SUPPLEMENTARY INFORMATION:

Background

Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) direct the Secretary of Commerce to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and either regulations are issued or, if the taking is limited to harassment, a notice of a proposed authorization is provided to the public for review.

An authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such takings are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.

Except with respect to certain activities not pertinent here, the MMPA defines “harassment” as: any act of pursuit, torment, or annoyance which: (i) has the potential to injure a marine mammal or marine mammal stock in the wild (Level A harassment); or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering (Level B harassment).

On January 19, 2021, we issued a final rule with regulations to govern the unintentional taking of marine mammals incidental to geophysical survey activities conducted by oil and gas industry operators, and those persons authorized to conduct activities on their behalf (collectively “industry operators”), in U.S. waters of the GOA ^[1] over the course of 5 years (86 FR 5322, January 19, 2021). The rule was based on our findings that the total taking from the specified activities over the 5-year period will have a negligible impact on the affected species or stock(s) of marine mammals and will not have an unmitigable adverse impact on the availability of those species or stocks for subsistence uses and became effective on April 19, 2021.

The regulations at 50 CFR 217.180 et seq. allow for the issuance of LOAs to industry operators for the incidental take of marine mammals during geophysical survey activities and prescribe the permissible methods of taking and other means of effecting the least practicable adverse impact on marine mammal species or stocks and their habitat (often referred to as mitigation), as well as requirements pertaining to the monitoring and reporting of such taking. Under 50 CFR 217.186(e), issuance of an LOA shall be ( printed page 58099) based on a determination that the level of taking will be consistent with the findings made for the total taking allowable under these regulations and a determination that the amount of take authorized under the LOA is of no more than small numbers.

NMFS subsequently discovered that the 2021 rule was based on erroneous take estimates. We conducted another rulemaking using correct take estimates and other newly available and pertinent information relevant to the analyses supporting some of the findings in the 2021 final rule and the taking allowable under the regulations. We issued a final rule in April 2024, effective May 24, 2024 (89 FR 31488, April 24, 2024).

On August 28, 2025, NMFS Office of Protected Resources received a request from NMFS Office of Policy for reimplementation of the current incidental take regulation (ITR) to avoid a lapse in ITRs offering incidental take coverage for GOA geophysical survey activities. On October 20, 2025, Bureau of Ocean Energy Management (the original petitioner for the current ITRs) submitted a request to be included in the process as a co-petitioner. In response to these requests, NMFS issued a new final rule, effective April 20, 2026, through April 19, 2031 (91 FR 20784, April 17, 2026).

The reimplementation of the regulations continues the established framework for authorization of incidental take through LOAs. The final rule made no changes to the specified activities or the specified geographical region in which those activities would be conducted, and there are no changes to the associated mitigation, monitoring, and reporting requirements.

Summary of Request and Analysis

TGS plans to conduct a three-dimensional (3D) ocean-bottom node (OBN) survey over approximately 600 lease blocks in the East Breaks and Alaminos Canyon areas, with water depths ranging from approximately 900 to 3,200 meters (m).

TGS plans to use a low-frequency airgun source known as Gemini (also referred to as a dual barbell source). Gemini airgun arrays will fire using the “Seismic Apparition” method, with a single-source vessel towing six sources (100-m separation), firing within 120 milliseconds with a predetermined dither to each source; no sources will fire simultaneously at any time.

Gemini was not included in the acoustic exposure modeling developed in support of the rule. However, Gemini was described and evaluated in support of a previous LOA, and we rely on that analysis here (88 FR 72739, October 23, 2023). For additional details regarding sources, see section C of the LOA application. Based on this information we have determined there will be no effects of magnitude or intensity different from those evaluated in support of the rule. NMFS therefore expects that use of modeling results supporting the final rule relating to use of airgun arrays is expected to be conservative as a proxy for use in evaluating potential impacts of use of Gemini.

Consistent with the preamble to the 2026 final rule, the survey effort proposed by TGS in its LOA request was used to develop LOA-specific take estimates based on the acoustic exposure modeling results described in the preamble (91 FR 20784, April 17, 2026). In order to generate the appropriate take number for authorization, the following information was considered: (1) survey type; (2) location (by modeling zone ⁱ ); (3) number of days; (4) source; and (5) month.ⁱⁱ To determine the most appropriate proxy array from the exposure modeling, the directionally dependent source level in a plane parallel to the sea surface was compared to the three airgun array sources which were originally modeled, including the 4,130-, 5,110-, and 8,000-in³ arrays. Out of these three proxies, the source which had the smallest relative error (arithmetic mean difference taken over the azimuthal or vessel bearing angle) was chosen as the most representative proxy. For a single 8,000-in³ Gemini source, surface affected waveforms were modeled by TGS using Nucleus+. To approximate the acoustic energy from six elements, the SEL for each frequency and aspect was adjusted by a factor of 10*log₁₀ ( N), where N in this case is 6. The resulting spectra were used in the comparison tool. The results showed that the most comparable source was the 4,130-in³ array. The Nucleus+ results indicate that the horizontal surface-affected SEL source level for a single 8,000-in³ array is approximately 218.2 dB, while the additional 10*log₁₀ (6) increases this to approximately 226 dB. Notably, the corresponding source level for the 4,130-in³ source is approximately 232 dB. Thus, the total acoustic energy from six 8,000-in³ Gemini sources remains lower than the conventional 4,130-in³ array. The acoustic exposure modeling performed in support of the rule provides 24-hour exposure estimates for each species, specific to each modeled source and survey type in each zone and month.

No OBN surveys were included in the modeled survey types, and use of existing proxies ( i.e., 2D, 3D NAZ, 3D WAZ, Coil) is generally conservative for use in evaluation of 3D OBN survey effort, largely due to the greater area covered by the modeled proxies. Summary descriptions of these modeled survey geometries are available in the preamble to the proposed rule (91 FR 9014, 9018, February 24, 2026). Coil was selected as the best available proxy survey type in this case because the spatial coverage of the planned survey is most similar to the coil survey pattern. Among the different parameters of the modeled survey patterns ( e.g., area covered, line spacing, number of sources, shot interval, total simulated pulses), NMFS considers area covered per day to be most influential on daily modeled exposures exceeding Level B harassment criteria. Although TGS is not proposing to perform a survey using the coil geometry, the coil proxy is most representative of the effort planned by TGS in terms of predicted Level B harassment exposures.

NMFS previously issued a LOA to TGS on June 26, 2026, for the take of marine mammals incidental to a 3D OBN survey in the East Breaks and Alaminos Canyon areas, effective September 1, 2026, through September 1, 2027. Please see the Federal Register notice of issuance (91 FR 39072, June 29, 2026) for additional details regarding the LOA and the proposed survey activity.

On August 25, 2026, TGS informed NMFS that its planned survey area had shifted and, accordingly, they requested a new LOA based on the updated survey area. This new LOA will replace the LOA previously issued to TGS.

The updated survey plan includes 102 total days of sound source operation with 74 days in zone 6 and 28 days in zone 7. The monthly distribution of survey days is not known in advance, though we assume that the planned 102 days of source operation would occur contiguously. Take estimates for each species are based on the time period that produces the greatest value and have been updated based on the revised survey plan.

Based on the results of our analysis, NMFS has determined that the level of taking expected for this survey and authorized through the LOA is consistent with the findings made for the total taking allowable under the regulations. See table 1 in this notice and table 7 of the rule (91 FR 20784, April 17, 2026).

Small Numbers Determination

Under the rule, NMFS may not authorize incidental take of marine mammals in an LOA if it will exceed “small numbers.” In short, when an ( printed page 58100) acceptable estimate of the individual marine mammals taken is available, if the estimated number of individual animals taken is up to, but not greater than, one-third of the best available abundance estimate, NMFS will determine that the numbers of marine mammals taken of a species or stock are small (91 FR 20784, April 17, 2026). For more information, please see NMFS' discussion of small numbers in the 2026 final rule (91 FR 20784, April 17, 2026).

The take numbers for authorization are determined as described above in the Summary of Request and Analysis section. Subsequently, the total incidents of harassment for each species are multiplied by scalar ratios (except in the cases where the take estimate has been rounded up to reflect a group size) to produce a derived product that better reflects the number of individuals likely to be taken within a survey (as compared to the total number of instances of take), accounting for the likelihood that some individual marine mammals may be taken on more than 1 day (91 FR 20784, April 17, 2026). The output of this scaling, where appropriate, is incorporated into adjusted total take estimates that are the basis for NMFS' small numbers determinations, as depicted in table 1.

This product is used by NMFS in making the necessary small numbers determinations through comparison with the best available abundance estimates (see discussion at 91 FR 20784, 20812, April 17, 2026). For this comparison, NMFS' approach is to use the maximum theoretical population, determined through review of current stock assessment reports (SAR; www.fisheries.noaa.gov/​national/​marine-mammal-protection/​marine-mammal-stock-assessments) and model-predicted abundance information ( seamap.env.duke.edu/​models/​SEFSC/​GOM/​). Information supporting the small numbers determinations is provided in table 1.

Based on the analysis contained herein of TGS's proposed survey activity described in its LOA request and the anticipated take of marine mammals, NMFS finds that small numbers of marine mammals will be taken relative to the affected species or stock sizes ( i.e., less than one-third of the best available abundance estimate) and therefore the taking is of no more than small numbers.

Authorization

NMFS has determined that the level of taking for this LOA request is consistent with the findings made for the total taking allowable under the incidental take regulations and that the amount of take authorized under the LOA is of no more than small numbers. Accordingly, we have issued a LOA to TGS, authorizing the take of marine mammals incidental to its geophysical survey activity, as described above.

91 FR 58098