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Federal Register / Vol. 86, No. 106 / Friday, June 4, 2021 / Notices
The Navy conducted comprehensive marine mammal surveys in theTMAA in 2009 and 2013. Additional survey effort was conducted in 2015. These surveys used systematic line-transect survey protocols including visual and acoustic detection methods Rone et al., 2010, 2014, 2017. The data were collected in four strata that were designed to encompass the four distinct habitats within the TMAA and greater GOA:
Inshore: All waters <1,000 m deep;
Slope: From 1,000 m water depth to the Aleutian trench/subduction zone;
Offshore: Waters offshore of the Aleutian trench/subduction zone;
Seamount: Waters within defined seamount areas. Density values for the slope and seamount regions of the TMAA are not relevant for the survey area considered herein. There were insufficient sightings data from the 2009, 2013, and 2015 line-transect surveys to calculate reliable density estimates for certain cetacean species in the GOA. In these cases, other available information supported development of density estimates. Additional sources of information include summer 2003
cetacean surveys near the Kenai Peninsula, within Prince William Sound and around Kodiak Island Waite, 2003
in DoN, 2021, summer 20102012 linetransect data collected over a broad area north of 40 N, south of the Aleutian Islands, and between 170 E and 135 W
during the International Whaling Commission-Pacific Ocean Whale and Ecosystem Research cruises Hakamada et al., 2017, and analysis of acoustic data from the 2013 Navy-funded survey effort in the TMAA Yack et al., 2015.
See DoN 2021 for additional detail.
When seasonal densities were available, the calculated exposures were based on summer densities, which are most representative of the proposed survey timing.
Pinniped numbers are commonly assessed by counting individuals at haul-outs or the number of pups weaned at rookeries. Translating these numbers to in-water densities presents challenges unique to pinnipeds. No in-water line transect survey data were available for harbor seal, Steller sea lion, or California sea lion in the GOA. Surveys conducted by Rone et al. 2014
recorded sightings of northern elephant seal and northern fur seal in the TMAA;
however, these data were insufficient to estimate a density for northern elephant seal, and were not used for northern fur seal due to the availability of more recent data. To account for the lack of in-water survey data for pinnipeds, published abundance estimates used in the density calculations were adjusted
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using a species-specific haul-out factor to estimate an in-water abundance for each species based on haul-out behavior. The calculated in-water abundance and an area of distribution specific to each species was used to estimate a density. See DoN 2021 for additional information. For pinnipeds, where monthly density estimates were available, the highest value from July or August was applied as most representative of the proposed survey timing.
Due to a lack of sighting data specific to the Behm Canal area, the Navy derived density estimates based on data collected from various surveys cetaceans and shore counts pinnipeds conducted within southeast Alaska and GOA. Pinniped density estimates for the Behm Canal region were additionally derived from publications, NMFS SARs, and consultation with subject matter experts DoN, 2019. Systematic ship surveys conducted in southeast Alaska waters from 1991 to 2012 provided data to develop stratified line-transect density estimates for harbor porpoise and Dalls porpoise in regions overlapping a portion of the Behm Canal area Dahlheim et al., 2015. Density information for the Behm Canal area is available for the following species:
Minke whale, fin whale, humpback whale, Pacific white-sided dolphin, killer whale, harbor porpoise, Dalls porpoise, and for all potentially affected pinniped species.
The general approach for cetaceans of applying Behm Canal density estimates to survey effort in shallow and intermediate depth strata and GOA
offshore density estimates to the deep depth stratum was applied for species for which appropriate estimates were available: Humpback whale, fin whale, minke whale, Pacific white-sided dolphin, killer whale, and Dalls porpoise. Note that, for killer whales, Behm Canal densities are provided specific to transient and resident whales. We apply the higher transient killer whale density value to estimate killer whale exposures in shallow and intermediate water depths. Behm Canal pinniped densities would be expected to overestimate pinniped occurrence off the coast, and so were not used for intermediate-depth waters, but were applied to shallow waters where available.
Certain species are not expected to occur in Behm Canal: Gray whale, blue whale, sei whale, sperm whale, beaked whales, northern fur seal, and northern elephant seal. For these species, we applied appropriate GOA density values to all depth strata i.e., inshore GOA

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values to shallow and intermediate water depths and offshore GOA density values to deep water depths. Note that, while DoN 2021 provides an inshore density estimate for sperm whales, that stratum corresponds to water depths <1,000 m. We assume here that sperm whales do not occur in shallow water depths <100 m.
Gray whale densities are provided for two zones, nearshore 02.25 nmi from shore and offshore from 2.2520 nmi from shore, based on density information in Carretta et al. 2000 and zones based on data from Shelden and Laake 2002. DoN 2021 assumes that gray whales do not occur in the region >20 nmi from shore. The nearshore density is used here to represent shallow and intermediate water <1,000
m deep. This approach assumes a higher density of gray whales across a larger area and is used as a precautionary approach.
Harbor porpoise densities in DoN
2021 were derived from survey data collected in summer 1997 in southeast Alaska and 1998 in the Gulf of Alaska and included correction factors for both perception and availability bias Hobbs and Waite, 2010. LDEO proposed to use density information from Hobbs and Waite 2010 specific to southeast Alaska, which better represents the survey area than the GOA information presented for harbor porpoise in DoN
2021. Following DoN 2021, we assume harbor porpoise will not occur in deep water >1,000 m.
No regional density information is available for the northern right whale dolphin. Becker et al. 2016 used linetransect survey data collected between 1991 and 2009 to develop predictive habitat-based models of cetacean densities in the California Current Ecosystem the region from Baja California to southern British Columbia. The modeled density estimates were available on the scale of 7 km by 10 km grid cells off California, Oregon, and Washington, and values were averaged for grid cells across Washington and Oregon corresponding with LDEOs shallow, intermediate, and deep water survey strata. These density values were applied to the portion of the survey area off Canada to calculate estimated exposures, as northern right whale dolphins do not typically occur beyond the California Current. The Rissos dolphin is only rarely observed in or near the Navys GOA survey area, and does not occur in Behm Canal, so minimal densities were used to represent their potential presence DoN, 2021. For California sea lion, density data is available in DoN
2021; however, it is likely that these
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