2024-23392. Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to U.S. Navy Repair and Replacement of the Q8 Bulkhead at Naval Station Norfolk

Table 1—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 Artiodactyla—Infraorder Cetacea—Mysticeti (baleen whales)
Family Balaenopteridae (rorquals):
Humpback whale	Megaptera novaeangliae	Gulf of Maine	-,-, N	1,396 (0, 1380, 2016)	22	12.15
Odontoceti (toothed whales, dolphins, and porpoises)
Family Physeteridae:
Bottlenose dolphin	Tursiops truncatus	Northern Migratory Coastal	-, -, Y	6,639 (0.41, 4,759, 2016)	48	12.2-21.5
		Southern Migratory Coastal	-, -, Y	3,751 (0.6, 2,353, 2016)	24	0-18.3
		Northern NC Estuarine	-, -, N	823 (0.06, 782, 2017)	7.8	7.2-30
Family Phocoenidae (porpoises):
Harbor porpoise	Phocoena phocoena	Gulf of Maine/Bay of Fundy	-, -, N	85,765 (0.53, 56,420, 2021)	649	145
Order Carnivora—Pinnipedia
Family Phocidae (earless seals):
Harbor Seal	Phoca vitulina	Western North Atlantic	-, -, N	61,336 (0.08, 57,637, 2018)	1,729	339
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://www.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/​. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable.
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, vessel strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range.

A detailed description of the species likely to be affected by the Navy's construction project, including brief introductions to the species and relevant stocks as well as available information regarding population trends and threats, and information regarding local occurrence, were provided in the Federal Register notice for the proposed rule (89 FR 55180, July 3, 2024); since that time, we are not aware of any changes in the status of these species and stocks; therefore, detailed descriptions are not provided here. Please refer to that Federal Register notice for these descriptions. Please also refer to NMFS' website ( https://www.fisheries.noaa.gov/​find-species) for generalized species accounts.

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 2.

Table 2—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.
( print page 81852)
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 and Holt, 2013).

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

Effects of Specified Activities on Marine Mammals and Their Habitat

The effects of underwater noise from the Navy's construction activities have the potential to result in behavioral harassment of marine mammals in the vicinity of the Project area. The proposed rule (89 FR 55180, July 3, 2024) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from the Navy's construction on marine mammals and their habitat. That information and analysis is referenced in this final rule and is not repeated here; please refer to the proposed rule (89 FR 55180, July 3, 2024).

Estimated Take of Marine Mammals

This section provides an estimate of the number of incidental takes that may be authorized, which will inform both NMFS' consideration of “small numbers,” and the negligible impact determinations.

Harassment is the only type of take expected to result from these activities. 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) (16 U.S.C. 1362(18)(A)(i)-(ii)).

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 sounds emitted from pile driving. Based on the nature of the activity and the anticipated effectiveness of the mitigation measures ( i.e., shutdown zones) discussed in detail below in the Mitigation section, Level A harassment is neither anticipated nor would be authorized.

As described previously, no serious injury or mortality is anticipated or authorized for this activity. Below we describe how the 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 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 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 state of the receiving animals ( e.g., 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 one micropascal (re one μPa)) for continuous ( e.g., vibratory pile driving) and above RMS SPL 160 dB re one 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 ( i.e., conspecific communication, predators, and prey) may result in changes in behavior patterns that would not otherwise occur.

The Navy's activity includes the use of continuous ( e.g., vibratory pile driving and removal) and impulsive ( e.g., impact pile driving) sources, and therefore the RMS SPL thresholds of 120 and 160 dB re one μPa are applicable.

The ensonified area associated with Level A harassment is more technically challenging to predict due to the need ( print page 81853) to account for a duration component. Therefore, NMFS developed an optional User Spreadsheet tool to accompany the Technical Guidance that can be used to relatively simply predict an isopleth distance for use in conjunction with marine mammal density or occurrence to help predict potential takes. We note that because of some of the assumptions included in the methods underlying this optional tool, we anticipate that the resulting isopleth estimates are typically going to be overestimates of some degree, which may result in an overestimate of potential take by Level A harassment. However, this optional tool offers the best way to estimate isopleth distances when more sophisticated modeling methods are not available or practical. For stationary sources impact or vibratory pile driving and removal, the optional User Spreadsheet tool predicts the distance at which, if a marine mammal remained at that distance for the duration of the activity, it would be expected to incur PTS. Inputs used in the optional User Spreadsheet tool, and the resulting estimated isopleths, are reported below. For concurrent activities where combined impact and vibratory hammer scenarios shown in table 9, the estimated Level A harassment distances reflect the impact driving activity and the estimated Level B harassment distances reflect the combined vibratory source levels for that activity.

On May 3, 2024, NMFS published (89 FR 36762) and solicited public comment on its draft updated Technical Guidance ( https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-acoustic-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. To best ensure we have considered an appropriate estimate of take by Level A harassment, in consideration of the best available science, we have conducted basic comparative calculations using the draft updated Technical Guidance for the purposes of understanding the number of takes by Level A harassment (auditory injury) that would be predicted if the draft updated Technical Guidance were finalized with no changes. The relevant draft updated thresholds and weighting functions may be found in the executive summary of the draft updated Technical Guidance, on pages 3 and 4. We have also considered whether modifications to mitigation zones would be appropriate in light of the draft updated Technical Guidance. Based on the outcome of these comparisons/analyses using the draft updated Technical Guidance, NMFS has made changes as appropriate to the required shutdown zones necessary to avoid Level A harassment. These updates to the estimated harassment zones (see table 8 and table 9) and resulting changes to the required shutdown zones (see table 11 and table 12) are minor and do not result in any changes to the take levels as described in the proposed rule and analyzed through this final rule.

These thresholds are provided in table 3 and table 4 below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS' 2018 Technical Guidance and the draft NMFS' 2024 Technical Guidance, both of which may be accessed at: https://www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-acoustic-technical-guidance.

Table 3—Thresholds Identifying the Onset of Auditory Injury

[NMFS 2018]

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 one 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 (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 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.

Table 4—Updated Thresholds Identifying the Onset of Auditory Injury (AUD INJ)

[NMFS 2024]

Hearing group	AUD INJ Onset Thresholds * (received level)
	Impulsive	Non-impulsive
Low-Frequency (LF) Cetaceans	Cell 1: Lp, 0-pk,flat : 222 dB; LE, p, LF,24h : 183 dB	Cell 2: LE , p, LF,24h : 197 dB.
High-Frequency (HF) Cetaceans	Cell 3: Lp, 0-pk,flat : 230 dB; LE , p, HF,24h : 193 dB	Cell 4: LE, p, HF,24h : 201 dB.
Very High-Frequency (VHF) Cetaceans	Cell 5: Lp, 0-pk,flat : 202 dB; LE , p, VHF,24h : 159 dB	Cell 6: LE, p, VHF,24h : 181 dB.
Phocid Pinnipeds (PW) (Underwater)	Cell 7: Lp, 0-pk,flat : 223 dB; LE, p, PW,24h : 183 dB	Cell 8: LE, p, PW,24h : 195 dB.
( print page 81854)
Otariid Pinnipeds (OW) (Underwater)	Cell 9: Lp, 0-pk,flat : 230 dB; LE, p, OW,24h : 185 dB	Cell 10: LE, p, OW,24h : 199 dB.
* Dual metric thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating AUD INJ onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive sounds, these thresholds are recommended for consideration.
Note: Peak sound pressure level ( Lp, 0-pk ) has a reference value of 1 µPa, and weighted cumulative sound exposure level ( LE, p ) has a reference value of 1µPa2 s. In this table, thresholds are abbreviated to be more reflective of International Organization for Standardization standards (ISO 2017). The subscript “flat” is being included to indicate peak sound pressure are flat weighted or unweighted within the generalized hearing range of marine mammals ( i.e., 7 Hz to 165 kHz). The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function (LF, HF, and VHF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The weighted 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 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.

The sound field in the Project area is the existing background noise plus additional construction noise from the Project. Marine mammals are expected to be affected via sound generated by the primary components of the Project ( i.e., impact pile driving and vibratory pile driving and removal). The maximum underwater area ensonified above the thresholds for individual activities of behavioral harassment referenced above is 93.5 square kilometers (km² )(36.1 miles (mi² )) and will consist of an area reaching the opposite shoreline of the river (see figures 6.6, 6.8, and 6.10 in the Navy's application for the Incidental Take Authorization for the Q8 bulkhead Project). The maximum (underwater) area ensonified above the thresholds for concurrent activities of behavioral harassment referenced above is 97.9 km² (37.8 mi² ) and will consist of a similar area reaching the opposite shoreline of the river as individual activities (see figures 6.11-6.16 in the Navy's application). Additionally, vessel traffic and other commercial and industrial activities in the Project area may contribute to elevated background noise levels which may mask sounds produced by the Project.

Transmission loss ( TL) is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source. TL parameters vary with frequency, temperature, sea conditions, current, source and receiver depth, water depth, water chemistry, and bottom composition and topography. The general formula for underwater TL is:

TL = B * Log₁₀ (R₁ /R₂)

Where

TL = transmission loss in dB

B = transmission loss coefficient

R₁ = the distance of the modeled SPL from the driven pile, and

R₂ = the distance from the driven pile of the initial measurement

This formula neglects loss due to scattering and absorption, which is assumed to be zero here. The degree to which underwater sound propagates away from a sound source is dependent on a variety of factors, most notably the water bathymetry and presence or absence of reflective or absorptive conditions including in-water structures and sediments. Spherical spreading occurs in a perfectly unobstructed ( i.e., free-field) environment not limited by depth or water surface, resulting in a 6-dB reduction in sound level for each doubling of distance from the source (20*log[range]). Cylindrical spreading occurs in an environment in which sound propagation is bounded by the water surface and sea bottom, resulting in a reduction of three dB in sound level for each doubling of distance from the source (10*log[range]). A practical spreading value of 15 is often used under conditions, such as the Project site, where water increases with depth as the receiver moves away from the shoreline, resulting in an expected propagation environment that will lie between spherical and cylindrical spreading loss conditions. Practical spreading loss is assumed here.

The intensity of pile driving sounds is greatly influenced by factors such as the type of piles, hammers, and the physical environment in which the activity takes place. In order to calculate the distances to the Level A harassment and the Level B harassment sound thresholds for the methods and piles being used in this Project, the Navy and NMFS used acoustic monitoring data from other locations to develop proxy source levels for the various pile types, sizes, and methods. The Project includes vibratory and impact installation of prestressed concrete and composite piles and vibratory removal of existing concrete piles. Steel sheet piles to make up the wall of the bulkhead will be installed with vibratory hammers. Source levels for each pile size and driving method for individual activities are presented in table 5. For concurrent activities where two noise sources have overlapping sound fields, there is potential for higher sound levels than for non-overlapping sources because the isopleth of one sound source encompasses the sound source of another isopleth. In such instances, the sources are considered additive and combined using the rules of decibel addition. For addition of two simultaneous sources, the difference between the two sound source levels is calculated, and: (1) if that difference is between zero and one dB, three dB are added to the higher sound source level; (2) if the difference is between two or three dB, two dB are added to the highest sound source level; (3) if the difference is between four to nine dB, one dB is added to the highest sound source level; and (4) with differences of 10 dB or more, there is no addition. Source levels for each pile size and vibratory driving for concurrent activities are presented in table 6. ( print page 81855)

Table 5—Proxy Sound Source Levels for Pile Sizes and Driving Methods

Pile size	Method	Proxy source level			Literature source
		dB RMS re 1µPa	dB SEL re 1µPa2 sec	dB peak re 1µPa
56-in sheet pile	Vibratory	168	N/A	N/A	Illingworth and Rodkin, 2017.
18-in concrete	Vibratory	162	N/A	N/A	Caltrans, 2020.
16-in composite	Vibratory	158	N/A	N/A	Illingworth and Rodkin, 2017.
18-in concrete	Impact	170	160	185	e4sciences, 2023.
16-in composite	Impact	169	157	177	Illingworth and Rodkin, 2017.

Table 6—Proxy Sound Source Levels for Concurrent Activities

Pile size and type	Vibratory installation source 1 [dB RMS]	Vibratory extract source 2 [dB RMS]	Revised SL to be used [dB RMS]
Source 1: Vibratory hammer 56-in steel sheet pile; Source 2: Vibratory extraction of 18-in concrete pile	168	162	169
Source 1: Vibratory hammer 18-in concrete pile; Source 2: Vibratory extraction of 18-in concrete pile	162	162	165
Source 1: Vibratory hammer 56-in steel sheet pile; Source 2: 16 in composite pile	168	158	168

Table 7—User Spreadsheet Input Parameters Used for Calculating Level A Harassment Isopleths

Phase (year)	Pile size and installation method	Spreadsheet tab used	Weighting factor adjustment (kHz)	Number of strikes per pile	Number of piles per day	Activity duration (minutes)
Phase 1 (Year 1)	18-in concrete impact installation	E.1 Impact pile driving	2	307	6	N/A
	18-in concrete vibratory extraction	A.1 Vibratory pile driving	2.5	N/A	6	14
	56-in sheet pile vibratory installation	A.1 Vibratory pile driving	2.5	N/A	6	24
Phase II (Year 2)	18-in concrete impact installation	E.1 Impact pile driving	2	499	6	N/A
	18-in concrete vibratory extraction	A.1 Vibratory pile driving	2.5	N/A	6	26
	56-in sheet pile vibratory installation	A.1 Vibratory pile driving	2.5	N/A	6	28
Phase III (Year 3)	16-in composite impact installation	E.1 Impact pile driving	2	540	6	N/A
	18-in concrete vibratory installation	E.1 Impact pile driving	2	540	6	N/A
	16-in composite vibratory extraction	A.1 Vibratory pile driving	2.5	N/A	6	20
	56-in sheet pile vibratory installation	A.1 Vibratory pile driving	2.5	N/A	6	38

Table 8—Calculated Level A and Level B Harassment Isopleths for Individual Activities

Phase (year)	Activity	Level A harassment zone (m) 1				Level B harassment zone(m)
		LF- cetaceans	HF (MF)- cetaceans	VHF (HF)- cetaceans	Phocids
Phase 1 (Year 1)	18-in concrete impact installation	43.9 (43.6)	5.6 (1.6)	67.8 (52.3)	38.9 (23.5)	46.4
	18-in concrete vibratory extraction	13.5 (10.0)	5.2 (0.9)	11.0 (14.7)	17.3 (6.1)	6,310
	56-in sheet pile vibratory installation	48.4 (35.9)	18.6 (3.2)	39.5 (53.0)	62.3 (21.8)	15,849
Phase II (Year 2)	18-in concrete impact installation	60.8 (60.8)	7.7 (2.2)	93.7 (72.4)	53.8 (32.5)	46.4
	18-in concrete vibratory extraction	20.3 (15.1)	7.8 (1.3)	16.6 (22.3)	26.2 (9.2)	6,310
	56-in sheet pile vibratory installation	53.7 (39.7)	20.6 (3.2)	43.8 (58.7)	69.1 (24.2)	15,849
Phase III (Year 3)	16-in composite impact installation	40.4 (40.4)	5.1 (1.4)	62.3 (48.1)	35.8 (21.6)	39.8
	18-in concrete impact installation	64.0 (64.0)	8.1 (2.3)	98.7 (76.3)	56.7 (34.3)	46.4
	16-in composite vibratory extraction	9.2 (6.8)	3.5 (0.6)	7.5 (10.1)	11.9 (4.2)	3,415
	56-in sheet pile vibratory installation	65.8 (48.7)	25.3 (4.3)	53.7 (72.0)	84.7 (29.6)	15,849
1  Harassment zones shown in parentheticals are based on the 2018 technical guidance and were presented in the proposed rule.

( print page 81856)

Table 9—Calculated Level A and Level B Harassment Isopleths for Concurrent Activities

Phase (year)	Activity	Level A harassment zone (m) 1				Level B harassment zone (m)
		LF- cetaceans	MF (HF)- cetaceans	HF (VHF)- cetaceans	Phocids
Phase 1 (Year 1)	Vibratory extract 18-in concrete piles and vibratory install 56-in steel sheet piles	56.4 (41.8)	21.7 (3.7)	46.1 (61.8)	72.7 (25.4)	18,478
	Vibratory extract 18-in concrete piles; vibratory install 56-in steel sheet piles; impact install 18-in concrete piles	43.9 (43.9)	5.6 (1.6)	67.8 (52.3)	38.9 (23.5)	18,478
Phase II (Year 2)	Vibratory extract 18-in concrete piles and vibratory install 56-in steel sheet piles	62.6 (46.3)	24.0 (4.1)	51.1 (68.5)	80.5 (28.2)	18,478
	Vibratory install 56-in steel sheet piles and impact install 18-in concrete piles	60.8 (60.8)	7.7 (2.2)	93.7 (72.4)	53.8 (32.5)	15,849
Phase III (Year 3)	Vibratory extract 18-in concrete piles and vibratory install 56-in steel sheet piles	65.8 (56.8)	25.3 (5.0)	53.7 (84.0)	84.7 (34.5)	18,478
	Vibratory install 56-in steel sheet piles and impact install 16-in composite piles	40.4 (40.4)	5.1 (1.4)	62.3 (48.1)	35.8 (21.6)	15,849
1  Harassment zones shown in parentheticals are based on the 2018 technical guidance and were presented in the proposed rule.

The maximum distance to the Level A harassment threshold during construction will be during the vibratory driving of 56-inch (in) concrete piles during Phase III of individual activities ( i.e., 84.7 m for harbor seals) and during the concurrent vibratory extraction of 18-in concrete piles and vibratory installation of 56-in steel sheet piles for concurrent activities of Phase III ( i.e., 84.7 m for harbor seals). Given these relatively small isopleths, if a marine mammal enters the shutdown zone during vibratory or impact pile driving it is expected that the construction activity will be shut down before any marine mammal would incur PTS. Therefore, no take by Level A harassment is expected during the construction activities associated with the Q8 bulkhead. The largest calculated Level B harassment isopleth extends out to 18,478 m, which will result from concurrent pile driving of the scenarios presented in table 9. The largest Level B harassment zone of 18,478 m is not an attainable observable distance in all directions, but in some areas the distance is smaller due to the zone being cut off by landmasses. The Level B harassment zone will be monitored to the maximum extent possible.

Marine Mammal Occurrence and Take Estimation

In this section we provide information about the occurrence of marine mammals, including density or other relevant information which will inform the take calculations. We describe how the information provided is synthesized to produce a quantitative estimate of the take that is reasonably likely to occur and may be authorized.

Humpback Whale

Humpback whales occur in the mouth of the Chesapeake Bay and nearshore waters of Virginia during winter and spring months. Several satellite tagged humpback whales were detected west of the Chesapeake Bay Bridge Tunnel, including two individuals with locations near NAVSTA Norfolk and Joint Expeditionary Base Little Creek (Aschettino et al., 2017). Group size was not reported in these surveys; however, most whales detected were juveniles. Although two individuals were detected in the vicinity of the Project area during shipboard surveys conducted in 2020, there is no evidence that they lingered for multiple days (Aschettino, 2020). Because no density estimates are available for the species in this area, the Navy estimated, and NMFS concurs, that one potential sighting of an average size group ( i.e., two individuals) could occur every 60 days of pile driving. Therefore, given the number of Project days expected in each year, NMFS will authorize a total of 16 takes by Level B harassment of humpback whale over the 5-year authorization, with no more than four takes by Level B harassment in a given year.

The largest Level A harassment zone for low-frequency cetaceans extends approximately 65.8 m from the source during concurrent activities for the vibratory extraction of 18-in concrete piles and vibratory install 56-in steel sheet piles (table 9). The Navy plans to shut down if a humpback whale is sighted within any of the Level A harassment zones for all activities. Therefore, NMFS will not authorize take by Level A harassment of humpback whales.

Bottlenose Dolphins

The expected number of bottlenose dolphins in the Project area was estimated using inshore seasonal densities provided in Engelhaupt et al. (2016) from vessel line-transect surveys near NAVSTA Norfolk and adjacent areas near Virginia Beach, Virginia, from August 2012 through August 2015. This density includes sightings inshore of the Chesapeake Bay from NAVSTA Norfolk west to the Thimble Shoals Bridge and is the most representative density for the Project area. To calculate potential Level B harassment takes of bottlenose dolphin, NMFS conservatively multiplied the density of 1.38 dolphin/km² (from Engelhaupt et al., 2016) by the largest Level B harassment isopleth for each activity (tables 7 and 8), and then by the number of days associated with that activity. For example, to calculate Level B harassment takes associated with work at the Q8 bulkhead in Phase I for the vibratory removal of 18-in concrete piles, NMFS multiplied the density ( i.e., 1.38 dolphins/km² ) by the Level B harassment zone for that activity ( i.e., 43.3 km² ) by the proportional number of pile driving days for that activity ( i.e., 24 days) for a total of 1,437 Level B harassment takes for that activity during Phase I. Takes by Level B harassment were calculated for both individual pile driving activities and concurrent pile driving activities, as authorized takes are conservatively based on the scenario that produces more takes by Level B harassment (table 9). Therefore, NMFS will authorize 14,191 takes by Level B ( print page 81857) harassment of bottlenose dolphin across all 5 years, with no more than 6,168 takes in a given year.

The largest Level A harassment zone for mid-frequency cetaceans extends approximately 25.3 m from the source during individual and concurrent activities during Phase III (table 8 and table 9). The Navy plans to shut down all activities if a bottlenose dolphin is sighted within the shutdown zones for mid-frequency cetaceans. Therefore, NMFS will not authorize take by Level A harassment of bottlenose dolphins.

Harbor Porpoise

Harbor porpoises are known to occur in the coastal waters near Virginia Beach (Hayes et al., 2019). Density data for this species within the Project vicinity do not exist or were not calculated because sample sizes were too small to produce reliable estimates of density. Harbor porpoise sighting data collected by the Navy near NAVSTA Norfolk and Virginia Beach from 2012 to 2015 (Engelhaupt et al. 2014; 2015; 2016) did not produce enough sightings to calculate densities. One group of two harbor porpoises was seen during spring 2015 (Engelhaupt et al. 2016). Elsewhere in their range, harbor porpoises typically occur in groups of two to three individuals (Carretta et al. 2001; Smultea et al. 2017).

Due to there being no density estimates for the species in the Project area, the Navy conservatively estimated one exposure of two porpoises for every 60 days of pile driving. Total pile driving days for Phase I will be 74 days, Phase II will be 37 days, and Phase III will be 101 days. Takes by Level B harassment were calculated for both individual pile driving activities and concurrent pile driving activities, as authorized takes are conservatively based on the scenario that produced the larger exposure estimate (table 11). Using the above methodology, NMFS calculated an exposure estimate of eight incidents of take for harbor porpoises.

NMFS does not expect any Level A harassment of harbor porpoise during this Project. The largest Level A harassment zone for high-frequency cetaceans extends approximately 98.7 m from the source during individual activities during Phase III (table 8). The Navy plans to shut down all activities if a harbor porpoise is sighted within the shutdown zones for high-frequency cetaceans. Therefore, NMFS will not authorize take by Level A harassment of harbor porpoise.

Harbor Seal

The expected number of harbor seals in the Project area was estimated using systematic land- and vessel-based survey data for in-water and hauled out seals collected by the Navy at the CBBT rock armor and portal islands from 2014 through 2019 (Jones et al., 2020). The average daily seal count from the field season ranged from eight to 23 seals, with an average of 13.6 harbor seals across all the field seasons.

NMFS expects that harbor seals are likely to be present from November to April and, consistent with other recent projects (88 FR 31633, May 18, 2023; 87 FR 15945, March 31, 2022; 86 FR 24340; May 6, 2021, and 86 FR 17458; April 2, 2021), NMFS calculated take by Level B harassment by multiplying 13.6 seals by the maximum number of pile driving days expected to occur from November through April. Therefore, we expect the total number of takes by Level B harassment for harbor seals to be 2,882.

NMFS does not expect any Level A harassment of harbor seals during this Project. The largest Level A harassment zone for phocids extends approximately 84.7 m from the source during individual and concurrent activities during Phase III (table 8 and table 9). The Navy plans to shut down all activities if a harbor porpoise is sighted within the shutdown zones for phocids. Therefore, NMFS will not authorize take by Level A harassment of harbor seals.

Table 10—Takes by Level B Harassment by Species and Stock in Comparison to Stock Abundance

LOA construction phase (year)	Species	Level B (individual activities)	Level B (concurrent activities)	Total	Stock abundance	Percentage of stock
Phase 1	Humpback	2	2	2	1,396	<1
	Bottlenose dolphin—Northern Migratory (NM)  1 2	5,414	2,888	2,607	6,639	39.27
	Bottlenose dolphin—Southern Migratory (SM)  1 2			2,607	3,751	69.50
	Bottlenose dolphin—NC Estuarine  1 2			200	823	24.30
	Harbor porpoise	4	2	4	85,765	<1
	Harbor seal	1,006	408	1,006	61,336	1.64
Phase 2	Humpback	2	2	2	1,396	<1
	Bottlenose dolphin—NM  1 2	2,609	2,179	1,205	6,639	18.15
	Bottlenose dolphin—SM  1 2			1,205	3,751	32.12
	Bottlenose dolphin—NC Estuarine  1 2			200	823	24.30
	Harbor porpoise	2	2	2	85,765	<1
	Harbor seal	503	653	653	61,336	1.06
Phase 3	Humpback	4	2	4	1,396	<1
	Bottlenose dolphin—NM  1 2	6,168	6,712	3,256	6,639	49.04
	Bottlenose dolphin—SM  1 2			3,256	3,751	85.80
	Bottlenose dolphin—NC Estuarine  1 2			200	823	24.30
	Harbor porpoise	4	2	4	85,765	<1
	Harbor seal	1,236	625	1,373	61,336	2.24
1  Take estimates are weighted based on the assumed percentages of population for each distinct stock, those percentages were also used to predict the proportion of animals present in the Project area from each stock. Please see Small Numbers section for additional information.
2  Assumes multiple repeated takes of the same individuals. Please see Small Numbers section for additional information.

( print page 81858)

Mitigation

In order to issue an IHA under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking pursuant to the activity, and other means of effecting the least practicable impact on the species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance. NMFS regulations require applicants for incidental take authorizations to include information about the availability and feasibility (economic and technological) of equipment, methods, and manner of conducting the activity or other means of effecting the least practicable adverse impact upon the affected species or stocks, and their habitat (50 CFR 216.104(a)(11)).

In evaluating how mitigation may or may not be appropriate to ensure the least practicable adverse impact on species or stocks and their habitat, as well as subsistence uses where applicable, NMFS considers two primary factors:

(1) The manner in which, and the degree to which, the successful implementation of the measure(s) is expected to reduce impacts to marine mammals, marine mammal species or stocks, and their habitat. This considers the nature of the potential adverse impact being mitigated ( e.g., likelihood, scope, range). It further considers the likelihood that the measure will be effective if implemented (probability of accomplishing the mitigating result if implemented as planned), the likelihood of effective implementation (probability implemented as planned); and

(2) The practicability of the measures for applicant implementation, which may consider such things as cost, impact on operations.

In addition to the measures described later in this section, the Navy will employ the following mitigation measures:

• The Navy will conduct briefings between construction supervisors and crews, the marine mammal monitoring team, and Navy staff prior to the start of all pile driving activity and when new personnel join the work, to explain responsibilities, communication procedures, marine mammal monitoring protocol, and operational procedures;
• If a marine mammal comes within 10 m of construction activities, including in-water heavy machinery work, operations shall cease and vessels shall reduce speed to the minimum level required to maintain steerage and safe working conditions; and
• Pile driving activity must be halted upon observation of either a species for which incidental take is not authorized or a species for which incidental take has been authorized but the authorized number of takes has been met, entering or is within the harassment zone.

The following mitigation measures apply to the Navy's in-water construction activities.

Establishment of Shutdown Zones —The Navy will establish shutdown zones for all pile driving and removal activities. The purpose of a shutdown zone is generally to define an area within which shutdown of the activity will occur upon sighting of a marine mammal (or in anticipation of an animal entering the defined area). Shutdown zones will vary based on the activity type and marine mammal hearing group (table 11 and table 12).

Protected Species Observers (PSO) —The placement of PSOs during all pile driving and removal activities (described in the Monitoring and Reporting section) will ensure that the entire shutdown zone is visible. A minimum of two PSOs will be used during all activities.

Monitoring for Level A and B Harassment —The Navy will monitor the Level B harassment zones ( i.e., areas where SPLs are equal to or exceed the 160 dB rms threshold for impact pile driving, and the 120 dB rms threshold during vibratory pile driving and removal) to the extent practicable, and all of the Level A harassment zones and shutdown zones, during all pile driving days. Monitoring zones provide utility for observing by establishing monitoring protocols for areas adjacent to the shutdown zones. Monitoring zones enable observers to be aware of and communicate the presence of marine mammals in the Project area outside the shutdown zone and thus prepare for a potential cessation of activity should the animal enter the shutdown zone.

Pre-Activity Monitoring —Prior to the start of daily in-water construction activity, or whenever a break in pile driving/removal of 30 minutes or longer occurs, PSOs will observe the shutdown and monitoring zones for a period of 30 minutes. Pile driving may commence following 30 minutes of observation when the determination is made that the shutdown zones are clear of marine mammals. If a marine mammal is observed within the shutdown zones listed in table 11 or table 12, pile driving activity must be delayed or halted. If pile driving is delayed or halted due to the presence of a marine mammal, the activity may not commence or resume until either the animal has voluntarily exited and been visually confirmed beyond the shutdown zones or 15 minutes have passed without re-detection of the animal. If work ceases for more than 30 minutes, the pre-activity monitoring of the shutdown zones will commence. A determination that the shutdown zone is clear must be made during a period of good visibility ( i.e., the entire shutdown zone and surrounding waters must be visible to the naked eye).

Soft Start —Soft start procedures are used to provide additional protection to marine mammals by providing warning and/or giving marine mammals a chance to leave the area prior to the hammer operating at full capacity. For impact pile driving, contractors will be required to provide an initial set of three strikes from the hammer at reduced energy, followed by a 30-second waiting period, then two subsequent reduced-energy strike sets. Soft starts will be implemented at the start of each day's impact pile driving and at any time following cessation of impact pile driving for a period of 30 minutes or longer.

Table 11—Shutdown and Monitoring Zones for Individual Activities

Phase (year)	Activity	Shutdown zones (m) 1			Level B monitoring zones all marine mammals
		LF- cetaceans	VHF (HF)- cetaceans	All other marine mammals
Phase 1 (Year 1)	18-in concrete impact installation	50 (50)	70 (60)	40 (30)	50
	18-in concrete vibratory extraction	20 (10)	20 (20)	20 (10)	6,310
	56-in sheet pile vibratory installation	50 (40)	40 (60)	60 (30)	15,850
Phase II (Year 2)	18-in concrete impact installation	70 (70)	100 (80)	60 (40)	50
	18-in concrete vibratory extraction	20 (20)	20 (30)	30 (10)	6,310
( print page 81859)
	56-in sheet pile vibratory installation	60 (40)	50 (60)	70 (30)	15,850
Phase III (Year 3)	16-in composite impact installation	50 (50)	70 (50)	40 (30)	40
	18-in concrete impact installation	70 (70)	100 (80)	60 (40)	50
	16-in composite vibratory extraction	10 (10)	10 (20)	20 (10)	3,415
	56-in sheet pile vibratory installation	70 (50)	60 (80)	90 (30)	15,850
1  Shutdown zones shown in parentheticals are based on the 2018 technical guidance and were presented in the proposed rule.

Table 12—Shutdown and Monitoring Zones for Concurrent Activities

Phase (year)	Activity	Shutdown zones (m) 1			Level B monitoring zones all marine mammals
		LF- cetaceans	HF- cetaceans	All other marine mammals
Phase 1 (Year 1)	Vibratory extract 18-in concrete piles and vibratory install 56-in steel sheet piles	60 (50)	50 (70)	80 (30)	18,480
	Vibratory extract 18-in concrete piles; vibratory install 56-in steel sheet piles; impact install 18-in concrete piles	50 (70)	70 (90)	40 (40)	18,480
Phase II (Year 2)	Vibratory extract 18-in concrete piles and vibratory install 56-in steel sheet piles	70 (50)	60 (70)	80 (30)	18,480
	Vibratory install 56-in steel sheet piles and impact install 18-in concrete piles	70 (50)	100 (80)	60 (30)	15,850
Phase III (Year 3)	Vibratory extract 18-in concrete piles and vibratory install 56-in steel sheet piles	70 (50)	60 (70)	90 (30)	18,480
	Vibratory install 56-in steel sheet piles and impact install 16-in composite piles	60 (50)	50 (80)	40 (30)	15,850
1  Shutdown zones shown in parentheticals are based on the 2018 technical guidance and were presented in the proposed rule.

Based on our evaluation of the applicant's mitigation measures, as well as other measures considered by NMFS, NMFS has determined that the mitigation measures provide the means of effecting the least practicable impact on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance.

Monitoring and Reporting

In order to issue an IHA for an activity, section 101(a)(5)(D) of the MMPA states that NMFS must set forth requirements pertaining to the monitoring and reporting of such taking. The MMPA implementing regulations at 50 CFR 216.104(a)(13) indicate that requests for authorizations must include the suggested means of accomplishing the necessary monitoring and reporting that will result in increased knowledge of the species and of the level of taking or impacts on populations of marine mammals that are expected to be present while conducting the activities. Effective reporting is critical both to compliance as well as ensuring that the most value is obtained from the required monitoring.

Monitoring and reporting requirements prescribed by NMFS should contribute to improved understanding of one or more of the following:

• Occurrence of marine mammal species or stocks in the area in which take is anticipated (e.g., presence, abundance, distribution, density);
• Nature, scope, or context of likely marine mammal exposure to potential stressors/impacts (individual or cumulative, acute or chronic), through better understanding of: (1) action or environment (e.g., source characterization, propagation, ambient noise); (2) affected species ( e.g., life history, dive patterns); (3) co-occurrence of marine mammal species with the activity; or (4) biological or behavioral context of exposure ( e.g., age, calving or feeding areas);
• Individual marine mammal responses (behavioral or physiological) to acoustic stressors (acute, chronic, or cumulative), other stressors, or cumulative impacts from multiple stressors;
• How anticipated responses to stressors impact either: (1) long-term fitness and survival of individual marine mammals; or (2) populations, species, or stocks;
• Effects on marine mammal habitat (e.g., marine mammal prey species, acoustic habitat, or other important physical components of marine mammal habitat); and
• Mitigation and monitoring effectiveness.

Visual Monitoring

Marine mammal monitoring during pile driving and removal must be conducted by qualified, NMFS approved PSOs, in accordance with the following:

• PSOs must be independent of the activity contractor (e.g., employed by a subcontractor) and have no other assigned tasks during monitoring periods;
• At least one PSO must have prior experience performing the duties of a PSO during construction activity pursuant to a NMFS-issued incidental take authorization;
• Other PSOs may substitute other relevant experience, education (i.e., a degree in biological science or related field), or training for prior experience performing the duties of a PSO during ( print page 81860) construction activity pursuant to a NMFS-issued incidental take authorization;
• PSOs must be approved by NMFS prior to beginning any activity subject to an LOA issued under this final rule; and
• A lead observer or monitoring coordinator must be designated. The lead observer must have prior experience performing the duties of a PSO during construction activity pursuant to a NMFS-issued incidental take authorization.

PSOs must have the following additional qualifications:

• Ability to conduct field observations and collect data according to assigned protocols;
• Experience or training in the field identification of marine mammals, including the identification of behaviors;
• Sufficient training, orientation, or experience with the construction operation to provide for personal safety during observations;
• Writing skills sufficient to prepare a report of observations including but not limited to: (1) The number and species of marine mammals observed; (2) dates and times when in-water construction activities were conducted; (3) dates, times, and reason for implementation of mitigation (or why mitigation was not implemented when required); and (4) marine mammal behavior; and
• Ability to communicate orally, by radio or in person, with Project personnel to provide real-time information on marine mammals observed in the area as necessary.

Given the configuration of the harassment zones, which vary depending on the pile type/size and the pile driver type (tables 9 and 10), it is assumed that 2 PSOs will be sufficient to monitor the zones for impact drivers, and 3 to 4PSOs will be sufficient to monitor the zones for vibratory drivers given the placement of the observers in the vicinity of the Project area. However, additional monitors may be added if warranted by the level of marine mammal activity in the area. PSOs will be placed at the best vantage point(s) practicable (figure 1) to monitor for marine mammals and implement shutdown/delay procedures when applicable by calling for the shutdown by the pile driver operator. PSOs will be deployed on the Green Mile Fishing Pier during vibratory driving of piles when monitoring zones are exceptionally large.

Monitoring will be conducted 30 minutes before, during, and after all in water construction activities. In addition, observers shall record all incidents of marine mammal occurrence, regardless of distance from activity, and shall document any behavioral reactions in concert with distance from piles being driven or removed. Pile driving activities include the time to install or remove a single pile or series of piles, as long as the time elapsed between uses of the pile driving equipment is no more than 30 minutes.

Figure 1 Protected Species Observer Locations at NAVSTA Norfolk at Norfolk, Virginia

Acoustic Monitoring

The Navy will implement in situ acoustic monitoring efforts to measure SPLs from in-water construction activities for pile types and methods that have not been previously collected at NAVSTA Norfolk (table 13). The Navy will collect and evaluate acoustic sound recording levels during pile driving activities. The Navy will collect data on 10 percent of the number of total piles driven for each pile type. Hydrophones will be placed at locations 33 feet (ft) from the noise source and, where the potential for Level A (PTS onset) harassment exists, at a second representative monitoring location that is a distance of 20 times the depth of water at the pile location, to the maximum extent practicable. For the pile driving events acoustically measured, 100 percent of the data will be analyzed. Please see the Navy's ( print page 81861) Acoustic Monitoring Plan and section 13.2 in the application for additional detail.

Table 13—Number of Piles for Hydroacoustic Monitoring

Pile type	Total piles	Method of install of removal	Number monitored
18-in concrete	200	Vibratory	20
18-in concrete	184	Impact	18
56-in steel sheet	547	Vibratory	55
16-in composite	178	Vibratory	18
16-in composite	105	Impact	11