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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations such impacts. We use the best available science to address this question. While we agree that there are likely local factors at a den site that could play a role in triggering when bears decide to depart the den site, those relationships have not been established, nor would there be any way to project those conditions to all future denning bears.
We use real-world data on den emergence dates and time spent at the den site post-emergence but prior to permanently departing the area. These observations already contain natural variation in the timing of these events, possibly based on the local conditions or the specific attributes of denning females e.g., nutritional condition.
Thus, drawing from these distributions should allow for the level of natural variation to be accounted for in the analysis. While its true a larger sample size would always be better, polar bears are difficult to study and we must therefore use what we have available. It is also worth mentioning that the sample sizes are not so small as to be unreliable. In fact they were deemed sufficient for inclusion into multiple peer-reviewed studies e.g., Rode et al.
2014, Smith et al. 2007.
Comment 59: One commenter suggested that the Service should consider the potential impacts of take by Level A harassment that may result from a mother abandoning her cubs in response to disturbance.
Response: The dataset that was used to analyze potential take from surface interactions encompassed all recorded human-polar bear interactions throughout the year, including the months when sows are moving toward the sea ice with cubs of the year. There are no recorded interactions in the 20142018 dataset between Industry and these bears that resulted in Level A
harassment. The Service has also accounted for these potential interactions when establishing mitigation measures. Under the mitigation measures established in the proposed rule, Industry must survey for maternal polar bear dens, create exclusion zones around known dens, and report all polar bear interactions including those with sows and cubs to the Service within 48 hours of the event.
Comment 60: One commenter suggested that the Service should consider the most recent evidence of cub survival and recruitment in the SBS
polar bear population as part of their baseline to assess impacts to SBS polar bears.
Response: We agree with the commenter that over the past 20 years, cub-of-the-year survival in the SBS has been low relative to other
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subpopulations and is the primary driver of concomitant decreases in abundance. Survival was especially low in the period 20042008 mean = 0.24, a period of marked population decline, but was relatively higher in the period 20092014 mean = 0.50, the last year for which estimates are available Atwood et al. 2020.
Comment 61: One commenter suggested that the Service should clarify the explanation for distinguishing lethal take of polar bear cubs if cubs are abandoned before 60 days of age and serious take by Level A harassment of cubs if cubs are abandoned after 60 of age.
Response: We disagree with the commenter that our different treatment of cubs emerging early during the early vs. late denning periods is inappropriate. We used 60 days based on published literature indicating that cubs have developed the basic functions to survive outside of the den by the time they reach 2 months 60 days of age.
Prior to 60 days, the literature indicates that survival of cubs outside of the den is not possible. Serious Level A
harassment is harassment that is likely to result in mortality. Based on the results of Rode et al. 2018, we know that early emergence from the den can lead to survival consequences for cubs.
However, it is clear from the results of Rode et al. 2018 that not all cubs die as a result of early emergence assuming they are >60 days old, thus, there is a different outcome to cubs emerging early during the early denning vs. the late denning periods. Hence, we treated early emergence during the late denning period as a serious Level A harassment because of the potential for a lethal outcome and lethal take for early emergence during the early denning period because of nearly 100%
probability of cubs dying then.
Comment 62: One commenter suggested that the Service should use systematically collected survey data that has been peer-reviewed in order to evaluate disturbance impacts to denning polar bears during Industry activities rather than use opportunistic observations of polar bear disturbance during Industry activities.
Response: The case studies include published literature and reports of observations made by Industry and research and provided to USFWS. The published literature includes peerreviewed literature, including literature by Amstrup 1993, which states that 10 of 12 polar bears tolerated exposure to exceptional levels of activity and most bears in this study showed substantial tolerance to activity. They also state . . . live capture and
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marking were probably more disruptive to bears than other possible perturbations. Yet recruitment of cubs through the time of emergence from the den and sizes of cubs were not affected. In our analysis, we utilized the best available information, which included internal reports and observations, as well as peer-reviewed literature e.g., Amstrup 1993. Thus, we used past reports to inform our findings, but the reports alone did not provide the basis for our findings as noted in the Info Source column of the AOGA
ITRCase Studies Summary Table 061621, document ID FWSR7ES
202100370011.
Comment 63: One commenter suggested that the Service should clarify the explanation for not classifying disturbance during early denning that did not result in den abandonment as take by Level A harassment.
Response: The early denning period begins with the birth of cubs and ends 60 days after birth. Because cubs cannot survive outside the den prior to reaching 60 days of age, any exposure during early denning that resulted in an emergence was classified as lethal take.
Of the 10 cases in the repeated-exposure category that occurred during the late denning period, 2 resulted in cub mortality; in the other 8 cases, exposures did not result in emergencesthe bears remained in their dens until after 13 February, the date that marked the end of the early denning period in cases where cub age was not known. Although possible, no studies have clearly demonstrated latent effects of disturbance on denning bears that did not respond to the disturbance in observable manners. In these eight cases, negative response e.g., early emergence were not observed during early denning. The purpose of evaluating these case studies was to inform the probabilities of responses to exposures during different periods. In this case, simulated dens that were exposed to repeated exposures before cubs reached 60 days of age had a 20%
probability, on average, of resulting in cub mortality and an 80% probability of remaining in the den until the beginning of the late denning period.
Comment 64: One commenter suggested that the Service should clarify their explanation for the dates assigned to the early denning period.
Response: We used the best available information to inform average parturition date of 15 December.
Messier et al. 1994 concluded that a majority of births occurred before or around 15 December as indicated by the drop in activity levels of instrumented females.

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