Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey in the Gulf of Alaska
Federal RegisterApr 9, 2019
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
RIN 0648-XG736
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey in the Gulf of Alaska
AGENCY:
National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce.
ACTION:
Notice; proposed incidental harassment authorization; request for comments on proposed authorization and possible renewal.
SUMMARY:
NMFS has received a request from the Lamont-Doherty Earth Observatory of Columbia University (L-DEO) for authorization to take marine mammals incidental to a marine geophysical survey in the Gulf of Alaska. 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 May 9, 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.redding@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:
Gray Redding, 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/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.
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.
The definitions of all applicable MMPA statutory terms cited above are included in the relevant sections below.
National Environmental Policy Act
To comply with the National Environmental Policy Act of 1969 (NEPA; 42 U.S.C. 4321
et seq.
) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed action (
i.e.,
the issuance of an incidental harassment authorization) with respect to potential impacts on the human environment.
Accordingly, NMFS plans to adopt the National Science Foundation's (NSF) EA, provided our independent evaluation of the document finds that it includes adequate information analyzing the effects on the human environment of issuing the IHA. NMFS is a cooperating agency on NSF's EA. NSF's EA will be made available for public comment at
https://www.nsf.gov/geo/oce/envcomp/
on approximately April 1, 2019. 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 November 20, 2018, NMFS received a request from L-DEO for an IHA to take marine mammals incidental to conducting seismic geophysical surveys in the Gulf of Alaska along the Alaska Peninsula subduction zone. On December 19, 2018, NMFS received a revised copy of the application, and that application was deemed adequate and complete on February 11, 2019. L-DEO's request is for take of a small number of 21 marine mammal species by Level B harassment and Level A harassment. Underwater sound associated with airgun use may result in the behavioral harassment or auditory injury of marine mammals in the ensonified areas. Neither L-DEO nor NMFS expects serious injury or mortality to result from this activity and, therefore, an IHA is appropriate.
NMFS previously issued an IHA to L-DEO for similar work (76 FR 38621; July 1, 2011). L-DEO complied with all the requirements (
e.g.,
mitigation, monitoring, and reporting) of the previous IHA and information regarding their monitoring results may be found in the “Description of Marine Mammals in the Area of Specified Activities.”
Description of Proposed Activity
Overview
The specified activity consists of a high energy geophysical seismic survey conducted in a portion of the Gulf of
Alaska. Researchers from Lamont-Doherty Earth Observatory (L-DEO), Cornell University, Colgate University, University of Washington, University of California Santa Cruz, University of Colorado Boulder, University of New Mexico, Washington University in St. Louis, and the United States Geological Survey (USGS), with funding from NSF, propose to conduct the seismic survey from the Research Vessel (R/V)
Marcus G. Langseth
(
Langseth
) in the Gulf of Alaska during 2019. The NSF-owned
Langseth
is operated by Columbia University's L-DEO under an existing Cooperative Agreement. The proposed seismic survey would likely occur off the Alaska Peninsula and the eastern Aleutian islands during late spring 2019 and would use a 36-airgun towed array with a total discharge volume of ~6600 in
3
. The survey would take place within the U.S. Exclusive Economic Zone (EEZ), in water ~15 to ~6,184 m deep.
The main goal of L-DEO's proposed seismic program is to conduct a 2D survey along the Alaska Peninsula subduction zone using airguns. The addition of active sources (airguns) to the existing seismic monitoring equipment in place would directly contribute to the overall project goals of imaging the architecture for the subduction zone and understanding the structures controlling how and where the planet's largest earthquakes occur.
Dates and Duration
The survey is expected to consist of up to 18 days of seismic operations and ~1 day of transit. The
Langseth
would leave from and return to port in Kodiak, likely during late spring (end of May/early June) 2019. Tentative sail dates are 1-19 June 2019.
Timing of the proposed survey will take advantage of the Alaska Amphibious Community Seismic Experiment (AACSE), which has deployed 75 ocean bottom seismometers (OBSs) offshore of the Alaska Peninsula. The survey needs to be conducted while the AACSE OBSs are on the sea floor (before 6 August 2019). The most value-added time window is mid-May through mid-June, when an on-shore seismic array, consisting of 400-450 onshore seismometers will also be deployed on Kodiak Island and which could record an unprecedented ship-to-shore dataset.
Specific Geographic Region
The proposed survey would occur within the area of ~52-58° N, ~150-162° W, within the EEZ of Alaska in water depths ranging from ~15 to ~6184 m. Representative survey tracklines are shown in Figure 1. As described further in this document, however, deviation in actual track lines, including order of survey operations, could be necessary for reasons such as science drivers, poor data quality, inclement weather, or mechanical issues with the research vessel and/or equipment. Thus, within the constraints of any federal authorizations issued for the activity, tracklines may shift from those shown in the application and could occur anywhere within the coordinates noted above and illustrated by the box in the inset map on Figure 1 of the IHA application.
EN09AP19.000
Detailed Description of Specific Activity
The procedures to be used for the proposed surveys would be similar to those used during previous seismic surveys by L-DEO and would use conventional seismic methodology. The surveys would involve one source vessel, the
Langseth,
which is owned by NSF and operated on its behalf by Columbia University's L-DEO. The
Langseth
would deploy an array of 36 airguns as an energy source with a total volume of ~6,600 in
3
. The receiving system would consist of previously deployed OBSs and onshore seismometers (See Figure 2 in IHA Application), as well as a single hydrophone streamer 5 kilometers (km) in length; no hydrophone streamer would be towed during the survey. As the airgun arrays are towed along the survey lines, the seismometers would receive and store the returning acoustic signals internally for later analysis and the hydrophone streamer would transfer the data to the on-board processing system.
For this proposed survey, a total of ~4400 km of transect lines would be surveyed in the Gulf of Alaska (GOA). There could be additional seismic operations associated with turns, airgun testing, and repeat coverage of any areas where initial data quality is sub-standard. To account for unanticipated delays, 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. During the survey, approximately 13 percent of the line km would take place in shallow water (<100 meter (m)), 27 percent would occur in intermediate water depths (100-1000 m), and the rest (60 percent) would occur in deep water (>1000 m).
In addition to the operations of the airgun array, the ocean floor would be mapped with a Kongsberg EM 122 multibeam echosounder (MBES) and a Knudsen Chirp 3260 sub-bottom profiler (SBP). A Teledyne RDI 75 kilohertz (kHz) Ocean Surveyor Acoustic Doppler Current Profiler (ADCP) would be used to measure water current velocities. These sources would be operated from the
Langseth
continuously during the seismic survey, but not during transit to and from the survey areas. All planned geophysical data acquisition activities would be conducted by L-DEO with on-board assistance by the scientists who have proposed the studies. The vessel would be self-contained, and the crew would live aboard the vessel.
During the survey, the
Langseth
would tow the full array, consisting of four strings with 36 airguns (plus 4 spares) and a total volume of ~6,600 in
3
. The 4-string array would be towed at a depth of 12 m, and the shot intervals would be 399.3 m for the entire survey.
Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (please see
Proposed Mitigation
and
Proposed Monitoring and Reporting
).
Description of Marine Mammals in the Area of Specified Activities
Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history, of the potentially affected species. Additional information regarding population trends and threats may be found in NMFS's Stock Assessment Reports (SAR;
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments
) and more general information about these species (
e.g.,
physical and behavioral descriptions) may be found on NMFS's website (
https://www.fisheries.noaa.gov/find-species
).
Table 1 lists all species with expected potential for occurrence in the Gulf of Alaska and summarizes information related to the population or stock, including regulatory status under the MMPA and ESA and potential biological removal (PBR), where known. For taxonomy, we follow Committee on Taxonomy (2017). PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as described in NMFS's SARs). While no mortality is anticipated or authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species and other threats.
Sixteen species of cetaceans and five species of pinnipeds could occur in the proposed Gulf of Alaska survey area. Cetacean species include seven species of mysticetes (baleen whales) and nine species of odontocetes (dolphins and small and large toothed whales).
Ferguson
et al.
(2015) described Biological Important Areas (BIAs) for cetaceans in the Gulf of Alaska. BIAs were delineated for four baleen whale species and one toothed whale species including fin, gray, North Pacific right, and humpback whales, and belugas in U.S. waters of the Gulf of Alaska. BIAs are described in the following sections for each marine mammal species, except for beluga whale BIAs, as these do not co-occur within L-DEO's proposed survey area and the species is not expected to be present there. BIAs are delineated for feeding, migratory corridors, and small and resident populations. Supporting evidence for these BIAs came from aerial-, land-, and vessel-based surveys; satellite tagging data; passive acoustic monitoring; traditional ecological knowledge; photo- and genetic-identification data; whaling data, including catch and sighting locations and stomach contents; prey studies; and observations from fishermen.
Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS's stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, stock abundance estimates are not available, and survey abundance estimates are used. This survey area may or may not align completely with a stock's geographic range as defined in the SARs. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS's U.S. Alaska and U.S. Pacific SARs (
e.g.,
Muto
et al.
2018, Carretta
et al.
2018). All values presented in Table 1 are the most recent available at the time of publication and are available in the 2017 SARs (Muto
et al.
2018, Carretta
et al.
2018) and draft 2018 SARs (available online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports
).
Table 1—Marine Mammals That Could Occur in the Project Area During the Specified Activity
Common name
Scientific name
Stock
ESA/MMPA status; strategic (Y/N)
1
Stock abundance (CV, N
min
,
most recent abundance
survey)
2
PBR
Annual
M/SI
3
Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)
Family Eschrichtiidae:
Gray whale
Eschrichtius robustus
Eastern North Pacific
-, -, N
26,960 (0.05, 25,849, 2016)
801
138
Western North Pacific
E, D, Y
175 (0.05, 167, 2016)
0.07
UNK
Family Balaenidae:
North Pacific right whale
Eubalaena japonica
Eastern North Pacific
E, D, Y
31 (0.226, 26, 2015)
0.05 b
0
Family Balaenopteridae (rorquals):
Blue whale
Balaenoptera musculus
Eastern North Pacific
E, D, Y
1,647 (0.07, 1,551, 2011)
2.3
≥0.2
Central North Pacific
E, D, Y
133 (1.09, 63, 2010)
0.1
0
Fin whale *
4
Balaenoptera physalus
Northeast Pacific
E, D, Y
3,168
4
5.1
0.6
Sei whale
Balaenoptera borealis
Eastern North Pacific
E, D, Y
519 (0.4, 374, 2014)
0.75
0
Minke whale *
5
Balaenoptera acutorostrata
Alaska
-, -, N
1,233
5
UND
0
Humpback whale
Megaptera novaeangliae
Central North Pacific
-, -, Y
10,103 (0.3, 7,890, 2006)
83
25
Western North Pacific
E, D, Y
1,107 (0.3, 865, 2006)
3
3.2
Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
Family Physeteridae:
Sperm whale *
Physeter macrocephalus
North Pacific
E, D, Y
N/A (see SAR, N/A, 2015)
see SAR
4.4
Family Ziphiidae (beaked whales):
Cuvier's beaked whale
Ziphius cavirostris
Alaska
-, -, N
N/A (see SAR, N/A, see SAR)
UND
0
Baird's beaked whale
Berardius bairdii
Alaska
-, -, N
N/A (see SAR, N/A, see SAR)
UND
0
Stejneger's beaked whale
Mesoplodon stejnegeri
Alaska
-, -, N
N/A (see SAR, N/A, see SAR)
UND
0
Family Delphinidae:
Killer whale
Orcinus orca
Eastern North Pacific Alaska Resident
-, -, N
2,347 c (N/A, 2347, 2012)
24
1
Gulf of Alaska, Aleutian Islands, and Bering Sea Transient
-, -, N
587 c (N/A, 587, 2012)
5.87
1
AT1 Transient
-, D, Y
7 c (N/A, 7, 2017)
0.01
0
Offshore
-, -, N
240 (0.49, 162, 2014)
1.6
0
Risso's dolphin
Grampus griseus
CA/WA/OR
-, -, N
6,336 (0.32, 4,817, 2014)
46
≥3.7
Pacific white-sided dolphin
Lagenorhynchus obliquidens
North Pacific
-, -, N
26,880 (N/A, N/A, 1990)
UND
0
Family Phocoenidae (porpoises):
Harbor porpoise
Phocoena phocoena
GOA
-, -, Y
31,046 (0.214, N/A, 1998)
UND
72
Southeast Alaska
-, -, Y
see SAR (see SAR, see SAR, 2012)
8.9
34
Dall's porpoise
Phocoenoides dalli
Alaska
-, -, N
83,400 (0.097, N/A, 1991)
UND
38
Order Carnivora—Superfamily Pinnipedia
Family Otariidae (eared seals and sea lions):
Steller sea lion
Eumetopias jubatus
Eastern U.S.
T, D, Y
41,638 a (see SAR, 41,638, 2015)
2,498
108
Western U.S.
E, D, Y
54,267 a (see SAR, 54,267, 2017)
326
252
California sea lion
Zalophus californianus
U.S.
-, -, N
296,750 (N/A, 153,337, 2011)
9,200
389
Northern fur seal
Callorhinus ursinus
Eastern Pacific
-, D, Y
620,660 (0.2, 525,333, 2016)
11,295
457
Family Phocidae (earless seals):
Northern elephant seal
Mirounga angustirostris
California Breeding
-, -, N
179,000 (N/A, 81,368, 2010)
4,882
8.8
Harbor seal
Phoca vitulina
South Kodiak
-, -, N
19,199 (see SAR, 17,479, 2011)
314
128
Cook Inlet/Shelikof Strait
-, -, N
27,386 (see SAR, 25,651, 2011)
770
234
Prince William Sound?
-, -, N
29,889 (see SAR, 27,936, 2011)
838
279
* Stocks marked with an asterisk are addressed in further detail in text below.
1
ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
2
NMFS marine mammal stock assessment reports online at:
https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.
CV is coefficient of variation; N
min
is the minimum estimate of stock abundance. In some cases, CV is not applicable (N/A).
3
These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (
e.g.,
commercial fisheries, ship strike).
4
Uncorrected estimate from Rone
et al.
(2017) based on a series of line-transect surveys off of Kodiak Island. The maximum estimate from the three surveys was selected. Based on the limited footprint of the surveys that lead to this estimate, the true abundance of the stock is expected to be much higher.
5
Uncorrected estimate from Zerbini
et al.,
(2006) based on a partial line-transect survey of the Gulf of Alaska.
Note
—Italicized species or stocks are not expected to be taken or proposed for authorization.
All species that could potentially occur in the proposed survey areas are included in Table 1. With the exception of AT1 transient killer whales, these species or stocks temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. However, the spatial occurrence of the AT1 transient is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here.
AT1 transient killer whales are a small, genetically distinct population of transient ecotype killer whales found in the Gulf of Alaska (Matkin
et al.
1999). The population has declined from a size of 22 whales in 1984, to just 7 today, and it is believed this decline was associated with the Exxon Valdez Oil Spill in 1989 (Matkin
et al.
2008). AT1 transients have only ever been seen in Prince William Sound and in the Kenai Fjords region (Muto
et al.
2018; Matkin
et al.
2008). Therefore, while the stock is present in the Gulf of Alaska, and deserved consideration, the limited range of the stock and the fact that this range does not overlap with L-DEO's proposed survey means take is not likely to occur for the AT1 stock of transient killer whales.
No comprehensive abundance estimate is available for the Alaska stock of minke whales. The best available estimate for the area comes from line-transect surveys conducted in shelf and nearshore waters (within 30-45 nautical miles of land) in 2001-2003 between the Kenai Peninsula (150° W) and Amchitka Pass (178° W). Minke whale abundance was estimated to be 1,233 (CV = 0.34) for this area (not been corrected for animals missed on the trackline) (Zerbini
et al.
2006). The majority of the sightings were in the Aleutian Islands, rather than in the Gulf of Alaska, and in water shallower than 200 m. This estimate cannot be used as an estimate of the entire Alaska stock of minke whales because only a portion of the stock's range was surveyed. Similarly, although a comprehensive abundance estimate is not available for the northeast Pacific stock of fin whales, there are provisional estimates representing relevant portions of the range. Zerbini
et al.
(2006) produced an estimate of 1,652 (95 percent CI: 1,142-2,389) fin whales for the area described above. Additionally, a series of line-transect surveys off of Kodiak Island and the in the northern Gulf of Alaska conducted in 2009, 2013, and 2015, generated a maximum estimate of 3,168 (CV = 0.26) (also not been corrected for animals missed on the trackline) (Rone
et al.
2017).
Kato and Miyashita (1998) reported 102,112 sperm whales (CV = 0.155) in the western North Pacific, however, with the caveat that their estimate is likely positively biased. From surveys in the Gulf of Alaska in 2009 and 2015, Rone
et al.
(2017) estimated 129 (CV = 0.44) and 345 sperm whales (CV = 0.43) in each year, respectively. The overall number of sperm whales occurring in Alaska waters is unknown (Muto
et al.
2018).
For the three species of beaked whale expected to occur in the area (Baird's, Cuvier's, and Stejneger's), there are no reliable estimates of abundance.
We have reviewed L-DEO's species descriptions, including life history information, distribution, regional distribution, diving behavior, and acoustics and hearing, for accuracy and completeness. Below, for the 21 species that are likely to be taken by the activities described, we offer a brief introduction to the species and relevant stock as well as available information regarding population trends and threats, and describe any information regarding local occurrence.
In addition, the northern sea otter (
Enhydra lutris
) and Pacific walrus (
Odobenus rosmarus divergens
) may be found in the Gulf of Alaska. However, northern sea otter and Pacific walrus are managed by the U.S. Fish and Wildlife Service and are not considered further in this document.
Mysticetes
North Pacific Right Whale (
Eubalaena japonica
)
North Pacific right whales summer in the northern North Pacific, primarily in the Okhotsk Sea (Brownell
et al.
2001) and in the Bering Sea (Shelden
et al.
2005; Wade
et al.
2006). This species is divided into western and eastern North Pacific stocks. The eastern North Pacific stock that occurs in U.S. waters numbers only ~31 individuals (Wade
et al.
2011b), and critical habitat has been designated in the eastern Bering Sea and in the GOA, south of Kodiak Island (NMFS 2017b). Wintering and breeding areas are unknown, but have been suggested to include the Hawaiian Islands, Ryukyu Islands, and Sea of Japan (Allen 1942; Banfield 1974; Gilmore 1978; Reeves
et al.
1978; Herman
et al.
1980; Omura 1986).
Since the 1960s, North Pacific right whale sightings have been relatively rare (
e.g.,
Clapham
et al.
2004; Shelden
et al.
2005). In the eastern North Pacific, south of 50 °N, only 29 reliable sightings were recorded from 1900 to 1994 (Scarff 1986, 1991; Carretta
et al.
1994). Starting in 1996, right whales have been sighted regularly in the southeast Bering Sea, including calves in some years (Goddard and Rugh 1998; LeDuc
et al.
2001; Moore
et al.
2000, 2002b; Wade
et al.
2006; Zerbini
et al.
2009); they have also been detected acoustically when sonobuoys were deployed (McDonald and Moore 2002; Munger
et al.
2003, 2005, 2008; Berchok
et al.
2009). Right whales are known to occur in the southeast Bering Sea from May to December (
e.g.,
Tynan
et al.
2001; Hildebrand and Munger 2005; Munger
et al.
2005, 2008). Call frequencies tended to be higher in July-October than from May-June or November-December (Munger
et al.
2008). Right whales seem to pass through the middle-shelf areas, without remaining there longer than a few days (Munger
et al.
2008).
Shelden
et al.
(2005) reported that the slope and abyssal plain in the western GOA were important areas for right whales until the late 1960s, but sightings and acoustic detections in this region in recent decades are rare. In March 1979, a group of four right whales was seen in Yakutat Bay (Waite
et al.
2003), but there were no further reports of right whale sightings in the GOA until July 1998, when a single whale was seen southeast of Kodiak Island (Waite
et al.
2003). Three sightings and one acoustic detection of right whales were made in Barnabas Trough south of Kodiak Island during NOAA surveys in 2004 to 2006 in areas with high densities of zooplankton (Wade
et al.
2011a). Those authors also report a fourth opportunistic sighting by a commercial fisher during that time in the same area. One right whale was sighted in the Aleutian Islands south of Unimak Pass in September 2004 (Wade
et al.
2011b). A BIA for feeding for North Pacific right whales was designated east of the Kodiak Archipelago, encompassing the GOA critical habitat and extending south of 56° N and north of 58° N and beyond the shelf edge (Ferguson
et al.
2015). Feeding primarily occurs in this BIA between June and September (Ferguson
et al.
2015)
Right whale acoustic detections were made south of the Alaska Peninsula and to the east of Kodiak Island in 2000 during August and September (see
Waite
et al.
2003; Mellinger
et al.
2004b), but no acoustic detections were made from April to August 2003 (Munger
et al.
2008) or in April 2009 (Rone
et al.
2010). Three right whales were acoustically detected in the Barnabas Trench area during a towed-PAM survey of the U.S. Navy training area east of Kodiak in the summer of 2013 but none were observed visually (Rone
et al.
2014). Right whales were not consistently detected acoustically from (2011-2015) with the fixed PAM monitoring in this region (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015), but there were detections on two days in June and August 2013 (Debich
et al.
2014). No right whales were visually observed during the three years of surveys (2009, 2013, and 2015) in this military area east of Kodiak (Rone
et al.
2017). There was one sighting of a single North Pacific right whale during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011). There was another sighting of a lone North Pacific right whale during a marine mammal cruise, approximately 130 miles east of Kodiak Island in July 2012 (Matsuoka
et al.
2013). Thus, it is possible that a right whale could be seen during the proposed survey.
Gray Whale (
Eschrichtius robustus
)
Two separate populations of gray whales have been recognized in the North Pacific (LeDuc
et al.
2002): The eastern North Pacific and western North Pacific (or Korean-Okhotsk) stocks. However, the distinction between these two populations has been recently debated owing to evidence that whales from the western feeding area also travel to breeding areas in the eastern North Pacific (Weller
et al.
2012, 2013; Mate
et al.
2015). Thus, it is possible that whales from both the endangered Western North Pacific and the delisted Eastern North Pacific distinction population segments (DPSs) could occur in the proposed survey area in the eastern North Pacific.
Gray whale populations were severely reduced by whaling, but the eastern North Pacific population is considered to have recovered. Punt and Wade (2012) estimated the eastern North Pacific population to be at 85 percent of its carrying capacity in 2009. The eastern North Pacific gray whale breeds and winters in Baja, California, and migrates north to summer feeding grounds in the northern Bering Sea, Chukchi Sea, and western Beaufort Sea (Rice and Wolman 1971; Rice 1998; Jefferson
et al.
2015). Most of the eastern Pacific population makes a round-trip annual migration of more than 18,000 km. From late May to early October, the majority of the population concentrates in the northern and western Bering Sea and in the Chukchi Sea. However, some individuals spend the summer months scattered along the coasts of southeast Alaska, B.C., Washington, Oregon, and northern California (Rice and Wolman 1971; Nerini 1984; Darling
et al.
1998; Dunham and Duffus 2001, 2002; Calambokidis
et al.
2002). Gray whales are found primarily in shallow water; most follow the coast during migration, staying close to the shoreline except when crossing major bays, straits, and inlets (Braham 1984).
It is difficult to determine precisely when the southbound migration begins; whales near Barrow were moving predominantly south in August (Maher 1960; Braham 1984). Gray whales leave the Bering Sea through Unimak Pass from late October through January (Braham 1984). From October to January, the main part of the population moves down the west coast of North America. Rugh
et al.
(2001) analyzed data collected from two sites in California to estimate the timing of the gray whale southward migration. They estimated that the median date for the migration past various sites was 1 December in the central Bering Sea (a nominal starting point), 12 December at Unimak Pass, 18 December at Kodiak Island, and 5 January for Washington.
By January and February, most of the whales are concentrated in the lagoons along the Pacific coast of the Baja Peninsula, Mexico. From late February to June, the population migrates northward to arctic and subarctic seas (Rice and Wolman 1971). The peak of northward migration in the GOA occurs in mid-April (Braham 1984). Most gray whales follow the coast during migration and stay within 2 km of the shoreline, except when crossing major bays, straits, and inlets from southeast Alaska to the eastern Bering Sea (Braham 1984). Gray whales use the nearshore areas of the Alaska Peninsula during the spring and fall migrations, and are often found within the bays and lagoons, primarily north of the peninsula, during the summer (Brueggeman
et al.
1989 in Waite
et al.
1999). However, gray whales are known to move further offshore between the entrance to Prince William Sound (PWS) and Kodiak Island and between Kodiak Island and the southern part of the Alaska Peninsula (Consiglieri
et al.
1982). During May-October, primary occurrence extends seaward 28 km from the shoreline. This is the main migratory corridor for gray whales.
In the summer, gray whales are seen in the southeast Bering Sea (Moore
et al.
2002b) and in the GOA, including around Kodiak Island (
e.g.,
Wade
et al.
2003; Calambokidis
et al.
2004; Calambokidis 2007; Moore
et al.
2007). In fact, gray whales have been seen feeding off southeast Kodiak Island, in particular near Ugak Bay, year-round (Moore
et al.
2007). Moore
et al.
(2007) noted monthly sighting rates that exceeded 100 sightings/h in January, June, September, and November, and >20 sightings/h in most other months. One feeding aggregation in July consisted of 350-400 animals, clustered in groups of 10-20 animals, from the mouth of Ugak Bay to 100 km ESE of Ugak Island (Moore
et al.
2007). Wade
et al.
(2003) reported a group size of 5.6 in the western GOA. A biologically important area (BIA) for feeding for gray whales has been identified in the waters east of the Kodiak Archipelago, with the greatest densities of gray whales occurring from June through August (Ferguson
et al.
2015). Additionally, a gray whale migratory corridor BIA has been established extending from Unimak Pass in the western GOA to the Canadian border in the eastern GOA (Ferguson
et al.
2015), including much of the landward side of the survey area. Gray whales occur in this area in high densities during November through January (southbound) and March through May (northbound).
Rone
et al.
(2017) sighted gray whales off Ugak Island, Kodiak, in all three years (2009, 2013, and 2015) of surveys in the military training area east of Kodiak. Gray whales were detected acoustically throughout the summer and fall at fixed hydrophones on the shelf off Kenai Peninsula and near Kodiak Island in this military training area in a 2014-2015 study (Rice
et al.
2015), but they were not detected at deeper slope or seamount sites and they were detected only once in prior years of study from 2011 to 2013 (Baumann-Pickering
et al.
2012; Debich
et al.
2013). Gray whales were neither observed visually nor detected acoustically during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011). Gray whales could be encountered during the proposed seismic survey in the GOA.
Humpback Whale (
Megaptera novaeangliae
)
The humpback whale is found throughout all oceans of the World (Clapham 2009), with recent genetic evidence suggesting three separate subspecies: North Pacific, North Atlantic, and Southern Hemisphere
(Jackson
et al.
2014). Nonetheless, genetic analyses suggest some gene flow (either past or present) between the North and South Pacific (
e.g.,
Jackson
et al.
2014; Bettridge
et al.
2015). Although considered to be mainly a coastal species, the humpback whale often traverses deep pelagic areas while migrating (
e.g.,
Mate
et al.
1999; Garrigue
et al.
2015).
North Pacific humpback whales migrate between summer feeding grounds along the Pacific Rim and the Bering and Okhotsk seas and winter calving and breeding areas in subtropical and tropical waters (Pike and MacAskie 1969; Rice 1978; Winn and Reichley 1985; Calambokidis
et al.
2000, 2001, 2008). In the North Pacific, humpbacks winter in four different breeding areas: (1) Along the coast of Mexico; (2) along the coast of Central America; (3) around the Main Hawaiian Islands; and (4) in the western Pacific, particularly around the Ogasawara and Ryukyu islands in southern Japan and the northern Philippines (Calambokidis
et al.
2008; Fleming and Jackson 2011; Bettridge
et al.
2015). These breeding areas are recognized as the Mexico, Central America, Hawaii, and Western Pacific DPSs (NMFS 2016b). Hawaii is the primary wintering area for whales from summer feeding areas in the Gulf of Alaska (Calambokidis
et al.
2008). Individuals from the Hawaii, Western Pacific, and Mexico DPSs could occur in the proposed survey area to feed. The Hawaii DPS is not listed and the Mexico DPS is listed as threatened under the ESA. Additionally, the Western North Pacific stock, analogous to the western Pacific DPS, is listed as endangered under the ESA.
There is potential for mixing of the western and eastern North Pacific humpback populations on their summer feeding grounds, and several sources suggest that this occurs to a limited extent (Muto
et al.
2018). NMFS is currently reviewing the global humpback whale stock structure in light of the recent revision to their ESA listing and identification of 14 DPSs (81 FR 62259; 8 September 2016). Currently, two stocks of humpback whales are recognized as occurring in Alaskan waters. The Central North Pacific Stock occurs from southeast Alaska to the Alaska Peninsula and the Western North Pacific Stock occurs from the Aleutians to the Bering Sea and Russia. These two stocks overlap on feeding grounds in the eastern Bering Sea and the western Gulf of Alaska (Muto
et al.
2018), encompassing the entire proposed survey area. BIAs for humpback whale feeding have been designated surrounding Kodiak Island and the Shumagin Islands (Ferguson
et al.
2015). The highest densities of humpback whales occur during July through September around Kodiak Island and during July through August in the Shumagin Islands.
Humpback whales are commonly sighted within the proposed survey area. Waite (2003) reported that 117 humpbacks were seen in 41 groups during their surveys in the western GOA in 2003, with aggregations seen off northeast Kodiak Island. During summer surveys from the Kenai Fjords to the central Aleutian Islands in 2001-2003, humpbacks were most abundant near Kodiak Island, the Shumagin Islands, and north of Unimak Pass (Zerbini
et al.
2006). Sightings of humpbacks around the Kodiak Islands were made most frequently in the fall, and aggregations were seen off Shuyak and Sitkalidak islands (Wynne and Witteveen 2005), as well as in Marmot and Chiniak bays (Baraff
et al.
2005). Waite
et al.
(1999) noted another aggregation area north of Unalaska Island. Offshore sightings of humpbacks have also been made south of the Alaska Peninsula, including ~280 km south of the Shumagin Islands (
e.g.,
Forney and Brownell 1996; Waite
et al.
1999). Humpback whales were sighted a total of 220 times (637 animals) during the three years of surveys (2009, 2013, and 2015) in and near the U.S. Navy training area east of Kodiak (Rone
et al.
2017). Humpback whales were also frequently detected acoustically during all years (2011-2015) of fixed-PAM studies in this area, with peak detections during late fall through early winter and detections at all shelf, slope, and seamount sites (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015). Humpback whales were the most frequently sighted cetacean during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey, comprising 50 percent of all cetacean sightings (RPS 2011). There were 92 sightings of this species, representing 288 animals during the 37 days of monitoring. The average group size was three and the maximum group size was 37. This species is likely to be common in the proposed survey area.
Calambokidis
et al.
(2008) reported an abundance estimate of 3,000-5,000 for the GOA. Rone
et al.
(2017) calculated an abundance estimate of 2,215 (uncorrected for missed animals) from a June-July 2013 survey in the U.S. Navy training area east of Kodiak Island, with the bulk of this estimate (2,927) found in the inshore stratum. NMFS provides best estimates of 1,107 for the Western North Pacific Stock and 10,103 for the Central North Pacific Stock (Muto
et al.
2018). Within the Central North Pacific stock, the Hawaii DPS is estimated to contain 11,398 animals where the Mexico DPS is estimated to contain 3,264 animals (81 FR 62259; effective October 11, 2016).
Minke Whale (
Balaenoptera acutorostrata
)
The minke whale has a cosmopolitan distribution ranging from the tropics and subtropics to the ice edge in both hemispheres (Jefferson
et al.
2015). In the Northern Hemisphere, minke whales are usually seen in coastal areas, but can also be seen in pelagic waters during northward migrations in spring and summer, and southward migration in autumn (Stewart and Leatherwood 1985). In the North Pacific, the summer range extends to the Chukchi Sea; in the winter, minke whales move further south to within 2° of the Equator (Perrin and Brownell 2009). The International Whaling Commission (IWC) recognizes three stocks in the North Pacific: The Sea of Japan/East China Sea, the rest of the western Pacific west of 180°N, and the remainder of the Pacific (Donovan 1991). NMFS recognizes a single stock in Alaskan waters and a second California/Oregon/Washington Stock (Muto
et al.
2016).
The minke whale tends to be solitary or in groups of 2-3 but can occur in much larger aggregations around prey resources (Jefferson
et al.
2008). Predominantly solitary animals were seen during surveys in Alaska (Wade
et al.
2003; Waite 2003; Zerbini
et al.
2006). The small size, inconspicuous blows, and brief surfacing times of minke whales mean that they are easily overlooked in heavy sea states, although they are known to approach vessels in some circumstances (Stewart and Leatherwood 1985). Little is known about the diving behavior of minke whales, but they are not known to make prolonged deep dives (Leatherwood and Reeves 1983).
Minke whales are relatively common in the Bering and Chukchi seas and in the inshore waters of the GOA (Mizroch 1992), but they are not considered abundant in any other part of the eastern Pacific (Brueggeman
et al.
1990). Waite (2003) sighted four minke whales in three groups during surveys in the western GOA in 2003, south of the Kenai Peninsula and south of PWS. Moore
et al.
(2002b) reported a minke whale sighting south of the Sanak Islands. Baraff
et al.
(2005) reported a single sighting near Kodiak Island in July 2002. During surveys in the western GOA and eastern Aleutians, minke whales occurred primarily in the Aleutians; a few sightings were made
south of the Alaska Peninsula and near Kodiak Island (Zerbini
et al.
2006). Rone
et al.
(2017) reported two sightings totaling three minke whales in 2009, three sightings totaling six minke whales in 2013, and no sightings of minke whales in 2015 in the U.S. Navy training area east of Kodiak. Minke whales were not detected acoustically during any year (2011-2015) of the fixed-PAM studies in the Department of the Navy (DoN) area east of Kodiak (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015). There was one sighting of a single minke whale during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Sei Whale (
Balaenoptera borealis
)
The sei whale occurs in all ocean basins (Horwood 2009) but appears to prefer mid-latitude temperate waters (Jefferson
et al.
2015). It undertakes seasonal migrations to feed in subpolar latitudes during summer and returns to lower latitudes during winter to calve (Horwood 2009). The sei whale is pelagic and generally not found in coastal waters (Harwood and Wilson 2001). It occurs in deeper waters characteristic of the continental shelf edge region (Hain
et al.
1985) and in other regions of steep bathymetric relief such as seamounts and canyons (Kenney and Winn 1987; Gregr and Trites 2001). On feeding grounds, sei whales associate with oceanic frontal systems (Horwood 1987) such as the cold eastern currents in the North Pacific (Perry
et al.
1999). Sei whales are frequently seen in groups of 2-5 (Jefferson
et al.
2008), although larger groups sometimes form on feeding grounds (Gambell 1985a).
In the U.S. Pacific, an Eastern North Pacific and a Hawaii stock are recognized (Carretta
et al.
2017). During summer in the North Pacific, the sei whale can be found from the Bering Sea to the northern GOA and south to California, and in the western Pacific from Japan to Korea. Its winter distribution is concentrated at about 20° N, and sightings have been made between southern Baja California and the Islas Revilla Gigedo (Rice 1998). No breeding grounds have been identified for sei whales; however, calving is thought to occur from September to March.
Moore
et al.
(2002b) made four sightings of six sei whales during summer surveys in the eastern Bering Sea, and one sighting south of the Alaska Peninsula between Kodiak and the Shumagin Islands. No sei whales were seen during surveys of the GOA by Wade
et al.
(2003), Waite (2003), or Zerbini
et al.
(2006). Rone
et al.
(2017) reported no sei whale sightings in 2009 or 2013 and a single sei whale sighting of one animal in 2015 in the U.S. Navy training area east of Kodiak. There was one sighting of two sei whales during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011). During a 2012 survey in summer and early fall, Matsuoka
et al.
(2013) reported 87 sei whale sightings of 1,647 individuals, however the majority of these sightings were far south of the action area. Sei whale sightings are likely to be uncommon in the proposed survey area.
Fin Whale (
Balaenoptera physalus
)
The fin whale is widely distributed in all the World's oceans (Gambell 1985b), although it is most abundant in temperate and cold waters (Aguilar 2009). Nonetheless, its overall range and distribution are not well known (Jefferson
et al.
2015). A recent review of fin whale distribution in the North Pacific noted the lack of sightings across the pelagic waters between eastern and western winter areas (Mizroch
et al.
2009). The fin whale most commonly occurs offshore but can also be found in coastal areas (Aguilar 2009). Most populations migrate seasonally between temperate waters where mating and calving occur in winter, and polar waters where feeding occurs in summer (Aguilar 2009). However, recent evidence suggests that some animals may remain at high latitudes in winter or low latitudes in summer (Edwards
et al.
2015).
The fin whale is known to use the shelf edge as a migration route (Evans 1987). Sergeant (1977) suggested that fin whales tend to follow steep slope contours, either because they detect them readily, or because the contours are areas of high biological productivity. However, fin whale movements have been reported to be complex (Jefferson
et al.
2015). Stafford
et al.
(2009) noted that sea-surface temperature is a good predictor variable for fin whale call detections in the North Pacific.
North Pacific fin whales summer from the Chukchi Sea to California and winter from California southwards (Gambell 1985b). In the United States, three stocks are recognized in the North Pacific: California/Oregon/Washington, Hawaii, and Alaska (Northeast Pacific) (Carretta
et al.
2017). Information about the seasonal distribution of fin whales in the North Pacific has been obtained from the detection of fin whale calls by bottom-mounted, offshore hydrophone arrays along the U.S. Pacific coast, in the central North Pacific, and in the western Aleutian Islands (Moore
et al.
1998, 2006; Watkins
et al.
2000a,b; Stafford
et al.
2007, 2009). Fin whale calls are recorded in the North Pacific year-round, including the GOA (
e.g.,
Moore
et al.
2006; Stafford
et al.
2007, 2009; Edwards
et al.
2015). Near the Alaska Peninsula in the western GOA, the number of calls received peaked in May-August, with few calls during the rest of the year (Moore
et al.
1998). In the central North Pacific, the GOA, and the Aleutian Islands, call rates peak during fall and winter (Moore
et al.
1998, 2006; Watkins
et al.
2000a,b; Stafford
et al.
2009).
Rice and Wolman (1982) encountered 19 fin whales during surveys in the GOA, including 10 aggregated near Middleton Island on 1 July 1980. During surveys from the Kenai Peninsula to the central Aleutian Islands, fin whales were most abundant near the Semidi Islands and Kodiak Island (Zerbini
et al.
2006). Numerous sightings of fin whales were also seen between the Semidi Islands and Kodiak Island during surveys by Waite (2003). Fin whale sightings around Kodiak Island were most numerous along the western part of the island in Uyak Bay and Kupreanof Straits, and in Marmot Bay (Wynne and Witteveen 2005; Baraff
et al.
2005). Fin whales were sighted around Kodiak Island year-round, but most sightings were made in the spring and summer (Wynne and Witteveeen 2005). A BIA for fin whale feeding has been designated southward from the Kenai Peninsula inshore of the Kodiak Archipelago and along the Alaska Peninsula to include the Semidi Islands (Ferguson
et al.
2015), overlapping with a proportion of the proposed survey area. Densities of fin whales are highest in this area during June through August.
Rone
et al.
(2017) reported 24 fin whale sightings (64 animals) in 2009, two hundred fin whale sightings (392 animals) in 2013, and 48 fin whale sightings (69 animals) in 2015 in the U.S. Navy training area east of Kodiak. That study also provided an abundance estimate of 3168 for this area. The density and abundance estimates were not corrected for missed animals. Fin whales were also frequently detected acoustically throughout the year during all years (2011-2015) of fixed-PAM studies in this area and detections occurred at all shelf, slope, and seamount sites (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015). Fin whales were the second most frequently sighted cetacean during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey, comprising
15.2 percent of all cetacean sightings (RPS 2011). There were 28 sightings of this species, representing 79 animals during the 37 days of monitoring. The average group size was three and the maximum group size was 10. Fin whales are likely to be common in the proposed survey area.
Blue Whale (
Balaenoptera musculus
)
The blue whale has a cosmopolitan distribution and tends to be pelagic, only coming nearshore to feed and possibly to breed (Jefferson
et al.
2015). Blue whale migration is less well defined than for some other rorquals, and their movements tend to be more closely linked to areas of high primary productivity, and hence prey, to meet their high energetic demands (Branch
et al.
2007). Generally, blue whales are seasonal migrants between high latitudes in the summer, where they feed, and low latitudes in the winter, where they mate and give birth (Lockyer and Brown 1981). Some individuals may stay in low or high latitudes throughout the year (Reilly and Thayer 1990; Watkins
et al.
2000b).
Although it has been suggested that there are at least five subpopulations in the North Pacific (Reeves
et al.
1998), analysis of calls monitored from the U.S. Navy Sound Surveillance System (SOSUS) and other offshore hydrophones (
e.g.,
Stafford
et al.
1999, 2001, 2007; Watkins
et al.
2000a; Stafford 2003) suggests that there are two separate populations: one in the eastern and one in the central North Pacific (Carretta
et al.
2017). The Eastern North Pacific Stock includes whales that feed primarily off California from June-November and winter off Central America (Calambokidis
et al.
1990; Mate
et al.
1999). The Central North Pacific Stock feeds off Kamchatka, south of the Aleutians and in the Gulf of Alaska during summer (Stafford 2003; Watkins
et al.
2000b), and migrates to the western and central Pacific (including Hawaii) to breed in winter (Stafford
et al.
2001; Carretta
et al.
2017). The status of these two populations could differ substantially, as little is known about the population size in the western North Pacific (Branch
et al.
2016).
In the North Pacific, blue whale calls are detected year-round (Stafford
et al.
2001, 2009; Moore
et al.
2002a, 2006; Monnahan
et al.
2014). Stafford
et al.
(2009) reported that sea-surface temperature is a good predictor variable for blue whale call detections in the North Pacific. In the GOA, no detections of blue whales had been made since the late 1960s (NOAA 2004b; Calambokidis
et al.
2009) until blue whale calls were recorded in the area during 1999-2002 (Stafford 2003; Stafford and Moore 2005; Moore
et al.
2006; Stafford
et al.
2007). Call types from both northeastern and northwestern Pacific blue whales were recorded from July through December in the GOA, suggesting that two stocks used the area at that time (Stafford 2003; Stafford
et al.
2007). Call rates peaked from August through November (Moore
et al.
2006). More recent acoustic studies using fixed PAM have confirmed the presence of blue whales from both the Central and Northeast Pacific stocks in the Gulf of Alaska concurrently (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015). Blue whale calls were recorded in all months; at all shelf, slope, and seamount sites; and during all years (2011-2015) of those studies.
In July 2004, three blue whales were sighted in the GOA. The first blue whale was seen on 14 July ~185 km southeast of PWS. Two more blue whales were seen ~275 km southeast of PWS (NOAA 2004b; Calambokidis
et al.
2009). These whales were thought to be part of the California feeding population (Calambokidis
et al.
2009). Western blue whales are more likely to occur in the western portion of the GOA, southwest of Kodiak, where their calls have been detected (see Stafford 2003). Two blue whale sightings were also made in the Aleutians in August 2004 (Calambokidis
et al.
2009). No blue whales were seen during surveys of the western GOA by Zerbini
et al.
(2006).
Rone
et al.
(2017) reported no blue whale sightings in 2009, five blue whale sightings (seven animals) in 2013, and 13 blue whale sightings (13 animals) in 2015 in the U.S. Navy training area east of Kodiak. Blue whales were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Odontocetes
Sperm Whale (
Physeter macrocephalus
)
The sperm whale is the largest of the toothed whales, with an extensive worldwide distribution from the edge of the polar pack ice to the Equator (Whitehead 2009). Sperm whale distribution is linked to its social structure: Mixed groups of adult females and juveniles of both sexes generally occur in tropical and subtropical waters at latitudes less than ~40° (Whitehead 2009). After leaving their female relatives, males gradually move to higher latitudes, with the largest males occurring at the highest latitudes and only returning to tropical and subtropical regions to breed. Sperm whales generally are distributed over large areas that have high secondary productivity and steep underwater topography, in waters at least 1000 m deep (Jaquet and Whitehead 1996). They are often found far from shore but can be found closer to oceanic islands that rise steeply from deep ocean waters (Whitehead 2009).
Most of the information regarding sperm whale distribution in the GOA (especially the eastern GOA) and southeast Alaska has come from observations from fishermen and reports from fisheries observers aboard commercial fishing vessels (
e.g.,
Dahlheim 1988). Fishery observers have identified interactions (
e.g.,
depredation) between longline vessels and sperm whales in the GOA and southeast Alaska since at least the mid-1970s (
e.g.,
Hill
et al.
1999; Straley
et al.
2005; Sigler
et al.
2008), with most interactions occurring in the West Yakutat and East Yakutat/Southeast regions (Perez 2006; Hanselman
et al.
2008). Sigler
et al.
(2008) noted high depredation rates in West Yakutat, East Yakutat/Southeast region, as well as the central GOA. Hill
et al.
(1999) found that most interactions in the GOA occurred to the east of Kodiak Island, even though there was substantial longline effort in waters to the west of Kodiak. Mellinger
et al.
(2004a) also noted that sperm whales occurred less often west of Kodiak Island.
Sperm whales are commonly sighted during surveys in the Aleutians and the central and western GOA (
e.g.,
Forney and Brownell 1996; Moore 2001; Waite 2003; Wade
et al.
2003; Zerbini
et al.
2004; Barlow and Henry 2005; Ireland
et al.
2005; Straley
et al.
2005). Waite (2003) and Wade
et al.
(2003) noted an average group size of 1.2 in the western GOA. In contrast, there are fewer reports on the occurrence of sperm whales in the eastern GOA (
e.g.,
Rice and Wolman 1982; Mellinger
et al.
2004a; MacLean and Koski 2005; Rone
et al.
2010). Rone
et al.
(2017) reported no sperm whale sightings in 2009, 19 sperm whale sightings (22 animals) in 2013, and 27 sperm whale sightings (45 animals) in 2015 in the U.S. Navy training area east of Kodiak. Additionally, there were 241 acoustic encounters with sperm whales during the 2013 towed-hydrophone survey in that study (Rone
et al.
2014). Sperm whales were also frequently detected acoustically throughout the year during all years (2011-2015) of fixed-PAM studies in this area and detections occurred at all shelf, slope, and seamount sites, but they were less common at the shelf site near Kenai Peninsula and most common on the
slope (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015).
Rone
et al.
(2017) provided an abundance estimate (uncorrected for missed animals) for the area of 129 sperm whales, most of which were found in slope waters. Sperm whales were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Cuvier's Beaked Whale (
Ziphius cavirostris
)
Cuvier's beaked whale is the most widespread of the beaked whales, occurring in almost all temperate, subtropical, and tropical waters and even some sub-polar and polar waters (MacLeod
et al.
2006). It is likely the most abundant of all beaked whales (Heyning and Mead 2009). Cuvier's beaked whale is found in deep water over and near the continental slope (Jefferson
et al.
2015).
Cuvier's beaked whale ranges north to the GOA, including southeast Alaska, the Aleutian Islands, and the Commander Islands (Rice 1986, 1998). Most reported sightings have been in the Aleutian Islands (
e.g.,
Leatherwood
et al.
1983; Forney and Brownell 1996; Brueggeman
et al.
1987). Waite (2003) reported a single sighting of four Cuvier's beaked whales at the shelf break east of Kodiak Island during the summer of 2003 and one stranded on Kodiak Island in January 1987 (Foster and Hare 1990). There was one sighting of a single Cuvier's beaked whale during a 2013 survey in the U.S. Navy training area east of Kodiak, but none during the 2009 and 2015 surveys in that region (Rone
et al.
2017). There were also five sightings (eight animals) of unidentified beaked whales during the 2013 survey and none during the other years. Additionally, there were 34 acoustic encounters with Cuvier's beaked whales during the 2013 towed-hydrophone survey in that study (Rone
et al.
2014). Cuvier's beaked whales were detected occasionally at deep-water sites (900-1,000 m) during the 2011-2015 fixed-PAM studies in the U.S. Navy training area. They were infrequently detected on the slope site but more commonly detected at Pratt and Quinn seamounts. Detections occurred May to July 2014 at Pratt Seamount and October 2014 to March 2015 at Quinn Seamount in one of those studies (Rice
et al.
2015). Beaked whales were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Stejneger's Beaked Whale (
Mesoplodon stejnegeri
)
Stejneger's beaked whale occurs in subarctic and cool temperate waters of the North Pacific (Mead 1989). Most records are from Alaskan waters, and the Aleutian Islands appear to be its center of distribution (Mead 1989; Wade
et al.
2003). There have been no confirmed sightings of Stejneger's beaked whale in the GOA since 1986 (Wade
et al.
2003). However, they have been detected acoustically in the Aleutian Islands during summer, fall, and winter (Baumann-Pickering
et al.
2014) and were detected year-round at deep-water sites during the 2011-2015 fixed-PAM studies in the U.S. Navy training area east of Kodiak (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015). In contrast to Cuvier's beaked whales, which were more prevalent at seamounts, Stejneger's beaked whales were detected most frequently at the slope site, with peak detections in September and October (Debich
et al.
2013; Rice
et al.
2015). There were no sightings of Stejneger's beaked whales during three years of surveys (2009, 2013, 2015) in this area (Rone
et al.
2017). However, there were five sightings (eight animals) of unidentified beaked whales during the 2013 survey. Additionally, there were six acoustic encounters with Stejneger's beaked whales during the 2013 towed-hydrophone survey in that study (Rone
et al.
2014). Beaked whales were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Baird's Beaked Whale (
Berardius bairdii
)
Baird's beaked whale has a fairly extensive range across the North Pacific north of 30° N, and strandings have occurred as far north as the Pribilof Islands (Rice 1986). Two forms of Baird's beaked whales have been recognized—the common slate-gray form and a smaller, rare black form (Morin
et al.
2017). The gray form is seen off Japan, in the Aleutians, and on the west coast of North America, whereas the black from has been reported for northern Japan and the Aleutians (Morin
et al.
2017). Recent genetic studies suggest that the black form could be a separate species (Morin
et al.
2017).
Baird's beaked whale is currently divided into three distinct stocks: Sea of Japan, Okhotsk Sea, and Bering Sea/eastern North Pacific (Balcomb 1989; Reyes 1991). Baird's beaked whales sometimes are seen close to shore, but their primary habitat is over or near the continental slope and oceanic seamounts in waters 1,000-3,000 m deep (Jefferson
et al.
1993; Kasuya and Ohsumi 1984; Kasuya 2009).
Baird's beaked whale is migratory, arriving in the Bering Sea in the spring, and remaining there throughout the summer; the winter distribution is unknown (Kasuya 2002). There are numerous sighting records from the central GOA to the Aleutian Islands and the southern Bering Sea (Leatherwood
et al.
1983; Kasuya and Ohsumi 1984; Forney and Brownell 1996; Brueggeman
et al.
1987; Moore
et al.
2002b; Waite 2003; Wade
et al.
2003). There were seven sightings of Baird's beaked whales (58 animals) during a 2013 survey in the U.S. Navy training area east of Kodiak (Rone
et al.
2017). Additionally, there were nine acoustic encounters with Baird's beaked whales during the 2013 towed-hydrophone survey in that study (Rone
et al.
2014). There were also five sightings (eight animals) of unidentified beaked whales during that survey. No beaked whales were observed in 2009 or 2015 surveys in the same area (Rone
et al.
2017). Baird's beaked whales were detected acoustically during fixed-PAM studies in this area during the 2011-2012 and 2012-2013 studies but not in 2014-2015 (Baumann-Pickering
et al.
2012; Debich
et al.
2013; Rice
et al.
2015). They were detected regularly at the slope site from November through and January and at the Pratt Seamount site during most months. Beaked whales were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Pacific White-Sided Dolphin (
Lagenorhynchus obliquidens
)
The Pacific white-sided dolphin is found throughout the temperate North Pacific, in a relatively narrow distribution between 38° N and 47° N (Brownell
et al.
1999). It is common both on the high seas and along the continental margins (Leatherwood
et al.
1984; Dahlheim and Towell 1994; Ferrero and Walker 1996). Pacific white-sided dolphins often associate with other species, including cetaceans (especially Risso's and northern right whale dolphins; Green
et al.
1993), pinnipeds, and seabirds.
Pacific white-sided dolphins were seen throughout the North Pacific during surveys conducted during 1983-1990 (Buckland
et al.
1993; Miyashita 1993b). During winter, this species is most abundant in California slope and offshore areas; as northern marine waters begin to warm in the spring, it appears to move north to slope and
offshore waters off Oregon/Washington (Green
et al.
1992, 1993; Forney 1994; Forney
et al.
1995; Buchanan
et al.
2001; Barlow 2003). During the summer, Pacific white-sided dolphins occur north into the GOA and west to Amchitka in the Aleutian Islands, but rarely in the southern Bering Sea (Allen and Angliss 2010). Moore
et al.
(2002b) documented a single sighting of eight Pacific white-sided dolphins in the southeast Bering Sea along the Alaska Peninsula. Sightings in the GOA and Aleutian Islands have been documented in the summer by Waite (2003) and Wade
et al.
(2003), and in the spring to the southeast of Kodiak Island by Rone
et al.
(2010). Dahlheim and Towell (1994) reported sightings for southeast Alaska. There was one sighting of 60 Pacific white-sided dolphins in 2009, no sightings in 2013, and 10 sightings of Pacific white-sided dolphins (986 animals) in 2015 during surveys in the U.S. Navy training area east of Kodiak (Rone
et al.
2017). Pacific white-sided dolphins were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011), but there was one sighting of two unidentified small odontocetes.
Risso's Dolphin (
Grampus griseus
)
Risso's dolphin is primarily a tropical and mid-temperate species distributed worldwide (Kruse
et al.
1999). It occurs between 60° N and 60° S, where surface water temperatures are at least 10° C (Kruse
et al.
1999). Water temperature appears to be an important factor affecting its distribution (Kruse
et al.
1999). Although it occurs from coastal to deep water, it shows a strong preference for mid-temperate waters of the continental shelf and slope (Jefferson
et al.
2014).
Throughout the region from California to Washington, the distribution and abundance of Risso's dolphins are highly variable, presumably in response to changing oceanographic conditions on both annual and seasonal time scales (Forney and Barlow 1998; Buchanan
et al.
2001; Becker 2007). Water temperature appears to be an important factor affecting their distribution (Kruse
et al.
1999; see also Becker 2007). Like the Pacific white-sided dolphin, Risso's dolphin is believed to make seasonal north-south movements related to water temperature, spending colder winter months off California and moving north to waters off Oregon/Washington during the spring and summer as northern waters begin to warm (Green
et al.
1992, 1993; Buchanan
et al.
2001; Barlow 2003; Becker 2007). Risso's dolphins are uncommon to rare in the GOA. Risso's dolphins have been sighted near Chirikof Island (southwest of Kodiak Island) and offshore in the GOA (Consiglieri
et al.
1980; Braham 1983). They were detected acoustically once, in January 2013, near Pratt Seamount during fixed-PAM studies from 2011-2015 in the U.S. Navy training area (Debich
et al.
2013). The DoN (2014) considers this species to be only an occasional visitor to their GOA training area. Risso's dolphins were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011). There was one sighting of two unidentified small odontocetes.
Killer Whale (
Orcinus orca
)
The killer whale is cosmopolitan and globally fairly abundant; it has been observed in all oceans of the World (Ford 2009). It is very common in temperate waters and also frequents tropical waters, at least seasonally (Heyning and Dahlheim 1988). High densities of the species occur in high latitudes, especially in areas where prey is abundant. Killer whale movements generally appear to follow the distribution of their prey, which includes marine mammals, fish, and squid.
Of eight killer whale stocks currently recognized in the Pacific U.S., six occur in Alaskan waters: (1) The Eastern North Pacific Alaska Resident Stock, from southeast Alaska to the Aleutians and Bering Sea, (2) the Eastern North Pacific Northern Resident Stock, from B.C. through parts of southeast Alaska, (3) the Eastern North Pacific Gulf of Alaska, Aleutian Islands, and Bering Sea Transient Stock, from PWS through to the Aleutians and Bering Sea, (4) the AT1 Transient Stock, from PWS through the Kenai Fjords, (5) the West Coast Transient Stock, from California through southeast Alaska, and (6) the Offshore Stock, from California through Alaska. The AT1 Transient Stock is considered depleted under the MMPA and therefore a strategic stock. Movements of resident groups between different geographic areas have also been documented (Leatherwood
et al.
1990; Dahlheim
et al.
1997; Matkin
et al.
1997, 1999 in Allen and Angliss 2010). In the proposed study area, individuals from one resident stock (Eastern North Pacific Alaska Resident Stock), the North Pacific Offshore Stock, and one transient stock (Eastern North Pacific Gulf of Alaska, Aleutian Islands, and Bering Sea Transient Stock), could be encountered during the survey. AT1 transients have only ever been seen in Prince William Sound and in the Kenai Fjords region (Muto et al., 2018; Matkin et al 2008). Therefore, while the stock is present in the Gulf of Alaska, the limited range of the stock and the fact that this range does not overlap with L-DEO's proposed survey means take is not likely to occur for the AT1 stock of transient killer whales.
During surveys of the western GOA and Aleutian Islands, transient killer whale densities were higher south of the Alaska Peninsula between the Shumagin Islands and the eastern Aleutians than in other areas (Wade
et al.
2003; Zerbini
et al.
2007). They were not seen between the Shumagin Islands and the eastern side of Kodiak Island during surveys in 2001-2003, but they were sighted there during earlier surveys (
e.g.,
Dahlheim 1997 in Zerbini
et al.
2007). Resident killer whales were most abundant near Kodiak Island, around Umnak and Unalaska Islands in the eastern Aleutians, and in Seguam Pass in the central Aleutians (Wade
et al.
2003; Zerbini
et al.
2007). No residents were seen between 156° W and 164° W, south of the Alaska Peninsula (Zerbini
et al.
2007).
Little is known about offshore killer whales in the GOA, but they could be encountered during the proposed survey. During summer surveys of the western GOA and Aleutian Islands in 2001-2003, two sightings of offshore killer whales were made, one northeast of Unalaska Island and another one south of Kodiak Island near the Trinity Islands (Wade
et al.
2003; Zerbini
et al.
2007). As the groups sighted were large, it suggests the number of offshore killer whales in the area is relatively high (Zerbini
et al.
2007). Dahlheim
et al.
(2008b) encountered groups of 20-60 killer whales in western Alaska; offshore killer whales encountered near Kodiak Island and the eastern Aleutians were also sighted in southeast Alaska and California. A group of at least 54 offshore killer whales was sighted in July 2003 during a survey in the eastern Aleutian Islands (Matkin
et al.
2007).
Rone
et al.
(2017) reported six killer whale sightings (119 animals) in 2009, 21 killer whale sightings (138 animals) in 2013, and 10 killer whale sightings (73 animals) in 2015 in the U.S. Navy training area east of Kodiak. Additionally, there were 32 acoustic encounters with killer whales and three acoustic encounters with offshore killer whales (based on known differences in their acoustic signals) during the 2013 towed-hydrophone survey in that study (Rone
et al.
2014). Killer whales were detected acoustically sporadiacally throughout the year at shelf, slope, and seamount sites in the U.S. Navy training area (Baumann-Pickering
et al.
2012;
Debich
et al.
2013). Rone
et al.
(2017) an abundance estimate (uncorrected for missed animals) for the area of 899 killer whales, most of which were found in slope waters. There was one sighting of a single killer whale during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Dall's Porpoise (
Phocoenoides dalli
)
Dall's porpoise is only found in the North Pacific and adjacent seas. It is widely distributed across the North Pacific over the continental shelf and slope waters, and over deep (>2,500 m) oceanic waters (Hall 1979), ranging from ~30-62° N (Jefferson
et al.
2015). In general, this species is common throughout its range (Buckland
et al.
1993). It is known to approach vessels to bowride (Jefferson 2009).
Dall's porpoise occurs throughout Alaska; the only apparent gaps in distribution in Alaskan waters south of the Bering Strait are for upper Cook Inlet and the Bering Sea shelf. Using a population estimate based on vessel surveys during 1987-1991, and correcting for the tendency of this species to approach vessels, which Turnock and Quinn (1991) suggested resulted in inflated abundance estimates perhaps by as much as five times, a population estimate of 83,400 was calculated for the Alaska stock of Dall's porpoise. Because this estimate is more than eight years old, NMFS considers it to be unreliable and reported that there are no reliable abundance estimates available for the Alaska Stock of this species when it was last reviewed (Muto
et al.
2016).
Numerous studies have documented the occurrence of Dall's porpoise in the Aleutian Islands and western GOA (Forney and Brownell 1996; Moore 2001; Wade
et al.
2003; Waite 2003; Baraff
et al.
2005; Ireland
et al.
2005) as well as in the Bering Sea (Moore
et al.
2002b). Dall's porpoise was one of the most frequently sighted species during summer seismic surveys in the central and eastern GOA and southeast Alaska (MacLean and Koski 2005; Hauser and Holst 2009). Rone
et al.
(2017) reported 10 Dall's porpoise sightings (59 animals) in 2009, 337 Dall's porpoise sightings (907 animals) in 2013, and 98 Dall's porpoise sightings (391 animals) in 2015 in the U.S. Navy training area east of Kodiak. Additionally, there were three acoustic encounters with Dall's porpoise during the 2013 towed-hydrophone survey in that study (Rone
et al.
2014). Rone
et al.
(2017) provided an abundance estimate for the area of 15,423 Dall's porpoises. This estimate was uncorrected for missed animals and did not account for their propensity to approach vessels. Dall's porpoise was the second most frequently sighted cetacean during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey, comprising 14.1 percent of all cetacean sightings (RPS 2011). There were 26 sightings of this species, representing 227 animals during the 37 days of monitoring. The average group size was nine and the largest group size was 35.
Harbor Porpoise (
Phocoena phocoena
)
The harbor porpoise inhabits temperate, subarctic, and arctic waters. It is typically found in shallow water (<100 m) nearshore but is occasionally sighted in deeper offshore water (Jefferson
et al.
2015); abundance declines linearly as depth increases (Barlow 1988). In the eastern North Pacific, its range extends from Point Barrow, Alaska, to Point Conception, California.
In Alaska, there are three separate stocks of harbor porpoise: Southeast Alaska, GOA, and Bering Sea. The Southeast Alaska Stock occurs from northern B.C. to Cape Suckling, and the GOA Stock ranges from Cape Suckling to Unimak Pass. The population estimates for the Southeast Alaska, GOA, and Bering Sea stocks are 11,146, 31,046, and 48,215, respectively (Muto
et al.
2016). The Southeast Alaska stock is
Harbor porpoise are seen regularly in the western GOA and Aleutian Islands (
e.g.,
Wade
et al.
2003; Waite 2003; Baraff
et al.
2005; Ireland
et al.
2005) and Bering Sea (Moore
et al.
2002b). Harbor porpoises are also sighted in the eastern and central GOA and southeast Alaska (Dahlheim
et al.
2000, 2008a; MacLean and Koski 2005; Rone
et al.
2010). There were 30 sightings (89 animals) of harbor porpoise in 2009, eight sightings (11 animals) of harbor porposie in 2013, and a single sighting of one harbor porpoise in 2015 during surveys in the U.S. Navy training area east of Kodiak (Rone
et al.
2017). Harbor porpoise were not observed during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011), but there was one sighting of two unidentified small odontocetes.
Pinnipeds
Northern Fur Seal (
Callorhinus ursinus
)
The northern fur seal is endemic to the North Pacific Ocean and occurs from southern California to the Bering Sea, Okhotsk Sea, and Honshu Island, Japan (Muto
et al.
2018). During the breeding season, most of the worldwide population of northern fur seals inhabits the Pribilof Islands in the southern Bering Sea (Lee
et al.
2014; Muto
et al.
2018). The rest of the population occurs at rookeries on Bogoslof Island in the Bering Sea, in Russia (Commander Islands, Robben Island, Kuril Islands), on San Miguel Island in southern California (NMFS 1993; Lee
et al.
2014), and on the Farallon Islands off central California (Muto
et al.
2018). In the United States, two stocks are recognized—the Eastern Pacific and the California stocks (Muto
et al.
2018). The Eastern Pacific stock ranges from the Pribilof Islands and Bogoslof Island in the Bering Sea during summer to California during winter (Muto
et al.
2018).
When not on rookery islands, northern fur seals are primarily pelagic but occasionally haul out on rocky shorelines (Muto
et al.
2018). During the breeding season, adult males usually come ashore in May-August and may sometimes be present until November; adult females are found ashore from June-November (Carretta
et al.
2017; Muto
et al.
2018). After reproduction, northern fur seals spend the next 7-8 months feeding at sea (Roppel 1984). Once weaned, juveniles spend 2-3 years at sea before returning to rookeries. Animals may migrate to the GOA, off Japan, and the west coast of the United States (Muto
et al.
2018). Pups travel through Aleutian passes and spend the first two years at sea before returning to their islands of origin.
In November, adult females and pups leave the Pribilof Islands and migrate into the North Pacific Ocean to areas including offshore Oregon and Washington (Ream
et al.
2005). Males usually migrate only as far south as the GOA (Kajimura 1984). Ream
et al.
(2005) showed that migrating females moved over the continental shelf as they migrated southeasterly. Instead of following depth contours, their travel corresponded with movements of the Alaska Gyre and the North Pacific Current (Ream
et al.
2005). Their foraging areas were associated with eddies, the subarctic-subtropical transition region, and coastal mixing (Ream
et al.
2005; Alford
et al.
2005). Some juveniles and non-pregnant females may remain in the GOA throughout the summer (Calkins 1986).
Robson
et al.
(2004) reported that female fur seals from St. Paul and St. George islands traveled in different directions. They also observed habitat separation among breeding sites on the same island (Robson
et al.
2004). Lactating females from the same breeding site share a foraging area,
whereas females from different sites tend to forage in different areas (Robson
et al.
2004). Females from both islands traveled for similar durations and maximum distances (Robson
et al.
2004).
Northern fur seals were seen throughout the North Pacific during surveys conducted during 1987-1990 (Buckland
et al.
1993). Tracked adult male fur seals that were tagged on St. Paul Island in the Bering Sea in October 2009, wintered in the Bering Sea or northern North Pacific Ocean; females migrated to the GOA and the California Current (Sterling
et al.
2014).
A total of 42 northern fur seals was seen during 3767 km of shipboard surveys in the northwestern GOA during June-July 1987 (Brueggeman
et al.
1988). Leatherwood
et al.
(1983) reported 14 sightings of 34 northern fur seals away from the breeding islands in the southeast Bering Sea during aerial surveys in 1982, mostly during July and August. No fur seals were seen during summer surveys in the GOA in 2004 and 2008 (MacLean and Koski 2005; Hauser and Holst 2009) or during spring surveys in 2009 (Rone
et al.
2010). None of the 42 female northern fur seals tagged on St Paul Island between August-October 2007 and 2008 traveled south of the Aleutian Islands (Kuhn
et al.
2010). Rone
et al.
(2014) reported 78 northern fur seal sightings (83 animals) in 2013 in the U.S. Navy training area east of Kodiak. They also provided an abundance estimate (uncorrected for missed animals) for the area of 1770 northern fur seals. There were seven sightings, representing 7 northern fur seals, during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Steller Sea Lion (
Eumetopias jubatus
)
The Steller sea lion occurs along the North Pacific Rim from northern Japan to California (Loughlin
et al.
1984). They are distributed around the coasts to the outer shelf from northern Japan through the Kuril Islands and Okhotsk Sea, through the Aleutian Islands, central Bering Sea, southern Alaska, and south to California (NMFS 2016c). There are two stocks, or DPSs, of Steller sea lions—the Western and Eastern DPSs, which are divided at 144° W longitude (NMFS 2016c). The Western DPS is listed as endangered and includes animals that occur in Japan and Russia (NMFS 2016c; Muto
et al.
2017); the Eastern DPS was delisted from threatened in 2013 (NMFS 2013a). Critical habitat has been designated 20 nmi around all major haulouts and rookeries, as well as three large foraging areas (NMFS 2017b). The critical habitat of both stocks is currently under review in light of the delisting of the Eastern DPS (Muto
et al.
2018). Critical habitat as well as “no approach” zones occur within the proposed study area. “No approach” zones are restricted areas wherein no vessel may approach within 3 nmi (5.6 km) of listed rookeries (50 CFR 223.202). Only individuals from the Western DPS are expected to occur in the proposed survey area. The Eastern DPS is estimated at 41,638 (Muto
et al.
2017) and appears to have increased at an annual rate of 4.76 percent between 1989 and 2015 (Muto
et al.
2018).
Rookeries of Steller sea lions from the Western DPS are located on the Aleutian Islands and along the Gulf of Alaska, as well as the east coast of Kamchatka, Commander Islands, and Kuril Islands (Burkanov and Loughlin 2005; Fritz
et al.
2016; Muto
et al.
2017). Breeding adults occupy rookeries from late-May to early-July (NMFS 2008). Non-breeding adults use haulouts or occupy sites at the periphery of rookeries during the breeding season (NMFS 2008). Pupping occurs from mid-May to mid July (Pitcher and Calkins 1981) and peaks in June (Pitcher
et al.
2002). Territorial males fast and remain on land during the breeding season (NMFS 2008). Females with pups generally stay within 30 km of the rookeries in shallow (30-120 m) water when feeding (NMFS 2008). Tagged juvenile sea lions showed localized movements near shore (Briggs
et al.
2005). Loughlin
et al.
(2003) reported that most (88 percent) at-sea movements of juvenile Steller sea lions in the Aleutian Islands were short (<15 km) foraging trips. The mean distance of juvenile sea lion trips at sea was 16.6 km and the maximum trip distance recorded was 447 km. Long-range trips represented 6 percent of all trips at sea, and trip distance and duration increase with age (Loughlin
et al.
2003; Call
et al.
2007). Although Steller sea lions are not considered migratory, foraging animals can travel long distances outside of the breeding season (Loughlin
et al.
2003; Raum-Suryan
et al.
2002).
Steller sea lions are present in Alaska year-round, with centers of abundance in the GOA and Aleutian Islands. There are five major rookery sites within the study area in the northern GOA: Chirikof, Chowiet, Atkins, Chernabura islands, and Pinnacle Rock. There are also numerous haulout sites located within the study area (see Figure 1 in the IHA Application); most haulout sites on Kodiak Island (and within the study area) are used year-round (
e.g.,
Wynne 2005). Counts are highest in late summer (Wynne 2005). Sea lion counts in the central GOA, including Kodiak Island, were reported to be declining between 1999 and 2003 (Sease and Gudmundson 2002; Wynne 2005). Evidence suggests that counts in Alaska were lowest in 2002 and 2003, but between 2003 and 2016 pup and non-pup counts have increased by 2.19 percent per year and 2.24 percent per year, respectively (Muto
et al.
2018). These rates vary regionally, with the highest rates of increase in the eastern Gulf of Alaska and a steadily decreasing rate of increase heading west to the Aleutian Islands.
Steller sea lions are an important subsistence resource for Alaska Natives from southeast Alaska to the Aleutian Islands. There are numerous communities along the shores of the GOA that participate in subsistence hunting. In 2008, 19 sea lions were taken in the Kodiak Island region and 9 were taken along the South Alaska Peninsula (Wolfe
et al.
2009). As of 2009, data on community subsistence harvests are no longer being collected consistently so no data are available. The most recent 5 years of data available (2004-2008) show an annual average catch of 172 steller sea lions for all areas in Alaska combined except the Pribilof Islands in the Bering Sea (Muto
et al.
2018).
There was one sighting of 18 Steller sea lions during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011).
Northern Elephant Seal (
Mirounga angustirostris
)
Northern elephant seals breed in California and Baja California, primarily on offshore islands (Stewart
et al.
1994), from December-March (Stewart and Huber 1993). Adult elephant seals engage in two long northward migrations per year, one following the breeding season, and another following the annual molt, with females returning earlier to molt (March-April) than males (July-August) (Stewart and DeLong 1995). Juvenile elephant seals typically leave the rookeries in April or May and head north, traveling an average of 900-1,000 km. Hindell and Perrin (2009) noted that traveling likely takes place in water depths >200 m.
When not breeding, elephant seals feed at sea far from the rookeries, ranging as far north as 60° N, into the GOA and along the Aleutian Islands (Le Boeuf
et al.
2000). Some seals that were tracked via satellite-tags for no more than 224 days traveled distances in excess of 10,000 km during that time (Le Beouf
et al.
2000). Northern elephant
seals that were satellite-tagged at a California rookery have been recorded traveling as far west as ~166.5-172.5° E (Le Boeuf
et al.
2000; Robinson
et al.
2012; Robinson 2016 in OBIS 2018; Costa 2017 in OBIS 2018). Post-molting seals traveled longer and farther than post-breeding seals (Robinson
et al.
2012). Rone
et al.
(2014) reported 16 northern fur seal sightings (16 animals) in a June-July 2013 survey in the U.S. Navy training area east of Kodiak. Northern elephant seal males could occur in the GOA throughout the year (Calkins 1986).
California Sea Lion (
Zalophus californianus
)
The primary range of the California sea lion includes the coastal areas and offshore islands of the eastern North Pacific Ocean from BC, Canada, to central Mexico, including the Gulf of California (Jefferson
et al.
2015). However, its distribution is expanding (Jefferson
et al.
2015), and its secondary range extends into the GOA where it is occasionally recorded (Maniscalco
et al.
2004) and southern Mexico (Gallo-Reynoso and Solórzano-Velasco 1991). California sea lions are coastal animals that often haul out on shore throughout the year. King (1983) noted that sea lions are rarely found more than 16 km offshore. During fall and winter surveys off Oregon/Washington, mean distance from shore was ~13 km (Bonnell
et al.
1992).
California sea lion rookeries are on islands located in southern California, western Baja California, and the Gulf of California (Carretta
et al.
2016). A single stock is recognized in U.S. waters: The U.S. Stock. Five genetically distinct geographic populations have been identified: (1) Pacific Temperate (includes rookeries in U.S. waters and the Coronados Islands to the south), (2) Pacific Subtropical, (3) Southern Gulf of California, (4) Central Gulf of California, and (5) Northern Gulf of California (Schramm
et al.
2009). Animals from the Pacific Temperate population occur in the proposed project area. California sea lions that are sighted in Alaska are typically seen at Steller sea lion rookeries or haulouts, with most sightings occurring between March and May, although they can be found in the GOA year-round (Maniscalco
et al.
2004).
Harbor Seal (
Phoca vitulina
)
The harbor seal is distributed in the North Atlantic and North Pacific. Two subspecies occur in the Pacific:
P.v. stejnegeri
in the northwest Pacific Ocean and
P.v. richardii
in the eastern Pacific Ocean. Eastern Pacific harbor seals occur in nearshore, coastal, and estuarine areas ranging from Baja California, Mexico, north to the Pribilof Islands in Alaska (Muto
et al.
2016). Harbor seals inhabit estuarine and coastal waters, hauling out on rocks, reefs, beaches, and glacial ice flows. They are generally non-migratory, but move locally with the tides, weather, season, food availability, and reproduction (Scheffer and Slipp 1944; Fisher 1952; Bigg 1969, 1981). Twelve stocks of harbor seals are recognized in Alaska (Muto
et al.
2016). The proposed survey would take place within the range of three of these stocks: North Kodiak, South Kodiak, and Cook Inlet/Shelikof Strait stocks. Nearby stocks are the Aleutian Islands, Prince William Sound, and Glacier Bay/Icy Strait stocks. There are two stocks in the Bering Sea (Bristol Bay and Pribilof Islands) and four stocks in southeast Alaska.
Female harbor seals give birth to a single pup while hauled out on shore or on glacial ice flows; pups are born from May to mid-July. The mother and pup remain together until weaning occurs at 3-6 weeks (Bishop 1967; Bigg 1969). When molting, which occurs primarily in late August, seals spend the majority of the time hauled out on shore, glacial ice, or other substrates. Juvenile harbor seals can travel significant distances (525 km) to forage or disperse, whereas adults were generally found within 190 km of their tagging location in Prince William Sound, Alaska (Lowry
et al.
2001). The smaller home range used by adults is suggestive of a strong site fidelity (Pitcher and Calkins 1979; Pitcher and McAllister 1981; Lowry
et al.
2001). Pups tagged in the GOA most commonly undertook multiple return trips of more than 75 km from natal areas, followed by movements of <25 km from the natal area (Small
et al.
2005). Pups tagged in Prince William Sound traveled a mean maximum distance of 43.2 km from their tagging location, whereas those tagged in the GOA moved a mean maximum distance of 86.6 km (Small
et al.
2005).
Harbor seals are an important subsistence resource for Alaska Natives in the northern GOA. In 2011-2012, 37 harbor seals were taken from the North Kodiak Stock and 126 harbor seals were taken from the South Kodiak Stock by communities on Kodiak Island (Muto
et al.
2016). The number taken from the Cook Inlet/Shelikof Strait Stock for 2011-2012 is unknown, but an average of 233 were taken from this stock annually during 2004-2008 (Muto
et al.
2016).
There was one sighting of nine harbor seals during the L-DEO seismic survey conducted in the summer of 2011 in the same area as the currently proposed survey (RPS 2011). Harbor seals could be encountered in the proposed survey 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 2.
Table 2—Marine Mammal Hearing Groups (NMFS, 2018)
Hearing group
Generalized hearing range *
Low-frequency (LF) cetaceans (baleen whales)
7 Hz to 35 kHz.
Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)
150 Hz to 160 kHz.
High-frequency (HF) cetaceans (true porpoises,
Kogia,
river dolphins, cephalorhynchid,
Lagenorhynchus cruciger
&
L. australis
)
275 Hz to 160 kHz.
Phocid pinnipeds (PW) (underwater) (true seals)
50 Hz to 86 kHz.
Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)
60 Hz to 39 kHz.
* Represents the generalized hearing range for the entire group as a composite (
i.e.,
all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65 dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall
et al.
2007) and PW pinniped (approximation).
The pinniped functional hearing group was modified from Southall
et al.
(2007) on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range (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. Twenty-one marine mammal species (16 cetacean and 5 pinniped (3 otariid and 2 phocid) species) have the reasonable potential to co-occur with the proposed survey activities. Please refer to Table 1. Of the 16 cetacean species that may be present, 7 are classified as low-frequency cetaceans (
i.e.,
all mysticete species), 7 are classified as mid-frequency cetaceans (
i.e.,
all delphinid and ziphiid species and the sperm whale), and 2 are classified as high-frequency cetaceans (
i.e.,
harbor porpoise and Kogia spp.).
Potential Effects of Specified Activities on Marine Mammals and Their Habitat
This section includes a summary and discussion of the ways that components of the specified activity may impact marine mammals and their habitat. The
Estimated Take 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 122 MBES, a Knudsen Chirp 3260 SBP, and a Teledyne RDI 75 kHz Ocean Surveyor ADCP would be operated continuously during the proposed surveys, but not during transit to and from the survey areas. Due to the lower source level of the Kongsberg EM 122 MBES relative to the
Langseth's
airgun array (242 dB re 1 μPa · m for the MBES versus a minimum of 258 dB re 1 μPa · m (rms) for the 36 airgun array (NSF-USGS, 2011)), sounds from the MBES are expected to be effectively subsumed by the sounds from the airgun array. Thus, any marine mammal potentially exposed to sounds from the MBES would already have been exposed to sounds from the airgun array, which are expected to propagate further in the water. 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 both the Knudsen Chirp 3260 SBP and the Teledyne RDI 75 kHz Ocean Surveyor ADCP relative to the
Langseth's
airgun array (maximum SL of 222 dB re 1 μPa · m for the SBP and maximum SL of 224 dB re 1 μPa · m for the ADCP, versus a minimum of 258 dB re 1 μPa · m for the 36 airgun array (NSF-USGS, 2011)), sounds from the SBP and ADCP are expected to be effectively subsumed by sounds from the airgun array. Thus, any marine mammal potentially exposed to sounds from the SBP and/or the ADCP 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, SBP or ADCP (beyond that which is already quantified as a result of exposure to the airguns) is discountable and therefore we do not consider noise from the MBES, SBP or ADCP further in this analysis.
Acoustic Effects
Here, we discuss the effects of active acoustic sources on marine mammals.
Potential Effects of Underwater Sound
—Please refer to the information given previously (“Description of Active Acoustic Sources”) regarding sound, characteristics of sound types, and
metrics used in this document. Anthropogenic sounds cover a broad range of frequencies and sound levels and can have a range of highly variable impacts on marine life, from none or minor to potentially severe responses, depending on received levels, duration of exposure, behavioral context, and various other factors. The potential effects of underwater sound from active acoustic sources can potentially result in one or more of the following: Temporary or permanent hearing impairment, non-auditory physical or physiological effects, behavioral disturbance, stress, and masking (Richardson
et al.,
1995; Gordon
et al.,
2004; Nowacek
et al.,
2007; Southall
et al.,
2007; Götz
et al.,
2009). The degree of effect is intrinsically related to the signal characteristics, received level, distance from the source, and duration of the sound exposure. In general, sudden, high level sounds can cause hearing loss, as can longer exposures to lower level sounds. Temporary or permanent loss of hearing will occur almost exclusively for noise within an animal's hearing range. We first describe specific manifestations of acoustic effects before providing discussion specific to the use of airgun arrays.
Richardson
et al.
(1995) described zones of increasing intensity of effect that might be expected to occur, in relation to distance from a source and assuming that the signal is within an animal's hearing range. First is the area within which the acoustic signal would be audible (potentially perceived) to the animal, but not strong enough to elicit any overt behavioral or physiological response. The next zone corresponds with the area where the signal is audible to the animal and of sufficient intensity to elicit behavioral or physiological responsiveness. Third is a zone within which, for signals of high intensity, the received level is sufficient to potentially cause discomfort or tissue damage to auditory or other systems. Overlaying these zones to a certain extent is the area within which masking (
i.e.,
when a sound interferes with or masks the ability of an animal to detect a signal of interest that is above the absolute hearing threshold) may occur; the masking zone may be highly variable in size.
We describe the more severe effects of certain non-auditory physical or physiological effects only briefly as we do not expect that use of airgun arrays are reasonably likely to result in such effects (see below for further discussion). Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton
et al.,
1973). Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions (
e.g.,
change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox
et al.,
2006; Southall
et al.,
2007; Zimmer and Tyack, 2007; Tal
et al.,
2015). The survey activities considered here do not involve the use of devices such as explosives or mid-frequency tactical sonar that are associated with these types of effects.
Threshold Shift
—Marine mammals exposed to high-intensity sound, or to lower-intensity sound for prolonged periods, can experience hearing threshold shift (TS), which is the loss of hearing sensitivity at certain frequency ranges (Finneran, 2015). TS can be permanent (PTS), in which case the loss of hearing sensitivity is not fully recoverable, or temporary (TTS), in which case the animal's hearing threshold would recover over time (Southall
et al.,
2007). Repeated sound exposure that leads to TTS could cause PTS. In severe cases of PTS, there can be total or partial deafness, while in most cases the animal has an impaired ability to hear sounds in specific frequency ranges (Kryter, 1985).
When PTS occurs, there is physical damage to the sound receptors in the ear (
i.e.,
tissue damage), whereas TTS represents primarily tissue fatigue and is reversible (Southall
et al.,
2007). In addition, other investigators have suggested that TTS is within the normal bounds of physiological variability and tolerance and does not represent physical injury (
e.g.,
Ward, 1997). Therefore, NMFS does not consider TTS to constitute auditory injury.
Relationships between TTS and PTS thresholds have not been studied in marine mammals, and there is no PTS data for cetaceans but such relationships are assumed to be similar to those in humans and other terrestrial mammals. PTS typically occurs at exposure levels at least several dBs above (a 40-dB threshold shift approximates PTS onset;
e.g.,
Kryter
et al.,
1966; Miller, 1974) that inducing mild TTS (a 6-dB threshold shift approximates TTS onset;
e.g.,
Southall
et al.
2007). Based on data from terrestrial mammals, a precautionary assumption is that the PTS thresholds for impulse sounds (such as airgun pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS cumulative sound exposure level thresholds are 15 to 20 dB higher than TTS cumulative sound exposure level thresholds (Southall
et al.,
2007). Given the higher level of sound or longer exposure duration necessary to cause PTS as compared with TTS, it is considerably less likely that PTS could occur.
For mid-frequency cetaceans in particular, potential protective mechanisms may help limit onset of TTS or prevent onset of PTS. Such mechanisms include dampening of hearing, auditory adaptation, or behavioral amelioration (
e.g.,
Nachtigall and Supin, 2013; Miller
et al.,
2012; Finneran
et al.,
2015; Popov
et al.,
2016).
TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 1985). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. Few data on sound levels and durations necessary to elicit mild TTS have been obtained for marine mammals.
Marine mammal hearing plays a critical role in communication with conspecifics, and interpretation of environmental cues for purposes such as predator avoidance and prey capture. Depending on the degree (elevation of threshold in dB), duration (
i.e.,
recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious. For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that occurs during a time where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts.
Finneran
et al.
(2015) measured hearing thresholds in three captive bottlenose dolphins before and after exposure to ten pulses produced by a seismic airgun in order to study TTS induced after exposure to multiple pulses. Exposures began at relatively low levels and gradually increased over a period of several months, with the highest exposures at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 193-195 dB.
No substantial TTS was observed. In addition, behavioral reactions were observed that indicated that animals can learn behaviors that effectively mitigate noise exposures (although exposure patterns must be learned, which is less likely in wild animals than for the captive animals considered in this study). The authors note that the failure to induce more significant auditory effects likely due to the intermittent nature of exposure, the relatively low peak pressure produced by the acoustic source, and the low-frequency energy in airgun pulses as compared with the frequency range of best sensitivity for dolphins and other mid-frequency cetaceans.
Currently, TTS data only exist for four species of cetaceans (bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless porpoise) exposed to a limited number of sound sources (
i.e.,
mostly tones and octave-band noise) in laboratory settings (Finneran, 2015). In general, harbor porpoises have a lower TTS onset than other measured cetacean species (Finneran, 2015). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species. There are no data available on noise-induced hearing loss for mysticetes.
Critical questions remain regarding the rate of TTS growth and recovery after exposure to intermittent noise and the effects of single and multiple pulses. Data at present are also insufficient to construct generalized models for recovery and determine the time necessary to treat subsequent exposures as independent events. More information is needed on the relationship between auditory evoked potential and behavioral measures of TTS for various stimuli. For summaries of data on TTS in marine mammals or for further discussion of TTS onset thresholds, please see Southall
et al.
(2007), Finneran and Jenkins (2012), Finneran (2015), and NMFS (2016a).
Behavioral Effects
—Behavioral disturbance may include a variety of effects, including subtle changes in behavior (
e.g.,
minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors (
e.g.,
species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
e.g.,
Richardson
et al.,
1995; Wartzok
et al.,
2003; Southall
et al.,
2007; Weilgart, 2007; Archer
et al.,
2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.,
2012), and can vary depending on characteristics associated with the sound source (
e.g.,
whether it is moving or stationary, number of sources, distance from the source). Please see Appendices B-C of Southall
et al.
(2007) for a review of studies involving marine mammal behavioral responses to sound.
Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok
et al.,
2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder
et al.,
2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure. As noted, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson
et al.,
1995; NRC, 2003; Wartzok
et al.,
2003). Controlled experiments with captive marine mammals have showed pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway
et al.,
1997). Observed responses of wild marine mammals to loud pulsed sound sources (typically seismic airguns or acoustic harassment devices) have been varied but often consist of avoidance behavior or other behavioral changes suggesting discomfort (Morton and Symonds, 2002; see also Richardson
et al.,
1995; Nowacek
et al.,
2007). However, many delphinids approach acoustic source vessels with no apparent discomfort or obvious behavioral change (
e.g.,
Barkaszi
et al.,
2012).
Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal. If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant (
e.g.,
Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 2005). However, there are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight.
Changes in dive behavior can vary widely, and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive (
e.g.,
Frankel and Clark, 2000; Ng and Leung, 2003; Nowacek
et al.,
2004; Goldbogen
et al.,
2013a, b). Variations in dive behavior may reflect interruptions in biologically significant activities (
e.g.,
foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response.
Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators (
e.g.,
bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance (
e.g.,
Croll
et al.,
2001; Nowacek
et al.;
2004; Madsen
et al.,
2006; Yazvenko
et al.,
2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationship between prey availability, foraging effort and success, and the life history stage of the animal.
Visual tracking, passive acoustic monitoring, and movement recording tags were used to quantify sperm whale behavior prior to, during, and following exposure to airgun arrays at received levels in the range 140-160 dB at distances of 7-13 km, following a phase-in of sound intensity and full array
exposures at 1-13 km (Madsen
et al.,
2006; Miller
et al.,
2009). Sperm whales did not exhibit horizontal avoidance behavior at the surface. However, foraging behavior may have been affected. The sperm whales exhibited 19 percent less vocal (buzz) rate during full exposure relative to post exposure, and the whale that was approached most closely had an extended resting period and did not resume foraging until the airguns had ceased firing. The remaining whales continued to execute foraging dives throughout exposure; however, swimming movements during foraging dives were 6 percent lower during exposure than control periods (Miller
et al.,
2009). These data raise concerns that seismic surveys may impact foraging behavior in sperm whales, although more data are required to understand whether the differences were due to exposure or natural variation in sperm whale behavior (Miller
et al.,
2009).
Variations in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure (
e.g.,
Kastelein
et al.,
2001, 2005, 2006; Gailey
et al.,
2007, 2016).
Marine mammals vocalize for different purposes and across multiple modes, such as whistling, echolocation click production, calling, and singing. Changes in vocalization behavior in response to anthropogenic noise can occur for any of these modes and may result from a need to compete with an increase in background noise or may reflect increased vigilance or a startle response. For example, in the presence of potentially masking signals, humpback whales and killer whales have been observed to increase the length of their songs (Miller
et al.,
2000; Fristrup
et al.,
2003; Foote
et al.,
2004), while right whales have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks
et al.,
2007). In some cases, animals may cease sound production during production of aversive signals (Bowles
et al.,
1994).
Cerchio
et al.
(2014) used passive acoustic monitoring to document the presence of singing humpback whales off the coast of northern Angola and to opportunistically test for the effect of seismic survey activity on the number of singing whales. Two recording units were deployed between March and December 2008 in the offshore environment; numbers of singers were counted every hour. Generalized Additive Mixed Models were used to assess the effect of survey day (seasonality), hour (diel variation), moon phase, and received levels of noise (measured from a single pulse during each ten minute sampled period) on singer number. The number of singers significantly decreased with increasing received level of noise, suggesting that humpback whale breeding activity was disrupted to some extent by the survey activity.
Castellote
et al.
(2012) reported acoustic and behavioral changes by fin whales in response to shipping and airgun noise. Acoustic features of fin whale song notes recorded in the Mediterranean Sea and northeast Atlantic Ocean were compared for areas with different shipping noise levels and traffic intensities and during a seismic airgun survey. During the first 72 h of the survey, a steady decrease in song received levels and bearings to singers indicated that whales moved away from the acoustic source and out of the study area. This displacement persisted for a time period well beyond the 10-day duration of seismic airgun activity, providing evidence that fin whales may avoid an area for an extended period in the presence of increased noise. The authors hypothesize that fin whale acoustic communication is modified to compensate for increased background noise and that a sensitization process may play a role in the observed temporary displacement.
Seismic pulses at average received levels of 131 dB re 1 μPa
2
-s caused blue whales to increase call production (Di Iorio and Clark, 2010). In contrast, McDonald
et al.
(1995) tracked a blue whale with seafloor seismometers and reported that it stopped vocalizing and changed its travel direction at a range of 10 km from the acoustic source vessel (estimated received level 143 dB pk-pk). Blackwell
et al.
(2013) found that bowhead whale call rates dropped significantly at onset of airgun use at sites with a median distance of 41-45 km from the survey. Blackwell
et al.
(2015) expanded this analysis to show that whales actually increased calling rates as soon as airgun signals were detectable before ultimately decreasing calling rates at higher received levels (
i.e.,
10-minute SEL
cum
of ~127 dB). Overall, these results suggest that bowhead whales may adjust their vocal output in an effort to compensate for noise before ceasing vocalization effort and ultimately deflecting from the acoustic source (Blackwell
et al.,
2013, 2015). These studies demonstrate that even low levels of noise received far from the source can induce changes in vocalization and/or behavior for mysticetes.
Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of disturbance in marine mammals (Richardson
et al.,
1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme
et al.,
1984). Humpback whales showed avoidance behavior in the presence of an active seismic array during observational studies and controlled exposure experiments in western Australia (McCauley
et al.,
2000). Avoidance may be short-term, with animals returning to the area once the noise has ceased (
e.g.,
Bowles
et al.,
1994; Goold, 1996; Stone
et al.,
2000; Morton and Symonds, 2002; Gailey
et al.,
2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur (
e.g.,
Bejder
et al.,
2006; Teilmann
et al.,
2006).
A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response (
e.g.,
directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (Evans and England, 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.
Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention (
i.e.,
when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fish and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates (
e.g.,
Beauchamp and Livoreil, 1997; Fritz
et al.,
2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness (
e.g.,
decline in body condition) and subsequent reduction in reproductive success, survival, or both (
e.g.,
Harrington and Veitch, 1992; Daan
et al.,
1996; Bradshaw
et al.,
1998). However, Ridgway
et al.
(2006) reported that increased vigilance in bottlenose dolphins exposed to sound over a five-day period did not cause any sleep deprivation or stress effects.
Many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle (24-hour cycle). Disruption of such functions resulting from reactions to stressors such as sound exposure are more likely to be significant if they last more than one diel cycle or recur on subsequent days (Southall
et al.,
2007). Consequently, a behavioral response lasting less than one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall
et al.,
2007). Note that there is a difference between multi-day substantive behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses.
Stone (2015) reported data from at-sea observations during 1,196 seismic surveys from 1994 to 2010. When large arrays of airguns (considered to be 500 in
3
or more) were firing, lateral displacement, more localized avoidance, or other changes in behavior were evident for most odontocetes. However, significant responses to large arrays were found only for the minke whale and fin whale. Behavioral responses observed included changes in swimming or surfacing behavior, with indications that cetaceans remained near the water surface at these times. Cetaceans were recorded as feeding less often when large arrays were active. Behavioral observations of gray whales during a seismic survey monitored whale movements and respirationspre-, 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
Langseth
could affect marine animals in the proposed survey areas. Houghton
et al.
(2015) proposed that vessel speed is the most important predictor of received noise levels, and Putland
et al.
(2017) also reported reduced sound levels with decreased vessel speed. Sounds produced by large vessels generally dominate ambient noise at frequencies from 20 to 300 Hz (Richardson
et al.
1995). However, some energy is also produced at higher frequencies (Hermannsen
et al.
2014); low levels of high-frequency sound from vessels has been shown to elicit responses in harbor porpoise (Dyndo
et al.
2015). Increased levels of ship noise have been shown to affect foraging by porpoise (Teilmann
et al.
2015; Wisniewska
et al.
2018); Wisniewska
et al.
(2018) suggest that a decrease in foraging success could have long-term fitness consequences.
Ship noise, through masking, can reduce the effective communication distance of a marine mammal if the frequency of the sound source is close to that used by the animal, and if the sound is present for a significant fraction of time (
e.g.,
Richardson
et al.
1995; Clark
et al.
2009; Jensen
et al.
2009; Gervaise
et al.
2012; Hatch
et al.
2012; Rice
et al.
2014; Dunlop 2015; Erbe
et al.
2015; Jones
et al.
2017; Putland
et al.
2017). In addition to the frequency and duration of the masking sound, the strength, temporal pattern, and location of the introduced sound also play a role in the extent of the masking (Branstetter
et al.
2013, 2016; Finneran and Branstetter 2013; Sills
et al.
2017). Branstetter
et al.
(2013) reported that time-domain metrics are also important in describing and predicting masking. In order to compensate for increased ambient noise, some cetaceans are known to increase the source levels of their calls in the presence of elevated noise levels from shipping, shift their peak frequencies, or otherwise change their vocal behavior (
e.g.,
Parks
et al.
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
Langseth
travels at a speed of 5 kn (approximately 9.3 km/h) while towing seismic survey gear (LGL 2018). At this speed, both the possibility of striking a marine mammal and the possibility of a strike resulting in serious injury or mortality are discountable. At average transit speed, the probability of serious injury or mortality resulting from a strike is less than 50 percent. However, the likelihood of a strike actually happening is again discountable. 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
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