# Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to Geophysical Surveys Related to Oil and Gas Activities in the Gulf of Mexico

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2020-27252

## Record

- **Collection:** Federal Register
- **Document type:** Rule
- **Published:** January 19, 2021
- **Citation:** 86 FR 5322

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
50 CFR Part 217
[Docket No. 201204-0326]
RIN 0648-BB38
Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to Geophysical Surveys Related to Oil and Gas Activities in the Gulf of Mexico

AGENCY:

National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce.

ACTION:

Final rule.

SUMMARY:

NMFS, upon request from the Bureau of Ocean Energy Management (BOEM), hereby issues 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 Federal waters of the U.S. Gulf of Mexico (GOM) over the course of five years. These regulations, which allow for the issuance of Letters of Authorization (LOA) to industry operators for the incidental take of marine mammals during the described activities and specified timeframe, 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, as well as requirements pertaining to the monitoring and reporting of such taking.

DATES:

Effective from April 19, 2021 through April 19, 2026.

ADDRESSES:

Electronic copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at:
www.fisheries.noaa.gov/action/incidental-take-authorization-oil-and-gas-industry-geophysical-survey-activity-gulf-mexico.
In case of problems accessing these documents, please call the contact listed below.

FOR FURTHER INFORMATION CONTACT:

Ben Laws, Office of Protected Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Purpose and Need for Regulatory Action

These incidental take regulations (ITR) establish a framework under the authority of the MMPA (16 U.S.C. 1361
et seq.
) to allow for the authorization of take of marine mammals incidental to the conduct of geophysical survey activities in the GOM. We received a petition from BOEM requesting the regulations. Subsequent LOAs may be requested by industry operators. Take is expected to occur by Level A and/or Level B harassment incidental to use of active acoustic sound sources. Please see the Background section below for definitions of harassment.

Legal Authority for the Action

Section 101(a)(5)(A) of the MMPA (16 U.S.C. 1371(a)(5)(A)) directs 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 for up to five years if, after notice and public comment, the agency makes certain findings and issues regulations that set forth permissible methods of taking pursuant to that activity and other means of effecting the “least practicable adverse impact” on the affected species or stocks and their habitat (see the discussion below in the Mitigation section), as well as monitoring and reporting requirements. Section 101(a)(5)(A) of the MMPA and the implementing regulations at 50 CFR part 216, subpart I, provide the legal basis for issuing this rule containing the regulations, and for any subsequent LOAs. As directed by this legal authority, the regulations contain mitigation, monitoring, and reporting requirements.

Summary of Major Provisions Within the Regulations

Following is a summary of the major provisions of these regulations regarding geophysical survey activities. These measures include:

• Standard detection-based mitigation measures, including use of visual and acoustic observation to detect marine mammals and shut down acoustic sources in certain circumstances;

• A time-area restriction designed to avoid effects to bottlenose dolphins in times and places believed to be of particular importance;

• Vessel strike avoidance measures; and

• Monitoring and reporting requirements.

These incidental take regulations govern and allow for the subsequent issuance of letters of authorization for the take of marine mammals incidental to the specified activity described in this Notice, within the upper bounds of take that was evaluated for this rule, and prescribe measures for mitigation, monitoring, and reporting. They do not preclude a U.S. citizen from applying for an incidental take authorization for a specified activity with different parameters or required measures through a separate request and process.

Background

Section 101(a)(5)(A) 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, regulations are issued, and notice is provided to the public.

An authorization for incidental taking 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 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.

The MMPA states that the term “take” means to harass, hunt, capture, or kill, or attempt to harass, hunt, capture, or kill, any marine mammal.

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).

Summary of Request

On October 17, 2016, BOEM submitted a revised petition
1

to NMFS for rulemaking under section 101(a)(5)(A) of the MMPA to authorize take of marine mammals incidental to conducting geophysical surveys during

oil and gas industry exploration and development activities in the GOM. This revised petition was deemed adequate and complete based on NMFS' implementing regulations at 50 CFR 216.104.

1
In the notice of proposed rulemaking (83 FR 29212; June 22, 2018), NMFS provided a brief history of prior petitions received from BOEM's predecessor agencies.

On December 8, 2016 (81 FR 88664), we published a notice of receipt of the petition in the
Federal Register
, requesting comments and information related to the request. This 30-day comment period was extended to January 23, 2017 (81 FR 92788), for a total review period of 45 days. The comments and information received during this public review period informed development of the proposed ITR, and all comments received are available online at
www.fisheries.noaa.gov/action/incidental-take-authorization-oil-and-gas-industry-geophysical-survey-activity-gulf-mexico.

In August 2017, BOEM produced a final Programmatic Environmental Impact Statement (PEIS) to evaluate potential significant environmental effects of geological and geophysical (G&G) activities on the Outer Continental Shelf (OCS) of the GOM, pursuant to the National Environmental Policy Act (NEPA). The PEIS is available online at:
www.boem.gov/Gulf-of-Mexico-Geological-and-Geophysical-Activities-Programmatic-EIS/.
NOAA participated as a cooperating agency in the development of the PEIS.

NMFS published a notice of proposed rulemaking in the
Federal Register
for a 60-day public review on June 22, 2018 (83 FR 29212). The comments and information received during this public review period informed development of the final ITR, and NMFS has responded to all comments received (see Comments and Responses).

On February 24, 2020, BOEM submitted a notice to NMFS of its “updated proposed action and action area for the ongoing [ITR] process[.]” This update consisted of removal of the area currently under a Congressional leasing moratorium under the Gulf of Mexico Energy Security Act (GOMESA) (Pub. L. 109-432, § 104) from consideration in the ITR. BOEM stated in its notice to NMFS that G&G activities are not likely to be proposed within the area subject to the leasing moratorium during the 5-year period of effectiveness for the ITR and, therefore, that the “number, type, and effects of any such proposed G&G activities are simply too speculative and uncertain for BOEM to predict or meaningfully analyze.” These Congressional leasing restrictions are in place until June 30, 2022. Based on this updated scope, BOEM on March 26, 2020, submitted revised projections of expected activity levels and corresponding changes to modeled acoustic exposure numbers. BOEM's notice and updated information are available online at:
www.fisheries.noaa.gov/action/incidental-take-authorization-oil-and-gas-industry-geophysical-survey-activity-gulf-mexico.
These changes are addressed as appropriate throughout this final ITR. On September 8, 2020, the President effectively extended this moratorium through withdrawal under the Outer Continental Shelf Lands Act (OCSLA) of the same area covered by the GOMESA moratorium from disposition by leasing for 10 years, beginning on July 1, 2022, and ending on June 30, 2032.

Geophysical surveys are conducted in support of hydrocarbon exploration and development in the GOM, typically by companies that provide such services to the oil and gas industry. Broadly, these surveys include (1) deep penetration surveys using large airgun arrays as the acoustic source; (2) shallow penetration surveys using a small airgun array, single airgun, or similar systems as the acoustic source; and (3) high-resolution surveys, which may use a variety of acoustic sources. Generally speaking, these surveys may occur within Federal territorial waters and waters of the U.S. Exclusive Economic Zone (EEZ) (
i.e.,
to 200 nautical miles (nmi)) within the GOM, and corresponding with BOEM's GOM OCS planning areas (
i.e.,
Western Planning Area (WPA), Central Planning Area (CPA), Eastern Planning Area (EPA)). The use of these acoustic sources is expected to produce underwater sound at levels that have the potential to result in harassment of marine mammals. Cetacean species with the potential to be present in the GOM are described below (see Table 4).

These regulations establish a framework under the authority of the MMPA (16 U.S.C. 1361
et seq.
) and NMFS' implementing regulations (50 CFR 216.101
et seq.
) to allow for the authorization, through LOAs, of take of marine mammals incidental to the conduct of geophysical surveys for oil and gas activities in the GOM. The regulations are effective for five years.

Description of the Specified Activity

Overview

The specified activity consists of geophysical surveys conducted by industry operators for a variety of reasons related to hydrocarbon exploration, development, and production. These operators are typically companies that provide geophysical services, such as data acquisition and processing, to the oil and gas industry, including exploration and production companies. The petition describes a five-year period of geophysical survey activity and provides estimates of the amount of effort by survey type and location. BOEM's PEIS (BOEM, 2017) describes a range of potential survey effort. The levels of effort in the petition (which form the basis for the modeling effort described later in the Estimated Take section) were the high-end estimates. Following BOEM's update of the petition's geographic scope, these estimates were revised accordingly. Actual total amounts of effort (including by survey type and location) would not be known in advance of receiving LOA requests from industry operators, but take in excess of what is analyzed for this rulemaking would not be authorized. As noted above, BOEM has updated the scope of the specified activity/specified geographical region by removing the area currently under leasing moratorium through GOMESA from consideration. The removed area largely covers the EPA, including areas in which NMFS had proposed time-area restrictions as mitigation, but also includes a portion of the CPA. Applicants seeking authorization for take of marine mammals incidental to survey activities within the GOMESA area during the 5-year period of effectiveness for this rule will need to pursue a separate MMPA incidental take authorization. See Figures 1 and 2.

Geophysical surveys are conducted to obtain information on marine seabed and subsurface geology for a variety of reasons, including to: (1) Obtain data for hydrocarbon and mineral exploration and production; (2) aid in siting of oil and gas structures, facilities, and pipelines; (3) identify possible seafloor or shallow depth geologic hazards; and (4) locate potential archaeological resources and benthic habitats that should be avoided. In addition, geophysical survey data inform Federal government decisions. For example, BOEM uses such data for resource estimation and bid evaluation to ensure that the government receives a fair market value for OCS leases, as well as to help to evaluate worst-case discharge for potential oil-spill analysis and to evaluate sites for potential hazards prior to drilling.

Deep penetration seismic surveys using airgun arrays as an acoustic source (sound sources are described in the “Detailed Description of Activities” section) are a primary method of obtaining geophysical data used to characterize subsurface structure. These surveys are designed to illuminate

deeper subsurface structures and formations that may be of economic interest as a reservoir for oil and gas exploitation. A deep penetration survey uses an acoustic source suited to provide data on geological formations that may be thousands of meters (m) beneath the seafloor, as compared with a shallow penetration or high resolution geophysical (HRG) survey that may be intended to evaluate shallow subsurface formations or the seafloor itself (
e.g.,
for hazards).

Deep penetration surveys may be two-dimensional (2D) or three-dimensional (3D) (see Figure 1-2 of the petition), and there are a variety of survey methodologies designed to provide the specific data of interest. 2D surveys are designed to acquire data over large areas (thousands of square miles) in order to screen for potential hydrocarbon prospectivity, and provide a cross-sectional image of the structure. In contrast, 3D surveys may use similar acoustic sources but are designed to cover smaller areas with greater resolution (
e.g.,
with closer survey line spacing), providing a volumetric image of underlying geological structures. Repeated 3D surveys are referred to as four-dimensional (4D), or time-lapse, surveys that assess the depletion of a reservoir.

Shallow penetration and high-resolution surveys are designed to highlight seabed and near-surface potential obstructions, archaeology, and geohazards that may have safety implications during rig installation or well and development facility siting. Shallow penetration surveys may use a small airgun array, single airgun, or similar sources, while high-resolution surveys (which are limited to imaging the seafloor itself) may use a variety of sources, such as sub-bottom profilers, single or multibeam echosounders, or side-scan sonars.

Dates and Duration

The specified activities may occur at any time during the five-year period of validity of these regulations. Actual dates and duration of individual surveys are not known. Survey activities are generally 24-hour operations. However, BOEM estimates that a typical seismic survey involves approximately 20 to 30 percent of non-operational downtime due to a variety of factors, including technical or mechanical problems, standby for weather or other interferences, and implementation of mitigation measures.

Specified Geographical Region

The OCS planning areas are depicted in Figure 1, and the overlap of the GOMESA moratorium area with the planning areas (as well as with the modeling zones, see discussion of modeling zones below) is depicted in Figure 2, showing the updated specified geographical region.

Only the northern portion of the GOM contains Federal waters. BOEM manages development of U.S. Federal OCS energy and mineral resources within OCS regions, which are divided into planning areas. Within planning areas are lease blocks, on which specific production activities may occur. Geophysical survey activities may occur on scales ranging from entire planning areas to multiple or specific lease blocks, or could occur at specific potential or existing facilities within a lease block. NMFS provided a detailed discussion of the specified geographical region in the notice of proposed rulemaking (83 FR 29212; June 22, 2018).

The prospective survey activities may occur in the U.S. waters of the GOM, within BOEM's Western, Central, and Eastern GOM OCS planning areas (approximately within the U.S. EEZ; Figure 1), but excluding the GOMESA moratorium area (Figure 2). Although survey activity in the GOMESA moratorium area is no longer being considered, the region has not changed compared with what was described, nor has substantive new information regarding the region become available. Therefore, we do not reprint that discussion here and refer the reader to that notice of proposed rulemaking for additional detail.

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Detailed Description of Activities

An airgun is a device used to emit acoustic energy pulses into the seafloor, and generally consists of a steel cylinder that is charged with high-pressure air. There are different types of airguns; differences between types of airguns are generally in the mechanical parts that release the pressurized air, and the bubble and acoustic energy released are effectively the same. Airguns are typically operated at a firing pressure of 2,000 pounds per square inch (psi). Release of the compressed air into the water column generates a signal that reflects (or refracts) off the seafloor and/or subsurface layers having acoustic impedance contrast. Individual airguns are available in different volumetric sizes and, for deep penetration seismic surveys, are towed in arrays (
i.e.,
a certain number of airguns of varying sizes in a certain arrangement) designed according to a given company's method of data acquisition, seismic target, and data processing capabilities.

Airgun arrays are typically configured in subarrays of 6-12 airguns each. Towed hydrophone streamers (described below) may follow the array by 100-200 m and can be 5-12 kilometer (km) long. The airgun array and streamers are typically towed at a speed of approximately 4.5 to 5 knots (kn). BOEM notes that arrays used for deep penetration surveys typically have between 20-80 individual elements, with a total volume of 1,500-8,460 in
3
. The output of an airgun array is directly proportional to airgun firing pressure or to the number of airguns, and is expressed as the cube root of the total volume of the array.

Airguns are considered to be low-frequency acoustic sources, producing sound with energy in a frequency range from less than 10 Hz to 2 kHz (though there may be energy at higher frequencies), with most energy radiated at frequencies below 500 Hz. Frequencies of interest to industry are below approximately 100 Hz. The amplitude of the acoustic wave emitted from the source is equal in all directions (
i.e.,
omnidirectional) for a single airgun, but airgun arrays do possess some directionality due to phase delays between guns in different directions. Airgun arrays are typically tuned to maximize functionality for data acquisition purposes, meaning that sound transmitted in horizontal directions and at higher frequencies is minimized to the extent possible.

When fired, a brief (~0.1 second) pulse of sound is emitted by all airguns in an array nearly simultaneously, in order to increase the amplitude of the overall source pressure signal. The combined signal amplitude and directivity is dependent on the number and sizes of individual airguns and their geometric positions within the array. The airguns are silent during the intervening periods, with the array typically fired on a fixed distance (or shot point) interval. The intervals are optimized for water depth and the distance of important geological features below seafloor, but a typical interval in relatively deep water might be approximately every 10-20 seconds (or 25-50 m, depending on vessel speed). The return signal is recorded by a listening device, and later analyzed with computer interpretation and mapping systems used to depict the subsurface. There must be enough time between shots for the sound signals to propagate down to and reflect from the feature of interest, and then to propagate upward to be received on hydrophones or geophones. Reverberation of sound from previous shots must also be given time to dissipate. The receiving hydrophones can be towed behind or in front of the airgun array (may be towed from the source vessel or from a separate receiver vessel), or geophone receivers can be deployed on the seabed. Receivers may be displaced several kilometers horizontally away from the source, so horizontal propagation time is also

considered in setting the interval between shots.

Sound levels for airgun arrays are typically modeled or measured at some distance from the source and a nominal source level then back-calculated. Because these arrays constitute a distributed acoustic source rather than a single point source (
i.e.,
the “source” is actually comprised of multiple sources with some predetermined spatial arrangement), the highest sound levels measurable at any location in the water will be less than the nominal source level. A common analogy is to an array of light bulbs; at sufficient distance—in the far field—the array will appear to be a single point source of light but individual sources, each with less intensity than that of the whole, may be discerned at closer distances (Caldwell and Dragoset (2000) define the far field as greater than 250 m). Therefore, back-calculated source levels are not typically considered to be accurate indicators of the true maximum amplitude of the output in the far field, which is what is typically of concern in assessing potential impacts to marine mammals. In addition, the effective source level for sound propagating in near-horizontal directions (
i.e.,
directions likely to impact most marine mammals in the vicinity of an array) is likely to be substantially lower (
e.g.,
15-24 decibels (dB); Caldwell and Dragoset, 2000) than the nominal source level applicable to downward propagation because of the directional nature of the sound from the airgun array. The horizontal propagation of sound is reduced by noise cancellation effects created when sound from neighboring airguns on the same horizontal plane partially cancel each other out.

Survey protocols generally involve a predetermined set of survey, or track, lines. The seismic acquisition vessel(s) (source vessel) will travel down a linear track for some distance until a line of data is acquired, then turn and acquire data on a different track. In some cases, data is acquired as the source vessel(s) turns continuously rather than moving on a linear track (
i.e.,
coil surveys). The spacing between track lines and the length of track lines can vary greatly, depending on the objectives of a survey. In addition to the line over which data acquisition is desired, full-power operation may include run-in and run-out. Run-in is approximately 1 km of full-power source operation before starting a new line to ensure equipment is functioning properly, and run-out is additional full-power operation beyond the conclusion of a trackline (
e.g.,
half the distance of the acquisition streamer behind the source vessel, when used) to ensure that all data along the trackline are collected by the streamer. Line turns can require two to six hours when towed hydrophones are used, due to the long trailing streamers, but may be much faster when streamers are not used. Spacing and length of tracks varies by survey. Survey operations often involve the source vessel(s), supported by a chase vessel. Chase vessels typically support the source vessel(s) by protecting the long hydrophone streamer (when used) from damage (
e.g.,
from other vessels) and otherwise lending logistical support (
e.g.,
returning to port for fuel, supplies, or any necessary personnel transfers). Chase vessels do not deploy acoustic sources for data acquisition purposes; the only potential effects of the chase vessels are those associated with normal vessel operations.

The general activities described here could occur pre- or post-leasing and/or on- or off-lease. Pre-lease surveys are more likely to involve larger-scale activity designed to explore or evaluate geologic formations. Post-lease activities may also include deep penetration surveys, but would be expected to be smaller in spatial and temporal scale as they are associated with specific leased blocks. Shallow penetration and HRG surveys are more likely to be associated with specific leased blocks and/or facilities, with HRG surveys used along pipeline routes and to search for archaeological resources and/or benthic communities. Specific types of surveys, including 2D and 3D surveys and various survey geometries typically associated with 3D surveys (
e.g.,
narrow- and wide-azimuth (NAZ and WAZ) and coil surveys), were described in summary in the notice of proposed rulemaking (83 FR 29212; June 22, 2018). We also described surveys involving the placement of seismic sensors in a drilled well or borehole, including various types of vertical seismic profiling and other types of borehole seismic surveys. For full detail, please refer to that notice or sections 1.2 and 1.3 of BOEM's petition.

Surveys may be designed as either multi-source (
i.e.,
multiple arrays towed by one or more source vessel(s)) or single source. Surveys may also be differentiated by the way in which they record the return signals using hydrophones and/or geophones. Hydrophones may be towed in streamers behind a vessel (either the source vessel(s) or a separate vessel) or in some cases may be placed in boreholes (called vertical seismic profiling) or spaced at various depths on vertical cables in the water column. Sensors may also be incorporated into ocean-bottom cables (OBC) or autonomous ocean-bottom nodes (OBN) and placed on the seafloor—these surveys are referred to generally as ocean-bottom seismic (OBS). Autonomous nodes can be tethered to coated lines and deployed from ships or remotely-operated vehicles, with current technology allowing use in water depths to approximately 3,000 m. OBS surveys are most useful to acquire data in shallow water and obstructed areas, as well as for acquisition of four-component survey data (
i.e.,
including pressure and 3D linear acceleration collected via geophone). For OBS surveys, one or two vessels usually are needed to lay out and pick up cables, one ship is needed to record data, one ship tows an airgun array, and two smaller utility boats support survey operations.

In summary, 3D survey design involves a vessel with one or more acoustic sources covering an area of interest with relatively tight spatial configuration (compared with 2D surveys). In order to provide richer, more useful data, particularly in areas with more difficult geology, survey designs become more complicated with additional source and/or receiver vessels operating in potentially increasingly complicated choreographies.

As compared with 2D and 3D deep penetration surveys, shallow penetration and HRG surveys are conducted to provide data informing initial site evaluation, drilling rig emplacement, and platform or pipeline design and emplacement. Identification of geohazards (
e.g.,
gas hydrates, buried channels) is necessary to avoid drilling and facilities emplacement problems, and operators are required to identify and avoid archaeological resources and certain benthic communities. These surveys may use single airguns or small airgun arrays, but generally use various types of electromechanical acoustic sources. Please see our notice of proposed rulemaking or BOEM's petition for additional detail regarding these survey types and electromechanical acoustic sources.

Summary of Representative Sound Sources

Because the specifics of acoustic sources to be used cannot be known in advance of receiving LOA requests from industry operators, it was necessary to define representative acoustic source parameters, as well as representative survey patterns. BOEM determined realistic representative proxy sound sources and survey patterns, which were used in acoustic exposure

modeling and more broadly to support the analysis, after discussions with individual geophysical companies. Acoustic exposure modeling is described in detail in “
Acoustic Propagation and Marine Mammal Exposure Modeling of Geological and Geophysical Sources in the Gulf of Mexico
” and “
Addendum to Acoustic Propagation and Marine Mammal Exposure Modeling of Geological and Geophysical Sources in the Gulf of Mexico
” (Zeddies
et al.,
2015, 2017a), hereafter referred to collectively as “the modeling report,” as well as in “
Gulf of Mexico Acoustic Exposure Model Variable Analysis
” (Zeddies
et al.,
2017b), which evaluated a smaller, alternative airgun array. The reports are available online at:
www.fisheries.noaa.gov/action/incidental-take-authorization-oil-and-gas-industry-geophysical-survey-activity-gulf-mexico.

Representative sources for the modeling include a single airgun, an airgun array, and multiple electromechanical sources. Two major survey types were considered: Large-area seismic (including 2D, 3D NAZ, 3D WAZ, and coil surveys) and small-area, high-resolution geotechnical (including single airgun surveys and surveys using a CHIRP sub-bottom profiler in combination with multibeam echosounder and side-scan sonar; the single airgun was used as a reasonable proxy for surveys using a boomer). The nominal airgun sources used for analysis of the proposed action include a small single airgun (90 in
3
airgun) and a large airgun array (8,000 in
3
). In addition, the supplemental Model Variable Analysis (Zeddies
et al.,
2017b) provides analysis of an alternative 4,130 in
3
array (see Letters of Authorization section). We note that while high-resolution geophysical sources were conservatively included for consideration in this rule to allow for take authorization if necessary, some of these types of sources would not necessarily be expected to cause the incidental take of marine mammals, depending on the source type and/or the manner in which it is operated (
e.g.,
operational settings, mitigation measures), and Letters of Authorization would not be necessary in those cases.

Additional characteristics of the representative acoustic sources and representative operational parameters of the different survey types that were used in the modeling simulations to predict the exposure of marine mammals to different received levels of sound are described in the modeling report and in our notice of proposed rulemaking. Please see those documents for additional detail.

We note that while it was necessary to identify representative sources for the purposes of modeling the number of takes to be included in the analysis under the rule, the analysis is intended to be, and is appropriately, applicable to takes resulting from the use of other sizes or configurations of airguns (
e.g.,
the alternative, smaller airgun array modeled in the “
Gulf of Mexico Acoustic Exposure Model Variable Analysis”
report (Zeddies
et al.,
2017b) referenced in the proposed rule and available for public review as supplementary material to the proposed rule).

While these descriptions reflect existing technologies and current practice, new technologies and/or uses of existing technologies may come into practice during the period of validity of these regulations. NMFS will evaluate any such developments on a case-specific basis to determine whether expected impacts on marine mammals are consistent with those described or referenced in this document and, therefore, whether any anticipated take incidental to use of those new technologies or practices may appropriately be authorized under the existing regulatory framework. We also note here that activities that may result in incidental take of marine mammals, and which would therefore appropriately require authorization under the MMPA, are not limited to those activities requiring permits from BOEM. There may be some activities that do not require permits from BOEM, such as certain ancillary activities, for which an LOA under this rule may be appropriate. Operators should consult NMFS regarding the appropriateness of applying for an LOA under this rule prior to conducting such activities.

Estimated Levels of Effort

As noted previously, actual total amounts of effort by survey type and location cannot be known in advance of receiving LOA requests from industry operators. Therefore, BOEM's PEIS provided projections of survey level of effort for the different survey types for a 10-year period (and BOEM's updated scope refined those projections to a five-year period). In order to construct a realistic scenario for future geophysical survey effort, BOEM evaluated trends in permit applications as well as industry estimates of future survey activity. In addition, GOMESA precludes leasing, pre-leasing, or any related activity (though not geophysical surveys) in the GOM east of 86°41′ W, in BOEM's Eastern Planning Area (EPA) and within 125 mi (201 km) of Florida, or in BOEM's Central Planning Area (CPA) and within 100 mi of Florida (and according to certain other detailed stipulations). These leasing restrictions are in place until June 30, 2022. On September 8, 2020, the President effectively extended this moratorium through withdrawal under OCSLA of the same area covered by the GOMESA moratorium from disposition by leasing for 10 years, beginning on July 1, 2022, and ending on June 30, 2032. This withdrawal prevents consideration of these areas for any leasing for purposes of exploration, development, or production during the 10-year period beginning on July 1, 2022, and ending on June 30, 2032. Although the withdrawal does not preclude geophysical survey activity, similar to the moratorium under GOMESA, the lack of leasing opportunities may be expected to curtail interest in exploratory surveys to some degree.

In order to provide some spatial resolution to the projections of survey effort and to provide reasonably similar areas within which acoustic modeling might be conducted, the geographic region was divided into seven zones, largely on the basis of water depth, seabed slope, and defined BOEM planning area boundaries. Shelf regions typically extend from shore to approximately 100-200 m water depths where bathymetric relief is gradual (off Florida's west coast, the shelf extends approximately 150 km). The slope starts where the seabed relief is steeper and extends into deeper water. In the GOM water deepens from 100-200 m to 1,500-2,500 m over as little as a 50 km horizontal distance. As the slope ends, water depths become more consistent, though depths can vary from 2,000-3,300 m. Three primary bathymetric areas were defined as shelf (0-200 m water depth), slope (200-2,000 m), and deep (>2,000 m).

Available information regarding cetacean density in the GOM (
e.g.,
Roberts
et al.,
2016) shows that, in addition to water depth, animal distribution tends to vary from east to west in the GOM and appears correlated with the width of shelf and slope areas from east to west. The western region is characterized by a relatively narrow shelf and moderate-width slope. The central region has a moderate-width shelf and moderate-width slope, and the eastern region has a wide shelf and a very narrow slope. Therefore, BOEM's western, central, and eastern planning area divisions provide appropriate longitudinal separations for the shelf and slope areas. Due to relative consistency in both physical properties

and predicted animal distribution, the deep area was not subdivided. As shown in Figure 3, Zones 1-3 represent the shelf area (from east to west), Zones 4-6 represent the slope area (from east to west), and Zone 7 is the deep area.

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ER19JA21.002

BILLING CODE 3510-22-C
Table 1 in the notice of proposed rulemaking provided the 10-year estimated levels of effort from BOEM's PEIS, estimated as 24-hr survey days, including annual totals by survey type and by zone for deep penetration and shallow penetration surveys, respectively. As the basis for the analysis supporting the proposed rulemaking, NMFS selected one high survey effort scenario and two each of moderate and low survey effort scenarios from the ten survey effort scenarios provided by BOEM. Of the ten “years” or effort scenarios, Year 1 (high), Years 4 and 5 (moderate), and Years 8 and 9 (low) were selected as representative effort scenarios and carried forward for further evaluation.

However, as noted previously, BOEM subsequently revised its proposed action by removing the area subject to leasing moratorium under GOMESA from consideration in the rule. In support of this revision, BOEM provided revised 5-year level of effort predictions and associated acoustic exposure estimates. BOEM's process for developing this information, described in detail in “Revised Modeled Exposure Estimates,” available online, was straightforward. Rather than using the PEIS's 10-year period, BOEM provided revised levels of effort for a 5-year period, using Years 1-5 of the original level of effort projections. BOEM stated that the first five years were selected to be carried forward “because they were contiguous, they included the three years with the most activity, and they were the best understood in relation to the historical data upon which they are based.” NMFS concurs with this choice. Levels of effort were revised based on the basic assumption that if portions of areas are removed from consideration, then the corresponding effort previously presumed to occur in those areas also is removed from consideration. Revised estimates of future effort and associated acoustic exposures draw upon the prior projections and modeling approach, which were subject to notice and comment. Table 1 shows the percentage reduction in survey area for each modeling zone that results from BOEM's scope revisions, and Table 2 provides the subsequent revised level of effort projections for the 5-year period.

Table 1—Percentage Reduction in Survey Area for Each Modeled Zone

Modeling zone

Percentage
reduction
in area

1
100.0

2
2.7

3
0.0

4
98.2

5
4.0

6
0.0

7
33.0

Table 2—Projected Levels of Effort in 24-hr Survey Days for Five Years, by Zone and Survey Type
1

Year

Zone
2

2D
3

3D NAZ
3

3D WAZ
3

Coil
3

VSP
3

Total

(deep)
3

Shallow

hazards
4

Boomer
4

HRG
4

Total

(shallow)
4

1
1
0
0
0
0
0
0
0
0
1
1

2
0
7
0
0
0
7
0
0
1
1

3
0
0
0
0
0
0
0
0
0
0

4
0
0
0
0
0
0
0
0
0
0

5
2
16
8
3
0
29
0
0
1
1

6
0
0
0
0
0
0
0
0
0
0

7
23
170
82
35
1
311
0
0
11
11

Total

25
193
90
38
1
347
0
0
14
14

2
1
0
0
0
0
0
0
0
0
1
1

2
0
10
1
0
0
11
0
0
1
1

3
0
0
0
0
0
0
0
0
0
0

4
27
0
0
0
0
27
0
0
0
0

5
0
16
8
3
0
27
0
0
1
1

6
0
0
0
0
0
0
0
0
0
0

7
10
166
79
34
1
290
0
0
11
11

Total

37
192
88
37
1
355
0
0
14
14

3
1
0
0
0
0
0
0
0
0
1
1

2
0
10
1
0
0
11
0
0
0
0

3
0
0
0
0
0
0
0
0
0
0

4
54
50
21
9
0
134
0
0
1
1

5
1
10
4
2
0
17
0
0
1
1

6
0
0
0
0
0
0
0
0
0
0

7
31
125
46
20
1
223
0
0
12
12

Total

86
195
72
31
1
385
0
0
12
12

4
1
0
0
0
0
0
0
0
0
0
0

2
0
10
1
0
0
11
0
0
0
0

3
0
0
0
0
0
0
0
0
0
0

4
54
50
21
9
0
134
0
0
1
1

5
1
10
4
2
0
17
0
0
1
1

6
0
0
0
0
0
0
0
0
0
0

7
31
125
46
20
1
223
0
0
12
12

Total

86
195
72
31
1
385
0
0
14
14

5
1
0
0
0
0
0
0
0
0
0
0

2
0
7
0
0
0
7
0
0
1
1

3
0
0
0
0
0
0
0
0
0
0

4
0
75
0
0
0
75
0
0
0
0

5
0
12
8
3
0
23
0
0
1
1

6
0
0
0
0
0
0
0
0
0
0

7
0
154
79
34
1
268
1
1
11
13

Total

0
248
87
37
1
373
1
1
13
15

1
Projected levels of effort in 24-hr survey days.

2
Zones follow the zones depicted in Figure 3.

3
Deep penetration survey types include 2D, which uses one source vessel with one large array (8,000 in
3
); 3D NAZ, which uses two source vessels using one large array each; 3D WAZ and coil, each of which uses four source vessels using one large array each (but with differing survey design); and VSP, which uses one source vessel with a large array. “Deep” refers to survey type, not to water depth.

4
Shallow penetration/HRG survey types include shallow hazards surveys, assumed to use a single 90 in
3
airgun or boomer, and high-resolution surveys using the multibeam echosounder, side-scan sonar, and chirp sub-bottom profiler systems concurrently. “Shallow” refers to survey type, not to water depth.

This description of the specified activity is a summary of critical information. The interested reader should refer to the notice of proposed rulemaking (83 FR 29212; June 22, 2018), as well as BOEM's petition (with recent addenda) and PEIS, for additional detail regarding these prospective activities and the region. Required mitigation, monitoring, and reporting measures are described in detail later in this document (please see Mitigation and Monitoring and Reporting).

Changes From the Proposed Rule

This section provides a summary of changes from the proposed rule. Each section in which changes were made (
e.g.,
Mitigation) includes a more detailed list of changes made and a fuller description of the rationale. The following Comments and Responses section also provides additional detail relating to changes, in cases where the change resulted from a public comment.

Most notably, as described in greater detail above, BOEM updated the scope of the specified activity/specified geographical region that is the subject of this rule by removing from consideration the area that is subject to the GOMESA leasing moratorium. In accordance with this updated spatial scope, BOEM provided revised activity level projections and revised estimated acoustic exposure numbers based on the same modeling that informed the numbers evaluated in the proposed rule. BOEM's revised activity level projections correspond with Years 1-5 of the original 10-year projections (see Table 1 of the notice of proposed rulemaking), which is a conservative choice as these years contained higher levels of effort than Years 6-10. In the proposed rule, NMFS selected years that were representative of different levels of effort as the basis for the total taking over five years, including one year of relatively high effort (Year 1), two years of relatively moderate effort (Years 4 and 5), and two years of relatively low effort (Years 8 and 9). This selection is now in part supplanted (with the two

representative “low effort” years replaced by one relatively high effort year and one relatively moderate effort year) by BOEM's selection of Years 1-5 and the associated updated levels of effort.

The revised acoustic exposure numbers form the basis for our analyses in this final rule. Of note, the maximum total taking, as well as the annual maximum, that would be allowable under the regulations has decreased for most species and stocks, with the exception of the annual maximums for Atlantic spotted dolphin and bottlenose dolphins, and the total taking over five years for the Atlantic spotted dolphin, which have increased slightly (please see Estimated Take for additional information). These changes (largely decreases) in the take numbers do not have a meaningful effect on the analysis (except where impacts are significantly reduced,
e.g.,
for Bryde's whales) and do not change any of the findings.

In the proposed rule, NMFS included several time-area restrictions, including a seasonal restriction on airgun survey activity in the “Bryde's whale core habitat” area (as well as alternatives to this proposal that were offered for public comment, including a year-round restriction in the same area). Following BOEM's update to the scope of the rule, two of these areas (the Bryde's whale area and the “Dry Tortugas” area that was, in part, designed to provide protection for sperm whales and beaked whales) were removed from consideration, as the specified activity/specified geographical region no longer includes surveys in the areas where these proposed restrictions are located.

A third time-area restriction—the “Coastal Restriction,” designed to protect bottlenose dolphins in coastal waters most heavily impacted by the Deepwater Horizon oil spill—has been modified in consideration of public comments. The restriction was proposed to be GOM-wide within coastal waters inside the 20-m isobath, and to be in effect from February through May. The area encompassed by the restriction has been reduced to match the assumed range of the northern coastal stock of bottlenose dolphins (
i.e.,
between 90-84° W, but in effect only to the eastern extent of the coastal waters portion of BOEM's updated specified geographic region) while the temporal window has been expanded to include January. In addition, a proposed 13-km buffer to this area has been removed.

In the proposed rule, NMFS defined “deep penetration” surveys as those using arrays greater than 400 in
3
total volume. That delineation has been revised to include surveys using arrays greater than 1,500 in
3
total volume, with arrays of 1,500 in
3
total volume and less considered “shallow penetration” surveys.

In the notice of proposed rulemaking, NMFS proposed an exception to the general shutdown requirements for certain species of dolphins in relation to airgun surveys, in which the acoustic source would be powered down to the smallest single element of the array. Power-down conditions would be maintained until the animal(s) is observed exiting the exclusion zone or for 15 minutes beyond the last observation of the animal, following which full-power operations may be resumed without ramp-up. NMFS also provided an alternative proposal for consideration by the public, in which no shutdown or power-down would be required upon observation of the same species of dolphins. Following review of public comments, NMFS removes the power-down measure for small delphinids, in favor of the no-shutdown and no power-down alternative. No shutdown or power-down is required for these species.

NMFS proposed a number of extended distance shutdown requirements on the basis of detections of certain species deemed particularly sensitive (
e.g.,
beaked whales) or of particular circumstances deemed to warrant the extended distance shutdown requirement (
e.g.,
whales with calves). These extended distance shutdowns were all conditioned upon observation or detection of these species or circumstances “at any distance” from the vessel. However, NMFS also included as an alternative proposal for public consideration a distance limit of 1,000 m for these shutdown requirements. Following review of public comments, NMFS determined that a distance limit on extended shutdown zones for relevant species or circumstances was appropriate, but determined 1,500 m was the appropriate distance (rather than 1,000 m).

The proposed rule included an extended distance shutdown for sperm whales that was applicable upon acoustic detection, but was not applicable to visual detection. Following review of public comments, the shutdown requirement has been expanded to include any detection of sperm whales within the extended distance shutdown zone, including visual detection.

For shallow penetration surveys, NMFS reduces the standard exclusion zone from 200 m to 100 m, while including an extended distance shutdown requirement mirroring the requirements for deep penetration surveys, but within a distance of 500 m. NMFS eliminates shutdown requirements for HRG surveys (defined here as surveys using electromechanical sources such as multi-beam echosounders, side-scan sonars, and chirp sub-bottom profilers). The proposed regulations required shutdown for marine mammals within the proposed exclusion zone for surveys operating in water depths greater than 200 m.

NMFS eliminates proposed requirements for visual observation during nighttime ramp-up and pre-clearance, and for the use of third-party PSOs aboard node retrieval vessels.

In the proposed rule, NMFS discussed the use of an extrapolation method recommended by the Marine Mammal Commission for use in estimating potential unobserved takes. NMFS agrees with public commenters that the appropriateness of the method for application to observations conducted from working source vessels (versus research vessels) is unknown and, as suggested through public comment, NMFS will not require use of this method but will continue to evaluate approaches for assessment of effects to marine mammal stocks, including those based on extrapolation of marine mammal detections, through the adaptive management process and subsequently apply them through LOAs as appropriate.

NMFS has revised requirements relating to reporting of injured or dead marine mammals and has added newly crafted requirements relating to actions that should be taken in response to notification of live stranding events in certain circumstances, in order to reflect current best practice.

The proposed rule indicated that LOA applications with take estimates based on modeling other than that specifically included in the modeling report used to support the EIS and the proposed rule (the modeling report; Zeddies
et al.,
2015, 2017a) would necessarily be published for public comment prior to the issuance of an LOA. Upon consideration of public comment and related supplemental materials, the final rule more flexibly allows that if applicants do not use the modeling provided by the rule, NMFS will publish a notice in the
Federal Register
soliciting public comment, when the model or inputs differ substantively from those that have been reviewed by NMFS and the public previously. Please see the Letters of Authorization section for more detail.

Comments and Responses

NMFS published a notice of proposed rulemaking in the
Federal Register
on June 22, 2018 (83 FR 29212), beginning a 60-day comment period. In that notice, we requested public input on the proposed rule and regulations, including the variations of the proposed rule, two economic baselines, and other information provided in the Regulatory Impact Analysis and associated appendices, and requested that interested persons submit relevant information, suggestions, and comments. In response to BOEM's change in scope and in consideration of public comments, we modified our action, as discussed in the following responses to comments. Please also see the Changes from the Proposed Rule section, above. We note that one area of significant concern for some members of the public was potential impacts to Bryde's whales and related mitigation measures. The reduced geographic scope eliminates the need to consider activity in the Bryde's whale “core habitat area” and eliminates the majority of the incidental take of Bryde's whale that was evaluated in the proposed rule.

During the 60-day comment period, we received 17 comment letters. A letter was submitted jointly by the International Association of Geophysical Contractors, the American Petroleum Institute, the National Ocean Industries Association, and the Offshore Operators Committee (hereafter, the “Associations”). A separate letter was submitted jointly by the Natural Resources Defense Council (NRDC), Center for Biological Diversity, Earthjustice, Gulf Restoration Network, Humane Society Legislative Fund, The Humane Society of the United States, and Sierra Club (hereafter, “NRDC”). Additional letters were submitted by the following: BP Exploration & Production Inc. (BP), Consumer Energy Alliance, CGG, Chevron USA Inc. (Chevron), the Center for Regulatory Effectiveness (CRE), the Florida Department of Environmental Protection, the Marine Mammal Commission (MMC), and eight private citizens. NMFS has reviewed all public comments received on the proposed rulemaking. All relevant comments and our responses are described below, with comment responses outlined by major categories. All comments received are available online at:
www.regulations.gov.
A direct link to these comments is provided at:
www.fisheries.noaa.gov/action/incidental-take-authorization-oil-and-gas-industry-geophysical-survey-activity-gulf-mexico.

General Comments

As an initial matter, we note that under the MMPA, NMFS generally does not have discretion regarding issuance of requested incidental take authorizations for small numbers of marine mammals, provided that (1) the total taking associated with a specified activity will have a negligible impact on the affected species or stock(s); (2) the total taking associated with a specified activity will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (not relevant here); and (3) mitigation, monitoring, and reporting of such takings are set forth, including mitigation measures sufficient to meet the standard of least practicable adverse impact on the affected species or stocks and their habitat.

In addition, NMFS' proposed action—the issuance of the ITR and any subsequent LOAs authorizing incidental take of marine mammals—addresses only marine mammals (and their habitat). As such, effects of the surveys on other aspects of the marine environment are not relevant to NMFS' analyses under the MMPA.

The MMPA does require that we evaluate potential effects to marine mammal habitat, which includes prey species (
e.g.,
zooplankton, fish, squid). However, consideration of potential effects to taxa other than marine mammals and their prey, or consideration of effects to potential prey species in a context other than the import of such effects on marine mammals, is not relevant to our action under the MMPA. We have appropriately considered effects to marine mammal habitat. Separately, BOEM evaluated effects to all relevant aspects of the human environment (including marine mammals and other taxa) through the analysis presented in BOEM's PEIS (available online at:
www.boem.gov/Gulf-of-Mexico-Geological-and-Geophysical-Activities-Programmatic-EIS/
), and effects to all potentially affected species that are listed under the Endangered Species Act (ESA) and any critical habitat designated for those species were addressed through consultation between BOEM and NMFS pursuant to section 7 of the ESA. That Biological Opinion, which evaluated NMFS' proposed action (issuance of the ITR and any subsequent LOAs) as well as all BOEM and Bureau of Safety and Environmental Enforcement (BSEE) approvals of activities associated with the OCS oil and gas program in the GOM, is available online at:
www.fisheries.noaa.gov/national/endangered-species-conservation/biological-opinions-issued-noaa-fisheries-office-protected.
We do not further address taxa other than marine mammals and marine mammal prey.

Comment:
The Associations comment that the proposed ITR is a well-structured and thorough document that appropriately concludes that geophysical activities in the GOM would have no more than a negligible impact on marine mammal populations, and that they appreciate NMFS' effort in preparing the proposed ITR and consideration of some of the Associations' previous comments.

Response:
NMFS appreciates the comment.

Comment:
The Associations comment that geophysical surveys play a critical role in the safe and orderly development of the oil and gas resources of the GOM.

Response:
We acknowledge the background operational information provided by the Associations.

Comment:
BP comments that the ITR is a much-needed process to govern the authorization of incidental takes of marine mammals associated with geophysical survey activity in the GOM. Chevron also indicates support for promulgation of the ITRs.

Response:
NMFS appreciates the comments.

Comment:
BP comments that projected survey efforts are underestimated but did not provide specific justification or recommendations.

Response:
Projected levels of survey effort were formulated by BOEM and included in their PEIS. BOEM's PEIS stated, “the scenarios contain projections based on the analysis of recent historic activity levels and trends made by BOEM's subject-matter experts who also considered industry-projected activity levels in their estimates.” These projected levels of survey effort were made available for public review on multiple occasions during the development of the PEIS, as well as during the notice of receipt comment period, in which the public was given the opportunity to review and comment on the petition itself (81 FR 88664; December 8, 2016). Neither BP nor other industry stakeholders submitted comments on the BOEM-developed effort levels, and no evidence was provided that projected survey efforts are underestimated. The projected levels of effort were subsequently updated by BOEM based on the removal of the GOMESA area from consideration.

Comment:
The Florida Department of Environmental Protection (FLDEP) expressed its concern regarding the potential impacts of OCS oil and gas

activities on marine and coastal environments and the biological resources and critical habitats associated with them. The FLDEP also indicated that former Secretary of the Interior Zinke had made a commitment to former Governor Scott to remove the State of Florida from future consideration for offshore drilling.

Response:
NMFS acknowledges the comments. Assuming that the requirements of the MMPA are met,
e.g.,
findings of negligible impact and small numbers are made, NMFS does not have discretion as to whether it may issue ITRs and LOAs under those ITRs, and NMFS has no authority to limit oil and gas activities outside of prescribing appropriate mitigation requirements.

Marine Mammal Impacts

Comment:
The Associations (as well as other industry commenters and the CRE) stated, in summary, that there is no scientific evidence that geophysical survey activities have caused adverse consequences to marine mammal stocks or populations, and that there are no known instances of injury to individual marine mammals as a result of such surveys, stating that similar surveys have been occurring for years without significant impacts. The Associations stated that surveys have been ongoing in the GOM for years and have not resulted in any negative impacts to marine mammals, including reducing fitness in individuals or populations. Referring to other regions, the commenters stated that bowhead whale numbers have increased in the Arctic despite survey activity. The Associations go further in claiming that “NMFS misconstrues its legal obligations” and “NMFS violates the MMPA's best available science requirement.”

Response:
Disruption of behavioral patterns (
i.e.,
Level B harassment) has been documented numerous times for marine mammals in the presence of airguns, in the form of avoidance of areas, notable changes in vocalization or movement patterns, or other shifts in important behaviors. See Potential Effects of the Specified Activity on Marine Mammals and Their Habitat in the notice of proposed rulemaking. In addition, there is growing scientific evidence demonstrating the connections between sub-lethal effects, such as behavioral disturbance, and population-level effects on marine mammals (
e.g.,
Lusseau and Bedjer, 2007; New
et al.,
2014; Pirotta
et al.,
2018). Disruptions of important behaviors, in certain contexts and scales, have been shown to have energetic effects that can translate to reduced survivorship or reproductive rates of individuals (
e.g.,
feeding is interrupted, so growth, survivorship, or ability to bring young to term may be compromised), which in turn can adversely affect populations depending on their health, abundance, and growth trends.

With specific regard to sound, as a 2017 report from the National Academy of Sciences noted, while it is true that “[n]o scientific studies have conclusively demonstrated a link between exposure to sound and adverse effects on a marine mammal population,” this is largely because such impacts are very difficult to demonstrate (NRC, 2005; NAS, 2017), not because they do not exist. Population‐level effects are inherently difficult to assess because of high variability, migrations, and multiple factors affecting the populations. Appropriate studies are exceedingly difficult to carry out, and no appropriate study and reference populations have yet been established. Nonetheless there is a growing body of literature and science illustrating the connections between prolonged behavioral disturbance and impacts to reproductive success and survivorship. Accordingly, it is not defensible to conclude that sub-lethal acoustic stressors cannot have population level consequences. Based on the available evidence, a sufficient analysis of the potential impacts of airgun noise requires consideration of impacts on individuals
and
the potential for population level effects. NMFS has carefully considered the available evidence in making the necessary determinations (see Negligible Impact Analysis and Determinations) and determining the most appropriate suite of mitigation measures.

Because some commenters repeatedly cite (and misunderstand) public statements by BOEM in support of a contention that there is “no harm from seismic,” we clarify the record by citing BOEM's own responses to similar comments on their PEIS (BOEM, 2017). BOEM stated: “It is critically important to understand that BOEM's . . . Science Note . . . refers to impacts on marine mammal . . . population sustainability rather than effects on individual animals. Studies have shown that marine mammals may and do react to sound through physical displacement from or avoidance of the area of ensonification and/or by altering their vocalizations. This [PEIS] acknowledges that significant acute physical injury to or death of marine mammals is not likely to be a direct result of seismic noise. It does, however, acknowledge that sublethal injurious effects are possible and may, over time, result in the eventual death of the individual(s) from these physical injuries and/or loss of hearing with (as in the case of marine mammals) the resultant inability to forage and communicate with conspecifics. Another prominent concern is whether anthropogenic sounds such as those generated during seismic survey activities may “mask” communications between some marine mammals. Depressed survival rates related to energetic effects or other impacts of noise are difficult to determine. BOEM, however, does not assume that lack of demonstrated adverse population-level effects from seismic surveys means that those effects may not occur.”

In support of assertions that there are “no effects” to marine mammals from seismic surveys and that there is a “lack of any harm” to marine mammals, CRE cites statements made by NMFS, in which we conclude that there is no evidence that serious injury, death, or stranding is reasonably likely to occur as a result of such surveys, and that Level A harassment is not reasonably likely to occur for mid-frequency cetaceans. CRE's assertion that there are “no effects” and “no harm” to marine mammals as a result of seismic surveys is based on the fact that marine mammals still exist in the GOM despite survey activity. CRE overlooks the evidence put forward for Level B harassment, and the potential effects of behavioral disruption, as well as the additional effects of noise that do not rise to the level of a take, but which nevertheless must be considered when evaluating the effects of a specified activity on a species or stock.

The Associations assert that we premise our decisions on the idea that we must act conservatively because effects that have not been conclusively proven—which the Associations claim, without evidence, do not and cannot occur—could occur in the future. The Associations state that we misconstrue our legal obligations via the application of “an additional layer of precautionary bias” beyond that established in the MMPA standards themselves, though they do not demonstrate that the bias exists. The Associations acknowledge that the MMPA requires mitigation sufficient to meet the standard of least practicable adverse impact. Therefore, some portion of the mitigation requirements contained in the proposed ITR would be necessary to meet that standard. However, they provide no analysis to support the contention that specific mitigation requirements exceed that standard. In fact, we have declined to adopt the recommendations of other commenters that are based on vague and unexplained standards of

“conservatism” that are not required in the MMPA. Here, we conducted the requisite analyses of mitigation and found that the requirements contained in this final ITR, as modified on the basis of new information and review of public comments, meet the least practicable adverse impact (LPAI) standard.

We base our conclusions, relating to the potential effects of the specified activity on the affected species and stocks, on reasonable interpretation of the available science, which we summarize in this preamble and described in detail in our notice of proposed rulemaking. While we acknowledge the lack of conclusive evidence for population-level consequences, this is an artifact of the extreme difficulty of empirically demonstrating such effects (as concluded by the National Academies of Science, stated above). The best available scientific information provides considerable evidence that the activities evaluated in this ITR have the potential to adversely affect the fitness of individual animals. The best available science clearly demonstrates that, given adverse impacts to an animal's fitness, population-level effects are plausible. The Associations' comments on this topic treat the lack of empirical evidence as evidence that such effects do not occur. However, NMFS does not agree that absence of evidence is evidence of absence of effects. The comments further incorrectly frame our decision-making as being premised on the idea that such effects could occur in the future, when they are actually based on a reasonable interpretation of the best available scientific information regarding what the effects of the specified activity are likely to be in the absence of prescribed mitigation. Despite the paucity of empirical research on population effects, the best available information demonstrates impacts at the individual level that, at a high enough level of take, have reasonably foreseeable population-level impacts.

Similarly, the Associations imply that our interpretation of the existing scientific information reflects speculation about what future research might demonstrate. The Associations' statements that NMFS dismissed current scientific findings and premised decisions on hypothesized future impacts are inaccurate, and their assertion that NMFS “has effectively required conclusive scientific proof that seismic surveys do not impact marine mammal populations” misunderstands NMFS' use of the scientific literature. The best available information demonstrates that the effects of seismic surveys on marine mammals may include adverse impacts on behavior in ways that can also have energetic consequences. To draw different conclusions regarding the need for the strong suite of mitigation requirements included in this final ITR, NMFS would require scientific evidence that demonstrates that seismic surveys do not have energetic consequences or, alternatively, do not reach a point where there are population-level consequences. NMFS is not aware of such evidence. NMFS' final rule is based on the best available scientific information and the requirements of the MMPA.

Chevron states that we do not account for “real-world” protected species observer (PSO) observations, calling this “arbitrary and capricious,” and seems to imply that these “ignored” PSO observations of marine mammals are evidence that seismic activities produce no more than “negligible effects on species.” Chevron does not provide evidence to support its comment or otherwise develop the suggestion to enable a specific response. However, we incorporated the best available scientific information for our analysis, as evidenced (for example) by our references in the notice of proposed rulemaking to BOEM's synthesis study of PSO data from 2002-08 (Barkaszi
et al.,
2012) (as well as other similar syntheses from other locations). In this final rulemaking, we have incorporated analysis of a newly available study of PSO data from 2009-15 (Barkaszi and Kelly, 2018). These data are also key to the evaluation of direct costs found in our RIA. We disagree with Chevron's apparent contention that we “ignore[d]” BOEM's earlier “admissions that no scientific evidence exists contradicting the real-world observations of negligible impact” (citing to BOEM's “Science Notes”). NMFS addressed BOEM's “Science Notes” in some detail in our notice of proposed rulemaking (83 FR 29264-65). Chevron misinterprets a statement from BOEM regarding the absence of evidence (“no documented evidence of noise from air guns . . . adversely affecting animal populations) as evidence itself of no adverse effects. According to Chevron, our “failure to account for” this is “arbitrary and capricious.” These issues have been addressed both above and in the notice of proposed rulemaking.

Comment:
NRDC referenced studies showing that noise from airgun surveys can travel great distances underwater, suggesting that due to the scale of this propagation, marine mammals in the GOM are consistently compromised in their ability to perform important life functions.

Response:
NMFS acknowledges that relatively loud, low-frequency noise (as is produced by airgun arrays) has the potential to propagate across large distances. However, propagation and received sound levels are highly variable based on many biological and environmental factors. For example, while one commonly cited study (Nieukirk
et al.,
2012) described detection of airgun sounds almost 4,000 km from the acoustic source, the sensors were located within the deep sound channel (SOFAR), where low-frequency signals may travel great distances due to the advantageous propagation environment. While sounds within this channel are unlikely to be heard by most marine mammals due to the depth of the SOFAR channel—which is dependent primarily on temperature and water pressure and therefore variable with latitude—it is arguable whether sounds that travel such distances may be heard by whales as a result of refraction to shallower depths (Nieukirk
et al.,
2012; McDonald
et al.,
1995). Regardless, while the extreme propagation distances cited in some comments may not be realistic, we acknowledge that contraction of effective communication space for Bryde's whales, which vocalize and hear at frequencies overlapping those emitted by airgun arrays, can occur at distances on the order of tens to hundreds of kilometers (
e.g.,
Hatch
et al.,
2012). However, attenuation to levels below which more acute effects are likely to occur is expected over much shorter distances (Zeddies
et al.,
2015, 2017a) and, therefore, we do not agree with the contention that the GOM would be ensonified to a degree that marine mammals would find it an unsuitable habitat or would be consistently compromised in their ability to perform important life functions. Rather, it is likely that displacement would occur within a much smaller region in the vicinity of the acoustic source (
e.g.,
within 10-20 km of the source, depending on season and location). Overall, the specific geographic region and marine mammal use of the area is sufficiently large that, although some displacement may occur (
i.e.,
Level B harassment as a result of acoustic exposure beyond the exclusion zone), the GOM offers enough habitat for marine mammals to seek temporary viable habitat elsewhere, if necessary. Many of the affected species occupy a wide portion of the GOM, and it is expected that individuals of these species can reasonably find temporary

foraging grounds or other suitable habitat areas consistent with their natural use of the region. Further, although the surveys are expected to occur over large portions of the GOM, they will only be transitory in any given area. Therefore, NMFS does not expect displacement to occur frequently or for long durations. Please see Negligible Impact Analysis and Determinations for additional analysis.

Comment:
NRDC states that airgun surveys have been linked to significant reductions in the probability of calf survival in western Pacific gray whales (an endangered baleen whale population), implying that these findings indicate that such surveys would similarly have significant negative effects on whales in the GOM.

Response:
Commenters cite a preliminary report (Cooke
et al.,
2015) that documented a reduction in calf survival that the authors suggested may be related to disruption of foraging from airgun survey activity and pile driving in Russia due to presumed avoidance of foraging areas. However, a more recent analysis (Cooke
et al.,
2017) invalidated these findings, showing that this was a sampling effect, as those calves that were assumed dead in the 2015 study have since been observed alive elsewhere. The new study found no significant annual variation in calf survival. Johnson
et al.
(2007) had previously reported that foraging gray whales exposed to airgun sounds during surveys in Russia did not experience any biologically significant or population-level effects.

Comment:
NRDC asserts that we have not adequately accounted for vessel collision risk, stating that the surveys will drive marine mammals into shipping lanes, thereby increasing their risk of ship strike. Relatedly, NRDC noted that NMFS' conclusion that ship strikes will not occur indicates an assumption that required ship-strike avoidance procedures will be effective. NRDC disagrees that the ship-strike avoidance measures will be effective.

Response:
NMFS is not aware of any scientific information suggesting that the surveys would drive marine mammals into shipping lanes and disagrees that this would be a reasonably anticipated effect of the specified activities. While the primary stressor to marine mammals from the specified activities is acoustic exposure to the sound source, NMFS takes seriously the risk of vessel strike and has prescribed measures sufficient to avoid the potential for ship strike to the extent practicable (see Mitigation). NMFS has required these measures despite a very low likelihood of vessel strike; vessels associated with the surveys will add a discountable amount of vessel traffic to the specific geographic region and, furthermore, vessels towing survey gear travel at very slow speeds (
i.e.,
roughly 4-5 kn).

Comment:
The MMC criticizes one aspect of the methodology for the analysis of chronic effects to Bryde's and sperm whales conducted by NMFS with the support of JASCO Applied Sciences (JASCO),
i.e.,
removing the top ten percent of the greatest pulse exposures. (JASCO is a consulting company contracted by NMFS and BOEM to model acoustic exposures of marine mammals to noise produced by industry survey activity.) The MMC recommends re-estimation of the various lost listening and communication space parameters without removing the greatest ten percent of pulse exposures.

Response:
The goal of this modeling exercise was to create a tool that could help evaluate loss of ability to detect signals of biological importance over spatial scales relevant to the sources and hearing capabilities of a wide variety of regional animals. In order to do so, we attempt to examine the portion of low-frequency acoustic energy lost from seismic surveys that has been empirically measured in many contexts around the world to generate higher chronic, longer-term average noise levels. Masking experienced by individual calling and receiving animals due to noise at relatively close proximity to a single intermittent source is an important but limited aspect of the real-world contexts within which populations of marine mammals are exposed to noise from multiple seismic surveys in a region like the GOM. This modeling sought to account for the known attributes of airgun noise, by which low-frequency energy lost laterally attenuates over large spatial scales with loss of impulsive features, leading to elevated background noise conditions, particularly when multiple surveys are concurrent within an acoustic region. Close range pulse energy would entirely drown out such evaluation, and would not account for the different acoustic characteristics of the signal and potential masking at such scales. Thus, while masking of specific signals relative to the near-field of operating airgun arrays is an impact that may occur, for the purposes of the analysis conducted for this rule, near-field impacts have been addressed through the modeling of acoustic exposures. The chronic and cumulative impacts analysis that is the subject of this comment addresses far-field chronic impacts. Additionally, there are technical concerns with modifying the analysis specifically as recommended and, accordingly, we disagree with the recommendation for purposes of this analysis of potential chronic effects.

The purpose of this modeling exercise was not to evaluate exposure implications for animals close to the modeling locations (
i.e.,
“acute” effects). Evaluation of acute effects, such as injury and behavioral disruption, was achieved through the primary acoustic exposure modeling effort (Zeddies
et al.,
2015, 2017a). These evaluated effects (evaluated through the primary acoustic modeling effort) are separate and separable from loss of hearing opportunities experienced by animals farther from source locations, which are evaluated through the chronic and cumulative effects modeling discussed here.

Marine Mammal Impacts—Habitat

Comment:
NRDC expressed concern regarding potential impacts to marine mammal prey and/or food webs from the planned surveys. NRDC provided numerous citations in claiming that the surveys could impact marine mammal prey through the following: (1) Cause severe physical injury and mortality; (2) damage hearing and sensory abilities of fish and marine invertebrates; (3) impede development of early life history stages; (4) induce stress that physically damages marine invertebrates and compromises fish health; (5) cause startle and alarm responses that interrupt vital behaviors; (6) alter predator avoidance behavior that may reduce probability of survival; (7) affect catchability of prey species; (8) mask important biological sounds essential to survival; (9) reduce reproductive success, potentially jeopardizing long-term sustainability of fish populations; (10) interrupt feeding behaviors and induce other species-specific effects that may increase risk of starvation, reduce reproduction, and alter community structure; and (11) compromise orientation of fish larvae with potential ecosystem-level effects. Additionally, NRDC cited a publication by McCauley
et al.
(2017) as evidence that the surveys could potentially impact zooplankton and consequently marine mammal food webs.

Response:
NMFS strongly disagrees with the suggestion that we ignored effects to prey species. In fact, we considered relevant literature (including that cited by NRDC) in finding that the most likely impact of survey activity to prey species such as fish and invertebrates would be temporary avoidance of an area, with a rapid return to pre-survey distribution and behavior,

and minimal impacts to recruitment or survival anticipated. While there is a lack of specific scientific information to allow an assessment of the duration, intensity, or distribution of effects to prey in specific locations at specific times and in response to specific surveys, NMFS' review of the available information does not indicate that such effects could be significant enough to impact marine mammal prey to the extent that marine mammal fitness would be affected. We agree that seismic surveys could affect certain marine mammal prey species, and addressed these potential effects, as well as the potential for those effects to impact marine mammal populations, in our notice of proposed rulemaking (83 FR 29241-29242). As stated in that notice, our review of the available information and the specific nature of the activities considered herein suggest that the activities evaluated in this ITR are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to prey species are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations. In support of this conclusion, we refer the commenter to discussion provided in our notice of proposed rulemaking. Additional information is summarized below.

In summary, fish react to sounds which are especially strong and/or intermittent low-frequency sounds, and behavioral responses such as flight or avoidance are the most likely effects. However, the reaction of fish to airguns depends on the physiological state of the fish, past exposures, motivation (
e.g.,
feeding, spawning, migration), and other environmental factors. While we agree that some studies have demonstrated that airgun sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs (
e.g.,
Fewtrell and McCauley, 2012; Pearson
et al.,
1992; Skalski
et al.,
1992; Santulli
et al.,
1999; Paxton
et al.,
2017), our review shows that the weight of evidence indicates either no or only a slight reaction to noise (
e.g.,
Miller and Cripps, 2013; Dalen and Knutsen, 1987; Pena
et al.,
2013; Chapman and Hawkins, 1969; Wardle
et al.,
2001; Sara
et al.,
2007; Jorgenson and Gyselman, 2009; Blaxter
et al.,
1981; Cott
et al.,
2012; Boeger
et al.,
2006), and that, most commonly, while there may be impacts to fish as a result of noise from nearby airguns, any effects will be temporary. For example, investigators reported significant, short-term declines in commercial fishing catch rate of gadid fishes during and for up to five days after seismic survey operations, but the catch rate subsequently returned to normal (Engas
et al.,
1996; Engas and Lokkeborg, 2002). Other studies have reported similar findings (
e.g.,
Hassel
et al.,
2004). Skalski
et al.
(1992) also found a reduction in catch rates—for rockfish (
Sebastes
spp.) in response to controlled airgun exposure—but suggested that the mechanism underlying the decline was not dispersal but rather decreased responsiveness to baited hooks associated with an alarm behavioral response. A companion study showed that alarm and startle responses were not sustained following the removal of the sound source (Pearson
et al.,
1992). Therefore, Skalski
et al.
(1992) suggested that the effects on fish abundance may be transitory, primarily occurring during the sound exposure itself. In some cases, effects on catch rates are variable within a study, which may be more broadly representative of temporary displacement of fish in response to airgun noise (
i.e.,
catch rates may increase in some locations and decrease in others) than any long-term damage to the fish themselves (Streever
et al.,
2016).

SPLs of sufficient strength have been known to cause injury to fish and fish mortality and, in some studies, fish auditory systems have been damaged by airgun noise (McCauley
et al.,
2003; Popper
et al.,
2005; Song
et al.,
2008). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen
et al.
(2012b) showed that a temporary threshold shift (TTS) of 4-6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long—both of which are conditions unlikely to occur for surveys that are necessarily transient in any given location and likely result in brief, infrequent noise exposure to prey species in any given area. For these surveys, the sound source is constantly moving, and most fish would likely avoid the sound source prior to receiving sound of sufficient intensity to cause physiological or anatomical damage. In addition, ramp-up may allow certain fish species the opportunity to move further away from the sound source.

NMFS considered the research provided by NRDC and disagrees with its interpretation of the literature. A recent comprehensive review (Carroll
et al.,
2017) found that results are mixed as to the effects of airgun noise on the prey of marine mammals. While some studies suggest a change in prey distribution and/or a reduction in prey abundance following the use of seismic airguns, others suggest no effects or even positive effects in prey abundance. As one specific example—regarding Paxton
et al.
(2017), which describes findings related to the effects of a 2014 seismic survey on a reef off of North Carolina—NRDC asserts that the study supports a conclusion that seismic surveys “cause significant shifts in distribution that may compromise life history behaviors.” However, our own review of this work shows that a reasonable interpretation leads to a more moderate conclusion. While the study did show a 78 percent decrease in observed nighttime abundance for certain species—which NRDC interprets as a significant shift in distribution that could compromise life history behaviors—it is important to note that the evening hours during which the decline in fish habitat use was recorded (via video recording) occurred on the same day that the seismic survey passed, and no subsequent data is presented to support an inference that the response was long-lasting. Additionally, given that the finding is based on video images, the lack of recorded fish presence does not support a conclusion that the fish actually moved away from the site or suffered any serious impairment because fish may remain present yet not be recorded on video. In summary, this particular study corroborates prior studies demonstrating a startle response or short-term displacement.

Available data suggest that cephalopods are capable of sensing the particle motion of sounds and detect low frequencies up to 1-1.5 kHz, depending on the species, and so are likely to detect airgun noise (Kaifu
et al.,
2008; Hu
et al.,
2009; Mooney
et al.,
2010; Samson
et al.,
2014). Auditory injuries (lesions occurring on the statocyst sensory hair cells) have been reported upon controlled exposure to low-frequency sounds, suggesting that cephalopods are particularly sensitive to low-frequency sound (Andre
et al.,
2011; Sole
et al.,
2013). Behavioral responses, such as inking and jetting, have also been reported upon exposure to low-frequency sound (McCauley
et al.,
2000b; Samson
et al.,
2014). Similar to fish, however, the transient nature of the surveys leads to an expectation that effects will be largely limited to

behavioral reactions and would occur as a result of brief, infrequent exposures.

We discussed impacts to benthic communities from impulsive sound generated by active acoustic sound sources in our notice of proposed rulemaking, including one study showing that exposure to airgun signals was found to significantly increase mortality in scallops, in addition to causing significant changes in behavioral patterns and disruption of hemolymph chemistry during exposure (although the authors state that the observed levels of mortality were not beyond naturally occurring rates) (Day
et al.,
2017). In addition, Fitzgibbon
et al.
(2017) found significant changes to hemolymph cell counts in spiny lobsters subjected to repeated airgun signals, with the effects lasting up to a year post-exposure. However, despite the high levels of exposure, direct mortality was not observed. Further, in reference to the study, Day
et al.
(2016) stated that “[s]eismic surveys appear to be unlikely to result in immediate large scale mortality [. . .] and, on their own, do not appear to result in any degree of mortality” and that “[e]arly stage lobster embryos showed no effect from air gun exposure, indicating that at this point in life history, they are resilient to exposure and subsequent recruitment should be unaffected.” A majority of the studies reviewed by NMFS have observed no increased mortality in invertebrates exposed to airgun noise (
e.g.,
Wardle
et al.,
2001; Parry
et al.,
2002; Christian
et al.,
2003; Andriguetto-Filho
et al.,
2005; Parry and Gason, 2006; Payne
et al.,
2007; Harrington
et al.,
2010; Przeslawski
et al.,
2018).

With regard to potential impacts on zooplankton, McCauley
et al.
(2017) found that exposure to airgun noise resulted in significant depletion for more than half the taxa present and that there were two to three times more dead zooplankton after airgun exposure compared with controls for all taxa, within 1 km of the airguns. However, the authors also stated that in order to have significant impacts on
r
-selected species (
i.e.,
those with high growth rates and that produce many offspring) such as plankton, the spatial or temporal scale of impact must be large in comparison with the ecosystem concerned, and it is possible that the findings reflect avoidance by zooplankton rather than mortality (McCauley
et al.,
2017). In addition, the results of this study are inconsistent with a large body of research that generally finds limited spatial and temporal impacts to zooplankton as a result of exposure to airgun noise (
e.g.,
Dalen and Knutsen, 1987; Payne, 2004; Stanley
et al.,
2011). Most prior research on this topic, which has focused on relatively small spatial scales, has showed minimal effects (
e.g.,
Kostyuchenko, 1973; Booman
et al.,
1996; Sætre and Ona, 1996; Pearson
et al.,
1994; Bolle
et al.,
2012).

A modeling exercise was conducted as a follow-up to the McCauley
et al.
(2017) study (as recommended by McCauley
et al.
), in order to assess the potential for impacts on ocean ecosystem dynamics and zooplankton population dynamics (Richardson
et al.,
2017). Richardson
et al.
(2017) found that a full-scale airgun survey would impact copepod abundance within the survey area, but that effects at a regional scale were minimal (2 percent decline in abundance within 150 km of the survey area and effects not discernible over the full region). The authors also found that recovery within the survey area would be relatively quick (3 days following survey completion), and suggest that the quick recovery was due to the fast growth rates of zooplankton, and the dispersal and mixing of zooplankton from both inside and outside of the impacted region. The authors also suggest that surveys in areas with more dynamic ocean circulation in comparison with the study region and/or with deeper waters (
i.e.,
typical GOM survey locations) would have less net impact on zooplankton.

Notably, a recently described study produced results inconsistent with those of McCauley
et al.
(2017). Researchers conducted a field and laboratory study to assess if exposure to airgun noise affects mortality, predator escape response, or gene expression of the copepod
Calanus finmarchicus
(Fields
et al.,
2019). Immediate mortality of copepods was significantly higher, relative to controls, at distances of 5 m or less from the airguns. Mortality one week after the airgun blast was significantly higher in the copepods placed 10 m from the airgun but was not significantly different from the controls at a distance of 20 m from the airgun. The increase in mortality, relative to controls, did not exceed 30 percent at any distance from the airgun. Moreover, the authors caution that even this higher mortality in the immediate vicinity of the airguns may be more pronounced than what would be observed in free-swimming animals due to increased flow speed of fluid inside bags containing the experimental animals. There were no sublethal effects on the escape performance or the sensory threshold needed to initiate an escape response at any of the distances from the airgun that were tested. Whereas McCauley
et al.
(2017) reported an SEL of 156 dB at a range of 509-658 m, with zooplankton mortality observed at that range, Fields
et al.
(2019) reported an SEL of 186 dB at a range of 25 m, with no reported mortality at that distance.

Regardless, if we assume a worst-case likelihood of severe impacts to zooplankton within approximately 1 km of the acoustic source, the typically wide dispersal of survey vessels and brief time to regeneration of the potentially affected zooplankton populations does not lead us to expect any meaningful follow-on effects to the prey base for odontocete predators (the region considered in this rule is not an important feeding area for taxa that feed directly on zooplankton,
i.e.,
mysticetes).

Given the inconsistency of the McCauley
et al.
(2017) results with prior research on impacts to zooplankton as a result of exposure to airgun noise and with the research of Fields
et al.
(2019), further validation of those findings would be necessary for NMFS to reach a determination that these impacts are likely to occur. Moreover, a single study is not sufficient to evaluate the potential impacts, and further study in additional locations must be conducted. Therefore, BOEM proposed to fund such a study as part of their 2019-21 Studies Development Plan (
www.boem.gov/FY-2019-2021-SDP/
).

A recent review article concluded that, while laboratory results provide scientific evidence for high-intensity and low-frequency sound-induced physical trauma and other negative effects on some fish and invertebrates, the sound exposure scenarios in some cases are not realistic to those encountered by marine organisms during routine seismic operations (Carroll
et al.,
2017). The review finds that there has been no evidence of reduced catch or abundance following seismic activities for invertebrates, and that there is conflicting evidence for fish with catch observed to increase, decrease, or remain the same. Further, where there is evidence for decreased catch rates in response to airgun noise, these findings provide no information about the underlying biological cause of catch rate reduction (Carroll
et al.,
2017).

NRDC's assertions regarding the likely effects of airgun survey noise on marine mammal prey include, for example, the assertion that the specified activity would harm fish and invertebrate species over the long-term, cause reductions in recruitment and effects to behavior that may reduce reproductive potential and foraging success and

increase the risk of predation, and induce changes in community composition via such population-level impacts. We have addressed these claims both in this response and in our review of the available literature. We also reviewed available information regarding populations of representative prey stocks in the northern GOM,
i.e.,
the only U.S. location where marine seismic surveys are a routinely occurring activity. While we recognize the need for caution in assuming correlation between the ongoing survey activity in the GOM and the health of assessed stocks there, we also believe this information has some value in informing the likelihood of population-level effects to prey species and, therefore, the likelihood that the specified activity would negatively impact marine mammal populations via effects to prey. We note that the information reported below is in context of managed commercial and recreational fishery exploitation, in addition to any other impacts (
e.g.,
noise) on the stocks. The species listed below are known prey species for marine mammals and represent groups with different life histories and patterns of habitat use. Numerous other managed stocks are similarly healthy.

• Red snapper (
Lutjanus campechanus
): Red snapper are bottom-dwelling fish generally found at approximately 10-190 m deep that typically live near hard structures on the continental shelf that have moderate to high relief (for example, coral reefs, artificial reefs, rocks, ledges, and caves), sloping soft-bottom areas, and limestone deposits. Larval snapper swim freely within the water column. Increases in total and spawning stock biomass are predicted beginning in about 1990 (Cass-Calay
et al.,
2015). Regional estimates suggest that recruitment in the west has generally increased since the 1980s, and has recently been above average, while recruitment in the east peaked in the mid-2000s, and has since declined. However, the most recent assessment suggests a less significant decline (to moderate levels) (Cass-Calay
et al.,
2015).

• Yellowfin tuna (
Thunnus albacares
): Yellowfin tuna are highly migratory, living in deep pelagic waters, and spawn in the GOM from May to August. However, we note that a single stock is currently assumed for the entire Atlantic, with additional spawning grounds in the Gulf of Guinea, Caribbean Sea, and off Cabo Verde. The most recent assessment indicates that spawning stock biomass for yellowfin tuna is stable or increasing somewhat and that, overall, the stock is near levels that produce the maximum sustainable yield (ICCAT, 2016).

• King mackerel (
Scomberomorus cavalla
): King mackerel are a coastal pelagic species, found in open waters near the coast in waters from approximately 35-180 m deep. King mackerel migrate in response to changes in water temperature, and spawn in shelf waters from May through October. Estimates of recruitment demonstrate normal cyclical patterns over the past 50 years, with a period of higher recruitment most recently (1990-2007) (SEDAR, 2014). Long-term spawning stock biomass patterns indicate that the spawning stock has been either rebuilding or remained relatively consistent over the last 20 years, with nothing indicating that the stock has declined in these recent decades (SEDAR, 2014).

In summary, the scientific literature demonstrates that impacts of seismic surveys on marine mammal prey species will likely be limited to behavioral responses, the majority of prey species will be capable of moving out of the area during surveys, a rapid return to normal recruitment, distribution, and behavior for prey species is anticipated, and, overall, impacts to prey species, if any, will be minor and temporary. Prey species exposed to sound might move away from the sound source, experience TTS, experience masking of biologically relevant sounds, or show no obvious direct effects. Mortality from decompression injuries is possible in close proximity to a sound, but only limited data on mortality in response to airgun noise exposure are available (Hawkins
et al.,
2014). The most likely impacts for most prey species in a given survey area would be temporary avoidance of the area. Surveys using towed airgun arrays move through an area relatively quickly, limiting exposure to multiple impulsive sounds. In all cases, sound levels would return to ambient once a survey moves out of the area or ends and the noise source is shut down and, when exposure to sound ends, behavioral and/or physiological responses are expected to end relatively quickly (McCauley
et al.,
2000b). The duration of fish avoidance of a given area after survey effort stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. While the potential for disruption of spawning aggregations or schools of important prey species can be meaningful on a local scale, the mobile and temporary nature of most surveys and the likelihood of temporary avoidance behavior suggest that impacts would be minor.

Finally, and relevant to NMFS' findings under the MMPA, NRDC does not demonstrate that even the asserted worst-case effects on prey species would have any meaningful impact on marine mammals or their respective populations. Referencing a single study on zooplankton effects (
i.e.,
McCauley
et al.,
2017), NRDC implies that airgun surveys will definitively reduce “the abundance and diversity of zooplankton over vast areas and induc[e] changes in community composition due to the aggregation of individual- and population-level impacts across multiple fish and invertebrate species,” thereby leading to ecosystem-level effects that would harm marine mammal populations. NMFS disagrees with this interpretation of the scientific literature and notes the presence of healthy stocks of marine mammal prey species currently found in the GOM, despite decades of routine geophysical survey operations, but also a devastating oil spill (discussed in detail in the notice of proposed rulemaking). NMFS believes that no evidence is presented to contradict our conclusions regarding likely impacts to marine mammals due to effects on prey species,
i.e.,
that impacts of the specified activity are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species, and that any effects that do occur are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.

Comment:
The Associations object to NMFS' use of an analysis of chronic and cumulative impacts of noise on marine mammals in the GOM (
i.e.,
the CCE report), which was described in detail in our notice of proposed rulemaking. The Associations state that “[c]oncepts such as “soundscape,” “communication space,” or “acoustic footprint” have no basis in any existing statutory or regulatory authorities, and are therefore inapplicable to this rulemaking.”

Response:
The purpose of the analysis was to evaluate the more cumulative nature of low-frequency, long-distance propagation of relatively low-intensity energy from multiple seismic surveys operating concurrently in a region, and to evaluate potential loss of ability to detect signals of biological importance over spatial scales relevant to the sources and hearing capabilities of representative species. NMFS is required to evaluate the effects of the specified activity on the potentially impacted marine mammal stocks and their habitat. Noise can disrupt marine mammals' behavioral patterns through the contraction of their communication

space, among other impacts. Moreover, NMFS is required to mitigate impacts on marine mammal species or stocks and their habitat. Concepts such as listening area and communication space are not novel, having been published in peer-reviewed literature and previously applied in impact assessment contexts. NMFS is required to consider these effects.

Comment:
NRDC argues that NMFS fails to consider chronic harm, including masking effects and impacts on acoustic habitat. For example, NRDC asserts that the consideration of masking in NMFS' negligible impact analysis was cursory in that it only came through the vulnerability ratings and “seems to misapprehend the spatial and temporal scope of the effects” of masking. Similarly, in addition to citing general concerns about chronic effects to Bryde's whales and other species, NRDC asserts that acoustic habitat is discussed, but not factored into the negligible impact analysis.

Response:
The potential impacts of masking were properly considered. NRDC significantly understates the consideration given to masking effects in the Expert Working Group (EWG) risk assessment framework (see Negligible Impact Analysis and Determinations). Broadly, the results of the EWG analysis for any given species are based on the integration of two components: The severity of the impacts (which reflects the extent of the activities overlaid with the presence and distribution of the given species) and the vulnerability of that species based on multiple biological and environmental risk factors, including explicit consideration of masking. The maximum possible vulnerability score any species can attain under the assessment across all of these factors is 30. The masking component of the vulnerability score considers communication masking, foraging masking, and navigation/orientation masking—for a total of seven points. The minimum score that any species assessed in the context of these survey activities could (and did) attain is 1, while the Bryde's whale was given the maximum scores across all types of masking for a score of 7. The differential across the highest and lowest possible masking scores is 6, out of a maximum possible total of 30 for the overall vulnerability score, which means that masking accounts for twenty percent of a species' vulnerability rating. Twenty percent is an appropriate and not insubstantial proportion of the vulnerability score, given that the total score (with its 30-point maximum) also accounts for behavioral impacts, whether there are biologically important areas or times overlaying the activities, whether there are additional chronic anthropogenic (
e.g.,
other anthropogenic noise) or chronic biological factors (
e.g.,
disease), and the status and trends of the population.

NMFS recognizes that masking is not necessarily co-extensive with harassment and explicitly recognizes this in our discussion of effects, although we also note that the distances at which behavioral harassment is quantified for this rule are farther than those contemplated in the past, due to the behavioral harassment thresholds used (see the Estimated Take section and comment responses later in this section for further discussion of acoustic thresholds). As discussed elsewhere, NMFS designed and supported the implementation of a chronic and cumulative effects analysis (the CCE report, discussed later in this preamble) for the specific purpose of addressing the effects of these activities on the listening space of all species and the communication space of Bryde's whales specifically. This modeling effort explicitly considered the effects of masking over realistic spatial scales. In their 2017 public comments on incidental harassment authorizations NMFS had proposed for seismic survey activities in the Atlantic Ocean, NRDC specifically recommended that NMFS conduct a modeling exercise like the effort conducted here for the GOM rule to better support those findings (see 83 FR 63268; December 7, 2018), yet they now suggest that this analysis is inadequate, even paired with the quantitative analysis included in the EWG analysis as it is here. See Potential Effects of the Specified Activities on Marine Mammals and Their Habitat in the notice of proposed rulemaking for additional discussion.

Comment:
A private citizen offers commentary and clarifications regarding the discussions of acoustic masking and acoustic habitat provided in our notice of proposed rulemaking.

Response:
We appreciate the discussion provided by the commenter, but note that no specific recommendations are provided towards an improved assessment of the effects of chronic aggregate noise from survey activity, as the commenter suggests is needed.

Cumulative Impacts and Related Issues

Comment:
NRDC expressed concern regarding cumulative impacts, claiming that NMFS' negligible impact determination underestimates impacts to marine mammal species and populations because it fails to consider the effects of other anticipated activities on the same marine mammal populations. NRDC also stated that NMFS must include geophysical surveys occurring within state waters within the scope of the ITR.

Response:
Neither the MMPA nor NMFS' codified implementing regulations address consideration of other unrelated activities and their impacts on populations. However, the preamble for NMFS' implementing regulations (54 FR 40338; September 29, 1989) states in response to comments that the impacts from other past and ongoing anthropogenic activities are to be incorporated into the negligible impact analysis via their impacts on the baseline. Consistent with that direction, NMFS has factored into its negligible impact analysis 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, the chronic and cumulative effects analysis (the “CCE report” discussed later in this preamble), and other relevant stressors. Some of these are addressed explicitly through the environmental risk factor scoring in the population vulnerability analysis of the Expert Working Group Assessment (including consideration of Deepwater Horizon (DWH) oil spill effects and risk from other anthropogenic activities). In addition, we consider these factors as relevant contextual elements of the analysis. See the Negligible Impact Analysis and Determinations section of this notice for full detail.

Our 1989 final rule for the MMPA implementing regulations also addressed public comments regarding cumulative effects from future, unrelated activities. There we stated that such effects are not considered in making findings under section 101(a)(5) concerning negligible impact. We indicated (1) that NMFS would consider cumulative effects that are reasonably foreseeable when preparing a NEPA analysis, and (2) that reasonably foreseeable cumulative effects would also be considered under section 7 of the ESA for ESA-listed species.

Here, we recognize the potential for cumulative impacts, as analyzed through BOEM's PEIS, which addressed the impacts of an extended time period of survey activity that may be permitted by BOEM (ten years versus the five years that the ITR is limited to), and which NMFS adopted as the basis for its Record of Decision. In that analysis, the assessment was focused on whether the predicted level of take from the forecasted level of survey effort, when considered in context, would have a

meaningful biological consequence at a species or population level. NMFS, therefore, assessed and integrated other contextual factors (
e.g.,
species' life history and biology, distribution, abundance, and status of the stock; mitigation and monitoring; characteristics of the surveys and sound sources) in determining the overall impact of issuance of the ITR and subsequent LOAs on the human environment. Key considerations included the nature of the surveys and the required mitigation. In all cases, it is expected that sound levels will return to previous background levels once the acoustic source moves a certain distance from the area, or the surveys cease. The proposed rule also identified several time-area restrictions to minimize risk or severity of impacts to the extent practicable, consistent with the MMPA's least practicable adverse impact standard. In the final rule, two of those areas were removed from consideration based on the reduction in the scope of the rule per BOEM's request. The other proposed mitigation area remains (as modified; see Mitigation). Although those two areas have been removed from consideration as mitigation due to the reduction in scope of the rule, the practical effect on GOM stocks is similar, in that no survey activity within those areas may be considered for take authorization pursuant to the rule. The similar result is a reduction in the overall numbers of take but also, importantly, elimination or minimization of impacts to marine mammal species or stocks in the areas most important to them for feeding, breeding, and other important functions. Therefore, the severity of takes that may occur pursuant to the rule is expected to be meaningfully lower due to the reduction in impacts that could reduce reproductive success or survivorship.

In summary, NMFS does not expect aggregate impacts from the forecast level of survey effort to affect rates of recruitment or survival for marine mammals, either alone or in combination with other past, present, or ongoing activities. The cumulative impacts of these surveys (
i.e.,
the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions) were addressed as required through the NEPA documents cited above. These documents, as well as the relevant Stock Assessment Reports, are part of NMFS' Administrative Record for this action, and provided the decision-maker with information regarding other activities in the action area that affect marine mammals, an analysis of cumulative impacts, and other information relevant to the determinations made under the MMPA.

Separately, cumulative effects were analyzed as required through NMFS' required intra-agency consultation under section 7 of the ESA, which concluded that NMFS' action of issuing the ITR and subsequent LOAs was not likely to jeopardize the continued existence of listed marine mammals.

We disagree with NRDC's suggestion that we include geophysical surveys in state waters within the scope of this rulemaking. Section 101(a)(5)(A) of the MMPA requires NMFS to make a determination that the take incidental to a “specified activity” will have a negligible impact on the affected species or stocks of marine mammals, and will not result in an unmitigable adverse impact on the availability of marine mammals for taking for subsistence uses. NMFS' implementing regulations require applicants to include in their request a detailed description of the specified activity or class of activities that can be expected to result in incidental taking of marine mammals. 50 CFR 216.104(a)(1). Thus, the “specified activity” for which incidental take coverage is being sought under section 101(a)(5)(A) is generally defined and described by the applicant. Here, BOEM is the applicant for the ITR in support of industry operators, and we are responding to the specified activity as described in that petition (and making the necessary findings on that basis). As BOEM's PEIS makes clear, BOEM does not have a regulatory role regarding surveys occurring in state waters. (See,
e.g.,
BOEM's PEIS, Chapter 1.1.3)

NRDC's representation of our action—“The agency's decision to evaluate the impacts of state water surveys separately as if they would occur in isolation”—also ignores the fact that we have no information about the possible extent of potential future geophysical survey activity in state waters, including type, amount, duration, timing, location, etc., even if such activity were to occur. Although it may be reasonable to assume that such activity occurs, we have no specific knowledge of any past, present, or reasonably foreseeable future survey activity in state waters. No prospective applicant has contacted NMFS to request incidental take authorization for any such survey activity planned or expected within state waters, on either a programmatic or specific basis. NRDC did not provide any information about the expected future extent of survey activity in state waters.

Acoustic Thresholds

Comment:
NRDC expressed concerns regarding NMFS' proposed use of the probabilistic response function described by Wood
et al.
(2012), in which 10 percent, 50 percent, and 90 percent of individuals exposed are assumed to produce a behavioral response (of a sufficient degree of severity to constitute Level B harassment) at exposures of 140, 160, and 180 dB root mean square (rms), respectively. (The function is shifted for the more behaviorally sensitive beaked whales such that 50 percent and 90 percent response probabilities are assumed to occur at 120 and 140 dB rms, respectively.) NRDC stated that the function is inconsistent with the best available science, asserting that behavioral disruptions occur at higher percentages at lower noise exposure levels than those suggested by Wood
et al.
(2012). NRDC's criticism of the function also focused on the use of horizontal displacement studies as the supposed basis of analysis for Wood
et al.
(2012), as well as on the function's nature as a series of step functions. In addition, NRDC expressed concerns that the use of frequency weighting in the Wood
et al.
(2012) approach is inappropriate. NRDC requested that NMFS revise the threshold as suggested in Nowacek
et al.
(2015), which recommended a similar function (but centered on 140 dB rms rather than 160 dB rms), while simultaneously stating that the use of such step-based risk functions is “biologically irrational.” Overall, NRDC claims that reliance on this function results in underestimation of impacts. A private citizen echoed some of NRDC's comments on this topic while CRE supports use of the Wood
et al.
approach.

Response:
NMFS has been criticized in the past for the use of the single-step 160-dB rms approach. Those criticisms are based on the idea that an approach reflecting a more complex multi-step probabilistic function would more effectively represent the known variation in responses at different levels due to differences in the receivers, the context of the exposure, and other factors, as well as the science indicating that animals may react in ways constituting Level B harassment when exposed to lower received levels. In developing the acoustic exposure analysis for the proposed rulemaking, we reviewed relevant past public comments as well as the best available science, determining that a more complex probabilistic function is indeed better reflective of available scientific information, and that it was appropriate

to take the fundamental step of recognizing the potential for Level B harassment occurring at exposures to received levels below 160 dB rms (as well as the potential for
no
Level B harassment occurring at exposures above 160 dB rms). This approach necessarily also accounts for differential hearing sensitivity by incorporating frequency-weighting functions, as behavioral responses in cetaceans are best explained by the interaction between sound source type and functional hearing group (Gomez
et al.,
2016). NMFS has determined that the general approach used for this rule—a probabilistic risk function that allows for the likelihood of differential response probability at given received levels on the basis of multiple factors, including behavioral context and distance from the source, and that addresses particularly sensitive species—is appropriate in light of the best available scientific information.

However, because behavioral responses to sound depend on the context in which an animal receives the sound, including the animal's behavioral mode when it hears sounds, prior experience, additional biological factors, and other contextual factors, defining sound levels that disrupt behavioral patterns is extremely difficult. Even experts have not previously been able to suggest specific new criteria due to these difficulties (
e.g.,
Southall
et al.
2007; Gomez
et al.,
2016). Agency expertise is appropriate in defining the particu

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2020-27252. Public record. Not legal advice.