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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules
was later observed with cubs i.e., 79
days had a litter size of 0. There were only 3 bears in the USGS 2018 data that met this criteria, leading to an assumed probability of a litter size of 0
at emergence being 0.07. We, therefore, assigned the probability of 0, 1, 2, or 3
cubs as 0.07, 0.15, 0.71, and 0.07, respectively.
Infrastructure and Human Activities The model developed by Wilson and Durner 2020 provides a template for estimating the level of potential impact to denning polar bears of proposed activities while also considering the natural denning ecology of polar bears in the region. The approach developed by Wilson and Durner 2020 also allows for the incorporation of uncertainty in both the metric associated with denning bears and in the timing and spatial patterns of proposed activities when precise information on those activities is unavailable. Below we describe the different sources of potential disturbance we considered within the
model. We considered infrastructure and human activities only within the area of proposed activity in the ITR
request. However, given that activity on the border of this region could still affect dens falling outside of the area defined in the ITR request, we also considered the impacts to denning bears within a 1-mile buffer outside of the proposed activity area.
Roads and Pads We obtained shapefiles of existing and proposed road and pad infrastructure associated with industrial activities from AOGA. Each attribute in the shapefiles included a monthly occupancy rate that ranged from 0 to 1.
For this analysis, we assumed that any road or pad with occupancy greater than 0 for a given month had the potential for human activity during the entire month unless otherwise noted.
Ice Roads and Tundra Travel We obtained shapefiles of proposed ice road and tundra travel routes from AOGA. We also received information on
the proposed start and end dates for ice roads and tundra routes each winter from AOGA with activity anticipated to occur at least daily along each.
Seismic Surveys Seismic surveys are planned to occur in the central region of the project area proposed by AOGA Figure 7. The region where seismic surveys would occur were split into two different portions representing relatively high and relatively low probabilities of polar bear dens being present Figure 7.
During any given winter, no more than 766 km2 and 1183 km2 will be surveyed in the highand low-density areas, respectively. Therefore, for this analysis, we estimated take rates by assuming that seismic surveys would occur in the portions of those areas with the highest underlying probabilities of denning occurring and covering the largest area proposed in each i.e., 766 km2 and 1183 km2. All seismic surveys could start as early as January 1 and operate until April 15.

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Figure 7-Depiction of areas where seismic surveys occurred in simulations with underlying map of relative den density. The high-density seismic area covers a region with relatively high probability of denning, and the low-density seismic area covers a region with relatively low probability of denning. During any given winter, no more than 766 km 2 and 1,183 km 2 will be surveyed in the high-density and low-density areas, respectively.
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