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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations
Pipelines We obtained shapefiles of existing and proposed pipelines, as well as which months and years each pipeline would be operational, from AOGA.
Based on the description in the Request, we assumed that all pipelines would have aerial surveys conducted weekly with aircraft flying at altitudes <457.2 m <1,500 ft and potentially exposing polar bears to disturbance.
Other Aircraft Activities Aside from flights to survey pipelines, the majority of aircraft flights are expected to occur at altitudes >457.2 m >1,500 ft. After reviewing current and proposed flight patterns for flights likely to occur at altitudes <457.2 m <1,500
ft, we found one flight path that we included in the model. The flight path is between the Oooguruk drill site and the onshore tie-in pad with at least daily flights between September 1 and January 31. We, therefore, also considered these flights as a continuous source of potential exposure to denning bears.
Aerial Infrared Surveys Based on AOGAs Request, we assumed that all permanent infrastructure i.e., roads, pipelines, and pads, tundra travel routes, and ice roads would receive two aerial infrared AIR surveys of polar bear den habitat within 1 mile of those features each
winter. The first survey could occur between December 1 and 25 and the second between December 15 through January 10 with at least 24 hours between the completion of the first survey and the beginning of the second.
During winters when seismic surveys occur, additional AIR surveys would be required. A total of three AIR surveys of any den habitat within 1 mile of the seismic survey area would be required prior to any seismic-related activities occurring e.g., advance crews checking ice conditions. The first AIR survey would need to occur between November 25 and December 15, the second between December 5 and 31, and the third between December 15 and January 15 with the same minimum of 24 hours between subsequent surveys. Similarly, during winters when seismic surveys occur, an additional AIR survey would be required of denning habitat within 1
mile of the pipeline between Badami and the road to Endicott Island. The additional survey of the pipeline to create a total of three would need to occur between December 5 and January 10.
During each iteration of the model, each AIR survey was randomly assigned a probability of detecting dens. Whereas previous analyses have used the results of Wilson and Durner 2020 to inform this detection probability, two additional studies Smith et al. 2020, Woodruff et al. in prep. have been
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from which we drew a detection probability for each of the simulated AIR surveys during each iteration of the model.

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Model Implementation For each iteration of the model, we first determined which dens were exposed to each of the simulated activities and infrastructure. We assumed that any den within 1.6 km 1
mi of infrastructure or human activities was exposed and had the potential to be disturbed as numerous studies have suggested a 1.6-km buffer is sufficient to reduce disturbance to denning polar bears MacGillivray et al. 2003, Larson et al. 2020, Owen et al. 2021. If, however, a den was detected by an AIR
survey prior to activity occurring within 1.6 km of it, we assumed a 1.6-km buffer would be established to restrict activity adjacent to the den and there would be no potential for future disturbance. If a den was detected by an AIR survey after activity occurred within 1.6 km of it, as
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long as the activity did not result in a Level A harassment or lethal take, we assumed a 1.6-km buffer would be applied to prevent disturbance during future denning periods. For dens exposed to human activity i.e., not detected by an AIR survey, we then identified the stage in the denning cycle when the exposure occurred based on the date range of the activities the den was exposed to. We then determined whether the exposure elicited a response by the denning bear based on probabilities derived from the reviewed case studies Table 7. Level B
harassment was applicable to both adults and cubs, if present, whereas Level A harassment i.e., serious injury and non-serious injury and lethal take were applicable only to cubs because the proposed activities had a discountable risk of running over dens and thus killing a female or impacting her future reproductive potential. The majority of proposed activities occur on established, permanent infrastructure
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conducted since Wilson and Durner 2020 was published that require an updated approach. The study by Woodruff et al. in prep. considered the probability of detecting heat signatures from artificial polar bear dens. They did not find a relationship between den snow depth and detection and estimated a mean detection rate of 0.24. A recent study by Smith et al. 2020 estimated that the detection rate for actual polar bear dens in northern Alaska was 0.45
and also did not report any relationship between detection and den snow depth.
Because the study by Wilson and Durner 2020 reported detection probability only for dens with less than 100 cm snow depth, we needed to correct it to also include those dens with greater than 100 cm snow depth.
Based on the distribution of snow depths used by Wilson and Durner 2020 derived from data in Durner et al.
2003, we determined that 24 percent of dens have snow depths greater than 100
cm. After taking these into account, the overall detection probability from Wilson and Durner 2020 including dens with snow depths greater than 100
cm was estimated to be 0.54. This led to a mean detection of 0.41 and standard deviation of 0.15 across the three studies. We used these values, and the method of moments Hobbs and Hooten 2015, to inform a Beta distribution i.e.,
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that would not be suitable for denning and therefore, pose no risk of being run over i.e., an existing road. For those activities off permanent infrastructure i.e., ice roads and tundra travel routes, crews will constantly be on the lookout for signs of denning, use vehicle-based forward looking infrared cameras to scan for dens, and will largely avoid crossing topographic features suitable for denning given operational constraints. Thus, the risk of running over a den was deemed to have a probability so low that it was discountable.
Based on AOGAs description of their proposed activities, we only considered AIR surveys and pipeline inspection surveys as discrete exposures given that surveys occur quickly i.e., the time for an airplane to fly over and infrequently.
For all other activities, we applied probabilities associated with repeated exposure Table 7. For the pipeline surveys, we made one modification to the probabilities applied compared to
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