4944 Federal Register / Vol. 90, No. 10 / Thursday, January 16, 2025 / Proposed Rules 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric 

Administration 

50 CFR Part 218 

[Docket No. 241220–0334] 

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: Final rule; notification of 

issuance of Letters of Authorization. 

SUMMARY: NMFS, upon request from the 

U.S. Navy (Navy), issues these 

regulations pursuant to the Marine 

Mammal Protection Act (MMPA) to 

govern the taking of marine mammals 

incidental to the training and testing 

activities conducted in the HawaiiSouthern 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 

Letters of Authorization (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 based on 

new information, including the three 

strikes, and authorizes 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). 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: Effective from January 16, 2025 

to December 20, 2025. 

ADDRESSES: Copies of the Navy’s 

applications, NMFS’ proposed and final 

rules and subsequent LOAs for these 

regulations, NMFS’ proposed and final 

rules and subsequent LOAs for the 

associated 5-year HSTT Study Area 

regulations, other supporting documents 

cited herein, and a list of the references 

cited in this document may be obtained 

online at: https://www.fisheries.

noaa.gov/national/marine-mammalprotection/incidental-takeauthorizations-military-readinessactivities. 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 regulations, promulgated under 

the authority of the MMPA (16 U.S.C. 

1361 et seq.), modify previous 

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 2020 HSTT 

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 2020 HSTT 

regulations and LOAs authorized 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 authorizes 

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 planned 

activities remain unchanged; however, 

this final rule includes two additional 

mitigation measures and revision of two 

existing mitigation measures to further 

reduce the probability of vessel strike, 

as well as two additional reporting 

measures (described below in the 

Changes from the Proposed Rule to the 

Final Rule section) from that included 

in the 2020 HSTT regulations. With the 

exception of these new mitigation 

measures and revisions to two existing 

mitigation measures, the required 

mitigation and monitoring measures 

remain unchanged from the 2020 HSTT 

regulations. 

Section 101(a)(5)(A) of the MMPA (16 

U.S.C. 1371(a)(5)(A)) directs 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, after notice and public comment, the 

agency makes certain findings and 

issues regulations that set forth 

permissible methods of taking pursuant 

to that activity, as well as monitoring 

and reporting requirements. Section 

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

implementing regulations at 50 CFR part 

216, subpart I, provide the legal basis for 

issuing this final rule and the 

subsequent LOAs. As directed by this 

legal authority, this final rule contains 

mitigation, monitoring, and reporting 

requirements. 

Summary of Major Provisions Within 

the Final Rule 

The following is a summary of the 

major provisions of this final rule 

regarding the Navy’s activities. Major 

provisions include, but are not limited 

to: 

• The use of defined powerdown and 

shutdown zones (based on activity); 

• Measures to reduce or eliminate the 

likelihood of ship strikes; 

• Activity limitations in certain areas 

and times that are biologically 

important (i.e., for foraging, migration, 

reproduction) for marine mammals; 

• Implementation of a Notification 

and Reporting Plan (for dead, live 

stranded, or marine mammals struck by 

a vessel); and 

• Implementation of a robust 

monitoring plan to improve our 

understanding of the environmental 

effects resulting from the Navy training 

and testing activities. 

Additionally, the rule includes an 

adaptive management component that 

allows for timely modification of 

mitigation or monitoring measures 

based on new information, when 

appropriate. 

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 


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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. 

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 

similar significance, and on the 

availability of such species or stocks for 

taking for certain subsistence uses 

(referred to in this rulemaking as 

‘‘mitigation’’); 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 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 final rule (83 FR 

66846, December 27, 2018) 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 (85 FR 41780) 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 proposed no changes to the nature 

of the specified activities covered by the 

2020 HSTT final rule. The Navy stated 

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 


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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 rule cover training and testing 

activities that would occur over the 

remainder of the effective period of the 

current regulations, valid from the 

publication date of this final rule 

through December 20, 2025. 

Summary of the Regulations 

NMFS is modifying 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 2020 HSTT 

regulations). In its 2022 application, the 

Navy proposed no additional changes 

and explained that its training and 

testing activities, including the level of 

vessel use, remain unchanged. Nearly 

all mitigation, monitoring, and reporting 

measures remain unchanged from the 

2020 HSTT regulations (85 FR 41780, 

July 10, 2020) with the exception of two 

additional mitigation measures (see the 

Mitigation Measures section of this final 

rule), revision of two existing mitigation 

measures (see the Mitigation Measures 

section of this final rule), and two 

additional reporting measures resulting 

from discussions between the Navy and 

NMFS (see the Reporting section of this 

final rule). 

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 authorize 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 

authorize these additional takes after 

analyzing the best available scientific 

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 require new and modified mitigation 

and also consider whether to require 

any new or modified mitigation for the 

entire specified activity. 

The regulatory language included at 

the end of this final rule, which is 

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 two new reporting 

measures. Therefore, in this final 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 final rule. 

The list indicates the short name by 

which the document is referenced in 

this final rule as well as the full titles 

of the cited documents. All of the 

documents can be found at: https://

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); 

• NMFS October 3, 2023, HawaiiSouthern California Training and 

Testing (HSTT) proposed rule (88 FR 

68290; 2023 HSTT proposed 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 requested 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 proposed 

no changes to the specified activities 


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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 final 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 final 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 

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 meters (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 when vessels would be dead 

in the water or moving slowly ahead to 

maintain steerage, such as launch and 

recovery of a small rigid hull inflatable 

boat; vessel boarding, search, and 

seizure training events; or retrieval of a 

target. 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 proposed 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 feet (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 knots (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 


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(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 

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 surface 

vessel 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). In 2023 (another non-RIMPAC 

year), there was no foreign vessel 

participation within SOCAL. Even in a 

RIMPAC year, the days at sea for foreign 

militaries engaged in a Navy-led 

training or testing activity accounts for 

a small, but variable, 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). During RIMPAC 2024, 

twenty-five foreign surface vessels 

participated for a combined 5,000 hours 

in U.S.-led training events. Therefore, 

foreign surface vessel activity is 

estimated to conservatively account for 

up to 10 percent of the U.S. Navy’s 

annual at sea time in HSTT (205 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 nautical miles (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. 

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. 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 Stock Assessment Reports (SARs). 

Second, NMFS considers foreign 

military activities, including recent 

strikes, qualitatively in this final 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 

2021 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. 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 

authorized take, as part of the negligible 

impact analysis. 

This final rule includes a new 

reporting measure that requires that the 

Navy’s annual HSTT reports shall 

include confirmation that foreign 

military use of sonar and explosives, 

when such militaries are participating 

in a U.S. Navy-led exercise or event, 

combined with the U.S. Navy’s use of 

sonar and explosives, would not cause 

exceedance of the analyzed levels 

(within each Navy Acoustic Effects 

Model (NAEMO) modeled sonar and 

explosive bin) used for estimating 

predicted impacts, which formed the 

basis of our acoustic impacts effects 

analysis that was used to estimate take 

in this final rule. This new reporting 

measure will allow NMFS to ensure that 

its analysis remains valid. 

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 

SOPs are essential to safety and mission 

success, the Navy considers them to be 

part of the proposed activities under the 

National Environmental Policy Act 


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(NEPA) and included them in the 

environmental analysis. We consider 

SOPs 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 SOPs 

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 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 Mitigation Measures section 

(September 2022). 

Comments and Responses 

We published a proposed rule in the 

Federal Register on October 3, 2023 (88 

FR 68290), with a 45-day comment 

period. That notice described, in detail, 

Navy’s request for modification of the 

2020 HSTT final rule and LOAs, new 

information regarding the occurrence of 

large whale strikes by naval vessels in 

the southern California portion of the 

HSTT Study Area and NMFS’ proposal 

to authorize two additional takes of 

large whales by serious injury or 

mortality. In that notice, we requested 

public input on the proposed 

promulgation of modified regulations 

and associated LOAs for the Navy 

governing this additional incidental 

taking of marine mammals. During the 

45-day comment period, we received 20 

comment submissions. Of this total, one 

submission was from a nongovernmental organization (NGO) and 

the remainder were from private 

citizens. NMFS has reviewed and 

considered all public comments 

received on the proposed rule and 

issuance of the LOAs. All substantive 

comments and our responses are 

described below. We organize our 

comment responses by major categories. 

Take Estimates 

Comment 1: A commenter 

recommended ensuring that any 

modifications to existing regulations or 

authorizations are based on recent and 

rigorous scientific evaluations. This can 

be achieved by conducting regular 

environmental impact assessments to 

account for changes in marine mammal 

populations and habitat conditions. 

Response: NMFS concurs with the 

commenter that modifications to 

existing regulations or authorizations 

must be based on rigorous scientific 

evaluations. NMFS has conducted a 

rigorous scientific evaluation in the 

promulgation of this rulemaking and 

has used the best available science to 

inform its analysis. These final 

regulations and LOAs include reporting 

provisions to ensure compliance and 

that the most value is obtained from the 

required monitoring. Monitoring results 

are considered annually through the 

adaptive management process described 

in the Adaptive Management section 

herein. Further, incidental take 

authorizations for military readiness 

activities can be effective for no more 

than 7 years. Therefore, at minimum, 

NMFS must reconduct its analysis every 

7 years, and in doing so, it considers 

changes in marine mammal populations 

and habitats in its analyses. However, 

during the effective period of an LOA(s), 

if NMFS were to find that the Navy’s 

activities are having more than a 

negligible impact on a species or stock, 

NMFS is required to withdraw or 

suspend the LOA(s) for a certain time 

(16 U.S.C. 1371(a)(5)(B)). 

Comment 2: A commenter stated that 

the 2022 Navy application is based on 

50 CFR 216.015 [the commenter is likely 

referring to section 216.105], which 

allows incidental take regulations to ‘‘be 

modified, in whole or in part, as new 

information is developed.’’ The 

commenter asserted that the only ‘‘new 

information’’ in the 2022 application is 

the information that the Navy has 

already reached its 7-year take limit and 

that failure to meet our own standards 

does not constitute ‘‘new information’’ 

in the sense of 50 CFR 216.015. The 

commenter stated that ‘‘new 

information’’ for this purpose would be 

either (1) evidence that allowing two 

additional takes (and relaxing mitigation 

procedures as requested in the 

application) during this time period will 

have no impact on threatened cetacean 

populations or (2) a dramatic increase in 

the level of military activity in HSTT. 

Response: The MMPA provides for 

the authorization of incidental take 

caused by specified activities at the 

request of an applicant, provided certain 

findings are made. The law directs 

NMFS to process adequate and 

complete applications for incidental 

take authorization, and issue the 

authorization provided all statutory 

findings and requirements, as well as all 

associated legal requirements, are met. 

Under 50 CFR 216.105, as new 

information is developed, through 

monitoring, reporting, or research, the 

regulations may be modified, in whole 

or in part, after notice and opportunity 

for public review. On March 31, 2022, 

NMFS received an adequate and 

complete 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 regulatory period based on 

probabilities derived from a Poisson 

distribution using new vessel strike data 

between 2009–2021 in the HSTT Study 

Area, as well as historical at-sea days in 

the HSTT Study Area from 2009–2015 

and estimated at-sea days for the period 

from 2016 to 2025, informed by 

monitoring and reporting. NMFS 

independently analyzed the request 

based on updated vessel strike data and 

days-at-sea, as well as using updated 

probability methodology, and also 

determined that the strike of up to two 

large whales could occur over the 

remaining duration of the regulations. 

NMFS, following its own analysis and 

proposed rule, has determined it is 

appropriate to promulgate a revised 

final rule and LOAs pursuant to 16 

U.S.C. 1371(a)(5)(A) and 50 CFR 

216.105. 

Comment 3: A commenter stated that 

Kuehne et al. (2020), referenced in the 

2023 HSTT proposed rule (88 FR 68290, 

October 3, 2023), indicates that noise 

from Navy aircraft penetrates more 

deeply into the water than the Navy or 

NMFS considered in their analyses. The 

commenter stated that the study found 

that noise from aircraft can permeate the 

water to at least 30 m and that the 

detected noise level (134 ± 3 dB re 1 mPa 

rms) exceeds volumes that can cause 

behavioral changes in marine mammals 

(Houser et al. 2013; Kastelein et al. 

2012; Kuehne et al. 2020; Williams et al. 

2002). The commenter asserted that, 

therefore, the Navy’s reliance on this 

paper to assert that aircrafts do not 

impact marine mammals is misplaced, 

and the proposed rule’s dismissal of the 


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study because it ‘‘did not include 

behavioral observations of wildlife, and 

the authors’ conclusions about potential 

impacts to wildlife were unsupported 

by data from the study’’ ignores the 

valid bases for these conclusions. 

Response: NMFS disagrees with the 

commenter that Kuehne et al. (2020) 

shows impacts to marine mammals from 

Navy’s HSTT activities that were not 

considered by NMFS and the Navy in 

their respective analyses. As stated in 

the comment, the strongest one-second 

window of underwater sound measured 

by Kuehne et al. (2020) was 134 ± 3 dB 

RMS re 1 mPa rms at 30 m below the sea 

surface. While sound levels between the 

hydrophone and the surface may have 

been stronger than those measured at 30 

m (Kuehne et al. 2020), for the reasons 

discussed in the 2023 HSTT proposed 

rule, there is no new information 

presented in this study to indicate that 

exposures closer to the surface or in air 

would have resulted in behavioral 

responses that would qualify as take by 

Level B harassment. 

We conclude that the information 

presented in Kuehne et al. (2020) does 

not reveal effects of the action on 

marine mammals in a manner or to an 

extent not already considered. 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 remain 

complete and supportable, as stated in 

the 2018 HSTT final rule and in the 

2023 HSTT proposed rule (88 FR 68290, 

October 3, 2023). Please see section 3.7 

(Marine Mammals) of the 2018 HSTT 

FEIS/OEIS for additional information. 

Of note, even if the sound level in the 

water were to exceed the Level B 

harassment threshold, a marine 

mammal would need to cross the path 

of the aircraft while the animal is 

relatively close to the surface in order 

for a take to occur, which is unlikely. 

In addition to Kuehne et al. (2020), 

the commenter referenced several other 

studies that it described as indicating 

that other Navy activities in the HSTT 

Study Area may affect listed species to 

an extent not previously considered. 

These studies include Goldbogen et al. 

(2013), Pirotta et al. (2019), Pirotta et al. 

(2021), Pirotta et al (2022), Simonis et 

al. (2020), Southall et al. (2019), 

Southall et al. (2021), and Szesciorka et 

al. (2019). NMFS considered Pirotta et 

al. (2021), Pirotta et al. (2022), and 

Southall et al. (2021) in its 2023 HSTT 

proposed rule (88 FR 68290, October 3, 

2023). NMFS considered Goldbogen et 

al. (2013) in the 2018 HSTT proposed 

rule (83 FR 29872, June 26, 2018) and 

2018 HSTT final rule (83 FR 66846, 

December 27, 2018), and NMFS 

considered Southall et al. (2019) in the 

2019 HSTT proposed rule (84 FR 48388, 

September 13, 2019). Pirotta et al. 

(2019) found that environmental 

changes could severely affect a 

population’s vital rates, but that, 

depending on the context of a 

disturbance, individuals were tolerant 

of anthropogenic disturbance. Simonis 

et al. (2020) correlated strandings in the 

Mariana islands with naval activities. 

NMFS is aware of this study and has 

considered it along with global 

information related to the correlation of 

sonar with strandings in our analysis. In 

a case study of a close vessel encounter 

with a blue whale, Szesciorka et al. 

(2019) noted that the ship’s reduced 

speed (i.e., 11.3 kn (20.9 km per hour)) 

may have played a role by giving the 

whale enough time to respond to the 

nearby vessel and that higher vessel 

speeds increase the risk that a whale 

could have been struck at the surface or 

get close enough to the ship’s draft that 

the propeller suction effect created by 

the ship’s hydrodynamic flow could 

pull the whale toward the hull. 

Additionally, feeding whales may be 

distracted and thus be less capable of 

detecting and avoiding approaching 

vessels (Szesciorka et al. 2019). NMFS 

determined that the information 

presented in these studies does not 

substantively affect our analysis of 

impacts on marine mammals and their 

habitat that appeared in the 2023 HSTT 

proposed 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 final 

rule. Please see NMFS’ response to 

Comment 14 regarding vessel speed 

restrictions. 

Comment 4: A commenter expressed 

support for Navy use of marine 

mammals for military purposes through 

its Marine Mammal Program. However, 

the commenter stated that to ‘‘take’’ 

mammals simply as a training 

opportunity via severe injury or 

mortality is unethical and to allow the 

killing of innocent animals as cross-fire 

or training shouldn’t be tolerated. 

Response: The actions the Navy takes 

through its Marine Mammal Program are 

outside the scope of this action; we note 

that no animals are intentionally 

exposed to serious injury or mortality 

through that program. For additional 

information about the Navy’s Marine 

Mammal Program, please see the Navy’s 

website at https://www.niwcpacific.

navy.mil/About/Departments/ 

Intelligence-Surveillance-andReconnaissance/Marine-MammalProgram/. 

Comment 5: A commenter stated that 

the recent whale deaths indicate that (1) 

NMFS’ earlier assumptions that vessel 

strikes would be unlikely and easily 

detected if they did occur were proven 

wrong, (2) vessel strikes are occurring at 

rates well-above that analyzed in NMFS’ 

analyses, (3) whales cannot avoid vessel 

strike at the level NMFS assumed in 

issuing the regulations, (4) and that 

sonar affects blue whales in ways not 

adequately considered. 

Response: In the 2018 HSTT final 

rule, 2020 HSTT final rule, and 2023 

HSTT proposed rule, NMFS described 

why a strike by a Navy vessel is unlikely 

in comparison to a strike by a non-Navy 

vessel, and that, overall, it is unlikely 

that the Navy would hit a large whale 

for these reasons. However, even in 

consideration of these factors that make 

vessel strike unlikely, given the history 

of vessel strike by the U.S. Navy in the 

HSTT Study Area, NMFS, in the 2018 

and 2020 HSTT final rules concluded 

that vessel strikes could occur and that 

authorization of three takes by vessel 

strike was appropriate. Therefore, 

NMFS disagrees that the recent vessel 

strikes disprove NMFS’ assumption that 

vessel strikes would be unlikely. 

To date, NMFS is aware of three 

confirmed vessel strikes of large whales 

by U.S. Navy vessels during the current 

regulatory period. Therefore, the strikes 

that have occurred to date have been 

within what NMFS anticipated could 

occur, though, NMFS’ current analysis 

suggests that two additional strikes may 

occur during the current regulatory 

period based on the best available 

scientific information since 

promulgation of the 2020 HSTT final 

rule. 

NMFS further disagrees that the 

recent vessel strikes disprove NMFS’ 

assumption that vessel strikes would be 

detected if they did occur. As 

demonstrated by the June 2021, July 

2021, and May 2023 U.S. Navy strikes, 

NMFS is confident that whales struck 

by Navy vessels are detected and 

reported, and Navy strikes are the 

numbers used in NMFS’ analysis to 

support the authorized number of 

strikes. Navy ships have multiple 

Lookouts, including on the forward part 

of the ship that can visually detect a hit 

whale (which has occasionally 

occurred), in the unlikely event ship 

personnel do not feel the strike. The 

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 


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chain of command give NMFS a high 

level of confidence that all strikes are 

reported. Accordingly, NMFS is 

confident that the information used to 

support the analysis is accurate and 

complete. Regarding the 2021 Royal 

Australian Navy vessel strikes, while 

the 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. 

While the 2018 HSTT final rule, the 

2020 HSTT final rule, and this final rule 

include mitigation to reduce the 

potential for vessel strike, NMFS neither 

states nor implies vessel strike 

avoidance of a particular ‘‘level’’. 

However, it is important that NMFS and 

the Navy consider the new information 

regarding vessel strikes in southern 

California consistent with 50 CFR 

216.105(c). Consideration of this new 

information in an updated analysis 

allows NMFS to reassess its negligible 

impact determination and to determine 

whether additional potential mortality 

would still constitute a negligible 

impact on the potentially affected 

stocks, as it has determined would be 

the case here. 

The commenter referenced several 

studies related to blue whales and 

sonar. Please see NMFS’ response to 

Comment 3. 

Comment 6: A commenter stated that 

NMFS should deny the Navy’s request 

for authorization of two additional takes 

of large whales by vessel strike because 

for at least two of the impacted marine 

mammal stocks (Eastern North Pacific 

stock of blue whale and Central 

America/Southern Mexico—California/ 

Oregon/Washington stock of humpback 

whale) mortality and serious injury 

already exceeds potential biological 

removal (PBR). The commenter stated 

that NMFS’ reasoning for authorizing 

the take amounts to ‘‘take by a thousand 

cuts’’ and defies the stated purpose and 

objectives of the MMPA. 

A commenter stated that NMFS may 

allow take of marine mammals 

incidental to military readiness 

activities only if the taking will have a 

‘‘negligible impact’’ on an affected 

species or stock. The commenter further 

stated that as one court has explained, 

‘‘[b]ecause any mortality level that 

exceeds PBR will not allow the stock to 

reach or maintain its optimum 

sustainable population (‘OSP’), such a 

mortality level could not be said to have 

only a ‘negligible impact’ on the stock.’’ 

(See Conservation Council for Hawai’i v. 

Nat’l Marine Fisheries Serv., 97 F. Supp. 

3d 1210, 1225 (D. Haw. 2015); see also 

54 FR 40338, 40341, 40342 (Sept. 29, 

1989) (‘‘In order to make a negligible 

impact finding, the proposed incidental 

take must not prevent a depleted 

population from increasing toward its 

OSP.’’)). Indeed, NMFS itself has 

previously recognized that when 

mortality of a species is above its PBR, 

‘‘a negligible impact finding under 

section 101(a)(5)(A) cannot be made’’ 

(61 FR 54,157, October 17, 1996). 

Response: The commenter is correct 

that PBR for the Eastern North Pacific 

stock of blue whales and the Central 

America/Southern Mexico—California/ 

Oregon/Washington stock of humpback 

whales is currently exceeded. However, 

NMFS is not authorizing take by 

mortality of the Central America/ 

Southern Mexico—California/Oregon/ 

Washington stock of humpback whales. 

In this final rule, NMFS is authorizing 

take of the Mainland Mexico-CA/OR/ 

WA stock of humpback whale, and PBR 

is not exceeded for this stock. A stock’s 

PBR is part of the best scientific 

information available and therefore, is 

considered in the negligible impact 

determination (see Conservation 

Council for Hawai’i v. Nat’l Marine 

Fisheries Serv., 97 F. Supp. 3d 1210, 

1228 (D. Haw. 2015)). However, 

exceedance of PBR does not inherently 

imply that a negligible impact 

determination cannot be made for an 

authorization that includes mortality or 

serious injury (M/SI) of that stock. As 

explained in the Serious Injury or 

Mortality subsection of the Analysis and 

Negligible Impact Determination section 

of the 2018 HSTT final rule and 2020 

HSTT final rule, and referenced in the 

same section of this final rule, in the 

commercial fisheries setting for 

Endangered Species Act (ESA)-listed 

marine mammals (which is similar to 

the non-fisheries incidental take setting, 

in that a negligible impact 

determination is required that is based 

on the assessment of take caused by the 

activity being analyzed), NMFS may 

find the impact of the authorized take 

from a specified activity to be negligible 

even if total human-caused mortality 

exceeds PBR, if the 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 in the section 

101(a)(5)(A) context here, the authorized 

lethal take (0.14 annually) of blue 

whales from the Eastern North Pacific 

stock is less than 10 percent of PBR (4.1) 

and there are management measures in 

place to address the mortality and 

serious injury from the activities other 

than those the Navy is conducting. For 

the complete discussion of how NMFS 

carefully considered potential 

mortalities from the Navy’s activities in 

light of PBR levels, including an 

explanation for why mortality above 

PBR will not necessarily induce 

population-level non-negligible impacts, 

see the discussion in the Analysis and 

Negligible Impact Determination section 

of this rule, the 2020 HSTT final rule, 

and the 2018 HSTT final rule. 

The commenter references a 1996 

NMFS notice of receipt and request for 

comments (61 FR 54,157; October 17, 

1996) that stated that a negligible impact 

finding under section 101(a)(5)(A) could 

not be made where PBR for the North 

Atlantic right whale stock was 0.4. The 

method that NMFS has articulated 

herein to evaluate negligible impact of 

potential mortality was adopted in 1999 

to evaluate negligible impact pursuant 

to MMPA section 101(a)(5)(E). NMFS 

uses these same criteria adopted in 1999 

to inform (i.e., it is not the sole factor 

considered) our negligible impact 

analysis of potential mortality under 

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

The 1996 decision that a negligible 

impact determination could not be 

made was regarding a request for take by 

mortality of North Atlantic right whale 

(61 FR 54,157; October 17, 1996)). PBR 

for North Atlantic right whale at that 

time was 0.4. If NMFS were to apply its 

current method for evaluating negligible 

impact of potential mortality to that 

request, the results would suggest that 

take by mortality should not be 

authorized (though again, the PBR 

evaluation is not the sole factor 

considered). 

Comment 7: A commenter stated that 

the Navy and NMFS must consider 

serious injury and mortality that results 

from joint training exercises the Navy 

engages in with foreign nations as 

‘‘take’’ under the regulations and that 

NMFS must reexamine the impacts of 

the Navy’s full suite of activities 

(including joint activities with foreign 

fleets) on marine mammals using the 

best available science. In the proposed 

rule, NMFS states that ‘‘[a]ccording 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. Navyled training exercise. The Royal 

Australian Navy vessel was adhering to 

its standard operating procedures at the 

time of the strike.’’ The commenter 

stated that this contradicts coverage of 


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the incident, including by the Navy 

Times/AP that reported: ‘‘[t]he Sydney 

has been holding joint exercises with 

the U.S. Navy in the area since early 

April’’ (The Navy Times, 2021). 

The commenter stated that elsewhere 

in the rule, NMFS appears to say that 

regardless of whether it considered 

vessel strikes that occurred during joint 

training or not, NMFS lets the Navy 

decide what activities it requests 

authorization for, and there is no 

reasoned explanation provided for this 

position. These joint activities led by 

the U.S. Navy pose serious threats to 

marine mammals, kill whales, and 

should be included as specified 

activities. The commenter 

recommended that NMFS not ‘‘defer to 

the applicant to describe the scope of its 

request for an authorization.’’ 

Response: Under the MMPA, only a 

U.S. Citizen may request NMFS 

authorize the incidental take of marine 

mammals (16 U.S.C. 1371(a)(5)(A)). 

Further, the MMPA requires NMFS to 

authorize the incidental take caused by 

the applicant’s specified activities, 

provided certain findings are made (Id.). 

In some cases, foreign militaries may 

participate in U.S. Navy training or 

testing activities in the HSTT Study 

Area. As stated in the proposed rule, the 

HMAS Sydney most likely struck the 

two fin whales around 6:25 a.m. the 

morning of May 7, 2021 while the 

HMAS Sydney was getting into position 

to participate in a U.S. Navy-led 

exercise later that day but was not 

actively engaged in an exercise at the 

presumed time of the strike. The Navy 

does not consider the Royal Australian 

Navy’s vessel movements at the time of 

strike as part of the ‘specified activity’ 

under the MMPA, as the strike did not 

occur while the HMAS Sydney was 

actively participating in a joint training 

exercise with the U.S. Navy. The MMPA 

is necessarily an applicant-driven 

process (Melone v. Coit, 100 F.4th 21, 32 

(1st Cir. 2024)) and NMFS has 

appropriately deferred to the Navy’s 

reasoned explanation of why the Royal 

Australian Navy’s operations were not 

part of the ‘‘specified activity.’’ 

As explained in the Foreign Navies 

section of this final rule, 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. Consistent with 

customary international law, U.S. Navy 

requests or encourages participating 

foreign entities to follow U.S. Navy’s 

mitigation measures for that particular 

event, depending on whether the 

activity is in the U.S.’s territorial sea or 

the EEZ. NMFS and the U.S. Navy also 

examined the Royal Australian Navy 

2021 strike report, and NMFS concurred 

with U.S. Navy’s conclusion that the 

strike most likely occurred before, but 

not during, a joint exercise, and the 

Royal Australian Navy vessel was 

adhering to its standard operating 

procedures at the time of the strike. 

As noted by the commenter in its 

letter, NMFS assessed the effects of 

foreign military activities. First, the 

impacts of all 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 its analysis, as 

described in the Foreign Navies section 

of this final rule. For instance, NMFS 

and the U.S. Navy examined the Royal 

Australian Navy 2021 strike report for 

any lessons that could inform U.S. Navy 

strike mitigation. 

This final rule includes a new 

reporting measure related to foreign 

vessels. The new measure requires that 

the Navy’s annual HSTT reports shall 

include confirmation that foreign 

military use of sonar and explosives, 

when such militaries are participating 

in a U.S. Navy-led exercise or event, 

combined with the U.S. Navy’s use of 

sonar and explosives, did not cause 

exceedance of the analyzed levels 

(within each NAEMO modeled sonar 

and explosive bin) used for estimating 

predicted impacts, which formed the 

basis of our acoustic impacts effects 

analysis that was used to estimate take 

in this final rule. This new reporting 

measure will allow NMFS to ensure that 

its analysis remains valid. 

Comment 8: A commenter stated that 

it supports the Navy’s request for two 

additional incidental takes of large 

whales by vessel strike. The commenter 

discussed a U.S. Supreme Court case, 

Winter v. NRDC, Inc., 555 U.S. 7 (2008), 

in support of its assertion that preparing 

for war still plainly outweighs the 

interests in the safety of marine life. 

Considering these interests, the 

commenter recommended that NMFS 

consider granting the Navy’s request for 

two additional incidental takes. 

Response: NMFS has made the 

required findings on the Navy’s request 

consistent with the statutory criteria 

under the MMPA and has authorized 

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). NMFS does not 

weigh the necessity of Navy training 

and testing against the risks to marine 

mammals as part of the required 

analysis for issuance of take regulations 

under the MMPA. The MMPA requires 

NMFS to authorize the incidental take 

of marine mammals caused by specified 

activities upon request, provided certain 

findings are made (16 U.S.C. 

1371(a)(5)(A)). NMFS’ least practicable 

adverse impact determination for 

military readiness activities must 

include consideration of personnel 

safety, practicality of implementation, 

and impact on the effectiveness of the 

military readiness activity (16 U.S.C. 

1371(a)(5)(a)(iii)). 

Comment 9: A commenter noted 

NMFS’ reference to Cure et al. (2021) 

and Isojunno et al. (2020) in the 2023 

HSTT proposed rule (88 FR 68290, 

October 3, 2023) discussing sperm 

whale behavioral responses to exposure 

to pulsed active sonar (PAS) and 

continuous active sonar (CAS). The 

commenter stated that physical trauma, 

sensory impairment (PTS, TTS, and 

acoustic masking), physiological 

responses (particularly stress 

responses), and behavioral disturbances 

are all part of the harassment of the 

whales and that these factors have not 

been included in the ‘‘take’’ of the three 

whales already, only the mortalities 

have been counted. The commenter 

stated that even brief and transient 

exposure to modest levels of midfrequency military sonar has been 

observed to cause whales to strand or 

perish at sea within hours (Dave, D.M., 

& Dave, M., 2023). These studies do not 

include the permanent injuries to these 

marine mammals’ hearing and sonar 

capabilities. The commenter stated that 

effects on marine mammal hearing are 

not mentioned outside of some studies 

on stranding and should include more 

study and data collection by marine 

mammal experts when it comes to PTS 

and sonar damage to these animals due 

to the impact of the U.S. Navy’s military 

ocean noise pollution. 

Response: In the 2023 HSTT proposed 

rule (88 FR 68290, October 3, 2023), 

NMFS included a discussion of relevant 

literature that had published since 

publication of the 2020 HSTT final rule 

(85 FR 41780, July 10, 2020), and in this 

final rule, NMFS has included a 

discussion of relevant literature that has 

published since publication of the 2023 

HSTT proposed rule. Herein, and in the 

2023 HSTT proposed rule, NMFS 

discussed all relevant literature, not just 

that related to vessel strike. (See the 

New Pertinent Science Since 

Publication of the 2020 HSTT Final 

Rule section of the 2023 HSTT proposed 

rule and the Potential Effects of 

Specified Activities on Marine 

Mammals and their Habitat section of 

this final rule.) 


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The commenter’s statement that 

‘‘even brief and transient exposure to 

modest levels of mid-frequency military 

sonar has been observed to cause whales 

to strand or perish at sea within hours’’ 

is not supported. The proposed rule 

discussed the limited examples of when 

tactical active sonar, in certain 

circumstances, have been found to have 

likely contributed to marine mammal 

stranding events. The reference that the 

commenter cites (Dave, D.M. & Dave, 

M., 2023) states that ‘‘even a brief and 

transient exposure to modest levels of 

mid-frequency military sonar has been 

observed to cause whales to strand or 

perish at sea within hours,’’ citing 

Ferna ́ndez et al. (2005) and NOAA and 

U.S. Department of the Navy (2001). 

These publications discuss two specific 

stranding events in the Canary Islands 

and the Bahamas, respectively. NMFS is 

aware of stranding events coincident 

with military MFAS use in which 

exposure to sonar is believed to have 

been a contributing factor and discussed 

these cases in detail in the 2018 HSTT 

proposed rule. While NMFS did not 

repeat this information in the 2023 

proposed rule as the analyses remain 

unchanged, NMFS stated in the rule that 

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. 

It is unclear what the commenter 

means by physical trauma, sensory 

impairment (PTS, TTS, and acoustic 

masking), physiological responses 

(particularly stress responses), and 

behavioral disturbances not having been 

included in the ‘‘take’’ of the three 

whales already, and that only the 

mortalities have been counted. In the 

2020 HSTT final rule, NMFS discussed 

all of the likely impacts to marine 

mammals, including PTS, TTS, 

masking, and stress, and authorized take 

of marine mammals by Level B 

harassment, Level A harassment, and 

mortality. The 2023 HSTT proposed 

rule and this final rule only discuss 

changes to NMFS’ analysis regarding 

mortality of marine mammals in detail, 

and refer back to the 2018 HSTT 

proposed and final rules and the 2020 

HSTT final rule regarding take by Level 

A harassment and Level B harassment. 

However, NMFS’ analysis, including its 

negligible impact determination, takes 

into consideration the total authorized 

take, not just mortality. 

Comment 10: A commenter stated that 

in addition to blue, humpback, and fin 

whales, the Navy also identifies other 

large whales in its request (Bryde’s 

whales, gray whales, minke whales, 

sperm whales, and sei whales) which 

are also all vulnerable to vessel strikes 

(Laist et al. 2001, Glass et al. 2008, and 

van der Hoop et al. 2015). NMFS’ 2023 

HSTT proposed rule (88 FR 68290, 

October 3, 2023) determined that the 

likelihood of vessel strikes to those 

whales is ‘‘discountable’’ due to their 

relatively low occurrence in the HSTT 

Study Area and the fact that they have 

rarely, if ever, been recorded struck by 

vessels. Due to the fact that reported 

collisions vastly underestimate actual 

strikes, the commenter asks NMFS and 

the Navy to approach vessel strikes and 

other harm very conservatively, 

particularly in light of how some of 

these whales are particularly vulnerable 

to vessel strike and at already-small 

population levels, as detailed in the 

commenter’s July 1, 2022 letter. 

Response: NMFS concurs with the 

commenter that all large whales are 

vulnerable to vessel strike, and that 

reported vessel strikes vastly 

underestimate actual strikes across 

many industries generally. However, 

NMFS has already conducted a 

conservative vessel strike analysis. 

While all large whales are vulnerable to 

vessel strike, it would be inappropriate 

to assume that all large whales that 

occur in the HSTT Study Area are likely 

to be struck by U.S. Navy vessels. 

Of note, the commenter is correct that 

NMFS does not anticipate vessel strike 

of Bryde’s whale, minke whale, or 

sperm whale. However, NMFS did 

propose to authorize take by M/SI by 

vessel strike of sei whale and Eastern 

North Pacific gray whale in the 2023 

HSTT proposed rule (88 FR 68290, 

October 3, 2023) and would authorize 

such take in this final rule. NMFS 

proposed authorizing one take (0.14 

takes annually) of sei whale (Eastern 

North Pacific stock) and four takes (0.57 

takes annually) of Eastern North Pacific 

gray whale. 

Regarding stocks for which take by M/ 

SI by vessel strike was not proposed, as 

stated in the proposed rule, 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. This includes Bryde’s whale, 

minke whale, and the CA/OR/WA stock 

of sperm whale raised by the commenter 

(an individual of the Hawaii stock of 

sperm whale was struck in 2007; see 

table 7 of this final 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. 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 in the Estimated 

Take From Vessel Strikes and 

Explosives by Serious Injury or Mortality 

Vessel Strike section of the proposed 

rule and the Authorized Take From 

Vessel Strikes and Explosives by Serious 

Injury or Mortality section in this final 

rule. Vessel strikes of the Hawaii stock 

of sperm whale are also unlikely given 

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). Given this 

analysis, NMFS concludes that the 

proposed take by M/SI by vessel strike 

included in the proposed rule remains 

appropriately conservative, and has not 

included take by M/SI by vessel strike 

of Bryde’s whale, Western North Pacific 

gray whale, minke whale, or sperm 

whale in this final rule. 

Comment 11: A commenter stated that 

aside from excluding impacts from 

foreign vessels, the proposed rule looks 

at the impacts of vessel strikes on large 

whales almost in isolation and does not 

adequately assess new science on the 

combined impacts of the Navy’s 

activities, in particular on large whales. 

The commenter asserted that while the 

Navy acknowledges that sonar and 

aircraft may affect whales, it does not 

adequately consider the extent of these 

impacts. Any analysis of the impacts of 

the Navy’s exercises must include, in 

addition to vessel strike impacts, the 

impacts from sonar activities of 

domestic vessels and foreign vessels 

involved in joint training exercises and 

any other stressor caused by the Navy’s 

activities. The commenter also asserted 

that the Navy’s literature review does 

not adequately focus on the large baleen 

whales that are of concern in this most 

recent request. 

The commenter stated that as it noted 

in its July 2022 letter, in its review of 

sound effects on animals, the Navy 

focuses heavily on pinnipeds (seals and 

sea lions) and odontocetes (dolphins 

and toothed whales), while their request 

for increased take focuses on mysticetes 


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(baleen whales). Mysticetes’ hearing 

systems are different from those of 

pinnipeds and odontocetes, and so 

while they are closely related one 

cannot infer that each group will 

experience the same effects from sound 

pollution (Southall et al. 2019). 

Mysticetes’ cochlea have their own 

unique shape, which in concert with the 

larger mass of baleen whales indicates 

that they are more sensitive to lowfrequency sound (Southall et al. 2019). 

Though auditory capabilities in baleen 

whales are understudied (Southall et al. 

2019), absence of literature on baleen 

whales does not indicate absence of 

effect. The commenter stated that 

furthermore, the Navy ignored key 

papers studying the effect of sonar on 

baleen whales. It specifically stated that 

the Navy failed to consider, and NMFS 

failed to address in its proposed rule, 

Goldbogen et al. (2013), and further 

references Southall et al. (2019) and 

Southall et al. (2021). 

Response: NMFS disagrees with the 

commenter that the proposed rule looks 

at the impacts of vessel strikes on large 

whales almost in isolation and does not 

adequately assess new science on the 

combined impacts of the Navy’s 

activities, in particular on large whales. 

While NMFS did not repeat discussion 

of a portion of the analysis that did not 

change (e.g., takes by harassment), this 

analysis was incorporated into the 

proposed rule and this final rule by 

reference, and NMFS considered those 

impacts in conjunction with the 

updated M/SI analysis in making its 

determinations. 

NMFS further disagrees that the 

literature review should have focused 

on large baleen whales. In the proposed 

rule (88 FR 68290, October 3, 2023), and 

in this final rule, NMFS’ literature 

review discussed recent literature 

concerning potential impacts from all of 

the Navy’s activities, not just those 

related to vessel strike. As the 

commenter has noted in its letter, NMFS 

must consider the full range of effects of 

the Navy’s activity, not just the potential 

for vessel strike of large whales in 

isolation. NMFS agrees with the 

commenter that an absence of literature 

on baleen whales does not indicate an 

absence of effects, nor has NMFS drawn 

such a conclusion. Rather, NMFS 

conducted a thorough analysis on the 

impacts of the Navy’s activities, 

including sonar and explosive use, on 

mysticetes, as well as other taxa, as 

described in the proposed rule and this 

final rule, which in some cases, 

reference the 2018 (83 FR 66846, 

December 27, 2018) and 2020 HSTT 

final rules (85 FR 41780, July 10, 2020). 

Regarding the specific studies that the 

commenter asserts NMFS failed to 

consider, while not directly cited to in 

the 2023 HSTT proposed rule (88 FR 

68290, October 3, 2023), NMFS 

considered and cited Goldbogen et al. 

(2013) in the 2018 (83 FR 66846, 

December 27, 2018) and 2020 HSTT 

final rules (85 FR 41780, July 10, 2020), 

and the Navy considered and cited this 

paper in the 2018 HSTT EIS/OEIS. 

NMFS considered and cited Southall et 

al. (2019) and Southall et al. (2021) in 

the 2023 HSTT proposed rule. 

Please see NMFS’ response to 

Comment 7 regarding foreign vessels. 

Comment 12: A commenter stated that 

the rule overlooks the likelihood that 

the Navy’s activities will take humpback 

whales from the endangered Central 

America distinct population segment 

(DPS). The commenter stated that its 

read of the science is that most of the 

humpback whale deaths that occur off 

California could be from the endangered 

Central America DPS. The commenter 

further stated that Wade et al. (2017) 

predicted a 67.2 percent movement 

probability for a whale in California to 

move to Central America. In other 

words, an estimated 7.056 Central 

America DPS humpback whales could 

die from vessel strikes off California 

annually (10.5 deaths * 0.672). The 

commenter stated in its letter that 

applying the Rockwood et al. (2021) 

model, 10.5 humpback mortalities occur 

annually off California from the January 

to April and July to November periods 

combined. The commenter stated that 

this does not include potential deaths 

from other sources or in other locations 

yet still represents a significant source 

of mortality for this already endangered 

population. 

Response: NMFS carefully considered 

the potential for each stock of large 

whales to be taken by serious injury or 

mortality by vessel strike. As stated in 

the 2023 HSTT proposed rule (88 FR 

68290, October 3, 2023), regarding the 

likelihood of striking a humpback whale 

from a particular DPS, NMFS 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 and 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. 

The commenter is correct that Wade 

et al. (2017) predicts that 67.2 percent 

of whales that summer in Oregon and 

California will move to Central America 

for the winter. However, NMFS 

disagrees with the commenter’s 

implication that it is more appropriate 

for NMFS to assume that 67.2 percent of 

humpbacks off of California are of the 

Central America DPS, and the 

commenter has not provided 

justification for doing so. (Of note, an 

updated paper from Wade (2021) shows 

that 58 percent of whales that summer 

in Oregon and California will move to 

Mexico (only 42 percent will move to 

Central America)). Rather, NMFS 

continues to find that it is appropriate 

to use the abundance estimates 

described above and the estimate that 

approximately 93 percent of humpbacks 

that winter in Central America will 

move to Oregon/California in the 

summer months to determine the 

relative abundance of each DPS off the 

coast of California. Therefore, NMFS 

continues to conclude that if a Navy 

vessel strike of a humpback whale were 

to occur within SOCAL, it would likely 

be from the Mexico DPS. 

Mitigation and Monitoring 

Comment 13: A commenter stated that 

in addition to strengthening the new 

and revised mitigation measures that 

NMFS included in the 2023 HSTT 

proposed rule, it should also require the 

following additional mitigation 

measures to ensure the least practicable 

adverse impact to marine mammals. The 

commenter noted that it and others have 

requested and expounded upon these 

measures in previous comment letters. 

1. Reinstating more protective 

mitigation areas and restricted training 

exercises in key migration corridors, 

feeding habitat, and other biologically 

important areas (BIAs) and creating/ 

expanding protective mitigation areas to 

protect newly recognized critical habitat 

and other BIAs. In a related comment, 

a separate commenter stated that the 

chances of an incidental take can be 

dramatically reduced by adjusting the 

time and location of exercises (e.g., 

minimizing activity in the vicinity of 

California’s Channel Islands during 

July–October) and reducing speed in 

mitigation areas. The commenter further 

asserted that additional BIAs identified 

by Kratofil et al. 2023 provide new 


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information that necessitates 

reevaluation of mitigation measures, yet 

NMFS rejects adding these new 

mitigation areas as ‘‘impracticable.’’ A 

third commenter stated that it is crucial 

to integrate scientific research, public 

awareness, and proactive measures to 

ensure the sustained well-being of gray 

whales and the preservation of their 

migratory habitats. 

2. Restricting activities when whale 

detection is particularly difficult, such 

as periods of low visibility (Williams et 

al. 2016). 

3. Improving detection of marine 

mammals by adding alternative 

detection methods, including safe/ 

environmentally-sound drone, thermal, 

and/or acoustic technologies, to 

lookouts/observers (Verfuss et al. 2018). 

In a related comment, a commenter 

recommended utilizing existing acoustic 

detection systems to track marine 

mammals in near real-time. 

4. Capping/reducing the level of naval 

activities authorized each year, in 

particular major exercises. In a related 

comment, a separate commenter stated 

that it is crucial to limit the [Navy]’s 

takes on marine mammals. 

5. Halting training exercises when 

whale presence in the area is ‘‘High’’ or 

‘‘Very High,’’ per WhaleSafe (see 

https://whalesafe.com). 

Response: Under the MMPA, NMFS’ 

least practicable adverse impact 

determination for military readiness 

activities must include consideration of 

personnel safety, practicality of 

implementation, and impact on the 

effectiveness of the military readiness 

activity (16 U.S.C. 1371(a)(5)(a)(iii)). 

NMFS has responded to these 

recommended measures, by 

corresponding number. 

1. In the 2023 HSTT proposed rule, 

NMFS discussed that 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, goosebeaked 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. 

Since publication of the 2023 HSTT 

proposed rule, Calambokidis et al. 

(2024) identified updated BIAs on the 

West Coast of the U.S. The HSTT Study 

Area overlaps feeding BIAs for blue 

whale and fin whale in SOCAL. 

Additionally, it overlaps a reproductive 

BIA as well as northbound and 

southbound migratory BIAs for gray 

whale. Please see Calambokidis et al. 

(2024) for additional details about the 

BIAs. 

NMFS and the Navy considered 

additional mitigation areas (beyond 

those already identified with associated 

measures to reduce impacts to marine 

mammals) to further protect marine 

mammals, including odontocetes with 

small or resident populations in the 

HSTT Study Area, and large whales 

with feeding, reproductive, and 

migratory BIAs in the HSTT Study Area. 

This includes consideration of new 

mitigation areas that could be based on 

newly identified BIAs in Hawaii 

(Kratofil et al. 2023) and on the West 

Coast (Calambokidis et al. 2024). The 

HRC overlaps BIAs identified in Kratofil 

et al. (2023) for humpback whale, 

spinner dolphin, short-finned pilot 

whale, rough-toothed dolphin, pygmy 

killer whale, pantropical spotted 

dolphin, melon-headed whale, false 

killer whale, dwarf sperm whale, goosebeaked whale, common bottlenose 

dolphin, and Blainville’s beaked whale. 

All of the BIAs that overlap the HRC are 

small and resident population BIAs, 

with the exception of the humpback 

whale reproductive BIA. SOCAL 

overlaps BIAs identified in 

Calambokidis et al. (2024) for blue 

whale (feeding area), fin whale (feeding 

area), and gray whale (migratory route). 

Additional restrictions in mitigation 

areas beyond those restrictions and 

areas included in the 2020 HSTT final 

rule (including mitigation to reduce 

vessel strike risk such as vessel speed 

restrictions, and in consideration of the 

newly identified BIAs (Kratofil et al. 

2023 and Calambokidis et al. 2024)) is 

impracticable given overlap with critical 

Navy training areas in the HRC and 

SOCAL, including areas around the 

Channel Islands in SOCAL. However, 

many of the BIAs identified in Kratofil 

et al. 2023 and Calambokidis et al. 

(2024) partially or fully overlap the 

mitigation areas included in the 2020 

HSTT final rule and this final rule and 

are aimed at reducing impacts to the 

same species for which Kratofil et al. 

2023 and Calambokidis et al. (2024) 

identified BIAs. In the HRC, the existing 

mitigation areas are targeted and 

expected to reduce impacts to 

humpback whales, false killer whales, 

dwarf sperm whales, pygmy killer 

whales, short-finned pilot whales, 

melon-headed whales, bottlenose 

dolphins, spotted dolphins, spinner 

dolphins, rough-toothed dolphins, 

goose-beaked whales, and Blainville’s 

beaked whales (i.e., all species for 

which Kratofil et al. (2023) identified 

BIAs). In SOCAL, the existing mitigation 

areas are aimed at reducing impacts to 

blue whales, fin whales, and gray 

whales (i.e., all species for which 

Calambokidis et al. (2024) identified 

BIAs). Further, as included in the 2023 

HSTT proposed rule, this final rule 

requires that 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 a select area of SOCAL, and 

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. Last, this 

final rule includes modification of two 

mitigation measures from the 2020 

HSTT final rule (85 FR 41780; July 10, 

2020) to further reduce the potential for 

vessel strike. 

Beyond the papers described herein, 

NMFS is not aware of, nor have 

commenters provided, additional 

research that suggests other areas 

warrant additional mitigation. While 

NMFS agrees with the commenter that 

public awareness can be an important 

part of gray whale conservation, NMFS 

does not anticipate that additional 

public awareness would assist in 

mitigating effects of Navy’s activities on 

gray whales, and therefore, has not 

required the Navy to implement 

measures related to public awareness. 

For a discussion of the mitigation 

measures required by this final rule, 

please see the Mitigation Measures 

section. 

Please see NMFS’ response to 

Comment 14 regarding vessel speed 

restrictions. 

2. Anti-submarine warfare training 

involving the use of mid-frequency 

active sonar (MFAS) typically involves 

the periodic use of active sonar to 

develop the ‘‘tactical picture,’’ or an 

understanding of the battle space (e.g., 

area searched or unsearched, presence 

of false contacts, and an understanding 

of the water conditions). Developing the 

tactical picture can take several hours or 

days, and typically occurs over vast 

waters with varying environmental and 

oceanographic conditions. Training 

during both high visibility (e.g., 

daylight, favorable weather conditions) 

and low visibility (e.g., nighttime, 

inclement weather conditions) is vital 

because sonar operators must be able to 

understand the environmental 

differences between day and night and 


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varying weather conditions and how 

they affect sound propagation and the 

detection capabilities of sonar. 

Temperature layers move up and down 

in the water column and ambient noise 

levels can vary significantly between 

night and day, affecting sound 

propagation and how sonar systems are 

operated. Reducing or securing power in 

low-visibility conditions as a mitigation 

would affect a commander’s ability to 

develop the tactical picture and would 

prevent sonar operators from training in 

realistic conditions. Further, during 

integrated training multiple vessels and 

aircraft may participate in an exercise 

using different dimensions of warfare 

simultaneously (e.g., submarine warfare, 

surface warfare, air warfare, etc.). If one 

of these training elements were 

adversely impacted (e.g., if sonar 

training reflecting military operations 

were not possible), the training value of 

other integrated elements would also be 

degraded. Additionally, failure to test 

such systems in realistic military 

operational scenarios increases the 

likelihood these systems could fail 

during military operations, thus 

unacceptably placing sailors’ lives and 

the Nation’s security at risk. Some 

systems have a nighttime testing 

requirement; therefore, these tests 

cannot occur only in daylight hours. 

Reducing or securing power in low 

visibility conditions would decrease the 

Navy’s ability to determine whether 

systems are operationally effective, 

suitable, survivable, and safe for their 

intended use by the fleet even in 

reduced visibility or difficult weather 

conditions. 

3. The Navy has compiled 

information related to the effectiveness 

of certain equipment to detect marine 

mammals in the context of their 

activities, as well as the practicality and 

effect on mission effectiveness of using 

various equipment. NMFS has reviewed 

this evaluation and concurs with the 

characterizations and the conclusions 

below. 

Thermal detection—Thermal 

detection systems are more useful for 

detecting marine mammals in some 

marine environments than others. 

Current technologies have limitations 

regarding water temperature and survey 

conditions (e.g., rain, fog, sea state, 

glare, ambient brightness), for which 

further effectiveness studies are 

required. Thermal detection systems are 

generally thought to be most effective in 

cold environments, which have a large 

temperature differential between an 

animal’s temperature and the 

environment. Current thermal detection 

systems have proven more effective at 

detecting large whale blows than the 

bodies of small animals, particularly at 

a distance. The effectiveness of current 

technologies has not been demonstrated 

for small marine mammals. Thermal 

detection systems exhibit varying 

degrees of false positive detections (i.e., 

incorrect notifications) due in part to 

their low sensor resolution and reduced 

performance in certain environmental 

conditions. False positive detections 

may incorrectly identify other features 

(e.g., birds, waves, boats) as marine 

mammals. In one study, a false positive 

rate approaching one incorrect 

notification per 4 min of observation 

was noted. 

The Navy has been investigating the 

use of thermal detection systems with 

automated marine mammal detection 

algorithms for future mitigation during 

training and testing, including on 

autonomous platforms. Thermal 

detection technology being researched 

by the Navy, which is largely based on 

existing foreign military grade 

hardware, is designed to allow observers 

and eventually automated software to 

detect the difference in temperature 

between a surfaced marine mammal 

(i.e., the body or blow of a whale) and 

the environment (i.e., the water and air). 

Although thermal detection may be 

reliable in some applications and 

environments, the current technologies 

are limited by their: (1) Low sensor 

resolution and a narrow field of view, 

(2) reduced performance in certain 

environmental conditions, (3) inability 

to detect certain animal characteristics 

and behaviors, and (4) high cost and 

uncertain long-term reliability. 

Thermal detection systems for 

military applications are deployed on 

various Department of Defense (DoD) 

platforms. These systems were initially 

developed for night time targeting and 

object detection such as a boat, vehicle, 

or people. Existing specialized DoD 

infrared/thermal capabilities on Navy 

aircraft and surface ships are designed 

for fine-scale targeting. Viewing arcs of 

these thermal systems are narrow and 

focused on a target area. Furthermore, 

sensors are typically used only in select 

training events, not optimized for 

marine mammal detection, and have a 

limited lifespan before requiring 

expensive replacement. Some sensor 

elements can cost upward of $300,000 

to $500,000 per device, so their use is 

predicated on a distinct military need. 

One example of trying to use existing 

DoD thermal systems is being proposed 

by the U.S. Air Force. The Air Force 

agreed to attempt to use specialized U.S. 

Air Force aircraft with military thermal 

detection systems for marine mammal 

detection and mitigation during a 

limited at-sea testing event. It should be 

noted, however, that these systems are 

specifically designed for and integrated 

into a small number of U.S. Air Force 

aircraft and cannot be added or 

effectively transferred universally to 

Navy aircraft. The effectiveness remains 

unknown in using a standard DoD 

thermal system for the detection of 

marine mammals without the addition 

of customized system-specific computer 

software to provide critical reliability 

(enhanced detection, cueing for an 

operator, reduced false positive, etc.) 

Finally, current DoD thermal sensors 

are not always optimized for marine 

mammal detections versus object 

detection, nor do these systems have the 

automated marine mammal detection 

algorithms the Navy is testing via its 

ongoing research program. The 

combination of thermal technology and 

automated algorithms are still 

undergoing demonstration and 

validation under Navy funding. 

Thermal detection systems 

specifically for marine mammal 

detection have not been sufficiently 

studied both in terms of their 

effectiveness within the environmental 

conditions found in the HSTT Study 

Area and their compatibility with Navy 

training and testing (i.e., polar waters vs. 

temperate waters). The effectiveness of 

even the most advanced thermal 

detection systems with technological 

designs specific to marine mammal 

surveys is highly dependent on 

environmental conditions, animal 

characteristics, and animal behaviors. 

At this time, thermal detection systems 

have not been proven to be more 

effective than, or equally effective as, 

traditional techniques currently 

employed by the Navy to observe for 

marine mammals (i.e., naked-eye 

scanning, hand-held binoculars, highpowered binoculars mounted on a ship 

deck). Focusing on thermal detection 

systems could also provide a distraction 

from and compromise to the Navy’s 

ability to implement its established 

observation and mitigation 

requirements. Last, the Navy does not 

have available manpower to add 

Lookouts to use thermal detection 

systems in tandem with existing 

Lookouts who are using traditional 

observation techniques. 

The Defense Advanced Research 

Projects Agency funded six initial 

studies to test and evaluate infraredbased thermal detection technologies 

and algorithms to automatically detect 

marine mammals on an unmanned 

surface vehicle. Based on the outcome 

of these initial studies, the Navy is 

pursuing additional follow-on research 

efforts. 


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The Office of Naval Research Marine 

Mammals and Biology program funded 

a project (2013–2019) to test the thermal 

limits of infrared-based automatic whale 

detection technology. That project 

focused on capturing whale spouts at 

two different locations featuring 

subtropical and tropical water 

temperatures, optimizing detector/ 

classifier performance on the collected 

data, and testing system performance by 

comparing system detections with 

concurrent visual observations. Results 

indicated that thermal detection systems 

in subtropical and tropical waters can 

be a valuable addition to marine 

mammal surveys within a certain 

distance from the observation platform 

(e.g., during seismic surveys, vessel 

movements), but have challenges 

associated with false positive detections 

of waves and birds (Boebel, 2017). 

While Zitterbart et al. (2020) reported 

on the results of land-based thermal 

imaging of passing whales, their 

conclusion was that thermal technology 

under the right conditions and from 

land can detect a whale within 3 km 

although there could also be lots of false 

positives, especially if there are birds, 

boats, and breaking waves at sea. 

The Navy’s Living Marine Resources 

program is funding one ongoing thermal 

imaging project entitled ‘‘Thermal 

Imaging for Vessel Strike Mitigation on 

Autonomous Vessels Project 68’’. The 

project is focused on adapting and 

testing two thermal imaging-based 

whale detection systems to reduce the 

potential for vessel strike during 

navigation of unmanned Navy surface 

vessels. Phase one is planned for 2024 

and 2025. The schedule for subsequent 

phases will be determined as work 

progresses. Project details are available 

at: https://exwc.navfac.navy.mil/ 

Portals/88/Documents/EXWC/ 

Environmental_Security/Living%20

Marine%20Resources/LMRFactSheet_

Project68.pdf. 

The Navy plans to continue 

researching thermal detection systems 

for marine mammal detection to 

determine their effectiveness and 

compatibility with Navy applications. If 

the technology matures to the state 

where thermal detection is determined 

to be an effective mitigation tool during 

training and testing, NMFS and the 

Navy will assess the practicability of 

using the technology during training 

and testing events and retrofitting the 

Navy’s observation platforms with 

thermal detection devices. The 

assessment will include an evaluation of 

the budget and acquisition process 

(including costs associated with 

designing, building, installing, 

maintaining, and manning the 

equipment); logistical and physical 

considerations for device installment, 

repair, and replacement (e.g., 

conducting engineering studies to 

ensure there is no electronic or power 

interference with existing shipboard 

systems); manpower and resource 

considerations for training personnel to 

effectively operate the equipment; and 

considerations of potential security and 

classification issues. New system 

integration on Navy assets can entail up 

to 5 to 10 years of effort to account for 

acquisition, engineering studies, and 

development and execution of systems 

training. The Navy will provide 

information to NMFS about the status 

and findings of Navy-funded thermal 

detection studies and any associated 

practicability assessments at the annual 

adaptive management meetings. 

Passive Acoustic Monitoring— 

Regarding the recommendation to 

utilize existing acoustic detection 

systems to track marine mammals in 

near real-time, the Navy does employ 

passive acoustic monitoring when 

practicable to do so (i.e., when assets 

that have passive acoustic monitoring 

capabilities are already participating in 

the activity). For other explosive events, 

there are no platforms participating that 

have passive acoustic monitoring 

capabilities. Adding a passive acoustic 

monitoring capability (either by adding 

a passive acoustic monitoring device to 

a platform already participating in the 

activity, or by adding a platform with 

integrated passive acoustic monitoring 

capabilities to the activity, such as a 

sonobuoy) for mitigation is not 

practicable. As discussed in chapter 5 

(Mitigation), section 5.5.3 (Active and 

Passive Acoustic Monitoring Devices) of 

the 2018 HSTT FEIS/OEIS, there are 

significant manpower and logistical 

constraints that make constructing and 

maintaining additional passive acoustic 

monitoring systems or platforms for 

each training and testing activity 

impracticable. Additionally, diverting 

platforms that have passive acoustic 

monitoring platforms would impact 

their ability to meet their Title 10 

requirements for maintaining military 

readiness and reduce the service life of 

those systems. 

The use of real-time PAM for 

mitigation at the Southern California 

Anti-submarine Warfare Range (SOAR) 

exceeds the capability of current 

technology. The Navy has a significant 

research investment in the Marine 

Mammal Monitoring on Navy Ranges 

(M3R) system at three ocean locations 

including SOAR. However, this system 

was designed and intended to support 

marine mammal research for select 

species, and not as a mitigation tool. 

Marine mammal PAM using 

instrumented hydrophones is still under 

development and while it has produced 

meaningful results for marine species 

monitoring, abundance estimation, and 

research, it was not developed for, nor 

is it appropriate for, real-time 

mitigation. The ability to detect, 

classify, and develop an estimated 

position (and the associated area of 

uncertainty) differs across species, 

behavioral context, animal location vs. 

receiver geometry, source level, etc. 

Based on current capabilities, and 

given adequate time, vocalizing animals 

within an indeterminate radius around 

a particular hydrophone are detected, 

but obtaining an estimated position for 

all individual animals passing through a 

predetermined area is not assured. 

Detecting vocalizations on a 

hydrophone does not determine 

whether vocalizing individuals would 

be within the established mitigation 

zone in the timeframes required for 

mitigation. Since detection ranges are 

generally larger than current mitigation 

zones for many activities, this would 

unnecessarily delay events due to 

uncertainty in the animal’s location and 

put at risk event realism. If an event 

were to be moved based upon lowconfidence localizations, it may 

inadvertently be moved to an area 

where non-vocalizing animals of 

undetermined species are present. 

To develop an estimated position for 

an individual, it must be vocalizing and 

its vocalizations must be detected on at 

least three hydrophones. The 

hydrophones must have the required 

bandwidth, and dynamic range to 

capture the signal. In addition, calls 

must be sufficiently loud so as to 

provide the required signal to noise 

ratio on the surrounding hydrophones. 

Typically, small odontocetes echolocate 

with a directed beam that makes 

detection of the call on multiple 

hydrophones difficult. Developing an 

estimated position of selected species 

requires the presence of whistles which 

may or may not be produced depending 

on the behavioral state. Beaked whales 

at SOAR vocalize only during deep 

foraging dives which occur at a rate of 

approximately 10 per day. They 

produce highly directed echolocation 

clicks that are difficult to 

simultaneously detect on multiple 

hydrophones. Current real-time systems 

cannot follow individuals and at best 

produce sparse positions with multiple 

false locations. The position estimation 

process must occur in an area with 

hydrophones spaced to allow the 

detection of the same echolocation click 

on at least three hydrophones. 

Typically, a spacing of less than 4 km 


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in water depths of approximately 2 km 

is preferred. In the absence of detection, 

the analyst can only determine with 

confidence if a group of beaked whales 

is somewhere within 6 km of a 

hydrophone. Beaked whales produce 

stereotypic click trains during deep (500 

m) foraging dives. The presence of a 

vocalizing group can be readily detected 

by an analyst by examining the click 

structure and repetition rate. However, 

estimating position is possible only if 

the same train of clicks is detected on 

multiple hydrophones which is often 

precluded by the animal’s narrow beam 

pattern. Currently, this is not an 

automated routine. 

In summary, the analytical and 

technical capabilities required to use 

PAM such as M3R at SOAR as a 

required mitigation tool are not 

sufficiently robust to rely upon due to 

limitations with near real-time 

classification and determining estimated 

positions. The level of uncertainty as to 

a species presence or absence and 

location are too high to provide the 

accuracy required for real-time 

mitigation. As discussed in chapter 5 

(Mitigation) of the 2018 HSTT FEIS/ 

OEIS, existing Navy visual mitigation 

procedures and measures, when 

performed by individual units at-sea, 

still remain the most effective and 

practical means of protection for marine 

species. 

NMFS is not requiring drones to be 

used at this time and the commenters 

did not provide information supporting 

the recommendation that they be used 

when considering the extensive 

monitoring by Lookouts required. 

4. The commenters neither offer a 

rationale for why a cap on the level of 

activities is needed nor do they suggest 

what an appropriate cap might be. The 

Navy is responsible under Title 10 of 

the U.S. Code for conducting the needed 

amount of testing and training to 

maintain military readiness, which is 

what they have proposed and NMFS has 

analyzed. Further, the MMPA states that 

NMFS shall issue MMPA authorizations 

if the necessary findings can be made, 

as they have been here. Importantly, as 

described in the Mitigation Measures 

section, the Navy has determined that it 

is practicable to limit activities (active 

sonar, explosive use, etc.) to varying 

degrees in five areas that are important 

to sensitive species or for important 

behaviors in order to minimize impacts 

that are more likely to lead to adverse 

effects on rates of recruitment or 

survival and is required by this final 

rule to do so. 

5. During the promulgation of this 

rule, NMFS and the Navy fully explored 

the potential for the Navy to incorporate 

WhaleSafe into its mitigation methods. 

However, the current WhaleSafe 

operational areas (Santa Barbara 

Channel and off the coast of San 

Francisco) do not overlap the HSTT 

Study Area. As such, while WhaleSafe 

can inform whale occurrence in other 

areas of Southern California, it is not an 

appropriate tool for determining 

mitigation actions in the HSTT Study 

Area, and NMFS has not required the 

Navy to halt training exercises when 

WhaleSafe indicates that whale 

presence in the area is ‘‘high’’ or ‘‘very 

high’’ as suggested by the commenter. 

However, NMFS has recommended to 

the Navy, including as a conservation 

recommendation in the 2024 reinitiated 

Biological and Conference Opinion, that 

it explore funding options and seek 

partnership opportunities for the 

development of a mapping and analysis 

tool that integrates acoustic and visual 

whale detections with model 

predictions to display near real-time 

whale presence data within the SOCAL 

and nearby surrounding areas. 

Information generated by such a tool 

could then be used by Navy, and 

potentially non-military, vessels to 

reduce the risk of large whale vessel 

strike in Southern California. 

Comment 14: A commenter stated that 

NMFS must substantially strengthen 

mitigation measures, including 

requiring more effective measures to 

protect large whales from vessel strikes, 

before issuing any additional take 

authorizations to the Navy. The 

commenter stated that NMFS rejected 

other mitigation measures, such as 

requiring vessels used in the Navy’s 

activities to slow to 10 kn (18.5 km per 

hour) or less in certain BIAs to reduce 

the risk of vessel strikes, by 

downplaying the risk of vessel strikes to 

endangered whales and other species 

impacted by the Navy’s activities. The 

commenter stated that NMFS’ proposed 

modifications to the mitigation 

measures fall short of meeting the least 

practicable adverse impact standard. 

Commenters provided several specific 

recommendations for mitigation 

measures. 

1. The 2023 HSTT proposed rule 

included a revised mitigation measure 

that states ‘‘if marine mammals are 

observed, Navy personnel must 

maneuver (which may include reducing 

speed as the mission or circumstances 

allow) to maintain distance.’’ The 

reference to reducing speed as the 

mission or circumstances allow is a 

revision from the measure in the 2020 

HSTT final rule. The commenter stated 

that this measure should be mandatory 

in important whale habitat, where 

whales are known to occur, and where 

vessel strikes have occurred or are 

expected to occur, and should be 

implemented in these areas even when 

whales have not been observed by 

Lookouts. Another commenter 

recommended focusing on vessel speeds 

and their impact on marine mammal 

safety to mitigate the risks associated 

with high-speed vessel travel and 

including revised protocols. 

2. The 2023 HSTT 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. 

The commenter stated that NMFS 

should attach specific actions required 

of other vessels in the area, including a 

10 kn (18.5 km per hour) ship speed, 

when a Navy vessel strike has been 

reported, in order to reduce the risk of 

further strikes. The commenter stated 

that these alerts should also go to nonNavy vessels in the vicinity that pose a 

risk to whales. 

3. The 2023 HSTT proposed rule 

modified the requirement for awareness 

messages disseminated in Southern 

California. The commenter stated that it 

supports the use of more accurate 

seasonal information to inform large 

whale awareness messages, but expects 

awareness and alerts to be tied to more 

robust mitigation action, and 

recommends that if a marine mammal is 

spotted, NMFS should require a 

mandatory 10 kn (18.5 km per hour) 

ship speed limit. 

4. The 2023 HSTT proposed rule also 

contains a new mitigation measure in 

which Navy personnel would issue realtime 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 yards (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)). The 

commenter recommended that (a) this 

should apply any time a whale is 

sighted (i.e., Navy should not have to 

observe at least four whales to trigger 

this measure), (b) this should have no 

geographic limitation, and (c) this 

should trigger a mandatory 10 kn (18.5 

km per hour) ship speed limit. 

5. A commenter stated that the Navy 

will evaluate future revisions to online 

or DVD Marine Species Awareness 

Training (MSAT) video training to 

emphasize that when a protected 

species is spotted, this may be an 

indicator that additional marine 


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mammals are present and nearby, and 

the vessel should take this into 

consideration when transiting. The 

commenter stated that this purported 

mitigation measure should be more 

forceful; when a protected species is 

spotted, protective actions must result. 

Response: Under the MMPA, NMFS’ 

least practicable adverse impact 

determination for military readiness 

activities must include consideration of 

personnel safety, practicality of 

implementation, and impact on the 

effectiveness of the military readiness 

activity (16 U.S.C. 1371(a)(5)(a)(iii)). 

The recommendation for NMFS to 

require, in some cases a reduction in 

speed, and in other cases a 10 kn (18.5 

km per hour) speed limit, generally 

speaking, is impracticable because these 

speed reductions and further reductions 

to Navy vessel speeds negatively impact 

mission effectiveness. The Navy is 

unable to impose a 10 kn (18.5 km per 

hour) ship speed limit because it would 

not be practical to implement and 

would impact the effectiveness of 

Navy’s activities by putting constraints 

on training and testing. The Navy 

requires flexibility in the use of variable 

ship speeds for training, testing, 

operational, safety, and engineering 

qualification requirements. Navy ships 

typically use the lowest speed practical 

given individual mission needs. NMFS 

has reviewed the Navy’s analysis of 

these additional restrictions and the 

impacts they would have on military 

readiness and concurs with the Navy’s 

assessment that they are impracticable. 

That said, NMFS has strengthened its 

mitigation requirement requiring Navy 

personnel to maneuver if marine 

mammals are observed to add ‘‘which 

may include reducing speed as the 

mission or circumstances allow’’ to 

emphasize that reduction of speeds 

should be considered where 

appropriate. Of note, current Navy 

Standard Operating Procedures and 

mitigations require a minimum of at 

least three Lookouts on duty on Navy 

cruisers and destroyers while underway 

and, so long as safety of navigation is 

maintained, to keep 500 yards away 

from large whales and 200 yards away 

from other marine mammals (except for 

bow-riding dolphins and pinnipeds 

hauled out on shore or man-made 

navigational structures, port structures, 

and vessels). 

Previously, the Navy commissioned a 

vessel density and speed report based 

on an analysis of Navy ship traffic in the 

HSTT Study Area between 2011 and 

2015. Median speed of all Navy vessels 

within the HSTT Study Area is typically 

already low, with median speeds 

between 5 and 12 kn (9.2 to 22.2 km per 

hour). Further, the presence and transits 

of commercial and recreational vessels, 

annually numbering in the thousands, 

poses a more significant risk to large 

whales than the presence of Navy 

vessels. The Vessel Strike subsection of 

the Estimated Take of Marine Mammals 

section of the 2020 HSTT final rule and 

this rule and the 2018 HSTT FEIS/OEIS 

chapter 3 (Affected Environment and 

Environmental Consequences) section 

3.7.3.4.1 (Impacts from Vessels and InWater Devices) and Appendix K, section 

K.4.1.6.2 (San Diego (Arc) Blue Whale 

Feeding Area Mitigation 

Considerations), explain the important 

differences between most Navy vessels 

and their operation and commercial 

ships that make Navy vessels much less 

likely to strike a whale. 

When developing Phase III mitigation 

measures, the Navy analyzed the 

potential for implementing additional 

types of mitigation, such as vessel speed 

restrictions within the HSTT Study 

Area. The Navy determined that based 

on how the training and testing 

activities will be conducted within the 

HSTT Study Area, vessel speed 

restrictions would be incompatible with 

practicability criteria for safety, 

sustainability, and training and testing 

missions, as described in chapter 5 

(Mitigation), section 5.3.4.1 (Vessel 

Movement) of the 2018 HSTT FEIS/ 

OEIS. NMFS fully reviewed this 

analysis and concurs with the Navy’s 

conclusions. During the promulgation of 

this final rule, NMFS again discussed 

the potential for vessel speed 

restrictions, including during limited 

times and areas, and Navy continued to 

assert that such restrictions are not 

practicable. After thorough discussion, 

NMFS again concurs with the Navy’s 

conclusions. 

Regarding the recommendation for 

Navy to send alerts of increased risk of 

strike to non-Navy vessels (such as 

through the WhaleAlert app), Navy has 

informed NMFS that transmitting 

information between Navy and civilian 

vessels poses security risks that make 

sending alerts to non-Navy vessels 

impracticable. 

Regarding the recommendations for 

the measure described in number 4 to be 

implemented when a single whale is 

sighted and in all areas, Navy asserts 

that doing so is not practicable as it 

would interfere with its mission 

success. Four whales was determined to 

be the appropriate trigger for this 

measure as it represents an increased 

strike risk without occurring so often 

that this measure becomes impracticable 

for the Navy to implement. Regarding 

the geographic limitations, 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. Given that 

this area includes the location where all 

known strikes have occurred, NMFS 

anticipates that this measure is of 

particular importance in this area, and 

Navy asserted that implementing this 

measure more broadly would be 

impracticable, as it could divert the 

attention of bridge personnel from other 

critical tasks. 

As stated by the commenter, the Navy 

will evaluate future revisions to online 

or DVD MSAT 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. NMFS 

does not dictate exactly what measure 

must be taken, as different situations 

warrant different actions and may have 

different safety and practicability 

considerations. 

The 2023 HSTT proposed rule and 

this final rule include two new 

mitigation measures beyond that 

required by the 2020 HSTT final rule 

and modification of two existing 

mitigation measures. Please see NMFS’ 

response to Comment 15. 

With the exception of the 

recommended mitigation measures 

discussed within this Comments and 

Responses section, the commenter has 

not demonstrated why NMFS has not 

met the least practicable adverse impact 

standard. As described in the Mitigation 

Measures section of this final rule, 

NMFS has included the mitigation 

requirements necessary to achieve the 

least practicable adverse impact on the 

affected species or stocks and their 

habitat. 

Comment 15: Multiple commenters 

stated that, rather than authorizing 

additional take by serious injury or 

mortality by vessel strike, NMFS should 

require the Navy to implement 

additional mitigation measures to avoid 

harassment and future vessel strikes of 

large whales. Commenters specifically 

referenced the 2021 Royal Australian 

Navy vessel strikes of fin whales, with 

one commenter referencing what it 

describes as NMFS’ acknowledgement 

of the susceptibility of fin whales to 

vessel strike year-round, and another 

stating that the Royal Australian Navy 

vessel strikes should be factored into the 

take calculation for the HSTT Study 

Area. 

In a related comment, a commenter 

questioned whether the Navy can 


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continuously keep asking for more takes 

if they continue to reach their 

authorized number. 

Response: Based on the available 

information at the time that the 2020 

HSTT final rule was promulgated, 

NMFS’ analysis suggested that three 

takes by serious injury or mortality by 

vessel strike over the 7-year duration of 

the HSTT rule could occur. To date, 

NMFS is aware of three confirmed 

vessel strikes of large whales by U.S. 

Navy vessels during the current 

regulatory period. While those three 

takes are within what NMFS anticipated 

could occur, given that three years 

remained of the effective period of the 

rule when the first two strikes occurred, 

the Navy reanalyzed the potential for 

take by mortality and serious injury by 

vessel strike over the duration of the 

rule, and that analysis suggested that 

additional takes could occur. NMFS’ 

subsequent analysis also suggested that 

two additional takes could occur over 

the remainder of the regulatory period. 

NMFS requires the Navy to implement 

mitigation measures to reduce the 

potential for vessel strike; however, this 

mitigation is not quantitatively 

incorporated into NMFS’ analysis, and 

therefore, does not reduce the number of 

takes that NMFS authorizes. 

Regarding mitigation, the 2023 HSTT 

proposed rule and this final rule include 

two new mitigation measures beyond 

that required by the 2020 HSTT final 

rule and modification of two existing 

mitigation measures. The new measures 

include: 

• Navy personnel must issue realtime 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; and 

• Navy personnel must send alerts to 

Navy vessels of increased risk of strike 

following any reported Navy vessel 

strike in the HSTT Study Area. 

Additionally, the 2020 HSTT final 

rule (85 FR 41780, July 10, 2020) 

requires Navy personnel to issue 

seasonal awareness notification 

messages to alert ships and aircraft to 

the possible presence of blue whales, 

humpback whales, gray whales, and fin 

whales in the seasons that they are most 

likely to occur in the HSTT Study Area. 

These messages assist in maintaining 

safety of navigation and in avoiding 

interactions with large whales during 

transits. This final 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), as included in 

the 2023 HSTT proposed rule. 

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. 

For vessel movement, the 2020 HSTT 

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

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, as 

included in the 2023 HSTT proposed 

rule. Please see the Mitigation Measures 

section for a full discussion of these 

new and revised measures. 

NMFS anticipates that additional 

vessel strike of large whales could still 

occur even in consideration of these 

additional and modified mitigation 

measures (noting that the mitigation 

measures are not quantitatively 

included in the vessel strike 

calculation). Therefore, NMFS is 

authorizing two additional takes of large 

whales by serious injury or mortality by 

vessel strike over the 7-year duration of 

the HSTT rule (two takes in addition to 

the three takes authorized in the current 

regulations). In the 2023 HSTT 

proposed rule and this final rule, NMFS 

describes factors that make fin whales 

particularly susceptible to vessel strike 

by the Navy in southern California (e.g., 

occurrence, Navy vessel strike history in 

SOCAL, year-round occurrence). As 

such, NMFS analysis suggests that of the 

five total takes by serious injury or 

mortality by vessel strike of large 

whales, up to four of those takes could 

be of the CA/OR/WA stock of fin whale. 

Regarding the suggestion that the Royal 

Australian Navy vessel strike of two fin 

whales should be factored into the take 

calculation for the HSTT Study Area, as 

explained in the 2023 HSTT proposed 

rule and in the Vessel Strike section of 

this final rule, 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. Navy-led 

training exercise, and the strike of those 

two fin whales is not included in the 

estimated take by vessel strike 

calculation. Instead, 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. 

Regarding a commenter’s concern 

about whether the Navy can 

continuously keep asking for more takes 

if they continue to reach their 

authorized number, as stated in the 

Background section of this final rule, an 

authorization for incidental takings 

shall be granted if NMFS finds that the 

taking will have a negligible impact on 

the species or stocks and will not have 

an unmitigable adverse impact on the 

availability of the species or stocks for 

taking for subsistence uses (where 

relevant) (16 U.S.C. 1371(a)(5)(A)). 

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 similar 

significance, and on the availability of 

such species or stocks for taking for 

certain subsistence uses (referred to in 

this rule as ‘‘mitigation measures’’); and 

requirements pertaining to the 

monitoring and reporting of such 

takings (16 U.S.C. 1371(a)(5)(A)). NMFS 

has made the required findings, and 

therefore, it must issue the requested 

incidental take authorization to the 

Navy. 

Comment 16: The 2023 HSTT 

proposed rule (88 FR 68290, October 3, 

2023) states: ‘‘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 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.’’ A commenter stated 

that NMFS should reject the Navy’s 

explanation for why three lookouts on 

cruisers and destroyers are not 

practicable. In a related comment, a 

commenter stated that the 2023 HSTT 

proposed rule seeks to reduce the 

number of lookouts (the simplest and 

cheapest mitigation strategy) from three 

to one, and recommended increased 

numbers of lookouts as a mitigation 

measure. This commenter also 

recommended enhancing bridge 

resource management. A commenter 

also recommended training for 

Lookouts. 

Response: Neither the 2023 HSTT 

proposed rule nor this final rule propose 

a reduction in the number of lookouts 

required on Navy vessels, and it is 

unclear what the commenter means by 

enhancing bridge resource management, 

though it is important to note that all 

bridge watchstanders including 

Lookouts take the Navy’s Marine 

Species Awareness Training that NMFS 

has reviewed and approved. The 


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commenter did not suggest what 

additional training Lookouts should 

receive. As a general matter, NMFS’ 

evaluation of least practicable adverse 

impact appropriately relies heavily on 

input from the applicant regarding the 

practicability of any given measure 

provided the explanation is reasonable 

and clear. Further, 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 and 

consultation with the Department of 

Defense on these considerations (see 16 

U.S.C. 1371(a)(5)(A)(iii)). The Navy has 

clearly indicated the need for flexibility 

to effectively carry out foreseeable 

military readiness activities, such that 

requiring additional Lookouts at all 

times would be impracticable, and we 

concur with that assessment. 

Comment 17: A commenter stated that 

if the Navy is allowed a greater number 

of incidental takes on marine life, it 

must enforce strategies to avoid such 

incidents and suggested that the Navy 

expand its existing precautions to 

protect marine life and minimize takes 

of marine animals. The commenter 

encourages the Navy to (1) continue 

implementing state-of-the-art 

technology and best practices to reduce 

underwater noise and disturbance 

during training exercises, particularly in 

areas where marine mammals are 

known to inhabit, (2) collaborate with 

marine biologists and conservation 

experts to continually monitor the 

effects of Navy activities on marine life 

and suggest corrective actions when 

necessary, (3) consider adjusting the 

timing or location of training exercises 

to minimize their impact on critical 

marine habitats and migration paths, 

and (4) promote transparency and 

cooperation by engaging with 

environmental organizations and local 

communities to develop and assess 

mitigation strategies collaboratively. In a 

related comment, another commenter 

stated that advanced technologies 

should allow the United States military 

to maintain readiness standards and 

protect wildlife. 

Response: NMFS worked closely with 

the Navy to investigate the recent vessel 

strikes and to identify ways to improve 

mitigation measures. This final rule 

includes revision to two existing 

mitigation measures and two new 

mitigation measures beyond that 

included in the 2020 HSTT final rule 

(85 FR 41780, July 10, 2020; described 

further in response to Comment 15). Of 

note, this final rule authorizes 

additional take by serious injury or 

mortality by vessel strike beyond that 

authorized by the 2020 HSTT final rule. 

This final rule does not authorize 

additional take by Level A or Level B 

harassment. However, as discussed in 

the Mitigation Measures section of this 

final rule, elsewhere in this section, and 

in chapter 5 (Mitigation) of the 2018 

HSTT FSEIS/OEIS, the Navy will 

implement extensive mitigation, both 

procedural mitigation and mitigation 

areas, to avoid or reduce potential 

impacts from the HSTT activities on 

marine mammals, including impacts 

from sonar and explosives. (Note that 

additional measures and revisions to 

some existing measures have been made 

since publication of this FEIS/OEIS). 

Specifically, the Navy would use a 

combination of delayed starts, 

powerdowns, and shutdowns to 

minimize the likelihood of M/SI, 

minimize the likelihood or severity of 

PTS or other injury, and reduce 

instances of TTS or more severe 

behavioral disruption caused by 

acoustic sources or explosives. The 

Navy will limit activities (active sonar, 

explosive use, major training exercises 

(MTEs), etc.) to varying degrees in 

multiple areas that are important to 

sensitive species or for critical behaviors 

in order to minimize impacts that are 

more likely to lead to adverse effects on 

rates of recruitment or survival. The 

mitigation measures would 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. Please see the Mitigation 

Measures section of this final rule for 

additional detail regarding required 

mitigation measures. 

Regarding best practices to reduce 

underwater noise, most of the Navy’s 

vessels already have state of the art 

quieting technologies employed to 

reduce their sound profile to assist them 

in avoiding detection by enemy forces, 

therefore, they are much quieter than 

commercial/recreational vessels of 

similar sizes. 

Regarding monitoring the effects of 

Navy activities on marine life and the 

commenter’s recommendation to take 

corrective actions when necessary, as 

required by this final rule, the Navy 

implements a robust monitoring 

program. Although the Navy has been 

conducting research and monitoring in 

the HSTT Study Area for over 20 years, 

it developed a formal marine species 

monitoring program in support of the 

MMPA and ESA authorizations for the 

Hawaii and Southern California range 

complexes in 2009. This robust program 

has resulted in hundreds of technical 

reports and publications on marine 

mammals that have informed Navy and 

NMFS analyses in environmental 

planning documents, rules, and 

Biological Opinions. The reports are 

made available to the public on the 

Navy’s marine species monitoring 

website 

(www.navymarinespeciesmonitoring.us) 

and the data on the Ocean 

Biogeographic Information System 

Spatial Ecological Analysis of 

Megavertebrate Populations (OBIS– 

SEAMAP) (www.seamap.env.duke.edu). 

For additional information about the 

Navy’s monitoring program, please see 

the Monitoring section herein and the 

websites listed above. 

Further, the regulations governing the 

take of marine mammals incidental to 

Navy training 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. Please see 

the Adaptive Management section of 

this final rule for additional 

information. 

Regarding transparency and 

cooperation, the MMPA does not 

require an independent review of 

mitigation measures. It does require 

notice and opportunity for public 

comment (16 U.S.C. 1371(a)(5)(A)(i)). 

The public comment period is a means 

by which the public (e.g., environmental 

organizations and local communities) 

are able to provide NMFS with 

mitigation measure recommendations 

supported by scientific evidence that 

NMFS takes into consideration when 

finalizing the rulemaking. 

Comment 18: A commenter stated that 

measures should be taken to cease any 

more actions potentially impacting 

marine mammals. The 2023 HSTT 

proposed rule (88 FR 68290, October 3, 

2023) states that results of a study 

indicated 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 whales beyond 200 yd (182.9 

m), compared with a 49 percent chance 

for trained marine mammal observers. 

The commenter recommended that the 

Navy hire trained marine mammal 

observers to keep the incidents of whale 

take to the original take numbers or less, 

and not need to have modifications to 

the LOA for additional animal take. The 


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commenter also recommended having 

experts that can accurately assess the 

physical and mental health of these 

animals. In a related comment, a 

commenter stated that the rule calls into 

question whether the three vessel strikes 

that have occurred were due to the crew 

not spotting the whales, not spotting 

them before the strike, or the Navy not 

emphasizing the importance of spotting 

and avoiding marine wildlife to its 

personnel. 

Response: As described in the 2023 

HSTT proposed rule (88 FR 68290, 

October 3, 2023), 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 

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. As noted by the commenter, 

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. While this study 

suggests that trained marine mammal 

observers are more effective than Navy 

Lookouts, the Navy has asserted that it 

is impracticable to station independent 

marine mammal observers on Navy 

vessels. When making the least 

practicable adverse impact 

determination for military readiness 

activities, NMFS must consider 

personnel safety, practicality of 

implementation, and impact on the 

effectiveness of the military readiness 

activities and must consult with the 

Department of Defense on these 

considerations (16 U.S.C. 

1371(a)(5)(A)(iii)). As described in 

section 5.5.5 (Third-Party Observers) of 

the 2018 HSTT FEIS/OEIS, use of thirdparty observers on Navy vessels or 

aircraft would result in safety and 

security clearance issues, berthing 

shortages or exceedance of other space 

limitations, impacts to Lookouts’ 

abilities to complete their other missionessential duties, and unsustainable 

costs, among other issues. Please see the 

2018 HSTT FEIS/OEIS for additional 

detail. 

Lookouts remain an important 

component of the Navy’s mitigation 

strategy, especially as it relates to 

minimizing exposure to the more 

harmful impacts that may occur within 

closer proximity to the source, where 

Lookouts are most effective. Further, 

NMFS and the Navy are also 

considering, through the adaptive 

management process, whether there are 

additional measures that would be 

practicable to implement that would 

improve effectiveness of Lookouts, such 

as enhanced personnel training. 

As described in the 2023 HSTT 

proposed rule (88 FR 68290, October 3, 

2023), the 2021 U.S. Navy vessel strikes 

were the first known U.S. Navy vessel 

strikes in the HSTT Study Area since 

2009. 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. 

Based on the Navy and NMFS’ 

investigation of these recent strike 

incidents, NMFS found that the Navy 

was substantially following the required 

mitigation protocols, consistent with 16 

U.S.C. 1371(a)(5)(B). These recent vessel 

strike reports (2021, 2023) 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. Given the size of Navy 

vessels and the need to maintain 

specific speeds during certain activities, 

even if a whale is detected, a U.S. Navy 

vessel may not be able to avoid a strike. 

Therefore, given the potential shift in 

factors contributing to vessel strike, and 

the challenges in avoiding potential 

strikes, it is important to ensure that the 

compliance process addresses the 

appropriate number of potential strikes 

and that they are considered in the 

negligible impact determination, which 

is why it was necessary to evaluate the 

authorization of an additional two takes 

by strike. The MMPA provides for the 

authorization of incidental take caused 

by specified activities, provided certain 

findings are made. The law directs 

NMFS to process adequate and 

complete applications for incidental 

take authorization, and issue the 

authorization provided all statutory 

findings and requirements, as well as all 

associated legal requirements, are met. 

It is unclear how having experts that 

can accurately assess the physical and 

mental health of these animals, as 

suggested by the commenter, would 

assist in mitigating the effects of the 

Navy’s activities, nor has the commenter 

provided detail explaining how. The 

required procedural mitigation 

measures are implemented within 

defined ranges based on established 

criteria, and implementation does not 

rely on a visual assessment of 

behavioral or physiological effects to 

animals. In its analysis, NMFS does 

consider the potential impacts of stress 

on marine mammals from exposure to 

the Navy’s activities. Please see the 

Stress Response section of the 2018 

HSTT Proposed Rule for a discussion of 

stress responses in marine mammals. 

Further, since that discussion, 

additional information about stress 

responses has become available (e.g., 

Houser et al. (2020); Houser et al. 

(2021)). However, the additional studies 

do not change the expected potential 

impacts of stress on marine mammals 

from exposure to the Navy’s activities. 

NMFS thoroughly discussed each of 

the strikes with the Navy, and 

summarized the circumstances 

surrounding each strike in the 

Estimated Take From Vessel Strikes and 

Explosives by Serious Injury or Mortality 

section of the 2023 HSTT proposed rule 

((88 FR 68290, October 3, 2023) and the 

Authorized Take From Vessel Strikes 

and Explosives by Serious Injury or 

Mortality section of this final rule. The 

circumstances surrounding whale 

detection ahead of each strike varied. 

However, of note, Navy vessels 

routinely successfully maneuver to 

avoid large whales. 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 


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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 

to avoid whales. 

Comment 19: A commenter, 

referencing two news articles, stated 

that new information indicates that the 

Navy is increasingly using unmanned 

systems, which cannot replace human 

monitoring, even if useful in addition to 

the lookouts and observers NMFS relies 

on to mitigate and monitor the impacts 

of the Navy’s activities on marine 

mammals. 

Response: As stated in the 2023 HSTT 

proposed rule (88 FR 68290, October 3, 

2023), the Navy’s proposed activities 

have not changed from that analyzed in 

the 2018 final rule (83 FR 66846, 

December 27, 2018) or the 2020 final 

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

Impacts from all unmanned systems that 

would be used in training and testing 

activities under this proposed rule have 

been accounted for in the analysis. 

Neither NMFS nor the Navy have 

proposed to replace human marine 

mammal monitoring with monitoring by 

unmanned systems. 

Determinations 

Comment 20: A commenter stated that 

NMFS has neither adequately evaluated 

nor met the negligible impact standard 

for the following reasons: 

1. The negligible impact 

determination dismisses the important 

fact that vessel strikes already pose a 

substantial threat to large whales in the 

region, and several populations are 

already exceeding PBR. Endangered 

blue whales, threatened and endangered 

humpback whales, and endangered fin 

whales off the coast of Southern 

California are particularly vulnerable, 

with even one additional ship strike 

constituting a significant impact. 

2. NMFS has failed to consider the 

impacts of the full scope of training 

exercises over 7 years on marine 

mammals, including joint training 

exercises with foreign fleets. The 

commenter further asserted that what is 

not unsaid in the rule, but is critically 

important, is that the Navy’s activities 

over 7 years (in contrast to the five 

already authorized) has never been 

evaluated under the MMPA, ESA, or 

NEPA. The commenter stated that this 

underscores that NMFS has not taken 

the measures needed to ensure the 

Navy’s activities in the HSTT Study 

Area will have no more than a negligible 

impact on endangered whales and other 

marine mammals in the Pacific Ocean 

over the full 7 years of the proposed 

authorization. NMFS must reexamine 

the increased risk and incidence of 

vessel strikes in light of the Navy’s full 

suite of impacts on large whales and 

other marine mammals (over this 

extended period of time) and decline to 

authorize this additional take. 

Response: NMFS disagrees with the 

commenter’s assertion that it has not 

adequately evaluated nor met the 

negligible impact standard. NMFS 

assessed all of the best available 

information about the relative risk of 

vessel strikes by commercial, 

recreational, and military vessels in the 

Vessel Strike section of this final rule. 

As explained in the Serious Injury or 

Mortality subsection of the Analysis and 

Negligible Impact Determination section 

of the 2018 HSTT final rule, the 2020 

HSTT final rule, and this final rule, 

NMFS may find the impact of the 

authorized take from a specified activity 

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

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, 

including vessel strike from other 

actions). When those considerations are 

applied in the section 101(a)(5)(A) 

context here, the authorized lethal take 

(0.14 annually) of humpback whales 

from the Mainland Mexico- CA/OR/WA 

stock, and blue whales from the Eastern 

North Pacific stock are less than 10 

percent of PBR (less than 1 percent for 

humpback whales from the Mainland 

Mexico- CA/OR/WA stock and 3 percent 

for blue whales from the Eastern North 

Pacific stock). The authorized lethal 

take (0.57 annually) of fin whales from 

the CA/OR/WA stock is less than 10 

percent of PBR also (less than 1 

percent). There are management 

measures in place to address the 

mortality and serious injury from the 

activities other than those the Navy is 

conducting. For the complete discussion 

of how NMFS carefully considered 

potential mortalities from the Navy’s 

activities in light of PBR levels, 

including an explanation for why 

mortality above PBR will not necessarily 

induce population-level non-negligible 

impacts, see the discussion in this rule, 

the 2020 HSTT final rule, and the 2018 

HSTT final rule. 

NMFS acknowledges that the removal 

of a reproductive female (or any female) 

could be more impactful to the status of 

a population than the removal of a male. 

However, the PBR framework that 

supports the negligible impact finding 

inherently considers the likelihood that 

the human-caused mortalities being 

considered may consist of a random 

distribution of individuals of different 

sex in different life stages. Also, beyond 

the low likelihood of striking a whale at 

all, the likelihood of hitting a female is 

even lower. 

It is important to note that the only 

change to the number of takes proposed 

by the 2023 HSTT proposed rule was to 

the take by vessel strike to account for 

new information since publication of 

the 2020 HSTT final rule. The 2020 

HSTT final rule analyzed and 

authorized take of marine mammals 

over a 7-year period, not 5 years as 

noted by the commenter, and NMFS 

conducted the appropriate level of 

MMPA, ESA, and NEPA analysis to 

comply with both statutes during the 

promulgation of the 2020 HSTT final 

rule. 

As stated in the Preliminary Analysis 

and Negligible Impact Determination 

section of the 2023 HSTT proposed rule 

(88 FR 68290, October 3, 2023) and the 

Analysis and Negligible Impact 

Determination section of this final rule, 

while this 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. In consideration of the 

total taking, including take by mortality, 

Level A harassment, and Level B 

harassment, NMFS finds that the 

incidental take from the specified 

activities will have a negligible impact 

on all affected marine mammal species 

and stocks. Consistent with 40 CFR 

1502.9 and the information and analysis 

contained in this final rule, the Navy 

and NMFS as a cooperating agency 

made a determination that this final rule 

and the subsequent LOAs will not result 

in significant impacts that were not 

fully considered in the 2018 HSTT 

FEIS/OEIS. As indicated in the 2023 

HSTT 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 and the Navy reinitiated 

consultation under the ESA. NMFS 

issued a reinitiated Biological and 

Conference Opinion on June 3, 2024 

concluding that the issuance of the 2024 

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 opinion is 


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available at https://doi.org/10.25923/ 

7y9x-vw84. 

Please also see NMFS’ response to 

Comment 7 regarding foreign vessels. 

Comment 21: Commenters stated that 

they oppose this proposed promulgation 

of modified regulations and associated 

LOAs for the Navy because it is not 

consistent with MMPA mandates that 

require NMFS to ensure activities have 

no more than a negligible impact on 

marine mammal species or stocks and 

that they have the least practicable 

adverse impact on marine mammal 

species, stocks, and habitat. In a related 

comment, a commenter stated that this 

rule would disregard the previously 

established boundaries between the 

Navy and NMFS and would also 

disregard the push the United States 

claims to have for the protection of 

marine wildlife. The commenter stated 

that it perceives the request to be 

heavily hypocritical of the same 

government that implemented 

regulations to protect marine wildlife 

that teeter on the edge of the endangered 

species list, to reach for an exception for 

its military, and further that the 

proposed amendment is unethical, 

hypocritical, and unnecessary. 

Response: The MMPA requires NMFS 

to authorize the incidental take of 

marine mammals by specified activities 

upon request if certain findings are 

made (16 U.S.C. 1371(a)(5)(A)). Here, 

the Navy submitted an application 

requesting two additional takes of large 

whales by serious injury or mortality by 

vessel strike through modification of the 

existing regulations and LOAs. As 

required by the MMPA, NMFS 

conducted the analysis described in the 

2023 HSTT proposed rule and this final 

rule and made all required findings 

(preliminarily, in the case of the 2023 

HSTT proposed rule), including finding 

that the Navy’s activities will have a 

negligible impact on marine mammals 

and that the required mitigation 

measures will effect the least practicable 

adverse impact on marine mammals. 

Therefore, promulgation of this final 

rule is appropriate. 

Please see the Mitigation Measures 

section of this final rule for additional 

discussion of the required mitigation 

measures and NMFS’ least practicable 

adverse impact finding. 

Other Regulatory Processes 

Comment 22: A commenter stated that 

the Navy issued an EIS purporting to 

analyze the environmental impacts of its 

training and testing activities in the 

HSTT Study Area. NMFS was a 

cooperating agency for the 2018 HSTT 

FEIS/OEIS. The EIS considered only 

three alternatives in detail: the No 

Action Alternative under which the 

Navy’s training activities would not 

occur; Alternative 1 that considered 

fluctuations in training cycles, testing 

requirements, and deployment 

schedules based on global demand and 

other factors and included the Navy’s 

entire suite of mitigation measures; and 

Alternative 2 that considered a higher 

number of training exercises and sonar 

hours than in Alternative 1 and 

included the Navy’s entire suite of 

mitigation measures. Alternative 1 was 

the preferred and adopted alternative. 

The commenter stated that none of the 

Navy’s alternatives considered in detail 

an alternative that would require 

mandatory speed limits to avoid 

collisions with endangered whales. 

Response: While none of the Navy’s 

alternatives considered in the 2018 

HSTT FEIS/OEIS include mandatory 

vessel speed limits, the Navy conducted 

an operational analysis of potential 

mitigation throughout the entire Study 

Area to consider a wide range of 

mitigation options, including but not 

limited to vessel speed restrictions. As 

discussed in chapter 3, section 

3.0.3.3.4.1 (Vessels and In-Water 

Devices) of the 2018 HSTT FEIS/OEIS, 

Navy ships transit at speeds that are 

optimal for fuel conservation or to meet 

operational requirements. Operational 

input indicated that implementing 

additional vessel speed restrictions 

beyond what is identified in chapter 5 

(Mitigation), section 5.4 (Mitigation 

Areas to be Implemented) of the 2018 

HSTT FEIS/OEIS would be 

impracticable to implement due to 

implications for safety and 

sustainability. In its assessment of 

potential mitigation, the Navy 

considered implementing additional 

vessel speed restrictions (e.g., 

expanding the 10 kn (18.5 km per hour) 

restriction to other activities). The Navy 

determined that implementing 

additional vessel speed restrictions 

beyond what is described in chapter 5 

(Mitigation), section 5.5.2.2 (Restricting 

Vessel Speed) of the 2018 HSTT FEIS/ 

OEIS would be impracticable due to 

implications for safety (the ability to 

avoid potential hazards), sustainability 

(maintain readiness), and the Navy’s 

ability to continue meeting its Title 10 

requirements to successfully accomplish 

military readiness objectives. 

Additionally, as described in chapter 5 

(Mitigation), section 5.5.2.2 (Restricting 

Vessel Speed) of the 2018 HSTT FEIS/ 

OEIS, any additional vessel speed 

restrictions would prevent vessel 

operators from gaining skill proficiency, 

would prevent the Navy from properly 

testing vessel capabilities, or would 

increase the time on station during 

training or testing activities as required 

to achieve skill proficiency or properly 

test vessel capabilities, which would 

significantly increase fuel consumption. 

As discussed in chapter 5 (Mitigation), 

section 5.3.4.1 (Vessel Movement) of the 

2018 HSTT FEIS/OEIS, the Navy 

implements mitigation to avoid vessel 

strikes throughout the Study Area. 

Additionally, this final rule includes 

two new mitigation measures beyond 

that required by the 2020 HSTT final 

rule and modification of two existing 

mitigation measures. These measures 

are described in response to Comment 

15 and the Mitigation Measures section 

of this final rule. 

Comment 23: A commenter stated that 

agencies must prepare supplemental 

EISs if: ‘‘(i) The agency makes 

substantial changes in the proposed 

action that are relevant to 

environmental concerns; or (ii) There 

are significant new circumstances or 

information relevant to environmental 

concerns and bearing on the proposed 

action or its impacts’’ (40 CFR 

1502.9(d)(1)). The commenter stated 

that because these triggers have been 

met, it urges NMFS to prepare a 

supplemental EIS on the basis of the 

new information that has come to light 

since 2018, including on the impacts of 

vessel strikes on large whales and on 

alternatives that reduce vessel strike 

impacts to marine mammals. 

Response: NMFS disagrees with the 

commenter that supplemental NEPA 

evaluation is warranted. As described in 

the National Environmental Policy Act 

section herein, consistent with 40 CFR 

1502.9(d) and the information and 

analysis contained in this rule, the Navy 

and NMFS as a cooperating agency have 

determined that this final 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 final rule and 

a supplemental information report 

prepared by NMFS, the Navy has made 

no substantial changes to the activities 

that are relevant to environmental 

concerns; nor are there substantial new 

circumstances or information about the 

significance of adverse effects that bear 

on the analysis. 

Comment 24: A commenter stated that 

despite the new 2020 authorization— 

and the additional extensive take and 

other impacts it enables—NMFS has not 

completed new ESA consultation or a 

supplemental NEPA evaluation. The 

Navy is operating under the 2018 BiOp 

and 2018 EIS. Since NMFS issued the 

2018 BiOp and EIS, a slew of new 

information—in addition to the 

expanded scope of the Navy’s 


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activities—indicates that the Navy’s 

activities in the HSTT Study Area are 

likely affecting ESA-listed species to an 

extent not previously considered. 

In a related comment regarding ESA 

compliance, a commenter stated that the 

proposed rule states, ‘‘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.’’ The 

commenter noted that when reinitiation 

is required, ‘‘the original opinion loses 

its validity, as does its accompanying 

incidental take statement, which then 

no longer shields the action agency from 

penalties for takings’’ (Ctr. for Biological 

Diversity v. BLM, 698 F.3d 1101, 1108 

(9th Cir. 2012)). A commenter stated 

that it awaits the conclusion of this 

reinitiated consultation and expects a 

revised biological opinion that fully 

complies with the ESA’s standards. 

Response: NMFS has fully complied 

with the ESA and NEPA. NMFS 

described the ESA section 7 

consultation history for this action in 

the Endangered Species Act section of 

the 2023 HSTT proposed rule and this 

final rule. As described in that section, 

NMFS 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 the revised 

regulations and LOAs under section 

101(a)(5)(A) of the MMPA. On June 3, 

2024, NMFS issued a 2024 reinitiated 

Biological and Conference Opinion 

concluding that the issuance of the rule 

and subsequent LOAs is 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 2024 

reinitiated Biological and Conference 

Opinion for this action is available at 

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

national/marine-mammal-protection/ 

incidental-take-authorizations-militaryreadiness-activities. 

NMFS is aware of the statement in 

Ctr. for Biological Diversity v. BLM, 698 

F.3d 1101, 1108 (9th Cir. 2012) 

referenced by the commenter. NMFS’ 

position is that a biological opinion, 

including its Incidental Take Statement, 

for which formal consultation has been 

re-initiated remains valid and effective 

during the consultation and until a new 

biological opinion is issued. When the 

new biological opinion with a new ITS 

is issued, it supersedes and replaces the 

previous opinion and ITS. 

Please see NMFS’ response to 

Comment 23 regarding NEPA 

compliance. 

Changes From the Proposed Rule to the 

Final Rule 

NMFS has added two additional 

reporting requirements since 

publication of the 2023 HSTT proposed 

rule. First, the Navy’s annual HSTT 

Training Exercise Report and Testing 

Activity Report must include 

information that tracks the Navy’s 

implementation of the new SOCAL large 

whale aggregation real-time reporting 

mitigation measure. The report must 

include the following information for 

each instance that an aggregation of 

large whales is reported: (1) the date, 

time and general location (e.g., 

approximately 10–12 nmi SE of San 

Clemente Island) of the whales when 

the aggregation was first sighted; (2) the 

total number of whales observed within 

1 nmi of a Navy vessel that make up the 

aggregation; and (3) the approximate 

distance (or distances if more than one 

group of whales is sighted) of the vessel 

from the whales in the aggregation when 

the whales were first sighted. To the 

extent practicable, this information 

should be provided in the Navy’s 

unclassified version of these reports. 

Second, the Navy’s annual HSTT 

Training Exercise Report and Testing 

Activity Report must include a 

confirmation that foreign military use of 

sonar and explosives, when such 

militaries are participating in a U.S. 

Navy-led exercise or event, combined 

with the U.S. Navy’s use of sonar and 

explosives, would not cause exceedance 

of the analyzed levels (within each 

NAEMO modeled sonar and explosive 

bin) used for estimating predicted 

impacts, which formed the basis of the 

acoustic impacts effects analysis used to 

estimate take in this final rule. 

NMFS has also made a nonsubstantive name change in the final 

rule. Ziphius cavirostris has multiple 

common names. In the 2018 HSTT final 

rule, 2020 HSTT final rule, and 2023 

HSTT proposed rule, NMFS used the 

common name Cuvier’s beaked whale. 

In this final rule, NMFS uses the 

common name goose-beaked whale 

instead. 

Last, NMFS made several nonsubstantive changes to the regulations to 

add clarity and improve readability. 

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, 

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 authorized. Two marine 

mammal species, the Hawaiian monk 

seal and the Main Hawaiian Islands 

Insular DPS of false killer whale, have 

critical habitat designated under the 

ESA (16 U.S.C. 1531 et seq.) in the 

HSTT Study Area. 

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), BIAs, national marine 

sanctuaries (NMSs), and unusual 


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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 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 final 

regulations. 

NMFS has reviewed the 2023 SARs 

(Carretta et al. 2024, Young et al. 2024). 

For all species except humpback whale, 

NMFS determined that neither the SARs 

nor any other new information changes 

our determination in the 2020 HSTT 

final rule of which species or stocks 

have the potential to be affected by the 

Navy’s activities. For humpback whale, 

the 2023 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 final 

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 2023 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, therefore, 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 

population MMPA ESA 

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 ................. - 791 (0.29)/623. 

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 Threatened 1 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.- 864 (0.40)/625. 

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

Depleted 

Endangered Hawaii ................. Summer 391 (0.9)/204. 

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. 


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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 

population MMPA ESA 

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

macrocephalus.

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

Depleted 

Endangered Southern California.- 2,606 (0.135)/ 

2,011. 

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. 

Goose-beaked whale 2 .. 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 ................. - 112 (0.24)/92. 

Oahu ............................. - - Hawaii ................. - 112 (0.17)/97. 

Maui Nui 3 ..................... - - Hawaii ................. - 64 (0.15)/56. 

Hawaii Island ................ - - Hawaii ................. - 136 (0.43)/96. 

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

Insular 4.

Strategic, 

Depleted 

Endangered Hawaii ................. - 167 (0.14)/149. 

Hawaii Pelagic .............. - - Hawaii ................. - 5,528 (0.35)/ 

4,152. 

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. 

Maui Nui 3 ..................... - - Hawaii ................. - unknown. 

Hawaii Island ................ - - Hawaii ................. - unknown. 

Hawaii Pelagic .............. - - Hawaii ................. - 67,313 (0.27)/ 

53,839. 

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 ................... - - Southern California.- 6,336 (0.32)/ 

4,817. 

Hawaii ........................... - - Hawaii ................. - 6,979 (0.29)/ 

5,283. 

Rough-toothed dolphin Steno bredanensis ....... NSD 5 ............................ - - Southern California.- unknown. 

Hawaii ........................... - - Hawaii ................. - 83,915 (0.49)/ 

56,782. 

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 ................. - 19,242 (0.23)/ 

15,894. 

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

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


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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 

population MMPA ESA 

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. 

Hawaii ........................... - - Hawaii ................. - 64,343 (0.28)/ 

51,055. 

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 ................. - 1,564 (0.05)/ 

1,444. 

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. 2Ziphius cavirostris has multiple common names. In the 2018 HSTT final rule, 2020 HSTT final rule, and 2023 HSTT proposed rule, NMFS used the common name 

Cuvier’s beaked whale. In this final rule, NMFS uses the common name goose-beaked whale instead. 3The ‘‘4-Islands’’ stocks of common bottlenose dolphin and pantropical spotted dolphin are now the ‘‘Maui Nui’’ stocks. 

4 NMFS relied on the 2022 final SAR for this stock. 

5 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. 

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. 

At the time of publication of the 2023 

HSTT proposed rule, there was an 

active UME for gray whales which 

NMFS fully considered in its analysis 

(88 FR 68290, October 3, 2023). This 

UME was closed on November 9, 2023. 

The UME involved 690 gray whale 

strandings, including 347 in the United 

States, 316 in Mexico, and 27 in Canada. 

Strandings occurred from Alaska to 

Mexico along the west coast of North 

America, including in the whale’s 

wintering, migratory, and feeding areas. 

The Investigative Team concluded that 

the preliminary cause of the UME was 

localized ecosystem changes in the 

whale’s Subarctic and Arctic feeding 

areas that led to changes in food, 

malnutrition, decreased birth rates, and 

increased mortality all documented 

during the UME. Please see https://

www.fisheries.noaa.gov/national/ 

marine-life-distress/2019-2023-easternnorth-pacific-gray-whale-ume-closed for 

additional information on this UME. 

Biologically Important Areas 

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, goose-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. 

Since publication of the 2023 HSTT 

proposed rule, Calambokidis et al. 

(2024) identified updated BIAs on the 

West Coast of the U.S. The HSTT Study 

Area overlaps feeding BIAs for blue 

whale and fin whale in SOCAL. 

Additionally, it overlaps a reproductive 

BIA as well as northbound and 

southbound migratory BIAs for gray 

whale. Please see Calambokidis et al. 

(2024) 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 Analysis and Negligible 

Impact Determination section considers 

the content of this section, the 

Estimated Take section, and the 

Mitigation Measures section, to draw 

conclusions regarding the likely impacts 

of these activities on the reproductive 

success or survivorship of individuals 

and whether those impacts are 

reasonably expected to, or reasonably 

likely to, adversely affect the species or 

stock through effects on annual rates of 

recruitment or survival. 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), 


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physiological responses (particularly 

stress responses), behavioral 

disturbance, or habitat effects. Further, 

in the 2023 HSTT proposed rule, we 

summarized any new relevant 

information from the scientific literature 

since publication of the 2020 HSTT 

final rule. We do not repeat the 

information here, all of which remains 

current and applicable, but 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 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 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 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). 

NMFS has reviewed new relevant 

information from the scientific literature 

since publication of the 2023 HSTT 

proposed rule. Further, in the 2023 

HSTT proposed rule, we summarized 

any 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 2023 

HSTT proposed rule are presented 

below. The literature generally falls into 

the following topic areas: Vessel Strike; 

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 

Dunlop (2024) studied migrating east 

Australian humpback whales’ response 

to approaching vessels to determine if 

individuals exhibited an avoidance 

response. While some select groups did 

display changes in their movements, the 

sampled collective did not display any 

consistent vessel avoidance response. 

Furthermore, the degree of avoidance 

was lower as vessels approached at 

faster speeds. Overall, the results 

showed that humpbacks were generally 

unresponsive to approaching vessels 

regardless of the speed or noise level at 

which they approached. Female-calf 

pairs proved to be the biggest exception 

to this pattern; though this demographic 

did not exhibit a consistent response as 

a whole, these pairs were more likely to 

change their travel pattern more than 

any other group. Due to the lack of 

response from the population, the 

results suggest that implementation of 

vessel strike avoidance protocols is 

critical for successfully conserving large 

whale populations. 

Redfern et al. (2024) developed a new 

metric for analyzing vessel strike risk 

reduction (‘‘PLETHd’’) and applied it to 

North Atlantic right, humpback, fin, and 

sei whale distributions along the U.S. 

East Coast. The metric is calculated 

using three parameters: the relationship 

between vessel speed and the 

probability that a strike is lethal, vessel 

transit distance, and whale 

distributions. The authors compared the 

impact of a 14 kn (25.9 km/hr) vs. 10 kn 

(18.5 km/hr) speed restriction and found 

that only the 10 kn (18.5 km/hr) 

reduction substantially reduced risk. 

The authors also found that applying a 

10 kn (18.5 km/hr) speed restriction 

within multiple whale species’ critical 

habitat zones was almost as effective as 

enacting the same speed restriction 

along the entire East Coast Exclusive 

Economic Zone (EEZ). The results 

suggest that 10 kn (18.5 km/hr) speed 

restrictions are a robust method for 

reducing vessel strike risk and that 

vessel restrictions within high-density 

core areas of a marine mammal’s habitat 

can be highly impactful. 

Hearing, Vocalization, and Masking 

Parnell et al. (2024) studied the 

soundscapes of four underwater 

Hawaiian monk seal critical habitats, 

including measurement of ambient 

noise and characterization of detected 

sound sources. The authors observed 

diel patterns in both anthropogenic and 

biological sound sources that mask 

acoustic communication in Hawaiian 

monk seals. The measurements 

collected for this study provide a 

baseline for future research on impacts 

of anthropogenic activities on these 

soundscapes. 

A multi-national team of scientists 

(U.S. and Norway) obtained the first 

hearing measurements of a mysticete 

species through auditory evoked 

potential (AEP) tests. During the 2023 

field season, AEP tests were conducted 

on two adolescent female minke whales 

in Norway (Houser et al. 2024). Houser 

et al. (2024) indicate that the minke 

whale’s upper-frequency limit of 

hearing occurs somewhere between 45 

to 90 kHz. Minke whale’s highfrequency sensitivity is hypothesized to 

support detection of the echolocation 

clicks of one their predators, the killer 

whale. The bandwidth of the tone-bursts 

used in the Houser et al. (2024) AEP 

testing was too broad to define the 

precise upper-frequency limit, but 

indicates this species is more sensitive 

to higher frequencies than previously 

predicted based on inner ear anatomy 

and vocalization data (Southall et al. 

2019; NMFS 2024). Results from their 

final 2024 field season, which included 

further examination of the upperfrequency limit of hearing, are expected 

to be published in 2025, with 

preliminary data from two additional 

whales indicating that minke whale 

hearing is best around 32 kHz. 

Hearing Loss (TTS and PTS) 

Gransier and Kastelein (2024) 

examined TTS susceptibility in harbor 

porpoises and harbor seals based on 

exposures varying in frequency range 

and level. Specifically, exposures 

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octave noise bands at frequencies 

covering the entire hearing range of each 

species. Despite these species having 

different audiograms and regions of best 

sensitivity (i.e., underwater pinnipeds 

are sensitive to sounds ranging from 

approximately 0.01 to 40–60kHz, while 

most odontocetes are sensitive sounds 

ranging from approximately 0.25 to 80– 

125kHz), the frequency-specific 

susceptibility to TTS was similar 

amongst both species, with the greatest 

susceptibility to TTS occurring at 

frequencies from 22.5 to 50 kHz and 

least susceptible to sounds below 10 

kHz. The frequency of minimum TTS 

for the harbor seal aligns with its 

frequency of best hearing, while 

frequency of minimum TTS for the 

harbor porpoise is well below the 

frequency of best hearing. This study 

illustrates that the audiogram does not 

always serve as a good predictor of 

frequency-dependent susceptibility to 

TTS, with the pattern of susceptibility 

to TTS in these two species being more 

comparable than their audiograms. 

Brewer et al. (2023) described 41 call 

types of Cook Inlet beluga vocal 

behavior and classified them into three 

categories: (1) whistles, (2) pulsed calls, 

and (3) combined calls. These are the 

first descriptions of vocal repertoire of 

this species in two critical habitat 

locations and across multiple seasons. 

Call types were then used to investigate 

the potential for masking from 

commercial ship noise. It was found 

that call types (0–12 kHz) were partially 

masked by distant ship noise and 

completely masked by close ship noise. 

This study provides evidence that ship 

noise can impact vocal communication 

of this population. Specifically Cook 

Inlet beluga vocalizations in the Susitna 

area, seven of the beluga’s most 

common calls are either partially or 

fully masked by commercial ship traffic. 

Kastelein et al. (2024) examined TTS 

in two California sea lions exposed to 

one-sixth-octave noise band centered at 

32 kHz for 60-minutes of exposure, 

resulting in cumulative sound exposure 

levels (SELcum) ranging from 168 to 192 

dB. Hearing after exposure was 

examined at the center frequency of the 

fatiguing sound (32 kHz) and at half an 

octave (44.8 kHz) and one octave above 

the center frequency (63 kHz). Higher 

SELcum resulted in greater threshold 

shifts. Furthermore, the greatest TTS 

occurred at half an octave above the 

center frequency, with TTS onset (6 dB 

threshold shift) measured at 44.8 kHz 

occurring at a 179 dB SELcum. TTS 

patterns and recovery was similar 

between the two individuals, with TTSs 

up to 6.7 dB recovering within 8 

minutes of exposure, TTSs up to 12 dB 

recovering within an hour, and only the 

highest TTS measured (12.9 dB) taking 

over an hour to recover. The results of 

this study were directly incorporated in 

the Navy’s updated Phase IV AUD INJ/ 

TTS criteria and indicate that California 

sea lions have lower AUD INJ/TTS onset 

than previously predicted (Southall et 

al. 2019). 

Behavioral Reactions 

Ceciarini et al. (2023) tested the 

efficacy of Acoustic Deterrent Devices 

for minimizing common bottlenose 

dolphin interactions with trammel nets 

in the Northern Tyrrhenian Sea. The 

authors used interactive pingers which 

emitted output signals ‘‘from 5 up to 

500 kHz at 168 dB re 1 mPa at 1 m as 

random high-speed tones FM ranging 

from 100 ms up to seconds’’. The study 

found that catch damage from dolphins 

was significantly lower in nets where 

pingers were used. 

Elmegaard et al. (2023) exposed six 

harbor porpoises to Acoustic 

Harassment Devices (AHDs), commonly 

referred to as ‘‘seal scarers’’, to 

determine if they would exhibit any 

physiological or behavioral reactions. 

The AHDs pulsed at 14 kHz with a 

source level of 189 dB re 1 mPa (rms) or 

sound exposure level of 184 dB re 1 

mPa2s, with porpoise RLs ranging from 

98–132 dB re 1 mPa. All individuals 

sampled exhibited a mixture of 

behavioral or physiological responses, 

including startling, increased distance 

from the sound source, increased swim 

speed, diving, altered echolocation 

patterns, cardiac responses, or altered 

respiration patterns. Overall, responses 

were observed in every individual up to 

7 km or down to an RL of 98 dB re 1 

mPa. 

Frankish et al. (2023) followed ten 

harbor porpoises for 5 to 10 days to 

observe their reactions to ship traffic 

around Denmark. The porpoises spent 

over half of the study period within 10 

km of a ship, and a third of the study 

period exposed to noise levels above 

ambient. The porpoises responded by 

moving away from ships during the day, 

and diving deep during the night. They 

had a higher likelihood of altering their 

movements when louder ships were 

nearby (maximum probability of 

deterrence = 12.2 percent during the day 

and 14.9 percent at night), and moved 

an average of 3.2 km away from 13.6 

different ships every day. Deeper dives 

occurred less frequently, at a rate of 5.7 

different ships per individual per night. 

The porpoises also reacted to loud ships 

that were far away (>2 km at 93 ± 14 dB 

re 1 mPa2), though responses occurred 

less frequently (5 to 9 percent of the 

time vs. up to 14.9 percent of the time 

at close range). 

Southall et al. (2023) used control 

exposure experiments (CEEs) to provide 

the first results in examining the impact 

of mid-frequency navy sonar (3.5–4.1 

kHz) or pseudorandom noise (similar 

frequency, duration and source and 

received level compared to midfrequency sonar) on fin whale behavior 

in feeding habitats of the Southern 

California Bight. Of the 15 exposed fin 

whales, only five individuals 

demonstrated a mild to moderate 

behavioral changes (avoidance, changes 

in feeding, diving, or respiration), with 

no changes demonstrated for whales in 

the six control exposures. Compared to 

blue whales, fin whale behavioral 

responses were more limited in 

occurrence, severity and duration and 

were found to be less dependent upon 

contextual aspects of exposure, with 

received level as the primary factor 

associated with behavioral responses. 

Additionally, foraging success was not 

compromised by exposures from this 

study. The authors note that differences 

observed between behavioral response 

in fin whales in this study and blue 

whales in previously published studies 

may be attributed to the smaller sample 

size associated with this study. 

However, as seen in blue whales, fin 

whale behavior returned to baseline 

conditions after noise exposure ended. 

Methodology for Assessing Acoustic 

Impacts 

Indeck et al. (2024) assessed North 

Atlantic right whale, fin, and blue whale 

detectability by Slocum gliders near 

heavily used shipping lanes in the Gulf 

of St. Lawrence, Canada. The goal of the 

study was to evaluate the gliders’ 

suitability as a passive acoustic 

monitoring platform for whale detection 

in areas with high anthropogenic noise 

levels. The authors found that shipping 

lane noise did not substantially impact 

whale detectability, as calls from the 

highly trafficked areas were not masked 

significantly more than calls in quieter 

areas nearby. The gliders were therefore 

identified as a viable PAM platform to 

use in and around busy shipping areas. 

These results suggest that gliders could 

be an important tool for monitoring 

mysticetes in highly industrialized areas 

and assisting in ongoing dynamic 

management initiatives. 

Conclusion for New Pertinent Science 

Since Publication of the 2023 HSTT 

Proposed Rule 

Having considered the best scientific 

information available, specifically new 

relevant information published since 

the 2023 HSTT proposed rule, we have 


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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 authorizing, 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 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 

authorized 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 

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). 

Authorized takes will 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) 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. 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) 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, 

either directly or via the effects of TTS 

(both equated to Level B harassment) or 

PTS of some degree (equated to Level A 

harassment). Thresholds have also been 

developed to identify the pressure levels 

above which animals may incur nonauditory injury from exposure to 

pressure waves from explosive 

detonation. We described the acoustic 

thresholds and the methods used to 

determine thresholds 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, and 2023 HSTT proposed 

rule, we described new relevant 

information from the scientific literature 

since publication of the 2018 HSTT 

final rule and 2020 HSTT final rule, 

respectively. Since publication of the 

2023 HSTT proposed rule, NMFS has 

updated our Technical Guidance 

(NMFS, 2024) containing updated 

acoustic criteria for auditory injury (89 

FR 36762, October 24, 2024). The 

Technical Guidance provides updated 

auditory injury thresholds, where 

appropriate, as well as revised 

weighting functions, in some cases. For 

impulsive sources, the Updated 

Technical Guidance’s auditory injury 

thresholds generally remain identical or 

are higher compared to our 2018 

Technical Guidance, meaning that 

received levels would need to be higher 

in order for marine mammals to be 

expected to incur auditory injury. The 

exceptions are for phocid pinnipeds 

(PW), where the cumulative SEL 

threshold, in the Updated Technical 

Guidance, is 2 dB lower and for otariid 

pinnipeds (OW) where the peak sound 

pressure level threshold is 2 dB lower 

and the cumulative SEL threshold is 18 

dB lower. As for the Updated Technical 

Guidance’s weighting functions, for MF 

cetaceans (now called HF cetaceans in 

the updated document) and HF 

cetaceans (now called VHF cetaceans in 

the updated document), the weighting 

functions reflect a higher susceptibility 

to auditory injury at frequencies below 

10 kHz, as compared to the 2018 

Technical Guidance. Other minor 

changes/shifts to weighting functions 

(e.g., for LF cetaceans, PW pinnipeds, 

OW pinnipeds) were also included. This 

new information was not available in a 

timeframe in which NMFS could have 

incorporated it into the quantitative 

analysis supporting this final 

rulemaking; however, NMFS did 

consider the information qualitatively. 

While these changes in the auditory 

injury thresholds and weighting 

functions could result in minor 

increases in PTS exposure estimates for 

some species, given the conservative 

assumptions built into the take estimate 

methodology, they would not be 

expected to result in meaningful, if any, 

changes in take estimates and would not 

be expected to change any of the 

findings. 

Navy’s Acoustic Effects Model 

The Navy proposed 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, and see the discussion of 

the 2024 Technical Guidance in the 

Acoustic Thresholds section above. 


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Range to Effects 

The Navy proposed 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 final rule, 

including equipment and sources used 

and exercises conducted. 

As described above in the Acoustic 

Thresholds section, since publication of 

the 2023 HSTT proposed rule, NMFS 

has updated our Technical Guidance 

(NMFS, 2024) containing updated 

acoustic criteria for auditory injury (89 

FR 36762). Please see that section for a 

full discussion of the updates. This new 

information was not available in a 

timeframe in which NMFS could have 

incorporated it into the quantitative 

analysis supporting this final 

rulemaking; however, NMFS did 

consider the information qualitatively. 

While these changes in the auditory 

injury thresholds and weighting 

functions could result in minor 

increases in PTS exposure estimates for 

some species, given the conservative 

assumptions built into the take estimate 

methodology, they would not be 

expected to result in meaningful, if any, 

changes in take estimates and would not 

be expected to change any of the 

findings. 

Therefore, the ranges to effects in this 

final 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. 

Marine Mammal Density 

The Navy proposed 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 2023 final SARs (Carretta 

et al. 2024, Young et al. 2024). 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 (Carretta 

et al. 2023, Young et al. 2023), 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 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 uses 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 


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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 

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 

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 Authorized 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 Authorized 

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 final 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 Authorized Harassment 

Take from Testing Activities and 

Authorized Harassment Take from 

Training Activities sections below for 

the authorized annual and 7-year total 

number and type of Level A harassment 

and Level B harassment for each 

humpback whale stock. 

Authorized 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 


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requested no change to this authorized 

take, though as described above, NMFS 

has since published the 2023 final, 

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. 

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. 

Authorized 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. 

Authorized 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 


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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 

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 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 

strikes of large whales in SOCAL 

attributed to 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 


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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 (176 km) 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 

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) 1 hour 

before the estimated strike time, at 10 

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 (129.6 km) 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 (9.3 km per hour) 

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 kn (31.5 km 

per hour) to 10 kn (18.5 km per hour) 

at 7:22 p.m. 

While in this incident a whale was 

discovered impinged on the bow of a 

Navy vessel, this incident is very 

different from the discovery of two fin 

whales discovered impinged on the 

sonar dome of a Royal Australian Navy 

vessel in 2021 when the vessel came to 

port at Naval Base San Diego. 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 March 2024 a dead fin whale was 

discovered off of Pier 10 in Naval 

Station San Diego within the Navy’s 

security barrier. The security barrier, 

which consists of a series of connected 

floating sections, is intended to 

discourage unauthorized boat entry to 

the piers. The necropsy indicated that 

vessel strike was the most likely cause 

of death. Given the location the whale 

was discovered, this could have been 

the result of a military vessel strike. 

However, the Navy reviewed its vessel 

activity during that time frame and 

available observations of those vessels 

coming and going to port, as well as at 

port, and determined it was unlikely 

that the whale was carried into port by 

a Navy vessel. Based on this and other 

information from Navy’s investigation, 

we cannot determine whether this 

whale was struck by a Navy vessel 

during HSTT activities or was struck by 

a commercial or other vessel and drifted 

into the Navy pier area. 

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 vessels 

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. The 

Navy has 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 


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chain of command give NMFS a high 

level of confidence that all strikes are 

reported. 

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 

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 2017–2023, 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 period 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 at the time that the 

analysis was conducted) 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 


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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 at 

the time the analysis was conducted 

(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 from mid-2023 

through 2025, and a 32, 9, and 2 percent 

chance that one, two, or three whales, 

respectively, would be struck over that 

period. Further, there is an estimated 11 

percent chance that the Navy would 

strike more than one large whale from 

mid-2023 through 2025. We have 

assessed these probabilities and 

determined that the strike of 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 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, porpoise, or small 

whale being struck by a vessel as a 

result of Navy activities. A 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 authorizing) 

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, 2020 HSTT final rule, and 2023 

HSTT proposed 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. 2024 and Young et al. 2024), 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. (Note that since publication of 

the 2023 HSTT proposed rule, Carretta 

et al. (2023), which includes vessel 

strike data through 2021 has published, 

but NMFS included this data in its 

analysis through the unpublished NMFS 

vessel strike data for 2019–2021, 

referenced above). 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 period of the rule (2.5 

years at the time of the analysis) 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 (since published in 

Caretta et al. (2023)) for California on 

known annual rates of large whale 

serious injury or mortality from vessel 

collisions (this data includes the strike 

of two 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 

2023 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 2023 SAR 

(or draft 2023 SAR, where relevant) 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). 


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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 

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).

1 b ........................ 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 

Hawaii ........................................................ ........................ 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 at the 

time of the analysis; 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) ............ 7.74 b 0.60 b

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 


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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—Continued 

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 

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 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 

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 authorized annual 

mortality. 

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 

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 .......................... 7.74 2 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 SOCAL 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 2023 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 


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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 one 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 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 (three gray whale 

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

two or three fin whale strikes by the 

U.S. Navy (2009, potentially 2023), and 

two 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 

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 period of the rule. 

Therefore, we find that, of the five total 

takes by serious injury or mortality by 

vessel strike of large whales authorized 

over the course of the 7-year rule, 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 expect that, of the five 

total takes by serious injury or mortality 

by vessel strike of large whales 

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 period 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 at the time of 

the analysis). 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 period 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 period 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 


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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 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 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 authorized. 

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 

period of the rule (more than twice that 

of the species with the next highest 

percentage, gray whale), NMFS 

authorizes 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 authorizing 

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 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 

HSTT Study 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., one, two, or four 

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 makes no changes to the 

authorization of take by M/SI as a result 

of explosive use as the Navy made no 

changes to its activities from that 

described in the 2018 HSTT final rule, 

and after reviewing all new information, 


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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). 

we find that our previous analyses 

remain applicable. Please refer to the 

2018 HSTT final rule and 2020 HSTT 

final rule for additional information. 

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 

describe below. This final rule includes 

all mitigation measures required by the 

2020 HSTT final rule (though two have 

been modified in this final 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 


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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 

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 will 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 

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 the 

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 final 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 final 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, 


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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, recently published 

West Coast BIAs (Calambokedis et al. 

2024), 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. 

This final 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) will be considered an 

aggregation under this measure)). This 

measure will 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. 

In addition to Lookouts required 

under this 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 Reporting section for additional 

detail on this 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 final 

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 

additional mitigation areas (beyond 

those already identified with associated 

measures to reduce impacts to marine 

mammals) to further protect marine 

mammals, including odontocetes with 

small or resident populations in the 

HSTT Study Area, and large whales 

with feeding, reproductive, and 

migratory BIAs in the HSTT Study Area. 

This includes consideration of new 

mitigation areas that could be based on 

newly identified BIAs in Hawaii 

(Kratofil et al. 2023) and on the West 

Coast (Calambokidis et al. 2024). The 

HRC overlaps BIAs identified in Kratofil 

et al. (2023) for humpback whale, 

spinner dolphin, short-finned pilot 

whale, rough-toothed dolphin, pygmy 

killer whale, pantropical spotted 

dolphin, melon-headed whale, false 

killer whale, dwarf sperm whale, goosebeaked whale, common bottlenose 

dolphin, and Blainville’s beaked whale. 

All of the BIAs that overlap the HRC are 

small and resident population BIAs, 

with the exception of the humpback 

whale reproductive BIA. SOCAL 

overlaps BIAs identified in 

Calambokidis et al. (2024) for blue 

whale (feeding area), fin whale (feeding 

area), and gray whale (migratory route). 

Additional restrictions in mitigation 

areas beyond those restrictions and 

areas included in the 2020 HSTT final 

rule (including mitigation to reduce 

vessel strike risk such as vessel speed 

restrictions, and in consideration of the 

newly identified BIAs (Kratofil et al. 

2023 and Calambokidis et al. 2024)) is 

impracticable given overlap with critical 

Navy training areas in the HRC and 

SOCAL. However, many of the BIAs 


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identified in Kratofil et al. 2023 and 

Calambokidis et al. (2024) partially or 

fully overlap the mitigation areas 

included in the 2020 HSTT final rule 

and this final rule and are aimed at 

reducing impacts to the same species for 

which Kratofil et al. 2023 and 

Calambokidis et al. (2024) identified 

BIAs. In the HRC, the existing 

mitigation areas are targeted and 

expected to reduce impacts to 

humpback whales, false killer whales, 

dwarf sperm whales, pygmy killer 

whales, short-finned pilot whales, 

melon-headed whales, bottlenose 

dolphins, spotted dolphins, spinner 

dolphins, rough-toothed dolphins, 

goose-beaked whales, and Blainville’s 

beaked whales (i.e., all species for 

which Kratofil et al. (2023) identified 

BIAs). In SOCAL, the existing mitigation 

areas are aimed at reducing impacts to 

blue whales, fin whales, and gray 

whales (i.e., all species for which 

Calambokidis et al. (2024) identified 

BIAs). Further, as included in the 2023 

HSTT proposed rule, this final rule 

requires that 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 a select area of SOCAL, and 

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. Last, this 

final rule includes modification of two 

mitigation measures from the 2020 

HSTT final rule (85 FR 41780; July 10, 

2020) to further reduce the potential for 

vessel strike. 

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: 

• 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 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 When a vessel is 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. 


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TABLE 8—SUMMARY OF PROCEDURAL MITIGATION—Continued 

Stressor or activity Mitigation zone sizes and other requirements 

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. These notifications would be issued to Navy vessels within this boundary only. 

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) 

• 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 spring 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 to personnel on vessels 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 is requiring 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 determined that the 

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 NMFS has included in 

this final rule, which ensures that 

mitigation is regularly assessed and 


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provides a mechanism to improve the 

mitigation, based on the factors above, 

through modification as appropriate. 

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 

proposed 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 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 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 

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 proposed 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. 

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 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 


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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, in 2023, we proposed 

requiring the Navy to report changes in 

its Lookout policies to NMFS as soon as 

practicable after a change is made. This 

final rule requires the Navy to 

implement that reporting measure, as 

well as two new measures that were not 

included in the 2023 HSTT proposed 

rule, described below. 

The Navy’s annual HSTT Training 

Exercise Report and Testing Activity 

Report must include information that 

tracks the Navy’s implementation of the 

new SOCAL large whale aggregation 

real-time reporting mitigation measure. 

The report must include the following 

information for each instance that an 

aggregation of large whales is reported: 

(1) the date, time and general location 

(e.g., approximately 10–12 nmi (18.5 to 

22.2 km) SE of San Clemente Island) of 

the whales when the aggregation was 

first sighted; (2) the total number of 

whales observed within 1 nmi (1.8 km) 

of a Navy vessel that make up the 

aggregation; and (3) the approximate 

distance (or distances if more than one 

group of whales is sighted) of the vessel 

from the whales in the aggregation when 

the whales were first sighted. To the 

extent practicable, this information 

should be provided in the Navy’s 

unclassified version of these reports. 

The Navy’s annual HSTT Training 

Exercise Report and Testing Activity 

Report must include a confirmation that 

foreign military use of sonar and 

explosives, when such militaries are 

participating in a U.S. Navy-led exercise 

or event, combined with the U.S. Navy’s 

use of sonar and explosives, would not 

cause exceedance of the analyzed levels 

(within each NAEMO modeled sonar 

and explosive bin) used for estimating 

predicted impacts, which formed the 

basis of the acoustic impacts effects 

analysis used to estimate take in this 

final rule. The purpose of this new 

reporting measure is for the Navy to 

confirm annually that the Navy has 

accounted for foreign military 

participation in its annual report, 

without requiring the Navy to 

quantitatively account for foreign 

military activity. The Navy informed 

NMFS that it would be difficult for the 

Navy to quantify foreign military 

activities as a subset of its total activities 

because the Navy does not track 

activities conducted by foreign vessels 

in this manner. Furthermore, the annual 

reported takes from Navy activities are 

calculated the same regardless of 

whether the activity was conducted by 

a foreign military or not. 

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 final 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 final rule and 

the 2020 HSTT final rule (where the 

activities, species and stocks, potential 

effects, and mitigation measures (except 

as modified above) are the same as for 

this rulemaking), we 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 fitness-level impacts to 

individuals, etc.). For this final rule, we 

evaluated the likely impacts of the 

enumerated maximum number of 

harassment takes that were reasonably 

expected to occur and are authorized, 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 proposed 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 and the 

additional reporting requirements 

described previously. 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 


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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 

recently closed 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 2023 Pacific and 

Alaska SARs (Carretta et al. 2024; 

Young et al. 2024). 

As described above, since publication 

of the 2023 HSTT proposed rule, NMFS 

has updated our Technical Guidance 

(NMFS, 2024) containing updated 

acoustic criteria for auditory injury (89 

FR 36762, October 24, 2024). The 

Technical Guidance provides updated 

auditory injury thresholds, where 

appropriate, as well as revised 

weighting functions, in some cases. For 

impulsive sources, the Updated 

Technical Guidance’s auditory injury 

thresholds generally remain identical or 

are higher compared to our 2018 

Technical Guidance, meaning that 

received levels would need to be higher 

in order for marine mammals to be 

expected to incur auditory injury. The 

exceptions are for phocid pinnipeds 

(PW), where the cumulative SEL 

threshold, in the Updated Technical 

Guidance, is 2 dB lower and for otariid 

pinnipeds (OW) where the peak sound 

pressure level threshold is 2 dB lower 

and the cumulative SEL threshold is 18 

dB lower. As for the Updated Technical 

Guidance’s weighting functions, for MF 

cetaceans (now called HF cetaceans in 

the updated document) and HF 

cetaceans (now called VHF cetaceans in 

the updated document), the weighting 

functions reflect a higher susceptibility 

to auditory injury at frequencies below 

10 kHz, as compared to the 2018 

Technical Guidance. Other minor 

changes/shifts to weighting functions 

(e.g., for LF cetaceans, PW pinnipeds, 

OW pinnipeds) were also included. This 

new information was not available in a 

timeframe in which NMFS could have 

incorporated it into the quantitative 

analysis supporting this final 

rulemaking; however, NMFS did 

consider the information qualitatively. 

While these changes in the auditory 

injury thresholds and weighting 

functions could result in minor 

increases in PTS exposure estimates for 

some species, given the conservative 

assumptions built into the take estimate 

methodology, they would not be 

expected to result in meaningful, if any, 

changes in take estimates and would not 

be expected to change any of the 

findings. 

Harassment 

As described in the Estimated Take of 

Marine Mammals section, the annual 

number of takes authorized 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 and gray whale UME, 

which have been closed since 

publication of the 2020 HSTT final rule 

and 2023 HSTT proposed rule, 

respectively, 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 

authorizing 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 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 MexicoCA/OR/WA stock, Mexico DPS), as 

described in table 7 (i.e., one, two, or 

four take(s) over 7 years divided by 

seven to get the annual number) could 

occur and are authorized. 

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 * 

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 ≥43.4 Y; ≥0.41 ............ Y, 43 ............... 80 36.6 ↑ ..................... N 

Gray whale (Eastern North 

Pacific stock).

26,960 0.57 131 Y, 9.3 ................ Y, 1.8 .............. 801 670 5↑ ................... Y; 690; 2019 

Humpback whale (Mainland Mexico-CA/OR/WA 

stock, Mexico DPS).

3,477 0.14 22 Y; 11.4 .............. 6Y, 10.15 ....... 65 7 43 Unknown ........ N 

Humpback whale (Hawaii 

stock).

11,278 0.29 27.09 Y; 8.39 .............. 8Y, 10.59 ....... 127 99.91 Unknown ........ Y; 52; 2015 


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TABLE 10—SUMMARY INFORMATION RELATED TO MORTALITIES REQUESTED FOR VESSEL STRIKE, 2018–2025— 

Continued 

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 * 

PBR * 

Residual 

PBR (PBR 

minus 

annual 

M/SI) 3

Stock trend * 4

Recent UME 

(Y/N); number 

and year 

(since 2007) 

Blue whale (Eastern North 

Pacific Stock).

1,898 0.14 ≥18.6 Y; ≥0.61 ............ Y, 18 ............... 4.1 ¥14.5 Unknown ........ Y; 3, 2007 

Sei whale (Eastern North 

Pacific Stock).

864 0.14 ≥0 N; 0 .................. Y, 0 ................. 1.25 1.25 Unknown ........ N 

* Presented in the 2023 final SARs. 

1 This column represents the annual take by serious injury or mortality (M/SI) by vessel collision and was calculated by the number of mortalities authorized divided 

by 7 years (the length of the rule and LOAs). 2 This 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. 3 This 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). 4 See relevant SARs for more information regarding stock status and trends. 5 The Pacific 2023 SAR indicates that the stock trend is increasing. However, recent (2023–2024) surveys conducted by NMFS’ Southwest Fisheries Science Center indicated that the estimated total abundance of gray whales during the 2023–2024 southbound migration was 19,260, 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. 2024). 6 Vessel 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. 7 For 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. 8 Annual vessel strike for this stock reported in the 2023 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 authorizing the following M/SI 

takes from explosives: five California 

sea lions and eight short-beaked 

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 

PBRPBR 

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 unknown N 

* Presented in the 2023 SARs. 

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. 

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, December 27, 2018) 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 

authorized, 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 Analysis and 

Negligible Impact 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 


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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 authorized 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 

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 

authorized M/SI and the UME inform 

the negligible impact determination 

immediately below. For the other five 

stocks with 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) 

The estimated and authorized lethal 

take of gray whale (Eastern North Pacific 

stock) is well below the insignificance 

threshold (0.57 as compared to a 

residual PBR of 670). Nonetheless, we 

consider here how the 2019–2023 West 

Coast Gray Whale UME informs our 

negligible impact determination. 

Strandings of eastern North Pacific gray 

whales occurred in the United States, 

Canada and Mexico along the west coast 

of North America. They occurred in 

wintering, migratory, and feeding areas. 

Stranding rates have returned back to 

normal and expected levels, and the 

prevalence of thin live or thin dead 

whales has also decreased. The 

Investigative Team concluded localized 

ecosystem changes, including both 

access to and quality of prey, in the 

northern Bering and Chukchi seas 

caused the UME. These changes 

contributed to the poor nutritional 

condition observed in live whales in the 

wintering areas of Mexico and dead 

stranded gray whales in all three 

countries. This malnutrition led to 

increased mortality during the whales’ 

annual northward migration (from 

Mexico to Alaska) and decreased 

production of calves. This resulted in an 

overall decline in population 

abundance. Because of the abundance 

and residual PBR of this stock, as well 

as the fact that the UME is closed and 

increased mortality stopped in late 2023 

(with peak strandings ending in 

December 2020), this UME is not 

expected to have any impacts on 

individuals during the period of this 

final rule, nor is it thought to have had 

impacts on the population rate when it 

was occurring that would influence our 

evaluation of the effects of the mortality 

authorized on the stock. 

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 18.6, yielding a 

residual PBR of ¥14.5. This is slightly 

higher than the 2020 HSTT final rule 

(¥16.7) and 2023 HSTT proposed rule 

(¥15.4). NMFS authorizes 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 14.5. 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 authorized take 

from a specified activity to be negligible 

even if total human-caused mortality 

exceeds PBR if the 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 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 0.6, 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 

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. 


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NMFS’ 2023 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 authorized) 

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 humancaused 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 authorized 

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 1.25. The 

total annual M/SI is estimated at greater 

than or equal to 0 in the 2023 SAR, 

yielding a residual PBR of 1.25. NMFS 

authorizes 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 1.11. 

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/ 


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OR/WA fin whale if both of the 2021 

U.S. Navy strikes were fin whales) 

which relies on the 2023 SARs. 

However, consideration of the 2023 

strike would not change the total M/SI 

which NMFS compares to PBR, as the 

2023 U.S. Navy strike occurred outside 

of the time period considered in the 

vessel strike analysis in the 2023 SAR. 

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. 

Immediately below, we explain the 

information that supports our finding 

that the Navy’s 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 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 2023 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– 

2021 across 9,246 observed fishing sets 

(Carretta et al. (2022)). 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 authorized 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 

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 final rule. 

See the Group and Species-Specific 

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 authorized 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 gray whale UME (now 

closed), 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 


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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 tables 12 and 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. Tables 12 

and 13 have been updated from tables 

18 and 19 in the 2020 HSTT final rule, 

as appropriate, with the 2023 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 rule unless 

specifically noted. 

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 


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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—Continued 

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 

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 3 864 2,633 9 

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 

Authorized Take From Vessel Strikes and Explosives by Serious Injury or Mortality section, 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 

determination that the Navy’s activities 

will 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 

authorizes 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 14.5. 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 

identified by Calambokidis et al. (2015). 

These areas overlap a portion of the blue 

whale feeding BIAs (parent and child; 

see Harrison et al. 2023) identified in 

Calambokidis et al. (2024) and 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 will 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 BIAs. 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 authorized mortality 

(which our earlier analysis indicated 

will 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 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take will 

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 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 will 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 determined, 

in consideration of all of the effects of 

the Navy’s activities combined, that the 

authorized take will 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 authorizes 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, Calambokidis et al. (2024) 

identifies feeding BIAs for fin whales in 

SOCAL. The Navy implements time/ 

area mitigation in SOCAL in blue whale 

BIAs identified by Calambokidis et al. 

(2015), and fin whales are known to 

sometimes feed in some of the same 

areas. Additionally, these mitigation 

areas designed for blue whales overlap 

a portion of the fin whale feeding BIAs 

(parent and child; see Harrison et al. 

2023) identified by Calambokidis et al. 

(2024) which means fin whales 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 will 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 

authorized mortality (which our earlier 

analysis indicated will 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 determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take will 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 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 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, 

these amounts are still not 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 will 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 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take will 

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 authorizes 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 


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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, 

these amounts are still not 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 will 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 

authorized mortality (which our earlier 

analysis indicated will 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 determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take will 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 authorized 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 Navy-estimated 

abundance and the SAR) is 568 and 101 

percent, respectively (table 13). 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 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). 

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 will 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 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take will 

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 authorizes 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 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 (measured against both the 

Navy-estimated abundance and the 

SAR) is 2,633 and 9 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, 

these amounts are still not 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 sei whale communication or other 

important low-frequency cues—and that 


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the associated lost opportunities and 

capabilities are not at a level that will 

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 authorized mortality (which 

our earlier analysis indicated will 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 determined, 

in consideration of all of the effects of 

the Navy’s activities combined, that the 

authorized take will 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 

authorizing 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 the insignificance threshold of 

residual PBR (670). We acknowledge 

that the 2021 vessel strikes by the U.S. 

Navy could have been Eastern North 

Pacific gray whales. If we presumed that 

the 2021 U.S. Navy strikes were both 

gray whales, M/SI of this stock would 

still fall well below PBR (801). 

We also consider here how the 2019– 

2023 West Coast Gray Whale UME 

informs our negligible impact 

determination. Because of the 

abundance and residual PBR of this 

stock, as well as the fact that the UME 

is closed and increased mortality 

stopped in late 2023 (with peak 

strandings ending in December 2020), 

this UME is not expected to have any 

impacts on individuals during the 

period of this final rule, nor is it thought 

to have had impacts on the population 

rate when it was occurring that would 

influence our evaluation of the effects of 

the mortality authorized on the stock. 

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 17 percent, 

respectively (table 13). (Note that in 

comparison to the recent Eguchi et al. 

2024 abundance estimate, the number of 

estimated total instances of take 

compared to the abundance would be 24 

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 will 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, these 

amounts are still not 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 will 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 

are 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 recent (now closed) 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 (2023–2024) surveys 

conducted by NMFS’ Southwest 

Fisheries Science Center estimated that 

the population has declined since the 

most recent Eastern North Pacific gray 

whale SAR was published (Eguchi et al. 

2024). Only a small portion of the stock 

is anticipated to be impacted and any 

individual gray 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 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 authorized mortality 

of four whales over the 7 year period 

(which our earlier analysis indicated 

will 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 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take will 

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 2023 final SAR but is listed as 

endangered under the ESA. No 

mortality or Level A harassment is 

anticipated or authorized. 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 13). These takes will likely 

accrue to different individuals, the 

behavioral disturbances will be of a lowmoderate 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 

determined, in consideration of all of 

the effects of the Navy’s activities 

combined, that the authorized take will 

have a negligible impact on the Western 

North Pacific stock of gray whales. 


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Humpback Whale (Hawaii Stock) 

The status of this stock is unknown. 

Animals in this stock are of the Hawaii 

DPS which is not listed under the ESA. 

No Level A harassment by tissue 

damage is authorized. NMFS authorizes 

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 areas 

(BIA, parent and child; see Harrison et 

al. 2023) identified in Kratofil et al. 

(2023) 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 will 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 are 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 

authorized mortality (which our earlier 

analysis indicated will 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 determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take will 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 authorized 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 will 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 determined, 

in consideration of all of the effects of 

the Navy’s activities combined, that the 

authorized take will 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 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 2,606 913 96 

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 

will 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 authorized 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 96 for 

sperm whales and 1,211 and 223 for 

Kogia spp., with a large proportion of 

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 


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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 will 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 are 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 2 stocks are 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 are 

not 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 3.5 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 

determined that the authorized take will 

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 

authorized. 

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 

will 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 will 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 determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

authorized take will 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 authorized. 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 14). 

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 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 


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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 will 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 are 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, are 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 determined, in 

consideration of all of the effects of the 

Navy’s activities combined, that the 

expected and authorized take will 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 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 

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 

Blainville’s 

beaked 

whale.

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

Goosebeaked 

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. a The 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. 

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 

Goose-beaked 

whale.

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


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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—Continued 

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 

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 

will 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, Goose-Beaked, 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 

authorized 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 goose-beaked 

and Blainville’s beaked whales 

identified in Kratofil et al. 2023), 

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 will 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 determined, 

in consideration of all of the effects of 

the Navy’s activities combined, that the 

authorized take will have a negligible 

impact on the Hawaii stocks of beaked 

whales. 

Baird’s Beaked Whale, Goose-Beaked 

Whale 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 authorized for 

any of these three stocks and only two 

takes by Level A harassment (PTS) are 

authorized. 

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 

150, 211, and 203 percent (measured 

against the SAR) for Baird’s beaked 

whales, goose-beaked beaked whales, 

and Mesoplodon spp., respectively 

(table 17). 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 goose-beaked)— 


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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 are not 

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 are 

not 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 goose-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 goose-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 goosebeaked 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 

goose-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 determined that the 

authorized take will have a negligible 

impact on the CA/OR/WA stocks of 

Baird’s and goose-beaked whales, as 

well as all six species included within 

the Mesoplodon spp. 

Small Whales and Dolphins 

In tables 18 and 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. Tables 18 and 

19 are updated from tables 24 and 25 in 

the 2020 HSTT final rule as appropriate 

with the 2023 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 rule unless specifically noted. 

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 


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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—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 

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 

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. 


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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 

will 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. 

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 

authorized 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 3 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 


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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 are not 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 is 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 

authorized, 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) are not 

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 determined that 

the authorized take will 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 

authorized 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 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 is unlikely to impact 


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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 are not 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 determined that the 

authorized take will 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 authorized 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 18). 

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. 

Within the Hawaii Island mitigation 

area (which overlaps a large portion of 

the BIAs for common bottlenose 

dolphin, dwarf sperm whale, false killer 

whale, melon-headed whale, 

pantropical spotted dolphin, pygmy 

killer whale, rough-toothed dolphin, 

short-finned pilot whale, and spinner 

dolphin identified in Kratofil et al. 

2023), the Navy will not use explosives 

and will limit the use of MF1 and MF4 

active sonar. The 4-Islands mitigation 

area overlaps a portion of the BIAs 

identified in Kratofil et al. (2023) for 

common bottlenose dolphin, false killer 

whale, pantropical spotted dolphin, 

rough-toothed dolphin, and spinner 

dolphin. Within the 4-Islands mitigation 

area (November 15–April 15), the Navy 

will not use MF1 surface ship hullmounted mid-frequency active sonar or 

explosives that could potentially result 

in takes of marine mammals. The 

mitigation required in these two areas 

will reduce the severity of impacts 

within these small and 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 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 are 

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 


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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 are 

not 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 determined that the 

authorized take will 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 2023 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 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 

will 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 

authorized for this stock. 

Most Level B harassments to Dall’s 

porpoise from hull-mounted sonar 

(MF1) in the HSTT Study Area will 

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. 

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 are not 

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 


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mean some small loss of opportunities 

or detection capabilities, the estimated 

209 takes by Level A harassment by PTS 

for Dall’s porpoise are 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 are not 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 determined that the 

authorized take will have a negligible 

impact on Dall’s porpoise. 

Pinnipeds 

In tables 21 and 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. Tables 21 and 

22 have been updated from tables 27 

and 28 in the 2020 HSTT final rule with 

the 2023 final SARs. For additional 

information and analysis supporting the 

negligible-impact analysis, see the 

Pinnipeds discussion in the Group and 

Species-Specific Analyses section of the 

2018 HSTT final rule, all of which 

remains applicable to this 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. 

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 


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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—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) 

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 

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 authorized and when this mortality 

is combined with the other humancaused 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 

authorized (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) are not 

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) is 

1,484 to 2,896 percent and 18 to 46 

percent, respectively (table 22). 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 are unlikely 

to impact behaviors, opportunities, or 

detection capabilities to a degree that 

would interfere with 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 


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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 will 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) are not 

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 2 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 determined that 

the authorized take will have a 

negligible impact on all pinniped 

species and stocks. 

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 additional take of two large 

whales by serious injury or mortality by 

vessel strike, and the required 

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 final 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 final 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 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 

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. 

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, fin whale, gray whale 

(Western North Pacific DPS), humpback 

whale (Mexico and Central America 

DPSs), sei whale, sperm whale, false 

killer whale (Main Hawaiian Islands 

Insular DPS), Hawaiian monk seal, and 


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Guadalupe fur seal. There is also ESAdesignated 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 

reinitiated consultation with NMFS 

pursuant to section 7 of the ESA for 

HSTT Study Area activities, and NMFS 

also reinitiated consultation internally 

on the issuance of these revised 

regulations and LOAs under section 

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

NMFS issued a reinitiated Biological 

and Conference Opinion on June 3, 2024 

concluding that the issuance of the 2024 

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 opinion is 

available at https://doi.org/10.25923/ 

7y9x-vw84. 

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 has 

fulfilled its responsibilities and 

completed all requirements under the 

NMSA. 

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 final rule, NMFS has 

determined that this final rule and any 

subsequent LOAs will not result in 

impacts that were not fully considered 

in the 2018 HSTT FEIS/OEIS. As 

indicated in this final rule, the Navy has 

made no substantial changes to the 

activities that are relevant to 

environmental concerns nor are there 

substantial new circumstances or 

information about the significance of 

adverse effects that bear on the analysis. 

Therefore, NMFS has determined that 

the 2018 HSTT FEIS/OEIS remains 

valid, and there is no need to 

supplement the document for this 

rulemaking. NOAA therefore, has 

adopted the 2018 HSTT FEIS/OEIS. 

NMFS has prepared a separate Record of 

Decision. NMFS’ Record of Decision for 

adoption of the 2018 HSTT FEIS/OEIS 

and issuance of this final rule and 

subsequent LOAs can be found at 

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

national/marine-mammal-protection/ 

incidental-take-authorizations-militaryreadiness-activities. 

Regulatory Flexibility Act 

The Office of Management and Budget 

has determined that this 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 during the 

proposed rule stage that this action 

would not have a significant economic 

impact on a substantial number of small 

entities. The factual basis for the 

certification was published in the 

proposed rule and is not repeated here. 

No comments were received regarding 

this certification. As a result, a 

regulatory flexibility analysis was not 

required and none was prepared. 

Waiver of Delay in Effective Date Under 

the Administrative Procedure Act 

NMFS has determined that there is 

good cause under the Administrative 

Procedure Act (5 U.S.C. 553(d)) to waive 

the 30-day delay of the effective date for 

this rule. This rule relieves the Navy 

from the restrictions of the take 

prohibitions under the MMPA by 

granting the Navy’s request for 

incidental take authorization under 

MMPA section 101(a)(5)(A). In addition, 

there is good cause to waive the 30-day 

effective date period because a delay 

would be contrary to the public interest 

and unnecessary. A delay in 

effectiveness is contrary to public 

interest because this rule allows the 

Navy to continue training and testing 

activities that are necessary for national 

security in compliance with the MMPA. 

Further, a delay is unnecessary because 

this rule is not generally applicable to 

the public. The Navy is the only entity 

affected by the regulations, the Navy 

specifically requested the modification 

to the regulations, and the Navy has 

fully agreed to the requirements 

included herein. The Navy is 

anticipating finalization of the rule and, 

as such, is ready to comply immediately 

upon publication. As such, there is good 

cause to waive the 30-day delay in 

effective date. 

List of Subjects in 50 CFR Part 218 

Administrative practice and 

procedure, Endangered and threatened 

species, Fish, Fisheries, Marine 

mammals, Penalties, Reporting and 

recordkeeping requirements, 

Transportation, Wildlife. 


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Dated: December 23, 2024. 

Samuel D. Rauch III, 

Deputy Assistant Administrator for 

Regulatory Programs, National Marine 

Fisheries Service. 

For reasons set forth in the preamble, 

50 CFR part 218 is amended 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: 

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 Hawaii-Southern 

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 (LOA). 

218.77 Renewals and modifications of 

Letters of Authorization. 

218.78–218.79 [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: 

(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. 

This subpart is effective from January 

16, 2025, 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 

Goose-beaked whale ................................................................................ CA/OR/WA 

Goose-beaked whale ................................................................................ Hawaii 

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

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


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TABLE 1 TO PARAGRAPH (b)—Continued 

Species Stock 

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 

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. 

Except for incidental takings 

contemplated in § 218.72(a) and 

authorized by LOAs issued under 

§§ 216.106 of this chapter and 218.76, it 

is unlawful for any person to do any of 

the following in connection with the 

activities listed in § 218.70(c): 

(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) after 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. 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 


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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). For active 

sonar subject mitigation requirements: 

(i) Number of Lookouts and 

observation platform—(A) Hullmounted sources. One Lookout is 

required for hull-mounted sources for 

platforms with space or manning 

restrictions while underway (at the 

forward part of a small boat or ship) and 

for platforms using active sonar while 

moored or at anchor (including 

pierside). Two Lookouts are required for 

hull mounted-sources 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 is required on the 

ship or aircraft conducting the activity 

for sources that are not hull-mounted. 

(ii) Mitigation zone and requirements. 

During active sonar use, the following 

requirements apply: 

(A) Powerdown for marine mammals 

at 1,000 yards. At 1,000 yards (yd) 

(914.4 m) from a marine mammal, Navy 

personnel must power down by 6 

decibels (dB). 

(B) Powerdown for marine mammals 

at 500 yards. At 500 yd (457.2 m) from 

a marine mammal, Navy personnel must 

power down by an additional 4 dB (for 

a total of 10 dB). 

(C) Shutdowns for marine mammals 

at 200 yards. At 200 yd (182.9 m) from 

a marine mammal, Navy personnel must 

shut down low-frequency active sonar 

≥200 dB and hull-mounted midfrequency active sonar; or Navy 

personnel must shut down lowfrequency active sonar <200 dB, midfrequency active sonar sources that are 

not hull-mounted, and high-frequency 

active sonar. 

(D) Prior to activity. Prior to the start 

of the active sonar activity (e.g., when 

maneuvering on station), Navy 

personnel must observe the 1,000 yd 

(914.4 m) mitigation zone for floating 

vegetation; if floating vegetation is 

observed in the mitigation zone, 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. 

(E) During the activity for lowfrequency active sonar at or above 200 

dB and hull-mounted mid-frequency 

active sonar. When using low-frequency 

active sonar at or above 200 dB and 

hull-mounted mid-frequency active 

sonar, Navy personnel must observe the 

1,000 yd (914.4 m) 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. 

(F) 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 1,000 yd 

(914.4 m) 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. 

(G) 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 indicated in § 218.74(a)(2)(ii) 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. For activities using air 

guns: 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned on a ship or pierside. 

(ii) Mitigation zone and requirements. 

The mitigation zone is 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. For 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. 

The mitigation zone is 100 yd (91.4 m) 

around the pile driver. 


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Federal Register / Vol. 90, No. 10 / Thursday, January 16, 2025 / Proposed Rules 5019 

(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 

(3) Clear from additional sightings. 

The mitigation zone has been clear from 

any additional sightings for 30 minutes. 

(5) Weapons firing noise. For 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. 

The mitigation zone is 30 degrees on 

either side of the firing line out to 70 yd 

(64 m) 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. For 

explosive sonobuoys: 

(i) Number of Lookouts and 

observation platform. One Lookout must 

be positioned in an aircraft or on a 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 

while performing their regular duties. 

(ii) Mitigation zone and requirements. 

The mitigation zone is 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. For explosive 

torpedoes: 

(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 while performing their 

regular duties. 

(ii) Mitigation zone and requirements. 

The mitigation zone is 2,100 yd (1,920.2 

m) 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 


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5020 Federal Register / Vol. 90, No. 10 / Thursday, January 16, 2025 / Proposed Rules 

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 

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. For gunnery 

activities using explosive mediumcaliber and large-caliber projectiles, the 

following 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 while performing their 

regular duties. 

(ii) Mitigation zone and 

requirements—(A) Air-to-surface 

activities. The mitigation zone is 200 yd 

(182.9 m) around the intended impact 

location for air-to-surface activities 

using explosive medium-caliber 

projectiles. 

(B) Surface-to-surface activities, 

medium-caliber. The mitigation zone is 

600 yd (548.6 m) around the intended 

impact location for surface-to-surface 

activities using explosive mediumcaliber projectiles. 

(C) Surface-to-surface activities, largecaliber. The mitigation zone is 1,000 yd 

(914.4 m) around the intended impact 

location for surface-to-surface activities 

using explosive large-caliber 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. For 

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 while performing their 

regular duties. 

(ii) Mitigation zone and 

requirements—(A) Missiles or rockets 

with 0.6–20 lb net explosive weight. The 

mitigation zone is 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. The mitigation zone is 

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 


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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. For explosive 

bombs: 

(i) Number of Lookouts and 

observation platform. One 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 

while performing their regular duties. 

(ii) Mitigation zone and requirements. 

The mitigation zone is 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. For 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 while 

performing their regular duties. 

(ii) Mitigation zone and requirements. 

The mitigation zone is 2.5 nautical 

miles (4.6 km) 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. For 

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) 


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5022 Federal Register / Vol. 90, No. 10 / Thursday, January 16, 2025 / Proposed Rules 

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 while performing their 

regular duties. 

(ii) Mitigation zone and 

requirements—(A) Activities using 0.1–5 

lb net explosive weight. The mitigation 

zone is 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. The mitigation zone is 

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, 

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. For 

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 while performing their 

regular duties. 

(ii) Mitigation zone and 

requirements—(A) Activities under 

positive control using 0.1–20 lb net 

explosive weight. The mitigation zone is 

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. The mitigation zone is 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 


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(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 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 

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. For 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 while performing their 

regular duties. 

(ii) Mitigation zone and requirements. 

The mitigation zone is 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 following 

requirements apply to vessel movement, 

except 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. The 

mitigation zone is 500 yd (457.2 m) 

around whales. 

(B) Marine mammals other than 

whales. The mitigation zone is 200 yd 

(182.9 m) around all other marine 

mammals (except bow-riding 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 


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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. The 

following mitigation applies to devices 

that are towed from a manned surface 

platform or manned aircraft, except 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. 

The mitigation zone is 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. For small-, medium-, and 

large-caliber non-explosive practice 

munitions, the following mitigation 

applies to activities using a surface 

target: 

(i) Number of Lookouts and 

observation platform. One Lookout must 

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. 

The mitigation zone is 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. For aircraft-deployed nonexplosive missiles and rockets, the 

following 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. 

The mitigation zone is 900 yd (823 m) 

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. For non-explosive bombs and 

non-explosive 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. 

The mitigation zone is 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: 


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(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, within the Hawaii Island 

Mitigation Area, 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 

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, within the 

4-Islands Region Mitigation Area, Navy 

personnel must not use MF1 surface 

ship hull-mounted mid-frequency active 

sonar from November 15–April 15 or 

explosives that could potentially result 

in takes of marine mammals at any time 

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 

Humpback Whale Special Reporting 

Areas established from December 15– 

April 15 in its annual training and 

testing activity reports submitted to 

NMFS. 

(D) Humpback Whale Awareness 

Notification Message Area (November– 

April). The following requirements 

apply in the Humpback Whale 

Awareness Notification Message Area 

established from 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, within the San Diego Arc, 

San Nicolas Island, and Santa Monica/ 

Long Beach Mitigation Areas from June 

1–October 31, 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, 


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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, within the Santa Barbara Island 

Mitigation Area, Navy personnel must 

not use MF1 surface ship hull-mounted 

mid-frequency active sonar during 

training or testing, or explosives that 

could potentially result in the take of 

marine mammals during mediumcaliber 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, 

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 during the spring to alert ships 

and aircraft within the eastern Pacific 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 instruct personnel on 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. 

The following requirements apply in the 

Gray Whale Awareness Notification 

Areas from November–March and Fin 

Whale Awareness Notification Message 

Areas from November–May. 

(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 personnel on 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 of marine 

mammals not identified in § 218.72(b). 

(b) Monitoring and reporting under 

the LOAs. The Navy must conduct all 

monitoring and reporting required 

under the LOAs. 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 comply with all 

notification and reporting requirements 

under the LOAs. 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, 


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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 

paragraphs (f)(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 (f)(1) through (9) 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. 

(F) Number and types of vessels, 

aircraft, and other platforms 

participating in each 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 the length of 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: 


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5028 Federal Register / Vol. 90, No. 10 / Thursday, January 16, 2025 / Proposed Rules 

(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 

Humpback Whale Special Reporting 

Area. 

(5) Mitigation areas. The Navy must 

report any use of restricted acoustic and 

explosive sources identified in 

§ 218.74(b). 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. 

(8) Large whale aggregations. For each 

instance that an aggregation of large 

whales (4 or more whales within 1 nmi 

(1.9 km)) is reported in the area between 

32–33 degrees North and 117.2–119.5 

degrees West, Navy personnel must 

report the following information and to 

the extent practicable, this information 

should be provided in the Navy’s 

unclassified version of these reports: 

(i) Date, time, and general location 

(e.g., approximately 10–12 nmi (18.5 to 

22.2 km) Southeast of San Clemente 

Island) of the whales when the 

aggregation was first sighted 

(ii) Total number of whales observed 

within 1 nmi (1.9 km) of a Navy vessel 

that make up the aggregation 

(iii) Approximate distance (or 

distances if more than 1 group of whales 

is sighted) of the vessel from the whales 

in the aggregation when the whales 

were first sighted. 

(9) Foreign military sonar and 

explosives. Navy personnel must 

confirm that foreign military use of 

sonar and explosives, when such 

militaries are participating in a U.S. 

Navy-led exercise or event, combined 

with the U.S. Navy’s use of sonar and 

explosives, would not cause exceedance 

of the analyzed levels within each 

NAEMO modeled sonar and explosive 

bin used for estimating predicted 

impacts. 

(g) 7-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 (LOA). 

(a) To incidentally take marine 

mammals pursuant to the regulations in 

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) 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. 


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(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) 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. 2024–31402 Filed 1–8–25; 4:15 pm] 

BILLING CODE 3510–22–P 


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