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Federal Register / Vol. 86, No. 157 / Wednesday, August 18, 2021 / Notices
array. We do not believe that Level A
harassment is a likely outcome for any lowor mid-frequency cetacean or phocid pinniped and are not authorizing any Level A harassment for these species. For high-frequency cetaceans, the larger estimated Level A
harassment zone associated with the high-energy array will be present for only 12 percent of total survey effort, and given the expected rarity of occurrence for harbor porpoise, no incidents of Level A harassment are expected.
Marine Mammal Occurrence Information about the presence, density, and group dynamics of marine mammals that informs the take calculations was provided in our notice of proposed IHA 86 FR 28787; May 28, 2021. Information that has remained unchanged is not reprinted here.
Density values are shown in Table 6.
The bowhead whale density value described in the notice of proposed IHA
86 FR 28787; May 28, 2021 was correct; however, the incorrect units were used. The value reported in the notice of proposed IHA 0.0124 whales/
km2 would correctly be stated as 0.0124
whales/100 km2, and the corrected density is used here.

TABLE 6DENSITY VALUES USED FOR determine the total ensonified area in TAKE ANALYSIS, CALCULATED BY each depth category. Estimated incidents of exposure above Level A and UAGI
Density individuals/km2

Species Bowhead whale
Gray whale
Fin whale
Humpback whale
Minke whale
Beluga whale
Killer whale
Narwhal
Harbor porpoise
Bearded seal
Ribbon seal
Ringed seal
Spotted seal

0.000124
0 0
0 0
0.0255
Unknown Unknown Unknown 0.0332
0.0677
0.376
0.0007

Take Calculation and Estimation Here we describe how the information provided above is brought together to produce a quantitative take estimate. In order to estimate the number of marine mammals predicted to be exposed to sound levels that would result in Level A or Level B harassment, radial distances from the airgun array to predicted isopleths corresponding to the Level A harassment and Level B
harassment thresholds are calculated, as described above. Those radial distances are then used to calculate the areas around the airgun array predicted to be ensonified to sound levels that exceed the Level A and Level B harassment thresholds. The distance for the 160-dB
threshold based on LDEO model results was used to draw a buffer around every transect line in GIS to
Level B harassment criteria are presented in Table 7. As noted previously, UAGI has added 25 percent in the form of operational days, which is equivalent to adding 25 percent to the line-kilometers to be surveyed. This accounts for the possibility that additional operational days are required, and is included in the estimates of actual exposures.
The number of individual marine mammals potentially exposed to airgun sounds with received levels 160 dB re 1 mParms Level B was estimated following NSFs take calculation method by multiplying the estimated densities by the total area expected to be ensonified above the Level threshold.
The total ensonified area was multiplied by 25 percent to account for any necessary additional operations, such as re-surveying segments where data quality was insufficient. This approach assumes that no marine mammals would move away or toward the trackline in response to increasing sound levels before the levels reach the threshold as R/V Sikuliaq approaches.
This value was then multiplied by the estimated densities for each species to produce estimated Level B takes. Given the location of the survey being far north in the Arctic, we expect that the density values, and thus estimated take numbers, are conservative estimates of what is likely to be encountered during the survey.

TABLE 7ESTIMATED TAKING BY LEVEL A AND LEVEL B HARASSMENT, AND PERCENTAGE OF POPULATION
Species
Stock 1

Estimated Level B
harassment
Estimated Level A
harassment
Authorized Level B
harassment
Authorized Level A
harassment
Total take
Percent of stock 1

Bowhead whale
Humpback whale 2
Fin whale 2 4
Gray whale 2
Minke whale 2 4
Beluga whale

Western Arctic
WN Pacific
NE Pacific
EN Pacific
Alaska
Beaufort Sea
Eastern Chukchi
Alaska Resident
Unidentified
Bering Sea
Beringia
Arctic
Bering
Unidentified

3
0 0
0 0
696
0
0 0
900
10,198
19
1,836

0
0 0
0 0
1
0 0
0 6
70
0 13

3
2 2
2 2
697
6
2 2
907
10,269
19
1,849

0
0 0
0 0
0
0 0
0 0
0 0
0

3
2 2
2 2
697
6
2 2
907
10,269
19
1,849

0.02
0.01
0.18
0.01
0.01
1.33
0.20
n/a 0.04
0.73
5.99
0.00
1.00

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Killer whale 2
Narwhal 3 4
Harbor porpoise 2 4
Bearded seal 5
Ringed seal 5
Spotted seal
Ribbon seal

1 In most 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 authorized takes occurred within each stock. Where necessary, additional discussion is provided in the Small Numbers Analysis section.
2 UAGI requests authorization of gray whale, humpback whale, fin whale, minke whale, killer whale, and harbor porpoise take equivalent to exposure of one group Clarke et al., 2016; Clarke et al., 2017; Clarke et al., 2018; Clarke et al., 2019.
3 UAGI requests authorization of two takes of narwhals.
4 As noted in Table 1, there is no estimate of abundance available for these species. See Small Numbers Analysis section for further discussion.
5 Due to rounding, the total estimated Level B harassment does not equal the sum of Level A harassment and Level B harassment.

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