Federal Register - August 5, 2021
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Source: Federal Register
43020
Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations
Table 4-Definitions of variables used in take estimates of polar bears on the coast of the North Slope of Alaska.
Variable Bes Ge Gi
ro eco eci eio
eii fi
fa
Bt Br
Definition bears encountered in an area of interest for the entire season coastal exposure area inland exposure area occupancy rate coastal open-water season bear-encounter rate in bears/season coastal ice season bear-encounter rate in bears/season inland open-water season bear-encounter rate in bears/season inland ice season bear-encounter rate in bears/season ice season harassment rate open-water season harassment rate number of estimated Level B harassment events total bears harassed for activit e
The variables defined above were used in a series of formulas to ultimately estimate the total harassment from surface-level interactions.
Encounter rates were originally calculated as bears encountered per square kilometer per season see North Slope Encounter Rates above. As a part of their Request, AOGA provided the Service with digital geospatial files that included the maximum expected human occupancy i.e., rate of occupancy ro for each individual structure e.g., each road, pipeline, well pad, etc. of their proposed activities for each month of the ITR period. Months were averaged to create open-water and ice-season occupancy rates. For example, occupancy rates for July 2022, August 2022, September 2022, October 2022,
and November 2022 were averaged to calculate the occupancy rate for a given structure during the open-water 2022
season. Using the buffer tool in ArcGIS, we created a spatial file of a 1.6-km 1mi buffer around all industrial structures. We binned the structures according to their seasonal occupancy rates by rounding them up into tenths 10 percent, 20 percent, etc.. We determined the impact area of each bin by first calculating the area within the buffers of 100 percent occupancy locations. We then removed the spatial footprint of the 100 percent occupancy buffers from the dataset and calculated the area within the 90 percent occupancy buffers. This iterative process continued until we calculated the area within all buffers. The areas of
impact were then clipped by coastal and inland zone shapefiles to determine the coastal areas of impact ac and inland areas of impact ai for each activity category. We then used spatial files of the coastal and inland zones to determine the area in coastal verse inland zones for each occupancy percentage. This process was repeated for each season from open-water 2021 to open-water 2026.
Impact areas were multiplied by the appropriate encounter rate to obtain the number of bears expected to be encountered in an area of interest per season Bes. The equation below Equation 3 provides an example of the calculation of bears encountered in the ice season for an area of interest in the coastal zone.
Equation 3
is occupied, the rate of occupancy, and the harassment rate Equation 4.
Equation 4
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bears in the area of interest per season by the proportion of the season the area
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To generate the number of estimated Level B harassments for each area of interest, we multiplied the number of
