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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations detection depending on people on the survey crew. Those differences are already incorporated into the estimates in Woodruff and Wilson 2021. All three surveyors had significant experience using AIR to detect polar bear dens. Thus, our estimate represents the average detection rates for people with training in the use of AIR to detect polar bear dens.
Comment 107: One commenter suggested that the Service underestimated the number of polar bear dens that would remain undetected, which may affect their take estimations.
Response: First, the den model does not assume only 52 dens are on the land in any given year. That is the mean value we used, but we accounted for the uncertainty in this estimate, so the number of dens simulated during each iteration is highly variable. We agree with the assessment by the commenter that the results of Woodruff and Wilson 2021 show that only 50% of dens were detected at least once during the study.
While that is not the correct metric to use in the analysis, our approach to estimating infrared efficacy took into account the lower detection rates for this study in combination with the two other studies that provide an aerial detection rate of dens with AIR.
Comment 108: Two commenters suggested that the Service should clarify the optimal weather conditions for AIR
surveys to be conducted in order to avoid AIR surveys being conducted in suboptimal conditions and affecting polar bear den detection rates.
Response: The estimates of AIR
detection used in the analysis were not obtained under optimal weather conditions, but under a range of weather conditions that AIR surveys are possible. Thus, optimal weather conditions are not required based on the estimates of detection we used. That said, it has been standard practice for Industry operators to conduct their AIR
surveys within parameters outlined by Amstrup et al., 2004 and York et al., 2004. This has been added to the Mitigation and Monitoring requirements in the ITR.
Comment 109: The regulatory text in the proposed rule at 18.120a describes the offshore boundary of the ITR as matching the boundary of the BOEM Beaufort Sea Planning area.
However, the preamble text and the maps in both the preamble and the proposed rule describe the geographic region as extending 80.5 km 50 mi offshore rather than matching the BOEM
Planning Area boundary. This discrepancy should be corrected.

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Response: We agree and have clarified this final rule so that the preamble text reflects the boundaries of the geographic area in the regulatory language.
Comment 110: One commenter suggested that the Service should request that helicopters be used for AIR
surveys because it has been reported that polar bear den detection rates are higher when helicopters are used compared to fixed-wing aircraft.
Response: Use of helicopters to survey active dens might actually lead to greater levels of disturbance and take than with fixed-wing aircraft. While its true that helicopters are more maneuverable than airplanes, we have not seen any published data only conjecture that detection rates for dens are higher when a helicopter is used vs.
a fixed-wing aircraft. Interestingly, Amstrup et al. 2004 used a helicopter and Smith et al. 2020 used a fixedwing, yet when accounting for likely undetectable dens, Amstrup et al. 2004
has a mean detection of 55% compared to Smith et al. 2020s 45%. These are likely statistically insignificant as the 95% CI for the Amstrup et al. 2004
estimate largely overlaps the Smith et al.
2004 point estimate, which does not provide an estimate of the associated uncertainty. Lastly, it is incorrect that fixed-wings create contrails and helicopters do not. We have run into issues with helicopters causing contrails, which impede visibility while circling bears during capture operations in the Arctic when temperatures are <0 F.
Comment 111: One commenter suggested that the Service overestimated their polar bear den detection rate for AIR surveys, which may underestimate take estimates resulting from den disturbance.
Response: We rely on the best available information to obtain estimates of AIR efficacy to detect established dens. The mean value used is in line with those studies, and the associated variability allows detection to be as low as 1.5% in some iterations of the model.
Comment 112: One commenter suggested that the Service overestimated their polar bear den detection rate for AIR surveys, which underestimates the number of undetected polar bear dens that may be potentially disturbed by Industry activities.
Response: We disagree with this characterization of the Wilson and Durner 2020 estimate derived from Amstrup et al. 2004. As noted in the ITR, the estimate derived by Wilson and Durner 2020, i.e., 74%, is only for dens available to be detected i.e., those with snow shallow enough to allow AIR

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detection. For the current analysis, given that Woodruff and Wilson 2021
didnt find a relationship between detection and snow depth, and Smith et al. 2020 did not account for dens unavailable to be detected e.g., due to snow depth, we corrected the Wilson and Durner 2020 estimate to be an average detection rate regardless of whether a den was available to be detected or not. That led to an estimate 55%, with confidence intervals that overlap the Smith et al. 2020 estimate.
Smith et al. 2020 did not provide an estimate of uncertainty for their mean den detection rate. But overall the estimates are very similar and not statistically different. The Wilson and Durner 2020 approach has been peerreviewed and published in the peerreviewed literature, so it constitutes the best available information and warrants inclusion in our analysis along with the two other studies that exist to estimate detection of dens using AIR.
Comment 113: One commenter suggested that the Service clarify their requirements for AIR survey flight paths in order to ensure all polar bear denning habitat is adequately surveyed.
Response: Our analysis is predicated on the fact that AOGA will survey all polar bear denning habitat that has been identified in the areas with proposed/
current infrastructure and industrial activities. We make this requirement clear in our description of our analytical approach. Thus, AOGA will be required to ensure that all denning habitat is surveyed the requisite number of times to be covered under the ITR.
Comment 114: One commenter suggested that the Service overestimated their polar bear den detection rate because they did not account for the depth of the dens in snow and deterioration of weather conditions during AIR surveys.
Response: As occurs during Industry surveys, AIR surveys were paused when conditions such as wind and fog affected visibility and/or safety of flying.
Because of the requirement for the surveys to be blind, Woodruff and Wilson 2021 did not measure snow depth at the time of den surveys. This would have made tracks in the snow alerting AIR observers to the den location. They did not find a relationship between snow depth and detection and highlight that the deepest den 145-cm snow ceiling thickness was detected whereas a nearby den with snow ceiling thickness of 66 cm was not. The authors acknowledge there may be other factors not accounted for in the study that are affecting den detection besides snow depth.

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