2024-18694. Takes of Marine Mammals Incidental to Specified Activities; Takes of Marine Mammals Incidental to Marine Site Characterization Surveys Off Rhode Island and Massachusetts

Table 1—Summary of Representative HRG Survey Equipment

Representative equipment type	Operating frequency ranges (kHz)	SL (SPL dB re 1µPa m)	SL (SEL dB re 1µPa2 m2 s)	SL (PK dBre 1µPa m)	Beamwidth ranges (degree)	Pulse duration (width) (millisecond)	Repetition rate (Hz)
Impulsive, Medium Sub-Bottom Profilers (Sparkers & Boomers)
AA, Dura-spark UHD Sparker (400 tips, 500 J) 1	0.3-1.2	203	174	211	180	1.1	4
AA, Dura-spark UHD Sparker Model 400 × 400 1	0.3-1.2	203	174	211	180	1.1	4
GeoMarine, Dual 400 Sparker, Model GeoSource 800 1  2	0.4-5	203	174	211	180	1.1	2
GeoMarine Sparker, Model GeoSource 200-400 1  2	0.3-1.2	203	174	211	180	1.1	4
GeoMarine Sparker, Model GeoSource 200 Lightweight 1  2	0.3-1.2	203	174	211	180	1.1	4
( print page 67601)
AA, triple plate SBoom (700-1,000 J) 3	0.1-5	205	172	211	80	0.6	4
1  The Dura-spark measurements and specifications provided in Crocker and Fratantonio (2016) were used for all sparker systems proposed for the survey. The data provided in Crocker and Fratantonio (2016) represent the most applicable data for similar sparker systems with comparable operating methods and settings when manufacturer or other reliable measurements are not available. Bay State Wind expects all equipment to operate at a comparable Joule-to-tip ratio as the 400 tip 500 J Dura-spark measured by Crocker and Fratantonio (2016) such that the proxy source levels provided in table 3 are realistically representative of sound levels that may be produced during sparker operations for the proposed survey.
2  The AA Dura-spark (500 J, 400 tips) was used as a proxy source for all proposed sparkers to represent the highest potential source level anticipated during the proposed survey. Though the power settings and number of tips may vary among of the sparker systems, all systems will operate with a comparable Joule-to-tip ratio which, as discussed above in section 1.3 of the Application, influences the source levels more than just power setting. Additionally, the survey would not utilize higher-powered sparker systems operating at ≥2,000 J so Dura-spark (500 J, 400 tips) is considered the best available proxy for source levels for these equipment.
3  Crocker and Fratantonio (2016) provide S-Boom measurements using two different power sources (CSP-D700 and CSP-N). The CSP-D700 power source was used in the 700 J measurements but not in the 1,000 J measurements. The CSP-N source was measured for both 700 J and 1,000 J operations but resulted in a lower SL; therefore, the single maximum SL value was used for both operational levels of the S-Boom.

Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (please see Proposed Mitigation and Proposed Monitoring and Reporting sections).

Description of Marine Mammals in the Area of Specified Activities

Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history of the potentially affected species. NMFS fully considered all of this information, and we refer the reader to these descriptions, instead of reprinting the information. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SARs; https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessments) and more general information about these species ( e.g., physical and behavioral descriptions) may be found on NMFS' website ( https://www.fisheries.noaa.gov/​find-species).

Table 2 lists all species or stocks for which take is expected and proposed to be authorized for this activity and summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act (ESA) and potential biological removal (PBR), where known. PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as described in NMFS' SARs). While no serious injury or mortality is anticipated or proposed to be authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species or stocks and other threats.

Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Atlantic and Gulf of Mexico SARs. All values presented in table 2 are the most recent available at the time of publication, including, as applicable, from the draft 2023 SARs (available online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessments).

Table 2—Species Likely Impacted by the Specified Activities ¹

Common name	Scientific name	Stock	ESA/MMPA status; strategic (Y/N) 2	Stock abundance (CV, N min , most recent abundance survey) 3	PBR	Annual M/SI 4
Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)
N Atlantic Right Whale	Eubalaena glacialis	Western Atlantic	E, D, Y	340 (0, 337, 2021) 5	0.7	27.2
Humpback Whale	Megaptera novaeangliae	Gulf of Maine	-, -, N	1,396 (0, 1380, 2016)	22	12.15
Fin Whale	Balaenoptera physalus	Western North Atlantic	E, D, Y	6,802 (0.24, 5,573, 2021)	11	2.05
Sei Whale	Balaenoptera borealis	Nova Scotia	E, D, Y	6,292 (1.02, 3,098, 2021)	6.2	0.6
Minke Whale	Balaenoptera acutorostrata	Canadian Eastern Coastal	-, -, N	21,968 (0.31, 17,002, 2021)	170	9.4
Order Cetartiodactyla—Cetacea—Superfamily Odontoceti (toothed whales, dolphins, and porpoises)
Sperm Whale	Physeter macrocephalus	North Atlantic	E, D, Y	5,895 (0.29, 4,639, 2021)	9.28	0.2
Long-Finned Pilot Whale 6	Globicephala melas	Western North Atlantic	-, -, N	39,215 (0.30, 30,627, 2021)	306	5.7
Striped Dolphin	Stenella coeruleoalba	Western North Atlantic	-, -, N	48,274 (0.29, 38,040, 2021)	529	0
Atlantic White-Sided Dolphin	Lagenorhynchus acutus	Western North Atlantic	-, -, N	93,233 (0.71, 54,443, 2021)	544	28
Bottlenose Dolphin	Tursiops truncatus	Western North Atlantic Offshore	-, -, N	64,587 (0.24, 52,801, 2021) 7	507	28
Common Dolphin	Delphinus delphis	Western North Atlantic	-, -, N	93,100 (0.56, 59,897, 2021)	1,452	414
Atlantic Spotted Dolphin	Stenella frontalis	Western North Atlantic	-, -, N	31,506 (0.28, 25,042, 2021)	250	0
Risso's Dolphin	Grampus griseus	Western North Atlantic	-, -, N	44,067 (0.19, 30,662, 2021)	307	18
White-Beaked Dolphin	Lagenorhynchus albirostris	Western North Atlantic	-, -, N	536,016 (0.31, 415,344, 2016)	4,153	0
Harbor Porpoise	Phocoena phocoena	Gulf of Maine/Bay of Fundy	-, -, N	85,765 (0.53, 56,420, 2021)	649	145
Order Carnivora—Superfamily Pinnipedia
Harbor Seal	Phoca vitulina	Western North Atlantic	-, -, N	61,336 (0.08, 57,637, 2018)	1,729	339
( print page 67602)
Gray Seal 8	Halichoerus grypus	Western North Atlantic	-, -, N	27,911 (0.20, 23,624, 2021)	1,512	4,570
1  Information on the classification of marine mammal species can be found on the web page for The Society for Marine Mammalogy's Committee on Taxonomy ( https://marinemammalscience.org/​science-and-publications/​list-marine-mammal-species-subspecies).
2  ESA status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.
3  NMFS marine mammal stock assessment reports online at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessment-reports-region. CV is coefficient of variation; N min is the minimum estimate of stock abundance.
4  These values, found in NMFS's SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined ( e.g., commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases.
5  The current SAR includes an estimated population (N best 340) based on sighting history through December 2021 (NMFS, 2024). In October 2023, NMFS released a technical report identifying that the North Atlantic right whale population size based on sighting history through 2022 was 356 whales, with a 95 percent credible interval ranging from 346 to 363 (Linden, 2023). Total annual average observed North Atlantic right whale mortality during the period 2017-2021 was 7.1 animals and annual average observed fishery mortality was 4.6 animals. Numbers presented in this table (27.2 total mortality and 17.6 fishery mortality) are 2016-2020 estimated annual means, accounting for undetected mortality and serious injury.
6  Key uncertainties exist in the population size estimate for this species, including uncertain separation between short-finned and long-finned pilot whales, small negative bias due to lack of abundance estimate in the region between US and the Newfoundland/Labrador survey area, and uncertainty due to unknown precision and accuracy of the availability bias correction factor that was applied.
7  Estimates may include sightings of the coastal form,
8  NMFS' stock abundance estimate (and associated PBR value) applies to the U.S. population only. Total stock abundance (including animals in Canada) is approximately 394,311. The annual M/SI value given is for the total stock.

As indicated above, all 17 species in table 2 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. All species that could potentially occur in the proposed survey areas are included in table 5 of the IHA application. While the blue whale ( Balaenoptera musculus), short-finned pilot whale ( Globicephala macrorhynchus), common bottlenose dolphin (western North Atlantic, northern migratory coastal stock; Tursiops truncatus), dwarf sperm whale ( Kogia sima), killer whale ( Orcinus orca), pygmy killer whale ( Feresa attenuata), false killer whale ( Pseudorca crassidens), northern bottlenose whale ( Hyperoodon ampullatus), Cuvier's beaked whale ( Ziphius cavirostris), Blainville's beaked whale ( Mesoplodon densirostris), Gervais beaked whale ( Mesoplodon europaeus), Sowerby's beaked whale ( Mesoplodon bidens), True's beaked whale ( Mesoplodon mirus), Melon-headed whale ( Peponocephala electra), Pantropical spotted dolphin ( Stenella attenuata), Fraser's dolphin ( Lagenodelphis hosei), rough toothed dolphin ( Steno bredanensis), Clymene dolphin ( Stenella clymene), spinner dolphin ( Stenella longirostri), harp seal ( Pagophilus groenlandica), and hooded seal ( Cystophora cristata) have been reported in the area, the temporal and/or spatial occurrence of these species is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here.

A description of the marine mammals in the area of the activities for which authorization of take is proposed here, including information on abundance, status, distribution, and hearing, may be found in the Federal Register notice of the proposed IHA for the 2022 IHA (87 FR 52515, August 26, 2022) addressing Lease Areas OCS-A 0486, 0487, and 0500. Significant new information is addressed below.

In addition, Bay State Wind is newly requesting authorization to take white-beaked dolphin. The white-beaked dolphin is considered rare in the Lease Area and potential ECRs, but two protected species observer (PSO) monitoring reports have reported the sighting of the species in the Rhode Island-Massachusetts Wind Energy Area (RI-MA WEA) where the Project Lease Area is located (EPI Group, 2021; RPS, 2021). Therefore, it is reasonable to anticipate take for this animal may occur and the take of the animal has been proposed for authorization accordingly. A detailed description of the white-beaked dolphin's status and trends, distribution and habitat preferences, and behavior and life history can be found in section 4.2.9 of the application.

North Atlantic Right Whale

In January 2024, NMFS released its draft 2023 SARs which updated the population estimate ( N_best) of North Atlantic right whales to 340 individuals; the annual mortality and serious injury (M/SI) value dropped from the final 2022 SAR of 31.2 to 27.2 in the draft 2023 SAR. Beginning in the 2022 SARs, the M/SI for North Atlantic right whale included the addition of estimated undetected mortality and serious injury, which had not been previously included in the SAR. The current population estimate is equal to the North Atlantic Right Whale Consortium's 2022 Annual Report Card, which identifies the population estimate as 340 individuals (Pettis et al. 2023).

Elevated North Atlantic right whale mortalities have occurred since June 7, 2017, along the U.S. and Canadian coast, with the leading category for the cause of death for this unusual mortality event (UME) determined to be “human interaction,” specifically from entanglements or vessel strikes. As of July 30, 2024, there have been 41 confirmed mortalities (dead, stranded, or floaters), 1 pending mortality, and 36 seriously injured free-swimming whales for a total of 78 whales. The UME also considers animals with sublethal injury or illness (called “morbidity”; n = 65) bringing the total number of whales in the UME to 142. More information about the North Atlantic right whale UME is available online at: https://www.fisheries.noaa.gov/​national/​marine-life-distress/​active-and-closed-unusual-mortality-events.

The proposed survey area is within a migratory corridor Biologically Important Area (BIA) for NARWs that extends from Massachusetts to Florida (LeBrecque et al. 2015). There is possible migratory behavior that could occur in this area between November and April. Right whale migration is not expected to be impacted by the proposed survey due to the very small size of the Lease Area and potential ECRs project area relative to the spatial extent of the available migratory habitat in the BIA.

Humpback Whale

Since January 2016, elevated humpback whale mortalities along the ( print page 67603) Atlantic coast from Maine to Florida led to the declaration of a UME. As of May 17, 2023, 227 humpback whales have stranded as part of this UME. Partial or full necropsy examinations have been conducted on approximately 90 of the known cases. Of the whales examined, about 40 percent had evidence of human interaction, either ship strike or entanglement. While a portion of the whales have shown evidence of pre-mortem vessel strike, this finding is not consistent across all whales examined and more research is needed. More information is available at: https://www.fisheries.noaa.gov/​national/​marine-life-distress/​active-and-closed-unusual-mortality-events.

Since December 1, 2022, the number of humpback strandings along the mid-Atlantic coast, from North Carolina to New York, has been elevated. In some cases, the cause of death is not yet known; in others, vessel strike has been deemed the cause of death. As the humpback whale population has grown, they are seen more often in the Mid-Atlantic. These whales may be following their prey (small fish) which were reportedly close to shore in the 2022-2023 winter. Changing distributions of prey impact larger marine species that depend on them, and result in changing distribution of whales and other marine life. These prey also attract fish that are targeted by recreational and commercial fishermen, which increases the number of boats and amount of fishing gear in these areas. This nearshore movement increases the potential for anthropogenic interactions, particularly.

The Lease Area and potential ECRs do not overlap any ESA-designated critical habitat, BIAs, or other important areas for the humpback whales. A humpback whale feeding BIA extends throughout the Gulf of Maine, Stellwagen Bank, and Great South Channel from May through December, annually (LaBrecque et al. 2015). However, this BIA is located further east and north of, and thus, does not overlap, the project area.

Marine Mammal Hearing

Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Not all marine mammal species have equal hearing capabilities ( e.g., Richardson et al. 1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall et al. (2007, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc.). Note that no direct measurements of hearing ability have been successfully completed for mysticetes ( i.e., low-frequency cetaceans). Subsequently, NMFS (2018) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65-decibel (dB) threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall et al. (2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in table 3.

Table 3—Marine Mammal Hearing Groups

[NMFS, 2018]

Hearing group	Generalized hearing range *
Low-frequency (LF) cetaceans (baleen whales)	7 Hz to 35 kHz.
Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)	150 Hz to 160 kHz.
High-frequency (HF) cetaceans (true porpoises, Kogia, river dolphins, Cephalorhynchid, Lagenorhynchus cruciger & L. australis)	275 Hz to 160 kHz.
Phocid pinnipeds (PW) (underwater) (true seals)	50 Hz to 86 kHz.
Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)	60 Hz to 39 kHz.
* Represents the generalized hearing range for the entire group as a composite ( i.e., all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65-dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall et al. 2007) and PW pinniped (approximation).

The pinniped functional hearing group was modified from Southall et al. (2007) on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range (Hemilä et al. 2006; Kastelein et al. 2009; Reichmuth et al. 2013).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information.

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

This section provides a discussion of the ways in which components of the specified activity may impact marine mammals and their habitat. The Estimated Take of Marine Mammals section later in this document includes a quantitative analysis of the number of individuals that are expected to be taken by this activity. The Negligible Impact Analysis and Determination section considers the content of this section, the Estimated Take of Marine Mammals section, and the Proposed Mitigation section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and whether those impacts are reasonably expected to, or reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.

A description of the potential effects of the specified activity on marine mammals and their habitat for the activities for which take is proposed here may be found in the Federal Register notice of the proposed IHA for the initial authorization proposed (87 FR 52515, August 26, 2022). NMFS has reviewed information on relevant Unusual Mortality Events, updated SARs, and other scientific literature and data, and preliminarily determined that there is no new information that affects our initial analysis of impacts on marine mammals and their habitat.

Estimated Take of Marine Mammals

This section provides an estimate of the number of incidental takes proposed for authorization through the IHA, which will inform NMFS' consideration of “small numbers,” the negligible impact determinations, and impacts on subsistence uses.

Harassment is the only type of take expected to result from these activities. ( print page 67604) Except with respect to certain activities not pertinent here, section 3(18) 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 be by Level B harassment only, in the form of disruption of behavioral patterns for individual marine mammals resulting from exposure to certain HRG sources. Based on the nature of the activity and the anticipated effectiveness of the mitigation measures ( i.e., shutdown measures, vessel strike avoidance procedures) discussed in detail below in the Proposed Mitigation section, Level A harassment is neither anticipated nor proposed to be authorized.

As described previously, no serious injury or mortality is anticipated or proposed to be authorized for this activity. Below we describe how the proposed take numbers are estimated.

For acoustic impacts, generally speaking, we estimate take by considering: (1) acoustic thresholds above which NMFS believes the best available science indicates marine mammals will likely 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) the number of days of activities. We note that while these factors can contribute to a basic calculation to provide an initial prediction of potential 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 proposed take estimates.

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 —Though 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 or exposure context ( e.g., frequency, predictability, duty cycle, duration of the exposure, signal-to-noise ratio, distance to the source), the environment ( e.g., bathymetry, other noises in the area, predators in the area), and the receiving animals (hearing, motivation, experience, demography, life stage, depth) and can be difficult to predict ( e.g., Southall et al. 2007, 2021; Ellison et al. 2012). Based on what the available science indicates and the practical need to use a threshold based on a metric that is both predictable and measurable for most activities, NMFS typically uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS generally predicts that marine mammals are likely to be behaviorally harassed in a manner considered to be Level B harassment when exposed to underwater anthropogenic noise above root-mean-squared pressure received levels (RMS SPL) of 120 dB (referenced to 1 micropascal (re 1 μPa)) for continuous ( e.g., vibratory pile driving, drilling) and above RMS SPL 160 dB re 1 μPa for non-explosive impulsive ( e.g., seismic airguns) or intermittent ( e.g., scientific sonar) sources. Generally speaking, Level B harassment take estimates based on these behavioral harassment thresholds are expected to include any likely takes by temporary threshold shift (TTS) as, in most cases, the likelihood of TTS occurs at distances from the source less than those at which behavioral harassment is likely. TTS of a sufficient degree can manifest as behavioral harassment, as reduced hearing sensitivity and the potential reduced opportunities to detect important signals (conspecific communication, predators, prey) may result in changes in behavior patterns that would not otherwise occur.

Bay State Wind's proposed activity includes the use of impulsive ( i.e., boomers and sparkers) and non-impulsive ( i.e., CHIRP SBPs) sources, and therefore the RMS SPL thresholds of 160 dB re 1 μPa is applicable.

Level A Harassment —NMFS' 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 non-impulsive).

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-technical-guidance.

On May 3, 2024, NMFS published (89 FR 36762) and solicited public comment on its draft Updated Technical Guidance, which includes updated thresholds and weighting functions to inform auditory injury estimates, and is intended to replace the 2018 Technical Guidance referenced above, once finalized. The public comment period ended on June 17, 2024, and although the Updated Technical Guidance is not final, we expect the Updated Technical Guidance to represent the best available science once it is.

Bay State Wind's HRG surveys include the use of impulsive ( i.e., boomers and sparkers) and non-impulsive ( i.e., CHIRP SBPs). However, as discussed above, NMFS has concluded that Level A harassment is not a reasonably likely outcome for marine mammals exposed to noise from the sources proposed for use here, and the potential for Level A harassment is not evaluated further in this document. The pending update to the Technical Guidance would not change NMFS' determination regarding the likelihood of take by Level A harassment. Please see Bay State Wind's application (section 1.4) for details of a quantitative exposure analysis exercise, ( i.e., calculated Level A harassment isopleths and estimated Level A harassment exposures). No take by Level A harassment is anticipated or proposed for authorization by NMFS. ( print page 67605)

Table 4—Thresholds Identifying the Onset of Permanent Threshold Shift

Hearing group	PTS onset acoustic thresholds * (received level)
	Impulsive	Non-impulsive
Low-Frequency (LF) Cetaceans	Cell 1:Lpk,flat : 219 dB; LE,LF,24h : 183 dB	Cell 2:LE,LF,24h : 199 dB.
Mid-Frequency (MF) Cetaceans	Cell 3:Lpk,flat : 230 dB; LE,MF,24h : 185 dB	Cell 4:LE,MF,24h : 198 dB.
High-Frequency (HF) Cetaceans	Cell 5:Lpk,flat : 202 dB; LE,HF,24h : 155 dB	Cell 6:LE,HF,24h : 173 dB.
Phocid Pinnipeds (PW) (Underwater)	Cell 7:Lpk,flat : 218 dB; LE,PW,24h : 185 dB	Cell 8:LE,PW,24h : 201 dB.
Otariid Pinnipeds (OW) (Underwater)	Cell 9:Lpk,flat : 232 dB; LE,OW,24h : 203 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 µPa, and cumulative sound exposure level ( LE ) has a reference value of 1µPa2 s. In this table, thresholds are abbreviated to reflect American National Standards Institute standards (American National Standards Institute, 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.

Ensonified Area

Here, we describe operational and environmental parameters of the activity that are used in estimating the area ensonified above the acoustic thresholds, including source levels and transmission loss coefficient.

NMFS has developed a user-friendly methodology for determining the rms sound pressure level at the 160-dB isopleth for the purpose of estimating the extent of Level B harassment isopleths associated with HRG survey equipment (NMFS, 2020). This methodology incorporates frequency and some directionality to refine estimated ensonified zones. Bay State Wind used NMFS's methodology, using the source level and operation mode of the equipment planned for use during the proposed survey, to estimate the maximum ensonified area over a 24-hour period, also referred to as the harassment area (table 5). Potential takes by Level B harassment are estimated within the ensonified area ( i.e., harassment area) as an SPL exceeding 160 dB re 1 µPa for impulsive sources ( e.g., sparkers, boomers) within an average day of activity.

The harassment zone is a representation of the maximum extent of the ensonified area around a sound source over a 24-hour period. The harassment zone was calculated for mobile sound sources per the following formula:

Harassment Zone = (Distance/day × 2 r) + π r²

where r is the linear distance from the source to the isopleth for Level A or Level B thresholds and day = 1 ( i.e., 24 hours).

The estimated potential daily active survey distance of 70 km was used as the estimated areal coverage over a 24-hour period. This distance accounts for the vessel traveling at roughly 4 knots (kn) and only for periods during which survey equipment that may result in take of marine mammals is in operation. A vessel traveling 4 kn can cover approximately 110 km per day; however, based on data from 2017, 2018, and 2019 surveys, survey coverage over a 24-hour period is closer to 70 km per day. For daylight only vessels, the distance is reduced to 35 km per day; however, to maintain the potential for 24-hour surveys, the corresponding Level B harassment zones provided in table 5 were calculated for each source category based on the Level B threshold distances in table 4 with a 24-hour (70 km) operational period.

NMFS considers the data provided by Crocker and Fratantonio (2016) to represent the best available information on source levels associated with HRG equipment and, therefore, recommends that source levels provided by Crocker and Fratantonio (2016) be incorporated in the method described above to estimate isopleth distances to harassment thresholds. In cases, when the source level for a specific type of HRG equipment is not provided in Crocker and Fratantonio (2016), NMFS recommends that either the source levels provided by the manufacturer be used, or, in instances where source levels provided by the manufacturer are unavailable or unreliable, a proxy from Crocker and Fratantonio (2016) be used instead. Table 2 shows the HRG equipment types that may be used during the proposed surveys and the source levels associated with those HRG equipment types.

Based upon modeling results, of the HRG survey equipment planned for use by Bay State Wind that has the potential to result in Level B harassment of marine mammals, the Applied Acoustics Dura-Spark UHD and GeoMarine Geo-Source sparkers would produce the largest Level B harassment isopleth (141 m) or Harassment Zone. Estimated distances to Level B harassment isopleths for all sources evaluated here, including the sparkers, are provided in table 5. Although Bay State Wind does not expect to use sparker sources on all planned survey days, Bay State Wind proposes to assume for purposes of analysis that the sparker would be used on all survey days. This is a conservative approach, as the actual sources used on individual survey days may produce smaller harassment distances.

Table 5—Distance to Level B Harassment Thresholds

[160 dB rms]

Source	Distance to Level B harassment threshold (m)
Boomers	76
Sparkers	141

Marine Mammal Occurrence

In this section we provide information about the occurrence of marine mammals, including density or other relevant information which will inform the take calculations. Habitat based density models produced by the Duke University Marine Geospatial Ecology Laboratory (Roberts et al. 2016, 2023) represent the best available information regarding marine mammal densities in the Lease Area and potential ECRs. The density data presented by Roberts et al. (2016, 2023) incorporate aerial and ( print page 67606) shipboard line-transect data from NMFS and other organizations and incorporate data from 8 physiographic and 16 dynamic oceanographic and biological covariates, and control for the influence of sea state, group size, availability bias, and perception bias on the probability of making a sighting. These density models were originally developed for all cetacean taxa in the U.S. Atlantic (Roberts et al. 2016). In subsequent years, certain models have been updated based on additional data as well as certain methodological improvements. More information is available online at https://seamap.env.duke.edu/​models/​Duke/​EC. Marine mammal density estimates in the Lease Area and potential ECRs (animals/km² ) were obtained using the most recent model results for all taxa (Roberts et al. 2023). The updated models incorporate sighting data, including sightings from NOAA's Atlantic Marine Assessment Program for Protected Species (AMAPPS) surveys.

For exposure analysis, density data from Roberts et al. (2023) were mapped using a geographic information system (GIS). Density grid cells that included any portion of the proposed Lease Area and potential ECRs were selected for all survey months (see figure 4 of Bay State Wind's application). The densities for each species as reported by Roberts et al. (2023) for each of the Lease Area and ECR were averaged by month; those values were then used to calculate the mean annual density for each species within the Lease Area and potential ECRs. Estimated mean monthly and annual densities (animals per km² ) of all marine mammal species that may be taken by the proposed survey are shown in table 7 of Bay State Wind's application. Please see table 6 for density values used in the exposure estimation process.

Due to limited data availability and difficulties identifying individuals to species level during visual surveys, individual densities are not able to be provided for all species and they are instead grouped into “guilds” (Roberts et al. 2023). These guilds include pilot whales, common bottlenose dolphins, and seals.

Long- and short-finned pilot whales are difficult to distinguish during shipboard surveys so individual habitat models were not able to be developed. However, as discussed in section 4.2.3 of Bay State Wind's application, all pilot whales in the Lease Area and potential ECRs are assumed to be long-finned pilot whales, so the densities and subsequent takes would apply only to this species.

The density models do not distinguish between common bottlenose dolphin stocks due to limited data regarding distributions of these stocks. As discussed in section 4.2.7 of Bay State Wind's application, only the western North Atlantic offshore stock is expected to occur in the Lease Area and potential ECRs. Therefore, the densities in table 6 and subsequent take calculations would only apply to this stock of bottlenose dolphins.

Gray seals and harbor seals are reasonably identifiable during shipboard visual surveys; therefore, it is expected that some sightings will be assigned to species rather than to the generalized seal guild. Additionally, seals tend to occur in very small numbers when away from haul out areas; therefore, sighting events are not likely to constitute large numbers of animals. For these reasons, the seal guild density was split evenly between both gray and harbor seal species.

Table 6—Average Annual Marine Mammal Density Estimates

Species	Average annual density (km2 )
Low-frequency Cetaceans
Fin whale	0.0022
Sei whale	0.0006
Minke whale	0.0056
Humpback whale	0.0014
North Atlantic right whale	0.0022
Mid-frequency cetaceans
Sperm whale	0.0002
Atlantic white-sided dolphin	0.0143
Atlantic spotted dolphin	0.0006
Common bottlenose dolphin (Offshore)	0.0093
Long-finned pilot whale	0.0016
Risso's dolphin	0.0006
Common dolphin	0.0846
Striped dolphin	0.0000
White-beaked dolphin	0.0000
High-frequency Cetaceans
Harbor porpoise	0.0423
Pinnipeds  1
Gray seal	0.0845
Harbor seal	0.0845
1  Seal species are not separated in the Roberts (2022) data therefore densities were evenly split between the two species expected to occur in the Lease Area and potential ECRs.

Take Estimation

Here we describe how the information provided above is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and proposed for authorization.

Level B harassment events were estimated by multiplying the average annual density of each species within the Lease Area and potential ECRs (table 6) by the largest harassment zone (141 m; table 5). That result was then multiplied by the number of survey days in that Lease Area or ECR (350 survey days), and rounded to the nearest whole number to arrive at estimated take. This final number equals the instances of take for the entire operational period. It was assumed the sparker systems were operating all 350 survey days as it is the sound source expected to produce the largest harassment zone. A summary of this method is illustrated in the following formula with the resulting proposed take of marine mammals is shown below in table 7:

Estimated take = Species Density × Harassment Zone × # of survey days

Table 7—Total Estimated and Requested Take Numbers

[By Level B harassment only]

Species	Abundance	Estimated Level B takes	Requested Level B takes	Max percent population
Low-frequency Cetaceans
Fin whale	6,802	15	15	0.22
Sei whale	6,292	4	4	0.06
( print page 67607)
Minke whale	21,968	39	39	0.18
Humpback whale	1,396	10	10	0.72
North Atlantic right whale	340	15	15	4.41
Mid-frequency Cetaceans
Sperm whale	5,895	2	2	0.03
Atlantic white-sided dolphin	93,233	99	99	0.11
Atlantic spotted dolphin	31,506	4	4	0.01
Common bottlenose dolphin (offshore stock)	64,587	65	65	0.10
Long-finned pilot whale	39,215	11	11	0.03
Risso's dolphin	44,067	4	4 (14)	0.03
Common dolphin	93,100	586	586 (1,485)	1.60
Striped dolphin	48,274	0	0 (46)	0.10
White-beaked dolphin	536,016	0	0 (12)	0.00
High-frequency Cetaceans
Harbor porpoise	85,765	293	293	0.34
Pinnipeds
Seals:
Gray seal	27,911	586	586	2.10
Harbor seal	61,336	586	586	0.96