Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Low-Energy Geophysical Survey in the Southwest Atlantic Ocean

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XR007

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Low-Energy Geophysical Survey in the Southwest Atlantic 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 has received a request from the Scripps Institute of Oceanography (SIO) for authorization to take marine mammals incidental to a low-energy marine geophysical survey in the Southwest Atlantic 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-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 authorizations and agency responses will be summarized in the final notice of our decision.

DATES:

Comments and information must be received no later than September 11, 2019.

ADDRESSES:

Comments should be addressed to Jolie Harrison, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service. Physical comments should be sent to 1315 East-West Highway, Silver Spring, MD 20910 and electronic comments should be sent to

ITP.Fowler@noaa.gov.

Instructions:

NMFS is not responsible for comments sent by any other method, to any other address or individual, or received after the end of the comment period. Comments received electronically, including all attachments, must not exceed a 25-megabyte file size. Attachments to electronic comments will be accepted in Microsoft Word or Excel or Adobe PDF file formats only. 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-under-marine-mammal-protection-act

without change. All personal identifying information (

e.g.,

name, address) voluntarily submitted by the commenter may be publicly accessible. Do not submit confidential business information or otherwise sensitive or protected information.

FOR FURTHER INFORMATION CONTACT:

Amy Fowler, Office of Protected Resources, NMFS, (301) 427-8401. Electronic copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at:

https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act.

In case of problems accessing these documents, please call the contact listed above.

SUPPLEMENTARY INFORMATION:

Background

The MMPA prohibits the “take” of marine mammals, with certain exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361

et seq.

) direct the Secretary of Commerce (as delegated to NMFS) to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and either regulations are issued or, if the taking is limited to harassment, a notice of a proposed incidental take authorization may be 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 such species or stocks for taking for certain subsistence uses (referred to in shorthand as “mitigation”); and requirements pertaining to the mitigation, monitoring and reporting of such takings are set forth.

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 incidental harassment authorization) with respect to potential impacts on the human environment.

This action is consistent with categories of activities identified in Categorical Exclusion B4 (incidental harassment authorizations with no anticipated serious injury or mortality) of the Companion Manual for NOAA Administrative Order 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.

We will review all comments submitted in response to this notice prior to concluding our NEPA process or making a final decision on the IHA request.

Summary of Request

On March 13, 2019, NMFS received a request from SIO for an IHA to take marine mammals incidental to conducting a low-energy marine geophysical survey in the Southwest Atlantic Ocean. The application was deemed adequate and complete on May 20, 2019. SIO's request is for take of a small number of 49 species of marine mammals by Level B harassment. Neither SIO nor NMFS expects serious injury or mortality to result from this activity and, therefore, an IHA is appropriate. The planned activity is not expected to exceed one year, hence, we do not expect subsequent MMPA incidental harassment authorizations would be issued for this particular activity.

Description of Proposed Activity

Overview

SIO plans to conduct low-energy marine seismic surveys in the Southwest Atlantic Ocean during September-October 2019. The seismic surveys would be conducted in the Exclusive Economic Zone (EEZ) of the Falkland Islands and International Waters, with water depths ranging from ~50-5700 meters (m) (See Figure 1 in the IHA application). The surveys would involve one source vessel, R/V

Thomas G. Thompson

(R/V

Thompson

). The

Thompson

would deploy up to two 45-in

3

GI airguns at a depth of 2-4 m with a maximum total volume of ~90 in

3

along predetermined tracklines associated with potential coring sites.

Dates and Duration

The seismic survey would be carried out for approximately 28 days. The

Thompson

would likely depart from Montevideo, Uruguay, on or about September 12, 2019 and would return to Montevideo on or about October 29, 2018. An additional 10 days are allotted to collecting cores and measuring water properties/collecting water samples and 5 contingency days have been allotted for adverse weather conditions. Transits from Montevideo to and from the project area would take approximately 2.5 days each, for a total of 5 transit days. Some deviation in timing could result from unforeseen events such as weather, logistical issues, or mechanical issues with the research vessel and/or equipment. Seismic activities would occur 24 hours per day during the proposed survey.

Specific Geographic Region

The proposed surveys would take place within the EEZ of the Falkland Islands and in International Waters of the Southwest Atlantic Ocean, between approximately 42.75° and 49.5° S, and 55.75° and 61.1° W. Work with occur over three survey areas, with these survey areas and representative tracklines shown in Figure 1 of the IHA application. The

Thompson

would depart from and return to Montevideo, Uruguay.

Detailed Description of Specific Activity

SIO proposes to conduct low-energy seismic surveys low-energy seismic surveys in the Southwest Atlantic Ocean in the EEZ of the Falkland Islands and in International Waters between approximately 42.75° and 49.5° S, and 55.75° and 61.1° W. Within this larger area, there are 3 separate survey areas with these survey areas and representative survey tracklines shown in Figure 1 in the IHA application. All data acquisition in Survey Areas 1 and 3 would occur in water >1,000 m deep. Area 2 ranges in depth from 50-5,700 m. The proposed surveys would be in support of a potential future International Ocean Discovery Program (IODP) project and would examine the histories of important deep ocean water masses that originate in the Southern Ocean and intersect the continental margin of Argentina. The proposed surveys would thus take place in an area that is of interest to the IODP. To achieve the program's goals, the Principal Investigators propose to collect low-energy, high-resolution multi-channel seismic (MCS) profiles and sediment cores, and measure water properties.

The procedures to be used for the seismic surveys would be similar to those used during previous seismic surveys by SIO and would use conventional seismic methodology. The surveys would involve one source vessel, R/V

Thompson,

which is managed by University of Washington (UW). The R/V

Thompson

would deploy up to two 45-in

3

GI airguns as an energy source with a maximum total volume of ~90 in

3

. The receiving system would consist of one hydrophone streamer, 200-1,600 m in length, as described below. As the airguns are towed along the survey lines, the hydrophone streamer would receive the returning acoustic signals and transfer the data to the on-board processing system.

The proposed cruise would consist of digital bathymetric, echosounding, and MCS surveys within three areas to collect data on ocean circulation and climate evolution and to enable the selection and analysis of potential future IODP drillsites (Survey Areas 1-3 in Fig. 1). The airgun array would be operated in one of two different types of array modes. The first would be highest-quality survey mode to collect the highest-quality seismic reflection data at approximately 18 potential IODP drill sites. The second mode would be a reconnaissance mode, which is quicker, and will occur at approximately 75 coring locations, primarily in Survey Area 2. The reconnaissance mode also allows for operations to occur in poor weather where the use of streamer longer than 200-m may not be possible safely.

The reconnaissance mode is carried out using either one or two 45-in

3

airguns, with airguns spaced 8 m apart (if 2 are being used) at a water depth of 2-4 m, with a 200 m hydrophone streamer and with the vessel traveling at 8 knots (kn). The highest-quality mode is carried out using a pair of 45-in

3

airguns, with airguns spaced 2 m apart at a depth of 2-4 m, with a 400, 800, or 1,600 m hydrophone streamer and with the vessel traveling at to 5 kn to achieve high-quality seismic reflection data.

At the three proposed Survey Areas, ~7,500 km of seismic data would be collected. All data acquisition in Areas 1 and 3 would occur in water >1,000 m deep. Area 2 ranges in depth from 50-5,700 m; most of the survey effort (60 percent) would occur in water >1,000 m deep; less than one percent would occur in shallow water <100 m deep. There could be additional seismic operations in the project area associated with equipment testing, re-acquisition due to reasons such as but not limited to equipment malfunction, data degradation during poor weather, or interruption due to shutdown or track deviation in compliance with IHA requirements. To account for these additional seismic operations, 25 percent has been added in the form of operational days, which is equivalent to adding 25 percent to the proposed line km to be surveyed.

In addition to the operations of the airgun array, a multibeam echosounder (MBES) and a sub-bottom profiler (SBP) would also be operated continuously throughout the survey, but not during transits to and from the project area. MBES and SBP data are essential for selecting core sites and for interpreting geological and oceanographic processes that affect the southern Argentine margin. A 12-kilohertz (kHz) pinger would be used during coring to track the depth. All planned geophysical data acquisition activities would be conducted by SIO and UW with on-board assistance by the scientists who have proposed the study. The vessel would be self-contained, and the crew would live aboard the vessel for the entire cruise.

R/V

Thompson

has a length of 83.5 m, a beam of 16 m, and a full load draft of 5.8 m. It is equipped with twin 360°-azimuth stern thrusters each powered by 3,000-hp DC motors and a water-jet bow thruster powered by a 1100-hp DC motor. An operation speed of ~9-15 km/h (~5-8 kn) would be used during seismic acquisition. When not towing seismic survey gear, R/V

Thompson

cruises at 22 km/h (12 kn) and has a maximum speed of 26.9 km/h (14.5 kn). It has a normal operating range of ~24,400 km. R/V

Thompson

would also serve as the platform from which vessel-based protected species visual observers (PSVO) would watch for marine mammals and before and during airgun operations.

During the survey, R/V

Thompson

would tow two 45-in

3

GI airguns and a streamer containing hydrophones. The generator chamber of each GI gun, the one responsible for introducing the sound pulse into the ocean, is 45 in

3

. The larger (105 in

3

) injector chamber injects air into the previously generated bubble to maintain its shape and does not introduce more sound into the water. The 45-in

3

GI airguns would be towed 21 m behind R/V

Thompson,

2 m (during 5-kn high-quality surveys) or 8 m (8-kn reconnaissance surveys) apart, side by side, at a depth of 2-4 m. High-

quality surveys with the 2-m airgun separation configuration would use a streamer up to 1,600-m long, whereas the reconnaissance surveys with the 8-m airgun separation configuration would use a 200-m streamer. Seismic pulses would be emitted at intervals of 25 m for the 5-kn surveys using the 2-m GI airgun separation and at 50 m for the 8-kn surveys using the 8-m airgun separation.

Table 1—Specifications of the R/V Thompson Airgun Array

Number of airguns

2.

Gun positions used

Two inline airguns 2- or 8-m apart.

Tow depth of energy source

2-4 m.

Dominant frequency components

0-188 hertz (Hz).

Air discharge volume

Approximately 90 in

3

.

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

Section 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. Additional information about these species (

e.g.,

physical and behavioral descriptions) may be found on NMFS's website (

https://www.fisheries.noaa.gov/find-species

).

The populations of marine mammals considered in this document do not occur within the U.S. EEZ and are therefore not assigned to stocks and are not assessed in NMFS' Stock Assessment Reports (SAR). As such, information on potential biological removal (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 on 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 are lacking; therefore estimates of abundance presented here are based on a variety of proxy sources including International Whaling Commission population estimates (IWC 2019), the U.S. Atlantic SARs (Hayes

et al.,

2018), and various literature estimates (see IHA application for further detail), as this is considered the best available information on potential abundance of marine mammals in the area. However, as described above, the marine mammals encountered by the proposed survey are not assigned to stocks. All abundance estimate values presented in Table 2 are the most recent available at the time of publication and are available in the 2018 U.S. Atlantic SARs (

e.g.,

Hayes

et al.

2018) available online at:

www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments,

except where noted otherwise.

Table 2 lists all species with expected potential for occurrence in the Argentine Basin, Southwest Atlantic Ocean, and summarizes information related to the population, including regulatory status under the MMPA and ESA. For taxonomy, we follow Committee on Taxonomy (2018).

Table 2—Marine Mammal Species Potentially Present in the Project Area Expected To Be Affected by the Specified Activities

Common name

Scientific name

Stock

1

ESA/

MMPA

status;

strategic

(Y/N)

2

Abundance

PBR

Relative

occurrence in

project area

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)

Family Balaenidae:

Southern right whale

Eubalaena australis

n/a

E/D;N

12,000

3

3,300

4

N.A.

Uncommon.

Family Cetotheriidae:

Pygmy right whale

Caperea marginata

n/a

N.A

N.A.

Rare.

Family Balaenopteridae (rorquals):

Blue whale

Balaenoptera musculus

n/a

E/D;Y

2,300 true

3

1,500 pygmy

5

N.A.

Rare.

Fin whale

Balaenoptera physalus

n/a

E/D;Y

15,000

5

N.A.

Uncommon.

Sei whale

Balaenoptera borealis

n/a

E

10,000

5

N.A.

Uncommon.

Common minke whale

Balaenoptera acutorostrata

n/a

-

515,000

3 6

N.A.

Common.

Antarctic minke whale

Balaenoptera bonaerensis

n/a

-

515,000

3 6

N.A.

Common.

Humpback whale

Megaptera novaeangliae

n/a

-

42,000

3

N.A.

Rare.

Superfamily Odontoceti (toothed whales, dolphins, and porpoises)

Family Physeteridae:

Sperm whale

Physeter macrocephalus

n/a

E

12,069

8

N.A.

Uncommon.

Family Kogiidae:

Pygmy sperm whale

Kogia breviceps

n/a

-

N.A.

N.A.

Rare.

Dwarf sperm whale

Kogia sima

n/a

-

N.A.

N.A.

Rare.

Family Ziphiidae (beaked whales):

Arnoux's beaked whale

Berardius arnuxii

n/a

-

599,300

9

N.A.

Uncommon.

Cuvier's beaked whale

Ziphius cavirostris

n/a

-

599,300

9

N.A.

Uncommon.

Southern bottlenose whale

Hyperoodon planifrons

n/a

-

599,300

9

N.A.

Uncommon.

Shepherd's beaked whale

Tasmacetus sheperdi

n/a

-

N.A.

N.A.

Uncommon.

Blainville's beaked whale

Mesoplodon densirostris

n/a

-

N.A.

N.A.

Rare.

Gray's beaked whale

Mesoplodon grayi

n/a

-

599,300

9

N.A.

Uncommon.

Hector's beaked whale

Mesoplodon hectori

n/a

-

N.A.

N.A.

Rare.

True's beaked whale

Mesoplodon mirus

n/a

-

N.A.

N.A.

Rare.

Strap-toothed beaked whale

Mesoplodon layardii

n/a

-

599,300

9

N.A.

Uncommon.

Andrews' beaked whale

Mesoplodon bowdoini

n/a

-

N.A.

N.A.

Rare.

Spade-toothed beaked whale

Mesoplodon traversii

n/a

-

N.A.

N.A.

Rare.

Family Delphinidae:

Risso's dolphin

Grampus griseus

n/a

-

18,250

10

N.A.

Uncommon.

Rough-toothed dolphin

Steno bredanensis

n/a

-

N.A

N.A.

Rare.

Common bottlenose dolphin

Tursiops truncatus

n/a

-

77,532

10

N.A.

Uncommon.

Pantropical spotted dolphin

Stenella attenuata

n/a

-

3,333

10

N.A.

Rare.

Atlantic spotted dolphin

Stenella frontalis

n/a

-

44,715

10

N.A.

Rare.

Spinner dolphin

Stenella longirostris

n/a

-

N.A

N.A.

Uncommon.

Clymene dolphin

Stenella clymene

n/a

-

N.A

N.A.

Rare.

Striped dolphin

Stenella coeruleoalba

n/a

-

54,807

10

N.A.

Uncommon.

Short-beaked common dolphin

Delphinus delphis

n/a

-

70,184

10

N.A.

Uncommon.

Fraser's dolphin

Lagenodelphis hosei

n/a

-

N.A

N.A.

Rare.

Dusky dolphin

Lagenorhynchus obscurus

n/a

-

7,252

11

N.A.

Uncommon.

Hourglass dolphin

Lagenorhynchus cruciger

n/a

-

150,000

5

N.A.

Common.

Peale's dolphin

Lagenorhynchus australis

n/a

-

20,000

12

N.A.

Common.

Southern right whale dolphin

Lissodelphis peronii

n/a

-

N.A

N.A.

Uncommon.

Commerson's dolphin

Cephalorhynchus commersonii

n/a

-

21,000

13

N.A.

Common.

Killer whale

Orcinus orca

n/a

-

25,000

14

N.A.

Uncommon.

Short-finned pilot whale

Globicephala macrorhynchus

n/a

-

200,000

5

N.A.

Rare.

Long-finned pilot whale

Globicephala melas

n/a

-

200,000

5

N.A.

Common.

False killer whale

Pseudorca crassidens

n/a

-

N.A

N.A.

Rare.

Family Phocoenidae (porpoises):

Spectacled porpoise

Phocoena dioptrica

n/a

-

N.A

N.A.

Uncommon.

Order Carnivora—Superfamily Pinnipedia

Family Otariidae (eared seals and sea lions):

Antarctic fur seal

Arctocephalus gazella

n/a

-

4.5-6.2 million

15

N.A.

Rare.

South American fur seal

Arctocephalus australis

n/a

-

99,000

16

N.A.

Common.

Subantarctic fur seal

Arctocephalus tropicalis

n/a

-

400,000

17

N.A.

Uncommon.

South American sea lion

Otaria flavescens

n/a

-

445,000

16

N.A.

Common.

Family Phocidae (earless seals):

Crabeater seal

Lobodon carcinophaga

n/a

-

5-10 million

18

N.A.

Rare.

Leopard seal

Hydrurga leptonyx

n/a

-

222,000-440,000

19

N.A.

Rare.

Southern elephant seal

Mirounga leonina

n/a

-

750,000

20

N.A.

Uncommon.

N.A. = data not available.

1

The populations of marine mammals considered in this document do not occur within the U.S. EEZ and are therefore not assigned to stocks.

2

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.

3

Southern Hemisphere (IWC 2019).

4

Southwest Atlantic (IWC 2019).

5

Antarctic (Boyd 2002).

6

Dwarf and Antarctic minke whales combined.

7

There are 14 distinct population segments (DPSs) of humpback whales recognized under the ESA; the Brazil DPS is not listed (NOAA 2017).

8

Estimate for the Antarctic, south of 60° S (Whitehead 2002).

9

All beaked whales south of the Antarctic Convergence; mostly southern bottlenose whales (Kasamatsu and Joyce 1995).

10

Estimate for the western North Atlantic (Hayes

et al.,

2018).

11

Estimate for Patagonian coast (Dans

et al.,

1997).

12

Estimate for Southern Patagonian waters, Argentina (Dellabianca

et al.,

2016).

13

Total world population (Dawson 2018).

14

Minimum estimate for Southern Ocean (Branch and Butterworth 2001).

15

South Georgia population (Dawson 2018).

16

Total population (Cárdenas-Alayza

et al.,

2016a).

17

Global population (Hofmeyr and Bester 2018).

18

Global population (Bengston and Stewart 2018).

19

Global population (Rogers 2018).

20

Total world population (Hindell

et al.,

2016).

All species that could potentially occur in the proposed survey areas are included in Table 2. As described below, all 49 species temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur, and we have proposed authorizing it.

Though other marine mammal species are known to occur in the Southwest Atlantic Ocean, the temporal and/or spatial occurrence of several of these species is such that take of these species is not expected to occur, and they are therefore not discussed further beyond the explanation provided here. An additional 11 species of marine mammals are known to occur in the Southwest Atlantic Ocean; however, they are unlikely to occur within the proposed project area because they are coastally-distributed (

e.g.,

Franciscana,

Pontoporia blainvillei;

Guiana dolphin,

Sotalia guianensis;

Chilean dolphin,

Cephalorhynchus eutropia;

Burmeister's porpoise,

Phocoena spinipinnis

); or their distributional range is farther south (Ross seal,

Ommatophoca rossii;

Weddell seal,

Leptonychotes weddellii

) or north (Bryde's whale,

Balaenoptera edeni;

Gervais' beaked whale,

Mesoplodon europaeus;

melon-headed whale,

Peponocephala electra;

pygmy killer whale,

Feresa attenuata;

long-beaked common dolphin,

Delphinus capensis

) of the proposed project area. None of these 11 species are discussed further here.

We have reviewed SIO's species descriptions, including life history information, distribution, regional distribution, diving behavior, and acoustics and hearing, for accuracy and completeness. We refer the reader to Section 4 of SIO's IHA application for

a complete description of the species, and offer a brief introduction to the species here, as well as information regarding population trends and threats, and describe information regarding local occurrence.

Mysticetes

Southern Right Whale

The southern right whale is circumpolar throughout the Southern Hemisphere between 20° S and 55° S (Jefferson et al. 2015), although it may occur further north where cold-water currents extend northwards (Best 2007). It migrates between summer foraging areas at high latitudes and winter breeding/calving areas in low latitudes (Jefferson et al. 2015). In the South Atlantic, known or historic breeding areas are located in the shallow coastal waters of South America, including Argentina and Brazil, as well as the Falkland Islands, Tristan de Cunha, Namibia, and South Africa (IWC 2001). Rowntree et al. (2013) reported that during 2009, primary calving grounds included an estimated 3,373 southern right whales off Argentina.

In the western South Atlantic Ocean, Península Valdés, Argentina, is the main breeding and calving area (Zerbini et al. 2018). It is located just over 200 km from the northwestern portion of the proposed project area. Right whales occurring in breeding and nursing grounds off southern Brazil and Península Valdés, Argentina, may comprise two separate subpopulations that exploit different habitats. Feeding also occurs at these grounds, with breeding success likely influenced by climate-induced variations in food (

i.e.,

krill) availability, such as reduced krill abundance due to global warming (Vighi et al. 2014; Seyboth et al. 2016). Areas with potential foraging importance include the outer shelf of southern South America (including the northwest portion of the proposed project area), the South Atlantic Basin, Scotia Sea, and Weddell Sea (Zerbini et al. 2016, 2018).

Pygmy Right Whale

The distribution of the pygmy right whale is circumpolar in the Southern Hemisphere between 30° S and 55° S in oceanic and coastal environments (Kemper 2018; Jefferson et al. 2015). The pygmy right whale appears to be non-migratory, although there may be some movement inshore in spring and summer (Kemper 2002; Jefferson et al. 2015), possibly related to food availability (Kemper 2018). Foraging areas are not known, but it seems likely that pygmy right whales may feed at productive areas in higher latitudes, such as near the Subtropical Convergence (Best 2007). There may be hotspots of occurrence where mesozooplankton, such as Nyctiphanes australis and Calanus tonsus, are plentiful (Kemper et al. 2013).

The project area is considered to be in the secondary distributional range for this species (Kemper 2018). In the South Atlantic, pygmy right whale records exist for southern Africa, Argentina, the Falkland Islands, and pelagic waters (Baker 1985). One stranding event of a single pygmy right whale occurred in the Falkland Islands during 1950 (Augé et al. 2018). There are no OBIS records of pygmy right whales within or near the project area, but one record exists west of South Georgia and the South Sandwich Islands (53.6° S, 40.6° W) (OBIS 2019).

Blue Whale

The blue whale has a cosmopolitan distribution, but tends to be mostly pelagic, only occurring nearshore to feed and possibly breed (Jefferson et al. 2015). It is most often found in cool, productive waters where upwelling occurs (Reilly and Thayer 1990). 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). Seamounts and other deep ocean structures may be important habitat for blue whales (Lesage et al. 2016). 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).

Brach et al. (2007) reported several catches near the proposed project area, particularly near the Falkland Islands, prior to 1974; however, most catches occurred in the waters of the Southern Ocean during January-March (Branch et al. 2007). There are two records in the OBIS database of blue whale sightings in the South Atlantic, including one off the Argentinian coast in 1993 and one northeast of Survey Area 3 in 1913 (42.15° S, 55.25° W) (OBIS 2019). Blue whale songs and ~500 sightings have been reported near South Georgia (Southeast of proposed survey area) (Sirovic et al. 2016; OBIS 2019). Blue whales were also acoustically detected south of the Falkland Islands during a recent Antarctic Circumnavigation Expedition (Bell 2017). A rare sighting of a mother and calf was made off Brazil in July 2014 (Rocha et al. 2019). One blue whale stranding event was reported in southern Brazil during the 2000s (Prado et al. 2016). Three standings events of individual blue whales occurred in the Falkland Islands during 1940-1962 (Augé et al. 2018).

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 García-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). The northern and southern fin whale populations likely do not interact owing to their alternate seasonal migration; the resulting genetic isolation has led to the recognition of two subspecies,

B. physalus quoyi

and

B. p. physalus

in the Southern and Northern hemispheres, respectively (Anguilar and García-Vernet 2018).

In the Southern Hemisphere, fin whales are typically distributed south of 50° S in the austral summer, migrating northward to breed in the winter (Gambell 1985). According to Edwards et al. (2015), the greatest number of sightings near the Falkland Islands (including the proposed project area) have been reported during December and January; however, sightings have also been made in the area from June through November. There were 27 sightings of 57 fin whales made during surveys in Falkland Islands waters during February 1998 to January 2001, including two sightings within the project area and at least three sightings immediately west of the project area (White et al. 2002). Sightings predominantly occurred during November-January in water depths >200 m, but some sightings were also made during September (White et al. 2002). Otherwise, there are four records west/south of the Falkland Islands, three off southeastern Brazil, and ~500 near South Georgia (OBIS 2019).

Sei Whale

The sei whale occurs in all ocean basins (Horwood 2018), predominantly inhabiting deep waters throughout their range (Acevedo et al. 2017a). It undertakes seasonal migrations to feed in sub-polar latitudes during summer, returning to lower latitudes during winter to calve (Horwood 2018). Recent observation records indicate that the sei whale may utilize the Vitória-Trindade

Chain off Brazil as calving grounds (Heissler et al. 2016). In the Southern Hemisphere, sei whales typically concentrate between the Subtropical and Antarctic convergences during the summer (Horwood 2018) between 40° S and 50° S, with larger, older whales typically travelling into the northern Antarctic zone while smaller, younger individuals remain in the lower latitudes (Acevedo et al. 2017a).

There were 31 sightings of 45 sei whales during surveys in Falkland Islands waters from February 1998 to January 2001, with one sighting within and one immediately west of the project area; most sightings occurred during March and November and none occurred from August-October (White et al. 2002). Twenty sightings of sei whales were made in the coastal waters of Argentina and in the Falkland Islands from 2004-2008, with the majority of sightings during August-September (Iñíguez et al. 2010). Sixty-five sightings of over 200 sei whales were made in the Magellan Strait and adjacent waters during November-May, during 2004-2015; the majority of sightings occurred during December and January (Acevedo et al. 2017a). Aerial and photographic surveys indicated a minimum of 87 sei whales present in Berkeley Sound, Falkland Islands, during February-May 2017, mostly occurring singly or in pairs and otherwise in groups of up to seven whales (Weir 2017).

There are no sei whale records within the proposed project area in the OBIS database; however, there are 32 records for the Southwest Atlantic, including eight sightings north of the project area during 2001-2014, ten west of Survey Area 2 during 2009-2013, nine near the southern tip of South America during 2012 and 2014, and five between the Falkland Islands and South Georgia during 2000-2001 (OBIS 2019). Nine sightings of 25 individuals were made in the Beagle Channel off the southeastern tip of South America during January 2015 and February 2016 (Reyes et al. 2016).

Common Minke Whale

The common minke whale has a cosmopolitan distribution ranging from the tropics and subtropics to the ice edge in both hemispheres (Jefferson et al. 2015). A smaller form (unnamed subspecies) of the common minke whale, known as the dwarf minke whale, occurs in the Southern Hemisphere, where its distribution overlaps with that of the Antarctic minke whale (B. bonaerensis) during summer (Perrin et al. 2018). The dwarf minke whale is generally found in shallower coastal waters and over the shelf in regions where it overlaps with B. bonaerensis (Perrin et al. 2018). The range of the dwarf minke whale is thought to extend as far south as 65° S (Jefferson et al. 2015) and as far north as 2° S in the Atlantic off South America, where it can be found nearly year-round (Perrin et al. 2018).

The waters of the proposed project area are considered to be within the primary range of the common (dwarf) minke whale (Jefferson et al. 2015). Sixty sightings of 68 minke whales were made during surveys in Falkland Islands waters from February 1998 to January 2001, including five sightings within the project area and ~20 sightings in the immediate vicinity; sightings occurred year-round (except during August), with most sightings during September-January (White et al. 2002).

Antarctic Minke Whale

The Antarctic minke whale has a circumpolar distribution in coastal and offshore areas of the Southern Hemisphere from ~7° S to the ice edge (Jefferson et al. 2015). It is found between 60° S and the ice edge during the austral summer; in the austral winter, it is mainly found at mid-latitude breeding grounds, including off western South Africa and northeastern Brazil, where it is primarily oceanic, occurring beyond the shelf break (Perrin et al. 2018). Antarctic minke whale densities are highest near pack ice edges, although they are also found amongst pack ice (Williams et al. 2014), where they feed almost entirely on krill (Tamura and Konishi 2009).

A sighting of two Antarctic minke whales was made off Brazil during an August-September 2010 survey from Vitória, at ~20° S, 40° W, to Trindade and Martim Vaz islands; the whales were seen in association with a group of rough-toothed dolphins near 19.1° S, 35.1° W on 21 August (Wedekin et al. 2014). There are no OBIS records of Antarctic minke whales within the project area, but two records exist for nearshore waters of Argentina west of Survey Area 2, and there are two records off southern South America (OBIS 2019). At least five strandings have been reported for southern Brazil, including two during the 1990s and three in the 2000s (Prado et al. 2016). One stranding of a single whale occurred in the Falkland Islands during May 2016 (Augé et al. 2018).

Humpback Whale

Humpback whales are found worldwide in all ocean basins. In winter, most humpback whales occur in the subtropical and tropical waters of the Northern and Southern Hemispheres (Muto et al., 2015). These wintering grounds are used for mating, giving birth, and nursing new calves. Humpback whales were listed as endangered under the Endangered Species Conservation Act (ESCA) in June 1970. In 1973, the ESA replaced the ESCA, and humpbacks continued to be listed as endangered. NMFS recently evaluated the status of the species, and on September 8, 2016, NMFS divided the species into 14 distinct population segments (DPS), removed the current species-level listing, and in its place listed four DPSs as endangered and one DPS as threatened (81 FR 62259; September 8, 2016). The remaining nine DPSs were not listed. The Brazil DPS, which is not listed under the ESA, is the only DPS of humpback whale that is expected to occur in the survey area.

In the Southern Hemisphere, humpback whales migrate annually from summer foraging areas in the Antarctic to breeding grounds in tropical seas (Clapham 2018). Whales migrating southward from Brazil have been shown to traverse offshore, pelagic waters within a narrow migration corridor to the east of the proposed project area (Zerbini et al. 2006, 2011) en route to feeding areas along the Scotia Sea, including the waters around Shag Rocks, South Georgia and the South Sandwich Islands (Stevick et al. 2006; Zerbini et al. 2006, 2011; Engel et al. 2008; Engel and Martin 2009).

The waters of the proposed project area are considered part of the humpback's secondary range (Jefferson et al. 2015). Four humpback sightings totaling five individuals were made during surveys in Falkland Islands waters, between February 1999 and March 2000 (White et al. 2002). For the South Atlantic, the OBIS database shows numerous sightings along the coast of South America, including one record within Survey Area 2 during February 2000, one record near the Argentinian coast during January 2008, and six historical records north of the project area (OBIS 2019).

Odontocetes

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). In general, it is distributed over large temperate and tropical areas that have high secondary productivity and steep underwater topography, such as volcanic islands (Jaquet and Whitehead 1996). Its distribution and relative

abundance can vary in response to prey availability, most notably squid (Jaquet and Gendron 2002). Females generally inhabit waters >1000 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 according to an unknown schedule (Whitehead 2018).

There were 21 sightings of 28 sperm whales during surveys in Falkland Islands waters from February 1998 to January 2001, with at least eight sightings within the proposed project area and one immediately west of the project area; sightings occurred year-round in water >200 m deep (White et al. 2002). Surveys conducted between January 2002 and May 2004 by observers on board longliners during hauling operations along the 1000-m isobath east and northeast of the Falkland Islands (including within the proposed project area) indicated that although sperm whales were present throughout the fishing areas, they were concentrated near the steepest depth gradients in north/east/southeast Burdwood Bank and northeast of the Falkland Islands (Yates and Brickle 2007). Yates and Brickle (2007) sighted sperm whales throughout the year, and observed a higher abundance south of 53° S during November-March and north of 50° S during May-September. Sperm whales were detected acoustically in Falkland Island waters during all seasons during monitoring from July 2012 to July 2013 (Premier Oil 2018).

In the OBIS database, there is one record of sperm whales within Survey Area 1, 84 records within Survey Area 2, and two within Survey Area 3 (OBIS 2019). An additional 89 records are near the project area, and 10 records are near the Falkland Islands (OBIS 2019). Sperm whales were sighted and/or acoustically detected off southern South America during the 2014-2017 Argentine Southern Ocean Research Partnership cruise (Melcon et al. 2017). Sixteen strandings totaling 39 sperm whales occurred in the Falkland Islands from 1957-2011 (Augé et al. 2018). There are ~30 stranding reports for southern Brazil from 1983-2014 (Prado et al. 2016; Vianna et al. 2016).

Pygmy and Dwarf Sperm Whales

Dwarf and pygmy sperm whales are distributed throughout tropical and temperate waters of the Atlantic, Pacific and Indian oceans, but their precise distributions are unknown because much of what we know of the species comes from strandings (McAlpine 2018). They are difficult to sight at sea, because of their dive behavior and perhaps because of their avoidance reactions to ships and behavior changes in relation to survey aircraft (Würsig et al. 1998). The two species are often difficult to distinguish from one another when sighted (McAlpine 2018). It has been suggested that the pygmy sperm whale is more temperate and the dwarf sperm whale more tropical, based at least partially on live sightings at sea from a large database from the eastern tropical Pacific (Wade and Gerrodette 1993; McAlpine 2018). This idea is also supported by the distribution of strandings in South American waters (Muñoz-Hincapié et al. 1998; Moura et al. 2016).

The proposed project area is located along the southern edge of the presumed distributional range of Kogia spp. There are no records of Kogia spp. in proposed project area (OBIS 2019). The only records in the OBIS database for the South Atlantic are for Africa; 57 records of

K. breviceps

and 22 records of

K. sima

(OBIS 2019). Both species have been reported off southern Brazil (

e.g.,

de Oliveira Santos et al. 2010; Costa-Silva et al. 2016). Approximately 60 dwarf sperm whale strandings have been reported in Brazil between 1965 and 2014 (Moura et al. 2016; Prado et al. 2016). Approximately 50 pygmy sperm whale strandings occurred in Brazil during the same time period (Moura et al. 2016; Prado et al. 2016; Vianna et al. 2016).

Arnoux's Beaked Whale

Arnoux's beaked whale is distributed in deep, cold, temperate, and subpolar waters of the Southern Hemisphere, occurring between 24° S and Antarctica (Thewissen 2018). Most records exist for southeastern South America, Falkland Islands, Antarctic Peninsula, South Africa, New Zealand, and southern Australia (MacLeod et al. 2006; Jefferson et al. 2015). There are no OBIS records for the Southwest Atlantic (OBIS 2019). At least three stranding events have been reported in southern Brazil since the 2000s (Prado et al. 2016). Stranding records also exist for the coast of Tierra del Fuego, Argentina (Riccialdelli et al. 2017).

Cuvier's Beaked Whale

Cuvier's beaked whale is probably the most widespread and common of the beaked whales, although it is not found in high-latitude polar waters (Heyning 1989; Baird 2018a). It is rarely observed at sea and is known mostly from strandings; it strands more commonly than any other beaked whale (Heyning 1989). Cuvier's beaked whale is found in deep water in the open-ocean and over and near the continental slope (Gannier and Epinat 2008; Baird 2018a).

In the South Atlantic, there are stranding records for Brazil, Uruguay, Argentina, Falkland Islands, and South Africa (MacLeod et al. 2006; Otley et al. 2012; Fisch and Port 2013; Bortolotto et al. 2016; Riccialdelli et al. 2017). Sighting records exist for nearshore Brazil, South Africa, and the central South Atlantic and Southern Ocean (Findlay et al. 1992; MacLeod et al. 2006; Prado et al. 2016). There are no OBIS records within or near the proposed project area; the nearest sighting record occurred off southeastern Brazil during 2001 (27.82° S, 45.2° W) (OBIS 2019).

Southern Bottlenose Whale

The southern bottlenose whale is found throughout the Southern Hemisphere from 30° S to the ice edge, with most sightings reported between ~57° S and 70° S (Jefferson et al. 2015; Moors-Murphy 2018). It is apparently migratory, occurring in Antarctic waters during summer (Jefferson et al. 2015). Several sighting and stranding records exist for southeastern South America, Falkland Islands, South Georgia Island, southeastern Brazil, and Argentina, and numerous sightings have been reported for the Southern Ocean (MacLeod et al. 2006; de Oliveira Santos and e Figueiredo 2016; Riccialdelli et al. 2017). The Falkland Islands/Tierra del Fuego area is considered a beaked whale key area (MacLeod and Mitchell 2006). Southern bottlenose whales were regularly seen there (18 sightings of 34 individuals) during September-February 1998-2001, including three sightings within the proposed project area (White et al. 2002). There are three records in the OBIS database of sightings in the Southwest Atlantic, one off eastern Brazil during November 2000 and two east of Survey Area 2 during November 2001 (45.75° S and 53.18° W) (OBIS 2019).

Shepherd's Beaked Whale

Based on known records, it is likely that Shepherd's beaked whale has a circumpolar distribution in the cold temperate waters of the Southern Hemisphere, between 33-50° S (Mead 2018). It is primarily known from strandings, most of which have been recorded in New Zealand and the Tristan da Cunha archipelago (Pitman et al. 2006; Mead 2018). Additional records in the South Atlantic include a sighting in the Scotia Sea and several strandings in Argentina (Grandi et al. 2005; MacLeod et al. 2006; Pitman et al. 2006; Riccialdelli et al. 2017; Mead

2018). Based on the known distributional range of Shepherd's beaked whale (MacLeod et al. 2006; Jefferson et al. 2015), the project area is within its possible range. There are no records for the Southwest Atlantic in the OBIS database (OBIS 2019).

Mesoplodont Beaked Whales (Including Blainville's, Gray's, Hector's, True's, Strapped-Toothed, Andrew's, and Spade-Toothed Beaked Whales)

Mesoplodont beaked whales are distributed throughout deep waters along the continental slopes of the Southwest Atlantic and the open ocean. Blainville's beaked whale is primarily found in tropical and warn temperate waters of all oceans (Pittman 2018), and the proposed project area is located at the southernmost extend of this species' distributional range (Jefferson et al. 2015). Gray's beaked whale, Hector's beaked whale, and Andrew's beaked whale are all thought to have a circumpolar distribution in temperate waters of the Southern Hemisphere (Pitman 2018). True's beaked whale has a disjunct, antitropical distribution (Jefferson et al. 2015) and in the Southern Hemisphere, is known to occur in South Africa, South America, and Australia (Findlay et al. 1992; MacLeod and Mitchell 2006; MacLeod et al. 2006). The strap-toothed beaked whale is thought to have a circumpolar distribution in temperate and subantarctic waters of the Southern Hemisphere, mostly between 32° and 63° S (MacLeod et al. 2006; Jefferson et al. 2015). It may undertake limited migration to warmer waters during the austral winter (Pitman 2018). The spade-toothed beaked whale is considered relatively rare and is known from only four records, three from New Zealand and one from Chile (Thompson et al. 2012), but based on latitude, the species could occur in the proposed project area.

Relatively few records exist of Mesoplodont beaked whale observations in the proposed survey area, with much of the evidence for Mesoplodont presence based on stranding records. Between February 1998 and January 2001, there were 7 sightings of 15 unidentified beaked whales during surveys in the Falkland Islands, and one of these whales was likely a Gray's beaked whale (White et al. 2002).

Risso's Dolphin

Risso's dolphin is distributed worldwide in mid-temperate and tropical oceans (Kruse et al. 1999), although it shows a preference for mid-temperate waters of the shelf and slope between 30° and 45° S (Jefferson et al. 2014). Although it occurs from coastal to deep water (~200-1000 m depth), it shows a strong preference for mid-temperate waters of upper continental slopes and steep shelf-edge areas (Hartman 2018). The variations in Risso's dolphin distribution and seasonal movement patterns near Argentina may be influenced by that of its primary prey, squid (Riccialdelli et al. 2011).

Sightings of Risso's dolphin have been reported on the Patagonian Shelf, Magellan Strait, and elsewhere around southern South America (Riccialdelli et al. 2011; Otley 2012; Jefferson et al. 2014). It has also been sighted during austral spring and fall surveys near southeastern Brazil from 2009 and 2014, in association with common bottlenose dolphins (Di Tullio et al. 2016). Retana and Lewis (2017) reported 11 records west of the project area. Although there are no records within the proposed project area in the OBIS database, 12 records exist along the southeastern Argentinian coast (OBIS 2019). Several dozen stranding events have been reported in coastal waters of southern Argentina (Riccialdelli et al. 2011; Otley 2012). Few stranding records also exist for northern/northeastern Brazil (Toledo et al. 2015; Sánchez-Sarmiento et al. 2018).

Rough-Toothed Dolphin

The rough-toothed dolphin is distributed worldwide in tropical and subtropical waters (Jefferson et al. 2015). It is generally seen in deep, oceanic water, although it is known to occur in coastal waters of Brazil (Jefferson et al. 2015; Cardoso et al. 2019). The proposed project area is located to the south of its primary distribution range (Jefferson et al. 2015); nonetheless, the rough-toothed dolphin could be encountered. Rough-toothed dolphins have been sighted in surveys off the coast of (Brazil Wedekin et al. 2014, de Oliveira Santos et al. 2017) and were also acoustically detected off southeastern Brazil during passive acoustic monitoring surveys in February 2016 (Bittencourt et al. 2018). There are no records of rough-toothed dolphin within the project area in the OBIS database; the nearest records occur of central-eastern Brazil (OBIS 2019). There have been ~40 reported strandings in southern Brazil from 1983-2014 (Baptista et al. 2016; Prado et al. 2016; Vianna et al. 2016).

Common Bottlenose Dolphin

The bottlenose dolphin occurs in tropical, subtropical, and temperate waters throughout the world (Wells and Scott 2018). In the South Atlantic, it occurs as far south Tierra del Fuego (Goodall et al. 2011; Vermeulen et al. 2017; Wells and Scott 2018). Although no sightings have been reported in OBIS (2019) for the proposed project area or the Falkland Islands, several stranding records exist (Otley 2012; Augé et al. 2018). In the OBIS database, there are 100 records within 700 km of the project area, including one nearshore southern Argentina and one near South Georgia (OBIS 2019).

Pantropical Spotted Dolphin

The pantropical spotted dolphin is distributed worldwide in tropical and some subtropical waters, between ~40° N and 40° S (Jefferson et al. 2015). It is one of the most abundant cetaceans and is found in coastal, shelf, slope, and deep waters (Perrin 2018a). Based on distribution maps (

e.g.,

Moreno et al. 2005; Jefferson et al. 2015), the proposed project area is located just south of its regular range; nonetheless, it is possible that pantropical spotted dolphins could be encountered. For the South Atlantic, there is one record for Brazil, observed during 2013 (OBIS 2019) and one reported stranding event in southern Brazil during the 1990s (Prado et al. 2016).

Atlantic Spotted Dolphin

The Atlantic spotted dolphin is distributed in tropical and warm temperate waters of the North Atlantic from Brazil to New England and to the coast of Africa (Jefferson et al. 2015). Based on distribution maps (

e.g.,

Moreno et al. 2005; Jefferson et al. 2015), the proposed project area is located just south of its regular range; nonetheless, it is possible that Atlantic spotted dolphins could be encountered. Moreno et al. (2005) summarized records for Brazil. For the South Atlantic, there is one record for Brazil in the OBIS database (OBIS 2019).

Spinner Dolphin

The spinner dolphin is pantropical in distribution, with a range nearly identical to that of the pantropical spotted dolphin, including oceanic tropical and sub-tropical waters between 40° N and 40° S (Jefferson et al. 2015). Spinner dolphins are extremely gregarious, and usually form large schools in the open sea and small ones in coastal waters (Perrin and Gilpatrick 1994).

Although its primary distributional range appears to be to the north of the proposed project area in the South Atlantic (Moreno et al. 2005; Jefferson et al. 2015), one sighting record has been reported east of Survey Area 2 and another north of the Falkland Islands

(OBIS 2019). Sightings off Brazil have also been reported (Moreno et al. 2005; OBIS 2019).

Clymene Dolphin

The clymene dolphin only occurs in tropical and subtropical waters of the Atlantic Ocean (Jefferson et al. 2015). It inhabits areas where water depths are 700-4500 m or deeper (Fertl et al. 2003). In the western Atlantic, it occurs from New Jersey to Florida, the Caribbean Sea, the Gulf of Mexico and south to Venezuela and Brazil (Würsig et al. 2000; Fertl et al. 2003).

Although currently available information indicates that the proposed project area likely does not overlap with its distributional range (Moreno et al. 2005; Jefferson et al. 2015), it is possible that clymene dolphins could be encountered. There are no OBIS records for the South Atlantic (OBIS 2019). Two stranding events of clymene dolphins were recorded in the Santa Catarina Coast of southern Brazil from 1983-2014 (Vianna et al. 2016).

Striped Dolphin

The striped dolphin has a cosmopolitan distribution in tropical to warm temperate waters from ~50° N to 40° S (Perrin et al. 1994; Jefferson et al. 2015). It occurs primarily in pelagic waters, but has been observed approaching shore where there is deep water close to the coast (Jefferson et al. 2015). In the South Atlantic, it is known to occur along the coast of South America, from Brazil to Argentina, and along the west coast of Africa (Jefferson et al. 2015).

The proposed project survey area is immediately south of its distributional range (Moreno et al. 2005; Jefferson et al. 2015). Sightings have been reported off the northern coast of Argentina (Moreno et al. 2005), with 10 records offshore Argentina north of the project area; the nearest record was located at 42.3° S, 62° W (OBIS 2019).

Short-Beaked Common Dolphin

The short-beaked common dolphin is found in tropical and warm temperate oceans around the world (Jefferson et al. 2015), ranging from ~60° N to ~50° S (Jefferson et al. 2015). It is the most abundant dolphin species in offshore areas of warm-temperate regions in the Atlantic and Pacific (Perrin 2018c).

Short-beaked common dolphins were observed on the outer-continental shelf off southeastern Brazil during spring and fall surveys during 2009-2014 (Di Tullio et al. 2016), and de Oliveira Santos et al. (2017) reported one sighting within the Parque Estadual Marinho da Laje de Santos MPA off Brazil's southeastern coast during boat-based cetacean surveys from 2013-2015. For the Southwest Atlantic, there are seven OBIS records for eastern South America, west and north of the proposed project area nearshore and offshore Argentina (OBIS 2019). There are at least 23 reported stranding events for short-beaked common dolphin in southern Brazil from 1983-2014 (Prado et al. 2016; Vianna et al. 2016). Strandings and incidental catches in fishing nets have been reported in Argentina (de Castro et al. 2016; Durante et al. 2016).

Fraser's Dolphin

Fraser's dolphin is a tropical oceanic species generally distributed between 30° N and 30° S that generally inhabits deeper, offshore water (Dolar 2018). The proposed project area is located south of the presumed distribution range (Jefferson et al. 2015), and strandings in more temperate waters, such as in Uruguay, are likely extralimital (Dolar 2018). However, there is one record in the OBIS database off central-eastern Argentina, west of the proposed project area (42.9° S, 65° W). Strandings and incidental captures in fishing nets have also been reported in Argentina (So et al. 2009; Durante et al. 2016).

Dusky Dolphin

The dusky dolphin occurs throughout the Southern Hemisphere, primarily over continental shelves and slopes and sometimes over deep water close to continents or islands (Van Waerebeek and Würsig 2018). Along the east coast of South America, it is present from ~36° S to Southern Patagonia and the Falkland Islands (Otley 2012; Van Waerebeek and Würsig 2018). It is the most common small cetacean near southeastern Argentina (Schiavini et al. 1999) and is incidentally captured in mid-water trawl fisheries in the region (Dans et al. 1997).

Dusky dolphins have been sighted during aerial and boat-based surveys from the southeastern Argentinian coast to the edge of the EEZ; there are also a few records for the proposed project area (Crespo et al. 1997). During the past decade, the presence of dusky dolphin has increased in the Beagle Channel, southern Argentina, suggesting at least a seasonally-resident population during austral summer and fall (Dellabianca et al. 2018). There are seven records ranging from counts of one to 30 dusky dolphins within Survey Area 2 in the OBIS database, and an additional ~80 records within the Southwest Atlantic beyond the proposed project area, including five records west of Survey Area 1 (OBIS 2019).

Hourglass Dolphin

The hourglass dolphin occurs in all parts of the Southern Ocean, with most sightings between ~45° S and 60° S (Cipriano 2018a). However, some sightings have been made as far north as 33° S (Jefferson et al. 2015). Although it is pelagic, it is also sighted near banks and islands (Cipriano 2018a). There were 177 sightings of 886 hourglass dolphins made during surveys in Falkland Islands waters from February 1998 to January 2001, including within the proposed project area; sightings predominantly occurred from September-February in water deeper than 200 m (White et al. 2002). There are two records in the OBIS database near the Falkland Islands, 12 records east and southeast of the southern tip of Argentina, and 17 records between Falkland Islands and South Georgia (OBIS 2019).

Peale's Dolphin

Peale's dolphin is endemic to southern South America and ranges from 38-59° S (Cipriano 2018b). It is known to breed in the Falkland Islands (White et al. 2002). Peale's dolphin was the most frequent and numerous cetacean recorded during surveys in Falkland Island waters from February 1998 to January 2001, with 864 sightings totaling 2617 individuals (White et al. 2002). There were 134 schools (465 individuals) observed during eight scientific cruises in southern Patagonian waters during November-April between 2009 and 2015, including sightings within and/or near the project area (Dellabianca et al. 2016). In the OBIS database, there are two sightings within Survey Area 2 and ~130 records near the project area (OBIS 2019). There are also reports of strandings historically from Southern Brazil to the Falkland Islands (Prado et al. 2016, Augé et al. 2018)

Southern Right Whale Dolphin

The southern right whale dolphin is distributed between the Subtropical and Antarctic convergences in the Southern Hemisphere, generally between ~30° S and 65° S (Jefferson et al. 2015; Lipsky and Brownell 2018). It is sighted most often in cool, offshore waters, although it is sometimes seen near shore where coastal waters are deep (Jefferson et al. 2015).

One sighting of 120 southern right whale dolphins was made in Survey Area 2 during September 1998; an additional two sightings of six and 20 individuals occurred southeast of the proposed project area during February and September 1999, respectively (White et al. 2002). Two strandings of

three southern right whale dolphins occurred in the Falkland Islands during February and September between 1945 and 2004 (Augé et al. 2018).

Commerson's Dolphin

Commerson's dolphin principally occurs near Argentina and the Falkland Islands, Strait of Magellan, and the Kerguelen Islands in the Indian Ocean (Dawson 2018). In the Falkland Islands, Commerson's dolphin are distributed mainly coastally and are also known to breed there (White et al. 2002).

Although these dolphins typically prefer water depths <100 m, there are two records within Survey Area 2 and over 500 records in the Southwest Atlantic in the OBIS database, with sightings particularly prevalent nearshore and offshore southeastern Argentina and the Falkland Islands (OBIS 2019). Commerson's dolphins have been observed year-round, except during May, with peak occurrence during April (White et al. 2002) in waters near the Falkland Islands, and in other surveys around Argentina.

Killer Whale

Killer whales have been observed in all oceans and seas of the world (Leatherwood and Dahlheim 1978). Based on sightings by whaling vessels between 1960 and 1979, killer whales are distributed throughout the South Atlantic (Budylenko 1981; Mikhalev et al. 1981). Although reported from tropical and offshore waters (Heyning and Dahlheim 1988), killer whales prefer the colder waters of both hemispheres, with greatest abundances found within 800 km of major continents (Mitchell 1975).

There are 48 records of killer whales for the Southwest Atlantic near the project area in the OBIS database, including one record of three individuals within Survey Area 2, three records totaling ten whales east of Survey Area 2, and one record of six whales northeast of Survey Area 3 (OBIS 2019). In addition to these sightings, there are numerous recorded observations from surveys in the area.

Short-Finned and Long-Finned Pilot Whale

The short-finned pilot whale is found in tropical and warm temperate waters, and the long-finned pilot whale is distributed antitropically in cold temperate waters (Olson 2018). The ranges of the two species show little overlap (Olson 2018). Short-finned pilot whale distribution does not generally range south of 40° S (Jefferson et al. 2008). Long-finned pilot whales are one of the most regular sighted species in the Falkland Islands (White et al. 2002).

There are eight records of long-finned pilot whales in Survey Area 2 and one record in Survey Area 3 in the OBIS database, in addition to ~100 records in the Southwest Atlantic beyond the project area; there is a single record of short-finned pilot whales off northeastern Brazil (OBIS 2019).

False Killer Whale

The false killer whale is found worldwide in tropical and temperate waters, generally between 50° N and 50° S (Odell and McClune 1999). It is widely distributed, but not abundant anywhere (Carwardine 1995). The proposed project area is within the primary range of the false killer whale in the Southwest Atlantic Ocean (Baird 2018b). Within this portion of its range, false killer whales are known to prey on fishes caught in the Uruguayan pelagic longline fishery (Passadore et al. 2015). Although there are no OBIS records of false killer whales within the project area, there are two records northeast of there, one record also exists west of South Georgia, and 18 records are located offshore northeastern Brazil (OBIS 2019).

Spectacled Porpoise

The spectacled porpoise is distributed in cool temperate, subantarctic, and Antarctic waters of the Southern Hemisphere (Goodall and Brownell 2018). In the Southwest Atlantic, it occurs from southern Brazil to Tierra del Fuego, Falkland Islands, and South Georgia, and its range extends southwards into the Drake Passage (Jefferson et al. 2015).

In the OBIS database, one record exists for the South Atlantic, west of Survey Area 2 at 47.5° S, 62.7° W during 2009 (OBIS 2019) and the species is generally observed in group sizes of one to five individuals (Goodall and Brownell 2018). Strandings of spectacled porpoises have been recorded around the region including the Falkland Islands, southern Brazil, and strand most frequently on the beaches of Tierra del Fuego where it is the second-most frequently stranding cetacean (Costa and Rojas 2017; Augé et al. 2018; Goodall and Brownell 2018).

Pinnipeds

Antarctic Fur Seal

The Antarctic fur seal is the only fur seal that lives south of the Antarctic Convergence (Acevedo et al. 2011). It has a circumpolar distribution around Antarctica and ranges as far north as the Falkland Islands and Argentina during the non-breeding season (Forcada and Staniland 2018).

Female Antarctic fur seals can disperse greater than 1,000 km onto the continental shelf of Patagonia once pups are weaned (Boyd et al. 2002), with tagged animals showing focused foraging activity in waters of the South American continental shelf, including waters of the proposed project area. There are thousands of records of Antarctic fur seals in the OBIS database (OBIS 2019), including 108 records for the proposed project area for May through October.

South American Fur Seal

The South American fur seal occurs along the Atlantic coast of South America from southern Brazil to the southernmost tip of Patagonia, extending out to include the Falkland Islands (Cárdenas-Alayza 2018a). There are no records of South American fur seals within the proposed offshore project area in the OBIS database (OBIS 2019). The closest record is ~270 km to the west and tagged individuals have undertaking foraging trips that bring them in waters near the project area (Baylis et al. 2018b), but with a tendency to be in waters less than 400 m deep.

Subantarctic Fur Seal

Subantarctic fur seals occur between 10° W and 170° E north of the Antarctic Polar Front in the Southern Ocean (Hofmeyr and Bester 2018). Breeding occurs on several islands, with Gough Island in the central South Atlantic accounting for about two thirds of pup production (Hofmeyr and Bester 2018), but adults take long foraging journeys away from these colonies. Subantarctic fur seals found in Brazil were most often seen there during the austral winter from July through October (de Moura and Siciliano 2007); most were males. There are no records of subantarctic fur seals within the proposed offshore project area in the OBIS database (OBIS 2019).

South American Sea Lion

The South American sea lion is widely distributed along the South American coastline from Peru in the Pacific to southern Brazil in the Atlantic (Cárdenas-Alayza 2018b). On the Atlantic coast, it occurs from Brazil to Tierra del Fuego, including the Falkland Islands (Cárdenas-Alayza 2018b). The northernmost rookery is located on the coast of Uruguay; South American sea lions are also known to breed on the Falkland Islands (Thompson et al. 2005).

There are 2,352 records for coastal and shelf waters of South America in the OBIS database; most records are for waters off Argentina (OBIS 2019). There are 80 records in the northwestern portion of the proposed project area and satellite tagged males have been recorded near Survey Area 2, but the animals tend to be found in waters 200 m deep or less.

Crabeater Seal

Crabeater seals have a circumpolar distribution off Antarctica and generally spend the entire year in the advancing and retreating pack ice; occasionally they are seen in the far southern areas of South America though this is uncommon (Bengtson and Stewart 2018). Vagrants are occasionally found as far north as Brazil (de Oliveira et al. 2006). There are no records of crabeater seals within the proposed offshore project area in the OBIS database (OBIS 2019). However, the species could possibly be present and Crabeater seals found on the coast of Brazil were most often observed during the austral summer and fall, but also in winter months (de Oliveira et al. 2006).

Leopard Seal

The leopard seal has a circumpolar distribution around the Antarctic continent where it is solitary and widely dispersed (Rogers 2018). Most leopard seals remain within the pack ice; however, members of this species regularly visit southern continents during the winter (Rogers 2018). On the Atlantic coast of South America, leopard seals have been reported in small groups on the Falkland Islands and as lone individuals in Brazil, Uruguay, Tierra del Fuego, Patagonia, and northern Argentina (summarized in Rodríguez et al. 2003). There are no records of leopard seals within the proposed offshore survey area in the OBIS database (OBIS 2019).

Southern Elephant Seal

The southern elephant seal has a near circumpolar distribution in the Southern Hemisphere (Jefferson et al. 2015), with breeding sites located on islands throughout the subantarctic (Hindell 2018). In the South Atlantic, southern elephant seals breed at Patagonia, South Georgia, and other islands of the Scotia Arc, Falkland Islands, Bouvet Island, and Tristan da Cunha archipelago (Bester and Ryan 2007). Península Valdés, Argentina is the sole continental South American large breeding colony, where tens of thousands of southern elephant seals congregate (Lewis et al. 2006).

Southern elephant seals are known to occur throughout the proposed project area (White et al. 2002; Campagna et al. 2008). All sightings north of 50° S were made during January−May, and all records south of 50° S were made during June, August, and November; most sightings were made near the 200-m isobath (White et al. 2002). For the South Atlantic, there are ~3,000 OBIS records for the nearshore and offshore waters of eastern South America (OBIS 2019); most of the records (2943) are for waters off Argentina and the Falkland Islands, including within and near the proposed project area, with the most records in survey Area 2.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Current data indicate that not all marine mammal species have equal hearing capabilities (

e.g.,

Richardson

et al.,

1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall

et al.

(2007) recommended that marine mammals be divided into functional hearing groups based on directly measured or estimated hearing ranges on the basis of available behavioral response data, audiograms derived using auditory evoked potential techniques, anatomical modeling, and other data. Note that no direct measurements of hearing ability have been successfully completed for mysticetes (

i.e.,

low-frequency cetaceans). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65 decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency 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 3.

Table 3—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 (Hemilä

et al.,

2006; Kastelein

et al.,

2009; Reichmuth and Holt, 2013).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information. Forty-nine marine mammal species (42 cetacean and 7 pinniped (4 otariid and 3 phocid) species) have the reasonable potential to co-occur with the proposed survey activities. Please refer to Table 2. Of the cetacean species that may be present, 8 are classified as low-frequency cetaceans (

i.e.,

all mysticete species), 28 are classified as mid-frequency cetaceans (

i.e.,

most delphinid and ziphiid species and the sperm whale), and 6 are classified as high-frequency cetaceans (

i.e.,

Kogia spp., hourglass dolphin, Peale's dolphin, Commerson's dolphin, spectacled porpoise).

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

This section includes a summary and discussion of the ways that components of the specified activity may impact marine mammals and their habitat. The

Estimated Take by Incidental Harassment

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 by Incidental Harassment

section, and the

Proposed Mitigation

section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and how those impacts on individuals are likely to impact marine mammal species or stocks.

Description of Active Acoustic Sound Sources

This section contains a brief technical background on sound, the characteristics of certain sound types, and on metrics used in this proposal inasmuch as the information is relevant to the specified activity and to a discussion of the potential effects of the specified activity on marine mammals found later in this document.

Sound travels in waves, the basic components of which are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks or corresponding points of a sound wave (length of one cycle). Higher frequency sounds have shorter wavelengths than lower frequency sounds, and typically attenuate (decrease) more rapidly, except in certain cases in shallower water. Amplitude is the height of the sound pressure wave or the “loudness” of a sound and is typically described using the relative unit of the dB. A sound pressure level (SPL) in dB is described as the ratio between a measured pressure and a reference pressure (for underwater sound, this is 1 microPascal (μPa)) 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 μPa) while the received level is the SPL at the listener's position (referenced to 1 μPa).

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 μPa

2

-s) represents the total energy contained within a pulse and considers both intensity and duration of exposure. Peak sound pressure (also referred to as zero-to-peak sound pressure or 0-p) is the maximum instantaneous sound pressure measurable in the water at a specified distance from the source and is represented in the same units as the rms sound pressure. Another common metric is peak-to-peak sound pressure (pk-pk), which is the algebraic difference between the peak positive and peak negative sound pressures. Peak-to-peak pressure is typically approximately 6 dB higher than peak pressure (Southall

et al.,

2007).

When underwater objects vibrate or activity occurs, sound-pressure waves are created. These waves alternately compress and decompress the water as the sound wave travels. Underwater sound waves radiate in a manner similar to ripples on the surface of a pond and may be either directed in a beam or beams or may radiate in all directions (omnidirectional sources), as is the case for pulses produced by the airgun arrays considered here. The compressions and decompressions associated with sound waves are detected as changes in pressure by aquatic life and man-made sound receptors such as hydrophones.

Even in the absence of sound from the specified activity, the underwater environment is typically loud due to ambient sound. Ambient sound is defined as environmental background sound levels lacking a single source or point (Richardson

et al.,

1995), and the sound level of a region is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical (

e.g.,

wind and waves, earthquakes, ice, atmospheric sound), biological (

e.g.,

sounds produced by marine mammals, fish, and invertebrates), and anthropogenic (

e.g.,

vessels, dredging, construction) sound. A number of sources contribute to ambient sound, including the following (Richardson

et al.,

1995):

•

Wind and waves:

The complex interactions between wind and water surface, including processes such as breaking waves and wave-induced bubble oscillations and cavitation, are a main source of naturally occurring ambient sound for frequencies between 200 Hz and 50 kHz (Mitson, 1995). In general, ambient sound levels tend to increase with increasing wind speed and wave height. Surf sound becomes important near shore, with measurements collected at a distance of 8.5 km from shore showing an increase of 10 dB in the 100 to 700 Hz band during heavy surf conditions;

•

Precipitation:

Sound from rain and hail impacting the water surface can become an important component of total sound at frequencies above 500 Hz, and possibly down to 100 Hz during quiet times;

•

Biological:

Marine mammals can contribute significantly to ambient sound levels, as can some fish and snapping shrimp. The frequency band for biological contributions is from approximately 12 Hz to over 100 kHz; and

•

Anthropogenic:

Sources of ambient sound related to human activity include transportation (surface vessels), dredging and construction, oil and gas drilling and production, seismic surveys, sonar, explosions, and ocean acoustic studies. Vessel noise typically dominates the total ambient sound for frequencies between 20 and 300 Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz and, if higher frequency sound levels are created, they attenuate rapidly. Sound from identifiable anthropogenic sources other than the activity of interest (

e.g.,

a passing vessel) is sometimes termed background sound, as opposed to ambient sound.

The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and human activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor, and is frequency-dependent. As a result of the dependence on a large number of varying factors, ambient sound levels can be expected to vary widely over both coarse and fine spatial and temporal scales. Sound levels at a given frequency and location can vary by 10-20 dB from day to day (Richardson

et al.,

1995). The result is that, depending on the source type and its intensity, sound from a given activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals.

Details of source types are described in the following text.

Sounds are often considered to fall into one of two general types: Pulsed and non-pulsed (defined in the following). The distinction between these two sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing (

e.g.,

Ward, 1997 in Southall

et al.,

2007). Please see Southall

et al.

(2007) for an in-depth discussion of these concepts.

Pulsed sound sources (

e.g.,

airguns, explosions, gunshots, sonic booms, impact pile driving) produce signals that are brief (typically considered to be less than one second), broadband, atonal transients (ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur either as isolated events or repeated in some succession. Pulsed sounds are all characterized by a relatively rapid rise from ambient pressure to a maximal pressure value followed by a rapid decay period that may include a period of diminishing, oscillating maximal and minimal pressures, and generally have an increased capacity to induce physical injury as compared with sounds that lack these features.

Non-pulsed sounds can be tonal, narrowband, or broadband, brief or prolonged, and may be either continuous or non-continuous (ANSI, 1995; NIOSH, 1998). Some of these non-pulsed 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.

As described above, a Kongsberg EM 300 MBES and a Knudsen Chirp 3260 SBP would be operated continuously during the proposed surveys, but not during transit to and from the survey areas. Additionally a 12-kHz pinger would be used during coring, when seismic airguns, are not in operation (more information on this pinger is available in NSF-USGS (2011). Each ping emitted by the MBES consists of eight (in water >1,000 m deep) or four (<1,000 m) successive fan-shaped transmissions, each ensonifying a sector that extends 1° fore-aft. Given the movement and speed of the vessel, the intermittent and narrow downward-directed nature of the sounds emitted by the MBES would result in no more than one or two brief ping exposures of any individual marine mammal, if any exposure were to occur.

Due to the lower source levels of the Knudsen Chirp 3260 SBP relative to the

Thompson's

airgun array (maximum SL of 222 dB re 1 μPa · m for the SBP, versus a minimum of 230.9 dB re 1 μPa · m for the 2 airgun array (LGL, 2019)), sounds from the SBP are expected to be effectively subsumed by sounds from the airgun array. Thus, any marine mammal potentially exposed to sounds from the SBP would already have been exposed to sounds from the airgun array, which are expected to propagate further in the water.

The use of pingers is also highly unlikely to affect marine mammals given their intermittent nature, short-term and transitory use from a moving vessel, relatively low source levels, and brief signal durations (NSF-USGS, 2011). As such, we conclude that the likelihood of marine mammal take resulting from exposure to sound from the MBES or SBP (beyond that which is already quantified as a result of exposure to the airguns) is discountable. Additionally the characteristics of sound generated by pingers means that take of marine mammals resulting from exposure to these pingers is discountable. Therefore we do not consider noise from the MBES, SBP, or pingers further in this analysis.

Acoustic Effects

Here, we discuss the effects of active acoustic sources on marine mammals.

Potential Effects of Underwater Sound

—Please refer to the information given previously (“Description of Active Acoustic Sources”) regarding sound, characteristics of sound types, and metrics used in this document. Anthropogenic sounds cover a broad range of frequencies and sound levels and can have a range of highly variable impacts on marine life, from none or minor to potentially severe responses, depending on received levels, duration of exposure, behavioral context, and various other factors. The potential effects of underwater sound from active acoustic sources can potentially result in one or more of the following: Temporary or permanent hearing impairment, non-auditory physical or physiological effects, behavioral disturbance, stress, and masking (Richardson

et al.,

1995; Gordon

et al.,

2004; Nowacek

et al.,

2007; Southall

et al.,

2007; Götz

et al.,

2009). The degree of effect is intrinsically related to the signal characteristics, received level, distance from the source, and duration of the sound exposure. In general, sudden, high level sounds can cause hearing loss, as can longer exposures to lower level sounds. Temporary or permanent loss of hearing will occur almost exclusively for noise within an animal's hearing range. We first describe specific manifestations of acoustic effects before providing discussion specific to the use of airgun arrays.

Richardson

et al.

(1995) described zones of increasing intensity of effect that might be expected to occur, in relation to distance from a source and assuming that the signal is within an animal's hearing range. First is the area within which the acoustic signal would be audible (potentially perceived) to the animal, but not strong enough to elicit any overt behavioral or physiological response. The next zone corresponds with the area where the signal is audible to the animal and of sufficient intensity to elicit behavioral or physiological responsiveness. Third is a zone within which, for signals of high intensity, the received level is sufficient to potentially cause discomfort or tissue damage to auditory or other systems. Overlaying these zones to a certain extent is the area within which masking (

i.e.,

when a sound interferes with or masks the ability of an animal to detect a signal of interest that is above the absolute hearing threshold) may occur; the masking zone may be highly variable in size.

We describe the more severe effects of certain non-auditory physical or physiological effects only briefly as we do not expect that use of airgun arrays are reasonably likely to result in such effects (see below for further discussion). Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton

et al.,

1973). Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions

(

e.g.,

change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox

et al.,

2006; Southall

et al.,

2007; Zimmer and Tyack, 2007; Tal

et al.,

2015). The survey activities considered here do not involve the use of devices such as explosives or mid-frequency tactical sonar that are associated with these types of effects.

Threshold Shift

—Marine mammals exposed to high-intensity sound, or to lower-intensity sound for prolonged periods, can experience hearing threshold shift (TS), which is the loss of hearing sensitivity at certain frequency ranges (Finneran, 2015). TS can be permanent (PTS), in which case the loss of hearing sensitivity is not fully recoverable, or temporary (TTS), in which case the animal's hearing threshold would recover over time (Southall

et al.,

2007). Repeated sound exposure that leads to TTS could cause PTS. In severe cases of PTS, there can be total or partial deafness, while in most cases the animal has an impaired ability to hear sounds in specific frequency ranges (Kryter, 1985).

When PTS occurs, there is physical damage to the sound receptors in the ear (

i.e.,

tissue damage), whereas TTS represents primarily tissue fatigue and is reversible (Southall

et al.,

2007). In addition, other investigators have suggested that TTS is within the normal bounds of physiological variability and tolerance and does not represent physical injury (

e.g.,

Ward, 1997). Therefore, NMFS does not consider TTS to constitute auditory injury.

Relationships between TTS and PTS thresholds have not been studied in marine mammals, and there is no PTS data for cetaceans but such relationships are assumed to be similar to those in humans and other terrestrial mammals. PTS typically occurs at exposure levels at least several dBs above (a 40-dB threshold shift approximates PTS onset;

e.g.,

Kryter

et al.,

1966; Miller, 1974) that inducing mild TTS (a 6-dB threshold shift approximates TTS onset;

e.g.,

Southall

et al.

2007). Based on data from terrestrial mammals, a precautionary assumption is that the PTS thresholds for impulse sounds (such as airgun pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS cumulative sound exposure level thresholds are 15 to 20 dB higher than TTS cumulative sound exposure level thresholds (Southall

et al.,

2007). Given the higher level of sound or longer exposure duration necessary to cause PTS as compared with TTS, it is considerably less likely that PTS could occur.

For mid-frequency cetaceans in particular, potential protective mechanisms may help limit onset of TTS or prevent onset of PTS. Such mechanisms include dampening of hearing, auditory adaptation, or behavioral amelioration (

e.g.,

Nachtigall and Supin, 2013; Miller

et al.,

2012; Finneran

et al.,

2015; Popov

et al.,

2016).

TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 1985). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. Few data on sound levels and durations necessary to elicit mild TTS have been obtained for marine mammals.

Marine mammal hearing plays a critical role in communication with conspecifics, and interpretation of environmental cues for purposes such as predator avoidance and prey capture. Depending on the degree (elevation of threshold in dB), duration (

i.e.,

recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious. For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that occurs during a time where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts.

Finneran

et al.

(2015) measured hearing thresholds in three captive bottlenose dolphins before and after exposure to ten pulses produced by a seismic airgun in order to study TTS induced after exposure to multiple pulses. Exposures began at relatively low levels and gradually increased over a period of several months, with the highest exposures at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 193-195 dB. No substantial TTS was observed. In addition, behavioral reactions were observed that indicated that animals can learn behaviors that effectively mitigate noise exposures (although exposure patterns must be learned, which is less likely in wild animals than for the captive animals considered in this study). The authors note that the failure to induce more significant auditory effects likely due to the intermittent nature of exposure, the relatively low peak pressure produced by the acoustic source, and the low-frequency energy in airgun pulses as compared with the frequency range of best sensitivity for dolphins and other mid-frequency cetaceans.

Currently, TTS data only exist for four species of cetaceans (bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless porpoise) exposed to a limited number of sound sources (

i.e.,

mostly tones and octave-band noise) in laboratory settings (Finneran, 2015). In general, harbor porpoises have a lower TTS onset than other measured cetacean species (Finneran, 2015). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species. There are no data available on noise-induced hearing loss for mysticetes.

Critical questions remain regarding the rate of TTS growth and recovery after exposure to intermittent noise and the effects of single and multiple pulses. Data at present are also insufficient to construct generalized models for recovery and determine the time necessary to treat subsequent exposures as independent events. More 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), Finneran and Jenkins (2012), Finneran (2015), and NMFS (2016a).

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; Weilgart, 2007; Archer

et al.,

2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source,

context, and numerous other factors (Ellison

et al.,

2012), and can vary depending on characteristics associated with the sound source (

e.g.,

whether it is moving or stationary, number of sources, distance from the source). Please see Appendices B-C of Southall

et al.

(2007) for a review of studies involving marine mammal behavioral responses to sound.

Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok

et al.,

2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder

et al.,

2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure. As noted, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson

et al.,

1995; NRC, 2003; Wartzok

et al.,

2003). Controlled experiments with captive marine mammals have showed pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway

et al.,

1997). Observed responses of wild marine mammals to loud pulsed sound sources (typically seismic airguns or acoustic harassment devices) have been varied but often consist of avoidance behavior or other behavioral changes suggesting discomfort (Morton and Symonds, 2002; see also Richardson

et al.,

1995; Nowacek

et al.,

2007). However, many delphinids approach acoustic source vessels with no apparent discomfort or obvious behavioral change (

e.g.,

Barkaszi

et al.,

2012).

Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal. If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant (

e.g.,

Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 2005). However, there are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight.

Changes in dive behavior can vary widely, and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive (

e.g.,

Frankel and Clark, 2000; Ng and Leung, 2003; Nowacek

et al.,

2004; Goldbogen

et al.,

2013a, b). Variations in dive behavior may reflect interruptions in biologically significant activities (

e.g.,

foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response.

Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators (

e.g.,

bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance (

e.g.,

Croll

et al.,

2001; Nowacek

et al.,

2004; Madsen

et al.,

2006; Yazvenko

et al.,

2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationship between prey availability, foraging effort and success, and the life history stage of the animal.

Visual tracking, passive acoustic monitoring, and movement recording tags were used to quantify sperm whale behavior prior to, during, and following exposure to airgun arrays at received levels in the range 140-160 dB at distances of 7-13 km, following a phase-in of sound intensity and full array exposures at 1-13 km (Madsen

et al.,

2006; Miller

et al.,

2009). Sperm whales did not exhibit horizontal avoidance behavior at the surface. However, foraging behavior may have been affected. The sperm whales exhibited 19 percent less vocal (buzz) rate during full exposure relative to post exposure, and the whale that was approached most closely had an extended resting period and did not resume foraging until the airguns had ceased firing. The remaining whales continued to execute foraging dives throughout exposure; however, swimming movements during foraging dives were 6 percent lower during exposure than control periods (Miller

et al.,

2009). These data raise concerns that seismic surveys may impact foraging behavior in sperm whales, although more data are required to understand whether the differences were due to exposure or natural variation in sperm whale behavior (Miller

et al.,

2009).

Variations in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in 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 (Miller

et al.,

2000; Fristrup

et al.,

2003; Foote

et al.,

2004), while right whales have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks

et al.,

2007). In some cases, animals may cease sound production during production of aversive signals (Bowles

et al.,

1994).

Cerchio

et al.

(2014) used passive acoustic monitoring to document the presence of singing humpback whales off the coast of northern Angola and to opportunistically test for the effect of seismic survey activity on the number of singing whales. Two recording units

were deployed between March and December 2008 in the offshore environment; numbers of singers were counted every hour. Generalized Additive Mixed Models were used to assess the effect of survey day (seasonality), hour (diel variation), moon phase, and received levels of noise (measured from a single pulse during each ten minute sampled period) on singer number. The number of singers significantly decreased with increasing received level of noise, suggesting that humpback whale breeding activity was disrupted to some extent by the survey activity.

Castellote

et al.

(2012) reported acoustic and behavioral changes by fin whales in response to shipping and airgun noise. Acoustic features of fin whale song notes recorded in the Mediterranean Sea and northeast Atlantic Ocean were compared for areas with different shipping noise levels and traffic intensities and during a seismic airgun survey. During the first 72 h 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 µPa

2

-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 SEL

cum

of ~127 dB). Overall, these results suggest that bowhead whales may adjust their vocal output in an effort to compensate for noise before ceasing vocalization effort and ultimately deflecting from the acoustic source (Blackwell

et al.,

2013, 2015). These studies demonstrate that even low levels of noise received far from the source can induce changes in vocalization and/or behavior for mysticetes.

Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of disturbance in marine mammals (Richardson

et al.,

1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme

et al.,

1984). Humpback whales showed avoidance behavior in the presence of an active seismic array during observational studies and controlled exposure experiments in western Australia (McCauley

et al.,

2000). Avoidance may be short-term, with animals returning to the area once the noise has ceased (

e.g.,

Bowles

et al.,

1994; Goold, 1996; Stone

et al.,

2000; Morton and Symonds, 2002; Gailey

et al.,

2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur (

e.g.,

Bejder

et al.,

2006; Teilmann

et al.,

2006).

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 five-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 one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall

et al.,

2007). Note that there is a difference between multi-day substantive behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses.

Stone (2015) reported data from at-sea observations during 1,196 seismic surveys from 1994 to 2010. When large arrays of airguns (considered to be 500 in

3

or more) were firing, lateral displacement, more localized avoidance, or other changes in behavior were evident for most odontocetes. However, significant responses to large arrays were found only for the minke whale and fin whale. Behavioral responses observed included changes in swimming or surfacing behavior, with indications that cetaceans remained near the water surface at these times. Cetaceans were recorded as feeding less often when large arrays were active. Behavioral observations of gray whales during a seismic survey monitored whale movements and respirations pre-, during and post-seismic survey (Gailey

et al.,

2016). Behavioral state and water depth were the best `natural' predictors of whale movements and respiration and, after considering

natural variation, none of the response variables were significantly associated with seismic survey or vessel sounds.

Stress Responses

—An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses (

e.g.,

Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness.

Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal system. Virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction, altered metabolism, reduced immune competence, and behavioral disturbance (

e.g.,

Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano

et al.,

2004).

The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose serious fitness consequences. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other functions. This state of distress will last until the animal replenishes its energetic reserves sufficiently to restore normal function.

Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses are well-studied through controlled experiments and for both laboratory and free-ranging animals (

e.g.,

Holberton

et al.,

1996; Hood

et al.,

1998; Jessop

et al.,

2003; Krausman

et al.,

2004; Lankford

et al.,

2005). Stress responses due to exposure to anthropogenic sounds or other stressors and their effects on marine mammals have also been reviewed (Fair and Becker, 2000; Romano

et al.,

2002b) and, more rarely, studied in wild populations (

e.g.,

Romano

et al.,

2002a). For example, Rolland

et al.

(2012) found that noise reduction from reduced ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003).

Auditory Masking

—Sound can disrupt behavior through masking, or interfering with, an animal's ability to detect, recognize, or discriminate between acoustic signals of interest (

e.g.,

those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson

et al.,

1995; Erbe

et al.,

2016). Masking occurs when the receipt of a sound is interfered with by another coincident sound at similar frequencies and at similar or higher intensity, and may occur whether the sound is natural (

e.g.,

snapping shrimp, wind, waves, precipitation) or anthropogenic (

e.g.,

shipping, sonar, seismic exploration) in origin. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest (

e.g.,

signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities (

e.g.,

sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions.

Under certain circumstances, marine mammals experiencing significant masking could also be impaired from maximizing their performance fitness in survival and reproduction. Therefore, when the coincident (masking) sound is man-made, it may be considered harassment when disrupting or altering critical behaviors. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect.

The frequency range of the potentially masking sound is important in determining any potential behavioral impacts. For example, low-frequency signals may have less effect on high-frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals (

e.g.,

Clark

et al.,

2009) and may result in energetic or other costs as animals change their vocalization behavior (

e.g.,

Miller

et al.,

2000; Foote

et al.,

2004; Parks

et al.,

2007; Di Iorio and Clark, 2009; Holt

et al.,

2009). Masking can be reduced in situations where the signal and noise come from different directions (Richardson

et al.,

1995), through amplitude modulation of the signal, or through other compensatory behaviors (Houser and Moore, 2014). Masking can be tested directly in captive species (

e.g.,

Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild (

e.g.,

Branstetter

et al.,

2013).

Masking affects both senders and receivers of acoustic signals and can potentially have long-term chronic effects on marine mammals at the population level as well as at the individual level. Low-frequency ambient sound levels have increased by as much as 20 dB (more than three times in terms of SPL) in the world's ocean from pre-industrial periods, with most of the increase from distant commercial shipping (Hildebrand, 2009). All anthropogenic sound sources, but especially chronic and lower-frequency signals (

e.g.,

from vessel traffic), contribute to elevated ambient sound levels, thus intensifying masking.

Masking effects of pulsed sounds (even from large arrays of airguns) on marine mammal calls and other natural sounds are expected to be limited, although there are few specific data on this. Because of the intermittent nature and low duty cycle of seismic pulses, animals can emit and receive sounds in the relatively quiet intervals between pulses. However, in exceptional situations, reverberation occurs for much or all of the interval between pulses (

e.g.,

Simard

et al.

2005; Clark and Gagnon 2006), which could mask calls. Situations with prolonged strong reverberation are infrequent. However, it is common for reverberation to cause some lesser degree of elevation of the

background level between airgun pulses (

e.g.,

Gedamke 2011; Guerra

et al.

2011, 2016; Klinck

et al.

2012; Guan

et al.

2015), and this weaker reverberation presumably reduces the detection range of calls and other natural sounds to some degree. Guerra

et al.

(2016) reported that ambient noise levels between seismic pulses were elevated as a result of reverberation at ranges of 50 km from the seismic source. Based on measurements in deep water of the Southern Ocean, Gedamke (2011) estimated that the slight elevation of background levels during intervals between pulses reduced blue and fin whale communication space by as much as 36-51 percent when a seismic survey was operating 450-2,800 km away. Based on preliminary modeling, Wittekind

et al.

(2016) reported that airgun sounds could reduce the communication range of blue and fin whales 2000 km from the seismic source. Nieukirk

et al.

(2012) and Blackwell

et al.

(2013) noted the potential for masking effects from seismic surveys on large whales.

Some baleen and toothed whales are known to continue calling in the presence of seismic pulses, and their calls usually can be heard between the pulses (

e.g.,

Nieukirk

et al.

2012; Thode

et al.

2012; Bröker

et al.

2013; Sciacca

et al.

2016). As noted above, Cerchio

et al.

(2014) suggested that the breeding display of humpback whales off Angola could be disrupted by seismic sounds, as singing activity declined with increasing received levels. In addition, some cetaceans are known to change their calling rates, shift their peak frequencies, or otherwise modify their vocal behavior in response to airgun sounds (

e.g.,

Di Iorio and Clark 2010; Castellote

et al.

2012; Blackwell

et al.

2013, 2015). The hearing systems of baleen whales are undoubtedly more sensitive to low-frequency sounds than are the ears of the small odontocetes that have been studied directly (

e.g.,

MacGillivray

et al.

2014). The sounds important to small odontocetes are predominantly at much higher frequencies than are the dominant components of airgun sounds, thus limiting the potential for masking. In general, masking effects of seismic pulses are expected to be minor, given the normally intermittent nature of seismic pulses.

Ship Noise

Vessel noise from the

Thompson

could affect marine animals in the proposed survey areas. Houghton

et al.

(2015) proposed that vessel speed is the most important predictor of received noise levels, and Putland

et al.

(2017) also reported reduced sound levels with decreased vessel speed. Sounds produced by large vessels generally dominate ambient noise at frequencies from 20 to 300 Hz (Richardson

et al.

1995). However, some energy is also produced at higher frequencies (Hermannsen

et al.

2014); low levels of high-frequency sound from vessels has been shown to elicit responses in harbor porpoise (Dyndo

et al.

2015). Increased levels of ship noise have been shown to affect foraging by porpoise (Teilmann

et al.

2015; Wisniewska

et al.

2018); Wisniewska

et al.

(2018) suggest that a decrease in foraging success could have long-term fitness consequences.

Ship noise, through masking, can reduce the effective communication distance of a marine mammal if the frequency of the sound source is close to that used by the animal, and if the sound is present for a significant fraction of time (

e.g.,

Richardson

et al.

1995; Clark

et al.

2009; Jensen

et al.

2009; Gervaise

et al.

2012; Hatch

et al.

2012; Rice

et al.

2014; Dunlop 2015; Erbe

et al.

2015; Jones

et al.

2017; Putland

et al.

2017). In addition to the frequency and duration of the masking sound, the strength, temporal pattern, and location of the introduced sound also play a role in the extent of the masking (Branstetter

et al.

2013, 2016; Finneran and Branstetter 2013; Sills

et al.

2017). Branstetter

et al.

(2013) reported that time-domain metrics are also important in describing and predicting masking. In order to compensate for increased ambient noise, some cetaceans are known to increase the source levels of their calls in the presence of elevated noise levels from shipping, shift their peak frequencies, or otherwise change their vocal behavior (

e.g.,

Parks

et al.

2011, 2012, 2016a,b; Castellote

et al.

2012; Melcón

et al.

2012; Azzara

et al.

2013; Tyack and Janik 2013; Luís

et al.

2014; Sairanen 2014; Papale

et al.

2015; Bittencourt

et al.

2016; Dahlheim and Castellote 2016; Gospić and Picciulin 2016; Gridley

et al.

2016; Heiler

et al.

2016; Martins

et al.

2016; O'Brien

et al.

2016; Tenessen and Parks 2016). Harp seals did not increase their call frequencies in environments with increased low-frequency sounds (Terhune and Bosker 2016). Holt

et al.

(2015) reported that changes in vocal modifications can have increased energetic costs for individual marine mammals. A negative correlation between the presence of some cetacean species and the number of vessels in an area has been demonstrated by several studies (

e.g.,

Campana

et al.

2015; Culloch

et al.

2016).

Baleen whales are thought to be more sensitive to sound at these low frequencies than are toothed whales (

e.g.,

MacGillivray

et al.

2014), possibly causing localized avoidance of the proposed survey area during seismic operations. Reactions of gray and humpback whales to vessels have been studied, and there is limited information available about the reactions of right whales and rorquals (fin, blue, and minke whales). Reactions of humpback whales to boats are variable, ranging from approach to avoidance (Payne 1978; Salden 1993). Baker

et al.

(1982, 1983) and Baker and Herman (1989) found humpbacks often move away when vessels are within several kilometers. Humpbacks seem less likely to react overtly when actively feeding than when resting or engaged in other activities (Krieger and Wing 1984, 1986). Increased levels of ship noise have been shown to affect foraging by humpback whales (Blair

et al.

2016). Fin whale sightings in the western Mediterranean were negatively correlated with the number of vessels in the area (Campana

et al.

2015). Minke whales and gray seals have shown slight displacement in response to construction-related vessel traffic (Anderwald

et al.

2013). Many odontocetes show considerable tolerance of vessel traffic, although they sometimes react at long distances if confined by ice or shallow water, if previously harassed by vessels, or have had little or no recent exposure to ships (Richardson

et al.

1995). Dolphins of many species tolerate and sometimes approach vessels (

e.g.,

Anderwald

et al.

2013). Some dolphin species approach moving vessels to ride the bow or stern waves (Williams

et al.

1992). Pirotta

et al.

(2015) noted that the physical presence of vessels, not just ship noise, disturbed the foraging activity of bottlenose dolphins. Sightings of striped dolphin, Risso's dolphin, sperm whale, and Cuvier's beaked whale in the western Mediterranean were negatively correlated with the number of vessels in the area (Campana

et al.

2015).

There are few data on the behavioral reactions of beaked whales to vessel noise, though they seem to avoid approaching vessels (

e.g.,

Würsig

et al.

1998) or dive for an extended period when approached by a vessel (

e.g.,

Kasuya 1986). Based on a single observation, Aguilar Soto

et al.

(2006) suggest foraging efficiency of Cuvier's beaked whales may be reduced by close approach of vessels.

In summary, project vessel sounds would not be at levels expected to cause anything more than possible localized and temporary behavioral changes in marine mammals, and would not be expected to result in significant negative

effects on individuals or at the population level. In addition, in all oceans of the world, large vessel traffic is currently so prevalent that it is commonly considered a usual source of ambient sound (NSF-USGS 2011).

Ship Strike

Vessel collisions with marine mammals, or ship strikes, can result in death or serious injury of the animal. Wounds resulting from ship strike may include massive trauma, hemorrhaging, broken bones, or propeller lacerations (Knowlton and Kraus, 2001). An animal at the surface may be struck directly by a vessel, a surfacing animal may hit the bottom of a vessel, or an animal just below the surface may be cut by a vessel's propeller. Superficial strikes may not kill or result in the death of the animal. These interactions are typically associated with large whales (

e.g.,

fin whales), which are occasionally found draped across the bulbous bow of large commercial ships upon arrival in port. Although smaller cetaceans are more maneuverable in relation to large vessels than are large whales, they may also be susceptible to strike. The severity of injuries typically depends on the size and speed of the vessel, with the probability of death or serious injury increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist

et al.,

2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013). Impact forces increase with speed, as does the probability of a strike at a given distance (Silber

et al.,

2010; Gende

et al.,

2011).

Pace and Silber (2005) also found that the probability of death or serious injury increased rapidly with increasing vessel speed. Specifically, the predicted probability of serious injury or death increased from 45 to 75 percent as vessel speed increased from 10 to 14 kn, and exceeded 90 percent at 17 kn. 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. The chances of a lethal injury decline from approximately 80 percent at 15 kn to approximately 20 percent at 8.6 kn. At speeds below 11.8 kn, the chances of lethal injury drop below 50 percent, while the probability asymptotically increases toward one hundred percent above 15 kn.

The

Thompson

travels at a speed of either 5 (9.3 km/hour) or 8 kn (14.8 km/hour) while towing seismic survey gear (LGL 2019). At these speeds, 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. Ship strikes, as analyzed in the studies cited above, generally involve commercial shipping, which is much more common in both space and time than is geophysical survey activity. Jensen and Silber (2004) summarized ship strikes of large whales worldwide from 1975-2003 and found that most collisions occurred in the open ocean and involved large vessels (

e.g.,

commercial shipping). No such incidents were reported for geophysical survey vessels during that time period.

It is possible for ship strikes to occur while traveling at slow speeds. For example, a hydrographic survey vessel traveling at low speed (5.5 kn) while conducting mapping surveys off the central California coast struck and killed a blue whale in 2009. The State of California determined that the whale had suddenly and unexpectedly surfaced beneath the hull, with the result that the propeller severed the whale's vertebrae, and that this was an unavoidable event. This strike represents the only such incident in approximately 540,000 hours of similar coastal mapping activity (

p

= 1.9 × 10

−6

; 95 percent CI = 0-5.5 × 10

−6

; NMFS, 2013b). In addition, a research vessel reported a fatal strike in 2011 of a dolphin in the Atlantic, demonstrating that it is possible for strikes involving smaller cetaceans to occur. In that case, the incident report indicated that an animal apparently was struck by the vessel's propeller as it was intentionally swimming near the vessel. While indicative of the type of unusual events that cannot be ruled out, neither of these instances represents a circumstance that would be considered reasonably foreseeable or that would be considered preventable.

Although the likelihood of the vessel striking a marine mammal is low, we require a robust ship strike avoidance protocol (see

Proposed Mitigation

), which we believe eliminates any foreseeable risk of ship strike. We anticipate that vessel collisions involving a seismic data acquisition vessel towing gear, while not impossible, represent unlikely, unpredictable events for which there are no preventive measures. Given the required mitigation measures, the relatively slow speed of the vessel towing gear, the presence of bridge crew watching for obstacles at all times (including marine mammals), and the presence of marine mammal observers, we believe that the possibility of ship strike is discountable and, further, that were a strike of a large whale to occur, it would be unlikely to result in serious injury or mortality. No incidental take resulting from ship strike is anticipated, and this potential effect of the specified activity will not be discussed further in the following analysis.

Stranding—

When a living or dead marine mammal swims or floats onto shore and becomes “beached” or incapable of returning to sea, the event is a “stranding” (Geraci

et al.,

1999; Perrin and Geraci, 2002; Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a stranding under the MMPA is that (A) a marine mammal is dead and is (i) on a beach or shore of the United States; or (ii) in waters under the jurisdiction of the United States (including any navigable waters); or (B) a marine mammal is alive and is (i) on a beach or shore of the United States and is unable to return to the water; (ii) on a beach or shore of the United States and, although able to return to the water, is in need of apparent medical attention; or (iii) in the waters under the jurisdiction of the United States (including any navigable waters), but is unable to return to its natural habitat under its own power or without assistance.

Marine mammals strand for a variety of reasons, such as infectious agents, biotoxicosis, starvation, fishery interaction, ship strike, unusual oceanographic or weather events, sound exposure, or combinations of these stressors sustained concurrently or in series. However, the cause or causes of most strandings are unknown (Geraci

et al.,

1976; Eaton, 1979; Odell

et al.,

1980; Best, 1982). Numerous studies suggest that the physiology, behavior, habitat relationships, age, or condition of cetaceans may cause them to strand or might pre-dispose them to strand when exposed to another phenomenon. These suggestions are consistent with the conclusions of numerous other studies that have demonstrated that combinations of dissimilar stressors commonly combine to kill an animal or dramatically reduce its fitness, even though one exposure without the other does not produce the same result (Chroussos, 2000; Creel, 2005; DeVries

et al.,

2003; Fair and Becker, 2000; Foley

et al.,

2001; Moberg, 2000; Relyea,

2005a; 2005b, Romero, 2004; Sih

et al.,

2004).

Use of military tactical sonar has been implicated in a majority of investigated stranding events. Most known stranding events have involved beaked whales, though a small number have involved deep-diving delphinids or sperm whales (

e.g.,

Mazzariol

et al.,

2010; Southall

et al.,

2013). In general, long duration (~1 second) and high-intensity sounds (>235 dB SPL) have been implicated in stranding events (Hildebrand, 2004). With regard to beaked whales, mid-frequency sound is typically implicated (when causation can be determined) (Hildebrand, 2004). Although seismic airguns create predominantly low-frequency energy, the signal does include a mid-frequency component. We have considered the potential for the proposed surveys to result in marine mammal stranding and have concluded that, based on the best available information, stranding is not expected to occur.

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. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pulsed sound on fish, although several are based on studies in support of construction projects (

e.g.,

Scholik and Yan, 2001, 2002; Popper and Hastings, 2009). Sound pulses at received levels of 160 dB may cause subtle changes in fish behavior. SPLs of 180 dB may cause noticeable changes in behavior (Pearson

et al.,

1992; Skalski

et al.,

1992). SPLs of sufficient strength have been known to cause injury to fish and fish mortality. The most likely impact to fish from survey activities at the project area would be temporary avoidance of the area. 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.

Information on seismic airgun impacts to zooplankton, which represent an important prey type for mysticetes, is limited. However, McCauley

et al.

(2017) reported that experimental exposure to a pulse from a 150 inch

3

airgun decreased zooplankton abundance when compared with controls, as measured by sonar and net tows, and caused a two- to threefold increase in dead adult and larval zooplankton. Although no adult krill were present, the study found that all larval krill were killed after air gun passage. Impacts were observed out to the maximum 1.2 km range sampled.

In general, impacts to marine mammal prey are expected to be limited due to the relatively small temporal and spatial overlap between the proposed survey and any areas used by marine mammal prey species. The proposed use of airguns as part of an active seismic array survey would occur over a relatively short time period (~28 days) and would occur over a very small area relative to the area available as marine mammal habitat in the Southwest Atlantic Ocean. We believe any impacts to marine mammals due to adverse effects to their prey would be insignificant due to the limited spatial and temporal impact of the proposed survey. However, adverse impacts may occur to a few species of fish and to zooplankton.

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 habitat-mediated 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 this one 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.

In summary, activities associated with the proposed action are not likely to have a permanent, adverse effect on any fish habitat or populations of fish species or on the quality of acoustic habitat. Thus, any impacts to marine mammal habitat are not expected to cause significant or long-term consequences for individual marine mammals or their populations.

Estimated Take

This section provides an estimate of the number of incidental takes proposed for authorization through this IHA, which will inform both NMFS' consideration of “small numbers” and the negligible impact determination.

Harassment is the only type of take expected to result from these activities. Except with respect to certain activities not pertinent here, section 3(18) of the MMPA defines “harassment” as any act of pursuit, torment, or annoyance, which (i) has the potential to injure a marine mammal or marine mammal stock in the wild (Level A harassment); or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering (Level B harassment).

Authorized takes would be by Level B harassment only, as use of the acoustic sources (

i.e.,

seismic airgun) has the potential to result in disruption of behavioral patterns for individual marine mammals. Based on the nature of the activity and the anticipated effectiveness of the mitigation measures (

i.e.,

marine mammal exclusion zones) discussed in detail below in Proposed Mitigation section, Level A harassment is neither anticipated nor proposed to be

authorized. As described previously, no mortality is anticipated or proposed to be authorized for this activity. Below we describe how the take is estimated.

Generally speaking, we estimate take by considering: (1) Acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and, (4) and the number of days of activities. We note that while these basic factors can contribute to a basic calculation to provide an initial prediction of takes, additional information that can qualitatively inform take estimates is also sometimes available (

e.g.,

previous monitoring results or average group size). Below, we describe the factors considered here in more detail and present the proposed take estimate.

Acoustic Thresholds

Using the best available science, NMFS has developed acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment).

Level B Harassment for non-explosive sources

—Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source (

e.g.,

frequency, predictability, duty cycle), the environment (

e.g.,

bathymetry), and the receiving animals (hearing, motivation, experience, demography, behavioral context) and can be difficult to predict (Southall

et al.,

2007, Ellison

et al.,

2012). Based on what the available science indicates, and the practical need to use a threshold based on a factor that is both predictable and measurable for most activities, NMFS uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS predicts that marine mammals are likely to be behaviorally harassed in a manner we consider Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 dB re 1 μPa (rms) for continuous (

e.g.,

vibratory pile-driving, drilling) and above 160 dB re 1 μPa (rms) for non-explosive impulsive (

e.g.,

seismic airguns) or intermittent (

e.g.,

scientific sonar) sources.

SIO's proposed activity includes the use of impulsive seismic sources, and therefore the 160 dB re 1 μPa (rms) is applicable.

Level A harassment for non-explosive sources

—NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual criteria to assess auditory injury (Level A harassment) to five different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). SIO's proposed activity includes the use of impulsive seismic sources.

These thresholds are provided in the table below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS 2018 Technical Guidance, which may be accessed at

https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

Table 4—Thresholds Identifying the Onset of Permanent Threshold Shift

Hearing group

PTS onset acoustic thresholds *

(received level)

Impulsive

Non-impulsive

Low-Frequency (LF) Cetaceans

Cell 1: L

pk,flat

:

219 dB;

L

E,LF,24h

:

183 dB

Cell 2: L

E,LF,24h

:

199 dB.

Mid-Frequency (MF) Cetaceans

Cell 3: L

pk,flat

:

230 dB;

L

E,MF,24h

:

185 dB

Cell 4: L

E,MF,24h

:

198 dB.

High-Frequency (HF) Cetaceans

Cell 5: L

pk,flat

:

202 dB;

L

E,HF,24h

:

155 dB

Cell 6: L

E,HF,24h

:

173 dB.

Phocid Pinnipeds (PW) (Underwater)

Cell 7: L

pk,flat

:

218 dB;

L

E,PW,24h

:

185 dB

Cell 8: L

E,PW,24h

:

201 dB.

Otariid Pinnipeds (OW) (Underwater)

Cell 9: L

pk,flat

:

232 dB;

L

E,OW,24h

:

203 dB

Cell 10: L

E,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 (

L

pk

) has a reference value of 1 µPa, and cumulative sound exposure level (

L

E

) has a reference value of 1µPa

2

s. In this Table, thresholds are abbreviated to reflect American National Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript “flat” is being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude of ways (

i.e.,

varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be exceeded.

Ensonified Area

Here, we describe operational and environmental parameters of the activity that will feed into identifying the area ensonified above the acoustic thresholds, which include source levels and transmission loss coefficient.

The proposed survey would entail the use of a 2-airgun array with a total discharge of 90 in

3

at a two depth of 2-4 m. Lamont-Doherty Earth Observatory (L-DEO) model results are used to determine the 160 dB

rms

radius for the 2-airgun array in deep water (>1,000 m) down to a maximum water depth of 2,000 m. Received sound levels were predicted by L-DEO's model (Diebold

et al.,

2010) as a function of distance from the airguns, for the two 45 in

3

airguns. 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 homogenous ocean layer, unbounded by a seafloor). In addition, propagation measurements of pulses from a 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 in 2007-2008 (Tolstoy

et al.,

2009; Diebold

et al.,

2010).

For deep and intermediate water cases, the field measurements cannot be used readily to derive the Level A and

Level B 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 maximum relevant water depth (~2,000 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, comparisons at short ranges between sound levels for direct arrivals recorded by the calibration hydrophone and model results for the same array tow depth are in good agreement (see Figures 12 and 14 in Appendix H of NSF-USGS 2011). Consequently, isopleths falling within this domain can be predicted reliably by the L-DEO model, although they may be imperfectly sampled by measurements recorded at a single depth. At greater distances, the calibration data show that seafloor-reflected and sub-seafloor-refracted arrivals dominate, whereas the direct arrivals become weak and/or incoherent. Aside from local topography effects, the region around the critical distance is where the observed levels rise closest to the model curve. However, the observed sound levels are found to fall almost entirely below the model curve. Thus, analysis of the Gulf of Mexico calibration measurements demonstrates that although simple, the L-DEO model is a robust tool for conservatively estimating isopleths.

The proposed surveys would acquire data with two 45-in

3

guns at a tow depth of 2-4 m. For deep water (>1000 m), we use the deep-water radii obtained from L-DEO model results down to a maximum water depth of 2000 m for the airgun array with 2-m and 8-m airgun separation. The radii for intermediate water depths (100-1000 m) are derived from the deep-water ones by applying a correction factor (multiplication) of 1.5, such that observed levels at very near offsets fall below the corrected mitigation curve (see Figure 16 in Appendix H of NSF-USGS 2011). The shallow-water radii are obtained by scaling the empirically derived measurements from the Gulf of Mexico calibration survey to account for the differences in source volume and tow depth between the calibration survey (6000 in

3

; 6-m tow depth) and the proposed survey (90 in

3

; 4-m tow depth); whereas the shallow water in the Gulf of Mexico may not exactly replicate the shallow water environment at the proposed survey sites, it has been shown to serve as a good and very conservative proxy (Crone

et al.,

2014). A simple scaling factor is calculated from the ratios of the isopleths determined by the deep-water L-DEO model, which are essentially a measure of the energy radiated by the source array.

L-DEO's modeling methodology is described in greater detail in SIO's IHA application. The estimated distances to the Level B harassment isopleths for the two proposed airgun configurations in each water depth category are shown in Table 5.

Table 5—Predicted Radial Distances From R/V

Thompson

Seismic Source to Isopleths Corresponding to Level B Harassment Threshold

Airgun configuration

Water depth

(m)

Predicted

distances (m)

to 160 dB

received

south level

Two 45 in

3

guns, 2-m separation

>1,000

a

539

100-1,000

b

809

<100

c

1,295

Two 45 in

3

guns, 8-m separation

>1,000

a

578

100-1,000

b

867

<100

c

1,400

a

Distance based on L-DEO model results.

b

Distance based on L-DEO model results with a 1.5 × correction factor between deep and intermediate water depths.

c

Distance based on empirically derived measurements in the Gulf of Mexico with scaling applied to account for differences in tow depth.

Predicted distances to Level A harassment isopleths, which vary based on marine mammal hearing groups, were calculated based on modeling performed by L-DEO using the NUCLEUS software program and the NMFS User Spreadsheet, described below. The updated acoustic thresholds for impulsive sounds (

e.g.,

airguns) contained in the Technical Guidance were presented as dual metric acoustic thresholds using both SEL

cum

and peak sound pressure metrics (NMFS 2016a). 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 SEL

cum

metric considers both level and duration of exposure, as well as auditory weighting functions by marine mammal hearing group. In recognition of the fact that the requirement to calculate Level A harassment ensonified areas could be more technically challenging to predict due to the duration component and the use of weighting functions in the new SEL

cum

thresholds, NMFS developed an optional User Spreadsheet that includes tools to help predict a simple isopleth that can be used in conjunction with marine mammal density or occurrence to facilitate the estimation of take numbers.

The SEL

cum

for the 2-GI 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 interactions of the two airguns that occur near the source center and is calculated as a point source (single airgun), the modified farfield signature is a more appropriate measure of the sound source level for large arrays. For this smaller array, the modified farfield changes will be correspondingly smaller as

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