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Federal Register / Vol. 86, No. 148 / Thursday, August 5, 2021 / Rules and Regulations
TABLE 9CALCULATION OF THE TOTAL NUMBER OF BARGE AND TUG VESSEL TRIP HOURS AND THE PROPORTION OF THE
SEASON POLAR BEARS MAY BE IMPACTED IN A 16.5-KM2 IMPACT AREA BY BARGE/TUG PRESENCE
Est. length km
Origin
Destination
Frequency
Time/trip hr
Total time hr
West Dock
Milne Point
West Dock
Endicott
Badami
Pt. Thomson

Milne Point
West Dock
Endicott
Badami
Pt. Thomson
West Dock

1
1 30
10
10
10

38
38
22
42
32
96

10
10
6 11
9 26

10
10
178
114
86
259

Total Hours

658

Proportion of Season Impacted by Barge/Tug Use
The number of estimated takes was then calculated using Equation 4, in which the impact area is multiplied by encounter rate, proportion of season, and harassment rate for the open-water season. The final number of estimated Level B harassment events from barge/
tug trips was 1.12 bears per year.
In-Water Construction Polar bears are neither known to vocalize underwater nor to rely substantially upon underwater sounds to locate prey. However, for any predator, loss of hearing is likely to be an impediment to successful foraging.
The Service has applied a 190 dB re 1
mPa threshold for TTS and a 180 dB
re1mPa threshold for Level B harassment arising from exposure of polar bears to underwater sounds for previous authorizations in the Beaufort and Chukchi Seas; seas. However, given the projection of polar bear TTS at 188 dB
by Southall et al. 2019 referenced in
0.24

Figure 1, we used a threshold of Level B harassment at 180 dB re 1 mPa in our analysis for these regulations.
The proposal for the 20212026 ITR
period includes several activities that will create underwater sound, including dredging, screeding, pile driving, gravel placement, and geohazard surveys.
Underwater sounds and the spatial extent to which they propagate are variable and dependent upon the sound source e.g., size and composition of a pile for pile driving, equipment type for geophysical surveys, etc., the installation method, substrate type, presence of sea ice, and water depth.
Source levels range from less than 160
dB re 1 mPa to greater than 200 dB re 1 mPa Rodkin and Pommerenck, 2014, meaning some sounds reach the level of TTS, however they do not reach the level of PTS Table 1. Although these activities result in underwater areas that are above the 180 dB Level B
harassment threshold for polar bears,
the areas above the threshold will be small and fall within the current impact area 1.6 km used to estimate polar bear harassment due to surface interactions.
Thus, additional harassment calculations based on in-water noise are not necessary. Similarly, any in-air sounds generated by underwater sources are not expected to propagate above the Level B harassment thresholds listed in Table 1 beyond the 1.6-km 1.0-mi impact area established in Polar Bear:
Surface Interactions.
Sum of Harassment From All Sources A summary of total numbers of estimated take by Level B harassments during the duration of the project by season and take category is provided in Table 10. The potential for lethal or Level A harassment was explored. The highest probability of greater than or equal to 1 lethal or serious Level A
harassment take of polar bears over the 5-year ITR period was 0.462.

TABLE 10TOTAL ESTIMATED LEVEL B HARASSMENT EVENTS OF POLAR BEARS PER YEAR AND SOURCE
Level B harassment of polar bears on the surface or in water Year
Open Open Open Open Open Open
water water water water water water
Surface activity
2021Ice 2021/2022
2022Ice 2022/2023
2023Ice 2023/2024
2024Ice 2024/2025
2025Ice 2025/2026
2026

56.54
83.77
84.28
84.23
84.48
12

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Critical Assumptions To conduct this analysis and estimate the potential amount of Level B
harassment, several critical assumptions were made.
Level B harassment is equated herein with behavioral responses that indicate harassment or disturbance. There is likely a portion of animals that respond in ways that indicate some level of disturbance but do not experience
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Vessel activity
1.94
1.94
1.94
1.94
1.94
0.00

1.12
1.12
1.12
1.12
1.12
1.12

significant biological consequences. Our estimates do not account for variable responses by polar bear age and sex;
however, sensitivity of denning bears was incorporated into the analysis. The available information suggests that polar bears are generally resilient to low levels of disturbance. Females with dependent young and juvenile polar bears are physiologically the most sensitive Andersen and Aars 2008 and
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Aircraft overflights 0.82
0.95
0.95
1.09
1.09
0.15

Total Denning bears 3.1
3.2
3.1
3.1
3.2
0

65
91
92
92
92
14

most likely to experience harassment from disturbance. There is not enough information on composition of the SBS
polar bear stock in the ITR area to incorporate individual variability based on age and sex or to predict its influence on harassment estimates. Our estimates are derived from a variety of sample populations with various age and sex structures, and we assume the exposed population will have a similar
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