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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules
Encounter rates were originally calculated as bears encountered per square kilometer per season see North Slope Encounter Rates above. As a part of their application, 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 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
To generate the number of estimated Level B harassments for each area of interest, we multiplied the number of
bears in the area of interest per season by the proportion of the season the area
is occupied, the rate of occupancy, and the harassment rate Equation 4.

Aircraft Impact to Surface Bears Polar bears in the project area will likely be exposed to the visual and auditory stimulation associated with AOGAs fixed-wing and helicopter flight plans; however, these impacts are likely to be minimal and not long-lasting to surface bears. Flyovers may cause disruptions in the polar bears normal behavioral patterns, thereby resulting in incidental Level B harassment. Sudden changes in direction, elevation, and movement may also increase the level of noise produced from the helicopter, especially at lower altitudes. This increased level of noise could disturb polar bears in the area to an extent that their behavioral patterns are disrupted
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and Level B harassment occurs.
Mitigation measures, such as minimum flight altitudes over polar bears and restrictions on sudden changes to helicopter movements and direction, will be required if these regulations are finalized to reduce the likelihood that polar bears are disturbed by aircraft.
Once mitigated, such disturbances are expected to have no more than shortterm, temporary, and minor impacts on individual bears.
Estimating Harassment Rates of Aircraft Activities To predict how polar bears will respond to fixed-wing and helicopter overflights during North Slope oil and gas activities, we first examined existing data on the behavioral responses of polar bears during aircraft surveys conducted by the Service and U.S.
Geological Survey USGS between August and October during most years from 2000 to 2014 Wilson et al. 2017, Atwood et al. 2015, and Schliebe et al.

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2008. Behavioral responses due to sight and sound of the aircraft have both been incorporated into this analysis as there was no ability to differentiate between the two response sources during aircraft survey observations. Aircraft types used for surveys during the study included a fixed-wing Aero-Commander from 2000
to 2004, a R44 helicopter from 2012 to 2014, and an A-Star helicopter for a portion of the 2013 surveys. During surveys, all aircraft flew at an altitude of approximately 90 m 295 ft and at a speed of 150 to 205 km per hour km/
h or 93 to 127 mi per hour mi/h.
Reactions indicating possible incidental Level B harassment were recorded when a polar bear was observed running from the aircraft or began to run or swim in response to the aircraft. Of 951 polar bears observed during coastal aerial surveys, 162 showed these reactions, indicating that the percentage of Level B harassments during these low-altitude
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The estimated harassment values for the open-water 2021 and open-water 2026 seasons were adjusted to account for incomplete seasons as the proposed regulations will be effective for only 85
and 15 percent of the open-water 2021
and 2026 seasons, respectively.

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Equation 4