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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations
Comment 65: One commenter suggested that the Service should collect more extensive followup information on polar bear den disturbance case studies in order to determine whether cubs survived a den disturbance event.
Response: For most of the case studies, we had documentation of only the immediate outcome of the exposure to a disturbance, which was sufficient for determining the immediate outcome.
For most cases, there is no documentation of the outcome of the cubs beyond the immediate timeframe of the disturbance. We used the best available information, and it would not be appropriate to assume an outcome in the absence of information.
Comment 66: Several commenters suggested that the Service did not adequately consider the possibility of lethal take or serious injury take by Level A harassment arising from direct contact of a vehicle with a den and varying reactions of denning animals to vehicles in close proximity.
Response: We do not use only Smith et al. 2020 for estimates of AIR
efficacy, but rather we include the results from Smith et al. 2020 and Amstrup et al. 2004 in our analysis, as well as a new study on artificial dens Woodruff and Wilson 2021. We do take into account potential disturbance from ground noise and vibrations from drill and exploration in the form of our disturbance probabilities derived from our review of relevant case studies.
While it is true that Amstrup et al.
2004 suggest helicopters may have higher detection rates than fixed-wing aircraft, the average detection rates from Amstrup et al. 2004 do not differ significantly from results obtained with a fixed-wing aircraft Smith et al. 2020
when accounting for the proportion of dens that are unlikely to be available for detection given snow depth.
Additionally, AOGA proposed using only fixed-wing aircraft, so that is what we considered in our analysis. The EA
serves to assess the impacts of the Federal action of issuing the ITR. The ITR does not authorize the specified activities; therefore, the EA focuses its discussion on the effects of takes to be authorized pursuant to the ITR. The impacts from the activities themselves could proceed without MMPA coverage at the discretion of the applicant and are not effects of the Proposed Action, but were nevertheless considered as part of the environmental baseline and in the cumulative impacts analysis.
Based on the output of the den disturbance analysis, we estimated the number of dens and probability of 1
den being run over by equipment used while driving off established roads in
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the project area. Because it is possible to run over dens only when driving off established roads, we restricted our analysis to only those simulated dens that occurred adjacent to proposed ice roads, tundra travel routes, and seismic grids. Because the applicant did not specify how seismic grids would be laid out, we followed a similar approach as Wilson and Durner 2020 and simulated seismic grids across the highand low-density seismic areas Fig. 7.
We simulated EW and NS seismic track lines, each separated by 201.2 m 660 ft. We assumed vehicles traveling seismic grids, ice roads, and tundra travel routes would have a width of 3.4
m 11.2 ft; Wilson and Durner 2020.
For each iteration of the model, we determined which dens occurred within the footprint i.e., 3.4 m of the different movement paths. We then determined if dens had been identified by AIR
surveys. If a den was identified on an AIR survey, we excluded it from further analysis. Lastly, we restricted the set of dens available to be run over to those that did not previously have a take by Level A harassment or lethal take assigned to it during the early or late denning periods. That is, those dens that did not previously respond to disturbance and, therefore, would be vulnerable to being run over by equipment. We did not consider the potential for running over dens during the den establishment period or postemergence period because during both of these periods bears are known to be on the surface and would likely be visible to operators and the bears would be able to readily detect the potential risk of the vehicles and respond appropriately.
Our approach for estimating the number of dens potentially run over by equipment can be considered conservative because it does not account for the fact that operators have stated they will avoid crossing denning habitat whenever possible, which would further reduce the probability of running over a den. Similarly, the seismic grids we simulated likely cover a greater area than a normal seismic layout, but because information was not provided by the applicant, we used the more liberal layout.
We found that the probability of running over a den is exceedingly low each year of the ITR. The probability of running over 1 den each winter ranged from 0.0041 to 0.0059. This makes sense given the existing mitigation measures analyzed take some dens off the table because they are found prior to the commencement of activities that could run over them. Additionally, the actual footprint of vehicles is very small
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compared to the scale of the project area, thus, there is a very low risk to begin with that a den would even overlap a vehicles footprint on the landscape.
When additional mitigation measures proposed by the applicant are considered, including the avoidance of steep terrain and the training of personnel for identifying den site characteristics, which cannot be quantified, the Service determined that the probability of running over a den was sufficiently small so that it could be dismissed and therefore was not included in this ITR.
Comment 67: One commenter suggested that the Service should use randomized case studies for their polar bear denning analysis.
Response: It is not clear exactly what the commenter means by the case studies used for the case studies are not randomized. There was no way to use randomized data in this case. The use of randomized data in this case would require conducting a study by radiocollaring denning females and then observing their response to any den disturbance. This runs the risk of substantial disturbance in both the capture and collaring see Amstrup 1993, Lunn et al. 2004 and the observation see Smith et al. 2007, 2010, 2013; Robinson 2014. Instead we relied on the case studies, the best available information, to inform our model and take probabilities.
Comment 68: One commenter suggested that the Service should reevaluate the most recent scientific evidence on the number of land-based dens for the SBS polar bear stock to avoid underestimating the number of dens used for the denning analysis.
Response: We are not sure what leads the commenter to believe that the results of Atwood et al. 2020 are an underestimate of the number of dens on shore. Atwood et al. 2020 represents the best available science and updates the approach developed by Wilson and Durner 2020 to incorporate newer data that was not available for Wilson and Durner 2020 and which does a better job incorporating uncertainty into the parameters used in the approach. The reason Atwood et al. 2020 is used over Wilson and Durner 2020 is two-fold.
First, an updated den catalogue i.e., Durner et al. 2020 wasnt available when Wilson and Durner 2020
conducted their analysis. This new set of dens is the primary reason that the estimate from Atwood et al. differs from Wilson and Durner. Second, multiple public comments on the analysis of Wilson and Durner noted that uncertainty in underlying parameters
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