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Federal Register / Vol. 86, No. 33 / Monday, February 22, 2021 / Notices
TABLE 5USER SPREADSHEET INPUT PARAMETERS USED FOR CALCULATING LEVEL A HARASSMENT ISOPLETHS
Continued
Number of strikes per pile
Propagation xLogR
Distance from source level measurement meters.

11.5-inch H-pile
14-inch H-pile
14-inch H-pile
48-inch pipe pile
19.69-inch sheet piles
1,000
15
10

1,000
15
10

15
10

1,000
15
10

15
10

25-inch sheet piles
15.
10.

a These estimates include contingencies for weather, equipment, work flow, and other factors that affect the number of piles per day, and are assumed to be a maximum anticipated per day. Given that AGDC plans to pile drive up to 24 hours per day, it is appropriate to assume that the number of piles installed within the 24hour period may not be a whole number.
b These averages assume that AGDC will drive 11.5-inch H-piles and sheet piles at a rate of 25 feet per day.

TABLE 6CALCULATED DISTANCES TO LEVEL A AND LEVEL B HARASSMENT ISOPLETHS
Activity
Level A harassment zone m
Hammer type
LF cetaceans 11.5-inch H-Pile
14-inch H-Pile
48-inch Pipe Pile
19.69-inch Sheet Piles
25-inch Sheet Piles

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Level A harassment zones are typically smaller than Level B
harassment zones. However, in rare cases such as the impact pile driving of the 11.5-inch and 14-inch H-piles in AGDCs project, the calculated Level A
harassment isopleth is greater than the calculated Level B harassment isopleth.
Calculation of Level A harassment isopleths include a duration component, which in the case of impact pile driving, is estimated through the total number of daily strikes and the associated pulse duration. For a stationary sound source such as impact pile driving, we assume here that an animal is exposed to all of the strikes expected within a 24-hour period. Calculation of a Level B
harassment zone does not include a duration component. Depending on the duration included in the calculation, the calculated Level A harassment isopleths can be larger than the calculated Level B harassment isopleth for the same activity.
Marine Mammal Occurrence In this section we provide the information about the presence, density, or group dynamics of marine mammals that will inform the take calculations.
Each fall and summer, NMFS and BOEM conduct an aerial survey in the Arctic, the ASAMM surveys Clarke et al., 2012, 2013a, 2014, 2015, 2017a, 2017b, 2018, 2019, 2020. The goal of these surveys is to document the distribution and relative abundance of bowhead, gray, right, fin and beluga whales and other marine mammals in areas of potential oil and natural gas exploration, development, and
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1,194
1,002
2 1,575
17
17

production activities in the Alaskan Beaufort and northeastern Chukchi Seas. Traditionally, only fall surveys were conducted but, in 2011, the first dedicated summer survey effort began in the ASAMM Beaufort Sea study area.
AGDC used these ASAMM surveys as the data source to estimate seasonal densities of cetaceans bowhead, gray and beluga whales in the project area.
The ASAMM surveys are conducted within blocks that overlay the Beaufort and Chukchi Seas oil and gas lease sale areas offshore of Alaska Figure 16 in AGDCs application, and provide sighting data for bowhead, gray, and beluga whales during summer and fall months. During the summer and fall, NMFS observed for marine mammals on effort for 13,484 km and 12,846 km, respectively, from 2011 through 2018, and an additional 1643 km during summer 2019 and 2055 km during fall 2019. Data from those surveys are used for this analysis. We note that the Prudhoe Bay portion of the AK LNG
project is in ASAMM survey Block 1a.
The inshore boundary of Block 1
terminates at the McClure Island group, and it was not until 2016 that on-effort surveys began inside the McClure Island group Block 1a; including Prudhoe Bay since bowhead whales, the focus of the surveys, are not likely to enter this area given its shallow depth. However, no bowhead whales and only one beluga whale have been observed in Block 1a including Prudhoe Bay. Therefore, the density estimates provided here, calculated using data from block 1, are likely an overestimate because they rely
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Phocids 639
536
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10
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Level B
harassment zone m 341
631
1,000
2,154
4,642
4,642

on offshore surveys where marine mammals are more likely to be present.
Bowhead Whale AGDC calculated density estimates for bowhead whale by dividing the average number of whales observed per km of transect effort from 2011 to 2018 in ASAMM Block 1 whales/km in Table 7
by two times the effective strip width ESW to encompass both sides of the transect line whales per km/2 ESW.
The ESW for bowhead whales from the Aero Commander aircraft is 1.15 km 0.71 mi Ferguson and Clarke 2013.
Therefore, the summer density estimate is 0.005 bowhead whales/km2, and the fall density estimate is 0.017 bowhead whales/km2. The resulting densities are expected to be overestimates for the AK
LNG analysis because the data is based on sighting effort outside of the barrier islands, and bowhead whales rarely occur within the barrier islands.
However, AGDC conservatively used the higher fall density to estimate potential Level B harassment takes, and NMFS
concurs. Note that inclusion of the 2019 ASAMM surveys reduces the fall bowhead density to 0.016 bowhead whales/km2. However, NMFS has conservatively used the higher density included in the proposed IHA to calculate Level B harassment take of bowhead whale, as described in the Take Calculation and Estimation section, below.
As noted in the Description of Marine Mammals in the Area of Specified Activities section of the proposed IHA
85 FR 43382; July 16, 2020, we do not expect bowhead whales to be present
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