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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules
TABLE 1TEMPORARY THRESHOLD SHIFT TTS AND PERMANENT THRESHOLD SHIFT PTS THRESHOLDS ESTABLISHED
BY SOUTHALL et al. 2019 THROUGH MODELING AND EXTRAPOLATION FOR OTHER MARINE CARNIVORES, WHICH
INCLUDES BOTH POLAR BEARS AND WALRUSES, IN DECIBELS dB. IMPULSIVE THRESHOLDS ARE PROVIDED FOR
SOUND ONSET.
TTS
non-impulsive
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Air
Water

During an FAA test, test aircraft produced sound at all frequencies measured 50 Hz to 10 kHz Healy 1974; Newman 1979. At frequencies centered at 5 kHz, jets flying at 300 m 984 ft produced 13 octave band noise levels of 84 to 124 dB, propeller-driven aircraft produced 75 to 90 dB, and helicopters produced 60 to 70 dB
Richardson et al. 1995. Thus, the frequency and level of airborne sounds typically produced by Industry is unlikely to cause temporary or permanent hearing damage unless marine mammals are very close to the sound source. Although temporary or permanent hearing damage is not anticipated, impacts from aircraft overflights have the potential to elicit biologically significant behavioral responses from polar bears.
Observations of polar bears during fall coastal surveys, which flew at much lower altitudes than typical Industry flights see Estimating Take Rates of Aircraft Activities, indicate that the reactions of non-denning polar bears is typically varied but limited to shortterm changes in behavior ranging from no reaction to running away. Bears associated with dens have been shown to increase vigilance, initiate rapid movement, and even abandon dens when exposed to low-flying aircraft see Effects to Denning Bears for further discussion. Aircraft activities can impact bears over all seasons; however, during the summer and fall seasons, aircraft have the potential to disturb both individuals and congregations of polar bears. These onshore bears spend most of their time resting and limiting their movements on land. Exposure to aircraft traffic is expected to result in changes in behavior, such as going from resting to walking or running and therefore, has the potential to be energetically costly. Mitigation measures, such as minimum flight elevations over polar bears and habitat areas of concern as well as flight restrictions around known polar bear aggregations when safe, are included in this proposed ITR to achieve least
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practicable adverse impact to polar bears by aircraft.
Polar Bear: Effects of In-Water Activities In-water sources of sound, such as pile driving, screeding, dredging, or vessel movement, may disturb polar bears. In the open-water season, Industry activities are generally limited to relatively ice-free, open water. During this time in the Beaufort Sea, polar bears are typically found either on land or on the pack ice, which limits the chances of the interaction of polar bears with offshore Industry activities. Though polar bears have been observed in open water miles from the ice edge or ice floes, the encounters are relatively rare although the frequency of such observations may increase due to sea ice change. However, if bears come in contact with Industry operations in open water, the effects of such encounters likely include no more than short-term behavioral disturbance.
While polar bears swim in and hunt from open water, they spend less time in the water than most marine mammals. Stirling 1974 reported that polar bears observed near Devon Island during late July and early August spent 4.1 percent of their time swimming and an additional 0.7 percent engaged in aquatic stalking of prey. More recently, application of tags equipped with timedepth recorders indicate that aquatic activity of polar bears is greater than was previously thought. In a study published by Lone et al. 2018, 75
percent of polar bears swam daily during open-water months, with animals spending 9.4 percent of their time in July in the water. Both coastaland pack-ice-dwelling animals were tagged, and there were no significant differences in the time spent in the water by animals in the two different habitat types. While polar bears typically swim with their ears above water, Lone et al. 2018 found polar bears in this study that were fitted with depth recorders n=6 spent approximately 24 percent of their time in the water with their head underwater.
The pile driving, screeding, dredging, and other in-water activities proposed
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non-impulsive 177 dB
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by Industry introduce substantial levels of noise into the marine environment.
Underwater sound levels from construction along the North Slope have been shown to range from 103 decibels dB at 100 m 328 ft for auguring to 143 dB at 100 m 328 ft for pile driving Greene et al. 2008 with most of the energy below 100 Hz. Airborne sound levels from these activities range from 65 dB at 100 m 328 ft for a bulldozer and 81 dB at 100 m 328 ft for pile driving, with most of the energy for inair levels also below 100 Hz Greene et al. 2008. Therefore, in-water activities are not anticipated to result in temporary or permanent damage to polar bear hearing.
In 2012, during the open-water season, Shell vessels encountered a few polar bears swimming in ice-free water more than 70 mi 112.6 km offshore in the Chukchi Sea. In those instances, the bears were observed to either swim away from or approach the Shell vessels. Sometimes a polar bear would swim around a stationary vessel before leaving. In at least one instance a polar bear approached, touched, and investigated a stationary vessel from the water before swimming away.
Polar bears are more likely to be affected by on-ice or in-ice Industry activities versus open-water activities.
From 2009 through 2014, there were a few Industry observation reports of polar bears during on-ice activities.
Those observations were primarily of bears moving through an area during winter seismic surveys on near-shore ice. The disturbance to bears moving across the surface is frequently minimal, short-term, and temporary due to the mobility of such projects and limited to small-scale alterations to bear movements.
Polar Bear: Effects to Denning Bears Known polar bear dens in the Beaufort Sea ITR region, whether discovered opportunistically or as a result of planned surveys such as tracking marked bears or den detection surveys, are monitored by the Service.
However, these known denning sites are only a small percentage of the total
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