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Federal Register / Vol. 86, No. 24 / Monday, February 8, 2021 / Notices 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.
The effect of needle guns is unclear as we have not recently authorized take by this method in these circumstances.
Given the relatively low source level for needle guns and small ensonified areas discussed below, there is some uncertainty about whether take will occur from this activity. However, in consideration of the applicants request and the predicted source levels, we conservatively authorize some take for this project.
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.
Thresholds have also been developed identifying the received level of in-air sound above which exposed pinnipeds would likely be behaviorally harassed.
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 decibel dB re 1
microPascal mPa root mean square rms for continuous e.g., vibratory pile-driving and above 160 dB re 1 mPa rms for non-explosive impulsive e.g., impact pile driving or intermittent e.g., scientific sonar sources. For in-air
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sounds, NMFS predicts that harbor seals exposed above received levels of 90 dB
re 20 mPa rms will be behaviorally harassed, and other pinnipeds will be harassed when exposed above 100 dB re 20 mPa rms.
WADOTs proposed activity includes the use of continuous vibratory piledriving and removal in water and needle guns in air sources, and therefore the 120 dB re 1 mPa rms threshold is applicable in water and the pinniped thresholds are applicable in air.
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. WADOTs activity includes the use of non-impulsive vibratory pile driving/removal sources.
These thresholds are provided in Table 2. 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/marinemammal-acoustic-technical-guidance.

TABLE 2THRESHOLDS IDENTIFYING THE ONSET OF PERMANENT THRESHOLD SHIFT
PTS onset acoustic thresholds received level
Hearing group
Non-impulsive Low-Frequency LF Cetaceans
Mid-Frequency MF Cetaceans
High-Frequency HF Cetaceans
Phocid Pinnipeds PW Underwater
Otariid Pinnipeds OW Underwater

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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.

Note: 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. 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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Ensonified Area Here, we describe operational and environmental parameters of the activity that will feed into identifying the area ensonified above the acoustic thresholds, which include source levels and transmission loss coefficient.
The sound field in the project area is the existing background noise plus additional construction noise from the
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proposed project. Marine mammals are expected to be affected via sound generated by the primary components of the project i.e., vibratory pile driving and removal and needle guns.
Vibratory hammers produce constant sound when operating, and produce vibrations that liquefy the sediment surrounding the pile, allowing it to penetrate to the required seating depth.
The actual durations of each installation
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method vary depending on the type and size of the pile.
In order to calculate distances to the Level A harassment and Level B
harassment sound thresholds for activities being used in this project, NMFS used acoustic monitoring data from other locations to develop source levels or the various pile types, sizes and methods see Table 3. Source levels for the 48-inch sheetpiles come from the
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