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 Department of Commerce National Oceanic and Atmospheric Administration [RTID 0648-XC041]
 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 Lamont-Doherty Earth Observatory (L-DEO) for authorization to take marine mammals incidental to geophysical surveys at the Cascadia Subduction Zone and Juan de Fuca Plate in the Northeast Pacific Ocean. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, 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 authorization and agency responses will be summarized in the final notice of our decision.
 DATES: Comments and information must be received no later than July 25, 2022.
 ADDRESSES: Comments should be addressed to Jolie Harrison, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service and should be submitted via email to 
                            *ITP.Corcoran@noaa.gov.* *Instructions:*
                             NMFS is not responsible for comments sent by any other method, to any other address or individual, or received after the end of the comment period. Comments, including all attachments, must not exceed a 25-megabyte file size. All comments received are a part of the public record and will generally be posted online at 
                            *www.fisheries.noaa.gov/​permit/​incidental-take-authorizations-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: Kim Corcoran, 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 proposed or, if the taking is limited to harassment, a notice of a proposed incidental harassment authorization is provided to the public for review. Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) and will not have an unmitigable adverse impact on the availability of the species or stock(s) for taking for subsistence uses (where relevant). Further, NMFS must prescribe the permissible methods of taking and other “means of effecting the least practicable adverse impact” on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stocks for taking for certain subsistence uses (referred to in shorthand as “mitigation”); and requirements pertaining to the mitigation, monitoring and reporting of the takings are set forth. The definitions of all applicable MMPA statutory terms cited above are included in the relevant sections below. National Environmental Policy Act To comply with the National Environmental Policy Act of 1969 (NEPA; 42 U.S.C. 4321 
                        *et seq.*) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed action (
                        *i.e.,*
                         the issuance of an IHA) with respect to potential impacts on the human environment. This action is consistent with categories of activities identified in Categorical Exclusion B4 (IHAs with no anticipated serious injury or mortality) of the Companion Manual for NOAA Administrative Order 216-6A, which do not individually or cumulatively have the potential for significant impacts on the quality of the human environment and for which we have not identified any extraordinary circumstances that would preclude this categorical exclusion. Accordingly, NMFS has preliminarily determined that the issuance of the proposed IHA qualifies to be categorically excluded from further NEPA review. Summary of Request On December 14, 2021, NMFS received a request from L-DEO for an IHA to take marine mammals incidental to a marine geophysical survey off the coasts of Oregon and Washington in the northeast Pacific Ocean. The application was deemed adequate and complete on April 4, 2022. L-DEO request is for take of small numbers of 23 species of marine mammals by Level B harassment only. 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 larger surveys in a similar location in the Northeast Pacific (
                        *e.g.,*86 FR 29090; May 28, 2021; 84 FR 35073; July 22, 2019). These surveys, however, included survey areas much closer to the coast. L-DEO complied with all the requirements (
                        *e.g.,*
                         mitigation, monitoring, and reporting) of the previous IHAs and information regarding their monitoring results may be found in the Description of Marine Mammals in the Area of Specified Activities section. Description of Proposed Activity Overview Researchers from New Mexico Institute of Mining and Technology (NMT) and Oregon State University (OSU), with funding from the U.S. National Science Foundation (NSF) propose to conduct low-energy seismic surveys from the Research Vessel (R/V) 
                        *Marcus G. Langseth*
                         (
                        *Langseth*), which is owned and operated by Lamont-Doherty Earth Observatory (L-DEO) of Columbia University, at the Cascadia subduction Zone and Juan de Fuca Plate in the 
                        ( print page 37561)
                        Northeast Pacific Ocean during Summer 2022. The proposed two-dimensional (2-D) seismic surveys would occur within the Exclusive Economic Zone (EEZ) of the United States, in waters deeper than 1600 meters (m). To complete this survey, the R/V 
                        *Langseth*
                         would tow a Generator-Injector (GI)-airgun cluster consisting of two 45 cubic inch (in3
                        ) GI guns spaced 2.46 m apart, with a total discharge volume of 90 in3
                        . The acoustic source would be towed at 2 to 4 m deep along the survey lines, while the receiving system is towed in an 800-1400 m long hydrophone streamer. The proposed study would acquire high-resolution 2-D seismic reflection data in conjunction with densely-spaced heat flow measurements to better understand the thermal structure of the Juan de Fuca plate as it enters the Cascadia subduction zone. The seismic and heat flow data would be acquired across several distinct structures that have not been previously studied, including a pseudofault, complex buried seamounts, and small outcrops that represent the summit of much larger buried seamounts. Dates and Duration The proposed survey is expect to last for 23 days, with approximately six days of seismic operations, three days of transit and 14 days of heat flow measurements. R/V 
                        *Langseth*
                         would likely leave out of and return to port in Newport, OR, during summer 2022. Specific Geographic Region The proposed survey would occur within ~42-47°N, ~125-127°W off the coast of Washington and Oregon in the Northeast Pacific ocean. Four regions where the surveys are proposed to occur are depicted in Figure 1; the tracklines could occur anywhere within the boxes shown in Figure 1. No representative survey tracklines are shown, as actual track lines and order of survey operations are dependent on science objectives and weather. The surveys are proposed to occur within the EEZ of the U.S., in waters >1600 m deep. 
 
  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, R/V 
                        *Langseth,*
                         which is owned and operated by L-DEO. R/V 
                        *Langseth*
                         would deploy two 45/105 in3
                         GI airguns as an energy source with a total volume of ~90 in3
                        . The receiving system would consist of one 800-1400 m long hydrophone streamer. As the airguns are towed along the survey lines, the hydrophone streamer would transfer data to the on-board processing system. Approximately 1135 kilometers (km) of transect lines would be surveyed in four survey regions in the Northeast Pacific Ocean; 200 km, 95 km, 440 km, and 400 km in the Coast, Nubbin, Pseudofault, and Oregon survey regions, respectively. All survey effort would occur in deep water >1600 m. In addition to the operations of the airgun array, the ocean floor would be mapped with the Kongsberg EM 122 multibeam echosounder (MBES), a Knudsen CHIRP 
                        ( print page 37563)
                        3260 (SBP) and an Acoustic Doppler Current Profiler (ADCP) would be operated from the vessel continuously. 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. Take of marine mammals is not expected to occur incidental to use of the MBES, SBP and ADCP, whether or not the airguns are operating simultaneously with the other sources. Given their characteristics (
                        *e.g.,*
                         narrow downward-directed beam), marine mammals would experience no more than one or two brief ping exposures, if any exposure were to occur. NMFS does not expect that the use of these sources presents any reasonable potential to cause take of marine mammals. Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (please see Proposed Mitigation and Proposed Monitoring and Reporting). Description of Marine Mammals in the Area of Specified Activities Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history of the potentially affected species. NMFS fully considered all of this information, and we refer the reader to these descriptions, incorporated here by reference, instead of reprinting the information. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SARs; 
                        *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' website (
                        *https://www.fisheries.noaa.gov/​find-species*). Table 1 lists all species or stocks for which take is expected and proposed to be authorized for this action, and summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act (ESA) and potential biological removal (PBR), where known. 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' SARs). While no serious injury or 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. 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 comprise that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS's U.S. Pacific SARs (Carretta et al., 2021). All values presented in Table 1 are the most recent available at the time of publication and are available in the 2020 SARs (Carretta et al., 2021) and draft 2021 SARs (available online at: 
                        *https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports*). Table 1—Species Likely Impacted by the Specified Activities
Common name
Scientific name
Stock
ESA/MMPA status; strategic 
                                 
                                    (Y/N) 1
Stock abundance (CV, Nmin, most recent abundance survey) 2
PBR
Annual M/SI 3**Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)**Family Balaenopteridae (rorquals):Humpback whale
*Megaptera novaeangliae*
California/Oregon/Washington
-,-,Y
4,973 (0.05, 4,776, 2018)
28.7
>48.6Minke whale
*Balaenoptera acutorostrata*
California/Oregon/Washington
-,-,N
915 (0.792, 509, 2018)
4.1
>0.59Sei whale
*Balaenoptera borealis*
Eastern North Pacific
E, D, Y
519 (0.4, 374, 2014)
0.75
>0.2Fin whale
*Balaenoptera physalus*
California/Oregon/Washington
E, D, Y
11,065 (0.405, 7,970, 2018)
80
>2.2Blue whale
*Balaenoptera musculus*
Eastern North Pacific
E, D, Y
1,898 (0.085, 1,767, 2018)
4.1
>19.4**Superfamily Odontoceti (toothed whales, dolphins, and porpoises)**Family Physeteridae:Sperm whale
*Physeter macrocephalus*
California/Oregon/Washington
E, D, Y
1,997 (0.57, 1270, 2014)
2.5
0.6Family Kogiidae:Pygmy sperm whale
*Kogia breviceps*
California/Oregon/Washington
-,-,N
4,111 (1.12, 1924, 2014)
19
0Dwarf sperm whale
*Kogia sima*
California/Oregon/Washington
-,-,N
UNK (UNK, UNK, 2014)
UND
0Family Ziphiidae (beaked whales):Baird's beaked whale
*Berardius Bairdii*
California/Oregon/Washington
-,-,N
1,363 (0.53, 894, 2018)
8.9
>0.2Cuvier's beaked whale
*Ziphius cavirostris*
California/Oregon/Washington
-,-,N
3,274 (0.67, 2,059, 2014)
21
<0.1Mesoplodont Beaked Whales
*Mesoplodon*
                                 spp.
California/Oregon/Washington
-,-,N
3,044 (0.54, 1,967, 2005)
20
0.1Family Delphinidae:Striped dolphin
*Stenella coeruleoalba*
California/Oregon/Washington
-,-,N
29,988 (0.3, 23,448, 2018)
225
>4Short-beaked common dolphin
*Delphinus delphis*
California/Oregon/Washington
-,-,N
1,056,308 (0.21, 888,971, 2018)
8,889
>30.5( print page 37564)Pacific white-sided dolphin
*Lagenorhynchus obliquidens*
California/Oregon/Washington
-,-,C
34,998 (0.222, 29,090, 2018)
279
7Northern right whale dolphin
*Lissodelphis borealis*
California/Oregon/Washington
-,-,N
29,285 (0.72, 17024, 2018)
163
>6.6Risso's dolphin
*Grampus griseus*
California/Oregon/Washington
-,-,N
6,336 (0.32, 4,817, 2014)
46
>3.7Killer whale
*Orcinus orca*
West Coast Transient
-,-,N
349 (N/A, 349, 2018)
3.5
0.4North Pacific Offshore
-,-,N
300 (0.1, 276, 2012)
2.8
0Family Phocoenidae (porpoises):Dall's porpoise
*Phocoenoides dalli*
California/Oregon/Washington
-,-,N
16,498 (0.61, 10,286, 2019)
99
>0.66**Order Carnivora—Superfamily Pinnipedia**Family Otariidae (eared seals and sea lions):Northern fur seal
*Callorhinus ursinus*
Eastern Pacific
-,D,Y
626,618 (0.2, 530,376, 2020)
11,403
373California
-,D,Y
14,050 (N/A, 7,524, 2013)
451
1.8Guadalupe fur seal
*Arctocephalus townsendi*
Mexico
T, D, Y
34,187 (N/A, 31,019, 2013)
1,062
>3.8Steller sea lion
*Eumetopias jubatus*
Eastern
-,-,N
43,201 (N/A, 43,201,2017)
2,592
112California sea lion
*Zalophus californianus*
United States
-,-,N
257,606 (N/A, 233,525, 2014)
14,011
>320Family Phocidae (earless seals):Northern elephant seal
*Mirounga angustirostris*
California Breeding
-,-,N
187,386 (N/A, 85,369, 2013)
5,122
5.31
                            —Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.2
                            —NMFS marine mammal stock assessment reports online at: 
                            *https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports.*
                             CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable.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). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases.
 As indicated above, all 23 species (with 25 managed stocks) in Table 1 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. While North Pacific right whales (
                        *Eubalaena japonica*), bottlenose dolphins (
                        *Tursiops truncatus),*
                         short-finned pilot whales (
                        *Globicephala macrorhynchus*), gray whales (
                        *Eschrichtius robustus*), and false killer whales (
                        *Pseudorca crassidens*) have been documented near the area, the temporal and/or spatial occurrence of these species is such that take is not expected to occur. Therefore, they are not discussed further beyond the explanation provided below. The North Pacific right whale is one of the rarest marine mammals in the world (Muto 
                        *et al.,*
                         2021). The species comprises of an eastern and western population that are largely or wholly discrete. The summer range of the eastern stock includes the Gulf of Alaska and the Bergin Sea, while the western stock is believed to feed in the Okhotsk Sea and in pelagic waters of the northwestern North Pacific (Muto 
                        *et al.,*
                         2021). Whaling records from the 19th century and recent Soviet catch data have shown that right whales were broadly distributed across the eastern North Pacific (Scarff 1986, Brownell 
                        *et al.,*
                         2001, Ivashchenko and Clapham 2012). There are sporadic records from below 20 degrees north, but the bulk of the data show right whales concentrated north of 35 degrees north, including coastal and offshore waters ranging from Washington state and British Columbia through the Gulf of Alaska, Alaska Peninsula, Aleutian Islands, and the Bering Sea (Muto 
                        *et al.,*
                         2021). The eastern North Pacific stock that occurs in the United States is estimated to contain 31 whales for the Bering sea and Aleutian Islands. A Biologically Important Area (BIA) for feeding for North Pacific right whales was designated east of the Kodiak Archipelago, which includes the Gulf of Alaska critical habitat and extends south of 56 degrees north and north of 58 degrees north and beyond the shelf edge. South of 50 degrees north, only 29 reliable sightings were recorded from 1900-1994 (Scarff 1986, 1991; Carretta 
                        *et al.,*
                        1994). Off the coast of California/Oregon/Washington, only seven documented sightings of right whales were made from 1990 through 2000. Two North Pacific right whale calls were detected on a bottom-mounted hydrophone (located in water 1390 m deep) off the Washington coast on June 29, 2013 (Sirovic 
                        *et al.,*
                         2014). During L-DEO's summer 2021 seismic survey in the Northeast Pacific, a sighting of two individuals was made northwest of the survey area in British Columbia, west of Haida Gwaii on July 27, 2021. Because of the small population size, and the fact that North Pacific right whales spend the summer feeding in high latitudes, the likelihood that the proposed survey would encounter a North Pacific right whale is discountable, and NMFS is not proposing to authorize take of this species. Bottlenose dolphins are distributed worldwide in tropical and warm-temperate waters. Bottlenose dolphins occur frequently off the coast of California, and sightings have been made as far north as 41 degrees north, but few records exist for Oregon and Washington (Carretta 
                        *et al.,*
                         2021). In California, separate coastal and offshore populations are known (Walker 1981; Ross and Cockcroft 1999; Van Waerebeek 
                        *et al.,*
                         1990; Lowther 2006). Three sightings and one stranding of bottlenose dolphins have been documented in Puget Sound since 2004 (Cascadia Research 2011 
                        *in*
                         U.S.C. 
                        ( print page 37565)
                        2015). L-DEO requested authorization for the incidental take of bottlenose dolphins (the request was for a total of 13 individuals). Although sightings of bottlenose dolphins in Puget Sound have increased considerably since 2016 (Cascadia Research Collective, 2020), given the far north and offshore placement of the proposed survey and the species' tendency to stay in coastal waters and in lower latitudes, we believe it is highly unlikely that bottlenose dolphins would be encountered in the proposed survey area, and NMFS is not proposing to authorize take of this species. Short-finned pilot whales are found in tropical and warm temperate waters (Olson 2018) and seen as far south as 40 degrees south and as far north as 50 degrees north (Jefferson 
                        *et al.,*
                         2015). Pilot whales are generally nomadic, but may reside in certain locations, including California and Hawaii (Olson 2018). The species were common off southern California (Dohl 
                        *et al.,*
                         1980) until an El Nino event occurred in 1982-1983 (Green 
                        *et al.,*
                         1992; Carretta and Forney 1993; Barlow 1997). Few sightings were made off California/Oregon/Washington in 1983-1984, but sightings remain rare (Barlow 1997; Buchanan 
                        *et al.,*
                         2001; Barlow 2010). No short-finned pilot whales were seen during surveys off Oregon and Washington in 1989-1990, 1992, 1996, and 2001 (Barolow 2003). Only one sighting has occurred off Oregon from 1991-2014 (Carretta 
                        *et al.,*
                         2021). Although zero Level B harassment exposure estimates were calculated, L-DEO requested authorization for the incidental take of 29 short-finned pilot whales based on the average group size produced by Barlow (2016). However, considering the species' historical occurrence in the proposed survey area, their preference for warmer tropical waters, and the best available information, the likelihood that L-DEO will encounter short-finned pilot whales in the proposed survey area is discountable, and NMFS is not proposing to authorize take of this species. Two separate populations of gray whales have been recognized in the North Pacific: the eastern North Pacific and western North Pacific stocks (LeDuc 
                        *et al.,*
                         2002; Weller 
                        *et al.,*
                         2013). 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). BIAs for feeding gray whales along the coasts of Washington, Oregon, and California have been identified, including northern Puget sound, Northwestern Washington, and Grays Harbor (WA); Depoe Bay and Cape Blanco and Orford Reef (OR), and Point St. George (CA); most of these areas are of importance from late spring through early fall (Calambokidis 
                        *et al.,*
                         2015); none occur within the proposed survey region. Resident gray whales have been observed foraging off the coast of Oregon from May through October and off Washington June through November (Newell and Cowles 2006; Scordino 
                        *et al.,*
                         2014). BIAs have also been identified for migrating gray whales along the entire coasts of Washington, Oregon, and California; although most whales travel within 10 km from shore, the BIAs were extended out to 47 km from the coastline (Calambokidis 
                        *et al.,*
                         2015); the proposed Oregon survey region is located adjacent to this BIA (see Figure 1). Gray whales from the far north begin to migrate south to breeding grounds on the west coast of Baja California and the southeastern Gulf of California in October and November (Braham 1984; Rugh 
                        *et al.,*
                         2001). Gray whales migrate closest to the Washington/Oregon coastline during spring (April-June), when most strandings are observed (Norman 
                        *et al.,*
                         2004). The species' stock range extends from as far south as Mexico all the way north to the Gulf of Alaska, primarily hugging the coastline (NMFS 2022). NOAA (2021b) declared an unusual mortality event (UME) for gray whales in 2019, as an elevated number of strandings have occurred along the coast of the Pacific Northwest since January 2019. As of 1 October 2021, a total of 212 dead gray whales have been reported, including 248 in the U.S. (55 in Washington; 12 in Oregon), 225 in Mexico, and 19 in B.C.; some of the whales were emaciated. A UME for gray whales was also declared for 1999-2000 (NOAA 2021c). The proposed survey is planned during the summer feeding season, when most individuals from the eastern North Pacific stock occur farther north. Although individuals, particularly from the Pacific Coast Feeding Group (PCFG), could be encountered in nearshore waters less than 10 km from shore, the likelihood that any gray whales will be encountered as far offshore as the proposed survey area is discountable. Gray whales have been observed to have a distinct ecological niche in nearshore and shallow waters (Darling 
                        *et al.,*
                         1998) and L-DEO's proposed activities to not overlap with this niche. L-DEO requested the incidental take of a singular gray whale, however NMFS does not propose to authorize any take of gray whales as it is temporally and spatially unlikely that they will be encountered. Lastly, the false killer whale is found worldwide in tropical and temperate waters, generally between 50 degrees north and 50 degrees south (Odell and McClune 1999). It is widely distributed, but not abundant anywhere (Carwardine 1995). The false killer whale generally inhabits deep, offshore waters, but sometimes is found over the continental shelf and occasionally moves into very shallow water (Jefferson 
                        *et al.,*
                         2015; Baird 2018b). In the eastern North Pacific, it has been reported only rarely north of Baja California (Leatherwood 
                        *et al.,*
                         1982, 1987; Mangels and Gerrodete 1994); however, the waters off the United States west coast all the way north to Alaska are considered part of its secondary range (Jefferson 
                        *et al.,*
                         2015). Its occurrence in Washington/Oregon is associated with warm-water incursions (Buchanan 
                        *et al.,*
                         2001). However, no sightings of false killer whales were made along the U.S. west coast during surveys conducted from 1986-2001 (Ferguson and Barlow 2001, 2003; Barlow 2003) or in 2005 and 2008 (Forney 2007; Barlow 2010). One pod of false killer whales occurred in Puget Sound for several months during the 1990s (USN 2015). Two false killer whales were reported stranded along the Washington coast during 1930-2002, both in El Niño years (Norman 
                        *et al.,*
                         2004). Based on the best available information, NMFS believes that the likelihood of the survey encountering a false killer whale is discountable and, although L-DEO requested incidental take of 5 whales based on their average group size (Mobley et al., 2000), NMFS does not propose authorizing any take of false killer whales. Humpback Whale The humpback whale is found throughout all of the oceans of the world (Clapham 2009). The worldwide population is divided into northern and southern ocean populations, but genetic analyses suggest some gene flow (either past or present) between the North and South Pacific (
                        *e.g.,*
                         Jackson 
                        *et al,.*
                         2014; Bettriddge 
                        *et al,.*
                         2015). Although considered to be mainly a coastal species, humpback whales often traverse deep pelagic areas while migrating (Calambokidis 
                        *et al.,*
                         2001; Garrigue 
                        *et al.,*
                         2002; Zerbini 
                        *et al.,*
                         2011). Humpbacks migrate between summer feeding grounds in high latitudes and winter calving and breeding grounds in tropical waters (Clapham and Mead 1999). Northern Pacific humpback whales summer in 
                        ( print page 37566)
                        feeding grounds along the Pacific Rim and in the Bering and Okhotsk seas (Pike and MacAskie 1969; Rice 1978; Winn and Reichley 1985; Calambokidis 
                        *et al.,*
                         2000, 2001, 2008; Bettridge 
                        *et al.,*
                         2015). Humpbacks in the north Pacific 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; Bettridge 
                        *et al.,*
                         2015). Prior to 2016, humpback whales were listed under the ESA as an endangered species worldwide. Following a 2015 global status review (Bettridge 
                        *et al.,*
                         2015), NMFS established 14 distinct population segments (DPS) with different listing statuses (81 FR 62259); September 8, 20216) pursuant to the ESA. The DPSs that occur in United States waters do not necessarily equate to the existing stocks designated under the MMPA and shown in Table 1. Because the MMPA stocks cannot be portioned (
                        *i.e,.*
                         parts managed as ESA-listed while other parts managed as non-ESA listed), until such time as the MMPA stock delineations are reviewed in light of the DPS designations, NMFS considers the existing humpback whale stocks under the MMPA to be endangered and depleted for MMPA management purposes (
                        *e.g.,*
                         selection of a recovery factor, stock status). NMFS has identified three DPSs of humpback whales that are found off the coasts of Washington, Oregon and California. These are: the Hawaii DPS (found predominately off Washington and southern British Columbia), which is not listed under the ESA; the Mexico DPS (found all along the west coast), which is listed as threatened under the ESA; and the Central America DPS (found all along the west coast, but most common off California and Oregon), which is listed as endangered under the ESA. According to Wade (2021), the probability that whales encountered in Oregon and California waters are from a given DPS are as follows: Central America DPS (42 percent); Mexico DPS (58 percent); Hawaii DPS (0 percent). The probability that humpback whales encountered in Washington and British Columbia waters are as follows: Central America DPS (6 percent); Mexico DPS (25 percent); Hawaii DPS (69 percent). Wade (2021) notes that the majority of humpback whales that may be found off of Washington are likely moving north of the United States border and feeding primarily off of southern British Columbia. Humpback whales are the most common species of large cetacean reported off the coasts of Oregon and Washington from May to November (Green 
                        *et al.,*
                         1992; Calambokidis 
                        *et al.,*
                         2000, 2004). Humpbacks occur primarily over the continental shelf and slope during the summer, but a few individuals have been reported in offshore pelagic waters (Green 
                        *et al.,*
                         1992; Calambokidis 
                        *et al.,*
                         2004, 2015; Becker 
                        *et al.,*
                         2012; Barlow 2016; Carretta 
                        *et al.,*
                         2021). Biologically Important Areas (BIAs) for feeding humpback whales along the coasts of Oregon and Washington, which have been designated from May through November, are all within approximately 80 kilometers (km) from shore, and include the waters off northern Washington, and Stonewall and Heceta Bank, OR (Calambokidis 
                        *et al.,*
                         2015). Six humpback whale sightings (eight animals) were made off Washington and Oregon during the June through July 2012 L-DEO Juan de Fuca plate seismic survey. There were 98 humpback whale sightings (213 animals) made during the July 2012 L-DEO seismic survey off Oregon (RPS 2012a), and 11 sightings (23 animals) during the July 2012 L-DEO seismic survey off Oregon (RPS 2012c). Numerous humpback whale sightings were made during L-DEO's Cascadia summer survey off Oregon and Washington in 2021 (RPS). On April 21, 2021, NMFS designated critical habitat in nearshore waters of the North Pacific Ocean for the endangered Central America and Western North Pacific DPSs and the threatened Mexico DPS of humpback whales (NMFS 2021). Critical habitat for the Central America and Mexico DPSs include waters within the California Current Ecosystem (CCE) off the coasts of California, Oregon, and Washington (Figure 1). Off Washington, critical habitat includes waters from the 50 m to 1200 m isobaths, as well as the strait of Juan de Fuca eastward to Angeles Point; however, there is an exclusion area of 1461 nautical square miles (nmi2
                        ) around the Navy's Quinault Range Site. Off Oregon, the critical habitat spans from the 50 m to 1200 m isobath until 42.17 degrees north where the critical habitat south of 42.17 degrees north extends out to the 2000 m isobath (NMFS 2021). There is no critical habitat designated within the proposed survey regions, and ensonified areas would not extend into critical habitat. Humpback whales are expected to be uncommon in the proposed offshore survey areas. Blue Whale The blue whale has a cosmopolitan distribution and tends to be pelagic, only coming nearshore to feed and possibly to breed (Jefferson 
                        *et al.,*
                         2015). Although it has been suggested that there are at least five subpopulations of blue whales in the North Pacific (NMFS 1998), analysis of blue whales calls monitored from the U.S. Navy Sound surveillance system (SOSUS) and other offshore hydrophones (see Stafford 
                        *et al.,*
                         1999, 2001, 2007; Watkins 
                        *et al.,*
                         2000; Stafford 2003) suggest that there are two separate populations: one in eastern and one in the western North Pacific (Sears and Perrin 2018). 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). Broad scale acoustic monitoring indicate that blue whales occurring in the northeast Pacific during summer and fall may winter in the eastern tropical Pacific (Stafford 
                        *et al.,*
                         1999, 2001). The distribution of the species, at least during times of the year when feeding is prevalent, occurs in areas that provide large seasonal concentrations of euphausiids (Yochem and Leatherwood 1985). The eastern North Pacific stock feeds in California waters from June through November (Calambokidis 
                        *et al.,*
                        1990; Mate 
                        *et al.,*
                         2015), and core areas have also been identified. Blue whales are considered rare off Oregon, Washington, and B.C. (Buchanan et al. 2001; Gregr 
                        *et al.,*
                         2006; Ford 2014), although satellite-tracked individuals have been reported off the coast (Bailey 
                        *et al.,*
                         2009). Based on modeling of the dynamic topography of the region, blue whales could occur in relatively high densities off Oregon during summer and fall (Pardo et al. 2015: Hazen et al. 2017). Recent phenology analysis of marine mammal sightings revealed a peak of blue whale density over the Oregon continental shelf in September, and their sighting rates in the region have increased over the past three decades as a response to environmental changes influencing prey availability shifting their range northward (Derville 
                        *et al.,*
                         2022). Densities along the U.S. west coast, including Oregon, were predicted to be highest in shelf waters, with lower densities in deeper offshore areas (Becker 
                        *et al.,*
                         2012; Calambokidis 
                        *et al.,*
                         2015). Blue whales have been detected acoustically off Oregon (McDonald 
                        *et al.,*
                         1995; Stafford 
                        *et al.,*
                         1998; Von Saunder and Barlow 1999). Blue whales could be encountered in the proposed survey areas.
                        ( print page 37567) Fin Whale 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 and García-Vernet 2018). Nonetheless, its overall range and distribution are not well known (Jefferson 
                        *et al.,*
                         2015). A review of fin whale distribution in the North Pacific noted the lack of sightings across pelagic waters between eastern and western winter areas (Mizroch 
                        *et al.,*
                         2009). Fin whales most commonly occur offshore, but can also be found in coastal areas (Jefferson 
                        *et al.,*
                         2015). Most populations migrate seasonally between temperate waters where mating and calving occur in winter, and polar waters where feeding occurs in summer (Aguilar and García-Vernet 2018). Some animals may remain at high latitudes in winter or low latitudes in summer (Edwards 
                        *et al.,*
                         2015). The northern and southern fin whale populations likely do not interact owing to their alternate seasonal migration; the resulting genetic isolation has led to the recognition of two subspecies, 
                        *B. physalus quoyi*
                         and 
                        *B. p. physalus*
                         in the Southern and Northern hemispheres, respectively (Anguilar and García-Vernet 2018). 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). 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 (
                        *e.g.,*
                         Moore 
                        *et al.,*
                         2006; Stafford 
                        *et al.,*
                         2007, 2009; Edwards 
                        *et al.,*
                         2015). In the central North Pacific, the Gulf of Alaska, and Aleutian Islands, call rates peak during fall and winter (Moore 
                        *et al.,*
                         1998, 2006; Watkins 
                        *et al.,*
                         2000a,b; Stafford 
                        *et al.,*
                         2009). Fin whales are routinely sighted during surveys off Oregon and Washington (Barlow and Forney 2007; Barlow 2010, 2016; Adams 
                        *et al.,*
                         2014; Calambokidis 
                        *et al.,*
                         2015; Edwards 
                        *et al.,*
                         2015; Carretta 
                        *et al.,*
                         2021), including in coastal as well as offshore waters. They have also been detected acoustically in those waters during June-August (Edwards 
                        *et al.,*
                         2015). Eight fin whale sightings (19 animals) were made off Washington/Oregon during the June-July 2012 L-DEO Juan de Fuca plate seismic survey; sightings were made in waters 2369-3940 m deep (RPS 2012b). Fourteen fin whale sightings (28 animals) were made during the July 2012 L-DEO seismic surveys off southern Washington (RPS 2012a). No fin whales were sighted during the July 2012 L-DEO seismic survey off Oregon (RPS 2012c). During L-DEO's Cascadia survey during June-July 2021, five sightings of seven fin whales were made off Oregon (RPS 2021b). Fine whales were also seen off southern Oregon during July 2012 in water >2000 m deep during surveys by Adams 
                        *et al.,*
                         (2014). Fin whales are likely to be encountered in the proposed survey area. Sei Whale The sei whale occurs in all ocean basins (Horwood 2018), 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 2018). 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 migrate from temperate zones occupied in winter to higher latitudes in the summer, where most feeding takes place (Gambell 1985a). During summer in the North Pacific, the sei whale can be found from the Bering Sea to the Gulf of Alaska and down to southern California, as well as in the western Pacific from Japan to Korea. Its winter distribution is concentrated at ~20° N (Rice 1998). Sei whales are rare in the waters off Washington, Oregon, and California (Brueggeman 
                        *et al.,*
                         1990; Green 
                        *et al.,*
                         1992; Barlow 1994, 1997). Less than 20 confirmed sightings were reported in that region during extensive surveys during 1991-2014 (Green 
                        *et al.,*
                         1992, 1993; Hill and Barlow 1992; Carretta and Forney 1993; Mangels and Gerrodette 1994; Von Saunder and Barlow 1999; Barlow 2003, 2010, 2014; Forney 2007; Carretta 
                        *et al.,*
                         2021). Based on surveys conducted in 1991-2008, the estimated abundance of sei whales off the coasts of Oregon and Washington was 52 (Barlow 2010); for 2014, the abundance estimate was 468 (Barlow 2016). Two sightings of four individuals were made during the June-July 2012 L-DEO Juan de Fuca plate seismic survey off Washington/Oregon (RPS 2012b). No sei whales were sighted during the summer 2012 or 2021 L-DEO seismic surveys off Oregon and Washington (RPS 2012a,c, 2021). Sei whales could be encountered during the proposed survey, although this species is considered rare in these waters. Minke Whale The minke whale has a cosmopolitan distribution that spans from tropical to polar regions in both hemispheres (Jefferson 
                        *et al.,*
                         2015). In the Northern Hemisphere, the minke whale is usually seen in coastal areas, but can also be seen in pelagic waters during its northward migration in spring and summer and southward migration in autumn (Stewart and Leatherwood 1985). In the North Pacific, the summer range of the minke whale extends to the Chukchi Sea; in the winter, the whales move south to within 2° of the Equator (Perrin 
                        *et al.,*
                         2018). The International Whaling Commission (IWC) recognizes three stocks of minke whales 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). Minke whales are relatively common in the Bering and Chukchi seas and in the Gulf of Alaska but are not considered abundant in any other part of the eastern Pacific (Brueggeman 
                        *et al.,*
                         1990). In the far north, minke whales are thought to be migratory, but they are believed to be year-round residents in nearshore waters off west coast of the U.S. (Dorsey 
                        *et al.,*
                         1990). Sightings have been made off Oregon and Washington in shelf and deeper waters (Green 
                        *et al.,*
                         1992; Adams 
                        *et al.,*
                         2014; Barlow 2016; Carretta 
                        *et al.,*
                         2021). An estimated abundance of 211 minke whales was reported for the Oregon/Washington region based on sightings data from 1991-2005 (Barlow and Forney 2007), whereas a 2008 survey did not record any minke whales while on survey effort (Barlow 2010). The abundance for Oregon/Washington for 2014 was estimated at 507 minke whales (Barlow 2016). There were no sightings of minke whales off Oregon/
                        ( print page 37568)
                        Washington during L-DEO's summer seismic surveys in 2012 or 2021 (RPS 2012b,c, 2021). One minke whale was seen during the July 2012 L-DEO seismic survey off southern Washington (RPS 2012a). Minke whales are expected to be uncommon in the proposed survey areas. Sperm Whale The sperm whale is the largest of the toothed whales, with an extensive worldwide distribution (Rice 1989). Sperm whale distribution is linked to social structure: Mixed groups of adult females and juveniles animals of both sexes generally occur in tropical and subtropical waters, whereas adult makes are commonly found alone or in the same-sex aggregations, often occurring in higher latitudes outside the breeding season (Best 1979; Watkins and Moore 1982; Arnbom and Whitehead 1989; Whitehead and Waters 1990). Males can migrate north in the summer to feed in the Gulf of Alaska, Bering Sea, and waters around the Aleutian Islands (Kasuya and Miyashita 1988). Females generally inhabit waters over 1000 m deep at latitudes under 40 degrees where sea surface temperatures are under 15 degrees Celsius; adult males move to higher latitudes as they grow older and larger in size, returning to warm-water breeding grounds according to an unknown schedule (Whitehead 2018). Sperm whales are distributed widely across the North Pacific (Rice 1989). Off California, they occur year-round (Dohl 
                        *et al.,*
                         1983: Barlow 1995; Forney 
                        *et al.,*
                         1995), with peak abundance from April to mid-June and from August to mid-November (Rice 1974). Off Oregon, sperm whales are seen in every season except winter (Green 
                        *et al.,*
                         1992). Sperm whales were sighted during surveys off Oregon in October 2011 and off Washington in June 2011 (Adams 
                        *et al.,*
                         2014). Sperm whale sightings were also made off Oregon and Washington during the 2014 Southwest Fisheries Science Center (SWFSC) vessel survey (Barlow 2016). Sperm whale were detected acoustically in waters off Oregon and Washington in August 2016 during the SWFSC Passive Acoustics Survey of Cetacean Abundance Levels (PASCAL) study using drifting acoustic recorders (Keating 
                        *et al.,*
                         2018). Oleson 
                        *et al.*
                         (2009) noted a significant diel pattern in the occurrence of sperm whale clicks at offshore and inshore monitoring locations off Washington, whereby clicks were more commonly heard during the day at the offshore site and at night at the inshore location, suggesting possible diel movements up and down the slope in search of prey. Sperm whale acoustic detections were also reported at an inshore site from June through January 2009, with an absence of calls during February through May (Sirovic 
                        *et al.,*
                         2012). Sperm whales are likely to be encountered in the proposed survey areas. Baird's Beaked Whale 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 were previously recognized—the common slate-gray form and a smaller, rare black form (Morin 
                        *et al.,*
                         2017), however the small body size of physically mature individuals in the latter form, as well as recent genetic studies (Morin 
                        *et al.,*
                         2017) have identified this form as a new species called Sato's beaked whale (
                        *Berardius minimus*) (Yamada 
                        *et al.,*
                         2019).The gray form is seen off Japan, in the Aleutians, and on the west coast of North America, whereas the black form has been reported for northern Japan and the Aleutians (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 1000-3000 m deep (Jefferson 
                        *et al.,*
                         2015). Along the U.S. west coast, Baird's beaked whales have been sighted primarily along the continental slope (Green 
                        *et al.,*
                         1992; Becker 
                        *et al.,*
                         2012; Carretta 
                        *et al.,*
                         2021) from late spring to early fall (Green 
                        *et al.,*
                         1992). The whales move out from those areas in winter (Reyes 1991). In the eastern North Pacific Ocean, Baird's beaked whales apparently spend the winter and spring far offshore, and in June, they move onto the continental slope, where peak numbers occur during September and October. Green 
                        *et al.,*
                         (1992) noted that Baird's beaked whales on the U.S. west coast were most abundant in the summer, and were not sighted in the fall or winter. MacLeod 
                        *et al.,*
                         (2006) reported numerous sightings and strandings of 
                        *Berardius*
                         spp. off the U.S. west coast. Green 
                        *et al.,*
                         (1992) sighted five groups during 75,050 km of aerial survey effort in 1989-1990 off Washington/Oregon spanning coastal to offshore waters: two in slope waters and three in offshore waters. Two groups were sighted during summer/fall 2008 surveys off Washington/Oregon, in waters >2000 m deep (Barlow 2010). Acoustic monitoring offshore Washington detected Baird's beaked whale pulses during January through November 2011, with peaks in February and July (ŝirović 
                        *et al.,*
                         2012b in USN 2015). Baird's beaked whales were detected acoustically in the waters off Oregon and Washington in August 2016 during the SWFSC PASCAL study using drifting acoustic recorders (Keating 
                        *et al.,*
                         2018). Baird's beaked whales could be encountered in the proposed survey regions. Cuvier's Beaked Whale Cuvier's beaked whale is probably the most widespread of the beaked whales, although it is not found in polar waters (Heyning 1989). Cuvier's beaked whale appears to prefer steep continental slope waters (Jefferson 
                        *et al.,*
                         2015) and is most common in water depths >1000 m (Heyning 1989). It is mostly known from strandings and strands more commonly than any other beaked whale (Heyning 1989). Its inconspicuous blows, deep-diving behavior, and tendency to avoid vessels all help to explain the infrequent sightings (Barlow and Gisiner 2006). The population in the California Current Large Marine Ecosystem seems to be declining (Moore and Barlow 2013). MacLeod 
                        *et al.,*
                         (2006) reported numerous sightings and strandings along the Pacific coast of the U.S. Cuvier's beaked whale is the most common beaked whale off the U.S. West Coast (Barlow 2010), and it is the beaked whale species that has stranded most frequently on the coasts of Oregon and Washington. From 1942-2010, there were 23 reported Cuvier's beaked whale strandings in Oregon and Washington (Moore and Barlow 2013). Most (75 percent) Cuvier's beaked whale strandings reported occurred in Oregon (Norman 
                        *et al.*
                         2004). Records of Cuvier's beaked whale in British Columbia are scarce, although 20 strandings, one incidental catch, and five sightings have been reported, including off western Vancouver Island (Ford 2014). Most strandings have been reported in summer (Ford 2014). Four beaked whale sightings were reported in water depths over 2000 m off Oregon/Washington during surveys in 2008 (Barlow 2010). None were seen in 1996 or 2001 (Barlow 2003), and several were recorded from 1991-1995 (Barlow 1997). One Cuvier's beaked whale sighting was made during surveys in 2014 (Barlow 2016). Acoustic monitoring in Washington offshore waters detected Cuvier's beaked whale calls between January and November 2011 (Sirovic 
                        *et al.,*
                         2012b in USN 2015). Cuvier's beaked whales were 
                        ( print page 37569)
                        detected acoustically in waters off Oregon and Washington in August 2016 during the SWFSC PASCAL study using drifting acoustic recorders (Keating 
                        *et al.,*
                         2018). Curvier's beaked whales could be encountered during the proposed surveys. Blainville's Beaked Whale Blainville's beaked whale is found in tropical and warm temperate waters of all oceans (Pitman 2018). It has the widest distribution throughout the world of all Mesoplodon species (Pitman 2018). Like other beaked whales, Blainville's beaked whale is generally found in waters 200-1400 m deep (Gannier 2000; Jefferson 
                        *et al.,*
                         2015). Occasional occurrences in cooler, higher-latitude waters are presumably related to warm-water incursions (Reeves 
                        *et al.,*
                         2002). MacLeod 
                        *et al.,*
                         (2006) reported stranding and sighting records in the eastern Pacific ranging from 37.3° N to 41.5° S. However, none of the 36 beaked whale stranding records in Oregon and Washington during 1930-2002 included Blainville's beaked whale (Norman 
                        *et al.,*
                         2004). One Blainville's beaked whale was found stranded (dead) on the Washington coast in November 2016 (COASST 2016). There was one acoustic encounter with Blainville's beaked whales recorded in Quinault Canyon off Washington in waters 1400 m deep during 2011 (Baumann-Pickering 
                        *et al.,*
                         2014). Blainville's beaked whales were not detected acoustically off Washington or Oregon during the August 2016 SWFSC PASCAL study using drifting acoustic recorders (Keating 
                        *et al.,*
                         2018). Although Blainville's beaked whales could be encountered during the proposed surveys, an encounter would be unlikely because the proposed survey regions are beyond the northern limits of this tropical species' usual distribution. Hubbs' Beaked Whale Hubbs' beaked whale occurs in temperate waters of the North Pacific (Mead 1989). Its distribution appears to be correlated with the deep subarctic current (Mead 
                        *et al.,*
                         1982). Numerous stranding records have been reported for the west coast of the U.S. (MacLeod 
                        *et al.,*
                         2006). Most are from California, but at least seven strandings have been recorded along the B.C. coast as far north as Prince Rupert (Mead 1989; Houston 1990a; Willis and Baird 1998; Ford 2014). Several strandings are known from Washington/Oregon (
                        *e.g.,*
                         Norman 
                        *et al.,*
                         2004; Griffiths 
                        *et al.,*
                         2019). In addition, at least two sightings off Oregon/Washington, but outside the U.S. EEZ, were reported by Carretta 
                        *et al.*
                         (2021), and one bycatch record off Oregon/Washington was reported by Griffiths 
                        *et al.*
                         (2019). During the 2016 SWFSC PASCAL study using drifting acoustic recorders, detections were made of beaked whale sounds presumed to be from Hubbs' beaked whales off Washington and Oregon during August (Griffiths 
                        *et al.,*
                         2019). This species seems to be less common in the region than some of the other beaked whales. Stejneger's Beaked Whale 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). After Cuvier's beaked whale, Stejneger's beaked whale was the second most commonly stranded beaked whale species in Oregon and Washington (Norman 
                        *et al.,*
                         2004). Stejneger's beaked whale calls were detected during acoustic monitoring offshore Washington between January and June 2011, with an absence of calls from mid-July-November 2011 (ŝirović 
                        *et al.,*
                         2012b in USN 2015). Analysis of these data suggest that this species could be more than twice as prevalent in this area than Baird's beaked whale (Baumann-Pickering 
                        *et al.,*
                         2014). Stejneger's beaked whales were also detected acoustically in waters off Oregon and Washington in August 2016 during the SWFSC PASCAL study using drifting acoustic recorders (Keating 
                        *et al.,*
                         2018). Striped Dolphin The striped dolphin has a cosmopolitan distribution in tropical to warm temperate waters from ~50° N to 40° S (Perrin 
                        *et al.,*
                         1994; Jefferson 
                        *et al.,*
                         2015). It occurs primarily in pelagic waters outside of the continental shelf, but has been observed approaching shore where there is deep water close to the coast (Jefferson 
                        *et al.,*
                         2015). Striped dolphins regularly occur off California (Becker 
                        *et al.,*
                         2012), including as far offshore as ~300 n.mi. during NOAA Fisheries vessel surveys (Carretta 
                        *et al.,*
                         2021). However, few sightings have been made off Oregon, and no sightings have been reported for Washington (Carretta 
                        *et al.,*
                         2021). However, strandings have occurred along the coasts of Oregon and Washington (Carretta 
                        *et al.,*
                         2016). During surveys off the U.S. west coast in 2014, striped dolphins were seen as far north as 44° N; based on those sightings, Barlow (2016) calculated an abundance estimate of 13,171 striped dolphins for Oregon/Washington. The abundance estimates for 2001, 2005, and 2008 were zero (Barlow 2016). It is possible, although unlikely, that striped dolphins could be encountered in the proposed survey area. Common Dolphin The common dolphin is found in tropical and warm temperate oceans around the world (Jefferson 
                        *et al.,*
                         2015), ranging from ~60° N to ~50° S (Jefferson 
                        *et al.,*
                         2015). It is the most abundant dolphin species in offshore areas of warm-temperate regions in the Atlantic and Pacific (Perrin 2018). It can be found in oceanic and coastal habitats; it is common in coastal waters 200-300 m deep and is also associated with prominent underwater topography, such as seamounts (Evans 1994). Short-beaked common dolphins have been sighted as far as 550 km from shore (Barlow 
                        *et al.,*
                         1997). The distribution of short-beaked common dolphins along the U.S. west coast is variable and likely related to oceanographic changes (Heyning and Perrin 1994; Forney and Barlow 1998). It is the most abundant cetacean off California; some sightings have been made off Oregon, in offshore waters (Carretta 
                        *et al.,*
                         2021). During surveys off the west coast in 2014 and 2017, sightings were made as far north as 44° N (Barlow 2016; SIO n.d.). Based on the absolute dynamic topography of the region, short-beaked common dolphins could occur in relatively high densities off Oregon during July-December (Pardo 
                        *et al.,*
                         2015). In contrast, habitat modeling predicted moderate densities of common dolphins off the Columbia River estuary during summer, with lower densities off southern Oregon (Becker 
                        *et al.,*
                         2014). A group of six common dolphins was sighted during L-DEO's Cascadia summer survey just south of the Columbia River off Oregon (RPS 2021b). Common dolphins could be encountered in the proposed survey regions. Pacific White-Sided Dolphin The Pacific white-sided dolphin is found in cool temperate waters of the North Pacific from the southern Gulf of California to Alaska. Across the North Pacific, it appears to have a relatively narrow distribution between 38° N and 47° N (Brownell 
                        *et al.,*
                         1999). In the eastern North Pacific Ocean, the Pacific white-sided dolphin is one of the most common cetacean species, occurring primarily in shelf and slope waters (Green 
                        *et al.,*
                         1993; Barlow 2003, 2010). It is known to occur close to shore in certain regions, including (seasonally) 
                        ( print page 37570)
                        southern California (Brownell 
                        *et al.,*
                         1999). Results of aerial and shipboard surveys strongly suggest seasonal north-south movements of the species between California and Oregon/Washington; the movements apparently are related to oceanographic influences, particularly water temperature (Green 
                        *et al.,*
                         1993; Forney and Barlow 1998; Buchanan 
                        *et al.,*
                         2001). During winter, this species is most abundant in California slope and offshore areas; as northern 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). The highest encounter rates off Oregon and Washington have been reported during March-May in slope and offshore waters (Green 
                        *et al.,*
                         1992). Similarly, Becker 
                        *et al.,*
                         (2014) predicted relatively high densities off southern Oregon in shelf and slope waters. Based on year-round aerial surveys off Oregon/Washington, the Pacific white-sided dolphin was the most abundant cetacean species, with nearly all (97%) sightings occurring in May (Green 
                        *et al.,*
                         1992, 1993). Barlow (2003) also found that the Pacific white-sided dolphin was one of the most abundant marine mammal species off Oregon/Washington during 1996 and 2001 ship surveys, and it was the second most abundant species reported during 2008 surveys (Barlow 2010). Adams 
                        *et al.,*
                         (2014) reported numerous offshore sightings off Oregon during summer, fall, and winter surveys in 2011 and 2012. Based on surveys conducted during 2014, the abundance was estimated at 20,711 for Oregon/Washington (Barlow 2016). Fifteen Pacific white-sided dolphin sightings (231 animals) were made off Washington/Oregon during the June-July 2012 L-DEO Juan de Fuca plate seismic survey (RPS 2012b). There were fifteen Pacific white-sided dolphin sightings (462 animals) made during the July 2012 L-DEO seismic surveys off southern Washington (RPS 2012a). This species was not sighted during the July 2012 L-DEO seismic survey off Oregon (RPS 2012c). Numerous Pacific white-sided dolphin sightings were made during L-DEO's Cascadia summer survey off Oregon and Washington (RPS 2021b). Pacific white-sided dolphins are likely to be common in the proposed survey regions. Northern Right-Whale Dolphin The northern right whale dolphin is found in cool temperate and sub-arctic waters of the North Pacific, from the Gulf of Alaska to near northern Baja California, ranging from 30° N to 50° N (Reeves 
                        *et al.,*
                         2002). In the eastern North Pacific Ocean, the northern right whale dolphin is one of the most common marine mammal species, occurring primarily in shelf and slope waters ~100 to >2000 m deep (Green 
                        *et al.,*
                         1993; Barlow 2003). The northern right whale dolphin comes closer to shore where there is deep water, such as over submarine canyons (Reeves 
                        *et al.,*
                         2002). Aerial and shipboard surveys suggest seasonal inshore-offshore and north-south movements in the eastern North Pacific Ocean between California and Oregon/Washington; the movements are believed to be related to oceanographic influences, particularly water temperature and presumably prey distribution and availability (Green 
                        *et al.,*
                         1993; Forney and Barlow 1998; Buchanan 
                        *et al.,*
                         2001). Green et al. (1992, 1993) found that northern right whale dolphins were most abundant off Oregon/Washington during fall, less abundant during spring and summer, and absent during winter, when this species presumably moves south to warmer California waters (Green 
                        *et al.,*
                         1992, 1993; Forney 1994; Forney 
                        *et al.,*
                         1995; Buchanan 
                        *et al.,*
                         2001; Barlow 2003). Becker et al. (2014) predicted relatively high densities off southern Oregon, and moderate densities off northern Oregon and Washington. Based on year-round aerial surveys off Oregon/Washington, the northern right whale dolphin was the third most abundant cetacean species, concentrated in slope waters but also occurring in water out to ~550 km offshore (Green 
                        *et al.,*
                         1992, 1993). Barlow (2003, 2010) also found that the northern right whale dolphin was one of the most abundant marine mammal species off Oregon/Washington during 1996, 2001, 2005, and 2008 ship surveys. Offshore sightings were made in the waters of Oregon during summer, fall, and winter surveys in 2011 and 2012 (Adams 
                        *et al.,*
                         2014). During L-DEO's Cascadia survey during June-July 2021, one sighting of 15 northern right whale dolphins was made off Washington, and another sighting of 12 individuals was made off Oregon (RPS 2021b). Northern right whale dolphins are likely to be encountered in the proposed survey regions. Risso's Dolphin Risso's dolphin is distributed worldwide in mid-temperate and tropical oceans (Kruse 
                        *et al.,*
                         1999). Although it shows a preference for mid-temperate waters of the shelf and slope between 30° and 45° (Jefferson 
                        *et al.,*
                         2014). Although it occurs from coastal to deep water (~200-1000 m depth), it shows a strong preference for mid-temperate waters of upper continental slopes and steep shelf-edge areas (Hartman 2018). Off the U.S. west coast, 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). The distribution and abundance of Risso's dolphins are highly variable from California to Washington, presumably in response to changing oceanographic conditions on both annual and seasonal time scales (Forney and Barlow 1998; Buchanan 
                        *et al.,*
                         2001). The highest densities were predicted along the coasts of Washington, Oregon, and central and southern California (Becker 
                        *et al.,*
                         2012). Off Oregon and Washington, Risso's dolphins are most abundant over continental slope and shelf waters during spring and summer, less so during fall, and rare during winter (Green 
                        *et al.,*
                         1992, 1993). Green 
                        *et al.,*
                         (1992, 1993) reported most Risso's dolphin groups off Oregon between ~45 and 47° N. Several sightings were made off southern Oregon during surveys in 1991-2014 (Barlow 2016; Carretta 
                        *et al.,*
                         2021). Sightings during ship surveys in summer/fall 2008 were mostly between ~30 and 38° N; none were reported in Oregon/Washington (Barlow 2010). Based on 2014 survey data, the abundance for Oregon/Washington was estimated at 430 (Barlow 2016). Risso's dolphins could be encountered in the proposed survey regions. Killer Whale The killer whale is cosmopolitan and globally fairly abundant, being observed in all oceans of the world (Ford 2018). It is very common in temperate waters and also frequents tropical waters, at least seasonally (Heyning and Dahlheim 1988). There are three distinct ecotypes, or forms, of killer whales recognized in the north Pacific: Resident, transient, and offshore. The three ecotypes differ morphologically, ecologically, behaviorally, and genetically. Resident killer whales exclusively prey upon fish, with a clear preference for salmon (Ford and Ellis 2006; Hanson 
                        *et al.,*
                         2010; Ford 
                        *et al.,*
                         2016), while transient killer whales exclusively prey upon marine mammals (Carretta 
                        *et al.,*
                         2019). Less is known about offshore killer whales, but they are believed to consume primarily fish, including several species of shark (Dahlheim 
                        *et 
                            ( print page 37571)
                            al.,*
                         2008). Killer whales occur in inshore inlets, along the coast, over the continental shelf, and in offshore waters (Ford 2014). Currently, there are eight killer whale stocks recognized in the U.S. Pacific: (1) Alaska Residents, occurring from Southeast Alaska to the Aleutians and Bering Sea; (2) Northern Residents, from British Columbia through parts of the Southeast Alaska; (3) Southern Residents, mainly in inland waters of Washington State and southern British Columbia; (4) Gulf of Alaska, Aleutians, and Bering Sea Transients, from Prince William Sound through the Aleutians and Bering Sea; (5) AT1 Transients, from Prince William Sound through the Kenai Fjords; (6) West Coast Transients, from California through Southeast Alaska; (7) Offshore, from California through Alaska; and (8) Hawaiian (Muto 
                        *et al.,*
                         2021; Carretta 
                        *et al.,*
                         2021). Individuals from the West Coast Transient and Offshore stocks could be encountered in the proposed project areas. It is unlikely that individuals from the endangered Eastern North Pacific Southern Resident stock would be encountered in the offshore survey regions, as they are primarily found along the coasts and the proposed survey is located in waters deeper than 1600 m and at least 46 km from the shoreline. The main diet of transient killer whales consists of marine mammals, in particular porpoises and seals. West coast transient killer whales (also known as Bigg's killer whales) range from Southeast Alaska to California (Muto 
                        *et al.,*
                         2021). The seasonal movements of transients are largely unpredictable (Baird 1994; Ford 2014). Green 
                        *et al.,*
                         (1992) noted that most groups seen during their surveys off Oregon and Washington were likely transients; during those surveys, killer whales were sighted only in shelf waters. Two of 17 killer whales that stranded in Oregon were confirmed as transient (Stevens 
                        *et al.,*
                         1989 in Norman 
                        *et al.,*
                         2004). Little is known about offshore killer whales, but they occur primarily over shelf waters and feed on fish, especially sharks (Ford 2014). Dahlheim 
                        *et al.,*
                         (2008) reported sightings in Southeast Alaska during spring and summer. Eleven sightings of approximately 536 individuals were reported off Oregon/Washington during the 2008 SWFSC vessel survey (Barlow 2010). Killer whales were sighted offshore Washington during surveys from August 2004 to September 2008 (Oleson 
                        *et al.,*
                         2009). Keating 
                        *et al.,*
                         (2015) analyzed cetacean whistles from recordings made during 2000-2012; several killer whale acoustic detections were made offshore Washington. Killer whales were sighted off Washington in July and September 2012 (Adams 
                        *et al.,*
                         2014). During L-DEO's Cascadia surveys during June through July 2021 in the Northeast Pacific Ocean, a sighting of 20 killer whales was made near the shelf edge off northern Oregon (RPS 2021b). Killer whales could be encountered during the proposed survey, although it is unlikely the endangered Southern Resident Killer whales would occur as far offshore as the survey regions. Pygmy and Dwarf Sperm Whale Dwarf and pygmy sperm whales are distributed throughout tropical and temperate waters of the Atlantic, Pacific, and Indian oceans, but their precise distributions are unknown because much of what we know of the species comes from strandings (McAlpine 2018). They are difficult to sight at sea, because of their dive behavior and perhaps because of their avoidance reactions to ships and behavior changes in relation to survey aircraft (Würsig 
                        *et al.,*
                         1998). The two species are often difficult to distinguish from one another when sighted (McAlpine 2018). Both 
                        *Kogia*
                         species are sighted primarily along the continental shelf edge and slope and over deeper waters off the shelf (Hansen 
                        *et al.,*
                         1994; Davis 
                        *et al.,*
                         1998; Jefferson 
                        *et al.,*
                         2015). Stomach content analyses from stranded whales further support this distribution (McAlpine 2018). Recent data indicate that both 
                        *Kogia*
                         species feed in the water column and on/near the seabed, likely using echolocation to search for prey (McAlpine 2018). Several studies have suggested that pygmy sperm whales live and feed mostly beyond the continental shelf edge, whereas dwarf sperm whales tend to occur closer to shore, often over the continental shelf and slope (Rice 1998; Wang 
                        *et al.,*
                         2002; MacLeod 
                        *et al.,*
                         2004; McAlpine 2018). It has also been suggested that the pygmy sperm whale is more temperate and the dwarf sperm whale more tropical, based at least partially on live sightings at sea from a large database from the eastern tropical Pacific (Wade and Gerrodette 1993; McAlpine 2018). Pygmy and dwarf sperm whales are rarely sighted off Oregon and Washington, with only one sighting of an unidentified 
                        *Kogia*
                         sp. beyond the U.S. EEZ, during the 1991-2014 NOAA vessel surveys (Carretta 
                        *et al.,*
                         2021). Norman 
                        *et al.,*
                         (2004) reported eight confirmed stranding records of pygmy sperm whales for Oregon and Washington, five of which occurred during autumn and winter. Despite the limited number of sightings, it is possible that pygmy or dwarf sperm whales could be encountered within the proposed project areas. Dall's Porpoise Dall's porpoise is found in temperate to subarctic waters of the North Pacific and adjacent seas (Jefferson 
                        *et al.,*
                         2015). It is widely distributed across the North Pacific over the continental shelf and slope waters, and over deep (>2500 m) oceanic waters (Hall 1979). It is probably the most abundant small cetacean in the North Pacific Ocean, and its abundance changes seasonally, likely in relation to water temperature (Becker 2007). Off Oregon and Washington, Dall's porpoise is widely distributed over shelf and slope waters, with concentrations near shelf edges, but is also commonly sighted in pelagic offshore waters (Morejohn 1979; Green 
                        *et al.,*
                         1992; Becker 
                        *et al.,*
                         2014; Fleming 
                        *et al.,*
                         2018; Carretta 
                        *et al.,*
                         2021). Combined results of various surveys out to ~550 km offshore indicate that the distribution and abundance of Dall's porpoise varies between seasons and years. North-south movements are believed to occur between Oregon/Washington and California in response to changing oceanographic conditions, particularly temperature and distribution and abundance of prey (Green 
                        *et al.,*
                         1992, 1993; Mangels and Gerrodette 1994; Barlow 1995; Forney and Barlow 1998; Buchanan 
                        *et al.,*
                         2001). Becker 
                        *et al.,*
                         (2014) predicted high densities off southern Oregon throughout the year, with moderate densities to the north. According to predictive density distribution maps, the highest densities off southern Washington and Oregon occur along the 500-m isobath (Menza 
                        *et al.,*
                         2016). Encounter rates reported by Green 
                        *et al.,*
                         (1992) during aerial surveys off Oregon/Washington were highest in fall, lowest during winter, and intermediate during spring and summer. Encounter rates during the summer were similarly high in slope and shelf waters, and somewhat lower in offshore waters (Green 
                        *et al.,*
                         1992). Dall's porpoise was the most abundant species sighted off Oregon/Washington during 1996, 2001, 2005, and 2008 ship surveys up to ~550 km from shore (Barlow 2003, 2010). Oleson 
                        *et al.,*
                         (2009) reported 44 sightings of 206 individuals off Washington during surveys form August 2004 to September 2008. Dall's porpoise were seen in the waters off Oregon during summer, fall, and winter surveys in 2011 and 2012 (Adams 
                        *et al.,*
                         2014). Nineteen Dall's porpoise sightings (144 animals) were made off Washington/Oregon during the June-
                        ( print page 37572)
                        July 2012 L-DEO Juan de Fuca plate seismic survey (RPS 2012b). There were 16 Dall's porpoise sightings (54 animals) made during the July 2012 L-DEO seismic surveys off southern Washington (RPS 2012a). This species was not sighted during the July 2012 L-DEO seismic survey off Oregon (RPS 2012c). During L-DEO's Cascadia survey during June-July 2021, one sighting of four individuals was made near the shelf edge off the Columbia River (RPS 2021b). Dall's porpoise is likely to be encountered during the proposed seismic surveys. Northern Fur Seal 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.,*
                         2021). During the breeding season, most of the worldwide population of northern fur seals inhabits the Pribilof Islands in the southern Bering Sea (NMFS 2007; Lee 
                        *et al.,*
                         2014; Muto 
                        *et al.,*
                         2021). 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.,*
                         2021). In the U.S., two stocks are recognized—the Eastern Pacific and the California stocks (Muto 
                        *et al.,*
                         2021). 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.,*
                         2021). When not on rookery islands, northern fur seals are primarily pelagic but occasionally haul out on rocky shorelines (Muto 
                        *et al.,*
                         2021). 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.,*
                         2021; Muto 
                        *et al.,*
                         2021). After reproduction, northern fur seals spend the next 7-8 months feeding at sea (Roppel 1984). Immature seals can remain in southern foraging areas year-round until they are old enough to mate (NMFS 2007). In November, females and pups leave the Pribilof Islands and migrate through the Gulf of Alaska to feeding areas primarily off the coasts of B.C., Washington, Oregon, and California before migrating north again to the rookeries in spring (Ream 
                        *et al.,*
                         2005; Pelland 
                        *et al.,*
                         2014). Males usually migrate only as far south as the Gulf of Alaska (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 Gulf of Alaska throughout the summer (Calkins 1986). The northern fur seals spends ~90% of its time at sea, typically in areas of upwelling along the continental slopes and over seamounts (Gentry 1981). The remainder of its life is spent on or near rookery islands or haulouts. Pups from the California stock also migrate to Washington, Oregon, and northern California after weaning (Lea 
                        *et al.,*
                         2009). Northern fur seals were seen throughout the North Pacific during surveys conducted during 1987-1990, including off Washington and Oregon (Buckland 
                        *et al.,*
                         1993). Tagged adult fur seals were tracked from the Pribilof Islands to the waters off Washington/Oregon/California, with recorded movement throughout the region (Pelland 
                        *et al.,*
                         2014). 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 Gulf of Alaska and the California Current (Sterling 
                        *et al.,*
                         2014). Some individuals reach California by December, after which time numbers increase off the west coast of North America (Ford 2014). The peak density shifts over the course of the winter and spring, with peak densities occurring in California in February, April off Oregon and Washington, and May off B.C. and Southeast Alaska (Ford 2014). The use of continental shelf and slope waters of B.C. and the northwestern U.S. by adult females during winter is well documented from pelagic sealing data (Bigg 1990). Bonnell 
                        *et al.,*
                         (1992) noted the presence of northern fur seals year-round off Oregon/Washington, with the greatest numbers (87%) occurring in January-May. Northern fur seals were seen as far out from the coast as 185 km, and numbers increased with distance from land; they were 5-6 times more abundant in offshore waters than over the shelf or slope (Bonnell 
                        *et al.,*
                         1992). The highest densities were seen in the Columbia River plume (~46° N) and in deep offshore waters (>2000 m) off central and southern Oregon (Bonnell 
                        *et al.,*
                         1992). The waters off Washington are a known foraging area for adult females, and concentrations of fur seals were also reported to occur near Cape Blanco, Oregon, at ~42.8° N (Pelland 
                        *et al.,*
                         2014). During L-DEO's Cascadia survey during June-July 2021, one northern fur seal was sighted off Washington near the shelf edge (RPS 2021b). Northern fur seals could be observed in the proposed survey regions, in particular females and juveniles. However, adult males are generally ashore during the reproductive season from May-August; adult females are generally ashore from June through November. Guadalupe Fur Seal Most breeding and births occur at Isla Guadalupe, Mexico; a secondary rookery exists at Isla Benito del Este (Maravilla-Chavez and Lowry 1999; Aurioles-Gamboa 
                        *et al.,*
                         2010). A few Guadalupe fur seals are known to occur at California sea lion rookeries in the Channel Islands, primarily San Nicolas and San Miguel islands, and sightings have also been made at Santa Barbara and San Clemente islands (Stewart 
                        *et al.,*
                         1987; Carretta 
                        *et al.,*
                         2021). Guadalupe fur seals prefer rocky habitat for breeding and hauling out. They generally haul out at the base of towering cliffs on shores characterized by solid rock and large lava blocks (Peterson 
                        *et al.,*
                         1968), although they can also inhabit caves and recesses (Belcher and Lee 2002). While at sea, this species usually is solitary but typically gathers in the hundreds to thousands at breeding sites. During the summer breeding season, most adults occur at rookeries in Mexico (Norris 2017 in USN 2019; Carretta 
                        *et al.,*
                         2021). Following the breeding season, adult males tend to move northward to forage. Females have been observed feeding south of Guadalupe Island, making an average round trip of 2375 km (Ronald and Gots 2003). Several rehabilitated Guadalupe fur seals that were satellite tagged and released in central California traveled as far north as B.C. (Norris 
                        *et al.,*
                         2015; Norris 2017 in USN 2019). Fur seals younger than two years old are more likely to travel to more northerly, offshore areas than older fur seals (Norris 2017 in USN 2019). Stranding data also indicates that fur seals younger than 2 years are more likely to occur in the proposed survey area, as this age class was most frequently reported (Lambourn 
                        *et al.,*
                         2012 in USN 2019). During 2015-2021, 724 Guadalupe fur seals stranded on the West Coast of the U.S., including 182 strandings along the coasts of Oregon and Washington during 2019-2021; NMFS declared this an unusual mortality event (NOAA 2021d). Guadalupe fur seals could be 
                        ( print page 37573)
                        encountered during the proposed seismic surveys, but most animals are likely to occur at their breeding sites farther south at the time of the surveys. California Sea Lion The primary range of the California sea lion includes the coastal areas and offshore islands of the eastern North Pacific Ocean from B.C. 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 Gulf of Alaska (Maniscalco 
                        *et al.,*
                         2004) and southern Mexico (Gallo-Reynoso and Solórzano-Velasco 1991), where it is occasionally recorded. California sea lion rookeries are on islands located in southern California, western Baja California, and the Gulf of California (Carretta 
                        *et al.,*
                         2021). 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. In California and Baja California, births occur on land from mid-May to late-June. During August and September, after the mating season, the adult males migrate northward to feeding areas as far north as Washington (Puget Sound) and B.C. (Lowry 
                        *et al.,*
                         1992). They remain there until spring (March-May), when they migrate back to the breeding colonies (Lowry 
                        *et al.,*
                         1992; Weise 
                        *et al.,*
                         2006). The distribution of immature California sea lions is less well known but some make northward migrations that are shorter in length than the migrations of adult males (Huber 1991). However, most immature seals are presumed to remain near the rookeries for most of the year, as are females and pups (Lowry 
                        *et al.,*
                         1992). California sea lions are coastal animals that often haul out on shore throughout the year, but peak numbers off Oregon and Washington occur during the fall (Bonnell 
                        *et al.,*
                         1992). During aerial surveys off the coasts of Oregon and Washington during 1989-1990, California sea lions were sighted at sea during the fall and winter, but no sightings were made during June-August (Bonnell 
                        *et al.,*
                         1992). Numbers off Oregon decrease during winter, as animals travel further north (Mate 1975 in Bonnell 
                        *et al.,*
                         1992). King (1983) noted that sea lions are rarely found more than 16 km offshore. During fall and winter surveys off Oregon and Washington, mean distance from shore was ~13 km and most were observed in water <200 m deep; however, sightings were made in water as deep as 356 m (Bonnell 
                        *et al.,*
                         1992). Weise 
                        *et al.,*
                         (2006) reported that males normally forage almost exclusively over the continental shelf, but during anomalous climatic conditions they can forage farther out to sea (up to 450 km offshore). During aerial surveys over the shelf and slope off Oregon and Washington (Adams 
                        *et al.,*
                         2014), California sea lions were seen during all survey months (January-February, June-July, September-October). Although most sightings occurred on the shelf, during February 2012, one sighting was made near the 2000-m depth contour, and during June 2011 and July 2012, sightings were made along the 200-m isobath off southern Oregon (Adams 
                        *et al.,*
                         2014). During October 2011, sightings were made off the Columbia River estuary near the 200-m isopleth and on the southern Oregon shelf; during September 2012, sightings occurred in nearshore waters off Washington and in shelf waters along the coast of Oregon (Adams 
                        *et al.,*
                         2014). Adams 
                        *et al.,*
                         (2014) reported sightings more than 60 km off the coast of Oregon. During L-DEO's Cascadia survey during June-July 2021, four sightings of nine California sea lions were made in nearshore waters off Oregon (RPS 2021b). California sea lions were also taken as bycatch off Washington and Oregon in the west coast groundfish fishery during 2002-2009 (Jannot 
                        *et al.,*
                         2011). California sea lions could be encountered in the proposed project regions. Steller Sea Lion The Steller sea lion occurs along the North Pacific Rim from northern Japan to California (Loughlin 
                        *et al.,*
                         1984). It is 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 (NOAA 2021e). There are two stocks, or DPSs, of Steller sea lions—the Western and Eastern DPSs, which are divided at 144° W longitude (Muto 
                        *et al.,*
                         2021). The Western DPS is listed as endangered and includes animals that occur in Japan and Russia (Muto 
                        *et al.,*
                         2021); the Eastern DPS was delisted from threatened in 2013 (NMFS 2013a). Only individuals from the Eastern DPS could occur in the proposed survey regions. Steller sea lions typically inhabit waters from the coast to the outer continental shelf and slope throughout their range; they are not considered migratory, although foraging animals can travel long distances (Loughlin 
                        *et al.,*
                         2003; Raum-Suryan 
                        *et al.,*
                         2002). Rookeries of Steller sea lions from the Eastern DPS are located in southeast Alaska, B.C., Oregon, and California; there are no rookeries in Washington (NMFS 2013a; Muto 
                        *et al.,*
                         2021). Breeding adults occupy rookeries from late-May to early-July (NMFS 2008). Federally designated critical habitat for Steller sea lions in Oregon and California includes all rookeries (NMFS 1993). Although the Eastern DPS was delisted from the ESA in 2013, the designated critical habitat remains valid (NOAA 2021e). The critical habitat in Oregon is located along the coast at Rogue Reef (Pyramid Rock) and Orford Reef (Long Brown Rock and Seal Rock). The critical habitat area includes aquatic zones that extend 0.9 km seaward and air zones extending 0.9 km above these terrestrial and aquatic zones (NMFS 1993). The nearest proposed seismic transect would be located 46 km from shore. 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%) 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% 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). During the summer, they mostly forage within 60 km from the coast; during winter, they can range up to 200 km from shore (Ford 2014). During surveys off the coasts of Oregon and Washington, Bonnell 
                        *et al.,*
                         (1992) noted that 89% of sea lions occurred over the shelf at a mean 
                        ( print page 37574)
                        distance of 21 km from the coast and near or in waters <200 m deep; the farthest sighting occurred ~40 km from shore, and the deepest sighting location was 1611 m deep. Sightings were made along the 200-m depth contour throughout the year (Bonnell 
                        *et al.,*
                         1992). During aerial surveys over the shelf and slope off Oregon and Washington, one Steller sea lion was seen on the Oregon shelf during January 2011, and two sightings totaling eight individuals were made on September 2012 off southern Oregon (Adams 
                        *et al.,*
                         2014). During a survey off Washington/Oregon June-July 2012, two Steller sea lions were seen from R/V 
                        *Langseth*
                         (RPS 2012b) off southern Oregon. Eight sightings of 11 individuals were made from R//V 
                        *Northern Light*
                         during a survey off southern Washington during July 2012 (RPS 2012a). No sightings were made during L-DEO's Cascadia summer survey off Oregon and Washington (RPS 2021b). Steller sea lions were also taken as bycatch off southern Oregon in the west coast groundfish fishery during 2002-2009 (Jannot 
                        *et al.,*
                         2011). Steller sea lions could be encountered in the proposed project regions. Northern Elephant Seal The northern elephant seal breeds in California and Baja California, primarily on offshore islands, from Cedros off the west coast of Baja California, north to the Farallons in Central California (Stewart 
                        *et al.,*
                         1994). Adult elephant seals engage in two long northward migrations per year, one following the breeding season, and another following the annual molt (Stewart and DeLong 1995). Between the two foraging periods, they return to land to molt, with females returning earlier than males (March-April vs. July-August). After the molt, adults then return to their northern feeding areas until the next winter breeding season. Breeding occurs from December-March (Stewart and Huber 1993). Females arrive in late December or January and give birth within ~1 week of their arrival. Juvenile elephant seals typically leave the rookeries in April or May and head north, traveling an average of 900-1000 km. Most elephant seals return to their natal rookeries when they start breeding (Huber 
                        *et al.,*
                         1991). When not at their breeding rookeries, adults feed at sea far from the rookeries. Adult females and juveniles forage in the California current off California to B.C. (Le Boeuf 
                        *et al.,*
                         1986, 1993, 2000). Bonnell 
                        *et al.*
                         (1992) reported that northern elephant seals were distributed equally in shelf, slope, and offshore waters during surveys conducted off Oregon and Washington, as far as 150 km from shore, in waters >2000 m deep. Telemetry data indicate that they range much farther offshore than that (Stewart and DeLong 1995). Males may feed as far north as the eastern Aleutian Islands and the Gulf of Alaska, whereas females feed south of 45° N (Le Boeuf 
                        *et al.,*
                         1993; Stewart and Huber 1993). Adult male elephant seals migrate north via the California current to the Gulf of Alaska during foraging trips, and could potentially be passing through the area off Washington in May and August (migrating to and from molting periods) and November and February (migrating to and from breeding periods), but likely their presence there is transient and short-lived. Most elephant seal sightings at sea off Washington were made during June, July, and September; off Oregon, sightings were recorded from November through May (Bonnell 
                        *et al.,*
                         1992). Northern elephant seal pups have been sighted at haulouts in the inland waters of Washington State (Jeffries 
                        *et al.,*
                         2000), and at least three were reported to have been born there (Hayward 2003). Pupping has also been observed at Shell Island (~43.3° N) off southern Oregon, suggesting a range expansion (Bonnell 
                        *et al.,*
                         1992; Hodder 
                        *et al.,*
                         1998). Northern elephant seals could be encountered during the proposed seismic surveys. Marine Mammal Hearing Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities (
                        *e.g.,*
                         Richardson 
                        *et al.,*
                         1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall 
                        *et al.,*
                         (2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc.). 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).
                        ( print page 37575) For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information. Potential Effects of Specified Activities on Marine Mammals and Their Habitat This section includes a discussion of the ways that L-DEO's specified activity may impact marine mammals and their habitat. The Estimated Take section later in this document includes a quantitative analysis of the number of individuals that are expected to be taken by this activity. The Negligible Impact Analysis and Determination section considers the content of this section, the Estimated Take section, and the Proposed Mitigation section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and how those impacts on individuals may or may not 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 a 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 μPa2
                        −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 this dependence on a large number of varying factors, ambient 
                        ( print page 37576)
                        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. Acoustic Effects Here, we discuss the effects of active acoustic sources on marine mammals. *Potential Effects of Underwater Sound*
                        —Please refer to the information given previously (“Description of Active Acoustic Sound Sources”) regarding sound, characteristics of sound types, and metrics used in this document. Note that, in the following discussion, we refer in many cases to Finneran (2015), a review article concerning studies of noise-induced hearing loss conducted from 1996-2015. For study-specific citations, please see Finneran (2015). 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, if it occurs at all, will occur almost exclusively in cases where a noise is within an animal's hearing frequency range. We first describe specific manifestations of acoustic effects before providing discussion specific to the use of airgun arrays. Richardson 
                        *et al.,*
                         (1995) described zones of increasing intensity of effect that might be expected to occur, in relation to distance from a source and assuming that the signal is within an animal's hearing range. First is the area within which the acoustic signal would be audible (potentially perceived) to the animal, but not strong enough to elicit any overt behavioral or physiological response. The next zone corresponds with the area where the signal is audible to the animal and of sufficient intensity to elicit behavioral or physiological response. Third is a zone within which, for signals of high intensity, the received level is sufficient to potentially cause discomfort or tissue damage to auditory or other systems. Overlaying these zones to a certain extent is the area within which masking (
                        *i.e.,*
                         when a sound interferes with or masks the ability of an animal to detect a signal of interest that is above the absolute hearing threshold) may occur; the masking zone may be highly variable in size. We describe the more severe effects of certain non-auditory physical or physiological effects only briefly as we do not expect that use of airgun arrays are reasonably likely to result in such effects (see below for further discussion). Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton 
                        *et al.,*
                         1973). Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions (
                        *e.g.,*
                         change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox 
                        *et al.,*
                         2006; Southall 
                        *et al.,*
                         2007; Zimmer and Tyack, 2007; Tal 
                        *et al.,*
                         2015). The survey activities considered here do not involve the use of devices such as explosives or 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 
                        ( print page 37577)
                        addition, other investigators have suggested that TTS is within the normal bounds of physiological variability and tolerance and does not represent physical injury (
                        *e.g.,*
                         Ward, 1997). Therefore, NMFS does not typically consider TTS to constitute auditory injury. Relationships between TTS and PTS thresholds have not been studied in marine mammals, 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 was likely due to the intermittent nature of exposure, the relatively low peak pressure produced by the acoustic source, and the low-frequency energy in airgun pulses as compared with the frequency range of best sensitivity for 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 direct 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, 2019), Finneran and Jenkins (2012), Finneran (2015), and NMFS (2018). *Behavioral Effects*
                        —Behavioral disturbance may include a variety of effects, including subtle changes in behavior (
                        *e.g.,*
                         minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses to sound are highly variable and context-specific, and any reactions depend on numerous intrinsic and extrinsic factors (
                        *e.g.,*
                         species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
                        *e.g.,*
                         Richardson 
                        *et al.,*
                         1995; Wartzok 
                        *et al.,*
                         2003; Southall 
                        *et al.,*
                         2007, 2019; Weilgart, 2007; Archer 
                        *et al.,*
                         2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison 
                        *et al.,*
                         2012), and can vary depending on characteristics associated with the sound source (
                        *e.g.,*
                         whether it is moving or stationary, number of sources, distance from the source). Please see Appendices B-C of Southall 
                        *et al.*
                         (2007) for a review of studies involving marine mammal behavioral responses to sound. Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok 
                        *et al.,*
                         2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder 
                        *et al.,*
                         2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure. As noted, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals 
                        ( print page 37578)
                        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 disruptions in biologically significant activities (
                        *e.g.,*
                         foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response. Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators (
                        *e.g.,*
                         bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance (
                        *e.g.,*
                         Croll 
                        *et al.,*
                         2001; Nowacek 
                        *et al.;*
                         2004; Madsen 
                        *et al.,*
                         2006; Yazvenko 
                        *et al.,*
                         2007). A determination of whether foraging disruptions 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 or amplitude of calls (Miller 
                        *et al.,*
                         2000; Fristrup 
                        *et al.,*
                         2003; Foote 
                        *et al.,*
                         2004; Holt 
                        *et al.,*
                         2012), while right whales have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks 
                        *et al.,*
                         2007). In some cases, animals may cease sound production during production of aversive signals (Bowles 
                        *et al.,*
                         1994). Cerchio 
                        *et al.,*
                         (2014) used passive acoustic monitoring to document the presence of singing humpback whales off the coast of northern Angola and to opportunistically test for the effect of seismic survey activity on the number of singing whales. Two recording units were deployed between March and December 2008 in the offshore environment; numbers of singers were counted every hour. Generalized Additive Mixed Models were used to assess the effect of survey day (seasonality), hour (diel variation), moon phase, and received levels of noise (measured from a single pulse during each 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, 
                        ( print page 37579)
                        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 μPa2
                        -s caused blue whales to increase call production (Di Iorio and Clark, 2010). In contrast, McDonald 
                        *et al.,*
                         (1995) tracked a blue whale with seafloor seismometers and reported that it stopped vocalizing and changed its travel direction at a range of 10 km from the acoustic source vessel (estimated received level 143 dB pk-pk). Blackwell 
                        *et al.,*
                         (2013) found that bowhead whale call rates dropped significantly at onset of airgun use at sites with a median distance of 41-45 km from the survey. Blackwell 
                        *et al.*
                         (2015) expanded this analysis to show that whales actually increased calling rates as soon as airgun signals were detectable before ultimately decreasing calling rates at higher received levels (
                        *i.e.,*
                         10-minute SELcum of ~127 dB). Overall, these results suggest that bowhead whales may adjust their vocal output in an effort to compensate for noise before ceasing vocalization effort and ultimately deflecting from the acoustic source (Blackwell 
                        *et al.,*
                         2013, 2015). These studies demonstrate that even low levels of noise received far from the source can induce changes in vocalization and/or behavior for mysticetes. Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of disturbance in marine mammals (Richardson 
                        *et al.,*
                         1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme 
                        *et al.,*
                         1984). Humpback whales showed avoidance behavior in the presence of an active seismic array during observational studies and controlled exposure experiments in western Australia (McCauley 
                        *et al.,*
                         2000). Avoidance may be short-term, with animals returning to the area once the noise has ceased (
                        *e.g.,*
                         Bowles 
                        *et al.,*
                         1994; Goold, 1996; Stone 
                        *et al.,*
                         2000; Morton and Symonds, 2002; Gailey 
                        *et al.,*
                         2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur (
                        *e.g.,*
                         Bejder 
                        *et al.,*
                         2006; Teilmann 
                        *et al.,*
                         2006). Forney 
                        *et al.,*
                         (2017) detail the potential effects of noise on marine mammal populations with high site fidelity, including displacement and auditory masking, noting that a lack of observed response does not imply absence of fitness costs and that apparent tolerance of disturbance may have population-level impacts that are less obvious and difficult to document. As we discuss in describing our proposed mitigation later in this document, avoidance of overlap between disturbing noise and areas and/or times of particular importance for sensitive species may be critical to avoiding population-level impacts because (particularly for animals with high site fidelity) there may be a strong motivation to remain in the area despite negative impacts. Forney 
                        *et al.,*
                         (2017) state that, for these animals, remaining in a disturbed area may reflect a lack of alternatives rather than a lack of effects. The authors discuss several case studies, including western Pacific gray whales, which are a small population of mysticetes believed to be adversely affected by oil and gas development off Sakhalin Island, Russia (Weller 
                        *et al.,*
                         2002; Reeves 
                        *et al.,*
                         2005). Western gray whales display a high degree of interannual site fidelity to the area for foraging purposes, and observations in the area during airgun surveys has shown the potential for harm caused by displacement from such an important area (Weller 
                        *et al.,*
                         2006; Johnson 
                        *et al.,*
                         2007). Forney 
                        *et al.,*
                         (2017) also discuss beaked whales, noting that anthropogenic effects in areas where they are resident could cause severe biological consequences, in part because displacement may adversely affect foraging rates, reproduction, or health, while an overriding instinct to remain could lead to more severe acute effects. A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response (
                        *e.g.,*
                         directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (Evans and England, 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response. Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in 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 arrays of large airguns (considered to be 500 in3
                         or more) were firing, lateral displacement, more localized avoidance, or other changes in behavior were evident for most odontocetes. However, significant responses to large arrays were found only for the minke whale and fin whale. Behavioral 
                        ( print page 37580)
                        responses observed included changes in swimming or surfacing behavior, with indications that cetaceans remained near the water surface at these times. Cetaceans were recorded as feeding less often when large arrays were active. Behavioral observations of gray whales during a seismic survey monitored whale movements and respirations pre-, during, and post-seismic survey (Gailey 
                        *et al.,*
                         2016). Behavioral state and water depth were the best `natural' predictors of whale movements and respiration and, after considering natural variation, none of the response variables were significantly associated with seismic survey or vessel sounds. *Stress Responses*
                        —An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses (
                        *e.g.,*
                         Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness. Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal system. Virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction, altered metabolism, reduced immune competence, and behavioral disturbance (
                        *e.g.,*
                         Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano 
                        *et al.,*
                         2004). The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose serious fitness consequences. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other functions. This state of distress will last until the animal replenishes its energetic reserves sufficiently to restore normal function. Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses are well-studied through controlled experiments and for both laboratory and free-ranging animals (
                        *e.g.,*
                         Holberton 
                        *et al.,*
                         1996; Hood 
                        *et al.,*
                         1998; Jessop 
                        *et al.,*
                         2003; Krausman 
                        *et al.,*
                         2004; Lankford 
                        *et al.,*
                         2005). Stress responses due to exposure to anthropogenic sounds or other stressors and their effects on marine mammals have also been reviewed (Fair and Becker, 2000; Romano 
                        *et al.,*
                         2002b) and, more rarely, studied in wild populations (
                        *e.g.,*
                         Romano 
                        *et al.,*
                         2002a). For example, Rolland 
                        *et al.,*
                         (2012) found that noise reduction from reduced ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003). *Auditory Masking*
                        —Sound can disrupt behavior through masking, or interfering with, an animal's ability to detect, recognize, or discriminate between acoustic signals of interest (
                        *e.g.,*
                         those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson 
                        *et al.,*
                         1995; Erbe 
                        *et al.,*
                         2016). Masking occurs when the receipt of a sound is interfered with by another coincident sound at similar frequencies and at similar or higher intensity, and may occur whether the sound is natural (
                        *e.g.,*
                         snapping shrimp, wind, waves, precipitation) or anthropogenic (
                        *e.g.,*
                         shipping, sonar, seismic exploration) in origin. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest (
                        *e.g.,*
                         signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities (
                        *e.g.,*
                         sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions. Under certain circumstances, significant masking could disrupt behavioral patterns, which in turn could affect fitness for survival and reproduction. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect. The frequency range of the potentially masking sound is important in predicting any potential behavioral impacts. For example, low-frequency signals may have less effect on 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 may be less in situations where the signal and noise come from different directions (Richardson 
                        *et al.,*
                         1995), through amplitude modulation of the signal, or through other compensatory behaviors (Houser and Moore, 2014). Masking can be tested directly in captive species (
                        *e.g.,*
                         Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild (
                        *e.g.,*
                         Branstetter 
                        *et al.,*
                         2013). Masking affects both senders and receivers of acoustic signals and can potentially have long-term chronic effects on marine mammals at the population level as well as at the individual level. Low-frequency ambient sound levels have increased by as much as 20 dB (more than three times in terms of SPL) in the world's ocean from pre-industrial periods, with most of the increase from distant commercial shipping (Hildebrand, 2009). All anthropogenic sound sources, but especially chronic and lower-frequency signals (
                        *e.g.,*
                         from vessel traffic), contribute to elevated ambient sound levels, thus intensifying masking. Masking effects of pulsed sounds (even from large arrays of airguns) on marine mammal calls and other natural sounds are expected to be limited, although there are few specific data on this. Because of the intermittent nature and low duty cycle of seismic pulses, 
                        ( print page 37581)
                        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.,*
                         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.
                        ( print page 37582) Sounds emitted by the 
                        *Langseth*
                         are low frequency and continuous, but would be widely dispersed in both space and time. Vessel traffic associated with the proposed survey is of low density compared to traffic associated with commercial shipping, industry support vessels, or commercial fishing vessels, and would therefore be expected to represent an insignificant incremental increase in the total amount of anthropogenic sound input to the marine environment, and the effects of vessel noise described above are not expected to occur as a result of this survey. In summary, project vessel sounds would not be at levels expected to cause anything more than possible localized and temporary behavioral changes in marine mammals, and would not be expected to result in significant negative effects on individuals or at the population level. In addition, in all oceans of the world, large vessel traffic is currently so prevalent that it is commonly considered a usual source of ambient sound (NSF-USGS 2011). Ship Strike Vessel collisions with marine mammals, or ship strikes, can result in death or serious injury of the animal. Wounds resulting from ship strike may include massive trauma, hemorrhaging, broken bones, or propeller lacerations (Knowlton and Kraus, 2001). An animal at the surface may be struck directly by a vessel, a surfacing animal may hit the bottom of a vessel, or an animal just below the surface may be cut by a vessel's propeller. Superficial strikes may not kill or result in the death of the animal. These interactions are typically associated with large whales (
                        *e.g.,*
                         fin whales), which are occasionally found draped across the bulbous bow of large commercial ships upon arrival in port. Although smaller cetaceans are more maneuverable in relation to large vessels than are large whales, they may also be susceptible to strike. The severity of injuries typically depends on the size and speed of the vessel, with the probability of death or serious injury increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist 
                        *et al.,*
                         2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013). Impact forces increase with speed, as does the probability of a strike at a given distance (Silber 
                        *et al.,*
                         2010; Gende 
                        *et al.,*
                         2011). Pace and Silber (2005) also found that the probability of death or serious injury increased rapidly with increasing vessel speed. Specifically, the predicted probability of serious injury or death 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*
                         will travel at a speed of 4.6 kn (8.5 km/h) while towing seismic survey gear. At this speed, both the possibility of striking a marine mammal and the possibility of a strike resulting in serious injury or mortality are discountable. At average transit speed, the probability of serious injury or mortality resulting from a strike is less than 50 percent. However, the likelihood of a strike actually happening is again discountable. 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 x 10−6; 95% CI = 0-5.5 x 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 propose a robust ship strike avoidance protocol (see Proposed Mitigation), which we believe eliminates any foreseeable risk of ship strike during transit. We anticipate that vessel collisions involving a seismic data acquisition vessel towing gear, while not impossible, represent unlikely, unpredictable events for which there are no preventive measures. Given the proposed mitigation measures, the relatively slow speed of the vessel towing gear, the presence of bridge crew watching for obstacles at all times (including marine mammals), and the presence of marine mammal observers, the possibility of ship strike is discountable and, further, were a strike of a large whale to occur, it would be unlikely to result in serious injury or mortality. No incidental take resulting from ship strike is anticipated, and this potential effect of the specified activity will not be discussed further in the following analysis. *Stranding*
                        —When a living or dead marine mammal swims or floats onto shore and becomes “beached” or incapable of returning to sea, the event is a “stranding” (Geraci 
                        *et al.,*
                         1999; Perrin and Geraci, 2002; Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a stranding under the MMPA is that “(A) a marine mammal is dead and is (i) on a beach or shore of the United States; or (ii) in waters under the jurisdiction of the United States (including any navigable waters); or (B) a marine mammal is alive and is (i) on a beach or shore of the United States and is unable to return to the water; (ii) on a beach or shore of the United States and, although able to return to the water, is in need of apparent medical attention; or (iii) in the waters under the jurisdiction of the United States (including any navigable waters), but is unable to return to its natural habitat under its own power or without assistance.” Marine mammals strand for a variety of reasons, such as infectious agents, biotoxicosis, starvation, fishery interaction, ship strike, unusual oceanographic or weather events, sound exposure, or combinations of these stressors sustained concurrently or in 
                        ( print page 37583)
                        series. However, the cause or causes of most strandings are unknown (Geraci 
                        *et al.,*
                         1976; Eaton, 1979; Odell 
                        *et al.,*
                         1980; Best, 1982). Numerous studies suggest that the physiology, behavior, habitat relationships, age, or condition of cetaceans may cause them to strand or might pre-dispose them to strand when exposed to another phenomenon. These suggestions are consistent with the conclusions of numerous other studies that have demonstrated that combinations of dissimilar stressors commonly combine to kill an animal or dramatically reduce its fitness, even though one exposure without the other does not produce the same result (Chroussos, 2000; Creel, 2005; DeVries 
                        *et al.,*
                         2003; Fair and Becker, 2000; Foley 
                        *et al.,*
                         2001; Moberg, 2000; Relyea, 2005a; 2005b, Romero, 2004; Sih 
                        *et al.,*
                         2004). There is no conclusive evidence that exposure to airgun noise results in behaviorally-mediated forms of injury. Behaviorally-mediated injury (
                        *i.e.,*
                         mass stranding events) has been primarily associated with beaked whales exposed to mid-frequency active (MFA) naval sonar. Tactical sonar and the alerting stimulus used in Nowacek 
                        *et al.,*
                         (2004) are very different from the noise produced by airguns. One should therefore not expect the same reaction to airgun noise as to these other sources. As explained below, military MFA sonar is very different from airguns, and one should not assume that airguns will cause the same effects as MFA sonar (including strandings). To understand why Navy MFA sonar affects beaked whales differently than airguns do, it is important to note the distinction between behavioral sensitivity and susceptibility to auditory injury. To understand the potential for auditory injury in a particular marine mammal species in relation to a given acoustic signal, the frequency range the species is able to hear is critical, as well as the species' auditory sensitivity to frequencies within that range. Current data indicate that not all marine mammal species have equal hearing capabilities across all frequencies and, therefore, species are grouped into hearing groups with generalized hearing ranges assigned on the basis of available data (Southall 
                        *et al.,*
                         2007, 2019). Hearing ranges as well as auditory sensitivity/susceptibility to frequencies within those ranges vary across the different groups. For example, in terms of hearing range, the high-frequency cetaceans (
                        *e.g., Kogia*
                         spp.) have a generalized hearing range of frequencies between 275 Hz and 160 kHz, while mid-frequency cetaceans—such as dolphins and beaked whales—have a generalized hearing range between 150 Hz to 160 kHz. Regarding auditory susceptibility within the hearing range, while mid-frequency cetaceans and high-frequency cetaceans have roughly similar hearing ranges, the high-frequency group is much more susceptible to noise-induced hearing loss during sound exposure, 
                        *i.e.,*
                         these species have lower thresholds for these effects than other hearing groups (NMFS, 2018). Referring to a species as behaviorally sensitive to noise simply means that an animal of that species is more likely to respond to lower received levels of sound than an animal of another species that is considered less behaviorally sensitive. So, while dolphin species and beaked whale species—both in the mid-frequency cetacean hearing group—are assumed to generally hear the same sounds equally well and be equally susceptible to noise-induced hearing loss (auditory injury), the best available information indicates that a beaked whale is more likely to behaviorally respond to that sound at a lower received level compared to an animal from other mid-frequency cetacean species that are less behaviorally sensitive. This distinction is important because, while beaked whales are more likely to respond behaviorally to sounds than are many other species (even at lower levels), they cannot hear the predominant, lower frequency sounds from seismic airguns as well as sounds that have more energy at frequencies that beaked whales can hear better (such as military MFA sonar). Navy MFA sonar affects beaked whales differently than airguns do because it produces energy at different frequencies than airguns. Mid-frequency cetacean hearing is generically thought to be best between 8.8 to 110 kHz, 
                        *i.e.,*
                         these cutoff values define the range above and below which a species in the group is assumed to have declining auditory sensitivity, until reaching frequencies that cannot be heard (NMFS, 2018). However, beaked whale hearing is likely best within a higher, narrower range (20-80 kHz, with best sensitivity around 40 kHz), based on a few measurements of hearing in stranded beaked whales (Cook 
                        *et al.,*
                         2006; Finneran 
                        *et al.,*
                         2009; Pacini 
                        *et al.,*
                         2011) and several studies of acoustic signals produced by beaked whales (
                        *e.g.,*
                         Frantzis 
                        *et al.,*
                         2002; Johnson 
                        *et al.,*
                         2004, 2006; Zimmer 
                        *et al.,*
                         2005). While precaution requires that the full range of audibility be considered when assessing risks associated with noise exposure (Southall 
                        *et al.,*
                         2007, 2019a2019), animals typically produce sound at frequencies where they hear best. More recently, Southall 
                        *et al.,*
                         (2019) suggested that certain species in the historical mid-frequency hearing group (beaked whales, sperm whales, and killer whales) are likely more sensitive to lower frequencies within the group's generalized hearing range than are other species within the group, and state that the data for beaked whales suggest sensitivity to approximately 5 kHz. However, this information is consistent with the general conclusion that beaked whales (and other mid-frequency cetaceans) are relatively insensitive to the frequencies where most energy of an airgun signal is found. Military MFA sonar is typically considered to operate in the frequency range of approximately 3-14 kHz (D'Amico 
                        *et al.,*
                         2009), 
                        *i.e.,*
                         outside the range of likely best hearing for beaked whales but within or close to the lower bounds, whereas most energy in an airgun signal is radiated at much lower frequencies, below 500 Hz (Dragoset, 1990). It is important to distinguish between energy (loudness, measured in dB) and frequency (pitch, measured in Hz). In considering the potential impacts of mid-frequency components of airgun noise (1-10 kHz, where beaked whales can be expected to hear) on marine mammal hearing, one needs to account for the energy associated with these higher frequencies and determine what energy is truly “significant.” Although there is mid-frequency energy associated with airgun noise (as expected from a broadband source), airgun sound is predominantly below 1 kHz (Breitzke 
                        *et al.,*
                         2008; Tashmukhambetov 
                        *et al.,*
                         2008; Tolstoy 
                        *et al.,*
                         2009). As stated by Richardson 
                        *et al.*
                         (1995), “[. . .] most emitted [seismic airgun] energy is at 10-120 Hz, but the pulses contain some energy up to 500-1,000 Hz.” Tolstoy 
                        *et al.,*
                         (2009) conducted empirical measurements, demonstrating that sound energy levels associated with airguns were at least 20 decibels (dB) lower at 1 kHz (considered “mid-frequency”) compared to higher energy levels associated with lower frequencies (below 300 Hz) (“all but a small fraction of the total energy being concentrated in the 10-300 Hz range” [Tolstoy 
                        *et al.,*
                         2009]), and at higher frequencies (
                        *e.g.,*
                         2.6-4 kHz), power might be less than 10 percent of the peak power at 10 Hz (Yoder, 2002). Energy levels measured by Tolstoy 
                        *et al.,*
                         (2009) were even lower at frequencies above 1 kHz. In addition, as sound propagates away from the source, it tends to lose higher-frequency components faster than low-frequency components (
                        *i.e.,*
                         low-frequency sounds 
                        ( print page 37584)
                        typically propagate longer distances than high-frequency sounds) (Diebold 
                        *et al.,*
                         2010). Although higher-frequency components of airgun signals have been recorded, it is typically in surface-ducting conditions (
                        *e.g.,*
                         DeRuiter 
                        *et al.,*
                         2006; Madsen 
                        *et al.,*
                         2006) or in shallow water, where there are advantageous propagation conditions for the higher frequency (but low-energy) components of the airgun signal (Hermannsen 
                        *et al.,*
                         2015). This should not be of concern because the likely behavioral reactions of beaked whales that can result in acute physical injury would result from noise exposure at depth (because of the potentially greater consequences of severe behavioral reactions). In summary, the frequency content of airgun signals is such that beaked whales will not be able to hear the signals well (compared to MFA sonar), especially at depth where we expect the consequences of noise exposure could be more severe. Aside from frequency content, there are other significant differences between MFA sonar signals and the sounds produced by airguns that minimize the risk of severe behavioral reactions that could lead to strandings or deaths at sea, 
                        *e.g.,*
                         significantly longer signal duration, horizontal sound direction, typical fast and unpredictable source movement. All of these characteristics of MFA sonar tend towards greater potential to cause severe behavioral or physiological reactions in exposed beaked whales that may contribute to stranding. Although both sources are powerful, MFA sonar contains significantly greater energy in the mid-frequency range, where beaked whales hear better. Short-duration, high energy pulses—such as those produced by airguns—have greater potential to cause damage to auditory structures (though this is unlikely for mid-frequency cetaceans, as explained later in this document), but it is longer duration signals that have been implicated in the vast majority of beaked whale strandings. Faster, less predictable movements in combination with multiple source vessels are more likely to elicit a severe, potentially anti-predator response. Of additional interest in assessing the divergent characteristics of MFA sonar and airgun signals and their relative potential to cause stranding events or deaths at sea is the similarity between the MFA sonar signals and stereotyped calls of beaked whales' primary predator: the killer whale (Zimmer and Tyack, 2007). Although generic disturbance stimuli—as airgun noise may be considered in this case for beaked whales—may also trigger antipredator responses, stronger responses should generally be expected when perceived risk is greater, as when the stimulus is confused for a known predator (Frid and Dill, 2002). In addition, because the source of the perceived predator (
                        *i.e.,*
                         MFA sonar) will likely be closer to the whales (because attenuation limits the range of detection of mid-frequencies) and moving faster (because it will be on faster-moving vessels), any antipredator response would be more likely to be severe (with greater perceived predation risk, an animal is more likely to disregard the cost of the response; Frid and Dill, 2002). Indeed, when analyzing movements of a beaked whale exposed to playback of killer whale predation calls, Allen 
                        *et al.,*
                         (2014) found that the whale engaged in a prolonged, directed avoidance response, suggesting a behavioral reaction that could pose a risk factor for stranding. Overall, these significant differences between sound from MFA sonar and the mid-frequency sound component from airguns and the likelihood that MFA sonar signals will be interpreted in error as a predator are critical to understanding the likely risk of behaviorally-mediated injury due to seismic surveys. The available scientific literature also provides a useful contrast between airgun noise and MFA sonar regarding the likely risk of behaviorally-mediated injury. There is strong evidence for the association of beaked whale stranding events with MFA sonar use, and particularly detailed accounting of several events is available (
                        *e.g.,*
                         a 2000 Bahamas stranding event for which investigators concluded that MFA sonar use was responsible; Evans and England, 2001). D'Amico 
                        *et al.,*
                         (2009) reviewed 126 beaked whale mass stranding events over the period from 1950 (
                        *i.e.,*
                         from the development of modern MFA sonar systems) through 2004. Of these, there were two events where detailed information was available on both the timing and location of the stranding and the concurrent nearby naval activity, including verification of active MFA sonar usage, with no evidence for an alternative cause of stranding. An additional ten events were at minimum spatially and temporally coincident with naval activity likely to have included MFA sonar use and, despite incomplete knowledge of timing and location of the stranding or the naval activity in some cases, there was no evidence for an alternative cause of stranding. The U.S. Navy has publicly stated agreement that five such events since 1996 were associated in time and space with MFA sonar use, either by the U.S. Navy alone or in joint training exercises with the North Atlantic Treaty Organization. The U.S. Navy additionally noted that, as of 2017, a 2014 beaked whale stranding event in Crete coincident with naval exercises was under review and had not yet been determined to be linked to sonar activities (U.S. Navy, 2017). Separately, the International Council for the Exploration of the Sea reported in 2005 that, worldwide, there have been about 50 known strandings, consisting mostly of beaked whales, with a potential causal link to MFA sonar (ICES, 2005). In contrast, very few such associations have been made to seismic surveys, despite widespread use of airguns as a geophysical sound source in numerous locations around the world. A more recent review of possible stranding associations with seismic surveys (Castellote and Llorens, 2016) states plainly that, “[s]peculation concerning possible links between seismic survey noise and cetacean strandings is available for a dozen events but without convincing causal evidence.” The authors' “exhaustive” search of available information found ten events worth further investigation via a ranking system representing a rough metric of the relative level of confidence offered by the data for inferences about the possible role of the seismic survey in a given stranding event. Only three of these events involved beaked whales. Whereas D'Amico 
                        *et al.,*
                         (2009) used a 1-5 ranking system, in which “1” represented the most robust evidence connecting the event to MFA sonar use, Castellote and Llorens (2016) used a 1-6 ranking system, in which “6” represented the most robust evidence connecting the event to the seismic survey. As described above, D'Amico 
                        *et al.*
                         (2009) found that two events were ranked “1” and ten events were ranked “2” (
                        *i.e.,*
                         12 beaked whale stranding events were found to be associated with MFA sonar use). In contrast, Castellote and Llorens (2016) found that none of the three beaked whale stranding events achieved their highest ranks of 5 or 6. Of the ten total events, none achieved the highest rank of 6. Two events were ranked as 5: one stranding in Peru involving dolphins and porpoises and a 2008 stranding in Madagascar. This latter ranking can only broadly be associated with the survey itself, as opposed to use of seismic airguns. An exhaustive investigation of this stranding event, which did not involve beaked whales, concluded that use of a high-frequency mapping system (12-kHz multibeam echosounder) was the most 
                        ( print page 37585)
                        plausible and likely initial behavioral trigger of the event, which was likely exacerbated by several site- and situation-specific secondary factors. The review panel found that seismic airguns were used after the initial strandings and animals entering a lagoon system, that airgun use clearly had no role as an initial trigger, and that there was no evidence that airgun use dissuaded animals from leaving (Southall 
                        *et al.,*
                         2013). However, one of these stranding events, involving two Cuvier's beaked whales, was contemporaneous with and reasonably associated spatially with a 2002 seismic survey in the Gulf of California conducted by L-DEO, as was the case for the 2007 Gulf of Cadiz seismic survey discussed by Castellote and Llorens (also involving two Cuvier's beaked whales). However, neither event was considered a “true atypical mass stranding” (according to Frantzis [1998]) as used in the analysis of Castellote and Llorens (2016). While we agree with the authors that this lack of evidence should not be considered conclusive, it is clear that there is very little evidence that seismic surveys should be considered as posing a significant risk of acute harm to beaked whales or other mid-frequency cetaceans. We have considered the potential for the proposed surveys to result in marine mammal stranding and have concluded that, based on the best available information, stranding is not expected to occur. *Entanglement*
                        —Entanglements occur when marine mammals become wrapped around cables, lines, nets, or other objects suspended in the water column. During seismic operations, numerous cables, lines, and other objects primarily associated with the airgun array and hydrophone streamers will be towed behind the 
                        *Langseth*
                         near the water`s surface. However, we are not aware of any cases of entanglement of mysticetes in seismic survey equipment. No incidents of entanglement of marine mammals with seismic survey gear have been documented in over 54,000 kt (100,000 km) of previous NSF-funded seismic surveys when observers were aboard (
                        *e.g.,*
                         Smultea and Holst 2003; Haley and Koski 2004; Holst 2004; Smultea 
                        *et al.,*
                         2004; Holst 
                        *et al.,*
                         2005a; Haley and Ireland 2006; SIO and NSF 2006b; Hauser 
                        *et al.,*
                         2008; Holst and Smultea 2008). Although entanglement with the streamer is theoretically possible, it has not been documented during tens of thousands of miles of NSF-sponsored seismic cruises or, to our knowledge, during hundreds of thousands of miles of industrial seismic cruises. There are a relative few deployed devices, and no interaction between marine mammals and any such device has been recorded during prior NSF surveys using the devices. There are no meaningful entanglement risks posed by the proposed survey, and entanglement risks are not discussed further in this document. Anticipated Effects on Marine Mammal Habitat *Physical Disturbance*
                        —Sources of seafloor disturbance related to geophysical surveys that may impact marine mammal habitat include placement of anchors, nodes, cables, sensors, or other equipment on or in the seafloor for various activities. Equipment deployed on the seafloor has the potential to cause direct physical damage and could affect bottom-associated fish resources. Placement of equipment, such as the heat flow probe in the seafloor, could damage areas of hard bottom where direct contact with the seafloor occurs and could crush epifauna (organisms that live on the seafloor or surface of other organisms). Damage to unknown or unseen hard bottom could occur, but because of the small area covered by most bottom-founded equipment and the patchy distribution of hard bottom habitat, contact with unknown hard bottom is expected to be rare and impacts minor. Seafloor disturbance in areas of soft bottom can cause loss of small patches of epifauna and infauna due to burial or crushing, and bottom-feeding fishes could be temporarily displaced from feeding areas. Overall, any effects of physical damage to habitat are expected to be minor and temporary. *Effects to Prey*
                        —Marine mammal prey varies by species, season, and location and, for some, is not well documented. Fish react to sounds which are especially strong and/or intermittent low-frequency sounds, and behavioral responses such as flight or avoidance are the most likely effects. However, the reaction of fish to airguns depends on the physiological state of the fish, past exposures, motivation (
                        *e.g.,*
                         feeding, spawning, migration), and other environmental factors. Several studies have demonstrated that airgun sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs (
                        *e.g.,*
                         Fewtrell and McCauley, 2012; Pearson 
                        *et al.,*
                         1992; Skalski 
                        *et al.,*
                         1992; Santulli 
                        *et al.,*
                         1999; Paxton 
                        *et al.,*
                         2017), though the bulk of studies indicate no or slight reaction to noise (
                        *e.g.,*
                         Miller and Cripps, 2013; Dalen and Knutsen, 1987; Pena 
                        *et al.,*
                         2013; Chapman and Hawkins, 1969; Wardle 
                        *et al.,*
                         2001; Sara 
                        *et al.,*
                         2007; Jorgenson and Gyselman, 2009; Blaxter 
                        *et al.,*
                         1981; Cott 
                        *et al.,*
                         2012; Boeger 
                        *et al.,*
                         2006), and that, most commonly, while there are likely to be impacts to fish as a result of noise from nearby airguns, such effects will be temporary. For example, investigators reported significant, short-term declines in commercial fishing catch rate of gadid fishes during and for up to five days after seismic survey operations, but the catch rate subsequently returned to normal (Engas 
                        *et al.,*
                         1996; Engas and Lokkeborg, 2002). Other studies have reported similar findings (Hassel 
                        *et al.,*
                         2004). Skalski 
                        *et al.,*
                         (1992) also found a reduction in catch rates—for rockfish (
                        *Sebastes*
                         spp.) in response to controlled airgun exposure—but suggested that the mechanism underlying the decline was not dispersal but rather decreased responsiveness to baited hooks associated with an alarm behavioral response. A companion study showed that alarm and startle responses were not sustained following the removal of the sound source (Pearson 
                        *et al.,*
                         1992). Therefore, Skalski 
                        *et al.,*
                         (1992) suggested that the effects on fish abundance may be transitory, primarily occurring during the sound exposure itself. In some cases, effects on catch rates are variable within a study, which may be more broadly representative of temporary displacement of fish in response to airgun noise (
                        *i.e.,*
                         catch rates may increase in some locations and decrease in others) than any long-term damage to the fish themselves (Streever 
                        *et al.,*
                         2016). SPLs of sufficient strength have been known to cause injury to fish and fish mortality and, in some studies, fish auditory systems have been damaged by airgun noise (McCauley 
                        *et al.,*
                         2003; Popper 
                        *et al.,*
                         2005; Song 
                        *et al.,*
                         2008). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen 
                        *et al.*
                         (2012b. (2012) showed that a TTS of 4-6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long—both of which are conditions unlikely to occur for this survey that is necessarily transient in any given location and likely result in brief, infrequent noise exposure to prey species in any given area. For this survey, the sound source is constantly moving, and most fish would likely avoid the sound source prior to receiving sound of sufficient intensity to cause physiological or anatomical damage. In addition, ramp-up may 
                        ( print page 37586)
                        allow certain fish species the opportunity to move further away from the sound source. A recent comprehensive review (Carroll 
                        *et al.,*
                         2017) found that results are mixed as to the effects of airgun noise on the prey of marine mammals. While some studies suggest a change in prey distribution and/or a reduction in prey abundance following the use of seismic airguns, others suggest no effects or even positive effects in prey abundance. As one specific example, Paxton 
                        *et al.,*
                         (2017), which describes findings related to the effects of a 2014 seismic survey on a reef off of North Carolina, showed a 78 percent decrease in observed nighttime abundance for certain species. It is important to note that the evening hours during which the decline in fish habitat use was recorded (via video recording) occurred on the same day that the seismic survey passed, and no subsequent data is presented to support an inference that the response was long-lasting. Additionally, given that the finding is based on video images, the lack of recorded fish presence does not support a conclusion that the fish actually moved away from the site or suffered any serious impairment. In summary, this particular study corroborates prior studies indicating that a startle response or short-term displacement should be expected. Available data suggest that cephalopods are capable of sensing the particle motion of sounds and detect low frequencies up to 1-1.5 kHz, depending on the species, and so are likely to detect airgun noise (Kaifu 
                        *et al.,*
                         2008; Hu 
                        *et al.,*
                         2009; Mooney 
                        *et al.,*
                         2010; Samson 
                        *et al.,*
                         2014). Auditory injuries (lesions occurring on the statocyst sensory hair cells) have been reported upon controlled exposure to low-frequency sounds, suggesting that cephalopods are particularly sensitive to low-frequency sound (Andre 
                        *et al.,*
                         2011; Sole 
                        *et al.,*
                         2013). Behavioral responses, such as inking and jetting, have also been reported upon exposure to low-frequency sound (McCauley 
                        *et al.,*
                         2000b; Samson 
                        *et al.,*
                         2014). Similar to fish, however, the transient nature of the survey leads to an expectation that effects will be largely limited to behavioral reactions and would occur as a result of brief, infrequent exposures. With regard to potential impacts on zooplankton, McCauley 
                        *et al.,*
                         (2017) found that exposure to airgun noise resulted in significant depletion for more than half the taxa present and that there were two to three times more dead zooplankton after airgun exposure compared with controls for all taxa, within 1 km of the airguns. However, the authors also stated that in order to have significant impacts on r-selected species (
                        *i.e.,*
                         those with high growth rates and that produce many offspring) such as plankton, the spatial or temporal scale of impact must be large in comparison with the ecosystem concerned, and it is possible that the findings reflect avoidance by zooplankton rather than mortality (McCauley 
                        *et al.,*
                         2017). In addition, the results of this study are inconsistent with a large body of research that generally finds limited spatial and temporal impacts to zooplankton as a result of exposure to airgun noise (
                        *e.g.,*
                         Dalen and Knutsen, 1987; Payne, 2004; Stanley 
                        *et al.,*
                         2011). Most prior research on this topic, which has focused on relatively small spatial scales, has showed minimal effects (
                        *e.g.,*
                         Kostyuchenko, 1973; Booman 
                        *et al.,*
                         1996; Sætre and Ona, 1996; Pearson 
                        *et al.,*
                         1994; Bolle 
                        *et al.,*
                         2012). A modeling exercise was conducted as a follow-up to the McCauley 
                        *et al.*
                         (2017) study (as recommended by McCauley 
                        *et al.,*), in order to assess the potential for impacts on ocean ecosystem dynamics and zooplankton population dynamics (Richardson 
                        *et al.,*
                         2017). Richardson 
                        *et al.,*
                         (2017) found that for copepods with a short life cycle in a high-energy environment, a full-scale airgun survey would impact copepod abundance up to three days following the end of the survey, suggesting that effects such as those found by McCauley 
                        *et al.,*
                         (2017) would not be expected to be detectable downstream of the survey areas, either spatially or temporally. Notably, a recently described study produced results inconsistent with those of McCauley 
                        *et al.,*
                         (2017). Researchers conducted a field and laboratory study to assess if exposure to airgun noise affects mortality, predator escape response, or gene expression of the copepod 
                        *Calanus finmarchicus*
                         (Fields 
                        *et al.,*
                         2019). Immediate mortality of copepods was significantly higher, relative to controls, at distances of 5 m or less from the airguns. Mortality one week after the airgun blast was significantly higher in the copepods placed 10 m from the airgun but was not significantly different from the controls at a distance of 20 m from the airgun. The increase in mortality, relative to controls, did not exceed 30 percent at any distance from the airgun. Moreover, the authors caution that even this higher mortality in the immediate vicinity of the airguns may be more pronounced than what would be observed in free-swimming animals due to increased flow speed of fluid inside bags containing the experimental animals. There were no sublethal effects on the escape performance or the sensory threshold needed to initiate an escape response at any of the distances from the airgun that were tested. Whereas McCauley 
                        *et al.*
                         (2017) reported an SEL of 156 dB at a range of 509-658 m, with zooplankton mortality observed at that range, Fields 
                        *et al.*
                         (2019) reported an SEL of 186 dB at a range of 25 m, with no reported mortality at that distance. Regardless, if we assume a worst-case likelihood of severe impacts to zooplankton within approximately 1 km of the acoustic source, the brief time to regeneration of the potentially affected zooplankton populations does not lead us to expect any meaningful follow-on effects to the prey base for marine mammals. A recent review article concluded that, while laboratory results provide scientific evidence for high-intensity and low-frequency sound-induced physical trauma and other negative effects on some fish and invertebrates, the sound exposure scenarios in some cases are not realistic to those encountered by marine organisms during routine seismic operations (Carroll 
                        *et al.,*
                         2017). The review finds that there has been no evidence of reduced catch or abundance following seismic activities for invertebrates, and that there is conflicting evidence for fish with catch observed to increase, decrease, or remain the same. Further, where there is evidence for decreased catch rates in response to airgun noise, these findings provide no information about the underlying biological cause of catch rate reduction (Carroll 
                        *et al.,*
                         2017). In summary, impacts of the specified activity on marine mammal prey species will likely be limited to behavioral responses, the majority of prey species will be capable of moving out of the area during the survey, a rapid return to normal recruitment, distribution, and behavior for prey species is anticipated, and, overall, impacts to prey species will be minor and temporary. Prey species exposed to sound might move away from the sound source, experience TTS, experience masking of biologically relevant sounds, or show no obvious direct effects. Mortality from decompression injuries is possible in close proximity to a sound, but only limited data on mortality in response to airgun noise exposure are available (Hawkins 
                        *et al.,*
                         2014). The most likely impacts for most prey species in the survey area would be temporary avoidance of the area. The proposed survey would move through an area relatively quickly, limiting exposure to multiple impulsive sounds. In all cases, 
                        ( print page 37587)
                        sound levels would return to ambient once the survey moves out of the area or ends and the noise source is shut down and, when exposure to sound ends, behavioral and/or physiological responses are expected to end relatively quickly (McCauley 
                        *et al.,*
                         2000b). The duration of fish avoidance of a given area after survey effort stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. While the potential for disruption of spawning aggregations or schools of important prey species can be meaningful on a local scale, the mobile and temporary nature of this survey and the likelihood of temporary avoidance behavior suggest that impacts would be minor. *Acoustic Habitat*
                        —Acoustic habitat is the soundscape—which encompasses all of the sound present in a particular location and time, as a whole—when considered from the perspective of the animals experiencing it. Animals produce sound for, or listen for sounds produced by, conspecifics (communication during feeding, mating, and other social activities), other animals (finding prey or avoiding predators), and the physical environment (finding suitable habitats, navigating). Together, sounds made by animals and the geophysical environment (
                        *e.g.,*
                         produced by earthquakes, lightning, wind, rain, waves) make up the natural contributions to the total acoustics of a place. These acoustic conditions, termed acoustic habitat, are one attribute of an animal's total habitat. Soundscapes are also defined by, and acoustic habitat influenced by, the total contribution of anthropogenic sound. This may include incidental emissions from sources such as vessel traffic, or may be intentionally introduced to the marine environment for data acquisition purposes (as in the use of airgun arrays). Anthropogenic noise varies widely in its frequency content, duration, and loudness and these characteristics greatly influence the potential habitat-mediated effects to marine mammals (please see also the previous discussion on masking under “Acoustic Effects”), which may range from local effects for brief periods of time to chronic effects over large areas and for long durations. Depending on the extent of effects to habitat, animals may alter their communications signals (thereby potentially expending additional energy) or miss acoustic cues (either conspecific or adventitious). For more detail on these concepts see, 
                        *e.g.,*
                         Barber 
                        *et al.,*
                         2010; Pijanowski 
                        *et al.,*
                         2011; Francis and Barber, 2013; Lillis 
                        *et al.,*
                         2014. Problems arising from a failure to detect cues are more likely to occur when noise stimuli are chronic and overlap with biologically relevant cues used for communication, orientation, and predator/prey detection (Francis and Barber, 2013). Although the signals emitted by seismic airgun arrays are generally low frequency, they would also likely be of short duration and transient in any given area due to the nature of these surveys. As described previously, exploratory surveys such as these cover a large area but would be transient rather than focused in a given location over time and therefore would not be considered chronic in any given location. Based on the information discussed herein, we conclude that impacts of the specified activity are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to marine mammal habitat are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations. Estimated Take This section provides an estimate of the number of incidental takes proposed for authorization through this IHA, which will inform both NMFS' consideration of “small numbers” and the negligible impact determinations. Harassment is the only type of take expected to result from these activities. Except with respect to certain activities not pertinent here, section 3(18) of the MMPA defines “harassment” as any act of pursuit, torment, or annoyance, which (i) has the potential to injure a marine mammal or marine mammal stock in the wild (Level A harassment); or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering (Level B harassment). Authorized takes would be by Level B harassment only, primarily in the form of behavioral disruption and including through Temporary Threshold Shift (TTS) for low frequency cetaceans resulting from exposure to sound from seismic airguns. TTS is not expected for all other hearing groups and is considered to be unlikely for low frequency cetaceans. Given the small size of the Level A harassment isopleths (28.6 m for LF cetaceans and less than one meter for all other species) and the anticipated effectiveness of the mitigation measures (
                        *i.e.,*
                         shutdown, ramp-up, 
                        *etc.*) discussed in detail below in Proposed Mitigation section, Level A harassment is neither anticipated nor proposed to be authorized. As described previously, no serious injury or mortality is anticipated or proposed to be authorized for this activity. Below we describe how the proposed take numbers are estimated. Generally speaking, we estimate take by considering: (1) Acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and (4) and the number of days of activities. We note that while these basic factors can contribute to a basic calculation to provide an initial prediction of takes, additional information that can qualitatively inform take estimates is also sometimes available (
                        *e.g.,*
                         previous monitoring results or average group size). Below, we describe the factors considered here in more detail and present the proposed take estimate. Acoustic Thresholds NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment). *Level B Harassment*
                        —Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source or exposure context (
                        *e.g.,*
                         frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment (
                        *e.g.,*
                         bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict (
                        *e.g.,*
                         Southall 
                        *et al.,*
                         2007, 2021, Ellison 
                        *et al.,*
                         2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment 
                        ( print page 37588)
                        when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 μPa)) for continuous (
                        *e.g.,*
                         vibratory pile-driving, drilling) and above RMS SPL 160 dB re 1 μPa (rms) for non-explosive impulsive (
                        *e.g.,*
                         seismic airguns) or intermittent (
                        *e.g.,*
                         scientific sonar) sources. L-DEO's proposed survey includes the use of impulsive seismic sources (
                        *e.g.,*
                         GI-airgun) and therefore the 160 dB re 1 μPa (rms) criteria is applicable for analysis of Level B harassment. *Level A harassment*
                        —NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual criteria to assess auditory injury (Level A harassment) to five different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). L-DEO's proposed survey includes the use of impulsive and intermittent sources. For more information, see NMFS' 2018 Technical Guidance, which may be accessed at: 
                        *www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-acoustic-technical-guidance.* Ensonified Area Here, we describe operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss coefficient. The proposed 2D survey would acquire data using a 2 GI-airgun cluster with a total discharge volume of 90 in3
                         at a maximum tow depth of 2-4 m. L-DEO model results are used to determine the 160 dB rms radius for the 2-GI airgun array in deep water (>1000 m) down to a maximum depth of 2000 m, as animals are generally not anticipated to dive below 2000 m (Costa and Williams, 1999). Received sound levels for the two 45 in3
                         GI airguns have been predicted by L-DEO's model (Diebold 
                        *et al.,*
                         2010) as a function of distance from the airguns. This modeling approach uses ray tracing for the direct wave traveling from the array to the receiver and its associated source ghost (reflection at the air-water interface in the vicinity of the array), in a constant-velocity half-space (infinite homogeneous ocean layer, unbounded by a seafloor). In addition, propagation measurements of pulses from a 36-airgun array at a tow depth of 6 m have been reported in deep water (~1600 m), intermediate water depth on the slope (~600-1100 m), and shallow water (~50) in the Gulf of Mexico in 2007-2008 (Tolstoy 
                        *et al.,*
                         2009; Diebold 
                        *et al.,*
                         2010). For deep and intermediate-water cases, the field measurements cannot be used readily to derive mitigation radii, as at those sites the calibration hydrophone was located at a roughly constant depth of 350-500 m, which may not intersect all the sound pressure level (SPL) isopleths at their widest point from the sea surface down to the maximum relevant water depth (~2000 m) for marine mammals. At short ranges, where the direct arrivals dominate and the effects of seafloor interactions are minimal, the data recorded at the deep sites are suitable for comparison with modeled levels at the depth of the calibration hydrophone. At longer ranges, the comparison with the mitigation model—constructed from the maximum SPL through the entire water column at varying distances from the airgun array—is the most relevant. In deep and intermediate-water depths, comparisons at short ranges between sound levels for direct arrivals recorded by the calibration hydrophone and model results for the same array tow depth are in good agreement (Fig. 12 and 14 in Appendix H of L-DEO's PEIS). Consequently, isopleths falling within this domain can be predicted reliably by the L-DEO model, although they may be imperfectly sampled by measurements recorded at a single depth. At greater distances, the calibration data show that seafloor-reflected and sub-seafloor-refracted arrivals dominate, whereas the direct arrivals become weak and/or incoherent. Aside from local topography effects, the region around the critical distance is where the observed levels rise closest to the mitigation model curve. However, the observed sound levels are found to fall almost entirely below the mitigation model curve. Thus, analysis of the Gulf of Mexico calibration measurements demonstrate that although simple, the L-DEO model is a robust tool for conservatively estimating isopleths and the deep water radii obtained from model results down to a maximum water depth of 2000 m. A recent retrospective analysis of acoustic propagation of R/V 
                        *Langseth*
                         sources in a coastal/shelf environment from the Cascadia Margin off Washington suggests that predicted (modeled) radii (using a similar approach) for R/V 
                        *Langseth*
                         sources were 2-3 times larger than measured in shallow water (Crone 
                        *et al.,*
                         2014). Similarly, data collected by Crone 
                        *et al.*
                         (2017) during a survey off New Jersey in 2014 and 2015 confirmed that in situ measurements and estimates of the 160- and 180-dB distances collected by R/V 
                        *Langseth*
                         hydrophone streamer were 2-3 times smaller than the predicted operational mitigation radii. Five separate comparisons conducted of the L-DEO model with in situ received level have confirmed that the L-DEO model generated conservative mitigation zones, resulting in significantly larger zones. The proposed surveys would acquire data with two 45 in3
                         GI funs at a tow depth of 2-4 m. As the entire survey occurs in deep water (>1000 m), L-DEO used the deep-water radii obtained from the model results explained above down to a maximum warter depth of 2000 m (see Figure A-1 in L-DEO's application). The estimated distances to the Level B harassment isopleth for the proposed survey are shown in Table 3. The acoustic propagation modeling methodologies are described in greater detail in L-DEO's IHA application. Table 3—Predicted Radial Distances to Isopleths Corresponding to the Level B Harassment Threshold
[160 dB re 1μPa (rms)]
Airgun configuration
Water depth 
                                 (m)
Predicted 
                                 distances (m) to  
                                 a received sound level  
                                 
                                    of 160 dB re 1 μPa
                                    rmsTwo 45-in3
                                 GI guns
>1,000
553
 
 
 Predicted distances to Level A harassment isopleths, which vary based on marine mammal hearing groups, were calculated based on modeling performed by L-DEO using the PGS Nucleus source modeling software program and the NMFS User Spreadsheet, described below. The acoustic thresholds for impulsive sounds (
                        *e.g.,*
                         airguns) contained in the Technical Guidance were presented as dual metric acoustic thresholds using both SELcum
                         and peak sound pressure metrics (NMFS 2018). As dual metrics, NMFS considers onset of PTS (Level A harassment) to have occurred when either one of the two metrics is exceeded (
                        *i.e.,*
                         metric resulting in the largest isopleth). The SELcum
                         metric considers both level and duration of exposure, as well as auditory weighting functions by marine mammal hearing group. In recognition of the fact that the requirement to calculate Level A harassment ensonified areas could be more technically challenging to predict due to the duration component and the use of weighting functions in the new SELcum
                         thresholds, NMFS developed an optional User Spreadsheet that includes tools to help predict a simple isopleth that can be used in conjunction with marine mammal density or occurrence to facilitate the estimation of take numbers. In order to more realistically incorporate the Technical Guidance's weighting functions over the seismic array's full acoustic band, unweighted spectrum data for the 
                        *Langseth's*
                         airgun array (modeled in 1 Hz bands) was used to make adjustments (dB) to the unweighted spectrum levels, by frequency, according to the weighting functions for each relevant marine mammal hearing group. These adjusted/weighted spectrum levels were then converted to pressures (μPa) in order to integrate them over the entire broadband spectrum, resulting in broadband weight source levels by hearing group that could be directly incorporated within the User Spreadsheet (
                        *i.e.,*
                         to override the Spreadsheet's more simple weighting factor adjustment). Using the User Spreadsheet's “safe distance” methodology for mobile sources (described by Sivle 
                        *et al.,*
                         2014) with the hearing group-specific weighted source levels, and inputs assuming spherical spreading propagation and source velocities (2.32 m/s) and shot intervals (every 2.69 s) specific to the planned survey, potential radial distances to auditory injury zones were then calculated for SELcum
                         thresholds. Outputs from the User Spreadsheet in the form of estimated distance to Level A harassment isopleths for the survey are shown in Table 4. NMFS considers onset of PTS (Level A harassment) to have occurred when either one of the dual metrics (SELcum
                         and Peakflat) is exceeded (
                        *i.e.,*
                         metric resulting in the largest isopleth). Table 4—Modeled Radial Distances (
                            m
                            ) to Isopleths Corresponding to Level A Harassment Thresholds
Source 
                                 (volume)
Level A harassment zones (m)LF
MF
HF
Phocid
OtariidTwo 45 cu in GI guns
28.6
0
0.1
0.3
0
 Note that because of some of the assumptions included in the methods used (
                        *e.g.,*
                         stationary receiver with no vertical or horizontal movement in response to the acoustic source), isopleths produced may be overestimates to some degree, which will ultimately result in some degree of overestimation of Level A harassment. However, these tools offer the best way to predict appropriate isopleths when more sophisticated modeling methods are not available. NMFS continues to develop ways to quantitatively refine these tools and will qualitatively address the output where appropriate. For mobile sources, such as the proposed seismic survey, the User Spreadsheet predicts the closest distance at which a stationary animal would not incur PTS if the sound source traveled by the animal in a straight line at a constant speed. Auditory injury for all species is unlikely to occur given the small modeled zones of injury (estimated zone less than 30 m for low-frequency cetaceans and near zero for all other species). Additionally, animals are expected to have aversive/compensatory behavior in response to the activity (Nachtigall 
                        *et al.,*
                         2018) further limiting the likelihood of auditory injury for all species. L-DEO did not request authorization of take by Level A harassment, and no take by Level A harassment is proposed for authorization by NMFS. Marine Mammal Occurrence In this section we provide information about the occurrence of marine mammals, including density or other relevant information, which will inform the take calculations. The U.S. Navy (USN) primarily use the Southwest Fishery Science Center (SWFSC) habitat-based cetacean density models to develop a marine species density database for the Northwest Training and Testing Study Area, which encompasses the proposed survey area (USN 2019). For species where density spatial modeling was unavailable, other data sources were used. The USN marine species density database is currently the most comprehensive density data set available for the California Current Ecosystem (CCE) which encompasses waters off the coast of California, Oregon, and Washington. However, GIS data layers are currently unavailable for this database; thus, in this analysis the USN data were only used for species for which density data were not available from an alternative spatially-explicit model (
                        *i.e.,*
                         minke, sei, and killer whales, 
                        *Kogia*
                         spp., and pinnipeds). For most pinnipeds, L-DEO used the highest densities for spring, summer, or fall from USN (2019), but corrected the estimates by projecting the most recent population growth/updated population estimates to 2022, when available. This same approach was used by NMFS for previous L-DEO surveys (
                        *e.g,.*
                         Northeast Pacific Ocean Survey (85 FR 19580; April 7, 2020)) in the region in 2021. For California sea lions, spring densities from USN (2019) were used directly, the density for the `40-70 km from shore' distance band was used for the Oregon survey region, and the density for the `70-450 km from shore' distance band was used for other survey regions. For the northern fur seal, the density for the spring for the `up to 70 km from shore' distance band was used for the Oregon survey region, and the spring density for the `>130 km from shore' distance band was used for the other survey regions. For the Guadalupe fur seal and Steller sea lion, summer densities for the `200 m isobath to 300 km from shore' were used. For the gray whale, the summer/fall density for the ‘10-47 km from shore' distance band (USN 2019) was used for the Oregon survey region and 
                        ( print page 37590)
                        a density of zero was used for all other survey regions. For killer whales, the annual density for all stocks occurring offshore was used from USN (2019). Spatially-explicit density data from summer/fall from the NOAA CetSound website (NOAA 2022) were used for most other species (
                        *i.e.,*
                         humpback, blue, fin, sperm, Baird's, beaked, and other small beaked whales; striped, short-beaked common, Pacific white-sided, Risso's, and northern right whale dolphins; and Dall's porpoise. CetMap (
                        *https://cetsound.noaa.gov/​cda)*
                         provides output of summer/fall habitat-based density models for cetaceans in the CCE (Becker 
                        *et al.,*
                         2020) in the form of GIS layers; these were used to calculate takes in the survey area. The density estimates were available in the form of a GIS grid with each cell in the grid measuring ~7 km east-west by 10 km north-south. This grid was intersected with a GIS layer of the area expected to be ensonified to >160 dB SPL from the survey area. North, west, and south boundaries are based on overlap/intersection with geographic extents of all four combined survey regions; eastern grid coverage limit was defined by inclusion of cells that contained >25 percent overlap with the angled boundary of the survey area polygon. The densities from all grid cells overlapping the ensonified areas were averaged to calculate an average species-specific density for each species (Table 5). Table 5—Modeled Marine Mammal Density Values and Daily Ensonified Area for L-DEO's Proposed Survey *
Species
Density 
                                 
                                    (#/km2
                                    )
Daily 
                                 ensonified area  
                                 
                                    (km2
                                    )
Number of 
                                 seismic days
SourceLF Cetaceans:Humpback whale
0.000464
221
6
Becker et al. (2020).*Blue whale*
0.000226
221
6
Becker et al. (2020).*Fin whale*
0.00241
221
6
Becker et al. (2020).*Sei whale*
0.0004
221
6
USN (2019).Minke whale
0.0013
221
6
USN (2019).MF Cetaceans:*Sperm whale*
0.002859
221
6
Becker et al. (2020).Baird's beaked whale
0.000407
221
6
Becker et al. (2020).Small beaked whale
0.002446
221
6
Becker et al. (2020).Striped dolphin
0.002095
221
6
Becker et al. (2020).Short-beaked common dolphin
0.004845
221
6
Becker et al. (2020).Pacific white-sided dolphin
0.059902
221
6
Becker et al. (2020).Northern right-whale dolphin
0.049535
221
6
Becker et al. (2020).Risso's dolphin
0.009917
221
6
Becker et al. (2020).Killer whale
0.00092
221
6
USN (2019).HF Cetaceans:Pygmy/dwarf sperm whale
0.00163
221
6
USN (2019).Dall's porpoise
0.093613
221
6
Becker et al. (2020).Otariid Seals:Northern fur seal
* 0.036115/0.032983
221
6
USN (2019).*Guadalupe fur seal*
0.02945
221
6
USN (2019).California sea lion
* 1.2951/0.0714
221
6
USN (2019).Steller sea lion
0.002573
221
6
USN (2019).Phocid Seal:Northern elephant seal
0.043301
221
6
USN (2019).* Species in this table differ slightly from those included in L-DEO's application as NMFS has determined that their occurrence in the survey area is rare and unlikely to be encountered. For more information, please see the Description of Marine Mammals in the Area of Specified Activity section of this notice.** Two different densities were used depending on water depth/distance from shore.
 Take Estimation Here we describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization. In order to estimate the number of marine mammals predicted to be exposed to sound levels that would result in Level B harassment, radial distances from the airgun array to the predicted isopleth corresponding to the Level B harassment thresholds are calculated, as described above. Those radial distances are then used to calculate the area(s) around the airgun array predicted to be ensonified to sound levels that exceed the Level B harassment threshold. The distance for the 160-dB threshold (based on L-DEO model results) was used to draw a buffer around the area expected to be ensonified (
                        *i.e.,*
                         the survey area). The ensonified areas were then increased by 25 percent to account for potential delays, which is the equivalent to adding 25 percent to the proposed line km to be surveyed. The density for each species in Table 5 were then multiplied by the daily ensonified areas expected to be ensonified, increased by 25 percent, and then multiplied by the number of survey days (6) to estimate the Level B takes. The marine mammals predicted to occur within these respective areas, based on the estimated densities, are assumed to be incidentally taken. Estimated exposures for the proposed survey are shown in Table 6.
                        ( print page 37591) Table 6—Estimated Take by Level B Harassment, and Percentage of Marine Mammal Stock Population
Species
MMPA stock
Estimated take by Level B 
                                 harassment
Take by level B 
                                 harassment  
                                 proposed for  
                                 authorization
Stock 
                                 abundance
Percent of 
                                 MMPA stockHumpback whale a
California/Oregon Washington
1
d
                                 2
4,973
0.04Blue whale
Eastern North Pacific
0
d
                                 2
1,898
0.11Fin whale
California/Oregon Washington
4
4
11,065
0.04Sei whale
Eastern North Pacific
1
d
                                 2
519
0.39Minke whale
California/Oregon Washington
2
2
915
0.22Sperm whale
California/Oregon Washington
5
d
                                 7
1,997
0.35Baird's beaked whale
California/Oregon Washington
1
d
                                 9
1,363
0.66Small beaked whale b
California/Oregon Washington
4
4
3,044
0.13Striped dolphin
California/Oregon Washington
3
d
                                 46
29,988
0.15Common dolphin
California/Oregon Washington
8
d
                                 179
1,056,308
0.02Pacific white-sided dolphin
California/Oregon Washington
99
99
34,998
0.28Northern right-whale dolphin
California/Oregon Washington
82
82
29,285
0.28Risso's dolphin
California/Oregon Washington
16
d
                                 22
6,336
0.35Killer whale
West Coast Transient
2
d
                                 7
349
0.00North Pacific Offshore


300
0.00Pygmy/dwarf sperm whale
California/Oregon Washington
3
3
4,111
0.07Dall's porpoise
California/Oregon Washington
155
155
16,498
0.94Northern fur seal c
Eastern Pacific
17
17
626,618
0.00California


530,376
0.00Guadalupe fur seal
Mexico
49
49
34,187
0.14California sea lion
United States
9
9
257,606
0.00Steller sea lion
Eastern
4
4
43,201
0.01Northern elephant seal
California Breeding
62
62
5,122
1.21a
                             Takes are allocated among the three DPSs in the area based on Wade 2021 (Oregon: 42 percent Central America DPS, 58 percent Mexico DPS; Washington: 6 percent Central America DPS, 25 percent Mexico DPS, 69 percent Hawaii DPS).b
                             Proposed takes include one each of Blainville's beaked whale, Stejneger's beaked whale, Cuvier's beaked whale, and Hubbs' beaked whale (see Appendix B of L-DEO's application for more information).c
                             In cases where multiple stocks are being affected, for the purposes of calculating the percentage of the stock impacted, the take is being analyzed as if all proposed takes occurred within each stock.d
                             Proposed take increased to mean group size from Barlow (2016).
 Proposed Mitigation In order to issue an IHA under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking pursuant to the activity, and other means of effecting the least practicable impact on the species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stock for taking for certain subsistence uses (latter not applicable for this action). NMFS regulations require applicants for incidental take authorizations to include information about the availability and feasibility (economic and technological) of equipment, methods, and manner of conducting the activity or other means of effecting the least practicable adverse impact upon the affected species or stocks, and their habitat (50 CFR 216.104(a)(11)). In evaluating how mitigation may or may not be appropriate to ensure the least practicable adverse impact on species or stocks and their habitat, as well as subsistence uses where applicable, NMFS considers two primary factors: (1) The manner in which, and the degree to which, the successful implementation of the measure(s) is expected to reduce impacts to marine mammals, marine mammal species or stocks, and their habitat. This considers the nature of the potential adverse impact being mitigated (likelihood, scope, range). It further considers the likelihood that the measure will be effective if implemented (probability of accomplishing the mitigating result if implemented as planned), the likelihood of effective implementation (probability implemented as planned), and; (2) The practicability of the measures for applicant implementation, which may consider such things as cost, impact on operations. L-DEO reviewed mitigation measures employed during seismic research surveys authorized by NMFS under previous incidental harassment authorizations, as well as recommended best practices in Richardson 
                        *et al.*
                         (1995), Pierson 
                        *et al.*
                         (1998), Weir and Dolman (2007), Nowacek 
                        *et al.*
                         (2013), Wright (2014), and Wright and Cosentino (2015), and has proposed mitigation measures based on the above sources. To reduce the potential for disturbance from acoustic stimuli associated with the activities, L-DEO proposed to implement mitigation measures for marine mammals. Mitigation measures that would be adopted during the planned survey include, but are not limited to: (1) Vessel speed or course alteration, provided that doing so would not compromise operation safety requirements. (2) GI-airgun shut down within EZs, and (3) ramp-up procedures. Vessel-Based Visual Mitigation Monitoring Visual monitoring requires the use of trained observers (herein referred to as visual protected species observers (PSOs)) to scan the ocean surface visually for the presence of marine mammals. The area to be scanned visually includes primarily the exclusion zone, within which observation of certain marine mammals requires shutdown of the acoustic source, but also the buffer zone. The buffer zone means an area beyond the exclusion zone to be monitored for the presence of marine mammals that may enter the exclusion zone. During pre-start clearance (
                        *i.e.,*
                         before ramp-up begins), the buffer zone also acts as an extension of the exclusion zone in that observations of marine mammals within the buffer zone would also prevent 
                        ( print page 37592)
                        airgun operations from beginning (
                        *i.e.,*
                         ramp-up). The buffer zone encompasses the area at and below the sea surface from the edge of the 100 m exclusion zone measured from the edges of the airgun array. Visual monitoring of the exclusion zone and adjacent waters is intended to establish and, when visual conditions allow, maintain zones around the sound source that are clear of marine mammals, thereby reducing or eliminating the potential for injury and minimizing the potential for more severe behavioral reactions for animals occurring closer to the vessel. Visual monitoring of the buffer zone is intended to (1) provide additional protection to naïve marine mammals that may be in the area during pre-clearance, and (2) during airgun use, aid in establishing and maintaining the exclusion zone by altering the visual observer and crew of marine mammals that are outside of, but may approach and enter, the exclusion zone. L-DEO must use independent, dedicated, trained visual PSOs, meaning that the PSOs must be employed by a third-party observer provider, must not have tasks other than to conduct observational effort, collect data, and communicate with and instruct relevant vessel crew with regard to the presence of protected species and mitigation requirements, and must have successfully completed an approved PSO training course. PSO resumes shall be provided to NMFS for approval. At least one visual PSO must have a minimum of 90 days at-sea experience working in that role during a shallow penetration or low-energy survey, with no more than 18 months elapsed since the conclusion of the at-sea experience. One PSO with such experience shall be designated as the lead for the entire protected species observation team. The lead PSO shall serve as primary point of contact for the vessel operator and ensure all PSO requirements per the IHA are met. To the maximum extent practicable, the experienced PSOs should be scheduled to be on duty with those PSOs with the appropriate training but who have not yet gained relevant experience. During survey operations (
                        *e.g.,*
                         any day on which use of the acoustic source is planned to occur, and whenever the acoustic source is in the water, whether activated or not), a minimum of two PSOs must be on duty and conducting visual observations at all times during daylight hours (
                        *i.e.,*
                         from 30 minutes prior to sunrise through 30 minutes following sunset) and 30 minutes prior to and during ramp-up of the airgun array. Visual monitoring of the exclusion and buffer zones must begin no less than 30 minutes prior to ramp-up and must continue until one hour after use of the acoustic source ceases or until 30 minutes past sunset. Visual PSOs must coordinate to ensure 360 degree visual coverage around the vessel from the most appropriate observation posts, and must conduct visual observations using binoculars and the naked eye while free from distractions and in a consistent, systematic, and diligent manner. PSOs shall establish and monitor the exclusion and buffer zones. These zones shall be based upon the radial distance from the edges of the acoustic source (rather than being based on the center of the array or around the vessel itself). During use of the acoustic source (
                        *i.e.,*
                         anytime airguns are active, including ramp-up) shall be communicated to the operator to prepare for the potential shutdown of the acoustic source. During use of the airgun, detections of marine mammals within the buffer zone (but outside the exclusion zone) should be communicated to the operator to prepare for the potential shutdown of the acoustic source. Visual PSOs will immediately communicate all observations to the on duty acoustic PSO(s), including any determination by the PSO regarding species identification, distance, and bearing and the degree of confidence in the determination. Any observations of marine mammals by crew members shall be relayed to the PSO team. During good conditions (
                        *e.g.,*
                         daylight hours; Beaufort sea state (BSS) 3 or less), visual PSOs shall conduct observations when the acoustic source is not operating for comparison of sightings rates and behavior with and without use of the acoustic source and between acquisition periods, to the maximum extent practicable. Visual PSOs may be on watch for a maximum of four consecutive hours followed by a break of at least one hour between watches and may conduct a maximum of 12 hours of observation per 24-hour period. Establishment of Exclusion and Buffer Zones An exclusion zone (EZ) is a defined area within which occurrence of a marine mammal triggers mitigation action intended to reduce the potential for certain outcome, 
                        *e.g.,*
                         auditory injury, disruption of critical behaviors. The PSOs would establish a minimum EZ with a 100 m radius with an additional 100 m buffer zone (total of 200 m). The 200m zone would be based on radial distance from the edge of the airgun array (rather than being based on the center of the array or around the vessel itself). With certain exceptions (described below), if a marine mammal appears within or enters this zone, the acoustic source would be shut down. The 100 m EZ, with additional 100 m buffer zone, is intended to be precautionary in the sense that it would be expected to contain sound exceeding the injury criteria for all cetacean hearing groups, (based on the dual criteria of SELcum
                         and peak SPL), while also providing a consistent, reasonably observable zone within which PSOs would typically be able to conduct effective observational effort. Additionally, a 100 m EZ is expected to minimize the likelihood that marine mammals will be exposed to levels likely to result in more severe behavioral responses. Although significantly greater distances may be observed from an elevated platform under good conditions, we believe that 100 m is regularly attainable for PSOs using the naked eye during typical conditions. An extended 500 m exclusion zone must be established for all beaked whales, dwarf and pygmy sperm whales, killer whales, a large whale with a calf, and groups of six or more large whales during all survey effort. No buffer zone is required. Pre-Clearance and Ramp-Up Ramp-up (sometimes referred to as “soft start”) is the gradual and systematic increase of emitted sound levels from an airgun array. Ramp-up would begin with one GI airgun 45 cu in first being activated, followed by the second after 5 minutes. The intent of pre-clearance observation (30 minutes) is to ensure no marine mammals are observed within the buffer zone prior to the beginning of ramp-up. During pre-clearance is the only time observations of marine mammals in the buffer zone would prevent operations (
                        *i.e.,*
                         the beginning of ramp-up). The intent of ramp-up is to warn protected species of pending seismic operations and to allow sufficient time for those animals to leave the immediate vicinity. A ramp-up procedure, involving a step-wise increase in the number of airguns are activated and the full volume is achieve, is required at all times as part of the activation of the acoustic source. All operators must adhere to the following pre-clearance and ramp-up requirements: The operator must notify a designated PSO of the planned start of ramp-up as agreed upon with the lead PSO; the notification time should not be less than 60 minutes prior to the planned ramp-up in order to allow PSOs time to monitor the exclusion and buffer( print page 37593)
                        zones for 30 minutes prior to the initiation of ramp-up (pre-clearance);
                    Ramp-ups shall be scheduled so as to minimize the time spent with the source activated prior to reaching the designated run-in;
                    One of the PSOs conducting pre-clearance observations must be notified again immediately prior to initiating ramp-up procedures and the operator must receive confirmation from the PSO to proceed;
                    Ramp-up may not be initiated if any marine mammal is within the applicable exclusion or buffer zone. If a marine mammal is observed within the applicable exclusion zone or the buffer zone during the 30 minutes pre-clearance period, ramp-up may not begin until the animal(s) has been observed exiting the zones or until an additional time period has elapsed with no further sightings (15 minutes for small odontocetes and pinnipeds, and 30 minutes for Mysticetes and all other odontocetes, including sperm whales, pygmy sperm whales, dwarf sperm whales, beaked whales, pilot whales, killer whales, Risso's dolphin);
                    PSOs must monitor the exclusion and buffer zones during ramp-up, and ramp-up must cease and the source must be shut down upon detection of a marine mammal within the applicable exclusion zone. Once ramp-up has begun, detections of marine mammals within the buffer zone do not require shutdown, but such observation shall be communicated to the operator to prepare for the potential shutdown.
                    If the acoustic source is shut down for brief periods (*i.e.,*
                         less than 30 minutes) for reasons other than that described for shutdown (
                        *e.g.,*
                         mechanical difficulty), it may be activated again without ramp-up if PSOs have maintained constant observation and no detections of marine mammals have occurred within the applicable exclusion zone. For any longer shutdown, pre-start clearance observation and ramp-up are required. For any shutdown at night or in periods of poor visibility (
                        *e.g.,*
                         BSS 4 or greater), ramp-up is required, but if the shutdown period was brief and constant observation was maintained, pre-start clearance watch is not required.
                    Testing of the acoustic source involving all elements requires ramp-up. Testing limited to individual source elements or strings does not require ramp-up but does require pre-start clearance watch. Shutdown The shutdown of an airgun array requires the immediate de-activation of all individual airgun elements of the array. Any PSO on duty will have the authority to delay the start of survey operations or to call for shutdown of the acoustic source if a marine mammal is detected within the applicable exclusion zone. The operator must also establish and maintain clear lines of communication directly between PSOs on duty and crew controlling the acoustic source to ensure that shutdown commands are conveyed swiftly while allowing PSOs to maintain watch. When both visual and acoustic PSOs are on duty, all detections will be immediately communicated to the remainder of the on-duty PSO team for potential verification of visual observations by the acoustic PSO or of acoustic detections by visual PSOs. When the airgun array is active (
                        *i.e.,*
                         anytime one or more airguns is active, including during ramp-up) and (1) a marine mammal appears within or enters the applicable exclusion zone and/or (2) a marine mammal (other than delphinids, see below) is detected acoustically and localized within the applicable exclusion zone, the acoustic source will be shut down. When shutdown is called for by a PSO, the acoustic source will be immediately deactivated and any dispute resolved only following deactivation. Following a shutdown, airgun activity would not resume until the marine mammal has clear the EZ. The animal would be considered to have cleared the EZ if it is visually observed to have departed the EZ, or it has not been seen within the EZ for 15 minutes in the case of small odontocetes and pinnipeds, and 30 minutes for Mysticetes and all other odontocetes, including sperm whales, beaked whales, pilot whales, killer whales, and Risso's dolphin) with no further observation of the marine mammal(s). The shutdown requirement can be waived for small dolphins if an individual is visually detected and localized within an exclusion zone. As defined here, the small dolphin group is intended to encompass those members of the Family Delphinidae most likely to voluntarily approach the source vessel for purposes of interacting with the vessel and/or airgun array (
                        *e.g.,*
                         bow riding). This exception to the shutdown requirement applies solely to specific genera of small dolphins-
                        *Delphinus, Stenella,*
                         and 
                        *Lissodelphis.* We propose this small dolphin exception because shutdown requirements for small dolphins under all circumstances represent practicability concerns without likely commensurate benefits for the animals in question. Small dolphins are generally the most commonly observed marine mammals in the specific geographic region and would typically be the only marine mammals likely to intentionally approach the vessel. As described above, auditory injury is extremely unlikely to occur for mid-frequency cetaceans (
                        *e.g.,*
                         delphinids), as this group is relatively insensitive to sound produced at the predominant frequencies in an airgun pulse while also having a relatively high threshold for the onset of auditory injury 
                        *(i.e.,*
                         permanent threshold shift). A large body of anecdotal evidence indicates that small dolphins commonly approach vessels and/or towed arrays during active sound production for purposes of bow riding, with no apparent effect observed in those delphinids (
                        *e.g.,*
                         Barkaszi 
                        *et al.,*
                         2012). The potential for increased shutdowns resulting from such a measure would require the 
                        *Langseth*
                         to revisit the missed track line to reacquire data, resulting in an overall increase in the total sound energy input to the marine environment and an increase in the total duration over which the survey is active in a given area. Although other mid-frequency hearing specialists (
                        *e.g.,*
                         large delphinids) are no more likely to incur auditory injury than are small dolphins, they are much less likely to approach vessels. Therefore, retaining a shutdown requirement for large delphinids would not have similar impacts in terms of either practicability for the applicant or corollary increase in sound energy output and time on the water. We do anticipate some benefit for a shutdown requirement for large delphinids in that it simplifies somewhat the total range of decision-making for PSOs and may preclude any potential for physiological effects other than to the auditory system as well as some more severe behavioral reactions for any such animals in close proximity to the source vessel. Visual PSOs shall use best professional judgment in making the decision to call for a shutdown if there is uncertainty regarding identification (
                        *i.e.,*
                         whether the observed marine mammal(s) belongs to one of the delphinid genera for which shutdown is waived or one of the species with a larger exclusion zone). Upon implementation of shutdown, the source may be reactivated after the marine mammal(s) has been observed exiting the applicable exclusion zone (
                        *i.e.,*
                         animal is not required to fully exit the buffer zone where applicable) or following a clearance period (15 minutes for small odontocetes and pinnipeds, and 30 minutes for mysticetes and all other odontocetes, including sperm whales, beaked whales, pilot whales, killer whales, and Risso's 
                        ( print page 37594)
                        dolphin) with no further observation of the marine mammal(s). L-DEO must implement shutdown if a marine mammal species for which take was not authorized, or a species for which authorization was granted but the takes have been met, approaches the Level B harassment zones. Vessel Strike Avoidance These measures apply to all vessels associated with the planned survey activity; however, we note that these requirements do not apply in any case where compliance would create an imminent and serious threat to a person or vessel or to the extent that a vessel is restricted in its ability to maneuver and, because of the restriction, cannot comply. These measures include the following: 1. Vessel operators and crews must maintain a vigilant watch for all marine mammals and slow down, stop their vessel, or alter course, as appropriate and regardless of vessel size, to avoid striking any marine mammal. A single marine mammal at the surface may indicate the presence of submerged animals in the vicinity of the vessel; therefore, precautionary measures should be exercised when an animal is observed. A visual observer aboard the vessel must monitor a vessel strike avoidance zone around the vessel (specific distances detailed below), to ensure the potential for strike is minimized. Visual observers monitoring the vessel strike avoidance zone can be either third-party observers or crew members, but crew members responsible for these duties must be provided sufficient training to distinguish marine mammals from other phenomena and broadly to identify a marine mammal to broad taxonomic group (
                        *i.e.,*
                         as a large whale or other marine mammal); 2. Vessel speeds must be reduced to 10 kn or less when mother/calf pairs, pods, or large assemblages of any marine mammal are observed near a vessel; 3. All vessels must maintain a minimum separation distance of 100 m from large whales (
                        *i.e.,*
                         sperm whales and all mysticetes); 4. All vessels must attempt to maintain a minimum separation distance of 50 m from all other marine mammals, with an exception made for those animals that approach the vessel; and 5. When marine mammals are sighted while a vessel is underway, the vessel should take action as necessary to avoid violating the relevant separation distance (
                        *e.g.,*
                         attempt to remain parallel to the animal's course, avoid excessive speed or abrupt changes in direction until the animal has left the area). If marine mammals are sighted within the relevant separation distance, the vessel should reduce speed and shift the engine to neutral, not engaging the engines until animals are clear of the area. This recommendation does not apply to any vessel towing gear. Based on our evaluation of the applicant's proposed measures, NMFS has preliminarily determined that the proposed mitigation measures provide the means of effecting the least practicable impact on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance. Proposed Monitoring and Reporting In order to issue an IHA for an activity, section 101(a)(5)(D) of the MMPA states that NMFS must set forth requirements pertaining to the monitoring and reporting of such taking. The MMPA implementing regulations at 50 CFR 216.104(a)(13) indicate that requests for authorizations must include the suggested means of accomplishing the necessary monitoring and reporting that will result in increased knowledge of the species and of the level of taking or impacts on populations of marine mammals that are expected to be present while conducting the activities. Effective reporting is critical both to compliance as well as ensuring that the most value is obtained from the required monitoring. Monitoring and reporting requirements prescribed by NMFS should contribute to improved understanding of one or more of the following: Occurrence of marine mammal species or stocks in the area in which take is anticipated (*e.g.,*
                         presence, abundance, distribution, density);
                    Nature, scope, or context of likely marine mammal exposure to potential stressors/impacts (individual or cumulative, acute or chronic), through better understanding of: (1) action or environment (*e.g.,*
                         source characterization, propagation, ambient noise); (2) affected species (
                        *e.g.,*
                         life history, dive patterns); (3) co-occurrence of marine mammal species with the action; or (4) biological or behavioral context of exposure (
                        *e.g.,*
                         age, calving or feeding areas);
                    Individual marine mammal responses (behavioral or physiological) to acoustic stressors (acute, chronic, or cumulative), other stressors, or cumulative impacts from multiple stressors;
                    How anticipated responses to stressors impact either: (1) long-term fitness and survival of individual marine mammals; or (2) populations, species, or stocks;
                    Effects on marine mammal habitat (*e.g.,*
                         marine mammal prey species, acoustic habitat, or other important physical components of marine mammal habitat); and,
                    Mitigation and monitoring effectiveness. Vessel-Based Visual Monitoring As described above, PSO observations would take place during daytime airgun operations. During seismic operations, at least three visual PSO would be based aboard the 
                        *Langseth.*
                         Two visual PSOs would be on duty at all time during daytime hours. Monitoring shall be conducted in accordance with the following requirements: PSOs shall be independent, dedicated and trained and must be employed by a third-party observer provider;
                    PSOs shall have no tasks other than to conduct visual observational effort, collect data, and communicate with and instruct relevant vessel crew with regard to the presence of protected species and mitigation requirements (including brief alerts regarding maritime hazards);
                    PSOs shall have successfully completed an approved PSO training course appropriate for their designated task (visual or acoustic);
                    NMFS must review and approve PSO resumes accompanied by a relevant training course information packet that includes the name and qualifications (*i.e.,*
                         experience, training completed, or educational background) of the instructor(s), the course outline or syllabus, and course reference material as well as a document stating successful completion of the course;
                    NMFS shall have one week to approve PSOs from the time that the necessary information is submitted, after which PSOs meeting the minimum requirements shall automatically be considered approved;
                    PSOs must successfully complete relevant training, including completion of all required coursework and passing (80 percent or greater) a written and/or oral examination developed for the training program;
                    PSOs must have successfully attained a bachelor's degree from an accredited college or university with a major in one of the natural sciences, a minimum of 30 semester hours or equivalent in the biological sciences, and at least one undergraduate course in math or statistics; and( print page 37595)
                    The educational requirements may be waived if the PSO has acquired the relevant skills through alternate experience. Requests for such a waiver shall be submitted to NMFS and must include written justification. Requests shall be granted or denied (with justification) by NMFS within one week of receipt of submitted information. Alternate experience that may be considered includes, but is not limited to (1) secondary education and/or experience comparable to PSO duties; (2) previous work experience conducting academic, commercial, or government-sponsored protected species surveys; or (3) previous work experience as a PSO; the PSO should demonstrate good standing and consistently good performance of PSO duties. PSOs must use standardized data collection forms, whether hard copy or electronic. PSOs must record detailed information about any implementation of mitigation requirements, including the distance of animals to the acoustic source and description of specific actions that ensued, the behavior of the animal(s), any observed changes in behavior before and after implementation of mitigation, and if shutdown was implemented, the length of time before any subsequent ramp-up of the acoustic source. If required mitigation was not implemented, PSOs should record a description of the circumstances. At a minimum, the following information must be recorded: Vessel name and call sign;
                    PSO names and affiliations;
                    Date and participants of PSO briefings (as discussed in General Requirement);
                    Dates of departure and return to port with port name;
                    Dates and times (Greenwich Mean Time) of survey effort and times corresponding with PSO effort;
                    Vessel location (latitude/longitude) when survey effort began and ended and vessel location at beginning and end of visual PSO duty shifts;
                    Vessel heading and speed at beginning and end of visual PSO duty shifts and upon any line change;
                    Environmental conditions while on visual survey (at beginning and end of PSO shift and whenever conditions changed significantly), including BSS and any other relevant weather conditions including cloud cover, fog, sun glare, and overall visibility to the horizon;
                    Factors that may have contributed to impaired observations during each PSO shift change or as needed as environmental conditions changed (*e.g.,*
                         vessel traffic, equipment malfunctions); and
                    Survey activity information, such as acoustic source power output while in operation, number and volume of airguns operating in the array, tow depth of the array, and any other notes of significance (*i.e.,*
                         pre-start clearance, ramp-up, shutdown, testing, shooting, ramp-up completion, end of operations, streamers, 
                        *etc.*). The following information should be recorded upon visual observation of any marine mammal: Watch status (sighting made by PSO on/off effort, opportunistic, crew, alternate vessel/platform);
                    PSO who sighted the animal;
                    Time of sighting;
                    Vessel location at time of sighting;
                    Water depth;
                    Direction of vessel's travel (compass direction);
                    Direction of animal's travel relative to the vessel;
                    Pace of the animal;
                    Estimated distance to the animal and its heading relative to vessel at initial sighting;
                    Identification of the animal (*e.g.,*
                         genus/species, lowest possible taxonomic level, or unidentified) and the composition of the group if there is a mix of species;
                    Estimated number of animals (high/low/best);
                    Estimated number of animals by cohort (adults, yearlings, juveniles, calves, group composition,*etc.*);
                    Description (as many distinguishing features as possible of each individual seen, including length, shape, color, pattern, scars or markings, shape and size of dorsal fin, shape of head, and blow characteristics);
                    Detailed behavior observations (*e.g.,*
                         number of blows/breaths, number of surfaces, breaching, spyhopping, diving, feeding, traveling; as explicit and detailed as possible; note any observed changes in behavior);
                    Animal's closest point of approach (CPA) and/or closest distance from any element of the acoustic source;
                    Platform activity at time of sighting (*e.g.,*
                         deploying, recovering, testing, shooting, data acquisition, other); and
                    Description of any actions implemented in response to the sighting (*e.g.,*
                         delays, shutdown, ramp-up) and time and location of the action. Reporting L-DEO must submit a draft comprehensive report to NMFS on all activities and monitoring results within 90 days of the completion of the survey or expiration of the IHA, whichever comes sooner. A final report must be submitted within 30 days following resolution of any comments on the draft report. The report would describe the operations that were conducted and sightings of marine mammals near the operations. The report would provide full documentation of methods, results, and interpretation pertaining to all monitoring. The 90-day report would summarize the dates and locations of seismic operations, and all marine mammal sightings (dates, times, locations, activities, associated seismic survey activities). The report would also include estimates of the number and nature of exposures that occurred above the harassment threshold based on PSO observations and including an estimate of those that were not detected, in consideration of both the characteristics and behaviors of the species of marine mammals that affect detectability, as well as the environmental factors that affect detectability. The draft report shall also include geo-referenced time-stamped vessel tracklines for all time periods during which airguns were operating. Tracklines should include points recording any change in airgun status (
                        *e.g.,*
                         when the airguns began operating, when they were turned off, or when they changed from full array to single gun or vice versa). GIS files shall be provided in ESRI shapefile format and include the UTC date and time, latitude in decimal degrees, and longitude in decimal degrees. All coordinates shall be referenced to the WGS84 geographic coordinate system. In addition to the report, all raw observational data shall be made available to NMFS. The report must summarize the information submitted in interim monthly reports as well as additional data collected as described above and in the IHA. A final report must be submitted within 30 days following resolution of any comments on the draft report. Reporting Injured or Dead Marine Mammals Discovery of injured or dead marine mammals—In the event that personnel involved in survey activities covered by the authorization discover an injured or dead marine mammal, the L-DEO shall report the incident to the Office of Protected Resources (OPR), NMFS and to the NMFS West Coast Regional Stranding Coordinator as soon as feasible. The report must include the following information: Time, date, and location (latitude/longitude) of the first discovery (and updated location information if known and applicable);
                    Species identification (if known) or description of the animal(s) involved;( print page 37596)
                    Condition of the animal(s) (including carcass condition if the animal is dead);
                    Observed behaviors of the animal(s), if alive;
                    If available, photographs or video footage of the animal(s); and
                    General circumstances under which the animal was discovered. Vessel strike—In the event of a ship strike of a marine mammal by any vessel involved in the activities covered by the authorization, L-DEO shall report the incident to OPR, NMFS and to the NMFS West Coast Regional Stranding Coordinator as soon as feasible. The report must include the following information: Time, date, and location (latitude/longitude) of the incident;
                    Vessel's speed during and leading up to the incident;
                    Vessel's course/heading and what operations were being conducted (if applicable);
                    Status of all sound sources in use;
                    Description of avoidance measures/requirements that were in place at the time of the strike and what additional measure were taken, if any, to avoid strike;
                    Environmental conditions (*e.g.,*
                         wind speed and direction, Beaufort sea state, cloud cover, visibility) immediately preceding the strike;
                    Species identification (if known) or description of the animal(s) involved;
                    Estimated size and length of the animal that was struck;
                    Description of the behavior of the animal immediately preceding and following the strike;
                    If available, description of the presence and behavior of any other marine mammals present immediately preceding the strike;
                    Estimated fate of the animal (*e.g.,*
                         dead, injured but alive, injured and moving, blood or tissue observed in the water, status unknown, disappeared); and
                    To the extent practicable, photographs or video footage of the animal(s). Actions To Minimize Additional Harm to Live-Stranded (or Milling) Marine Mammals In the event of a live stranding (or near-shore atypical milling) event within 50 km of the survey operations, where the NMFS stranding network is engaged in herding or other interventions to return animals to the water, the Director of OPR, NMFS (or designee) will advise L-DEO of the need to implement shutdown procedures for all active acoustic sources operating within 50 km of the stranding. Shutdown procedures for live stranding or milling marine mammals include the following: If at any time, the marine mammal the marine mammal(s) die or are euthanized, or if herding/intervention efforts are stopped, the Director of OPR, NMFS (or designee) will advise the IHA-holder that the shutdown around the animals' location is no longer needed. Otherwise, shutdown procedures will remain in effect until the Director of OPR, NMFS (or designee) determines and advises L-DEO that all live animals involved have left the area (either of their own volition or following an intervention). If further observations of the marine mammals indicate the potential for re-stranding, additional coordination with the IHA-holder will be required to determine what measures are necessary to minimize that likelihood (
                        *e.g.,*
                         extending the shutdown or moving operations farther away) and to implement those measures as appropriate. Additional Information Requests—if NMFS determines that the circumstances of any marine mammal stranding found in the vicinity of the activity suggest investigation of the association with survey activities is warranted, and an investigation into the stranding is being pursued, NMFS will submit a written request to L-DEO indicating that the following initial available information must be provided as soon as possible, but no later than 7 business days after the request for information: Status of all sound source use in the 48 hours preceding the estimated time of stranding and within 50 km of the discovery/notification of the stranding by NMFS; and
                    If available, description of the behavior of any marine mammal(s) observed preceding (*i.e.,*
                         within 48 hours and 50 km) and immediately after the discovery of the stranding. In the event that the investigation is still inconclusive, the investigation of the association of the survey activities is still warranted, and the investigation is still being pursued, NMFS may provide additional information requests, in writing, regarding the nature and location of survey operations prior to the time period above. Reporting Species of Concern To support NMFS's goal of improving our understanding of occurrence of marine mammal species or stocks in the area (
                        *e.g.,*
                         presence, abundance, distribution, density), L-DEO will immediately report observations of Southern Resident killer whales or North Pacific right whales to OPR, NMFS. Although, the likelihood of encountering either species is considered to be rare and unexpected. Negligible Impact Analysis and Determination NMFS has defined negligible impact as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival (50 CFR 216.103). A negligible impact finding is based on the lack of likely adverse effects on annual rates of recruitment or survival (
                        *i.e.,*
                         population-level effects). An estimate of the number of takes alone is not enough information on which to base an impact determination. In addition to considering estimates of the number of marine mammals that might be “taken” through harassment, NMFS considers other factors, such as the likely nature of any impacts or responses (
                        *e.g.,*
                         intensity, duration), the context of any impacts or responses (
                        *e.g.,*
                         critical reproductive time or location, foraging impacts affecting energetics), as well as effects on habitat, and the likely effectiveness of the mitigation. We also assess the number, intensity, and context of estimated takes by evaluating this information relative to population status. Consistent with the 1989 preamble for NMFS' implementing regulations (54 FR 40338; September 29, 1989), the impacts from other past and ongoing anthropogenic activities are incorporated into this analysis via their impacts on the baseline (
                        *e.g.,*
                         as reflected in the regulatory status of the species, population size and growth rate where known, ongoing sources of human-caused mortality, or ambient noise levels). To avoid repetition, the discussion of our analysis applies to all the species listed in Table 6, given that the anticipated effects of this activity on these different marine mammal stocks are expected to be similar, except where a species- or stock-specific discussion is warranted. NMFS does not anticipate that serious injury or mortality would occur as a result from low-energy surveys, even in the absence of mitigation, and no serious injury or mortality is proposed to be authorized. As discussed in the Potential Effects of Specified Activities on Marine Mammals and their Habitat section, non-auditory physical effects and vessel strike are not expected to occur. NMFS expects that all potential take would be in the form of Level B behavioral harassment in the form of temporary avoidance of the area or decreased 
                        ( print page 37597)
                        foraging (if such activity was occurring), responses that are considered to be of low severity, and with no lasting biological consequences (
                        *e.g.,*
                         Southall 
                        *et al.,*
                         2007, 2021). TTS is not expect for most hearing groups (HF, MF, otariids and phocids) and is considered to be highly unlikely for LF cetaceans. Even repeated Level B harassment of some small subset of an overall stock is unlikely to result in any significant realized decrease in viability for the affected individuals, and thus would not result in any adverse impact to the stock as a whole. As described above, Level A harassment is not expected to occur given the estimated small size of the Level A harassment zones. In addition to being temporary, the maximum expected Level B harassment zone around the survey vessel is 553 m. Therefore, the ensonified area surrounding the vessel is relatively small compared to the overall distribution of animals in the area and their use of the habitat. Feeding behavior is not likely to be significantly impacted as prey species are mobile and are broadly distributed throughout the survey area; therefore, marine mammals that may be temporarily displaced during survey activities are expected to be able to resume foraging once they have moved away from areas with disturbing levels of underwater noise. Because of the short duration (6 days) and temporary nature of the disturbance and the availability of similar habitat and resources in the surrounding area, the impacts to marine mammals and the food sources that they utilize are not expected to cause significant or long-term consequences for individual marine mammals or their populations. The entire U.S. West Coast within 47 km of the coast is a BIA for migrating gray whale potential presence January to July and October to December. The BIA for northbound gray whale migration is broken into two phases, Phase A (within 8 km of shore) and Phase B (within 5 km of shore), which are active from January to July and March to July, respectively. The BIA for southbound migration includes waters within 10 km of shore and is active from October to March. All planned survey areas are outside of all gray whale BIAs and no takes of gray whales are proposed for authorization. There are also two humpback whale feeding BIAs (Stonewall and Heceta Bank) adjacent to the survey area, however no overlap occurs between the survey area and the BIAs. There are no rookeries, mating or calving grounds known to be biologically important to marine mammals within the proposed survey area. Critical habitat for the Mexico and Central America DPSs of humpback whales has been established along the U.S. West Coast (86 FR 21082; May 5, 2021), and NMFS has expanded the Southern Resident killer whale critical habitat to include coastal waters of Washington, Oregon, and California (86 FR 41668; August 2, 2021). No part of L-DEO's proposed seismic survey will occur in or near these critical habitats. No permanent hearing impairment (Level A harassment) is anticipated or proposed to be authorized. Authorized takes of killer whales is expected to comprise almost entirely of the West Coast Transient and/or North Pacific Offshore stocks as Southern Resident killer whales are typically confined to coastal and inland waters. Therefore take of Southern Resident killer whales is unlikely given the far offshore location of the proposed survey, and no take of Southern Resident killer whales is proposed for authorization. In summary and as described above, the following factors primarily support our preliminary determination that the impacts resulting from this activity are not expected to adversely affect any of the species or stocks through effects on annual rates of recruitment or survival: No serious injury or mortality is anticipated or authorized;
                    The proposed activity is temporary and of relatively short duration (6 days);
                    The anticipated impacts of the proposed activity on marine mammals would be temporary behavioral changes due to avoidance of the area around the vessel;
                    No take by Level A harassment is proposed for authorization;
                    The availability of alternative areas of similar habitat value for marine mammals to temporarily vacate the survey area during the proposed survey to avoid exposure to sounds from the activity is readily abundant;
                    The potential adverse effects on fish or invertebrate species that serve as prey species for marine mammals from the proposed survey would be temporary and spatially limited, and impacts to marine mammal foraging would be minimal; and
                    The proposed mitigation measures, including visual, shutdowns, and enhanced measures for areas of biological importance (*e.g.,*
                         additional monitoring vessel, daylight operations only) are expected to minimize potential impacts to marine mammals (both amount and severity). Based on the analysis contained herein of the likely effects of the specified activity on marine mammals and their habitat, and taking into consideration the implementation of the proposed monitoring and mitigation measures, NMFS preliminarily finds that the total marine mammal take from the proposed activity will have a negligible impact on all affected marine mammal species or stocks. Small Numbers As noted above, only small numbers of incidental take may be authorized under sections 101(a)(5)(A) and (D) of the MMPA for specified activities other than military readiness activities. The MMPA does not define small numbers and so, in practice, where estimated numbers are available, NMFS compares the number of individuals taken to the most appropriate estimation of abundance of the relevant species or stock in our determination of whether an authorization is limited to small numbers of marine mammals. When the predicted number of individuals to be taken is fewer than one-third of the species or stock abundance, the take is considered to be of small numbers. Additionally, other qualitative factors may be considered in the analysis, such as the temporal or spatial scale of the activities. The amount of take NMFS proposes to authorize is below one third of the estimated stock abundance for all species (in fact, take of individuals is less than ten percent of the abundance of the affected stocks, see Table 6). This is likely a conservative estimate because we assume all takes are of different individual animals, which is likely not the case. Some individuals may be encountered multiple times in a day, but PSOs would count them as separate individuals if they cannot be identified. Based on the analysis contained herein of the proposed activity (including the proposed mitigation and monitoring measures) and the anticipated take of marine mammals, NMFS preliminarily finds that small numbers of marine mammals would be taken relative to the population size of the affected species or stocks. Unmitigable Adverse Impact Analysis and Determination There are no relevant subsistence uses of the affected marine mammal stocks or species implicated by this action. Therefore, NMFS has determined that the total taking of affected species or stocks would not have an unmitigable adverse impact on the availability of such species or stocks for taking for subsistence purposes. Endangered Species Act Section 7(a)(2) of the Endangered Species Act of 1973 (ESA: 16 U.S.C. 1531 
                        *et seq.*) requires that each Federal 
                        ( print page 37598)
                        agency insure that any action it authorizes, funds, or carries out is not likely to jeopardize the continued existence of any endangered or threatened species or result in the destruction or adverse modification of designated critical habitat. To ensure ESA compliance for the issuance of IHAs, NMFS consults internally whenever we propose to authorize take for endangered or threatened species, in this case with the ESA Interagency Cooperation Division within NMFS' Office of Protected Resources (OPR). NMFS is proposing to authorize take of blue whales, fin whales, sei whales, sperm whales, Central America DPS humpback whales, Mexico DPS humpback whales, and Guadalupe fur seal, which are listed under the ESA. The NMFS OPR Permits and Conservation Division has requested initiation of Section 7 consultation with the NMFS OPR ESA Interagency Cooperation Division for the issuance of this IHA. NMFS will conclude the ESA consultation prior to reaching a determination regarding the proposed issuance of the authorization. Proposed Authorization As a result of these preliminary determinations, NMFS proposes to issue an IHA to L-DEO for conducting geophysical surveys in the Northeast Pacific Ocean during Summer 2022, provided the previously mentioned mitigation, monitoring, and reporting requirements are incorporated. A draft of the proposed IHA can be found at: 
                        *https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​incidental-take-authorizations-research-and-other-activities.* Request for Public Comments We request comment on our analyses, the proposed authorization, and any other aspect of this notice of proposed IHA for the proposed survey. We also request comment on the potential renewal of this proposed IHA as described in the paragraph below. Please include with your comments any supporting data or literature citations to help inform decisions on the request for this IHA or a subsequent renewal IHA. On a case-by-case basis, NMFS may issue a one-time, one-year renewal IHA following notice to the public providing an additional 15 days for public comments when (1) up to another year of identical or nearly identical activities as described in the Description of Proposed Activities section of this notice is planned or (2) the activities as described in the Description of Proposed Activities section of this notice would not be completed by the time the IHA expires and a renewal would allow for completion of the activities beyond that described in the 
                        *Dates and Duration*
                         section of this notice, provided all of the following conditions are met: A request for renewal is received no later than 60 days prior to the needed renewal IHA effective date (recognizing that the renewal IHA expiration date cannot extend beyond one year from expiration of the initial IHA).
                    The request for renewal must include the following: (1) An explanation that the activities to be conducted under the requested renewal IHA are identical to the activities analyzed under the initial IHA, are a subset of the activities, or include changes so minor (
                        *e.g.,*
                         reduction in pile size) that the changes do not affect the previous analyses, mitigation and monitoring requirements, or take estimates (with the exception of reducing the type or amount of take). (2) A preliminary monitoring report showing the results of the required monitoring to date and an explanation showing that the monitoring results do not indicate impacts of a scale or nature not previously analyzed or authorized. Upon review of the request for renewal, the status of the affected species or stocks, and any other pertinent information, NMFS determines that there are no more than minor changes in the activities, the mitigation and monitoring measures will remain the same and appropriate, and the findings in the initial IHA remain valid. Dated: June 16, 2022. Kimberly Damon-Randall, Director, Office of Protected Resources, National Marine Fisheries Service.


BILLING CODE 3510-22-P BILLING CODE 3510-22-C [FR Doc. 2022-13328 Filed 6-22-22; 8:45 am]