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Federal Register / Vol. 86, No. 157 / Wednesday, August 18, 2021 / Notices Estimated Take This section provides an estimate of the number of incidental takes for authorization through this IHA, which informed 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 will be by Level B
harassment, as use of seismic airguns may result, either directly or as a result of TTS, in disruption of behavioral patterns of marine mammals. The mitigation and related monitoring measures are expected to minimize the severity of such taking to the extent practicable. Moreover, based on the nature of the activity and the anticipated effectiveness of the mitigation measures i.e., implementation of extended shutdown distances for certain species discussed in detail below in the Mitigation sectionLevel A harassment is neither anticipated nor authorized.
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 Permanent Threshold Shift 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, the receiving animals hearing, motivation, experience, demography, behavioral context, and the distance between the sound source and the animal, and can be difficult to predict Southall et al., 2007, Ellison et al., 2012. NMFS uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS predicts that marine mammals may be behaviorally harassed i.e., Level B harassment when exposed to underwater anthropogenic noise above received levels 160 dB re 1 mPa rms for the impulsive sources i.e., seismic airguns evaluated here.
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. UAGIs seismic survey includes the use of impulsive sources seismic airgun.
These thresholds are provided in Table 3 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
Impulsive
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Low-Frequency LF Cetaceans
Mid-Frequency MF Cetaceans
High-Frequency HF Cetaceans
Phocid Pinnipeds PW
Underwater
Otariid Pinnipeds OW
Underwater

Cell Cell Cell Cell
Non-impulsive
1: Lpk,flat: 219; dB; LE,LF,24h: 183 dB
3: Lpk,flat: 230 dB; LE,MF,24h: 185 dB
5 Lpk,flat: 202 dB; LE,HF,24h: 155 dB
7: Lpk,flat: 218 dB; LE,PW,24h: 185 dB

Cell 9: Lpk,flat: 232 dB; LE,OW,24h: 203 dB

Cell Cell Cell Cell
2:
4:
6:
8:

LE,LF,24h: 199 dB.
LE,MF,24h: 198 dB.
LE,HF,24h: 173 dB.
LE,PW,24h: 201 dB.

Cell 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.
Note: Peak sound pressure Lpk has a reference value of 1 Pa, and cumulative sound exposure level LE has a reference value of 1Pa2s.
In this Table, thresholds are abbreviated to reflect American National Standards Institute standards ANSI 2013. However, peak sound pressure is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript flat is being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function LF, MF, and HF
cetaceans, and PW and OW pinnipeds and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude of ways i.e., varying exposure levels and durations, duty cycle. When possible, it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be exceeded.

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