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Federal Register / Vol. 86, No. 33 / Monday, February 22, 2021 / Notices In order to generate a summer density, as AGDC expects that the majority of their work will occur during the summer, we first began with the spring density. Summer densities in the project area are expected to significantly decrease as ringed seals range considerable distances during the open water season. Summer density was estimated to be 50 percent of the spring density 0.548 seals/km2, resulting in a summer density estimate of 0.274 ringed seals/km2. Like summer density estimates, fall density data are limited.
Ringed seals remain in the water through the fall and into the winter.
Given the lack of data, fall density is
assumed the same as the summer density of 0.274 ringed seals/km2.
During the winter months, ringed seals create subnivean lairs and maintain breathing holes in the landfast ice. Tagging data suggest that ringed seals utilize multiple lairs and Kelly et al. 1986 determined that, on average, one seal used 2.85 lairs, although the authors suggested that this is likely an underestimate. Density estimates for the number of ringed seal ice structures have been calculated Frost and Burns 1989; Kelly et al. 1986; Williams et al.
2001, and the average density of ice structures from these reports is 1.58/
km2.

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To estimate ringed seal density in the winter, the average ice structure density 1.58/km2 was divided by the average number of structures used by the seals 2.85 structures. The estimated density is 0.509 ringed seals/km2 in the winter;
however, this is likely an overestimate as the average number of ice structures utilized is thought to be an underestimate Kelly et al., 1986.
While more recent ASAMM surveys have been conducted in the project area 20162019, these surveys did not identify observed pinnipeds to species, and therefore were not used to calculate take of pinnipeds.

TABLE 11RINGED SEAL ICE STRUCTURE DENSITY IN THE VICINITY OF THE PROJECT AREA
Ice structure density structures per km2

Year
tkelley on DSKBCP9HB2PROD with NOTICES2

1982
1983
1999
2000
Average Density

3.6
0.81
0.71
1.2
1.58.

Source
Frost and Burns 1989.
Kelly et al., 1986.
Williams et al., 2001.
Williams et al., 2001.

Given that AGDC will only pile drive during the winter if they are unable to complete the work during the summer and fall open water season, AGDC
estimated ringed seal takes using summer densities, rather than winter.
NMFS concurs with this approach.

percent of the pinniped sightings during these monitoring efforts. Therefore, summer spotted seal density was calculated as 20 percent of the ringed seal density of 0.274 seals/km2. This results in an estimated spotted seal summer density of 0.055 seals/km2.

Spotted Seal
Bearded Seal
The spotted seal occurs in the Beaufort Sea in small numbers during the summer open water period. At the onset of freeze-up in the fall, spotted seals return to the Chukchi and then Bering Sea to spend the winter and spring. As such, we do not expect spotted seals to occur in the project area during AGDCs winter/spring contingency period.
Only a few of the studies referenced in calculating the ringed seal densities also include data for spotted seals.
Given the limited spotted seal data, NMFS expects that relying on this data may result in an underestimate, and that it is more conservative to calculate the spotted seal density as a proportion of the ringed seal density. Therefore, summer spotted seal density was estimated as a proportion of the ringed seal summer density based on the percentage of pinniped sightings observed during monitoring projects in the region Harris et al., 2001; Aerts et al., 2008; Hauser et al., 2008; HDR
2012. Spotted seals comprised 20

The majority of bearded seals spend the winter and spring in the Chukchi and Bering seas; however, some remain in the Beaufort Sea year-round. A
reliable population estimate for the bearded seal stock is not available, and occurrence in the Beaufort Sea is less known than that in the Bering Sea.
Spring aerial surveys conducted as part of industry monitoring for the Northstar production facility provide limited sighting numbers from 19992002
Moulton et al., 2000, Moulton et al., 2001, Moulton et al., 2002a, Moulton et al., 2003. During the 4 years of survey, an average of 11.75 bearded seals were observed during 3,997.5 km2 of effort.
Using this data, winter and spring density are estimated to be 0.003
bearded seals/km2.
Bearded seals occur in the Beaufort Sea more frequently during the open water season, rather than other parts of the year. Only a few of the studies referenced in calculating the ringed seal densities also include data for bearded seals. Given the limited bearded seal
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data, NMFS expects that relying on this data may result in an underestimate, and that it is more conservative to calculate the bearded seal density as a proportion of the ringed seal density.
Therefore, summer density was estimated as a proportion of the ringed seal summer density based on the percentage of pinniped sightings observed during monitoring projects in the region Harris et al., 2001; Aerts et al., 2008; Hauser et al., 2008; HDR
2012. Bearded seals comprised 17
percent of the pinniped sightings during these monitoring efforts. Therefore, summer bearded seal density was calculated as 17 percent of the ringed seal density of 0.274 seals/km2. This results in an estimated bearded seal summer density of 0.047 seals/km2. The same estimate is assumed for bearded seal fall density.
As noted in the Description of Marine Mammals in the Area of Specified Activities section and in Table 12, bearded seals could potentially occur in the project area during AGDCs winter/
spring contingency period. However, we would expect very few, if any, bearded seals to be present during this time. In consideration of this species presence information, and AGDCs plan to conduct most construction during the open-water season, NMFS used the summer density in the take calculation described below.

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