# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Military Readiness Activities in the Hawaii-California Training and Testing Study Area > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2025-23088 ## Record - **Collection:** Federal Register - **Document type:** Rule - **Published:** December 17, 2025 - **Citation:** 90 FR 58810 ## Text DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration 50 CFR Part 218 [Docket No. 251211-0182] RIN 0648-BN44 Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Military Readiness Activities in the Hawaii-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. Department of the Navy (including the U.S. Navy and the U.S. Marine Corps (Navy)) and on behalf of the U.S. Coast Guard (Coast Guard) and U.S. Army (Army; hereafter, Navy, Coast Guard, and Army are collectively referred to as Action Proponents), issues these regulations pursuant to the Marine Mammal Protection Act (MMPA) to govern the taking of marine mammals incidental to training and testing activities and modernization and sustainment of ranges conducted in the Hawaii-California Training and Testing (HCTT) Study Area over the course of 7 years from December 2025 through December 2032. These regulations allow for the issuance of letters of authorization (LOAs) for the incidental take of marine mammals during specified activities and timeframes, prescribe the permissible methods of taking and other means of effecting the least practicable adverse impact on marine mammal species and their habitat, and establish requirements pertaining to the monitoring and reporting of such taking. The Action Proponents' activities are considered military readiness activities pursuant to the MMPA, as amended by the National Defense Authorization Act for Fiscal Year 2004 (2004 NDAA) and the NDAA for Fiscal Year 2019 (2019 NDAA). DATES: Effective from December 21, 2025, through December 20, 2032. ADDRESSES: A copy of the Action Proponents' incidental take authorization (ITA) application and supporting documents, as well as a list of the references cited in this document, may be obtained online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-military-readiness-activities. In case of problems accessing these documents, please call the contact listed below (see FOR FURTHER INFORMATION CONTACT ). FOR FURTHER INFORMATION CONTACT: Leah Davis, Office of Protected Resources, NMFS, (301) 427-8401. SUPPLEMENTARY INFORMATION: Purpose and Need for Regulatory Action These regulations, issued under the authority of the MMPA (16 U.S.C. 1361 et seq. ), allow for the authorization of take of marine mammals incidental to the Action Proponents' training and testing activities and modernization and sustainment of ranges (that qualify as military readiness activities) involving the use of active sonar and other transducers, air guns, and explosives (also referred to as “in-water detonations”); pile driving and vibratory extraction; land-based missile and target launches; and vessel movement in the HCTT Study Area. The HCTT Study Area includes areas in the north-central Pacific Ocean, from California west to Hawaii and the International Date Line, and including the Hawaii Range Complex (HRC) and Temporary Operating Area (TOA), Southern California (SOCAL) Range Complex, Point Mugu Sea Range (PMSR), Silver Strand Training Complex (SSTC), areas along the Southern California coastline from approximately Dana Point to Port Hueneme, and the Northern California (NOCAL) Range Complex. Also included in the HCTT 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 training and testing may occur (see figure 1 of the proposed rulemaking and figure 1.1-1 of the application). Please see the Legal Authority for the Proposed Action section for relevant definitions. Legal Authority for the Final Action The MMPA prohibits the “take” of marine mammals, with certain exceptions. Section 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq. ) 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 certain findings are made and either regulations are proposed or, if the taking is limited to harassment, a notice of a proposed authorization is provided to the public for review and the opportunity to submit comment. 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; 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 the species or stocks for taking for certain subsistence uses (collectively referred to as “mitigation”); and requirements pertaining to the monitoring and reporting of the 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 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 and amended the definition of “harassment” as applied to a “military readiness activity” to read as follows (section 3(18)(B) of the MMPA): (1) 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 (2) 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). The 2004 NDAA also amended section 101(a)(5)(A)(iii) of the MMPA establishing that “[f]or military readiness activity . . . , 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.” On August 13, 2018, the 2019 NDAA (Pub. L. 115-232) amended the section 101(a)(5)(A)(ii) of the MMPA to allow incidental take regulations (ITRs) for military readiness activities to be issued for up to 7 years. Summary of Major Provisions Within the Final Rule The major provisions of this rule are: • Take of marine mammals by Level A harassment and/or Level B harassment; • Take of marine mammals by mortality or serious injury (M/SI); • Use of defined powerdown and shutdown zones (based on activity); • Measures to reduce the likelihood of vessel 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 any vessel engaged in military readiness activities); and • Implementation of a robust monitoring plan to improve our understanding of the environmental effects resulting from the Action Proponents' training and testing activities and modernization and sustainment of ranges. This rule includes an adaptive management component that allows for timely modification of mitigation, monitoring, and/or reporting measures based on new information, when appropriate. Summary of Request On September 16, 2024, NMFS received an application from the Action Proponents requesting authorization to take marine mammals, by Level A and B harassment, incidental to training, testing, and modernization and sustainment of ranges (characterized as military readiness activities) including the use of sonar and other transducers, explosives, air guns, impact and vibratory pile driving and extraction, and land-based missile and target launches conducted within the HCTT Study Area. The Action Proponents also requested authorization to take, by serious injury or mortality, a limited number of marine mammal species incidental to the use of explosives and vessel movement during military readiness activities conducted within the HCTT Study Area. The Action Proponents requested multiple 7-year LOAs for Navy training activities, Coast Guard training activities, Army training activities, and Navy testing activities. In response to our comments and following an information exchange, the Action Proponents submitted a revised application, deemed adequate and complete on December 13, 2024. Also on that same date (December 13, 2024), NMFS published a notice of receipt of the application (NOR) in the Federal Register (89 FR 100982), requesting comments and information related to the Action Proponents' specified activities. During the 30-day public comment period, NMFS received one public comment from the Center for Biological Diversity. On July 16, 2025, NMFS published a proposed rule (90 FR 32118) and requested comments and information related to the Action Proponents' request for 30 days. All relevant comments received during the NOR and the proposed rulemaking comment periods were considered in this final rule. Comments received on the proposed rule are addressed in this final rule in the Comments and Responses section. NMFS previously promulgated ITRs pursuant to the MMPA relating to similar military readiness activities in areas located within the HCTT Study Area. NMFS published the first rule effective from January 5, 2009 through January 5, 2014, (74 FR 1456, January 12, 2009) for incidental take relating to military readiness activities in the HRC and January 14, 2009 through January 14, 2014 (74 FR 3882) for SOCAL. The second rule, effective from December 24, 2013 through December 24, 2018 (78 FR 78106, December 24, 2013), combined the Hawaii and Southern California range complexes, as well as the SSTC, pierside locations in San Diego Bay and Pearl Harbor, and the transit corridor between SOCAL and Hawaii, and throughout San Diego Bay. The third rule was effective from December 21, 2018 through December 20, 2023 (83 FR 66846, December 27, 2018), which was subsequently amended, extending the effective date from December 20, 2023 until December 20, 2025 (85 FR 41780, July 10, 2020) pursuant to the 2019 NDAA and NMFS later amended that rule to increase the take of large whales by vessel strike and modify the mitigation, monitoring, and reporting measures to reduce the occurrence of vessel strikes involving large whales (90 FR 4944, January 16, 2025). For this rulemaking, the Action Proponents plan to conduct substantially similar training and testing activities within the HCTT Study Area that were conducted under previous rules (noting that the Study Area has been expanded, as described in the Geographic Region section of the proposed rulemaking). The Action Proponents' application reflects the most up-to-date compilation of training and testing activities, and modernization and sustainment of ranges deemed necessary to accomplish military readiness requirements. The types and numbers of activities included in this rule account for interannual variability in training and testing to meet evolving or emergent military readiness requirements. As explained herein, these regulations also consolidate several actions conducted by the Navy that were previously authorized by NMFS and include some new military readiness activities carried out by the Action Proponents. In particular, these regulations cover incidental take during military readiness activities in the HCTT Study Area that will occur for a 7-year period following the expiration of the pre-existing MMPA authorization which expires on December 20, 2025 (85 FR 41780, as amended by 90 FR 4944). In addition, this rule includes PMSR activities for which incidental take was previously authorized under separate authorizations and will supersede that recent PMSR regulations (87 FR 40888, July 8, 2022). This rule also includes areas along the Southern California coastline from approximately Dana Point to Port Hueneme and supersedes the incidental harassment authorization (IHA) allowing incidental take of marine mammals during pile driving training activities at Port Hueneme (90 FR 20283, May 13, 2025). In this rule, we have undertaken a comprehensive assessment of the risks/impacts of all military training and testing activities on marine mammals likely to be present within the entire range of the Study Area. Description of Specified Activity The Action Proponents requested authorization to take marine mammals incidental to conducting military readiness activities. The Action Proponents have determined that acoustic and explosives stressors are likely to result in take of marine mammals in the form of Level A and B harassment, and that a limited number of takes by serious injury or mortality may result from vessel movement and use of explosives (including ship shock trials). Detailed descriptions of these activities are provided in chapter 2 and appendix A of the 2025 HCTT Environmental Impact Statement/Overseas Environmental Impact Statement (2025 HCTT EIS/OEIS) ( https://www.nepa.navy.mil/hctteis/ ) and in the Action Proponents' application ( https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-military-readiness-activities ). Of note, the U.S. Air Force (USAF) is a joint lead agency for the 2025 HCTT EIS/OEIS; USAF activities consist of air combat maneuvers and air-to-air gunnery (a gunnery exercise in which fixed-wing aircraft fire medium caliber guns at air targets). The Action Proponents determined that USAF activities would not result in the taking of marine mammals, and therefore these activities are not included in the Action Proponents' application. NMFS concurs that these activities are not anticipated to result in incidental take of marine mammals. As such, no authorization for taking marine mammals incidental to USAF activities is required and no LOA will be issued by NMFS for such USAF activities. A detailed description of the specified activities was provided in our proposed rulemaking (90 FR 32118, July 16, 2025). NMFS hereby refers to the information and analysis provided in the proposed rule which continue to apply to this final rule. Since that time, no changes have been made to the planned activities, with the exception of a reduction in the number of launch events at PMSR as described in the Changes from the Proposed Rule to the Final Rule section. Therefore, a detailed description is not provided here. Please refer to the proposed rulemaking for the complete description of the specified activity. Foreign Navies In furtherance of national security objectives, foreign militaries may participate in multinational training and testing events in the Study Area. Foreign military activities that are planned by and under the substantial control and responsibility of the Action Proponents are included in the specified activity. These participants could be in various training or testing events described in appendix A of the 2025 HCTT EIS/OEIS, and their effects are analyzed in this final rule. However, when foreign military vessels and aircraft operate independently within the Study Area as sovereign vessels outside the planning, control, and responsibility of the Action Proponents, those activities are not considered part of the specified activity. There are many reasons why foreign military vessels may traverse U.S. waters or come into a U.S. port, or foreign aircraft may enter U.S. airspace, not all of which are at the request of any of the Action Proponents. Foreign military vessels and aircraft operate pursuant to their own national authorities and have independent rights under customary international law, embodied in the principle of sovereign immunity, to engage in various activities on the world's oceans and in associated airspace. The most significant joint training event is the Rim of the Pacific (RIMPAC), a multi-national training exercise held biennially 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 (U.S. Department of the Navy, 2021c). 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. 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, 25 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 HCTT (205 days out of an estimated 2,056 days at sea). In RIMPAC 2024, 21 U.S. Navy maritime patrol aircraft participated, as did 12 foreign maritime patrol aircraft. When foreign militaries are participating in a U.S. Navy-led exercise or event, foreign military use of sonar and explosives, when combined with the Action Proponents' use of sonar and explosives, would not result in 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. Please see the Mitigation Measures section and Reporting section of this final rule for information about mitigation and reporting related to foreign navy activities in the HCTT Study Area. Comments and Responses We published the proposed rule in the Federal Register on July 16, 2025 (90 FR 32118) with a 30-day comment period. In that proposed rule, we requested public input on our analyses, our preliminary findings, and the proposed regulations, and requested that interested persons submit relevant information and comments. During the 30-day comment period, we received six comments. Of this total, one submission was from the Marine Mammal Commission (Commission), and the remaining comments were from non-governmental organizations (NGO) and private citizens. The majority of the comments either opposed or recommended revisions to the proposed rule. NMFS has reviewed and considered all relevant public comments received on the proposed rule and issuance of the LOAs. All substantive, relevant comments and our responses are described below. We organize our comment responses by major categories. Impact Analysis and Thresholds Comment 1 (ref 20, 21): The Commission stated that a 5-minute accumulation time for an entire day of pile driving is insufficient, particularly because of the Commission's assertion that the Navy does not implement, and NMFS has not proposed to require, soft-start procedures during pile-driving training activities. The Commission also noted differences in pile driving between the proposed rule and another recent military readiness activity involving pile driving (90 FR 20283, May 13, 2025). The Commission recommended that NMFS revise: (1) the range to effects for pile driving for temporary threshold shift (TTS) and auditory injury (AUD INJ) based on the number of piles of each pile type and installation method that would be installed on a given day, the number of minutes or strikes needed to install each pile to depth, and the correct source levels, including for vibratory installation of 24-inch (in; 0.61 meters (m)) sheet piles; (2) the range to effects for pile driving for behavioral response for vibratory installation of 24-in (0.61 m) sheet piles based on a source level of 159 decibel referenced to 1 microPascal (dB re 1 μPa) at 11 m; and (3) the numbers of takes accordingly for the final rule. Response: NMFS disagrees with the Commission's assertion that the source levels used for vibratory installation of 24-inch (0.61 m) sheet piles are incorrect. As indicated in the proposed rule and technical report “Quantifying Acoustic Impacts on Marine Mammals and Sea Turtles: Methods and Analytical Approach for Phase IV Training and Testing” (U.S. Department of the Navy, 2024a), hereafter referred to as the Acoustic Impacts Technical Report, a source level of 159 dB root-mean-square (RMS) for vibratory driving of 24-inch (0.61 m) steel sheet piles measured at 10 m (32.8 ft) (NAVFAC, 2020) is a reasonable representation of likely sound levels. The Navy assumed and NMFS concurred that most animals in the area of pile driving activities would avoid higher sound levels that could cause injury over periods of time shorter than 5 minutes. Furthermore, criteria for AUD INJ and TTS are conservative in that they do not account for recovery of hearing effects during breaks in sound exposure ( e.g., silent periods as the hammer is repositioned, when pinnipeds lift their heads out of the water or haul out). The Navy considers soft-start procedures for impact pile driving to be part of its standard operating procedures. As such, the 2025 HCTT EIS/OEIS, 2024 HCTT Draft EIS/OEIS, application, and the HCTT proposed rule (90 FR 32118, July 16, 2025) do not list soft start as a mitigation measure. The Navy states that its standard operating procedures are essential to safety and mission success and are implemented regardless of their secondary benefits, whereas its mitigation measures are designed entirely for the purpose of avoiding or reducing impacts to marine mammals. As such, the Action Proponents did not include a description of the soft-start procedure in the mitigation section of the application, and NMFS did not propose to include soft start as a mitigation measure in the proposed rule. However, NMFS agrees with the Commission that it is appropriate to require soft-start procedures as a mitigation measure, and this final rule clarifies that the Navy must implement soft start techniques for impact pile driving. Comment 2 (ref 12, 79): The Commission highlighted multiple points regarding the behavioral response functions (BRF) following its review of the technical report “Criteria and Thresholds for U.S. Navy Acoustic and Explosive Effects Analysis (Phase 4)” (U.S. Department of the Navy, 2025a). These points generally relate to the upper bound of the BRFs, Southall et al. data, odontocete BRFs, sensitive species BRFs, harbor porpoise data, pinniped BRFs, response severity denotation, and inconsistencies in some tables and figures. Please see the Commission's letter for a detailed discussion of its recommendation. The Commission recommended that NMFS require the Navy to revise Department of the Navy (2025a) to clarify and address these points, as that document underpins the current and future Phase IV rulemakings. The Commission also stated that to increase efficiency for all of the agencies involved and to ensure accurate information is being provided for public comment, the Commission would welcome the opportunity to informally review future versions of the Navy's criteria and threshold documents. The Commission further recommended that NMFS work with the Navy to use the dose-response functions that were developed from all of the raw data rather than those that were regenerated for only moderate and severe responses and to refrain from extrapolating beyond the bounds of the underlying data when revising the BRFs. In a related comment, a commenter stated that NMFS has not incorporated recent behavioral response data on common dolphins (Southall et al., 2024), and other important studies highlighted by the Commission, into its biphasic risk functions. The commenter references a fuller description of its concern in a comment on the 2024 Hawaii-California Training and Testing (HCTT) Draft EIS/OEIS. Response: Regarding the upper bound of the BRFs, the Navy adjusted the upper bound of the BRFs in Phase IV to more accurately reflect observed behavioral data, particularly at higher received levels. For example, sonar received levels between 170 and 182 dB re 1 µPa for humpback whales during the 3S2 study (the second phase of the Sea Mammals, Sonar, Safety (3S) project) and between 175 and 186 dB re 1 µPa for sperm whales during the 3S3 study (the third phase of the 3S project) did not elicit observable responses. See section 3.1.6.1.2 of the Criteria and Thresholds Technical Report for discussion of the 3S and 3S2 study, and section and 3.1.6.1.3 for discussion of the 3S3 study. Please see table E-1 in the Criteria and Thresholds Technical Report for details of all individual responses documented during studies in conjunction with received levels of sonar and sonar like sources. The descriptions of responses in appendix E (Behavioral Responses to Sonar and Sonar-Like Sources: All Individuals Included) of the Criteria and Thresholds Technical Report were updated to include additional information on the observed responses. Extending the upper bound to 200 dB re 1 µPa allows the BRFs to account for this lack of response at higher received levels. This adjustment does not arbitrarily shift the entire curve to the right, as the Commission suggests. For groups like pinnipeds, where responses are consistently observed at lower received levels, the BRF approaches 100 percent response probability at 185 dB re 1 µPa. Therefore, the upper bound adjustment primarily impacts the odontocete and mysticete BRFs, reflecting the observed data at higher exposures. It is also important to note that the lower bound of the BRFs were extended to 90 dB re 1 µPa in Phase IV (compared to the 100 dB re 1 µPa lower limit used in Phase III), further demonstrating that the adjustments were not solely focused on increasing the upper bound. The Commission's observation of a flat slope between 185 and 200 dB re 1 µPa for the Phase III BRFs shown in figure 42 (U.S. Department of the Navy, 2024a) was a result of anchoring the Phase III BRFs at 185 dB re 1 µPa and then extending them to 200 dB re 1 µPa for plotting purposes. Finally, regarding the point that the upper level of the mysticete BRF exceeds the TTS onset, it is important to emphasize that auditory and behavioral criteria are not directly linked. The Navy recognizes the evolving nature of acoustic science and will continue to refine its effects criteria as new data and understanding become available. Regarding data from Southall et al. (2024), the Navy develops its BRFs using the best available scientific data. While data from the Atlantic behavioral response study (BRS) cited by the Commission were collected during the timeframe referenced, these data are not available for use in the development of the BRFs for Phase IV. These functions are always developed in close consultation with scientists conducting BRS/controlled exposure experiment (CEE) studies, but when the data are not yet published, the researchers determine the appropriate time at which to share data with the Navy. In this case, Atlantic BRS behavioral response results have not been shared in time for the development of the Navy risk thresholds. The Navy did consider data from Southall et al. (2024) in appendix D of the 2025 HCTT EIS/OEIS, indicating the potential responses observed in this study occurred at received levels and distances assessed for potentially significant behavioral responses in the analysis of Phase IV; however, the findings of this study do not change the conclusions made by the Navy nor NMFS' determination. The Navy remains committed to incorporating the best available scientific data into its impact assessments and will revisit its BRFs as new information, including the published results of the Atlantic BRS, becomes available. Regarding the odontocete BRF, all the data from Houser et al. (2013a, 2013b) were included in the modified risk functions developed for subsampling in the Navy's BRFs. However, low-severity responses were classified as “non- responses” when deriving the BRFs (see also Southall et al. (2021) for a description of severity scoring). This approach, consistent with Phase III, reflects that low-severity behavioral responses are not typically considered “harassment” under the MMPA during military readiness activities. To balance field and captive study data, a subsampling method was used. This involved creating modified risk functions incorporating the new scoring values (classifying low-severity responses as non-responses) at different received levels. Thirty data points were then randomly selected from the bottlenose dolphin risk function generated using this method. This subsampling approach, similar to that used for beaked whale data in both Phase III and Phase IV, ensures each individual animal from the captive study receives equal weight, comparable to individuals from field studies. This allows for a more comprehensive consideration of exposures and responses for each species, unlike Phase III's selection of a single response level per individual. The Navy clarified this methodology in the Criteria and Thresholds Technical Report. Further, the Navy's current Odontocete BRF considers the potential for behavioral responses that may qualify as `harassment' under the MMPA for military readiness activities at the estimated received levels in Southall et al. (2024). Regarding the sensitive species BRF, while the generalized additive model (GAM) published in Jacobson et al. (2022) only extended to 165 dB, the Navy requested that authors rerun their model to 200 dB to create a new curve that could be subsampled for the Navy Phase IV risk function; the same was done for the Moretti et al. (2014) data. Therefore, the two beaked whale range-based risk functions extended to the same bandwidth as the Navy BRF and the subsampling matched the rest of the data. Navy updated the Criteria and Thresholds Technical Report to reflect that the published GAMs were rerun with the broader bandwidth. Both Moretti et al. (2014) and Jacobson et al. (2022) were subsampled 10 times each. To be included in the BRF, data sets need to relate known or estimable received levels to observations of individual or group behavior. The data in Falcone et al. (2017) was not included in the development of the BRFs because it is not possible to reasonably estimate the received levels in this study; however, this data was considered in developing the distance conditions for the application of the Sensitive Species BRF. The Navy and NMFS are committed to ensuring scientific integrity in datasets used for BRF development. Using data that do not meet these criteria could result in unreliable or misleading risk assessments. A risk function has not yet been fit to Southern California Anti-Submarine Warfare Range (SOAR) data for beaked whales, nor has one been fit for minke whales at Pacific Missile Range Facility (PMRF). The BRFs in Phase IV utilized only individual response-RL data outside of the four pre-existing risk functions that were subsampled. There were no individual response-RL data available for beaked whales at SOAR nor for minke whales at PMRF, therefore those data were not used in the Phase IV BRFs. As science continues to evolve, the Navy and NMFS will continue to refine the effects criteria. The Navy remains committed to incorporating new data and analyses, including those from SOAR and PMRF, as they become available and meet the rigorous standards required for robust BRF development. Regarding the Kastelein harbor porpoise data, when the same individuals were tested at multiple received levels for the same source within a single study, only the lowest received level eliciting a response was included in the data used for BRF development. However, in some studies, Kastelein tested the same sources using different parameters, such as an upsweep versus a downsweep signal ( e.g., Kastelein et al. (2014b), where both low frequency and mid frequency active sonar signals were tested as both a downsweep and upsweep), or as a continuous versus pulsed active sonar signal ( e.g., Kastelein et al., 2018). In that case, the response to both signal parameters would have been used in the BRF as those would be considered different signals. The citations for the relevant Kastelein studies, previously provided in tables 19 and 20, were added to table E-1 in the Criteria and Thresholds Technical Report. Regarding the pinniped BRFs, the Navy confirms that all data from the Houser et al. (2013a) California sea lion controlled exposure experiment were considered in developing the Phase IV BRFs. However, as with the odontocete BRF, low-severity responses were classified as “non-responses” when deriving the BRF. This decision aligns with the Navy's approach to assessing potential harassment under the MMPA during military readiness activities, where low-severity responses are not typically considered indicative of harassment. The original curves developed by Houser et al. (2013a) were not used because they included the low-severity responses as responses indicative of harassment. The Navy clarified this approach in the Criteria and Thresholds Technical Report. Regarding the identified inconsistencies in some data, tables, and figures, NMFS and the Navy have carefully reviewed those identified in the Commission's comments and the Navy made the necessary corrections to the Criteria and Thresholds Technical Report. These revisions ensure consistency in the reported ranges of received levels, distances, and significant responses across the executive summary, tables, figures, and accompanying text. Specifically, the Navy updated table E-1 in the Criteria and Thresholds Technical Report to include data for Blainville's beaked whales from Tyack et al. (2011). The studies by Moretti et al. (2014) and Jacobson et al. (2022) involved aggregated and modeled data rather than individual animal responses and were therefore incorporated into the BRFs through a random subsampling process, as described in the Criteria and Thresholds Technical Report, rather than being presented directly in table E-1, which focuses on individual-level data. The Navy also addressed inconsistencies between Curé et al. (2025) and table E-1 of Criteria and Thresholds Technical Report identified by the Commission. The Navy updated the closest points of approach so that the onset closest point of approach is given for signals that elicited significant responses, while the closest point of approach of the overall exposure session is given for signals that did not elicit a significant response. These corrections only affect the way data was presented in table E-1 and do not change the BRFs. Finally, the Navy has confirmed to NMFS that it used the data from Houser et al. (2013a) and Houser et al. (2013b) to develop the new risk functions. As noted previously, low-severity responses were scored as “non-responses” within these functions to align with the Navy's approach to assessing potential harassment under the MMPA. These new risk functions were then subsampled using the same method applied to the beaked whale range risk functions in both Phase III and Phase IV, ensuring consistency in the Navy's treatment of such data. This subsampling approach, described in detail within those reports, ensures appropriate weighting of individual responses and contributes to the robustness of the Navy's BRFs. Regarding the Commissions' offer to informally review future versions of the criteria and threshold reports, NMFS recommends that the Commission coordinate directly with the Navy for any potential early reviews as the Navy is the primary author. Comment 3 (ref 13): The Commission recommended that NMFS work with the Navy in a concerted manner to incorporate data that support criteria and threshold development more often than on a decadal cycle and to revise NAEMO to implement the relevant criteria and thresholds at a true post-processing stage so that animat ( i.e., a virtual animal) dosimeter data can be re-queried if thresholds change, rather than needing to remodel the animat-portion of NAEMO. Response: The Criteria and Thresholds are typically updated at the beginning of each at-sea Phase. This is a significant effort that involves collecting published data, working with marine mammal researchers to collect and understand emergent data, developing methods to incorporate the data, writing and publishing the technical report, and seeking approvals from Navy leadership and NMFS. Nevertheless, emergent data is continuously assessed against the current criteria and thresholds to ascertain whether it would create significant changes to the Navy's analysis. If so, the analysis would be altered to reflect this emergent data. The Navy is continuously reassessing and evolving its analytical methods including the need to more frequently update criteria and threshold and the feasibility for NAEMO to more rapidly incorporate such changes. For example, the Navy has undertaken efforts to investigate the feasibility of moving the weighting functions to the post-processor for impulsive modeling, which would allow added flexibility to the modeling process when new data emerges outside of the normal criteria and threshold timeline. NMFS supports such efforts. Comment 4 (ref 10): The Commission recommended that NMFS determine whether inclusion of data from Kastelein et al. (2024a, 2025a, 2025b) would alter the weighting functions and/or thresholds for the functional hearing groups and, if so, whether those modifications would be sufficient to warrant revision of the weighting functions and associated thresholds for non-impulsive sources as stipulated in the Criteria and Thresholds Technical Report. Response: Whether and when to share data for ongoing research is at the discretion of the researchers and funding agencies. Since the specific data from Kastelein et al. (2024a) were not shared with the Navy prior to peer review and publication, the data could not be incorporated into the development of the Phase IV Criteria and Thresholds. However, the Navy's current approach using the existing Phase IV criteria remains protective even when compared to the findings of Kastelein et al. (2024a). Specifically, incorporating the TTS onset value of 169 dB sound exposure level (SEL) reported by Kastelein et al. (2024a) would raise the very high frequency (VHF) non-impulse exposure function by 4 dB. The impact on other impulsive and non-impulsive exposure functions is negligible (1 dB or less). NMFS has also reviewed the data from Kastelein et al. (2024b, 2025a, 2025b). Kastelein et al. (2025a) evaluated the effect of one-sixth octave band noise centered at 40 kilohertz (kHz) on TTS in two California sea lions ( Zalophus californianus ). Results indicate that TTS onset (6 dB threshold shift) occurred at approximately 169 dB cumulative SEL, which is lower than predicted by the current Phase IV TTS threshold and weighting function. Interestingly, this TTS onset level is lower than what was measured during exposure to 32 kHz in a previous study (179 dB cumulative SEL; Kastelein et al. (2024b)). So, despite hearing sensitivity decreasing at higher frequencies, Kastelein et al. (2025a) indicate that TTS onset occurs at a lower level than predicted, which contradicts typical trends in TTS onset previously measured in marine mammals. Thus, these data suggest a need to evaluate exposures at potentially higher frequencies to examine whether this disparate trend continues. Kastelein et al. (2025b) examined TTS in two harbor seals ( Phoca vitulina ) exposed to one-sixth octave band noise centered at 8 kHz. In this study, TTS onset (6 dB threshold shift) occurred at approximately 181 dB cumulative SEL, which is higher than what is predicted with the current Navy Phase IV criteria. In consideration of the information discussed above, NMFS and Navy have concluded that revisions to the Phase IV criteria and thresholds are not warranted at this time. Comment 5 (ref 11, 78): The Commission recommended that NMFS determine whether the low frequency (LF) cetacean weighting function has been shifted far enough to the higher frequencies to reflect that 32 kHz was the most sensitive frequency tested in minke whales, determine whether use of the phocid carnivore in water (PCW) composite audiogram, weighting function, and threshold parameters are more representative of very low-frequency (VLF) and LF cetaceans than medians and means of the five other functional hearing groups, and work with the Navy to revise the VLF and LF cetacean composite audiograms, weighting functions, and thresholds as needed for impulsive and non-impulsive sources for the final rule and 2025 HCTT EIS/OEIS. In a related comment, a commenter stated that NMFS has applied a patently unrealistic, non-conservative auditory weighting scheme for “low frequency cetaceans” and references a similar comment on the 2024 HCTT Draft EIS/OEIS. Response: The lack of data on mysticete hearing, especially in terms of the impacts of noise on hearing, has made this a challenging group for which to develop acoustic criteria. The Navy has split the mysticetes into two hearing groups for its Phase IV analyses: VLF and LF cetaceans (see appendix B of the Criteria and Thresholds Technical Report). This decision is outlined in detail within the documentation and includes the best available science including the recommendations of Southall et al. (2019c) and the minke whale study by Houser et al. (2024). Navy was given access to pre-published data on the 2023/2024 minke whale field season and was able to incorporate into their Phase IV criteria (noting, as the commenter did, that the 2023 field season data was published in November 2024). In their Phase IV criteria, the Navy separated VLF cetaceans ( i.e., blue, fin, right, and bowhead) whales from LF cetaceans (all other mysticetes). Thus, they are acknowledging differences among mysticetes species. NMFS and the Navy disagree that wholesale adoption of the PCW parameters or shifting the LF weighting function solely based on the 32 kHz sensitivity of minke whales is scientifically justified. There is no scientific evidence to support the exclusive use of the PCW composite audiogram and weighting function parameters for the LF and VLF groups. Adolescent minke whales were tested by Houser et al. (2024) specifically because of their small size compared to other baleen whales. Smaller head size generally facilitates hearing at higher frequencies, so a shift of the entire LF curve (intended to represent all species within the hearing group) to a center frequency of 32 kHz is not likely representative of most baleen whales, which are larger in size compared to adolescent minke whales. Therefore, the Navy maintains, and NMFS concurs, that based on the weight of the evidence, the existing LF weighting function and the use of medians and means from multiple functional hearing groups provide a more representative and protective approach for assessing acoustic impacts on VLF and LF cetaceans. This approach incorporates data from a broader range of species and avoids overreliance on data from a single species or functional hearing group. NMFS' approach has remained consistent throughout our Technical Guidance development (2016, 2018, 2024), and we have addressed comments on the LF cetacean weighting function in our previous Federal Register notices finalizing these documents (81 FR 51693, August 4, 2016; 89 FR 84872, October 24, 2024). NMFS' 2024 Technical Acoustic Guidance does not incorporate the recent data on minke whale hearing. However, NMFS has committed to incorporating this data into future versions, as indicated in our 2024 Updated Technical Guidance. NMFS is awaiting publication of results from the 2024 field season before re-evaluating our acoustic criteria for mysticetes. Comment 6 (ref 14): The Commission recommended that NMFS work with the Navy to reprogram NAEMO to implement densities at a post-processing stage so that densities can be easily revised rather than needing to remodel the animat-portion of NAEMO when density estimates change. The Commission states that such an improvement was recommended by Simmons et al. (2025) to be addressed through modifications to animat seeding and investigating runs by hearing group within NAEMO. Response: NMFS concurs that it is appropriate to explore whether NAEMO can be reprogrammed to implement densities at a post-processing stage so that densities can be easily revised rather than needing to remodel the animat-portion of NAEMO when density estimates change. The Navy has undertaken work in Fiscal Year 2025 to explore standardization of animat distributions and statistical considerations of applying species' densities after the NAEMO post-processor to scale results. If the Navy, in coordination with NMFS, finds that this proves feasible and appropriate, the Navy hopes to implement this for Phase V. Comment 7 (ref 17, 18): The Commission recommended that NMFS work with the Navy to use an avoidance swim speed of no more than 2 m per second (m/second) for harbor porpoises and 1 m/second for pinnipeds and to revise the NAEMO modeling and take estimates appropriately for the final rule. The Commission further recommended that NMFS work with the Navy to incorporate moving animats into NAEMO that can actively avoid sound sources based on species-specific dive profiles and swim speeds for Phase V activities (which would occur in HCTT from 2032 to 2039) and, if that is not feasible, incorporate species-specific swim speeds and the actual modeled sound propagation into NAEMO to simulate avoidance for a given event. The Commission stated that both creating an emulator and running simulation studies outside of NAEMO, as recommended by Simmons et al. (2025), should inform how best to deal with moving animats and implementing avoidance within NAEMO. Response: NMFS and the Navy acknowledge the importance of using appropriate swim speeds in the avoidance analysis in NAEMO, which assesses the potential for marine mammals to mitigate high-intensity sound exposures that could lead to auditory injury. While baseline swim speeds can be informative, the Navy prioritized data on swim behavior observed near and during anthropogenic disturbance because these data were considered more representative of how animals might respond to acoustic stimuli and potentially reduce injury risk. NMFS concurs with this approach. The Commission referenced a study by Kastelein et al. (2018) as support for a lower harbor porpoise swim speed. However, the cited speed of 7.1 kilometers per hour (km/hr) represents the sustained average speed of a single captive harbor porpoise in a relatively small pool during a pile driving playback study at exposures below those causing auditory injury. This specific observation does not accurately reflect the full range of harbor porpoise swim capabilities. As documented in table 8 of the appendix to the Acoustic Impacts Technical Report, data from free-swimming harbor porpoises indicate swim speeds up to and exceeding 3 m/second, supporting the Navy's chosen value for modeling avoidance. For pinnipeds, the avoidance analysis used a reasonable swim speed of 2 m/second for a limited duration (10 minutes), acknowledging the lack of observed data on their swim behavior during acoustic exposures. This assumption balances the need for a realistic representation of potential avoidance behavior with the limited data availability, contributing to a conservative assessment of potential impacts. The Navy's approach to modeling impacts is described in the Acoustic Impacts Technical Report. NMFS has reviewed the Acoustic Impacts Technical Report and concurs with the Navy that the approach is based on the best available science. In early NAEMO development, the Navy compared the number of exposures ( i.e., >120 dB) using the Marine Mammal Movement and Behavior (3MB) model versus horizontally stationary animats and concluded that there was no significant difference in behavioral exposures between the two distribution methods. Thus, horizontally stationary animats were selected for computational efficiency. NMFS and the Navy recognize the evolving nature of modeling techniques and acknowledge the Commission's desire for more dynamic and species-specific avoidance behaviors in future iterations of NAEMO. NMFS has encouraged the Navy to continue to explore NAEMO enhancements, and the Navy has indicated that it will consider species-specific swim speeds and potentially more complex movement models, as data availability and computational capabilities allow. Currently, however, detailed avoidance data for many species are limited, necessitating the use of surrogate data and generalized approaches, as is also the case with dive profiles. The Navy states that it will continue to prioritize research and development efforts to enhance the accuracy of its impact modeling tools, ensuring the best available science informs its environmental assessments. Comment 8 (ref 19): The Commission recommended that NMFS work with the Navy to use its Range-Dependent Acoustic Model and the Navy's Standard Parabolic Equation (RAM/PE) model for non-impulsive sources to model all underwater detonations ( i.e., impulsive sources) for Phase IV activities for which modeling has not been completed and for all Phase V activities, until such time that Comprehensive Acoustic Simulation System/Gaussian Ray Bundle (CASS/GRAB) and the similitude equation have been validated for the range of detonation sizes and environmental parameters ( i.e., water depth and receiver range) in which it would be used. They supported this recommendation by stating that, given the comparability of the modeled zones from the Peregrine version of RAM/PE to the measured values and that RAM/PE is already used by the Navy for modeling non-impulsive sources that operate at less than 100 Hz and in shallow water, the Navy has the data to conduct a rigorous comparison of CASS/GRAB and the similitude equation and the in situ measurements of the USS Ford ship shock trial from Seger et al. (2023) to fulfill the project's intent and to inform future rulemakings. Response: Navy has indicated that it plans to conduct a verification of the impulsive propagation methods in NAEMO using the Seger et al. (2023) data, which was published by Madhusudhana et al. (2024). The NAEMO impulsive modeling methods, as described in the Acoustic Impacts Technical Report, require arrival times, sound levels, and phases to be output from the propagation model. RAM/PE does not output the time information necessary for simulation and is thus not a suitable option for impulsive modeling in NAEMO. The limitations of the similitude equation are discussed in section 4.1.3.2 of the Acoustic Impacts Technical Report and comparisons between the peak pressure computed at various ranges against the theoretical value based on the similitude equation showed agreement, providing confidence that the similitude equation was appropriate for use in NAEMO. The Navy states that it is committed to ensuring the accuracy of its impulsive propagation models and recognizes the importance of ongoing validation efforts. While the similitude equation has been evaluated and demonstrated good agreement with measured data, as detailed in section 4.1.3.2 of the Acoustic Impacts Technical Report, the Navy is open to exploring alternative approaches to meet NAEMO's requirements. Comment 9 (ref 16): The Commission continues to maintain that NMFS has not provided adequate justification for dismissing the possibility that single underwater detonations can cause a behavioral response, and, therefore, again recommended that it estimate and authorize takes by Level B harassment of marine mammals during all explosive activities, including those that involve single detonations and gunnery exercises that have several detonations occurring within a few seconds. The Commission further recommends that NMFS encourage the Navy to invest resources in conducting BRSs on marine mammals' responses, including pinniped responses, to underwater detonations for the derivation of explosive BRFs, or at the very least a source-specific step-function threshold, noting that the Navy's Living Marine Resources program has provided funding for a few opportunistic studies involving behavioral response of cetaceans exposed to underwater detonations. Response: NMFS acknowledges the possibility that single underwater detonations (including some multiple explosive events, such as certain naval gunnery exercises, that may be treated as a single event because a few explosions occur closely spaced within a very short time (a few seconds)) can cause a behavioral response. The current take estimate framework allows for the consideration of animals exhibiting behavioral disturbance during single explosions as they are counted as “taken by Level B harassment” if they are exposed above the TTS threshold, which is 5 dB higher than the behavioral harassment threshold for multiple detonations. We acknowledge in our analysis that individuals exposed above the TTS threshold may also be harassed by behavioral disruption and those potential impacts are considered in the Analysis and Negligible Impact Determination section. Neither NMFS nor the Navy are aware of evidence to support the assertion that animals will have multiple significant behavioral responses ( i.e., those that would qualify as take) to temporally and spatially isolated explosions at received levels below the TTS threshold. However, if any such responses were to occur, they would be expected to be rare and since separated in space and time, would most likely result only in isolated startle responses ( i.e., additional behavioral responses would not be expected to add cumulatively or in severity). Furthermore, these rare responses would not be expected to occur at received levels below TTS onset. Thus, they would occur at received levels already bounded by the single detonation criteria ( i.e., TTS is used as the Level B harassment criteria for single detonations) and would therefore already be accounted for in the current take estimates. The derivation of the explosive injury criteria is provided in the Criteria and Thresholds Technical Report. There is limited information upon which to estimate behavioral response thresholds specific to explosives. Therefore, as described in the Criteria and Thresholds Technical Report, the behaviors exhibited by animals exposed to brief intense tones in the Schlundt et al. (2000) study continue to inform the behavioral response threshold for explosives. Some of the observed behaviors in that study would be considered moderate severity for captive animals with trained behaviors and thus may be potentially significant in the context of wild animals. Appropriate threshold metrics are applied for this criterion given the supporting data. Additionally, RMS sound pressure levels (SPLs) are not a preferred metric for explosives due to the challenge of identifying the appropriate time window. Most explosive activities, including all explosive gunnery activities, analyzed in the rule and the 2025 HCTT EIS/OEIS include multiple detonations. For these activities, significant behavioral responses are assumed to occur if the cumulative SELs are greater than or equal to 5 dB less than the threshold for onset of TTS. For single detonations, the analysis in appendix E of the 2025 HCTT EIS/OEIS assumes that any auditory impact (TTS or AUD INJ) may have a concurrent significant behavioral response. This assumption for single detonations has been clarified in the Criteria and Thresholds Technical Report. BRSs on marine mammal responses to underwater detonations would support future analyses, and NMFS will consider such a recommendation to the Navy relative to other new and ongoing research priorities. The Navy supports a wide range of research to inform the development of criteria. The Navy is supporting new research into marine mammal behavioral responses to detonations through its Living Marine Resources program ( https://exwc.navfac.navy.mil/Products-and-Services/Environmental-Security/LMR/ ). The findings of this research will be incorporated into the behavioral response criteria when available. To clarify, the Navy has specifically monitored shock trial detonations since the 1990s. Madhusudhana et al. (2024) present data on pre- and post-detonation vocalizations at monitoring sites in the vicinity of the 2021 full ship shock trial. Most sites showed no significant changes in vocalization activity for the timeframes analyzed. Comment 10 (ref 66): A commenter recommended that, in addition to the designation of geographic mitigation areas identified above, efforts should be undertaken in an iterative manner to identify additional important habitat areas across the HCTT Study Area, using the full range of data and information available ( e.g., habitat-based density models, NMFS-recognized Biologically Important Areas (BIAs), Endangered Species Act (ESA) critical habitat designations, passive acoustic monitoring data, other survey data, oceanographic and other environmental data). Response: NMFS and the Navy used the best available scientific information ( e.g., stock assessment reports (SARs) and numerous study reports from Navy-funded monitoring and research in the specific geographic region) in assessing density, distribution, and other information regarding marine mammal use of habitats in the HCTT Study Area. In addition, NMFS consulted Calambokidis et al. (2024) and Kratofil et al. (2023), which provides a specific, detailed assessment of known BIAs, which may be region-, species-, and/or time-specific, include reproductive areas, feeding areas, migratory corridors, and areas in which small and resident populations are concentrated. While the science of marine mammal occurrence, distribution, and density resides as a core NMFS mission, the Navy does provide extensive support to the NMFS mission via ongoing HCTT specific monitoring as detailed in this final rule. Also included are direct Navy funding support to NMFS for programmatic marine mammal surveys in Hawaii and the U.S. West Coast, and spatial habitat model improvements. Comment 11 (ref 68): A commenter stated that there is a need for the Navy to compile more information regarding the number, nature, and timing of testing and training events that take place within, or in close proximity to, important habitat areas, and to refine its scale of analysis of operations to match the scale of the habitat areas that are considered to be important. The commenter states that while the 2024 HCTT Draft EIS/OEIS, in assessing environmental impacts on marine mammals, breaks down estimated impacts by region, the resolution is seldom greater than range complex or homeport and is not specifically focused on areas of higher biological importance. Current and ongoing efforts to identify important habitat areas for marine mammals should be used by the Navy as a guide to the most appropriate scale(s) for the analysis of operations. Response: In their take request and effects analysis provided to NMFS, the Action Proponents considered historic use (number and nature of training and testing activities) and locational information of training and testing activities when developing modeling boxes. The timing of training cycles and testing needs varies based on deployment requirements to meet current and emerging threats. Due to the variability, the Action Proponents' description of the specified activities is structured to provide flexibility in training and testing locations, timing, and number. In addition, information regarding the exact location of sonar usage is classified. Due to the variety of factors, many of which influence locations that cannot be predicted in advance ( e.g., weather), the analysis is completed at a scale that is necessary to allow for flexibility. The purpose of the Action Proponents' quantitative acoustic analysis is to provide the best estimate of impact/take to marine mammals and ESA-listed species for the regulatory and ESA section 7 consultation analyses. Specifically, the analysis must take into account multiple training and testing activities over large areas of the ocean for multiple years; therefore, analyzing activities in multiple locations over multiple seasons produces the best estimate of impacts/take to inform the 2025 HCTT EIS/OEIS and regulators. Also, the scale at which spatially explicit marine mammal density models are structured is determined by the data collection method and the environmental variables that are used to build the model. Therefore, altogether, given the variables that determine when and where the Action Proponents train and test, as well as the resolution of the density data, the analysis of potential impacts is scaled to the level that the data fidelity will support. NMFS has worked with the Navy over the years to increase the spatio-temporal specificity of the descriptions of activities planned in or near areas of biological importance, when possible ( e.g., in BIAs or Sanctuaries, where possible). The HCTT analysis in the Action Proponents' application (see appendix A of the application) includes improved modeling since Phase III to predict the number of expected takes, by effect type, within important habitat areas such as identified BIAs and ESA-designated critical habitat. NMFS is confident that the granularity of information provided sufficiently allows for an accurate assessment of both the impacts of the Action Proponents' activities on marine mammal populations and the protective measures evaluated to mitigate those impacts. NMFS and the Action Proponents will continue to consider how to appropriately refine our future analyses. Comment 12 (ref 77): A commenter stated that NMFS has relied improperly on means and medians in establishing its thresholds for auditory impacts and references a similar comment on the 2024 HCTT Draft EIS/OEIS. In that comment, the commenter recommends implementation of a 6 dB reduction to its TTS and PTS thresholds in line with the suggestions by Tougaard et al. (2015). The commenter states that a 6 dB adjustment would accord with the minimum level of “non-trivial” TTS required to evaluate onset, effectively adjusting the exposure functions to more closely match the point where TTS begins. Response: The technical guidance appropriately uses measures of central tendency based on an onset level of 6 dB TTS. No reduction is necessary or supported by the scientific literature, especially considering numerous other conservative methods in the auditory criteria. For example, the proposed and final rules assume no recovery of hearing during time intervals between intermittent exposures. However, multiple studies from humans, terrestrial mammals, and marine mammals have demonstrated less TTS from intermittent exposures compared to continuous exposures with the same total energy because hearing is known to experience some recovery in between noise exposures. Therefore, NMFS' approach in the proposed and final rules is known to overestimate the effects of intermittent noise sources such as tactical sonars. Further, marine mammal TTS data have shown that, for two exposures with equal energy, the longer duration exposure tends to produce a larger amount of TTS. Since most marine mammal TTS data have been obtained using exposure durations up to an hour, much longer than the durations of many tactical sources, the use of the existing marine mammal TTS data tends to over-estimate the effects of sonars with shorter duration signals. Comment 13 (ref 15, 80): The Commission recommended that NMFS refrain from using cut-off distances in conjunction with the Bayesian BRFs and re-estimate the numbers of marine mammal takes based solely on the Bayesian BRFs for the final rule. In a related comment, a commenter stated that NMFS reduces the Navy's modeled take estimates through the application of cut-off distances that do not make sense conceptually, that are based on little or no data from the behavioral response literature, and that contradict data that are available, including Falcone et al. (2017) and Melcón et al. (2012). The commenter refers to a description of their concern in a comment on the 2025 HCTT Draft EIS/OEIS, in which they state that they agree with the Commission's recommendation that the Navy refrain from using cut-off distances and rely instead on the take estimates produced through its response functions. Response: The consideration of proximity (cut-off distances) was part of the criteria developed in consultation between the Navy and NMFS, and is appropriate based on the best available science, which shows that marine mammal responses to sound vary based on both sound level and distance. Therefore, these cut-off distances were applied within NAEMO. The derivation of the BRFs and associated cut-off distances is provided in the Criteria and Thresholds Technical Report. The Phase IV approach represents a refinement in assessing potential behavioral impacts. It employs a probability of response condition for high source level exposures, addressing previous concerns from the Commission about potentially cutting off responses when the probability remained above 50 percent. This approach, combined with the distance cut-off, provides a more nuanced and protective assessment compared to the Phase III methodology, which relied solely on distance cut-offs. Therefore, directly comparing Phase III and Phase IV cut-off distances is not appropriate. NMFS and the Navy are confident that this combined distance and probability threshold approach is well-substantiated by available data and effectively avoids underestimating potential behavioral responses to acoustic sources. To clarify, section 3.1.4 (Dose and Contextual Responses) of the Criteria and Thresholds Technical Report explains that at low received levels, distance to the sound source factors into the likelihood of a behavioral response. Although distance was investigated as a covariate in the Bayesian BRF model, most BRSs to date have used similar source levels making received level and source-receiver distance tightly correlated (see section 3.1.9 (Behavioral Cut-off Conditions) of the Criteria and Thresholds Technical Report). Therefore, including distance in the BRF model using the available response-received level data did not improve the BRFs. Still, NMFS and the Navy agree that distance is an important contextual factor. Since it was not possible to directly account for distance in the Bayesian model at this time, the Navy incorporated the behavioral cut-off conditions, beyond which significant behavioral reactions are assumed to be unlikely. As described in section 3.1.9 of the Criteria and Thresholds Technical Report, the distance cut-off conditions were conservatively estimated based on observations from multiple cited studies. Applying the distance cut-off condition is appropriate to reasonably estimate significant impacts. In addition, high source level exposures are addressed by also using a probability of response condition rather than the dual distance cut-off applied in Phase III. This method was devised in part to address public comments, including those from the Commission received in Phase III that were focused on cutting off behavioral responses, in some cases, where the probability of response was still above 50 percent. The probability of response cut-off condition in Phase IV allows for prediction of significant impacts beyond the distance cut-off. Regarding the studies cited by a commenter, Melcón et al. (2012) found that the probability of recording blue whale “D calls” decreased with higher received levels at the high-frequency acoustic recording package (HARP) buoy averaged over many hours; however, this study does not provide any information about the distance between the sound source and any animals and cannot be used to derive cut-off distances. Falcone et al. (2017) was reviewed by the Navy and discussed in the Criteria and Thresholds Technical Report: “. . . Falcone et al. (2017) modeled apparent responses to mid-powered sources out to 50 km (27 nautical miles (nmi)) and responses to high-powered sources at distances as great as 100 km (54 nmi). However, the models were not developed to estimate distances to response, and care needs to be taken when interpreting the results in that context.” Responses at 100 km (54 nmi) were generally mild, such as a slight ( i.e., less than 2 minutes) increase in the duration of shallow dives that was similar to the range of duration variability found in dives when no mid-frequency active sonar (MFAS) was present. The inter-deep dive interval duration also increased for both mid- and high-powered MFAS sources starting at 100 km (54 nmi); however, the inter-deep dive interval duration only exhibited the strongest increase within 20 km (10.8 nmi) of the source. As described in section 3.1.9 of the Criteria and Thresholds Technical Report, the cut-off conditions are applied to predict significant behavioral responses. The data used to inform the BRFs includes observations beyond 10 km (5.4 nmi) and studies cited in section 3.1.9 of the Criteria and Thresholds Technical Report. This includes data on exposures to other sound sources which is informative when data on exposure to sonars is limited. All the identified significant behavioral responses that were used to develop the BRFs are within the cut-offs (either by distance or SPL). Although behavioral responses are predicted beyond the cut-off conditions, these are not expected to rise to the level of harassment under the MMPA as defined for military readiness activities. NMFS and the Navy acknowledge the Commission's perspective but maintain that the combined use of cut-off distances and BRFs provides a more accurate and realistic assessment of potential behavioral impacts, particularly for military readiness activities. While Tyack and Thomas (2019) cautioned against using step functions anchored to the 50 percent response level of dose-response curves, the Navy's methodology does not employ such an approach. Instead, the cut-off distances, informed by the farthest observed distances of significant behavioral reactions in the available data (including those exceeding 10 km (5.4 nmi)), serve as a threshold for identifying responses reasonably likely to qualify as harassment under the MMPA. This approach prevents underestimating significant impacts while acknowledging that responses occurring beyond these distances, while possible, are less likely to reach this level of concern. The Navy's Phase IV approach, incorporating both BRFs and scientifically informed cut-off distances, offers a more realistic assessment of potential behavioral impacts compared to relying solely on BRFs. This approach balances the statistical probabilities derived from the BRFs with empirical observations of behavioral responses in the field. NMFS and the Navy are confident that this combined approach, while still incorporating conservatism to account for uncertainty, does not underestimate potential take by Level B harassment under the MMPA during military readiness activities and provides a more accurate representation of potential impacts. NMFS has independently assessed the thresholds used by the Navy to identify Level B harassment by behavioral disturbance and finds that they appropriately apply the best available science and it is not necessary to recalculate take estimates. As the science related to marine mammal behavior advances, NMFS and the Navy will continue to refine consideration of contextual factors, such as distance, in its assessment of behavioral responses. Comment 14 (ref 81): A commenter stated that NMFS wholly discounted gas-bubble pathology as a mechanism of harm to marine mammals due to the specified activities, and that the Action Proponents must assume that a number of beaked whales are subject to injury and mortality from gas-bubble formation. Response: The commenter's characterization of NMFS' analysis is incorrect. NMFS does not disregard the fact that it is possible for naval activities using hull-mounted tactical sonar to contribute to the death of marine mammals in certain circumstances (that are not present in the HCTT Study Area) via strandings resulting from behaviorally mediated physiological impacts or other gas-related injuries. In the Potential Effects of Specified Activities on Marine Mammals and Their Habitat section of the proposed rule, NMFS discusses these potential causes and outlines the few cases where active naval sonar (in the U.S. or, largely, elsewhere) has either potentially contributed to or, as with the Bahamas example, been more definitively causally linked to marine mammal strandings. As noted, there are a suite of factors that have been associated with these specific cases of strandings directly associated with sonar (steep bathymetry, multiple hull-mounted platforms using sonar simultaneously, constricted channels, strong surface ducts, etc.). These factors are not present together in the HCTT Study Area during the specified activities. Further, there have never been any strandings associated with Navy sonar use in the HCTT Study Area. For these reasons, NMFS does not anticipate that the Action Proponents' training or testing activities will result in marine mammal strandings, and none are authorized. Furthermore, ongoing Navy funded beaked whale monitoring at a heavily used training and testing area in the SOCAL Range Complex has not documented mortality or habitat abandonment by beaked whales. Passive acoustic detections of beaked whales have not significantly changed over 10 years of monitoring (DiMarzio et al., 2018; DiMarzio et al., 2019; DiMarzio et al., 2020). From visual surveys in the area since 2006 there have been repeated sightings of the same individual beaked whales, beaked whale mother-calf pairs, and beaked whale mother-calf pairs with mothers on their second calf (Schorr et al., 2018; Schorr et al., 2020). Satellite tracking studies of beaked whales documented high site fidelity to this area even though the study area is located in one of the most used Navy areas in the Pacific (Schorr et al., 2018; Schorr et al., 2020). Comment 15 (ref 82): A commenter stated that NMFS failed to present a meaningful analysis of the Navy's aggregate effects on marine mammal populations and refers to its comment on the 2024 HCTT Draft EIS/OEIS. Response: NMFS fully analyzed and considered the potential for aggregate effects from all of the Action Proponents' specified activities, and has applied a reasoned and comprehensive approach to evaluating the effects of these activities on marine mammal species or stocks and their habitat. This analysis was detailed in the Preliminary Analysis and Negligible Impact Determination section of the proposed rule and is included here in the Analysis and Negligible Impact Determination section of this final rule. Our analysis includes consideration of unusual mortality events (UMEs) and previous environmental impacts, where appropriate, to inform the baseline levels of both individual health and susceptibility to additional stressors, as well as stock status. Further, the species and stock-specific assessments in the Analysis and Negligible Impact Determination section (which have been updated and expanded since the previous HCTT rulemaking to consider additional species- and stock-specific factors) present and address the combined mortality, injury, behavioral harassment, and other effects of the aggregate activities, including impacts anticipated in important habitats such as ESA-designated critical habitat and known BIAs (and in consideration of applicable mitigation), as well as other information that supports our determinations that the Action Proponents' activities will not adversely affect any species or stocks via impacts on annual rates of recruitment or survival. We refer the reader to the Analysis and Negligible Impact Determination section for this analysis. Further, widespread, extensive monitoring since 2006 on Navy ranges that have been used for training and testing for decades has demonstrated no evidence of population-level impacts (see https://www.navymarinespeciesmonitoring.us/regions/pacific/current-projects/ for results, e.g., “Cuvier's Beaked Whale and Fin Whale Population Dynamics and Impact Assessment at the Southern California Offshore Antisubmarine Warfare Range (SOAR)”). Based on the best available research from NMFS and Navy-funded marine mammal studies, there is no evidence that “population-level harm” to marine mammals, including beaked whales, is occurring in the HCTT Study Area. Comment 16 (31): A commenter stated that the Eastern North Pacific stock of gray whale has been declining for years since the recent UME, and that NOAA estimates 13,000 Eastern North Pacific gray whales, rather than 26,960 whales as reported in the proposed rule. The commenter stated that this makes the other species estimates, impacts, and information in the draft very questionable. The commenter further states that there should be no harassment or takes of the Eastern North Pacific gray whales, nor the Southern Resident killer whales, nor other endangered or threatened species. The commenter also stated that more research is needed on the unknown impacts to multiple species of which the proposed rule proposed to authorize take, particularly research on new technologies, impulsive and continuous sonar broadcast, and uncrewed sea craft. Response: The 2023 Pacific SAR indicates the Eastern North Pacific stock of gray whales is increasing and has an abundance of 26,960 animals. However, recent (2024-2025) surveys conducted by NMFS' Southwest Fisheries Science Center (SWFSC) indicated that the estimated total abundance of gray whales during the 2024-2025 southbound migration was 12,950 (Eguchi et al., 2025). NMFS has updated its analysis to consider both abundance estimates, and has determined the authorized take of the Eastern North Pacific stock of gray whale will have a negligible impact on the stock, including in consideration of the Eguchi et al. (2025) estimate. As described in the Analysis and Negligible Impact Determination section, this stock is not listed under the ESA and is not considered as depleted or strategic under the MMPA and there are no UMEs or other for this stock. Any takes in the form of TTS are expected to be lower-level, of short duration (from minutes to, at most, several hours or less than a day), and mostly not in a frequency band that would be expected to interfere with gray whale communication or other important low-frequency cues. Any associated lost opportunities or capabilities individuals might experience as a result of TTS would not be at a level or duration that would be expected to impact reproductive success or survival. For similar reasons, while auditory injury impacts last longer, the low anticipated levels of AUD INJ that could be reasonably expected to result from these activities are unlikely to have any effect on fitness. Regarding the likely severity of any single instance of take by behavioral disturbance, as described above, the majority of the predicted exposures are expected to be below 172 dB SPL and last from a few minutes to a few hours, at most, with associated responses most likely in the form of moving away from the source, foraging interruptions, vocalization changes, or disruption of other social behaviors, lasting from a few minutes to several hours. Gray whales are large-bodied capital breeders with a slow pace of life and are therefore generally less susceptible to impacts from shorter duration foraging disruptions. Further, as described in the Group and Species-Specific Analyses section and the Mitigation Measures section, mitigation measures are expected to further reduce the potential severity of impacts through real-time operational measures that minimize higher level/longer duration exposures and time/area measures that reduce impacts in high value habitat. Given the number of takes by harassment as compared to the stock/species abundance (see table 54), and the fact that a portion of the takes of the Eastern North Pacific occur in BIAs, it is likely that some portion of the individuals taken are taken repeatedly over a limited number of days. However, given the variety of activity types that contribute to take across separate exercises conducted at different times and in different areas, and the fact that many result from transient activities conducted at sea, it is unlikely that repeated takes would occur either in numbers across sequential days in a manner likely to impact foraging success and energetics or other behaviors such that reproduction or survival of any individuals is likely to be impacted. Given the status of the stock and in consideration of other ongoing anthropogenic mortality (fisheries interactions, vessel strike), the authorized M/SI (three over the course of the 7-year rule, or 0.43 annually) will not, alone, nor in combination with the impacts of the take by harassment discussed above (which is not expected to impact the reproduction or survival of any individuals), be expected to adversely affect rates of recruitment and survival for any of this stock. NMFS did not propose to authorize take of southern resident killer whale (90 FR 32118, July 16, 2025), and this final rule does not authorize take of that stock. This rule does, however, authorize take of certain species that are listed as threatened or endangered under the ESA, as indicated in table 1. 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. As described in the Analysis and Negligible Impact Determination section, based on the analysis contained herein of the likely effects of the specified activities on marine mammals and their habitat, and taking into consideration the implementation of the proposed monitoring and mitigation measures, NMFS finds that the total marine mammal take from the specified activity will have a negligible impact on all affected marine mammal species or stocks. On September 16, 2024, NMFS received an application from the Action Proponents requesting authorization to take marine mammals incidental to training, testing, and modernization and sustainment of ranges (characterized as military readiness activities) within the HCTT Study Area. In response to our comments and following an information exchange, the Action Proponents submitted a revised application, deemed adequate and complete on December 13, 2024. NMFS, following its own analysis and proposed rule, has determined it is appropriate to promulgate a final rule and LOAs pursuant to 16 U.S.C. 1371(a)(5)(A) and 50 CFR 216.105. Regarding the commenter's assertion that more research is needed on the unknown impacts to multiple species of which the proposed rule proposed to authorize take, particularly research on new technologies, impulsive and continuous sonar broadcast, and uncrewed sea craft, this final rule requires the Action Proponents to conduct all monitoring and reporting required under the LOAs, including abiding by the HCTT Study Area monitoring program. Details on program goals, objectives, project selection process, and current projects are available at https://www.navymarinespeciesmonitoring.us. The commenter appears to imply that NMFS should not authorize take of marine mammals prior to completion of the research it states is needed. However, as stated in the Legal Authority for the Final Action 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 17 (32-3): A commenter recommended that NMFS integrate Indigenous and local ecological knowledge into baseline data collection and cumulative impact assessments. In a related comment, the commenter stated the proposed rule evaluates impacts primarily from the military readiness activities themselves but does not meaningfully incorporate the cumulative effects of commercial shipping, climate change-driven habitat shifts, and prior authorization of incidental take in the same region. Response: It is unclear what the commenter is referring to regarding baseline data collection, and the commenter has not identified, with any degree of specificity, which Indigenous or local ecological knowledge it recommends NMFS consider. The MMPA requires that NMFS issue an incidental take authorization, provided the necessary findings are made for the specified activity put forth in the application and appropriate mitigation and monitoring measures are set forth, as described in the Legal Authority for the Final Action section of this rule. As described in the proposed rule (90 FR 32118, July 16, 2025) and this final rule, the preamble for NMFS' implementing regulations under section 101(a)(5) (54 FR 40338, September 29, 1989) explains in response to comments that the impacts from other past and ongoing anthropogenic activities are incorporated into the negligible impact analysis via their impacts on the environmental baseline. Consistent with that direction, NMFS has factored into its negligible impact analyses the impacts of other past and ongoing anthropogenic activities via their impacts on the baseline ( e.g., as reflected in the density/distribution and status of the species, population size and growth rate, and other relevant stressors (such as UMEs)). See the Analysis and Negligible Impact Determination section of this rule. Our 1989 final rule for the MMPA implementing regulations also addressed how cumulative effects from unrelated activities would be considered. There we stated that such effects are not separately considered in making findings under section 101(a)(5) concerning negligible impact, but that NMFS would consider cumulative effects that are reasonably foreseeable when preparing a NEPA analysis and also that reasonably foreseeable cumulative effects would be considered under section 7 of the ESA for ESA-listed species. The cumulative effects of the incremental impact of the proposed action when added to other past, present, and reasonably foreseeable future actions (as well as the effects of ocean pollution and ecosystem alteration trends; see Table 4-2) were evaluated against the appropriate resources and regulatory baselines in the 2025 HCTT EIS/OEIS. The best available science and a comprehensive review of past, present, and reasonably foreseeable actions (including commercial shipping, ecosystem alteration trends, and other activities for which incidental take of marine mammals may occur) was used to develop the Cumulative Impacts analysis. This analysis is contained in chapter 4 of the 2025 HCTT EIS/OEIS. As required under NEPA, the level and scope of the analysis is commensurate with the scope of potential impacts of the action and the extent and character of the potentially-impacted resources ( e.g., the geographic boundaries for cumulative impacts analysis for some resources are expanded to include activities outside the HCTT Study Area that might impact migratory or wide-ranging animals), as reflected in the resource-specific discussions in chapter 3 (Affected Environment and Environmental Consequences) of the 2025 HCTT EIS/OEIS. The 2025 HCTT EIS/OEIS considered the proposed training activities alongside other actions in the region whose impacts may be additive to those of the proposed training. Past and present actions are also included in the analytical process as part of the affected environmental baseline conditions presented in chapter 3 of the 2025 HCTT EIS/OEIS. Further, cumulative effects to listed species of the specified activity in combination with other activities are analyzed in the ESA biological opinion. This analysis is contained in section 7 (Cumulative Effects). The opinion states that it assumes effects in the future would be similar to those in the past and, therefore, are reflected in the anticipated trends described in the Species and Designated Critical Habitat that May be Affected and Environmental Baseline sections of the biological opinion (sections 4 and 5, respectively). Marine Mammal Densities Comment 18 (ref 1): The Commission recommended that NMFS use an abundance estimate of 72,631 rather than 48,780 for April-June and 63,850 rather than 43,360 for July-March, along with a 75 percent assumption for the core area and 30 percent assumption for the geographic area to revise the density estimates and resulting numbers of takes of Guadalupe fur seals for the final rule. Response: Juárez-Ruiz et al. (2022) revised abundance estimate became available after the densities were derived for the Navy's acoustic and explosive impact modeling. The Navy worked with one of the co-authors on the paper by Juárez-Ruiz et al. (2022) to develop the density estimates used in the analysis, which included identifying the most appropriate abundance estimate for Guadalupe fur seal. During the process of calculating pinniped densities for the pending Northwest Training and Testing Phase IV Supplemental EIS/OEIS Study Area, The Marine Mammal Center reported to the Navy a revised unpublished abundance for Guadalupe fur seals of 96,468. Considering that this is a two-fold increase in the abundance estimate used to derive densities, the Navy decided that the Guadalupe fur seal densities should be revised and take estimates recalculated based on the adjusted densities. Since there are only two uniform density strata for Guadalupe fur seal, the Navy determined that remodeling to estimate takes would not be necessary and that the increase in takes can be estimated by calculating a multiplier equal to the ratio between the initial and recalculated densities. Two multipliers were calculated and used to revise take estimates: (1) a warm season multiplier of 2.07945; and (2) a cold season multiplier of 2.05908. This was a reasonable approach given that remodeling is not feasible at this point because exposure estimates from previous analyses in at-sea study areas have shown that changes in densities result in approximately proportional changes in predicted exposures. The “U.S. Navy Marine Species Density Database Phase IV for the Hawaii-California Training and Testing Study Area” (U.S. Department of the Navy, 2024b), hereafter referred to as the Density Technical Report, was amended with the revised densities in September 2025 and is hereafter referred to as the revised Density Technical Report (U.S. Department of the Navy, 2025b), and NMFS concurs with that revision. The HCTT proposed rule and this final rule include the resulting take numbers. Comment 19 (ref 2): The Commission recommended that NMFS use the monk seal abundance estimates from the 2022 SAR to derive its density estimates and re-estimate the numbers of takes for the final rule. Response: The abundance of 1,437 monk seals published in the 2021 SAR (Carretta et al., 2022) was the latest abundance estimate available when the Navy calculated densities. The 2022 SAR (Carretta et al., 2023b) was published in August 2023, over 1 year after densities were finalized. The Navy revised the density estimates for Hawaiian monk seal using the latest abundance estimates reported in the 2024 draft SAR (Carretta et al., in review) for each island where separate abundances were reported. The total abundance reported by Carretta et al. (in review) is 1,605 monk seals. In order to account for the increase in total abundance, the Navy calculated multipliers for each island by taking the ratio of the revised and initial densities. An analysis of the acoustic effects modeling results showed that all predicted exposures of Hawaiian monk seals occurred in the Main Hawaiian Islands (MHI) and no exposures occurred in the Northwestern Hawaiian Islands. Therefore, the Navy used the highest multiplier derived for the MHI of 1.2919 to increase the estimated takes in waters both greater than and less than 200 m. NMFS concurs with this method. Comment 20 (ref 3): The Commission recommended that NMFS: (1) revise the elephant seal density estimates by increasing the (a) in-water percentage of females from 0-25 percent for May and June, (b) percentage of females off California from 80-100 percent for January, February, and May, (c) in-water percentage of males from 0-25 percent for August, and (d) percentage of females off California in September and October from 5 percent and males off California in April, May, June, and October from 0-10 percent to the percentage of the population expected to be comprised of yearlings and juveniles and the sex-based ratios provided in table 9-12 of the Density Technical Report; and (2) re-estimate the numbers of takes accordingly for the final rule. The Commission stated that these revisions are particularly important, because NMFS relies on the Navy's density estimates for authorizing the taking associated with many other activities off California and will do so for at least the next 7 years until the Phase V densities are available. Response: The Navy used the kernel density distribution areas shown in figure 4 in Robinson et al. (2012) to approximate the spatial strata to use in density calculations. The Navy recognized that the data in Figure 4 indicated a higher relative density of female elephant seals off California in May and June; however, that is the time during which females return to natal rookeries and are hauled out molting and fasting and not expected to spend much, if any, time in the water. The sex and age class haulout behavior of northern elephant seals is complex and difficult to represent in this type of calculation where some portion of seals of each age and sex class is hauled out at different but overlapping time periods that span partial months. For 7 months (males) or 8 months (females) out of the year, the Navy assumes 100 percent of seals are in the water, which is undoubtedly an overestimate considering that seals are known to haulout during foraging periods. While the Navy strives to improve density estimates to accurately represent pinniped haulout behavior, the level of precision is limited by both the available and sometimes conflicting data on species' behavior and the large scale of the study area over which behavior may vary. The assumptions made for the purposes of calculating monthly densities at this scale were reasonable and generally representative of the species behavior. While the majority of tagged elephant seals reported by Robinson et al. (2012) were from Año Nuevo Island, a few were tagged on Islas San Benito, Mexico and followed similar migration patterns. Seals from all other breeding and haulout sites are expected to follow similar migration patterns ( i.e., move north or northwest after breeding and molting periods) and to follow similar annual breeding and molting haulout cycles. For females, this means hauling out to molt in May and June and spending little to no time in the water. Again, the information in Robinson et al. (2012) was primarily used to define strata for calculating densities. It's clear from Robinson et al. (2012) figure 4 that 100 percent of females do not occur off CA in January, February, and May; the Navy considers 80 percent to be a reasonable estimate. It's not clear how the Commission determined that 10 percent instead of 5 percent of females would be off California in September and October. While the density estimates do not distinguish abundance by age class, the entire population abundance is used in the calculations, which includes all age classes. Furthermore, the analyzed abundance of elephant seals includes 22,000 seals from the Mexico breeding population (a likely overestimate for that declining population as noted in the Density Technical Report and revised Density Technical Report and exceeds the abundance of the California breeding stock managed by NMFS. This conservative abundance estimate puts more seals in the water during the majority of the year and likely inflates predicted exposure estimates. Lastly, the majority of sonar and explosive use occurs in the SOCAL Range Complex located south of the elephant seal at-sea distribution following both the post-breeding and post-molting migrations, which extend north and northwest of the Channel Islands and into the North Pacific. As such, the Navy has not revised the density estimates as recommended by the Commission. NMFS concurs, and has not revised the number of estimated takes of this stock. Comment 21 (ref 4, 5): The Commission recommended that NMFS: (1) revise the harbor seal density estimates by using (a) the 2.86 correction factor from Harvey and Goley (2011) rather than 2.44 for the Channel Islands and 1.15 for Point Mugu and La Jolla to estimate the total abundances at the various locations in Table 9-21 of Density Technical Report, (b) the 65 percent in-water percentage from Harvey and Goley (2011) for Point Mugu, La Jolla, and all of the Channel Islands except for San Nicolas and San Miguel Islands for the entire year, and (c) 40 km from shore from Calambokidis (2004) and the 200-m isobath based on Stewart and Yochem (1994) rather than 20 km from shore and the 120-m isobath as stratum demarcations for areas where harbor seals could occur; and (2) re-estimate the numbers of takes accordingly for the final rule. The Commission further recommended that NMFS: (1) contact the SWFSC to obtain the maximum harbor seal abundance estimate from Santa Catalina Island during which the relevant haul-out sites were surveyed and use the 2.86 correction factor to estimate the total abundance at Santa Catalina Island; (2) estimate the total abundance of harbor seals from La Jolla to Point Mugu and from Point Mugu around past Pt. Conception based on the number of harbor seals of the 30,968 abundance estimate for the California stock from Harvey and Goley (2011) that remains after subtracting the Channel Islands, Point Mugu, and La Jolla abundance estimates; (3) use the 65 percent in-water percentage from Harvey and Goley (2011), 40 km from shore from Calambokidis (2004), and the 200-m isobath based on Stewart and Yochem (1994) to estimate the harbor seal density for Santa Catalina Island, from La Jolla to Point Mugu, and from Point Mugu around past Pt. Conception; and (4) re-estimate the numbers of takes accordingly for the final rule. Response: Regarding the Commission's recommendation to use the 2.86 correction factor from Harvey and Goley (2011), the correction factor for San Nicolas Island from Stewart and Yochem (1983) of 59 percent in-water is the most appropriate haulout factor ( i.e., with one exception it is the highest percentage of seals in the water) compared with other available haulout factors. Harvey and Goley (2011) recommend a factor of 1.54 (or 35 percent in water) for all of California. A factor of 2.86 (65 percent in-water) for southern California was also reported by the authors, but was based only on one survey, so the authors recommended using the mean of 1.54 (35 percent in-water) for California over the 2.86 factor. Note that the authors describe the single survey from southern California as “a poor sample estimate of the proportion ashore.” The Navy used 2.44 (59 percent in-water), which is higher than most other factors including all three of the mean haulout factors derived by Harvey and Goley (2011) (see table 2 in the paper), which would also have been reasonable alternatives. Haulout factors were also chosen to be specific to season (breeding/molting vs. non-breeding/molting) as well as location where data were available. The survey data reported by Lowry et al. (2021) that were used to estimate abundances and densities were conducted in summer, so Navy used the most conservative haulout factor for summer (59 percent in-water) from Stewart and Yochem (1983) for the in-water abundance estimate, and NMFS concurs. The 87 percent ashore estimate was a typo in the Navy's 2024 Marine Species Density Database (NMSDD) which has been superseded by the revised Density Technical Report. It should have been 83 percent ashore equating to 17 percent in-water, as shown in table 9-20 in the revised Density Technical Report. The factor of 1.2 or 17 percent in-water is from table 1 in Huber et al. (2001) which cites the source as Hanan (1996), a Ph.D. dissertation. The Navy corrected the typo in the revised Density Technical Report. The Navy selected the 1.2 haulout factor for the two mainland locations in Southern California because several of the sites used in the research were located along the mainland coast and the Navy sought out correction factors specific to seals along the mainland, and NMFS concurs with this approach. Below table 9-25 in the revised Density Technical Report, the following text states which correction factor was used for the September-February time period, “For the September through February time period, the in-water abundance was estimated as 86 percent of the total abundance, based on data from San Miguel Island reported by Yochem et al. (1987) and included in a summary by Huber et al. (2001).” Table 9-24 shows an in-water percentage range of 81-86 percent; the Navy selected 86 percent in-water as a more conservative approach. NMFS concurs with this decision. The Navy used the 59 percent in-water factor for March through August for all Channel Islands except for San Miguel Island, which used 23 percent based on a tagging study conducted with seals on the island, and NMFS concurs. As a conservative measure, the Navy used the highest counts from 2016 to 2019 by Lowry et al. (2021) to estimate in-water abundances instead of using a multi-year average or counts from the most recent year ( i.e., 2019) (refer to table 9-25 in the revised Density Technical Report). Both alternative options would have been reasonable to select, but instead the Navy chose to use the maximum count over the 4 year survey period. Note that the maximum counts for six of the eight islands occurred in 2016 (the other two occurred in 2019), suggesting that the overall harbor seal abundance in the Channel Islands may be declining and that the Navy's density estimates may be high for predicting takes beyond the year 2019. NMFS concurs with this approach. Regarding the strata, harbor seals are well known for remaining close to haulouts and foraging in relatively shallow waters, as documented in the half dozen sources cited on page 237 of the revised Density Technical Report. The sources also demonstrate that while habitat use is generally similar in multiple regions, there is variability in the depth and distance from shore characteristics of harbor seal distribution in various studies. The Navy reviewed the sources and attempted to define strata that captured the general and expected distribution of the species. Expanding strata farther offshore into deeper waters to capture extralimital and infrequent excursions by individual seals (as recommended by the Commission) would have the effect of reducing the density in the nearshore habitat where harbor seals predominantly occur. Stewart and Yochem (1994) reported the 20 km distance-from-shore metric used in the analysis. The 120 m depth contour used to define strata encompassed the vast majority of reported foraging depths without expanding the strata farther offshore ( e.g., to the 200 m depth contour representing the shelf break as the Commission recommended) and reducing the densities. The density estimates are intended to represent the predominant occurrence and distribution of the population rather than capture all possible areas where wide-ranging individuals have been sighted. The Channel Islands are part of the Continental Borderland region in the Southern California Bight which exhibits a complex bathymetry without a clearly distinct shelf break. While the shelf break (often represented by the 200 m depth contour) is a reasonable boundary to choose in more conventional continental margins, it does not accurately demarcate the shelf break in the Southern California Bight. As noted above, the harbor seal abundances were based on counts reported by Lowry et al. (2021), which reported eight harbor seals off Santa Catalina island in 2019 only; no counts were reported in 2016 through 2018. Using a haulout factor of 59 percent results in a total abundance of 20 seals associated with the island and in-water abundance estimates of 12 seals (March-August) and 17 seals (September-February). The area around Santa Catalina Island extending from shore to the 120 m isobath is approximately 42,205 square kilometers (km 2 ), which results in densities of 0.0003 to 0.0004 seals/km 2 for March-August and September-February, respectively. The densities are about three orders of magnitude lower than densities around the other islands where the Navy conducts more activities ( e.g., San Nicolas, San Miguel, San Clemente). Based on these factors, the Navy has determined that adding a density for Santa Catalina Island and remodeling would not contribute substantively, if at all, to the current take estimates, and NMFS concurs. The Navy worked with scientists from the NMFS SWFSC to derive the pinniped density estimates, including estimates for harbor seals. There is a lack of survey data between La Jolla and Point Mugu along the mainland coast, which is why densities are not provided along that part of the coast. It is also noteworthy that the majority of training and testing activities using sonar and other transducers or explosives would occur beyond 12 nmi (22.2 km) from shore along the mainland coast. The adjacent warning area (W-291) begins approximately 12 nmi (22.2 km) from shore along the coast between La Jolla and Point Mugu. Therefore, any harbor seals occurring along the coast in this area are unlikely to be affected, and calculating the density using the method suggested by the Commission is not warranted. Calambokidis et al. (2004) reported harbor seal sightings off the Washington coast from 1995 to 2002. While not as relevant to more recently reported harbor seal behavior off California, the authors reported a mean depth for the 15 sightings of 102 m and a mean distance from shore of 15.5 km, which further supports the Navy's decision to use the 120 m depth contour and a distance of 20 km from shore to define the strata used in the Navy's HCTT density estimates rather than greater depths and distances from shore recommended by the Commission. Given that the densities remain unchanged, re-estimating the number of takes for this final rule was not required. Comment 22 (6, 7): The Commission recommended that NMFS work with the Navy to derive harbor seal and bottlenose dolphin density estimates for both within San Diego Bay and the SSTC area based on sightings data from the numerous monitoring reports available, while also considering the area beyond the Coronado Bridge in San Diego Bay. Response: The Navy has derived densities for bottlenose dolphin for the SSTC, located south of the entrance to San Diego Bay (see figure 6-53 in the Density Technical Report). The Navy recognizes that in addition to the regularly occurring California sea lion, other marine mammal species, such as harbor seal and common bottlenose dolphin occasionally enter San Diego Bay; however, those species tend to remain near the mouth of the Bay, with only a few moving farther into the Bay. The planned activities involving in-water sound sources within San Diego Bay occur well into the Bay, typically south of the Coronado Bridge, and do not include pile driving. The monitoring report for the Naval Base Point Loma Pier 302 Replacement Project (available at https://www.fisheries.noaa.gov/action/incidental-take-authorization-naval-base-point-loma-pier-302-replacement-project ) cited by the Commission reported observation of 1 bottlenose dolphin and 13 harbor seals over 181 observer hours. It is not unusual for individuals of both species that occur in nearshore waters to be sighted at the mouth of San Diego Bay near Point Loma. The Naval Base San Diego (NBSD) Pier 6 Replacement Project monitoring report (available at https://www.fisheries.noaa.gov/action/incidental-take-authorization-naval-base-san-diego-pier-6-replacement-project-san-diego ) recorded species during two IHA periods over approximately 15 months (October 2021-January 2023). Only two harbor seals were observed over 450 monitoring days under the first IHA and no harbor seals were observed over 88 monitoring days under the second IHA. These few observations are not indicative of regular occurrence in the central or southern part of San Diego Bay and do not support the need for a density estimate in San Diego Bay. The report also shows 86 bottlenose dolphin observations under the first IHA and 0 bottlenose dolphin observations under the second IHA (table 3-3). The report qualifies the total number of observations by quantifying re-sightings in table 3-5 ( i.e., sightings of the same individual multiple times based on identifiable markings on dorsal fins ( e.g., cuts, scrapes, shape, etc. )). The data indicate approximately 72 percent of individuals observed were resights. Table 3-12 in the report shows that bottlenose dolphins were only sighted in January, February, and March of 2022 and were not sighted during any other month. Monitoring also occurred in January 2023 with zero bottlenose dolphin observations; however, no monitoring occurred in February or March of 2023. It is possible that the occurrence in San Diego Bay from January to March of 2022 was an anomaly; the report noted that bottlenose dolphins were not expected to occur in San Diego Bay at all. Observer bias may have also contributed to the increased sightings, as noted in section 3.2.2 of the report, which discussed a similar trend in observations of California sea lions. The Commission references 15 IHAs issued to the Navy in the last decade, but aside from the two noted above, the Commission does not clearly state which other projects are referenced. The non-systematic observations reported in the monitoring reports mentioned previously do not support robust density estimates for San Diego Bay. Additional data would be required to better quantify abundance and seasonal occurrence in the bay to support a density estimate. Therefore, given their occasional presence and the limitations of the observational data, the Navy did not develop density estimates for harbor seal and bottlenose dolphin specific to San Diego Bay for the HCTT EIS/OEIS, and NMFS concurs such density estimates are not necessary. Comment 23 (ref 8): The Commission recommended that NMFS work with the Navy to derive the California sea lion density estimates south of the Coronado Bridge based on sightings data from the numerous monitoring reports rather than Graham and Saunders (2015). Response: While the observations of California sea lions during pier replacement activities at NBSD confirm the presence of sea lions south of the Coronado Bridge, the observations were not based on line transect surveys unlike the data reported by Graham and Saunders (2015). Naval Facilities Engineering Command Southwest (2024) reported 237 observations over 493 monitor days, or 0.48 animals per day, and also acknowledged that the observations included repeat sightings (approximately 26 percent of individuals), making the data less useful for estimating densities. As with the bottlenose dolphin sightings, the report noted that sightings of California sea lions increased substantially in January, February, and March of 2022, and the increase was likely due to the presence of additional observers. This suggests a bias in the data that limits its usefulness for deriving densities representative of species distribution and occurrence. These non-systematic observations reported in both in the Naval Facilities Engineering Command Southwest (2024) monitoring report do not support robust density estimates for south and central San Diego Bay. Additional data would be required to better quantify abundance and seasonal occurrence in the bay to support a density estimate. Furthermore, the proposed military readiness activities in San Diego Bay do not include pile driving or other sound-producing activities that would require a density for analysis. Comment 24 (ref 9): The Commission noted the following points related to the pinniped densities provided in the Density Technical Report. The Commission recommended that NMFS work with the Navy to revise the Density Technical Report to clarify and address these points since the densities will inform the numbers of takes for the final rule and other incidental take authorizations for activities conducted by the Navy and other applicants. • The Navy stated that, on average, post-partum female northern fur seals spent 180 hours in the water for every 40 hours on land, equating to 78 percent of time in the water, which equated to 78 percent of adult females being in the water from June through November. The in-water percentage would be 82 rather than 78 percent. • The Navy incorrectly identified the various in-water percentages for California sea lions in Table 9-25 as haul-out correction factors in the table heading and underlying text. The heading and text should indicate that those are indeed in-water percentages, similar to table 9-20 for harbor seals. • The Navy did not include the California sea lion juveniles and pups specified in table 9-25 in the non-breeding season abundance estimate for the California breeding strata. Juveniles and pups should be included in the abundance estimate as was done for the breeding season density. • The Navy specified that the in-water percentages for Steller sea lions were correction factors for estimation of the in-water abundances. The percentages should be specified as in-water percentages rather than correction factors, similar to harbor seals. Response: Regarding the Commission's first point, Antonelis et al. (1990) states that the average foraging trip was 180.6 hours (standard deviation (SD) = 37 hours) and the average time on land was 39.6 hours (SD = 10 hours). The Navy interpreted that as a ratio of 40 hours on land to 180 hours in water or 40:180 = 40/180 = 22 percent on land (78 percent in water). The Navy acknowledges a different interpretation of the source is reasonable, but notes that any difference in the resulting percentages (78 percent vs. 82 percent) is within the range of the SD in both measurements. As such, the Navy has not adjusted the percentage, and NMFS concurs no adjustment is warranted. Regarding the Commission's second and fourth points, the Navy changed the heading on table 9-25 in the Density Technical Report and adjusted related text on correction factors in the sections on California sea lions and Steller sea lions and in the revised Density Technical Report. NMFS concurs with this change. Regarding the Commission's third point, the abundance estimate used to calculate densities for the non-breeding season was based on the total stock abundance and therefore considered all lifestages, even though they were not specifically called out in the calculation. The in-water percentages reported in table 9-25 were based on data on haulout behavior for each lifestage, but not all percentages were used to calculate densities. For example, for the non-breeding season female pups were effectively assigned the in-water percentage of 75 percent characteristic of adult females, but used for all females, rather than the 34 percent in-water percentage representing pup haulout behavior. Using this approach helped to simplify the calculation somewhat but also resulted in a more conservative density estimate. Also, the abundance used was based on data reported by Hernández-Camacho et al. (2021) and exceeded the current abundance for the California Stock reported in the SAR. As such, no change is warranted. Mitigation Comment 25 (ref 32-1): A commenter recommended that NMFS expand the exclusion and shutdown zones to reflect what the author suggests is “current science on behavioral harassment thresholds.” Response: The comment is vague, and the commenter does not provide citations or otherwise support the assertion that the proposed zones do not adequately reflect current science. The mitigation zones and the shutdown requirements included in the proposed rule and this final rule considered the current science regarding behavioral response, as well as practicability for implementation. The practicability assessment criteria are described in table 5-1 of the 2025 HCTT EIS/OEIS. Comment 26 (ref 33): A commenter stated that for mitigation areas to effectively protect marine mammals they must be properly sited, and the management objectives for each mitigation area must be based on best available scientific information. The commenter stated, when uncertainty exists and options are proposed that risk overprotection or underprotection, the MMPA requires the permitting agency to consider “whether the precautionary approach would give more protection to marine mammals, and then whether that protection would impede military training to a degree making that mitigation not practi [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2025-23088. Public record. Not legal advice.