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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations were not adequately accounted for.
Atwood et al. 2020 overcame this problem to present a more robust estimate. We agree with the commenter that, in the long term, land-based denning is likely to increase due to loss of sea ice. However, the most recent study of land-based denning in the SBS, Olson et al. 2017 found that rates of land-based denning have been constant i.e., not statistically different between the periods 19962006 and 20072013.
Given that the lowest sea ice minimum extent was observed in 2012, its unlikely that there has been a significant increase in land-based denning since the data used in Olson et al. 2017.
Comment 69: One commenter suggested the Service should consider including more recent years of denning data in their denning analysis in order to account for the increased number of land-based dens.
Response: Atwood et al. 2020 are clear about their methods and what data they used to calculate the 54% of dens occurring on land. This estimate conforms to those found in Olson et al.
2017, which is the most recently published study on the percent of SBS
bears denning on land. Olson et al.
2017 found that on average, in the period 19962006, 54% of bears in the SBS denned on land, and in the period 20072013, 55% denned on land. Thus, these data nearly perfectly conform to the values used by Atwood et al. 2020;
which also included uncertainty around those estimates. The reason Atwood only used data through 2015 is because that is the last year when bears received GPS collars, which are required to obtain an unbiased estimate of the distribution of denning. The graph the commenters present in their letter is not an accurate way to represent the data in the den catalogue. While its true that there are additional years of dens in the den catalogue, beyond 2015 they are based on firsthand observations, which are going to show a positive bias towards land-based dens given that limited search effort is conducted offshore. Thus, the best available data are used by Atwood et al. 2020, and the approach used by the commenters is likely biased high and not a proper way to summarize the data.
Comment 70: One commenter suggested that the Service should clarify their methods for accounting for the variation and uncertainty in their polar bear population estimate and the interannual variation in the number of denning female polar bears that was used in the denning analysis.
Response: We agree that Wilson and Durner 2020 failed to account for uncertainty associated with many of the
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underlying parameters used to estimate the number of dens on shore. That is why we relied on the estimate provided by Atwood et al. 2020 that does account for that uncertainty. The uncertainty accounted for by Atwood et al. 2020 incorporates annual variability in environmental conditions, which could lead to differences in the use of land. So, the Atwood et al. 2020
methods and results are robust to the issues presented by the commenter.
Comment 71: One commenter suggested that the Service should consider accounting for the number of dens containing females without cubs and reevaluating the den emergence date to include only successful dens in order to not underestimate the number of takes for denning polar bears.
Response: We disagree that the model does not account for dens with only a female bear. In fact we provide some probability 7% for a den to have 0
cubs. So, we do account for the probability of a female emerging without cubs. As for the incorrect skew of emergence dates, we again disagree with the commenter. We use den emergence data from Rode et al. 2018
and restrict the data to only those that were in the den for a sufficient amount of time to indicate the den was more than a shelter den. Additionally, even though Rode et al. identify some of the dens as not being observed with cubs 100 days after emergence, it does not indicate that the dens were unsuccessful, only that they were later observed without cubs. Cubs could easily have been lost between emergence and subsequent reobservation. There is currently no way to know if a bear emerged without a cub. If those data were available, we would include them, but they dont exist.
Comment 72: One commenter suggested that the Services denning analysis using the Wilson and Durner 2020 model framework does not accurately predict impacts to denning polar bears throughout the geographic scope for project activities and the model does not account for uncertainty in the timing and location of Industry activities that may impact denning polar bears.
Response: We disagree with the commenter that the general framework provided by Wilson and Durner 2020
is not suitable for use in this ITR. The approach developed by Wilson and Durner 2020 provides a general framework for how to incorporate different sources of information as well as associated uncertainty to analyze how different types of activity and infrastructure might affect denning
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polar bears. The specific model discussed in Wilson and Durner 2020
has been significantly modified to account for the proposed activities in this Request as well as additional sources of information e.g., different denning periods to increase the realism of the model. While it is true that Wilson and Durner 2020 only used the model to analyze impacts to polar bears over a smaller activity area, with one type of industrial activity, the model we published as part of this ITR clearly shows that it is capable of being applied to a larger area and suite of activities.
We also disagree that the ITR does not provide reliable information on where and when activities will occur. Both the code and objects associated with the den disturbance model and the associated shapefiles published with the proposed ITR provide both spatial and temporal information on when/where activities will occur. In instances where specific dates or areas were unknown e.g., seismic surveys, we accounted for that uncertainty by analyzing the seismic to occur in the worst place possible for polar bears within the range provided by AOGA in their Request as well as accounting for variability in the timing of activity within prescribed bounds. We also disagree with the commenter that the Service did not account for the possibility of a larger seismic survey.
This is not true. We clearly state on page 29410 of the Federal Register publication of the Proposed ITR that during any given winter, the areas surveyed would be <766 km2 and <1,183 km2 in the areas identified as relatively high and relatively low den probabilities, respectively.
Comment 73: Commenters suggested that the Service should reevaluate their take determination for early den departures as potentially lethal take for polar bear cubs.
Response: We do allow for potential survival consequence from early emergence. In fact, if a den is disturbed that leads to early emergence, cubs are always given a serious take by Level A
harassment. There are currently no data to support that an early departure from the den itself leads to reduced survival.
That would take a similar-type analysis that Rode et al. 2018 conducted. While we agree cubs have been observed being killed by conspecifics and other predators after leaving the den site, there is currently no linkage with time spent at the den post-emergence and pre-departure.
Comment 74: One commenter suggested that the Service should clarify their explanation for how non-serious take by Level A harassment was
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