner dolphin 

(whitebelly) ............... 121 0 121 0 121 a 186,906 0.06 

Spinner dolphin (eastern) ........................... 8,173 16 8,189 0 8189 a 186,906 4.38 

Striped dolphin ............. 2,209 3 2212 0 2212 a 128,867 1.72 

Short-beaked common 

dolphin ...................... 2,812 6 2818 0 2818 a 283,196 1.00 

Fraser’s dolphin ........... 856 2 858 0 858 c 289,300 0.30 

Short-finned pilot whale 244 0 244 0 244 a 3,348 7.29 

Killer whale ................... 25 0 25 0 25 a 852 2.93 

False killer whale ......... 118 0 118 0 118 c 39,600 0.30 

Pygmy killer whale ....... 116 0 116 0 116 c 38,900 0.30 

Melon-headed whale .... 135 0 135 0 135 c 45,400 0.30 

Kogia spp ..................... 33 1 33 1 34 c d 11,200 0.30 

Guadalupe fur seal ...... 415 1 416 0 416 c 34,187 1.22 

California sea lion ........ 349 16 365 0 365 c 105,000 0.35 

aEstimated population in Pacific waters of Mexico (Gerrodette and Palacios (1996)). 

bProposed take increased to maximum group size. 

cPopulation in ETP or wider Pacific (NMFS 2015b). 

dPopulation of Kogia species guild. 

Proposed Mitigation 

In order to issue an IHA under section 

101(a)(5)(D) of the MMPA, NMFS must 

set forth the permissible methods of 

taking pursuant to the activity, and 

other means of effecting the least 

practicable impact on the species or 

stock and its habitat, paying particular 

attention to rookeries, mating grounds, 

and areas of similar significance, and on 

the availability of the species or stock 

for taking for certain subsistence uses 

(latter not applicable for this action). 

NMFS regulations require applicants for 

incidental take authorizations to include 

information about the availability and 

feasibility (economic and technological) 

of equipment, methods, and manner of 

conducting the activity or other means 

of effecting the least practicable adverse 

impact upon the affected species or 

stocks and their habitat (50 CFR 

216.104(a)(11)). 

In evaluating how mitigation may or 

may not be appropriate to ensure the 

least practicable adverse impact on 

species or stocks and their habitat, as 

well as subsistence uses where 

applicable, we carefully consider two 

primary factors: 

(1) The manner in which, and the 

degree to which, the successful 

implementation of the measure(s) is 

expected to reduce impacts to marine 

mammals, marine mammal species or 

stocks, and their habitat. This considers 

the nature of the potential adverse 

impact being mitigated (likelihood, 

scope, range). It further considers the 

likelihood that the measure will be 

effective if implemented (probability of 

accomplishing the mitigating result if 

implemented as planned) and the 

likelihood of effective implementation 

(probability implemented as planned); 

and 

(2) The practicability of the measures 

for applicant implementation, which 

may consider such things as cost, 

impact on operations, and, in the case 

of a military readiness activity, 

personnel safety, practicality of 

implementation, and impact on the 

effectiveness of the military readiness 

activity. 

In order to satisfy the MMPA’s least 

practicable adverse impact standard, 

NMFS has evaluated a suite of basic 

mitigation protocols for seismic surveys 

that are required regardless of the status 

of a stock. Additional or enhanced 

protections may be required for species 

whose stocks are in particularly poor 

health and/or are subject to some 

significant additional stressor that 

lessens that stock’s ability to weather 

the effects of the specified activities 

without worsening its status. We 

reviewed seismic mitigation protocols 

required or recommended elsewhere 


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(e.g., HESS, 1999; DOC, 2013; IBAMA, 

2018; Kyhn et al., 2011; JNCC, 2017; 

DEWHA, 2008; BOEM, 2016; DFO, 

2008; GHFS, 2015; MMOA, 2016; 

Nowacek et al., 2013; Nowacek and 

Southall, 2016), recommendations 

received during public comment 

periods for previous actions, and the 

available scientific literature. We also 

considered recommendations given in a 

number of review articles (e.g., Weir and 

Dolman, 2007; Compton et al., 2008; 

Parsons et al., 2009; Wright and 

Cosentino, 2015; Stone, 2015b). This 

exhaustive review and consideration of 

public comments regarding previous, 

similar activities has led to development 

of the protocols included here. 

Vessel-Based Visual Mitigation 

Monitoring 

Visual monitoring requires the use of 

trained observers (herein referred to as 

visual protected species observers 

(PSOs)) to scan the ocean surface for the 

presence of marine mammals. The area 

to be scanned visually includes 

primarily the exclusion zone (EZ), 

within which observation of certain 

marine mammals requires shutdown of 

the acoustic source, but also a buffer 

zone and, to the extent possible 

depending on conditions, the 

surrounding waters. The buffer zone 

means an area beyond the EZ to be 

monitored for the presence of marine 

mammals that may enter the EZ. During 

pre-start clearance monitoring (i.e., 

before ramp-up begins), the buffer zone 

also acts as an extension of the EZ in 

that observations of marine mammals 

within the buffer zone would also 

prevent airgun operations from 

beginning (i.e., ramp-up). The buffer 

zone encompasses the area at and below 

the sea surface from the edge of the 0– 

500 m EZ, out to a radius of 1,000 m 

from the edges of the airgun array (500– 

1,000 m). This 1,000-m zone (EZ plus 

buffer) represents the pre-start clearance 

zone. Visual monitoring of the EZ and 

adjacent waters is intended to establish 

and, when visual conditions allow, 

maintain zones around the sound source 

that are clear of marine mammals, 

thereby reducing or eliminating the 

potential for injury and minimizing the 

potential for more severe behavioral 

reactions for animals occurring closer to 

the vessel. Visual monitoring of the 

buffer zone is intended to (1) provide 

additional protection to marine 

mammals that may be in the vicinity of 

the vessel during pre-start clearance, 

and (2) during airgun use, aid in 

establishing and maintaining the EZ by 

alerting the visual observer and crew of 

marine mammals that are outside of, but 

may approach and enter, the EZ. 

L–DEO must use dedicated, trained, 

NMFS-approved PSOs. The PSOs must 

have no tasks other than to conduct 

observational effort, record 

observational data, and communicate 

with and instruct relevant vessel crew 

with regard to the presence of marine 

mammals and mitigation requirements. 

PSO resumes shall be provided to 

NMFS for approval. 

At least one of the visual and two of 

the acoustic PSOs (discussed below) 

aboard the vessel must have a minimum 

of 90 days at-sea experience working in 

those roles, respectively, with no more 

than 18 months elapsed since the 

conclusion of the at-sea experience. One 

visual PSO with such experience shall 

be designated as the lead for the entire 

protected species observation team. The 

lead PSO shall serve as primary point of 

contact for the vessel operator and 

ensure all PSO requirements per the 

IHA are met. To the maximum extent 

practicable, the experienced PSOs 

should be scheduled to be on duty with 

those PSOs with appropriate training 

but who have not yet gained relevant 

experience. 

During survey operations (e.g., any 

day on which use of the acoustic source 

is planned to occur, and whenever the 

acoustic source is in the water, whether 

activated or not), a minimum of two 

visual PSOs must be on duty and 

conducting visual observations at all 

times during daylight hours (i.e., from 

30 minutes prior to sunrise through 30 

minutes following sunset). Visual 

monitoring of the pre-start clearance 

zone must begin no less than 30 minutes 

prior to ramp-up, and monitoring must 

continue until one hour after use of the 

acoustic source ceases or until 30 

minutes past sunset. Visual PSOs shall 

coordinate to ensure 360° visual 

coverage around the vessel from the 

most appropriate observation posts, and 

shall conduct visual observations using 

binoculars and the naked eye while free 

from distractions and in a consistent, 

systematic, and diligent manner. 

PSOs shall establish and monitor the 

exclusion and buffer zones. These zones 

shall be based upon the radial distance 

from the edges of the acoustic source 

(rather than being based on the center of 

the array or around the vessel itself). 

During use of the acoustic source (i.e., 

anytime airguns are active, including 

ramp-up), detections of marine 

mammals within the buffer zone (but 

outside the EZ) shall be communicated 

to the operator to prepare for the 

potential shutdown of the acoustic 

source. Visual PSOs will immediately 

communicate all observations to the on 

duty acoustic PSO(s), including any 

determination by the PSO regarding 

species identification, distance, and 

bearing and the degree of confidence in 

the determination. Any observations of 

marine mammals by crew members 

shall be relayed to the PSO team. During 

good conditions (e.g., daylight hours; 

Beaufort sea state (BSS) 3 or less), visual 

PSOs shall conduct observations when 

the acoustic source is not operating for 

comparison of sighting rates and 

behavior with and without use of the 

acoustic source and between acquisition 

periods, to the maximum extent 

practicable. 

Visual PSOs may be on watch for a 

maximum of 4 consecutive hours 

followed by a break of at least one hour 

between watches and may conduct a 

maximum of 12 hours of observation per 

24-hour period. Combined observational 

duties (visual and acoustic but not at 

same time) may not exceed 12 hours per 

24-hour period for any individual PSO. 

Passive Acoustic Monitoring 

Acoustic monitoring means the use of 

trained personnel (sometimes referred to 

as passive acoustic monitoring (PAM) 

operators, herein referred to as acoustic 

PSOs) to operate PAM equipment to 

acoustically detect the presence of 

marine mammals. Acoustic monitoring 

involves acoustically detecting marine 

mammals regardless of distance from 

the source, as localization of animals 

may not always be possible. Acoustic 

monitoring is intended to further 

support visual monitoring (during 

daylight hours) in maintaining an EZ 

around the sound source that is clear of 

marine mammals. In cases where visual 

monitoring is not effective (e.g., due to 

weather, nighttime), acoustic 

monitoring may be used to allow certain 

activities to occur, as further detailed 

below. 

PAM would take place in addition to 

the visual monitoring program. Visual 

monitoring typically is not effective 

during periods of poor visibility or at 

night, and even with good visibility, is 

unable to detect marine mammals when 

they are below the surface or beyond 

visual range. Acoustic monitoring can 

be used in addition to visual 

observations to improve detection, 

identification, and localization of 

cetaceans. The acoustic monitoring 

would serve to alert visual PSOs (if on 

duty) when vocalizing cetaceans are 

detected. It is only useful when marine 

mammals vocalize, but it can be 

effective either by day or by night, and 

does not depend on good visibility. It 

would be monitored in real time so that 

the visual observers can be advised 

when cetaceans are detected. 

The R/V Langseth will use a towed 

PAM system, which must be monitored 


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by at a minimum one on duty acoustic 

PSO beginning at least 30 minutes prior 

to ramp-up and at all times during use 

of the acoustic source. Acoustic PSOs 

may be on watch for a maximum of 4 

consecutive hours followed by a break 

of at least one hour between watches 

and may conduct a maximum of 12 

hours of observation per 24-hour period. 

Combined observational duties (acoustic 

and visual but not at same time) may 

not exceed 12 hours per 24-hour period 

for any individual PSO. 

Survey activity may continue for 30 

minutes when the PAM system 

malfunctions or is damaged, while the 

PAM operator diagnoses the issue. If the 

diagnosis indicates that the PAM system 

must be repaired to solve the problem, 

operations may continue for an 

additional 5 hours without acoustic 

monitoring during daylight hours only 

under the following conditions: 

• Sea state is less than or equal to 

BSS 4; 

• No marine mammals (excluding 

delphinids) detected solely by PAM in 

the applicable EZ in the previous 2 

hours; 

• NMFS is notified via email as soon 

as practicable with the time and 

location in which operations began 

occurring without an active PAM 

system; and 

• Operations with an active acoustic 

source, but without an operating PAM 

system, do not exceed a cumulative total 

of 5 hours in any 24-hour period. 

Establishment of Exclusion and PreStart Clearance Zones 

An EZ is a defined area within which 

occurrence of a marine mammal triggers 

mitigation action intended to reduce the 

potential for certain outcomes, e.g., 

auditory injury, disruption of critical 

behaviors. The PSOs would establish a 

minimum EZ with a 500-m radius. The 

500-m EZ would be based on radial 

distance from the edge of the airgun 

array (rather than being based on the 

center of the array or around the vessel 

itself). With certain exceptions 

(described below), if a marine mammal 

appears within or enters this zone, the 

acoustic source would be shut down. 

The pre-start clearance zone is 

defined as the area that must be clear of 

marine mammals prior to beginning 

ramp-up of the acoustic source, and 

includes the EZ plus the buffer zone. 

Detections of marine mammals within 

the pre-start clearance zone would 

prevent airgun operations from 

beginning (i.e., ramp-up). 

The 500-m EZ is intended to be 

precautionary in the sense that it would 

be expected to contain sound exceeding 

the injury criteria for all cetacean 

hearing groups, (based on the dual 

criteria of SELcum and peak SPL), while 

also providing a consistent, reasonably 

observable zone within which PSOs 

would typically be able to conduct 

effective observational effort. 

Additionally, a 500-m EZ is expected to 

minimize the likelihood that marine 

mammals will be exposed to levels 

likely to result in more severe 

behavioral responses. Although 

significantly greater distances may be 

observed from an elevated platform 

under good conditions, we believe that 

500 m is likely regularly attainable for 

PSOs using the naked eye during typical 

conditions. The pre-start clearance zone 

simply represents the addition of a 

buffer to the EZ, doubling the EZ size 

during pre-clearance. 

An extended EZ of 1,500 m must be 

enforced for all beaked whales and 

Kogia species. No buffer of this 

extended EZ is required. 

Pre-Start Clearance and Ramp-Up 

Ramp-up (sometimes referred to as 

‘‘soft start’’) means the gradual and 

systematic increase of emitted sound 

levels from an airgun array. Ramp-up 

begins by first activating a single airgun 

of the smallest volume, followed by 

doubling the number of active elements 

in stages until the full complement of an 

array’s airguns are active. Each stage 

should be approximately the same 

duration, and the total duration should 

not be less than approximately 20 

minutes. The intent of pre-start 

clearance observation (30 minutes) is to 

ensure no protected species are 

observed within the pre-clearance zone 

(or extended EZ, for beaked whales and 

Kogia spp.) prior to the beginning of 

ramp-up. During pre-start clearance 

period is the only time observations of 

marine mammals in the buffer zone 

would prevent operations (i.e., the 

beginning of ramp-up). The intent of 

ramp-up is to warn marine mammals of 

pending seismic survey operations and 

to allow sufficient time for those 

animals to leave the immediate vicinity. 

A ramp-up procedure, involving a stepwise increase in the number of airguns 

firing and total array volume until all 

operational airguns are activated and 

the full volume is achieved, is required 

at all times as part of the activation of 

the acoustic source. All operators must 

adhere to the following pre-start 

clearance and ramp-up requirements: 

• The operator must notify a 

designated PSO of the planned start of 

ramp-up as agreed upon with the lead 

PSO; the notification time should not be 

less than 60 minutes prior to the 

planned ramp-up in order to allow the 

PSOs time to monitor the pre-start 

clearance zone (and extended EZ) for 30 

minutes prior to the initiation of rampup (pre-start clearance); 

• Ramp-ups shall be scheduled so as 

to minimize the time spent with the 

source activated prior to reaching the 

designated run-in; 

• One of the PSOs conducting prestart clearance observations must be 

notified again immediately prior to 

initiating ramp-up procedures and the 

operator must receive confirmation from 

the PSO to proceed; 

• Ramp-up may not be initiated if any 

marine mammal is within the applicable 

exclusion or buffer zone. If a marine 

mammal is observed within the pre-start 

clearance zone (or extended EZ, for 

beaked whales and Kogia species) 

during the 30 minute pre-start clearance 

period, ramp-up may not begin until the 

animal(s) has been observed exiting the 

zones or until an additional time period 

has elapsed with no further sightings 

(15 minutes for small odontocetes and 

pinnipeds, and 30 minutes for all 

mysticetes and all other odontocetes, 

including sperm whales, beaked whales, 

and large delphinids, such as killer 

whales); 

• Ramp-up shall begin by activating a 

single airgun of the smallest volume in 

the array and shall continue in stages by 

doubling the number of active elements 

at the commencement of each stage, 

with each stage of approximately the 

same duration. Duration shall not be 

less than 20 minutes. The operator must 

provide information to the PSO 

documenting that appropriate 

procedures were followed; 

• PSOs must monitor the pre-start 

clearance zone (and extended EZ) 

during ramp-up, and ramp-up must 

cease and the source must be shut down 

upon detection of a marine mammal 

within the applicable zone. Once rampup has begun, detections of marine 

mammals within the buffer zone do not 

require shutdown, but such observation 

shall be communicated to the operator 

to prepare for the potential shutdown; 

• Ramp-up may occur at times of 

poor visibility, including nighttime, if 

appropriate acoustic monitoring has 

occurred with no detections in the 30 

minutes prior to beginning ramp-up. 

Acoustic source activation may only 

occur at times of poor visibility where 

operational planning cannot reasonably 

avoid such circumstances; 

• If the acoustic source is shut down 

for brief periods (i.e., less than 30 

minutes) for reasons other than that 

described for shutdown (e.g., 

mechanical difficulty), it may be 

activated again without ramp-up if PSOs 

have maintained constant visual and/or 

acoustic observation and no visual or 


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acoustic detections of marine mammals 

have occurred within the applicable EZ. 

For any longer shutdown, pre-start 

clearance observation and ramp-up are 

required. For any shutdown at night or 

in periods of poor visibility (e.g., BSS 4 

or greater), ramp-up is required, but if 

the shutdown period was brief and 

constant observation was maintained, 

pre-start clearance watch of 30 minutes 

is not required; and 

• Testing of the acoustic source 

involving all elements requires rampup. Testing limited to individual source 

elements or strings does not require 

ramp-up but does require pre-start 

clearance of 30 min. 

Shutdown 

The shutdown of an airgun array 

requires the immediate de-activation of 

all individual airgun elements of the 

array. Any PSO on duty will have the 

authority to delay the start of survey 

operations or to call for shutdown of the 

acoustic source if a marine mammal is 

detected within the applicable EZ. The 

operator must also establish and 

maintain clear lines of communication 

directly between PSOs on duty and 

crew controlling the acoustic source to 

ensure that shutdown commands are 

conveyed swiftly while allowing PSOs 

to maintain watch. When both visual 

and acoustic PSOs are on duty, all 

detections will be immediately 

communicated to the remainder of the 

on-duty PSO team for potential 

verification of visual observations by the 

acoustic PSO or of acoustic detections 

by visual PSOs. When the airgun array 

is active (i.e., anytime one or more 

airguns is active, including during 

ramp-up) and (1) a marine mammal 

appears within or enters the applicable 

EZ and/or (2) a marine mammal (other 

than delphinids, see below) is detected 

acoustically and localized within the 

applicable EZ, the acoustic source will 

be shut down. When shutdown is called 

for by a PSO, the acoustic source will 

be immediately deactivated and any 

dispute resolved only following 

deactivation. Additionally, shutdown 

will occur whenever PAM alone 

(without visual sighting), confirms 

presence of marine mammal(s) in the 

EZ. If the acoustic PSO cannot confirm 

presence within the EZ, visual PSOs 

will be notified but shutdown is not 

required. 

Following a shutdown, airgun activity 

would not resume until the marine 

mammal has cleared the EZ. The animal 

would be considered to have cleared the 

EZ if it is visually observed to have 

departed the EZ (i.e., animal is not 

required to fully exit the buffer zone 

where applicable), or it has not been 

seen within the EZ for 15 minutes for 

small odontocetes and pinnipeds, or 30 

minutes for all mysticetes and all other 

odontocetes, including sperm whales, 

beaked whales, Kogia species, and large 

delphinids, such as killer whales. 

The shutdown requirement is waived 

for small dolphins if an individual is 

detected within the EZ. As defined here, 

the small dolphin group is intended to 

encompass those members of the Family 

Delphinidae most likely to voluntarily 

approach the source vessel for purposes 

of interacting with the vessel and/or 

airgun array (e.g., bow riding). This 

exception to the shutdown requirement 

applies solely to specific genera of small 

dolphins (Delphinus, Lagenodelphis, 

Lissodelphis, Stenella, Steno, and 

Tursiops). 

We include this small dolphin 

exception because shutdown 

requirements for small dolphins under 

all circumstances represent 

practicability concerns without likely 

commensurate benefits for the animals 

in question. Small dolphins are 

generally the most commonly observed 

marine mammals in the specific 

geographic region and would typically 

be the only marine mammals likely to 

intentionally approach the vessel. As 

described above, auditory injury is 

extremely unlikely to occur for midfrequency cetaceans (e.g., delphinids), 

as this group is relatively insensitive to 

sound produced at the predominant 

frequencies in an airgun pulse while 

also having a relatively high threshold 

for the onset of auditory injury (i.e., 

permanent threshold shift). 

A large body of anecdotal evidence 

indicates that small dolphins commonly 

approach vessels and/or towed arrays 

during active sound production for 

purposes of bow riding, with no 

apparent effect observed in those 

delphinoids (e.g., Barkaszi et al., 2012, 

Barkaszi and Kelly, 2018). The potential 

for increased shutdowns resulting from 

such a measure would require the 

Langseth to revisit the missed track line 

to reacquire data, resulting in an overall 

increase in the total sound energy input 

to the marine environment and an 

increase in the total duration over 

which the survey is active in a given 

area. Although other mid-frequency 

hearing specialists (e.g., large 

delphinids) are no more likely to incur 

auditory injury than are small dolphins, 

they are much less likely to approach 

vessels. Therefore, retaining a shutdown 

requirement for large delphinids would 

not have similar impacts in terms of 

either practicability for the applicant or 

corollary increase in sound energy 

output and time on the water. We do 

anticipate some benefit for a shutdown 

requirement for large delphinids in that 

it simplifies somewhat the total range of 

decision-making for PSOs and may 

preclude any potential for physiological 

effects other than to the auditory system 

as well as some more severe behavioral 

reactions for any such animals in close 

proximity to the Langseth. 

Visual PSOs shall use best 

professional judgment in making the 

decision to call for a shutdown if there 

is uncertainty regarding identification 

(i.e., whether the observed marine 

mammal(s) belongs to one of the 

delphinid genera for which shutdown is 

waived or one of the species with a 

larger EZ). 

L–DEO must implement shutdown if 

a marine mammal species for which 

take was not authorized, or a species for 

which authorization was granted but the 

takes have been met, approaches the 

Level A or Level B harassment zones. L– 

DEO must also implement shutdown if 

any large whale (defined as a sperm 

whale or any mysticete species) with a 

calf (defined as an animal less than twothirds the body size of an adult observed 

to be in close association with an adult) 

and/or an aggregation of six or more 

large whales are observed at any 

distance. 

Vessel Strike Avoidance 

Vessel operators and crews must 

maintain a vigilant watch for all 

protected species and slow down, stop 

their vessel, or alter course, as 

appropriate and regardless of vessel 

size, to avoid striking any marine 

mammal. A visual observer aboard the 

vessel must monitor a vessel strike 

avoidance zone around the vessel 

(distances stated below). Visual 

observers monitoring the vessel strike 

avoidance zone may be third-party 

observers (i.e., PSOs) or crew members, 

but crew members responsible for these 

duties must be provided sufficient 

training to (1) distinguish marine 

mammals from other phenomena and 

(2) broadly to identify a marine mammal 

as a whale or other marine mammal. 

Vessel speeds must be reduced to 10 

knots or less when mother/calf pairs, 

pods, or large assemblages of cetaceans 

are observed near a vessel. 

All vessels must maintain a minimum 

separation distance of 100 m from 

sperm whales and all other baleen 

whales. 

All vessels must, to the maximum 

extent practicable, attempt to maintain a 

minimum separation distance of 50 m 

from all other marine mammals, with an 

understanding that at times this may not 

be possible (e.g., for animals that 

approach the vessel). 


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When marine mammals are sighted 

while a vessel is underway, the vessel 

shall take action as necessary to avoid 

violating the relevant separation 

distance (e.g., attempt to remain parallel 

to the animal’s course, avoid excessive 

speed or abrupt changes in direction 

until the animal has left the area). If 

marine mammals are sighted within the 

relevant separation distance, the vessel 

must reduce speed and shift the engine 

to neutral, not engaging the engines 

until animals are clear of the area. This 

does not apply to any vessel towing gear 

or any vessel that is navigationally 

constrained. 

These requirements do not apply in 

any case where compliance would 

create an imminent and serious threat to 

a person or vessel or to the extent that 

a vessel is restricted in its ability to 

maneuver and, because of the 

restriction, cannot comply. 

We have carefully evaluated the suite 

of mitigation measures described here 

and considered a range of other 

measures in the context of ensuring that 

we prescribe the means of effecting the 

least practicable adverse impact on the 

affected marine mammal species and 

stocks and their habitat. Based on our 

evaluation of the proposed measures, as 

well as other measures considered by 

NMFS described above, NMFS has 

preliminarily determined that the 

mitigation measures provide the means 

of effecting the least practicable impact 

on the affected species or stocks and 

their habitat, paying particular attention 

to rookeries, mating grounds, and areas 

of similar significance. 

Mitigation Measures in Mexican Waters 

As stated previously, NMFS cannot 

authorize the incidental take of marine 

mammals in the territorial seas of 

foreign nations, as the MMPA does not 

apply in those waters. L–DEO is 

required to adhere to the mitigation 

measures described above while 

operating within the Mexican EEZ and 

International Waters. The requirements 

do not apply within Mexican territorial 

waters. Mexico may prescribe mitigation 

measures that would apply to survey 

operations within the Mexican EEZ and 

territorial waters but NMFS is currently 

unaware of any specific potential 

requirements. While operating within 

the Mexican EEZ but outside Mexican 

territorial waters, if mitigation 

requirements prescribed by NMFS differ 

from the requirements established under 

Mexican law, L–DEO would adhere to 

the most protective measure. For 

operations in Mexican territorial waters, 

L–DEO would implement measures 

required under Mexican law (if any). If 

information regarding measures 

required under Mexican law becomes 

available prior to NMFS’ final decision 

on this request for IHA, NMFS will 

consider it as appropriate in making its 

negligible impact determination. 

Proposed Monitoring and Reporting 

In order to issue an IHA for an 

activity, section 101(a)(5)(D) of the 

MMPA states that NMFS must set forth 

requirements pertaining to the 

monitoring and reporting of such taking. 

The MMPA implementing regulations at 

50 CFR 216.104(a)(13) indicate that 

requests for authorizations must include 

the suggested means of accomplishing 

the necessary monitoring and reporting 

that will result in increased knowledge 

of the species and of the level of taking 

or impacts on populations of marine 

mammals that are expected to be 

present in the proposed action area. 

Effective reporting is critical both to 

compliance as well as ensuring that the 

most value is obtained from the required 

monitoring. 

Monitoring and reporting 

requirements prescribed by NMFS 

should contribute to improved 

understanding of one or more of the 

following: 

• Occurrence of marine mammal 

species or stocks in the area in which 

take is anticipated (e.g., presence, 

abundance, distribution, density); 

• Nature, scope, or context of likely 

marine mammal exposure to potential 

stressors/impacts (individual or 

cumulative, acute or chronic), through 

better understanding of: (1) Action or 

environment (e.g., source 

characterization, propagation, ambient 

noise); (2) affected species (e.g., life 

history, dive patterns); (3) co-occurrence 

of marine mammal species with the 

action; or (4) biological or behavioral 

context of exposure (e.g., age, calving or 

feeding areas); 

• Individual marine mammal 

responses (behavioral or physiological) 

to acoustic stressors (acute, chronic, or 

cumulative), other stressors, or 

cumulative impacts from multiple 

stressors; 

• How anticipated responses to 

stressors impact either: (1) Long-term 

fitness and survival of individual 

marine mammals; or (2) populations, 

species, or stocks; 

• Effects on marine mammal habitat 

(e.g., marine mammal prey species, 

acoustic habitat, or other important 

physical components of marine 

mammal habitat); and 

• Mitigation and monitoring 

effectiveness. 

Vessel-Based Visual Monitoring 

As described above, PSO observations 

would take place during daytime airgun 

operations. During seismic survey 

operations, at least five visual PSOs 

would be based aboard the Langseth. 

Two visual PSOs would be on duty at 

all time during daytime hours. 

Monitoring shall be conducted in 

accordance with the following 

requirements: 

• The operator shall provide PSOs 

with bigeye binoculars (e.g., 25 x 150; 

2.7 view angle; individual ocular focus; 

height control) of appropriate quality 

(i.e., Fujinon or equivalent) solely for 

PSO use. These shall be pedestalmounted on the deck at the most 

appropriate vantage point that provides 

for optimal sea surface observation, PSO 

safety, and safe operation of the vessel; 

and 

• The operator will work with the 

selected third-party observer provider to 

ensure PSOs have all equipment 

(including backup equipment) needed 

to adequately perform necessary tasks, 

including accurate determination of 

distance and bearing to observed marine 

mammals. 

PSOs must have the following 

requirements and qualifications: 

• PSOs shall be independent, 

dedicated, trained visual and acoustic 

PSOs and must be employed by a thirdparty observer provider; 

• PSOs shall have no tasks other than 

to conduct observational effort (visual or 

acoustic), collect data, and 

communicate with and instruct relevant 

vessel crew with regard to the presence 

of protected species and mitigation 

requirements (including brief alerts 

regarding maritime hazards); 

• PSOs shall have successfully 

completed an approved PSO training 

course appropriate for their designated 

task (visual or acoustic). Acoustic PSOs 

are required to complete specialized 

training for operating PAM systems and 

are encouraged to have familiarity with 

the vessel with which they will be 

working; 

• PSOs can act as acoustic or visual 

observers (but not at the same time) as 

long as they demonstrate that their 

training and experience are sufficient to 

perform the task at hand; 

• NMFS must review and approve 

PSO resumes accompanied by a relevant 

training course information packet that 

includes the name and qualifications 

(i.e., experience, training completed, or 

educational background) of the 

instructor(s), the course outline or 

syllabus, and course reference material 

as well as a document stating successful 

completion of the course; 


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• PSOs must successfully complete 

relevant training, including completion 

of all required coursework and passing 

(80 percent or greater) a written and/or 

oral examination developed for the 

training program; 

• PSOs must have successfully 

attained a bachelor’s degree from an 

accredited college or university with a 

major in one of the natural sciences, a 

minimum of 30 semester hours or 

equivalent in the biological sciences, 

and at least one undergraduate course in 

math or statistics; and 

• The educational requirements may 

be waived if the PSO has acquired the 

relevant skills through alternate 

experience. Requests for such a waiver 

shall be submitted to NMFS and must 

include written justification. Requests 

shall be granted or denied (with 

justification) by NMFS within 1 week of 

receipt of submitted information. 

Alternate experience that may be 

considered includes, but is not limited 

to (1) secondary education and/or 

experience comparable to PSO duties; 

(2) previous work experience 

conducting academic, commercial, or 

government-sponsored protected 

species surveys; or (3) previous work 

experience as a PSO; the PSO should 

demonstrate good standing and 

consistently good performance of PSO 

duties. 

For data collection purposes, PSOs 

shall use standardized data collection 

forms, whether hard copy or electronic. 

PSOs shall record detailed information 

about any implementation of mitigation 

requirements, including the distance of 

animals to the acoustic source and 

description of specific actions that 

ensued, the behavior of the animal(s), 

any observed changes in behavior before 

and after implementation of mitigation, 

and if shutdown was implemented, the 

length of time before any subsequent 

ramp-up of the acoustic source. If 

required mitigation was not 

implemented, PSOs should record a 

description of the circumstances. At a 

minimum, the following information 

must be recorded: 

• Vessel names (source vessel and 

other vessels associated with survey) 

and call signs; 

• PSO names and affiliations; 

• Dates of departures and returns to 

port with port name; 

• Date and participants of PSO 

briefings; 

• Dates and times (Greenwich Mean 

Time) of survey effort and times 

corresponding with PSO effort; 

• Vessel location (latitude/longitude) 

when survey effort began and ended and 

vessel location at beginning and end of 

visual PSO duty shifts; 

• Vessel heading and speed at 

beginning and end of visual PSO duty 

shifts and upon any line change; 

• Environmental conditions while on 

visual survey (at beginning and end of 

PSO shift and whenever conditions 

changed significantly), including BSS 

and any other relevant weather 

conditions including cloud cover, fog, 

sun glare, and overall visibility to the 

horizon; 

• Factors that may have contributed 

to impaired observations during each 

PSO shift change or as needed as 

environmental conditions changed (e.g., 

vessel traffic, equipment malfunctions); 

and 

• Survey activity information, such as 

acoustic source power output while in 

operation, number and volume of 

airguns operating in the array, tow 

depth of the array, and any other notes 

of significance (i.e., pre-start clearance, 

ramp-up, shutdown, testing, shooting, 

ramp-up completion, end of operations, 

streamers, etc.). 

The following information should be 

recorded upon visual observation of any 

protected species: 

• Watch status (sighting made by PSO 

on/off effort, opportunistic, crew, 

alternate vessel/platform); 

• PSO who sighted the animal; 

• Time of sighting; 

• Vessel location at time of sighting; 

• Water depth; 

• Direction of vessel’s travel (compass 

direction); 

• Direction of animal’s travel relative 

to the vessel; 

• Pace of the animal; 

• Estimated distance to the animal 

and its heading relative to vessel at 

initial sighting; 

• Identification of the animal (e.g., 

genus/species, lowest possible 

taxonomic level, or unidentified) and 

the composition of the group if there is 

a mix of species; 

• Estimated number of animals (high/ 

low/best); 

• Estimated number of animals by 

cohort (adults, yearlings, juveniles, 

calves, group composition, etc.); 

• Description (as many distinguishing 

features as possible of each individual 

seen, including length, shape, color, 

pattern, scars or markings, shape and 

size of dorsal fin, shape of head, and 

blow characteristics); 

• Detailed behavior observations (e.g., 

number of blows/breaths, number of 

surfaces, breaching, spyhopping, diving, 

feeding, traveling; as explicit and 

detailed as possible; note any observed 

changes in behavior); 

• Animal’s closest point of approach 

(CPA) and/or closest distance from any 

element of the acoustic source; 

• Platform activity at time of sighting 

(e.g., deploying, recovering, testing, 

shooting, data acquisition, other); and 

• Description of any actions 

implemented in response to the sighting 

(e.g., delays, shutdown, ramp-up) and 

time and location of the action. 

If a marine mammal is detected while 

using the PAM system, the following 

information should be recorded: 

• An acoustic encounter 

identification number, and whether the 

detection was linked with a visual 

sighting; 

• Date and time when first and last 

heard; 

• Types and nature of sounds heard 

(e.g., clicks, whistles, creaks, burst 

pulses, continuous, sporadic, strength of 

signal); and 

• Any additional information 

recorded such as water depth of the 

hydrophone array, bearing of the animal 

to the vessel (if determinable), species 

or taxonomic group (if determinable), 

spectrogram screenshot, and any other 

notable information. 

Reporting 

A report would be submitted to NMFS 

within 90 days after the end of the 

cruise. The report would summarize the 

dates and locations of seismic survey 

operations, and all marine mammal 

sightings (dates, times, locations, 

activities, associated seismic survey 

activities), and provide full 

documentation of methods, results, and 

interpretation pertaining to all 

monitoring. 

The draft report shall also include 

geo-referenced time-stamped vessel 

tracklines for all time periods during 

which airguns were operating. 

Tracklines should include points 

recording any change in airgun status 

(e.g., when the airguns began operating, 

when they were turned off, or when 

they changed from full array to single 

gun or vice versa). GIS files shall be 

provided in ESRI shapefile format and 

include the UTC date and time, latitude 

in decimal degrees, and longitude in 

decimal degrees. All coordinates shall 

be referenced to the WGS84 geographic 

coordinate system. In addition to the 

report, all raw observational data shall 

be made available to NMFS. The report 

must summarize the data collected as 

described above and in the IHA. A final 

report must be submitted within 30 days 

following resolution of any comments 

on the draft report. 

Reporting Injured or Dead Marine 

Mammals 

Discovery of injured or dead marine 

mammals—In the event that personnel 

involved in survey activities covered by 


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the authorization discover an injured or 

dead marine mammal, the L–DEO shall 

report the incident to the Office of 

Protected Resources (OPR), NMFS and 

to the NMFS West Coast Regional 

Stranding Coordinator as soon as 

feasible. The report must include the 

following information: 

• Time, date, and location (latitude/ 

longitude) of the first discovery (and 

updated location information if known 

and applicable); 

• Species identification (if known) or 

description of the animal(s) involved; 

• Condition of the animal(s) 

(including carcass condition if the 

animal is dead); 

• Observed behaviors of the 

animal(s), if alive; 

• If available, photographs or video 

footage of the animal(s); and 

• General circumstances under which 

the animal was discovered. 

Vessel strike—In the event of a ship 

strike of a marine mammal by any vessel 

involved in the activities covered by the 

authorization, L–DEO shall report the 

incident to OPR, NMFS and to the 

NMFS West Coast Regional Stranding 

Coordinator as soon as feasible. The 

report must include the following 

information: 

• Time, date, and location (latitude/ 

longitude) of the incident; 

• Vessel’s speed during and leading 

up to the incident; 

• Vessel’s course/heading and what 

operations were being conducted (if 

applicable); 

• Status of all sound sources in use; 

• Description of avoidance measures/ 

requirements that were in place at the 

time of the strike and what additional 

measure were taken, if any, to avoid 

strike; 

• Environmental conditions (e.g., 

wind speed and direction, Beaufort sea 

state, cloud cover, visibility) 

immediately preceding the strike; 

• Species identification (if known) or 

description of the animal(s) involved; 

• Estimated size and length of the 

animal that was struck; 

• Description of the behavior of the 

animal immediately preceding and 

following the strike; 

• If available, description of the 

presence and behavior of any other 

marine mammals present immediately 

preceding the strike; 

• Estimated fate of the animal (e.g., 

dead, injured but alive, injured and 

moving, blood or tissue observed in the 

water, status unknown, disappeared); 

and 

• To the extent practicable, 

photographs or video footage of the 

animal(s). 

Actions To Minimize Additional Harm 

to Live-Stranded (or Milling) Marine 

Mammals 

In the event of a live stranding (or 

near-shore atypical milling) event 

within 50 km of the survey operations, 

where the NMFS stranding network is 

engaged in herding or other 

interventions to return animals to the 

water, the Director of OPR, NMFS (or 

designee) will advise L–DEO of the need 

to implement shutdown for all active 

acoustic sources operating within 50 km 

of the stranding. Procedures related to 

shutdowns for live stranding or milling 

marine mammals include the following: 

• If at any time, the marine 

mammal(s) die or are euthanized, or if 

herding/intervention efforts are stopped, 

the Director of OPR, NMFS (or designee) 

will advise L–DEO that the shutdown 

around the animals’ location is no 

longer needed. 

• Otherwise, shutdown procedures 

will remain in effect until the Director 

of OPR, NMFS (or designee) determines 

and advises L–DEO that all live animals 

involved have left the area (either of 

their own volition or following an 

intervention). 

• If further observations of the marine 

mammals indicate the potential for restranding, additional coordination with 

L–DEO will be required to determine 

what measures are necessary to 

minimize that likelihood (e.g., 

extending the shutdown or moving 

operations farther away) and to 

implement those measures as 

appropriate. 

Additional Information Requests—If 

NMFS determines that the 

circumstances of any marine mammal 

stranding found in the vicinity of the 

activity suggest investigation of the 

association with survey activities is 

warranted, and an investigation into the 

stranding is being pursued, NMFS will 

submit a written request to L–DEO 

indicating that the following initial 

available information must be provided 

as soon as possible, but no later than 7 

business days after the request for 

information: 

• Status of all sound source use in the 

48 hours preceding the estimated time 

of stranding and within 50 km of the 

discovery/notification of the stranding 

by NMFS; and 

• If available, description of the 

behavior of any marine mammal(s) 

observed preceding (i.e., within 48 

hours and 50 km) and immediately after 

the discovery of the stranding. 

In the event that the investigation is 

still inconclusive, the investigation of 

the association of the survey activities is 

still warranted, and the investigation is 

still being pursued, NMFS may provide 

additional information requests, in 

writing, regarding the nature and 

location of survey operations prior to 

the time period above. 

Negligible Impact Analysis and 

Determination 

NMFS has defined negligible impact 

as an impact resulting from the 

specified activity that cannot be 

reasonably expected to, and is not 

reasonably likely to, adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival 

(50 CFR 216.103). A negligible impact 

finding is based on the lack of likely 

adverse effects on annual rates of 

recruitment or survival (i.e., populationlevel effects). An estimate of the number 

of takes alone is not enough information 

on which to base an impact 

determination. In addition to 

considering estimates of the number of 

marine mammals that might be ‘‘taken’’ 

through harassment, NMFS considers 

other factors, such as the likely nature 

of any responses (e.g., intensity, 

duration), the context of any responses 

(e.g., critical reproductive time or 

location, migration), as well as effects 

on habitat, and the likely effectiveness 

of the mitigation. We also assess the 

number, intensity, and context of 

estimated takes by evaluating this 

information relative to population 

status. Consistent with the 1989 

preamble for NMFS’s implementing 

regulations (54 FR 40338; September 29, 

1989), the impacts from other past and 

ongoing anthropogenic activities are 

incorporated into this analysis via their 

impacts on the environmental baseline 

(e.g., as reflected in the regulatory status 

of the species, population size and 

growth rate where known, ongoing 

sources of human-caused mortality, or 

ambient noise levels). 

To avoid repetition, our analysis 

applies to all species listed in Table 1, 

given that NMFS expects the anticipated 

effects of the planned geophysical 

survey to be similar in nature. Where 

there are meaningful differences 

between species or stocks, or groups of 

species, in anticipated individual 

responses to activities, impact of 

expected take on the population due to 

differences in population status, or 

impacts on habitat, NMFS has identified 

species-specific factors to inform the 

analysis. 

As described above, we propose to 

authorize only the takes estimated to 

occur outside of Mexican territorial 

waters (Table 7); however, for the 

purposes of our negligible impact 

analysis and determination, we consider 

the total number of takes that are 


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anticipated to occur as a result of the 

entire survey (including the portion of 

the survey that would occur within the 

Mexican territorial waters 

(approximately 6 percent of the survey) 

(Table 8). 

TABLE 8—TOTAL ESTIMATED TAKE INCLUDING MEXICAN TERRITORIAL WATERS

Species 

Level B 

harassment 

(excluding 

Mexican 

territorial 

waters) 

Level A 

harassment 

(excluding 

Mexican 

territorial 

waters) 

Level B 

harassment 

(Mexican 

territorial 

waters) 

Level A 

harassment 

(Mexican 

territorial 

waters) 

Total Level B 

harassment 

Total Level A 

harassment 

Humpback whale ..................................... 8 0 1 0 9 0 

Minke whale ............................................. 2 0 0 0 2 0 

Bryde’s whale ........................................... 27 1 2 0 29 1 

Fin whale .................................................. 2 0 0 0 2 0 

Sei whale ................................................. 3 0 0 0 3 0 

Blue whale ............................................... 5 0 0 0 5 0 

Sperm whale ............................................ 12 0 1 0 13 0 

Cuvier’s beaked whale ............................. 69 0 69 0 138 0 

Longman’s beaked whale ........................ 3 0 0 0 3 0 

Mesoplodon spp ....................................... 23 0 1 0 24 0 

Risso’s dolphin ......................................... 328 0 22 0 350 0 

Rough-toothed dolphin ............................. 597 0 38 0 635 0 

Common bottlenose dolphin .................... 2,274 0 196 0 2,470 0 

Pantropical spotted dolphin ..................... 7,988 0 519 0 8,507 0 

Spinner dolphin (whitebelly) ..................... 121 0 7 0 128 0 

Spinner dolphin (eastern) ........................ 8,189 0 557 0 8,746 0 

Striped dolphin ......................................... 2,212 0 122 0 2,334 0 

Short-beaked common dolphin ................ 2,818 0 209 0 3,027 0 

Fraser’s dolphin ....................................... 858 0 58 0 916 0 

Short-finned pilot whale ........................... 244 0 15 0 259 0 

Killer whale ............................................... 25 0 2 0 27 0 

False killer whale ..................................... 118 0 8 0 126 0 

Pygmy killer whale ................................... 116 0 8 0 124 0 

Melon-headed whale ................................ 135 0 9 0 144 0 

Kogia spp ................................................. 33 1 2 0 35 1 

Guadalupe fur seal .................................. 416 0 1 0 417 0 

California sea lion .................................... 365 0 693 0 1,058 0 

NMFS does not anticipate that serious 

injury or mortality would occur as a 

result of L–DEO’s planned survey, even 

in the absence of mitigation, and none 

are proposed for authorization. Nonauditory physical effects, stranding, and 

vessel strike are also not expected to 

occur. 

We are proposing to authorize a 

limited number of instances of Level A 

harassment of two species (Bryde’s 

whale and dwarf sperm whales, which 

are members of the low- and highfrequency cetacean hearing groups, 

respectively) in the form of PTS, and 

Level B harassment only of the 

remaining marine mammal species. We 

believe that any PTS incurred in marine 

mammals as a result of the planned 

activity would be in the form of only a 

small degree of PTS, not total deafness, 

because of the constant movement of 

both the R/V Langseth and of the marine 

mammals in the project areas, as well as 

the fact that the vessel is not expected 

to remain in any one area in which 

individual marine mammals would be 

expected to concentrate for an extended 

period of time. Additionally, L–DEO 

would shut down the airgun array if 

marine mammals approach within 500 

m (with the exception of specific genera 

of dolphins, see Proposed Mitigation), 

further reducing the expected duration 

and intensity of sound, and therefore 

the likelihood of marine mammals 

incurring PTS. Since the duration of 

exposure to loud sounds will be 

relatively short it would be unlikely to 

affect the fitness of any individuals. 

Also, as described above, we expect that 

marine mammals would likely move 

away from a sound source that 

represents an aversive stimulus, 

especially at levels that would be 

expected to result in PTS, given 

sufficient notice of the R/V Langseth’s 

approach due to the vessel’s relatively 

low speed when conducting seismic 

surveys. Accordingly, we expect that the 

majority of takes would be in the form 

of short-term Level B behavioral 

harassment in the form of temporary 

avoidance of the area or decreased 

foraging (if such activity were 

occurring), reactions that are considered 

to be of low severity and with no lasting 

biological consequences (e.g., Southall 

et al., 2007, Ellison et al., 2012). 

Marine mammal habitat may be 

impacted by elevated sound levels, but 

these impacts would be temporary. Prey 

species are mobile and are broadly 

distributed throughout the project areas; 

therefore, marine mammals that may be 

temporarily displaced during survey 

activities are expected to be able to 

resume foraging once they have moved 

away from areas with disturbing levels 

of underwater noise. Because of the 

relatively short duration (up to 24 days) 

and temporary nature of the 

disturbance, the availability of similar 

habitat and resources in the surrounding 

area, the impacts to marine mammals 

and the food sources that they utilize 

are not expected to cause significant or 

long-term consequences for individual 

marine mammals or their populations. 

Yazvenko et al. (2007) reported no 

apparent changes in the frequency of 

feeding activity in Western gray whales 

exposed to airgun sounds in their 

feeding grounds near Sakhalin Island. 

Goldbogen et al. (2013) found blue 

whales feeding on highly concentrated 

prey in shallow depths were less likely 

to respond and cease foraging than 

whales feeding on deep, dispersed prey 

when exposed to simulated sonar 

sources, suggesting that the benefits of 

feeding for humpbacks foraging on highdensity prey may outweigh perceived 


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harm from the acoustic stimulus, such 

as the seismic survey (Southall et al., 

2016). Additionally, L–DEO will shut 

down the airgun array upon observation 

of an aggregation of six or more large 

whales, which would reduce impacts to 

cooperatively foraging animals. For all 

habitats, no physical impacts to habitat 

are anticipated from seismic activities. 

While SPLs of sufficient strength have 

been known to cause injury to fish and 

fish and invertebrate mortality, in 

feeding habitats, the most likely impact 

to prey species from survey activities 

would be temporary avoidance of the 

affected area and any injury or mortality 

of prey species would be localized 

around the survey and not of a degree 

that would adversely impact marine 

mammal foraging. The duration of fish 

avoidance of a given area after survey 

effort stops is unknown, but a rapid 

return to normal recruitment, 

distribution and behavior is expected. 

Given the short operational seismic time 

near or traversing specific habitat areas, 

as well as the ability of cetaceans and 

prey species to move away from 

acoustic sources, NMFS expects that 

there would be, at worst, minimal 

impacts to animals and habitat within 

these areas. The proposed survey 

tracklines do not overlap with any 

designated critical habitat for ESA-listed 

species or areas of known importance 

for any species. 

Negligible Impact Conclusions 

The proposed survey would be of 

short duration (up to 25 days of seismic 

operations), and the acoustic ‘‘footprint’’ 

of the proposed survey would be small 

relative to the ranges of the marine 

mammals that would potentially be 

affected. Sound levels would increase in 

the marine environment in a relatively 

small area surrounding the vessel 

compared to the range of the marine 

mammals within the proposed survey 

area. Short term exposures to survey 

operations are not likely to significantly 

disrupt marine mammal behavior, and 

the potential for longer-term avoidance 

of important areas is limited. 

The proposed mitigation measures are 

expected to reduce the number of takes 

by Level A harassment (in the form of 

PTS) by allowing for detection of marine 

mammals in the vicinity of the vessel by 

visual and acoustic observers. The 

proposed mitigation measures are also 

expected to minimize the severity of any 

potential behavioral disturbance (Level 

B harassment) via shutdowns of the 

airgun array. Based on previous 

monitoring reports for substantially 

similar activities that have been 

previously authorized by NMFS 

(available at https://www.fisheries.

noaa.gov/national/marine-mammalprotection/incidental-takeauthorizations-research-and-otheractivities), we expect that the proposed 

mitigation will be effective in 

preventing, at least to some extent, 

potential PTS in marine mammals that 

may otherwise occur in the absence of 

the proposed mitigation (although all 

authorized PTS has been accounted for 

in this analysis). 

NMFS concludes that exposures to 

marine mammal species and stocks due 

to L–DEO’s proposed seismic survey 

activities would result in only shortterm (temporary and short in duration) 

effects to individuals exposed, over 

relatively small areas of the affected 

animals’ ranges. Animals may 

temporarily avoid the immediate area, 

but are not expected to permanently 

abandon the area. Major shifts in habitat 

use, distribution, or foraging success are 

not expected. NMFS does not anticipate 

the proposed take estimates to impact 

annual rates of recruitment or survival. 

In summary and as described above, 

the following factors primarily support 

our preliminary determination that the 

impacts resulting from this activity are 

not expected to adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival: 

• No serious injury or mortality is 

anticipated or proposed to be 

authorized, even absent mitigation; 

• The proposed activity is temporary 

and of relatively short duration (up to 

25 days); 

• The anticipated impacts of the 

proposed activity on marine mammals 

would primarily be temporary 

behavioral changes due to avoidance of 

the area around the survey vessel; 

• The number of instances of 

potential PTS that may occur are 

expected to be very small in number. 

Instances of potential PTS that are 

incurred in marine mammals are 

expected to be of a low level, due to 

constant movement of the vessel and of 

the marine mammals in the area, and 

the nature of the survey design (not 

concentrated in areas of high marine 

mammal concentration); 

• The availability of alternate areas of 

similar habitat value for marine 

mammals to temporarily vacate the 

survey area during the proposed survey 

to avoid exposure to sounds from the 

activity; 

• The potential adverse effects on fish 

or invertebrate species that serve as prey 

species for marine mammals from the 

proposed survey would be temporary 

and spatially limited, and impacts to 

marine mammal foraging would be 

minimal; and 

• The proposed mitigation measures, 

including visual and acoustic 

monitoring and shutdowns are expected 

to minimize potential impacts to marine 

mammals (both amount and severity). 

Based on the analysis contained 

herein of the likely effects of the 

specified activity on marine mammals 

and their habitat, and taking into 

consideration the implementation of the 

proposed mitigation and monitoring 

measures, NMFS preliminarily finds 

that the total marine mammal take from 

the proposed activity will have a 

negligible impact on all affected marine 

mammal species or stocks. 

Small Numbers 

As noted above, only small numbers 

of incidental take may be authorized 

under sections 101(a)(5)(A) and (D) of 

the MMPA for specified activities other 

than military readiness activities. The 

MMPA does not define small numbers 

and so, in practice, where estimated 

numbers are available, NMFS compares 

the number of individuals taken to the 

most appropriate estimation of 

abundance of the relevant species or 

stock in our determination of whether 

an authorization is limited to small 

numbers of marine mammals. When the 

predicted number of individuals to be 

taken is fewer than one third of the 

species or stock abundance, the take is 

considered to be of small numbers. 

Additionally, other qualitative factors 

may be considered in the analysis, such 

as the temporal or spatial scale of the 

activities. 

The amount of take NMFS proposes to 

authorize is below one third of the 

estimated population abundance of all 

species (Gerrodette and Palacios 1996); 

NMFS 2015b). In fact, take of 

individuals is less than 8 percent of the 

abundance of any affected population. 

Based on the analysis contained 

herein of the proposed activity 

(including the proposed mitigation and 

monitoring measures) and the 

anticipated take of marine mammals, 

NMFS preliminarily finds that small 

numbers of marine mammals will be 

taken relative to the population size of 

the affected species or stocks. 

Unmitigable Adverse Impact Analysis 

and Determination 

There are no relevant subsistence uses 

of the affected marine mammal stocks or 

species implicated by this action. 

Therefore, NMFS has determined that 

the total taking of affected species or 

stocks would not have an unmitigable 

adverse impact on the availability of 

such species or stocks for taking for 

subsistence purposes. 


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Endangered Species Act 

Section 7(a)(2) of the Endangered 

Species Act of 1973 (ESA: 16 U.S.C. 

1531 et seq.) requires that each Federal 

agency insure that any action it 

authorizes, funds, or carries out is not 

likely to jeopardize the continued 

existence of any endangered or 

threatened species or result in the 

destruction or adverse modification of 

designated critical habitat. To ensure 

ESA compliance for the issuance of 

IHAs, NMFS consults internally 

whenever we propose to authorize take 

for endangered or threatened species. 

NMFS is proposing to authorize take 

of blue whales, fin whales, sei whales, 

sperm whales, Mexico DPS humpback 

whales, Central America DPS humpback 

whales, and Guadalupe fur seals, which 

are listed under the ESA. The NMFS 

OPR Permits and Conservation Division 

has requested initiation of Section 7 

consultation with the NMFS OPR ESA 

Interagency Cooperation Division for the 

issuance of this IHA. NMFS will 

conclude the ESA consultation prior to 

reaching a determination regarding the 

proposed issuance of the authorization. 

Proposed Authorization 

As a result of these preliminary 

determinations, NMFS proposes to issue 

an IHA to L–DEO for conducting marine 

geophysical surveys in the ETP, 

beginning in spring 2022, provided the 

previously mentioned mitigation, 

monitoring, and reporting requirements 

are incorporated. A draft of the 

proposed IHA can be found at https:// 

www.fisheries.noaa.gov/permit/ 

incidental-take-authorizations-undermarine-mammal-protection-act. 

Request for Public Comments 

We request comment on our analyses, 

the proposed authorization, and any 

other aspect of this notice of proposed 

IHA for the proposed geophysical 

surveys. We also request at this time 

comment on the potential Renewal of 

this proposed IHA as described in the 

paragraph below. Please include with 

your comments any supporting data or 

literature citations to help inform 

decisions on the request for this IHA or 

a subsequent Renewal IHA. 

On a case-by-case basis, NMFS may 

issue a one-time, one-year Renewal IHA 

following notice to the public providing 

an additional 15 days for public 

comments when (1) up to another year 

of identical or nearly identical activities 

as described in the Description of 

Proposed Activities section of this 

notice is planned or (2) the activities as 

described in the Description of 

Proposed Activities section of this 

notice would not be completed by the 

time the IHA expires and a Renewal 

would allow for completion of the 

activities beyond that described in the 

Dates and Duration section of this 

notice, provided all of the following 

conditions are met: 

(1) A request for renewal is received 

no later than 60 days prior to the needed 

Renewal IHA effective date (recognizing 

that the Renewal IHA expiration date 

cannot extend beyond one year from 

expiration of the initial IHA); 

(2) The request for renewal must 

include the following: 

• An explanation that the activities to 

be conducted under the requested 

Renewal IHA are identical to the 

activities analyzed under the initial 

IHA, are a subset of the activities, or 

include changes so minor (e.g., 

reduction in pile size) that the changes 

do not affect the previous analyses, 

mitigation and monitoring 

requirements, or take estimates (with 

the exception of reducing the type or 

amount of take); and 

• A preliminary monitoring report 

showing the results of the required 

monitoring to date and an explanation 

showing that the monitoring results do 

not indicate impacts of a scale or nature 

not previously analyzed or authorized. 

(3) Upon review of the request for 

Renewal, the status of the affected 

species or stocks, and any other 

pertinent information, NMFS 

determines that there are no more than 

minor changes in the activities, the 

mitigation and monitoring measures 

will remain the same and appropriate, 

and the findings in the initial IHA 

remain valid. 

Dated: January 7, 2022. 

Catherine Marzin, 

Acting Director, Office of Protected Resources, 

National Marine Fisheries Service. 

[FR Doc. 2022–00455 Filed 1–7–22; 4:15 pm] 

BILLING CODE 3510–22–P 


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