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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations allow us to refine our treatment of early emergences e.g., separating those that ultimately resulted in mortality from those that did not. See below for our response to the known outcomes statement.
Comment 78: One commenter suggested that the Service should consider followup information from den case studies and reevaluate take determinations based on latent effects of den disturbance to polar bear cubs.
Response: The commenter does not indicate which cases they consider to have known outcomes or followup, so we cannot address those directly. We are also unclear about which cases correspond to claims about observer opinion on cub size and survival. For example, the commenter states that observers thought the cub of another female was too small to survive, and the outcome for this case was an observed behavioral response. This statement seems to correspond with a case where the final outcome was insufficient information and was not used in calculating the response probabilities. It is possible that the cases the commenter is referring to elicited no observable response in a particular period but were subjected to disturbances in later periods that did elicit negative responses the commenters claim that a bear that departed a den without cubs was classified as a non-serious response supports this possibility because that classification would not be possible during a period when the bear left the den.
The general argument the commenter is expressing seems to be that latent effects from disturbance could manifest later, and, therefore, our harassment classifications for early departure in the post-emergence period should be higher presumably serious take by Level A
harassment as opposed to non-serious take by Level A harassment. Survival of cubs-of-the-year is often low, and this is especially true in the Southern Beaufort Sea subpopulation, even for those cubs from undisturbed dens. It should be expected, therefore, that some cubs that departed den sites early during the postemergence period would die before reaching independence and others would not. Although an early departure from a den due to disturbance may incur a fitness cost hence the nonserious take by Level A harassment classification, the probability or degree of that cost has not been evaluated.
Consequently, assigning a higher level of take i.e., serious take by Level A
harassment is inappropriate because that would signify an injury that is likely to result in mortality.

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Comment 79: One commenter suggested that the Service should clarify their explanation for the dates to distinguish the early denning period from the late denning period because this date may be later.
Response: The specific data range cited by the commenter is only related to the review of case studies because individual birth dates couldnt be known. We therefore had to rely on means obtained from the scientific literature to represent the natural range of den phenology data. The actual analysis to estimate disturbance and take to denning bears allowed for variability in denning phenology dates that match the published range of values. The actual start/end dates for the given denning periods in the analysis are based on the simulated dates for specific life history events. For example, bears are given a simulated birth date ranging from 1 December to 15 January i.e., the start of the early denning period. The late denning period then begins on the date those simulated cubs turn 60 days old.
Comment 80: One commenter suggested that the Service should consider whether climate change may cause a greater impact on polar bears that relocate their dens in response to disturbance.
Response: While we agree with the commenter that these types of relationships are conceivable, we are unaware of any information to support or document these claims. Further, these statements are just conjectures, and its equally feasible that females have sufficient energetic reserves to find a new den site given that they already spend energy scouting for ideal den sites. We are therefore required to use the currently best-available information, which indicates minimal impacts to denning females if forced to find a new den site after being disturbed.
Comment 81: One commenter suggested that the Service should consider whether the opportunistically collected data on polar bear dens is an accurate representation of polar bear responses to den disturbance and whether the Service developed accurate model assumptions based on polar bear responses to den disturbance.
Response: We use the best available information to calculate the probabilities of different levels of response to industrial activities. It is important to consider the variability across individuals and how they respond. The Service does not assume only minor behavioral responses, but provides estimates varying from lethal take of cubs to minor behavioral responses because that is the range of
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responses observed in real-world examples.
Comment 82: One commenter suggested that the Service should classify all cases in which denning polar bears are disturbed by industry activities as take by Level A harassment.
Response: We agree that there are sufficient data to show variability in responses to human activity. That is what we show with our case study assessment i.e., see table 7 with disturbance probabilities. Theres always some probability of no response and others of varying levels of disturbance. We also agree that the case study review didnt allow for accounting for bears that chose not to den near existing infrastructure/activity nor every single den that may have been adjacent to activities but going undetected. There is no way to ever detect all dens. However, we do account for bears that avoid denning near infrastructure. We detail this on pages 86 FR 2940729408 of the proposed rule June 1, 2021. Using historical den data, we found that dens occurred less frequently than expected adjacent to existing infrastructure, so that is accounted for in the model. It is simply an assumption with no published information to back it up that bears choosing to den away from Industry would be more sensitive to disturbance.
Again, it may be the case, but its also possible that it is not. So, without any data to support this claim, it would be inappropriate to incorporate it into the analysis. We disagree that we should treat all bears that are exposed to disturbance as having the potential for injury or death. The case study data and other published studies e.g., Amstrup 1993, Larson et al. 2020 clearly show this is not the case. And, as the commenter suggests, we know that there is a great deal of variability in responses to human activity. So, it would be inappropriate, and not based on the best-available science, to assume all bears are subject to potential injury or death.
Comment 83: One commenter suggested that the Service should consider that specific Industry activities may have different levels of impact on denning polar bears.
Response: The probabilities in Table 7
are drawn from a wide range of activities ranging from very minimal human activity, to very invasive. In our model framework, the varied and multiple sources of activity are accounted for. Briefly, a den is allowed to be exposed to disturbance until it is either disturbed and assigned a take by Level A harassment or greater, or bears emerge and depart their den by the
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