Federal Register / Vol. 89, No. 195 / Tuesday, October 8, 2024 / Notices 81429 

enterprises (SMEs), the academic 

community, and civil society 

organizations) stakeholders to cooperate 

in order to advance U.S. economic 

competitiveness and national security. 

In this RFI, NIST is seeking 

information about existing awards and 

recognition programs that can be 

leveraged by the U.S. Government and 

U.S. standards community to encourage 

and support standards participation and 

leadership in CET areas in alignment 

with the actions called out in the USG 

NSSCET Implementation Roadmap. 

NIST is also requesting information that 

will help inform the work of the U.S. 

Government and the U.S. standards 

community to educate and empower the 

standards workforce and business and 

technology decision-makers. Finally, 

NIST is seeking to maintain an open 

dialogue and sustained communication 

with the U.S. CET and standards 

communities regarding the ongoing 

implementation of the roadmap. 

Information gathered through this RFI 

and other stakeholder engagements will 

support key activities to optimize the 

USG NSSCET impact and further 

enhance the U.S. Government’s ability 

to support a private sector-led, open, 

consensus-based international standards 

system in which the U.S. Government is 

an active stakeholder and participant. 

NIST is requesting comments on the 

following questions and encourages 

responses from the public, including 

key stakeholders from the private sector 

(i.e., industry, including start-ups and 

SMEs, the academic community, 

professional societies, and civil society 

organizations), standards developing 

organizations (SDOs), and international 

standards community. 

The questions on awards and 

recognition, as well as on workforce 

development, address specific aspects of 

the USG NSSCET where further input 

from the stakeholder community will 

help the short- and long-term outcomes 

in the implementation roadmap. The 

inclusion of these two topics on this RFI 

is not intended to indicate a particular 

relationship between the two topics, nor 

are they intended to limit the topics that 

may be addressed by the public in 

response to this RFI. Responses to the 

open feedback question may include 

any topic believed to have implications 

for the ongoing implementation. 

When responding, commenters may 

address the practices of their 

organization(s) or a group of 

organizations with which they are 

familiar. Commenters may also provide 

information about the type, size, and 

location of the organization(s). Provision 

of such information is optional and will 

not affect NIST’s consideration. 

Existing Awards and Recognition 

Programs for Standards Development 

1. How can the U.S. Government and 

the U.S. standards community leverage 

existing awards and recognition 

programs or establish new programs to 

support standards participation and 

leadership in CET areas? 

2. What types of awards and 

recognition programs for standards 

development further standards 

engagement, especially with respect to 

CET? 

Best Practices for Standards Workforce 

Development 

1. What types of support could 

improve professional development for 

early-career professionals, mid-career 

professionals, or those who are new to 

standards development? 

2. What type of educational outreach 

to business and technology decisionmakers on why, how, and when to 

engage in standards development could 

increase their engagement? 

3. How can the U.S. Government and 

the U.S. standards community more 

effectively work together to share best 

practices for standards workforce 

development? 

Open Feedback on the Implementation 

of the USG NSSCET 

1. Please describe any additional 

observations of how the U.S. 

Government can effectively implement 

the vision set forth in the USG NSSCET 

and associated Implementation 

Roadmap. 

Alicia Chambers, 

NIST Executive Secretariat. 

[FR Doc. 2024–23174 Filed 10–7–24; 8:45 am] 

BILLING CODE 3510–13–P 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric 

Administration 

[RTID 0648–XE162] 

Takes of Marine Mammals Incidental to 

Specified Activities; Taking Marine 

Mammals Incidental to a Marine 

Geophysical Survey in the Nauru Basin 

of Greater Micronesia in the Northwest 

Pacific Ocean 

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 received a request from 

the Scripps Institution of Oceanography 

(SIO) for authorization to take marine 

mammals incidental to a marine 

geophysical survey in the Nauru Basin 

of greater Micronesia in the northwest 

(NW) Pacific Ocean. 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, 1-year 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 November 7, 

2024. 

ADDRESSES: Comments should be 

addressed to Jolie Harrison, Chief, 

Permits and Conservation Division, 

Office of Protected Resources, National 

Marine Fisheries Service and should be 

submitted via email to 

ITP.wachtendonk@noaa.gov. 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/national/ 

marine-mammal-protection/incidentaltake-authorizations-research-and-otheractivities. In case of problems accessing 

these documents, please call the contact 

listed below. 

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 

https://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: 

Rachel Wachtendonk, Office of 

Protected Resources, NMFS, (301) 427– 

8401. 

SUPPLEMENTARY INFORMATION: 


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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 specific 

geographic region if certain findings are 

made and either regulations are 

proposed or, if the taking is limited to 

harassment, a notice of a proposed IHA 

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 monitoring and 

reporting of the takings. 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. 

This action is consistent with 

categories of activities identified in 

Categorical Exclusion B4 (IHAs with no 

anticipated serious injury or mortality) 

of the Companion Manual for NAO 216– 

6A, which do not individually or 

cumulatively have the potential for 

significant impacts on the quality of the 

human environment and for which we 

have not identified any extraordinary 

circumstances that would preclude this 

categorical exclusion. Accordingly, 

NMFS has preliminarily determined 

that the issuance of the proposed IHA 

qualifies to be categorically excluded 

from further NEPA review. 

Summary of Request 

On June 6, 2024, NMFS received a 

request from the Scripps Institution of 

Oceanography (SIO) for an IHA to take 

marine mammals incidental to a marine 

geophysical survey in the Nauru Basin 

of greater Micronesia in the northwest 

(NW) Pacific Ocean. The application 

was deemed adequate and complete on 

July 30, 2024. SIO’s request is for take 

of 27 species of marine mammals, by 

Level B harassment only. Neither SIO 

nor NMFS expect serious injury or 

mortality to result from this activity 

and, therefore, an IHA is appropriate. 

Description of Proposed Activity 

Overview 

Researchers from the Woods Hole 

Oceanographic Institution (WHOI) and 

University of Houston, with funding 

from the National Science Foundation 

(NSF), and implementation by SIO, 

propose to conduct a low-energy marine 

seismic survey using airguns as the 

acoustic source from the research vessel 

(R/V) Sikuliaq (Sikuliaq), which is 

owned by NSF and operated by the 

University of Alaska Fairbanks (UAF). 

The proposed survey would occur in the 

Nauru Basin of greater Micronesia in the 

NW Pacific Ocean from approximately 

December 2024 to January 2025. The 

proposed survey would occur in 

International Waters and within the 

Exclusive Economic Zone (EEZ) of the 

Republic of Marshall Islands, in water 

depths ranging from approximately 

4,000–6,000 meters (m). To complete 

this 2-dimensional (2–D) multi-channel 

seismic (MCS) reflection survey, the 

Sikuliaq would tow a 4-airgun array 

with a total discharge volume of ∼420 

cubic inches (in3) at a depth of 3 m, 

operated by marine technicians from 

SIO. The airgun array receiver would 

consist of a 1,200 m long solid-state 

hydrophone streamer. The airguns 

would fire at a shot interval of 30 m. 

Approximately 3,158 kilometers (km) of 

seismic acquisition is planned. Airgun 

arrays would introduce underwater 

sounds that may result in take, by Level 

B harassment, of marine mammals. 

The purpose of the proposed survey is 

to examine magnetic reversals to help 

determine the process that causes 

changes in the Earth’s magnetic field. 

The proposed seismic surveys are a 

prerequisite for processing magnetic 

data, as they will provide crucial 

information on the structure of the 

oceanic crust that is used to model the 

source of the magnetic signals. 

Dates and Duration 

The R/V Sikuliaq would likely 

mobilize from Honolulu, Hawaii, on 

December 7, 2024, and demobilize in 

Pohnpei, Federated States of 

Micronesia, on January 6, 2025, after the 

survey is completed. The survey is 

expected to last 27 days, including 

approximately 14 days of seismic 

operations and 13 days of transit. 

Specific Geographic Region 

The proposed survey would occur 

within approximately 6–20° N, 154– 

167° E, in International Waters and 

within the EEZ of the Republic of 

Marshall Islands, in water depths 

ranging from approximately 4,000 to 

6,000 m. The region where the survey is 

proposed to occur is depicted in figure 

1; the tracklines could occur anywhere 

within the polygon shown in figure 1. 

Representative survey tracklines are 

shown; however, some deviation in 

actual tracklines, 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 R/V 

Sikuliaq would likely mobilize from 

Honolulu, Hawaii and demobilize in 

Pohnpei, Federated States of 

Micronesia. 


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Figure 1—Location of the Proposed 

Seismic Survey in the Nauru Basin of 

Greater Micronesia in the NW Pacific 

Ocean 

Representative survey tracklines are 

included in the figure; however, the 

tracklines could occur anywhere within 

the survey area. 

Detailed Description of the Specified 

Activity 

The procedures to be used for the 

proposed survey would be similar to 

those used during previous seismic 

surveys by SIO and would use 

conventional seismic methodology. The 

survey would involve one source vessel, 

R/V Sikuliaq, which is owned by NSF 

and operated by UAF. During the lowenergy MCS seismic reflection survey, 

R/V Sikuliaq would tow two strings, 

each with two Generator-Injector (GI) 

airguns. During the survey, both strings, 

totaling four active airguns with a total 

discharge volume of 420 in3, would be 

used. The two airgun strings would be 

spaced 11 m apart and would be towed 

approximately 25 m behind the vessel. 

The airgun array configurations are 

illustrated in figure 2–11 of NSF and the 

U.S. Geological Survey’s (USGS) 

Programmatic Environmental Impact 

Statement (PEIS; NSF–USGS, 2011). 

(The PEIS is available online at: https:// 

www.nsf.gov/geo/oce/envcomp/usgsnsf-marine-seismic-research/nsf-usgsfinal-eis-oeis_3june2011.pdf). The 

receiving system would consist of a 

1,200 m long solid-state hydrophone 

streamer. As the airgun arrays are towed 

along the survey lines, the hydrophone 

streamer would transfer the data to the 

on-board processing system. 

Approximately 3,158 km of seismic 

acquisition are planned. The survey 

would take place in water depths 

ranging from approximately 4,000 to 

6,000 m. In addition to the operations of 

the airgun array, the ocean floor would 

be mapped with the Kongsberg EM 304 

and the Kongsberg EM 710 multibeam 

echosounder (MBES), and a Knudsen 

Chirp 3260 sub-bottom profiler (SBP). A 

Teledyne RDI 75 kilohertz (kHz) Ocean 

Surveyor Acoustic Doppler Current 

Profiler (ADCP) would be used to 

measure water current velocities, and a 

passive sea surface magnetometer and a 

shipboard gravitometer would also be 

used. Take of marine mammals is not 

expected to occur incidental to use of 

the MBES, SBP, and ADCP, whether or 

not the airguns are operating 

simultaneously with the other sources. 

Given their characteristics (e.g., narrow 

downward-directed beam), marine 

mammals would experience no more 

than one or two brief ping exposures, if 

any exposure were to occur. NMFS does 

not expect that the use of these sources 

presents any reasonable potential to 

cause take of marine mammals. 

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. NMFS fully considered 

all of this information, and we refer the 

reader to these descriptions, instead of 

reprinting the information. Additional 

information about these species (e.g., 

physical and behavioral descriptions) 

may be found on NMFS’ website 

(https://www.fisheries.noaa.gov/findspecies). NMFS refers the reader to the 

aforementioned source for general 

information regarding the species listed 

in table 1. 

The populations of marine mammals 

found in the survey area do not occur 

within the U.S. EEZ and therefore, are 

not assessed in NMFS’ Stock 

Assessment Reports (SARs). For most 

species, there are no stocks defined for 

management purposes in the survey 

area, and NMFS is evaluating impacts at 


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the species level and ranges for most 

species evaluated here are considered to 

be the North Pacific. As such, 

information on potential biological 

removal level (PBR; 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) and 

annual levels of serious injury and 

mortality from anthropogenic sources 

are not available for these marine 

mammal populations. Abundance 

estimates for marine mammals in the 

survey location were calculated using 

density data for marine mammals from 

a US Navy Technical Report for the 

region (DoN, 2018). The area covered in 

this report include the Mariana Islands 

Training and Testing (MITT) Study 

Area, within approximately 6–23° N, 

122–150° E, and the Transit Corridor 

which spans from the MITT Study Area 

to the International Date Line.These 

abundance estimates are considered the 

best scientific information available on 

the abundance of marine mammal 

populations in the area. 

Table 1 lists all species or stocks for 

which take is expected and proposed to 

be authorized for this activity and 

summarizes information related to the 

population or stock, including 

regulatory status under the MMPA and 

Endangered Species Act (ESA). 

TABLE 1—SPECIES LIKELY IMPACTED BY THE SPECIFIED ACTIVITIES

Common name Scientific name 

Stock/distinct 

population 

segment 

(DPS) 

ESA/MMPA 

status; strategic 

(Y/N) 1

Abundance 2

Order Artiodactyla—Cetacea—Mysticeti (baleen whales) 

Family Balaenopteridae (rorquals) 

Blue Whale .......................................... Balaenoptera musculus ............................. NA E, D, Y 150 

Bryde’s Whale ..................................... Balaenoptera edeni ................................... NA -, -, N 1,596 

Fin Whale ............................................ Balaenoptera physalus .............................. NA E, D, Y 46 

Humpback Whale ................................ Megaptera novaeangliae ........................... Western North 

Pacific DPS 

E, D, Y 2,673 

Humpback Whale ................................ Megaptera novaeangliae ........................... Oceania DPS -, -, N 2,673 

Minke Whale ........................................ Balaenoptera acutorostrata ....................... NA -, -, N 450 

Sei Whale ............................................ Balaenoptera borealis ................................ NA E, D, Y 821 

Omura’s Whale .................................... Balaenoptera omurai ................................. NA -, -, N 160 

Odontoceti (toothed whales, dolphins, and porpoises) 

Family Physeteridae 

Sperm Whale ....................................... Physeter macrocephalus ........................... NA E, D, Y 5,146 

Family Kogiidae 

Dwarf Sperm Whale ............................ Kogia sima ................................................. NA -, -, N 27,395 

Pygmy Sperm Whale .......................... Kogia breviceps ......................................... NA -, -, N 11,168 

Family Ziphiidae (beaked whales) 

Blainville’s Beaked Whale ................... Mesoplodon densirostris ............................ NA -, -, N 3,376 

Cuvier’s Beaked Whale ....................... Ziphius cavirostris ...................................... NA -, -, N 2,642 

Longman’s Beaked Whale .................. Indopacetus pacificus ................................ NA -, -, N 11,253 

Ginko-Toothed Beaked Whale ............ Mesoplodon ginkgodens ............................ NA -, -, N 7,567 

Deraniyagala’s Beaked Whale ............ Mesoplodon hotaula .................................. NA -, -, N NA 

Family Delphinidae 

False Killer Whale ............................... Pseudorca crassidens ............................... NA -, -, N 4,218 

Killer Whale ......................................... Orcinus orca .............................................. NA -, -, N 253 

Melon-Headed Whale .......................... Peponocephala electra .............................. NA -, -, N 16,551 

Pygmy Killer Whale ............................. Feresa attenuata ....................................... NA -, -, N 527 

Short-Finned Pilot Whale .................... Globicephala macrorhynchus .................... NA -, -, N 6,583 

Bottlenose Dolphin .............................. Tursiops truncatus ..................................... NA -, -, N 1,076 

Fraser’s Dolphin .................................. Lagenodelphis hosei .................................. NA -, -, N 76,476 

Pantropical Spotted Dolphin ................ Stenella attenuata ...................................... NA -, -, N 85,755 

Risso’s Dolphin .................................... Grampus griseus ....................................... NA -, -, N 17,184 

Rough-Toothed Dolphin ...................... Steno bredanensis ..................................... NA -, -, N 1,815 

Spinner Dolphin ................................... Stenella longirostris ................................... NA -, -, N 5,232 

Striped Dolphin .................................... Stenella coeruleoalba ................................ NA -, -, N 24,528 

1 Endangered 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 Abundance estimates for marine mammals in the survey location were calculated using density data for marine mammals from the U.S. Navy 

Marine Species Density Database Phase III for the Mariana Islands Training and Testing Study Area report (DoN 2018). 

As indicated above, all 27 species in 

table 1 temporally and spatially cooccur with the activity to the degree that 

take is reasonably likely to occur. All 

species that could potentially occur in 

the proposed survey areas are included 

in table 3 of the IHA application. While 

common dolphins have been reported in 

the area, the temporal and/or spatial 

occurrence of these species is such that 

take is not expected to occur, and they 

are not discussed further beyond the 

explanation provided here. The 

proposed study area is not a part of the 

common dolphin range. Studies have 

noted that common dolphins are rare in 

the Mariana Islands, and this species 

was not included in the U.S. Navy’s 


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Marine Species Density Database for the 

Mariana Islands Training and Testing 

Study area. Katsumata and Matsuoka 

(2021, 2022) recorded sightings of 

common dolphins north of 35° N, 

approximately 1,665 km north of the 

study area. 

In addition to what is included in 

sections 3 and 4 of the IHA application, 

and NMFS’ website, further detail 

informing the regional occurrence for 

select species of particular or unique 

vulnerability (i.e., information regarding 

ESA listed species) is provided below. 

Blue Whale 

The blue whale has a cosmopolitan 

distribution and tends to be pelagic, 

only coming nearshore to feed and 

possibly to breed (Jefferson et al., 2015). 

The distribution of the species, at least 

during times of the year when feeding 

is a major activity, occurs in areas that 

provide large seasonal concentrations of 

euphausiids (Yochem and Leatherwood, 

1985). Blue whales are most often found 

in cool, productive waters where 

upwelling occurs (Reilly and Thayer, 

1990). Generally, blue whales are 

seasonal migrants between high 

latitudes in summer, where they feed, 

and low latitudes in winter, where they 

mate and give birth (Lockyer and 

Brown, 1981). The current distribution 

of blue whales in the western North 

Pacific is largely unknown; however, 

central North Pacific blue whales are 

known to migrate to the western and 

central Pacific to breed during winters. 

Blue whales are listed as endangered 

under the ESA. 

Blue whales are rare in Micronesia; 

during a 2007 Mariana Islands survey 

that took place from January to April, no 

blue whales were detected visually or 

acoustically (DoN, 2007; Fulling et al., 

2011). However, blue whales were 

detected acoustically on recorders 

deployed in the Northern Mariana 

Islands from 2010 to 2013 (Oleson et al., 

2015) and there are confirmed records of 

blue whales near the Republic of the 

Marshall Islands and Wake Island 

(Wiles, 2005; SPREP, 2022; Miller, 

2023). 

Fin Whale 

The fin whale is widely distributed in 

all the world’s oceans (Gambell, 1985), 

although it is most abundant in 

temperate and cold waters (Aguilar and 

Garcı ́a-Vernet, 2018). Nonetheless, its 

overall range and distribution is not 

well known (Jefferson et al., 2015). Fin 

whales most commonly occur offshore, 

but can also be found in coastal areas 

(Jefferson et al., 2015). Most populations 

migrate seasonally between temperate 

waters where mating and calving occur 

in winter, and polar waters where 

feeding occurs in the summer; they are 

known to use the shelf edge as a 

migration route (Evans, 1987). 

In the North Pacific, fin whales are 

found in summer from the Chukchi Sea 

to California and in winter from 

California southwards in the eastern 

Pacific (Gambell, 1985). The current 

distribution of fin whales in the western 

North Pacific is largely unknown, but 

they are known to winter in the Yellow, 

East China, and South China seas 

(Parsons et al., 1995; Rudolph and 

Smeenk, 2002). Fin whale calls are 

recorded in the North Pacific year-round 

(e.g., Moore et al., 2006; Stafford et al., 

2007, 2009), including the western 

North Pacific (Edwards et al., 2015). 

They were detected acoustically near 

Wake Island during January 2010 

(Oleson and Hill, 2010). However, no fin 

whales were sighted or detected 

acoustically during the January to April 

2007 surveys in the waters of the 

Mariana Islands (DoN, 2007; Fulling et 

al., 2011) or during NOAA surveys of 

the Mariana Islands (Hill et al., 2020c; 

Yano et al., 2022). Fin whales have been 

detected acoustically on recorders 

deployed in the Northern Mariana 

Islands from 2010 to 2013 (Oleson et al., 

2015). 

Humpback Whale 

The humpback whale is found 

throughout all oceans of the world 

(Clapham, 2018). Although considered 

to be mainly a coastal species, 

humpback whales often traverse deep 

pelagic areas while migrating 

(Calambokidis et al., 2001; Garrigue et 

al., 2002, 2015; Zerbini et al., 2011). 

Humpbacks migrate between summer 

feeding grounds in high latitudes and 

winter calving and breeding grounds in 

tropical waters (Clapham and Mead, 

1999). Humpback whales were 

previously listed as endangered under 

the ESA at the species level. NMFS reevaluated the status of the species in 

2015, and on September 8, 2016, NMFS 

divided the species into 14 DPS, 

removed the current species-level 

listing, and listed 4 DPSs as endangered 

and 1 DPS as threatened (81 FR 62259, 

September 8, 2016). The remaining nine 

DPSs were not listed. If humpback 

whales are encountered during the 

proposed survey, they would most 

likely be from the Western North Pacific 

DPS, which is listed as endangered 

under the ESA. It is unlikely that whales 

from the Oceania DPS, which is not 

listed under the ESA, would be 

encountered during the proposed 

survey. The longitudinal distribution 

boundaries of humpback whales 

wintering in Oceania lie between ∼160° 

E (west of New Caledonia) and ∼120° W 

(east of French Polynesia) and 

latitudinally between 0° and 30° S. 

Humpback whales occur throughout 

most of the Pacific, but are rare in the 

equatorial region (Jefferson et al., 2015). 

North Pacific humpback whales summer 

in feeding grounds along the Pacific Rim 

and in the Bering and Okhotsk seas 

(Pike and MacAskie, 1969; Rice 1978; 

Winn and Reichley, 1985; Calambokidis 

et al., 2000, 2001, 2008; Bettridge et al., 

2015). The Western North Pacific DPS 

winters in the western Pacific, 

particularly around the Ogasawara and 

Ryukyu islands in southern Japan and 

the northern Philippines (Calambokidis 

et al., 2008; Bettridge et al., 2015) and 

typically feed in Russia during the 

summer (Calambokidis et al., 2008; 

Ransome et al., 2023). At least five 

sightings of humpback whales were 

made from 1978 to 1996 in the Mariana 

Islands; including one sighting of a 

mother-calf pair (Eldredge, 2003). There 

were no humpback sightings during the 

January–April 2007 surveys in the 

Mariana Islands (DoN, 2007; Norris et 

al., 2012). However, humpbacks were 

detected acoustically in the Mariana 

Islands, including just west of the 

proposed survey area, during January– 

April 2007 (DoN, 2007; Norris et al., 

2012), during acoustic recorder 

deployments in 2010–2013 (Oleson et 

al., 2015), and during glider surveys in 

the southern Mariana Trench region 

during September–November 2014 

(Klink et al., 2015). Forty-two sightings 

were made during NOAA’s Pacific 

Islands Fisheries Science Center (PIFSC) 

surveys of the southern Mariana Islands 

between 2010 and 2019 (Hill et al., 

2020c) and in May 2021 (Yano et al., 

2022). 

Sei Whale 

Sei whales are found in all ocean 

basins (Horwood, 2018) but appear to 

prefer mid-latitude temperate waters 

(Jefferson et al., 2015). Habitat 

suitability models indicate that sei 

whale distribution is related to cool 

water with high chlorophyll levels 

(Palka et al., 2017; Chavez-Rosales et al., 

2019). They occur in deeper waters 

characteristic of the continental shelf 

edge region (Hain et al., 1985) and in 

other regions of steep bathymetric relief 

such as seamounts and canyons 

(Kenney and Winn, 1987; Gregr and 

Trites, 2001). 

In the North Pacific during summer, 

the sei whale can be found from the 

Bering Sea to the Gulf of Alaska and 

down to the Baja California Peninsula, 

as well as in the western Pacific from 

Japan to Korea. On summer feeding 

grounds, sei whales associate with 


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oceanic frontal systems (Horwood, 

1987) such as the cold eastern currents 

in the North Pacific (Perry et al., 1999). 

Its winter distribution is concentrated at 

∼20° N (Rice, 1998). Three sightings of 

sei whales were made within the 

proposed survey area during the NOAA 

PIFSC transit from Hawaii to Guam from 

January to February 2010 (PIFSC, 2010a; 

Hill, 2023a). During the January to April 

2007 surveys of the Mariana Islands, the 

sei whale was one of the most 

frequently sighted baleen whales (DoN, 

2007; Fulling et al., 2011), including 

sightings just west of the proposed 

survey area. All sei whale sightings 

were south of Saipan in water depths 

greater than 1,000 m deep, with a 

number of sightings directly over the 

Mariana Trench; 32 acoustic detections 

were also recorded (Norris et al., 2012). 

No sei whales were detected during 

surveys of the southern Mariana Islands 

from 2010 to 2019 (Hill et al., 2020c). 

Sperm Whale 

The sperm whale is widely 

distributed, occurring from the edge of 

the polar pack ice to the Equator in both 

hemispheres, with the sexes occupying 

different distributions (Whitehead, 

2018). Their distribution and relative 

abundance can vary in response to prey 

availability, most notably squid (Jaquet 

and Gendron, 2002). Females generally 

inhabit waters >1,000 m deep at 

latitudes <40° where sea surface 

temperatures are <15° C; adult males 

move to higher latitudes as they grow 

older and larger in size, returning to 

warm-water breeding grounds 

(Whitehead, 2018). 

The sperm whale is the most common 

large toothed whale in the Pacific 

Islands region (Reeves et al., 1999). 

There are historical whaling records 

throughout the region in the months of 

April through September, including 

within the proposed survey area 

(Townsend, 1935). Two sightings were 

made within the proposed survey area 

during the NOAA PIFSC transit from 

Hawaii to Guam from January to 

February 2010 (PIFSC, 2010a; Hill, 

2023a), and three sightings were made 

east of the proposed survey area during 

a transit by PIFSC from Guam to Hawaii 

in April–May 2010 (PIFSC, 2010b; Hill, 

2023b). Additionally, sperm whales 

have been sighted just north of the 

proposed survey area during summer 

surveys in 2014 (Matsuoka et al., 2015). 

The Bismarck Sea in Papua New Guinea 

appears to be an important breeding 

ground for sperm whales as mother/calf 

pairs and mature males have been seen 

in this area (Madsen et al., 2002). During 

the 2007 surveys, there were multiple 

sightings of groups that included calves 

(DoN, 2007). Observations were made of 

several large bulls with fresh tooth 

marks (one male rammed the survey 

ship) in 2007, which suggests that these 

males were engaged in competition for 

mates (Fulling and Salinas Vega, 2009). 

Thus, there is evidence that this area is 

used for breeding and calving by sperm 

whales. The sperm whale was the most 

frequently sighted cetacean during the 

January–April 2007 survey in the waters 

of the Mariana Island, and acoustic 

detections were three times higher than 

visual detections (DoN, 2007; Fulling et 

al., 2011; Norris et al., 2012); sperm 

whales were detected in deep waters 

throughout most of Mariana Islands, as 

well as just west of the proposed survey 

area. Additionally, acoustic detections 

were made on recorders in the Northern 

Mariana Islands from 2010 to 2013 

(Oleson et al., 2015) and during glider 

surveys in the southern Mariana Trench 

from September to November 2014 

(Klink et al., 2015). Seven sightings of 

sperm whales were made during 

surveys conducted in the southern 

Mariana Islands during 2010–2019, 

three encounters were made during the 

Mariana Archipelago Cetacean Survey 

(MACS) 2015, and two sightings were 

recorded during MACS 2018 (Hill et al., 

2020c). Sperm whales were also seen 

and detected acoustically during May– 

July 2021 surveys in the Mariana Islands 

(Yano et al., 2022). 

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. 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, 2019) recommended that marine 

mammals be divided into hearing 

groups based on directly measured 

(behavioral or auditory evoked potential 

techniques) or estimated hearing ranges 

(behavioral response data, anatomical 

modeling, etc.). 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. 

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 et al., 2013). 

For more detail concerning these 

groups and associated frequency ranges, 

please see NMFS (2018) for a review of 

available information. 


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On May 3, 2024, NMFS published (89 

FR 36762) and solicited public comment 

on its draft Updated Technical 

Guidance, which includes updated 

thresholds and weighting functions to 

inform auditory injury estimates, and is 

intended to replace the 2018 Technical 

Guidance referenced above, once 

finalized. The public comment period 

ended on June 17, 2024. Although the 

Updated Technical Guidance is not yet 

final, NMFS considers the updated 

hearing group in this proposed IHA, 

along the existing Technical Guidance 

(NMFS, 2018), because at the time of the 

final agency decision on this request 

NMFS anticipates the Updated 

Technical Guidance will become final 

agency action and represent the best 

available science. The updated hearing 

groups are presented below (table 3). 

The references, analysis, and 

methodology used in the development 

of the hearing groups are described in 

NMFS’ 2024 Technical Guidance, which 

may be accessed at: https://

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/marinemammal-acoustic-technical-guidance. 

TABLE 3—MARINE MAMMAL HEARING GROUPS (NMFS, 2024) 

Hearing Group ∧ Generalized Hearing Range * 

UNDERWATER 

Low-frequency (LF) cetaceans (baleen whales) .................................................................................................. 7 Hz to 36 * kHz. 

High-frequency (HF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales) ...................... 150 Hz to 160 kHz. 

Very High-frequency (VHF) cetaceans (true porpoises, Kogia, river dolphins, Cephalorhynchid, 

Lagenorhynchus cruciger & L. australis).

200 Hz to 165 kHz. 

Phocid pinnipeds (PW) (underwater) (true seals) ................................................................................................ 40 Hz to 90 kHz. 

Otariid pinnipeds (OW) (underwater) (sea lions and fur seals) ........................................................................... 60 Hz to 68 kHz. 

∧Southall et al. 2019 indicates that as more data become available there may be separate hearing group designations for Very Low-Frequency 

cetaceans (blue, fin, right, and bowhead whales) and Mid-Frequency cetaceans (sperm, killer, and beaked whales). However, at this point, all baleen whales are part of the LF cetacean hearing group, and sperm, killer, and beaked whales are part of the HF cetacean hearing group. Additionally, recent data indicates that as more data become available for Monachinae seals, separate hearing group designations may be appropriate for the two phocid subfamilies (Ruscher et al. 2021; Sills et al. 2021). 

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

hearing ranges may not be as broad. Generalized hearing range chosen based on ∼65 dB threshold from composite audiogram, previous analysis in NMFS 2018, and/or data from Southall et al. 2007; Southall et al. 2019. Additionally, animals are able to detect very loud sounds above 

and below that ‘‘generalized’’ hearing range. 

+ NMFS is aware that the National Marine Mammal Foundation successfully collected preliminary hearing data on two minke whales during 

their third field season (2023) in Norway. These data have implications for not only the generalized hearing range for low-frequency cetaceans 

but also on their weighting function. However, at this time, no official results have been published. Furthermore, a fourth field season (2024) is 

proposed, where more data will likely be collected. Thus, it is premature for us to propose any changes to our current Updated Technical Guidance. However, mysticete hearing data is identified as a special circumstance that could merit re-evaluating the acoustic criteria in this document. Therefore, we anticipate that once the data from both field seasons are published, it will likely necessitate updating this document (i.e., 

likely after the data gathered in the summer 2024 field season and associated analysis are published). 

Potential Effects of Specified Activities 

on Marine Mammals and Their Habitat 

This section provides a discussion of 

the ways in which components of the 

specified activity may impact marine 

mammals and their habitat. The 

Estimated Take of Marine Mammals 

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 of Marine Mammals 

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 whether those 

impacts are reasonably expected to, or 

reasonably likely to, adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival. 

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 


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1Please refer to the information given previously 

(‘‘Description of Active Acoustic Sound Sources’’) 

regarding sound, characteristics of sound types, and 

metrics used in this document. 

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 array 

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., 

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 

anthropogenic 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 this 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. 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., 

NMFS, 2018; 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 (American National 

Standards Institute (ANSI), 1986, 2005; 

Harris, 1998; National Institute for 

Occupational Health and Safety 

(NIOSH), 1998; International 

Organization for Standardization (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 1—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 


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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, if it occurs at all, will 

occur almost exclusively in cases where 

a noise is within an animal’s hearing 

frequency 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 

to elicit behavioral or physiological 

response. 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). Threshold shift 

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 typically 

consider TTS to constitute auditory 

injury. 

Relationships between TTS and PTS 

thresholds have not been studied in 

marine mammals. 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 impulsive 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. 

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 3 captive 

bottlenose dolphins before and after 

exposure to 10 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 was 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 


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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. 

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 

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 shown 

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). 

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). 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 disruptions 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 affect 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. 

Visual tracking, passive acoustic 

monitoring (PAM), 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, or 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, 


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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). 

Changes in respiration naturally vary 

with different behaviors and alterations 

to breathing rate as a function of 

acoustic exposure can be expected to cooccur 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 

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 PAM 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 minutes sampled period) 

on singer number. The number of 

singers significantly decreased with 

increasing received level of noise, 

suggesting that humpback whale 

communication 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 cumulative sound 

exposure level (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 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 show 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. 

Avoidance of overlap between 

disturbing noise and areas and/or times 

of particular importance for sensitive 

species may be critical to avoiding 

population-level impacts because 

(particularly for animals with high site 

fidelity) there may be a strong 

motivation to remain in the area despite 

negative impacts. 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. 

Forney et al. (2017) specifically 

discuss beaked whales, stating that until 

recently most knowledge of beaked 

whales was derived from strandings, as 

they have been involved in atypical 

mass stranding events associated with 

mid-frequency active sonar (MFAS) 

training operations. Given these 

observations and recent research, 

beaked whales appear to be particularly 

sensitive and vulnerable to certain types 

of acoustic disturbance relative to most 

other marine mammal species. 

Individual beaked whales reacted 

strongly to experiments using simulated 

MFAS at low received levels, by moving 

away from the sound source and 

stopping foraging for extended periods. 


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These responses, if on a frequent basis, 

could result in significant fitness costs 

to individuals (Forney et al., 2017). 

Additionally, difficulty in detection of 

beaked whales due to their cryptic 

surfacing behavior and silence when 

near the surface pose problems for 

mitigation measures employed to 

protect beaked whales. Forney et al. 

(2017) specifically states that failure to 

consider both displacement of beaked 

whales from their habitat and noise 

exposure could lead to more severe 

biological consequences. 

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 

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 5-day 

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 1 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 arrays 

of large airguns (considered to be 500 

in3 or more in that study) 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 


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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, 

significant masking could disrupt 

behavioral patterns, which in turn could 

affect fitness for survival and 

reproduction. 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 

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 

predicting 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 may be less 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 noise levels during intervals 

between seismic 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 2,000 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). 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 more sensitive to lowfrequency 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 Sikuliaq 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. 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). 

Vessel 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; 


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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. 

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. 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 vessels (Richardson et al. 1995). 

Pirotta et al. (2015) noted that the 

physical presence of vessels, not just 

ship noise, disturbed the foraging 

activity of bottlenose dolphins. There is 

little 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). 

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). 

Vessel Strike 

Vessel collisions with marine 

mammals, or vessel strikes, can result in 

death or serious injury of the animal. 

Wounds resulting from vessel 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 vessels 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 

increased from 45 to 75 percent as 

vessel speed increased from 10 to 14 

knots (kn (26 kilometer per hour (kph)), 

and exceeded 90 percent at 17 kn (31 

kph). 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 kn (28 kph). 

The chances of a lethal injury decline 

from approximately 80 percent at 15 kn 

(28 kph) to approximately 20 percent at 

8.6 kn (16 kph). At speeds below 11.8 

kn (22 kph), the chances of lethal injury 

drop below 50 percent, while the 

probability asymptotically increases 

toward one hundred percent above 15 

kn (28 kph). 

The Sikuliaq will travel at a speed of 

5 kn (9 kph) while towing seismic 

survey gear. At this speed, both the 

possibility of striking a marine mammal 

and the possibility of a strike resulting 

in serious injury or mortality are 

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 discountable. Vessel 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. Jensen and Silber (2004) 

summarized vessel 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). No 

such incidents were reported for 

geophysical survey vessels during that 

time period. 

It is possible for vessel strikes to occur 

while traveling at slow speeds. For 

example, a hydrographic survey vessel 

traveling at low speed (5.5 kn (10 kph)) 

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 confidence interval = 0–5.5 

× 10¥6; NMFS, 2013). In addition, a 

research vessel 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 

propose a robust vessel strike avoidance 

protocol (see Proposed Mitigation), 

which we believe eliminates any 

foreseeable risk of vessel 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 

proposed 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, 

the possibility of vessel strike is 

discountable and, further, 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 vessel 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 marine mammal is dead 

and is on a beach or shore of the United 

States; or in waters under the 

jurisdiction of the United States 

(including any navigable waters); or a 

marine mammal is alive and is on a 

beach or shore of the United States and 


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is unable to return to the water; 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 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, vessel 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 predispose 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. MFA 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 military 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 noiseinduced 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 mid-frequency 

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). 

Military 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 

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 in the historical midfrequency 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 ‘‘midVerDate Sep<11>2014 17:23 Oct 07, 2024 Jkt 265001 PO 00000 Frm 00027 Fmt 4703 Sfmt 4703 E:\FR\FM\08OCN1.SGM 08OCN1

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frequency’’) 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., MFA sonar) 

will likely be closer to the whales 

(because attenuation limits the range of 

detection of mid-frequencies) 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 10 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 

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 review of possible stranding 

associations with seismic surveys 

(Castellote and Llorens, 2016) states 

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’ 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 10 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. 


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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 be broadly 

associated with the survey itself, as 

opposed to use of seismic airguns. An 

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 LamontDoherty Earth Observatory (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). 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, based on the 

best available information, do not 

expect a stranding to occur. 

Entanglement—Entanglements occur 

when marine mammals become 

wrapped around cables, lines, nets, or 

other objects suspended in the water 

column. During seismic operations, 

numerous cables, lines, and other 

objects primarily associated with the 

airgun array and hydrophone streamers 

will be towed behind the Sikuliaq near 

the water’s surface. However, we are not 

aware of any cases of entanglement of 

marine mammals in seismic survey 

equipment. No incidents of 

entanglement of marine mammals with 

seismic survey gear have been 

documented in over 54,000 nautical 

miles (100,000 km) of previous NSFfunded 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., 2005a; 

Haley and Ireland 2006; SIO and NSF 

2006b; 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. There are relatively 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 

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., 

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). 

Sound pressure levels 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. (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 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. 


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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 longlasting. 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 3 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 recently described 

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 1 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, 

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 review article concluded that, while 

laboratory results provide scientific 

evidence for high-intensity and lowfrequency 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 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 generally 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. 


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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 of Marine Mammals 

This section provides an estimate of 

the number of incidental takes proposed 

for authorization through the IHA, 

which will inform NMFS’ consideration 

of ‘‘small numbers,’’ the negligible 

impact determinations, and impacts on 

subsistence uses. 

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). 

Proposed authorized takes would be 

by Level B harassment only, in the form 

behavioral reactions and/or TTS for 

individual marine mammals resulting 

from exposure to noise from the use of 

seismic airguns. Based on the nature of 

the activity and the anticipated 

effectiveness of the mitigation measures 

(i.e., shutdown) discussed in detail 

below in the Proposed Mitigation 

section, Level A harassment is neither 

anticipated nor proposed to be 

authorized. 

As described previously, no serious 

injury or mortality is anticipated or 

proposed to be authorized for this 

activity. Below, we describe how the 

proposed take numbers are estimated. 

For acoustic impacts, generally 

speaking, we estimate take by 

considering: (1) acoustic thresholds 

above which NMFS believes the best 

available science indicates marine 

mammals will likely 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 factors can 

contribute to a basic calculation to 

provide an initial prediction of potential 

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 estimates. 

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—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 or exposure 

context (e.g., frequency, predictability, 

duty cycle, duration of the exposure, 

signal-to-noise ratio, distance to the 

source), the environment (e.g., 

bathymetry, other noises in the area, 

predators in the area), and the receiving 

animals (hearing, motivation, 

experience, demography, life stage, 

depth) and can be difficult to predict 

(e.g., Southall et al., 2007, 2021, Ellison 

et al., 2012). Based on what the 

available science indicates and the 

practical need to use a threshold based 

on a metric that is both predictable and 

measurable for most activities, NMFS 

typically uses a generalized acoustic 

threshold based on received level to 

estimate the onset of behavioral 

harassment. NMFS generally predicts 

that marine mammals are likely to be 

behaviorally harassed in a manner 

considered to be Level B harassment 

when exposed to underwater 

anthropogenic noise above root-meansquared pressure received levels (RMS 

SPL) of 120 dB (referenced to 1 

micropascal (re 1 mPa)) for continuous 

(e.g., vibratory pile driving, drilling) and 

above RMS SPL 160 dB re 1 mPa for nonexplosive impulsive (e.g., seismic 

airguns) or intermittent (e.g., scientific 

sonar) sources. Generally speaking, 

Level B harassment take estimates based 

on these behavioral harassment 

thresholds are expected to include any 

likely takes by TTS as, in most cases, 

the likelihood of TTS occurs at 

distances from the source less than 

those at which behavioral harassment is 

likely. TTS of a sufficient degree can 

manifest as behavioral harassment, as 

reduced hearing sensitivity and the 

potential reduced opportunities to 

detect important signals (conspecific 

communication, predators, prey) may 


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result in changes in behavior patterns 

that would not otherwise occur. 

SIO’s proposed activity includes the 

use of impulsive seismic sources (i.e., 

airguns), and therefore the 160 dB re 1 

mPa is applicable. 

Level A harassment—NMFS’ 

Technical Guidance for Assessing the 

Effects of Anthropogenic Sound on 

Marine Mammal Hearing (Version 2.0; 

NMFS, 2018) and the draft Updated 

Technical Guidance (NMFS, 2024) 

identify 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). This proposed IHA 

estimates Level A harassment using the 

existing Technical Guidance (NMFS, 

2018) as well as the draft Updated 

Technical Guidance (NMFS, 2024) 

because at the time of the final agency 

decision on this request for incidental 

take, NMFS may have made a final 

agency decision on the draft Guidance. 

These thresholds are provided in the 

tables below. The references, analysis, 

and methodology used in the 

development of the thresholds are 

described in NMFS’ 2018 Technical 

Guidance and NMFS’ 2024 draft 

Updated Technical Guidance, both of 

which may be accessed at: https://

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/marinemammal-acoustic-technical-guidance. 

SIO’s proposed activity includes the 

use of impulsive seismic sources (i.e. 

airguns). 

TABLE 4—NMFS’ 2018 THRESHOLDS IDENTIFYING THE ONSET OF PERMANENT THRESHOLD SHIFT (PTS) 

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. 

Based on the outcome of these 

comparisons/analyses using the draft 

Updated Technical Guidance, the lowfrequency cetacean isopleth is slightly 

higher using the updated guidance, and 

the mid-frequency cetacean (renamed 

high-frequency cetacean) and highfrequency cetacean (renamed very-high 

frequency cetacean) are the same as 

those calculated using the 2018 

Technical Guidance. Given that the 

updated Level A harassment isopleths 

are smaller than the proposed mitigation 

zone for all species (see the Proposed 

Mitigation section), there will be no 

change to the proposed take numbers or 

mitigation zones if/when the 2024 draft 

Technical Guidance is finalized. 

TABLE 5—NMFS’ 2024 THRESHOLDS IDENTIFYING THE ONSET OF AUDITORY INJURY (AUD INJ) 

Hearing group 

PTS onset acoustic thresholds * 

(received level) 

Impulsive Non-impulsive 

Low-Frequency (LF) Cetaceans ...................................... Cell 1: Lp, 0-pk,flat: 222 dB; LE, p, LF,24h: 183 dB .............. Cell 2: LE, P, LF,24h: 197 dB. 

High-Frequency (HF) Cetaceans ..................................... Cell 3: Lp, 0-pk,flat: 230 dB; LE,HF,24h : 193 dB ................. Cell 4: LE, p, HF,24h: 201 dB. 

Very High-Frequency (VHF) Cetaceans .......................... Cell 5: Lpk, 0-pk, flat: 202 dB; LE, p, VHF,24hr: 159 dB ........ Cell 6: LE, p, VHF, 24h: 181 

dB. 

Phocid Pinnipeds (PW) (Underwater) ............................. Cell 7: Lp 0-pk,flat: 223 dB; LE,PW,24h: 185 dB .................. Cell 8: LE, p, PW,24h: 195 

dB. 

Otariid Pinnipeds (OW) (Underwater) ............................. Cell 9: Lp 0-pk,flat: 230 dB; LE, p, OW,24h: 185 dB ............. Cell 10: LE, p, OW,24h: 199 

dB. 

* Dual metric criteria for impulsive sounds: Use whichever criteria results in the larger isopleth for calculating AUD INJ onset. If a non-impulsive 

sound has the potential of exceeding the peak sound pressure level criteria associated with impulsive sounds, the PK SPL criteria are recommended for consideration for non-impulsive sources. 

Note: Peak sound pressure level (Lp,0-pk) has a reference value of 1 μPa (underwater) and 20 μPa (in air), and weighted cumulative sound exposure level (LE,p) has a reference value of 1 μPa2s (underwater) and 20 μPa2s (in air). In this Table, criteria are abbreviated to be more reflective of International Organization for Standardization standards (ISO 2017; ISO 2020). The subscript ‘‘flat’’ is being included to indicate peak 

sound pressure are flat weighted or unweighted within the generalized hearing range of marine mammals underwater (i.e., 7 Hz to 165 kHz) or in 

air (i.e., 42 Hz to 52 kHz). The subscript associated with cumulative sound exposure level criteria indicates the designated marine mammal auditory weighting function (LF, HF, and VHF cetaceans, and PW, OW, PA, and OA pinnipeds) and that the recommended accumulation period is 24 

hours. The weighted cumulative sound exposure level criteria 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 criteria will be exceeded. 


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Ensonified Area 

Here, we describe operational and 

environmental parameters of the activity 

that are used in estimating the area 

ensonified above the acoustic 

thresholds, including source levels and 

transmission loss coefficient. 

When the Technical Guidance was 

published (NMFS, 2016), in recognition 

of the fact that ensonified area/volume 

could be more technically challenging 

to predict because of the duration 

component in the new thresholds, we 

developed a user spreadsheet that 

includes tools to help predict a simple 

isopleth that can be used in conjunction 

with marine mammal density or 

occurrence to help predict takes. We 

note that because of some of the 

assumptions included in the methods 

used for these tools, we anticipate that 

isopleths produced are typically going 

to be overestimates of some degree, 

which may result in some degree of 

overestimation of Level A harassment 

take. However, these tools offer the best 

way to predict appropriate isopleths 

when more sophisticated 3D modeling 

methods are not available, and NMFS 

continues to develop ways to 

quantitatively refine these tools and will 

qualitatively address the output where 

appropriate. 

The proposed survey would entail the 

use of a 4-airgun array with a total 

discharge volume of 420 in3 at a tow 

depth of 3 m. SIO used modeling by the 

L–DEO, which determines the 160 dBrms

radius for the airgun source down to a 

maximum depth of 2,000 m. Received 

sound levels have been predicted by L– 

DEO’s model (Diebold et al. 2010) as a 

function of distance from the 4-airgun 

array. This modeling approach 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 constant-velocity 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 

(∼1,600 m), intermediate water depth on 

the slope (∼600–1,100 m), and shallow 

water (∼50 m) in the Gulf of Mexico 

(Tolstoy et al. 2009; Diebold et al. 2010). 

For deep and intermediate water 

cases, the field measurements cannot be 

used readily to derive the harassment 

isopleths, as at those sites the 

calibration hydrophone was located at a 

roughly constant depth of 350–550 m, 

which may not intersect all the SPL 

isopleths at their widest point from the 

sea surface down to the assumed 

maximum relevant water depth (∼2000 

m) for marine mammals. At short 

ranges, where the direct arrivals 

dominate and the effects of seafloor 

interactions are minimal, the data at the 

deep 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 at short ranges, sound levels for 

direct arrivals recorded by the 

calibration hydrophone and L–DEO 

model results for the same array tow 

depth are in good alignment (see figures 

12 and 14 in Diebold et al. 2010). 

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 

seafloor-reflected and sub-seafloorrefracted arrivals dominate, whereas the 

direct arrivals become weak and/or 

incoherent (see figures 11, 12, and 16 in 

Diebold et al. 2010). 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. 

The proposed low-energy survey 

would acquire data with the 4-airgun 

array at a tow depth of 3 m. For deep 

water (>1,000 m), we use the deep-water 

radii obtained from L–DEO model 

results down to a maximum water depth 

of 2,000 m for the airgun array. 

L–DEO’s modeling methodology is 

described in greater detail in SIO’s 

application. The estimated distances to 

the Level B harassment isopleth for the 

proposed airgun configuration are 

shown in table 6. 

TABLE 6—PREDICTED RADIAL DISTANCES FROM THE R/V SIKULIAQ SEISMIC SOURCE TO ISOPLETH CORRESPONDING TO

LEVEL B HARASSMENT THRESHOLD

Airgun configuration Tow depth 

(m) 

Water depth 

(m) 

Predicted 

distances (in m) 

to the Level B 

harassment 

threshold 

4 105-in3 airguns ....................................................................................................... 3 >1,000 1,408 

TABLE 7—MODELED RADIAL DISTANCE TO ISOPLETHS CORRESPONDING TO LEVEL A HARASSMENT THRESHOLDS

Low 

frequency 

cetaceans 

Mid 

frequency 

cetaceans 

High 

frequency 

cetaceans 

PTS SELcum ................................................................................................................................. 38.5 0 0.1 

PTS Peak ..................................................................................................................................... 12.4 NA/0 85.8 

The largest distance (in bold) of the dual criteria (SEL cum or Peak) was used to estimate threshold distances and potential takes by Level A 

harassment. 

NA not applicable or available and assumed to be 0. 

Table 7 presents the modeled PTS 

isopleths for each cetacean hearing 

group based on L–DEO modeling 

incorporated in the companion user 

spreadsheet, for the low-energy surveys 

with the shortest shot interval (i.e., 

greatest potential to cause PTS based on 

accumulated sound energy) (NMFS 

2018). 

Predicted distances to Level A 

harassment isopleths, which vary based 


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on marine mammal hearing groups, 

were calculated based on modeling 

performed by L–DEO using the Nucleus 

software program and the NMFS user 

spreadsheet, described below. The 

acoustic thresholds for impulsive 

sounds contained in the NMFS 

Technical Guidance were presented as 

dual metric acoustic thresholds using 

both SELcum and peak sound pressure 

metrics (NMFS, 2016). 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. 

The SELcum for the 4-airgun array is 

derived from calculating the modified 

farfield signature. The farfield signature 

is often used as a theoretical 

representation of the source level. To 

compute the farfield signature, the 

source level is estimated at a large 

distance (right) 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, it has been recognized that the 

source level from the theoretical farfield 

signature is never physically achieved at 

the source when the source is an array 

of multiple airguns separated in space 

(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 farfield 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 farfield signature. 

Because the farfield signature does not 

take into account the large array effect 

near the source and is calculated as a 

point source, the farfield signature is not 

an appropriate measure of the sound 

source level for large arrays. See SIO’s 

application for further detail on acoustic 

modeling. 

Auditory injury is unlikely to occur 

for mid-frequency cetaceans, given the 

very small modeled zones of injury for 

those species (all estimated zones are 

less than 15 m for mid-frequency 

cetaceans), in context of distributed 

source dynamics. 

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 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 anticipate that 

Level A harassment is a likely outcome 

for any mid-frequency cetacean and do 

not propose to authorize any take by 

Level A harassment for these species. 

The Level A and Level B harassment 

estimates are based on a consideration 

of the number of marine mammals that 

could be within the area around the 

operating airgun array where received 

levels of sound ≥160 dB re 1 mPa rms 

are predicted to occur. The estimated 

numbers are based on the densities 

(numbers per unit area) of marine 

mammals expected to occur in the area 

in the absence of seismic surveys. To 

the extent that marine mammals tend to 

move away from seismic sources before 

the sound level reaches the criterion 

level and tend not to approach an 

operating airgun array, these estimates 

likely overestimate the numbers actually 

exposed to the specified level of sound. 

Marine Mammal Occurrence 

In this section we provide information 

about the occurrence of marine 

mammals, including density or other 

relevant information which will inform 

the take calculations. 

For the proposed survey area, SIO 

used density data from the U.S. Navy’s 

Marine Species Density Database Phase 

III for the Mariana Islands Training and 

Testing (MITT) Study Area (DoN, 2018). 

The U.S. Navy modeled densities for 

two areas within the MITT: the Mariana 

Islands Training and Testing 

Representative Study Area, ∼580 km to 

the west of the proposed survey area, 

and the Transit Corridor Representative 

Study Area surrounding Wake Island, 

∼120 km to the east of the proposed 

survey area (DoN, 2018). The proposed 

survey area lies between the two MITT 

modeled areas and does not overlap 

either area. As the proposed tracklines 

are located closer to Wake Island than 

the Mariana Islands, the MITT seasonal 

density estimates for the Transit 

Corridor Representative Study Area 

were used here. As the survey is 

proposed for December 2024 to January 

2025, the densities for winter (December 

through February) were used to 

calculate takes for marine mammals. No 

densities were available for 

Deraniyagala’s beaked whale. However, 

the density for ginkgo-toothed beaked 

whale was applied to Deraniyagala’s 

beaked whale and ginkgo-toothed 

beaked whale as a combined group, as 

these two species are difficult to 

distinguish. 

Take Estimation 

Here, we describe how the 

information provided above is 

synthesized to produce a quantitative 

estimate of the take that is reasonably 

likely to occur and proposed for 

authorization. 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 the predicted isopleth 

corresponding to the Level A 

harassment and Level B harassment 

thresholds are calculated, as described 

above. Those radial distances were then 

used to calculate the area(s) around the 

airgun array predicted to be ensonified 

to sound levels that exceed the 

harassment thresholds. The distance for 

the 160-dB Level B harassment 

threshold and PTS (Level A harassment) 

thresholds (based on L–DEO model 

results) was used to draw a buffer 

around the area expected to be 

ensonified (i.e., the survey area). The 

ensonified areas were then increased by 

25 percent to account for potential 

delays, which is equivalent to adding 25 

percent to the proposed line km to be 

surveyed. The density for each species 

was then multiplied by the daily 

ensonified areas (increased as described 

above) and then multiplied by the 

number of survey days (14) to estimate 

potential takes (see appendix B of SIO’s 

application for more information). 

SIO assumed that their estimates of 

marine mammal exposures above 

harassment thresholds equate to take 

and requested authorization of those 

takes. Those estimates in turn form the 

basis for our proposed take 

authorization numbers. Based on the 

nature of the activity and the 

anticipated effectiveness of the 

mitigation measures (i.e., shutdown) 

discussed in detail below in the 

Proposed Mitigation section, Level A 

harassment is neither anticipated nor 

proposed to be authorized. Therefore we 

have added SIO’s estimated exposures 

above Level A harassment thresholds to 

their estimated exposures above the 

Level B harassment threshold to 

produce a total number of incidents of 

take by Level B harassment that is 

proposed for authorization. Estimated 

exposures and proposed take numbers 

for authorization are shown in table 8. 


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TABLE 8—ESTIMATED TAKE PROPOSED FOR AUTHORIZATION

Common name 

Estimated take Proposed 

authorized 

take 1 Abundance Percent of 

abundance Level B Level A 

Level B 

Blue Whale ............................................................................................................ 1 0 1 150 0.37 

Bryde’s Whale ....................................................................................................... 3 0 3 1,596 0.21 

Fin Whale .............................................................................................................. 1 0 1 46 1.44 

Humpback Whale 2 ................................................................................................ 10 0 10 2,673 0.37 

Minke Whale ......................................................................................................... 2 0 2 450 0.37 

Sei Whale .............................................................................................................. 1 0 3 2 821 0.24 

Omura’s Whale ..................................................................................................... 0 0 3 1 160 0.63 

Sperm Whale ........................................................................................................ 25 0 25 5,146 0.48 

Dwarf Sperm Whale .............................................................................................. 45 3 48 27,395 0.17 

Pygmy Sperm Whale ............................................................................................ 18 1 19 11,168 0.17 

Blainville’s Beaked Whale ..................................................................................... 8 0 8 3,376 0.23 

Cuvier’s Beaked Whale ......................................................................................... 41 0 41 2,642 1.56 

Longman’s Beaked Whale .................................................................................... 3 0 3 11,253 0.02 

Ginko-Toothed Beaked Whale .............................................................................. 21 0 21 7,567 0.16 

Deraniyagala’s Beaked Whale.

False Killer Whale ................................................................................................. 6 0 3 10 4,218 0.24 

Killer Whale ........................................................................................................... 1 0 3 5 253 1.98 

Melon-Headed Whale ........................................................................................... 30 0 3 95 16,551 0.57 

Pygmy Killer Whale ............................................................................................... 1 0 3 6 527 1.14 

Short-Finned Pilot Whale ...................................................................................... 23 0 23 6,583 0.04 

Bottlenose Dolphin ................................................................................................ 9 0 9 1,076 0.79 

Fraser’s Dolphin .................................................................................................... 28 0 28 76,476 0.04 

Pantropical Spotted Dolphin ................................................................................. 125 0 125 85,755 0.15 

Risso’s Dolphin ..................................................................................................... 5 0 27 17,184 0.16 

Rough-Toothed Dolphin ........................................................................................ 20 0 20 1,815 1.13

Spinner Dolphin ..................................................................................................... 21 0 3 98 5,232 1.87 

Striped Dolphin ...................................................................................................... 65 0 65 24,528 0.26 

1 Requested take authorization for marine mammals is Level A plus Level B calculated takes. 

2All takes are assumed to be from the Western North Pacific DPS. 

3Takes have been increased to mean group size for the Mariana Islands based on Fulling et al. (2011) where available or for Hawaii (e.g., Risso’s dolphin and killer whale) as reported by Bradford et al. (2017), or Jefferson et al. (2015). 

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, NMFS considers 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), 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, and 

impact on operations. 

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 shutdown zone (SZ), 

within which observation of certain 

marine mammals requires shutdown of 

the acoustic source, a buffer zone, and 

to the extent possible depending on 

conditions, the surrounding waters. The 

buffer zone means an area beyond the 

SZ to be monitored for the presence of 

marine mammals that may enter the SZ. 

During pre-start clearance monitoring 

(i.e., before ramp-up begins), the buffer 

zone also acts as an extension of the SZ 

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– 

100 m SZ, out to a radius of 200 m from 

the edges of the airgun array (100–200 

m). This 200-m zone (SZ plus buffer) 

represents the pre-start clearance zone. 

Visual monitoring of the SZ and 

adjacent waters (buffer plus surrounding 

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 SZ by alerting the 

visual observer and crew of marine 

mammals that are outside of, but may 

approach and enter, the SZ. 

During survey operations (e.g., any 

day on which use of the airgun array is 

planned to occur and whenever the 

airgun array is in the water, whether 


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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 1 hour after use of the 

airgun array 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 

SZ and buffer zone. These zones shall 

be based upon the radial distance from 

the edges of the airgun array (rather than 

being based on the center of the array 

or around the vessel itself). During use 

of the airgun array (i.e., anytime airguns 

are active, including ramp-up), 

detections of marine mammals within 

the buffer zone (but outside the SZ) 

shall be communicated to the operator 

to prepare for the potential shutdown of 

the airgun array. 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 airgun array is not operating for 

comparison of sighting rates and 

behavior with and without use of the 

airgun array 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 1 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. 

Establishment of Shutdown and PreStart Clearance Zones 

A SZ 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 SZ with a 100-m radius. The 

100-m SZ 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 

airgun array 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 airgun array and 

includes the SZ 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 100-m SZ 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 100-m SZ 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 expect that 

100 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 SZ, doubling the SZ size 

during pre-clearance. 

An extended SZ of 500 m must be 

implemented for all beaked whales, a 

large whale with a calf, and groups of 

six or more large whales. No buffer of 

this extended SZ is required, as NMFS 

concludes that this extended SZ is 

sufficiently protective to mitigate 

harassment to these groups. 

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. The intent 

of pre-start clearance observation (30 

minutes) is to ensure no marine 

mammals are observed within the prestart clearance zone (or extended SZ, for 

beaked whales, a large whale with a 

calf, and groups of six or more large 

whales) prior to the beginning of rampup. During the 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 the 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 prior to the 

sound source reaching full intensity. 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 airgun array. 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 SZ) 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 

shutdown or buffer zone. If a marine 

mammal is observed within the pre-start 

clearance zone (or extended SZ, for 

beaked whales, a large whale with a 

calf, and groups of six or more large 

whales) 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 30 minutes for 

all mysticetes and all other odontocetes, 

including sperm whales, beaked whales, 

and large delphinids, such as pilot 

whales); 

• Ramp-up must begin by activating 

one GI airgun and shall continue in 

stages, doubling the number of active 

elements at the commencement of each 

stage, with each stage lasting no less 

than 5 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 SZ 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 ramp-up 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 


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minutes prior to beginning ramp-up. 

Airgun array activation may only occur 

at times of poor visibility where 

operational planning cannot reasonably 

avoid such circumstances; 

• If the airgun array is shut down for 

brief periods (i.e., less than 30 minutes) 

for reasons other than implementation 

of prescribed mitigation (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 

acoustic detections of marine mammals 

have occurred within the pre-start 

clearance zone (or extended SZ, where 

applicable). For any longer shutdown, 

pre-start clearance observation and 

ramp-up are required; and 

• Testing of the airgun array 

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 minutes. 

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 call for shutdown of the 

airgun array if a marine mammal is 

detected within the applicable SZ. The 

operator must also establish and 

maintain clear lines of communication 

directly between PSOs on duty and 

crew controlling the airgun array 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 

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

than delphinids, see below) is detected 

acoustically and localized within the 

applicable SZ, the airgun array will be 

shut down. When shutdown is called 

for by a PSO, the airgun array will be 

immediately deactivated and any 

dispute resolved only following 

deactivation. 

Following a shutdown, airgun activity 

would not resume until the marine 

mammal has cleared the SZ. The animal 

would be considered to have cleared the 

SZ if it is visually observed to have 

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

required to fully exit the buffer zone 

where applicable), or it has not been 

seen within the SZ for 15 minutes for 

small odontocetes or 30 minutes for all 

mysticetes and all other odontocetes, 

including sperm whales, beaked whales, 

and large delphinids, such as pilot 

whales. 

The shutdown requirement is waived 

for specific genera of small dolphins if 

an individual is detected within the SZ. 

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 the specific genera of 

small dolphins (Lagenodelphis, 

Stenella, Steno, and Tursiops). 

We include this small dolphin 

exception because shutdown 

requirements for these species 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 mid-frequency 

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 (e.g., Barkaszi 

et al., 2012; Barkaszi and Kelly, 2018). 

The potential for increased shutdowns 

resulting from such a measure would 

require the Sikuliaq 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 midfrequency 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 Sikuliaq. 

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 SZ). 

SIO must implement shutdown if a 

marine mammal species for which take 

was not authorized or a species for 

which authorization was granted but the 

authorized takes have been met 

approaches the Level A or Level B 

harassment zones. SIO 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 two-thirds 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 Mitigation 

Measures 

Vessel personnel should use an 

appropriate reference guide that 

includes identifying information on all 

marine mammals that may be 

encountered. Vessel operators must 

comply with the below measures except 

under extraordinary circumstances 

when the safety of the vessel or crew is 

in doubt or the safety of life at sea is in 

question. 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. 

Vessel operators and crews must 

maintain a vigilant watch for all marine 

mammals and slow down, stop their 

vessel, or alter course, as appropriate 

and regardless of vessel size, to avoid 

striking any marine mammal. A single 

marine mammal at the surface may 

indicate the presence of submerged 

animals in the vicinity of the vessel; 

therefore, precautionary measures 

should always be exercised. A visual 

observer aboard the vessel must monitor 

a vessel strike avoidance zone around 

the vessel (separation 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) 


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distinguish marine mammals from other 

phenomena and (2) broadly to identify 

a marine mammal as a right whale, 

other whale (defined in this context as 

sperm whales or baleen whales other 

than right whales), or other marine 

mammals. 

Vessel speeds must be reduced to 10 

kn (18.5 kph) 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). 

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. 

Based on our evaluation of the 

applicant’s proposed measures, as well 

as other measures considered by NMFS, 

NMFS has preliminarily determined 

that the proposed 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. 

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 while conducting the activities. 

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 

activity; 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 Sikuliaq. 

Two visual PSOs would be on duty at 

all times during daytime hours. 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. SIO must use dedicated, 

trained, and NMFS-approved PSOs. At 

least one visual PSO 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. 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. Monitoring shall be 

conducted in accordance with the 

following requirements: 

• 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); and 

• PSOs shall have successfully 

completed an approved PSO training 

course appropriate for their designated 

task (visual). 

• 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; 

• 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 


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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 electronic data 

collection forms. PSOs shall record 

detailed information about any 

implementation of mitigation 

requirements, including the distance of 

animals to the airgun array 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 airgun array. If required 

mitigation was not implemented, PSOs 

should record a description of the 

circumstances. At a minimum, the 

following information must be recorded: 

Æ Vessel name, vessel size and type, 

maximum speed capability of vessel; 

Æ Dates (MM/DD/YYYY) of 

departures and returns to port with port 

name; 

Æ PSO names and affiliations, PSO ID 

(initials or other identifier); 

Æ Date (MM/DD/YYYY) and 

participants of PSO briefings; 

Æ Visual monitoring equipment used 

(description); 

Æ PSO location on vessel and height 

(meters) of observation location above 

water surface; 

Æ Watch status (description); 

Æ Dates (MM/DD/YYYY) and times 

(Greenwich Mean Time/UTC) of survey 

on/off effort and times (GMC/UTC) 

corresponding with PSO on/off effort; 

Æ Vessel location (decimal degrees) 

when survey effort began and ended and 

vessel location at beginning and end of 

visual PSO duty shifts; 

Æ Vessel location (decimal degrees) at 

30-second intervals if obtainable from 

data collection software, otherwise at 

practical regular interval; 

Æ Vessel heading (compass heading) 

and speed (knots) at beginning and end 

of visual PSO duty shifts and upon any 

change; 

Æ Water depth (meters) (if obtainable 

from data collection software); 

Æ 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; 

Æ Factors that may have contributed 

to impaired observations during each 

PSO shift change or as needed as 

environmental conditions changed 

(description) (e.g., vessel traffic, 

equipment malfunctions); and 

Æ Vessel/Survey activity information 

(and changes thereof) (description), 

such as airgun 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.). 

• Upon visual observation of any 

marine mammals, the following 

information must be recorded: 

Æ Sighting ID (numeric); 

Æ Watch status (sighting made by 

PSO on/off effort, opportunistic, crew, 

alternate vessel/platform); 

Æ Location of PSO/observer 

(description); 

Æ Vessel activity at the time of the 

sighting (e.g., deploying, recovering, 

testing, shooting, data acquisition, 

other); 

Æ PSO who sighted the animal/ID; 

Æ Time/date of sighting (GMT/UTC, 

MM/DD/YYYY); 

Æ Initial detection method 

(description); 

Æ Sighting cue (description); 

Æ Vessel location at time of sighting 

(decimal degrees); 

Æ Water depth (meters); 

Æ Direction of vessel’s travel 

(compass direction); 

Æ Speed (knots) of the vessel from 

which the observation was made; 

Æ Direction of animal’s travel relative 

to the vessel (description, compass 

heading); 

Æ Bearing to sighting (degrees); 

Æ 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; 

Æ Species reliability (an indicator of 

confidence in identification) (1 = 

unsure/possible, 2 = probable, 3 = 

definite/sure, 9 = unknown/not 

recorded); 

Æ Estimated distance to the animal 

(meters) and method of estimating 

distance; 

Æ Estimated number of animals (high/ 

low/best) (numeric); 

Æ Estimated number of animals by 

cohort (adults, yearlings, juveniles, 

calves, group composition, etc.); 

Æ 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); 

Æ 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); 

Æ Animal’s closest point of approach 

(meters) and/or closest distance from 

any element of the airgun array; 

Æ Description of any actions 

implemented in response to the sighting 

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

time and location of the action; 

Æ Photos (Yes/No); 

Æ Photo Frame Numbers (List of 

numbers); and 

Æ Conditions at time of sighting 

(Visibility; Beaufort Sea State). 

Reporting 

SIO shall submit a draft 

comprehensive report on all activities 

and monitoring results within 90 days 

of the completion of the survey or 

expiration of the IHA, whichever comes 

sooner. The report must describe all 

activities conducted and sightings of 

marine mammals, must provide full 

documentation of methods, results, and 

interpretation pertaining to all 

monitoring, and must summarize the 

dates and locations of survey operations 

and all marine mammal sightings (dates, 

times, locations, activities, associated 

survey activities). The draft report shall 

also include geo-referenced timestamped vessel tracklines for all time 

periods during which airgun arrays 

were operating. Tracklines should 

include points recording any change in 

airgun array status (e.g., when the 

sources began operating, when they 

were turned off, or when they changed 

operational status such as from full 

array to single gun or vice versa). 

Geographic Information System files 

shall be provided in Environmental 

Systems Research Institute 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. The report must summarize 

data collected as described above in 

Proposed Monitoring and Reporting. 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 the survey activities 

discover an injured or dead marine 

mammal, the SIO shall report the 


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incident to the Office of Protected 

Resources (OPR) and NMFS 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 strike 

of a marine mammal by any vessel 

involved in the activities covered by the 

authorization, SIO shall report the 

incident to OPR and NMFS 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, BSS, 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 

marine mammal 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). 

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 impacts or responses (e.g., 

intensity, duration), the context of any 

impacts or responses (e.g., critical 

reproductive time or location, foraging 

impacts affecting energetics), 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’ 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 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, the discussion of 

our analysis applies to all the species 

listed in table 1, given that the 

anticipated effects of this activity on 

these different marine mammal stocks 

are expected to be similar, except where 

a species- or stock-specific discussion is 

warranted. NMFS does not anticipate 

that serious injury or mortality would 

occur as a result of SIO’s planned 

survey, even in the absence of 

mitigation, and no serious injury or 

mortality is proposed to be authorized. 

As discussed in the Potential Effects of 

Specified Activities on Marine 

Mammals and Their Habitat section 

above, non-auditory physical effects and 

vessel strike are not expected to occur. 

NMFS expects that all potential take 

would be in the form of Level B 

behavioral harassment in the form of 

temporary avoidance of the area or 

decreased foraging (if such activity was 

occurring), responses that are 

considered to be of low severity, and 

with no lasting biological consequences 

(e.g., Southall et al., 2007, 2021). These 

low-level impacts of behavioral 

harassment are not likely to impact the 

overall fitness of any individual or lead 

to population level effects of any 

species. As described above, Level A 

harassment is not expected to occur 

given the estimated small size of the 

Level A harassment zones. 

In addition, the maximum expected 

Level B harassment zone around the 

survey vessel is 1,408 m. Therefore, the 

ensonified area surrounding the vessel 

is relatively small compared to the 

overall distribution of animals in the 

area and their use of the habitat. 

Feeding behavior is not likely to be 

significantly impacted as prey species 

are mobile and are broadly distributed 

throughout the survey area; 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 

short duration (14 survey days) and 

temporary nature of the disturbance and 

the availability of similar habitat and 

resources in the surrounding area, the 

impacts to marine mammals and marine 

mammal prey species are not expected 

to cause significant or long-term fitness 

consequences for individual marine 

mammals or their populations. 

Additionally, the acoustic ‘‘footprint’’ 

of the proposed survey would be very 

small relative to the ranges of all 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. The seismic array would be active 

24 hours per day throughout the 

duration of the proposed survey. 

However, the very brief overall duration 

of the proposed survey (14 survey days) 

would further limit potential impacts 

that may occur as a result of the 

proposed activity. 

Of the marine mammal species that 

are likely to occur in the project area, 

the following species are listed as 

endangered under the ESA: humpback 

whales (Western North Pacific DPS), 

blue whales, fin whales, sei whales, and 

sperm whales. The take numbers 

proposed for authorization for these 

species (table 6) are minimal relative to 

their modeled population sizes; 

therefore, we do not expect populationlevel impacts to any of these species. 

Moreover, the actual range of the 

populations extends past the area 

covered by the model, so modeled 

population sizes are likely smaller than 

their actual population size. The other 

marine mammal species that may be 

taken by harassment during SIO’s 

seismic survey are not listed as 

threatened or endangered under the 

ESA. There is no designated critical 


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habitat for any ESA-listed marine 

mammals within the project area. 

There are no rookeries, mating, or 

calving grounds known to be 

biologically important to marine 

mammals within the survey area, and 

there are no feeding areas known to be 

biologically important to marine 

mammals within the survey area. 

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 any of 

the species or stocks through effects on 

annual rates of recruitment or survival: 

• No serious injury or mortality is 

anticipated or authorized; 

• The proposed activity is temporary 

and of relatively short duration (27 days 

total with 14 days of planned survey 

activity); 

• The anticipated impacts of the 

proposed activity on marine mammals 

would be temporary behavioral changes 

due to avoidance of the ensonified area, 

which is relatively small (see tables 4 

and 5); 

• The availability of alternative 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 is readily abundant; 

• 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 

are expected to reduce the number and 

severity of takes, to the extent 

practicable, by visually and/or 

acoustically detecting marine mammals 

within the established zones and 

implementing corresponding mitigation 

measures (e.g., delay; shutdown). 

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 monitoring and mitigation 

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 previously, only take of 

small numbers of marine mammals 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 number of takes NMFS proposes 

to authorize is below one-third of the 

modeled abundance for all relevant 

populations (specifically, take of 

individuals is less than 2 percent of the 

modeled abundance of each affected 

population, see table 6). This is 

conservative because the modeled 

abundance represents a population of 

the species and we assume all takes are 

of different individual animals, which is 

likely not the case. Some individuals 

may be encountered multiple times in a 

day, but PSOs would count them as 

separate individuals if they cannot be 

identified. 

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 would 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. 

Endangered Species Act 

Section 7(a)(2) of the ESA of 1973 (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 humpback whales (Western North 

Pacific DPS), blue whales, fin whales, 

sei whales, and sperm whales, which 

are listed under the ESA. The NMFS 

Office of Protected Resources (OPR) 

Permits and Conservation Division has 

requested initiation of section 7 

consultation with the 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 SIO for conducting a marine 

geophysical survey in the Nauru Basin 

of greater Micronesia in the NW Pacific 

Ocean from December 2024-January 

2025, 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/national/ 

marine-mammal-protection/incidentaltake-authorizations-research-and-otheractivities. 

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 marine 

geophysical survey. We also request 

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, 1-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 Activity section of this notice 

is planned or (2) the activities as 

described in the Description of 

Proposed Activity 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: 

• 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 1 year from 

expiration of the initial IHA). 


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• The request for renewal must 

include the following: 

(1) 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). 

(2) 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. 

• 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: October 3, 2024. 

Kimberly Damon-Randall, 

Director, Office of Protected Resources, 

National Marine Fisheries Service. 

[FR Doc. 2024–23250 Filed 10–7–24; 8:45 am] 

BILLING CODE 3510–22–P 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric 

Administration 

[RTID 0648–XE296] 

Takes of Marine Mammals Incidental to 

Specified Activities; Takes of Marine 

Mammals Incidental to Marine Site 

Characterization Surveys Off Rhode 

Island and Massachusetts 

AGENCY: National Marine Fisheries 

Service (NMFS), National Oceanic and 

Atmospheric Administration (NOAA), 

Commerce. 

ACTION: Notice; issuance of an incidental 

harassment authorization. 

SUMMARY: In accordance with the 

regulations implementing the Marine 

Mammal Protection Act (MMPA) as 

amended, notification is hereby given 

that NMFS has issued an incidental 

harassment authorization (IHA) to Bay 

State Wind, LLC (Bay State Wind), to 

incidentally harass marine mammals 

during marine site characterization 

surveys off the coast of Rhode Island 

and Massachusetts in the Bureau of 

Ocean Energy Management (BOEM) 

Commercial Lease of Submerged Lands 

for Renewable Energy Development on 

the Outer Continental Shelf (OCS) Lease 

Area OCS–A 0500 and the associated 

export cable route (ECR) area. 

DATES: The authorization is effective 

from October 6, 2024, to October 5, 

2025. 

ADDRESSES: 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/national/

marine-mammal-protection/incidentaltake-authorizations-other-energyactivities-renewable. In case of problems 

accessing these documents, please call 

the contact listed below. 

FOR FURTHER INFORMATION CONTACT: 

Rachel Hilt, Office of Protected 

Resources, NMFS, (301) 427–8401. 

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 IHA 

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 monitoring and 

reporting of the takings. The definitions 

of all applicable MMPA statutory terms 

cited above are included in the relevant 

sections below. 

History of Request 

On October 6, 2022, NMFS issued an 

IHA to ;rsted (parent company of Bay 

State Wind) to take marine mammals 

incidental to marine site 

characterization surveys in Lease Areas 

OCS–A 0486, 0487, 0500 off the coasts 

from New York to Massachusetts and 

along potential ECRs to landfall 

locations between Raritan Bay (part of 

the New York Bight) and Falmouth, 

Massachusetts (87 FR 61575; October 

12, 2022). On May 26, 2023, NMFS 

received a request for a renewal of that 

initial IHA because ;rsted’s marine site 

characterization surveys under the 

initial IHA had not yet been completed 

and more time was required. The 

renewal IHA was issued on September 

29, 2023 (88 FR 62337, October 5, 2023). 

;rsted has complied with all the 

requirements (e.g., mitigation, 

monitoring, and reporting) of the 

previous IHAs in Lease Areas OCS–A 

0486, 0487, and 0500. 

On March 27, 2024, NMFS received a 

request from Bay State Wind for an IHA 

to take marine mammals incidental to 

conducting marine site characterization 

surveys off the coasts of Rhode Island 

and Massachusetts. This request was 

limited to planned survey activity in 

OCS–A 0500 (i.e., ;rsted’s planned Bay 

State Wind development) and the 

associated ECR area. Following NMFS’ 

review of the application, Bay State 

Wind submitted a revised version on 

June 10, 2024. Following additional 

review of the application, Bay State 

Wind submitted another revised version 

on July 29, 2024, which was deemed 

adequate and complete on August 1, 

2024. Bay State Wind’s request is for 

take of 17 species of marine mammals, 

by Level B harassment only. Neither Bay 

State Wind nor NMFS expect serious 

injury or mortality to result from this 

activity and, therefore, an IHA is 

appropriate. There are no changes from 

the proposed IHA to the final IHA. 

Description of the Activity and 

Anticipated Impacts 

Overview 

Bay State Wind will conduct marine 

site characterization surveys, including 

high-resolution geophysical (HRG) 

surveys and geotechnical surveys, in 

BOEM Lease Area OCS–A 0500, and the 

associated ECR. The purpose of the 

marine site characterization surveys is 

to collect data concerning seabed 

(geophysical, geotechnical, and 

geohazard), ecological, and 

archeological conditions within the 

footprint of the offshore wind facility 

development. Surveys are also 

conducted to support engineering 


ddrumheller on DSK120RN23PROD with NOTICES1