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Federal Register / Vol. 86, No. 23 / Friday, February 5, 2021 / Notices injury or loss of life for individuals.
There are two scenarios, approaching pile refusal and pile instability, where this imminent risk could be a factor.
These scenarios are considered unlikely and it is expected that shutdowns will predominately be practicable during operations. See the Proposed Mitigation section for shutdown procedural details.
Although the exposure modeling indicated that Level A harassment takes are only expected for a three species of baleen whales fin whale, minke whale, and humpback whale, South Fork Wind requested authorization of take by Level A harassment of one sei whale based on the occurrence of sei whales in the project area documented during prior and ongoing HRG surveys of the SFWF.
South Fork Wind requested authorization of take equal to the mean group size for Level B harassment, based on the best available data seals, Herr et al., 2009; blue whale, long-finned pilot whale, Kenney and Vigness-Raposa, 2010; sperm whale, and Rissos dolphin, Barkaszi and Kelly, 2018. NMFS agrees
that this approach is appropriate in cases where instantaneous exposure is expected to result in harassment, e.g., Level B harassment and calculated take estimates are either zero or less than the group size.
Cofferdam Installation and Removal Animal movement and exposure modeling was not used to determine potential exposures from vibratory pile driving. Rather, the modeled acoustic range distances to isopleths corresponding to the Level A
harassment and Level B harassment threshold values were used to calculate the area around the cofferdam predicted to be ensonified daily to levels that exceed the thresholds, or the ZOI. ZOI
is calculated as the following:
ZOI = pr2, where r is the linear acoustic range distance from the source to the isopleth for Level A harassment or Level B harassment thresholds. This area was adjusted to account for the portion of the ZOI
truncated by the coastline of Long Island, NY.

The daily area was then multiplied by the maximum monthly density of a given marine mammal species. Roberts et al. 2018 produced density models for all seals but did not differentiate by seal species. Because the seasonality and habitat use by gray seals roughly overlaps with that of harbor seals in the survey areas, it was assumed that the mean annual density of seals could refer to either of the respective species and was, therefore, divided equally between the two species.
Finally, the resulting value was multiplied by the number of proposed activity days which is, for cofferdam installation and removal, conservatively estimated as two days. Modeling of the Level A harassment exposures resulting from two 18-hrs periods of vibratory pile driving and removal resulted in less than one exposure for all species for each month between October 1 and May 31. Modeled potential Level B
harassment exposures resulting from installation and extraction of the cofferdam are shown in Table 19.

TABLE 19MODELED LEVEL B HARASSMENT EXPOSURES RESULTING FROM VIBRATORY PILE DRIVING AND REMOVAL OF
THE COFFERDAM
Species
Jan
Fin whale
Minke whale
Sei whale
Humpback whale
North Atlantic right whale
Atlantic white-sided dolphin
Common dolphin
Common bottlenose dolphin
Harbor porpoise
Gray seal
Harbor seal

0
2 0
1 6
0 1
289
3 1,305
1,305

Feb 0
3 0
1 6
0 0
123
2 1,305
1,305

Mar 1
3 0
1 5
0 0
65
2 1,305
1,305

Apr 2
0 0
0 3
1 1
197
5 1,305
1,305

May
Oct
1 0
0 0
1 1
3 1,509
3 1,305
1,305

1
0 0
0 0
1 3
2,007
11
1,305
1,305

Nov 0
2 0
0 1
1 4
1,088
1 1,305
1,305

Dec 0
2 0
1 3
1 3
337
2 1,305
1,305

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Maximum 18-hour periods of vibratory pile driving or removal will be separated by at least 24 hours of no vibratory sound source operating at the cofferdam.

Modeled vibratory pile driving activities for the SFEC SFWF COP
Appendix J1 Denes et al., 2018
resulted in mean acoustic ranges to the PTS threshold for low frequency cetaceans, ranging from 742 m for 6 hrs of piling to 1,470 m for 18 hrs of piling Denes et al., 2018. Maximum acoustic ranges to PTS thresholds for other marine mammal hearing groups are all under 103 m. Level A harassment exposures are not expected due to low population densities of LFC species in the project area, animal movement and required accumulation periods Denes et al., 2019, the short duration of vibratory pile driving, and proposed mitigation measures see Proposed Mitigation section.
Vibratory pile driving during cofferdam installation and removal for
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the SFEC does have the potential to elicit behavioral responses in marine mammals. However, predicting Level B
harassment exposure estimates resulting from vibratory pile driving is complicated by the nearshore location, short duration of cofferdam installation and removal, and static species density data that are not indicative of animals transiting the nearshore environment.
Marine mammal densities at the near shore export cable area were estimated from the 10 x 10 km habitat density block from Roberts et al. 2016 and Roberts et al. 2018 that contained the anticipated location of the temporary cofferdam. However, the density estimates are not provided for the area adjacent to the shoreline, although some density blocks do intersect the shore.
Due to this structure, densities are
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artificially weighted to the nearest 100
km2 offshore and do not adequately represent the low numbers expected for some groups like large whales. In addition, the species densities represented in the Roberts et al. 2016
and Robert et al. 2018 are provided as monthly estimates and are, therefore, not indicative of a single-day distribution of animals within the potential ensonified zone. The modeled behavioral harassment threshold acoustic ranges extend beyond 36 km from the source Table 11; despite this extensive Level B harassment zone, only bottlenose dolphin, harbor seal, and gray seal exposure estimates are relatively large. However, the low densities of most species nearshore, the seasonality of occurrence, and the transitory nature of marine mammals
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