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

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XR056

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Low-Energy Geophysical Survey in the South 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 South 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 October 30, 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.Egger@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:

Stephanie Egger, 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 May 15, 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 Southeast Atlantic Ocean. The application was deemed adequate and complete on August 12, 2019. SIO's request is for take of a small number of 48 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.

Description of Proposed Activity

Overview

SIO plans to conduct low-energy marine seismic surveys in the Southeast Atlantic Ocean during November-December 2019. The seismic surveys would be conducted to understand the volcanic and tectonic development of Walvis Ridge and Rio Grande Rise in the South Atlantic Ocean. The seismic surveys would be conducted in International Waters with water depths ranging from approximately 500 to 5700 m. The surveys would involve one source vessel, R/V

Thomas G. Thompson

(

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.

Dates and Duration

The R/V

Thompson

would likely depart from Montevideo, Uruguay, on or about November 3, 2019 and would arrive in Walvis Bay, Namibia, on or about 5 December 5, 2019. If the arrival port is Cape Town instead of Walvis Bay, an additional two days would be required for transit. Seismic operations would occur for approximately 14 days. Transit to and from the project area and between surveys would occur from approximately 16 days. Equipment deployment and recovery would take approximately 3 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 majority of the survey would take place in the Southeast Atlantic Ocean between ~33.2°-21° S and 1° W-8° E (see Figure 1). A small survey area is proposed for the Southwest Atlantic Ocean between ~33.2°-34.3° S and 30.8°-31.8° W (see Figure 1). Seismic surveys would occur in five survey areas including Libra Massif in the Southwest Atlantic and Valdivia Bank, Gough, Tristan, and Central survey areas in the Southeast Atlantic; representative survey tracklines are shown in Figure 1.

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Detailed Description of Specific Activity

SIO proposes to conduct low-energy seismic surveys in five areas in the South Atlantic Ocean. Reconnaissance Surveys are planned for three survey areas (Gough, Tristan, Central) and High Quality Surveys are planned to take place along the proposed seismic transect lines in the main survey area (Valdivia Bank) and Libra Massif survey area (Figure 1). However, High-Quality Surveys may be replaced by Reconnaissance Surveys depending on weather conditions and timing (

e.g.,

10 percent of survey effort at Valdivia Bank is expected to consist of Reconnaissance Surveys). All data acquisition in the Tristan survey area would occur in water >1,000 m deep; all other survey areas have effort in intermediate (100-1,000 m) and deep (>1,000 m) water. Most of the survey effort (97 percent) would occur in water >1,000 m deep. The proposed surveys would be in support of a potential future International Ocean Discovery Program (IODP) project and to improve our understanding of volcanic and tectonic development of oceanic ridges and to enable the selection and analysis of potential future IODP drill sites. To achieve the program's goals, the Principal Investigators propose to collect low-energy, high-resolution multi-channel seismic (MCS) profiles. The proposed cruise would consist of digital bathymetric, echosounding, and MCS surveys.

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 to 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 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. The second mode would be a reconnaissance mode, which are quicker and less impacted by adverse weather. The reconnaissance mode also allows for operations to occur in poor weather where the use of streamer longer than 400-m may not be possible safely.

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 knots (5 kn) to achieve high-quality seismic reflection data. 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 kn.

Seismic data would be collected first as a single profile over the rift at Libra Massif, the most southeastern edifice of Rio Grande Rise. After crossing the Atlantic, data would be collected over three seamounts (Gough, Tristan, Central) in the “Guyot Province” of Walvis Ridge. Approximately 24 hr of seismic profiling is proposed at each location, before moving on to the Valdivia Bank survey area, where most survey effort (75 percent) would occur.

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 shut-down 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 hull-mounted multibeam echosounder (MBES) and a sub-bottom profiler (SBP) would also be operated from the

Thompson

continuously throughout the seismic surveys, but not during transits to and from the project area. All planned data acquisition and sampling activities would be conducted by SIO and UW with on board assistance by the scientists who have proposed the project. The vessel would be self-contained, and the crew would live aboard the vessel for the entire cruise.

The

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 1,100-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, the

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. The

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, the

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 the

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) for a few dolphin species, 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).

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All species that could potentially occur in the proposed survey areas are included in Table 2. As described below, all 48 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 13 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.,

Atlantic humpback dolphin,

Sousa teuszii;

Heaviside's dolphin,

Cephalorhynchus heavisidii;

Chilean dolphin,

C. eutropia;

long-beaked common dolphin,

Delphinus capensis;

Franciscana,

Pontoporia blainvillei;

Guiana dolphin,

Sotalia guianensis;

Burmeister's porpoise,

Phocoena spinipinnis;

West Indian manatee,

Trichechus manatus;

African manatee,

T. senegalensis;

South American fur seal,

Arctocephalus australis

); or (2) occur further south (spectacled porpoise,

Phocoena dioptrica;

Ross seal,

Ommatophoca rossii;

Weddell seal,

Leptonychotes weddellii

). Although a gray whale (

Eschrichtius robustus

) was sighted off Namibia in 2013 (Elwen and Gridley 2013), and the remains of a stranded Omura's whale (

Balaenoptera omurai

) were reported for Mauritania in western Africa (Jung

et al.

2016), these species are not considered further as they typically do not occur in the Atlantic Ocean. None of these 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 3,864 southern right whales off South Africa.

Although southern right whale calving/breeding areas are located in nearshore waters, feeding grounds in the Southern Ocean apparently are located mostly in highly-productive pelagic waters (Kenney 2018). Waters south of South Africa are believed to be a nursery area for southern right whales, as females and calves are seen there (Barendse and Best 2014). Right whales with calves are seen in nearshore waters of South Africa during July-November (Best 2007). Nearshore waters off western South Africa might be used as a year-round feeding area (Barendse and Best 2014). The highest sighting rates off western South Africa occur during early austral summer, and the lowest rates have been reported from autumn to mid-winter (Barendse and Best 2014). Although right whales were depleted in the early 19th century by whaling, they are now reappearing off Namibia; this likely indicates a range expansion of the stock from South Africa rather than a separate stock (Roux

et al.

2001, 2015). Numerous sightings were made in the area from 1971 through 1999; most sightings were made from July through November, with one sighting during December (Roux

et al.

2001). A total of 10 calves were born off Namibia between 1996 and 1999 (Roux

et al.

2001). However, Roux

et al.

(2015) postulated that Namibian waters currently serve as mating grounds rather than a calving area. Best (2007) reported a summer feeding concentration between 30° and 40° S, including the Guyot Province of Walvis Ridge, where three proposed survey areas (Gough, Tristan, Central) are located.

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).

In the South Atlantic, pygmy right whale records exist for southern Africa, Argentina, Falkland Islands, and pelagic waters (Baker 1985). Leeney

et al.

(2013) reported 12 strandings and 8 records of skeletal remains for Namibia since 1978. Most of the records are for Walvis Bay; strandings have only been reported during austral summer (November-March). The large number of juveniles suggests that the area may be a nursery ground (Leeney

et al.

2013). Best (2007) reported records between 30° S and 40° S, including near the Central survey area. Bester and Ryan (2007) suggested that pygmy right whales occur in the Tristan da Cunha archipelago. One pygmy right whale was taken by whalers at 35° S and 8° W on 30 November 1970 (Budylenko

et al.

1973

in

Best

et al.

2009). There are no OBIS records of pygmy right whales for the offshore waters of the proposed survey area, but 10 records exist off southwestern Africa (OBIS 2019). Pygmy right whales could be seen in any of the proposed project area at the time of the surveys, in particular in the Gough, Tristan, and Central survey areas.

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).

An extensive data review and analysis by Branch

et al.

(2007a) showed that blue whales are essentially absent from the central regions of major ocean basins, including the South Atlantic. Blue whales were captured by the thousands off Angola, Namibia, and South Africa between 1908 and 1967 (Branch

et al.

2007a; Figueiredo and Weir 2014), including several catches near the proposed project area during 1958-1973 (including in November and December) and a few sightings off South Africa. However, whales were nearly extirpated in this region, and sightings are now rare (Branch

et al.

2007a). At least four records exist for Angola; all sightings were made in 2012, with at least one sighting in July, two in August, and one in October (Figueiredo and Weir 2014). Sightings were also made off Namibia in 2014 from seismic vessels (Brownell

et al.

2016). Waters off Namibia may serve as a possible wintering and possible breeding ground for Antarctic blue whales (Best 1998, 2007; Thomisch

et al.

2017). Antarctic blue whale calls were detected on acoustic recorders that were deployed northwest of Walvis Ridge (just to the north of the Valdivia Bank survey area) from November 2011 through May 2013 during all months except during September and October, indicating that not all whales migrate to higher latitudes during the summer (Thomisch

et al.

2017). Most blue whales in southeastern Africa are expected to be Antarctic blue whales; however, ~4 percent may be pygmy blue whales (Branch

et al.

2007b, 2008). In fact, pygmy blue whale vocalizations were detected off northern Angola in October 2008; these calls were attributed to the Sri Lanka population (Cerchio

et al.

2010). One offshore sighting of a blue whale was made at 13.4° S, 26.8° W and the other at 15.9° S, 4.6° W (Branch

et al.

2007a; OBIS 2019). The occurrence of blue whales in the Tristan da Cunha archipelago also seems likely (Bester and Ryan 2007). There are ~1845 blue whale records for the South Atlantic in the OBIS database; however, no records occur within the proposed project area (OBIS 2019). Blue whales could be encountered during the proposed surveys, in particular in the Valdivia Bank survey area.

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). Historical whaling data showed several catches for the Tristan da Cunha archipelago (Best

et al.

2009), as well as off Namibia and southern Africa (Best 2007). Fin whales appear to be somewhat common in the Tristan da Cunha archipelago from October-December (Bester and Ryan 2007). According to Edwards

et al.

(2015), sightings have been made south of South Africa from December-February; they did not report any sightings or acoustic detections near the proposed project area. Several fin whales sightings and strandings have been reported for Namibia in the last decade (NDP unpublished data

in

Pisces Environmental Services 2017). Fin whale calls were detected on acoustic recorders that were deployed northwest of Walvis Ridge from November 2011 through May 2013 during the months of November, January, and June through August, indicating that the waters off Namibia serve as wintering grounds (Thomisch

et al.

2017). Similarly, Best (2007) also suggested that waters off Namibia may be wintering grounds.

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). 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). Best (2007) showed summer concentrations between 30° S and 50° S, including near the three proposed survey areas (Central, Tristan, Gough) in the Guyot Province of Walvis Ridge. Waters off northern Namibia may serve as wintering grounds (Best 2007).

A sighting of a mother and calf were made off Namibia in March 2012, and one stranding was reported in July 2013 (NDP unpublished data in Pisces Environmental Services 2017). One sighting was made during seismic surveys off the coast of northern Angola between 2004 and 2009 (Weir 2011). A group of 2-4 sei whales was seen near St. Helena during April 2011 (Clingham

et al.

2013). Although the occurrence of sei whales is likely in the Tristan da Cunha archipelago (Bester and Ryan 2007), there have been no recent records of sei whales in the region; however, sei whale catches were made here in the 1960s (Best

et al.

2009). Sei whales were also taken off southern Africa during the 1960s, with some catches reported just to the southeast of the proposed survey area; catches were made during the May-July northward migration as well as during the August-October southward migration (Best and Lockyer 2002). In the OBIS database, there are 40 sei whale records for the South Atlantic; the closest records were reported at 33.3° S, 8.0° W and 35.1° S, 6.4° W (OBIS 2019). Sei whales could be encountered in any of the proposed survey areas at the time of the surveys, in particular in the Gough, Tristan, and Central survey areas.

Bryde's Whale

Bryde's whale occurs in all tropical and warm temperate waters in the Pacific, Atlantic and Indian oceans, between 40° N and 40° S (Jefferson

et al.

2015). It is one of the least known large baleen whales, and it remains uncertain how many species are represented in this complex (Kato and Perrin 2018).

B. brydei

is commonly used to refer to the larger form or “true” Bryde's whale and

B. edeni

to the smaller form; however, some authors apply the name B. edeni to both forms (Kato and Perrin 2018). Bryde's whale remains in warm (>16 °C) water year-round (Kato and Perrin 2018), but analyses have shown that it prefers water <20.6 °C in the eastern tropical Atlantic (Weir

et al.

2012). Seasonal movements have been recorded towards the Equator in winter and offshore in summer (Kato and Perrin 2018). It is frequently observed in biologically productive areas such as continental shelf breaks (Davis

et al.

2002) and regions subjected to coastal upwelling (Gallardo

et al.

1983; Siciliano

et al.

2004). Central oceanic waters of the South Atlantic, including the proposed project area, are considered part of its secondary range (Jefferson

et al.

2015).

In southern Africa, there are likely three populations of Bryde's whales—an inshore population, a pelagic population of the Southeast Atlantic stock, and the Southwest Indian Ocean stock (Best 2001). The Southeast Atlantic stock ranges from the equator to ~34° S and migrates north in the fall and south during the spring, with most animals occurring off Namibia during the austral summer (Best 2001). Numerous sightings have been made off Gabon (Weir 2011), Angola (Weir 2010, 2011), and South Africa (Findlay

et al.

1992), including in deep slope waters. Strandings have also been reported along the Namibian coast (Pisces Environmental Services 2017). Bryde's whale was sighted in the offshore waters of the South Atlantic during a cruise from Spain to South Africa in November 2009, near 22° S, 6° W (Shirshov Institut n.d.). In the OBIS database, there are 12 records off the coast of South Africa (OBIS 2019). Bryde's whales are not expected to occur in the Libra Massif survey area. However, they could be encountered in the rest of the proposed project area, in particular the eastern portions of the Valdivia Bank survey area.

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).

It is known to occur off South Africa during autumn and winter (Perrin

et al.

2018), but has not been reported for the waters off Angola or Namibia (Best 2007). It is likely to occur in the waters of the Tristan da Cunha archipelago (Bester and Ryan 2007). There are 36 records for the South Atlantic in the OBIS database, including records off South America and along the coast of Namibia and South Africa; there are no records in the proposed project area (OBIS 2019). Dwarf minke whales could be encountered in the proposed project area at the time of the surveys.

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).

In the Southeast Atlantic, Antarctic minke whales have been reported for the waters of South Africa, Namibia, and Angola (Best 2007). Antarctic minke whale calls were detected on acoustic recorders that were deployed northwest of Walvis Ridge from November 2011 through May 2013 during the months of November, December, January, and June through August, indicating that not all whales migrate to higher latitudes during the summer (Thomisch

et al.

2017). Sightings have also been made along the coast of Namibia, in particular during summer (NPD unpublished data

in

Pisces Environmental Services 2017). Antarctic minke whales are also likely to occur in the Tristan da Cunha archipelago (Bester and Ryan 2007). Two groups totaling seven whales were sighted at 36.4° S, 8.5° W on 7 October 1988 (Best

et al.

2009). A sighting of two 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 five OBIS records for the South Atlantic, including along the coast of South America and South Africa; there are no records for the proposed project area (OBIS 2019). Antarctic minke whales could be encountered in the proposed project area at the time of the surveys.

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.

In the Southern Hemisphere, humpback whales migrate annually from summer foraging areas in the Antarctic to breeding grounds in tropical seas (Clapham 2018). Two of the breeding grounds are in the South Atlantic, off Brazil and West Africa (Engel and Martin 2009). Bettridge

et al.

(2015) identified humpback whales at these breeding locations as the Brazil and Gabon/Southwest Africa DPSs. There may be two breeding substocks in Gabon/Southwest Africa, including individuals in the main breeding area in the Gulf of Guinea and those animals migrating past Namibia and South Africa (Rosenbaum

et al.

2009; Barendse

et al.

2010a; Branch 2011; Carvalho

et al.

2011). Migration rates are relatively high between populations within the southeastern Atlantic (Rosenbaum

et al.

2009). However, Barendse

et al.

(2010a) reported no matches between individuals sighted in Namibia and South Africa based on a comparison of tail flukes. In addition, wintering humpbacks have also been reported on the continental shelf of northwest Africa, which may represent the northernmost humpback whales that are known to winter in the Gulf of Guinea (Van Waerebeek

et al.

2013). Feeding areas for this stock include Bouvet Island (Rosenbaum

et al.

2014) and waters of the Antarctic Peninsula (Barendse

et al.

2010b).

Humpbacks have been seen on breeding grounds around São Tomé in the Gulf of Guinea from August through November; off Gabon, whales occur from late June-December (Carvalho

et al.

2011). The west coast of South Africa might not be a `typical' migration corridor, as humpbacks are also known to feed in the area; they are known to occur in the region during the northward migration (July-August), the southward migration (October-November), and into February (Barendse

et al.

2010b; Carvalho

et al.

2011; Seakamela

et al.

2015). The highest sighting rates in the area occurred during mid-spring through summer (Barendse

et al.

2010b). Off Namibia, the main peak of occurrence is during winter (July), with another peak during spring (September); however, this area is unlikely to be a breeding area (Elwen

et al.

2014). Elwen

et al.

(2014) suggested that humpbacks are migrating northward past Namibia during winter and migrate closer to shore during a southward migration during spring/summer. Humpback whale calls were detected on acoustic recorders that were deployed northwest of Walvis Ridge from November 2011 through May 2013 during the months of November, December, January, and May through August, indicating that not all whales migrate to higher latitudes during the summer (Thomisch

et al.

2017). Based on whales that were satellite-tagged in Gabon in winter 2002, migration routes southward include offshore waters along Walvis Ridge (Rosenbaum

et al.

2014). Hundreds of sightings have been made during seismic surveys off the coast of Angola between 2004 and 2009, including in deep slope water; most sightings were reported during winter and spring (Weir 2011). Best

et al.

(1999) reported some sightings off the coast of Angola during November 1995. Humpback whale acoustic detections were made in the area from June through December 2008 (Cerchio

et al.

2014).

Humpbacks occur occasionally around the Tristan da Cunha archipelago (Bester and Ryan 2007). Three records exist for Tristan waters, all south of 37° S (Best

et al.

2009). Humpback whales have also been sighted off St. Helena (MacLeod and Bennett 2007; Clingham

et al.

2013). Numerous humpbacks were detected visually and acoustically during a survey off Brazil from Vitória at ~20° S, 40° W, to Trindade and Martim Vaz islands during August-September 2010 (Wedekin

et al.

2014). One adult humpback was seen on 31 August near Trindade Island, at 20.5° S, 29.3° W in a water depth of 150 m, but no acoustic detections were made east of 35° W (Wedekin

et al.

2014). Numerous sightings were also made near Trindade Island during July-August 2007 and before that date (Siciliano

et al.

2012). For the South Atlantic, the OBIS database shows over 700 records for the South Atlantic, including along the coast of South America and western Africa, and in offshore waters of the central Atlantic (OBIS 2019). The closest sightings to the proposed survey areas in the southeastern Atlantic occur near the Gough survey area at 33.8° S, 2.1° E and 32.5° S, 3.8° E (OBIS 2019). The waters of the proposed project area are considered part of the humpback's secondary range (Jefferson

et al.

2015). However, humpback whales could be encountered at the time of the proposed surveys, in particular in the Valdivia Bank survey area.

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 >1,000 m deep at latitudes <40° where sea surface temperatures are <15° C; adult males move to higher latitudes as they grow older and larger in size, returning to warm-water breeding grounds according to an unknown schedule (Whitehead 2018).

Whaling data from the South Atlantic indicate that sperm whales may be migratory off South Africa, with peak abundances reported in the region during autumn and late winter/spring (Best 2007). The waters of northern Namibia and Angola were also historical whaling grounds (Best 2007; Weir 2019). Sperm whales were the most frequently sighted cetacean during seismic surveys off the coast of northern Angola between 2004 and 2009; hundreds of sightings were made off Angola and a few sightings were reported off Gabon (Weir 2011). Sperm whales have also been sighted off South Africa during surveys of the Southern Ocean (Van Waerebeek

et al.

2010). In addition, a sighting was made at 30.1° S, 14.3° E (Clingham

et al.

2013). Bester and Ryan (2007) reported that sperm whales might be common in the Tristan da Cunha archipelago. Catches of sperm whales in the 19th century were made in Tristan waters between October and January (Townsend 1935

in

Best

et al.

2009), and catches also occurred there in the 1960s (Best

et al.

2009). One group was seen at St. Helena during July 2009 (Clingham

et al.

2013). There are ~3,080 records of sperm whales for the South Atlantic in the OBIS database, including nearshore waters of South American and Africa and offshore waters (OBIS 2019). Most (3,069) records are from historical catch data, which include captures within the proposed project area (OBIS 2019). Sperm whales could be encountered in the proposed project area at the time of the surveys.

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).

Both species are known to occur in the South Atlantic, occurring as far south as northern Argentina in the west and South Africa in the east (Jefferson

et al.

2015). There are 30 records of

Kogia

sp. for Namibia; most of these are strandings of pygmy sperm whales, but one live stranding of a dwarf sperm whale has also been reported (Elwen

et al.

2013). Twenty-six sightings of dwarf sperm whales were made during seismic surveys off the coast Angola between 2004 and 2009 (Weir 2011). Findlay

et al.

(1992) reported numerous records of dwarf sperm whales for South Africa.

Kogia

sp. were sighted during surveys off St. Helena during August-October 2004 (Clingham

et al.

2013). There are no records of

Kogia

sp. in the offshore waters of the proposed survey area (OBIS 2019). The only records in the OBIS database for the South Atlantic are for Africa; there are 57 records of

K. breviceps

and 22 records of

K. sima

exist for southwestern Africa (OBIS 2019). Both pygmy and dwarf sperm whales could be encountered in the proposed project area at the time of the surveys.

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). One sighting was made south of Africa at ~40° S during surveys of the Southern Ocean (Van Waerebeek

et al.

2010). Arnoux's beaked whales likely occur in the Tristan da Cunha archipelago (Bester and Ryan 2007). There are three OBIS records for the Southeast Atlantic in South Africa and no records for the Southwest Atlantic (OBIS 2019). Based on information presented in Best (2007), it is more likely to be encountered in the southern Central, Gough, and Tristan survey areas than in the more northern survey area.

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), as well as for Gabon (Weir 2007) and Angola (Best 2007; Weir 2019). UNEP/CMS (2012) reported its presence in Namibia. Bester and Ryan (2007) suggested that Cuvier's beaked whales likely occur in the Tristan da Cunha archipelago. There are 11 OBIS records for the South Atlantic, including Brazil, Namibia, and South Africa; however, there are no records within or near the proposed project area (OBIS 2019). Cuvier's beaked whale could be encountered in the proposed project area at the time of the surveys.

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). Southern bottlenose whales were sighted near 45° S and south of there during surveys of the Southern Ocean (Van Waerebeek

et al.

2010). There are eight records in the OBIS database for the South Atlantic, including one in the central South Atlantic at 37.1° S, 12.3° W, as well as Brazil, Namibia, and South Africa (OBIS 2019). Based on limited information on its distributional range (Best 2007; Jefferson

et al.

2015),

the southern bottlenose whale is more likely to occur in the southern survey areas than the Valdivia Bank survey area.

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). The Tristan da Cunha archipelago has the second highest number of strandings (Mead 2018) and is thought to be a concentration area for Shepherd's beaked whales (Bester and Ryan 2007; Best

et al.

2009). Pitman

et al.

(2006) and Best

et al.

(2009) reported six stranding records for Tristan da Cunha and possible sightings on the Tristan Plateau (2 sightings of 10 whales on 17 November 1985 near 37.3° S, 12.5° W) and Gough Island (one sighting of 4-5 animals). Another stranding of two whales on Tristan da Cunha occurred on 13 January 2012 (Best

et al.

2014). Shepherd's beaked whales were sighted south of Africa during surveys of the Southern Ocean (Van Waerebeek

et al.

2010). There are three records for the South Atlantic in the OBIS database, all southwest of South Africa (OBIS 2019). Based on limited information on its distributional range (Best 2007; Jefferson

et al.

2015), Shepherd's beaked whale is more likely to occur in the southern survey areas than the Valdivia Bank survey area.

Blainville's Beaked Whale

Blainville's beaked whale is found in tropical and warm temperate waters of all oceans (Pitman 2018). It has the widest distribution throughout the world of all

Mesoplodon

species (Pitman 2018). In the South Atlantic, strandings have been reported for southern Brazil and South Africa (Findlay

et al.

1992; Secchi and Zarzur 1999; MacLeod

et al.

2006; Prado

et al.

2016). A sighting was made during a boat survey off St. Helena in November 2007 (Clingham

et al.

2013). There are 20 OBIS records for South Africa, but none for the offshore waters of the proposed project area (OBIS 2019). Based on limited information on its distributional range (Best 2007; Jefferson

et al.

2015), Blainville's beaked whale could be encountered in the proposed project area.

Gray's Beaked Whale

Gray's beaked whale is thought to have a circumpolar distribution in temperate waters of the Southern Hemisphere (Pitman 2018). It primarily occurs in deep waters beyond the edge of the continental shelf (Jefferson

et al.

2015). Some sightings have been made in very shallow water, usually of sick animals coming in to strand (Gales

et al.

2002; Dalebout

et al.

2004). There are numerous sighting records from Antarctic and sub-Antarctic waters (MacLeod

et al.

2006); in summer months, Gray's beaked whales appear near the Antarctic Peninsula and along the shores of the continent (sometimes in the sea ice).

In the South Atlantic, several stranding records exist for Brazil, the southeast coast of South America, Falkland Islands, Namibia, and South Africa (Findlay

et al.

1992; MacLeod

et al.

2006; Otley 2012; Otley

et al.

2012; Prado

et al.

2016; Riccialdelli

et al.

2017). Additionally, one sighting was reported off the southwestern tip of South Africa (MacLeod

et al.

2006). A sighting was also made south of Arica near 45° S during surveys of the Southern Ocean (Van Waerebeek

et al.

2010). UNEP/CMS (2012) reported their presence in Namibia. Gray's beaked whales likely occur in the Tristan da Cunha archipelago (Bester and Ryan 2007). However, there are no OBIS records for the offshore waters of the proposed project area, but there are records for Argentina and South Africa (OBIS 2019). Based on limited information on its distributional range (Best 2007; Jefferson

et al.

2015). Gray's beaked whale is more likely to occur in the southern survey areas than the Valdivia Bank survey area.

Hector's Beaked Whale

Hector's beaked whale is thought to have a circumpolar distribution in temperate waters of the Southern Hemisphere (Pitman 2018). Like other Mesoplodonts, Hector's beaked whale likely inhabits deep waters (200-2000 m) in the open ocean or continental slopes (Pitman 2018). To date, Hector's beaked whales have only been identified from strandings and have not been observed in the wild (Pitman 2018). Based on the number of stranding records for the species, it appears to be relatively rare. Nonetheless, in the South Atlantic, strandings have been reported for southern Brazil, Argentina, Falkland Islands, and South Africa (MacLeod

et al.

2006; Otley

et al.

2012; Prado

et al.

2016; Riccialdelli

et al.

2017). However, there are no OBIS records for this species for the South Atlantic (OBIS 2019). Based on limited information on its distributional range (Best 2007; Jefferson

et al.

2015). Hector's beaked whale is more likely to occur in the southern survey areas than the Valdivia Bank survey area.

Gervais' Beaked Whale

Although Gervais' beaked whale is generally considered to be a North Atlantic species, it likely occurs in deep waters of the temperate and tropical Atlantic Ocean in both the northern and southern hemispheres (Jefferson

et al.

2015). Stranding records have been reported for Brazil and Ascension Island in the central South Atlantic (MacLeod

et al.

2006). The southernmost stranding record was reported for São Paulo, Brazil, possibly expanding the known distributional range of this species southward (Santos

et al.

2003). Although the distribution range of Gervais' beaked whale is not generally known to extend as far south as the proposed project area, this species might range as far south as Angola or northern Namibia in the South Atlantic (MacLeod

et al.

2006; Best 2007; Jefferson

et al.

2015). In fact, one stranding has been reported for Namibia (Bachara and Norman 2014). There are no OBIS records for the South Atlantic (OBIS 2019). Gervais' beaked whale could be encountered in the proposed project area at the time of the surveys.

True's Beaked Whale

True's beaked whale has a disjunct, antitropical distribution (Jefferson

et al.

2015). In the Southern Hemisphere, it is known to occur in South Africa, South America, and Australia (Findlay

et al.

1992; Souza

et al.

2005; MacLeod and Mitchell 2006; MacLeod

et al.

2006; Best

et al.

2009). These areas may comprise three separate populations; the region of South Africa in the Indian Ocean is considered a key beaked whale area (MacLeod and Mitchell 2006). In the South Atlantic, True's beaked whale has stranded on Tristan da Cunha (Best

et al.

2009). Based on stranding and sighting data, the proposed southern project area, including southern waters of Valdivia Bank survey area, is part of the possible range of True's beaked whale (MacLeod

et al.

2006; Best 2007; Jefferson

et al.

2015). There are 14 OBIS records for the South Atlantic, all for the off South Africa (OBIS 2019). True's beaked whale could be encountered in the proposed project area at the time of the surveys.

Strap-Toothed Beaked Whale

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). Strap-toothed beaked whales are thought to migrate northward from Antarctic and subantarctic latitudes during April-September (Sekiguchi

et al.

1995).

In the South Atlantic, stranding records have been reported for Brazil, Uruguay, Argentina, Falkland Islands, South Georgia, Namibia, and South Africa (Findlay

et al.

1992; Pinedo

et al.

2002; MacLeod

et al.

2006; Otley

et al.

2012; Prado

et al.

2016; Riccialdelli

et al.

2017). In addition, sightings have been reported off the southern tip of Africa, near Bouvet Island, and in the Southern Ocean (Finlay

et al.

1992; MacLeod

et al.

2006). One sighting was made south of Africa during surveys of the Southern Ocean (Van Waerebeek

et al.

2010). Bester and Ryan (2007) suggested that strap-toothed beaked whales likely occur in the Tristan da Cunha archipelago (Bester and Ryan 2007). There are 38 OBIS records for the South Atlantic, including for Argentina, Namibia, and South Africa; however, there are no records in the offshore waters of the proposed project area (OBIS 2019). Based on limited information on its distributional range (Best 2007; Jefferson

et al.

2015), strap-toothed beaked whales are more likely to occur in the southern survey areas than the Valdivia Bank survey area.

Andrew's Beaked Whale

Andrew's beaked whale has a circumpolar distribution in temperate waters of the Southern Hemisphere (Baker 2001; Pitman 2018). It is known only from stranding records between 32° S and 55° S, with more than half of the strandings occurring in New Zealand (Jefferson

et al.

2015). In the South Atlantic, Andrew's beaked whales have also stranded in the Tristan da Cunha archipelago, Falkland Islands, Argentina, and Uruguay (Baker 2001; Laporta

et al.

2005; MacLeod

et al.

2006; Best

et al.

2009; Otley

et al.

2012; Riccialdelli

et al.

2017). There are no OBIS records for the South Atlantic (OBIS 2019). Based on limited information on its distributional range (Best 2007; Jefferson

et al.

2015), Andrew's beaked whale is more likely to occur in the southern survey areas than the Valdivia Bank survey area.

Spade-Toothed Beaked Whale

The spade-toothed beaked whale is the name proposed for the species formerly known as Bahamonde's beaked whale (

M. bahamondi

); genetic evidence has shown that it belongs to the species first identified by Gray in 1874 (Van Helden

et al.

2002). 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). Although no records currently exist for the South Atlantic, the known records at similar latitudes suggest that the spade-toothed beaked whale could occur in the proposed project area.

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). In the southeastern Atlantic Ocean, there are records spanning from Gabon to South Africa (Jefferson

et al.

2014). It appears to be relatively common off Angola; 75 sightings were made during seismic surveys off the coast of northern Angola between 2004 and 2009, including in deep slope waters (Weir 2011). Four sightings were also made off Gabon (Weir 2011). It was also sighted during surveys off southern Africa, and there are stranding records for Namibia (Findlay

et al.

1992). There are 54 records for the South Atlantic in the OBIS database, including for Argentina, Namibia, and South Africa; however, there are no records in the proposed project area. Risso's dolphin could be encountered in the proposed survey areas at the time of the surveys.

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). In the Southeast Atlantic, rough-toothed dolphins have been sighted off Namibia (Findlay

et al.

1992), Gabon (de Boer 2010), and Angola (Weir 2007, 2010). Eighteen sightings were made during seismic surveys off the coast of northern Angola between 2004 and 2009, including in deep slope waters; one sighting was also made off Gabon (Weir 2011). Rough-toothed dolphins have also been sighted at St. Helena (MacLeod and Bennett 2007; Clingham

et al.

2013), near the Central survey area at 32.5° S, 2.0° W (Peters 1876

in

Best

et al.

2009), and near 37° S, 15° E (Scheidat

et al.

2011). One rough-toothed dolphin sighting was made during an August-September 2010 survey off Brazil from Vitória at ~20° S, 40° W to Trindade and Martim Vaz islands; the group of 30 individuals was seen in association with two minke whales at ~19.1° S, 35.1° W on 21 August (Wedekin

et al.

2014). For the South Atlantic, there are 42 records of rough-toothed dolphin in the OBIS database, including off Brazil, central West Africa, and South Africa (OBIS 2019). Rough-toothed dolphins could be encountered in the proposed project area during the surveys.

Common Bottlenose Dolphin

The bottlenose dolphin occurs in tropical, subtropical, and temperate waters throughout the world (Wells and Scott 2018). Although it is more commonly found in coastal and shelf waters, it can also occur in deep offshore waters (Jefferson

et al.

2015). Jefferson

et al.

(2015) reported central pelagic waters of the South Atlantic Ocean (within the proposed project area) as secondary range for the bottlenose dolphin. In the southeastern South Atlantic, common bottlenose dolphins occur off Gabon (de Boer 2010), Angola (Weir 2007, 2010), Namibia (Findlay

et al.

1992; Peddemors 1999), and South Africa (Findlay

et al.

1992). Off Namibia, there is likely an inshore and an offshore ecotype (Peddemors 1999). Numerous sightings were made during seismic surveys off the coast of northern Angola between 2004 and 2009, including in deep slope waters; sightings were also made off Gabon (Weir 2011).

Three sightings of common bottlenose dolphins were made at Trindade Island during December 2009-February 2010 surveys; two sightings of 15 individuals were made during December and a single bottlenose dolphin was sighted on 23 February (Carvalho and Rossi-Santos 2011). Additionally, two sightings of common bottlenose dolphins were made during an August-September 2010 survey from Vitória at ~20° S, 40° W to Trindade and Martim Vaz islands; both groups were seen on 30 August at Trindade Island, near 20.5° S, 29.3° W (Wedekin

et al.

2014). Common bottlenose dolphins have also been sighted near St. Helena (MacLeod and Bennett 2007; Clingham

et al.

2013). There are 132 OBIS records for the western and eastern South Atlantic; however, there are no records in the offshore waters of the proposed project area (OBIS 2019). Common bottlenose dolphins could be encountered in the

proposed project area during the surveys (Jefferson

et al.

2015).

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). In the South Atlantic, pantropical spotted dolphins have been sighted off Brazil (Moreno

et al.

2005), Gabon (de Boer 2010), Angola (Weir 2007, 2010), and St. Helena (MacLeod and Bennett 2007; Clingham

et al.

2013). Four sightings were made during seismic surveys off the coast off northern Angola between 2004 and 2009, including in deep slope waters; and additional four sightings were made off Gabon (Weir 2011). Findlay

et al

(1992) reported sightings off the east coast of South Africa. In the OBIS database, there is one record for Brazil and one record for South Africa (OBIS 2019). Based on its distributional range (Best 2007; Jefferson

et al.

2015), pantropical spotted dolphins could be encountered during the proposed surveys.

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). Although its distributional range appears to be just to the north of the proposed project area (Best 2007; Jefferson

et al.

2015), Culik (2004) reported its presence in Namibia. These dolphins were one of the most frequently sighted cetaceans during seismic surveys off the coast of northern Angola between 2004 and 2009, including in deep slope waters; about 100 sightings were made off Angola and several sightings were also made off Gabon (Weir 2011). For the South Atlantic, there is one record for Brazil in the OBIS database (OBIS 2019). Atlantic spotted dolphins could be encountered in the proposed project area during the surveys.

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).

Its distributional range appears to be to the north of the proposed survey area in the South Atlantic (Best 2007; Jefferson

et al.

2015). One group of three individuals was seen near the 1000-m isobath during seismic surveys off the coast of northern Angola between 2004 and 2009 (Weir 2011). There are two OBIS records for the South Atlantic: One sighting north of the Falkland Islands at 47.4° S, 54.2° W and another off Brazil (OBIS 2019). Based on distributional information (Best 2007; Jefferson

et al.

2015), spinner dolphins could be encountered during the proposed surveys, most likely in the northern parts of the Valdivia Bank survey area.

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 700-4,500 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).

In the eastern Atlantic, they have been sighted as far south as Angola (Weir 2006; Weir

et al.

2014). One sighting was made during seismic surveys off the coast of northern Angola between 2004 and 2009 (Weir 2011). Currently available information indicates that only the northern-most proposed project area might overlap with its distributional range (

e.g.,

Fertl

et al.

2003; Best 2007; Jefferson

et al.

2015), although Weir

et al.

(2014) noted that it is unlikely that this species occurs farther south than Angola due to the cold Benguela Current there. There are no OBIS records for the South Atlantic (OBIS 2019). Based on distributional information (Best 2007; Jefferson

et al.

2015), Clymene dolphins could be encountered in the northern parts of the Valdivia Bank survey area.

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).

Sightings have been made on the west coast of South Africa (Findlay

et al.

1992). Sixty-six sightings were made during seismic surveys off the coast of northern Angola between 2004 and 2009, including in deep slope waters (Weir 2011). There are approximately 60 OBIS records for the South Atlantic, including nearshore waters of Brazil, Uruguay, Argentina, Angola, and South Africa, and 19 records for offshore waters near 8.4° S, 24.4° W (OBIS 2019). Based on distributional information (Best 2007; Jefferson

et al.

2015), striped dolphins could be encountered during the proposed surveys.

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).

In the South Atlantic, the short-beaked common dolphin occurs along the coasts of South America and Africa (Perrin 2018c). Although according to Jefferson

et al.

(2015) and Perrin (2018c), its occurrence in central oceanic waters of the South Atlantic is uncertain, Best (2007) reported a few records between 30-41° S, 15° W-10° E. Sightings have also been reported along the coast of Namibia (Best 2007; NDP unpublished data

in

Pisces Environmental Services 2017). Sightings have been reported off the west coast of southern Africa during summer and winter, and there are stranding records for Namibia (Findlay

et al.

1992). About 100 sightings of

Delphinus

sp. were made during seismic surveys off the coast of northern Angola between 2004 and 2009, including in deep slope waters; sightings were also made off Gabon (Weir 2011). For the South Atlantic, there are 7 OBIS records for waters off Argentina and nearly 80 records for southwestern Africa, including Namibia and South Africa (OBIS 2019). Short-beaked common dolphins could be encountered in the proposed project area at the time of the surveys.

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). Strandings in more temperate waters, such as in Uruguay, are likely extralimital (Dolar 2018). Three sightings were made during seismic surveys off the coast of northern Angola between 2004 and 2009, all in water deeper than 1000 m; one sighting was made in the Gulf of Guinea (Weir

et al.

2008; Weir 2011). Fraser's dolphin has

also been sighted off the east coast of South Africa (Findlay

et al.

1992). There are 24 OBIS records for the South Atlantic, all along the coast of South America (OBIS 2019). Based on its distribution (Jefferson

et al.

2015), Fraser's dolphin could be encountered during the proposed surveys, but is more likely to be seen in the northern portions of the Valdivia Bank survey area than elsewhere.

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). In the southeastern Atlantic, it occurs along the coast of Angola, Namibia, and South Africa, as well as Tristan da Cunha (Findlay

et al.

1992; Culik 2004; Weir 2019). It appears to occur off the west coast of southern Africa year-round (Findlay

et al.

1982). According to Jefferson

et al.

(2015), it is unlikely to occur in the deep waters of the proposed project area.

It has been observed in groups of 10 to 20 individuals preying on Cape horse mackerel off Namibia (Bernasconi

et al.

2011), and it has been seen in mixed groups with southern right whale dolphins there (Culik 2004). It was sighted during spring surveys off west coast of South Africa during 2014 (Seakamala

et al.

2015). It has also been reported near Gough Island; animals there likely make up a disjunct oceanic population rather than suggesting movement of individuals between South America and southern Africa (Cassens

et al.

2005). There are ~150 OBIS records for the South Atlantic, but none occur within the proposed project area. The dusky dolphin is unlikely to be encountered in the proposed survey areas in the southeastern Atlantic, and is not expected to occur in the Libra Massif survey area.

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 are approximately 45 records in the OBIS database for the Southwest Atlantic, but none within the Libra Massif survey area (OBIS 2019). Based on its known distributional range (Best 2007; Jefferson

et al.

2015), it could occur in the southern-most portions of the proposed project area.

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). It is also known to occur off Namibia (Findlay

et al.

1992; Culik 2004), where it has been seen out to the 1000-m isobath (Rose and Payne 1991); it is thought to occur in the region year-round (Rose and Payne 1991). However, Best (2007) did not report any sightings in the Valdivia Bank survey area. There are no records for the South Atlantic in the OBIS database (OBIS 2019). Bester and Ryan (2007) suggested that southern right whale dolphins might be visitors to the southern waters of the Tristan da Cunha archipelago. One was captured near Tristan da Cunha on 10 December 1847 at 37.1° S, 11.6° W (Cruickshank and Brown 1981

in

Best

et al.

2009). There are no records for the South Atlantic in the OBIS database (OBIS 2019). According its distribution range (Best 2007; Jefferson

et al.

2015), southern right whale dolphins could occur in the proposed project area, although they are more likely to be encountered in the more southerly survey areas.

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). In the southeastern Atlantic, killer whales are known to occur off Gabon (de Boer 2010; Weir 2010), Angola (Weir 2007, 2010, 2011), as well as Namibia and South Africa (Findlay

et al.

1992; Best 2007; Elwen and Leeney 2011). Sightings of killer whale pods of 1 to >100 individuals have been made near the proposed survey areas during November and December (Budylenko 1981; Mikhalev

et al.

1981). Eighteen sightings were made during seismic surveys off northern Angola between 2004 and 2009, including in deep slope waters; one sighting was made off Gabon (Weir 2011). The number of sightings are thought to decrease north of Cape Town, South Africa, but sightings have been made year round, including in offshore waters (up to 600 km from shore), but not within the proposed project area (Rice and Saayman 1987). Killer whales are known to prey on longline catches in the waters off South Africa (Williams

et al.

2009). Sightings of killer whale pods of 1 to >100 individuals have been made near the Libra Massif survey area during November (Budylenko 1981; Mikhalev

et al.

1981). A sighting was made south of the proposed survey areas at approximately 45° S, 8° W (Scheidat

et al.

2011). There are about 55 records of killer whales for the South Atlantic in the OBIS database, including records for offshore and nearshore waters of South America, as well as South Africa (OBIS 2019); however, there are no records near the proposed survey areas.

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). Short-finned pilot whales were the most frequently sighted cetacean during seismic surveys off the coast of Angola between 2004 and 2009; more than 100 sightings were off Angola including in deep slope waters and several sightings were also reported off Gabon (Weir 2011). There are records of long-finned pilot whales for South Africa and Namibia (Findlay

et al.

1992; Best 2007). Long-finned pilot whales are considered uncommon in Tristan waters (Bester and Ryan 2007); pilot whales have stranded on the islands of the Tristan da Cunha archipelago, although it is uncertain what species they were (Best

et al.

2009). There is a single record of short-finned pilot whales in the Southwest Atlantic Ocean, but there are >100 long-finned pilot whale records for the waters off South America, Namibia, South Africa, and the central Atlantic Ocean (OBIS 2019). Based on their distributional ranges (Best 2007; Jefferson

et al.

2015), short-finned pilot whales are more likely to occur in the Valdivia Bank survey area, whereas long-finned pilot whales are more likely to occur in the more southern survey areas.

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 false killer whales occurs throughout the South Atlantic. In the southeast Atlantic Ocean, 13 sightings were made during seismic surveys off the coast of northern Angola between 2004 and 2009, all in water deeper than 1000 m (Weir 2011). Stranding records and sightings also exist for Namibia and South Africa (Findlay

et al.

1992). They have also been recorded around St. Helena (Clingham

et al.

2013). Predation events by killer whales or false killer whales in the Uruguayan longline fishery were recorded north of the Libra Massif survey area (Passadore

et al.

2014, 2015). Although there are no OBIS records of false killer whales for the offshore waters of the proposed project area, there are 91 records for the South Atlantic, including offshore waters off South America and nearshore waters of Namibia and South Africa; however, there are no records near the proposed survey areas (OBIS 2019). Based on its distributional range (Best 2007; Jefferson

et al.

2015), the false killer whale could be encountered in the proposed project areas.

Pygmy Killer Whale

The pygmy killer whale has a worldwide distribution in tropical and subtropical waters, generally not ranging south of 35° S (Jefferson

et al.

2015). It is known to inhabit the warm waters of the Indian, Pacific, and Atlantic oceans (Jefferson

et al.

2015). It can be found in nearshore areas where the water is deep and in offshore waters (Jefferson

et al.

2015). In the southeast Atlantic, there are stranding records along the coast of southern Africa, including Namibia (Findlay

et al.

1992). There is one stranding record for Brazil (Santos

et al.

2010). There are seven OBIS records for the Southeast Atlantic Ocean, but no records for the offshore waters of the proposed survey areas (OBIS 2019). Based on its distributional range (Best 2007; Jefferson

et al.

2015), the pygmy killer whale could be encountered in the proposed survey areas.

Melon-Headed Whale

The melon-headed whale is an oceanic species found worldwide in tropical and subtropical waters from ~40° N to 35° S (Jefferson

et al.

2015). It occurs most often in deep offshore waters and occasionally in nearshore areas where the water is deep (Jefferson

et al.

2015). Off the west coast of Africa, melon-headed whales have been recorded off Gabon (de Boer 2010; Weir 2011) and Angola (Weir 2007a, 2010, 2011). Four sightings were made during seismic surveys off the coast of northern Angola between 2004 and 2009, all in water deeper than 1000 m (Weir 2011). Extralimital record exists for South Africa (Peddemors 1999; Jefferson

et al.

2015). There is one OBIS record for South Africa (OBIS 2019). Based on its distributional range (Best 2007; Jefferson

et al.

2015), melon-headed whale could be encountered in the northern portion of the Valdivia Bank survey area.

Pinnipeds

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. Vagrant subantarctic fur seals have been reported in South Africa (Shaughnessy and Ross 1980). The at-sea distribution of subantarctic fur seals is poorly understood, although they are often seen in the waters between Tristan da Cunha and South Africa (Bester and Ryan 2007). There are 35 OBIS records for the South Atlantic, including in nearshore and offshore waters of South Africa, and 21 records at 40.3° S, 9.9° W; however, there are no records for the proposed project area (OBIS 2019).

Cape Fur Seal

The Cape fur seal is endemic to the west coast of southern Africa, occurring from Algoa Bay, South Africa to Ilha dos Tigres, Angola (Kirkman

et al.

2013). The population severely declined between the 17th and 19th century, due to sealing and guano collection on many of the breeding islands (Kirkman

et al.

2007). However, the population recovered when sealing limits were imposed in the early 20th century, and the population is now estimated to number ~2 million individuals (Kirkman

et al.

2007). There have also been two mass die-offs of Cape fur seals in Namibia that were related to poor environmental conditions and reduced prey (Roux

et al.

2002

in

Kirkman

et al.

2007).

The Cape fur seal currently breeds at 40 colonies along the coast of South Africa, Namibia, and Angola, including on the mainland and nearshore islands (Kirkman

et al.

2013). There have been several new breeding colonies established in recent years, as the population has shifted northward (Kirkman

et al.

2013). More than half of the seal population occurs in Namibia (Wickens

et al.

1991). High densities have been observed between 30 and 60 n.mi. from shore, with densities dropping farther offshore (Thomas and Schülein 1988). Cape fur seals typically forage over the shelf up to ~220 km offshore (Shaughnessy 1979), but they are known to travel distances up to 1970 km along the coast of South America (Oosthuizen 1991). Breeding occurs during November and December (Warneke and Shaughnessy 1985

in

Kirkman and Arnould 2018). There are over 2000 OBIS records along the coasts of Namibia and South Africa, but no records for the offshore survey areas. As Cape fur seals typically remain over the shelf to forage and are breeding during the time of the survey, they are unlikely to be encountered in the offshore project area.

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 (Oliveira

et al.

2006). Telemetry studies show that crabeater seals are generally confined to the pack ice, but spend ~14 percent of their time in open water outside of the breeding season (reviewed in Southwell

et al.

2012). During the breeding season crabeater seals were most likely to be present within 5° or less (~550 km) of the shelf break in the south, though non-breeding animals ranged further north. Pupping season peaks in mid- to late-October and adults are observed with their pubs as late as mid-December (Bengtson and Stewart 2018). There are two records of crabeater seals for South Africa in the OBIS database (OBIS 2019).

Leopard Seal

The leopard seal has a circumpolar distribution around the Antarctic continent where it is solitary and widely dispersed (Rogers 2018). Leopard seals are top predators, consuming everything from krill and fish to penguins and other seals (

e.g.,

Hall-Aspland and Rogers 2004; Hirukie

et al.

1999). Pups are born during October to mid-November and weaned approximately one month later (Rogers 2018). Mating occurs in the water during December and January. There is one record for South Africa 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). Breeding colonies are otherwise island-based, with the occasional exception of the Antarctic mainland (Hindell 2018).

When not breeding (September-October) or molting (November-April), southern elephant seals range throughout the Southern Ocean from areas north of the Antarctic Polar Front to the pack ice of the Antarctic, spending >80 percent of their time at sea each year, up to 90 percent of which is spent submerged while hunting, travelling and resting in water depths ≥200 m (Hindell 2018). Males generally feed in continental shelf waters, while females preferentially feed in ice-free Antarctic Polar Front waters or the marginal ice zone in accordance with winter ice expansion (Hindell 2018). Southern elephant seals tagged at South Georgia showed long-range movements from ~April through October into the open Southern Ocean and to the shelf of the Antarctic Peninsula (McConnell and Fedak 1996). One adult male that was sighted on Gough Island had previously been tagged at Marion Island in the Indian Ocean (Reisinger and Bester 2010). Vagrant southern elephant seals, mainly consisting of juvenile and subadult males, have been documented in Uruguay, Brazil, Argentina, Falkland Islands, and South Georgia (Lewis

et al.

2006a; Oliveira

et al.

2011; Mayorga

et al.

2015). For the South Atlantic, there are more than 2000 OBIS records for the nearshore and offshore waters of South America and along the coasts of Namibia and South Africa (OBIS 2019). Most of the records (1793) are for waters of the Patagonian Large Marine Ecosystem (Campagna

et al.

2006), but none occur within the proposed project area.

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-eight marine mammal species (43 cetacean and 5 pinniped (2 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, 9 are classified as low-frequency cetaceans (

i.e.,

all mysticete species), 31 are classified as mid-frequency cetaceans (

i.e.,

most delphinid and ziphiid species and the sperm whale), and 3 are classified as high-frequency cetaceans (

i.e.,

Kogia spp., hourglass dolphin).

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. 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.

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. Therefore, we do not consider noise from the MBES or SBP 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 Sound Sources

section) 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 (2018).

Behavioral Effects

—Behavioral disturbance may include a variety of effects, including subtle changes in behavior (

e.g.,

minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors (

e.g.,

species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (

e.g.,

Richardson

et al.,

1995; Wartzok

et al.,

2003; Southall

et al.,

2007; 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, l

et al

one 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 some 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. 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.

A modeling exercise was conducted as a follow-up to the McCauley

et al.

(2017) study (as recommended by McCauley

et al.

), in order to assess the potential for impacts on ocean ecosystem dynamics and zooplankton population dynamics (Richardson

et al.,

2017). Richardson

et al.

(2017) found that for copepods with a short life cycle in a high-energy environment, a full-scale airgun survey would impact copepod abundance up to three days following the end of the survey, suggesting that effects such as those found by McCauley

et al.

(2017) would not be expected to be detectable downstream of the survey areas, either spatially or temporally.

Notably, a recently described study produced results inconsistent with those of McCauley

et al.

(2017). Researchers conducted a field and laboratory study to assess if exposure to airgun noise affects mortality, predator escape response, or gene expression of the copepod

Calanus finmarchicus

(Fields

et al.,

2019). Immediate mortality of copepods was significantly higher, relative to controls, at distances of 5 m or less from the airguns. Mortality one week after the airgun blast was significantly higher in the copepods placed 10 m from the airgun but was not significantly different from the controls at a distance of 20 m from the airgun. The increase in mortality, relative to controls, did not exceed 30 percent at any distance from the airgun. Moreover, the authors caution that even this higher mortality in the immediate vicinity of the airguns may be more pronounced than what would be observed in free-swimming animals due to increased flow speed of fluid inside bags containing the experimental animals. There were no sublethal effects on the escape performance or the sensory threshold needed to initiate an escape response at any of the distances from the airgun that were tested. Whereas McCauley

et al.

(2017) reported an SEL of 156 dB at a range of 509-658 m, with zooplankton mortality observed at that range, Fields

et al.

(2019) reported an SEL of 186 dB at a range of 25 m, with no reported mortality at that distance.

Regardless, if we assume a worst-case likelihood of severe impacts to zooplankton within approximately 1 km of the acoustic source, the typically wide dispersal of survey vessels and brief time to regeneration of the potentially affected zooplankton populations does not lead us to expect any meaningful follow-on effects to the prey base for odontocete predators. Given t

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