68290 Federal Register / Vol. 88, No. 190 / Tuesday, October 3, 2023 / Proposed Rules 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric 

Administration 

50 CFR Part 218 

[Docket No. 230817–0197] 

RIN 0648–BL72 

Taking and Importing Marine 

Mammals; Taking Marine Mammals 

Incidental to the U.S. Navy Training 

and Testing Activities in the HawaiiSouthern California Training and 

Testing Study Area 

AGENCY: National Marine Fisheries 

Service (NMFS), National Oceanic and 

Atmospheric Administration (NOAA), 

Commerce. 

ACTION: Proposed rule; request for 

comments and information. 

SUMMARY: NMFS has received a request 

from the U.S. Navy (Navy) to modify the 

regulations and Letters of Authorization 

(LOAs) authorizing the take of marine 

mammals incidental to Navy training 

and testing activities conducted in the 

Hawaii-Southern California Training 

and Testing (HSTT) Study Area between 

2018 and 2025. In 2021, two separate 

U.S. Navy vessels struck unidentified 

large whales on two separate occasions, 

one whale in June 2021 and one whale 

in July 2021, in waters off Southern 

California. The takes by vessel strike of 

the two whales by the U.S. Navy were 

covered by the existing regulations and 

LOAs, which authorize the U.S. Navy to 

take up to three large whales by serious 

injury or mortality by vessel strike 

between 2018 and 2025. The Navy 

reanalyzed the potential of vessel strike 

in the HSTT Study Area, including the 

recent strikes and as a result, requested 

two additional takes of large whales by 

serious injury or mortality by vessel 

strike for the remainder of the current 

regulatory period. In May 2023, a U.S. 

Navy vessel struck a large whale in 

waters off Southern California. NMFS 

reanalyzed the potential for vessel strike 

following the May 2023 strike and 

proposes to authorize two additional 

takes of large whales by serious injury 

or mortality by vessel strike for the 

remainder of the current regulatory 

period (two takes in addition to the 

three takes authorized in the current 

regulations). Pursuant to the Marine 

Mammal Protection Act (MMPA), NMFS 

is requesting comments on the proposed 

promulgation of modified regulations 

and associated LOAs for the Navy 

governing this additional incidental 

taking of marine mammals. NMFS will 

consider public comments prior to 

issuing any final rule and making final 

decisions on the issuance of the 

requested LOAs. Agency responses to 

public comments will be provided in 

the notice of the final decision. The 

Navy’s activities qualify as military 

readiness activities pursuant to the 

MMPA, as amended by the National 

Defense Authorization Act for Fiscal 

Year 2004 (2004 NDAA). 

DATES: Comments and information must 

be received no later than November 17, 

2023. 

ADDRESSES: Submit all electronic public 

comments via the Federal e-Rulemaking 

Portal. Go to https://

www.regulations.gov and enter NOAA– 

NMFS–2023–0102 in the Search box. 

Click on the ‘‘Comment’’ icon, complete 

the required fields, and enter or attach 

your comments. 

Instructions: Comments sent by any 

other method, to any other address or 

individual, or received after the end of 

the comment period may not be 

considered by NMFS. All comments 

received are a part of the public record 

and will generally be posted for public 

viewing on www.regulations.gov 

without change. All personal identifying 

information (e.g., name, address), 

confidential business information, or 

otherwise sensitive information 

submitted voluntarily by the sender will 

be publicly accessible. NMFS will 

accept anonymous comments (enter ‘‘N/ 

A’’ in the required fields if you wish to 

remain anonymous). 

A copy of the Navy’s applications, 

NMFS’ proposed and final rules and 

subsequent LOAs for the existing (2020) 

and previous (2018) regulations, and 

other supporting documents and 

documents cited herein may be obtained 

online at: www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

incidental-take-authorizations-militaryreadiness-activities. In case of problems 

accessing these documents, please use 

the contact listed here (see FOR FURTHER

INFORMATION CONTACT). 

FOR FURTHER INFORMATION CONTACT: 

Leah Davis, Office of Protected 

Resources, NMFS, (301) 427–8401. 

SUPPLEMENTARY INFORMATION: 

Purpose of Regulatory Action 

These proposed regulations, issued 

under the authority of the MMPA (16 

U.S.C. 1361 et seq.), would modify the 

current regulations, which allow for the 

authorization of take of marine 

mammals incidental to the Navy’s 

training and testing activities (which 

qualify as military readiness activities) 

from the use of sonar and other 

transducers, in-water detonations, air 

guns, impact pile driving/vibratory 

extraction, and the movement of vessels 

throughout the HSTT Study Area (50 

CFR part 218, subpart H; hereafter 

‘‘2020 HSTT regulations’’). 

NMFS received a request from the 

Navy to modify the existing regulations 

and LOAs to authorize two additional 

takes of large whales by serious injury 

or mortality by vessel strike over the 

remainder of the HSTT regulatory 

period. The current HSTT regulations 

and LOAs authorize the incidental take, 

by serious injury or mortality, of three 

large whales by vessel strike. Here, in 

consideration of the best available 

science, including updated information 

related to vessel strikes, NMFS analyzes 

and proposes to authorize the incidental 

serious injury or mortality by vessel 

strike of five large whales over the 

effective period of the regulations 

(December 2018–December 2025). The 

effective period remains unchanged 

from the existing regulations. Further, 

the Navy’s proposed activities remain 

unchanged; however, this proposed rule 

includes two additional mitigation 

measures and revision of two existing 

mitigation measures to further reduce 

the probability of vessel strike. With the 

exception of these new mitigation 

measures and revisions to two existing 

mitigation measures, the required 

mitigation and monitoring measures 

remain unchanged. 

Background 

The MMPA prohibits the ‘‘take’’ of 

marine mammals, with certain 

exceptions. Sections 101(a)(5)(A) and 

(D) of the MMPA (16 U.S.C. 1361 et 

seq.) direct the Secretary of Commerce 

(as delegated to NMFS) to allow, upon 

request, the incidental, but not 

intentional, taking of small numbers of 

marine mammals by U.S. citizens who 

engage in a specified activity (other than 

commercial fishing) within a specified 

geographical region if certain findings 

are made and either regulations are 

issued or, if the taking is limited to 

harassment, the public is provided with 

notice of the proposed incidental take 

authorization and the opportunity to 

review and submit comments. 

An authorization for incidental 

takings shall be granted if NMFS finds 

that the taking will have a negligible 

impact on the species or stock(s) and 

will not have an unmitigable adverse 

impact on the availability of the species 

or stock(s) for taking for subsistence 

uses (where relevant). Further, NMFS 

must prescribe the permissible methods 

of taking and other means of effecting 

the least practicable adverse impact on 

the affected species or stocks and their 

habitat, paying particular attention to 

rookeries, mating grounds, and areas of 


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similar significance, and on the 

availability of such species or stocks for 

taking for certain subsistence uses 

(referred to in this rulemaking as 

‘‘mitigation measures’’); and 

requirements pertaining to the 

monitoring and reporting of such 

takings. The MMPA defines ‘‘take’’ to 

mean to harass, hunt, capture, or kill, or 

attempt to harass, hunt, capture, or kill 

any marine mammal. The Preliminary 

Analysis and Negligible Impact 

Determination section below discusses 

the definition of ‘‘negligible impact.’’ 

The 2004 NDAA (Pub. L. 108–136) 

amended section 101(a)(5) of the MMPA 

to remove the ‘‘small numbers’’ and 

‘‘specified geographical region’’ 

provisions indicated above and 

amended the definition of ‘‘harassment’’ 

as applied to a ‘‘military readiness 

activity.’’ The definition of harassment 

for military readiness activities (section 

3(18)(B) of the MMPA) is (i) any act that 

injures or has the significant potential to 

injure a marine mammal or marine 

mammal stock in the wild (Level A 

Harassment); or (ii) any act that disturbs 

or is likely to disturb a marine mammal 

or marine mammal stock in the wild by 

causing disruption of natural behavioral 

patterns, including, but not limited to, 

migration, surfacing, nursing, breeding, 

feeding, or sheltering, to a point where 

such behavioral patterns are abandoned 

or significantly altered (Level B 

harassment). In addition, the 2004 

NDAA amended the MMPA as it relates 

to military readiness activities such that 

the least practicable adverse impact 

analysis shall include consideration of 

personnel safety, practicality of 

implementation, and impact on the 

effectiveness of the military readiness 

activity. 

The NDAA for Fiscal Year 2019 (2019 

NDAA) (Pub. L. 115–232), amended the 

MMPA to allow incidental take rules for 

military readiness activities under 

section 101(a)(5)(A) to be issued for up 

to 7 years. Prior to this amendment, all 

incidental take rules under section 

101(a)(5)(A) were limited to 5 years. 

Under the MMPA implementing 

regulations, incidental take regulations 

may be modified, in whole or in part, as 

new information is developed and after 

notice and opportunity for public 

comment (50 CFR 216.105). An LOA 

must be withdrawn or suspended if, 

after notice and opportunity for public 

comment, NMFS determines that the 

regulations are not being substantially 

complied with, or the taking is having, 

or may have, more than a negligible 

impact on species or stock. Id. at 

216.106(e). Note, in its application, 

Navy relied on §§ 218.76, and 218.77. 

These sections outline the process for 

modification of an LOA without 

modifying the applicable incidental take 

regulation. These sections do not apply 

here because the Navy requested 

modification of the 2020 HSTT 

regulations. 

Summary of Request 

On December 27, 2018, NMFS issued 

a 5-year final rule governing the taking 

of marine mammals incidental to Navy 

training and testing activities conducted 

in the HSTT Study Area (83 FR 66846; 

hereafter ‘‘2018 HSTT final rule’’). 

Previously, on August 13, 2018, and 

towards the end of the time period in 

which NMFS was processing the Navy’s 

request for the 2018 regulations, the 

2019 NDAA amended the MMPA for 

military readiness activities to allow 

incidental take regulations to be issued 

for up to 7 years instead of the previous 

5 years. The Navy’s training and testing 

activities conducted in the HSTT Study 

Area qualify as military readiness 

activities pursuant to the MMPA, as 

amended by the 2004 NDAA. On March 

11, 2019, the Navy submitted an 

application requesting that NMFS 

extend the 2018 HSTT regulations and 

associated LOAs such that they would 

cover take incidental to 7 years of 

training and testing activities instead of 

5, extending the expiration date from 

December 20, 2023 to December 20, 

2025. On July 10, 2020, NOAA Fisheries 

issued regulations to govern the taking 

of marine mammals incidental to the 

training and testing activities conducted 

in the HSTT Study Area over the course 

of 7 years, effectively extending the 

effective period from December 20, 2023 

to December 20, 2025. 

On March 31, 2022, NMFS received 

an adequate and complete application 

(2022 Navy application) from the Navy 

requesting that NMFS modify the 

existing regulations and LOAs to 

authorize two additional takes of large 

whales by serious injury or mortality by 

vessel strike over the remainder of the 

HSTT authorization period. The 2020 

HSTT regulations (50 CFR part 218, 

subpart H) and LOAs authorize the take 

of marine mammals from the Navy’s 

training and testing activities in the 

HSTT Study Area through December 20, 

2025. These regulations and LOAs 

authorize the take of three large whales 

by serious injury or mortality by vessel 

strike. 

The Navy’s 2022 request is based 

upon new information regarding U.S. 

Navy vessel strikes off the coast of 

Southern California. As described in the 

2022 Navy application, in 2021, two 

separate U.S. Navy vessels struck 

unidentified large whales off the coast 

of Southern California on two separate 

occasions, one whale in June 2021 and 

one whale in July 2021. Separately, a 

foreign naval vessel struck two fin 

whales off the coast of Southern 

California in May 2021. 

In the 2022 Navy application, the 

Navy proposes no changes to the nature 

of the specified activities covered by the 

2020 HSTT final rule. The Navy states 

that the level of activity within and 

between years would be consistent with 

that previously analyzed in the 2020 

HSTT final rule, and all activities would 

be conducted within the same 

boundaries of the HSTT Study Area 

identified in the 2020 HSTT final rule. 

The training and testing activities (e.g., 

equipment and sources used, exercises 

conducted) are identical to those 

described and analyzed in the 2020 

HSTT final rule, and the mitigation, 

monitoring, and reporting measures are 

similar to those described and analyzed 

in the 2020 HSTT final rule. The only 

changes included in the Navy’s request 

are for additional take by serious injury 

or mortality by vessel strike. 

The Navy’s mission is to organize, 

train, equip, and maintain combat-ready 

naval forces capable of winning wars, 

deterring aggression, and maintaining 

freedom of the seas. This mission is 

mandated by Federal law (10 U.S.C. 

8062), which ensures the readiness of 

the naval forces of the United States. 

The Navy executes this responsibility by 

establishing and executing training 

programs, including at-sea training and 

exercises, and ensuring naval forces 

have access to the ranges, operating 

areas (OPAREAs), and airspace needed 

to develop and maintain skills for 

conducting naval activities. 

For a summary of the training and 

testing activities within the HSTT Study 

Area, see the Navy’s previous 

rulemaking and LOA applications 

submitted for HSTT Phase III activities 

(October 13, 2017 initial rulemaking and 

LOA application (hereafter ‘‘2017 Navy 

application’’) and March 11, 2019 

extension rulemaking and LOA 

application (hereafter ‘‘2019 Navy 

application’’)) and the 2020 HSTT 

regulations that were subsequently 

promulgated, which can be found at: 

https://www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

incidental-take-authorizations-militaryreadiness-activities. These activities are 

deemed by the Navy necessary to 

accomplish military readiness 

requirements and are anticipated to 

continue into the reasonably foreseeable 

future. The 2022 Navy application and 

this proposed rule cover training and 

testing activities that would occur over 

the remainder of the effective period of 

the current regulations, valid from the 


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publication date of the final rule, if 

issued, through December 20, 2025. 

Summary of the Proposed Regulations 

NMFS is proposing to modify the 

incidental take regulations and 

associated LOAs to cover the same Navy 

activities covered by the 2020 HSTT 

regulations but authorize five takes of 

large whales by serious injury or 

mortality by vessel strike (two takes in 

addition to the three takes authorized in 

the current regulations). In its 2022 

application, the Navy proposes no 

additional changes and explains that its 

training and testing activities, including 

the level of vessel use, remain 

unchanged. Nearly all mitigation, 

monitoring, and reporting measures 

remain unchanged with the exception of 

two additional mitigation measures, 

revision of two existing mitigation 

measures, and an additional reporting 

measure resulting from discussions 

between the Navy and NMFS. 

In response to the Navy’s request, we 

focus our analysis on the new 

information related to vessel strike. We 

also review any new information that 

may be pertinent to our analysis of the 

impacts from all other activities that 

comprise Navy’s specified activity, and 

our analysis of mitigation, monitoring, 

and reporting. Where there is any new 

information pertinent to the 

descriptions, analyses, or findings 

required to authorize the incidental take 

for military readiness activities under 

MMPA section 101(a)(5)(A), that 

information is provided in the 

appropriate sections below. Where there 

is no new information or any new 

information does not change our 

previous analysis or findings, we 

indicate as such and refer the reader to 

the original analysis in the 2018 HSTT 

proposed and final rule, 2020 HSTT 

final rule or the 2019 HSTT Final 

Environmental Impact Statement (FEIS)/ 

Overseas Environmental Impact 

Statement (OEIS). 

After reviewing all new information 

and as discussed below, we largely find 

that our previous analyses and findings 

remain current and applicable. For 

vessel strike, we provide a new analysis 

and propose authorizing two additional 

takes of large whales, for a total of five 

takes by serious injury or mortality by 

vessel strike over the 7-year period. We 

consider authorizing these additional 

takes after analyzing the best available 

information and after considering the 

effects of the entire specified activity 

and the total taking as required by 

MMPA section 101(a)(5)(A). When 

setting forth the permissible methods of 

taking pursuant to the activity and other 

means of effecting the least practicable 

adverse impact on the species or stock, 

we propose requiring new and modified 

mitigation and also consider whether to 

require any new or modified mitigation 

for the entire specified activity. 

The proposed regulatory language 

included at the end of this proposed 

rule, which would be published at 50 

CFR part 218, subpart H, remains largely 

the same as that under the HSTT 2020 

regulations, except for a small number 

of technical changes related to the 

Navy’s 2022 request, new and revised 

mitigation measures, and a new 

reporting measure. Therefore, in this 

proposed rule, we refer the reader to 

complete analyses described in the 2018 

HSTT final rule or an updated analysis 

in the 2020 HSTT final rule, where 

appropriate. 

Below is a list of the regulatory 

documents referenced in this proposed 

rule. The list indicates the short name 

by which the document is referenced in 

this proposed rule as well as the full 

titles of the cited documents. All of the 

documents can be found at: 

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/incidentaltake-authorizations-military-readinessactivities and http://www.hstteis.com/. 

• NMFS June 26, 2018, HawaiiSouthern California Training and 

Testing (HSTT) proposed rule (83 FR 

29872; 2018 HSTT proposed rule); 

• NMFS December 27, 2018, HawaiiSouthern California Training and 

Testing (HSTT) final rule (83 FR 66846; 

2018 HSTT final rule); 

• NMFS September 13, 2019, HawaiiSouthern California Training and 

Testing (HSTT) proposed rule (84 FR 

48388; 2019 HSTT proposed rule); 

• NMFS July 10, 2020, HawaiiSouthern California Training and 

Testing (HSTT) final rule (85 FR 41780; 

2020 HSTT final rule); 

• Navy October 13, 2017, MMPA 

rulemaking and LOA application (2017 

Navy application); 

• Navy March 11, 2019, MMPA 

rulemaking and LOA extension 

application (2019 Navy application); 

• Navy March 31, 2022, MMPA 

rulemaking and LOA revision 

application (2022 Navy application); 

and 

• October 26, 2018, Hawaii-Southern 

California Training and Testing (HSTT) 

Final Environmental Impact Statement/ 

Overseas Environmental Impact 

Statement (FEIS/OEIS) (2018 HSTT 

FEIS/OEIS). 

Description of the Specified Activity 

The Navy requests authorization to 

take marine mammals incidental to 

conducting training and testing 

activities. The Navy has determined that 

acoustic and explosives stressors are 

most likely to result in impacts on 

marine mammals that could rise to the 

level of harassment. In addition to take 

by harassment, the Navy has determined 

that vessel movement may result in 

serious injury or mortality to marine 

mammals. Detailed descriptions of these 

activities are provided in chapter 2 of 

the 2018 HSTT FEIS/OEIS and in the 

2017 Navy application. 

Overview of Training and Testing 

Activities 

The Navy routinely trains in the 

HSTT Study Area in preparation for 

national defense missions. Training and 

testing activities and components 

covered in the 2022 Navy application 

are described in detail in the Overview 

of Training and Testing Activities 

sections of the 2018 HSTT proposed 

rule, the 2018 HSTT final rule, and 

chapter 2 (Description of Proposed 

Action and Alternatives) of the 2018 

HSTT FEIS/OEIS (http://

www.hstteis.com/). Each military 

training and testing activity described 

meets mandated Fleet requirements to 

deploy ready forces. The Navy proposes 

no changes to the specified activities 

described and analyzed in the 2018 

HSTT final rule and subsequent 2020 

HSTT final rule. The boundaries of the 

HSTT Study Area (see figure 2–1 of the 

2019 Navy application); the dates and 

duration of the activities; and the 

training and testing activities (e.g., 

equipment and sources used, exercises 

conducted) analyzed in this proposed 

rule are identical to those described and 

analyzed in the 2020 HSTT final rule 

and therefore, are not repeated herein. 

Please see the 2020 HSTT final rule for 

more information. The manner of vessel 

movement presented in this proposed 

rule is also identical to that analyzed in 

the 2020 HSTT final rule. 

Vessel Strike 

Vessel strikes are not specific to any 

particular training or testing activity but 

rather, a limited, sporadic, and 

incidental result of Navy vessel 

movement within the HSTT Study Area. 

Vessel strikes from commercial, 

recreational, and military vessels are 

known to seriously injure and 

occasionally kill cetaceans (Abramson et 

al. 2011; Berman-Kowalewski et al. 

2010; Calambokidis, 2012; Douglas et al. 

2008; Laggner, 2009; Lammers et al. 

2003; Van der Hoop et al. 2012; Van der 

Hoop et al. 2013; Crum et al. 2019), 

although reviews of the literature on 

vessel strikes mainly involve collisions 

between commercial vessels and whales 

(Jensen and Silber, 2003; Laist et al. 

2001). Vessel speed, size, and mass are 


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all important factors in determining 

both the potential likelihood and 

impacts of a vessel strike to marine 

mammals (Conn and Silber, 2013; 

Gende et al. 2011; Silber et al. 2010; 

Vanderlaan and Taggart, 2007; Wiley et 

al. 2016). For large vessels, speed and 

angle of approach can influence the 

severity of a strike. 

Navy vessels transit at speeds that are 

optimal for fuel conservation or to meet 

training and testing requirements. Small 

craft (for purposes of this analysis, less 

than 18 m in length) have much more 

variable speeds (0–50+ knots (kn; 0–92.6 

kilometers (km) per hour), dependent on 

the activity). Submarines generally 

operate at speeds in the range of 8–13 

kn (14.8–24.1 km per hour), and the 

average speed of large Navy ships range 

between 10 and 15 kn (18.5 and 27.8 km 

per hour). While these speeds are 

considered averages and representative 

of most events, some vessels need to 

operate outside of these parameters for 

certain times or during certain activities. 

For example, to produce the required 

relative wind speed over the flight deck, 

an aircraft carrier engaged in flight 

operations must adjust its speed through 

the water accordingly. Also, there are 

other instances such as launch and 

recovery of a small rigid hull inflatable 

boat; vessel boarding, search, and 

seizure training events; or retrieval of a 

target when vessels would be dead in 

the water or moving slowly ahead to 

maintain steerage. There are a few 

specific events, including high-speed 

tests of newly constructed vessels, 

where vessels would operate at higher 

speeds. By comparison, this is slower 

than most commercial vessels where 

full speed for a container ship is 

typically 24 kn (44.4 km per hour; 

Bonney and Leach, 2010). 

Large Navy vessels (greater than 18 m 

in length) within the offshore areas of 

range complexes and testing ranges 

operate differently from commercial 

vessels in ways that may reduce the 

probability of whale collisions. Surface 

ships operated by or for the Navy have 

multiple personnel assigned to stand 

watch at all times when a ship or 

surfaced submarine is moving through 

the water (underway). A primary duty of 

personnel standing watch on surface 

ships is to detect and report all objects 

and disturbances sighted in the water 

that may indicate a threat to the vessel 

and its crew, such as debris, a 

periscope, surfaced submarine, or 

surface disturbance. Per vessel safety 

requirements, personnel standing watch 

also report any marine mammals sighted 

in the path of the vessel as a standard 

collision avoidance procedure. All 

vessels proceed at a safe speed so they 

can take proper and effective action to 

avoid a collision with any sighted object 

or disturbance and can be stopped 

within a distance appropriate to the 

prevailing circumstances and 

conditions. As described in the 

Standard Operating Procedures section, 

the Navy utilizes Lookouts to avoid 

collisions, and Lookouts are also trained 

to spot marine mammals so that vessels 

may change course or take other 

appropriate action to avoid collisions. 

Should a vessel strike occur, we 

consider that it would likely result in 

incidental take in the form of serious 

injury and/or mortality and, 

accordingly, for the purposes of the 

analysis, we assume that any vessel 

strike would result in serious injury or 

mortality. 

The Navy proposes no changes to the 

nature of the specified activities, the 

training and testing activities, the 

manner of vessel movement, the speeds 

at which vessels operate, the number of 

vessels that would be used during 

various activities, or the locations in 

which Navy vessel activity would be 

concentrated within the HSTT Study 

Area described in the 2018 HSTT final 

rule and referenced in the 2020 HSTT 

final rule. 

Vessel Movement 

Vessels used as part of the planned 

activities include ships, submarines, 

unmanned vessels, and boats ranging in 

size from small, 22 ft (7 m) rigid hull 

inflatable boats to aircraft carriers with 

lengths up to 1,092 ft (333 m). The 

average speed of large Navy ships ranges 

between 10 and 15 kn (18.5 and 27.8 km 

per hour) and submarines generally 

operate at speeds in the range of 8–13 

kn (14.8–24.1 km per hour) while a few 

specialized vessels can travel at faster 

speeds. Small craft (for purposes of this 

analysis, less than 18 m in length) have 

much more variable speeds (0–50+ kn 

(0–92.6 km per hour), dependent on the 

activity) but generally range from 10 to 

14 kn (18.5 to 25.9 km per hour). From 

unpublished Navy data, average median 

speed for large Navy ships in the HSTT 

Study Area from 2011–2015 varied from 

5–10 kn (9.2–18.5 km per hour) with 

variations by ship class and location 

(i.e., slower speeds close to the coast). 

While these speeds for large and small 

craft are representative of most events, 

some vessels need to temporarily 

operate outside of these parameters. 

Typical speed of Navy vessels in HSTT 

core high use areas from 2014–2018 

were between 10 and 15 kn (18.5 and 

27.8 km per hour; Starcovic and Mintz 

2021). This core area is a region 

including the approaches to San Diego, 

and immediate offshore areas west of 

San Diego, centered north and south of 

San Clemente Island. A full description 

of Navy vessels that are used during 

training and testing activities can be 

found in the 2017 Navy application and 

chapter 2 (Description of Proposed 

Action and Alternatives) of the 2018 

HSTT FEIS/OEIS. 

The number of Navy vessels used in 

the HSTT Study Area varies based on 

military training and testing 

requirements, deployment schedules, 

annual budgets, and other dynamic 

factors. Most training and testing 

activities involve the use of vessels. 

These activities could be widely 

dispersed throughout the HSTT Study 

Area but would typically be conducted 

near naval ports, piers, and range areas. 

Navy vessel traffic would be especially 

concentrated near San Diego, California 

and Pearl Harbor, Hawaii. Based on 

historical data, we anticipate the annual 

number of at-sea hours by U.S. Navy 

vessels in the HSTT action area will be 

around 26,800 hours per year (Starcovic 

and Mintz 2021). We expect that about 

25 percent of this vessel activity would 

occur within the Hawaii Range Complex 

(HRC) and 75 percent within the 

Southern California Range Complex 

(SOCAL; Mintz 2016). There is no 

seasonal differentiation in Navy vessel 

use because of continual operational 

requirements from Combatant 

Commanders. The majority of large 

vessel traffic occurs between the 

installations and the OPAREAs. The 

transit corridor, notionally defined by 

the great circle route (e.g., shortest 

distance) from San Diego to the center 

of the HRC, as depicted in the 2018 

HSTT FEIS/OEIS, is generally used by 

ships transiting between SOCAL and 

HRC. While in transit, ships and aircraft 

would, at times, conduct basic and 

routine unit-level activities such as 

gunnery, bombing, and sonar training 

and maintenance. Of note, support craft 

would be more concentrated in the 

coastal waters in the areas of naval 

installations, ports, and ranges. 

Activities involving vessel movements 

occur intermittently and are variable in 

duration, ranging from a few hours up 

to weeks. More information on Navy 

and non-Navy vessel traffic patterns in 

the HSTT Study Area may be found in 

several studies prepared by the Navy 

(Starcovic and Mintz 2021; Mintz, 2016; 

Mintz and Filadelfo, 2011; Mintz, 2012; 

Mintz and Parker, 2006). 

Foreign Navies 

In addition, we note that in some 

cases, foreign militaries may participate 

in U.S. Navy training or testing 

activities in the HSTT Study Area. The 

Navy does not consider these foreign 


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military activities as part of the 

‘‘specified activity’’ under the MMPA, 

and NMFS defers to the applicant to 

describe the scope of its request for an 

authorization. 

The participation of foreign navies 

varies from year to year, but overall is 

infrequent compared with Navy’s total 

training and testing activities. The most 

significant joint training event is the 

Rim of the Pacific (RIMPAC), a multinational training exercise held everyother-year primarily in the HRC. The 

participation level of foreign military 

vessels in U.S. Navy-led training or 

testing events within the HRC and 

within SOCAL differs greatly between 

RIMPAC and non-RIMPAC years. For 

example, in 2019 (a non-RIMPAC year), 

there were 0.1 foreign navy at-sea days 

(i.e., 1 day = 24 hours) within HRC and 

20 foreign navy at-sea days within 

SOCAL (Navy 2021). Out of 56 U.S.-led 

training events in 2019, 4 involved 

foreign navy vessels, with an average 

time per event of 8.7 hours. In 2020, a 

RIMPAC year, foreign vessels 

participating in U.S. Navy-led events 

accounted for 32 at-sea days in the HRC 

from August through September (some 

of this activity occurred after the 

RIMPAC exercise). During RIMPAC 

2022, foreign vessels operated and/or 

transited through the HRC for 576 hours 

(24 days). Even in a RIMPAC year, the 

days at sea for foreign militaries engaged 

in a Navy-led training or testing activity 

accounts for a very small percentage 

compared to the U.S. Navy activities. 

For instance, the 2020 foreign military 

participation (a RIMPAC-year) was 1.5 

percent of the U.S. Navy’s average days 

at sea (32 days out of an estimated 2,056 

days at sea). 

According to the U.S. Navy, 

consistent with customary international 

law, when a foreign military vessel 

participates in a U.S. Navy exercise 

within the U.S. territorial sea (i.e., 0 to 

12 nmi (0 to 22.2 km) from shore), the 

U.S. Navy will request that the foreign 

vessel follow the U.S. Navy’s mitigation 

measures for that particular event. 

When a foreign military vessel 

participates in a U.S. Navy exercise 

beyond the U.S. territorial sea but 

within the U.S. Exclusive Economic 

Zone, the U.S. Navy will encourage the 

foreign vessel to follow the U.S. Navy’s 

mitigation measures for that particular 

event (Navy 2022a; Navy 2022b). In 

either scenario (i.e., both within and 

beyond the territorial sea), U.S. Navy 

personnel will provide the foreign 

vessels participating with a description 

of the mitigation measures to follow. If 

a foreign military is not participating in 

a U.S. Navy training or testing exercise, 

foreign military vessels operating within 

the HSTT Study Area are expected to 

adhere to their own standard operating 

procedures and environmental 

mitigation measures. 

According to the U.S. Navy, the May 

2021 vessel strike of two fin whales by 

an Australian navy vessel did not occur 

while that vessel was participating in a 

U.S. Navy-led training exercise. The 

Royal Australian Navy vessel was 

adhering to its standard operating 

procedures at the time of the strike. The 

Royal Australian Navy provided a report 

of the incident, which is discussed 

below to inform our analysis. 

NMFS analyzes the effects of these 

foreign military activities in two ways. 

First, effects of all past foreign military 

activities are captured in the baseline 

for the analysis, through marine 

mammal abundance estimates and 

population trends found in the SARs. 

Second, NMFS considers foreign 

military activities, including recent 

strikes, qualitatively in this proposed 

rule. For instance, in preparing this 

rulemaking, NMFS and the U.S. Navy 

discussed the nature, frequency, and 

control over joint or U.S. Navy-led 

training and testing activities with 

foreign entities to identify opportunities 

to encourage foreign militaries to adopt 

mitigation. NMFS and the U.S. Navy 

examined the Royal Australian Navy 

strike report for any lessons that could 

inform U.S. Navy strike mitigation. 

NMFS considered the Royal Australian 

Navy strikes along with other recent 

U.S. Navy strikes to determine whether 

these strikes indicate an increased risk 

of strike by the U.S. Navy in this region 

during the early summer months. NMFS 

also considered the species struck in 

this incident, fin whales, along with 

other literature, when considering the 

likelihood of certain species to be struck 

by the U.S. Navy. Finally, NMFS 

considered the fact that two fin whales 

were struck by the Royal Australian 

Navy qualitatively when considering 

other fin whale population and 

mortality trends, as well as the take 

proposed for authorization, as part of 

the negligible impact analysis. 

Standard Operating Procedures 

For training and testing to be 

effective, personnel must be able to 

safely use their sensors and weapon 

systems as they are intended to be used 

in a real-world situation and to their 

optimum capabilities. While standard 

operating procedures (SOPs) are 

designed for the safety of personnel and 

equipment and to ensure the success of 

training and testing activities, their 

implementation often yields additional 

benefits on environmental, 

socioeconomic, public health and 

safety, and cultural resources. Because 

standard operating procedures are 

essential to safety and mission success, 

the Navy considers them to be part of 

the proposed activities under NEPA and 

included them in the environmental 

analysis. We consider standard 

operating procedures as part of Navy’s 

specified activity for the purposes of 

MMPA but also, where procedures are 

utilized (even in part) to reduce impacts 

to marine mammal species and Navy’s 

commitment to follow the measures are 

practicable, certain SOPs may also be 

required as mitigation. Details on 

standard operating procedures were 

provided in the 2018 HSTT proposed 

rule; please see the 2018 HSTT 

proposed rule, the 2017 Navy 

application, and Chapter 2 (Description 

of Proposed Action and Alternatives) of 

the 2018 HSTT FEIS/OEIS for more 

information. 

As stated in its 2022 application, in 

2018, the Navy updated its SOPs related 

to vessel safety to incorporate revised 

procedures regarding Lookouts for 

certain ship classes as per the 2021 

Surface Ship Navigation Department 

Organization and Regulations Manual 

(NAVDORM). The 2021 NAVDORM 

requires the use of three Lookouts on 

Navy cruisers and destroyers as 

compared to the previous requirement 

of one Lookout when a vessel was 

underway and not engaged in sonar 

training or testing. However, as 

discussed in the Proposed Mitigation 

Measures section below, the Navy 

informed NMFS that requiring the 

additional Lookouts as mitigation is not 

practicable because this SOP may 

change in response to manning issues 

and national security needs. Further, 

since submission of its 2022 

application, the Navy has updated its 

Lookout Training Handbook and 

implemented other training 

improvements, as described in the 

Proposed Mitigation Measures section 

(September 2022). 

Description of Marine Mammals and 

Their Habitat in the Area of the 

Specified Activities 

Marine mammal species and their 

associated stocks that have the potential 

to occur in the HSTT Study Area are 

presented in table 1 along with the best/ 

minimum abundance estimate and 

associated coefficient of variation value. 

Consistent with the 2018 HSTT final 

rule and 2020 HSTT final rule, the Navy 

anticipates the take of individuals from 

38 marine mammal species by Level A 

harassment and Level B harassment 

incidental to training and testing 

activities from the use of sonar and 

other transducers, in-water detonations, 


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air guns, and impact pile driving/ 

vibratory extraction activities. As 

described in detail later, serious injury 

or mortality of six species is also 

analyzed and proposed for 

authorization. 

In the 2018 HSTT proposed rule and 

2018 HSTT final rule, we presented a 

detailed discussion of marine mammals 

and their occurrence in the HSTT Study 

Area, inclusive of important marine 

mammal habitat (e.g., ESA-designated 

critical habitat), biologically important 

areas (BIAs), national marine 

sanctuaries (NMSs), and unusual 

mortality events (UMEs). Please see 

these rules and the 2017 and 2019 Navy 

applications for additional information 

beyond what is provided herein. While 

there have been some minor changes 

described here, there have been no 

changes to important marine mammal 

habitat, NMSs, or ESA designated 

critical habitat since the issuance of the 

2018 HSTT final rule that change our 

determination of which species or 

stocks have the potential to be affected 

by the Navy’s activities or the 

information in the Description of Marine 

Mammals and Their Habitat in the Area 

of the Specified Activities section in the 

2019 HSTT proposed rule and 2020 

HSTT final rule. Therefore, the 

information presented in those sections 

of the 2019 HSTT proposed rule and 

2020 HSTT final rule remains current 

and valid with the exception of the 

information about UMEs, BIAs, and 

revised humpback whale stock 

structures, discussed below. 

On April 21, 2021, NMFS designated 

critical habitat for the endangered 

Western North Pacific Distinct 

Population Segment (DPS), the 

endangered Central America DPS, and 

the threatened Mexico DPS of 

humpback whales (86 FR 21082). Areas 

proposed as critical habitat include 

specific marine areas located off the 

coasts of California, Oregon, 

Washington, and Alaska. None of the 

designated critical habitat overlaps with 

the HSTT Study Area. One of the 

proposed areas, critical habitat Unit 19, 

would have overlapped with the SOCAL 

range in the HSTT Study Area but was 

excluded after consideration of potential 

national security and economic impacts 

of designation. NMFS, in the final rule 

designating critical habitat for 

humpback whales, identified prey 

species, primarily euphausiids and 

small pelagic schooling fishes of 

sufficient quality, abundance, and 

accessibility within humpback whale 

feeding areas to support feeding and 

population growth, as an essential 

habitat feature. NMFS, through a critical 

habitat review team (CHRT), also 

considered inclusion of migratory 

corridors and passage features, as well 

as sound and the soundscape, as 

essential habitat features. NMFS did not 

include either in the final critical 

habitat, however, as the CHRT 

concluded that the best available 

science did not allow for identification 

of any consistently used migratory 

corridors or definition of any physical, 

essential migratory or passage 

conditions for whales transiting 

between or within habitats of the three 

DPSs. The best available science also 

currently does not enable NMFS to 

identify particular sound levels or to 

describe a certain soundscape feature 

that is essential to the conservation of 

humpback whales. Regardless of 

whether critical habitat is designated for 

a particular area, NMFS has considered 

all applicable information regarding 

marine mammals and their habitat in 

the analysis supporting these proposed 

regulations. 

NMFS has reviewed the 2022 final 

Stock Assessment Reports (SARs; 

Carretta et al. 2023, Young et al. 2023). 

For all species except humpback whale, 

NMFS determined that neither the SARs 

nor any other new information changes 

our determination of which species or 

stocks have the potential to be affected 

by the Navy’s activities. For humpback 

whale, the 2022 final SARs include a 

revision to the humpback whale stock 

structure in the Pacific Ocean. In the 

2020 HSTT final rule, NMFS authorized 

take of the CA/OR/WA stock and 

Central North Pacific stock of humpback 

whale. Given the revised stock 

structure, in this proposed rule, NMFS 

has reanalyzed the potential for take of 

each stock of humpback whale and 

determined that the Central America/ 

Southern Mexico-CA/OR/WA, Mainland 

Mexico—CA/OR/WA stock, and Hawaii 

stocks are likely to be taken by the 

Navy’s activities. Please refer to the 

2022 Alaska and Pacific Ocean SARs for 

additional information about these new 

stocks.) 

The species considered but not 

carried forward for analysis are two 

American Samoa stocks of spinner 

dolphins—(1) the Kure and Midway 

stock and (2) the Pearl and Hermes 

stock. There is no potential for overlap 

with any stressors from Navy activities 

and therefore there would be no 

incidental takes, in which case, these 

stocks are not considered further. 

TABLE 1—MARINE MAMMAL OCCURRENCE WITHIN THE HSTT STUDY AREA

Common name Scientific name Stock 

Status 

Occurrence Seasonal 

absence 

Stock abundance 

(CV)/minimum 

MMPA ESA population 

Blue whale ..................... Balaenoptera musculus Eastern North Pacific ... Strategic, 

Depleted 

Endangered Southern 

California 

— 1,898 (0.085)/1,767. 

Central North Pacific .... Strategic, Depleted ...... Endangered Hawaii Summer 133 (1.09)/ 

63. 

Bryde’s whale ................ Balaenoptera brydei/ 

edeni.

Eastern Tropical Pacific — — Southern 

California 

— unknown. 

Hawaii .......................... — — Hawaii — 602 (0.22)/501. 

Fin whale ....................... Balaenoptera physalus CA/OR/WA ................... Strategic, 

Depleted 

Endangered Southern 

California 

— 11,065 (0.405)/7,970. 

Hawaii .......................... Strategic, 

Depleted 

Endangered Hawaii Summer 203 (0.99)/101. 

Humpback whale ........... Megaptera 

novaeangliae.

Central America/Southern Mexico—CA/OR/ 

WA.

Strategic Endangered 1 Southern 

California 

Winter 1,496 (0.171)/1,284. 

Mainland Mexico—CA/ 

OR/WA.

Strategic Threatened1 Southern 

California 

Winter 3,477 (0.101)/3,185. 

Hawai1i .......................... — —1 Hawaii Summer 11,278 (0.56)/7,265. 

Minke whale .................. Balaenoptera 

acutorostrata.

CA/OR/WA ................... — — Southern 

California 

— 915 (0.792)/509. 

Hawaii .......................... — — Hawaii Summer 438 (1.05)/212. 

Sei whale ....................... Balaenoptera borealis .. Eastern North Pacific ... Strategic, 

Depleted 

Endangered Southern 

California 

— 519 (0.40)/374. 

Hawaii .......................... Strategic, 

Depleted 

Endangered Hawaii Summer 391 (0.9)/204. 


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TABLE 1—MARINE MAMMAL OCCURRENCE WITHIN THE HSTT STUDY AREA—Continued 

Common name Scientific name Stock 

Status 

Occurrence Seasonal 

absence 

Stock abundance 

(CV)/minimum 

MMPA ESA population 

Gray whale .................... Eschrichtius robustus ... Eastern North Pacific ... — — Southern 

California 

— 26,960 (0.05)/25,849. 

Western North Pacific .. Strategic, 

Depleted 

Endangered Southern 

California 

— 290 (NA)/271. 

Sperm whale ................. Physeter 

macrocephalus.

CA/OR/WA ................... Strategic, 

Depleted 

Endangered Southern 

California 

— 1,997 (0.57)/1,270. 

Hawaii .......................... Strategic, 

Depleted 

Endangered Hawaii — 5,707 (0.23)/4,486. 

Pygmy sperm whale ...... Kogia breviceps ........... CA/OR/WA ................... — — Southern 

California 

Winter and 

Fall 

4,111 (1.12)/1,924. 

Hawaii .......................... — — Hawaii — 42,083 (0.64) 25,695. 

Dwarf sperm whale ....... Kogia sima ................... CA/OR/WA ................... — — Southern 

California 

— unknown. 

Hawaii .......................... — — Hawaii — unknown. 

Baird’s beaked whale .... Berardius bairdii ........... CA/OR/WA ................... — — Southern 

California 

— 1,363 (0.53)/894. 

Blainville’s beaked 

whale.

Mesoplodon 

densirostris.

Hawaii .......................... — — Hawaii — 1,132 (0.99)/564. 

Cuvier’s beaked whale .. Ziphius cavirostris ........ CA/OR/WA ................... — — Southern 

California 

— 5,454 (0.27)/4,214. 

Hawaii .......................... — — Hawaii — 4,431 0.41/3,180. 

Longman’s beaked 

whale.

Indopacetus pacificus .. Hawaii .......................... — — Hawaii — 2,550 (0.67)/1,527. 

Mesoplodont beaked 

whales.

Mesoplodon spp ........... CA/OR/WA ................... — — Southern 

California 

— 3,044 (0.54)/1,967. 

Common Bottlenose dolphin.Tursiops truncatus ....... California Coastal ......... — — Southern 

California 

— 453 (0.06)/346. 

CA/OR/WA Offshore .... — — Southern 

California 

— 3,477 (0.696)/2,048. 

Hawaii Pelagic ............. — — Hawaii — unknown. 

Kauai and Niihau ......... — — Hawaii — NA NA/97. 

Oahu ............................ — — Hawaii — NA. 

4-Islands ....................... — — Hawaii — NA. 

Hawaii Island ................ — — Hawaii — unknown. 

False killer whale .......... Pseudorca crassidens .. Main Hawaiian Islands 

Insular.

Strategic, 

Depleted 

Endangered Hawaii — 167 (0.14)/149. 

Hawaii Pelagic ............. — — Hawaii — 2,086 (0.35)/1,567. 

Northwestern Hawaiian 

Islands.

— — Hawaii — 477 (1.71)/178. 

Fraser’s dolphin ............. Lagenodelphis hosei .... Hawaii .......................... — — Hawaii — 40,960 (0.7)/24,068. 

Killer whale .................... Orcinus orca ................. Eastern North Pacific 

Offshore.

— — Southern 

California 

— 300 (0.1)/276. 

West Coast Transient .. — — Southern 

California 

— 349 (N/A)/349. 

Hawaii .......................... — — Hawaii — 161 (1.06)/78. 

Long-beaked common 

dolphin.

Delphinus capensis ...... California ...................... — — Southern 

California 

— 83,379 (0.216)/69,636. 

Melon-headed whale ..... Peponocephala electra Hawaiian Islands .......... — — Hawaii — 40,647 (0.74)/23,301. 

Kohala Resident ........... — — Hawaii — unknown. 

Northern right whale dolphin.Lissodelphis borealis .... CA/OR/WA ................... — — Southern 

California 

— 29,285 (0.72)/17,024. 

Pacific white-sided dolphin.Lagenorhynchus 

obliquidens.

CA/OR/WA ................... — — Southern 

California 

— 34,999 (0.222)/29,090. 

Pantropical spotted dolphin.Stenella attenuata ........ Oahu ............................ — — Hawaii — unknown. 

4-Islands ....................... — — Hawaii — unknown. 

Hawaii Island ................ — — Hawaii — unknown. 

Hawaii Pelagic ............. — — Hawaii — 39,768 (0.51)/25,548. 

Pygmy killer whale ........ Feresa attenuata .......... Tropical ........................ — — Southern 

California 

Winter & 

Spring 

unknown. 

Hawaii .......................... — — Hawaii — 10,328 (0.75)/5,885. 

Risso’s dolphins ............ Grampus griseus .......... CA/OR/WA ...................

Hawaii ..........................

— 

— 

— 

— 

Southern 

California 

Hawaii 

— 

— 

6,336 (0.32)/4,817. 

7,385 (0.22)/6,150. 

Steno bredanensis ....... NSD 2 ........................... — — Southern 

California 

— unknown. 

Rough-toothed dolphin .. Hawaii .......................... — — Hawaii — 76,357 (0.41)/54,804. 

Short-beaked common 

dolphin.

Delphinus delphis ........ CA/OR/WA ................... — — Southern 

California 

— 1,056,308 (0.21)/ 

888,971. 

Short-finned pilot whale Globicephala 

macrorhynchus.

CA/OR/WA ................... — — Southern 

California 

— 836 (0.79)/466. 

Hawaii .......................... — — Hawaii — 12,607 (0.18)/10,847. 

Spinner dolphin ............. Stenella longirostris ...... Hawaii Pelagic ............. — — Hawaii — unknown. 

Hawaii Island ................ — — Hawaii — 665 (0.09)/617. 

Oahu and 4-Islands ..... — — Hawaii — unknown. 

Kauai and Niihau ......... — — Hawaii — unknown. 

Kure and Midway ......... — — Hawaii — unknown. 

Pearl and Hermes ........ — — Hawaii — unknown. 

Striped dolphin .............. Stenella coeruleoalba .. CA/OR/WA ................... — — Southern 

California 

— 29,988 (0.3)/23,448. 


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TABLE 1—MARINE MAMMAL OCCURRENCE WITHIN THE HSTT STUDY AREA—Continued 

Common name Scientific name Stock 

Status 

Occurrence Seasonal 

absence 

Stock abundance 

(CV)/minimum 

MMPA ESA population 

Hawaii .......................... — — Hawaii — 35,179 (0.23)/29,058. 

Dall’s porpoise ............... Phocoenoides dalli ....... CA/OR/WA ................... — — Southern 

California 

— 16,498 (0.61)/10,286. 

Harbor seal .................... Phoca vitulina .............. California ...................... — — Southern 

California 

— 30,968 (NA)/27,348. 

Hawaiian monk seal ...... Neomonachus 

schauinslandi.

Hawaii .......................... Strategic, 

Depleted 

Endangered Hawaii — 1,465 3 (0.03)/1,431. 

Northern elephant seal .. Mirounga angustirostris California ...................... — — Southern 

California 

— 187,386 (NA)/85,369. 

California sea lion ......... Zalophus californianus U.S. Stock .................... — — Southern 

California 

— 257,606 (NA)/233,515. 

Guadalupe fur seal ........ Arctocephalus 

townsendi.

Mexico to California ..... Strategic, 

Depleted 

Threatened Southern 

California 

— 34,187 (NA)/31,019. 

Northern fur seal ........... Callorhinus ursinus ...... California ...................... Depleted — Southern 

California 

— 14,050 (NA)/7,524. 

Note: A ‘‘—’’ indicates that this column does not apply. 1The Mainland Mexico-CA–OR–WA stock and the Mexico-North Pacific stock (which does not occur in the HSTT Study Area) of humpback whale comprise the 

Mexico DPS. The Hawai1i stock comprises the Hawai1i DPS. The Central America/Southern Mexico-CA–OR–WA stock comprises the Central America DPS. 2 NSD—No stock designation. Rough-toothed dolphin has a range known to include the waters off Southern California, but there is no recognized stock or data 

available for the U.S. West Coast. 3The best official estimate of the total population size from the NMFS 2022 Stock Assessment Report (Carretta et al. 2023) is 1,465. This estimate is based on 

available data through 2020 data for Kure and Midway Atolls, Nihoa Island, and the MHI, and through 2019 for all other subpopulations. More recent survey data for 

2021 and 2022 indicate an increasing trend in population size. NMFS estimates a total population size for 2022 of 1,605 (NOAA 2023). 

Unusual Mortality Events 

An UME is defined under section 

410(6) of the MMPA as a stranding that 

is unexpected, involves a significant 

die-off of any marine mammal 

population, and demands immediate 

response. From 1991 to the present, 

there have been 17 formally recognized 

UMEs affecting marine mammals in 

California and Hawaii and involving 

species under NMFS’ jurisdiction. There 

is one UME that is applicable to our 

evaluation of the Navy’s activities in the 

HSTT Study Area. The gray whale UME 

along the west coast of North America 

is active and involves ongoing 

investigations. At the time of 

publication of the 2020 HSTT final rule, 

there was an active UME for Guadalupe 

fur seal, which NMFS fully considered 

in its analysis (85 FR 41780, July 10, 

2020). This UME was closed on 

September 2, 2021, and therefore, it is 

not discussed further beyond the 

information provided here. The UME 

was closed because conditions under 

which the UME was declared are no 

longer occurring or have become 

persistent. Scientists documented a 

reduction in strandings compared to 

peak UME years. The team of scientists 

who investigated this UME determined 

the cause of the UME as being due to 

malnutrition in Guadalupe fur seal pups 

and yearlings from ecological factors 

(e.g., warm water events) in the Pacific 

Ocean causing suboptimal prey 

conditions. Please see https://

www.fisheries.noaa.gov/national/ 

marine-life-distress/unusual-mortalityevent-2015-2021-guadalupe-fur-sealand-2015 for additional information on 

this UME. 

Gray Whale UME 

Since January 1, 2019, elevated gray 

whale strandings have occurred along 

the west coast of North America, from 

Mexico to Canada. As of June 25, 2023, 

there have been a total of 674 strandings 

along the coasts of the U.S., Canada, and 

Mexico, with 333 of those strandings 

occurring along the U.S. coast. Of the 

strandings on the U.S. coast, 135 have 

occurred in Alaska, 83 in Washington, 

22 in Oregon, and 93 in California. Full 

or partial necropsy examinations were 

conducted on a subset of the whales. 

Preliminary findings in several of the 

whales have shown evidence of 

emaciation. These findings are not 

consistent across all of the whales 

examined, so more research is needed. 

As part of the UME investigation 

process, NOAA has assembled an 

independent team of scientists to 

coordinate with the Working Group on 

Marine Mammal Unusual Mortality 

Events to review the data collected, 

sample stranded whales, consider 

possible causal-linkages between the 

mortality event and recent ocean and 

ecosystem perturbations, and determine 

the next steps for the investigation. 

Please refer to: https://

www.fisheries.noaa.gov/national/ 

marine-life-distress/2019-2023-graywhale-unusual-mortality-event-alongwest-coast-and for more information on 

this UME. See the Preliminary Analysis 

and Negligible Impact Determination 

section for additional information on 

how NMFS has considered this UME in 

this proposed rule. 

Biologically Important Areas 

Since publication of the 2020 HSTT 

final rule, Kratofil et al. (2023) 

identified updated BIAs in Hawaii. The 

HSTT Study Area overlaps the updated 

BIAs for small and resident populations 

of the following species in Hawaii: 

spinner dolphin, short-finned pilot 

whale, rough-toothed dolphin, pygmy 

killer whale, pantropical spotted 

dolphin, melon-headed whale, false 

killer whale, dwarf sperm whale, 

Cuvier’s beaked whale, common 

bottlenose dolphin, and Blainville’s 

beaked whale. Further, the HSTT Study 

Area overlaps updated BIAs for 

humpback whale reproduction in 

Hawaii. The updated BIAs overlap 

critical Navy training and testing areas 

within the HSTT Study Area, including 

most of the internal Navy operating 

areas. Please see Kratofil et al. (2023) for 

additional details about the BIAs. 

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 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 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 


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survival. In the Potential Effects of 

Specified Activities on Marine 

Mammals and Their Habitat section of 

the 2018 HSTT proposed and final 

rules, and as updated by the 2020 HSTT 

final rule, NMFS provided a description 

of the ways marine mammals may be 

affected by the same activities that the 

Navy will be conducting during the 7- 

year period analyzed in this rulemaking 

in the form of serious injury or 

mortality, physical trauma, sensory 

impairment (permanent and temporary 

threshold shifts and acoustic masking), 

physiological responses (particularly 

stress responses), behavioral 

disturbance, or habitat effects. We do 

not repeat the information here, all of 

which remains current and applicable, 

and instead summarize any new 

relevant information from the scientific 

literature. For more information we refer 

the reader to those rules and the 2018 

HSTT FEIS/OEIS (Chapter 3, Section 3.7 

Marine Mammals), which NMFS 

participated in the development of via 

our cooperating agency status and 

adopted to meet our NEPA 

requirements. 

In the Potential Effects of Specified 

Activities on Marine Mammals and 

Their Habitat section of the 2018 HSTT 

final rule, we stated that it has been 

speculated for some time that beaked 

whales might have unusual sensitivities 

to sonar sound due to their likelihood 

of stranding in conjunction with midfrequency active sonar (MFAS) use, 

although few definitive causal 

relationships between MFAS use and 

strandings have been documented, and 

no such findings have been documented 

with Navy use in Hawaii and southern 

California. On March 25, 2022, a beaked 

whale (species unknown) stranded in 

Honaunau Bay, Hawaii. The animal was 

observed swimming into shore and over 

rocks. Bystanders intervened to turn the 

animal off of the rocks, and it swam 

back out of the Bay on its own. Locals 

reported hearing a siren or alarm type of 

sound underwater on the same day, and 

a Navy vessel was observed from shore 

on the following day. The Navy 

confirmed it used continuous active 

sonar (CAS) within 50 km (27 nmi) and 

48 hours of the time of stranding, 

though the stranding has not been 

definitively linked to the Navy’s CAS 

use. 

An initial study of another deep 

diving odontocete, the sperm whale, 

found similar behavioral responses and 

reductions in foraging when whales 

were exposed to pulsed active sonar 

(PAS) and CAS at similar cumulative 

Sound Exposure Levels (SELcum), even 

though the CAS signal had a lower 

source level than the PAS signal. This 

may indicate that animals were, in this 

case, responding to the cumulative 

energy of a signal rather than the 

instantaneous amplitude (Cure et al. 

2021, Isojunno et al. 2020). If a beaked 

whale were inshore of a Navy vessel 

using either PAS or CAS MFAS, and 

responded by moving away from the 

vessel, they could find themselves in 

shallow water and become disoriented, 

as may have happened in the case of 

Honaunau Bay. In addition, the animal 

was not seen after it returned to sea, so 

blood tissue samples could not be 

obtained. There has been a growing 

body of literature about the impacts of 

new pathogens on the health and 

stranding of marine mammals, 

including beaked whales in Hawaii and 

other locations in the Pacific (e.g., 

Clifton et al. 2023 and West et al. 2013). 

New Pertinent Science Since 

Publication of the 2020 HSTT Final 

Rule 

NMFS has reviewed new relevant 

information from the scientific literature 

since publication of the 2020 HSTT 

final rule. Summaries of the new key 

scientific literature reviewed since 

publication of the 2020 HSTT final rule 

are presented below. The literature 

generally falls into the following topic 

areas: Vessel Strike; Aircraft Noise; 

Hearing, Vocalization, and Masking; 

Hearing Loss (Temporary Threshold 

Shift (TTS) and Permanent Threshold 

Shift (PTS)); Behavioral Reactions; 

Stranding; Population Consequences of 

Disturbance and Cumulative Stressors; 

Methodology for Assessing Acoustic 

Impacts. 

Vessel Strike 

Crum et al. (2019) analyzed a 

modeling framework using encounter 

theory to estimate the risk of lethal 

commercial vessel strike to North 

Atlantic right whales. Seasonal 

mortality rates of right whales decreased 

by 22 percent on average after a speed 

rule was implemented, indicating that 

the rule is effective at reducing lethal 

collisions. The rule’s effect on risk was 

greatest where right whales were 

abundant and vessel traffic was heavy 

but varied considerably across time and 

space. 

Keen et al. (2019) compared vessel 

traffic patterns in the Southern 

California Bight, San Francisco, and the 

Pacific Northwest and found fin whales 

had a higher risk of nighttime vessel 

strikes with the nighttime risk being 

double daytime risk. The authors 

concluded that the shipping lanes 

contained 14 percent of all traffic 

volume and contributed 13 percent of 

all strike risk similar to conclusions 

reached by Rockwood et al. (2017). 

However, the authors also point out that 

a California Current Ecosystem (CCE) 

wide shipping speed reductions would 

not be practicable. Instead, they 

proposed 24-hour speed restrictions 

around and within shipping lanes 

would be more effective and feasible 

than nighttime only speed restrictions 

elsewhere. Keen et al. (2019b) reported 

high fin whale habitat suitability 

throughout the Southern California 

Bight, in particular inshore in winter 

and in southern portions of the Bight, 

which include HSTT SOCAL Study 

Area. 

Leaper (2019) estimated that a global 

10 percent reduction in shipping speeds 

could result in a reduction of 

underwater sound associated with 

shipping by approximately 40 percent 

and vessel strike risk by around 50 

percent by 2050. The vessel strike risk 

reduction done by the author is highly 

variable based solely on the relationship 

between ship speed and risk, qualitative 

in its findings, and speculative. 

Redfern et al. (2019) compared risk of 

vessel strike to baleen whales around 

the Santa Barbara Channel based on 8 

years of shipping data (2008–2015). 

Species evaluated include blue whales, 

fin whales, and humpback whales using 

available spatial habitat models and 

satellite tagging results. Spatial habitat 

modeling data included the years 1991, 

1993, 1996, 2001, 2005, 2008, and 2009. 

The authors defined collision risk based 

on the co-occurrence of whales and 

ships for various management scenarios 

focused on adding shipping routes, 

expanding existing area to be avoided, 

and reducing shipping speed associated 

with these areas. Encounter rate theory 

was used to predict relative mortality 

resulting from vessel strikes by 

estimating (a) the encounter rate; (b) the 

number of encounters that result in a 

collision; and (c) the probability that a 

collision is lethal (Martin et al. 2016, 

Rockwood et al. 2017, Crum et al. 2019). 

The authors concluded that expanding 

the existing areas to be avoided and 

speed reductions within shipping lanes 

and their approaches would be the most 

effective solutions. Ship speeds 

declined in the Bight from 2008 to 2015 

because California air pollution 

regulations and economic factors made 

slow-steaming strategies more favorable, 

therefore reduction in risk from slowing 

ships was greatest in 2008 and lowest in 

2015. 

Rockwood and Jahncke (2019) 

estimated that humpback whale 

mortality from January to April in 

Southern California alone was 6.5 

whales (1.63/month), based upon 

modeling using updated abundance 


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estimates for humpback whales off 

Southern California. When added to the 

estimated mortality from July to 

November, the total estimated annual 

humpback mortality from vessel strikes 

in California alone was 23.4 deaths (16.9 

+ 6.5). This study did not include 

information for January to April for fin 

or blue whales and did not estimate 

humpback mortality in central or 

Northern California. Thus, even this 

updated study may underestimate 

whale mortality. The author’s focus was 

exclusively on shipping approaches to 

San Francisco Bay (Northern California) 

and Los Angeles/Long Beach (Southern 

California) based on Rockwood et al. 

2017 with new local fine scale analysis. 

The paper postulated potential mortality 

from models, not actual reported strikes. 

The model is used to predict whale 

mortality based on factors listed in 

Rockwood et al. 2017. In the model 

results, cargo vessels, especially 

container ships, accounted for more 

than half of the predicted mortality for 

all whale species in both Northern and 

Southern California with oil tankers 

accounting for the second highest 

mortality. The author’s recommendation 

concludes with commercial industrywide shipping speed reduction 

recommendations given the model is 

biased on mortality as a function of 

speed. In summary, Rockwood and 

Jahncke (2019) only addresses 

commercial shipping strike risk 

associated with major California 

commercial ports, and therefore, the 

paper may have limited applicability to 

how the Navy trains and tests in 

SOCAL. 

Se`be et al. (2019) assesses previous 

publications on whale vessel strike risk 

methodology and proposed a systematic 

approach to addressing the issue called 

the Formal Safety Assessment: (1) 

identification of hazards, (2) assessment 

of risks, (3) risk control options, (4) costbenefit assessment, and (5) 

recommendations for decision-making. 

The authors provided a case study based 

on data from Rockwood et al. (2017). No 

new data analysis is presented in the 

paper. Caveats to Se`be et al. (2019) are 

similar to those mentioned for 

Rockwood et al. (2017, 2019): older 

marine mammal data that may not be 

reflective of current or future 

distribution and focus on limited 

navigation within shipping approaches 

by commercial ships means that this 

study may have somewhat limited 

applicability to how the Navy trains and 

tests in SOCAL. 

Szesciorka et al. (2019) concluded 

that while whales have some cues to 

avoid ships, this is true only at close 

range, under certain oceanographic 

conditions and if the whale is not 

otherwise distracted by feeding, 

breeding, or other behaviors. The paper 

is based on a single blue whale reaction 

observed in the Santa Barbara Channel, 

north of, and outside of, SOCAL. The 

blue whale was tagged as part of the 

U.S. Navy-funded Southern California 

Behavioral Response Study (SOCAL 

BRS) 2010–2015 and exposed to 

simulated MFAS when a closest point of 

approach of 93 m from a passing 

commercial container ship was noted. 

The whale was only tagged for a couple 

of hours before tag detachment. As other 

published papers report from the 

SOCAL BRS and as cited in the 2018 

HSTT FEIS/OEIS, there can be 

significant individual variation in 

response to anthropogenic sources, 

which in this case would include vessel 

transit. 

Blondin et al. (2020) estimated blue 

whale vessel strike risk in the Southern 

California Bight by combining predicted 

daily whale distributions with 

continuous vessel movement data for 4 

years (2011, 2013, 2015, 2017). The 

study focuses on the northern Southern 

California Bight associated with the 

commercial vessel traffic separation 

zone through Santa Barbara Channel 

approaching the Port of Los Angeles/ 

Long Beach. This area is north of and 

outside of SOCAL. The authors found 

that vessel traffic activity across years 

(2011, 2013, 2015, 2017) was variable 

and whale spatial probability was also 

variable based on inter-annual 

fluctuations in environmental 

conditions. Similar to previous 

monitoring efforts in Southern 

California, blue whales are typically in 

higher concentrations north of SOCAL 

from July-November (Mate et al. 2018), 

and Blondin et al. (2021) also picked up 

on this seasonal variability in their 

analysis. Oceanographic conditions 

favorable for krill development and 

concentration (i.e., cool water periods) 

would lead to increased blue whale 

occurrence and higher strike risk as 

evidenced during the higher number of 

blue whale strikes in 2007 (BermanKowalewski et al. 2010). Finally, the 

coarse level of data analyzed by the 

authors does not account for short-term 

patchy prey conditions influencing blue 

whale occurrence and may result in 

overestimation of average risk. 

Redfern et al. (2020) revised their 

2019 assessments of vessel strike risk off 

California using interannual variability 

of risk across multiple years for blue 

whale, fin whale and humpback whale. 

The authors showed higher 

concentrations of both blue and fin 

whales along the Central California 

coast as compared to within SOCAL. 

Magnitude of vessel strike risk was 

influenced by the ship traffic scenario. 

In addition, interannual species 

variability (1991, 1993, 1996, 2001, 

2005, 2008, and 2009) also influenced 

the magnitude of vessel strike risk, but 

did not change whether nearshore or 

offshore scenarios had higher risk. The 

author’s conclusions were similar to 

Redfern et al. (2019). Figure 2 from 

Redfern et al. (2020) illustrates mean 

blue whale, fin whale, and humpback 

whale vessel strike risk for California 

based on data through 2009. Results 

from more recent NMFS surveys in 2014 

and 2018 may or may not change this 

assessment in the future. 

Rockwood et al. (2020b) calculated 

expected blue whale and humpback 

whale mortality for hypothetical 

compliance scenarios by imposing 

speed caps within and adjacent to vessel 

traffic lanes leading to the Port of San 

Francisco in Central California, 400 

miles (643.7 km) north of SOCAL. 

Rookwood et al. (2020a) had already 

demonstrated this area off Central 

California had concentrated krill prey 

with associated higher distributions of 

blue whales and humpback whales. 

Rookwood et al. (2020b) used better 

temporal resolution density data than 

previous modeling efforts reported by 

Rookwood et al. (2017). Biological data 

analysis for Rookwood et al. (2020b) 

was based on regional monthly krill and 

whale surveys from 2004–2017. 

Rockwood et al.’s (2020b) overall 

modeling conclusions were that lower 

commercial ship speeds within the 

vessel traffic lanes could potentially 

reduce whale mortality from vessel 

strike. The authors acknowledge that 

local changes in whale abundance can 

have strong effects on both inter-annual 

and long-term patterns of ship-strike 

mortality. 

Bernknopf et al. (2021) examined the 

socioeconomic benefits of using 

remotely-sensed information instead of 

in situ observations for determining 

blue whale occurrence in the eastern 

North Pacific Ocean. Their analysis 

used blue whale spatial distribution 

through 1991–2009 projects as 

representative of 2017 densities (Becker 

et al. 2012) combined with automatic 

identification system (AIS) derived 

measures of civilian commercial vessel 

traffic to predict blue whale vessel strike 

risk, called the Reference Case by the 

authors. The authors then compared 

estimated blue whale strike risk in a 

second analysis that, instead of using 

empirically measured blue whale 

observations converted into spatial 

habitat maps, used satellite tracking and 

environmental data to identify the 

spatial and temporal distribution of blue 


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whales, called the Counterfactual Case 

by the authors (Hazen et al. 2017). 

Estimated mean fatal strikes to blue 

whales for the Reference Case based on 

empirical density data from 1991–2009 

ranged from 0.0490 to 2.5877 (max. 

values >1.000 between June to October) 

(see Table 2 in Bernknopf et al. 2021). 

Estimated mean fatal strikes to blue 

whales for the Counterfactual Case 

based on environmental estimates of 

blue whale density in 2017 ranged from 

0.0286 to 2.1556 (max. values >1.000 

between August to October). An 

important caveat to this research is that 

the two approaches result in different 

strike risks due to using different blue 

whale density estimates. 

Barkaszi et al. (2021) designed a 

model to estimate risks to large whales 

from shipping associated with offshore 

wind development along the U.S. 

Atlantic Coast. A key caveat for the 

model is that it is based on civilian 

vessel types associated with wind 

energy construction (e.g., tugs, service 

craft, etc.) with relatively fixed, direct 

routes to offshore wind sites. Therefore, 

while lower vessel speeds can reduce 

mortality, prediction and 

implementation of reduced speed zones 

are a far more complex challenge 

(Barkaszi et al. 2021). Vessel speed has 

less effect on strike risk over a fixed 

distance with fixed target density when 

there are no behavioral components 

considered (Yin et al. 2019). Vessel 

speed has a significant effect on strike 

risk only when behavioral components 

are considered, thus the ability for the 

user to input animal or vessel aversion 

is an important variable that can 

provide insights to the encounter risk 

based on vessel speeds. 

Cusato (2021) discusses the merits of 

vessel traffic separation changes or 

mandatory commercial ship speed 

reductions in the Santa Barbara Channel 

to reduce the risk of vessel strikes to 

large whales. The author compares it to 

similar restrictions on the U.S. East 

Coast for North Atlantic right whales. 

The paper is a policy discussion rather 

than an analysis of current biological 

distribution of large whales and 

associated risk. Cusato (2021) focuses on 

reducing risk from commercial ships in 

the current vessel traffic separation 

scheme within the Santa Barbara 

Channel. Speed restrictions in the 

Channel would need to be implemented 

through either Federal regulations or 

Federal statute. The author also 

correctly points out legitimate concerns 

that operating large vessels at slow 

speeds in certain conditions could pose 

a safety risk because large vessels are 

more difficult to control and steer at 

slower speeds. 

Hausner et al. (2021) examined 

tradeoffs of blue whale vessel strikes 

and speed reduction mitigation over a 

17-year period from 2002 to 2018 in the 

Southern California Bight under two 

management scenarios verses a ‘‘fixed 

strategy’’ that implements speed 

reductions for a fixed time period each 

year. The two management strategies 

were (1) a ‘‘daily strategy’’ 

implementing speed reductions in 

response to whale habitat conditions on 

a daily basis, and (2) a ‘‘seasonal 

strategy’’ implementing speed 

reductions in response to whale habitat 

conditions on a seasonal basis. The 

period of the author’s data analysis also 

covers the abnormal marine heat wave 

along the U.S. West Coast (2014–2016). 

The study’s focus was exclusively with 

the traffic separation lanes leading from 

the Santa Barbara Channel to the Ports 

of Los Angeles and Long Beach, a 

narrow corridor north of and outside of 

SOCAL. The daily and seasonal 

management strategies were more 

effective in reducing blue whale strike 

risk in the Santa Barbara channel than 

the fixed strategy. The daily 

management strategy had the highest 

protective effect. This apparent 

difference in strategies also applied 

during and after the 2014–2016 marine 

heat wave where the daily strategy 

added even extra protection. The 

authors acknowledged that interannual 

variation on blue whale presence in the 

shipping lanes added some variability to 

their analysis. In addition, their study 

only considered blue whales sighted 

within the Traffic Separation Scheme, 

as opposed to the broader region where 

vessels transit through or a blue whale 

could occur. 

Ransome et al. (2021) documented 40 

vessel strikes to large whales in the 

Eastern Tropical Pacific Ocean between 

1905 and 2017 off the coasts of 10 

Central and South American countries 

(Mexico to Columbia). The authors 

concluded that vessel strikes to large 

whales are more prolific in this region 

than previously reported. For instance, 

the author’s findings of 40 vessel strikes 

was over three times greater than 

previous reporting and still is likely 

under reporting total whale strikes. The 

majority of whale strikes occurred from 

the 1950s onward with the growth of 

modern shipping and whale watching. 

Humpback whales were the most 

commonly struck species (45 percent) 

although 30 percent of the species were 

not identified in their data. 

Rockwood et al. (2021), similar to 

Rockwood et al. (2020b), calculated 

potential whale strike mortalities using 

AIS vessel data and whale density data 

to estimate mortality under several 

management scenarios within the 

commercial shipping lanes passing 

through Santa Barbara Channel and San 

Pedro Channel to and from the Ports of 

Los Angeles and Long Beach. While the 

Santa Barbara Channel is approximately 

100 miles (160.9 km) north of SOCAL, 

Rockwood et al.’s study area also 

included the southern vessel traffic 

approach to Los Angeles and Long 

Beach which did extend into the 

northeast coastal portion of SOCAL. 

Recent whale surveys were not available 

for this effort, so the authors used longterm average blue, fin, and humpback 

whale densities from Becker et al. 

(2016). The author’s model also 

predicted a higher level of whale vessel 

strikes from commercial ships than 

Rockwood et al. (2017), although the 

authors acknowledged that for the 2020 

publication they included more vessel 

classes than for the 2017 publication. 

Silber et al. (2021) examined the risk 

to gray whales from commercial 

shipping in the North Pacific. Vessel 

strike risk was highest for gray whales 

including the Western North Pacific 

Distinct Population Segment (WNP 

DPS) along most of the migratory routes. 

Highest risk to the WNP DPS of gray 

whales was outside of the SOCAL in the 

western Bering Sea, along the east coast 

of the Kamchatka peninsula (Russia), 

and coastlines of Japan. For both Eastern 

North Pacific and WNP DPSs of gray 

whales, the greatest vessel strike risk 

along the U.S. West Coast was from 

Washington to Central California. 

Helm et al. (2023) looked at strike risk 

to foraging humpback whales surfacing 

around large cruise ships transiting 

Glacier Bay National Park, Alaska. The 

authors concluded that the probability 

of foraging humpback whales remaining 

near the surface after first sightings was 

relatively high. While this puts 

humpback whales at increased risk of 

ship strike, it also allows shipboard 

observers more time to spot whales in 

order to maneuver the ship to avoid a 

strike. 

Lookout Effectiveness 

A recent study by Oedekoven and 

Thomas (2022) was designed to evaluate 

the effectiveness of Navy Lookouts at 

detecting marine mammals before they 

entered a defined set of mitigation zones 

(i.e., 200, 500, and 1,000 yd (182.9, 

457.2, and 914.4 m)) during MFAS 

training activities. This study also 

compared Lookout effectiveness with 

that of trained marine mammal 

observers. Lookout teams were 

comprised of varying numbers of 

Lookouts depending on the type of ship 

and the training activity that was 

occurring (noting that the data was 


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collected prior to the Navy’s change in 

its SOPs to require the use of three 

Lookouts on Navy cruisers and 

destroyers.) Marine mammal observer 

teams consisted of two dedicated 

observers. Results of this study indicate 

that Navy Lookout Teams, which 

include Lookouts and other crew 

members, have approximately an 80 

percent chance of failing to detect a pod 

of large baleen whales (rorquals) before 

they come closer than a mitigation range 

of 200 yd (182.9 m), compared with a 

49 percent chance for trained marine 

mammal observers. The probability of a 

pod remaining undetected by Lookouts 

was greater for larger mitigation zones 

(i.e., 85 percent at 500 yd (457.2 m); 91 

percent at 1,000 yd (914.4 m)). These 

values require some level of 

interpretation with regard to the 

numerical results. For instance, the 

study’s statistical model assumed that 

Navy ships moved in a straight line at 

a set speed for the duration of the field 

trials, and that animals could not move 

in a direction perpendicular to a ship. 

Violation of this model assumption 

would underestimate Lookout 

effectiveness for some data points. The 

values for both Navy Lookouts and the 

Marine Mammal Observers include 

animals under the water that would not 

have been available for detection by a 

Lookout. This study suggests that 

detection of marine mammals is less 

certain than previously assumed at 

certain distances. 

Hearing, Vocalization, and Masking 

Branstetter et al. (2021) measured 

underwater, masked hearing thresholds 

for frequencies between 0.5 and 80 

kilohertz (kHz) in two killer whales. 

Critical ratios computed from the 

threshold measurements ranged from 16 

to 32 decibels (dB). For communication 

signals in the 1.5–15 kHz range, killer 

whales would require the signal to be 

up to 26 dB above background Gaussian 

noise to be detected. The authors noted 

that ambient background noise in the 

marine environment is not Gaussian, the 

tones used in this study do not contain 

as much frequency information as 

biologically relevant signals, and the 

temporal and spectral characteristics of 

actual signals and noise may result in 

some degree of release from masking. 

These results are consistent with critical 

ratio measurements from other 

odontocete species, despite differences 

in hearing ability and head size. 

Fournet et al. (2021) measured call 

amplitudes from male bearded seals in 

the Beaufort Sea under different 

ambient noise conditions. The results 

showed that estimated source levels of 

seal calls increased with ambient noise 

up to approximately 100–105 dB rootmean-squared (rms), above which no 

further Lombard effect was observed. 

This suggests that masking of bearded 

seal mating calls may occur, resulting in 

reduced communication range, which 

could reduce the ability of bearded seals 

to detect one another, mate, and 

reproduce. 

Mercado (2021) aimed to characterize 

how units within humpback whale 

songs were systematically varied using 

a large dataset of recordings from off the 

coast of Kona, Hawaii. The data showed 

that narrowband, reverberant units 

repeated at regular time intervals and 

dominated most song sessions, while 

broadband units were less predictable 

and occupied frequency bands that did 

not overlap with the narrowband units. 

The persistent production of 

narrowband units at regular time 

intervals resulted in consistent 

reverberation, which could either 

function to increase the range at which 

the song can be detected, or listen for 

fluctuations in echoes to indicate the 

presence of whale-sized targets. 

Rey-Baquero et al. (2021) collected 

theodolite and passive acoustic data on 

humpback whales in a pristine 

environment along the Colombian 

Pacific for 2 months. When acoustic 

data (n=34 files) were analyzed for unit 

duration and inter-unit interval before 

and after boats passed, song unit lengths 

were shorter and more variable when 

boats were present. The second aim of 

this study was to model the whales’ 

communication space during ambient 

noise or one to two boats traveling 

slowly. The most common peak 

frequency of this stock’s song (350 Hz) 

was used in the model, and, along with 

a whale’s location along the coast, 

informed calculations of transmission 

loss. However, the source level of 

‘‘typical whale-watching boats’’ (145 dB 

re 1 uPa (decibels referenced to 1 

micropascal) at 1 m; (Erbe et al. 2012)) 

and humpback whales (153 dB re 1 uPa 

at 1 m; (Au et al. 2006)) were taken from 

previous studies. Authors found that the 

infrequent addition of ecotour boat 

noise could temporarily reduce the 

‘‘very audible area’’ (>10 dB SNR) in 

their song’s commonly used peak 

frequency (350 Hz) by 63 percent. 

Ruscher et al. (2021) measured aerial 

behavioral hearing thresholds in a 

Hawaiian monk seal (Neomonachus 

schauinslandi). The results showed a 

hearing range between 0.1 and 33 kHz 

with relatively poor sensitivity 

compared to Phocinae seals. The most 

sensitive thresholds were 40 dB re 20 

mPa measured at 800 Hz and 3.2 kHz. 

The resulting audiogram was most 

similar to the northern elephant seal, 

which is the only other species of 

Monachinae seal with audiogram data 

(Reichmuth et al. 2013). This study 

suggested that hearing sensitivity of 

Monachinae seals is substantially 

reduced compared to other species 

within their functional hearing group 

(phocid carnivores in air; PCA); 

therefore, the use of the PCA weighting 

function to predict auditory impacts is 

likely conservative for Hawaiian monk 

seals. 

Sills et al. (2021) measured 

underwater auditory detection 

thresholds in a male Hawaiian monk 

seal, and the range of most sensitive 

hearing was between 0.2 and 33 kHz. 

Peak hearing sensitivity of 73 dB re 1 

mPa was observed at 1.6 kHz. The 

audiogram for this individual was 

similar but narrower and elevated 

compared to the hearing group (phocid 

carnivores in water; PCW) composite 

audiogram used to assess impacts to this 

species. Underwater vocalizations were 

also measured, and 6 call types were 

identified, which had peak energy 

between 55 and 400 Hz. The number of 

calls produced per minute fluctuated 

seasonally and peaked in the breeding 

season with the highest call rates 

recorded in December. 

Sweeney et al. (2022) examined the 

difference between noise impact 

analyses using unweighted broadband 

sound pressure levels (SPLs) and 

analyses using auditory weighting 

functions. The recordings used to 

conduct parallel analyses in three 

marine mammal species groups were 

from a shipping route in Canada. Since 

shipping noise was predominantly in 

the low-frequency spectrum, bowhead 

whales perceived similar weighted and 

unweighted SPLs while narwhals and 

ringed seals experienced lower SPLs 

when auditory weighting functions were 

used. The data provide a real-world 

example to support the use of weighting 

functions based on hearing sensitivity 

when estimating audibility and 

potential impact of vessel noise on 

marine mammals. 

A study by von Benda-Beckmann et 

al. (2021) modeled the effect of pulsed 

and continuous 1–2 kHz active sonar on 

sperm whale echolocation clicks and 

found that the presence of upper 

harmonics in the sonar signal increased 

masking of clicks produced in the 

search phase of foraging compared to 

buzz clicks produced during prey 

capture. Different levels of sonar caused 

intermittent to continuous masking (120 

to 160 dB re 1 mPa2, respectively), but 

varied based on click level, whale 

orientation, and prey target strength. 

CAS resulted in a greater percentage of 


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time that echolocation clicks were 

masked compared to PAS. 

Kastelein et al. (2021c) compared the 

ability of harbor porpoises to detect 

signals in constant-amplitude noise 

with amplitude-modulated noise. 

Underwater, behavioral hearing 

thresholds were measured from harbor 

porpoises at 4 kHz under three 

conditions: ambient noise (control), 

sinusoidally amplitude modulated 

(SAM) masking noise, and Gaussian 

(constant amplitude) masking noise. 

Both masker types were centered at 4 

kHz with a one-third octave bandwidth 

and were tested at various SPLs. The 

SAM noise was also tested at 

modulation rates from 1–90 hertz (Hz). 

The 4 kHz hearing test signals were 0.5, 

1, and 2 seconds in duration. The 

results showed that, compared to 

Gaussian noise, up to 14.5 dB of 

masking release (from ‘‘dip listening’’) 

was observed in lower-modulation rate 

(1–5 Hz) SAM noise. The effect of 

masking on communication space is 

often modeled using constant-amplitude 

noise, whereas most Navy sources 

contain gaps, more like amplitudemodulated noise. This study suggests 

that the signal duration, masker level, 

and masker modulation rate and depth 

should be considered when modeling 

the effect of noise on signal detection. 

Isojunno et al. (2021) used data from 

15 tagged sperm whales (Isojunno et al. 

2020) to evaluate odontocete 

echolocation behavior as a function of 

received sonar exposures. Statistical 

analysis revealed small reductions in 

the number of buzzes and movement 

during sonar, but the most apparent 

change in echolocation behavior was a 

Lombard effect observed during higher 

sea states (increased surface noise). No 

behavioral changes in orientation 

relative to the sonar source were 

observed that would suggest an antimasking strategy for spatial release from 

masking. Theoretical modeling of 

masking potential in terms of detection 

range revealed that search phase clicks 

would likely be masked during both 

PAS and CAS, but the buzz clicks 

would not. For regular search phase 

clicks to be continuously masked, SELs 

would have to be equal to or greater 

than 160 and 173 dB re 1 mPa2s (dB 

referenced to 1 micropascal squared 

seconds) for PAS and CAS, respectively. 

Overall, the data showed more evidence 

for masking by increases in ambient 

noise (surface noise from higher sea 

states), than for sonar. This result could 

be due, in part, to the 1–2 kHz 

narrowband sonar masker, which is not 

comparable to broadband maskers such 

as ambient noise or shipping noise. 

Matthews and Parks (2021) reviewed 

the existing literature on North Atlantic 

right whale acoustic behavior and 

summarize information on acoustic 

behavior of the Southern right whale, 

North Pacific right whale, and bowhead 

whale. The authors reviewed primary 

literature on whale vocalizations, 

anatomical modeling, and behavioral 

responses to playbacks to conclude that 

the North Atlantic right whale might 

have a hearing range of 20 Hz to 22 kHz. 

However, vocalization data cannot be 

used to directly estimate audible range 

since there are many examples of 

mammals (including marine mammals) 

that vocalize with energy below the 

frequency of best hearing, and calls can 

also contain high-frequency harmonics 

that are above the upper limit of 

hearing. The anatomical model 

developed by Ketten (1994) was used by 

Parks et al. (2007) to estimate a 

functional hearing range of 15 Hz to 18 

kHz for this species. 

Jacobson et al. (2022) modeled the 

probability of Blainville’s beaked whale 

group vocal periods (GVPs) on the 

Pacific Missile Range Facility during 

periods of no naval activity, naval 

activity without hull-mounted MFAS, 

and naval activity with hull-mounted 

MFAS. Data were collected from 

bottom-mounted hydrophones on the 

range before, during, and after six 

Submarine Commanders Course (SCC) 

exercises. At an MFAS received level of 

150 dB re 1 mPa rms (root mean square), 

the probability of GVP detection 

decreased by 77 percent (95 percent CI: 

67 percent–84 percent) compared to 

periods when general training activity 

was ongoing and by 87 percent (95 

percent CI: 81 percent–91 percent) 

compared to baseline conditions. This 

study found a greater reduction in 

p(GVP) with MFAS than observed in a 

prior study of Blainville’s beaked 

whales at the Atlantic Undersea Test 

and Evaluation Center (AUTEC) (Moretti 

et al. 2014). The authors suggest that 

this may be due to the baseline period 

in the AUTEC study including naval 

activity without MFAS, potentially 

lowering the baseline p(GVP), or due to 

differences in the residency of the 

populations at each range. 

Branstetter and Sills (2022) reviewed 

direct laboratory (i.e., psychoacoustic) 

studies of marine mammal hearing in 

noise. Psychoacoustic studies of 

auditory masking in marine mammals 

were described in detail and categorized 

by the type of signal and masker (e.g., 

tone in white noise), and specific 

conditions under which masking is 

reduced (i.e., release from masking). 

Specifically, comodulation masking 

release, or the reduction in masking due 

to amplitude or frequency modulation 

differences between the signal and 

noise, and spatial release from masking, 

or the reduction in masking due to 

spatial separation between signal and 

noise and the directional hearing ability 

of the listener, are discussed. Finally, 

energetic masking, or the ability of the 

listener to detect a signal was compared 

to informational masking, or the ability 

of the listener to comprehend the signal 

was reviewed. The authors point out 

that while the body of scientific 

evidence thus far shows that processes 

of the ear result in energetic masking, 

more research on informational masking 

is needed to develop realistic 

communication space models. This is 

because current communication space 

models are based on 50 percent signal 

detection rather than some threshold of 

successful signal recognition or 

interpretation by the listener. 

Hearing Loss (TTS and PTS) 

Houser (2021) reviews existing 

literature on the relationship between 

auditory threshold shift and tissue 

destruction in mammals. According to 

small terrestrial mammal literature, 

TTSs of approximately 30–50 dB 

measured 24 hours after sound exposure 

induced progressive tissue damage 

despite the return of normal hearing 

thresholds. Although large TTSs allow 

for full recovery of hearing, pathological 

tissue destruction may occur; however, 

smaller-magnitude TTSs are unlikely to 

result in tissue damage. The author 

concludes that the current criteria of 40 

dB of TTS measured within minutes of 

the noise exposure as the onset of injury 

is likely to encompass recoverable 

auditory threshold shift without tissue 

damage. This publication supports the 

use of current definitions of auditory 

injury in marine mammals. 

Kastelein et al. (2022a) measured 

underwater behavioral hearing 

thresholds in two California sea lions at 

0.6, 0.85, and 1.2 kHz before and after 

exposure to a one-sixth-octave noise 

band centered at 0.6 kHz for 60-minutes. 

Hearing tests were also conducted at 1, 

1.4, and 2 kHz after exposure to a onesixth-octave noise band centered at 1 

kHz for 60-minutes. For the 0.6 kHz 

exposure, the maximum TTS was 7.5 dB 

(6.7 dB mean) for a 210 dB cumulative 

SEL (SELcum) exposure at the hearing 

test frequency one-half octave above the 

center frequency of the fatiguing 

stimulus (0.85 kHz), which recovered 

after approximately 12 minutes. For the 

1 kHz exposure, the maximum TTS was 

10.6 dB (9.6 dB mean) after a 195 dB 

SELcum exposure at the hearing test 

frequency one-half octave above the 

center frequency of the fatiguing 


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stimulus (1.4 kHz). Mean threshold shift 

(TS) greater than 6 dB (mean = 8.0 dB, 

min = 7.2 dB, max = 8.5 dB) was also 

observed after exposure to the 1 kHz 

fatiguing stimulus at 195 dB SELcum for 

the 1 kHz hearing test frequency. For 

this exposure frequency, hearing 

recovered within 24 minutes. The 

results of this study show individuals 

exhibiting onset of TTS in water at 

lower received levels than the otariid 

thresholds in ‘‘Criteria and Thresholds 

for U.S. Navy Acoustic and Explosive 

Effects Analysis (Phase III)’’ (Navy, 

2017). 

Kastelein et al. (2022b) measured 

underwater behavioral hearing 

thresholds in two California sea lions at 

8, 11.3, and 16kHz before and after 

exposure to a one-sixth-octave noise 

band centered at 8 kHz for 60-minutes. 

Hearing tests were also conducted at 32 

kHz after exposure to a one-sixth-octave 

noise band centered at 16 kHz for 60- 

minutes. For the 8kHz exposure, the 

maximum TTS was 20.2 dB (18 dB 

mean) for a 190 dB SELcum exposure at 

the hearing test frequency one-half 

octave above the center frequency of the 

fatiguing stimulus (11.3 kHz), which 

recovered after approximately 12 

minutes. For the 16 kHz exposure, the 

maximum TTS was 19.7 dB (16.3 dB 

mean) after a 207 dB SELcum exposure at 

the hearing test frequency one-half 

octave above the center frequency of the 

fatiguing stimulus (22.4 kHz). For these 

exposure frequencies and scenarios, 

hearing recovered within 72 minutes or 

less. The results of this study show TTS 

onset in-water occurred at lower 

received levels than what the current 

otariid criteria in ‘‘Criteria and 

Thresholds for U.S. Navy Acoustic and 

Explosive Effects Analysis (Phase III’’) 

(Navy, 2017) suggest. 

Kastelein et al. (2021a) measured 

underwater behavioral hearing 

thresholds at 0.5, 0.71, and 1 kHz in one 

harbor porpoise before and after 

exposure to one-sixth-octave band noise 

centered at 0.5 kHz. Maximum TTS was 

8.9 dB (mean = 7.6 dB) at the 0.5 kHz 

hearing test frequency after a 205-dB 

SELcum exposure. For the 0.71 and 1 kHz 

hearing test frequencies, no mean TTS 

> 6 dB was observed. However, at 0.71 

kHz, maximum TTS was 6.5 dB (mean 

= 5.8 dB) was observed after a 205-dB 

SELcum exposure. At 1 kHz, a maximum 

of 6.3 dB of TTS (mean = 5.7 dB) 

occurred after 206-dB SELcum exposures. 

All shifts < 5 dB recovered within 12 

minutes and shifts > 6 dB recovered 

within 60 minutes. These results are 

consistent with the criteria and 

thresholds described in ‘‘Criteria and 

Thresholds for U.S. Navy Acoustic and 

Explosive Effects Analysis (Phase III)’’ 

(Navy, 2017). 

Kastelein et al. (2021b) measured 

behavioral, underwater hearing 

thresholds at 2, 2.8, and 4.2 kHz in two 

sea lions before and after exposure to 

band-limited noise centered at 2 kHz. 

Sea lion hearing was also tested at 4.2, 

5.6, 8 kHz before and after exposure to 

noise centered at 4 kHz. Maximum TTS 

was 24.1 dB (22.4 dB mean) at the 5.6 

kHz test frequency after a 205-dB SELcum

exposure centered at 4 kHz. Threshold 

shifts greater than or equal to 6 dB 

occurred at 187, 181, and 187 dB SELcum

for 4.2, 5.6, and 8 kHz test frequencies 

respectively. After exposure to the 2- 

kHz noise, maximum TTS of 11.1 dB 

(10.5 dB mean) occurred for 203 dB 

SELcum at the 2 kHz test frequency. 

Threshold shifts greater than or equal to 

6 dB occurred at SELcum of 192, 186, and 

198 dB for test frequencies 2, 2.8, and 

4.2 kHz respectively. These data suggest 

that one-half octave above the exposure 

frequency is the most sensitive to noise 

exposure. TTS between 6 and 10 dB 

recovered within 60 minutes, 10–15 dB 

of TTS recovered within 120 min, and 

TTS up to 24.1 dB recovered after 240 

minutes. The results of this study show 

individuals exhibiting onset of TTS inwater at lower received levels than the 

current otariid criteria (‘‘Criteria and 

Thresholds for U.S. Navy Acoustic and 

Explosive Effects Analysis (Phase III)’’ 

(Navy, 2017)). 

Kastelein et al. (2020a) measured 

underwater, behavioral hearing 

thresholds in one harbor porpoise before 

and after exposure to playbacks of onesixth-octave band noise centered at 1.5 

kHz and a 6.5 kHz continuous wave. 

Following exposure to the 1.5 kHz noise 

band at 201 dB SELcum, a maximum of 

a 7.8 dB, 9.8 dB, and 7 dB TTS was 

observed for 1.5, 2.1, and 3 kHz hearing 

frequencies respectively. After exposure 

to the 6.5 kHz continuous wave at 184 

dB SELcum, a maximum of a 7.5, 16.7, 

and 11.8 dB TTS was observed for 6.5, 

9.2, and 13 kHz hearing frequencies 

respectively. For the 6.5 kHz exposure, 

a mean TTS > 6 dB was observed for the 

178 and 180 dB SELcum when the 

hearing test frequency was 9.2 kHz, and 

for the 180 dB SELcum when the hearing 

test frequency was 13 kHz. The results 

of this study show that the animal 

incurred onset of TTS at higher received 

levels than what the current HF 

cetacean criteria in ‘‘Criteria and 

Thresholds for U.S. Navy Acoustic and 

Explosive Effects Analysis (Phase III)’’ 

(Navy, 2017) indicate for both 1.5 and 

6.5 kHz. 

Kastelein et al. (2020b) measured 

underwater, behavioral hearing 

thresholds in two harbor seals before 

and after exposure to playbacks of onesixth-octave band noise centered at 0.5, 

1, and 2 kHz. Hearing tests were 

conducted at the center frequency, onehalf octave above, and 1 octave above 

center frequency. No TTS > 6 dB was 

observed for any hearing frequency after 

204, 210, or 211 dB SELcum exposures to 

the 0.5 kHz noise band. For the 1 kHz 

exposure frequency, max TTS of 7.4 dB 

(6.1 mean) was observed after a 207 dB 

SELcum exposure at a hearing frequency 

of 1.4 kHz. For this exposure frequency, 

no other test condition produced TTS > 

6 dB; although, a 5.9 dB shift (at 1.4 

kHz) occurred at 206 dB SELcum. For the 

2 kHz noise band, after a 201 dB SELcum

exposure, max TTS of 12 dB was 

measured one octave above the center 

frequency (4 kHz). For this exposure 

frequency, TTS > 6 dB was observed at 

SELcum > 201, 198, and 192 dB for 

hearing frequencies 2, 2.8, and 4 kHz 

respectively. All shifts recovered within 

1 hour. These results of this study show 

that the animal incurred lower TTS (i.e., 

smaller threshold shifts) at higher 

received levels than what the current 

phocid pinniped criteria in ‘‘Criteria 

and Thresholds for U.S. Navy Acoustic 

and Explosive Effects Analysis (Phase 

III)’’ (Navy, 2017) indicate. 

Kastelein et al. (2020c) measured 

underwater, behavioral hearing 

thresholds in one harbor porpoise before 

and after exposure to playbacks of onesixth-octave band noise centered at 88.4 

kHz. Maximum TTS of 13.6 dB was 

observed at 197 dB SELcum for the 100 

kHz hearing test frequency. No TTS > 6 

dB was observed for any SELcum at the 

88.4 kHz test frequency. For 125 kHz, 

shifts > 6 dB were observed for 191, 194, 

and 197 dB SELcum exposures, with a 

mean TTS of 5.4, 6.1, and 5.9 dB, 

respectively. The results of this study 

show that the animal incurred TTS at 

higher received levels than what the 

current HF cetacean criteria in ‘‘Criteria 

and Thresholds for U.S. Navy Acoustic 

and Explosive Effects Analysis (Phase 

III)’’ (Navy, 2017) suggest. 

Kastelein et al. (2020d) measured 

underwater, behavioral hearing 

thresholds in one harbor porpoise before 

and after exposure to airgun impulses 

(‘‘shots’’). Exposure conditions varied 

with regard to number of airguns, 

number of shots, light cues, and 

position of the dolphin relative to the 

airguns. Hearing test frequencies were 2, 

4, and 8 kHz, and no TTS > 6 dB was 

observed. The results of this study show 

that the animal would incur TTS onset 

at higher received levels than what the 

current HF cetacean criteria in ‘‘Criteria 

and Thresholds for U.S. Navy Acoustic 

and Explosive Effects Analysis (Phase 

III)’’ (Navy, 2017) suggest. 


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Kastelein et al. (2020e) measured 

underwater, behavioral hearing 

thresholds in two harbor seals before 

and after exposure to playbacks of onesixth-octave band noise centered at 40 

kHz. For the 50 kHz hearing test 

frequency, a maximum TTS of 30.7 dB 

was observed 12–16 minutes after the 

189 dB SELcum, and a mean TTS > 6 dB 

was observed for all SELcum 177 dB and 

above. The 30-dB shift recovered after 3 

days. No TTS > 6 dB was observed for 

any SELcum at the 63 kHz test frequency 

for either seal. At 40 kHz, mean TTS of 

9.2 dB was observed after a 189-dB SEL. 

The results of this study show that the 

animal incurred TTS at lower received 

levels than what the current phocid 

criteria in ‘‘Criteria and Thresholds for 

U.S. Navy Acoustic and Explosive 

Effects Analysis (Phase III)’’ (Navy, 

2017) suggest. 

Sills et al. (2020) exposed one 

bearded seal to multiple impulsive 

underwater noise exposures (seismic air 

gun ‘‘shots’’). Hearing tests were 

conducted at 100 Hz and 400 Hz after 

exposures to 2, 4, and 10 shots. After a 

4-shot (191 dB SELcum) exposure, max 

TTS of 9.4 dB was observed, but no 

other TTS > 6 dB was demonstrated, 

despite four 10-shot (194–195 dB 

SELcum) exposures. It is possible that 

TTS recovered during the 

measurements, as quantified by a mean 

‘‘first miss’’ of 7.5 dB for the 10-shot 

exposures (mean TTS was 2.2 dB). The 

results of this study show that the 

animal incurred TTS onset at lower 

received levels than what the current 

criteria in ‘‘Criteria and Thresholds for 

U.S. Navy Acoustic and Explosive 

Effects Analysis (Phase III)’’ (Navy, 

2017) suggest. Behavioral responses 

were also scored and averaged across 

three observers. For most exposures, the 

seal exhibited mild/detectable 

responses, and all scores indicated that 

the seal did not move more than half his 

body and consistently participated in 

the study. 

Tougaard et al. (2022) reviewed the 

most recent temporary TTS data from 

phocid seals and harbor porpoises and 

compared empirical data to the 

predictive exposure functions put forth 

by Southall et al. (2019), which were 

based on data collected prior to 2015. 

The authors concluded that more recent 

data supports the thresholds used for 

harbor porpoises (categorized as ‘very 

high frequency’, or VHF cetaceans), 

which over-estimated the hearing 

impact for sounds above 20 kHz in 

frequency. Similarly, the new data for 

phocid seals show TTS onset thresholds 

that are well-above the predicted levels 

for sounds below 5 kHz in frequency. 

However, phocid seals might be more 

sensitive to higher frequency sound 

exposures than predicted, as the TTS 

onset data for frequencies higher than 

20 kHz was below the predicted levels. 

von Benda-Beckmann et al. (2022) 

assessed whether correcting for kurtosis, 

a measure of sound impulsiveness, 

improved the ability to predict TTS in 

a marine mammal. Two different 

kurtosis correction factors were tested 

by applying them to frequency-weighted 

sound exposure levels (SELcum) and 

fitting (linear least squares) previously 

collected harbor porpoise TTS data to 

create dose-response functions, then 

comparing the resulting R2 values to 

that of the standard function used to fit 

TTS growth data. TTS data from both 

continuous and intermittent sound 

exposures were used. For intermittent 

and continuous 1–2 kHz exposures 

combined, kurtosis-corrected fits were 

poorer (R2 = 0.47, 0.68) than SELcumbased fits (R2 = 0.73). For intermittent 

exposures of different types, one of the 

kurtosis-corrections resulted in a better 

fit (R2 = 0.84) than SELcum (R2 = 0.64), 

but only when a model fitting parameter 

denoting the relationship between 

SELcum and risk of permanent hearing 

loss was specifically derived from 

harbor porpoise TTS growth data. The 

conclusions from this study were that 

the kurtosis-corrected SELs did not 

explain differences in TTS between 

intermittent and continuous sound 

exposures, likely because silent 

intervals provided an opportunity for 

hearing recovery that could not be 

accounted for by these models. Kurtosis 

might still be useful for evaluating 

sound exposure criteria for different 

types of sounds having various degrees 

of impulsiveness. 

Behavioral Reactions 

In a study by Benti et al. (2021), 

vocalizations from Northeast Atlantic 

herring-feeding killer whales and 

Northeast Pacific mammal-eating killer 

whales were played back to humpback 

whales in Norwegian waters while their 

behavior was monitored through 

animal-borne tags and visual 

observations. In five of six cases the 

humpback whales approached the fisheating killer whales, suggesting some 

attraction. The response to the mammaleating killer whales varied with the 

behavioral context of the humpback 

whales. The results suggested that the 

calls of the fish-eating killer whales may 

have acted like a dinner-bell and 

initiated approach and foraging 

behavior in the humpback whales, 

while the unfamiliar sounds of the 

mammal-eating killer whales may have 

been perceived as a threat in offshore 

waters, but led to mixed behavior 

during inshore herring foraging by 

humpback whales. These results 

indicated that the humpback whales 

were able to discriminate between the 

different call types and respond with 

different behavioral strategies. 

Boisseau et al. (2021) exposed 

foraging minke whales in Icelandic 

waters to an acoustic deterrent device 

that emitted 15 kHz pure tones with a 

source level of 198 dB rms. Pulse length 

and the number of pulses in a block 

were randomized but average pulse 

length was 752 millisecond (ms) with a 

10 percent duty cycle. The source was 

deployed from a Zodiac boat 500 m 

away from an animal for the first two 

exposures, and 1000 m away in the 

remaining 8 exposures (max received 

level of 150 dB RMS at a minimum 

distance of 338 m). Video-range tracking 

was used to track animals before, 

during, and after the exposures and dive 

duration (sec), swim speed (km/h), 

reoxygenation rate (blows/min), and 

path predictability were also examined. 

During the exposure, animal speed and 

dive duration increased, measures of 

path predictability increased indicating 

straighter paths, and reoxygenation rate 

decreased. Path predictability had a 

strong relationship with received level 

whereas speed and dive duration did 

not, which suggested those two metrics 

were more influenced by the presence of 

the exposure signal than the received 

sound level. 

Cure ́ et al. (2021) conducted 

controlled exposure experiments using 

both PAS (5 percent duty cycle) and 

CAS (95 percent duty cycle) to measure 

and score tagged sperm whale 

behavioral responses. No sonar control 

exposures resulted in significantly fewer 

and less severe behavioral responses 

than sonar exposures. No significant 

differences were observed between 

sonar types, but the presence of killer 

whales or pilot whales did significantly 

increase the number of responses. The 

probability of observing low and 

medium severity responses increased 

with cumulative sound exposure level 

(SEL, dB re 1 mPa2 s), reaching a 

probability of 0.5 at approximately 173 

dB SEL for low severity responses. 

Medium severity responses reached a 

probability of approximately 0.35 at 

cumulative SELs between 179 and 189 

dB. This study suggested that both PAS 

and CAS exposure resulted in a greater 

number of behavioral changes in sperm 

whales as compared to the vessel 

(control) alone, and the types of 

behavioral responses might differ across 

sonar types. 

Czapanskiy et al. (2021) modeled 

energetic costs associated with 

behavioral response to MFAS using 


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datasets from 11 cetaceans’ feeding 

rates, prey characteristics, avoidance 

behavior, and metabolic rates. Authors 

found that the short-term energetic cost 

was influenced more by lost foraging 

opportunities than increased locomotor 

effort during avoidance. Additionally, 

the model found that mysticetes 

incurred more energetic cost than 

odontocetes, even during mild 

behavioral responses to sonar. 

Durbach et al. (2021) analyzed 

acoustic tracks from minke whales 

detected on the Pacific Missile Range 

Facility (PMRF) in Hawaii in 3 years 

before, during, and after major Navy 

training exercises. These tracks were fit 

using a continuous-time correlated 

random walk at 5-minute interpolated 

locations. During sonar periods, fast 

movement became more northerly and 

more directed (less turning), with less 

movement south and east in the 

direction of the training activity, and 

this more northerly movement 

continued after sonar cessation. 

Specifically, whales to the north of the 

training activity were more likely to 

head north, while whales that were west 

of the activity were more likely to head 

west. Headings did not appear to change 

for slow, undirected movement during 

sonar. In addition, fast movement was 

more likely to occur during sonar than 

during any other period (70 percent 

during vs 35–41 percent in the other 

periods). Finally, whales were more 

likely to stop calling when in the fast 

state although not necessarily more 

during sonar than in other periods; in 

contrast, slow moving whales were 

more likely to stop calling during sonar 

than other periods. These results 

demonstrated that minke whales moved 

faster and movements were more 

directed during periods of active sonar. 

Minke whales also avoided the locations 

of the ships producing the sonar and 

were more likely to cease calling during 

sonar. 

Fernandez-Betelu et al. (2021) used 

passive acoustic data recorded over a 

10-year time period to assess the effects 

of impulsive noise produced during 

offshore activities on coastal bottlenose 

dolphin occurrence. Offshore activities 

included seismic surveys and pile 

driving from wind farm construction. 

Echolocation detections of dolphins 

were compared across years with and 

without offshore activity and also across 

days with and without impulsive noise. 

The effect of distance from the noiseproducing activities on dolphin 

detections was also investigated by 

placing recorders (CPODs) at locations 

expected to be the most (impact areas) 

and least (reference areas) impacted by 

noise. No consistent relationship was 

found between annual dolphin 

occurrence and impulsive noise, but 

significantly more detections were 

observed on days with impulsive noise. 

The results showed that dolphins were 

not displaced by impulsive noise levels 

up to 141 dB re 1 mPa and as close as 

20 km (10.8 nmi) from the impact area. 

These results suggest that the increase 

in dolphin detections during far-field 

noise was likely due to an increase in 

the number and/or amplitude of 

echolocation vocalizations. 

Hastie et al. (2021) studied how the 

number and severity of avoidance 

events may be an outcome of marine 

mammal cognition and risk assessment. 

Five captive grey seals were given the 

option to forage in a high- or lowdensity prey patch while continuously 

exposed to silence, pile driving, or tidal 

turbine playbacks (source levels = 148 

dB re 1 mPa at 1 m) for 1 hour. One prey 

patch was closer to the speaker, so had 

a higher received level in experimental 

exposures. Overall, seals avoided both 

anthropogenic noise playback 

conditions with higher received levels 

when the prey density was limited but 

would forage successfully and for as 

long as control conditions when the 

prey density was higher, demonstrating 

a classic cognitive approach utilized 

with predation risk and profit balancing. 

In a study by Holt et al. (2021a), 

DTAGs (miniature sound and movement 

recording tags) were attached with 

suction cups to Southern Resident Killer 

Whales in the Salish Sea to investigate 

the relationship between probability of 

prey capture and vessel and sound 

variables. The predicted probability of 

prey capture was lower when vessels 

increased their speed. Received noise 

level did not significantly affect the 

probability of prey capture. The rate of 

descent during dives was slower when 

echosounders were on. The observed 

effects of echosounders suggest that 

whales prolonged their foraging efforts 

to successfully hunt, which could be 

caused by acoustic masking or increased 

attention to vessels. The rate of descent 

increased with increasing broadband 

noise levels and decreasing vessel 

distance. Decrease prey abundance also 

decreased the probability of predicted 

prey capture. 

Holt et al. (2021b) attached DTAGs to 

23 Southern Resident Killer Whales in 

the San Juan Islands over 3 field seasons 

in order to investigate the effects of 

vessel distance on underwater foraging 

behavior. When vessels were less than 

366 m away, whales (n=13) decreased 

the number of dives associated with 

prey capture and the amount of time 

spent in these dives. Additionally, 

female killer whales were more likely to 

stop foraging, socializing, and preysharing and instead start traveling when 

vessels approached at this distance. At 

the same distance from vessels, male 

orcas were more likely to transition 

from close prey capture to socializing 

and prey-sharing, but would not stop 

general foraging behavior, such as 

searching for prey at deeper depths. 

Female orcas may therefore be at greater 

risk than males during close vessel 

interactions. 

Kates Varghese et al. (2021) analyzed 

the effect of two separate surveys using 

a 12 kHz multibeam echosounder (i.e., 

downward directed, unlike ASW sonar) 

over the Southern California 

Antisubmarine Warfare Range (SOAR) 

hydrophone array on Cuvier’s beaked 

whale foraging. The authors conducted 

a spatial analysis, building off a 

temporal analysis of a previously 

presented dataset (Varghese et al. 2020). 

There were differences in spatial use of 

the SOAR for foraging between the 2 

survey years. While no change in overall 

foraging effort was detected before, 

during, and after the surveys each year, 

some localized spatial shifts in foraging 

hot spots were detected during and after 

the survey in the second year. Because 

of the known heterogeneity of prey 

patches on SOAR, lack of evidence of 

avoidance of the sound source, and no 

observed change in overall foraging 

effort, the authors suggest that the 

observed spatial shifts were most likely 

due to prey dynamics. 

Ko ̈nigson et al. (2021) tested the 

efficacy of Banana Pingers (300 ms, 59– 

130 kHz frequency modulated, 133–139 

dB rms re 1 mPa at 1 m source level) as 

a deterrent for harbor porpoise in 

Sweden. As described previously, these 

pingers were designed to avoid potential 

pinniped responses. Authors used 

recorded echolocation clicks with C– 

PODs to measure the presence or 

absence of porpoise in the area. 

Porpoise were less likely to be detected 

at 0 m and within 100 m of an active 

pinger, but a pinger at 400 m appeared 

to have no effect. 

In a study by Laborie et al. (2021), 

unmanned aerial vehicles (UAVs) were 

flown at three altitudes (25, 20, and 15 

m) over Weddell seals, including adult 

males and females and females with 

pups. There was generally little 

response; 88 percent of the time the 

animals showed mild vigilance or no 

responses, and mothers rarely ended 

nursing. Agitation or escape responses 

only occurred in 12 percent of 

observations. The strongest response 

was in females with pups when wind 

speeds were lowest and therefore 

ambient noise levels were at their 

lowest. The probability of response 


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increased with lower altitude flights, so 

at altitudes over 25 m a low level of 

impact to Weddell seal behavior would 

be expected. 

Manzano-Roth et al. (2022) found that 

cross seamount beaked whales reduced 

clusters of foraging pulses (Group Vocal 

Periods) during Submarine Command 

Course events and remained low for a 

minimum of 3 days after the MFA sonar 

activity. 

An analysis subsequent to Varghese et 

al. (2020) suggested that the observed 

spatial shifts of Cuvier’s beaked whales 

during multibeam echosounder activity 

on the Southern California 

Antisubmarine Warfare Range were 

most likely due to prey dynamics (Kates 

Varghese et al. 2021). 

Ramesh et al. (2021) explored 

environmental drivers and the impact of 

shipping noise on fin whale 

vocalizations in Ireland. Approximately 

3 months of passive acoustic fin whale 

call data from spring 2016 used in the 

habitat model found that fin whale calls 

increased at night, along with signs of 

higher prey availability. Fin whale calls 

were also less likely to be detected for 

every 1 dB re 1 mPa/minute increase in 

shipping noise levels (rms). However, 

these results should be used cautiously 

since the model was more likely to 

predict the absence of fin whale 

detections, rather than their presence. 

Santos-Carvallo et al. (2021) 

monitored fin whale behavior before, 

during, and after the presence of whale 

watching vessels in Caleta Chan ̃ aral de 

Aceituno to determine if the whale 

watching activity was having any 

adverse impacts on the fin whales. 

Whale watching activities were only 

conducted by local artisanal fishers; 39 

boats have permission but less than 20 

conduct the whale watching activity. 

Land-based observations were 

conducted in January and February of 

2015–2018 via binocular scans and focal 

follow tracking using a theodolite. 

Groups of whales were tracked through 

the area with continuous sampling of 

position, behavior, and presence of 

boats for every surfacing until they were 

no longer visible. Behavior was 

classified as traveling or resting, and the 

groups’ swim speed, reorientation, and 

directness index, and these were 

modeled relative to the number of boats 

and whether the time period was before, 

during, or after the boats were present. 

Most observations occurred within the 

presence of at least one boat, but no 

more than three boats at one time. 

Travel swim speeds increased in the 

after period, while reorientation 

increased and directness decreased 

during and after the presence of boats. 

During rest behavior, reorientation 

increased during the presence of boats 

compared to before the boats were 

present, and directness decreased 

during the presence of boats. These 

results indicate that when whale 

watching vessels were present, the fin 

whales changed their direction of 

movement more frequently, with less 

linear movement than occurred before 

the boats arrived; this behavior may 

represent evasion or avoidance of the 

boats. The increase in travel swim 

speeds after the boats left the area may 

be related to the vessel’s rapid speeds 

when leaving, sometimes in front of 

animals, leading to more avoidance 

behavior after the boats departed. 

Arranz et al. (2021) conducted a noise 

exposure experiment which compared 

behavioral reactions of resting shortfinned pilot whale mother-calf pairs 

during controlled approaches by a tour 

boat with two electric (136–140 dB) or 

petrol engines (139–150 dB). Approach 

speed (<4 kn (7.4 km per hour)), 

distance of passes (60 m (65.6 yd)), and 

vessel features other than engine noise 

remained the same between the two 

experimental conditions. Behavioral 

data was collected via unmanned aerial 

vehicle (UAV) and activity budgets were 

calculated from continuous focal 

follows. Mother pilot whales rested less, 

and calves nursed less, in response to 

both types of boat engines compared to 

control conditions (vessel >300 m (328 

yd), stationary in neutral). However, 

they found no significant impact on 

whale behaviors when the boat 

approached with the quieter electric 

engine, while resting behavior 

decreased 29 percent and nursing 

decreased 81 percent when the louder 

petrol engine was installed in the same 

vessel. 

Hiley et al. (2021) exposed groups of 

harbor porpoises to ‘‘startle sounds’’, 

which were 200-ms in duration and 

were band limited (5.5–20.5 kHz) with 

a peak frequency of 10.5 kHz and a 

source level of 176 dB re 1 mPa. There 

were 13 exposure sequences in which 

the startle sound was repeated for 15 

minutes at a 0.6 percent duty cycle, and 

11 control sequences in which vessels 

operated but no startle sounds were 

played. Despite a larger distance 

between porpoise groups and vessels 

during sound exposure trials (152 m) as 

compared to control trials (90 m), 

avoidance responses during exposures 

were significant whereas no avoidance 

was observed for controls. Porpoises 

avoided the area where sound exposures 

took place for approximately 30–60 

minutes, and no long-term exclusion 

effect was observed. 

Pellegrini et al. (2021) examined how 

boat presence impacts a unique 

subspecies of bottlenose dolphin 

(Tursiops truncatus gephyreus, Lahille’s 

bottlenose) that vocalizes while foraging 

cooperatively with local fishermen who 

cast nets onto dolphin-herded fish while 

standing in coastal waters in Brazil. 

Dolphin vocalizations changed in 

response to the number, type, and speed 

of boats within 250 m. When more than 

one boat was present, dolphins 

produced fewer whistles and had a 

lower click rate and a longer whistle 

duration; initial and maximum 

frequency increased as well, especially 

when group size or calf presence 

increased. Whistles were longer 

duration when boat speed increased as 

well. 

Martin et al. (2022) exposed a wild 

Cape fur seal breeding colony in Africa 

to playback recordings of boat noise and 

sea-side car traffic. Focal groups of at 

least six seals were approached by an 

experimenter who crawled within 6 m 

to avoid disturbing the seals. Seals were 

exposed to low (60–64 dB re 20 mPa rms 

SPL, broadcast at 6 m), medium (64–70 

dB, broadcast at 3 m), or high (70–80 

dB, broadcast at 1 m) levels, depending 

on the individual’s distance to the 

speaker. No behavioral differences were 

found between low, medium, and highlevel groups. Video recorded behavioral 

analysis demonstrated that mother-pup 

pairs spent less time nursing (15–31 

percent) and more time awake (13–26 

percent), vigilant (7–31 percent), and 

mobile (2–4 percent) during boat noise 

conditions compared to control 

conditions. Mothers were more vigilant 

(26 percent) than pups (7 percent) to 

medium levels of boat noise. 

Jones-Todd et al. (2021) analyzed the 

movement of seven Blainville’s beaked 

whales tagged at (AUTEC) relative to 

MFAS use during the SCC training 

event. Data from these tags was 

previously reported by Joyce et al. 

(2019). A continuous time correlated 

random walk movement model 

accounted for location accuracy by 

modeling 100 track imputations for each 

tag and arranged samples in equal time 

intervals. The probability of whale 

presence within the boundary of the 

instrumented range (on range), and 

outside the boundary of the 

instrumented range (off range) was 

modeled relative to the time since the 

last MFAS transmission. Results show 

there was a higher probability that 

whales on the range would go off range 

when there were MFAS transmissions, 

and that whales off the range would stay 

off the range when there were MFAS 

transmissions. These results indicate a 

response to MFAS that lasted for 3 days 

since transition rates on-off and off-on 

the range returned to baseline levels 


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after that amount of time. There was 

also variability in transition rates and 

time spent on/off range between 

individuals, which highlights the need 

to analyze a larger sample size of 

whales. 

Durban et al. (2022) tested new 

methods of observing behavioral 

responses of groups of small delphinids 

to sonar, where the use of tags is 

challenging, and the response of the 

group is more salient than that of the 

individual. They tested the use of a 

land-based observation platform 

coupled with a drone and multiple 

acoustic recorders to observe the vocal 

behavior, group cohesion, group size, 

and group behavior before, during, and 

after a simulated sonar exposure. In a 

group of short-beaked common 

dolphins, the authors found the number 

of whistles and sub-groups to increase 

during the exposure period, but the 

directivity of the tracked subgroup did 

not change much. 

Ko ̈nigson et al. (2022) tested the 

efficacy of Banana Pingers (300 ms, 59– 

130 kHz frequency modulated, 133–139 

dBrms re 1 mPa at 1 m source level) as 

a deterrent for harbor porpoise in 

Sweden. As described previously, these 

pingers were designed to avoid potential 

pinniped responses. Authors used 

recorded echolocation clicks with C– 

PODs to measure the presence or 

absence of porpoise in the area. 

Porpoise were less likely to be detected 

at 0 m and within 100 m of an active 

pinger, but a pinger 400 m appeared to 

have no effect. 

Miller et al. (2022) investigated the 

risk disturbance hypothesis that an 

animal’s response decision is a trade-off 

between perceived risk and the cost of 

a missed opportunity (the reward of 

foraging). The authors predicted that 

species that are more vulnerable to 

predation would be more likely to 

respond to both predator sounds and 

anthropogenic stressors. Using data 

collected from 2008 to 2017 during the 

3S project in Norway, changes in 

foraging duration during killer whale 

playbacks and changes in foraging 

duration during mid-frequency sonar 

were positively correlated across the 

four species examined (listed in order of 

increasing sensitivity to foraging 

disruption: sperm whales, long-finned 

pilot whales, humpback whales, and 

northern bottlenose whales). This 

suggests that tolerance of predation risk 

may play a role in sensitivity to sonar 

disturbance. 

Paitach et al. (2022) tested the efficacy 

of Banana Pingers (300 ms, 50–120 kHz 

frequency modulated, 145 dB +/¥ 3 dB 

at 1 m source level) as a deterrent and 

entanglement mitigation for Franciscana 

dolphins in Brazil. These pingers were 

designed to emit sound outside of the 

best hearing range for pinnipeds and 

were therefore less likely to incite a 

‘‘dinner bell’’ effect. Authors used 

recorded echolocation clicks with C– 

PODs to measure the presence or 

absence of dolphins in the area. 

Dolphins were 19 percent and 15 

percent less likely to be detected nearby 

and within 100 m of an active pinger 

respectively, but dolphins 400 m from 

the pinger did not appear to avoid it. 

While a reduction in vocalizations does 

not always equate to a reduction in 

presence, this species has been 

previously seen departing from areas 

with active pingers. Authors did not 

witness any habituation to the pinger 

during the length of the experiment (64 

days), and although they recorded fewer 

dolphins in the area over time, they 

believe this was due to seasonality 

rather than habitat displacement. 

Siegal et al. (2022) used Dtag data 

from 15 northern bottlenose whales 

tagged during 3S efforts off Norway 

(2013–2016) to estimate body density (to 

represent body condition by lipid 

energy stores) using hydrodynamic 

models and obtain foraging and antipredator indicators based on vocal 

behavior and dive metrics. The authors 

compared relative anti-predator/foraging 

indices to body condition and found 

that relative anti-predator to foraging 

indices typically did not depend on 

body condition. This finding is 

inconsistent with the needs/assets 

hypothesis; an individual in poor 

condition would accept more risk (i.e., 

engage in less anti-predator behavior) 

for foraging opportunities, whereas 

healthy animals can afford to be more 

risk averse (i.e., have a relatively higher 

anti-predator to foraging index ratio). 

The authors suggest that this result may 

be due to an insufficient range of body 

conditions in the data set to determine 

a relationship, or a selection of bolder 

individuals in the tagging effort. The 

authors also suggest that animals in 

good condition may take greater 

predation risks because they may 

successfully flee. Three of the 15 whales 

were exposed to sonar (presented in 

prior 3S publications). The authors 

compared foraging and anti-predator 

metrics pre- and post-exposure, showing 

that all three animals increased their 

anti-predator index and reduced their 

foraging index. 

Stanistreet et al. (2022) used passive 

acoustic recordings during a 

multinational navy activity to assess 

marine mammal acoustic presence and 

behavioral response to especially long 

bouts of sonar lasting up to 13 

consecutive hours, occurring repeatedly 

over 8 days (median and maximum SPL 

= 120 dB and 164 dB). Cuvier’s beaked 

whales and sperm whales substantially 

reduced how often they produced clicks 

during sonar, indicating a decrease or 

cessation in foraging behavior. Few 

previous studies have shown sustained 

changes in foraging or displacement of 

sperm whales, but there was an absence 

of sperm whale clicks for 6 consecutive 

days of sonar activity. Sperm whales 

returned to baseline levels of clicks 

within days after the activity, but 

beaked whale detection rates remained 

low even 7 days after the exercise. In 

addition, there were no detections from 

a Mesoplodon beaked whale species 

within the area during and at least 7 

days after the sonar activity. Clicks from 

northern bottlenose whales and 

Sowerby’s beaked whales were also 

detected but were not frequent enough 

at the recording site used to compare 

clicks between baseline and sonar 

conditions. 

Benhemma-Le Gall et al. (2021) 

compared harbor porpoise presence and 

foraging activity between periods of 

baseline and construction at two 

Scottish offshore windfarms with arrays 

of echolocation click detectors (C– 

PODs). Noise levels were measured with 

calibrated noise recorders, and vessel 

presence was tracked with AIS data. 

Authors found an 8–17 percent decline 

in porpoise presence compared to 

baseline, with more porpoises (more 

buzzing) further from vessels, 

construction sites, and related higher 

levels of noise. The probability of 

porpoise occurrence by source vessels 

decreased by 9–23 percent without 

piling activity, and by 40–54 percent 

during pile driving. Porpoises were 

displaced up to 12 km (6.5 nmi) from 

pile driving and 4 km (2.2 nmi) from 

construction vessels. At an average 

vessel distance of 2 km (1.1 nmi), 

porpoise occurrence decreased by up to 

35 percent. Outside piling hours, 

porpoise detection decreased by 17 

percent (0.26), and foraging (buzzes) 

decreased by up to 41.5 percent (0.03) 

with increasing noise levels (159 and 

155 dB re 1 mPa, respectively). During 

piling activities, porpoise occurrence 

began lower (0.16, 102 dB) but 

occurrence still decreased by 9 percent 

(0.07), and foraging (buzzes, beginning 

at 0.76, 104 dB) also decreased by 61.8 

percent (0.15) with increasing noise 

levels (161 and 155 dB re 1 mPa, 

respectively). 

Kastelein et al. (2022c) recorded pile 

driving sounds 100 m from construction 

for an offshore windfarm turbine, and 

six versions of the sound were created 

with varying frequency content using 

low-pass filters at 44.1, 6.3, 3.2, 1.5, 1.0, 


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and 0.5 kHz, at levels of 135 dB re 1 

mPa2s. When authors played these 

impulsive sounds back to a single 

harbor porpoise in a pool, she increased 

swim speed, respiration rate, distance 

from the transducer, and occasionally 

jumped in response to the sounds with 

higher frequencies present (i.e., the 

sounds with a wider bandwidth, 

especially sounds low-pass filtered at 

44.1 and 6.3 kHz). However, the 

porpoise still moved away from the 

three most narrowband sounds, just not 

as far. Results indicate that frequency 

weighting of SEL may improve 

prediction of harbor porpoise behavioral 

responses, and authors present the 

argument that weighted SELs should be 

used for reporting behavioral response 

threshold levels for criteria. 

Todd et al. (2022) detected harbor 

porpoises with C–PODS before, during, 

and after pile driving for an oil and gas 

platform from 2015–2020. Pile driving 

single strike SEL at 750 m was 160–164 

dB re 1 mPa2s. Porpoise detections 

significantly decreased at the beginning 

of the construction project, but 

detections appeared to return to 

baseline levels within 5 months. 

According to the authors, the lack of 

significant trend over years indicated 

that porpoises returned to the area and 

did not experience habitat displacement 

for the entire 5-year period. 

Physiological Responses and Stress 

Elmegaard et al. (2021) exposed two 

captive harbor porpoises to sonar 

sweeps (6–9 kHz, 500 msec duration, 

50–100 msec rise time, varying received 

levels (RL)) and pulsed sounds (50 msec 

duration, peak frequency 40 kHz, half 

power bandwidth of ∼5 kHz, rise time 

< 5 msec, varying RL) to investigate 

startle reflex and changes in heart rate. 

The sonar exposures did not elicit 

startle responses; the initial two to three 

exposures induced bradycardia (a slow 

heart rate), with subsequent habituation. 

This habituation was conserved after a 

3-year pause in exposures. The authors 

suggest that the initial bradycardia 

allows ‘‘a prolonged breath-hold to 

assess the nature of a novel stimuli or 

flee in crypsis if needed;’’ in naı ̈ve wild 

cetaceans, the reduced peripheral 

perfusion caused by this response may 

reduce N2 diffusion from supersaturated 

tissues during dive ascents, increasing 

risk of decompression sickness. Startle 

responses to the pulse exposures were 

directly correlated to RL. The 50 percent 

motor-startle probability threshold was 

around 130 dB re 1 mPa (rms50). This is 

∼85 dB above hearing threshold and is 

similar to that observed in bottlenose 

dolphins (∼90 dB over hearing 

threshold) (Gotz et al. 2020). No 

significant change in heart rate was 

observed. The authors suggest that the 

parasympathetic cardiac dive response 

may override any transient sympathetic 

response, or that diving mammals may 

not have the cardiac startle response 

seen in terrestrial mammals in order to 

maintain volitional cardiovascular 

control at depth. 

Fahlman et al. (2021) reviews 

decompression theory and the 

mechanisms dolphins have evolved to 

prevent high N2 levels and gas emboli 

(i.e., bends-like symptoms) in normal 

conditions. However, in times of high 

stress, the selective gas exchange 

hypothesis states that this mechanism 

can break down. In addition, circulating 

microparticles may be useful biomarkers 

for decompression stress in cetaceans. 

Yang et al. (2021) measured cortisol 

concentrations in blood samples of two 

captive bottlenose dolphins and found 

significantly higher levels after exposure 

to high sound level (140 dB re 1 mPa) 

impulsive noise playbacks, compared to 

control and low sound levels (0 and 120 

dB re 1 mPa, respectively). Six cytokine 

gene transcriptions were also measured 

in blood samples and two (IL–10 and 

IFN-g) showed significant changes at 

high sound level exposure, compared to 

control and low sound levels. Results 

suggest that repeated exposures or 

sustained stress response to impulsive 

sounds may increase an affected 

individual’s susceptibility to pathogens, 

affect growth and reproduction, etc. In 

addition, no avoidance behavior was 

observed during the trials, indicating 

that stress-induced physiological 

changes could be present despite the 

absence of behavioral changes. 

Williams et al. (2022) measured 

physiological and behavioral responses 

in narwhals in the Arctic during seismic 

airgun impulse exposure compared to 

control conditions. Responses were 

measured using heart rateaccelerometer-depth recorders and 

changes in locomotor, cardiovascular, 

and respiratory responses were observed 

following exposure. Airgun SELs, as 

received at 10 m depth during sound 

source verifications, were 

approximately 152 dB re 1 mPa2s at 1 km 

(0.5 nmi) range and decreased to 

approximately 120 dB re 1 mPa2s at 10 

km (5.4 nmi) dives. The response to 

seismic and vessel noise was a 

reduction in gliding descents and 

prolonged periods of high intensity 

activity associated with periods of 

elevated stroke frequencies. Noise 

exposure also resulted in periods of 

prolonged and intense bradycardia (i.e., 

slowed heart rate). An increase in postdive respiratory rates occurred during 

recovery from noise-exposed dives 

compared to control dives. 

Stranding 

Danil et al. (2021) document the 

findings of NOAA’s investigation of the 

strandings of three coastal bottlenose 

dolphins in 2015 at Silver Strand 

Training Complex in NOAA Technical 

Memorandum NMFS–SWFSC–641. On 

October 21, 2015, two dolphins were 

found stranded dead near each other on 

the beach. Because a Navy major 

training exercise (MTE) was underway, 

these strandings met the criteria of an 

Uncommon Stranding Event in 

accordance with the Southern California 

Stranding Response Plan in the Navy’s 

Phase 2 LOA for HSTT. A third 

decomposed dolphin was found in the 

same area 10 days later. Examination of 

the dolphins resulted in findings 

indicative of severe acute trauma, 

including lower jaw subcutaneous 

hemorrhage, emphysema, and cervical 

blubber hemorrhage. Additional signs of 

injury to the cerebrum and heart, or 

lipids in the lungs were also discovered. 

No hemorrhage was found near the ears. 

At least two of the dolphins showed 

signs of feeding before stranding, and all 

were in robust condition. There were no 

external signs of strike or entanglement. 

These observations and lack of others 

did not clearly determine the cause of 

the acute trauma. Based on previous 

case studies, the investigators 

determined that underwater detonation, 

peracute underwater entrapment (i.e., 

fisheries interaction), or sonar were the 

most plausible causes. The Navy notes 

that sonar has not been associated with 

these kinds of symptoms before, nor has 

there ever been any association between 

dolphin mortality and sonar. No antisubmarine (ASW) sonar or explosive use 

was associated with the Navy MTE; 

however, unit level training with MF1 

sonar occurred on October 19 (for 35 

minutes) and October 20 (62 minutes in 

total), with sonar use as close as 6 nmi 

(11.1 km) to the stranding location. No 

known squid or bait fishing efforts 

within U.S. waters occurred in the 

vicinity preceding the strandings. The 

Navy notes that it is unknown what 

fishing efforts occurred in Mexican 

territorial waters immediately south of 

the stranding location. 

Wang et al. (2021) conducted an 

auditory-evoked potential (AEP) hearing 

test on a single stranded 19-year-old 

male melon-headed whale in the 9.5— 

181 kHz frequency range. Tone pip 

trains were presented underwater at a 

depth of 0.3 m and 1 m distance from 

the whale, and AEPs were recorded by 

suction cup electrodes on the skin 

surface. Hearing was measured in this 


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individual after it had been stranded 

and during attempted rehabilitation in a 

concrete pool. Eighteen frequencies 

were measured once, and eight 

frequencies were measured twice, 

yielding an audiogram that showed 

elevated hearing thresholds (compared 

to the pygmy killer whale) between 10 

and 100 kHz. There are no data from 

normal-hearing individuals of the 

melon-headed whale species to which 

this study’s data can be compared. 

Population Consequences of 

Disturbance and Cumulative Stressors 

Southall et al. (2021) provided 

updated guidance and methods to assess 

the severity of behavioral responses by 

marine mammals to several types of 

anthropogenic noise sources. The 

criteria developed in the 2007 effort 

were updated by explicitly 

distinguishing between captive and 

field studies, decoupling their 

respective severity scales, and splitting 

the severity scale into three categories of 

foraging, survival, and reproduction. In 

addition, the updated guidance changed 

the categorization of noise sources and 

began to consider long term 

consequences of exposures rather than 

just immediate responses. Additional 

and consistent metrics to be reported in 

behavioral response studies are 

recommended, including subjectspecific metrics (e.g., functional hearing 

group, age class, sex, behavioral state, 

presence of calf), exposure context 

metrics (e.g., exposure type, range to 

source, source and animal depth, 

presence of other species or other noise 

sources), and noise exposure metrics 

(e.g. exposure duration, rise time, 

number of exposures, SPL [rms and pp], SEL, SNR). The authors then applied 

the severity scale to acute exposure 

studies using sonar sources, continuous 

(industrial) sources, pile driving 

sources, and airgun sources. For the 

long-term exposure analysis, a set of 

factors developed by Bejder and 

Samuels (2003) were applied to longterm studies on whale-watching and 

other long-term exposure or multiexposure datasets. These factors 

included metrics of short-term impacts 

and long-term survival measures, 

characteristics of the studies, and 

sources of anthropogenic disturbance. 

The applied examples of scoring both 

acute and long-term studies of 

behavioral response provide a 

framework for other researchers to apply 

the same metrics to their own studies. 

Migrating humpback whale mothercalf pairs’ responses to seismic surveys 

were modeled by Dunlop et al. (2021) 

using both a forwards and backward 

approach. While a typical forwards 

approach can determine if a stressor 

would have population-level 

consequences, authors demonstrated 

that working backwards through a 

population consequences of disturbance 

(PCoD) model can be used to assess the 

‘‘worst case’’ scenario for an interaction 

of a target species and stressor. 

Assumptions for the extreme scenario 

were likely exaggerated (e.g., in area for 

> 48 hours, exposed to > 3 air gun 

events) but lack data to inform 

humpback nursing behavior and calf 

survivability during acoustic stressors. 

The results demonstrated that migrating 

whales would not likely experience 

enough of a delay as a result of 

disturbance to result in population 

consequences, but whales disturbed in 

breeding or resting areas would be more 

vulnerable to consequences of 

disturbance. 

Greenfield et al. (2020) demonstrated 

that bottlenose dolphins who had been 

injured from boat strike or entanglement 

experienced a decline in their social 

network’s preferred associations, and as 

a result were more vulnerable to 

predation and less fecund. 

Hin et al. (2021) used a previously 

published energy budget model for pilot 

whales (Hin et al. 2019) to examine how 

lost foraging days affect individuals in 

a population at carrying capacity. In this 

model, depletion of prey is dependent 

on whale density, and prey density 

limits the energy available for growth, 

reproduction, and survival. The authors 

assumed extreme disturbance events for 

this study: consecutive days of no 

foraging affecting all individuals in a 

population. The undisturbed whale 

population was regulated through the 

effect of prey availability on calf 

survival and pregnancy rates and on age 

at first reproduction of females. During 

a disturbance event, population decline 

was generally attributed to loss of 

lactating females and calves due to 

reduced body condition. The 

subsequent increase in prey density and 

per capita prey availability, however, 

resulted in improved body condition in 

the population overall and decreased 

age at first calf. As disturbance duration 

was increased (∼40 days of no foraging), 

the population would enter extreme 

decline towards extinction. 

Murray et al. (2021) conducted a 

cumulative effects assessment on 

Northern and Southern Resident killer 

whales, which involved both a 

Pathways of Effects conceptual model 

and a Population Viability Analysis 

quantitative simulation model. Authors 

found that both populations were highly 

sensitive to prey abundance and were 

also impacted by the interaction of low 

prey abundance with vessel strike, 

vessel noise, and polychlorinated 

biphenyls contaminants. However, more 

research is needed to validate the 

mechanisms of vessel disturbance and 

environmental contaminants. 

Pirotta et al. (2020) reformulated their 

previous dynamic energy budget model 

(Pirotta et al. 2018) to investigate the 

state-dependent life history strategies of 

female long-finned pilot whales and 

trade-offs between their body condition 

(i.e., ability to offset starvation during 

pregnancy and provide milk), prey 

availability, and decision to reproduce 

in situations with and without 

disturbance. Many whales in this model 

attempted to reproduce young, and 

while that had no cost in situations 

without disturbance, young mothers 

would starve and die when foraging was 

prevented by some disturbance event or 

because resources were low (winter). 

Whale reproductive strategies resulted 

in lower lifetime reproductive output, 

compared to the model used in Hin et 

al. (2019). 

Pirotta et al. (2021) integrated 

different sources of data (e.g., controlled 

exposure data, activity monitoring, 

telemetry tracking, and prey sampling) 

into a bioenergetic model, which was 

used to predict effects from sonar on a 

blue whale’s daily energy intake. 

Approximately half of the simulated 

whales had no change in daily net 

energy intake because they either had 

no response or were not exposed. 

However, the other half experienced a 

decrease in net energy intake. A portion 

(11 percent) of those simulated whales 

had negative net energy even after brief 

(e.g., 6–30 min) or weak (e.g., 160–180 

dB re 1 mPa source level) events, which 

indicated that they would not be able to 

cover that day’s energetic cost. This 

dichotomy in results was due to the 

variation in activity budgets, lunging 

rates and ranging patterns between 

tagged whales. This evidence suggests 

that context can influence the predicted 

costs of disturbance even more than 

body size or prey density distribution 

on a daily scale (although prey 

availability and abundance affected 

behavioral patterns). 

Pirotta et al. (2022) evaluated 

potential long-term effects of changing 

environmental conditions and military 

sonar by modeling vital rates of Eastern 

North Pacific blue whales. Previous 

work from Pirotta et al. (2021) was used 

as a foundation for incorporating the 

most recent best available science into 

the vital rate model presented in this 

study. Using data and underlying 

models of behavioral patterns, energy 

budgets, body condition, contextual 

responses to noise, and prey resources, 

the model predicted female vital rates 


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including survival (age at death), and 

reproductive success (number of female 

calves). The model simulation results 

showed that ‘‘[e]nvironmental changes 

were predicted to severely affect vital 

rates, while the current regime of sonar 

activities was not.’’ The case study used 

an annual sonar regime in SOCAL based 

on the description of the action in the 

Navy’s 2018 HSTT FEIS/OEIS. 

Additional military sonar scenarios 

were modeled, and a ten-fold increase 

in sonar activity combined with a shift 

in geographical location to overlap with 

main feeding areas of blue whales 

resulted in a moderate decrease in 

lifetime reproductive success (Cohen’s d 

= 0.47). However, there was no effect on 

survival (Cohen’s d = 0.05). 

Pirotta (2022) covered the 

development of bioenergetic models 

[‘‘any mechanistic model where the 

principles of metabolic ecology are used 

to describe how an individual animal 

acquires energy from food resources 

(i.e., energy intake) and allocates 

assimilated energy to various life history 

functions (i.e., energy costs, including 

maintenance and survival, growth and 

reproduction)’’] with a focus on 

applications to marine mammals. This 

article provided a thorough overview of 

the history of marine mammal 

bioenergetic models, defined relevant 

terminology, and explained the 

differences between general types of 

models. 

McHuron et al. (2021) developed a 

state-dependent behavioral and life 

history model to predict the probability 

of Western gray whale mother-calf pair 

survival with and without acoustic 

disturbance and with or without 

adequate prey availability on their 

summer foraging grounds. Pregnant 

mother movement, feeding behavior, fat 

mass and fetal length were input data 

for the model. Since prey availability 

was co-dependent on whales having 

access to high-density offshore areas by 

mid-July, nearshore seismic surveys had 

no impact on population fecundity or 

mother-calf survival. This model 

overcomes a key challenge in PCoD 

literature by providing a link between 

behavioral responses and vital rates; 

authors recommend focusing on species 

that are data rich to accurately 

characterize the biology of the focal 

species, metrics of fitness, and key 

qualities of their environment. 

Joy et al. (2022) presented a 

hypothetical case study for fin whales 

off Southern California exposed to 

stationary single-ship 53C sonar events 

over the course of a year, using the 

Navy’s Phase 3 behavioral response 

function (BRF). Two model runs were 

compared: using a = 0.05 (average 20- 

minute movement disruption) and a= 

0.99 (average 3 days movement 

disruption). When animals returned to 

baseline behavior after a short 

disturbance (a = 0.05), there was less 

regional displacement and thus more 

instances of behavioral disturbance over 

the course of a year. When animals 

returned to baseline behavior after a 

longer period (a=0.99), there were fewer 

instances of behavioral disturbances 

over the course of a year due to 

cumulative displacement from habitat 

near the sonar source. 

Keen et al. (2021) reviewed 15+ years 

of PCoD modeling and identified the 

most critical factors for determining 

long-term impacts to populations. 

Critical factors include life-history 

traits, disturbance source 

characteristics, and environmental 

conditions. No specific model or 

quantitative assessment was proposed. 

Methodology for Assessing Acoustic 

Impacts 

Palmer et al. (2022) recorded North 

Atlantic right whale upcalls using 10 

Marine Autonomous Recording Units 

deployed in Cape Cod Bay from 

February to May 2009. A modified 

equation was provided for determining 

the effective survey area, including a 

Lombard coefficient, for single sensor 

applications. The authors state manual 

annotation or verification is nearly 

always used to confirm automated 

detector outputs prior to near-real-time 

conservation measures due to 

limitations in automatic detector 

capabilities. 

Aircraft Noise 

Kuehne et al. (2020) measured in-air 

and underwater sound from lowaltitude EA–18G Growler flights in the 

immediate vicinity of Ault Field at 

Naval Air Station Whidbey Island 

(NASWI). Data were collected by two inair recorders and one hydrophone 

placed just off the runway at a depth of 

30 meters. The underwater 10-flight 

average sound measurement was 134 ± 

3 dB re 1 mPa rms in the highest 1- 

second window. The results showed 

that the peak frequency range of the 

Growler overflight noise both in air and 

underwater was between 50 and 1,000 

Hz, which is typically a frequency range 

with high background noise underwater, 

particularly in areas with large amounts 

of vessel traffic (Erbe et al. 2012). The 

study did not include behavioral 

observations of wildlife, and the 

authors’ conclusions about potential 

impacts to wildlife were unsupported 

by data from the study. In a separate 

effort, Kuehne and Olden (2020) relied 

on volunteers to identify military 

aircraft noise in recordings taken on 

land on the Olympic Peninsula. This 

study also did not examine impacts to 

or responses by wildlife to aircraft. 

We reiterate that NMFS reviewed the 

Navy’s analysis and conclusions that 

aircraft noise will not result in 

incidental take of marine mammals, and 

finds the analysis and conclusions 

complete and supportable, as stated in 

the 2018 HSTT final rule. Please see 

section 3.7 (Marine Mammals) of the 

2018 HSTT FEIS/OEIS for additional 

information. 

Conclusion for New Pertinent Science 

Since Publication of the 2020 HSTT 

Final Rule 

Having considered the best scientific 

information available, specifically new 

relevant information published since 

the 2020 HSTT final rule, we have 

preliminarily determined that there is 

no new information that substantively 

affects our analysis of impacts on 

marine mammals and their habitat that 

appeared in the 2020 HSTT final rule, 

all of which remains applicable and 

valid for our assessment of the effects of 

the Navy’s activities during the 7-year 

period of this rulemaking. 

Estimated Take of Marine Mammals 

This section indicates the number of 

takes that NMFS is proposing for 

authorization, which are based on the 

amount of take that NMFS anticipates 

could occur or is likely to occur, 

depending on the type of take and the 

methods used to estimate it, as 

described below. NMFS coordinated 

closely with the Navy in the 

development of their incidental take 

application and preliminarily agrees 

that the methods the Navy has put forth 

described herein, in the 2019 HSTT 

proposed rule, 2020 HSTT final rule, 

and in the 2018 HSTT proposed and 

final rules to estimate take (including 

the model, thresholds, and density 

estimates), and the resulting numbers 

are based on the best available science 

and appropriate for authorization, with 

the exception of that of humpback 

whales, discussed further below. The 

number and type of incidental takes that 

could occur or are likely to occur 

annually remain identical to those 

authorized in the 2018 HSTT 

regulations and 2020 HSTT regulations, 

with the exception of proposed takes by 

serious injury or mortality by vessel 

strike and harassment takes of 

humpback whale stocks in Southern 

California (due to the new stock 

structure). 

Takes are predominantly in the form 

of harassment, but a small number of 

serious injuries or mortalities could 


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occur. For military readiness activities, 

the MMPA defines ‘‘harassment’’ as (i) 

any act that injures or has the significant 

potential to injure a marine mammal or 

marine mammal stock in the wild (Level 

A harassment); or (ii) any act that 

disturbs or is likely to disturb a marine 

mammal or marine mammal stock in the 

wild by causing disruption of natural 

behavioral patterns, including, but not 

limited to, migration, surfacing, nursing, 

breeding, feeding, or sheltering, to a 

point where such behavioral patterns 

are abandoned or significantly altered 

(Level B harassment). 

Proposed authorized takes would 

primarily be in the form of Level B 

harassment, as use of the acoustic and 

explosive sources (i.e., sonar, air guns, 

pile driving, explosives) and is more 

likely to result in the disruption of 

natural behavior patterns to a point 

where they are abandoned or 

significantly altered (as defined 

specifically at the beginning of this 

section but referred to generally as 

behavioral disturbance) or TTS for 

marine mammals. There is also the 

potential for Level A harassment in the 

form of auditory injury and/or tissue 

damage (the latter from explosives only) 

to result from exposure to the sound 

sources utilized in training and testing 

activities. Additionally, serious injuries 

or mortalities of mysticetes (except for 

sei whales, minke whales, Bryde’s 

whales, Central North Pacific stock of 

blue whales, Hawaii stock of fin whales, 

Western North Pacific stock of gray 

whales, and sperm whales) could occur 

through vessel strike. Proposed 

mitigation and monitoring measures are 

expected to minimize the severity of the 

taking to the extent practicable. 

Generally speaking, for acoustic 

impacts, NMFS estimates the amount 

and type of harassment by considering: 

(1) acoustic thresholds above which 

NMFS believes the best available 

science indicates marine mammals 

would experience behavioral 

disturbance or incur some degree of 

temporary or permanent hearing 

impairment; (2) the area or volume of 

water that will be ensonified above 

these levels in a day or event; (3) the 

density or occurrence of marine 

mammals within these ensonified areas; 

and (4) and the number of days of 

activities or events. 

Acoustic Thresholds 

Using the best available science, 

NMFS, in coordination with the Navy, 

has established acoustic thresholds that 

identify the most appropriate received 

level of underwater sound above which 

marine mammals exposed to these 

sound sources could be reasonably 

expected to experience a disruption in 

behavior patterns to a point where they 

are abandoned or significantly altered or 

to incur TTS (equated to Level B 

harassment) or permanent threshold 

shift (PTS) of some degree (equated to 

Level A harassment). Thresholds have 

also been developed to identify the 

pressure levels above which animals 

may incur non-auditory injury from 

exposure to pressure waves from 

explosive detonation. 

We described the acoustic thresholds 

and the methods used to determine 

thresholds, none of which have 

changed, in detail in the Acoustic 

Thresholds section of the 2018 HSTT 

final rule; please see the 2018 HSTT 

final rule for detailed information. 

Further, in the 2020 HSTT final rule, we 

described new relevant information 

from the scientific literature since 

publication of the 2018 HSTT final rule. 

Since publication of the 2020 HSTT 

final rule, a number of additional 

studies have published, including 

several associated with TTS in harbor 

porpoises and seals (e.g., Kastelein et al. 

2020d; Kastelein et al. 2021a and 2021b; 

Sills et al. 2020). NMFS is aware of 

these recent papers, summarized above 

in the New Pertinent Science Since 

Publication of the 2020 HSTT Final 

Rule section. NMFS is currently 

working with the Navy to update NMFS’ 

Technical Guidance for Assessing the 

Effects of Anthropogenic Sound on 

Marine Mammal Hearing Version 2.0 

(Acoustic Technical Guidance; NMFS 

2018) to reflect relevant papers that 

have been published since the 2018 

update on our 3–5 year update schedule 

in the Acoustic Technical Guidance. 

First, we note that the recent peerreviewed updated marine mammal 

noise exposure criteria by Southall et al. 

(2019) provide identical PTS and TTS 

thresholds and weighting functions to 

those provided in NMFS’ Acoustic 

Technical Guidance. 

NMFS will continue to review and 

evaluate new relevant data as it becomes 

available and consider the impacts of 

those studies on the Acoustic Technical 

Guidance to determine what revisions 

or updates may be appropriate. 

However, any such revisions must 

undergo peer and public review before 

being adopted, as described in the 

Acoustic Technical Guidance 

methodology. While some of the 

relevant data may potentially suggest 

changes to TTS/PTS thresholds for some 

species, any such changes would not be 

expected to change the predicted take 

estimates in a manner that would 

change the necessary determinations 

supporting the issuance of these 

regulations, and the data and values 

used in this proposed rule reflect the 

best available science. 

Navy’s Acoustic Effects Model 

The Navy proposes no changes to the 

Acoustic Effects Model as described in 

the 2018 HSTT final rule (and 

incorporated by reference in the 2020 

HSTT final rule), and there is no new 

information that would affect the 

applicability or validity of the model. 

Please see the 2018 HSTT final and 

proposed rules and Appendix E of the 

2018 HSTT FEIS/OEIS for detailed 

information. 

Range to Effects 

The Navy proposes no changes from 

the 2018 HSTT final rule (and 

subsequent 2020 HSTT final rule) to the 

type and nature of the specified 

activities to be conducted during the 7- 

year period analyzed in this proposed 

rule, including equipment and sources 

used and exercises conducted. NMFS 

has reviewed and will continue to 

review and evaluate new relevant data 

as it becomes available and consider the 

impacts of those studies on the Acoustic 

Technical Guidance to determine what 

revisions/updates may be appropriate. 

However, any such revisions must 

undergo peer and public review before 

being adopted, as described in the 

Acoustic Guidance methodology. While 

some of the relevant data may 

potentially suggest changes to TTS/PTS 

thresholds for some species (e.g., 

Kastelein et al. (2020a) shows onset of 

TTS incurred by a harbor porpoise at 

higher received levels than would have 

been anticipated based on the existing 

criteria, while Kastelein et al. (2022a) 

shows onset of TTS in otariids in water 

at lower received levels than the 

existing criteria), our assessment 

suggests that any such changes would 

not be expected to change the predicted 

take estimates in a manner that would 

change the necessary determinations 

supporting the issuance of these 

regulations, and the data and values 

used in the 2018 HSTT final rule, 2020 

HSTT final rule, and this proposed rule 

reflect the best available science. 

Therefore, the ranges to effects in this 

proposed rule are identical to those 

described and analyzed in the 2018 

HSTT final rule and 2020 HSTT final 

rule, including received sound levels 

that may cause onset of significant 

behavioral response and TTS and PTS 

in hearing for each source type or 

explosives that may cause non-auditory 

injury. Please see the Range to Effects 

section and tables 24 through 40 of the 

2018 HSTT final rule for detailed 

information. 


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Marine Mammal Density 

The Navy proposes no changes to the 

methods used to estimate marine 

mammal density described in the 2018 

HSTT final rule, and there is no new 

information that would affect the 

applicability or validity of these 

methods or change the results in a 

manner that would change the 

necessary determinations supporting the 

issuance of these regulations. The 

Navy’s estimate of marine mammal 

density as described in the 2018 HSTT 

final rule remains valid, though, as 

described herein, NMFS has 

incorporated new information regarding 

humpback whale stock structure into its 

analysis. Please see the 2018 HSTT final 

rule, and below, for detailed 

information. 

As noted above, NMFS regularly 

updates SARs, and in this rulemaking 

considers the 2022 final SARs (Carretta 

et al. 2023, Young et al. 2023). While 

these SARs contain updated 

information, the Navy’s estimate of 

marine mammal density as described in 

the 2018 HSTT final rule remains valid 

for the following reasons. The Navy uses 

its Marine Species Density Database 

(NMSDD) for its analysis, which is 

derived from multiple sources, 

including but not limited to SARs. In 

contrast, for most cetacean species, the 

SAR is estimated using line-transect 

surveys or mark-recapture studies (e.g., 

Barlow, 2010; Barlow and Forney, 2007; 

Calambokidis et al. 2008). The result 

provides one single abundance value for 

each species across broad geographic 

areas, but it does not provide 

information on the species density or 

concentrations within that area, and it 

does not estimate density for other 

timeframes or seasons that were not 

surveyed. A change in a stock’s 

abundance indicated in a SAR does not 

necessarily indicate a change in that 

stock’s density in any given area. 

Therefore, stocks in the HSTT Study 

Area with higher abundance estimates 

in the most recent SARs in comparison 

to the abundance estimates at the time 

that marine mammal densities were 

derived for the HSTT Study Area do not 

necessarily now occur in higher 

densities in the HSTT Study Area. For 

humpback whale, while the stock 

structure in the Pacific Ocean was 

revised in the 2022 final SARs, the 

discussion above remains true regarding 

density of humpback whales in the 

HSTT Study Area across all stocks. 

Take Requests 

As in the 2018 HSTT final rule and 

2020 HSTT final rule, the Navy 

determined that the three stressors 

below could result in the incidental 

taking of marine mammals. NMFS has 

reviewed the Navy’s data and analysis 

and determined that it is complete and 

accurate, and NMFS agrees that the 

following stressors have the potential to 

result in takes of marine mammals from 

the Navy’s planned activities: 

• Acoustics (sonar and other 

transducers; air guns; pile driving/ 

extraction); 

• Explosives (explosive shock wave 

and sound, assumed to encompass the 

risk due to fragmentation); and 

• Physical Disturbance and Strike 

(vessel strike). 

NMFS reviewed and agrees with the 

Navy’s conclusion that acoustic and 

explosive sources have the potential to 

result in incidental takes of marine 

mammals by harassment, serious injury, 

or mortality. NMFS carefully reviewed 

the Navy’s analysis and conducted its 

own analysis of vessel strikes, 

determining that the likelihood of any 

particular species of large whale being 

struck is quite low. However, as noted 

previously, in 2021, two separate U.S. 

Navy vessels struck unidentified large 

whales on two separate occasions, one 

whale in June 2021 and one whale in 

July 2021. In May 2023, the U.S. Navy 

struck a large whale, which based on 

available photos and video, NMFS and 

the Navy have determined was either a 

fin whale or sei whale. NMFS agrees 

that vessel strikes have the potential to 

result in incidental take from serious 

injury or mortality for certain species of 

large whales, and the Navy has 

specifically requested coverage for these 

species. Therefore, the likelihood of 

vessel strikes, and later the effects of the 

incidental take that is being proposed to 

be authorized, has been fully analyzed 

and is described below. 

Regarding the quantification of 

expected takes from acoustic and 

explosive sources (by Level A and Level 

B harassment, as well as mortality 

resulting from exposure to explosives), 

the number of takes are based directly 

on the level of activities (days, hours, 

counts, etc., of different activities and 

events) in a given year. In the 2020 

HSTT final rule, take estimates across 

the 7 years were based on the Navy 

conducting 4 years of a representative 

level of activity and 3 years of 

maximum level of activity. As in the 

2020 HSTT final rule, the Navy 

proposes to use the maximum annual 

level to calculate annual takes (which 

would remain identical to what was 

determined in the 2020 HSTT final rule, 

with the exception of attribution of 

takes to humpback whale stocks), and 

the sum of all years (4 representative 

and 3 maximum) to calculate the 7-year 

totals for this rulemaking. 

The quantitative analysis process 

used for the 2018 HSTT FEIS/OEIS and 

the 2017 and 2019 Navy applications to 

estimate potential exposures to marine 

mammals resulting from acoustic and 

explosive stressors is detailed in the 

technical report titled Quantifying 

Acoustic Impacts on Marine Mammals 

and Sea Turtles: Methods and 

Analytical Approach for Phase III 

Training and Testing (U.S. Department 

of the Navy, 2018). The Navy Acoustic 

Effects Model estimates acoustic and 

explosive effects without taking 

mitigation into account; therefore, the 

model overestimates predicted impacts 

on marine mammals within mitigation 

zones. To account for mitigation for 

marine species in the take estimates, the 

Navy conducts a quantitative 

assessment of mitigation. The Navy 

conservatively quantifies the manner in 

which procedural mitigation is expected 

to reduce the risk for model-estimated 

PTS for exposures to sonars and for 

model-estimated mortality for exposures 

to explosives, based on species 

sightability, observation area, visibility, 

and the ability to exercise positive 

control over the sound source. Where 

the analysis indicates mitigation would 

effectively reduce risk, the modelestimated PTS are considered reduced 

to TTS and the model-estimated 

mortalities are considered reduced to 

injury. For a complete explanation of 

the process for assessing the effects of 

mitigation, see the 2017 Navy 

application and the Take Requests 

section of the 2018 HSTT final rule. The 

extent to which the mitigation areas 

reduce impacts on the affected species 

and stocks is addressed separately in the 

Preliminary Analysis and Negligible 

Impact Determination section. 

No changes have been made to the 

quantitative analysis process to estimate 

potential exposures to marine mammals 

resulting from acoustic and explosive 

stressors and calculate take estimates, 

with the exception of take of humpback 

whales to account for the change in 

stock structure. Please see the 

documents described in the paragraph 

above, the 2018 HSTT proposed rule, 

the 2018 HSTT final rule, and below for 

detailed descriptions of these analyses. 

While Oedekoven and Thomas (2022) 

suggest that detection of marine 

mammals is less certain than previously 

assumed at certain distances, NMFS has 

independently evaluated the Navy’s 

method for application of mitigation 

effectiveness in estimating take and 

agrees that it is appropriately applied to 

augment the model in the prediction 

and authorization of injury and 


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mortality as described in the rule, 

including after consideration of 

Oedekoven and Thomas (2022). In 

summary, we believe the Navy’s 

methods, including the method for 

incorporating mitigation and avoidance, 

are the most appropriate methods for 

predicting PTS, TTS, and behavioral 

disturbance. But even with the 

consideration of mitigation and 

avoidance, given some of the more 

conservative components of the 

methodology (e.g., the thresholds do not 

consider ear recovery between pulses), 

we would describe the application of 

these methods as identifying the 

maximum number of instances in which 

marine mammals would be reasonably 

expected to be taken through PTS, TTS, 

or behavioral disturbance. 

Summary of Requested Take From 

Training and Testing Activities 

Based on the methods discussed in 

the previous sections and the Navy’s 

model and quantitative assessment of 

mitigation, the Navy provided its take 

estimate and request for authorization of 

takes incidental to the use of acoustic 

and explosive sources for training and 

testing activities both annually (based 

on the maximum number of activities 

that could occur per 12-month period) 

and over the 7-year period in its 2019 

rulemaking/LOA application. With the 

exception of changes to humpback 

whale take, described below, annual 

takes (based on the maximum number of 

activities that could occur per 12-month 

period) from the use of acoustic and 

explosive sources are identical to those 

presented in tables 41 and 42 and in the 

Explosives subsection of the Take 

Requests section of the 2018 HSTT final 

rule. The 2022 Navy application 

includes the Navy’s updated take 

estimate and request for take by vessel 

strike due to vessel movement in the 

HSTT Study Area. NMFS reviewed the 

Navy’s data, methodology, and analysis 

and determined that it was complete, 

but NMFS has reanalyzed the potential 

for vessel strike following the May 2023 

strike, as described in the Estimated 

Take from Vessel Strikes and Explosives 

by Serious Injury or Mortality section. 

NMFS agrees that the estimates for 

incidental takes by harassment from all 

sources as well as the incidental takes 

by serious injury or mortality from 

explosives requested for authorization 

are the maximum number of instances 

in which marine mammals are 

reasonably expected to be taken at the 

time of Navy’s request, and continues to 

be for all stocks other than humpback 

whales, for which changes are described 

below. NMFS also agrees that the takes 

by serious injury or mortality as a result 

of vessel strikes could occur. Note that, 

consistent with the 2020 HSTT final 

rule, the total amount of estimated 

incidental take from acoustic and 

explosive sources over the total 7-year 

period covered by the 2019 Navy 

application is less than the annual total 

multiplied by seven. Although the 

annual estimates are based on the 

maximum number of activities per year 

and therefore, the maximum possible 

estimated takes, the 7-year total take 

estimates are based on the sum of 3 

maximum years and 4 representative 

years, with the exception of humpback 

whale stocks that occur in SOCAL for 

which 7-year total take is conservatively 

estimated as the annual total multiplied 

by seven. Not all activities occur every 

year. Some activities would occur 

multiple times within a year, and some 

activities would occur only a few times 

over the course of the 7-year period. 

Using 7 years of the maximum number 

of activities each year would vastly 

overestimate the amount of incidental 

take that would occur over the 7-year 

period where the Navy knows that it 

will not conduct the maximum number 

of activities each and every year for the 

7 years. 

As described above in the Description 

of Marine Mammals and Their Habitat 

in the Area of the Specified Activities 

section, the 2022 final SARs include a 

revision to the humpback whale stock 

structure in the Pacific Ocean. In the 

2020 HSTT final rule, NMFS authorized 

take of the CA/OR/WA stock and 

Central North Pacific stock of humpback 

whale. Given the revised stock 

structure, in this proposed rule, NMFS 

has reanalyzed the potential for take of 

each stock of humpback whale and 

determined that the Central America/ 

Southern Mexico-CA/OR/WA, Mainland 

Mexico—CA/OR/WA stock, and Hawaii 

stocks are likely to be taken by the 

Navy’s activities. 

Under the new stock structure, the 

Hawaii stock (Hawaii DPS) is the only 

stock that would occur in Hawaii. 

Therefore, the Hawaii stock of 

humpback whale is the only humpback 

whale stock anticipated to be taken by 

the Navy’s activities in the HRC, and all 

takes of the Central North Pacific stock 

of humpback whale that were 

authorized in the 2020 HSTT final rule 

are anticipated to be of individuals from 

the new Hawaii stock. In SOCAL, the 

takes of individuals from the former CA/ 

OR/WA stock that were authorized in 

the 2020 HSTT final rule are anticipated 

to be of individuals from the new 

Central America/Southern Mexico-CA/ 

OR/WA and Mainland Mexico-CA/OR/ 

WA stock. 

Please see the Estimated Harassment 

Take from Testing Activities and 

Estimated Harassment Take from 

Training Activities sections below for 

the estimated annual and 7-year total 

number and type of Level A harassment 

and Level B harassment for each 

humpback whale stock. 

Estimated Harassment Take From 

Training Activities 

For training activities, table 11 of the 

2020 HSTT final rule summarizes the 

Navy’s take estimate and request in the 

2019 Navy application and the 

maximum amount and type of Level A 

harassment and Level B harassment that 

NMFS concurred is reasonably expected 

to occur by species or stock and 

authorized in the 2020 HSTT LOA. In 

the 2022 Navy application, the Navy 

requested no change to this authorized 

take, though as described above, NMFS 

has since published the 2022 final 

SARs, which include a revision to 

humpback whale stock structure. For 

the estimated 7-year total amount and 

type of Level A harassment and Level B 

harassment, see table 11 of the 2020 

HSTT final rule for all species other 

than humpback whale. For the 

estimated amount and type of Level A 

harassment and Level B harassment 

annually, see table 41 in the 2018 HSTT 

final rule for all species other than 

humpback whale. Note that take by 

Level B harassment includes both 

behavioral disturbance and TTS. Navy 

Figures 6–12 through 6–50 in Section 6 

of the 2017 Navy application illustrate 

the comparative amounts of TTS and 

behavioral disturbance for each species 

annually, noting that if a modeled 

marine mammal was ‘‘taken’’ through 

exposure to both TTS and behavioral 

disturbance in the model, it was 

recorded as a TTS. 


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TABLE 2—HUMPBACK WHALE TAKE FROM ACOUSTIC AND EXPLOSIVE EFFECTS FOR ALL TRAINING ACTIVITIES IN THE

HSTT STUDY AREA

Species Stock 

Annual 7-Year total 

Level B 

harassment 

Level A 

harassment 

Level B 

harassment 

Level A 

harassment 

Humpback whale a ................ Hawaii ........................................................... 5,604 1 34,437 12 

Central America/Southern Mexico-CA/OR/ 

WA (Central America DPS).

585 0 b 4,095 0 

Mainland Mexico—CA/OR/WA (Mexico 

DPS).

669 1 b 4,683 7 

a Combined, takes from the Central America/Southern Mexico- CA/OR/WA stock and the Mainland Mexico CA/OR/WA stock are equal to takes 

of the CA/OR/WA stock authorized in the 2020 HSTT final rule. b Unlike other species and stocks, for the Central America/Southern Mexico-CA/OR/WA stock and Mainland Mexico-CA/OR/WA stock, NMFS 

estimated the 7-year take by Level B harassment by multiplying the annual estimated take by seven. However, between the two stocks, NMFS 

does not anticipate that the total number of takes by Level B harassment across all 7 years would exceed the 7,962 takes by Level B harassment from training activities that were authorized for the CA/OR/WA stock of humpback whales in the 2020 HSTT final rule. 

Estimated Harassment Take From 

Testing Activities 

For testing activities, table 12 of the 

2020 HSTT final rule summarizes the 

Navy’s take estimate and request in the 

2019 Navy application and the 

maximum amount and type of Level A 

harassment and Level B harassment that 

NMFS concurred is reasonably expected 

to occur by species or stock and 

authorized in the 2020 HSTT LOA. In 

the 2022 Navy application, the Navy 

requested no change to this authorized 

take. For the estimated 7-year total 

amount and type of Level A harassment 

and Level B harassment, see table 12 of 

the 2020 HSTT final rule. For the 

estimated amount and type of Level A 

harassment and Level B harassment 

annually, see table 42 in the 2018 HSTT 

final rule. Note that take by Level B 

harassment includes both behavioral 

disturbance and TTS. Navy Figures 6– 

12 through 6–50 in section 6 of the 2017 

Navy application illustrate the 

comparative amounts of TTS and 

behavioral disturbance for each species 

annually, noting that if a modeled 

marine mammal was ‘‘taken’’ through 

exposure to both TTS and behavioral 

disturbance in the model, it was 

recorded as a TTS. 

TABLE 3—HUMPBACK WHALE TAKE FROM ACOUSTIC AND EXPLOSIVE EFFECTS FOR ALL TESTING ACTIVITIES IN THE

HSTT STUDY AREA

Species Stock 

Annual 7-Year total 

Level B 

harassment 

Level A 

harassment 

Level B 

harassment 

Level A 

harassment 

Humpback whale a ................ Hawaii ........................................................... 3,522 2 23,750 19 

Central America/Southern Mexico—CA/OR/ 

WA.

291 0 b 2,037 0 

Mainland Mexico—CA/OR/WA .................... 449 0 b 3,143 0 

a Combined, takes from the Central America/Southern Mexico-CA/OR/WA stock and the Mainland Mexico CA/OR/WA stock are equal to takes 

of the CA/OR/WA stock authorized in the 2020 HSTT final rule. b Unlike other species and stocks, for the Central America/Southern Mexico-CA/OR/WA stock and Mainland Mexico-CA/OR/WA stock, NMFS 

estimated the 7-year take by Level B harassment by multiplying the annual estimated take by seven. However, between the two stocks, NMFS 

does not anticipate that the total number of takes by Level B harassment across all 7 years would exceed the 4,961 takes by Level B harassment from testing activities that were authorized for the CA/OR/WA stock of humpback whales in the 2020 HSTT final rule. 

Estimated Take From Vessel Strikes and 

Explosives by Serious Injury or Mortality 

Vessel Strike 

Vessel strikes from commercial, 

recreational, and military vessels are 

known to affect large whales and have 

resulted in serious injury and fatalities 

to cetaceans (Abramson et al. 2011; 

Berman-Kowalewski et al. 2010; 

Calambokidis, 2012; Douglas et al. 2008; 

Laggner, 2009; Lammers et al. 2003; Van 

der Hoop et al. 2012; Van der Hoop et 

al. 2013; Crum et al. 2019). Records of 

collisions date back to the early 17th 

century, and the worldwide number of 

collisions appears to have increased 

steadily during recent decades (Laist et 

al. 2001; Ritter 2012) due to increases in 

the number and speed of large vessels, 

increased reporting of strikes, and 

increased abundance of some large 

whales (Ransome et al. 2021), among 

other factors. 

Numerous studies of interactions 

between surface vessels and marine 

mammals have demonstrated that freeranging marine mammals often, but not 

always (e.g., McKenna et al. 2015; 

Smultea et al. 2022; Szesciorka et al. 

2019), engage in avoidance behavior 

when surface vessels move toward 

them. It is not clear whether these 

responses are caused by the physical 

presence of a surface vessel, the 

underwater noise generated by the 

vessel, or an interaction between the 

two (Amaral and Carlson, 2005; Au and 

Green, 2000; Bain et al. 2006; Bauer 

1986; Bejder et al. 1999; Bejder and 

Lusseau, 2008; Bejder et al. 2009; Bryant 

et al. 1984; Corkeron, 1995; Erbe, 2002; 

Fe ́lix, 2001; Goodwin and Cotton, 2004; 

Lemon et al. 2006; Lusseau, 2003; 

Lusseau, 2006; Magalhaes et al. 2002; 

Nowacek et al. 2001; Richter et al. 2003; 

Scheidat et al. 2004; Simmonds, 2005; 

Watkins, 1986; Williams et al. 2002; 

Wursig et al. 1998). Several authors 

suggest that the noise generated during 

vessel movement is probably an 

important factor (Blane and Jaakson, 

1994; Evans et al. 1992; Evans et al. 

1994). Water disturbance may also be a 

factor. These studies suggest that the 

behavioral responses of marine 

mammals to surface vessels are similar 

to their behavioral responses to 


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predators. Avoidance behavior is 

expected to be even stronger in the 

subset of instances during which the 

Navy is conducting training or testing 

activities using active sonar or 

explosives. 

The marine mammals most vulnerable 

to vessel strikes are those that spend 

extended periods of time at the surface 

to restore oxygen levels within their 

tissues after deep dives (e.g., sperm 

whales). In addition, some baleen 

whales seem generally unresponsive to 

vessel sound, making them more 

susceptible to vessel collisions 

(Nowacek et al. 2004). These species are 

primarily large, slow-moving whales. 

Some researchers have suggested the 

relative risk of a vessel strike can be 

assessed as a function of animal density 

and the magnitude of vessel traffic (e.g., 

Fonnesbeck et al. 2008; Vanderlaan et 

al. 2008). Differences among vessel 

types also influence the probability of a 

vessel strike. The ability of any ship to 

detect a marine mammal and avoid a 

collision depends on a variety of factors, 

including environmental conditions, 

ship design, size, speed, and ability and 

number of personnel observing, as well 

as the behavior of the animal. Vessel 

speed, size, and mass are all important 

factors in determining if injury or death 

of a marine mammal is likely due to a 

vessel strike. For large vessels, speed 

and angle of approach can influence the 

severity of a strike. For example, 

Vanderlaan and Taggart (2007) found 

that between vessel speeds of 8.6 and 15 

kn (15.9 and 27.8 km per hour), the 

probability that a vessel strike is lethal 

increases from 0.21 to 0.79. Large 

whales also do not have to be at the 

water’s surface to be struck. Silber et al. 

(2010) found when a whale is below the 

surface (about one to two times the 

vessel draft), there is likely to be a 

pronounced propeller suction effect. 

This suction effect may draw the whale 

into the hull of the ship, increasing the 

probability of propeller strikes. 

There are some key differences 

between the operation of military and 

non-military vessels, which make the 

likelihood of a military vessel striking a 

whale lower than some other vessels 

(e.g., commercial merchant vessels). Key 

differences include: 

• Many military ships have their 

bridges positioned closer to the bow, 

offering better visibility ahead of the 

ship (compared to a commercial 

merchant vessel); 

• There are often aircraft associated 

with the training or testing activity 

(which can serve as Lookouts), which 

can more readily detect cetaceans in the 

vicinity of a vessel or ahead of a vessel’s 

present course before crew on the vessel 

would be able to detect them; 

• Military ships are generally more 

maneuverable than commercial 

merchant vessels, and if cetaceans are 

spotted in the path of the ship, could be 

capable of changing course more 

quickly; 

• The crew size on military vessels is 

generally larger than merchant ships, 

allowing for stationing more trained 

Lookouts on the bridge. At all times 

when vessels are underway, trained 

Lookouts and bridge navigation teams 

are used to detect objects on the surface 

of the water ahead of the ship, including 

cetaceans. Additional Lookouts, beyond 

those already stationed on the bridge 

and on navigation teams, are positioned 

as Lookouts during some training 

events; and 

• When submerged, submarines are 

generally slow moving (to avoid 

detection), and therefore, marine 

mammals at depth with a submarine are 

likely able to avoid collision with the 

submarine. When a submarine is 

transiting on the surface, there are 

Lookouts serving the same function as 

they do on surface ships. 

Vessel strike to marine mammals is 

not associated with any specific training 

or testing activity but is rather a limited 

and sporadic, but possible, accidental 

result of Navy vessel movement within 

the HSTT Study Area or while in 

transit. 

In 2009, the Navy began 

implementing additional mitigation 

measures to further reduce the 

likelihood of vessel strikes. Prior to the 

recent strikes in 2021 and 2023, there 

were two recorded U.S. Navy vessel 

strikes of large whales in the HSTT 

Study Area between 2009 and April 

2021, a period of approximately 12 

years. 

Since 2021 there have been five 

documented strikes of large whales in 

SOCAL by naval vessels, three by the 

U.S. Navy and two by the Royal 

Australian Navy. As stated previously, 

the U.S. Navy struck a large whale in 

waters off Southern California in May 

2023. Based on available photos and 

video, NMFS and the Navy have 

determined this whale was either a fin 

whale or sei whale. The U.S. Navy 

struck two unidentified large whales 

during the months of June and July 

2021, and prior to that, on May 7, 2021, 

the Royal Australian Navy HMAS 

Sydney, a 147.5 m (161.3 yd) Hobart 

Class Destroyer, struck and killed two 

fin whales (a mother and her calf) while 

operating within SOCAL. In the case of 

the Royal Australian Navy strike, the 

carcasses were first sighted under the 

bow of the vessel while it was 

approaching the Naval Base in San 

Diego. The whales had been pinned to 

a sonar dome in the front of the vessel 

due to the force of water as the ship was 

underway. Based on interviews with 

HMAS Sydney personnel, the most 

likely time of impact with the two 

whales would have been around 6:25 

a.m. when the vessel was located near 

Cortes Bank, and visibility was poor. 

The reported vessel speed at the 

estimated time of strike was 9 kn (16.7 

km per hour). One minute before the 

estimated strike time a lookout reported 

whales off the starboard bow. The 

officer on-watch verbally acknowledged 

the report, slowed speed, and visually 

tracked the whales passing clear down 

the starboard side until they were clear 

of the ship. The morning of the strike, 

the HMAS Sydney was getting into 

position to participate in a U.S. Navyled exercise later that day. Of note, 

throughout the remainder of the day 

visibility was poor and the vessel had 

implemented mitigation measures in 

multiple instances due to whale 

occurrence. In addition to being the 

only documented occurrence of a 

foreign military vessel strike of a large 

whale within the HSTT Study Area, the 

HMAS Sydney vessel strike was also 

somewhat unique, as compared to other 

reported military vessel strikes, in that 

two whales were apparently struck at 

one time, and both remained pinned to 

the front of the vessel until the vessel 

approached the port. 

On June 29, 2021, a U.S. Navy cruiser 

struck an unknown whale species 

approximately 95 nmi west of San 

Diego. The ship was returning from 

Hawaii, heading to a rendezvous with a 

fuel replenishment vessel (oiler) for an 

Underway Replenishment. Off-duty 

sailors noticed a group of whales 

approaching the ship from the port 

quarter (i.e., left rear of the ship), an area 

unique to cruisers with some equipment 

structures blocking close aboard sight. 

The first indication of a whale within 

the 500-yd mitigation zone immediately 

prior to the strike was when an off-duty 

sailor on the flight deck witnessed the 

whale briefly surface on the aft port 

quarter before diving. Shortly after this 

occurred blood was noticed in the wake, 

and a floating whale body was 

eventually observed behind the ship. 

The ship’s speed was 25 kn (46.3 km per 

hour) at the estimated time the strike 

occurred. The Navy also noted that, on 

the morning before the strike occurred, 

the ship had maneuvered several times 

to avoid whale blows beyond the 500- 

yd (457.2 m) mitigation zone, closer to 

1,000 yd (914.4 m). 

On July 11, 2021, a U.S. Navy cruiser 

struck an unknown whale species 


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approximately 90 nmi (166.7 km) southsouthwest of San Diego. The vessel was 

a participant in a MTE (Large Integrated 

Anti-Submarine Warfare—Composite 

Unit Training Exercise) within the 

SOCAL portion of the action area. The 

vessel was maneuvering for pending 

flight operations to receive an inbound 

helicopter. At 2:27 p.m., the starboard 

lookout sighted what they believed to be 

a whale crossing immediately under the 

vessel’s bow. The conning officer 

attempted to maneuver the vessel by 

turning to port but internal 

watchstanders subsequently felt the 

ship shudder aft. The vessel’s combat 

center observed a red slick 600 yd 

(548.6 m) astern on a flight deck camera 

and a brief surfacing of the whale itself, 

but no carcass was observed. There had 

not been any sightings of large whales 

off the bow leading up to the incident. 

Although the ship was traveling at 25– 

30 kn (46.3–55.6 km per hour) one hour 

before the estimated strike time, at ten 

minutes before, the vessel changed 

course and reduced its speed to 17 kn 

(31.5 km per hour). These 2021 

incidents were the first known U.S. 

Navy vessel strikes in the HSTT Study 

Area since 2009. 

On May 20, 2023, a U.S. Navy aircraft 

carrier was at sea conducting 

independent, unit-level flight training 

for the embarked airwing approximately 

70 nmi west of San Diego. Training 

exercises concluded for the day at 

approximately 7:44 p.m. local time. 

Navy personnel discovered a whale 

impinged on the bow of the vessel at 

approximately 8:00 p.m. local time. The 

vessel was traveling at approximately 5 

kn and had recently made a turn to reset 

position for the evening when the Navy 

personnel discovered the whale. Navy 

personnel captured video and photos of 

the carcass, and based on those images, 

NMFS and the Navy have determined 

this whale was either a fin whale or sei 

whale; the two species are very similar 

morphologically and are difficult to 

distinguish from one another at sea. 

Navy personnel stopped the vessel to 

allow lack of momentum to dislodge the 

carcass from the bow, and based on lack 

of further observations after the carcass 

dislodged, it is believed to have sunk 

around 9:30 p.m. local time. Navy 

personnel on board the vessel reported 

that they did not feel an impact from 

striking the whale. Prior to the strike, 

between 6:45 p.m. and 7:45 p.m., the 

forward Lookouts on the vessel 

observed two whales crossing the 

vessel’s bow but did not provide a 

distance between the vessel and the 

whales. One Lookout reported seeing 

the blow and the other reported seeing 

‘humps’ (presumably the dorsal of the 

animal). Both whales were sighted past 

the ship’s course to the northwest. 

Within the same time window, one of 

the aft Lookouts observed a single whale 

swimming parallel to the ship and soon 

passed astern of the ship. During the 

same time, independent of the sightings 

and for general movement reasons, the 

ship changed speed from 17 knots to 10 

knots at 7:22 p.m. 

For the same reasons listed above 

describing why the likelihood of a 

military vessel striking a whale is lower 

than that of some other vessels striking 

whales, it is also highly unlikely that a 

Navy vessel would strike a whale, 

dolphin, porpoise, or pinniped without 

detecting it. Specifically, Navy ships 

have Lookouts, including on the 

forward part of the ship that can 

visually detect a hit animal in the event 

ship personnel do not feel the strike 

(which has occurred). Accordingly, 

NMFS is confident that the Navy’s 

reported strikes are accurate and 

appropriate for use in the analysis. 

Navy’s strict internal procedures and 

mitigation requirements include 

reporting of any vessel strikes of marine 

mammals, and the Navy’s discipline, 

extensive training (not only for 

detecting marine mammals, but for 

detecting and reporting any potential 

navigational obstruction), and strict 

chain of command give NMFS a high 

level of confidence that all strikes 

actually get reported. 

As noted above, the 2021 Royal 

Australian Navy vessel strikes were first 

observed when the vessel came to port 

at Naval Base San Diego. However, such 

a scenario is unlikely on a U.S. Navy 

vessel. While U.S. Navy cannot 

speculate on the configurations of other 

ships bows and even sonar dome 

specifications (that may be at the bow), 

the Navy believes it would be 

implausible for a marine mammal to 

become lodged on the sonar dome of a 

U.S. Navy ship and remain undetected 

due to a technological standard 

operating procedure. Sonar domes on 

U.S. Navy ships have a pressurized 

rubber window that maintains 150 

pound-force per square inch (PSI) 

through the ship’s fire main. If anything 

affects the pressure, an alarm sounds in 

the sonar control room. In the event of 

a whale strike in that location, this 

alarm would alert personnel that 

something hit the sonar dome. Further, 

the shape, hydrodynamic design, 

construction using a non-abrasive 

material, and regular hull cleaning 

procedures to remove barnacles and 

other growth on U.S. Navy ships also 

make it unlikely that a whale would 

become lodged and remain undetected 

on a U.S. Navy ship’s bow or even sonar 

dome. While in the case of the May 

2023 strike, described above, a whale 

also became lodged on the ship’s bow, 

the aircraft carrier that struck the whale 

does not have active or passive sonar 

capabilities (i.e., no sonar dome), nor 

does it have a bulbous bow, and the 

whale was more quickly discovered by 

Navy personnel. 

In order to better account for the 

accidental nature of vessel strikes to 

large whales in general and the potential 

risk from U.S. Navy vessel movement 

within the HSTT Study Area during the 

remaining period of the HSTT rule in 

particular, the Navy requested the HSTT 

rule be modified to authorize additional 

incidental takes by vessel strike based 

on probabilities derived from a Poisson 

distribution using vessel strike data 

between 2009–2021 in the HSTT Study 

Area (the time period from when 

current mitigations were instituted until 

the Navy conducted the analysis for the 

2022 Navy application), as well as 

historical at-sea days in the HSTT Study 

Area from 2009–2015 and estimated atsea days for the period from 2016 to 

2025 covered by the current regulations. 

This distribution predicted the 

probabilities of a specific number of 

strikes (n=0, 1, 2, etc.) over the 

remaining period of the regulations at 

the time of the Navy’s analysis (2022– 

2025). 

The Navy used the two fin whale 

strikes (2009) and two unidentified large 

whale strikes (2021) in their 

calculations to determine the number of 

strikes likely to result from its activities 

over the remaining 3 years of the rule 

(2023–2025, although worldwide strike 

information from all Navy activities and 

other sources was used to inform the 

species that may be struck). The Navy 

evaluated data beginning in 2009 as that 

was the start of the Navy’s Marine 

Species Awareness Training and 

adoption of additional mitigation 

measures to address vessel strike, which 

will remain in place along with 

additional and modified mitigation 

measures during the 7 years of this 

rulemaking. From this analysis, the 

Navy concluded that there was a 27 

percent chance that zero whales would 

be struck by Navy vessels over the 

remaining period of the rule (which, at 

the time that the application was 

submitted, was 4 years), and a 35, 23, 

and 10 percent chance that one, two, or 

three whales, respectively, would be 

struck over the remaining 4 years of the 

rule. Therefore, the Navy estimated that 

there was some probability that the 

Navy could strike, and take by serious 

injury or mortality, up to three large 

whales incidental to training and testing 


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activities within the HSTT Study Area 

over what would have been the 

remaining 4 years of the current 

authorization, and the Navy requested 

authorization of two additional takes of 

large whales by serious injury or 

mortality by vessel strike, beyond the 

three takes authorized by the 2020 

HSTT final rule (85 FR 41780, July 10, 

2020). 

NMFS has since updated this analysis 

to reflect that an additional strike of an 

unidentified large whale occurred in 

May 2023 (either a fin whale or sei 

whale, as stated above) and that 

additional time has passed since the 

Navy submitted the 2022 Navy 

application. Based on further 

discussions with the Navy, NMFS has 

also updated the way it calculated at-sea 

days. This is a different manner of 

calculating at-sea days for the purposes 

of the strike analysis rather than a 

change in Navy’s activity levels. For 

2010–2015, the at-sea days used in 

NMFS’ calculation reflected historic atsea days in the HSTT action area based 

on positional vessel data records (Mintz, 

2016). While the actual annual at-sea 

days from 2016-present are currently 

classified, NMFS’ updated calculation 

reflects an extrapolation of the 2010– 

2015 at-sea days (using the formula y = 

¥64x + 131555) to estimate the number 

of at-sea days in 2016 (Navy, 2022). The 

number of at-sea days derived for 2016 

was 2,056 at-sea days, which reflects the 

downward trend in HSTT vessel activity 

from 2010–2015. Since we do not have 

sufficient information to say whether or 

not this downward trend continued for 

the years 2017–2022, we conservatively 

estimate the average over these years 

was the same as the 2016 extrapolated 

value of 2,056 at-sea days. This analysis 

only included at-sea days for Navy 

warships greater than 65 feet (i.e., 

destroyers are the smallest ship class 

included). Navy vessels smaller than 65 

feet have never reported a whale strike 

in the Pacific, and therefore, we 

consider it unlikely that this would 

occur in the remaining 2.5 years of the 

regulations. 

TABLE 4—HSTT 2009 THROUGH MID-2023 AT-SEA DAYS USED FOR THE VESSEL STRIKE PROBABILITY CALCULATION

Year At-sea days Derivation 

2009 .......................................... 4,233 Estimated average based on 2010–2015 data. 

2010 .......................................... 5,207 Based on positional vessel data. 

2011 .......................................... 4,483 Based on positional vessel data. 

2012 .......................................... 4,081 Based on positional vessel data. 

2013 .......................................... 4,041 Based on positional vessel data. 

2014 .......................................... 4,272 Based on positional vessel data. 

2015 .......................................... 3,311 Based on positional vessel data. 

2016 .......................................... 2,056 Extrapolated from 2010–2015 regression. 

2017 .......................................... 2,056 Extrapolated from 2010–2015 regression. 

2018 .......................................... 2,056 Extrapolated from 2010–2015 regression. 

2019 .......................................... 2,056 Extrapolated from 2010–2015 regression. 

2020 .......................................... 2,056 Extrapolated from 2010–2015 regression. 

2021 .......................................... 2,056 Extrapolated from 2010–2015 regression. 

2022 .......................................... 2,056 Extrapolated from 2010–2015 regression. 

2023 (first half of year) ............. 1,028 Extrapolated from 2010–2015 regression, then reduced by half. 

2009–Mid-2023 total .......... 45,048 

NMFS then used the number of past 

Navy vessel strikes and the at-sea days 

to calculate a vessel strike rate for 2009 

through mid-2023. The estimated total 

number of Navy at-sea days (for vessels 

greater than 65 feet) for 2009 through 

mid-2023 was 45,048 days. Dividing the 

five known strikes during that period by 

the at-sea days (i.e., 5 strikes/45,048 atsea days) results in a strike rate of 

0.000111 strikes per day. 

As described above, NMFS 

conservatively assumed that the average 

number of at-sea days from mid-2023 

through 2025 (the remaining period of 

the regulations) will be the same as the 

2016 extrapolated value of 2,056. 

Therefore, the estimated at-sea days 

within the action area for the period 

from mid-2023 through 2025 is 5,140 

days. NMFS multiplied the historic 

daily strike rate by the estimated at-sea 

days from mid-2023 through 2025 

(0.000111 strikes per day × 5,140 days) 

to estimate the number of whale strikes 

anticipated during that period. This 

calculation predicts an estimated 0.57 

strikes over the remaining 2.5 years of 

the regulations (mid-2023 through 

2025). 

As explained above, according to the 

U.S. Navy, the May 2021 vessel strike of 

two fin whales by a Royal Australian 

Navy vessel did not occur while that 

vessel was participating in a U.S. Navyled training exercise, and the strike of 

those two fin whales is not included in 

the estimated take by vessel strike 

calculation. Instead, as noted below, 

NMFS considered the 2021 vessel strike 

by the Royal Australian Navy along with 

other strike information when 

determining which species could be 

among the estimated large whales 

struck. 

NMFS used a Poisson distribution to 

derive the probabilities of a specific 

number of strikes (n=0, 1, 2, etc.) from 

mid-2023 through 2025, given the 

estimated 0.57 strikes during that 

period. NMFS’ probability analysis 

concluded that there is a 57 percent 

chance that zero whales would be struck 

by U.S. Navy vessels over the remaining 

period of the rule (mid-2023 through 

2025), and a 32, 9, and 2 percent chance 

that one, two, or three whales, 

respectively, would be struck over the 

remaining 2.5 years of the regulations. 

Further, there is an estimated 11 percent 

chance that the Navy would strike more 

than one large whale over the remaining 

period of the rule (mid-2023 through 

2025). We have assessed these 

probabilities and determined that the 

strike up to two large whales could 

occur over the remaining duration of the 

regulations, for a total of five takes by 

serious injury or mortality of large 

whales by vessel strike total over the 7- 

year duration of the regulations (three 

takes authorized in the 2020 HSTT final 

rule (85 FR 41780, July 10, 2020) which 

have occurred, plus two additional 

takes). 

In addition to the reasons listed above 

that make it unlikely that the Navy will 

hit a large whale (more maneuverable 

ships, larger crew, etc.), vessel strike of 

dolphins, small whales, porpoises, and 

pinnipeds is considered very unlikely. 

Dating back more than 20 years and for 

as long as it has kept records, the Navy 

has no records of any small whales or 


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pinnipeds being struck by a vessel as a 

result of Navy activities. Over the same 

time period, NMFS and the Navy have 

only one record of a dolphin being 

struck by a vessel as a result of Navy 

activities. The dolphin was accidentally 

struck by a Navy small boat in fall 2021 

in Saint Andrew’s Pass, Florida. The 

smaller size and maneuverability of 

dolphins, small whales, and pinnipeds 

generally make such strikes very 

unlikely. Other than this one reported 

strike of a dolphin in 2021, NMFS has 

never received any reports from other 

LOA or Incidental Harassment 

Authorization holders indicating that 

these species have been struck by 

vessels. In addition, worldwide vessel 

strike records show little evidence of 

strikes of these groups from the 

shipping sector and larger vessels, and 

the majority of the Navy’s activities 

involving faster-moving vessels (that 

could be considered more likely to hit 

a marine mammal) are located in 

offshore areas where smaller delphinid, 

porpoise, and pinniped densities are 

lower. Based on this information, NMFS 

concurs with the Navy’s assessment and 

recognizes the potential for (and is 

proposing for authorization) incidental 

take by vessel strike of large whales only 

(i.e., no dolphins, small whales, 

porpoises, or pinnipeds) over the course 

of the 7-year regulations from training 

and testing activities as discussed 

below. 

Next, after determining that take of up 

to five large whales could occur, NMFS 

considered which species could be 

among the five large whales struck. As 

noted in the 2018 HSTT proposed and 

final rules, the 2019 HSTT proposed 

rule, and 2020 HSTT final rule, in the 

2017 Navy rulemaking/LOA 

application, the Navy initially 

considered a weight of evidence 

approach that considered relative 

abundance, historical strike data over 

many years, and the overlap of Navy 

activities with the stock distribution in 

their request. NMFS updated this 

analysis to consider several factors, in 

addition to the overlap of Navy 

activities with stock distribution: (1) 

The relative likelihood of striking one 

stock versus another based on available 

strike data from all vessel types as 

denoted in the Carretta et al. (2021; 

referenced in the Pacific SARs), the 

Pacific and Alaska SARs (Carretta et al. 

2023 and Young et al. 2023), and 

unpublished NMFS vessel strike data 

for 2019–2021; and (2) whether the 

Navy has ever struck an individual from 

a particular species or stock in the 

HSTT Study Area, and if so, how many 

times. NMFS did not consider relative 

abundance, as was considered in 

previous analyses, given that the 

relative abundance of a stock does not 

necessarily inform its occurrence in a 

specific area. Further, NMFS did not 

consider the historical strike data from 

older years (prior to 2015), given that 

more recent data is more relevant to 

determining occurrence of, and strike 

risk to, various stocks. NMFS updated 

the analysis with NMFS’ vessel strike 

probability analysis for the remaining 

2.5 years of the rule and included new/ 

updated vessel strike data from the 

SARs and NMFS records for California 

and Hawaii. 

To address number (1) above, for 

SOCAL, NMFS compiled information 

from Carretta et al. (2021) and 

unpublished NMFS vessel strike data 

for 2020–2021 for California on known 

annual rates of large whale serious 

injury or mortality from vessel 

collisions (this data includes the strike 

of 2 fin whales by the Royal Australian 

Navy in 2021, but does not include 

Navy strikes in 2021 and 2023 because 

the species struck is not known). Use of 

Carretta et al. (2021) rather than the 

Pacific SAR allows NMFS to separate 

strikes that occurred in California from 

strikes to the same stocks that occurred 

in other locations. For the HRC, NMFS 

compiled information from the Pacific 

and Alaska SARs and unpublished 

NMFS vessel strike data for 2019–2021 

for Hawaii on known annual rates of 

large whale serious injury or mortality 

from vessel collisions. The annual rates 

of large whale serious injury or 

mortality from vessel collisions from 

those sources help inform the relative 

susceptibility of large whale species to 

vessel strike in SOCAL and the HRC; 

therefore, we considered only reported 

strikes where the species struck was 

identified with sufficient certainty (i.e., 

‘‘known strikes’’). Additionally, the M/ 

SI in the 2022 SAR considers modeled 

takes for some, but not most species and 

stocks (i.e., M/SI for humpback whale 

includes modeled takes from Rockwood 

et al. (2017)). Using known strike data 

for all species and stocks allows us to 

consider-like metrics for this 

comparative analysis. (Note we rely on 

the M/SI estimates from the 2022 SAR 

in our Negligible Impact Analysis. We 

also consider modeled takes of species 

from Rockwood et al. (2017) in table 7). 

We summed the annual rates of serious 

injury or mortality from vessel 

collisions in California and Hawaii as 

calculated above and then divided each 

species’ annual rate by this sum to get 

the proportion of strikes for each 

species/stock (table 5). 

TABLE 5—ANNUAL RATES OF SERIOUS INJURY AND MORTALITY FROM VESSEL STRIKE AND PERCENTAGE OF TOTAL

STRIKES BY SPECIES IN SOCAL AND THE HRC 

ESA status Species Stock 

SOCAL 

annual known 

strikes 

(2015–2021) 

HRC 

annual known 

strikes 

(2015–2021) 

Percentage 

of total 

annual strikes 

Listed .............. Blue whale .......................... Central North Pacific ................................. ........................ 0 0.0 

Eastern North Pacific ................................ 0.57 ........................ 6.5 

Fin whale a .......................... California, Oregon, & Washington ............ 1.57 ........................ 17.8 

Hawaiian .................................................... ........................ 0 0.0 

Humpback whale ................ Central America/Southern Mexico-CA/OR/ 

WA (Central America DPS).

b 1 ........................ 11.3 

Mainland Mexico-CA/OR/WA (Mexico 

DPS).

Sei whale ............................ Eastern North Pacific ................................ 0.14 ........................ 1.6 

Hawaiian .................................................... ........................ 0 0.0 

Gray whale .......................... Western North Pacific ............................... 0 ........................ 0.0 

Sperm whale ....................... California, Oregon, & Washington ............ 0 ........................ 0.0 

Hawaiian .................................................... ........................ 0 0.0 

Not listed ........ Gray whale .......................... Eastern North Pacific ................................ 2.14 ........................ 24.3 

Bryde’s whale ..................... ETP stock .................................................. 0 ........................ 0.0 

Hawaiian .................................................... ........................ 0 0.0 

Minke whale ........................ CA/OR/WA ................................................ 0 ........................ 0.0 


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TABLE 5—ANNUAL RATES OF SERIOUS INJURY AND MORTALITY FROM VESSEL STRIKE AND PERCENTAGE OF TOTAL

STRIKES BY SPECIES IN SOCAL AND THE HRC—Continued 

ESA status Species Stock 

SOCAL 

annual known 

strikes 

(2015–2021) 

HRC 

annual known 

strikes 

(2015–2021) 

Percentage 

of total 

annual strikes 

Hawaiian .................................................... ........................ 0 0.0 

Humpback whale ................ Hawaii (Hawaii DPS) ................................. ........................ 3.4 38.5 

Total ........ ............................................. .................................................................... 8.82 ............................

aThis includes the two fin whales struck by the Royal Australian Navy in May 2021. 

bThis strike occurred to an individual of the CA/OR/WA stock under the previous stock structure. As such, in its analysis, NMFS assumed that 

this strike could have been of either stock. 

To inform the likelihood of striking a 

particular species of large whale, we 

multiplied the percent of total annual 

strikes for a given species in table 5, by 

the total percent likelihood of striking at 

least one whale during the remaining 

period of the rule (2023–2025; i.e., 43 

percent, as described by the probability 

analysis above). We also calculated the 

percent likelihood of striking a 

particular species of large whale twice 

during the remaining period of the rule 

by squaring the value estimated for the 

probability of striking a particular 

species of whale once (i.e., to calculate 

the probability of an event occurring 

twice, multiply the probability of the 

first event by the second). The results of 

these calculations are reflected in the 

last two columns of table 6. We note 

that these probabilities vary from year to 

year as the average annual mortality 

changes depending on the specific range 

of time considered; however, over the 

years and through updated data in the 

SARs and unpublished NMFS records, 

stocks tend to consistently maintain a 

relatively higher or relatively lower 

likelihood of being struck. 

TABLE 6—PERCENT LIKELIHOOD OF STRIKING EACH STOCK ONE OR TWO TIMES OVER 2.5 YEARS AND TOTAL KNOWN

U.S. NAVY STRIKES IN THE HSTT STUDY AREA

Species Stock Total known U.S. Navy strikes in 

HSTT study area 

Percent 

likelihood of 

1 strike over 

2.5 years 

Percent 

likelihood of 

2 strikes over 

2.5 years 

Blue whale ...................................... Central North Pacific ...................... 0 ..................................................... 0.00 0.00 

Eastern North Pacific ..................... 1 in SOCAL (2004) ........................ 2.81 0.08 

Fin whale ........................................ CA/OR/WA ..................................... 3 in SOCAL (2009, 2023 a) ............ b 7.74 b 0.60 

Hawaiian ........................................ 0 ..................................................... 0.00 0.00 

Humpback whale ............................ Central America/Southern MexicoCA/OR/WA (Central America 

DPS).

0 ..................................................... 4.93 0.24 

Mainland Mexico-CA/OR/WA 

(Mexico DPS).

Sei whale ........................................ Eastern North Pacific ..................... 1 in SOCAL (2023 a) ...................... 0.69 0.00 

Hawaiian ........................................ 0 ..................................................... 0.00 0.00 

Gray whale ..................................... Western North Pacific .................... 0 ..................................................... 0.00 0.00 

Sperm whale ................................... CA/OR/WA ..................................... 0.00 ................................................ 0.00 

Hawaiian ........................................ 1 in HRC (2007) ............................. 0.00 0.00 

Gray whale ..................................... Eastern North Pacific ..................... 3 in SOCAL (1993, 1998) .............. 10.55 1.11 

Bryde’s whale ................................. ETP stock ....................................... 0 ..................................................... 0.00 0.00 

Hawaiian ........................................ 0 ..................................................... 0.00 0.00 

Minke whale .................................... CA/OR/WA ..................................... 0 ..................................................... 0.00 0.00 

Hawaii ............................................ 0 ..................................................... 0.00 0.00 

Humpback whale ............................ Hawaii (Hawaii DPS) ..................... 2 in HRC (2003) ............................. 16.76 2.81 

aBased on available photos and video, NMFS and the Navy have determined the May 2023 strike was of either a fin whale or sei whale. In 

the analysis herein, NMFS has assumed that this strike could have been of either species, and has therefore, accounted for it in both the fin 

whale and sei whale strike totals. Given that we are unable to identify the species of the whales struck by the U.S. Navy in 2021, NMFS did not 

include the two 2021 strikes in this part of the analysis. bThis includes the two fin whales struck by the Royal Australian Navy in May 2021. 

The percent likelihood calculated as 

described above are then considered in 

combination with the information 

indicating the known species that the 

Navy has hit in the HSTT Study Area 

since 1991 (since they started tracking 

consistently; table 6). We note that for 

the lethal take of species specifically 

denoted in table 7 below, 47 percent of 

those struck by the Navy (8 of 17 in the 

Pacific) remained unidentified 

(including the May 2023 strike, which 

as stated above, NMFS and the Navy 

have determined was of either a fin 

whale or sei whale). However, given the 

information on known stocks struck, the 

analysis below remains appropriate. We 

also note that Rockwood et al. (2017) 

modeled the likelihood of vessel strike 

of blue whales, fin whales, and 

humpback whales on the U.S. West 

Coast (discussed in more detail in the 

Serious Injury or Mortality subsection of 

the Preliminary Analysis and Negligible 

Impact Determination section), and 

those numbers help inform the relative 

likelihood that the Navy could hit those 

stocks. 

For each indicated stock, table 7 

includes the percent likelihood of 


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striking an individual whale from a 

particular stock during the remaining 

2.5 years of the rule once based on SAR 

data, Carretta et al. (2021), and 

unpublished NMFS vessel strike data 

from 2019–2021 for Hawaii; total strikes 

from Navy vessels in the HSTT Study 

Area, and modeled vessel strikes from 

Rockwood et al. (2017). The last column 

indicates the annual mortality proposed 

to be authorized. 

TABLE 7—SUMMARY OF FACTORS CONSIDERED IN DETERMINING THE NUMBER OF INDIVIDUALS IN EACH STOCK

POTENTIALLY STRUCK BY A VESSEL

ESA status Species Stock 

Percent 

likelihood 

of one 

strike over 

2.5 years 

Total known U.S. Navy 

strikes in HSTT study area 

(1993–2009) 

Rockwood 

et al. 2017 

modeled 

vessel 

strikes 1

Annual 

authorized 

take from 

2020 HSTT 

final rule 

Proposed 

annual 

authorized 

take 

Listed ............. Blue whale .......................... Central North Pacific .......... 0.00 0 .......................................... .................... .................... 0 

Eastern North Pacific .......... 2.81 1 in SOCAL (2004) ............. 18 0.14 0.14 

Fin whale ............................ CA/OR/WA .......................... 2 7.74 3 in SOCAL (2009, 2023 3) 43 0.29 0.57 

Hawaii ................................. 0.00 0 .......................................... .................... .................... 0 

Humpback whale 4 .............. Central America/Southern 

Mexico-CA/OR/WA (Central America DPS).

4.93 0 .......................................... 22 0.14 0 

Mainland Mexico-CA/OR/ 

WA (Mexico DPS).

0.14 

Sei whale ............................ Eastern North Pacific .......... 0.69 1 in SOCAL(2023) 3 ............ .................... .................... 0.14 

Hawaii ................................. 0.00 0 .......................................... .................... .................... 0 

Gray whale ......................... Western North Pacific ......... 0.00 0 .......................................... .................... .................... 0 

Sperm whale ....................... CA/OR/WA .......................... 0.00 0 .......................................... .................... .................... 0 

Hawaii ................................. 0.00 1 in HRC (2007) ................. .................... 0.14 0 

Not listed ....... Gray whale ......................... Eastern North Pacific .......... 10.55 3 in SOCAL (1993, 1998) ... .................... 0.29 0.57 

Bryde’s whale ..................... Eastern Tropical Pacific ...... 0.00 0 .......................................... .................... .................... 0 

Hawaii ................................. 0.00 0 .......................................... .................... .................... 0 

Minke whale ........................ CA/OR/WA .......................... 0.00 0 .......................................... .................... .................... 0 

Hawaii ................................. 0.00 0 .......................................... .................... .................... 0 

Humpback whale ................ Hawaii (Hawaii DPS) 5 ........ 16.76 2 in HRC (2003) ................. .................... 0.29 0.29 

1 Rockwood et al. modeled likely annual vessel strikes off the West Coast for these three species only. 2This includes the two fin whales struck by the Royal Australian Navy in May 2021. 

3Based on available photos and video, NMFS and the Navy have determined the May 2023 strike was of either a fin whale or sei whale. In the analysis herein, 

NMFS has assumed that this strike could have been of either species, and has therefore, accounted for it in both the fin whale and sei whale strike totals. 4 In the 2020 HSTT final rule, take of humpback whale by serious injury and mortality by vessel strike in Southern California was attributed to the former CA/OR/WA 

stock and the Mexico DPS. Text explains why takes in SOCAL come from the Mexico DPS, and therefore the Mainland Mexico-CA/OR/WA stock. 5The 2022 final SAR reports vessel strike data for the Hawaii stock of humpback whales in Alaska, Washington, and Hawaii. Only vessel strike data from Hawaii 

was incorporated into our analysis as Alaska and Washington are outside of the HSTT Study Area. 

Accordingly, stocks that have no 

record of ever having been struck by any 

vessel are considered to have a zero 

percent likelihood of being struck by the 

Navy in the 7-year period of the rule. 

Stocks that have never been struck by 

the Navy, have rarely been struck by 

other vessels, and have a low percent 

likelihood based on the historical vessel 

strike calculation are also considered to 

have a zero percent likelihood to be 

struck by the Navy during the 7-year 

rule. We note that while vessel strike 

records have not differentiated between 

Eastern North Pacific and Western 

North Pacific gray whales, given their 

small population size and the 

comparative rarity with which 

individuals from the Western North 

Pacific stock are detected off the U.S. 

West Coast, it is highly unlikely that 

they would be encountered, much less 

struck. This rules out all but seven 

stocks. Further, it is unlikely that the 

Hawaii stock of sperm whale would be 

struck given the zero percent likelihood 

of striking a sperm whale as indicated 

by the quantitative analysis above, the 

fact that the last U.S. Navy strike of a 

Hawaii stock sperm whale was in 2007, 

before the mitigation updates discussed 

above, and that, with the exception of 

humpback whales, vessel strikes (both 

military and non-military) of other large 

whale species in the HRC are extremely 

rare events (Carretta 2021b; Carretta 

2022). (The 2020 HSTT final rule 

authorized 1 take (0.14 annual take) by 

mortality of the Hawaii stock of sperm 

whale.) 

As stated previously, based on 

available photos and video of the whale 

struck by the U.S. Navy in Southern 

California in 2023, NMFS and the Navy 

have determined this whale was either 

a fin whale or sei whale. While the 

species of the two whales struck by the 

U.S. Navy in 2021 are unknown, given 

the following factors, NMFS expects 

these strikes may have been CA/OR/WA 

fin whales or Eastern North Pacific 

(ENP) gray whales, or some combination 

of these two stocks. These species have 

the highest annual rates of mortality/ 

serious injury (M/SI) from vessel 

collision in California (1.57, 2.14, 

respectively, as noted above; which is 

approximately one and a half to two 

times higher than the species with the 

next highest strike rate, humpback 

whale, and approximately two to four 

times higher than the strike rate of blue 

whale). Additionally, gray whale and fin 

whale have the most recorded vessel 

strike incidents by military vessels in 

SOCAL and are the only stocks known 

to have been hit more than one time by 

naval vessels in the SOCAL portion of 

the HSTT Study Area (3 gray whale 

strikes by the U.S. Navy (1993, 1998), 2 

or 3 fin whale strikes by the U.S. Navy 

(2009, potentially 2023), and 2 fin whale 

strikes by the Royal Australian Navy 

(2021)). Further, accounting for 

undocumented vessel strikes, Rockwood 

et al. (2021) estimated that in their study 

area off Southern California from 2012– 

2018, on average 8.9 blue, 4.6 

humpback, and 9.7 fin whales were 

killed by civilian vessel strikes from 

June to November each year. In 

addition, they estimated that, on 

average, 5.7 humpback whales were 

killed by civilian vessel strike from 

January–April per year (Rockwood et al. 

2021). For fin whales in particular, 

model-predicted densities of large 

whales in the Southern California Bight 

from May to July 2021 (the time period 

during which the 2021 strikes of two 

unidentified whales by the U.S. Navy 

occurred) estimated fin whale 

abundance as being nearly an order of 

magnitude higher than either blue or 

humpback whale abundance during this 

time period (Becker et al. 2020; Zickel 


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et al. 2021). Ship-whale encounter 

models for the U.S. West Coast 

Exclusive Economic Zone also indicated 

that vessel strike mortality estimates for 

fin whales were significantly higher 

than for blue whales and humpback 

whales (Rockwood et al. 2017). The 

comparatively higher modeled vessel 

strike rates for fin whales result from 

both the larger population as well as the 

more offshore distribution that overlaps 

significantly with several major 

shipping routes for a much greater 

spatial extent (Rockwood et al. 2017). 

Based on 1,243 visual boat-based 

sightings of 2,638 fin whales from 1991– 

2011, Calambokidis et al. (2015) found 

fin whale concentration areas included 

the San Clemente Basin where the 2021 

Navy vessel strikes occurred (Tanner 

and Cortez Banks area and the shelf 

edge west of San Nicolas Island were 

also reported as fin whale concentration 

areas). There are two different 

populations of fin whales that occur in 

the Southern California Bight: a 

seasonal population, and a population 

that occurs year-round with offshore/ 

inshore movements (Campbell et al. 

2015; Falcone et al. 2022). This would 

likely make fin whales more susceptible 

to vessel strike year-round, as compared 

to other large whale species that may 

occur seasonally within SOCAL. Based 

on all of these factors, there is a 

reasonable likelihood that the CA/OR/ 

WA stock of fin whales or ENP stock of 

gray whales could be struck twice 

during the remaining 2.5 years of the 

rule. Therefore, we propose that, of the 

five total takes by serious injury or 

mortality by vessel strike of large whales 

proposed to be authorized, up to four of 

those takes could be of the CA/OR/WA 

stock of fin whale or the ENP stock of 

gray whale given that the two strikes of 

unidentified large whales in 2021 could 

have been of either stock. Further, 

consistent with the 2020 HSTT final 

rule, we propose that, of the five total 

takes by serious injury or mortality by 

vessel strike of large whales proposed to 

be authorized, up to two of those takes 

could occur in Hawaii, and therefore be 

of individuals of the Hawaii stock of 

humpback whale. 

Based on the information summarized 

in table 7 and the fact that there is the 

potential for up to two large whales to 

be struck over the remaining 2.5 years 

of the rule (five strikes over the full 7- 

year rule period), one individual from 

the Eastern North Pacific stock of blue 

whale, Mainland Mexico-CA/OR/WA 

stock of humpback whale, or Eastern 

North Pacific stock of sei whale could 

be among the two whales struck during 

the remaining effective period of the 

regulations (2023–2025). The total 

strikes of Eastern North Pacific blue 

whales and the percent likelihood of 

striking one based on the historic strike 

calculation above can both be 

considered moderate compared to other 

stocks, and the Navy struck a blue 

whale in 2004 (based on the historic 

strike calculation, the likelihood of 

striking two blue whales is well below 

one percent (table 6)). Therefore, we 

consider it reasonably likely that the 

Navy could strike one individual over 

the course of the 7-year rule, and given 

that we do not expect that the 2023 

strike nor either of the 2021 U.S. Navy 

strikes of unidentified large whales were 

blue whales, we expect that this strike 

could occur during the remaining 2.5 

years of the rule. The total strikes of 

Eastern North Pacific sei whales are low 

compared to other stocks, but NMFS 

and the Navy think it is possible that the 

Navy may have struck a sei whale in 

SOCAL in 2023. Therefore, we consider 

it reasonably likely that the Navy could 

strike a sei whale over the remaining 2.5 

years of the rule. The Navy has not hit 

a humpback whale in the SOCAL 

portion of the HSTT Study Area. 

However, in 2016 a U.S. Coast Guard 

vessel participating in a Navy event 

struck a humpback whale in Hood 

Canal, and as a species, humpbacks 

have a moderate to high number of total 

strikes and percent likelihood of being 

struck. Although the likelihood of 

Central America/Southern Mexico-CA/ 

OR/WA (Central America DPS) or 

Mainland Mexico-CA/OR/WA (Mexico 

DPS) humpback whales being struck by 

any vessel type is moderate to high 

relative to other stocks, the distribution 

of the Mexico DPS versus the Central 

America DPS, as well as the distribution 

of overall vessel strikes inside versus 

outside of the SOCAL area (the majority 

are outside), supports the reasonable 

likelihood that the Navy could strike 

one individual humpback whale from 

the Mainland Mexico-CA/OR/WA stock 

(Mexico DPS) over the 7-year duration 

of the rule, as described below. 

Regarding the likelihood of striking a 

humpback whale from a particular DPS, 

we evaluated the relative abundance of 

each of these DPS in California waters. 

Curtis et al. (2022) estimated the 

abundance of the Central America DPS 

to be 1,496 whales. From Wade et al. 

(2017), about 93 percent (or 1,391 

whales) of these humpbacks that winter 

in Central America will move to 

Oregon/California in the summer 

months. While there is currently no 

abundance estimate for the Mexico DPS, 

an estimated 3,477 whales from the 

Mexico DPS feed off the U.S. West Coast 

(Calambokidis and Barlow 2020; Curtis 

2022). Based on this information, we 

estimate that approximately 30 percent 

of the humpback whales off the coast of 

California may be from the Central 

America DPS with the remaining 70 

percent are expected to be from the 

Mexico DPS. Therefore, we anticipate 

that if a Navy vessel strike of a 

humpback whale were to occur within 

SOCAL, it would likely be from the 

Mexico DPS. Last, Rockwood et al. 

(2017) supports a relative likelihood of 

1:1:2 for striking blue whales, 

humpback whales, and fin whales off 

the U.S West Coast (though as noted 

above, more recent data suggests that 

the relative likelihood of striking a fin 

whale is higher and suggests that the 

two 2021 U.S. Navy vessel strikes of 

unidentified large whales may have 

been fin whales), which, in 

consideration of more recent data also 

supports the proposed authorized take 

included in this rule, which is 1, 1, and 

4, respectively over the 7-year period. 

For these reasons, one lethal take of a 

Mainland Mexico-CA/OR/WA 

humpback whale (Mexico DPS) could 

occur and is proposed for authorization. 

For Hawaii stocks, given that all 

known vessel strikes between 2015 and 

2021 were of humpback whales, we 

anticipate that any vessel strike of a 

large whale in Hawaii would be of the 

Hawaii stock of humpback whale. Given 

that this stock has the highest 

percentage of total annual strikes (38.5 

percent) and a 2.81 percent chance of 

being struck twice over the remaining 

2.5 years (more than twice that of the 

species with the next highest 

percentage, gray whale), NMFS 

proposes to authorize two lethal takes of 

Hawaii humpback whales. 

As described above, the Navy’s 

analysis suggests and NMFS’ analysis 

concurs that the likelihood of vessel 

strikes to the stocks below is 

discountable due to the stocks’ 

relatively low occurrence in the HSTT 

Study Area, particularly in core HSTT 

training and testing subareas, and the 

fact that the stocks have not been struck 

by the Navy and are rarely, if ever, 

recorded struck by other vessels. 

Therefore, NMFS is not proposing to 

authorize lethal take for the following 

stocks: Blue whale (Central North 

Pacific stock), Bryde’s whale (Eastern 

Tropical Pacific stock and Hawaii 

stock), fin whale (Hawaii stock), gray 

whale (Western North Pacific stock), 

humpback whale (Central America/ 

Southern Mexico-CA/OR/WA stock, 

Central America DPS), minke whale 

(CA/OR/WA stock and Hawaii stock), 

sei whale (Hawaii stock), and sperm 


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1Outside of the military readiness context, 

mitigation may also be appropriate to ensure 

compliance with the ‘‘small numbers’’ language in 

MMPA sections 101(a)(5)(A) and (D). 

whale (CA/OR/WA stock and Hawaii 

stock). 

Also of note, while information on 

past Navy vessel strikes can serve as a 

reasonable indicator of future vessel 

strike risk, future conditions may differ 

from the past in ways that could 

influence the likelihood of a large whale 

vessel strike occurring. In general, the 

magnitude of vessel strike risk may be 

increasing over time as many whale 

populations are gradually recovering 

from centuries of commercial whaling 

(Redfern et al. 2020). Increased vessel 

strike risk off California in recent 

decades has been associated with 

increases in the abundance of fin and 

humpback whale populations in the 

North Pacific (Redfern et al. 2020). It has 

also been suggested that the blue whale 

population in the Eastern North Pacific, 

inclusive of the SOCAL portion of the 

action area, is at carrying capacity and 

recovered to pre-whaling levels 

(Monnahan et al. 2014). In addition, the 

magnitude of risk may also be affected 

by shifts in whale distributions over 

time in response to environmental 

factors including climate change, 

marine heatwaves, and associated 

changes in prey distribution. 

Historically, military vessel strikes of 

large whales within the HSTT Study 

Area have been rare events with only 

seven such strikes occurring over the 

past 14 years, five U.S. Navy strikes, and 

two Royal Australian Navy strikes. 

However, the fact that four of these 

strikes occurred within a 3-month 

period (May–July) in 2021, and two 

occurred within a 4-month period 

(February–May) in 2009, suggests that 

military vessel strikes in SOCAL can be 

both highly episodic and clustered. The 

four large whale strikes in 2021 (two 

strikes of unidentified large whales by 

the U.S. Navy and two fin whale strikes 

by the Royal Australian Navy) appear to 

be outliers in the time series of military 

vessel strikes in SOCAL for that period. 

However, particularly in consideration 

of the 2023 U.S. Navy strike, these 

strikes could also represent an early 

indicator of an increased military vessel 

strike risk within SOCAL based on the 

factors discussed above. Results from a 

survey of whale watching vessel 

operators and crew in Southern 

California, combined with remote 

sensing data in the area, suggest that the 

number of large whales may have been 

greater in May through July of 2021 

compared with previous years in certain 

high military vessel traffic and ‘‘core’’ 

use HSTT areas off southern California, 

particularly farther offshore as well as 

closer to shore off San Diego Bay (Zickel 

MJ et al. 2021). 

In conclusion, while take by vessel 

strike across any given year is sporadic, 

based on the information and analysis 

above, including consideration of the 

2021 and 2023 strikes by the U.S. Navy, 

NMFS anticipates no more than five 

takes of large whales by M/SI could 

occur over the 7-year period of the rule. 

Of those five whales over the 7-years, no 

more than four may come from the 

following stocks: gray whale (Eastern 

North Pacific stock) and fin whale (CA/ 

OR/WA stock). No more than two may 

come from the Hawaii stock of 

humpback whales. No more than one 

may come from the following stocks: 

blue whale (Eastern North Pacific stock), 

sei whale (Eastern North Pacific), and 

humpback whale (Mexico-North Pacific 

stock or Mainland Mexico-CA/OR/WA, 

Mexico DPS). Accordingly, NMFS has 

evaluated under the negligible impact 

standard the M/SI of 0.14, 0.29, or 0.57 

whales annually from each of these 

species or stocks (i.e., 1, 2, or 4 takes, 

respectively, divided by 7 years to get 

the annual number), along with the 

expected incidental takes by 

harassment. 

Explosives 

The Navy’s model and quantitative 

analysis process used for the 2018 HSTT 

FEIS/OEIS and in the Navy’s 2017 and 

2019 applications to estimate potential 

exposures of marine mammals to 

explosive stressors is detailed in the 

technical report titled Quantifying 

Acoustic Impacts on Marine Mammals 

and Sea Turtles: Methods and 

Analytical Approach for Phase III 

Training and Testing report (U.S. 

Department of the Navy, 2018). 

Specifically, over the course of a 

modeled maximum year of training and 

testing, the Navy’s model and 

quantitative analysis process estimates 

M/SI of two short-beaked common 

dolphin and one California sea lion as 

a result of exposure to explosive 

training and testing activities (please see 

section 6 of the 2017 Navy application 

where it is explained how maximum 

annual estimates are calculated). Over 

the 7-year period of the 2020 HSTT 

regulations, M/SI of 8 short-beaked 

common dolphins and 5 California sea 

lions (13 marine mammals in total) is 

estimated as a result of exposure to 

explosive training and testing activities. 

NMFS proposes no changes to the 

authorization of take by M/SI as a result 

of explosive use as the Navy proposes 

no changes to its activities from that 

described in the 2018 HSTT final rule, 

and after reviewing all new information, 

we find that our previous analyses 

remain applicable. Please refer to the 

2018 HSTT final rule and 2020 HSTT 

final rule for additional information. 

Proposed Mitigation Measures 

Under section 101(a)(5)(A) of the 

MMPA, NMFS must set forth the 

permissible methods of taking pursuant 

to the activity, and other means of 

effecting the least practicable adverse 

impact on the species or stock(s) and its 

habitat, paying particular attention to 

rookeries, mating grounds, and areas of 

similar significance, and on the 

availability of the species or stock(s) for 

subsistence uses (‘‘least practicable 

adverse impact’’). NMFS does not have 

a regulatory definition for least 

practicable adverse impact. The 2004 

NDAA amended the MMPA as it relates 

to military readiness activities and the 

incidental take authorization process 

such that a determination of ‘‘least 

practicable adverse impact’’ shall 

include consideration of personnel 

safety, practicality of implementation, 

and impact on the effectiveness of the 

military readiness activity. For the full 

discussion of how NMFS interprets least 

practicable adverse impact, including 

how it relates to the negligible-impact 

standard, see the Mitigation Measures 

section in the 2018 HSTT final rule. 

Section 101(a)(5)(A)(i)(II) requires 

NMFS to issue, in conjunction with its 

authorization, binding—and 

enforceable—restrictions (in the form of 

regulations) setting forth how the 

activity must be conducted, thus 

ensuring the activity has the ‘‘least 

practicable adverse impact’’ on the 

affected species or stocks. In situations 

where mitigation is specifically needed 

to reach a negligible impact 

determination, section 101(a)(5)(A)(i)(II) 

also provides a mechanism for ensuring 

compliance with the ‘‘negligible 

impact’’ requirement. Finally, the least 

practicable adverse impact standard also 

requires consideration of measures for 

marine mammal habitat, with particular 

attention to rookeries, mating grounds, 

and other areas of similar significance, 

and for subsistence impacts, whereas 

the negligible impact standard is 

concerned solely with conclusions 

about the impact of an activity on 

annual rates of recruitment and 

survival.1 In evaluating what mitigation 

measures are appropriate, NMFS 

considers the potential impacts of the 

Specified Activities, the availability of 

measures to minimize those potential 

impacts, and the practicability of 

implementing those measures, as we 


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describe below. This proposed rule 

includes all mitigation measures 

required by the 2020 HSTT final rule 

(though two have been modified in this 

proposed rule), and our discussion in 

that rule remains complete and accurate 

(including reference to the 2018 HSTT 

final rule), except as described below. 

Implementation of Least Practicable 

Adverse Impact Standard 

Our evaluation of potential mitigation 

measures includes consideration of two 

primary factors: 

(1) The manner in which, and the 

degree to which, implementation of the 

potential measure(s) is expected to 

reduce adverse impacts to marine 

mammal species or stocks, their habitat, 

and their availability for subsistence 

uses (where relevant). This analysis 

considers such things as the nature of 

the potential adverse impact (such as 

likelihood, scope, and range), the 

likelihood that the measure will be 

effective if implemented, and the 

likelihood of successful 

implementation; and 

(2) The practicability of the 

measure(s) for applicant 

implementation. Practicability of 

implementation may consider such 

things as cost, impact on activities, and, 

in the case of a military readiness 

activity, specifically considers 

personnel safety, practicality of 

implementation, and impact on the 

effectiveness of the military readiness 

activity. 

While the language of the least 

practicable adverse impact standard 

calls for minimizing impacts to affected 

species or stocks, we recognize that the 

reduction of impacts to those species or 

stocks accrues through the application 

of mitigation measures that limit 

impacts to individual animals. 

Accordingly, NMFS’ analysis focuses on 

measures that are designed to avoid or 

minimize impacts on individual marine 

mammals that are likely to increase the 

probability or severity of populationlevel effects. 

While direct evidence of impacts to 

species or stocks from a specified 

activity is rarely available, and 

additional study is still needed to 

understand how specific disturbance 

events affect the fitness of individuals of 

certain species, there have been 

improvements in understanding the 

process by which disturbance effects are 

translated to the population. With 

recent scientific advancements (both 

marine mammal energetic research and 

the development of energetic 

frameworks), the relative likelihood or 

degree of impacts on species or stocks 

may often be inferred given a detailed 

understanding of the activity, the 

environment, and the affected species or 

stocks—and the best available science 

has been used here. This same 

information is used in the development 

of mitigation measures and helps us 

understand how mitigation measures 

contribute to lessening effects (or the 

risk thereof) to species or stocks. We 

also acknowledge that there is always 

the potential that new information, or a 

new recommendation could become 

available in the future and necessitate 

reevaluation of mitigation measures 

(which may be addressed through 

adaptive management) to see if further 

reductions of population impacts are 

possible and practicable. 

In the evaluation of specific measures, 

the details of the specified activity will 

necessarily inform each of the two 

primary factors discussed above 

(expected reduction of impacts and 

practicability), and are carefully 

considered to determine the types of 

mitigation that are appropriate under 

the least practicable adverse impact 

standard. Analysis of how a potential 

mitigation measure may reduce adverse 

impacts on a marine mammal stock or 

species, consideration of personnel 

safety, practicality of implementation, 

and consideration of the impact on 

effectiveness of military readiness 

activities are not issues that can be 

meaningfully evaluated through a yes/ 

no lens. The manner in which, and the 

degree to which, implementation of a 

measure is expected to reduce impacts, 

as well as its practicability in terms of 

these considerations, can vary widely. 

For example, a time/area restriction 

could be of very high value for 

decreasing population-level impacts 

(e.g., avoiding disturbance of feeding 

females in an area of established 

biological importance) or it could be of 

lower value (e.g., decreased disturbance 

in an area of high productivity but of 

less firmly established biological 

importance). Regarding practicability, a 

measure might involve restrictions in an 

area or time that impede the Navy’s 

ability to certify a strike group (higher 

impact on mission effectiveness), or it 

could mean delaying a small in-port 

training event by 30 minutes to avoid 

exposure of a marine mammal to 

injurious levels of sound (lower impact). 

A responsible evaluation of ‘‘least 

practicable adverse impact’’ will 

consider the factors along these realistic 

scales. Accordingly, the greater the 

likelihood that a measure will 

contribute to reducing the probability or 

severity of adverse impacts to the 

species or stock or its habitat, the greater 

the weight that measure is given when 

considered in combination with 

practicability to determine the 

appropriateness of the mitigation 

measure, and vice versa. In the 

evaluation of specific measures, the 

details of the specified activity will 

necessarily inform each of the two 

primary factors discussed above 

(expected reduction of impacts and 

practicability), and will be carefully 

considered to determine the types of 

mitigation that are appropriate under 

the least practicable adverse impact 

standard. For more detail on how we 

apply these factors, see the discussion 

in the Mitigation Measures section of 

the 2018 HSTT final rule. 

Assessment of Mitigation Measures for 

HSTT Rule 

NMFS fully reviewed the Navy’s 

specified activities and the mitigation 

measures for the 2020 HSTT final rule 

and determined, with the addition of 

the new and modified measures 

discussed herein, and after 

consideration of the new information 

and studies described above, that the 

proposed mitigation measures would 

result in the least practicable adverse 

impact on marine mammals (see the 

2019 Navy application and the 2018 

HSTT final rule for detailed information 

on the Navy’s mitigation measures, with 

the exception of the new and modified 

measures described herein). NMFS 

worked with the Navy in the 

development of the Navy’s mitigation 

measures, which were informed by 

years of implementation and 

monitoring. A complete discussion of 

the Navy’s evaluation process used to 

develop, assess, and select mitigation 

measures, which was informed by input 

from NMFS, can be found in Chapter 5 

(Mitigation) of the 2018 HSTT FEIS/ 

OEIS. The process described in Chapter 

5 (Mitigation) of the 2018 HSTT FEIS/ 

OEIS robustly supports NMFS’ 

independent evaluation of whether the 

mitigation measures would meet the 

least practicable adverse impact 

standard. The Navy has implemented 

the mitigation measures under the 2020 

HSTT regulations and would be 

required to continue implementation of 

the mitigation measures identified in 

this rulemaking for the full 7 years it 

covers to avoid or reduce potential 

impacts from acoustic, explosive, and 

physical disturbance and vessel strike 

stressors. 

The Navy also evaluated numerous 

measures in the 2018 HSTT FEIS/OEIS 

that were not included in the 2017 Navy 

application, and NMFS independently 

reviewed and considered all new 

information, and continues to concur 

with Navy’s analysis that their inclusion 


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68324 Federal Register / Vol. 88, No. 190 / Tuesday, October 3, 2023 / Proposed Rules 

was not appropriate under the least 

practicable adverse impact standard. 

The Navy considered these additional 

potential mitigation measures in two 

groups. First, Chapter 5 (Mitigation) of 

the 2018 HSTT FEIS/OEIS, in the 

Measures Considered but Eliminated 

section, includes an analysis of an array 

of different types of mitigation that have 

been recommended over the years by 

NGOs or the public, through scoping or 

public comment on environmental 

compliance documents. Appendix K 

(Geographic Mitigation Assessment) of 

the 2018 HSTT FEIS/OEIS includes an 

in-depth analysis of time/area 

restrictions that have been 

recommended over time or previously 

implemented as a result of litigation. 

Below, we summarize the mitigation 

measures (organized into procedural 

measures and mitigation areas) that 

NMFS has determined will ensure the 

least practicable adverse impact on all 

affected species and stocks and their 

habitat, including the specific 

considerations for military readiness 

activities, and including several 

measures that are new or modified since 

publication of the 2020 HSTT final rule. 

In its 2022 application, the Navy 

proposed no changes to the procedural 

or geographic mitigation measures in 

the 2020 HSTT final rule. NMFS 

reviewed new information potentially 

pertinent to mitigation of the Navy’s 

training and testing activities. While 

Lookouts are essential to detecting the 

potential for and potentially avoiding a 

vessel strike of a marine mammal, 

NMFS and the Navy have always 

acknowledged that Lookouts cannot 

prevent all vessel strikes. The recent 

U.S. Navy and Royal Australian Navy 

vessel strikes appear to confirm this, as 

these strikes occurred when Lookouts 

were posted. As acknowledged above, 

these recent incidents may represent an 

early indicator of an increased military 

vessel strike risk within SOCAL. Recent 

reports appear to reflect the sporadic, 

episodic, or clustered nature of vessel 

strike or may reflect a trend of increased 

large whale presence in this area in the 

early summer months. NMFS and Navy 

have discussed the circumstances of 

each of the recent strikes, including the 

Royal Australian Navy strike, and 

discussed ways of improving strike 

mitigation. In these further 

conversations, NMFS and the Navy 

developed several new and modified 

mitigation measures in comparison to 

those included in the 2020 HSTT final 

rule. 

For vessel movement, the 2020 HSTT 

final rule required that ‘‘When 

underway Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must 

maneuver to maintain distance.’’ This 

measure has been updated to state that 

reducing speed may be an appropriate 

way to maneuver. The revised measure 

states that ‘‘When underway, Navy 

personnel must observe the mitigation 

zone for marine mammals; if marine 

mammals are observed, Navy personnel 

must maneuver (which may include 

reducing speed as the mission or 

circumstances allow) to maintain 

distance.’’ Of note, between 2009 and 

2021 (the most recent year for which 

data is available), U.S. Navy vessels in 

the SOCAL portion of the HSTT Study 

Area maneuvered 316 times to avoid 

large whales during MTEs. The years 

2017 and 2021 had the highest number 

of maneuvers (n=64 and n=82, 

respectively). In all years for which data 

is available (2009 to 2021), Navy 

cruisers and destroyers account for 51 to 

100 percent of maneuvers during MTEs. 

With this modified measure, NMFS is 

emphasizing that Navy personnel 

should consider reducing speed (as 

mission or circumstances allow) when 

maneuvering to avoid marine mammals, 

though this modified measure does not 

require reduction of vessel speed for 

reasons explained in Chapter 5 

(Mitigation) of the 2018 HSTT FEIS/ 

OEIS, in the Measures Considered but 

Eliminated section (i.e., requirements to 

reduce vessel speeds would have 

significant direct negative effects on 

mission effectiveness). 

This proposed rule also requires that 

Navy personnel must send alerts to 

Navy vessels of increased risk of strike 

following any reported Navy vessel 

strike in the HSTT Study Area. 

Further, the 2020 HSTT final rule 

included a requirement for Navy 

personnel to issue seasonal awareness 

notification messages to alert ships and 

aircraft to the possible presence of blue 

whales (June–October), humpback 

whales (November–April), gray whales 

(November–March), or fin whales 

(November–May). These messages assist 

in maintaining safety of navigation and 

in avoiding interactions with large 

whales during transits. Platforms must 

use the information from the awareness 

notification messages to assist their 

visual observation of applicable 

mitigation zones during training and 

testing activities and to aid in the 

implementation of procedural 

mitigation. This proposed rule requires 

the Navy to re-title the spring blue 

whale message (released in June) to a 

large whale awareness message 

inclusive of typical spring-summer large 

whales in southern California (mainly 

blue, fin, and humpback whales). 

Furthermore, rather than tying the 

message release to a specific month, the 

message would be for a period based on 

predicted oceanographic conditions for 

a given year (e.g., May–November, 

April–November, etc.). The Navy will 

also evaluate information obtained from 

NMFS’ Southwest Fisheries Science 

Center scientists, soon to be 

promulgated revised West Coast BIAs, 

and other oceanographic or predictive 

models for guiding message text 

descriptions of whale occurrence in 

Southern California. The improvement 

will emphasize that when a marine 

mammal is spotted, this may be an 

indicator that additional marine 

mammals are present and nearby, and 

increased vigilance and awareness of 

Navy personnel is warranted. 

The proposed rule also contains a 

new mitigation measure in which Navy 

personnel would issue real-time 

notifications to Navy vessels of large 

whale aggregations (four or more 

whales) within 1 nmi (1.9 km) of a Navy 

vessel in a select area of SOCAL (Of 

note, the four whales do not have to be 

the same species and do not have to be 

part of the same group (e.g., two whales 

of one species sighted at a distance off 

the port side at 500 yd (457.2 m) and 

two more whales of another species 

sighted off the starboard side at 500 yd 

(457.2 m) would be considered an 

aggregation under this measure)). This 

measure would apply to the area 

between 32–33 degrees North and 

117.2–119.5 degrees West, which 

includes the locations where recent 

(2009, 2021, 2023) strikes occurred, and 

historic locations where strikes occurred 

when precise latitude and longitude 

were known. 

Of note, in order to improve 

mitigation effectiveness, in fall 2022 the 

Navy made several changes to its 

Lookout training. The Navy revised its 

basic Lookout training materials to 

improve marine mammal awareness and 

spotting techniques through updates to 

the Marine Mammal chapter of the 

Navy’s September 2022 Lookout 

Training Handbook. Further, the Navy 

integrated improved Lookout training 

into a new generation of a shipboard 

simulator at its recruit training center in 

the Great Lakes. This simulator 

enhances new sailor knowledge and 

skill under realistic training scenarios. 

Last, the Navy will evaluate future 

revisions to online or DVD Marine 

Species Awareness Training video 

training to emphasize that when a 

protected species is spotted, this may be 

an indicator that additional marine 

mammals are present and nearby, and 

the vessel should take this into 

consideration when transiting. 


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In addition to Lookouts required 

under this proposed rule, the Navy 

mandates the number of Lookouts on 

underway vessels per internal policy 

documents, including the Surface Ship 

NAVDORM. As described in the 

Standard Operating Procedures section, 

in 2021, NAVDORM policy changed to 

require three Lookouts on most classes 

of surface ship, including destroyers 

and cruisers. However, the Navy asserts 

that always including three Lookouts on 

these vessels in the future as a required 

mitigation measure is not practicable 

because lookout numbers are subject to 

change based on national security 

needs, including manning and staffing 

requirements. As such, although the 

Navy describes these additional 

Lookouts in its application under the 

mitigation section, NMFS has not 

considered the potential presence of two 

additional lookouts when considering 

Navy’s mitigation effectiveness. Please 

see the Proposed Reporting section for 

additional detail on this proposed 

requirement. 

With the exception of Oedekoven and 

Thomas (2022) described above, there is 

no new information that affects NMFS’ 

assessment of the applicability or 

effectiveness of the measures included 

in the 2018 HSTT final rule over the 

remainder of the 7-year period. As 

stated above in the Potential Effects of 

Specified Activities on Marine 

Mammals and Their Habitat section, 

while (Oedekoven and Thomas, 2022) 

suggests that detection of marine 

mammals is less certain than previously 

assumed at certain distances, model 

assumptions may still underestimate 

Lookout effectiveness in some cases. 

Additionally, maneuvering data 

summarized above demonstrates that 

Navy vessels are successfully 

maneuvering to avoid striking sighted 

marine mammals in most cases, despite 

the Oedekoven and Thomas (2022) 

results. Further, as described above, 

Navy and NMFS have developed 

modified or new mitigation in this 

proposed rule which are anticipated to 

further reduce the risk of vessel strike of 

large whales. 

In summary, and as described in more 

detail above regarding vessel strike, the 

Navy has agreed to procedural 

mitigation measures that will reduce the 

probability and/or severity of impacts 

expected to result from acute exposure 

to acoustic sources or explosives, vessel 

strike, and impacts to marine mammal 

habitat. Specifically, the Navy will use 

a combination of delayed starts, 

powerdowns, and shutdowns to 

minimize or avoid M/SI and minimize 

the likelihood or severity of PTS or 

other injury, and reduce instances of 

TTS or more severe behavioral 

disturbance caused by acoustic sources 

or explosives. The Navy will also 

implement multiple time/area 

restrictions (several of which were 

added in the 2018 HSTT final rule since 

the previous HSTT MMPA incidental 

take rule) that would reduce take of 

marine mammals in areas or at times 

where they are known to engage in 

important behaviors, such as feeding or 

calving, where the disruption of those 

behaviors would have a higher 

probability of resulting in impacts on 

reproduction or survival of individuals 

that could lead to population-level 

impacts. Table 8 provides the Navy’s 

required procedural mitigation 

measures for environmental awareness 

and education and vessel movement as 

well as summaries of the Navy’s 

procedural mitigation measures for 

other activities. Table 9 provides 

summaries of mitigation areas for the 

HSTT Study Area. 

NMFS and the Navy considered 

mitigation areas to protect marine 

mammals, including odontocetes with 

small or resident populations in the 

HSTT Study Area. This included 

consideration of new mitigation areas 

based on newly identified BIAs in 

Hawaii (Kratofil et al. 2023). Including 

additional mitigation areas beyond that 

included in the 2020 HSTT final rule is 

impracticable given overlap with critical 

Navy training areas in the HRC. 

However, many of the BIAs identified in 

Kratofil et al. 2023 partially or fully 

overlap the mitigation areas included in 

the 2020 HSTT final rule and proposed 

herein. 

TABLE 8—SUMMARY OF PROCEDURAL MITIGATION

Stressor or activity Mitigation zone sizes and other requirements 

Environmental Awareness and Education ................................................................ • This mitigation applies to all training and testing activities, as applicable. 

• Mitigation Requirements: 

Æ Appropriate Navy personnel (including civilian personnel) involved in mitigation and training or testing activity reporting under the specific activities 

must complete one or more modules of the U.S. Navy Afloat Environmental Compliance Training Series, as identified in their career path training plan. Modules include: 

D Introduction to the U.S. Navy Afloat Environmental Compliance Training Series. The introductory module provides information on environmental laws (e.g., ESA, MMPA) and the corresponding responsibilities 

that are relevant to Navy training and testing activities. The material 

explains why environmental compliance is important in supporting the 

Navy’s commitment to environmental stewardship. 

D Marine Species Awareness Training. All bridge watch personnel, 

Commanding Officers, Executive Officers, maritime patrol aircraft aircrews, anti-submarine warfare and mine warfare rotary-wing aircrews, 

Lookouts, and equivalent civilian personnel must successfully complete the Marine Species Awareness Training prior to standing watch 

or serving as a Lookout. The Marine Species Awareness Training provides information on sighting cues, visual observation tools and techniques, and sighting notification procedures. Navy biologists developed Marine Species Awareness Training to improve the effectiveness of visual observations for biological resources, focusing on marine mammals and sea turtles, and including floating vegetation, jellyfish aggregations, and flocks of seabirds. 

D U.S. Navy Protective Measures Assessment Protocol. This module 

provides the necessary instruction for accessing mitigation requirements during the event planning phase using the Protective Measures 

Assessment Protocol software tool. 

D U.S. Navy Sonar Positional Reporting System and Marine Mammal Incident Reporting. This module provides instruction on the procedures 

and activity reporting requirements for the Sonar Positional Reporting 

System and marine mammal incident reporting. 

Active Sonar .............................................................................................................. Depending on sonar source: 


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TABLE 8—SUMMARY OF PROCEDURAL MITIGATION—Continued 

Stressor or activity Mitigation zone sizes and other requirements 

• 1,000 yd (914.4 m) power down, 500 yd (457.2 m) power down, and 200 

yd (182.9 m) shut down 

• 200 yd (182.9 m) shut down. 

Air Guns ..................................................................................................................... • 150 yd (137.2 m). 

Pile Driving ................................................................................................................ • 100 yd (91.4 m). 

Weapons Firing Noise ............................................................................................... • 30 degrees on either side of the firing line out to 70 yd (64 m). 

Explosive Sonobuoys ................................................................................................ • 600 yd (548.6 m). 

Explosive Torpedoes ................................................................................................. • 2,100 yd (1,920.2 m). 

Explosive Medium-Caliber and Large-Caliber Projectiles ......................................... • 1,000 yd (914.4 m; large-caliber projectiles). 

• 600 yd (548.6 m; medium-caliber projectiles during surface-to-surface activities). 

• 200 yd (182.9 m; medium-caliber projectiles during air-to-surface activities). 

Explosive Missiles and Rockets ................................................................................ • 2,000 yd (1,828.8 m; 21–500 lb. net explosive weight). 

• 900 yd (823 m; 0.6–20 lb. net explosive weight). 

Explosive Bombs ....................................................................................................... • 2,500 yd (2,286 m). 

Sinking Exercises ...................................................................................................... • 2.5 nmi (4.6 km). 

Explosive Mine Countermeasure and Neutralization Activities ................................. • 2,100 yd (1,929.2 m; 6–650 lb net explosive weight). 

• 600 yd (548.6 m; 0.1–5 lb net explosive weight). 

Explosive Mine Neutralization Activities Involving Navy Divers ................................ • 1,000 yd (914.4 m; 21–60 lb net explosive weight for positive control charges 

and charges using time-delay fuses). 

• 500 yd (457.2 m; 0.1–20 lb net explosive weight for positive control charges). 

Underwater Demolition Multiple Charge—Mat Weave and Obstacle Loading ......... • 700 yd (640.1 m). 

Maritime Security Operations—Anti-Swimmer Grenades ......................................... • 200 yd (182.9 m). 

Vessel Movement ...................................................................................................... • The mitigation must not be applied if: (1) The vessel’s safety is threatened, (2) 

the vessel is restricted in its ability to maneuver (e.g., during launching and recovery of aircraft or landing craft, during towing activities, when mooring), (3) 

the vessel is operated autonomously, or (4) when impractical based on mission 

requirements (e.g., during Amphibious Assault—Battalion Landing exercises). 

• Number of Lookouts and Observation Platform: 

Æ 1 Lookout must be on the vessel that is underway.1

• Mitigation Requirements: 

Æ Mitigation zones:—500 yd (457.2 m) around whales.—200 yd (182.9 m) 

around other marine mammals (except bow-riding dolphins and pinnipeds 

hauled out on man-made navigational structures, port structures, and vessels). 

Æ During the activity:—When underway, Navy personnel must observe the 

mitigation zone for marine mammals; if marine mammals are observed, 

Navy personnel must maneuver (which may include reducing speed as the 

mission or circumstances allow) to maintain distance. 

• Additional requirements: 

Æ If a marine mammal vessel strike occurs, Navy personnel must follow the 

established incident reporting procedures. Navy personnel must also send 

alerts to Navy vessels of increased risk of strike following any reported 

Navy vessel strike in the HSTT Study Area. 

Æ Navy personnel must issue real-time notifications to Navy vessels of large 

whale aggregations (four or more whales) within 1 nmi (1.9 km) of a Navy 

vessel in the area between 32–33 degrees North and 117.2–119.5 degrees West. 

Towed In-Water Devices ........................................................................................... • 250 yd (228.6 m; marine mammals). 

Small-, Medium-, and Large-Caliber Non-Explosive Practice Munitions .................. • 200 yd (182.9 m). 

Non-Explosive Missiles and Rockets ........................................................................ • 900 yd (823 m). 

Non-Explosive Bombs and Mine Shapes .................................................................. • 1,000 yd (914.4 m). 

Note:lb: pounds; nmi: nautical miles; yd: yards; m: meters. 1 Underway vessels will maintain at least one Lookout. For ship classes required to maintain more than one Lookout, the specific requirement is subject to change 

over time in accordance with Navy navigation instruction (e.g., the Surface Ship NAVDORM). Navy personnel will notify NMFS as soon as practicable should its Lookout policies change, including in the NAVDORM. 

TABLE 9—SUMMARY OF MITIGATION AREAS FOR MARINE MAMMALS

Summary of mitigation area requirements 

Hawaii Island Mitigation Area (year-round): 

• Navy personnel must not conduct more than 300 hours of MF1 surface ship hull-mounted mid-frequency active sonar or 20 hours of MF4 dipping sonar, or 

use explosives that could potentially result in takes of marine mammals during training and testing.1

4-Islands Region Mitigation Area (November 15–April 15 for active sonar; year-round for explosives): 

• Navy personnel must not use MF1 surface ship hull-mounted mid-frequency active sonar or explosives that could potentially result in takes of marine mammals during training and testing.1

Humpback Whale Special Reporting Areas (December 15–April 15): 

• Navy personnel must report the total hours of surface ship hull-mounted mid-frequency active sonar used in the special reporting areas in its annual training 

and testing activity reports submitted to NMFS. 

San Diego Arc, San Nicolas Island, and Santa Monica/Long Beach Mitigation Areas (June 1–October 31): 

• Navy personnel must not conduct more than a total of 200 hours of MF1 surface ship hull-mounted mid-frequency active sonar in the combined areas, excluding normal maintenance and systems checks, during training and testing.1

• Within the San Diego Arc Mitigation Area, Navy personnel must not use explosives that could potentially result in the take of marine mammals during largecaliber gunnery, torpedo, bombing, and missile (including 2.75′′ rockets) activities during training and testing.1

• Within the San Nicolas Island Mitigation Area, Navy personnel must not use explosives that could potentially result in the take of marine mammals during 

mine warfare, large-caliber gunnery, torpedo, bombing, and missile (including 2.75′′ rockets) activities during training.1

• Within the Santa Monica/Long Beach Mitigation Area, Navy personnel must not use explosives that could potentially result in the take of marine mammals 

during mine warfare, large-caliber gunnery, torpedo, bombing, and missile (including 2.75′′ rockets) activities during training and testing.1

Santa Barbara Island Mitigation Area (year-round): 


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TABLE 9—SUMMARY OF MITIGATION AREAS FOR MARINE MAMMALS—Continued 

Summary of mitigation area requirements 

• Navy personnel must not use MF1 surface ship hull-mounted mid-frequency active sonar during training and testing, or explosives that could potentially result 

in the take of marine mammals during medium-caliber or large-caliber gunnery, torpedo, bombing, and missile (including 2.75′′ rockets) activities during training.1

Awareness Notification Message Areas (seasonal according to species): 

• Navy personnel must issue awareness notification messages to alert ships and aircraft to the possible presence of large whales during a period based on predicted oceanographic conditions for a given year. The message must emphasize that when a marine mammal is spotted, this may be an indicator that additional marine mammals are present and nearby, and increased vigilance and awareness of Navy personnel is warranted. Navy personnel must also issue 

awareness notification messages to alert ships and aircraft to the possible presence of gray whales (November–March) and fin whales (November–May). 

1 If Naval units need to conduct more than the specified amount of training or testing, they will obtain permission from the appropriate designated Command authority prior to commencement of the activity. The Navy will provide NMFS with advance notification and include the information in its annual activity reports submitted to 

NMFS. 

Mitigation Conclusions 

NMFS has carefully evaluated the 

Navy’s mitigation measures from the 

2020 rule—many of which were 

developed with NMFS’ input during the 

previous phases of Navy training and 

testing authorizations and none of 

which have changed since our 

evaluation during the 2018 HSTT 

rulemaking, with the exception of the 

changes described herein—and 

considered a broad range of other 

measures (i.e., the measures considered 

but eliminated in the 2018 HSTT FEIS/ 

OEIS, which reflect many of the 

comments that have arisen via NMFS or 

public input in past years) in the 

context of ensuring that NMFS 

prescribes the means of effecting the 

least practicable adverse impact on the 

affected marine mammal species and 

stocks and their habitat. Our evaluation 

of potential measures included 

consideration of the following factors in 

relation to one another: the manner in 

which, and the degree to which, the 

successful implementation of the 

mitigation measures is expected to 

reduce the likelihood and/or magnitude 

of adverse impacts to marine mammal 

species and stocks and their habitat; the 

proven or likely efficacy of the 

measures; and the practicability of the 

measures for applicant implementation, 

including consideration of personnel 

safety, practicality of implementation, 

and impact on the effectiveness of the 

military readiness activity. After 

considering all new information, 

including consideration of new 

information regarding vessel strike, 

NMFS proposes two additional 

mitigation measures and revision of two 

existing mitigation measures as 

described above. 

Based on our evaluation of the Navy’s 

current mitigation measures (which are 

being implemented under the 2020 

HSTT regulations), as well as modified 

and new measures described above, 

NMFS has preliminarily determined 

that the proposed mitigation measures 

are appropriate means of effecting the 

least practicable adverse impact on 

marine mammal species or stocks and 

their habitat, paying particular attention 

to rookeries, mating grounds, and areas 

of similar significance, and considering 

specifically personnel safety, 

practicality of implementation, and 

impact on the effectiveness of the 

military readiness activity. 

Additionally, as described in more 

detail below, the 2020 HSTT final rule 

includes an adaptive management 

provision, which the Navy proposes to 

extend, which ensures that mitigation is 

regularly assessed and provides a 

mechanism to improve the mitigation, 

based on the factors above, through 

modification as appropriate. 

The proposed rule comment period 

provides the public an opportunity to 

submit recommendations, views, and/or 

concerns regarding the Navy’s activities 

and the proposed mitigation measures. 

While NMFS has preliminarily 

determined that the proposed mitigation 

measures would effect the least 

practicable adverse impact on the 

affected species or stocks and their 

habitat, NMFS will consider all public 

comments to help inform our final 

decision. Consequently, the proposed 

mitigation measures may be refined, 

modified, removed, or added to prior to 

the issuance of the final rule based on 

public comments received, and where 

appropriate, further analysis of any 

additional mitigation measures. 

Proposed Monitoring 

Section 101(a)(5)(A) of the MMPA 

states that in order to authorize 

incidental take for an activity, 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 incidental take 

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. 

In its 2022 application, the Navy 

proposes no changes to the monitoring 

described in the 2018 HSTT final rule 

and 2020 HSTT final rule. They would 

continue implementation of the robust 

Integrated Comprehensive Monitoring 

Program and Strategic Planning Process 

described in the 2018 HSTT final rule. 

The Navy’s monitoring strategy, 

currently required by the 2018 HSTT 

regulations, is well-designed to work 

across Navy ranges to help better 

understand the impacts of the Navy’s 

activities on marine mammals and their 

habitat by focusing on learning more 

about marine mammal occurrence in 

different areas and exposure to Navy 

stressors, marine mammal responses to 

different sound sources, and the 

consequences of those exposures and 

responses on marine mammal 

populations. Similarly, these proposed 

modified regulations would include 

identical adaptive management 

provisions and reporting requirements 

as the 2018 HSTT regulations. There is 

no new information that would indicate 

that the monitoring measures put in 

place under the 2018 HSTT final rule 

would not remain applicable and 

appropriate for the 7-year period of this 

proposed rule. See the Monitoring 

section of the 2018 HSTT final rule for 

more details on the monitoring program 

that would be required under this rule. 

In addition, please see the 2019 Navy 

application, which references Chapter 

13 of the 2017 Navy application for full 

details on the monitoring and reporting 

proposed by the Navy. 

Within the SOCAL portion of HSTT, 

the Navy has been primarily focused on 

beaked whale monitoring since 2018 

through two separate ongoing projects 

that are expected to continue until 2025. 

These projects use passive acoustic 

devices, visual surveys, satellite tagging, 

genetic analysis, photoID, and response 

to anthropogenic sounds to refine 

population status of beaked whales in 

SOCAL. There is also one concurrent 

project with fin whales using visual 

surveys, satellite tagging, and photoID to 

gather additional data on fin whale 


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populations in Southern California. 

Finally, the Navy continues to fund 

marine mammal sighting data collected 

during California Cooperative Oceanic 

Fisheries Investigations (CALCOFI) 

https://calcofi.org/. These data are 

collected on a much more frequent basis 

than NMFS’ West Coast visual survey 

which typically occur once every 5 

years in the summer. CALCOFI surveys 

occur quarterly every year to include 

winter and spring seasons NMFS does 

not survey. Sufficient marine mammal 

sightings have been accumulated since 

the Navy started funding in 2004 for the 

data to be incorporated into ongoing 

NMFS spatial habitat models, including 

new models for select species. The Navy 

also annually funds continued NMFS 

spatial habitat model improvements as 

new data and techniques become 

available. These models benefit the 

Navy and other Federal partners such as 

the Bureau of Ocean Energy 

Management and NMFS, for use in 

future regional marine mammal density 

derivation. For additional information, 

please see the Navy’s Marine Species 

Monitoring program website, https://

www.navymarinespeciesmonitoring.us/ 

regions/pacific/current-projects/. 

Adaptive Management 

The 2020 HSTT regulations governing 

the take of marine mammals incidental 

to Navy training and testing activities in 

the HSTT Study Area contain an 

adaptive management component. Our 

understanding of the effects of Navy 

training and testing activities (e.g., 

acoustic and explosive stressors) on 

marine mammals continues to evolve, 

which makes the inclusion of an 

adaptive management component both 

valuable and necessary within the 

context of 7-year regulations. The 2022 

Navy application proposes no changes 

to the adaptive management component 

included in the 2020 HSTT final rule. 

The reporting requirements associated 

with this rule are designed to provide 

NMFS with monitoring data from the 

previous year to allow NMFS to 

consider whether any changes to 

existing mitigation and monitoring 

requirements are appropriate. The use of 

adaptive management allows NMFS to 

consider new information from different 

sources to determine (with input from 

the Navy regarding practicability) on an 

annual or biennial basis if mitigation or 

monitoring measures should be 

modified (including additions or 

deletions). Mitigation measures could be 

modified if new data suggests that such 

modifications would have a reasonable 

likelihood of more effectively 

accomplishing the goals of the 

mitigation and monitoring and if the 

measures are practicable. If the 

modifications to the mitigation, 

monitoring, or reporting measures are 

substantial, NMFS will publish a notice 

of the planned LOA in the Federal 

Register and solicit public comment. 

The following are some of the 

possible sources of applicable data to be 

considered through the adaptive 

management process: (1) results from 

monitoring and exercises reports, as 

required by MMPA authorizations; (2) 

compiled results of Navy funded R&D 

studies; (3) results from specific 

stranding investigations; (4) results from 

general marine mammal and sound 

research; and (5) any information which 

reveals that marine mammals may have 

been taken in a manner, extent, or 

number not authorized by these 

regulations or subsequent LOAs. The 

results from monitoring reports and 

other studies may be viewed at https:// 

www.navymarinespeciesmonitoring.us. 

Proposed Reporting 

In order to issue incidental take 

authorization for an activity, section 

101(a)(5)(A) of the MMPA states that 

NMFS must set forth requirements 

pertaining to the monitoring and 

reporting of such taking. Effective 

reporting is critical both to compliance 

as well as ensuring that the most value 

is obtained from the required 

monitoring. Reports from individual 

monitoring events, results of analyses, 

publications, and periodic progress 

reports for specific monitoring projects 

will be posted to the Navy’s Marine 

Species Monitoring web portal: http://

www.navymarinespeciesmonitoring.us. 

The 2019 Navy application and 2022 

Navy application proposed no changes 

to the reporting requirements, though as 

noted above, the Navy has since 

proposed to report changes to Lookout 

SOPs to NMFS. Except as discussed 

below, reporting requirements would 

remain identical to those described in 

the 2018 HSTT final rule and 2020 

HSTT final rule, and there is no new 

information that would indicate that the 

reporting requirements put in place 

under the 2020 HSTT final rule would 

not remain applicable and appropriate 

for the remaining duration of the 7-year 

period of this proposed rule. See the 

Reporting section of the 2018 HSTT 

final rule for more details on the 

reporting that would be required under 

this rulemaking. In addition, the 2018 

HSTT proposed and final rules 

unintentionally failed to include the 

requirement for the Navy to submit a 

final activity ‘‘close out’’ report at the 

end of the regulatory period. That 

oversight was corrected through the 

2020 HSTT final rule. Please see the 

2020 HSTT final rule for the detailed 

requirements for that report. 

In addition to the reporting 

requirements included in the 2020 

HSTT final rule, the Navy must report 

changes in its Lookout policies to NMFS 

as soon as practicable after a change is 

made. 

Preliminary Analysis and Negligible 

Impact Determination 

NMFS has defined negligible impact 

as an impact resulting from the 

specified activity that cannot be 

reasonably expected to, and is not 

reasonably likely to, adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival 

(50 CFR 216.103). A negligible impact 

finding is based on the lack of likely 

adverse effects on annual rates of 

recruitment or survival (i.e., populationlevel effects). While this proposed rule 

consists of a modification of take by M/ 

SI by vessel strike, NMFS considers the 

impacts of the entire specified activity 

and the total taking in the negligible 

impact determination. An estimate of 

the number of takes alone is not enough 

information on which to base an impact 

determination. In addition to 

considering estimates of the number of 

marine mammals that might be taken 

through mortality, serious injury, and 

Level A or Level B harassment (as 

presented in tables 11 and 12 of the 

2020 HSTT final rule), NMFS considers 

other factors, such as the likely nature 

of any responses (e.g., intensity, 

duration), the context of any responses 

(e.g., critical reproductive time or 

location, migration), as well as effects 

on habitat, and the likely effectiveness 

of the mitigation. We also assess the 

number, intensity, and context of 

estimated takes by evaluating this 

information relative to population 

status. Consistent with the 1989 

preamble for NMFS’ implementing 

regulations (54 FR 40338; September 29, 

1989), the impacts from other past and 

ongoing anthropogenic activities 

(including foreign military activities) are 

incorporated into this analysis via their 

impacts on the environmental baseline 

(e.g., as reflected in the regulatory status 

of the species, population size and 

growth rate where known, other ongoing 

sources of human-caused mortality, 

ambient noise levels, and specific 

consideration of take by Level A 

harassment or M/SI previously 

authorized for other NMFS activities). 

In the Estimated Take of Marine 

Mammals sections of this proposed rule 

and the 2020 HSTT final rule (where the 

activities, species and stocks, potential 

effects, and mitigation measures are the 

same as for this rulemaking), we 


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identified the subset of potential effects 

that would be expected to rise to the 

level of takes both annually and over the 

7-year period covered by this 

rulemaking and then identified the 

number of each of those mortality takes 

that we believe could occur or the 

maximum number of harassment takes 

that are reasonably expected to occur 

based on the methods described. The 

impact that any given take will have is 

dependent on many case-specific factors 

that need to be considered in the 

negligible impact analysis (e.g., the 

context of behavioral exposures such as 

duration or intensity of a disturbance, 

the health of impacted animals, the 

status of a species that incurs fitnesslevel impacts to individuals, etc.). For 

this proposed rule, we evaluated the 

likely impacts of the enumerated 

maximum number of harassment takes 

that are reasonably expected to occur 

and proposed for authorization, in the 

context of the specific circumstances 

surrounding these predicted takes. We 

also assessed M/SI takes that could 

occur, as well as considering the traits 

and statuses of the affected species and 

stocks. Last, we collectively evaluated 

this information, as well as other more 

taxa-specific information and mitigation 

measure effectiveness, in group-specific 

assessments that support our negligible 

impact conclusions for each stock or 

species. Because all of the Navy’s 

specified activities would occur within 

the ranges of the marine mammal stocks 

identified in the rule, all negligible 

impact analyses and determinations are 

at the stock level (i.e., additional 

species-level determinations are not 

needed). 

The Navy proposes no changes to the 

nature or level of the specified activities 

or the boundaries of the HSTT Study 

Area, and therefore, the training and 

testing activities (e.g., equipment and 

sources used, exercises conducted) are 

the same as those analyzed in the 2020 

HSTT final rule. In addition, the 

mitigation, monitoring, and nearly all 

reporting measures are identical to those 

described and analyzed in the 2018 

HSTT final rule with the exception of 

changes to mitigation measures 

described previously and the additional 

reporting requirement for Navy to report 

changes in its Lookout policies to NMFS 

as soon as practicable after a change is 

made. There is no new information 

since the publication of the 2020 HSTT 

final rule regarding the impacts of the 

specified activities on marine mammals, 

the status and distribution of any of the 

affected marine mammal species or 

stocks, or the effectiveness of the 

mitigation and monitoring measures 

that would change the content of our 

analyses, with the exception of that 

described below. First, naval vessel 

strikes have occurred in the HSTT and 

Atlantic Fleet Training and Testing 

(AFTT) Study Areas since publication of 

the 2020 HSTT final rule (one fin or sei 

whale struck by the U.S. Navy in the 

HSTT Study Area (2023), two 

unidentified large whales struck by the 

U.S. Navy in the HSTT Study Area 

(2021), two fin whales struck by a 

foreign navy in the HSTT Study Area 

(2021), and one dolphin struck by the 

U.S. Navy in the AFTT Study Area 

(2021)). Second, for gray whales, we 

have considered the latest effects of the 

UME on the west coast of North 

America along with the effects of the 

Navy’s activities in the negligible 

impact analysis. Third, a new study 

suggests that Lookout detection of 

marine mammals is less certain than 

previously assumed (Oedekoven and 

Thomas, 2022). Fourth, stock 

assessments have been updated for 

multiple stocks in the 2022 Pacific and 

Alaska SARs (Carretta et al. 2023; 

Young et al. 2023). 

As described above and in the 2022 

Navy application, a number of 

additional studies have been published, 

including several studies associated 

with TTS in harbor porpoises and seals 

(e.g., Kastelein et al. 2020d; Kastelein et 

al. 2021a and 2021b; Sills et al. 2020). 

NMFS is aware of these recent papers 

and is currently working with the Navy 

to update NMFS’ Technical Guidance 

for Assessing the Effects of 

Anthropogenic Sound on Marine 

Mammal Hearing Version 2.0 (Acoustic 

Technical Guidance; NMFS 2018) to 

reflect relevant papers that have been 

published since the 2018 update on our 

3–5 year update schedule in the 

Acoustic Technical Guidance. We note 

that the recent peer-reviewed, updated 

marine mammal noise exposure criteria 

by Southall et al. (2019) provide 

identical PTS and TTS thresholds and 

weighting functions to those provided 

in NMFS’ Acoustic Technical Guidance. 

NMFS will continue to review and 

evaluate new relevant data as it becomes 

available and consider the impacts of 

those studies on the Acoustic Technical 

Guidance to determine what revisions/ 

updates may be appropriate. However, 

any such revisions must undergo peer 

and public review before being adopted, 

as described in the Acoustic Guidance 

methodology. While some of the 

relevant data may potentially suggest 

changes to TTS/PTS thresholds for some 

species, any such changes would not be 

expected to change the predicted take 

estimates in a manner that would 

change the necessary determinations 

supporting the issuance of these 

regulations, and the data and values 

used in this rulemaking reflect the best 

available science. 

Harassment 

As described in the Estimated Takes 

of Marine Mammals section, the annual 

number of takes proposed for 

authorization and reasonably expected 

to occur by Level A harassment and 

Level B harassment (based on the 

maximum number of activities per 12- 

month period) are identical to those 

presented in tables 41 and 42 in the 

Take Requests section of the 2018 HSTT 

final rule, with the exception of 

humpback whale, which are presented 

in tables 2 and 3 herein. As such, the 

negligible impact analyses and 

determinations of the effects of the 

estimated Level A harassment and Level 

B harassment takes on annual rates of 

recruitment or survival for each species 

and stock are nearly identical to and 

substantively unchanged from those 

presented in the 2020 HSTT final rule. 

The differences in the analysis is our 

removal of consideration of California 

Sea Lion UME, which has been closed 

since publication of the 2020 HSTT 

final rule, and incorporation of the 

revised stock structure for humpback 

whales. This does not affect the results 

of the analyses or our determinations. 

For detailed discussion of the impacts 

that affected individuals may 

experience given the specific 

characteristics of the specified activities 

and required mitigation (e.g., from 

behavioral disruption, masking, and 

temporary or permanent threshold 

shift), along with the effects of the 

expected Level A harassment and Level 

B harassment take on reproduction and 

survival, see the applicable subsections 

in the Analysis and Negligible Impact 

Determination section of the 2018 HSTT 

final rule (83 FR 66977–67018; also 

incorporated by reference in the 2020 

HSTT final rule). 

Serious Injury or Mortality 

Based on the information and 

methods discussed in the Estimated 

Take of Marine Mammals section 

(which are identical to those used in the 

2018 HSTT final rule for explosives and 

revised for vessel strike), NMFS is 

proposing to authorize five mortalities 

of large whales due to vessel strike over 

the 7-year period of this rulemaking, 

two more strikes than what was 

authorized in the 2018 HSTT final rule 

and 2020 HSTT final rule. Across the 7- 

year duration of the rule, take of an 

annual average of 0.57 gray whales 

(Eastern North Pacific stock) and fin 


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whales (CA/OR/WA stock), an annual 

average of 0.29 humpback whales 

(Hawaii stock) and an annual average of 

0.14 blue whales (Eastern North Pacific 

stock), sei whales (Eastern North Pacific 

stock) and humpback whales (Mainland 

Mexico-CA/OR/WA stock, Mexico DPS), 

as described in table 8 (i.e., one, two, or 

four take(s) over 7 years divided by 

seven to get the annual number) could 

occur and are proposed for 

authorization. 

TABLE 10—SUMMARY INFORMATION RELATED TO MORTALITIES REQUESTED FOR VESSEL STRIKE

[2018–2025] 

Species (stock) 

Stock 

abundance 

(Nbest) * 

Annual 

authorized 

take by 

serious 

injury or 

mortality 1

Total 

annual 

M/SI * 2

Fisheries interactions (Y/N); 

annual rate of 

M/SI from 

fisheries 

interactions * 

Annual rate of 

M/SI from 

vessel 

collision * 

Potential 

biological 

removal 

(PBR) * 

Residual 

PBR (PBR 

minus 

annual 

M/SI) 3

Stock trend * 4

Recent UME 

(Y/N); number 

and year 

(since 2007) 

Fin whale (CA/OR/WA 

stock).

11,065 0.57 ≥43.6 Y; ≥0.64 ............ Y, 43 ............... 80 36.4 ↑ ..................... N. 

Gray whale (Eastern North 

Pacific stock).

26,960 0.57 131 Y, 9.3 ................ Y, 1.8 .............. 801 670 5↑ ................... Y; 674; 2019 

(as of June 

25, 2023). 

Humpback whale (Mainland Mexico-CA/OR/WA 

stock, Mexico DPS).

3,477 0.14 22 Y; 11.4 .............. Y, 10.15 .......... 65 6 43 Unknown ........ N. 

Humpback whale (Hawaii 

stock).

11,278 0.29 27.09 Y; 8.39 .............. 7Y, 10.59 ....... 127 99.91 Unknown ........ Y; 2015; 52.] 

Blue whale (Eastern North 

Pacific Stock).

1,898 0.14 ≥19.5 Y; ≥1.54 ............ Y, 0.8 .............. 4.1 -15.4 Unknown ........ Y; 3, 2007. 

Sei whale (Eastern North 

Pacific Stock).

519 0.14 ≥0.2 N; 0 .................. Y, 0.2 .............. 0.75 0.55 Unknown ........ N. 

* Presented in the 2022 final SARs. 

1This column represents the annual take by serious injury or mortality (M/SI) by vessel collision and was calculated by the number of mortalities proposed for authorization divided by 7 years (the length of the rule and LOAs). 2This column represents the total number of incidents of M/SI that could potentially accrue to the specified species or stock. This number comes from the SAR, but 

deducts the takes accrued from either Navy strikes or NMFS’ Southwest Fisheries Science Center (SWFSC) takes in the SARs to ensure not double-counted against 

PBR. However, for these species, there were no takes from either other Navy activities or SWFSC in the SARs to deduct that would be considered double-counting. 3This value represents the calculated PBR less the average annual estimate of ongoing anthropogenic mortalities (i.e., total annual human-caused M/SI, which is 

presented in the SARs). 4See relevant SARs for more information regarding stock status and trends. 

5The Pacific 2022 SAR indicates that the stock trend is increasing. However, recent (2021–2022) surveys conducted by NMFS’ Southwest Fisheries Science Center estimated that the population has declined to 16,650 whales, though the authors note that this stock has historically shown a pattern of population growth and decline that has not impacted the population in the long term (Eguchi et al. 2022). 6Vessel strike of the Mainland Mexico-CA/OR/WA stock was calculated by applying a prorated portion of humpback whale strikes modeled by Rockwood et al. 

(2017) to this stock. 7For this stock, PBR is currently set at 43 for U.S. waters and 65 for the stock’s entire range. As the HSTT Study Area extends beyond U.S. waters and activities 

have the potential to impact the entire stock, we present the analysis using the PBR for the stock’s entire range. 8Annual vessel strike for this stock reported in the 2022 final SAR was calculated by summing vessel strike data from Hawaii, Alaska, and Washington. All observed strikes in Hawaii were assigned to the Hawaii stock, and a portion of observed strikes in Alaska were assigned to the Hawaii stock. Vessel strike of the Hawaii 

stock in Washington waters was calculated by applying a prorated portion of humpback whale strikes modeled by Rockwood et al. (2017) to the Hawaii stock. 

The Navy also requested a small 

number of takes by M/SI from 

explosives in the 2017 Navy 

application. To calculate the annual 

average of mortalities for explosives in 

table 11, we used the same method as 

described for vessel strikes. The annual 

average is the total number of takes over 

7 years divided by seven. Specifically, 

NMFS is proposing to authorize the 

following M/SI takes from explosives: 

five California sea lions and eight shortbeaked common dolphins over the 7- 

year period (therefore 0.71 mortalities 

annually for California sea lions and 

1.14 mortalities annually for shortbeaked common dolphin), as described 

in table 11. As this annual number is the 

same as that analyzed and authorized in 

the 2020 HSTT final rule, and no other 

relevant information about the status, 

abundance, or effects of mortality on 

each species or stock has changed, the 

analysis of the effects of explosives is 

identical to that presented in the 2020 

HSTT final rule. 

TABLE 11—SUMMARY INFORMATION RELATED TO MORTALITIES FROM EXPLOSIVES

[2018–2025] 

Species 

(stock) 

Stock 

abundance 

(Nbest) * 

Annual 

authorized 

take by 

serious 

injury or 

mortality 1

Total 

annual 

M/SI* 2

Fisheries interactions (Y/N); 

annual rate of 

M/SI from 

fisheries 

interactions * 

PBR * 

SWFSC 

authorized 

take 

(annual) 3

Residual 

PBR—PBR 

minus 

annual M/SI 

and 

SWFSC 4

Stock 

trend* 5

UME 

(Y/N); 

number 

and year 

California sea lion (U.S. stock) .............. 257,606 0.71 ≥321 Y; ≥197 ............. 14,011 6 13,684 ↑ N 

Short-beaked common dolphin (CA/OR/ 

WA stock).

1,056,308 1.14 ≥30.5 Y; ≥30.5 ............ 8,889 2.8 8,855.7 ? N 

* Presented in the 2022 draft SARs or most recent SAR. 

1This column represents the annual take by serious injury or mortality (M/SI) during explosive detonations and was calculated by the number of mortalities planned 

for authorization divided by 7 years (the length of the rule and LOAs). 2This column represents the total number of incidents of M/SI that could potentially accrue to the specified species or stock. This number comes from the SAR. 

3This column represents annual take authorized through NMFS’ SWFSC rulemaking/LOAs (86 FR 3840; January 15, 2021). 

4This value represents the calculated PBR less the average annual estimate of ongoing anthropogenic mortalities (i.e., total annual human-caused M/SI column 

and the annual authorized take from the SWFSC column. In the case of California sea lion the M/SI column (321) and the annual authorized take from the SWFSC 

(6) were subtracted from the calculated PBR of 14,011. In the case of short-beaked common dolphin the M/SI column (30.5) and the annual authorized take from the 

SWFSC (2.8) were subtracted from the calculated PBR of 8,889. 5See relevant SARs for more information regarding stock status and trends. 


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See the Serious Injury or Mortality 

subsection in the Analysis and 

Negligible Impact Determination section 

of the 2018 HSTT final rule (83 FR 

66985–66993) for detailed discussions 

of the impacts of M/SI, including a 

description of how the agency uses the 

PBR metric and other factors to inform 

our analysis and an analysis of the 

impacts on each species and stock for 

which M/SI is proposed for 

authorization, including the 

relationship of potential mortality for 

each species to the insignificance 

threshold and residual PBR, except as 

updated below. 

Stocks With M/SI Below the 

Insignificance Threshold 

As noted in the Serious Injury or 

Mortality subsection of the Negligible 

Impact Analysis and Determination 

section in the 2018 HSTT final rule and 

2020 HSTT final rule, for a species or 

stock with incidental M/SI less than 10 

percent of residual PBR, we consider M/ 

SI from the specified activities to 

represent an insignificant incremental 

increase in ongoing anthropogenic M/SI 

that alone (i.e., in the absence of any 

other take and barring any other 

unusual circumstances) will clearly not 

adversely affect annual rates of 

recruitment and survival. In this case, as 

shown in table 10 and table 11, the 

following species or stocks have 

potential or estimated M/SI from vessel 

strike and explosive takes, respectively, 

and proposed for authorization below 

their insignificance threshold: fin whale 

(CA/OR/WA stock), gray whale (Eastern 

North Pacific stock), humpback whale 

(Hawaii stock and Mainland MexicoCA/OR/WA stock), California sea lion 

(U.S stock), and short-beaked common 

dolphin (CA/OR/WA stock). While the 

proposed authorized M/SI of gray 

whales (Eastern North Pacific stock) is 

below the insignificance threshold, 

because of the recent UME, we further 

address how the proposed authorized 

M/SI and the UME inform the negligible 

impact determination immediately 

below. For the other four stocks with 

proposed authorized M/SI below the 

insignificance threshold, there are no 

other known factors, information, or 

unusual circumstances that indicate 

anticipated M/SI below the 

insignificance threshold could have 

adverse effects on annual rates of 

recruitment or survival and they are not 

discussed further. For the remaining 

stocks with anticipated potential M/SI 

above the insignificance threshold, how 

that M/SI compares to residual PBR, as 

well as additional factors, as 

appropriate, are discussed below as 

well. 

Gray Whales (Eastern North Pacific 

Stock) 

Since January 2019, gray whale 

strandings along the west coast of North 

America have been significantly higher 

than the previous 18-year averages. 

Preliminary findings from necropsies 

have shown evidence of emaciation. 

These findings are not consistent across 

all of the whales examined, so more 

research is needed. The seasonal pattern 

of elevated strandings in the spring and 

summer months is similar to that of the 

previous gray whale UME in 1999–2000. 

If strandings continue to follow a 

similar pattern, we would anticipate a 

decrease in strandings in late summer 

and fall. However, combined with other 

annual human-caused mortalities and 

viewed through the PBR lens (for 

human-caused mortalities), total 

human-caused mortality would still fall 

below residual PBR. Given the small 

number of takes by serious injury or 

mortality proposed for authorization, 

the proposed takes are not anticipated to 

exacerbate the ongoing UME. 

Stocks With M/SI Above the 

Insignificance Threshold 

Blue Whale (Eastern North Pacific 

Stock) 

For blue whales (Eastern North Pacific 

stock), PBR is currently set at 4.1 and 

the total annual M/SI is estimated at 

greater than or equal to 19.5, yielding a 

residual PBR of ¥15.4. This is slightly 

higher than the 2020 HSTT final rule 

(was ¥16.7). NMFS proposes to 

authorize one M/SI for the Navy over 

the 7-year duration of the rule 

(indicated as 0.14 annually for the 

purposes of comparing to PBR and 

evaluating overall effects on annual 

rates of recruitment and survival), 

which means that residual PBR is 

exceeded by 15.54. However, as 

described in the 2018 and 2020 rules, 

given that the negligible impact 

determination is based on the 

assessment of take of the activity being 

analyzed, when total annual mortality 

from human activities is higher, but the 

impacts from the specific activity being 

analyzed are very small, NMFS may still 

find the impact of the proposed 

authorized take from a specified activity 

to be negligible even if total humancaused mortality exceeds PBR if the 

proposed authorized mortality is less 

than 10 percent of PBR and management 

measures are being taken to address 

serious injuries and mortalities from the 

other activities causing mortality (i.e., 

other than the specified activities 

covered by the incidental take 

authorization in consideration). When 

those considerations are applied here, 

the authorized lethal take (0.14 

annually) of blue whales from the 

Eastern North Pacific stock is less than 

10 percent of PBR (which is 4.1), and 

there are management measures in place 

to address M/SI from activities other 

than those the Navy is conducting (as 

discussed below). Perhaps more 

importantly, the available data suggests 

that the current number of vessel strikes 

is not likely to have an adverse impact 

on the population, despite the fact that 

it exceeds PBR, with the Navy’s 

minimal additional mortality of one 

whale in the 7 years not creating the 

likelihood of adverse impact. 

Immediately below, we explain the 

information that supports our finding 

that the Navy’s proposed authorized M/ 

SI is not expected to result in more than 

a negligible impact on this stock. As 

described previously, NMFS must also 

ensure that impacts by the applicant on 

the species or stock from other types of 

take (i.e., harassment) do not combine 

with the impacts from mortality to 

adversely affect the species or stock via 

impacts on annual rates of recruitment 

or survival, which occurs further below 

in the stock-specific conclusion 

sections. 

As discussed in the 2018 HSTT final 

rule and the 2020 HSTT final rule, the 

2018 draft SAR and the more recent 

SARs rely on a new method to estimate 

annual deaths by vessel strike utilizing 

an encounter theory model that 

combined species distribution models of 

whale density, vessel traffic 

characteristics, and whale movement 

patterns obtained from satellite-tagged 

animals in the region to estimate 

encounters that would result in 

mortality (Rockwood et al. 2017). The 

model predicts 18 annual mortalities of 

blue whales from vessel strikes, which, 

with the additional M/SI of 1.54 from 

fisheries interactions, results in the 

current estimate of residual PBR being 

¥15.4. Although NMFS’ Permits and 

Conservation Division in the Office of 

Protected Resources has independently 

reviewed the vessel strike model and its 

results and agrees that it is appropriate 

for estimating blue whale mortality by 

vessel strike on the U.S. West Coast, for 

analytical purposes we also note that if 

the historical method were used to 

predict vessel strike (i.e., using observed 

mortality by vessel strike, or 0.8, instead 

of 18), then total human-caused 

mortality including the Navy’s potential 

take would not exceed PBR. We further 

note that the authors (Rockwood et al. 

2017) do not suggest that vessel strike 

suddenly increased to 18 recently. In 

fact, the model is not specific to a year, 

but rather offers a generalized 


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prediction of vessel strike off the U.S. 

West Coast. Therefore, if the Rockwood 

et al. (2017) model is an accurate 

representation of vessel strike, then 

similar levels of vessel strike have been 

occurring in past years as well. Put 

another way, if the model is correct, for 

some number of years total-humancaused mortality has been significantly 

underestimated and PBR has been 

similarly exceeded by a notable amount, 

and yet, the Eastern North Pacific stock 

of blue whales remains stable 

nevertheless. 

NMFS’ 2022 final SAR states that the 

current population trend is unknown, 

though there may be evidence of a 

population size increase since the 

1990s. The SAR further cites to 

Monnahan et al. (2015), which used a 

population dynamics model to estimate 

that the Eastern North Pacific blue 

whale population was at 97 percent of 

carrying capacity in 2013 and to suggest 

that the observed lack of a population 

increase since the early 1990s was 

explained by density dependence, not 

impacts from vessel strike. This would 

mean that this stock of blue whales 

shows signs of stability and is not 

increasing in population size because 

the population size is at or nearing 

carrying capacity for its available 

habitat. In fact, we note that this 

population has maintained this status 

throughout the years that the Navy has 

consistently tested and trained at 

similar levels (with similar vessel 

traffic) in areas that overlap with blue 

whale occurrence, which would be 

another indicator of population 

stability. 

Monnahan et al. (2015) modeled 

vessel numbers, vessel strikes, and the 

population of the Eastern North Pacific 

blue whale population from 1905 out to 

2050 using a Bayesian framework to 

incorporate informative biological 

information and assign probability 

distributions to parameters and derived 

quantities of interest. The authors tested 

multiple scenarios with differing 

assumptions, incorporated uncertainty, 

and further tested the sensitivity of 

multiple variables. Their results 

indicated that there is no immediate 

threat (i.e., through 2050) to the 

population from any of the scenarios 

tested, which included models with 10 

and 35 strike mortalities per year. 

Broadly, the authors concluded that, 

unlike other blue whale stocks, the 

Eastern North Pacific blue whales have 

recovered from 70 years of whaling and 

are in no immediate threat from vessel 

strikes. They further noted that their 

conclusion conflicts with the depleted 

and strategic designation under the 

MMPA as well as PBR specifically. 

As discussed, we also take into 

consideration management measures in 

place to address M/SI caused by other 

activities. The Channel Islands NMS 

staff coordinates, collects, and monitors 

whale sightings in and around the 

Vessel Speed Reduction (VSR) zones 

and the Channel Islands NMS region. 

Redfern et al. (2013) note that the most 

risky area for blue whales is the Santa 

Barbara Channel, where shipping lanes 

intersect with common feeding areas. 

The seasonally established Southern 

California VSR zone spans from Point 

Arguello to Dana Point, including the 

Traffic Separation Schemes in the Santa 

Barbara Channel and San Pedro 

Channel. Vessels transiting the area 

from May 1 through December 15, 2023 

are recommended to exercise caution 

and voluntarily reduce speed to 10 kn 

(18.5 km per hour) or less for blue, 

humpback, and fin whales. (Note this is 

an expanded timeframe from the Whale 

Advisory Zone discussed in the 2020 

HSTT final rule, which spanned June 

through November, though the effective 

period could change in future years.) 

Channel Island NMS observers collect 

information from aerial surveys 

conducted by NOAA, the U.S. Coast 

Guard, California Department of Fish 

and Game, and U.S. Navy chartered 

aircraft. Information on seasonal 

presence, movement, and general 

distribution patterns of large whales is 

shared with mariners, NMFS Office of 

Protected Resources, U.S. Coast Guard, 

California Department of Fish and 

Game, the Santa Barbara Museum of 

Natural History, the Marine Exchange of 

Southern California, and whale 

scientists. Real time and historical 

whale observation data collected from 

multiple sources can be viewed on the 

Point Blue Whale Database. 

In this case, 0.14 M/SI means one 

mortality in 1 of the 7 years and zero 

mortalities in 6 of those 7 years. 

Therefore, the Navy would not be 

contributing to the total human-caused 

mortality at all in 6 of the 7, or 85.7 

percent, of the years covered by this 

rulemaking. That means that even if a 

blue whale were to be struck, in 6 of the 

7 years there could be no effect on 

annual rates of recruitment or survival 

from Navy-caused M/SI. Additionally, 

the loss of a male would have far less, 

if any, effect on population rates and 

absent any information suggesting that 

one sex is more likely to be struck than 

another, we can reasonably assume that 

there is a 50 percent chance that the 

single strike authorized by this 

rulemaking would be a male, thereby 

further decreasing the likelihood of 

impacts on the population rate. In 

situations like this where potential M/ 

SI is fractional, consideration must be 

given to the lessened impacts 

anticipated due to the absence of M/SI 

in 6 of the 7 years and the fact that the 

single strike could be a male. Lastly, we 

reiterate that PBR is a conservative 

metric and also not sufficiently precise 

to serve as an absolute predictor of 

population effects upon which mortality 

caps would appropriately be based. This 

is especially important given the minor 

difference between zero and one across 

the 7-year period covered by this 

rulemaking, which is the smallest 

distinction possible when considering 

mortality. As noted above, Wade et al. 

(1998), authors of the paper from which 

the current PBR equation is derived, 

note that ‘‘Estimating incidental 

mortality in 1 year to be greater than the 

PBR calculated from a single abundance 

survey does not prove the mortality will 

lead to depletion; it identifies a 

population worthy of careful future 

monitoring and possibly indicates that 

mortality-mitigation efforts should be 

initiated.’’ The information included 

here indicates that the current 

population trend of this blue whale 

stock is unknown but likely 

approaching carrying capacity and has 

leveled off because of densitydependence, not human-caused 

mortality, in spite of what might be 

otherwise indicated from the calculated 

PBR. Further, potential (and proposed 

for authorization) M/SI is below 10 

percent of PBR and management actions 

are in place to minimize vessel strike 

from other vessel activity in one of the 

highest-risk areas for strikes. Based on 

the presence of the factors described 

above, we do not expect lethal take from 

Navy activities, alone, to adversely 

affect Eastern North Pacific blue whales 

through effects on annual rates of 

recruitment or survival. Nonetheless, 

the fact that total human-caused 

mortality exceeds PBR necessitates close 

attention to the remainder of the 

impacts (i.e., harassment) on the Eastern 

North Pacific stock of blue whales from 

the Navy’s activities to ensure that the 

total authorized takes have a negligible 

impact on the species or stock. 

Therefore, this information will be 

considered in combination with our 

assessment of the impacts of proposed 

harassment takes in the Group and 

Species-Specific Analyses section that 

follows. 

Sei Whale (Eastern North Pacific Stock) 

For sei whales (Eastern North Pacific 

stock), PBR is currently set at 0.75. The 

total annual M/SI is estimated at greater 

than or equal to 0.2 in the 2022 final 

SAR, which reflects one strike over 5 


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years, yielding a residual PBR of 0.55. 

However, more recent information 

suggests that the total annual M/SI 

reflected in the SAR may be 

overestimated because the one mortality 

considered in the calculation may not 

have been caused by a vessel strike. 

Carretta et al. (2021) elected to omit this 

strike from its report summarizing 

sources of human-related injury and 

mortality for U.S. Pacific west coast 

marine mammal stock assessments after 

reviewing the stranding narrative. The 

narrative indicated that the strike likely 

occurred post-mortem, evidenced by a 

lack of hemorrhaging in the whale’s 

tissues. NMFS proposes to authorize 

one M/SI for the Navy over the 7-year 

duration of the rule (indicated as 0.14 

annually for the purposes of comparing 

to PBR and evaluating overall effects on 

annual rates of recruitment and 

survival), which means that residual 

PBR is 0.41 with the conservative 

inclusion of the likely post-mortem 

strike discussed above. 

We acknowledge that the 2023 vessel 

strike by the U.S. Navy could have been 

of a sei whale or a CA/OR/WA fin 

whale, and this strike is not 

quantitatively included in this PBR 

analysis (nor is it quantitatively 

included in the PBR analysis for CA/ 

OR/WA fin whale if both of the 2021 

U.S. Navy strikes were fin whales) 

which rely on the 2022 final SARs. 

However, consideration of the 2023 

strike would not change the total M/SI 

which NMFS compares to PBR, as the 

single strike from 2012–2016 used to 

calculate the vessel strike rate in the 

2022 final SAR occurred in 2015 

(which, as noted above, likely occurred 

post-mortem, and therefore, inclusion of 

this strike in the annual total M/SI is 

inherently conservative), and the 2023 

U.S. Navy strike occurred outside of the 

2012–2016 time period. Therefore, 

while we acknowledge the 2023 U.S. 

Navy strike, in the quantitative analysis 

it is treated the same as other non-U.S. 

Navy strikes that occurred outside of the 

timeframe reflected in the total M/SI 

(2012–2016). 

Immediately below, we explain the 

information that supports our finding 

that the Navy’s proposed authorized M/ 

SI is not expected to result in more than 

a negligible impact on this stock. As 

described previously, NMFS must also 

ensure that impacts by the applicant on 

the species or stock from other types of 

take (i.e., harassment) do not combine 

with the impacts from mortality to 

adversely affect the species or stock via 

impacts on annual rates of recruitment 

or survival, which occurs further below 

in the stock-specific conclusion 

sections. 

Of note, management measures are in 

place to address M/SI caused by other 

activities. The Channel Islands NMS 

staff coordinates, collects, and monitors 

whale sightings in and around the 

Vessel Speed Reduction (VSR) zones 

and the Channel Islands NMS region. 

The seasonally established Southern 

California VSR zone spans from Point 

Arguello to Dana Point, including the 

Traffic Separation Schemes in the Santa 

Barbara Channel and San Pedro 

Channel. Vessels transiting the area 

from May 1 through December 15, 2023 

are recommended to exercise caution 

and voluntarily reduce speed to 10 kn 

(18.5 km per hour) or less. While the 

VSR zone is aimed at reducing risk of 

fatal vessel strike of blue, humpback, 

and fin whales, this measure is also 

anticipated to reduce risk to sei whales 

(note, this is an expanded timeframe 

from the Whale Advisory Zone 

discussed in the 2020 HSTT final rule, 

which spanned June through November, 

though the effective period could 

change in future years). Channel Island 

NMS observers collect information from 

aerial surveys conducted by NOAA, the 

U.S. Coast Guard, California Department 

of Fish and Game, and U.S. Navy 

chartered aircraft. Information on 

seasonal presence, movement, and 

general distribution patterns of large 

whales is shared with mariners, NMFS 

Office of Protected Resources, U.S. 

Coast Guard, California Department of 

Fish and Game, the Santa Barbara 

Museum of Natural History, the Marine 

Exchange of Southern California, and 

whale scientists. Real time and 

historical whale observation data 

collected from multiple sources can be 

viewed on the Point Blue Whale 

Database. 

Further, as stated in the 2022 final 

SAR, the California swordfish drift 

gillnet fishery is the most likely U.S. 

fishery to interact with Eastern North 

Pacific sei whales, though there are zero 

estimated annual takes from this fishery 

given no observed entanglements from 

1990–2016 across 8,845 monitored 

fishing sets (Carretta et al. (2018b)). 

NMFS established the Pacific Offshore 

Cetacean Take Reduction Team in 1996 

and prepared an associated Plan 

(PCTRP) to reduce the risk of M/SI via 

fisheries interactions. In 1997, NMFS 

published final regulations formalizing 

the requirements of the PCTRP, 

including the use of pingers following 

several specific provisions and the 

employment of Skipper education 

workshops. 

In this case, 0.14 M/SI means one 

authorized mortality in 1 of the 7 years 

and zero authorized mortalities in 6 of 

those 7 years. Therefore, the Navy’s 

authorized take would not be 

contributing to the total human-caused 

mortality at all in 6 of the 7, or 85.7 

percent, of the years covered by this 

rulemaking. That means that even if a 

sei whale were to be struck, in 6 of the 

7 years there could be no effect on 

annual rates of recruitment or survival 

from Navy-caused M/SI. Additionally, 

the loss of a male would have far less, 

if any, effect on population rates and 

absent any information suggesting that 

one sex is more likely to be struck than 

another, we can reasonably assume that 

there is a 50 percent chance that the 

single strike authorized by this 

rulemaking would be a male, thereby 

further decreasing the likelihood of 

impacts on the population rate. In 

situations like this where potential M/ 

SI is fractional, consideration must be 

given to the lessened impacts 

anticipated due to the absence of M/SI 

in 6 of the 7 years and the fact that the 

single strike could be a male. 

Lastly, we reiterate that PBR is a 

conservative metric and also not 

sufficiently precise to serve as an 

absolute predictor of population effects 

upon which mortality caps would 

appropriately be based. This is 

especially important given the minor 

difference between zero and one across 

the 7-year period covered by this 

rulemaking, which is the smallest 

distinction possible when considering 

mortality. As noted above, Wade et al. 

(1998), authors of the paper from which 

the current PBR equation is derived, 

note that ‘‘Estimating incidental 

mortality in 1 year to be greater than the 

PBR calculated from a single abundance 

survey does not prove the mortality will 

lead to depletion; it identifies a 

population worthy of careful future 

monitoring and possibly indicates that 

mortality-mitigation efforts should be 

initiated.’’ Even after qualitatively 

considering the possibility that the 

whale struck by Navy in 2023 was a sei 

whale, and based on the presence of the 

factors described above, we do not 

expect one authorized lethal take from 

Navy activities, alone, to adversely 

affect Eastern North Pacific sei whales 

through effects on annual rates of 

recruitment or survival. This 

information will be considered in 

combination with our assessment of the 

impacts of proposed harassment takes in 

the Group and Species-Specific 

Analyses section that follows. 

Group and Species-Specific Analyses 

In addition to broader analyses of the 

impacts of the Navy’s activities on 

mysticetes, odontocetes, and pinnipeds, 

the 2018 HSTT final rule contained 

detailed analyses of the effects of the 


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Navy’s activities in the HSTT Study 

Area on each affected species and stock 

and was updated, as appropriate, in the 

2020 HSTT final rule. All of that 

information and analyses remain 

applicable and valid for our analyses of 

the effects of the same Navy activities 

on the same species and stocks, with the 

exception of humpback whale, for 

which the stock structure has been 

revised, and NMFS has updated its 

analyses accordingly for this proposed 

rule. See the Group and SpeciesSpecific Analyses subsection in the 

Analysis and Negligible Impact 

Determination section of the 2018 HSTT 

final rule (83 FR 66993–67018). In 

addition, apart from the additional 

proposed incidental take by vessel strike 

of two large whales, the resulting 

changes to the average annual mortality 

estimates discussed above, and the 

revised humpback whale stock 

structure, no new information has been 

received since the publication of the 

2020 HSTT final rule that significantly 

changes the analyses of the effects of the 

Navy’s activities on each species and 

stock presented in the 2020 HSTT final 

rule (new information regarding vessel 

strike, the potential impact of the new 

gray whale UME, and the revised 

humpback whale stock structure were 

discussed earlier in the rule). 

In the discussions below, the 

estimated Level B harassment takes 

represent instances of take, not the 

number of individuals taken (the much 

lower and less frequent Level A 

harassment takes are far more likely to 

be associated with separate individuals), 

and in many cases, some individuals are 

expected to be taken more than one time 

while in other cases, a portion of 

individuals will not be taken at all. 

Below, we compare the total take 

numbers (including PTS, TTS, and 

behavioral disturbance) for species or 

stocks to their associated abundance 

estimates to evaluate the magnitude of 

impacts across the species or stock and 

to individuals. Specifically, when an 

abundance percentage comparison is 

below 100, it means that percentage or 

less of the individuals in the stock will 

be affected (i.e., some individuals will 

not be taken at all), that the average for 

those taken is 1 day per year, and that 

we would not expect any individuals to 

be taken more than a few times in a 

year. When it is more than 100 percent, 

it means there will definitely be some 

number of repeated takes of individuals. 

For example, if the percentage is 300, 

the average would be each individual is 

taken on 3 days in a year if all were 

taken, but it is more likely that some 

number of individuals will be taken 

more than three times and some number 

of individuals fewer times or not at all. 

While it is not possible to know the 

maximum number of days across which 

individuals of a stock might be taken, in 

acknowledgement of the fact that it is 

more than the average, for the purposes 

of this analysis, we assume a number 

approaching twice the average. For 

example, if the percentage of take 

compared to the abundance is 800, we 

estimate that some individuals might be 

taken as many as 16 times. Those 

comparisons are included in the 

sections below. For some stocks, these 

numbers have been adjusted slightly 

(with these adjustments being in the 

single digits) so as to more consistently 

apply this approach, but these minor 

changes did not change the analysis or 

findings. 

To assist in understanding what this 

analysis means, we clarify a few issues 

related to estimated takes and the 

analysis here. An individual that incurs 

a PTS or TTS take may sometimes, for 

example, also be subject to behavioral 

disturbance at the same time. As 

described in the Harassment subsection 

of the Analysis and Negligible Impact 

Determination section of the 2018 HSTT 

final rule, the degree of PTS, and the 

degree and duration of TTS, expected to 

be incurred from the Navy’s activities 

are not expected to impact marine 

mammals such that their reproduction 

or survival could be affected. Similarly, 

data do not suggest that a single 

instance in which an animal accrues 

PTS or TTS and is also subjected to 

behavioral disturbance would result in 

impacts to reproduction or survival. 

Alternately, we recognize that if an 

individual is subjected to behavioral 

disturbance repeatedly for a longer 

duration and on consecutive days, 

effects could accrue to the point that 

reproductive success is jeopardized (as 

discussed below in the stock-specific 

summaries). Accordingly, in analyzing 

the number of takes and the likelihood 

of repeated and sequential takes (which 

could result in reproductive impacts), 

we consider the total takes, not just the 

Level B harassment takes by behavioral 

disturbance, so that individuals 

potentially exposed to both threshold 

shift and behavioral disturbance are 

appropriately considered. We note that 

the same reasoning applies with the 

potential addition of behavioral 

disturbance to tissue damage from 

explosives, the difference being that we 

do already consider the likelihood of 

reproductive impacts whenever tissue 

damage occurs. Further, the number of 

Level A harassment takes by either PTS 

or tissue damage are so low compared 

to abundance numbers that it is 

considered highly unlikely that any 

individual would be taken at those 

levels more than once. 

Having considered all of the 

information and analyses previously 

presented in the 2018 HSTT final rule, 

including the Group and SpeciesSpecific Analyses discussions organized 

by the different groups and species, 

below we present tables showing 

instances of total take as a percentage of 

stock abundance for each group, 

updated with the new vessel strike 

calculations and humpback stock 

structure. We then summarize the 

information for each species or stock, 

considering the analysis from the 2018 

HSTT final rule, 2020 HSTT final rule, 

and any new analysis. The analyses 

below in some cases address species 

collectively if they occupy the same 

functional hearing group (i.e., low, mid, 

and high-frequency cetaceans and 

pinnipeds in water), share similar life 

history strategies, and/or are known to 

behaviorally respond similarly to 

acoustic stressors. Because some of 

these groups or species share 

characteristics that inform the impact 

analysis similarly, it would be 

duplicative to repeat the same analysis 

for each species or stock. In addition, 

animals belonging to each stock within 

a species typically have the same 

hearing capabilities and behaviorally 

respond in the same manner as animals 

in other stocks within the species. 

Mysticetes 

In table 12 and table 13 below for 

mysticetes, we indicate the total annual 

mortality, Level A harassment, and 

Level B harassment, and a number 

indicating the instances of total take as 

a percentage of abundance. Table 12 and 

table 13 have been updated from tables 

18 and 19 in the 2020 HSTT final rule, 

as appropriate, with the 2022 final SARs 

and updated information on mortality, 

as discussed above. For additional 

information and analysis supporting the 

negligible-impact analysis, see the 

Mysticetes discussion in the Group and 

Species-Specific Analyses section of the 

2018 HSTT final rule, all of which 

remains applicable to this proposed rule 

unless specifically noted. 


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TABLE 12—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR

MYSTICETES IN THE HRC PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF TOTAL

TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total takes a Abundance Instance of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality b

Total 

takes 

(entire 

study 

area) 

Takes 

(within 

Navy 

EEZ) 

Total Navy 

abundance 

inside and 

outside of 

EEZ 

(HRC) 

Within EEZ 

Navy 

abundance 

(HRC) 

Total 

take as 

percentage 

of total 

Navy 

abundance 

(HRC) 

EEZ 

take as 

percentage 

of Navy 

EEZ 

abundance 

(HRC) 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Blue whale Central 

North 

Pacific.

15 33 0 0 0 48 40 43 33 112 121 

Bryde’s 

whale.

Hawaii ..... 40 106 0 0 0 146 123 108 89 135 138 

Fin whale Hawaii ..... 21 27 0 0 0 48 41 52 40 92 103 

Humpback 

whale.

Hawaii ..... 2,837 6,289 3 0 0.29 9,129 7,389 5,078 4,595 180 161 

Minke 

whale.

Hawaii ..... 1,233 3,697 2 0 0 4,932 4,030 3,652 2,835 135 142 

Sei whale Hawaii ..... 46 121 0 0 0 167 135 138 107 121 126 

Note: For the Hawaii take estimates, we compare predicted takes to abundance estimates generated from the same underlying density estimates (as described in 

the Estimated Take of Marine Mammals section of the 2018 HSTT final rule), both in and outside of the U.S. EEZ. Because the portion of the Navy’s study area inside the U.S. EEZ is generally concomitant with the area used to generate the abundance estimates in the SARs, and the abundance predicted by the same underlying density estimates is the preferred abundance to use, there is no need to separately compare the take to the SARs abundance estimate. aTotal takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. bThe annual mortality of 0.29 is the result of no more than two mortalities over the course of 7 years from vessel strikes as described above in the Estimated Take 

of Marine Mammals section. 

TABLE 13—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR

MYSTICETES IN THE SOCAL PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF

TOTAL TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total 

takes a

Abundance Instance of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality b

Total 

takes 

(entire 

study 

Area) 

Navy 

abundance 

in action 

area (SOCAL) 

NMFS 

SARS 

abundance 

Total 

take as 

percentage 

of total 

Navy 

abundance 

in action 

area 

Total 

take as 

percentage 

of total 

SAR 

abundance 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Blue whale ......... Eastern North 

Pacific.

792 1,196 1 0 0.14 1,989 785 1,898 253 105 

Bryde’s whale .... Eastern Tropical 

Pacific.

14 27 0 0 0 41 1.3 unknown 3,154 unknown 

Fin whale ........... CA/OR/WA ........ 835 1,390 1 0 0.57 2,227 363 11,065 613 20 

Humpback whale Central America/ 

Southern Mexico-CA/OR/WA.

282 594 0 0 0 876 c 74 1,496 1,184 59 

Mainland 

Mexico- CA/ 

OR/WA.

198 920 1 0 0.14 1,119 c 173 3,477 647 32 

Minke whale ...... CA/OR/WA ........ 259 666 1 0 0 926 163 915 568 101 

Sei whale ........... Eastern North 

Pacific.

27 52 0 0 0.14 79 3 519 2,633 15 

Gray whale ........ Eastern North 

Pacific.

1,316 3,355 7 0 0.57 4,679 193 26,960 2,424 17 

Gray whale ........ Western North 

Pacific.

2 4 0 0 0 6 0 290 0 2 

Note: For the SOCAL take estimates, because of the manner in which the Navy study area overlaps the ranges of many MMPA stocks (i.e., a stock may range far 

north to Washington state and beyond and abundance may only be predicted within the U.S. EEZ, while the Navy study area is limited to Southern California and 

northern Mexico, but extends beyond the U.S. EEZ), we compare predicted takes to both the abundance estimates for the study area, as well as the SARs (as described in the Estimated Take of Marine Mammals section of the 2018 HSTT final rule). aTotal takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. bThe annual mortality of 0.14 is the result of no more than one mortality over the course of 7 years from vessel strikes as described above in the Estimated Take 

of Marine Mammals section. The annual mortality of 0.57 is the result of no more than four mortalities over the course of 7 years from vessel strikes. c In the 2020 HSTT final rule, NMFS reported a Navy abundance in Action Area (SOCAL) of 247 CA/OR/WA humpback whales. As explained in more detail in the 

Estimated Take from Vessel Strikes and Explosives by Serious Injury or Mortality, NMFS estimates that approximately 30 percent of the humpback whales off the 

coast of California may be from the Central America DPS with the remaining 70 percent are expected to be from the Mexico DPS. Therefore, of the estimated 247 

humpback whales in SOCAL, NMFS anticipates that 74 would be of the Central America/Southern Mexico-CA/OR/WA stock (Central America DPS), and 173 would 

be of the Mainland Mexico-CA/OR/WA stock (Mexico DPS). 


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Below we compile and summarize the 

information that supports our 

preliminary determination that the 

Navy’s activities would not adversely 

affect any species or stocks through 

effects on annual rates of recruitment or 

survival for any of the affected mysticete 

species and stocks. 

Blue Whale (Eastern North Pacific 

Stock) 

Blue whales are listed as endangered 

under the ESA, and the current 

population trend for the Eastern North 

Pacific stock is unknown. We further 

note that this stock was originally listed 

under the ESA as a result of the impacts 

from commercial whaling, which is no 

longer affecting the species. NMFS 

proposes to authorize one mortality over 

the 7 years covered by this rulemaking 

or 0.14 mortality annually. With the 

addition of this 0.14 annual mortality, 

residual PBR is exceeded, resulting in 

the total human-caused mortality 

exceeding PBR by 15.54. However, as 

described in more detail in the Serious 

Injury or Mortality section above, when 

total human-caused mortality exceeds 

PBR, we consider whether the 

incremental addition of a small amount 

of authorized mortality from the 

specified activity may still result in a 

negligible impact, in part by identifying 

whether it is less than 10 percent of 

PBR. In this case, the authorized 

mortality is well below 10 percent of 

PBR, management measures are in place 

to reduce mortality from other sources, 

and the incremental addition of a single 

mortality over the course of the 7-year 

Navy rule is not expected to, alone, lead 

to adverse impacts on the stock through 

effects on annual rates of recruitment or 

survival. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 253 and 105 percent, 

respectively (table 13). Given the range 

of blue whales, this information 

suggests that only some portion of 

individuals in the stock are likely 

impacted, but that there will likely be 

some repeat exposure (maybe 5 or 6 

days within a year) of some subset of 

individuals that spend extended time 

within SOCAL. Regarding the severity 

of those individual Level B harassment 

takes by behavioral disturbance, the 

duration of any exposure is expected to 

be between minutes and hours (i.e., 

relatively short) and the received sound 

levels largely below 172 dB with a 

portion up to 178 dB (i.e., of a moderate 

or lower level, less likely to evoke a 

severe response). Additionally, the Navy 

implements time/area mitigation in 

SOCAL in the majority of the BIAs, 

which will reduce the severity of 

impacts to blue whales by reducing 

interference in feeding that could result 

in lost feeding opportunities or 

necessitate additional energy 

expenditure to find other good 

opportunities. Regarding the severity of 

TTS takes, we have explained in the 

2018 HSTT final rule that they are 

expected to be low-level, of short 

duration, and mostly not in a frequency 

band that would be expected to interfere 

with blue whale communication or 

other important low-frequency cues— 

and that the associated lost 

opportunities and capabilities are not at 

a level that would impact reproduction 

or survival. For similar reasons (as 

described in the 2018 HSTT final rule) 

the single estimated Level A harassment 

take by PTS for this stock is unlikely to 

have any effect on the reproduction or 

survival of that one individual, even if 

it were to be experienced by an animal 

that also experiences one or more Level 

B harassment takes by behavioral 

disturbance. 

Altogether, only a small portion of the 

stock is anticipated to be impacted and 

any individual blue whale is likely to be 

disturbed at a low-moderate level, with 

likely many animals exposed only once 

or twice and a subset potentially 

disturbed across 5 or 6 days but 

minimized in biologically important 

areas. This low magnitude and severity 

of harassment effects is not expected to 

result in impacts on the reproduction or 

survival of any individuals and, 

therefore, when combined with the 

proposed authorized mortality (which 

our earlier analysis indicated would not, 

alone, have more than a negligible 

impact on this stock of blue whales), the 

total take is not expected to adversely 

affect this stock through impacts on 

annual rates of recruitment or survival. 

For these reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on the Eastern North Pacific 

stock of blue whales. 

Bryde’s Whale (Eastern Tropical Pacific 

Stock) 

Little is known about this stock or its 

status, and it is not listed under the 

ESA. No mortality or Level A 

harassment is anticipated or proposed to 

be authorized. Regarding the magnitude 

of Level B harassment takes (TTS and 

behavioral disturbance), the number of 

estimated total instances of take 

compared to the abundance is 3,154 

percent; however, the abundance upon 

which this percentage is based (1.3 

whales from the Navy estimate, which 

is extrapolated from density estimates 

based on very few sightings) is clearly 

erroneous and the SAR does not include 

an abundance estimate because all of 

the survey data is outdated (table 13). 

However, the abundance in the early 

1980s was estimated as 22,000 to 

24,000, a portion of the stock was 

estimated at 13,000 in 1993, and the 

minimum number in the Gulf of 

California was estimated at 160 in 1990. 

Given this information and the fact that 

41 total takes of Bryde’s whales were 

estimated, this information suggests that 

only a small portion of the individuals 

in the stock are likely impacted, and 

few, if any, are likely taken over more 

than 1 day. Regarding the severity of 

those individual Level B harassment 

takes by behavioral disturbance, the 

duration of any exposure is expected to 

be between minutes and hours (i.e., 

relatively short) and the received sound 

levels largely below 172 dB with a 

portion up to 178 dB (i.e., of a moderate 

or lower level, less likely to evoke a 

severe response). Regarding the severity 

of TTS takes, they are expected to be 

low-level, of short duration, and mostly 

not in a frequency band that would be 

expected to interfere with Bryde’s whale 

communication or other important lowfrequency cues. Any associated lost 

opportunities and capabilities are not at 

a level that would impact reproduction 

or survival. 

Altogether, only a small portion of the 

stock is anticipated to be impacted and 

any individual Bryde’s whale is likely to 

be disturbed at a low-moderate level, 

with few, if any, individuals exposed 

over more than 1 day in the year. This 

low magnitude and severity of 

harassment effects is not expected to 

result in impacts on individual 

reproduction or survival, much less 

annual rates of recruitment or survival. 

For these reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on the Eastern Tropical Pacific 

stock of Bryde’s whales. 

Fin Whale (CA/OR/WA Stock) 

The SAR identifies this stock as 

‘‘increasing,’’ even though the larger 

species is listed as endangered under 

the ESA. NMFS proposes to authorize 

four mortalities over the 7 years covered 

by this rulemaking, or 0.57 mortality 

annually. The addition of this 0.57 

annual mortality still leaves the total 

human-caused mortality well under 

residual PBR. 


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We acknowledge the 2021 vessel 

strike of two fin whales by the Royal 

Australian Navy, and that the 2021 and 

2023 vessel strikes by the U.S. Navy 

could have been CA/OR/WA fin whales. 

While the Royal Australian Navy strikes 

are not quantitatively included in the 

estimated take by vessel strike, even if 

they were, and if we presumed that the 

2021 and 2023 U.S. Navy strikes were 

all fin whales, M/SI of this stock would 

still fall well below PBR (80). 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 613 and 20 percent, respectively 

(table 13). This information suggests 

that only some portion (less than 25 

percent) of individuals in the stock are 

likely impacted but that there is likely 

some repeat exposure (perhaps up to 12 

days within a year) of some subset of 

individuals that spend extended time 

within the SOCAL complex. Some of 

these takes could occur on a few 

sequential days for some small number 

of individuals, for example, if they 

resulted from a multi-day exercise on a 

range while individuals were in the area 

for multiple days feeding. Regarding the 

severity of those individual Level B 

harassment takes by behavioral 

disturbance, the duration of any 

exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 

dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

Additionally, while there are no known 

BIAs for fin whales in the SOCAL range, 

the Navy implements time/area 

mitigation in SOCAL in blue whale 

BIAs, and fin whales are known to 

sometimes feed in some of the same 

areas, which means they could 

potentially accrue some benefits from 

the mitigation. Regarding the severity of 

TTS takes, they are expected to be lowlevel, of short duration, and mostly not 

in a frequency band that would be 

expected to interfere with fin whale 

communication or other important lowfrequency cues—and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. For similar 

reasons (as described in the 2018 HSTT 

final rule) the single estimated Level A 

harassment take by PTS for this stock is 

unlikely to have any effects on the 

reproduction or survival of that one 

individual. 

Altogether, this population is 

increasing, only a small portion of the 

stock is anticipated to be impacted, and 

any individual fin whale is likely to be 

disturbed at a low-moderate level, with 

the taken individuals likely exposed 

between 1 and 12 days, with a few 

individuals potentially taken on a few 

sequential days. This low magnitude 

and severity of harassment effects is not 

expected to result in impacts on 

individual reproduction or survival, and 

therefore, when combined with the 

proposed authorized mortality (which 

our earlier analysis indicated would not, 

alone, have more than a negligible 

impact on this stock of fin whales), the 

total take is not expected to adversely 

affect this stock through impacts on 

annual rates of recruitment or survival. 

For these reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on the CA/OR/WA stock of fin 

whales. 

Humpback Whale (Central America/ 

Southern Mexico-CA/OR/WA Stock) 

The SAR identifies this stock as 

increasing, though the growth rate is 

uncertain. Animals in this stock are of 

the Central America DPS which is 

designated as endangered under the 

ESA. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 1,184 and 59 percent, 

respectively (table 11). Given the range 

of humpback whales, this information 

suggests that only some portion of 

individuals in the stock are likely 

impacted but that there is likely some 

repeat exposure (perhaps up to 23 days 

within a year) of some subset of 

individuals that spend extended time 

within the SOCAL complex. Regarding 

the severity of those individual Level B 

harassment takes by behavioral 

disturbance, the duration of any 

exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 

dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

Some of these takes could occur on 

several sequential days for some small 

number of individuals, for example, if 

they resulted from a multi-day exercise 

on a range while individuals were in the 

area for multiple days feeding. However, 

in these amounts, it would still not be 

expected to adversely impact 

reproduction or survival of any 

individuals. 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with humpback whale 

communication or other important lowfrequency cues—and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. Altogether, 

only a small portion of the stock is 

anticipated to be impacted and any 

individual humpback whale is likely to 

be disturbed at a low-moderate level, 

with likely many animals exposed only 

once or twice and a subset potentially 

disturbed up to 23 days, but with no 

reason to think that more than a few of 

those days would be sequential. This 

low magnitude and severity of 

harassment effects is not expected to 

result in impacts on the reproduction or 

survival of any individuals and, 

therefore, the total take is not expected 

to adversely affect this stock through 

impacts on annual rates of recruitment 

or survival. For these reasons, we have 

preliminarily determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take proposed would have a 

negligible impact on the Central 

America/Southern Mexico-CA/OR/WA 

stock of humpback whales. 

Humpback Whale (Mainland MexicoCA/OR/WA Stock) 

The status of this stock is unknown. 

Animals in this stock are of the Mexico 

DPS which is designated as threatened 

under the ESA. NMFS proposes to 

authorize one mortality over the 7 years 

covered by this rulemaking, or 0.14 

mortality annually. The addition of this 

0.14 annual mortality still leaves the 

total human-caused mortality well 

under residual PBR. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 647 and 32 percent, respectively 

(table 13). Given the range of humpback 

whales, this information suggests that 

only some portion of individuals in the 

stock are likely impacted but that there 

is likely some repeat exposure (perhaps 

up to 13 days within a year) of some 

subset of individuals that spend 

extended time within the SOCAL 

complex. Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 


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dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

Some of these takes could occur on 

several sequential days for some small 

number of individuals, for example, if 

they resulted from a multi-day exercise 

on a range while individuals were in the 

area for multiple days feeding. However, 

in these amounts, it would still not be 

expected to adversely impact 

reproduction or survival of any 

individuals. 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with humpback whale 

communication or other important lowfrequency cues—and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. For similar 

reasons (as described in the 2018 HSTT 

final rule) the single estimated Level A 

harassment take by PTS for this stock is 

unlikely to have any effects on the 

reproduction or survival of that one 

individual. 

Altogether, only a small portion of the 

stock is anticipated to be impacted and 

any individual humpback whale is 

likely to be disturbed at a low-moderate 

level, with likely many animals exposed 

only once or twice and a subset 

potentially disturbed up to 13 days, but 

with no reason to think that more than 

a few of those days would be sequential. 

This low magnitude and severity of 

harassment effects is not expected to 

result in impacts on the reproduction or 

survival of any individuals and, 

therefore, when combined with the 

proposed authorized mortality (which 

our earlier analysis indicated would not, 

alone, have more than a negligible 

impact on this stock of humpback 

whales), the total take is not expected to 

adversely affect this stock through 

impacts on annual rates of recruitment 

or survival. For these reasons, we have 

preliminarily determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take proposed would have a 

negligible impact on the CA/OR/WA 

stock of humpback whales. 

Minke Whale (CA/OR/WA Stock) 

The status of this stock is unknown 

and it is not listed under the ESA. No 

mortality from vessel strike or tissue 

damage from explosive exposure is 

anticipated or proposed for 

authorization for this species. Regarding 

the magnitude of Level B harassment 

takes (TTS and behavioral disturbance), 

the number of estimated total instances 

of take compared to the abundance 

(measured against both the Navyestimated abundance and the SAR) is 

568 and 101 percent, respectively (table 

11). Based on the behaviors of minke 

whales, which often occur along 

continental shelves and sometimes 

establish home ranges along the West 

Coast, this information suggests that 

only a portion of individuals in the 

stock are likely impacted but that there 

is likely some repeat exposure (perhaps 

up to 11 days within a year) of some 

subset of individuals that spend 

extended time within the SOCAL 

complex. Some of these takes could 

occur on a few sequential days for some 

small number of individuals, for 

example, if they resulted from a multiday exercise on a range while 

individuals were in the area for multiple 

days feeding. Regarding the severity of 

those individual Level B harassment 

takes by behavioral disturbance, the 

duration of any exposure is expected to 

be between minutes and hours (i.e., 

relatively short) and the received sound 

levels largely below 172 dB with a 

portion up to 178 dB (i.e., of a moderate 

or lower level, less likely to evoke a 

severe response). Regarding the severity 

of TTS takes, they are expected to be 

low-level, of short duration, and mostly 

not in a frequency band that would be 

expected to interfere with minke whale 

communication or other important lowfrequency cues—and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. For similar 

reasons (as described in the 2018 HSTT 

final rule) the single estimated Level A 

harassment take by PTS for this stock is 

unlikely to have any effects on the 

reproduction or survival of that 

individual. 

Altogether, only a portion of the stock 

is anticipated to be impacted and any 

individual minke whale is likely to be 

disturbed at a low-moderate level, with 

the taken individuals likely exposed 

between 1 and 11 days, with a few 

individuals potentially taken on a few 

sequential days. This low magnitude 

and severity of harassment effects is not 

expected to result in impacts on 

individual reproduction or survival, 

much less annual rates of recruitment or 

survival. For these reasons, we have 

preliminarily determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take proposed would have a 

negligible impact on the CA/OR/WA 

stock of minke whales. 

Sei Whale (Eastern North Pacific Stock) 

The status of this stock is unknown, 

and sei whales are listed under the ESA. 

NMFS proposes to authorize one 

mortality over the 7 years covered by 

this rulemaking or 0.14 mortality 

annually. The addition of this 0.14 

annual mortality still leaves the total 

human-caused mortality under residual 

PBR. After additionally considering 

several qualitative factors described 

above, including that the 2023 strike 

could have been a sei whale (or fin 

whale), we do not expect one authorized 

lethal take from Navy activities, alone, 

to adversely affect Eastern North Pacific 

sei whales through effects on annual 

rates of recruitment or survival. No 

Level A harassment is anticipated or 

proposed for authorization. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 2,633 and 15 percent, 

respectively (table 13), however, the 

abundance upon which the Navy 

percentage is based (3 from the Navy 

estimate, which is extrapolated from 

density estimates based on very few 

sightings) is likely an underestimate of 

the number of individuals in the HSTT 

study Area, resulting in an 

overestimated percentage. Given this 

information and the large range of sei 

whales, and the fact that only 79 total 

Level B harassment takes of sei whales 

were estimated, it is likely that some 

very small number of sei whales would 

be taken repeatedly, potentially up to 15 

days in a year (typically 2,633 percent 

would lead to the estimate of 52 days/ 

year, however, given that there are only 

79 sei whale total takes, we used the 

conservative assumption that five 

individuals might be taken up to 15 

times, with the few remaining takes 

distributed among other individuals). 

Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 

dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

Some of these takes could occur on a 

few sequential days for some small 

number of individuals, for example, if 

they resulted from a multi-day exercise 

on a range while individuals were in the 

area for multiple days feeding, however, 

in these amounts it would still not be 

expected to adversely impact 

reproduction or survival of any 

individuals. Regarding the severity of 

TTS takes, they are expected to be lowlevel, of short duration, and mostly not 

in a frequency band that would be 

expected to interfere with sei whale 


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communication or other important lowfrequency cues—and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. 

Altogether, only a small portion of the 

stock is anticipated to be impacted and 

any individual sei whale is likely to be 

disturbed at a low-moderate level, with 

only a few individuals exposed over one 

to 15 days in a year, with no more than 

a few sequential days. This low 

magnitude and severity of harassment 

effects is not expected to result in 

impacts on individual reproduction or 

survival, and therefore, when combined 

with the proposed authorized mortality 

(which our earlier analysis indicated 

would not, alone, have more than a 

negligible impact on this stock of sei 

whales), the total take is not expected to 

adversely affect this stock through 

impacts on annual rates of recruitment 

or survival. For these reasons, we have 

preliminarily determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take proposed would have a 

negligible impact on the Eastern North 

Pacific stock of sei whales. 

Gray Whale (Eastern North Pacific 

Stock) 

The Eastern North Pacific stock of 

gray whale is not ESA-listed and the 

SAR indicates that the stock is 

increasing. However, recent (2021– 

2022) surveys conducted by NMFS’ 

Southwest Fisheries Science Center 

estimated that the population has 

declined to 16,650 whales, though the 

authors note that this stock has 

historically shown a pattern of 

population growth and decline that has 

not impacted the population in the long 

term (Eguchi et al. 2022). NMFS is 

proposing to authorize four mortalities 

over the 7 years covered by this 

rulemaking, or 0.57 mortality annually. 

The addition of this 0.57 annual 

mortality still leaves the total humancaused mortality well under the 

insignificance threshold of residual PBR 

(670). On May 31, 2019, NMFS declared 

the unusual spike in strandings of gray 

whales along the west coast of North 

America since January 1, 2019 an UME. 

As of June 25, 2023, 674 gray whales 

have stranded along the west coast of 

North America (in the U.S., Canada, and 

Mexico) under this UME. Given the 

small number of takes by serious injury 

or mortality proposed for authorization, 

the proposed takes are not anticipated to 

exacerbate the ongoing UME. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 2,424 and 16 percent, 

respectively (table 13). (Note that in 

comparison to the recent Eguchi et al. 

2022 abundance estimate, the number of 

estimated total instances of take 

compared to the abundance would be 28 

percent.) This information suggests that 

only some small portion of individuals 

in the stock are likely impacted (less 

than 17 percent) but that there is likely 

some level of repeat exposure of some 

subset of individuals that spend 

extended time within the SOCAL 

complex. Typically 2,424 percent would 

lead to the estimate of 48 days/year, 

however, given that a large number of 

gray whales are known to migrate 

through the SOCAL complex and the 

fact that there are 4,679 total takes, we 

believe that it is more likely that a larger 

number of individuals would be taken 

one to a few times, while a small 

number staying in an area to feed for 

several days may be taken on 5–10 days. 

Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 

dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

Some of these takes could occur on a 

couple of sequential days for some small 

number of individuals; however, in 

these amounts it would still not be 

expected to adversely impact 

reproduction or survival of any 

individuals. 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with gray whale 

communication or other important lowfrequency cues and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. For these same 

reasons (low level and frequency band), 

while a small permanent loss of hearing 

sensitivity may include some degree of 

energetic costs for compensating or may 

mean some small loss of opportunities 

or detection capabilities, at the expected 

scale the seven estimated Level A 

harassment takes by PTS for gray whales 

would be unlikely to impact behaviors, 

opportunities, or detection capabilities 

to a degree that would interfere with 

reproductive success or survival of any 

individuals. 

Altogether, we have considered the 

impacts of the gray whale UME, the 

Eastern North Pacific stock of gray 

whales is not endangered or threatened 

under the ESA. The SAR indicates that 

the stock is increasing. However, recent 

(2021–2022) surveys conducted by 

NMFS’ Southwest Fisheries Science 

Center estimated that the population has 

declined (Eguchi et al. 2022). Only a 

small portion of the stock is anticipated 

to be impacted and any individual gray 

whale is likely to be disturbed at a lowmoderate level, with likely many 

animals exposed only once or twice and 

a subset potentially disturbed across 5 

to 10 days. This low magnitude and 

severity of harassment effects is not 

expected to result in impacts to 

reproduction or survival for any 

individuals and, therefore, when 

combined with the proposed authorized 

mortality of four whales over the 7 year 

period (which our earlier analysis 

indicated would not, alone, have more 

than a negligible impact on this stock of 

gray whales), the total take is not 

expected to adversely affect this stock 

through impacts on annual rates of 

recruitment or survival. For these 

reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on the Eastern North Pacific 

stock of gray whales. 

Gray Whale (Western North Pacific 

stock) 

The Western North Pacific stock of 

gray whales is reported as increasing in 

the 2022 final SAR but is listed as 

endangered under the ESA. No 

mortality or Level A harassment is 

anticipated or proposed for 

authorization. This stock is expected to 

incur the very small number of 6 Level 

B harassment takes (2 behavioral 

disruption and 4 TTS) to a stock with 

a SAR-estimated abundance of 290 

(table 11). These takes will likely accrue 

to different individuals, the behavioral 

disturbances will be of a low-moderate 

level, and the TTS instances will be at 

a low level and short duration. This low 

magnitude and severity of harassment 

effects is not expected to result in 

impacts on individual reproduction or 

survival, much less to adversely affect 

this stock through impacts on annual 

rates of recruitment or survival. For 

these reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on the Western North Pacific 

stock of gray whales. 

Humpback Whale (Hawaii Stock) 

The status of this stock is unknown. 

Animals in this stock are of the Hawaii 


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DPS which is not listed under the ESA. 

No Level A harassment by tissue 

damage is proposed for authorization. 

NMFS proposes to authorize two 

mortalities over the 7 years covered by 

this rulemaking, or 0.29 mortalities 

annually. The addition of this 0.29 

annual mortality still leaves the total 

human-caused mortality well under the 

insignificance threshold for residual 

PBR. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

instances of take compared to the 

abundance, both throughout the HSTT 

Study Area and within the U.S. EEZ, 

respectively, is 180 and 161 percent 

(table 12). This information and the 

complicated far-ranging nature of the 

stock structure suggests that some 

portion of the stock (but not all) are 

likely impacted, over 1 to several days 

per year, with little likelihood of take 

across sequential days. Regarding the 

severity of those individual Level B 

harassment takes by behavioral 

disturbance, the duration of any 

exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 

dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

Additionally, as noted above, there are 

two mitigation areas implemented by 

the Navy that span a large area of the 

important humpback reproductive area 

(BIA) and minimize impacts by limiting 

the use of MF1 active sonar and 

explosives, thereby reducing both the 

number and severity of takes of 

humpback whales. Regarding the 

severity of TTS takes, they are expected 

to be low-level, of short duration, and 

mostly not in a frequency band that 

would be expected to interfere with 

humpback whale communication or 

other important low-frequency cues, 

and that the associated lost 

opportunities and capabilities are not at 

a level that would impact reproduction 

or survival. For these same reasons (low 

level and frequency band), while a small 

permanent loss of hearing sensitivity 

may include some degree of energetic 

costs for compensating or may mean 

some small loss of opportunities or 

detection capabilities, at the expected 

scale the 3 estimated Level A 

harassment takes by PTS for humpback 

whales would be unlikely to impact 

behaviors, opportunities, or detection 

capabilities to a degree that would 

interfere with reproductive success or 

survival of any individuals. 

Altogether, this stock’s status is 

unknown and the DPS is not listed as 

endangered or threatened under the 

ESA. Only a small portion of the stock 

is anticipated to be impacted and any 

individual humpback whale is likely to 

be disturbed at a low-moderate level, 

with the taken individuals likely 

exposed between 1 to several days per 

year, with little likelihood of take across 

sequential days. This low magnitude 

and severity of harassment effects is not 

expected to result in impacts on 

individual reproduction or survival, and 

therefore, when combined with the 

proposed authorized mortality (which 

our earlier analysis indicated would not, 

alone, have more than a negligible 

impact on this stock of humpback 

whales), the total take is not expected to 

adversely affect this stock through 

effects on annual rates of recruitment or 

survival. For these reasons, we have 

preliminarily determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take proposed would have a 

negligible impact on the Hawaii stock of 

humpback whales. 

Blue Whale (Central North Pacific 

Stock) and the Hawaii Stocks of Bryde’s 

Whale, Fin Whale, Minke Whale, and 

Sei Whale 

The status of these stocks are not 

identified in the SARs. Blue whale 

(Central North Pacific stock) and the 

Hawaii stocks of fin whale and sei 

whale are listed as endangered under 

the ESA; the Hawaii stocks of minke 

whales and Bryde’s whales are not 

listed under the ESA. No mortality or 

Level A harassment by tissue damage is 

anticipated or proposed for 

authorization for any of these stocks. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

instances of take compared to the 

abundance, both throughout the HSTT 

Study Area and within the U.S. EEZ, 

respectively, is 92–135 and 103–142 

percent (table 12). This information 

suggests that some portion of the stocks 

(but not all) are likely impacted, over 1 

to several days per year, with little 

likelihood of take across sequential 

days. Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 

dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with mysticete 

communication or other important lowfrequency cues—and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. For similar 

reasons (as described in the 2018 HSTT 

final rule) the two estimated Level A 

harassment takes by PTS for the Hawaii 

stock of minke whales are unlikely to 

have any effects on the reproduction or 

survival of any individuals. 

Altogether, only a portion of these 

stocks are anticipated to be impacted 

and any individuals of these stocks are 

likely to be disturbed at a low-moderate 

level, with the taken individuals likely 

exposed between 1 and several days, 

with little chance that any are taken 

across sequential days. This low 

magnitude and severity of harassment 

effects is not expected to result in 

impacts on individual reproduction or 

survival, much less have impacts on 

annual rates of recruitment or survival. 

For these reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on these stocks. 

Odontocetes 

Sperm Whale, Dwarf Sperm Whale, and 

Pygmy Sperm Whale 

In table 14 and table 15 below for 

sperm whale, dwarf sperm whale, and 

pygmy sperm whale, we indicate the 

total annual mortality (0 for all stocks; 

the 2020 HSTT final rule included 0.14 

annual takes by mortality of the Hawaii 

stock of sperm whale), Level A and 

Level B harassment, and a number 

indicating the instances of total take as 

a percentage of abundance. Table 14 and 

table 15 are unchanged from tables 20 

and 21 in the 2020 HSTT final rule, 

except for updated information on 

mortality for the Hawaii stock of sperm 

whales, as discussed above. For 

additional information and analysis 

supporting the negligible-impact 

analysis, see the Odontocetes discussion 

as well as the Sperm Whales, Dwarf 

Sperm Whales, and Pygmy Sperm 

Whales discussion in the Group and 

Species-Specific Analyses section of the 

2018 HSTT final rule, all of which 

remains applicable to this proposed rule 

unless specifically noted. 


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TABLE 14—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR SPERM

WHALES, DWARF SPERM WHALES, AND PYGMY SPERM WHALES IN THE HRC PORTION OF THE HSTT STUDY AREA

AND NUMBER INDICATING THE INSTANCES OF TOTAL TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take 

(not all takes represent separate individuals, 

especially for disturbance) 

Total takes Abundance Instances of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment Mortality 

Total 

takes 

(entire 

study 

area) 

Takes 

(within 

NAVY 

EEZ) 

Total Navy 

abundance 

inside and 

outside 

EEZ 

(HRC) 

Within 

EEZ 

Navy 

abundance 

(HRC) 

Total 

take as 

percentage 

of total 

Navy 

abundance 

(HRC) 

EEZ 

take as 

percentage 

of EEZ 

abundance 

(HRC) 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Dwarf 

sperm 

whale.

Hawaii .... 5,870 14,550 64 0 0 20,484 15,310 8,218 6,379 249 240 

Pygmy 

sperm 

whale.

Hawaii .... 2,329 5,822 29 0 0 8,180 6,098 3,349 2,600 244 235 

Sperm 

whale.

Hawaii .... 2,466 30 0 0 0 2,496 1,317 1,656 1,317 151 147 

Note: For the Hawaii take estimates, we compare predicted takes to abundance estimates generated from the same underlying density estimates (as described in 

the Estimated Take of Marine Mammals section of the 2018 HSTT final rule), both in and outside of the U.S. EEZ. Because the portion of the Navy’s study area inside the U.S. EEZ is generally concomitant with the area used to generate the abundance estimates in the SARs, and the abundance predicted by the same underlying density estimates is the preferred abundance to use, there is no need to separately compare the take to the SARs abundance estimate. 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. 

TABLE 15—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR SPERM

WHALES, DWARF SPERM WHALES, AND PYGMY SPERM WHALES IN THE SOCAL PORTION OF THE HSTT STUDY

AREA AND NUMBER INDICATING THE INSTANCES OF TOTAL TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take 

(not all takes represent separate individuals, 

especially for disturbance) 

Total takes Abundance Instances of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

takes 

(entire 

study 

area) 

Navy 

abundance 

in action 

area 

NMFS 

SARS 

abundance 

Total 

take as 

percentage 

of total 

Navy 

abundance 

in Action 

Area 

Total 

take as 

percentage 

of total 

SAR 

abundance 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Kogia whales ... CA/OR/WA ...... 2,779 6,353 38 0 0 9,170 757 4,111 1,211 223 

Sperm whale ... CA/OR/WA ...... 2,437 56 0 0 0 2,493 273 1,997 913 125 

Note: For the SOCAL take estimates, because of the manner in which the Navy study area overlaps the ranges of many MMPA stocks (i.e., a stock may range far 

north to Washington state and beyond and abundance may only be predicted within the U.S. EEZ, while the Navy study area is limited to Southern California and 

northern Mexico, but extends beyond the U.S. EEZ), we compare predicted takes to both the abundance estimates for the study area, as well as the SARs (as described in the Estimated Take of Marine Mammals section of the 2018 HSTT final rule). 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. 

Below we compile and summarize the 

information that supports our 

preliminary determination that the 

Navy’s activities would not adversely 

affect any species or stocks through 

effects on annual rates of recruitment or 

survival for any of the affected species 

and stocks addressed in this section. 

Sperm Whale, Dwarf Sperm Whale, and 

Pygmy Sperm Whale (CA/OR/WA 

Stocks) 

The SAR identifies the CA/OR/WA 

stock of sperm whales as ‘‘stable’’, and 

the species is listed as endangered 

under the ESA. The status of the CA/ 

OR/WA stocks of pygmy and dwarf 

sperm whales is unknown and neither 

are listed under the ESA. Neither 

mortality nor Level A harassment by 

tissue damage from exposure to 

explosives is expected or proposed for 

authorization for any of these three 

stocks. 

Due to their pelagic distribution, 

small size, and cryptic behavior, pygmy 

sperm whales and dwarf sperm whales 

are rarely sighted during at-sea surveys 

and are difficult to distinguish between 

when visually observed in the field. 

Many of the relatively few observations 

of Kogia spp. off the U.S. West Coast 

were not identified to species. All at-sea 

sightings of Kogia spp. have been 

identified as pygmy sperm whales or 

Kogia spp. Stranded dwarf sperm and 

pygmy sperm whales have been found 

on the U.S. West Coast, however dwarf 

sperm whale strandings are rare. NMFS 

SARs suggest that the majority of Kogia 

sighted off the U.S. West Coast were 

likely pygmy sperm whales. As such, 

the stock estimate in the NMFS SAR for 

pygmy sperm whales is the estimate 

derived for all Kogia spp. in the region 

(Barlow, 2016), and no separate 

abundance estimate can be determined 

for dwarf sperm whales, though some 

low number likely reside in the U.S. 

EEZ. Due to the lack of abundance 

estimate, it is not possible to predict the 

take of dwarf sperm whales and take 

estimates are identified as Kogia spp. 

(including both pygmy and dwarf sperm 

whales). We assume only a small 

portion of those takes are likely to be 

dwarf sperm whales as the density and 

abundance in the U.S. EEZ is thought to 

be low. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is, respectively, 913 and 125 for 

sperm whales and 1,211 and 223 for 

Kogia spp., with a large proportion of 


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these anticipated to be pygmy sperm 

whales due to the low abundance and 

density of dwarf sperm whales in the 

HSTT Study Area. (Table 15). Given the 

range of these stocks (which extends the 

entire length of the West Coast, as well 

as beyond the U.S. EEZ boundary), this 

information suggests that some portion 

of the individuals in these stocks will 

not be impacted but that there is likely 

some repeat exposure (perhaps up to 24 

days within a year for Kogia spp. and 18 

days a year for sperm whales) of some 

small subset of individuals that spend 

extended time within the SOCAL Range. 

Additionally, while interrupted feeding 

bouts are a known response and concern 

for odontocetes, we also know that there 

are often viable alternative habitat 

options in the relative vicinity. 

Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB (i.e., of a lower, to 

occasionally moderate, level and less 

likely to evoke a severe response). 

However, some of these takes could 

occur on a fair number of sequential 

days for some number of individuals. 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with sperm whale 

communication or other important lowfrequency cues, and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. For these same 

reasons (low level and frequency band), 

while a small permanent loss of hearing 

sensitivity (PTS) may include some 

degree of energetic costs for 

compensating or may mean some small 

loss of opportunities or detection 

capabilities, at the expected scale the 

estimated Level A harassment takes by 

PTS for the dwarf and pygmy sperm 

whale stocks would be unlikely to 

impact behaviors, opportunities, or 

detection capabilities to a degree that 

would interfere with reproductive 

success or survival of any individuals. 

Thus, the 38 total Level A harassment 

takes by PTS for these two stocks would 

be unlikely to affect rates of recruitment 

and survival for the stocks. 

Altogether, most members of the 

stocks will likely be taken by Level B 

harassment (at a low to occasionally 

moderate level) over several days a year, 

and some smaller portion of the stocks 

are expected to be taken on a relatively 

moderate to high number of days (up to 

18 or 24) across the year, some of which 

could be sequential days. Though the 

majority of impacts are expected to be 

of a lower to sometimes moderate 

severity, the larger number of takes for 

a subset of individuals makes it more 

likely that a small number of 

individuals could be interrupted during 

foraging in a manner and amount such 

that impacts to the energy budgets of 

females (from either losing feeding 

opportunities or expending considerable 

energy to find alternative feeding 

options) could cause them to forego 

reproduction for a year. Energetic 

impacts to males are generally 

meaningless to population rates unless 

they cause death, and it takes extreme 

energy deficits beyond what would ever 

be likely to result from these activities 

to cause the death of an adult marine 

mammal. As discussed in the 2020 

HSTT final rule, however, foregone 

reproduction (especially for 1 year, 

which is the maximum predicted 

because the small number anticipated in 

any 1 year makes the probability that 

any individual would be impacted in 

this way twice in 7 years very low) has 

far less of an impact on population rates 

than mortality and a small number of 

instances of foregone reproduction 

would not be expected to adversely 

affect these stocks through effects on 

annual rates of recruitment or survival. 

We also note that residual PBR is 19 for 

pygmy sperm whales and 1.9 for sperm 

whales. Both the abundance and PBR 

are unknown for dwarf sperm whales, 

however, we know that take of this 

stock is likely significantly lower in 

magnitude and severity (i.e., lower 

number of total takes and repeated takes 

any individual) than pygmy sperm 

whales. For these reasons, in 

consideration of all of the effects of the 

Navy’s activities combined, we have 

preliminarily determined that the 

authorized take proposed would have a 

negligible impact on the CA/OR/WA 

stocks of sperm whales and pygmy and 

dwarf sperm whales. 

Sperm Whale (Hawaii Stock) 

The SAR does not identify a trend for 

this stock and the species is listed as 

endangered under the ESA. No 

mortality or Level A harassment by PTS 

or tissue damage is expected or 

proposed for authorization. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

instances of take compared to the 

abundance, both throughout the HSTT 

Study Area and within the U.S. EEZ, 

respectively, is 151 and 147 percent 

(table 14). This information and the 

sperm whale stock range suggest that 

likely only a smaller portion of the stock 

would be impacted, over 1 to several 

days per year, with little likelihood of 

take across sequential days. Regarding 

the severity of those individual Level B 

harassment takes by behavioral 

disturbance, the duration of any 

exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB (i.e., of a lower, to 

occasionally moderate, level and less 

likely to evoke a severe response). 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with sperm whale 

communication or other important lowfrequency cues, and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. 

Altogether, a relatively small portion 

of this stock is anticipated to be 

impacted and any individuals are likely 

to be disturbed at a low-moderate level, 

with the taken individuals likely 

exposed between 1 and several days, 

with little chance that any are taken 

across sequential days. This low 

magnitude and severity of harassment 

effects is not expected to result in 

impacts on individual reproduction or 

survival, much less annual rates of 

recruitment or survival. For these 

reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on the Hawaii stock of sperm 

whales. 

Pygmy and Dwarf Sperm Whales 

(Hawaii Stocks) 

The SAR does not identify a trend for 

these stocks and the species are not 

listed under the ESA. No Level A 

harassment by tissue damage is 

anticipated or proposed for 

authorization. Regarding the magnitude 

of Level B harassment takes (TTS and 

behavioral disturbance), the number of 

estimated instances of take compared to 

the abundance, both throughout the 

HSTT Study Area and within the U.S. 

EEZ, respectively, is 244–249 and 235– 

240 percent (table 12). This information 

and the pygmy and dwarf sperm whale 

stock ranges (at least throughout the 

U.S. EEZ around the entire Hawaiian 

Islands) suggest that likely a fair portion 

of each stock is not impacted, but that 

a subset of individuals may be taken 

over one to perhaps 5 days per year, 

with little likelihood of take across 

sequential days. Regarding the severity 

of those individual Level B harassment 

takes by behavioral disturbance, the 

duration of any exposure is expected to 


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be between minutes and hours (i.e., 

relatively short) and the received sound 

levels largely below 172 dB (i.e., of a 

lower, to occasionally moderate, level 

and less likely to evoke a severe 

response). Additionally, as discussed 

earlier, within the Hawaii Island 

Mitigation Area, explosives are not used 

and the use of MF1 and MF4 active 

sonar is limited, greatly reducing the 

severity of impacts within the small and 

resident population BIA for dwarf 

sperm whales (Kratofil et al., 2023), 

which is entirely contained within this 

mitigation area. 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with sperm whale 

communication or other important lowfrequency cues—and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. For these same 

reasons (low level and frequency band), 

while a small permanent loss of hearing 

sensitivity may include some degree of 

energetic costs for compensating or may 

mean some small loss of opportunities 

or detection capabilities, at the expected 

scale, estimated Level A harassment 

takes by PTS for dwarf and pygmy 

sperm whales would be unlikely to 

impact behaviors, opportunities, or 

detection capabilities to a degree that 

would interfere with reproductive 

success or survival of any individuals, 

even if it were to be experienced by an 

animal that also experiences one or 

more instances of Level B harassment by 

behavioral disturbance. Thus the 29 and 

64 total Level A harassment takes by 

PTS for dwarf and pygmy sperm whales, 

respectively, would be unlikely to affect 

rates of recruitment and survival for 

these stocks. 

Altogether, a portion of these stocks 

are likely to be impacted and any 

individuals are likely to be disturbed at 

a low-moderate level, with the taken 

individuals likely exposed between 1 

and 5 days, with little chance that any 

are taken across sequential days. This 

low magnitude and severity of Level A 

and Level B harassment effects is not 

expected to result in impacts on 

individual reproduction or survival, 

much less impacts on annual rates of 

recruitment or survival. For these 

reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the expected and 

authorized take proposed would have a 

negligible impact on the Hawaii stocks 

of pygmy and dwarf sperm whales. 

Beaked Whales 

In table 16 and table 17 below for 

beaked whales, we indicate the total 

annual mortality, Level A and Level B 

harassment, and a number indicating 

the instances of total take as a 

percentage of abundance. Table 16 and 

table 17 are unchanged from table 22 

and table 23 in the 2020 HSTT final 

rule, with the exception of a correction 

to a rounding error as noted. For 

additional information and analysis 

supporting the negligible-impact 

analysis, see the Odontocetes discussion 

as well as the Beaked Whales discussion 

in the Group and Species-Specific 

Analyses section of the 2018 HSTT final 

rule, all of which remains applicable to 

this proposed rule unless specifically 

noted. 

TABLE 16—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR BEAKED

WHALES IN THE HRC PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF TOTAL

TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate 

individuals, especially for disturbance) 

Total takes Abundance Instances of total take 

as percent of 

abundance 

Level B harassment 

Level A harassment 

Total 

Takes 

(entire 

Study 

Area) 

Takes 

(within 

Navy 

EEZ) 

Total 

Navy 

abundance 

inside 

and 

outside 

EEZ 

(HRC) 

Within 

EEZ 

Navy 

abundance 

(HRC) 

Total 

take as 

percentage 

of total 

Navy 

abundance 

(HRC) 

EEZ 

take as 

percentage 

of EEZ 

abundance 

(HRC) 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage Mortality 

Blainville’s 

beaked 

whale.

Hawaii 5,369 16 0 0 0 5,385 4,140 989 768 a 544 539 

Cuvier’s 

beaked 

whale.

Hawaii 1,792 4 0 0 0 1,796 1,377 345 268 521 514 

Longman’s 

beaked 

whale.

Hawaii 19,152 81 0 0 0 19,233 14,585 3,568 2,770 539 527 

Note: For the Hawaii take estimates, we compare predicted takes to abundance estimates generated from the same underlying density estimates (as described in 

the Estimated Take of Marine Mammals section of the 2018 HSTT final rule), both in and outside of the U.S. EEZ. Because the portion of the Navy’s study area inside the U.S. EEZ is generally concomitant with the area used to generate the abundance estimates in the SARs, and the abundance predicted by the same underlying density estimates is the preferred abundance to use, there is no need to separately compare the take to the SARs abundance estimate. 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. aThe 2020 final rule unintentionally presented this percentage as 545. The correct value is provided here. This error does not affect the conclusions in the 2020 

HSTT final rule. 


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TABLE 17—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR BEAKED

WHALES IN THE SOCAL PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF TOTAL

TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take 

(not all takes represent 

separate individuals, especially for disturbance) 

Total takes Abundance Instances of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

Takes 

(entire 

study 

area) 

Navy 

abundance 

in 

action 

area 

NMFS 

SARS 

abundance 

Total 

take as 

percentage 

of total 

Navy 

abundance 

in action 

area 

Total 

take as 

percentage 

of total 

SAR 

abundance 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Baird’s beaked 

whale.

CA/OR/WA ...... 2,030 14 0 0 0 2,044 74 1,363 2,762 150 

Cuvier’s beaked 

whale.

CA/OR/WA ...... 11,373 127 1 0 0 11,501 520 5,454 2,212 211 

Mesoplodon 

species.

CA/OR/WA ...... 6,125 68 1 0 0 6,194 89 3,044 6,960 203 

Note: For the SOCAL take estimates, because of the manner in which the Navy study area overlaps the ranges of many MMPA stocks (i.e., a stock may range far 

north to Washington state and beyond and abundance may only be predicted within the U.S. EEZ, while the Navy study area is limited to Southern California and 

northern Mexico, but extends beyond the U.S. EEZ), we compare predicted takes to both the abundance estimates for the study area, as well as the SARs (as described in the Estimated Take of Marine Mammals section of the 2018 HSTT final rule). 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. 

Below we compile and summarize the 

information that supports our 

determination that the Navy’s activities 

would not adversely affect any species 

or stocks through effects on annual rates 

of recruitment or survival for any of the 

affected species or stocks addressed in 

this section. 

Blainville’s, Cuvier’s, and Longman’s 

Beaked Whales (Hawaii Stocks) 

The SAR does not identify a trend for 

these stocks and the species are not 

listed under the ESA. No mortality or 

Level A harassment are expected or 

proposed for authorization for any of 

these three stocks. Regarding the 

magnitude of Level B harassment takes 

(TTS and behavioral disturbance), the 

number of estimated instances of take 

compared to the abundance, both 

throughout the HSTT Study Area and 

within the U.S. EEZ, respectively, is 

521–544 and 514–539 percent (table 16). 

This information and the stock ranges 

(at least of the small, resident island 

associated stocks around Hawaii) 

suggest that likely a fair portion of the 

stocks (but not all) will be impacted, 

over 1 to perhaps 11 days per year, with 

little likelihood of much take across 

sequential days. Regarding the severity 

of those individual Level B harassment 

takes by behavioral disturbance, the 

duration of any exposure is expected to 

be between minutes and hours (i.e., 

relatively short) and the received sound 

levels largely below 160 dB, though 

with beaked whales, which are 

considered somewhat more sensitive, 

this could mean that some individuals 

will leave preferred habitat for a day or 

2 (i.e., moderate level takes). However, 

while interrupted feeding bouts are a 

known response and concern for 

odontocetes, we also know that there are 

often viable alternative habitat options 

nearby. Additionally, as noted earlier, 

within the Hawaii Island mitigation area 

(which overlaps a large portion of the 

BIAs for Cuvier’s and Blainville’s 

beaked whales), explosives are not used 

and the use of MF1 and MF4 active 

sonar is limited, greatly reducing the 

severity of impacts within these two 

small resident populations. 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 

to interfere with beaked whale 

communication or other important lowfrequency cues, and that the associated 

lost opportunities and capabilities are 

not at a level that would impact 

reproduction or survival. 

Altogether, a fair portion of these 

stocks are anticipated to be impacted 

and any individuals are likely to be 

disturbed at a moderate level, with the 

taken individuals likely exposed 

between 1 and 11 days, with little 

chance that individuals are taken across 

more than a few sequential days. This 

low, to occasionally moderate, 

magnitude and severity of harassment 

effects is not expected to result in 

impacts on individual reproduction or 

survival, much less have impacts on 

annual rates of recruitment or survival. 

For these reasons, we have preliminarily 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take 

proposed would have a negligible 

impact on the Hawaii stocks of beaked 

whales. 

Baird’s and Cuvier’s Beaked Whales and 

Mesoplodon Species (All CA/OR/WA 

Stocks) 

The species are not listed under the 

ESA and their populations have been 

identified as ‘‘increasing,’’ ‘‘decreasing,’’ 

and ‘‘increasing,’’ respectively. No 

mortality is expected or proposed for 

authorization for any of these three 

stocks and only two takes by Level A 

harassment (PTS) are proposed for 

authorization. 

No methods are available to 

distinguish between the six species of 

Mesoplodon beaked whale CA/OR/WA 

stocks (Blainville’s beaked whale (M. 

densirostris), Perrin’s beaked whale (M. 

perrini), Lesser beaked whale (M. 

peruvianus), Stejneger’s beaked whale 

(M. stejnegeri), Gingko-toothed beaked 

whale (M. gingkodens), and Hubbs’ 

beaked whale (M. carlhubbsi)) when 

observed during at-sea surveys (Carretta 

et al. 2018a). Bycatch and stranding 

records from the region indicate that the 

Hubbs’ beaked whale is most commonly 

encountered (Carretta et al. 2008, Moore 

and Barlow, 2013). As indicated in the 

SAR, no species-specific abundance 

estimates are available, the abundance 

estimate includes all CA/OR/WA 

Mesoplodon spp, and the six species are 

managed as one unit. Due to the lack of 

species-specific abundance estimates, it 

is not possible to predict the take of 

individual species and take estimates 

are identified as Mesoplodon spp. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance for these stocks is 2,762, 

2,212, and 6,960 percent (measured 

against Navy-estimated abundance) and 


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150, 211, and 203 percent (measured 

against the SAR) for Baird’s beaked 

whales, Cuvier’s beaked whales, and 

Mesoplodon spp., respectively (table 

15). Given the ranges of these stocks, 

this information suggests that some 

smaller portion of the individuals of 

these stocks will be taken, and that 

some subset of individuals within the 

stock will be taken repeatedly within 

the year (perhaps up to 20–25 days, and 

potentially more for Cuvier’s)— 

potentially over a fair number of 

sequential days, especially where 

individuals spend extensive time in the 

SOCAL Range. Note that we predict 

lower days of repeated exposure for 

these stocks than their percentages 

might have suggested because of the 

number of overall takes—i.e., using the 

higher percentage would suggest that an 

unlikely portion of the takes are taken 

up by a small portion of the stock 

incurring a very large number of repeat 

takes, with little room for take resulting 

from few or moderate numbers of 

repeats, which is unlikely. While 

interrupted feeding bouts are a known 

response and concern for odontocetes, 

we also know that there are often viable 

alternative habitat options in the 

relative vicinity. Regarding the severity 

of those individual Level B harassment 

takes by behavioral disturbance, we 

have explained that the duration of any 

exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 160 dB, though with beaked 

whales, which are considered somewhat 

more sensitive, this could mean that 

some individuals will leave preferred 

habitat for a day or 2 (i.e., of a moderate 

level). In addition, as noted, some of 

these takes could occur on a fair number 

of sequential days for these stocks. 

The severity of TTS takes is expected 

to be low-level, of short duration, and 

mostly not in a frequency band that 

would be expected to interfere 

significantly with conspecific 

communication, echolocation, or other 

important low-frequency cues. 

Therefore, the associated lost 

opportunities and capabilities would 

not be expected to impact reproduction 

or survival. For similar reasons (as 

described in the 2020 HSTT final rule) 

the single estimated Level A harassment 

take by PTS for this stock is unlikely to 

have any effects on the reproduction or 

survival of any individuals. 

Altogether, a portion of these stocks 

will likely be taken (at a moderate or 

sometimes low level) over several days 

a year, and some smaller portion of the 

stock is expected to be taken on a 

relatively moderate to high number of 

days across the year, some of which 

could be sequential days. Though the 

majority of impacts are expected to be 

of a moderate severity, the repeated 

takes over a potentially fair number of 

sequential days for some individuals 

makes it more likely that a small 

number of individuals could be 

interrupted during foraging in a manner 

and amount such that impacts to the 

energy budgets of females (from either 

losing feeding opportunities or 

expending considerable energy to find 

alternative feeding options) could cause 

them to forego reproduction for a year. 

Energetic impacts to males are generally 

meaningless to population rates unless 

they cause death, and it takes extreme 

energy deficits beyond what would ever 

be likely to result from these activities 

to cause the death of an adult marine 

mammal. As noted previously, however, 

foregone reproduction (especially for 1 

year, which is the maximum predicted 

because the small number anticipated in 

any 1 year makes the probability that 

any individual would be impacted in 

this way twice in 7 years very low) has 

far less of an impact on population rates 

than mortality and a small number of 

instances of foregone reproduction 

would not be expected to adversely 

affect these stocks through effects on 

annual rates of recruitment or survival, 

especially given the residual PBR of 

these three beaked whale stocks (8.7, 

41.9, and 19.9, respectively). 

Further, Navy activities have been 

conducted in SOCAL for many years at 

similar levels and the SAR considers 

Mesoplodon spp. and Baird’s beaked 

whales as increasing. While NMFS’ SAR 

indicates that Cuvier’s beaked whales 

on the U.S. West Coast are declining 

based on a Bayesian trend analysis of 

NMFS’ survey data collected from 1991 

through 2014, results from passive 

acoustic monitoring and other research 

have estimated regional Cuvier’s beaked 

whale densities that were higher than 

indicated by NMFS’ broad-scale visual 

surveys for the U.S. West Coast (Debich 

et al. 2015a; Debich et al. 2015b; 

Falcone and Schorr, 2012, 2014; 

Hildebrand et al. 2009; Moretti, 2016; 

Sˇirovic ́ et al. 2016; Smultea and 

Jefferson, 2014). Research also indicates 

higher than expected residency in the 

Navy’s instrumented Southern 

California Anti-Submarine Warfare 

Range in particular (Falcone and Schorr, 

2012) and photo identification studies 

in the SOCAL have identified 

approximately 100 individual Cuvier’s 

beaked whale individuals with 40 

percent having been seen in one or more 

prior years, with re-sightings up to 7 

years apart (Falcone and Schorr, 2014). 

The documented residency by many 

Cuvier’s beaked whales over multiple 

years suggests that a stable population 

may exist in that small portion of the 

stock’s overall range (Falcone et al. 

2009; Falcone and Schorr, 2014; Schorr 

et al. 2017). 

For these reasons, in consideration of 

all of the effects of the Navy’s activities 

combined, we have preliminarily 

determined that the authorized take 

proposed would have a negligible 

impact on the CA/OR/WA stocks of 

Baird’s and Cuvier’s beaked whales, as 

well as all six species included within 

the Mesoplodon spp. 

Small Whales and Dolphins 

In table 18 and table 19 below for 

dolphins and small whales, we indicate 

the total annual mortality, Level A and 

Level B harassment, and a number 

indicating the instances of total take as 

a percentage of abundance. Table 18 and 

table 19 are updated from tables 24 and 

25 in the 2020 HSTT final rule as 

appropriate with the 2022 final SARs. 

For additional information and analysis 

supporting the negligible-impact 

analysis, see the Odontocetes discussion 

as well as the Small Whales and 

Dolphins discussion in the Group and 

Species-Specific Analyses section of the 

2018 HSTT final rule, all of which 

remains applicable to this proposed rule 

unless specifically noted. 


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TABLE 18—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR DOLPHINS

AND SMALL WHALES IN THE HRC PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF

TOTAL TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total takes Abundance Instance of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

takes 

(entire 

study 

area) 

Takes 

(within 

Navy 

EEZ) 

Total 

Navy 

abundance 

inside and 

outside 

of EEZ 

(HRC) 

Within 

EEZ 

Navy 

abundance 

(HRC) 

Total 

take as 

percentage 

of total 

Navy 

abundance 

(HRC) 

EEZ 

take as 

percentage 

of Navy 

EEZ 

abundance 

(HRC) 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Bottlenose 

dolphin.

Hawaii 

Pelagic.

3,196 132 0 0 0 3,328 2,481 1,528 1,442 218 172 

Bottlenose 

dolphin.

Kauai & 

Niihau.

534 31 0 0 0 565 264 184 184 307 143 

Bottlenose 

dolphin.

Oahu ...... 8,600 61 1 0 0 8,662 8,376 743 743 a 1,166 a 1,127 

Bottlenose 

dolphin.

4-Island .. 349 10 0 0 0 359 316 189 189 190 167 

Bottlenose 

dolphin.

Hawaii .... 74 6 0 0 0 80 42 131 131 61 32 

False killer 

whale.

Hawaii 

Pelagic.

999 42 0 0 0 1,041 766 645 507 161 151 

False killer 

whale.

Main Hawaiian 

Islands 

Insular.

572 17 0 0 0 589 476 147 147 b 401 324 

False killer 

whale.

Northwestern 

Hawaiian Islands.

365 16 0 0 0 381 280 215 169 177 166 

Fraser’s 

dolphin.

Hawaii .... 39,784 1,289 2 0 0 41,075 31,120 5,408 18,763 760 166 

Killer 

whale.

Hawaii .... 118 6 0 0 0 124 93 69 54 180 172 

Melonheaded 

whale.

Hawaii Islands.3,261 231 0 0 0 3,492 2,557 1,782 1,782 196 143 

Melonheaded 

whale.

Kohala 

Resident.

341 9 0 0 0 350 182 447 447 78 41 

Pantropical spotted dolphin.Hawaii Island.3,767 227 0 0 0 3,994 2,576 2,405 2,405 166 107 

Pantropical spotted dolphin.Hawaii 

Pelagic.

9,973 476 0 0 0 10,449 7,600 5,462 4,637 191 164 

Pantropical spotted dolphin.Oahu ...... 4,284 45 0 0 0 4,329 4,194 372 372 1,164 1,127 

Pantropical spotted dolphin.4-Island .. 701 17 0 0 0 718 634 657 657 109 96 

Pygmy 

killer 

whale.

Hawaii .... 8,122 402 0 0 0 8,524 6,538 4,928 3,931 173 166 

Pygmy 

killer 

whale.

Tropical .. 710 50 0 0 0 760 490 159 23 478 2,130 

Risso’s 

dolphin.

Hawaii .... 8,950 448 0 0 0 9,398 7,318 1,210 4,199 777 174 

Roughtoothed 

dolphin.

Hawaii .... 6,112 373 0 0 0 6,485 4,859 3,054 2,808 212 173 

Shortfinned 

pilot 

whale.

Hawaii .... 12,499 433 0 0 0 12,932 9,946 6,433 5,784 201 172 

Spinner 

dolphin.

Hawaii Island.279 12 0 0 0 291 89 629 629 46 14 

Spinner 

dolphin.

Hawaii 

Pelagic.

4,332 202 0 0 0 4,534 3,491 2,885 2,229 157 157 

Spinner 

dolphin.

Kauai & 

Niihau.

1,683 63 0 0 0 1,746 812 604 604 289 134 


ddrumheller on DSK120RN23PROD with PROPOSALS2
Federal Register / Vol. 88, No. 190 / Tuesday, October 3, 2023 / Proposed Rules 68347 

TABLE 18—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR DOLPHINS

AND SMALL WHALES IN THE HRC PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF

TOTAL TAKE AS A PERCENTAGE OF STOCK ABUNDANCE—Continued 

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total takes Abundance Instance of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

takes 

(entire 

study 

area) 

Takes 

(within 

Navy 

EEZ) 

Total 

Navy 

abundance 

inside and 

outside 

of EEZ 

(HRC) 

Within 

EEZ 

Navy 

abundance 

(HRC) 

Total 

take as 

percentage 

of total 

Navy 

abundance 

(HRC) 

EEZ 

take as 

percentage 

of Navy 

EEZ 

abundance 

(HRC) 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Spinner 

dolphin.

Oahu & 4- 

Island.

1,790 34 1 0 0 1,825 1,708 354 354 516 482 

Striped 

dolphin.

Hawaii .... 7,379 405 0 0 0 7,784 6,034 4,779 3,646 163 165 

Note: For the Hawaii take estimates, we compare predicted takes to abundance estimates generated from the same underlying density estimates (as described in 

the Estimated Take of Marine Mammals section of the 2018 HSTT final rule), both in and outside of the U.S. EEZ. Because the portion of the Navy’s study area inside the U.S. EEZ is generally concomitant with the area used to generate the abundance estimates in the SARs, and the abundance predicted by the same underlying density estimates is the preferred abundance to use, there is no need to separately compare the take to the SARs abundance estimate. 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. aThe 2020 final rule unintentionally presented these percentages as 1,169 and 1,130. The correct values are provided here. These errors do not affect the conclusions in the 2020 HSTT final rule. bThe 2020 final rule unintentionally presented this percentage as 400. The correct value is provided here. This rounding error does not affect the conclusions in the 

2020 HSTT final rule. 

TABLE 19—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR DOLPHINS

AND SMALL WHALES IN THE SOCAL PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES

OF TOTAL TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total takes Abundance Instance of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

takes 

(entire 

study 

area) 

Navy 

abundance 

in action 

area (SOCAL) 

NMFS 

SARS 

abundance 

Total 

take as 

percentage 

of total 

Navy 

abundance 

in action 

area 

Total 

take as 

percentage 

of total 

SAR 

abundance 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Bottlenose dolphin.California 

Coastal.

1,771 38 0 0 0 1,809 238 453 760 399 

Bottlenose dolphin.CA/OR/WA 

Offshore.

51,727 3,695 3 0 0 55,425 5,946 3,477 932 1,594 

Killer whale .... ENP Offshore 96 11 0 0 0 107 4 300 2,675 36 

Killer whale .... ENP Transient/West 

Coast Transient.

179 20 0 0 0 199 30 349 663 57 

Long-beaked 

common 

dolphin.

California ....... 233,485 13,787 18 2 0 247,292 10,258 83,379 2,411 297 

Northern right 

whale dolphin.

CA/OR/WA .... 90,052 8,047 10 1 0 98,110 7,705 29,285 1,273 335 

Pacific whitesided dolphin.CA/OR/WA .... 69,245 6,093 5 0 0 75,343 6,626 34,999 1,137 215 

Risso’s dolphin CA/OR/WA .... 116,143 10,118 9 0 0 126,270 7,784 6,336 1,622 1,993 

Short-beaked 

common 

dolphin.

CA/OR/WA .... 1,374,048 118,525 79 10 1.14 1,492,664 261,438 1,056,308 571 141 

Short-finned 

pilot whale.

CA/OR/WA .... 1,789 124 1 0 0 1,914 208 836 920 229 

Striped dolphin CA/OR/WA .... 163,640 11,614 3 0 0 175,257 39,862 29,988 440 584 

Note: For the SOCAL take estimates, because of the manner in which the Navy study area overlaps the ranges of many MMPA stocks (i.e., a stock may range far 

north to Washington state and beyond and abundance may only be predicted within the U.S. EEZ, while the Navy study area is limited to Southern California and 

northern Mexico, but extends beyond the U.S. EEZ), we compare predicted takes to both the abundance estimates for the study area, as well as the SARs (as described in the Estimated Take of Marine Mammals section of the 2018 HSTT final rule). 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. 

For mortality takes there is an annual average of 1.14 short-beaked common dolphins (i.e., where eight takes could potentially occur divided by 7 years to get the 

annual number of mortalities/serious injuries). 

Below we compile and summarize the 

information that supports our 

determination that the Navy’s activities 

would not adversely affect any species 

or stocks through effects on annual rates 

of recruitment or survival for any of the 

affected species or stocks addressed in 

this section. 


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Long-Beaked Common Dolphin 

(California Stock), Northern Right 

Whale Dolphin (CA/OR/WA Stock), and 

Short-Beaked Common Dolphin (CA/ 

OR/WA Stock) 

None of these stocks are listed under 

the ESA and their stock statuses are 

considered ‘‘increasing,’’ ‘‘unknown,’’ 

and ‘‘increasing,’’ respectively. Eight 

mortalities or serious injuries of shortbeaked common dolphins are proposed 

for authorization over the 7-year rule, or 

1.14 M/SI annually. The addition of this 

1.14 annual mortality still leaves the 

total human-caused mortality well 

under the insignificance threshold for 

residual PBR. The three stocks are 

expected to accrue 2, 1, and 10 Level A 

harassment takes from tissue damage 

resulting from exposure to explosives, 

respectively. As described in detail in 

the 2018 HSTT final rule, the impacts of 

a Level A harassment take by tissue 

damage could range in impact from 

minor to something just less than M/SI 

that could seriously impact fitness. 

However, given the Navy’s procedural 

mitigation, exposure closer to the source 

and more severe end of the spectrum is 

less likely and we cautiously assume 

some moderate impact for these takes 

that could lower the affected 

individual’s fitness within the year such 

that a female (assuming a 50 percent 

chance of it being a female) might forego 

reproduction for 1 year. As noted 

previously, foregone reproduction has 

less of an impact on population rates 

than death (especially for only 1 year in 

7, which is the maximum predicted 

because the small number anticipated in 

any 1 year makes the probability that 

any individual would be impacted in 

this way twice in 7 years very low), and 

1 to 10 instances would not be expected 

to impact annual rates of recruitment or 

survival for these stocks. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 2,411, 1,273, and 571 percent 

(respective to the stocks listed in the 

heading) and 297, 335, and 141 percent 

(respective to the stocks listed in the 

heading) (table 19). Given the range of 

these stocks, this information suggests 

that likely some portion (but not all or 

even the majority) of the individuals in 

the northern right whale dolphin and 

short-beaked common dolphin stocks 

are likely impacted while it is entirely 

possible that most or all of the rangelimited long-beaked common dolphin is 

taken. All three stocks likely will 

experience some repeat Level B 

harassment exposure (perhaps up to 48, 

25, or 11 days within a year, respective 

to the stocks listed in the heading) of 

some subset of individuals that spend 

extended time within the SOCAL range 

complex. While interrupted feeding 

bouts are a known response and concern 

for odontocetes, we also know that there 

are often viable alternative habitat 

options in the relative vicinity. 

Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB with a portion up to 178 

dB (i.e., of a moderate or lower level, 

less likely to evoke a severe response). 

However, some of these takes could 

occur on a fair number of sequential 

days for long-beaked common dolphins 

or northern right whale dolphins, or 

even some number of short-beaked 

common dolphins, given the high 

number of total takes (i.e., the 

probability that some number of 

individuals get taken on a higher 

number of sequential days is higher, 

because the total take number is 

relatively high, even though the 

percentage is not that high). 

The severity of TTS takes is expected 

to be low-level, of short duration, and 

mostly not in a frequency band that 

would be expected to interfere 

significantly with conspecific 

communication, echolocation, or other 

important low-frequency cues, and the 

associated lost opportunities and 

capabilities would not be expected to 

impact reproduction or survival. For 

these same reasons (low level and 

frequency band), while a small 

permanent loss of hearing sensitivity 

may include some degree of energetic 

costs for compensating or may mean 

some small loss of opportunities or 

detection capabilities, as discussed in 

the 2020 HSTT final rule, it would be 

unlikely to impact behaviors, 

opportunities, or detection capabilities 

to a degree that would interfere with 

reproductive success or survival of any 

individuals. 

Altogether and as described in more 

detail above, 1.14 annual lethal takes of 

short-beaked common dolphins are 

proposed for authorization, all three 

stocks may experience a very small 

number of takes by tissue damage or 

PTS (relative to the stock abundance 

and PBR), and a moderate to large 

portion of all three stocks will likely be 

taken (at a low to occasionally moderate 

level) over several days a year, and some 

smaller portion of these stocks is 

expected to be taken on a relatively 

moderate to high number of days across 

the year, some of which could be 

sequential days. Though the majority of 

impacts are expected to be of a lower to 

sometimes moderate severity, the larger 

number of takes (in total and for certain 

individuals) makes it more likely 

(probabilistically) that a small number 

of individuals could be interrupted 

during foraging in a manner and amount 

such that impacts to the energy budgets 

of females (from either losing feeding 

opportunities or expending considerable 

energy to find alternative feeding 

options) could cause them to forego 

reproduction for a year. Energetic 

impacts to males are generally 

meaningless to population rates unless 

they cause death, and it takes extreme 

energy deficits beyond what would ever 

be likely to result from these activities 

to cause the death of an adult marine 

mammal. As noted previously, however, 

foregone reproduction (especially for 

only 1 year out of 7, which is the 

maximum predicted because the small 

number anticipated in any 1 year makes 

the probability that any individual 

would be impacted in this way twice in 

7 years very low) has far less of an 

impact on population rates than 

mortality and a small number of 

instances of foregone reproduction 

(including in combination with that 

which might result from the small 

number of tissue damage takes) would 

not be expected to adversely affect the 

stocks through effects on annual rates of 

recruitment or survival, especially given 

the very high residual PBRs of these 

stocks (638.3, 156.4, and 8,858.5, 

respectively). For these reasons, in 

consideration of all of the effects of the 

Navy’s activities combined (mortality, 

Level A harassment, and Level B 

harassment), we have preliminarily 

determined that the authorized take 

proposed would have a negligible 

impact on these three stocks of 

dolphins. 

All Other SOCAL Dolphin Stocks 

(Except Long-Beaked Common Dolphin, 

Northern Right Whale Dolphin, and 

Short-Beaked Common Dolphin) 

None of these stocks are listed under 

the ESA and their stock statuses are 

considered ‘‘unknown,’’ except for the 

bottlenose dolphin (California coastal 

stock) and killer whale (Eastern North 

Pacific stock), which are considered 

‘‘stable.’’ No M/SI or Level A 

harassment via tissue damage from 

exposure to explosives is expected or 

proposed for authorization for these 

stocks. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 


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abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is from 440 to 2,675 percent and 

36 to 1,993 percent, respectively (table 

19). Given the range of these stocks 

(along the entire U.S. West Coast, or 

even beyond, with some also extending 

seaward of the HSTT Study Area 

boundaries), this information suggests 

that some portion (but not all or even 

the majority) of the individuals of any 

of these stocks will be taken, with the 

exception that most or all of the 

individuals of the more range-limited 

California coastal stock of bottlenose 

dolphin may be taken. It is also likely 

that some subset of individuals within 

most of these stocks will be taken 

repeatedly within the year (perhaps up 

to 10–15 days within a year) but with 

no more than several potentially 

sequential days, although the CA/OR/ 

WA stocks of bottlenose dolphins, 

Pacific white-sided dolphins, and 

Risso’s dolphins may include 

individuals that are taken repeatedly 

within the year over a higher number of 

days (up to 57, 22, and 40 days, 

respectively) and potentially over a fair 

number of sequential days, especially 

where individuals spend extensive time 

in the SOCAL range complex. Note that 

though percentages are high for the 

Eastern North Pacific stock of killer 

whales and short-finned pilot whales, 

given the low overall number of takes, 

it is highly unlikely that any individuals 

would be taken across the number of 

days their percentages would suggest. 

While interrupted feeding bouts are a 

known response and concern for 

odontocetes, we also know that there are 

often viable alternative habitat options 

in the relative vicinity. Regarding the 

severity of those individual Level B 

harassment takes by behavioral 

disturbance, we have explained that the 

duration of any exposure is expected to 

be between minutes and hours (i.e., 

relatively short) and the received sound 

levels largely below 172 dB (i.e., of a 

lower, or sometimes moderate level, less 

likely to evoke a severe response). 

However, as noted, some of these takes 

could occur on a fair number of 

sequential days for the three stocks 

listed earlier. 

The severity of TTS takes is expected 

to be low-level, of short duration, and 

mostly not in a frequency band that 

would be expected to interfere 

significantly with conspecific 

communication, echolocation, or other 

important low-frequency cues. For these 

same reasons (low level and frequency 

band), while a small permanent loss of 

hearing sensitivity may include some 

degree of energetic costs for 

compensating or may mean some small 

loss of opportunities or detection 

capabilities, it would be unlikely to 

impact behaviors, opportunities, or 

detection capabilities to a degree that 

would interfere with reproductive 

success or survival of any individuals. 

Altogether, a portion of all of these 

stocks will likely be taken (at a low to 

occasionally moderate level) over 

several days a year, and some smaller 

portion of CA/OR/WA stocks of 

bottlenose dolphins, Pacific white-sided 

dolphins, and Risso’s dolphins, 

specifically, are expected to be taken on 

a relatively moderate to high number of 

days across the year, some of which 

could be sequential days. Though the 

majority of impacts are expected to be 

of a lower to sometimes moderate 

severity, the larger number of takes (in 

total and for certain individuals) for the 

CA/OR/WA stocks of bottlenose 

dolphins, Pacific white-sided dolphins, 

and Risso’s dolphins makes it more 

likely (probabilistically) that a small 

number of individuals could be 

interrupted during foraging in a manner 

and amount such that impacts to the 

energy budgets of females (from either 

losing feeding opportunities or 

expending considerable energy to find 

alternative feeding options) could cause 

them to forego reproduction for a year. 

Energetic impacts to males are generally 

meaningless to population rates unless 

they cause death, and it takes extreme 

energy deficits beyond what would ever 

be likely to result from these activities 

to cause the death of an adult marine 

mammal. As noted previously, however, 

foregone reproduction (especially for 

only 1 year in 7, which is the maximum 

predicted because the small number 

anticipated in any 1 year makes the 

probability that any individual would 

be impacted in this way twice in 7 years 

very low) has far less of an impact on 

population rates than mortality and a 

small number of instances of foregone 

reproduction would not be expected to 

adversely affect the stocks through 

effects on annual rates of recruitment or 

survival, especially given the residual 

PBRs of the CA/OR/WA stocks of 

bottlenose dolphins, Pacific white-sided 

dolphins, and Risso’s dolphins (18.9, 

272, and 42.3, respectively). For these 

reasons, in consideration of all of the 

effects of the Navy’s activities 

combined, we have preliminarily 

determined that the authorized take 

proposed would have a negligible 

impact on these stocks of dolphins. 

All HRC Dolphin Stocks 

With the exception of the Main 

Hawaiian Island stock of false killer 

whales (listed as endangered under the 

ESA, with the MMPA stock identified as 

‘‘decreasing’’), none of these stocks are 

listed under the ESA and their stock 

statuses are considered ‘‘unknown.’’ No 

M/SI or Level A harassment via tissue 

damage from exposure to explosives is 

expected or proposed for authorization 

for these stocks. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is from 46 to 1,166 percent and 14 

to 2,130 percent, respectively (table 16). 

Given the ranges of these stocks (many 

of them are small, resident, islandassociated stocks), this information 

suggests that a fairly large portion of the 

individuals of many of these stocks will 

be taken but that most individuals will 

only be impacted across a smaller to 

moderate number of days within the 

year (1–15), and with no more than 

several potentially sequential days, 

although two stocks (the Oahu stocks of 

bottlenose dolphin and pantropical 

spotted dolphin) have a slightly higher 

percentage, suggesting they could be 

taken up to 23 days within a year, with 

perhaps a few more of those days being 

sequential. We note that although the 

percentage is higher for the tropical 

stock of pygmy killer whale within the 

U.S. EEZ (2,130), given (1) the low 

overall number of takes (760) and (2) the 

fact that the small within-U.S. EEZ 

abundance is not a static set of 

individuals, but rather individuals 

moving in and out of the U.S. EEZ 

making it more appropriate to use the 

percentage comparison for the total 

takes versus total abundance—it is 

highly unlikely that any individuals 

would be taken across the number of 

days the within-U.S. EEZ percentage 

suggests (42). While interrupted feeding 

bouts are a known response and concern 

for odontocetes, we also know that there 

are often viable alternative habitat 

options in the relative vicinity. 

Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB (i.e., of a lower, or 

sometimes moderate level, less likely to 

evoke a severe response). However, as 

noted, some of these takes could occur 

on a fair number of sequential days for 

the Oahu stocks of bottlenose dolphin 

and pantropical spotted dolphins. 

Regarding the severity of TTS takes, 

they are expected to be low-level, of 

short duration, and mostly not in a 

frequency band that would be expected 


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to interfere significantly with 

conspecific communication, 

echolocation, or other important lowfrequency cues. For these same reasons 

(low level and frequency band), while a 

small permanent loss of hearing 

sensitivity may include some degree of 

energetic costs for compensating or may 

mean some small loss of opportunities 

or detection capabilities, they would be 

unlikely to impact behaviors, 

opportunities, or detection capabilities 

to a degree that would interfere with 

reproductive success or survival of any 

individuals, even if accrued to 

individuals that are also taken by 

behavioral harassment at the same time. 

Altogether, most of these stocks (all 

but the Oahu stocks of bottlenose 

dolphin and pantropical spotted 

dolphins) will likely be taken (at a low 

to occasionally moderate level) over 

several days a year, with some smaller 

portion of the stock potentially taken on 

a more moderate number of days across 

the year (perhaps up to 15 days for 

Fraser’s dolphin, though others notably 

less), some of which could be across a 

few sequential days, which is not 

expected to affect the reproductive 

success or survival of individuals. For 

the Oahu stocks of bottlenose dolphin 

and pantropical spotted dolphins, some 

subset of individuals could be taken up 

to 23 days in a year, with some small 

number being taken across several 

sequential days, such that a small 

number of individuals could be 

interrupted during foraging in a manner 

and amount such that impacts to the 

energy budgets of females (from either 

losing feeding opportunities or 

expending considerable energy to find 

alternative feeding options) could cause 

them to forego reproduction for a year. 

Energetic impacts to males are generally 

meaningless to population rates unless 

they cause death, and it takes extreme 

energy deficits beyond what would ever 

be likely to result from these activities 

to cause the death of an adult marine 

mammal. As noted previously, however, 

foregone reproduction (especially for 1 

year, which is the maximum predicted 

because the small number anticipated in 

any 1 year makes the probability that 

any individual would be impacted in 

this way twice in 7 years very low) has 

far less of an impact on population rates 

than mortality and a small number of 

instances of foregone reproduction 

would not be expected to adversely 

affect these two stocks through effects 

on annual rates of recruitment or 

survival. For these reasons, in 

consideration of all of the effects of the 

Navy’s activities combined, we have 

preliminarily determined that the 

authorized take proposed would have a 

negligible impact on all of the stocks of 

dolphins found in the vicinity of the 

HRC. 

Dall’s Porpoise 

In table 20 below for porpoises, we 

indicate the total annual mortality, 

Level A harassment and Level B 

harassment, and a number indicating 

the instances of total take as a 

percentage of abundance. Table 20 is 

updated from table 26 in the 2020 HSTT 

final rule with the 2022 final SARs. For 

additional information and analysis 

supporting the negligible-impact 

analysis, see the Odontocetes discussion 

as well as the Dall’s Porpoise discussion 

in the Group and Species-Specific 

Analyses section of the 2018 HTT final 

rule, all of which remains applicable to 

this proposed rule unless specifically 

noted. 

TABLE 20—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR PORPOISES IN THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF TOTAL TAKE AS A PERCENTAGE OF

STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total 

takes 

Abundance Instances of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

takes 

(entire 

study 

area) 

Navy 

abundance 

in action 

area 

NMFS 

SARS 

abundance 

Total 

take as 

percentage 

of total 

Navy 

abundance 

in action 

area 

Total 

take as 

percentage 

of total 

SAR 

abundance 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

Dall’s porpoise CA/OR/WA ...... 14,482 29,891 209 0 0 44,582 2,054 16,498 2,170 270 

Note: For the SOCAL take estimates, because of the manner in which the Navy study area overlaps the ranges of many MMPA stocks (i.e., a stock may range far 

north to Washington state and beyond and abundance may only be predicted within the U.S. EEZ, while the Navy study area is limited to Southern California and 

northern Mexico, but extends beyond the U.S. EEZ), we compare predicted takes to both the abundance estimates for the study area, as well as the SARs (as described in the Estimated Take of Marine Mammals section of the 2018 HSTT final rule). 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. 

Below we compile and summarize the 

information that supports our 

determination that the Navy’s activities 

would not adversely affect Dall’s 

porpoises through effects on annual 

rates of recruitment or survival. 

Dall’s porpoise is not listed under the 

ESA and the stock status is considered 

‘‘unknown.’’ No M/SI or Level A 

harassment via tissue damage from 

exposure to explosives is expected or 

proposed for authorization for this 

stock. 

Most Level B harassments to Dall’s 

porpoise from hull-mounted sonar 

(MF1) in the HSTT Study Area would 

result from received levels between 154 

and 166 dB SPL (85 percent). While 

harbor porpoises have been observed to 

be especially sensitive to human 

activity, the same types of responses 

have not been observed in Dall’s 

porpoises. Dall’s porpoises are typically 

notably longer than and weigh more 

than twice as much as harbor porpoises 

making them generally less likely to be 

preyed upon and likely differentiating 

their behavioral repertoire somewhat 

from harbor porpoises. Further, they are 

typically seen in large groups and 

feeding aggregations or exhibiting bowriding behaviors, which is very different 

from the group dynamics observed in 

the more typically solitary, cryptic 

harbor porpoises, which are not often 

seen bow-riding. For these reasons, 

Dall’s porpoises are not treated as 

especially sensitive species (as 

compared to harbor porpoises, which 

have a lower threshold for Level B 

harassment by behavioral disturbance 

and more distant cutoff) but, rather, are 

analyzed similarly to other odontocetes. 

Therefore, the majority of Level B 

harassment takes are expected to be in 

the form of milder responses compared 

to higher level exposures. As discussed 

more fully in the 2018 HSTT final rule, 

we anticipate more severe effects from 

takes when animals are exposed to 

higher received levels. 


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Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), the number of estimated 

total instances of take compared to the 

abundance (measured against both the 

Navy-estimated abundance and the 

SAR) is 2,170 and 270 percent, 

respectively (table 20). Given the range 

of this stock (up the U.S. West Coast 

through Washington and sometimes 

beyond the U.S. EEZ), this information 

suggests that some smaller portion of 

the individuals of this stock will be 

taken, and that some subset of 

individuals within the stock will be 

taken repeatedly within the year 

(perhaps up to 42 days)—potentially 

over a fair number of sequential days, 

especially where individuals spend 

extensive time in the SOCAL range 

complex. While interrupted feeding 

bouts are a known response and concern 

for odontocetes, we also know that there 

are often viable alternative habitat 

options in the relative vicinity. 

Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB (i.e., of a lower, or 

sometimes moderate level, less likely to 

evoke a severe response). However, as 

noted, some of these takes could occur 

on a fair number of sequential days for 

this stock. 

The severity of TTS takes is expected 

to be low-level, of short duration, and 

mostly not in a frequency band that 

would be expected to interfere 

significantly with conspecific 

communication, echolocation, or other 

important low-frequency cues. 

Therefore, the associated lost 

opportunities and capabilities would 

not be expected to impact reproduction 

or survival. For these same reasons (low 

level and the likely frequency band), 

while a small permanent loss of hearing 

sensitivity may include some degree of 

energetic costs for compensating or may 

mean some small loss of opportunities 

or detection capabilities, the estimated 

209 takes by Level A harassment by PTS 

for Dall’s porpoise would be unlikely to 

impact behaviors, opportunities, or 

detection capabilities to a degree that 

would interfere with reproductive 

success or survival for most individuals. 

Because of the high number of PTS 

takes, however, we acknowledge that a 

few animals could potentially incur 

permanent hearing loss of a higher 

degree that could potentially interfere 

with their successful reproduction and 

growth. Given the status of the stock, 

even if this occurred, it would not 

adversely impact rates of recruitment or 

survival. 

Altogether, a portion of this stock will 

likely be taken (at a low to occasionally 

moderate level) over several days a year, 

and some smaller portion of the stock is 

expected to be taken on a relatively 

moderate to high number of days across 

the year, some of which could be 

sequential days. Though the majority of 

impacts are expected to be of a lower to 

sometimes moderate severity, the larger 

number of takes (in total and for certain 

individuals) for the Dall’s porpoise 

makes it more likely (probabilistically) 

that a small number of individuals 

could be interrupted during foraging in 

a manner and amount such that impacts 

to the energy budgets of females (from 

either losing feeding opportunities or 

expending considerable energy to find 

alternative feeding options) could cause 

them to forego reproduction for a year. 

Energetic impacts to males are generally 

meaningless to population rates unless 

they cause death, and it takes extreme 

energy deficits beyond what would ever 

be likely to result from these activities 

to cause the death of an adult marine 

mammal. Similarly, we acknowledge 

the potential for this to occur to a few 

individuals out of the 209 total that 

might incur a higher degree of PTS. As 

noted previously, however, foregone 

reproduction (especially for only 1 year 

in 7, which is the maximum predicted 

because the small number anticipated in 

any 1 year makes the probability that 

any individual would be impacted in 

this way twice in 7 years very low) has 

far less of an impact on population rates 

than mortality. Further, the small 

number of instances of foregone 

reproduction that could potentially 

result from PTS and/or the few 

repeated, more severe Level B 

harassment takes by behavioral 

disturbance would not be expected to 

adversely affect the stock through effects 

on annual rates of recruitment or 

survival, especially given the status of 

the species (not endangered or 

threatened; minimum population of 

10,286 just within the U.S. EEZ) and 

residual PBR of Dall’s porpoise (98.3). 

For these reasons, in consideration of all 

of the effects of the Navy’s activities 

combined, we have preliminarily 

determined that the authorized take 

proposed would have a negligible 

impact on Dall’s porpoise. 

Pinnipeds 

In table 21 and table 22 below for 

pinnipeds, we indicate the total annual 

mortality, Level A harassment and Level 

B harassment, and a number indicating 

the instances of total take as a 

percentage of abundance. Table 21 and 

table 22 have been updated from tables 

27 and 28 in the 2020 HSTT final rule 

with the 2022 final SARs, as 

appropriate. For additional information 

and analysis supporting the negligibleimpact analysis, see the Pinnipeds 

discussion in the Group and SpeciesSpecific Analyses section of the 2018 

HSTT final rule, all of which remains 

applicable to this proposed rule unless 

specifically noted. 

TABLE 21—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR

PINNIPEDS IN THE HRC PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF TOTAL

TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total takes Abundance Instance of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

takes 

(entire 

study 

area) 

Takes 

(within 

Navy 

EEZ) 

Total 

Navy 

abundance 

inside and 

outside of 

EEZ 

(HRC) 

Within 

EEZ 

Navy 

abundance 

(HRC) 

Total 

take as 

percentage 

of total 

Navy 

abundance 

(HRC) 

EEZ 

take as 

percentage 

of Navy 

EEZ 

abundance 

(HRC) 

Behavioral 

disturbance 

TTS (may 

also include 

disturbance) PTS Tissue damage 

Hawaiian monk seal .... 143 62 1 0 0 206 195 169 169 122 115 

Note: For the Hawaii take estimates, we compare predicted takes to abundance estimates generated from the same underlying density estimates (as described in 

the Estimated Take of Marine Mammals section of the 2018 HSTT final rule), both in and outside of the U.S. EEZ. Because the portion of the Navy’s study area inside the U.S. EEZ is generally concomitant with the area used to generate the abundance estimates in the SARs, and the abundance predicted by the same underlying density estimates is the preferred abundance to use, there is no need to separately compare the take to the SARs abundance estimate. 

Total takes inside and outside U.S. EEZ represent the sum of annual Level A and Level B harassment from training and testing activities. 


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TABLE 22—ANNUAL ESTIMATED TAKES BY LEVEL B HARASSMENT, LEVEL A HARASSMENT, AND MORTALITY FOR

PINNIPEDS IN THE SOCAL PORTION OF THE HSTT STUDY AREA AND NUMBER INDICATING THE INSTANCES OF TOTAL

TAKE AS A PERCENTAGE OF STOCK ABUNDANCE

Species Stock 

Instances of indicated types of incidental take (not all takes 

represent separate individuals, especially for disturbance) 

Total 

takes 

Abundance Instance of total take 

as percent of 

abundance 

Level B harassment Level A 

harassment 

Mortality 

Total 

takes 

(entire 

study 

area) 

Navy 

abundance 

in action 

area (SOCAL) 

NMFS 

SARS 

abundance 

Total 

take as 

percentage 

of total 

Navy 

abundance 

in action 

area 

Total 

take as 

percentage 

of total 

SAR 

abundance 

Behavioral 

disturbance 

TTS 

(may also 

include 

disturbance) PTS Tissue damage 

California sea 

lion.

U.S .................. 113,419 4,789 87 9 0.71 118,305 4,085 257,606 2,896 46 

Guadalupe fur 

seal.

Mexico ............. 1,442 15 0 0 0 1,457 1,171 34,187 124 4 

Northern fur 

seal.

California ......... 15,167 124 1 0 0 15,292 886 14,050 1,726 109 

Harbor seal ...... California ......... 2,450 2,994 8 0 0 5,452 321 30,968 1,698 18 

Northern elephant seal.California ......... 42,916 17,955 97 2 0 60,970 4,108 187,386 1,484 33 

Note: For the SOCAL take estimates, because of the manner in which the Navy action area overlaps the ranges of many MMPA stocks (i.e., a stock may range far 

north to Washington state and beyond and abundance may only be predicted within the U.S. EEZ, while the Navy action area is limited to Southern California and 

northern Mexico, but extends beyond the U.S. EEZ), we compare predicted takes to both the abundance estimates for the action area, as well as the SARs. 

For mortality takes there is an annual average of 0.71 California sea lions (i.e., where five takes could potentially occur divided by 7 years to get the annual number 

of mortalities/serious injuries). 

Below we compile and summarize the 

information that supports our 

determination that the Navy’s activities 

would not adversely affect any 

pinnipeds through effects on annual 

rates of recruitment or survival for any 

of the affected species or stocks 

addressed in this section. 

Five M/SI takes of California sea lions 

are proposed for authorization and 

when this mortality is combined with 

the other human-caused mortality from 

other sources, it still falls well below the 

insignificance threshold for residual 

PBR (13,684). A small number of Level 

A harassment takes by tissue damage are 

also proposed for authorization (nine 

and two for California sea lions and 

northern elephant seals, respectively), 

which, as discussed in the 2020 HSTT 

final rule, could range in impact from 

minor to something just less than M/SI 

that could seriously impact fitness. 

However, given the Navy’s mitigation, 

exposure at the closer to the source and 

more severe end of the spectrum is less 

likely. Nevertheless, we cautiously 

assume some moderate impact on the 

individuals that experience these small 

numbers of take that could lower the 

individual’s fitness within the year such 

that a female (assuming a 50 percent 

chance of it being a female) might forego 

reproduction for 1 year. As noted 

previously, foregone reproduction has 

less of an impact on population rates 

than death (especially for only one 

within 7 years, which is the maximum 

predicted because the small number 

anticipated in any 1 year makes the 

probability that any individual would 

be impacted in this way twice in 7 years 

very low) and these low numbers of 

instances (especially assuming the 

likelihood that only 50 percent of the 

takes would affect females) would not 

be expected to impact annual rates of 

recruitment or survival, especially given 

the population sizes of these species. 

Regarding the magnitude of Level B 

harassment takes (TTS and behavioral 

disturbance), for Hawaiian monk seals 

and Guadalupe fur seals, the two 

species listed under the ESA, the 

estimated instances of takes as 

compared to the stock abundance does 

not exceed 124 percent, which suggests 

that some portion of these two stocks 

would be taken on 1 to a few days per 

year. For the remaining stocks, the 

number of estimated total instances of 

take compared to the abundance 

(measured against both the Navyestimated abundance and the SAR) for 

these stocks is 1,484 to 2,896 percent 

and 18 to 46 percent, respectively (table 

21). Given the ranges of these stocks 

(i.e., very large ranges, but with 

individuals often staying in the vicinity 

of haulouts), this information suggests 

that some very small portion of the 

individuals of these stocks will be 

taken, but that some subset of 

individuals within the stock will be 

taken repeatedly within the year 

(perhaps up to 58 days)—potentially 

over a fair number of sequential days. 

Regarding the severity of those 

individual Level B harassment takes by 

behavioral disturbance, the duration of 

any exposure is expected to be between 

minutes and hours (i.e., relatively short) 

and the received sound levels largely 

below 172 dB, which is considered a 

relatively low to occasionally moderate 

level for pinnipeds. However, as noted, 

some of these takes could occur on a fair 

number of sequential days for this stock. 

As described in the 2018 HSTT final 

rule and 2020 HSTT final rule, the 

Hawaii and 4-Islands mitigation areas 

protect (by not using explosives and 

limiting MFAS within) a significant 

portion of the designated critical habitat 

for Hawaiian monk seals in the Main 

Hawaiian Islands, including all of it 

around the islands of Hawaii and Lanai, 

most around Maui, and good portions 

around Molokai and Kaho’olawe. As 

discussed, this protection reduces the 

overall number of takes and further 

reduces the severity of effects by 

minimizing impacts near pupping 

beaches and in important foraging 

habitat. 

The severity of TTS takes are 

expected to be low-level, of short 

duration, and mostly not in a frequency 

band that would be expected to interfere 

significantly with conspecific 

communication, echolocation, or other 

important low-frequency cues that 

would affect the individual’s 

reproduction or survival. For these same 

reasons (low level and frequency band), 

while a small permanent loss of hearing 

sensitivity may include some degree of 

energetic costs for compensating or may 

mean some small loss of opportunities 

or detection capabilities, the one to 

eight estimated Level A harassment 

takes by PTS for monk seals, northern 

fur seals, and harbor seals would be 

unlikely to impact behaviors, 

opportunities, or detection capabilities 

to a degree that would interfere with 


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reproductive success or survival of any 

individuals. Because of the high number 

of PTS takes for California sea lions and 

northern elephant seals (87 and 97, 

respectively), we acknowledge that a 

few animals could potentially incur 

permanent hearing loss of a higher 

degree that could potentially interfere 

with their successful reproduction and 

growth. Given the status of the stocks, 

even if this occurred, it would not 

adversely impact rates of recruitment or 

survival (residual PBR of 13,684 and 

5,108, respectively). 

Altogether, an individual Hawaiian 

monk seal and Guadalupe fur seal 

would be taken no more than a few days 

in any year with none of the expected 

take anticipated to affect individual 

reproduction or survival, let alone 

annual rates of recruitment and 

survival. With all other stocks, only a 

very small portion of the stock will be 

taken in any manner. Of those taken, 

some individuals will be taken by Level 

B harassment (at a moderate or 

sometimes low level) over several days 

a year, and some smaller portion of 

those taken will be on a relatively 

moderate to high number of days across 

the year (up to 58), a fair number of 

which would likely be sequential days. 

Though the majority of impacts are 

expected to be of a lower to sometimes 

moderate severity, the repeated takes 

over a potentially fair number of 

sequential days for some individuals 

makes it more likely that some number 

of individuals could be interrupted 

during foraging in a manner and amount 

such that impacts to the energy budgets 

of females (from either losing feeding 

opportunities or expending considerable 

energy to find alternative feeding 

options) could cause them to forego 

reproduction for a year (energetic 

impacts to males are generally 

meaningless to population rates unless 

they cause death, and it takes extreme 

energy deficits beyond what would ever 

be likely to result from these activities 

to cause the death of an adult marine 

mammal). As noted previously, 

however, foregone reproduction 

(especially for only 1 year within 7, 

which is the maximum predicted 

because the small number anticipated in 

any 1 year makes the probability that 

any individual would be impacted in 

this way twice in 7 years very low) has 

far less of an impact on population rates 

than mortality and a relatively small 

number of instances of foregone 

reproduction (as compared to the stock 

abundance and residual PBR) would not 

be expected to adversely affect the stock 

through effects on annual rates of 

recruitment or survival, especially given 

the status of these stocks. Accordingly, 

we do not anticipate the relatively small 

number of individual northern fur seals 

or harbor seals that might be taken over 

repeated days within the year in a 

manner that results in 1 year of foregone 

reproduction to adversely affect the 

stocks through effects on rates of 

recruitment or survival, given the status 

of the stocks, which are respectively 

increasing and stable with abundances 

and residual PBRs of 14,050/30,968 and 

449/1,598. 

For California sea lions, given the 

very high abundance and residual PBR 

(257,606 and 13,684, respectively), as 

well as the increasing status of the stock 

in the presence of similar levels of Navy 

activities over past years—the impacts 

of 0.71 annual mortalities, potential 

foregone reproduction for up to nine 

individuals in a year taken by tissue 

damage, and some relatively small 

number of individuals taken as a result 

of repeated behavioral harassment over 

a fair number of sequential days are not 

expected to adversely affect the stock 

through effects on annual rates of 

recruitment or survival. Similarly, for 

northern elephant seals, given the very 

high abundance and residual PBR 

(187,386 and 5,108, respectively), as 

well as the increasing status of the stock 

in the presence of similar levels of Navy 

activities over past years, the impacts of 

potential foregone reproduction for up 

to two individuals in a year taken by 

tissue damage and some relatively small 

number of individuals taken as a result 

of repeated behavioral harassment over 

a fair number of sequential days are not 

expected to adversely affect the stock 

through effects on annual rates of 

recruitment or survival. For these 

reasons, in consideration of all of the 

effects of the Navy’s activities combined 

(M/SI, Level A harassment, and Level B 

harassment), we have preliminarily 

determined that the authorized take 

proposed would have a negligible 

impact on all pinniped species and 

stocks. 

Preliminary Determination 

The 2018 HSTT final rule included a 

detailed discussion of all of the 

anticipated impacts on the affected 

species and stocks from serious injury 

or mortality, Level A harassment, and 

Level B harassment; impacts on habitat; 

and how the Navy’s mitigation and 

monitoring measures reduce the number 

and/or severity of adverse effects. We 

have evaluated how these impacts as 

well as an additional proposed take of 

two large whales by serious injury or 

mortality by vessel strike, and the 

proposed mitigation measures are 

expected to combine, annually, to affect 

individuals of each species and stock. 

Those effects were then evaluated in the 

context of whether they are reasonably 

likely to impact reproductive success or 

survivorship of individuals and then, if 

so, further analyzed to determine 

whether there would be effects on 

annual rates of recruitment or survival 

that would adversely affect the species 

or stock. 

As described above, the basis for the 

negligible impact determination is the 

assessment of effects on annual rates of 

recruitment and survival. Accordingly, 

the analysis included in the 2018 HSTT 

final rule and 2020 HSTT final rule used 

annual activity levels, the best available 

science, and approved methods to 

predict the annual impacts to marine 

mammals, which were then analyzed in 

the context of whether each species or 

stock would incur more than a 

negligible impact based on anticipated 

adverse impacts to annual rates of 

recruitment or survival. As we have 

described above, none of the factors 

upon which the conclusions in the 2020 

HSTT final rule were based have 

changed, with the exception of 

estimated take by vessel strike. 

Therefore, even though this proposed 

rule includes two additional takes by 

vessel strike, little has changed that 

would change our 2018 HSTT final rule 

and subsequent 2020 HSTT final rule 

analyses, and it is appropriate to rely on 

those analyses, as well as the new 

information and analysis discussed 

above, for this proposed rule. 

Based on the applicable information 

and analysis from the 2018 HSTT final 

rule and 2020 HSTT final rule, as 

updated with the information and 

analysis contained herein on the 

potential and likely effects of the 

specified activities on the affected 

marine mammals and their habitat, and 

taking into consideration the 

implementation of the monitoring and 

mitigation measures, NMFS 

preliminarily finds that the incidental 

take from the specified activities will 

have a negligible impact on all affected 

marine mammal species and stocks. 

Subsistence Harvest of Marine 

Mammals 

There are no subsistence uses or 

harvest of marine mammals in the 

geographic area affected by the specified 

activities. Therefore, NMFS has 

preliminarily determined that the total 

taking affecting species or stocks would 

not have an unmitigable adverse impact 

on the availability of such species or 

stocks for taking for subsistence 

purposes. 


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Classification 

Endangered Species Act 

There are nine marine mammal 

species under NMFS jurisdiction that 

are listed as endangered or threatened 

under the ESA with confirmed or 

possible occurrence in the HSTT Study 

Area: blue whale (Eastern and Central 

North Pacific stocks), fin whale (CA/OR/ 

WA and Hawaii stocks), gray whale 

(Western North Pacific stock), 

humpback whale (Mexico and Central 

America DPSs), sei whale (Eastern 

North Pacific and Hawaii stocks), sperm 

whale (CA/OR/WA and Hawaii stocks), 

false killer whale (Main Hawaiian 

Islands Insular), Hawaiian monk seal 

(Hawaii stock), and Guadalupe fur seal 

(Mexico to California). There is also 

ESA-designated critical habitat for 

Hawaiian monk seals and Main 

Hawaiian Islands Insular false killer 

whales. The Navy consulted with NMFS 

pursuant to section 7 of the ESA for 

HSTT activities. NMFS also consulted 

internally on the issuance of the 2018 

HSTT regulations and LOAs under 

section 101(a)(5)(A) of the MMPA. 

NMFS issued a Biological Opinion on 

December 10, 2018 concluding that the 

issuance of the 2018 HSTT final rule 

and subsequent LOAs are not likely to 

jeopardize the continued existence of 

the threatened and endangered species 

under NMFS’ jurisdiction and are not 

likely to result in the destruction or 

adverse modification of critical habitat 

in the HSTT Study Area. The 2018 

Biological Opinion included specified 

conditions under which NMFS would 

be required to reinitiate section 7 

consultation. NMFS reviewed these 

specified conditions for the 2020 HSTT 

rulemaking and determined that 

reinitiation of consultation was not 

warranted. The incidental take 

statement that accompanied the 2018 

Biological Opinion was amended to 

cover the 7-year period of the 2020 

HSTT rule. The 2018 Biological Opinion 

for this action is available at https:// 

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/incidentaltake-authorizations-military-readinessactivities. 

The 2018 Biological Opinion 

reinitiation clause (2), states that formal 

consultation should be reinitiated if 

‘‘new information reveals effects of the 

agency action that may affect ESA-listed 

species or critical habitat in a manner or 

to an extent not previously considered.’’ 

Given the new information regarding 

the recent occurrence of large whale 

strikes by naval vessels in the southern 

California portion of the HSTT Study 

Area, as described herein, the Navy has 

reinitiated consultation with NMFS 

pursuant to section 7 of the ESA for 

HSTT Study Area activities, and NMFS 

has also reinitiated consultation 

internally on the issuance of these 

proposed, revised regulations and LOAs 

under section 101(a)(5)(A) of the 

MMPA. 

National Marine Sanctuaries Act 

Federal agency actions that are likely 

to injure national marine sanctuary 

resources are subject to consultation 

with the Office of National Marine 

Sanctuaries (ONMS) under section 

304(d) of the National Marine 

Sanctuaries Act (NMSA). There are two 

national marine sanctuaries in the HSTT 

Study Area, the Hawaiian Islands 

Humpback Whale National Marine 

Sanctuary and the Channel Islands 

National Marine Sanctuary. NMFS will 

work with NOAA’s ONMS to fulfill our 

responsibilities under the NMSA as 

warranted and will complete any NMSA 

requirements prior to a determination 

on the issuance of the final rule and 

LOAs. 

National Environmental Policy Act 

To comply with the National 

Environmental Policy Act of 1969 

(NEPA; 42 U.S.C. 4321 et seq.) and 

NOAA Administrative Order (NAO) 

216–6A, NMFS must evaluate our 

proposed actions and alternatives with 

respect to potential impacts on the 

human environment. NMFS 

participated as a cooperating agency on 

the 2018 HSTT FEIS/OEIS (published 

on October 26, 2018, http://

www.hstteis.com) which evaluated 

impacts from Navy training and testing 

activities in the HSTT Study Area for 

the reasonably foreseeable future 

(including through 2025). In accordance 

with 40 CFR 1506.3, NMFS 

independently reviewed and evaluated 

the 2018 HSTT FEIS/OEIS and 

determined that it was adequate and 

sufficient to meet our responsibilities 

under NEPA for the issuance of the 2018 

HSTT final rule and associated LOAs. 

NMFS therefore adopted the 2018 HSTT 

FEIS/OEIS. 

In accordance with 40 CFR 1502.9 

and the information and analysis 

contained in this proposed rule, the 

Navy and NMFS as a cooperating 

agency have made a preliminary 

determination that this proposed rule 

and any subsequent LOAs would not 

result in significant impacts that were 

not fully considered in the 2018 HSTT 

FEIS/OEIS. As indicated in this 

proposed rule, the Navy has made no 

substantial changes to the activities nor 

are there significant new circumstances 

or information relevant to 

environmental concerns or their 

impacts. NMFS will make a final NEPA 

determination prior to a decision 

whether to issue a final rule. 

Regulatory Flexibility Act 

The Office of Management and Budget 

has determined that this proposed rule 

is not significant for purposes of 

Executive Order 12866. 

Pursuant to the Regulatory Flexibility 

Act (RFA), the Chief Counsel for 

Regulation of the Department of 

Commerce has certified to the Chief 

Counsel for Advocacy of the Small 

Business Administration that this 

proposed rule, if adopted, would not 

have a significant economic impact on 

a substantial number of small entities. 

The RFA requires Federal agencies to 

prepare an analysis of a rule’s impact on 

small entities whenever the agency is 

required to publish a notice of proposed 

rulemaking. However, a Federal agency 

may certify, pursuant to 5 U.S.C. 605(b), 

that the action will not have a 

significant economic impact on a 

substantial number of small entities. 

The Navy is the sole entity that would 

be affected by this rulemaking, and the 

Navy is not a small governmental 

jurisdiction, small organization, or small 

business, as defined by the RFA. Any 

requirements imposed by an LOA 

issued pursuant to these regulations, 

and any monitoring or reporting 

requirements imposed by these 

regulations, would be applicable only to 

the Navy. NMFS does not expect the 

issuance of these regulations or the 

associated LOAs to result in any 

impacts to small entities pursuant to the 

RFA. Because this action, if adopted, 

would directly affect the Navy and not 

a small entity, NMFS concludes the 

action would not result in a significant 

economic impact on a substantial 

number of small entities. 

List of Subjects in 50 CFR Part 218 

Exports, Fish, Imports, Incidental 

take, Indians, Labeling, Marine 

mammals, Navy, Penalties, Reporting 

and recordkeeping requirements, 

Seafood, Sonar, Transportation. 

Dated: September 26, 2023. 

Samuel D. Rauch III, 

Deputy Assistant Administrator for 

Regulatory Programs, National Marine 

Fisheries Service. 

For reasons set forth in the preamble, 

NMFS proposes to amend 50 CFR part 

218 as follows: 

PART 218—REGULATIONS 

GOVERNING THE TAKING AND 

IMPORTING OF MARINE MAMMALS 

■ 1. The authority citation for part 218 

continues to read as follows: 


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Authority: 16 U.S.C. 1361 et seq. 

■ 2. Revise subpart H to read as follows: 

Subpart H—Taking and Importing 

Marine Mammals; U.S. Navy’s HawaiiSouthern California Training and 

Testing (HSTT) 

Sec. 

218.70 Specified activity and geographical 

region. 

218.71 Effective dates. 

218.72 Permissible methods of taking. 

218.73 Prohibitions. 

218.74 Mitigation requirements. 

218.75 Requirements for monitoring and 

reporting. 

218.76 Letters of Authorization. 

218.77 Renewals and modifications of 

Letters of Authorization. 

218.78 and 218.79 [Reserved] 

Subpart H—Taking and Importing 

Marine Mammals; U.S. Navy’s HawaiiSouthern California Training and 

Testing (HSTT) 

§ 218.70 Specified activity and 

geographical region. 

(a) Regulations in this subpart apply 

only to the U.S. Navy (Navy) for the 

taking of marine mammals that occurs 

in the area described in paragraph (b) of 

this section and that occurs incidental 

to the activities listed in paragraph (c) 

of this section. 

(b) The taking of marine mammals by 

the Navy under this subpart may be 

authorized in Letters of Authorization 

(LOAs) only if it occurs within the 

Hawaii-Southern California Training 

and Testing (HSTT) Study Area, which 

includes established operating and 

warning areas across the north-central 

Pacific Ocean, from the mean high tide 

line in Southern California west to 

Hawaii and the International Date Line. 

The HSTT Study Area includes the atsea areas of three existing range 

complexes, the Hawaii Range Complex 

(HRC), the Southern California Range 

Complex (SOCAL), and the Silver 

Strand Training Complex, and overlaps 

a portion of the Point Mugu Sea Range 

(PMSR). Also included in the HSTT 

Study Area are Navy pierside locations 

in Hawaii and Southern California, 

Pearl Harbor, San Diego Bay, and the 

transit corridor on the high seas where 

sonar training and testing may occur. 

(c) The taking of marine mammals by 

the Navy is only authorized if it occurs 

incidental to the Navy conducting 

training and testing activities, including: 

(1) Training. (i) Amphibious warfare; 

(ii) Anti-submarine warfare; 

(iii) Electronic warfare; 

(iv) Expeditionary warfare; 

(v) Mine warfare; 

(vi) Surface warfare; and 

(vii) Pile driving. 

(2) Testing. (i) Naval Air Systems 

Command Testing Activities; 

(ii) Naval Sea System Command 

Testing Activities; 

(iii) Office of Naval Research Testing 

Activities; and 

(iv) Naval Information Warfare 

Systems Command. 

§ 218.71 Effective dates. 

Regulations in this subpart are 

effective from [date of publication of a 

final rule in the Federal Register] 

through December 20, 2025. 

§ 218.72 Permissible methods of taking. 

(a) Under LOAs issued pursuant to 

§§ 216.106 of this chapter and 218.76, 

the Holder of the LOAs (hereinafter 

‘‘Navy’’) may incidentally, but not 

intentionally, take marine mammals 

within the area described in § 218.70(b) 

by Level A harassment and Level B 

harassment associated with the use of 

active sonar and other acoustic sources 

and explosives as well as serious injury 

or mortality associated with vessel 

strikes and explosives, provided the 

activity is in compliance with all terms, 

conditions, and requirements of these 

regulations in this subpart and the 

applicable LOAs. 

(b) The incidental take of marine 

mammals by the activities listed in 

§ 218.70(c) is limited to the following 

species: 

TABLE 1 TO PARAGRAPH (b) 

Species Stock 

Blue whale ................................................................................................ Central North Pacific. 

Blue whale ................................................................................................ Eastern North Pacific. 

Bryde’s whale ........................................................................................... Eastern Tropical Pacific. 

Bryde’s whale ........................................................................................... Hawaii. 

Fin whale .................................................................................................. CA/OR/WA. 

Fin whale .................................................................................................. Hawaii. 

Humpback whale ...................................................................................... Central America/Southern Mexico—CA/OR/WA. 

Humpback whale ...................................................................................... Mainland Mexico—CA/OR/WA. 

Humpback whale ...................................................................................... Hawaii. 

Minke whale .............................................................................................. CA/OR/WA. 

Minke whale .............................................................................................. Hawaii. 

Sei whale .................................................................................................. Eastern North Pacific. 

Sei whale .................................................................................................. Hawaii. 

Gray whale ............................................................................................... Eastern North Pacific.

Gray whale ............................................................................................... Western North Pacific.

Sperm whale ............................................................................................. CA/OR/WA. 

Sperm whale ............................................................................................. Hawaii. 

Dwarf sperm whale ................................................................................... Hawaii. 

Pygmy sperm whale ................................................................................. Hawaii. 

Kogia whales ............................................................................................ CA/OR/WA. 

Baird’s beaked whale ............................................................................... CA/OR/WA. 

Blainville’s beaked whale ......................................................................... Hawaii. 

Cuvier’s beaked whale ............................................................................. CA/OR/WA. 

Cuvier’s beaked whale ............................................................................. Hawaii. 

Longman’s beaked whale ......................................................................... Hawaii. 

Mesoplodon spp ....................................................................................... CA/OR/WA. 

Bottlenose dolphin .................................................................................... California Coastal. 

Bottlenose dolphin .................................................................................... CA/OR/WA Offshore. 

Bottlenose dolphin .................................................................................... Hawaii Pelagic. 

Bottlenose dolphin .................................................................................... Kauai & Niihau. 

Bottlenose dolphin .................................................................................... Oahu. 

Bottlenose dolphin .................................................................................... 4-Island. 


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TABLE 1 TO PARAGRAPH (b)—Continued 

Species Stock 

Bottlenose dolphin .................................................................................... Hawaii. 

False killer whale ...................................................................................... Hawaii Pelagic. 

False killer whale ...................................................................................... Main Hawaiian Islands Insular. 

False killer whale ...................................................................................... Northwestern Hawaiian Islands. 

Fraser’s dolphin ........................................................................................ Hawaii. 

Killer whale ............................................................................................... Eastern North Pacific (ENP) Offshore. 

Killer whale ............................................................................................... ENP Transient/West Coast Transient. 

Killer whale ............................................................................................... Hawaii. 

Long-beaked common dolphin ................................................................. California. 

Melon-headed whale ................................................................................ Hawaiian Islands. 

Melon-headed whale ................................................................................ Kohala Resident. 

Northern right whale dolphin .................................................................... CA/OR/WA. 

Pacific white-sided dolphin ....................................................................... CA/OR/WA. 

Pantropical spotted dolphin ...................................................................... Hawaii Island. 

Pantropical spotted dolphin ...................................................................... Hawaii Pelagic. 

Pantropical spotted dolphin ...................................................................... Oahu. 

Pantropical spotted dolphin ...................................................................... 4-Island. 

Pygmy killer whale .................................................................................... Hawaii. 

Pygmy killer whale .................................................................................... Tropical. 

Risso’s dolphin ......................................................................................... CA/OR/WA. 

Risso’s dolphin ......................................................................................... Hawaii. 

Rough-toothed dolphin ............................................................................. Hawaii. 

Short-beaked common dolphin ................................................................ CA/OR/WA. 

Short-finned pilot whale ............................................................................ CA/OR/WA. 

Short-finned pilot whale ............................................................................ Hawaii. 

Spinner dolphin ......................................................................................... Hawaii Island. 

Spinner dolphin ......................................................................................... Hawaii Pelagic. 

Spinner dolphin ......................................................................................... Kauai & Niihau. 

Spinner dolphin ......................................................................................... Oahu & 4-Island. 

Striped dolphin .......................................................................................... CA/OR/WA. 

Striped dolphin .......................................................................................... Hawaii. 

Dall’s porpoise .......................................................................................... CA/OR/WA. 

California sea lion ..................................................................................... U.S. 

Guadalupe fur seal ................................................................................... Mexico. 

Northern fur seal ....................................................................................... California. 

Harbor seal ............................................................................................... California. 

Hawaiian monk seal ................................................................................. Hawaii. 

Northern elephant seal ............................................................................. California. 

Note to Table 1: CA/OR/WA = California/Oregon/Washington. 

§ 218.73 Prohibitions. 

Notwithstanding incidental takings 

contemplated in § 218.72(a) and 

authorized by LOAs issued under 

§§ 216.106 of this chapter and 218.76, 

no person in connection with the 

activities listed in § 218.70(c) may: 

(a) Violate, or fail to comply with, the 

terms, conditions, and requirements of 

this subpart or an LOA issued under 

§§ 216.106 of this chapter and 218.76; 

(b) Take any marine mammal not 

specified in § 218.72(b); 

(c) Take any marine mammal 

specified in § 218.72(b) in any manner 

other than as specified in the LOAs; or 

(d) Take a marine mammal specified 

in § 218.72(b) if NMFS determines such 

taking results in more than a negligible 

impact on the species or stocks of such 

marine mammal. 

§ 218.74 Mitigation requirements. 

When conducting the activities 

identified in § 218.70(c), the mitigation 

measures contained in any LOAs issued 

under §§ 216.106 of this chapter and 

218.76 must be implemented. These 

mitigation measures include, but are not 

limited to: 

(a) Procedural mitigation. Procedural 

mitigation is mitigation that the Navy 

must implement whenever and 

wherever an applicable training or 

testing activity takes place within the 

HSTT Study Area for each applicable 

activity category or stressor category and 

includes acoustic stressors (i.e., active 

sonar, air guns, pile driving, weapons 

firing noise), explosive stressors (i.e., 

sonobuoys, torpedoes, medium-caliber 

and large-caliber projectiles, missiles 

and rockets, bombs, sinking exercises, 

mines, anti-swimmer grenades, and mat 

weave and obstacle loading), and 

physical disturbance and strike stressors 

(i.e., vessel movement; towed in-water 

devices; small-, medium-, and largecaliber non-explosive practice 

munitions; non-explosive missiles and 

rockets; and non-explosive bombs and 

mine shapes). 

(1) Environmental awareness and 

education. Appropriate Navy personnel 

(including civilian personnel) involved 

in mitigation and training or testing 

activity reporting under the specified 

activities will complete one or more 

modules identified in their career path 

training plan, as specified in the LOAs. 

(2) Active sonar. Active sonar 

includes low-frequency active sonar, 

mid-frequency active sonar, and highfrequency active sonar. For vessel-based 

activities, mitigation applies only to 

sources that are positively controlled 

and deployed from manned surface 

vessels (e.g., sonar sources towed from 

manned surface platforms). For aircraftbased activities, mitigation applies only 

to sources that are positively controlled 

and deployed from manned aircraft that 

do not operate at high altitudes (e.g., 

rotary-wing aircraft). Mitigation does 

not apply to active sonar sources 

deployed from unmanned aircraft or 

aircraft operating at high altitudes (e.g., 

maritime patrol aircraft). 

(i) Number of Lookouts and 

observation platform—(A) Hullmounted sources. One Lookout for 


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platforms with space or manning 

restrictions while underway (at the 

forward part of a small boat or ship) and 

platforms using active sonar while 

moored or at anchor (including 

pierside); and two Lookouts for 

platforms without space or manning 

restrictions while underway (at the 

forward part of the ship). 

(B) Sources that are not hull-mounted 

sources. One Lookout on the ship or 

aircraft conducting the activity. 

(ii) Mitigation zone and requirements. 

During the activity, at 1,000 yards (yd) 

Navy personnel must power down 6 

decibels (dB), at 500 yd (457.2 m) Navy 

personnel must power down an 

additional 4 dB (for a total of 10 dB), 

and at 200 yd (182.9 m) Navy personnel 

must shut down for low-frequency 

active sonar ≥200 dB and hull-mounted 

mid-frequency active sonar; or at 200 yd 

(182.9 m) Navy personnel must shut 

down for low-frequency active sonar 

<200 dB, mid-frequency active sonar 

sources that are not hull-mounted, and 

high-frequency active sonar. 

(A) Prior to activity. Prior to the start 

of the activity (e.g., when maneuvering 

on station), Navy personnel must 

observe the mitigation zone for floating 

vegetation; if floating vegetation is 

observed, Navy personnel must relocate 

or delay the start of active sonar 

transmission until the mitigation zone is 

clear. Navy personnel must also observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must relocate 

or delay the start of active sonar 

transmission. 

(B) During the activity for lowfrequency active sonar at or above 200 

dB and hull-mounted mid-frequency 

active sonar. During the activity for lowfrequency active sonar at or above 200 

dB and hull-mounted mid-frequency 

active sonar, Navy personnel must 

observe the mitigation zone for marine 

mammals and power down active sonar 

transmission by 6 dB if marine 

mammals are observed within 1,000 yd 

(914.4 m) of the sonar source; power 

down by an additional 4 dB (for a total 

of 10 dB total) if marine mammals are 

observed within 500 yd (457.2 m) of the 

sonar source; and cease transmission if 

marine mammals are observed within 

200 yd (182.9 m) of the sonar source. 

(C) During the activity for lowfrequency active sonar below 200 dB, 

mid-frequency active sonar sources that 

are not hull mounted, and highfrequency active sonar. During the 

activity for low-frequency active sonar 

below 200 dB, mid-frequency active 

sonar sources that are not hull mounted, 

and high-frequency active sonar, Navy 

personnel must observe the mitigation 

zone for marine mammals and cease 

active sonar transmission if marine 

mammals are observed within 200 yd 

(182.9 m) of the sonar source. 

(D) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing or 

powering up active sonar transmission) 

until one of the following conditions 

has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the sonar source; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 minutes 

(min) for aircraft-deployed sonar 

sources or 30 min for vessel-deployed 

sonar sources; 

(4) Sonar source transit. For mobile 

activities, the active sonar source has 

transited a distance equal to double that 

of the mitigation zone size beyond the 

location of the last sighting; or 

(5) Bow-riding dolphins. For activities 

using hull-mounted sonar where a 

dolphin(s) is observed in the mitigation 

zone, the Lookout concludes that the 

dolphin(s) are deliberately closing in on 

the ship to ride the ship’s bow wave, 

and are therefore out of the main 

transmission axis of the sonar (and there 

are no other marine mammal sightings 

within the mitigation zone). 

(3) Air guns—(i) Number of Lookouts 

and observation platform. One Lookout 

positioned on a ship or pierside. 

(ii) Mitigation zone and requirements. 

150 yd (137.2 m) around the air gun. 

(A) Prior to activity. Prior to the initial 

start of the activity (e.g., when 

maneuvering on station), Navy 

personnel must observe the mitigation 

zone for floating vegetation; if floating 

vegetation is observed, Navy personnel 

must relocate or delay the start until the 

mitigation zone is clear. Navy personnel 

must also observe the mitigation zone 

for marine mammals; if marine 

mammals are observed, Navy personnel 

must relocate or delay the start of air 

gun use. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease air 

gun use. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing air 

gun use) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the air gun; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 30 min; or 

(4) Air gun transit. For mobile 

activities, the air gun has transited a 

distance equal to double that of the 

mitigation zone size beyond the location 

of the last sighting. 

(4) Pile driving. Pile driving and pile 

extraction sound during Elevated 

Causeway System training. 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned on the shore, the elevated 

causeway, or a small boat. 

(ii) Mitigation zone and requirements. 

100 yd (91.4 m) around the pile driver. 

(A) Prior to activity. Prior to the initial 

start of the activity (for 30 min), Navy 

personnel must observe the mitigation 

zone for floating vegetation; if floating 

vegetation is observed, Navy personnel 

must delay the start until the mitigation 

zone is clear. Navy personnel also must 

observe the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must delay 

the start of pile driving or vibratory pile 

extraction. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease 

impact pile driving or vibratory pile 

extraction. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing pile 

driving or pile extraction) until one of 

the following conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the pile driving 

location; or 


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(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 30 minutes. 

(5) Weapons firing noise. Weapons 

firing noise associated with large-caliber 

gunnery activities. 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned on the ship conducting 

the firing. Depending on the activity, the 

Lookout could be the same as the one 

provided for under ‘‘Explosive mediumcaliber and large-caliber projectiles’’ or 

under ‘‘Small-, medium-, and largecaliber non-explosive practice 

munitions’’ in paragraphs (a)(8)(i) and 

(a)(18)(i) of this section. 

(ii) Mitigation zone and requirements. 

Thirty degrees on either side of the 

firing line out to 70 yd from the muzzle 

of the weapon being fired. 

(A) Prior to activity. Prior to the start 

of the activity, Navy personnel must 

observe the mitigation zone for floating 

vegetation; if floating vegetation is 

observed, Navy personnel must relocate 

or delay the start of weapons firing until 

the mitigation zone is clear. Navy 

personnel must also observe the 

mitigation zone for marine mammals; if 

marine mammals are observed, Navy 

personnel must relocate or delay the 

start of weapons firing. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease 

weapons firing. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

weapons firing) until one of the 

following conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the firing ship; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 30 min; or 

(4) Firing ship transit. For mobile 

activities, the firing ship has transited a 

distance equal to double that of the 

mitigation zone size beyond the location 

of the last sighting. 

(6) Explosive sonobuoys—(i) Number 

of Lookouts and observation platform. 

One Lookout must be positioned in an 

aircraft or on small boat. If additional 

platforms are participating in the 

activity, Navy personnel positioned in 

those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and requirements. 

600 yd (548.6 m) around an explosive 

sonobuoy. 

(A) Prior to activity. Prior to the initial 

start of the activity (e.g., during 

deployment of a sonobuoy field, which 

typically lasts 20–30 min), Navy 

personnel must observe the mitigation 

zone for floating vegetation; if floating 

vegetation is observed, Navy personnel 

must relocate or delay the start of 

sonobuoy or source/receiver pair 

detonations until the mitigation zone is 

clear. Navy personnel must conduct 

passive acoustic monitoring for marine 

mammals and use information from 

detections to assist visual observations. 

Navy personnel also must visually 

observe the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must relocate 

or delay the start of sonobuoy or source/ 

receiver pair detonations. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease 

sonobuoy or source/receiver pair 

detonations. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

detonations) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the sonobuoy; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min 

when the activity involves aircraft that 

have fuel constraints (e.g., helicopter), 

or 30 min when the activity involves 

aircraft that are not typically fuel 

constrained. 

(D) After activity. After completion of 

the activity (e.g., prior to maneuvering 

off station), when practical (e.g., when 

platforms are not constrained by fuel 

restrictions or mission-essential followon commitments), Navy personnel must 

observe for marine mammals in the 

vicinity of where detonations occurred; 

if any injured or dead marine mammals 

are observed, Navy personnel must 

follow established incident reporting 

procedures. If additional platforms are 

supporting this activity (e.g., providing 

range clearance), these Navy assets must 

assist in the visual observation of the 

area where detonations occurred. 

(7) Explosive torpedoes—(i) Number 

of Lookouts and observation platform. 

One Lookout positioned in an aircraft. If 

additional platforms are participating in 

the activity, Navy personnel positioned 

in those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and requirements. 

2,100 yd around the intended impact 

location. 

(A) Prior to activity. Prior to the initial 

start of the activity (e.g., during 

deployment of the target), Navy 

personnel must observe the mitigation 

zone for floating vegetation and jellyfish 

aggregations; if floating vegetation or 

jellyfish aggregations are observed, Navy 

personnel must relocate or delay the 

start of firing until the mitigation zone 

is clear. Navy personnel must conduct 

passive acoustic monitoring for marine 

mammals and use the information from 

detections to assist visual observations. 

Navy personnel also must visually 

observe the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must relocate 

or delay the start of firing. 

(B) During activity. During the 

activity, Navy personnel must observe 

for marine mammals and jellyfish 

aggregations; if marine mammals or 

jellyfish aggregations are observed, Navy 

personnel must cease firing. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

firing) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended 

impact location; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min 

when the activity involves aircraft that 

have fuel constraints, or 30 min when 


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the activity involves aircraft that are not 

typically fuel constrained. 

(D) After activity. After completion of 

the activity (e.g., prior to maneuvering 

off station), Navy personnel must when 

practical (e.g., when platforms are not 

constrained by fuel restrictions or 

mission-essential follow-on 

commitments), observe for marine 

mammals in the vicinity of where 

detonations occurred; if any injured or 

dead marine mammals are observed, 

Navy personnel must follow established 

incident reporting procedures. If 

additional platforms are supporting this 

activity (e.g., providing range clearance), 

these Navy assets must assist in the 

visual observation of the area where 

detonations occurred. 

(8) Explosive medium-caliber and 

large-caliber projectiles. Gunnery 

activities using explosive mediumcaliber and large-caliber projectiles. 

Mitigation applies to activities using a 

surface target. 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be on the vessel or aircraft conducting 

the activity. For activities using 

explosive large-caliber projectiles, 

depending on the activity, the Lookout 

could be the same as the one described 

in ‘‘Weapons firing noise’’ in paragraph 

(a)(5)(i) of this section. If additional 

platforms are participating in the 

activity, Navy personnel positioned in 

those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and 

requirements—(A) Air-to-surface 

activities. 200 yd (182.9 m) around the 

intended impact location for air-tosurface activities using explosive 

medium-caliber projectiles. 

(B) Surface-to-surface activities, 

medium-caliber. 600 yd (548.6 m) 

around the intended impact location for 

surface-to-surface activities using 

explosive medium-caliber projectiles. 

(C) Surface-to-surface activities, largecaliber. 1,000 yd (914.4 m) around the 

intended impact location for surface-tosurface activities using explosive largecaliber projectiles. 

(D) Prior to activity. Prior to the start 

of the activity (e.g., when maneuvering 

on station), Navy personnel must 

observe the mitigation zone for floating 

vegetation; if floating vegetation is 

observed, Navy personnel must relocate 

or delay the start of firing until the 

mitigation zone is clear. Navy personnel 

also must observe the mitigation zone 

for marine mammals; if marine 

mammals are observed, Navy personnel 

must relocate or delay the start of firing. 

(E) During activity. During the 

activity, Navy personnel must observe 

for marine mammals; if marine 

mammals are observed, Navy personnel 

must cease firing. 

(F) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

firing) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended 

impact location; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min for 

aircraft-based firing or 30 min for vesselbased firing; or for activities using 

mobile targets, the intended impact 

location has transited a distance equal 

to double that of the mitigation zone 

size beyond the location of the last 

sighting. 

(G) After activity. After completion of 

the activity (e.g., prior to maneuvering 

off station), Navy personnel must, when 

practical (e.g., when platforms are not 

constrained by fuel restrictions or 

mission-essential follow-on 

commitments), observe for marine 

mammals in the vicinity of where 

detonations occurred; if any injured or 

dead marine mammals are observed, 

Navy personnel must follow established 

incident reporting procedures. If 

additional platforms are supporting this 

activity (e.g., providing range clearance), 

these Navy assets must assist in the 

visual observation of the area where 

detonations occurred. 

(9) Explosive missiles and rockets. 

Aircraft-deployed explosive missiles 

and rockets. Mitigation applies to 

activities using a surface target. 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned in an aircraft. If additional 

platforms are participating in the 

activity, Navy personnel positioned in 

those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and 

requirements—(A) Missiles or rockets 

with 0.6–20 lb net explosive weight. 900 

yd (823 m) around the intended impact 

location for missiles or rockets with 0.6– 

20 lb net explosive weight. 

(B) Missiles with 21–500 lb net 

explosive weight. 2,000 yd (1,828.8 m) 

around the intended impact location for 

missiles with 21–500 lb net explosive 

weight. 

(C) Prior to activity. Prior to the initial 

start of the activity (e.g., during a flyover of the mitigation zone), Navy 

personnel must observe the mitigation 

zone for floating vegetation; if floating 

vegetation is observed, Navy personnel 

must relocate or delay the start of firing 

until the mitigation zone is clear. Navy 

personnel also must observe the 

mitigation zone for marine mammals; if 

marine mammals are observed, Navy 

personnel must relocate or delay the 

start of firing. 

(D) During activity. During the 

activity, Navy personnel must observe 

for marine mammals; if marine 

mammals are observed, Navy personnel 

must cease firing. 

(E) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

firing) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended 

impact location; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min 

when the activity involves aircraft that 

have fuel constraints, or 30 min when 

the activity involves aircraft that are not 

typically fuel constrained. 

(F) After activity. After completion of 

the activity (e.g., prior to maneuvering 

off station), Navy personnel must, when 

practical (e.g., when platforms are not 

constrained by fuel restrictions or 

mission-essential follow-on 

commitments), observe for marine 

mammals in the vicinity of where 

detonations occurred; if any injured or 

dead marine mammals are observed, 

Navy personnel must follow established 

incident reporting procedures. If 

additional platforms are supporting this 

activity (e.g., providing range clearance), 

these Navy assets will assist in the 

visual observation of the area where 

detonations occurred. 

(10) Explosive bombs—(i) Number of 

Lookouts and observation platform. One 


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Lookout must be positioned in an 

aircraft conducting the activity. If 

additional platforms are participating in 

the activity, Navy personnel positioned 

in those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and requirements. 

2,500 yd (2,286 m) around the intended 

target. 

(A) Prior to activity. Prior to the initial 

start of the activity (e.g., when arriving 

on station), Navy personnel must 

observe the mitigation zone for floating 

vegetation; if floating vegetation is 

observed, Navy personnel must relocate 

or delay the start of bomb deployment 

until the mitigation zone is clear. Navy 

personnel also must observe the 

mitigation zone for marine mammals; if 

marine mammals are observed, Navy 

personnel must relocate or delay the 

start of bomb deployment. 

(B) During activity. During the activity 

(e.g., during target approach), Navy 

personnel must observe the mitigation 

zone for marine mammals; if marine 

mammals are observed, Navy personnel 

must cease bomb deployment. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing bomb 

deployment) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended 

target; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min; or 

for activities using mobile targets, the 

intended target has transited a distance 

equal to double that of the mitigation 

zone size beyond the location of the last 

sighting. 

(D) After activity. After completion of 

the activity (e.g., prior to maneuvering 

off station), Navy personnel must, when 

practical (e.g., when platforms are not 

constrained by fuel restrictions or 

mission-essential follow-on 

commitments), observe for marine 

mammals in the vicinity of where 

detonations occurred; if any injured or 

dead marine mammals are observed, 

Navy personnel must follow established 

incident reporting procedures. If 

additional platforms are supporting this 

activity (e.g., providing range clearance), 

these Navy assets must assist in the 

visual observation of the area where 

detonations occurred. 

(11) Sinking exercises—(i) Number of 

Lookouts and observation platform. 

Two Lookouts (one must be positioned 

in an aircraft and one must be 

positioned on a vessel). If additional 

platforms are participating in the 

activity, Navy personnel positioned in 

those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and requirements. 

2.5 nautical miles (nmi) around the 

target ship hulk. 

(A) Prior to activity. Prior to the initial 

start of the activity (90 min prior to the 

first firing), Navy personnel must 

conduct aerial observations of the 

mitigation zone for floating vegetation 

and jellyfish aggregations; if floating 

vegetation or jellyfish aggregations are 

observed, Navy personnel must delay 

the start of firing until the mitigation 

zone is clear. Navy personnel also must 

conduct aerial observations of the 

mitigation zone for marine mammals; if 

marine mammals are observed, Navy 

personnel must delay the start of firing. 

(B) During activity. During the 

activity, Navy personnel must conduct 

passive acoustic monitoring for marine 

mammals and use the information from 

detections to assist visual observations. 

Navy personnel must visually observe 

the mitigation zone for marine mammals 

from the vessel; if marine mammals are 

observed, Navy personnel must cease 

firing. Immediately after any planned or 

unplanned breaks in weapons firing of 

longer than 2 hours, Navy personnel 

must observe the mitigation zone for 

marine mammals from the aircraft and 

vessel; if marine mammals are observed, 

Navy personnel must delay 

recommencement of firing. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

firing) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the target ship 

hulk; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 30 minutes. 

(D) After activity. After completion of 

the activity (for 2 hours after sinking the 

vessel or until sunset, whichever comes 

first), Navy personnel must observe for 

marine mammals in the vicinity of 

where detonations occurred; if any 

injured or dead marine mammals are 

observed, Navy personnel must follow 

established incident reporting 

procedures. If additional platforms are 

supporting this activity (e.g., providing 

range clearance), these Navy assets will 

assist in the visual observation of the 

area where detonations occurred. 

(12) Explosive mine countermeasure 

and neutralization activities—(i) 

Number of Lookouts and observation 

platform—(A) Smaller mitigation zone. 

One Lookout must be positioned on a 

vessel or in an aircraft when 

implementing the smaller mitigation 

zone. 

(B) Larger mitigation zone. Two 

Lookouts (one must be positioned in an 

aircraft and one must be on a small boat) 

when implementing the larger 

mitigation zone. 

(C) Additional platforms. If additional 

platforms are participating in the 

activity, Navy personnel positioned in 

those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and requirements. 

(A) Activities using 0.1–5 lb net 

explosive weight. 600 yd (548.6 m) 

around the detonation site for activities 

using 0.1–5 lb net explosive weight. 

(B) Activities using 6–650 lb net 

explosive weight. 2,100 yd (1,920.2 m) 

around the detonation site for activities 

using 6–650 lb net explosive weight 

(including high explosive target mines). 

(C) Prior to activity. Prior to the initial 

start of the activity (e.g., when 

maneuvering on station; typically, 10 

min when the activity involves aircraft 

that have fuel constraints, or 30 min 

when the activity involves aircraft that 

are not typically fuel constrained), Navy 

personnel must observe the mitigation 

zone for floating vegetation; if floating 

vegetation is observed, Navy personnel 

must relocate or delay the start of 

detonations until the mitigation zone is 

clear. Navy personnel also must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must relocate 

or delay the start of detonations. 

(D) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals, concentrations of seabirds, 


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and individual foraging seabirds; if 

marine mammals, concentrations of 

seabirds, or individual foraging seabirds 

are observed, Navy personnel must 

cease detonations. 

(E) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity or 

a sighting of seabird concentrations or 

individual foraging seabirds during the 

activity. Navy personnel must allow a 

sighted animal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

detonations) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to detonation site; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min 

when the activity involves aircraft that 

have fuel constraints, or 30 min when 

the activity involves aircraft that are not 

typically fuel constrained. 

(F) After activity. After completion of 

the activity (typically 10 min when the 

activity involves aircraft that have fuel 

constraints, or 30 min when the activity 

involves aircraft that are not typically 

fuel constrained), Navy personnel must 

observe for marine mammals in the 

vicinity of where detonations occurred; 

if any injured or dead marine mammals 

are observed, Navy personnel must 

follow established incident reporting 

procedures. If additional platforms are 

supporting this activity (e.g., providing 

range clearance), these Navy assets must 

assist in the visual observation of the 

area where detonations occurred. 

(13) Explosive mine neutralization 

activities involving Navy divers—(i) 

Number of Lookouts and observation 

platform—(A) Smaller mitigation zone. 

Two Lookouts (two small boats with one 

Lookout each, or one Lookout must be 

on a small boat and one must be in a 

rotary-wing aircraft) when 

implementing the smaller mitigation 

zone. 

(B) Larger mitigation zone. Four 

Lookouts (two small boats with two 

Lookouts each), and a pilot or member 

of an aircrew must serve as an 

additional Lookout if aircraft are used 

during the activity, when implementing 

the larger mitigation zone. 

(C) Divers. All divers placing the 

charges on mines will support the 

Lookouts while performing their regular 

duties and will report applicable 

sightings to their supporting small boat 

or Range Safety Officer. 

(D) Additional platforms. If additional 

platforms are participating in the 

activity, Navy personnel positioned in 

those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and 

requirements—(A) Activities under 

positive control using 0.1–20 lb net 

explosive weight. 500 yd (457.2 m) 

around the detonation site during 

activities under positive control using 

0.1–20 lb net explosive weight. 

(B) Activities under positive control 

using 21–60 lb net explosive weight 

charges. 1,000 yd (914.4 m) around the 

detonation site during all activities 

using time-delay fuses (0.1–29 lb net 

explosive weight) and during activities 

under positive control using 21–60 lb 

net explosive weight charges. 

(C) Prior to activity. Prior to the initial 

start of the activity (e.g., when 

maneuvering on station for activities 

under positive control; 30 min for 

activities using time-delay firing 

devices), Navy personnel must observe 

the mitigation zone for floating 

vegetation; if floating vegetation is 

observed, Navy personnel must relocate 

or delay the start of detonations or fuse 

initiation until the mitigation zone is 

clear. Navy personnel also must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must relocate 

or delay the start of detonations or fuse 

initiation. 

(D) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals, concentrations of seabirds, 

and individual foraging seabirds (in the 

water and not on shore); if marine 

mammals, concentrations of seabirds, or 

individual foraging seabirds are 

observed, Navy personnel must cease 

detonations or fuse initiation. To the 

maximum extent practicable depending 

on mission requirements, safety, and 

environmental conditions, Navy 

personnel must position boats near the 

mid-point of the mitigation zone radius 

(but outside of the detonation plume 

and human safety zone), must position 

themselves on opposite sides of the 

detonation location (when two boats are 

used), and must travel in a circular 

pattern around the detonation location 

with one Lookout observing inward 

toward the detonation site and the other 

observing outward toward the perimeter 

of the mitigation zone. If used, Navy 

aircraft must travel in a circular pattern 

around the detonation location to the 

maximum extent practicable. Navy 

personnel must not set time-delay firing 

devices (0.1–29 lb net explosive weight) 

to exceed 10 minutes. 

(E) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity or 

a sighting of seabird concentrations or 

individual foraging seabirds during the 

activity. Navy personnel must allow a 

sighted animal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

detonations) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the detonation 

site; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min 

during activities under positive control 

with aircraft that have fuel constraints, 

or 30 min during activities under 

positive control with aircraft that are not 

typically fuel constrained and during 

activities using time-delay firing 

devices. 

(F) After activity. After completion of 

an activity (for 30 min), the Navy must 

observe for marine mammals for 30 

minutes. Navy personnel must observe 

for marine mammals in the vicinity of 

where detonations occurred; if any 

injured or dead marine mammals are 

observed, Navy personnel must follow 

established incident reporting 

procedures. If additional platforms are 

supporting this activity (e.g., providing 

range clearance), these Navy assets must 

assist in the visual observation of the 

area where detonations occurred. 

(14) Maritime security operations— 

anti-swimmer grenades—(i) Number of 

Lookouts and observation platform. One 

Lookout must be positioned on the 

small boat conducting the activity. If 

additional platforms are participating in 

the activity, Navy personnel positioned 

in those assets (e.g., safety observers, 

evaluators) must support observing the 

mitigation zone for applicable biological 

resources while performing their regular 

duties. 

(ii) Mitigation zone and requirements. 

200 yd (182.9 m) around the intended 

detonation location. 

(A) Prior to activity. Prior to the initial 

start of the activity (e.g., when 

maneuvering on station), Navy 

personnel must observe the mitigation 

zone for floating vegetation; if floating 

vegetation is observed, Navy personnel 


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must relocate or delay the start of 

detonations until the mitigation zone is 

clear. Navy personnel also must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must relocate 

or delay the start of detonations. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease 

detonations. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

detonations) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended 

detonation location; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 30 min; or 

(4) Detonation location transit. The 

intended detonation location has 

transited a distance equal to double that 

of the mitigation zone size beyond the 

location of the last sighting. 

(D) After activity. After completion of 

the activity (e.g., prior to maneuvering 

off station), Navy personnel must, when 

practical (e.g., when platforms are not 

constrained by fuel restrictions or 

mission-essential follow-on 

commitments), observe for marine 

mammals in the vicinity of where 

detonations occurred; if any injured or 

dead marine mammals are observed, 

Navy personnel must follow established 

incident reporting procedures. If 

additional platforms are supporting this 

activity (e.g., providing range clearance), 

these Navy assets will assist in the 

visual observation of the area where 

detonations occurred. 

(15) Underwater demolition multiple 

charge—mat weave and obstacle 

loading exercises—(i) Number of 

Lookouts and observation platform. 

Two Lookouts (one must be positioned 

on a small boat and one must be 

positioned on shore from an elevated 

platform). If additional platforms are 

participating in the activity, Navy 

personnel positioned in those assets 

(e.g., safety observers, evaluators) must 

support observing the mitigation zone 

for applicable biological resources while 

performing their regular duties. 

(ii) Mitigation zone and requirements. 

700 yd (640.1 m) around the intended 

detonation location. 

(A) Prior to activity. Prior to the initial 

start of the activity, or 30 min prior to 

the first detonation, the Lookout 

positioned on a small boat must observe 

the mitigation zone for floating 

vegetation and marine mammals; if 

floating vegetation or marine mammals 

are observed, Navy personnel must 

delay the start of detonations until the 

mitigation zone is clear. For 10 min 

prior to the first detonation, the Lookout 

positioned on shore must use binoculars 

to observe the mitigation zone for 

marine mammals; if marine mammals 

are observed, Navy personnel must 

delay the start of detonations. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease 

detonations. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

detonations) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the detonation 

location; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min (as 

determined by the Navy shore observer). 

(D) After activity. After completion of 

the activity (for 30 min), the Lookout 

positioned on a small boat must observe 

for marine mammals in the vicinity of 

where detonations occurred; if any 

injured or dead marine mammals are 

observed, Navy personnel must follow 

established incident reporting 

procedures. If additional platforms are 

supporting this activity (e.g., providing 

range clearance), these Navy assets must 

assist in the visual observation of the 

area where detonations occurred. 

(16) Vessel movement. The mitigation 

will not be applied if: the vessel’s safety 

is threatened; the vessel is restricted in 

its ability to maneuver (e.g., during 

launching and recovery of aircraft or 

landing craft, during towing activities, 

when mooring); the vessel is operated 

autonomously; or when impracticable 

based on mission requirements (e.g., 

during Amphibious Assault—Battalion 

Landing exercise). 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be on the vessel that is underway. 

(ii) Mitigation zone and 

requirements—(A) Whales. 500 yd 

(457.2 m) around whales. 

(B) Marine mammals other than 

whales. 200 yd (182.9 m) around all 

other marine mammals (except bowriding dolphins and pinnipeds hauled 

out on man-made navigational 

structures, port structures, and vessels). 

(iii) During the activity. When 

underway, Navy personnel must 

observe the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must 

maneuver (which may include reducing 

speed as the mission or circumstances 

allow) to maintain distance. 

(iv) Incident reporting procedures. If a 

marine mammal vessel strike occurs, 

Navy personnel must follow the 

established incident reporting 

procedures. 

(v) Post-strike alerts. Navy personnel 

must send alerts to Navy vessels of 

increased risk of strike following any 

reported Navy vessel strike in the HSTT 

Study Area. 

(vi) Large whale aggregation alerts. 

Navy personnel must issue real-time 

notifications to Navy vessels of large 

whale aggregations (four or more 

whales) within 1 nmi (1.9 km) of a Navy 

vessel in the area between 32–33 

degrees North and 117.2–119.5 degrees 

West. 

(17) Towed in-water devices. 

Mitigation applies to devices that are 

towed from a manned surface platform 

or manned aircraft. The mitigation will 

not be applied if the safety of the towing 

platform or in-water device is 

threatened. 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned on a manned towing 

platform. 

(ii) Mitigation zone and requirements. 

250 yd (228.6 m) around marine 

mammals. 

(iii) During the activity. During the 

activity (i.e., when towing an in-water 

device), Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must 

maneuver to maintain distance. 

(18) Small-, medium-, and largecaliber non-explosive practice 

munitions. Mitigation applies to 

activities using a surface target. 

(i) Number of Lookouts and 

observation platform. One Lookout must 


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be positioned on the platform 

conducting the activity. Depending on 

the activity, the Lookout could be the 

same as the one described for ‘‘Weapons 

firing noise’’ in paragraph (a)(5)(i) of 

this section. 

(ii) Mitigation zone and requirements. 

200 yd (182.9 m) around the intended 

impact location. 

(A) Prior to activity. Prior to the start 

of the activity (e.g., when maneuvering 

on station), Navy personnel must 

observe the mitigation zone for floating 

vegetation; if floating vegetation is 

observed, Navy personnel must relocate 

or delay the start of firing until the 

mitigation zone is clear. Navy personnel 

also must observe the mitigation zone 

for marine mammals; if marine 

mammals are observed, Navy personnel 

must relocate or delay the start of firing. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease 

firing. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting before or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

firing) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended 

impact location; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min for 

aircraft-based firing or 30 min for vesselbased firing; or 

(4) Impact location transit. For 

activities using a mobile target, the 

intended impact location has transited a 

distance equal to double that of the 

mitigation zone size beyond the location 

of the last sighting. 

(19) Non-explosive missiles and 

rockets. Aircraft-deployed nonexplosive missiles and rockets. 

Mitigation applies to activities using a 

surface target. 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned in an aircraft. 

(ii) Mitigation zone and requirements. 

900 yd around the intended impact 

location. 

(A) Prior to activity. Prior to the initial 

start of the activity (e.g., during a flyover of the mitigation zone), Navy 

personnel must observe the mitigation 

zone for floating vegetation; if floating 

vegetation is observed, Navy personnel 

must relocate or delay the start of firing 

until the mitigation zone is clear. Navy 

personnel also must observe the 

mitigation zone for marine mammals; if 

marine mammals are observed, Navy 

personnel must relocate or delay the 

start of firing. 

(B) During activity. During the 

activity, Navy personnel must observe 

the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must cease 

firing. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting prior to or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing 

firing) until one of the following 

conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended 

impact location; or 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min 

when the activity involves aircraft that 

have fuel constraints, or 30 min when 

the activity involves aircraft that are not 

typically fuel constrained. 

(20) Non-explosive bombs and mine 

shapes. Non-explosive bombs and nonexplosive mine shapes during mine 

laying activities. 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned in an aircraft. 

(ii) Mitigation zone and requirements. 

1,000 yd (914.4 m) around the intended 

target. 

(A) Prior to activity. Prior to the initial 

start of the activity (e.g., when arriving 

on station), Navy personnel must 

observe the mitigation zone for floating 

vegetation; if floating vegetation is 

observed, Navy personnel must relocate 

or delay the start of bomb deployment 

or mine laying until the mitigation zone 

is clear. Navy personnel also must 

observe the mitigation zone for marine 

mammals; if marine mammals are 

observed, Navy personnel must relocate 

or delay the start of bomb deployment 

or mine laying. 

(B) During activity. During the activity 

(e.g., during approach of the target or 

intended minefield location), Navy 

personnel must observe the mitigation 

zone for marine mammals and, if marine 

mammals are observed, Navy personnel 

must cease bomb deployment or mine 

laying. 

(C) Commencement/recommencement 

conditions after a marine mammal 

sighting prior to or during the activity. 

Navy personnel must allow a sighted 

marine mammal to leave the mitigation 

zone prior to the initial start of the 

activity (by delaying the start) or during 

the activity (by not recommencing bomb 

deployment or mine laying) until one of 

the following conditions has been met: 

(1) Observed exiting. The animal is 

observed exiting the mitigation zone; 

(2) Thought to have exited. The 

animal is thought to have exited the 

mitigation zone based on a 

determination of its course, speed, and 

movement relative to the intended target 

or minefield location; 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 10 min; or 

(4) Target transit. For activities using 

mobile targets, the intended target has 

transited a distance equal to double that 

of the mitigation zone size beyond the 

location of the last sighting. 

(b) Mitigation areas. In addition to 

procedural mitigation, Navy personnel 

must implement mitigation measures 

within mitigation areas to avoid or 

reduce potential impacts on marine 

mammals. 

(1) Mitigation areas for marine 

mammals in the Hawaii Range Complex 

for sonar, explosives, and vessel 

strikes—(i) Mitigation area 

requirements—(A) Hawaii Island 

Mitigation Area (year-round)—(1) MF1 

surface ship hull-mounted midfrequency active sonar, MF4 dipping 

sonar, or explosives. Except as provided 

in paragraph (b)(1)(i)(A)(2) of this 

section, Navy personnel must not 

conduct more than 300 hours of MF1 

surface ship hull-mounted midfrequency active sonar or 20 hours of 

MF4 dipping sonar annually, or use 

explosives that could potentially result 

in takes of marine mammals during 

training and testing. 

(2) National security exception. 

Should national security require 

conduct of more than 300 hours of MF1 

surface ship hull-mounted midfrequency active sonar or 20 hours of 

MF4 dipping sonar, or use of explosives 

that could potentially result in the take 

of marine mammals during training or 

testing, Naval units must obtain 

permission from the appropriate 

designated Command authority prior to 

commencement of the activity. Navy 

personnel must provide NMFS with 

advance notification and include the 


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information (e.g., sonar hours or 

explosives usage) in its annual activity 

reports submitted to NMFS. 

(B) 4-Islands Region Mitigation Area 

(November 15–April 15 for active sonar; 

year-round for explosives)—(1) MF1 

surface ship hull-mounted midfrequency active sonar or explosives. 

Except as provided in paragraph 

(b)(1)(i)(B)(2) of this section, Navy 

personnel must not use MF1 surface 

ship hull-mounted mid-frequency active 

sonar or explosives that could 

potentially result in takes of marine 

mammals during training and testing. 

(2) National security exception. 

Should national security require use of 

MF1 surface ship hull-mounted midfrequency active sonar or explosives 

that could potentially result in the take 

of marine mammals during training or 

testing, Naval units must obtain 

permission from the appropriate 

designated Command authority prior to 

commencement of the activity. Navy 

personnel must provide NMFS with 

advance notification and include the 

information (e.g., sonar hours or 

explosives usage) in its annual activity 

reports submitted to NMFS. 

(C) Humpback Whale Special 

Reporting Areas (December 15–April 

15). Navy personnel must report the 

total hours of surface ship hull-mounted 

mid-frequency active sonar used in the 

special reporting areas in its annual 

training and testing activity reports 

submitted to NMFS. 

(D) Humpback Whale Awareness 

Notification Message Area (November– 

April)—(1) Seasonal awareness 

notification message. Navy personnel 

must issue a seasonal awareness 

notification message to alert ships and 

aircraft operating in the area to the 

possible presence of concentrations of 

large whales, including humpback 

whales. 

(2) Vessel instruction. To maintain 

safety of navigation and to avoid 

interactions with large whales during 

transits, Navy personnel must instruct 

vessels to remain vigilant to the 

presence of large whale species 

(including humpback whales). 

(3) Awareness notification message 

use. Platforms must use the information 

from the awareness notification message 

to assist their visual observation of 

applicable mitigation zones during 

training and testing activities and to aid 

in the implementation of procedural 

mitigation. 

(ii) [Reserved] 

(2) Mitigation areas for marine 

mammals in the southern California 

portion of the study area for sonar, 

explosives, and vessel strikes—(i) 

Mitigation area requirements—(A) San 

Diego Arc, San Nicolas Island, and 

Santa Monica/Long Beach Mitigation 

Areas (June 1–October 31)—(1) MF1 

surface ship hull-mounted midfrequency active sonar. Except as 

provided in paragraph (b)(2)(i)(A)(2) of 

this section, Navy personnel must not 

conduct more than a total of 200 hours 

of MF1 surface ship hull-mounted midfrequency active sonar in the combined 

areas, excluding normal maintenance 

and systems checks, during training and 

testing. 

(2) National security exception. 

Should national security require 

conduct of more than 200 hours of MF1 

surface ship hull-mounted midfrequency active sonar in the combined 

areas during training and testing 

(excluding normal maintenance and 

systems checks), Naval units must 

obtain permission from the appropriate 

designated Command authority prior to 

commencement of the activity. Navy 

personnel must provide NMFS with 

advance notification and include the 

information (e.g., sonar hours) in its 

annual activity reports submitted to 

NMFS. 

(3) Explosives in San Diego Arc 

Mitigation Area. Except as provided in 

paragraph (b)(2)(i)(A)(4) of this section, 

within the San Diego Arc Mitigation 

Area, Navy personnel must not use 

explosives that could potentially result 

in the take of marine mammals during 

large-caliber gunnery, torpedo, bombing, 

and missile (including 2.75-inch 

rockets) activities during training and 

testing. 

(4) National security exception. 

Should national security require use of 

explosives that could potentially result 

in the take of marine mammals during 

large-caliber gunnery, torpedo, bombing, 

and missile (including 2.75-inch 

rockets) activities during training or 

testing within the San Diego Arc 

Mitigation Area, Naval units must 

obtain permission from the appropriate 

designated Command authority prior to 

commencement of the activity. Navy 

personnel must provide NMFS with 

advance notification and include the 

information (e.g., explosives usage) in 

its annual activity reports submitted to 

NMFS. 

(5) Explosives in San Nicolas Island 

Mitigation Area. Except as provided in 

paragraph (b)(2)(i)(A)(6) of this section, 

within the San Nicolas Island Mitigation 

Area, Navy personnel must not use 

explosives that could potentially result 

in the take of marine mammals during 

mine warfare, large-caliber gunnery, 

torpedo, bombing, and missile 

(including 2.75-inch rockets) activities 

during training. 

(6) National security exception. 

Should national security require use of 

explosives that could potentially result 

in the take of marine mammals during 

mine warfare, large-caliber gunnery, 

torpedo, bombing, and missile 

(including 2.75-inch rockets) activities 

during training in the San Nicolas 

Island Mitigation Area, Naval units 

must obtain permission from the 

appropriate designated Command 

authority prior to commencement of the 

activity. Navy personnel must provide 

NMFS with advance notification and 

include the information (e.g., explosives 

usage) in its annual activity reports 

submitted to NMFS. 

(7) Explosives in the Santa Monica/ 

Long Beach Mitigation Area. Except as 

provided in paragraph (b)(2)(i)(A)(8) of 

this section, within the Santa Monica/ 

Long Beach Mitigation Area, Navy 

personnel must not use explosives that 

could potentially result in the take of 

marine mammals during mine warfare, 

large-caliber gunnery, torpedo, bombing, 

and missile (including 2.75-inch 

rockets) activities during training and 

testing. 

(8) National security exception. 

Should national security require use of 

explosives that could potentially result 

in the take of marine mammals during 

mine warfare, large-caliber gunnery, 

torpedo, bombing, and missile 

(including 2.75-inch rockets) activities 

during training or testing in the Santa 

Monica/Long Beach Mitigation Area, 

Naval units must obtain permission 

from the appropriate designated 

Command authority prior to 

commencement of the activity. Navy 

personnel must provide NMFS with 

advance notification and include the 

information (e.g., explosives usage) in 

its annual activity reports submitted to 

NMFS. 

(B) Santa Barbara Island Mitigation 

Area (year-round)—(1) MF1 surface ship 

hull-mounted mid-frequency active 

sonar or explosives. Except as provided 

in paragraph (b)(2)(i)(B)(2) of this 

section, Navy personnel must not use 

MF1 surface ship hull-mounted midfrequency active sonar during training 

or testing, or explosives that could 

potentially result in the take of marine 

mammals during medium-caliber or 

large-caliber gunnery, torpedo, bombing, 

and missile (including 2.75-inch 

rockets) activities during training. 

(2) National security exception. 

Should national security require use of 

MF1 surface ship hull-mounted midfrequency active sonar during training 

or testing, or explosives that could 

potentially result in the take of marine 

mammals during medium-caliber or 

large-caliber gunnery, torpedo, bombing, 


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and missile (including 2.75-inch 

rockets) activities during training, Naval 

units must obtain permission from the 

appropriate designated Command 

authority prior to commencement of the 

activity. Navy personnel must provide 

NMFS with advance notification and 

include the information (e.g., sonar 

hours or explosives usage) in its annual 

activity reports submitted to NMFS. 

(C) Spring Large Whale Awareness 

Notification Message—(1) Awareness 

notification message. Navy personnel 

must issue an awareness notification 

message to alert ships and aircraft 

operating in the area to the possible 

presence of concentrations of large 

whales, including blue whales, fin 

whales, and humpback whales. 

(2) Applicable period. This message 

must apply to a period that is based on 

predicted oceanographic conditions for 

a given year. 

(3) Marine mammals and vessel 

transit. To maintain safety of navigation 

and to avoid interactions with large 

whales during transits, Navy personnel 

must emphasize to vessels that when a 

marine mammal is spotted, this may be 

an indicator that additional marine 

mammals are present nearby, and 

increased vigilance and awareness of 

Navy personnel is warranted. 

(4) Platform use of message. Platforms 

must use the information from the 

awareness notification messages to 

assist their visual observation of 

applicable mitigation zones during 

training and testing activities and to aid 

in the implementation of procedural 

mitigation. 

(D) Gray Whale (November–March) 

and Fin Whale (November–May) 

Awareness Notification Message 

Areas—(1) Seasonal awareness 

message. Navy personnel must issue a 

seasonal awareness notification message 

to alert ships and aircraft operating in 

the area to the possible presence of 

concentrations of large whales, 

including gray whales, and fin whales. 

(2) Marine mammals and vessel 

transit. To maintain safety of navigation 

and to avoid interactions with large 

whales during transits, Navy personnel 

must instruct vessels to remain vigilant 

to the presence of large whale species. 

(3) Platform use of message. Platforms 

must use the information from the 

awareness notification messages to 

assist their visual observation of 

applicable mitigation zones during 

training and testing activities and to aid 

in the implementation of procedural 

mitigation. 

(ii) [Reserved] 

§ 218.75 Requirements for monitoring and 

reporting. 

(a) Unauthorized take. Navy 

personnel must notify NMFS 

immediately (or as soon as operational 

security considerations allow) if the 

specified activity identified in § 218.70 

is thought to have resulted in the 

mortality or serious injury of any marine 

mammals, or in any Level A harassment 

or Level B harassment take of marine 

mammals not identified in this subpart. 

(b) Monitoring and reporting under 

the LOAs. The Navy must conduct all 

monitoring and reporting required 

under the LOAs, including abiding by 

the HSTT Study Area monitoring 

program. Details on program goals, 

objectives, project selection process, and 

current projects are available at 

www.navymarinespeciesmonitoring.us. 

(c) Notification of injured, live 

stranded, or dead marine mammals. 

The Navy must consult the Notification 

and Reporting Plan, which sets out 

notification, reporting, and other 

requirements when dead, injured, or 

live stranded marine mammals are 

detected. The Notification and 

Reporting Plan is available at https://

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/incidentaltake-authorizations-military-readinessactivities. 

(d) Changes in Lookout Policies. The 

Navy must report changes in its Lookout 

policies to NMFS as soon as practicable 

after a change is made. 

(e) Annual HSTT Study Area marine 

species monitoring report. The Navy 

must submit an annual report of the 

HSTT Study Area monitoring describing 

the implementation and results from the 

previous calendar year. Data collection 

methods must be standardized across 

range complexes and study areas to 

allow for comparison in different 

geographic locations. The report must 

be submitted to the Director, Office of 

Protected Resources, NMFS, either 

within 3 months after the end of the 

calendar year, or within 3 months after 

the conclusion of the monitoring year, 

to be determined by the Adaptive 

Management process. This report will 

describe progress of knowledge made 

with respect to intermediate scientific 

objectives within the HSTT Study Area 

associated with the Integrated 

Comprehensive Monitoring Program 

(ICMP). Similar study questions must be 

treated together so that progress on each 

topic can be summarized across all 

Navy ranges. The report need not 

include analyses and content that does 

not provide direct assessment of 

cumulative progress on the monitoring 

plan study questions. As an alternative, 

the Navy may submit a multi-Range 

Complex annual Monitoring Plan report 

to fulfill this requirement. Such a report 

will describe progress of knowledge 

made with respect to monitoring study 

questions across multiple Navy ranges 

associated with the ICMP. Similar study 

questions must be treated together so 

that progress on each topic can be 

summarized across multiple Navy 

ranges. The report need not include 

analyses and content that does not 

provide direct assessment of cumulative 

progress on the monitoring study 

question. This will continue to allow 

the Navy to provide a cohesive 

monitoring report covering multiple 

ranges (as per ICMP goals), rather than 

entirely separate reports for the HSTT, 

Gulf of Alaska, Mariana Islands, and 

Northwest Study Areas. 

(f) Annual HSTT Study Area training 

exercise report and testing activity 

report. Each year, the Navy must submit 

two preliminary reports (Quick Look 

Report) detailing the status of 

authorized sound sources within 21 

days after the anniversary of the date of 

issuance of each LOA to the Director, 

Office of Protected Resources, NMFS. 

Each year, the Navy must submit 

detailed reports to the Director, Office of 

Protected Resources, NMFS, within 3 

months after the 1-year anniversary of 

the date of issuance of the LOA. The 

HSTT annual Training Exercise Report 

and Testing Activity Report can be 

consolidated with other exercise reports 

from other range complexes in the 

Pacific Ocean for a single Pacific 

Exercise Report, if desired. The annual 

reports must contain information on 

major training exercises (MTEs), Sinking 

Exercise (SINKEX) events, and a 

summary of all sound sources used, 

including within specific mitigation 

reporting areas, as described in 

paragraph (e)(3) through (5) of this 

section. The analysis in the detailed 

reports must be based on the 

accumulation of data from the current 

year’s report and data collected from 

previous reports. The detailed reports 

must contain information identified in 

paragraphs (e)(1) through (7) of this 

section. 

(1) MTEs. This section of the report 

must contain the following information 

for MTEs conducted in the HSTT Study 

Area. 

(i) Exercise information (for each 

MTE). 

(A) Exercise designator. 

(B) Date that exercise began and 

ended. 

(C) Location. 

(D) Number and types of active sonar 

sources used in the exercise. 

(E) Number and types of passive 

acoustic sources used in exercise. 


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68366 Federal Register / Vol. 88, No. 190 / Tuesday, October 3, 2023 / Proposed Rules 

(F) Number and types of vessels, 

aircraft, and other platforms 

participating in exercise. 

(G) Total hours of all active sonar 

source operation. 

(H) Total hours of each active sonar 

source bin. 

(I) Wave height (high, low, and 

average) during exercise. 

(ii) Individual marine mammal 

sighting information for each sighting in 

each exercise where mitigation was 

implemented: 

(A) Date, time, and location of 

sighting. 

(B) Species (if not possible, indication 

of whale/dolphin/pinniped). 

(C) Number of individuals. 

(D) Initial Detection Sensor (e.g., 

sonar, Lookout). 

(E) Indication of specific type of 

platform observation was made from 

(including, for example, what type of 

surface vessel or testing platform). 

(F) Length of time observers 

maintained visual contact with marine 

mammal. 

(G) Sea state. 

(H) Visibility. 

(I) Sound source in use at the time of 

sighting. 

(J) Indication of whether animal was 

less than 200 yd (182.9 m), 200 to 500 

yd (182.9 to 457.2 m), 500 to 1,000 yd 

(457.2 m to 914.4 m), 1,000 to 2,000 yd 

(914.4 m to 1,828.8 m), or greater than 

2,000 yd (1,828.8 m) from sonar source. 

(K) Whether operation of sonar sensor 

was delayed, or sonar was powered or 

shut down, and how long the delay. 

(L) If source in use was hull-mounted, 

true bearing of animal from the vessel, 

true direction of vessel’s travel, and 

estimation of animal’s motion relative to 

vessel (opening, closing, parallel). 

(M) Lookouts must report, in plain 

language and without trying to 

categorize in any way, the observed 

behavior of the animal(s) (such as 

animal closing to bow ride, paralleling 

course/speed, floating on surface and 

not swimming, etc.) and if any calves 

were present. 

(iii) An evaluation (based on data 

gathered during all of the MTEs) of the 

effectiveness of mitigation measures 

designed to minimize the received level 

to which marine mammals may be 

exposed. This evaluation must identify 

the specific observations that support 

any conclusions the Navy reaches about 

the effectiveness of the mitigation. 

(2) SINKEXs. This section of the 

report must include the following 

information for each SINKEX completed 

that year. 

(i) Exercise information (gathered for 

each SINKEX). 

(A) Location. 

(B) Date and time exercise began and 

ended. 

(C) Total hours of observation by 

Lookouts before, during, and after 

exercise. 

(D) Total number and types of 

explosive source bins detonated. 

(E) Number and types of passive 

acoustic sources used in exercise. 

(F) Total hours of passive acoustic 

search time. 

(G) Number and types of vessels, 

aircraft, and other platforms 

participating in exercise. 

(H) Wave height in feet (high, low, 

and average) during exercise. 

(I) Narrative description of sensors 

and platforms utilized for marine 

mammal detection and timeline 

illustrating how marine mammal 

detection was conducted. 

(ii) Individual marine mammal 

observation (by Navy Lookouts) 

information for each sighting where 

mitigation was implemented. 

(A) Date/Time/Location of sighting. 

(B) Species (if not possible, indicate 

whale, dolphin, or pinniped). 

(C) Number of individuals. 

(D) Initial detection sensor (e.g., sonar 

or Lookout). 

(E) Length of time observers 

maintained visual contact with marine 

mammal. 

(F) Sea state. 

(G) Visibility. 

(H) Whether sighting was before, 

during, or after detonations/exercise, 

and how many minutes before or after. 

(I) Distance of marine mammal from 

actual detonations (or target spot if not 

yet detonated): Less than 200 yd (182.9 

m), 200 to 500 yd (182.9 to 457.2 m), 

500 to 1,000 yd (457.2 m to 914.4 m), 

1,000 to 2,000 yd (914.4 m to 1,828.8 

m), or greater than 2,000 yd (1,828.8 m). 

(J) Lookouts must report, in plain 

language and without trying to 

categorize in any way, the observed 

behavior of the animal(s) (such as 

animal closing to bow ride, paralleling 

course/speed, floating on surface and 

not swimming etc.), including speed 

and direction and if any calves were 

present. 

(K) The report must indicate whether 

explosive detonations were delayed, 

ceased, modified, or not modified due to 

marine mammal presence and for how 

long. 

(L) If observation occurred while 

explosives were detonating in the water, 

indicate munition type in use at time of 

marine mammal detection. 

(3) Summary of sources used. This 

section of the report must include the 

following information summarized from 

the authorized sound sources used in all 

training and testing events: 

(i) Total annual hours or quantity (per 

the LOA) of each bin of sonar or other 

acoustic sources (e.g., pile driving and 

air gun activities); and 

(ii) Total annual expended/detonated 

ordinance (missiles, bombs, sonobuoys, 

etc.) for each explosive bin. 

(4) Humpback Whale Special 

Reporting Area (December 15–April 15). 

The Navy must report the total hours of 

operation of surface ship hull-mounted 

mid-frequency active sonar used in the 

special reporting area. 

(5) HSTT Study Area Mitigation 

Areas. The Navy must report any use 

that occurred as specifically described 

in these areas. Information included in 

the classified annual reports may be 

used to inform future adaptive 

management of activities within the 

HSTT Study Area. 

(6) Geographic information 

presentation. The reports must present 

an annual (and seasonal, where 

practical) depiction of training and 

testing bin usage (as well as pile driving 

activities) geographically across the 

HSTT Study Area. 

(7) Sonar exercise notification. The 

Navy must submit to NMFS (contact as 

specified in the LOA) an electronic 

report within 15 calendar days after the 

completion of any MTE indicating: 

(i) Location of the exercise; 

(ii) Beginning and end dates of the 

exercise; and 

(iii) Type of exercise. 

(g) Seven-year close-out 

comprehensive training and testing 

activity report. This report must be 

included as part of the 2025 annual 

training and testing report. This report 

must provide the annual totals for each 

sound source bin with a comparison to 

the annual allowance and the 7-year 

total for each sound source bin with a 

comparison to the 7-year allowance. 

Additionally, if there were any changes 

to the sound source allowance, this 

report must include a discussion of why 

the change was made and include the 

analysis to support how the change did 

or did not result in a change in the 2018 

HSTT FEIS/OEIS and final rule 

determinations. The draft report must be 

submitted within 3 months after the 

expiration of this subpart to the 

Director, Office of Protected Resources, 

NMFS. NMFS must submit comments 

on the draft close-out report, if any, 

within 3 months of receipt. The report 

will be considered final after the Navy 

has addressed NMFS’ comments, or 3 

months after the submittal of the draft 

if NMFS does not provide comments. 

§ 218.76 Letters of Authorization. 

(a) To incidentally take marine 

mammals pursuant to the regulations in 


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Federal Register / Vol. 88, No. 190 / Tuesday, October 3, 2023 / Proposed Rules 68367 

this subpart, the Navy must apply for 

and obtain LOAs in accordance with 

§ 216.106 of this chapter. 

(b) LOAs, unless suspended or 

revoked, may be effective for a period of 

time not to exceed December 20, 2025. 

(c) If an LOA expires prior to 

December 20, 2025, the Navy may apply 

for and obtain a renewal of the LOA. 

(d) In the event of projected changes 

to the activity or to mitigation, 

monitoring, or reporting (excluding 

changes made pursuant to the adaptive 

management provision of § 218.77(c)(1)) 

required by an LOA issued under this 

subpart, the Navy must apply for and 

obtain a modification of the LOA as 

described in § 218.77. 

(e) Each LOA must set forth: 

(1) Permissible methods of incidental 

taking; 

(2) Geographic areas for incidental 

taking; 

(3) Means of effecting the least 

practicable adverse impact (i.e., 

mitigation) on the species or stocks of 

marine mammals and their habitat; and 

(4) Requirements for monitoring and 

reporting. 

(f) Issuance of the LOA(s) must be 

based on a determination that the level 

of taking is consistent with the findings 

made for the total taking allowable 

under the regulations in this subpart. 

(g) Notice of issuance or denial of the 

LOA(s) must be published in the 

Federal Register within 30 days of a 

determination. 

§ 218.77 Renewals and modifications of 

Letters of Authorization. 

(a) An LOA issued under §§ 216.106 

of this chapter and 218.76 for the 

activity identified in § 218.70(c) may be 

renewed or modified upon request by 

the applicant, provided that: 

(1) The planned specified activity and 

mitigation, monitoring, and reporting 

measures, as well as the anticipated 

impacts, are the same as those described 

and analyzed for the regulations in this 

subpart (excluding changes made 

pursuant to the adaptive management 

provision in paragraph (c)(1) of this 

section); and 

(2) NMFS determines that the 

mitigation, monitoring, and reporting 

measures required by the previous 

LOA(s) were implemented. 

(b) For LOA modification or renewal 

requests by the applicant that include 

changes to the activity or to the 

mitigation, monitoring, or reporting 

measures (excluding changes made 

pursuant to the adaptive management 

provision in paragraph (c)(1) of this 

section) that do not change the findings 

made for the regulations or result in no 

more than a minor change in the total 

estimated number of takes (or 

distribution by species or stock or 

years), NMFS may publish a notice of 

planned LOA in the Federal Register, 

including the associated analysis of the 

change, and solicit public comment 

before issuing the LOA. 

(c) An LOA issued under §§ 216.106 

of this chapter and 218.76 may be 

modified by NMFS under the following 

circumstances: 

(1) Adaptive management. After 

consulting with the Navy regarding the 

practicability of the modifications, 

NMFS may modify (including adding or 

removing measures) the existing 

mitigation, monitoring, or reporting 

measures if doing so creates a 

reasonable likelihood of more 

effectively accomplishing the goals of 

the mitigation and monitoring. 

(i) Possible sources of data that could 

contribute to the decision to modify the 

mitigation, monitoring, or reporting 

measures in an LOA include: 

(A) Results from the Navy’s 

monitoring from the previous year(s); 

(B) Results from other marine 

mammal and/or sound research or 

studies; or 

(C) Any information that reveals 

marine mammals may have been taken 

in a manner, extent, or number not 

authorized by the regulations in this 

subpart or subsequent LOAs. 

(ii) If, through adaptive management, 

the modifications to the mitigation, 

monitoring, or reporting measures are 

substantial, NMFS will publish a notice 

of planned LOA in the Federal Register 

and solicit public comment. 

(2) Emergencies. If NMFS determines 

that an emergency exists that poses a 

significant risk to the well-being of the 

species or stocks of marine mammals 

specified in LOAs issued pursuant to 

§§ 216.106 of this chapter and 218.76, 

an LOA may be modified without prior 

notice or opportunity for public 

comment. Notice would be published in 

the Federal Register within 30 days of 

the action. 

§§ 218.78–218.79 [Reserved] 

[FR Doc. 2023–21499 Filed 10–2–23; 8:45 am] 

BILLING CODE 3510–22–P 


ddrumheller on DSK120RN23PROD with PROPOSALS2