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Federal Register / Vol. 86, No. 33 / Monday, February 22, 2021 / Notices
potential to result in behavioral harassment of marine mammals in the vicinity of the survey area. The notice of proposed IHA 85 FR 43382; July 16, 2020 included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from AGDCs construction activities on marine mammals and their habitat. That information and analysis is incorporated by reference into this final IHA
determination and is not repeated here;
please refer to the notice of proposed IHA 85 FR 43382; July 16, 2020.
Estimated Take This section provides an estimate of the number of incidental takes authorized through this IHA, which will inform both NMFS consideration of small numbers and the negligible impact determination.
Harassment is the only type of take expected to result from these activities.
Except with respect to certain activities not pertinent here, section 318 of the MMPA defines harassment as any act of pursuit, torment, or annoyance, which i has the potential to injure a marine mammal or marine mammal stock in the wild Level A harassment;
or ii has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering Level B harassment. Authorized takes would primarily be by Level B
harassment, as use of the acoustic source i.e., vibratory and impact pile driving has the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury Level A harassment to result, primarily for phocids, due to their lack of visibility and the size of the Level A
harassment zones. Auditory injury is unlikely to occur to cetaceans for the reasons described in the Take Calculation and Estimation section,
below. The mitigation and monitoring measures are expected to minimize the severity of the taking to the extent practicable.
As described previously, no mortality is anticipated or authorized for this activity. Below we describe how the take is estimated.
Generally speaking, we estimate take by considering: 1 Acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; 2 the area or volume of water that will be ensonified above these levels in a day; 3 the density or occurrence of marine mammals within these ensonified areas;
and, 4 and the number of days of activities. We note that while these basic factors can contribute to a basic calculation to provide an initial prediction of takes, additional information that can qualitatively inform take estimates is also sometimes available e.g., previous monitoring results or average group size. Below, we describe the factors considered here in more detail and present the take estimate.
Acoustic Thresholds NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed equated to Level B harassment or to incur PTS of some degree equated to Level A harassment.
Level B Harassment for non-explosive sourcesThough significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source e.g., frequency, predictability, duty cycle, the environment e.g., bathymetry, and the receiving animals hearing, motivation, experience, demography, behavioral context and can be difficult to predict Southall et
al., 2007, Ellison et al., 2012. Based on what the available science indicates and the practical need to use a threshold based on a factor that is both predictable and measurable for most activities, NMFS uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS predicts that marine mammals are likely to be behaviorally harassed in a manner we consider Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 dB re 1 mPa rms for continuous e.g., vibratory piledriving, drilling and above 160 dB re 1
mPa rms for non-explosive impulsive e.g., seismic airguns or intermittent e.g., scientific sonar sources.
AGDCs construction activity includes the use of continuous vibratory pile driving and impulsive impact pile driving sources, and therefore the 120
and 160 dB re 1 mPa rms are applicable.
Level A harassment for non-explosive sourcesNMFS Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing Version 2.0
Technical Guidance, 2018 identifies dual criteria to assess auditory injury Level A harassment to five different marine mammal groups based on hearing sensitivity as a result of exposure to noise from two different types of sources impulsive or nonimpulsive. AGDCs construction activity includes the use of impulsive impact pile driving and non-impulsive vibratory pile driving sources.
These thresholds are provided in the table below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS 2018 Technical Guidance, which may be accessed at https www.fisheries.noaa.gov/
national/marine-mammal-protection/
marine-mammal-acoustic-technicalguidance.

TABLE 3THRESHOLDS IDENTIFYING THE ONSET OF PERMANENT THRESHOLD SHIFT
PTS onset acoustic thresholds
received level
Hearing group
tkelley on DSKBCP9HB2PROD with NOTICES2

Impulsive Low-Frequency LF Cetaceans
Mid-Frequency MF Cetaceans
High-Frequency HF Cetaceans
Phocid Pinnipeds PW Underwater
Otariid Pinnipeds OW Underwater

Cell Cell Cell Cell Cell
1:
3:
5:
7:
9:

Lpk,flat:
Lpk,flat:
Lpk,flat:
Lpk,flat:
Lpk,flat:

219
230
202
218
232

dB;
dB;
dB;
dB;
dB;

Non-impulsive
LE,LF,24h: 183 dB
LE,MF,24h: 185 dB
LE,HF,24h: 155 dB
LE,PW,24h: 185 dB
LE,OW,24h: 203 dB

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2: LE,LF,24h: 199 dB.
4: LE,MF,24h: 198 dB.
6: LE,HF,24h: 173 dB.
8: LE,PW,24h: 201 dB.
10: LE,OW,24h: 219 dB.

Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive sounds, these thresholds should also be considered.

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