5322 Federal Register / Vol. 86, No. 11 / Tuesday, January 19, 2021 / Rules and Regulations 

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. 

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-oiland-gas-industry-geophysical-surveyactivity-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 


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Federal Register / Vol. 86, No. 11 / Tuesday, January 19, 2021 / Rules and Regulations 5323 

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. 

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-andgas-industry-geophysical-surveyactivity-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/Gulfof-Mexico-Geological-and-GeophysicalActivities-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-andgas-industry-geophysical-surveyactivity-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 


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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 twodimensional (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 crosssectional 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 highresolution 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. 

BILLING CODE 3510–22–P 


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BILLING CODE 3510–22–C 

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 in3. 

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 lowfrequency 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 


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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, backcalculated 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 runout. 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 fourcomponent 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 


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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-andgas-industry-geophysical-surveyactivity-gulf-mexico. 

Representative sources for the 

modeling include a single airgun, an 

airgun array, and multiple 

electromechanical sources. Two major 

survey types were considered: Largearea 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 in3 airgun) and 

a large airgun array (8,000 in3). In 

addition, the supplemental Model 

Variable Analysis (Zeddies et al., 2017b) 

provides analysis of an alternative 4,130 

in3 array (see Letters of Authorization 

section). We note that while highresolution 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 casespecific 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 fiveyear 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 


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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. 

BILLING CODE 3510–22–P 

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 


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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 VSP3 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 

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

2Zones 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 in3); 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. 4Shallow penetration/HRG survey types include shallow hazards surveys, assumed to use a single 90 in3 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 


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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 in3 total 

volume. That delineation has been 

revised to include surveys using arrays 

greater than 1,500 in3 total volume, with 

arrays of 1,500 in3 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 preclearance, 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. 


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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-andgas-industry-geophysical-surveyactivity-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-MexicoGeological-and-Geophysical-ActivitiesProgrammatic-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-noaafisheries-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 wellstructured 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 


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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 populationlevel 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 


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‘‘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 


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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 lowfrequency 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, nearfield 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 speciesspecific 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, 


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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 longterm 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, shortterm 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 


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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; S#tre 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 freeswimming 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/FY2019-2021-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 


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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 populationlevel 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 bottomdwelling 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 longterm 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 


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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 peerreviewed 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 


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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 


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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 particular steps at which 

specific response probabilities are 

assumed to occur, and while we 

acknowledge our approach reduces a 

complex suite of interactions to make 

reasonable inferences, it is consistent 

with the best available science. 

NRDC expressed concerns regarding 

our approach by noting the size 

discrepancy between the area ensonified 

to 140 dB versus that ensonified to 160 

dB, implying that we ignore potential 

responses at the lower received level. To 

clarify, the difference between our 

approach and NRDC’s recommendation 

is solely in the proportion of a 

population assumed to be taken upon 

exposure to the specified received level 

which, as stated above, is determined on 

the basis of expert judgement based on 

the best available science. We believe 

that the Wood et al. (2012) function is 

consistent with the best available 

science, and is therefore an appropriate 

approach. Below, we address NRDC’s 

concerns in greater detail. 

NRDC referenced ‘‘recent’’ research 

they claim is not consistent with the 

recommendations of Wood et al. (2012). 

We note that, of the nine studies cited 

by NRDC, five were published prior to 

the Wood et al. (2012) study, and were 

therefore available for those authors’ 

consideration (and some were 

specifically referenced by those authors 

in discussion of their 

recommendations). Further, we disagree 

that the referenced findings are 

inconsistent with Wood et al. (2012). 

First, a mere reaction to noise exposure 

does not mean that a take by Level B 

harassment, as defined by the MMPA, 

has occurred. For a take to occur 

requires that an act have ‘‘the potential 

to disturb by causing disruption of 

behavioral patterns,’’ not simply result 

in a detectable change in motion or 

vocalization. NRDC also suggests that 

some of these studies were not 

incorporated into Wood et al.’s 

recommendations, or our consideration 

of those and other potential approaches 

in context of the available science, and 

criticize what they view as an overreliance on horizontal displacement 

studies as the supposed basis of 

analysis. While it is true that the 

majority of available behavioral data 

focus on avoidance responses, Wood et 

al. (2012) does not mention excluding 

behavioral studies involving vocal 

changes, and the precedent Southall et 

al. (2007) specifically incorporates 

numerous studies that do mention 

changes in vocalization associated with 

sound exposure. Thus, these datasets 

were not excluded and, as discussed in 

our notice of proposed rulemaking, we 

adequately considered all studies 

addressed by NRDC. 

Regarding baleen whales, we 

acknowledge that changes in 

vocalization have been observed in 

association with exposure to airgun 

surveys within migratory and nonmigratory contexts (e.g., Castellote et al., 

2012; Blackwell et al., 2013; Cerchio et 

al., 2014). The potential for such effects 

to occur over relatively large spatial 

scales is not surprising for species with 

large communication spaces (e.g., Clark 

et al., 2009), but we reiterate our 

disagreement with NRDC’s apparent 

contention that every detected change to 

vocalizations rises to the level of a take. 

NRDC cites reports of changes in 

vocalization, typically for baleen 

whales, as evidence in support of lower 

thresholds, claiming these reactions 

result in biological consequences 

indicating that the reaction was indeed 

a take. However, NMFS is not aware of 

research that provides a well-supported 

link between the reported reactions at 

lower received levels and the putative 

consequences. In conflict with NRDC’s 

interpretation of the literature are 

documented instances of marine 

mammal exposure to greater received 

levels that did not elicit any response 

(e.g., Malme et al., 1983, 1984, 1985, 

1988; McCauley et al., 1998, 2000a, 

2000b; Barkaszi et al., 2012; Stone, 

2015a; Gailey et al., 2016; Barkaszi and 

Kelly, 2018). 

The received level associated with 

stoppage of calling for bowhead whales 

(Balaena mysticetus) observed by 

Blackwell et al. (2013, 2015)—a 

response that may arguably rise to the 

level of harassment—is consistent with 

the Wood et al. (2012) scheme, in which 

the potential for take upon exposure to 

received levels as low as 140 dB is 

accounted for. Similarly, the findings of 

Pirotta et al. (2014) for harbor porpoise 

(Phocoena phocoena) are consistent 

with the treatment of behaviorally 

sensitive species by Wood et al., in 

which the potential for take at even 

lower received levels is accounted for 

(though irrelevant here, as harbor 

porpoise are not found in the GOM). 

The response levels reported by 

McDonald et al. (1995) and Di Iorio and 

Clark (2009) for blue whales 

(Balaenoptera musculus) also comport 

with the Wood et al. function, if we 

assume that the observed responses 

equate to harassment (though it is not 

clear that they do). With regard to 

NRDC’s citation of Clark and Gagnon 

(2006), a non-peer reviewed white 

paper, NRDC incorrectly overestimated 

the area over which the effect was 

observed by an order of magnitude (the 

paper discusses an area of 100 x 100 

nmi, which equates to 10,000 nmi2—not 

100,000 nmi2). 

In regard to Cerchio et al. (2014), it is 

important to note that received levels 

provided in this study are those 

recorded at locations of their 

underwater recording devices. The 

authors indicated ‘‘we did not have the 

ability to locate the singers or the 

seismic survey vessel, estimate the 

source level of the pulses, the distance 

between the source and potentially 

impacted singers, or the received level 

of the pulses at the singers.’’ The same 

situation, i.e., actual received levels at 

the location of the animals are 

unknown, is true for Castellote et al. 

(2012) and Clark and Gagnon (2006), 

which provide average background 

sound levels with and without the 

presence of airgun surveys. Thus, not 

having the location of the animals at the 

time of exposure makes it difficult to 

draw conclusions based strictly on 

received level. NMFS has evaluated the 

papers and determined they are not 

informative about appropriate Level B 

harassment thresholds. 

Regarding sperm whales, NMFS 

disagrees that assuming a 100 percent 


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probability of take of sperm whales 

upon exposure to survey noise at 135 

dB—as suggested by NRDC—is an 

accurate reflection of the results of the 

Miller et al. (2009) study. While we 

agree that the work of Miller et al. 

(2009) suggests that sperm whales in the 

GOM may be susceptible to disruption 

of foraging behavior upon exposure to 

relatively moderate sound levels, NRDC 

incorrectly interprets results of the 

study in claiming that sperm whale 

‘‘foraging success’’ was found to 

‘‘decline significantly.’’ Instead, the 

authors report that buzz rates (a proxy 

for attempts to capture prey) were 

approximately 20 percent lower, 

meaning that the appropriate 

interpretation would be that foraging 

activity (versus foraging success) was 

reduced by 20 percent (Jochens et al., 

2008). Of the eight whales tagged in that 

study, only one was observed to actually 

cease foraging. 

Moreover, while we do believe that 

these results support a conclusion that 

exposure to survey noise can impact 

foraging activity, other commenters 

have interpreted them differently, e.g., 

by focusing on the finding that exposed 

whales did not change behavioral state 

during exposure or show horizontal 

avoidance (a finding replicated in other 

studies, e.g., Madsen et al., 2002a; 

Winsor et al., 2017). Importantly, the 

observed effect was not statistically 

significant and, as reported by the 

authors, constituted ‘‘subtle effects on 

their foraging behavior.’’ Furthermore, 

the authors of the Wood et al. (2012) 

study explicitly described their 

consideration of Miller et al. (2009) in 

the development of their recommended 

criteria. Therefore, the Wood et al. 

(2012) recommendation is indeed 

consistent with the Miller et al. (2009) 

study. 

In referencing Bowles et al. (1994), 

NRDC fails to state that the observed 

cessation of vocalization was likely in 

response to a low-frequency tone 

(dissimilar to airgun signals), though a 

distant airgun survey was noted as 

producing signals that were detectable 

above existing background noise. NRDC 

recommends that NMFS base a sperm 

whale threshold on the findings of a 

separate study of exposure of sperm 

whales and other species to sonar 

signals (Miller et al., 2012). NMFS 

disagrees that behavioral response data 

for sperm whales exposed to midfrequency active sonar (Miller et al., 

2012) is more appropriate than using 

data from the airgun exposures 

described by Miller et al. (2009) and 

already considered within the Wood et 

al. function. Furthermore, the 

alternative recommendation of Nowacek 

et al. (2015), which is repeatedly 

mentioned by NRDC as a more 

appropriate alternative to Wood et al. 

(2012), does not make a distinction 

between sperm whales and other 

odontocetes and instead advocates for a 

criteria that treats all marine mammal 

species the same (we address this in 

greater detail below). 

Regarding other odontocetes, NRDC’s 

representation of the available scientific 

information is also inaccurate. Miller et 

al. (2005) specifically state that 

‘‘[s]ighting rates at distances of 10–20 

km from the airgun array were 

significantly lower than those in areas 

20–30 km from the airgun array, where 

sighting rates were unexpectedly high’’ 

(i.e., the study indicates sighting rates of 

beluga whales (Delphinapterus leucas) 

were lower, not ‘‘100% avoidance’’ as 

claimed by NRDC). Miller et al. (2005) 

reported seven aerial beluga whale 

sightings from 8 to 18 km from the 

survey vessel and two vessel-based 

beluga whale sightings at 1.5 and 2.5 km 

from the survey vessel. Furthermore, 

Southall et al. (2007) described the 

findings of the Miller et al. (2005) study 

as temporary avoidance behaviors at 

these lower received levels, while 

Gomez et al. (2016) (which NRDC agrees 

reflects the best available science) 

evaluated Miller et al. (2005) based on 

a received level of 150 dB. Thus, the 

Wood et al. (2012) approach does 

capture responses associated with this 

study. 

Additionally, Wood et al. (2012) has 

the advantage of accounting for 

sensitive species such as beaked whales, 

meaning that a response of a beaked 

whale at 140 dB (as cited by NRDC) is 

covered within the Wood et al. (2012) 

recommended criteria (e.g., Wood et al. 

assumes 90 percent of an exposed 

beaked whale population will respond 

at 140 dB). If Nowacek et al. (2015) was 

instead used, as advocated by NRDC, 

the probability of response would only 

be 50 percent at 140 dB. 

It should be noted that the systematic 

review by Gomez et al. (2016), cited by 

NRDC in support of their position, 

found that received level was not 

appropriate as the sole indicator of 

behavioral response. For example, this 

review shows that ‘‘low’’ effects were 

actually found to reach peak probability 

at a higher received level than 

‘‘moderate’’ effects for baleen whales. 

As we discussed in our notice of 

proposed rulemaking, the results of the 

Gomez et al. (2016) review are not 

inconsistent with Wood et al. (2012). 

With regard to NRDC’s comment that 

the authors consider their results ‘‘nonconservative,’’ Gomez et al. (2016) only 

indicates that they may have scored the 

severity of vocal responses higher if 

they had more information on the 

ecological significance of these types of 

responses. There is no indication 

elsewhere in Gomez et al. (2016) that 

their overall results and analysis are 

‘‘non-conservative.’’ 

NRDC repeatedly cites Nowacek et al. 

(2015) in public comments. We note 

first that while NRDC repeatedly refers 

to this paper as a ‘‘study’’ (implying that 

it presents new scientific data or the 

results of new analyses of existing 

scientific data), the paper (which is coauthored by the author of NRDC’s 

comment letter) in fact makes policy 

recommendations rather than presenting 

any new science. The more substantive 

reviews presented by Southall et al. 

(2007) and Gomez et al. (2016) were 

unable to present any firm 

recommendations, as noted above. We 

addressed the Nowacek et al. (2015) 

approach relative to the Wood et al. 

(2012) approach, in context of the best 

available scientific information, in 

detail in our notice of proposed 

rulemaking. Then, as now, we found 

that those recommendations are not 

justified by the available scientific 

evidence. 

Other than suggesting a 50 percent 

midpoint for a probabilistic function, 

Nowacek et al. (2015) offer minimal 

detail on how their recommended 

probabilistic function should be 

derived/implemented or exactly how 

this midpoint value (i.e., 140 dB rms) 

was derived (i.e., what studies support 

this point). In contrast with elements of 

a Level B harassment function that 

NRDC indicates as important, Nowacek 

et al. (2015) does not make distinctions 

between any species or species groups 

and provides no quantitative 

recommendations for acknowledging 

that behavioral responses can vary by 

species group and/or behavioral context. 

In summary, little substantive support is 

provided by Nowacek et al. (2015) for 

the proposal favored by NRDC. Few 

studies are offered in support of the 

recommended midpoint and the 

proposal is offered only in a one-page 

supplementary document. The Nowacek 

et al. (2015) approach is not wellsupported scientific consensus, as 

NRDC’s comment suggests. 

Additionally, the application of the 

Nowacek et al. (2015) approach 

disregards the important role that 

distance from a source plays in the 

likelihood that an animal will respond 

to a given received level from that 

source type in a particular manner. By 

assuming, for example, a 50 percent 

midpoint at 140 dB rms, the approach 

implies an unrealistically high 

probability of marine mammal response 


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2NMFS. 2018. 2018 revision to: Technical 

guidance for assessing the effects of anthropogenic 

sound on marine mammal hearing (Version 2.0). NOAA Technical Memorandum NMFS–OPR–59, 

National Marine Fisheries Service: 178. 

to signals received at very far distances 

from a source (e.g., greater than 50 km). 

DeRuiter et al. (2013) found that beaked 

whales exposed to similar received 

levels responded when the sound was 

coming from a closer source and did not 

respond to the same level received from 

a distant source. Although the Wood et 

al. (2012) approach does not specifically 

include a distance cut-off, the distances 

at which marine mammals are predicted 

to respond better comport with the 

distances at which behavioral responses 

have been detected and reported in the 

literature. 

NRDC also criticizes the use of 

weighting functions in evaluating 

potential Level B harassment, and 

specifically criticizes use of the Mweighting scheme of Southall et al. 

(2007). Gomez et al. (2016) suggest that 

incorporation of frequency-weighting is 

necessary to account for differential 

hearing sensitivity, as behavioral 

responses in cetaceans are best 

explained by the interaction between 

sound source type and functional 

hearing group. That is, implementing 

weighting functions allows for 

consideration that different marine 

mammal groups do not hear varying 

frequencies of sound equally well. Thus, 

it is appropriate to account for sounds 

below a group’s best hearing range 

having a lower likelihood of resulting in 

a behavioral response (let alone that 

animals are likely unable to effectively 

detect sounds at frequencies completely 

outside their hearing range). 

The M-weighting functions are 

described in Southall et al. (2007) as 

‘‘intentionally precautionary (wide)’’ (as 

opposed to the weighting functions used 

in NMFS’ 2018 Revised Technical 

Guidance 2 to account for noise-induced 

hearing loss) and are used to account for 

the functional hearing ranges of 

different marine mammal hearing 

groups. This frequency weighting 

scheme was intentionally selected 

because it is more conservative in 

accounting for hearing sensitivity (as is 

appropriate in evaluating potential 

Level B harassment) than are more 

recently developed filters designed to 

better assess potential noise-induced 

hearing loss. 

NRDC asserts that because Mweighting assumes that mid- and highfrequency (MF and HF) cetaceans are 

relatively insensitive to noise below 1 

kHz, it is likely that the incorporation of 

M-weighting has a significant 

downwards effect on take estimates. 

This is incorrect. The table below 

illustrates the impact of M-weighting 

functions on frequencies ranging from 

100 Hz to 1 kHz. 

TABLE 3—IMPACT OF M-WEIGHTING FUNCTIONS ON FREQUENCIES RANGING FROM 100 Hz TO 1 kHz 

Weighting (¥dB) 

Hearing group 1 kHz 500 Hz 250 Hz 100 Hz 

Mid-frequency Cetaceans ................................................................................ ¥0.186 dB ¥0.76 dB ¥2.77 dB ¥10 dB. 

High-frequency Cetaceans .............................................................................. ¥0.034 dB ¥1.33 dB ¥4.45 dB ¥13.6 dB. 

We see that, at 250 Hz and above, the 

M-weighting functions do not result in 

a significant reduction (less than 3 dB 

for MF cetaceans and less than 5 dB for 

HF cetaceans). Furthermore, the lower 

bound of the functional hearing range of 

these groups is 150 Hz for MF cetaceans 

and 275 Hz for HF cetaceans (i.e., 

sounds below 100 Hz, where most 

energy in airgun noise is found and 

where M-weighting results in the 

greatest reductions, are outside 

functional hearing range). At 1 kHz, 

where these species are most likely to be 

able to detect and respond to airgun 

noise, there is very little assumed 

reduction in sensitivity. 

Finally, NRDC advocates for the use 

of a linear risk function as opposed to 

the multiple step function of Wood et al. 

(2012), stating that linear risk functions 

are scientifically accepted methodology 

that better acknowledge individuals 

may vary in responsiveness. Although 

NRDC does not specifically define what 

they mean by ‘‘linear risk function,’’ 

NMFS assumes a linear risk function is 

a smooth, continuous function, as 

opposed to a function defined by 

multiple steps, as is the case of Wood 

et al. (2012) (and Nowacek et al. (2015), 

which NRDC recommends as an 

alternative to Wood et al.). NRDC states 

that Wood et al. (2012) ‘‘has a 

significant negative bias on take 

estimates’’ where ‘‘all exposures from 

140 dB to 159.9 dB are considered to 

produce the same risk.’’ While it is true 

that relying upon Wood et al. (2012) 

results in all exposures within a 

particular step (e.g., 140 dB and 159.9 

dB) having the same risk, and future risk 

functions may be further refined by 

incorporating more steps, Wood et al. 

(2012) better represents known variation 

in behavioral responses at different 

received levels than Nowacek et al. 

(2015), which provides only a suggested 

midpoint for a risk function without any 

guidance on what should be done above 

or below this midpoint, much less the 

linear risk function NRDC states should 

be used. Wood et al. (2012) does 

acknowledge that responsiveness varies 

with received levels, while relying on 

broad steps, rather than a continuous 

function. These broad steps allow for 

easier implementation of a risk function 

and are more practical for most users, 

which is an important consideration, 

especially in the context of users that 

may not have the ability or access to 

more sophisticated modeling (i.e., nonNavy users). Therefore, if new linear 

risk functions become available, NMFS 

may still provide a more simplistic 

function broken down in broad steps, so 

that it can be applied by all users. 

In referencing NMFS’ proposal to use 

the recommendations of Wood et al., 

and prior to even attempting to 

characterize the scientific evidence, 

NRDC states, ‘‘Incredibly [NMFS’] 

approach produces take estimates that 

are substantially lower than the muchcriticized, non-conservative, 160 dB 

threshold [. . .].’’ NRDC (1) 

mischaracterizes criticism of the historic 

160-dB threshold as being about the 

results of its use, rather than being about 

whether it adequately represents the 

best available science; (2) introduces an 

MMPA standard that does not exist in 

the statute (implying that NMFS is being 

unlawfully or improperly ‘‘nonconservative’’); and (3) suggests that 

NRDC favors whichever method of 

evaluating potential Level B harassment 

returns the highest estimate. This is 

repeated later in their comment when 

they assert that use of the Wood et al. 

recommendations are ‘‘arbitrary and 

capricious’’ because use of the 

recommendations ‘‘appears, in its 

results, even less conservative than the 

outdated 160 dB threshold.’’ However, 


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selection of an evaluation scheme on the 

basis of the results it returns, rather than 

on how well the scheme reflects the 

available scientific literature, would be 

truly arbitrary and capricious and run 

counter to our mandates. 

Overall, we reiterate the lack of 

scientific consensus regarding what 

criteria might be most appropriate for 

evaluating Level B harassment. Defining 

sound levels that disrupt behavioral 

patterns is difficult because responses 

depend on complex, difficult to predict 

contextual factors much more so than 

received level. Therefore, levels at 

which responses occur are not 

necessarily consistent and can be 

difficult to predict. However, although 

better methods of assessing likely 

behavioral response to acoustic stimuli 

than the relatively simple multi-step 

function used here may be forthcoming 

from the scientific community, NMFS is 

compelled to move forward with the 

best available information. We believe 

the recommendations of Wood et al. 

(2012) reflect the best available science. 

Comment: NRDC notes NMFS’ 

reference to a ‘‘preliminary analysis’’ in 

the discussion of acoustic thresholds for 

Level B harassment and asserts that 

NMFS must make the analysis publicly 

available and allow opportunity for 

public comment before finalizing the 

rule. 

Response: Our use of the phrase 

‘‘preliminary analysis’’ in the notice of 

proposed rulemaking merits some 

clarification. The particular analysis we 

referred to is not in and of itself predecisional or preliminary. Rather, it is a 

discrete analytical product with a result 

that will not change—it is one way 

(non-parametric regression method) of 

looking at one subset (Malme et al., 

1984, 1988; Houser et al., 2013; Antunes 

et al., 2014; Moretti et al., 2014) of the 

data related to marine mammal 

behavioral responses to intermittent 

sound. NMFS conducted an analysis of 

relevant data starting with the premise 

of deriving a generic exposure-response 

curve using previously published 

exposure-response curves. This exercise 

was conducted as part of an ongoing 

separate and broader agency effort to 

evaluate behavioral response data. We 

also clarify that the Level B harassment 

criteria for this rule did not 

substantively rely upon that analysis. 

Comment: NRDC claims that NMFS 

misapplies the MMPA’s statutory 

definition of harassment by adopting a 

probability standard other than 

‘‘potential’’ in setting thresholds for 

auditory injury, stating that a take 

estimate based on ‘‘potential’’ should 

either count take from the lowest 

exposure level at which hearing loss can 

occur or establish a probability function 

that accounts for variability in the 

acoustic sensitivity of individual marine 

mammals. NRDC states that NMFS 

instead derived auditory injury 

thresholds from average exposure levels 

at which tested marine mammals 

experience hearing loss, which 

discounts instances of hearing loss at 

lower levels of exposure. The comment 

further states that for purposes of take 

estimation, thresholds based on mean or 

median values will lead to roughly half 

of an exposed cohort experiencing the 

impacts that the threshold is designed to 

avoid, at levels that are considered 

‘‘safe,’’ therefore resulting in substantial 

underestimates of auditory injury. 

NRDC makes similar statements with 

regard to the criteria for Level B 

harassment. 

Response: The 2018 Revised 

Technical Guidance’s (NMFS, 2018) 

onset thresholds for TTS for nonimpulsive sounds encompass more than 

90 percent of available TTS data (i.e., for 

mid-frequency cetaceans, only two data 

points are below the onset threshold, 

with maximum point only 2 dB below), 

and in some situations 100 percent of 

TTS data (e.g., high-frequency 

cetaceans; although this group is datalimited). Thus, the 2018 Revised 

Technical Guidance thresholds provide 

realistic predictions, based on currently 

available data, of noise-induced hearing 

loss in marine mammals. For impulsive 

sounds, data are limited to two studies, 

and NMFS directly adopted the TTS 

onset levels from these two studies for 

the applicable hearing groups. 

Our Federal Register notice 

announcing the availability of the 

original 2016 Technical Guidance (81 

FR 51694; August 4, 2016; NMFS, 2016), 

indicated that onset of auditory injury 

(i.e., permanent threshold shift (PTS)) 

equates to Level A harassment under the 

MMPA. We explained in that notice that 

because the acoustic thresholds for PTS 

conservatively predict the onset of PTS, 

they are inclusive of the ‘‘potential’’ 

language contained in the definition of 

Level A harassment. See 81 FR 51697, 

51721. 

Regarding Level B harassment, based 

on the language and structure of the 

definition of Level B harassment, we 

interpret the concept of ‘‘potential to 

disturb’’ as embedded in the assessment 

of the behavioral response that results 

from an act of pursuit, torment, or 

annoyance (collectively referred to 

hereafter as an ‘‘annoyance’’). The 

definition refers to a ‘‘potential to 

disturb’’ by causing disruption of 

behavioral patterns. Thus, an analysis 

that indicates a disruption in behavioral 

patterns establishes the ‘‘potential to 

disturb.’’ A separate analysis of 

‘‘potential to disturb’’ is not needed. In 

the context of an ITR such as this, our 

analysis is forward-looking. The inquiry 

is whether we would reasonably expect 

a disruption of behavioral patterns; if so, 

we would conclude a potential to 

disturb and therefore expect Level B 

harassment. We addressed NRDC’s 

concerns regarding the scientific 

support for the Level B harassment 

criteria in a previous comment 

response. 

Comment: NRDC raised concerns 

regarding use of NMFS’ 2018 Revised 

Technical Guidance (NMFS, 2018), 

claiming that the guidance is not based 

on the best available science and 

underestimates potential auditory 

injury. We also note that NRDC’s 

comment references an attachment that 

was not provided. 

Response: The 2018 Revised 

Technical Guidance (NMFS, 2018) is a 

compilation, interpretation, and 

synthesis of the scientific literature that 

provides the best available information 

regarding the effects of anthropogenic 

sound on marine mammals’ hearing. 

The 2016 Technical Guidance was 

classified as a Highly Influential 

Scientific Assessment and, as such, 

underwent three independent peer 

reviews, at three different stages in its 

development, including a follow-up to 

one of the peer reviews, prior to its 

dissemination by NMFS. In addition, 

there were three separate public 

comment periods, during which time 

NMFS received and responded to 

similar comments on the guidance (81 

FR 51694), and more recent public and 

interagency review under Executive 

Order 13795. While new information 

may help to improve the guidance in the 

future, and NMFS will review the 

available literature to determine when 

revisions are appropriate, the final 

guidance reflects the best available 

science and all information received 

through peer review and public 

comment. The concerns raised by NRDC 

have been addressed by NMFS in 

responses associated with the guidance 

(see www.fisheries.noaa.gov/national/ 

marine-mammal-protection/marinemammal-acoustic-technical-guidance). 

In light of these considerations, NRDC’s 

argument that use of the guidance is 

‘‘arbitrary and capricious’’ is 

unpersuasive. As was stated in our 

notice of proposed rulemaking, NMFS 

considers the 2018 Revised Technical 

Guidance to represent the best scientific 

information currently available and, 

given the incorporation of multiple peer 

reviews and public comment 

opportunities during its development, 

we did not solicit and are not 


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responding in detail to comments 

concerning the contents of the 

Technical Guidance (NMFS, 2016, 

2018), as such comments are outside the 

scope of this rulemaking. 

NRDC also referenced information 

related to occupational noise standards 

established by the National Institute of 

Occupational Safety and Health 

(NIOSH). Human noise risk assessments 

(NIOSH, 1998) are not equivalent (or 

applicable) to thresholds provided in 

the guidance, because they are used to 

predict hearing loss based on a daily 8- 

h exposure over 40 years (i.e., current 

marine mammal TTS data are only 

available to predict exposure periods of 

24-h or less and cannot be used to assess 

or predict risk associated with a lifetime 

of exposure) and are based on larger 

sample sizes of human listeners (e.g., 

NIOSH 1972 and 1997 risk assessments 

were based on a sample size of 1,172 

people). As pointed out in Wright 

(2015), NIOSH criteria provide a 95 

percent confidence interval for their 

human noise standards but also allow 

for an excess risk of material hearing 

impairment, defined as an average 

threshold elevation for both ears that 

exceeds 25 dB, of eight percent (i.e., 

human noise standards limits do allow 

for some risk; risk is not zero percent 

and specifically that eight percent of the 

population is still capable of developing 

noise-induced hearing loss exceeding 25 

dB when exposed to the 85 dB NIOSH 

level). 

Finally, we note that a group of 

scientists recently published an update 

to their original, seminal publication 

concerning noise exposure criteria to 

predict the onset of auditory effects in 

marine mammals (Southall et al., 2007, 

2019a), the topic of this comment. The 

newer publication evaluates the 

recommendations of the original 

publication in light of subsequent 

scientific findings, including those 

findings that form the basis for the 

recommendations of NMFS (2018). 

While Southall et al. (2019a) provide 

recommendations for future research 

that could lead to revisions, the 

fundamental aspects of an evaluation of 

the onset of auditory effects for the 

marine mammals considered in this ITR 

(i.e., auditory weighting functions and 

noise exposure criteria) are identical to 

those presented by NMFS (2018) and 

incorporated into the modeling process 

developed for this ITR. 

Sound Field Modeling 

Comment: NRDC asserts that NMFS 

has not appropriately accounted for 

hard-bottom habitat in our propagation 

analysis, stating that there are areas of 

hard bottom in the GOM and that we 

cannot assume that proposed surveys 

will take place entirely in areas with 

soft or sandy bottoms. 

Response: Sound propagation 

modeling performed in support of 

BOEM’s PEIS and this ITR was 

developed to adequately represent a 

wide range of conditions for a variety of 

parameters, including bottom 

composition. NMFS does not assume 

that hard bottom does not exist in the 

GOM, but rather that it is not 

sufficiently predominant to warrant 

specific representation in a propagation 

modeling exercise covering the whole 

GOM. As shown in Figure 50 of the 

modeling report—depicting a 

compilation of surficial sediment 

composition available through a 

hydrographic survey database from 

NOAA’s National Ocean Service and its 

predecessor, the U.S. Coast and 

Geodetic Survey—muds and sands are 

the dominant substrate types throughout 

the GOM (as stated in our notice of 

proposed rulemaking), with only small, 

scattered areas of hard bottom. The 

Minerals Management Service (MMS) 

report cited by NRDC, which concerns 

conversion of seafloor maps existing at 

the time to MMS-approved GIS format 

for use in geohazards evaluations, does 

not contradict this. 

Substrate types for propagation 

modeling are based on grain size, 

porosity, and shear velocity, etc., and do 

not include ‘‘hard’’ or ‘‘coral’’ bottom. It 

is also important to note that, while 

some hard bottom habitats would 

increase propagation due to increased 

reflectivity, NRDC’s statement that coral 

bottom can ‘‘significantly increase 

propagation of airgun noise’’ is 

erroneous. In fact, the roughness of the 

coral habitat would cause severe bottom 

loss due to scattering. As noted above, 

bottom composition in the region is 

mostly mud and sand and, therefore, 

selection of parameter values associated 

with these bottom types for propagation 

modeling is appropriate. We also note 

that, for the shelf region of the eastern 

GOM, where sand is predominant, a 

larger grain size value was selected to 

account for this. The acoustic modeling 

provided by Zeddies et al. (2015, 2017a) 

appropriately and reasonably accounts 

for variability in bottom composition 

throughout the region. 

The modeling process requires the use 

of simplifying assumptions about 

oceanographic and seabed parameters, 

and these assumptions carry some 

uncertainty, which may lead to 

uncertainty in the form of variance or 

error in individual model outputs and 

in the final estimates of marine mammal 

acoustic exposures. It is for this reason 

that parametric uncertainty analysis was 

performed to evaluate the effects of this 

uncertainty ‘‘envelope.’’ (This analysis 

was summarized in our notice of 

proposed rulemaking and described in 

detail in the modeling report. NRDC 

does not reference this assessment.) 

Uncertainties in the results of acoustic 

propagation modeling were estimated 

by examining the variation in model 

outputs when model inputs were offset 

by realistic errors. The environmental 

properties were selected so that the 

median, or expected, value could be 

compared to a worst-case outcome (e.g., 

assuming an extreme case of a more 

reflective bottom), which was generated 

by selecting extreme values for several 

input parameters. These comparisons 

represent the maximum errors in the 

predicted sound fields that result from 

incorrect specification of the parameters 

tested. As described in the modeling 

report, the greatest uncertainty due to 

geoacoustic parameters of the sea 

bottom is 4 dB (in the deep zone). The 

effect of the geoacoustic uncertainty 

increased when the sound speed profile 

was downwardly refracting. In the case 

of a surface channel (slope zone, winter 

season), the average difference between 

the median and worst-case was only 0.5 

dB, i.e., in this case the geoacoustic 

parameters had virtually no effect on the 

sound levels at the top of the water 

column (where marine mammals are 

likely to be present). 

Marine Mammal Densities 

Comment: NRDC criticized NMFS’ 

use of the Roberts et al. (2016) model 

outputs for purposes of deriving 

abundance estimates, as used for 

comparison to exposure estimates 

herein. NRDC states that we should use 

the NMFS Stock Assessment Report 

(SAR) abundance estimates for this 

purpose, while allowing that modelpredicted abundance estimates may be 

used for ‘‘data-deficient’’ stocks. NRDC 

implies that use of model-predicted 

abundances would overestimate actual 

abundances, apparently based on the 

fact that the density models are 

informed by many years of data rather 

than only the most recent year of data. 

Where model-predicted abundance 

estimates are used, NRDC recommends 

that we adjust the averaged model 

outputs to the lower bound of the 

standard deviation estimated by the 

model for each grid cell. 

Response: The approach 

recommended by NRDC is 

inappropriate. Comparing take estimates 

generated through use of the outputs of 

a density model to an unrelated 

abundance estimate provides a 

meaningless comparison. As explained 

in our notice of proposed rulemaking, 


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we compare the take estimates 

generated through use of the density 

outputs to the abundance predicted 

through use of the model precisely to 

provide a meaningful comparison of 

predicted takes to predicted population. 

The two potential sources of 

abundance data—the output of cetacean 

density models (Roberts et al., 2016) 

and the available SARs data—provide 

different results, with the SARs 

estimates typically much lower. 

Differences between the two separate 

sets of abundance estimates result from 

key methodological differences. In order 

to produce sufficiently reliable and 

detailed density surfaces (maps), 

Roberts et al. (2016) combined multiple 

NMFS cetacean surveys and modeled 

density using a habitat-based approach 

(Miller et al., 2013), while the SARs 

estimates utilized only the most recent 

NMFS survey and estimated density 

using traditional distance sampling 

(Buckland et al., 2001). The two 

approaches, while compatible and based 

on a common statistical framework 

(distance sampling), can yield different 

results, depending on complex factors 

such as whether population sizes have 

changed, or species habitat preferences 

have shifted over time. Neither 

approach will necessarily yield a higher 

abundance estimate than the other, but 

use of multiple years of data in 

developing an abundance estimate 

minimizes the influence of interannual 

variation in over- or underestimating 

actual abundance. By linking sightings 

with environmental conditions, habitatbased density layers represent smoothed 

surfaces that are not biased by 

anomalous conditions. This makes them 

particularly appropriate for the five-year 

timeframe of this ITR, which will span 

varying environmental conditions. 

To illustrate why this smoothing of 

interannual variation helps to create a 

meaningful comparison to take 

estimates, we provide the extreme 

example of the GOM Clymene dolphin. 

NMFS’ three most recent SAR 

abundance estimates for this stock have 

fluctuated between 129 and 17,355 

animals, i.e., varying by a maximum 

factor of more than 100. For most 

species, such fluctuations across these 

‘‘snapshot’’ abundance estimates (i.e., 

that are based on only the most recent 

year of survey data) reflect interannual 

variations in dynamic oceanographic 

characteristics that influence whether 

animals will be seen when surveying in 

predetermined locations, rather than 

any true increase or decline in 

population abundance. In fact, NMFS’ 

SARs typically caution that trends 

should not be inferred from multiple 

such estimates, that differences in 

temporal abundance estimates are 

difficult to interpret without an 

understanding of range-wide stock 

abundance, and that temporal shifts in 

abundance or distribution cannot be 

effectively detected by surveys that only 

cover portions of a stock’s range (i.e., 

U.S. waters). The corresponding density 

model for Clymene dolphins predicts a 

mean abundance of 11,000 dolphins. 

Therefore, in this example, NRDC 

would have us compare takes predicted 

by a model in which 11,000 dolphins 

are assumed to exist against an 

abundance estimate of 129 dolphins. 

Our goal in assessing predicted takes is 

to generate a meaningful comparison, 

which is accomplished through use of 

the model-predicted abundance. 

A second key methodological 

difference explains the tendency for the 

model-predicted abundance estimates to 

be higher than the SARs estimates. SAR 

abundance estimates are typically 

underestimates of actual abundance 

because they do not account for bias on 

the ability of observers to detect 

animals—in contrast, Roberts et al. 

(2016) do account for availability bias 

and perception bias on the probability 

of sighting an animal. Availability bias 

occurs when a model assumes that 

animals are always available to be 

observed by the survey team when, in 

fact, they are not. Cetaceans are diving 

animals; while submerged, they are 

unavailable. Assuming diving animals 

are always available results in an 

underestimation of abundance, because 

while they are diving they are present 

but not counted by the survey team. 

Perception bias occurs when a model 

assumes that animals will always be 

detected when they are on the survey 

trackline, when, in fact, detection is not 

certain. 

With regard to bias correction, NRDC 

suggests that such corrections are 

incorporated into NMFS’ GOM SARs. 

However, some correction has been 

performed only for the more-recently 

surveyed shelf and coastal stocks of 

bottlenose dolphin, i.e., four out of the 

25 stocks of GOM marine mammals 

considered herein. NRDC also strangely 

suggests that ‘‘NMFS doesn’t show that 

applying trackline correction factors 

consistent with Barlow (2015), who 

reported trackline detection 

probabilities for marine mammals in the 

Pacific, would result in population 

estimates consistent with the ones the 

agency has derived from Roberts et al. 

(2016).’’ We can safely assume that 

these would be consistent, given that 

the models developed by Roberts et al. 

(2016) considered, and in some cases 

directly incorporated, the correction 

factors of Barlow (1999) and Barlow and 

Forney (2007) (the original work upon 

which Barlow (2015) builds). 

These issues, which are typical for 

NMFS’ SAR abundance estimates, are 

particularly exacerbated for GOM 

stocks. For the majority of stocks, the 

most recent abundance estimates are 

derived from the results of vessel-based 

surveys in 2009, i.e., even if one 

believes that such ‘‘snapshot’’ estimates 

are most appropriate, the GOM 

estimates are out of date and NMFS’ 

guidelines state that data greater than 

eight years old should not be used for 

abundance estimates. (We note that 

more recent survey effort has been 

conducted, but corresponding 

abundance estimates have only recently 

been made available via unpublished 

draft SARs for most stocks that have yet 

to be available for public comment or 

finalized at the time the analyses were 

completed for these regulations.) More 

important for cryptic species, i.e., those 

species that spend little time at the 

surface and/or are difficult to detect 

when at the surface, is the lack of any 

bias correction. For example, the 

Cuvier’s beaked whale—a cosmopolitan 

species and perhaps the most 

widespread and most commonly 

observed species of beaked whale—is 

officially estimated by NMFS to number 

74 individuals in the GOM, a clear 

underestimate. For purposes of 

reference, current abundance estimates 

for the U.S. Pacific and Atlantic 

stocks—for which some bias corrections 

have been made—are 3,274 and 5,744 

individuals, respectively. Marine 

mammal scientists working in the GOM 

have acknowledged that the likely 

abundance of beaked whales (and other 

cryptic species, such as Kogia spp.) 

should be expected to be closer to the 

values predicted by Roberts et al. (2016) 

than those given in the SARs. For 

example, Dias and Garrison (2016) state 

that current abundance estimates for 

Kogia spp. may be considerably 

underestimated due to the cryptic 

behavior of these species and difficulty 

of detection in Beaufort sea state greater 

than one, while density estimates for 

certain species derived from long-term 

passive acoustic monitoring are much 

higher than are estimates derived from 

visual observations (e.g., Hildebrand et 

al., 2015). Separately, NMFS’ 

announcement of a negative 90-day 

finding on a petition to list the GOM 

Cuvier’s beaked whale as endangered 

(84 FR 11058) included adoption of the 

abundance estimate of Roberts et al. 

(2016) as being most appropriate. 

Roberts et al. (2015b) summarize this 

situation: ‘‘Because [NMFS’ SAR] 

estimates are very low relative to the 


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abundance we estimated, it is likely that 

if our [density] results are used to 

estimate population-level impacts from 

potentially harmful human activities 

(i.e. ‘‘takes’’, as defined by the Marine 

Mammal Protection Act), the estimated 

impacts will be very high [. . .].’’ 

NRDC suggests that the SARs are an 

appropriate representation of ‘‘actual’’ 

abundance, whereas the Roberts et al. 

(2016) predictions are not. NRDC also 

appears to claim, without 

substantiation, that an abundance 

estimate derived from multiple years of 

data would typically overestimate actual 

abundance. However, these estimates 

are not directly comparable—not 

because one represents a ‘‘snapshot,’’ 

while one represents multiple years of 

data—but because one does not correct 

for one or more known biases against 

the probability of observing animals 

during survey effort, while the other 

does. Because of this important caveat, 

NMFS’ SAR abundance estimates 

should not be considered ‘‘actual’’ 

abundance more than any other 

accepted estimate. Therefore, when 

multiple estimates of a stock’s 

abundance are available, they should be 

evaluated based on quality, e.g., does 

the estimate account for relevant biases, 

does it minimize the effect of 

interannual variability, and, 

importantly, should provide a 

meaningful comparison. In this light, 

our use of the Roberts et al. (2016) 

abundance estimates are not a ‘‘radical 

departure from past practice,’’ as 

claimed by NRDC. Our practice, as 

mandated by our implementing 

regulations, is to use the best scientific 

evidence available. NRDC states that 

‘‘NMFS cannot simply discard this 

Congressionally mandated estimate in 

favor of the larger population estimates 

derived from its misapplication of the 

[. . .] model.’’ The statute does not 

mandate use of the SARs for comparison 

with take estimates. 

Aside from their failure to explain the 

claim of ‘‘misapplication,’’ and the 

unwarranted implication that we must 

make use of the model-generated 

abundance estimates simply because 

they are larger (and not because they are 

the best available scientific 

information), NRDC errs in asserting 

that the MMPA requires that we use 

SAR abundance estimates. Section 117 

of the MMPA requires the development 

of SARs, and dictates certain 

information that SARs must provide. 

However, there is no part of the MMPA 

that requires the population abundance 

estimates given in a SAR to be used in 

any specific application and, 

importantly, the MMPA does not even 

require that the SAR include a best 

population estimate. The MMPA 

requires only that SARs provide a 

minimum population estimate, which is 

used in the formulation of a potential 

biological removal (PBR) level, which is 

then required by section 118 of the 

MMPA for certain uses in the 

management of marine mammal take 

incidental to commercial fisheries. In 

summary, NRDC’s comment reflects an 

inaccurate interpretation of the available 

information, and NMFS disagrees with 

the approach recommended by the 

comment. 

Take Estimates 

Comment: The Associations state that 

‘‘NMFS substantially overestimates the 

number of incidental takes predicted to 

result’’ from the specified activity. The 

comment goes on to discuss the 

modeling that is ‘‘intentionally designed 

to overestimate takes,’’ and discusses 

the findings of the Acoustic Exposure 

Model Variable Analysis (Zeddies et al., 

2017b) (which was provided for public 

review in association with the proposed 

rule). Other industry commenters and 

the CRE echo these points. 

Response: The commenters’ 

statements that NMFS has substantially 

overestimated takes are incorrect. We 

used current scientific information and 

state-of-the-art acoustic propagation and 

animal movement modeling to 

reasonably estimate potential exposures 

to noise. Chevron stated that the 

modeling used ‘‘admittedly erroneous 

models’’ but provides no supporting 

information or citation. Chevron further 

describes ‘‘errors in methodology’’ and 

‘‘admissions’’ that the modeling 

methodology and the data used are not 

‘‘rigorous science,’’ while asserting that 

NMFS ‘‘repeatedly rejects and omits 

science that is available.’’ Chevron’s 

comments do not provide any 

illumination as to what specifically 

these errors may be, what data it 

believes is flawed, or what ‘‘science’’ 

NMFS has rejected or omitted. NMFS 

has considered all relevant available 

scientific information. 

To summarize in a basic way, it is 

foreseeable that a large amount of noiseproducing activity, such as BOEM’s 

application and PEIS describe, results in 

a substantial number of predicted 

acoustic exposures. Despite 

recommending that ‘‘a better approach 

would be to use the best and most likely 

values for all of the input variables to 

the model,’’ the Associations’ comments 

do not include substantive 

recommendations for improvement. 

They do not specify which of the many 

data inputs are ‘‘conservative’’ or to 

what degree, nor do they recommend 

alternatives to the choices that were 

painstakingly documented in 

developing the modeling. 

As was noted in the notice of 

proposed rulemaking, NMFS disagrees 

with the Associations’ characterization 

of the modeling and with certain 

statements in BOEM’s draft PEIS 

regarding the modeling that are 

frequently cited by the Associations. As 

we stated in the notice, BOEM’s draft 

PEIS included unsupported and 

erroneous statements that characterized 

the modeling results—which BOEM and 

NMFS developed collaboratively—as 

‘‘unrealistically high,’’ ‘‘overly 

conservative,’’ and representative of a 

‘‘worst-case scenario,’’ among other 

things. These statements were included 

in that document without NMFS’ prior 

knowledge. Importantly, as a result of 

NOAA’s public comments on that draft 

PEIS in its role as a cooperating agency, 

the statements referenced by the 

commenters were properly removed 

from the final PEIS, which more 

accurately characterizes the modeling 

process and results. 

The Associations take out of context 

a number of statements from the 

discussion in NMFS’ notice of proposed 

rulemaking of the modeling process, 

data inputs, and user selections. We 

address these in turn: 

• The Associations quote NMFS as 

stating that our modeling likely ‘‘leads 

to substantial overestimates of the 

numbers of individuals potentially 

disturbed [and] . . . to an 

overestimation of the population-level 

consequences of the estimated 

exposures’’ and that, even with the 

application of a correction factor, the 

modeling still represents an 

‘‘overestimate.’’ (83 FR 29261, 29291). 

But the full statement in our notice is as 

follows: ‘‘While the modeling provides 

reasonable estimates of the total number 

of instances of exposure exceeding 

Level B harassment criteria, it is likely 

that it leads to substantial overestimates 

of the numbers of individuals 

potentially disturbed, given that all 

animals within the areas modeled are 

unlikely to be completely replaced on a 

daily basis. Therefore, in assuming an 

increased number of individuals 

impacted, these results would lead to an 

overestimation of the potential 

population-level consequences of the 

estimated exposures.’’ Our point was 

that, although the modeling provides 

reasonable estimates of the total amount 

of acoustic exposures, it would be an 

overestimate to interpret this total as 

representative of the number of 

individuals impacted. We then 

discussed our development of a 

correction factor to address this issue 


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3The Associations misunderstand the timeline 

relating to the availability of the report for NMFS’ 

consideration for developing the proposed rule. 

(‘‘NMFS inexplicably dismisses [the report] as being 

provided too late despite the fact that it was 

provided to NMFS 11 months ago’’). We must 

correct the record on this point. The analysis was 

submitted by IAGC for NMFS’ consideration on 

September 6, 2017, well after the total 45-day 

comment period on the petition had closed (81 FR 

88664 (December 8, 2016, notice of receipt of 

petition providing for 30-day comment period); 81 

FR 92788 (extending comment period an additional 

15 days to January 23, 2017)). The final PEIS was 

then issued in August 2017. Subsequent materials 

could no longer be considered as NMFS prepared 

(see Table 12 of the notice of proposed 

rulemaking). 

• The Associations highlight our 

‘‘admission’’ that the modeling is 

purposely conservative. We address this 

below by explaining why, in some 

cases, it is appropriate to make 

reasonably conservative choices. 

• The Associations mischaracterize 

the Wood et al. (2012) Level B 

harassment criteria as ‘‘expressly 

rejecting the best available science.’’ In 

discussing different versions of 

frequency weighting functions, we 

stated that ‘‘Type III filters’’ are better 

designed to predict the onset of auditory 

injury, while explaining why use of 

‘‘Type I filters’’ (or M-weighting) was 

appropriate for use in evaluation of 

Level B harassment (83 FR 29248). The 

Type III filters, as adopted by NMFS 

(2018), were appropriately used for 

evaluation of Level A harassment 

(which includes auditory injury). 

• Although characterized as 

‘‘conservative’’ NMFS has made 

reasonable choices through the 

application of professional judgment by 

subject matter experts. For example, 

using single airgun modeling results in 

lieu of boomer results was a choice 

made for computational efficiency 

precisely because it was not 

significantly influential on the results. 

(83 FR 29251). And selecting an 

estimate for standard deviation in an 

investigation of model sensitivity to 

source level variance was in response to 

a concern of the commenters—overall 

sensitivity of the model to uncertainty 

in input parameters and the resulting 

uncertainty in model results—and had 

no bearing on the model results (83 FR 

29257). 

• The Associations also highlight our 

statement that ‘‘the lack of aversion 

within the animal movement modeling 

process results in overestimates of 

potential injurious exposure,’’ without 

noting that we corrected this issue 

through a post-hoc correction to 

reasonably account for aversion. 

The modeling required that a number 

of assumptions and choices be made by 

subject matter experts and, in most 

cases, the most representative data or 

methods were used. As we 

acknowledged, in some cases, some 

assumptions or choices are purposely 

conservative (where the conservative 

choice is reasonable) to minimize the 

likelihood of underestimating the 

potential impacts on marine mammals 

represented by a specified level of 

survey effort. These are reasonable, 

scientifically acceptable choices that do 

not create, as the Associations state, 

‘‘multiplicatively accumulating bias as 

the conservative assumptions interact 

with each other to multiply 

uncertainty’’). To the extent that the 

results of the modeling may be 

conservative, they are the most credible, 

science-based information available at 

this time (assuming the notional 8,000 

in3 array and activity level projections 

specified by BOEM in the petition). 

These comments provide no 

reasonable justification as to why the 

modeling results in overestimates of 

take. The Associations instead seem to 

rely on the incorrect premise that realtime mitigation would somehow reduce 

actual levels of acoustic exposure 

(versus reducing the duration and/or 

intensity of exposure). NMFS disagrees 

that ‘‘each of the inputs is purposely 

developed to be conservative’’—again, 

the Associations do not provide any 

support for this assertion, and none is 

to be found in the administrative record 

for this action. Although it may be 

correct that some conservativeness 

accumulates throughout the analysis, 

the Associations do not adequately 

describe the nature of conservativeness 

associated with model inputs or the 

degree to which such conservativeness 

‘‘accumulates’’ (either quantitatively or 

qualitatively), nor do they offer more 

appropriate alternatives. 

The modeling effort incorporated 

representative sound sources and 

projected survey scenarios (both based 

on the best available information 

obtained by BOEM), physical and 

geological oceanographic parameters at 

multiple locations within the GOM and 

during different seasons, the best 

available information regarding marine 

mammal distribution and density, and 

available information regarding known 

behavioral patterns of the affected 

species. Current scientific information 

and state-of-the-art acoustic propagation 

and animal movement modeling were 

used to reasonably estimate potential 

exposures to noise. The notice of 

proposed rulemaking described all 

aspects of the modeling effort in 

significant detail, including numerous 

investigations (test scenarios) designed 

by the agencies to understand various 

model sensitivities and the effects of 

certain choices on model results. The 

modeling report itself was provided for 

public review, in association with both 

BOEM’s PEIS and NMFS’ notice of 

proposed rulemaking. 

We quote the Marine Mammal 

Commission’s public comment on this 

topic: ‘‘Complex sound propagation and 

animat modeling was used to estimate 

the numbers of potential takes from 

various types of geophysical surveys in 

the Gulf. NMFS received comments 

from industry operators suggesting that 

the modeling results were overly 

conservative and that the take estimates 

were ‘higher than BOEM expects would 

actually occur in a real world 

environment.’ However, the 

Commission has reviewed the modeling 

approach and parameters used to 

estimate takes and believes they 

represent the best available information 

regarding survey scenarios, sound 

sources, physical and oceanographic 

conditions in the Gulf, and marine 

mammal densities and behavior. As 

such, the Commission agrees with 

NMFS and BOEM that the resulting take 

estimates were conservative but 

reasonable, thereby minimizing the 

likelihood that actual takes would be 

underestimated.’’ 

The CRE says, absent citation or 

reference, that ‘‘everyone agrees’’ that 

takes are overestimated. Their assertion 

that we ‘‘greatly overestimate both 

exposures and takes’’ is based on their 

view that we relied on ‘‘flawed models 

and on Risk Assessment Frameworks 

that are unfinished and have not been 

peer reviewed.’’ While the Associations 

focus on supposed conservatism built 

into the modeling process, the CRE 

appears to believe that there is some 

unknown process by which modeled 

exposures are ‘‘converted’’ to takes. 

(‘‘These take overestimates stem 

primarily from [NMFS’] use of various 

models to convert exposures to takes 

[. . .]. They have no credible framework 

for converting exposure to takes.’’) We 

believe the CRE is likely referring to the 

EWG risk assessment framework, which 

is a systematic analysis used as an aid 

to understanding the significance of the 

modeled takes to the affected stocks. 

However, this framework plays no role 

in the estimation of takes (takes are an 

input to the EWG framework) and is not 

itself a ‘‘model.’’ CRE also makes the 

claim, addressed elsewhere in this 

response, that the take estimates ‘‘do not 

include the impact of mitigation 

measures.’’ 

Regarding the modeling variable 

analysis submitted by the Associations 

(Zeddies et al., 2017b), we have fully 

considered the results in developing 

this final ITR,3 but do not find that the 


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the draft proposed rule for interagency review. The 

rule was submitted to OMB on October 3, 2017. 

Upon submission, no further changes could be 

made to the rule other than those arising pursuant 

to the interagency review. The Office of Information 

and Regulatory Affairs cleared the proposed rule on 

June 11, 2018, whereupon it was submitted to the 

Federal Register on June 12 and published on June 

22. Therefore, the analysis was not able to be 

considered by NMFS in the notice of proposed 

rulemaking despite the length of time between 

submission of the report to NMFS and publication 

of the proposed rule. 

analysis supports any changes to the 

modeling. IAGC and API contracted 

with JASCO Applied Sciences, which 

performed the original modeling effort, 

to conduct additional analysis regarding 

the effect that various acoustic model 

parameters or inputs have on the 

outputs used to estimate numbers of 

animals exposed to threshold levels of 

sound from geophysical sources used in 

the GOM. The analysis investigated five 

factors: 

• Airgun array size (including total 

volume, number of array elements, 

element air pressure, array geometry 

and spacing) used in source and 

propagation models; 

• Acoustic threshold criteria and 

associated weighting used to calculate 

exposures; 

• Animal densities used for adjusting 

simulated computer model exposures to 

potential real-world animal exposures; 

• Natural aversive behaviors of 

marine mammals; and 

• The addition of mitigative measures 

that lessen the potential for animals’ 

exposure to threshold levels of seismic 

sound. 

The primary finding of the Acoustic 

Exposure Model Variable Analysis is 

that use of appropriate acoustic injury 

criteria (i.e., NMFS, 2016, 2018) 

decreased predictions of injurious 

exposure. At the time the Associations 

submitted this report, they were 

apparently unaware that, as described 

herein, NMFS had already made the 

change that the Associations’ analysis 

indicates is most significant: The 

appropriate acoustic injury criteria (i.e., 

NMFS, 2016, 2018), representing the 

best available science, were used in 

NMFS’ analysis in the proposed rule. 

Other significant investigations in the 

Associations’ modeling variable analysis 

included an alternative array size and 

quantitative consideration of animal 

aversion and mitigation effectiveness. 

We address these below. 

The Associations state that the 

selected array (8,000 in3) is 

unrealistically large, resulting in an 

overestimation of likely source levels 

and, therefore, size of the sound field 

with which marine mammals would 

interact. Zeddies et al. (2017b) 

evaluated the use of a substitute 4,130 

in3 array, finding that reduction in array 

volume reduces the number of predicted 

exposures. Use of a smaller airgun array 

volume with lower source level 

unsurprisingly creates a smaller 

ensonified area resulting in fewer 

numbers of animals expected to exceed 

exposure thresholds. However, selection 

of the representative array to be used in 

the modeling was directed by the ITR 

applicant (i.e., BOEM). Given that the 

array used was selected by the applicant 

and included in the petition for the ITR 

(which was available for public 

comment in our Federal Register notice 

of receipt of BOEM’s application), any 

complaint regarding this or other 

aspects of the specified activity, 

including activity level projections and 

representative source characteristics or 

survey geometry, should be addressed to 

BOEM. According to BOEM, the 

particular array was selected as a 

realistic representative proxy after 

BOEM’s discussions with individual 

geophysical companies. An 8,000-in3

array was considered reasonable, as it 

falls within the range of typical airgun 

arrays currently used in the GOM, 

which are roughly 4,000–8,475 in3

(BOEM, 2017). According to BOEM’s 

permitting records, approximately onethird of arrays used in a recent year 

were 8,000 in3 or greater. Also, as noted 

previously, regardless of the 

representative airgun array size used to 

model the number of takes of marine 

mammals for the purposes of the 

analysis conducted in this rule, the 

analysis of the take and the associated 

findings are applicable to take incurred 

from the use of other sizes of airgun 

arrays, including smaller ones such as 

those modeled in the Acoustic Exposure 

Model Variable Analysis report. 

The Associations’ comments also 

focus significantly on the need to 

incorporate quantitative adjustments to 

account for aversion and mitigation. As 

discussed in the notice of proposed 

rulemaking, the effects of mitigation and 

aversion on exposure estimates were 

investigated via test scenarios, and 

NMFS acknowledges that both of these 

factors would lead to a reduction in 

likely injurious exposure to some 

degree. (As noted above, the issue of 

aversion was addressed via post-hoc 

quantitative adjustment). Ultimately 

these factors were not quantified in the 

modeling because, in summary, there is 

too much inherent uncertainty regarding 

the effectiveness of detection-based 

mitigation for these activities to support 

any reasonable quantification of its 

effect in reducing injurious exposure, 

and there is too little information 

regarding the likely level of onset and 

degree of aversion to justify its use in 

the modeling via precise quantitative 

control of animat movements (as 

compared to post-hoc adjustment of the 

modeling results, as is done here). 

Zeddies et al. (2017b) found that 

incorporation of aversion into the 

modeling process appears to reduce the 

number of predicted injurious 

exposures, though the magnitude of the 

effect was variable. The authors state 

that this variability is likely because 

there are few samples of injurious 

exposure exceedance, meaning that the 

statistical variability of re-running 

simulations is evident. 

While aversion and mitigation 

implementation are expected to reduce 

somewhat the modeled levels of 

injurious exposure, it is important to 

note that they would not be expected to 

result in any meaningful reduction in 

assumed exposures resulting in Level B 

harassment, nor in total takes by 

harassment, as any averted injurious 

(Level A harassment) takes would not be 

alleviated, but rather would be 

appropriately changed to behavioral 

disturbance (Level B harassment) takes. 

The Associations, acknowledging the 

analysis we have done to produce more 

realistic estimates of potential Level A 

harassment, are focused on the 

supposed overestimation of Level B 

harassment. Yet their focal areas of 

complaint are limited to array size, 

which is a decision made by BOEM, and 

mitigation effectiveness, a factor that 

would have no effect on the amount of 

predicted Level B harassment. With 

regard to the large number of other data 

inputs and/or choices made in the 

modeling, the Associations conclude 

that ‘‘NMFS has admittedly chosen 

conservative numerical values to assess 

allegedly uncertain variables to 

overestimate adverse effects,’’ without 

specifically identifying a single issue 

where they feel a meaningful data or 

process error was made. 

Comment: The CRE recommends a 

different method of estimating potential 

take of marine mammals, stating that 

NMFS ‘‘should continue to use Line 

Transect to estimate exposures and 

takes.’’ 

Response: Although CRE does not 

actually describe the method they 

recommend, we infer that they are 

referencing a relatively simplistic 

method historically used in estimating 

acoustic exposures, typically on a 

survey-specific basis. Essentially, this 

methodology consists of: (1) 

Determination of estimated isopleth 

ranges from the source for a specified 

acoustic threshold (nominally this 

threshold was historically the 160 dB 


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rms received level for Level B 

harassment); (2) assumption that a 

cylinder whose radius matched the 

range to these isopleths and 

encompassed the entire water column 

was ensonified to that threshold; (3) 

calculating the surface area ensonified 

by this water column as the source 

moved along its track; and (4) 

multiplying that resultant ensonified 

surface area by the density of each 

marine mammal species present to 

estimate potential harassment takes. 

(Note that this process is somewhat 

more complicated for evaluation of 3D 

surveys.) In this case, following a 

modeling workshop held in 2014 as a 

collaborative effort between the 

American Petroleum Institute (API) and 

the International Association of 

Geophysical Contractors (IAGC), NMFS, 

and BOEM, the agencies determined 

that it would be most appropriate to 

collaborate on a more sophisticated 

approach, in which more detailed 

modeling of the source and its 

properties, the acoustic propagation 

field in three dimensions, and three 

dimensional animal placement and 

movement is used to better calculate the 

potential impacts to marine mammals. 

To summarize aspects of the process: 

• Operational Scenario Development: 

According to BOEM, the source and 

operations scenarios presented in the 

petition and which underlie the 

modeling effort were based on historical 

permit information. BOEM sought 

industry input and used historical data 

to develop the specification of the 

nominal airgun array. The array 

specifications and level of survey effort 

were intended to be representative of 

future activity, not a conservative overestimate. 

• Acoustic Modeling: The 

propagation model output has been 

compared with measured data and been 

shown to be reliable. The physical 

inputs to the model are the best 

available data. The full sound field was 

used to predict exposures, not a 

‘maximum over depth’ simplification. 

• Animal Modeling: The animal 

movement model used is one of the few 

models available that incorporates full 

four-dimensional movement. Properly 

applied, such models provide the most 

accurate predictions of acoustic 

exposure. 

• Animal Density: The density and 

distribution data used were the best 

available and represent the latest 

synthesis and analysis. 

• Effects Criteria: The historical Level 

B harassment threshold of 160 dB has 

been criticized for multiple reasons, and 

the use of the Wood et al. (2012) criteria 

in this analysis allows for the 

application of current scientific 

information to address some of the 

issues raised. The best available science 

relating to potential auditory injury, as 

synthesized in NMFS (2018) and more 

recently described by Southall et al. 

(2019a), was used in the modeling 

effort. 

Taking advantage of these more 

sophisticated tools allows for a more 

accurate and detailed model of the 

exposures of a population of marine 

animals in the three dimensions and 

time, and also provides: (1) Statistical 

data on each individually modeled 

animal and the population as a whole; 

(2) rate of exposure (threshold 

exceedance per unit time) over the 

duration of a survey; and (3) the data 

necessary to determine effects based on 

more sophisticated thresholds, such as 

cumulative sound exposure level. A 

comparison of these methods—animat 

method involving three-dimensional 

animal movement modeling and static 

distribution, in which a static twodimensional density is overlaid on a 

simplified representation of the sound 

field—found that differences 

consistently arise between the two 

methods. The static distribution method 

was found to consistently underestimate 

the number of takes by Level B 

harassment compared with the animat 

method. In addition, repeating many 

simulations with the animat method 

provides a more robust risk assessment 

and provides a better measure of 

variability (Schecklman et al., 2011). 

We agree with CRE (and our own 

statements, as cited by CRE) that 

sophisticated modeling is not a 

requirement of the MMPA process. 

However, all take estimation requires 

the use of modeling; the difference 

between various approaches to 

estimating take is the degree of 

sophistication of the modeling approach 

employed. We note that the National 

Science Foundation (NSF) typically 

utilizes the method espoused by CRE in 

take authorization requests for specific 

surveys. In order to derive the necessary 

estimated isopleth distance, NSF 

applications typically use Nucleus (a 

source model) in conjunction with ray 

trace modeling to approximate 

propagation of the acoustic signatures. 

The modeling developed by BOEM and 

NMFS supports both BOEM’s 2017 PEIS 

and the analyses conducted for this 

rulemaking, and additionally is 

available for use in supporting LOA 

applications to maximize efficiency of 

the LOA process for disparate 

applicants. However, we have made 

clear that LOA applicants are free to 

pursue a different method of estimating 

takes than the modeling effort 

developed collaboratively by NMFS and 

BOEM. Use of a different analytical 

method in support of an LOA 

application will necessarily require 

additional review. 

CRE compares ‘‘Line Transect’’ 

modeling performed in support of a 

2004 Minerals Management Service 

Environmental Assessment to that 

developed in support of this effort, 

stating that the take estimates generated 

in that effort are ‘‘orders of magnitude 

smaller than the take estimates’’ 

evaluated here. CRE’s erroneous 

implication is that the only difference 

between the two efforts is the modeling 

approach. (‘‘The great difference 

between GOM takes as estimated by 

Line Transect, and as estimated by 

[NMFS]’s current models, demonstrates 

just how inaccurate and exaggerated the 

model take estimates are.’’) However, 

the inputs to the two efforts are 

significantly different. Most notably, the 

assumptions relating to projected effort, 

animal occurrence, and sound source 

output are not comparable. Effort 

projections for the 2004 modeling were 

roughly 53 percent of those given by 

BOEM for the high effort scenario in the 

PEIS, and included only relatively 

archaic 3D survey geometries, versus the 

more complex azimuth designs and coil 

surveys considered herein. Advances in 

cetacean density modeling provide 

estimates for use here that are, in some 

cases, multiple orders of magnitude 

greater than the poor estimates used in 

the 2004 effort. The 15-year old 

modeling held up by CRE as a good 

example assumed a 4,550 in3 acoustic 

source with a uniform 3 km isopleth 

distance to the 160-dB rms threshold. 

BOEM specified use of an 8,000 in3

acoustic source for the modeling effort 

here, with a mean distance to the 160 

dB isopleths of 12.7 km, but even more 

recent modeling of a more comparable 

source (4,130 in3) shows that the 

isopleth distance may be as large as 8.4 

km, depending on the season (Zeddies 

et al., 2017b). Moreover, the 2004 

modeling reduced even that ensonified 

area by an arbitrary 50 percent to 

account for an ‘‘elliptical zone of 

ensonification.’’ It is clear that the two 

modeling efforts are in no way 

comparable. 

Comment: NRDC asserts that NMFS 

fails to account for forms of injury that 

are reasonably anticipated, stating that 

permanent hearing loss (i.e., Level A 

harassment) may occur through 

mechanisms other than PTS, and that 

behaviorally-mediated injury may occur 

as a result of exposure to airgun noise. 

NRDC states that NMFS must account 

for these mechanisms in its assessment 

of potential injury. 


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Response: NMFS is aware of the work 

by Kujawa and Liberman (2009), which 

is cited by NRDC. The authors report 

that in mice, despite completely 

reversible threshold shifts that leave 

cochlear sensory cells intact, there were 

synaptic level changes and delayed 

cochlear nerve degeneration. However, 

the large threshold shifts measured (i.e., 

maximum 40 dB) that led to the 

synaptic changes shown in this study 

are within the range of the large shifts 

used by Southall et al. (2007, 2019a) and 

in NMFS’ 2018 Revised Technical 

Guidance to define PTS onset (i.e., 40 

dB). It is unknown whether smaller 

levels of TTS would lead to similar 

changes or what may be the long-term 

implications of irreversible neural 

degeneration. The effects of sound 

exposure on the nervous system are 

complex, and this will be re-examined 

as more data become available. It is 

important to note that NMFS’ 2018 

Revised Technical Guidance 

incorporated various conservative 

factors, such as a 6-dB threshold shift to 

represent TTS onset (i.e., minimum 

amount of threshold shift that can be 

differentiated in most experimental 

conditions); the incorporation of 

exposures only with measured levels of 

TTS (i.e., did not incorporate exposures 

where TTS did not occur); and assumed 

no potential of recovery between 

intermittent exposures. NMFS disagrees 

that consideration of likely PTS is not 

sufficient to account for reasonably 

expected incidents of auditory injury. 

There is no conclusive evidence that 

exposure to airgun noise results in 

behaviorally-mediated forms of injury. 

Behaviorally-mediated injury (i.e., mass 

stranding events) has been primarily 

associated with beaked whales exposed 

to mid-frequency active (MFA) navy 

sonar. Military tactical sonar and the 

alerting stimulus used in Nowacek et al. 

(2004) are very different from the noise 

produced by airguns. One should 

therefore not expect the same reaction to 

airgun noise as to these other sources. 

Yet NRDC infers that because strandings 

of beaked whales have been correlated 

with navy MFA sonar use, strandings 

are also likely to occur due to seismic 

surveys. As explained below, navy MFA 

sonar is very different from airguns, and 

it is not reasonable to assume that 

airguns will cause the same effects as 

navy MFA sonar (including strandings). 

To understand why navy MFA sonar 

affects beaked whales differently than 

airguns do, it is important to note the 

distinction between behavioral 

sensitivity and susceptibility to auditory 

injury. To understand the potential for 

auditory injury in a particular marine 

mammal species in relation to a given 

acoustic signal, the frequency range the 

species is able to hear is critical, as well 

as the species’ auditory sensitivity to 

frequencies within that range. Current 

data indicate that not all marine 

mammal species have equal hearing 

capabilities across all frequencies and, 

therefore, species are grouped into 

hearing groups with generalized hearing 

ranges assigned on the basis of available 

data (Southall et al., 2007, 2019a). 

Hearing ranges as well as auditory 

sensitivity/susceptibility to frequencies 

within those ranges vary across the 

different groups. For example, in terms 

of hearing range, the high-frequency 

cetaceans (e.g., Kogia spp.) have a 

generalized hearing range of frequencies 

between 275 Hz and 160 kHz, while 

mid-frequency cetaceans—such as 

dolphins and beaked whales—have a 

generalized hearing range between 150 

Hz to 160 kHz. Regarding auditory 

susceptibility within the hearing range, 

while mid-frequency cetaceans and 

high-frequency cetaceans have roughly 

similar hearing ranges, the highfrequency group is much more 

susceptible to noise-induced hearing 

loss during sound exposure, i.e., these 

species have lower thresholds for these 

effects than other hearing groups 

(NMFS, 2018). Referring to a species as 

behaviorally sensitive to noise simply 

means that an animal of that species is 

more likely to respond to lower received 

levels of sound than an animal of 

another species that is considered less 

behaviorally sensitive. So, while 

dolphin species and beaked whale 

species—both in the mid-frequency 

cetacean hearing group—are assumed to 

(generally) hear the same sounds 

equally well and be equally susceptible 

to noise-induced hearing loss (auditory 

injury), the best available information 

indicates that a beaked whale is more 

likely to behaviorally respond to that 

sound at a lower received level 

compared to an animal from other midfrequency cetacean species that is less 

behaviorally sensitive. This distinction 

is important because, while beaked 

whales are more likely to respond 

behaviorally to sounds than are many 

other species (even at lower levels), they 

cannot hear the predominant, lower 

frequency sounds from seismic airguns 

as well as sounds that have more energy 

at frequencies that beaked whales can 

hear better (such as navy MFA sonar). 

Navy MFA sonar affects beaked 

whales differently than airguns do 

because it produces energy at different 

frequencies than airguns. Mid-frequency 

cetacean hearing is generically thought 

to be best between 8.8 to 110 kHz, i.e., 

these cutoff values define the range 

above and below which a species in the 

group is assumed to have declining 

auditory sensitivity, until reaching 

frequencies that cannot be heard 

(NMFS, 2018). However, beaked whale 

hearing is likely best within a higher, 

narrower range (20–80 kHz, with best 

sensitivity around 40 kHz), based on a 

few measurements of hearing in 

stranded beaked whales (Cook et al., 

2006; Finneran et al., 2009; Pacini et al., 

2011) and several studies of acoustic 

signals produced by beaked whales (e.g., 

Frantzis et al., 2002; Johnson et al., 

2004, 2006; Zimmer et al., 2005). While 

precaution requires that the full range of 

audibility be considered when assessing 

risks associated with noise exposure 

(Southall et al., 2007, 2019a), animals 

typically produce sound at frequencies 

where they hear best. More recently, 

Southall et al. (2019a) suggested that 

certain species amongst the historical 

mid-frequency hearing group (beaked 

whales, sperm whales, and killer 

whales) are likely more sensitive to 

lower frequencies within the group’s 

generalized hearing range than are other 

species within the group and state that 

the data for beaked whales suggest 

sensitivity to approximately 5 kHz. 

However, this information is consistent 

with the general conclusion that beaked 

whales (and other mid-frequency 

cetaceans) are relatively insensitive to 

the frequencies where most energy of an 

airgun signal is found. Navy MFA sonar 

is typically considered to operate in the 

frequency range of approximately 3–14 

kHz (D’Amico et al., 2009), i.e., outside 

the range of likely best hearing for 

beaked whales but within or close to the 

lower bounds, whereas most energy in 

an airgun signal is radiated at much 

lower frequencies, below 500 Hz 

(Dragoset, 1990). 

It is important to distinguish between 

energy (loudness, measured in dB) and 

frequency (pitch, measured in Hz). In 

considering the potential impacts of 

mid-frequency components of airgun 

noise (1–10 kHz, where beaked whales 

can be expected to hear) on marine 

mammal hearing, one needs to account 

for the energy associated with these 

higher frequencies and determine what 

energy is truly ‘‘significant.’’ Although 

there is mid-frequency energy 

associated with airgun noise (as 

expected from a broadband source and 

as we acknowledged in the notice of 

proposed rulemaking), airgun sound is 

predominantly below 1 kHz (Breitzke et 

al., 2008; Tashmukhambetov et al., 

2008; Tolstoy et al., 2009). As stated by 

Richardson et al. (1995), ‘‘[. . .] most 

emitted [seismic airgun] energy is at 10– 

120 Hz, but the pulses contain some 


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4The U.S. Navy has publicly stated its agreement 

that five such events since 1996 were associated in 

time and space with MFA sonar use, either by the 

U.S. Navy alone or in joint training exercises with 

the North Atlantic Treaty Organization. The U.S. 

Navy additionally noted that, as of 2017, a 2014 

beaked whale stranding event in Crete coincident 

with naval exercises was under review and had not 

yet been determined to be linked to sonar activities 

(DoN, 2017). 

energy up to 500–1,000 Hz.’’ Tolstoy et 

al. (2009) conducted empirical 

measurements, demonstrating that 

sound energy levels associated with 

airguns were at least 20 decibels (dB) 

lower at 1 kHz (considered ‘‘midfrequency’’) compared to higher energy 

levels associated with lower frequencies 

(below 300 Hz) (‘‘all but a small fraction 

of the total energy being concentrated in 

the 10–300 Hz range’’ [Tolstoy et al., 

2009]), and at higher frequencies (e.g., 

2.6–4 kHz), power might be less than 10 

percent of the peak power at 10 Hz 

(Yoder, 2002). Energy levels measured 

by Tolstoy et al. (2009) were even lower 

at frequencies above 1 kHz. In addition, 

as sound propagates away from the 

source, it tends to lose higher-frequency 

components faster than low-frequency 

components (i.e., low-frequency sounds 

typically propagate longer distances 

than high-frequency sounds) (Diebold et 

al., 2010). Although higher-frequency 

components of airgun signals have been 

recorded, it is typically in surfaceducting conditions (e.g., DeRuiter et al., 

2006; Madsen et al., 2006) or in shallow 

water, where there are advantageous 

propagation conditions for the higher 

frequency (but low-energy) components 

of the airgun signal (Hermannsen et al., 

2015). This should not be of concern 

because the likely behavioral reactions 

of beaked whales that can result in acute 

physical injury would result from noise 

exposure at depth (because of the 

potentially greater consequences of 

severe behavioral reactions) and 

because, even if near-surface exposure 

to such higher-frequency components 

were of concern, oceanographic 

conditions in the GOM do not 

consistently support such ducting 

conditions. In summary, the frequency 

content of airgun signals is such that 

beaked whales will not be able to hear 

the signals well (compared to MFA 

sonar), especially at depth where we 

expect the consequences of noise 

exposure could be more severe. 

Aside from frequency content, there 

are other significant differences between 

MFA sonar signals and the sounds 

produced by airguns that minimize the 

risk of severe behavioral reactions that 

could lead to strandings or deaths at sea, 

e.g., significantly longer signal duration, 

horizontal sound direction, typical fast 

and unpredictable source movement. 

All of these characteristics of MFA 

sonar tend towards greater potential to 

cause severe behavioral or physiological 

reactions in exposed beaked whales that 

may contribute to stranding. Although 

both sources are powerful, MFA sonar 

contains significantly greater energy in 

the mid-frequency range, where beaked 

whales hear better. Short-duration, high 

energy pulses—such as those produced 

by airguns—have greater potential to 

cause damage to auditory structures 

(though this is unlikely for midfrequency cetaceans, as explained later 

in this document), but it is longer 

duration signals that have been 

implicated in the vast majority of 

beaked whale strandings. Faster, less 

predictable movements in combination 

with multiple source vessels are more 

likely to elicit a severe, potentially antipredator response. Of additional interest 

in assessing the divergent characteristics 

of MFA sonar and airgun signals and 

their relative potential to cause 

stranding events or deaths at sea is the 

similarity between the MFA sonar 

signals and stereotyped calls of beaked 

whales’ primary predator: The killer 

whale (Zimmer and Tyack, 2007). 

Although generic disturbance stimuli— 

as airgun noise may be considered in 

this case for beaked whales—may also 

trigger antipredator responses, stronger 

responses should generally be expected 

when perceived risk is greater, as when 

the stimulus is confused for a known 

predator (Frid and Dill, 2002). In 

addition, because the source of the 

perceived predator (i.e., MFA sonar) 

will likely be closer to the whales 

(because attenuation limits the range of 

detection of mid-frequencies) and 

moving faster (because it will be on 

faster-moving vessels), any antipredator 

response would be more likely to be 

severe (with greater perceived predation 

risk, an animal is more likely to 

disregard the cost of the response; Frid 

and Dill, 2002). Indeed, when analyzing 

movements of a beaked whale exposed 

to playback of killer whale predation 

calls, Allen et al. (2014) found that the 

whale engaged in a prolonged, directed 

avoidance response, suggesting a 

behavioral reaction that could pose a 

risk factor for stranding. Overall, these 

significant differences between sound 

from MFA sonar and the mid-frequency 

sound component from airguns and the 

likelihood that MFA sonar signals will 

be interpreted in error as a predator are 

critical to understanding the likely risk 

of behaviorally-mediated injury due to 

seismic surveys. 

The available scientific literature also 

provides a useful contrast between 

airgun noise and MFA sonar regarding 

the likely risk of behaviorally-mediated 

injury. There is strong evidence for the 

association of beaked whale stranding 

events with MFA sonar use, and 

particularly detailed accounting of 

several events is available (e.g., a 2000 

Bahamas stranding event for which 

investigators concluded that MFA sonar 

use was responsible; Evans and 

England, 2001). D’Amico et al. (2009) 

reviewed 126 beaked whale mass 

stranding events over the period from 

1950 (i.e., from the development of 

modern MFA sonar systems) through 

2004. Of these, there were two events 

where detailed information was 

available on both the timing and 

location of the stranding and the 

concurrent nearby naval activity, 

including verification of active MFA 

sonar usage, with no evidence for an 

alternative cause of stranding. An 

additional ten events were at minimum 

spatially and temporally coincident 

with naval activity likely to have 

included MFA sonar use and, despite 

incomplete knowledge of timing and 

location of the stranding or the naval 

activity in some cases, there was no 

evidence for an alternative cause of 

stranding.4 Separately, the International 

Council for the Exploration of the Sea 

reported in 2005 that, worldwide, there 

have been about 50 known strandings, 

consisting mostly of beaked whales, 

with a potential causal link to MFA 

sonar (ICES, 2005). In contrast, very few 

such associations have been made to 

seismic surveys, despite widespread use 

of airguns as a geophysical sound source 

in numerous locations around the 

world. 

A more recent review of possible 

stranding associations with seismic 

surveys (Castellote and Llorens, 2016) 

states plainly that, ‘‘[s]peculation 

concerning possible links between 

seismic survey noise and cetacean 

strandings is available for a dozen 

events but without convincing causal 

evidence.’’ The authors’ ‘‘exhaustive’’ 

search of available information found 

ten events worth further investigation 

via a ranking system representing a 

rough metric of the relative level of 

confidence offered by the data for 

inferences about the possible role of the 

seismic survey in a given stranding 

event. Only three of these events 

involved beaked whales. Whereas 

D’Amico et al. (2009) used a 1–5 

ranking system, in which ‘‘1’’ 

represented the most robust evidence 

connecting the event to MFA sonar use, 

Castellote and Llorens (2016) used a 1– 

6 ranking system, in which ‘‘6’’ 

represented the most robust evidence 


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5Of the ten total events, none achieved the 

highest rank of 6. Two events were ranked as 5: One 

stranding in Peru involving dolphins and porpoises 

and a 2008 stranding in Madagascar. This latter 

ranking can only broadly be associated with the 

survey itself, as opposed to use of seismic airguns. 

An exhaustive investigation of this stranding event, 

which did not involve beaked whales, concluded 

that use of a high-frequency mapping system (12- 

kHz multibeam echosounder) was the most 

plausible and likely initial behavioral trigger of the 

event, which was likely exacerbated by several siteand situation-specific secondary factors. The review 

panel found that seismic airguns were used after the 

initial strandings and animals entering a lagoon 

system, that airgun use clearly had no role as an 

initial trigger, and that there was no evidence that 

airgun use dissuaded animals from leaving 

(Southall et al., 2013). 

connecting the event to the seismic 

survey. As described above, D’Amico et 

al. (2009) found that two events were 

ranked ‘‘1’’ and ten events were ranked 

‘‘2’’ (i.e., 12 beaked whale stranding 

events were found to be associated with 

MFA sonar use). In contrast, Castellote 

and Llorens (2016) found that none of 

the three beaked whale stranding events 

achieved their highest ranks of 5 or 6.5

However, we acknowledged in the 

notice of proposed rulemaking that one 

of these stranding events, involving two 

Cuvier’s beaked whales, was 

contemporaneous with and reasonably 

associated spatially with a 2002 seismic 

survey in the Gulf of California, and 

here acknowledge the same for the 2007 

Gulf of Cadiz seismic survey discussed 

by Castellote and Llorens (also 

involving two Cuvier’s beaked whales). 

However, neither event was considered 

a ‘‘true atypical mass stranding’’ 

(according to Frantzis [1998]) as used in 

the analysis of Castellote and Llorens 

(2016). While we agree with the authors 

that this lack of evidence should not be 

considered conclusive, it is clear that 

there is very little evidence that seismic 

surveys should be considered as posing 

a significant risk of acute harm to 

marine mammals. 

Comment: NRDC asserts that NMFS 

has failed to account adequately for the 

effects of stress on marine mammals. 

Response: As NRDC acknowledges, 

we addressed the available literature 

regarding potential impacts of stress 

resulting from noise exposure in marine 

mammals. As described in that 

discussion, stress responses are 

complicated and may or may not have 

meaningful impacts on marine 

mammals. NRDC implies that NMFS 

must (1) enumerate takes resulting from 

stress alone and (2) specifically address 

stress in its negligible impact analysis. 

The effects of stress are not 

straightforward, and there is no 

information available to inform an 

understanding of whether it is 

reasonably likely that an animal may 

experience a stress response upon noise 

exposure that would not be accounted 

for in NMFS’ existing enumeration of 

takes via exposure to noise, which 

includes an accounting for exposures 

above received levels as low as 140 dB 

rms (and as low as 120 dB rms for 

beaked whales). NRDC provides nothing 

informative regarding how such an 

analysis might be carried out. With 

regard to NMFS’ negligible impact 

analysis, we believe that the potential 

effects of stress are addressed and 

subsumed within NMFS’ considerations 

of severity of effect and vulnerability of 

affected populations. Similarly, NRDC 

provides no justification as to why 

stress would appropriately be 

considered separately in this analysis, 

and no useful recommendation as to 

how to do so, if appropriate. We believe 

we have appropriately acknowledged 

the potential effects of stress, and that 

these potential effects are accounted for 

within our overall assessment of 

potential effects on marine mammals. 

Comment: NRDC states that masking 

results in take of marine mammals and 

that NMFS must account for this in its 

take estimates. 

Response: We addressed our 

consideration of masking in greater 

detail in a previous response. We 

acknowledge that masking may impact 

marine mammals, particularly baleen 

whales such as the Bryde’s whale, and 

particularly when considered in the 

context of the full suite of regulated and 

unregulated anthropogenic sound 

contributions overlaying an animal’s 

acoustic habitat. We acknowledge that 

masking can constitute a take, 

depending on the particular 

circumstances, but do not agree that 

masking effects from the incremental 

noise contributions of individual 

activities or sound sources always rise 

to the level of take. Further, not all takes 

are readily quantifiable. In this case, 

while masking is considered in the 

analysis, we do not believe it will result 

in take of marine mammals beyond 

those that have already been quantified 

as taken by behavioral harassment. 

Specifically, in the case of these 

proposed activities, in the event that 

some masking incidents rise to the level 

of a take, we would expect them to be 

accounted for in the quantified 

exposures above the harassment 

thresholds. Given the short duration of 

expected noise exposures, any take by 

masking in the case of these surveys 

would be most likely to be incurred by 

individuals either exposed briefly to 

notably higher levels or those that are 

generally in the wider vicinity of the 

source for comparatively longer times. 

Both of these situations would be 

captured in the enumeration of takes by 

Level B harassment, which accounts for 

takes that may occur upon exposure at 

relatively low levels of received sound 

(e.g., 140 dB). 

Comment: MMC commented that the 

aversion adjustment applied to 

estimates of Level A harassment 

proposed by NMFS for low- and highfrequency cetaceans is not supported. 

NRDC provided similar comments. 

Response: NMFS disagrees with these 

comments, and clarifies our position 

given the misunderstanding evident in 

the comments. The MMC cites NMFS’ 

statements that ‘‘too little is known 

about the factors that lead to avoidance 

of sounds to quantify aversive behavior 

for survey activities when modeling 

marine mammal exposure to sound’’ 

and that ‘‘aversion is a contextdependent behavioral response affected 

by biological factors, including energetic 

and reproductive state, sociality, and 

health status of individual animals’’ in 

characterizing our subsequent use of a 

post-hoc correction factor to account for 

aversion as an ‘‘apparent contradiction.’’ 

Similarly, NRDC cites NMFS’ statement 

that aversion was not quantified in the 

modeling process due to lack of 

information regarding species-specific 

degree of aversion and level of onset in 

criticizing the adjustment that was later 

made. 

Aversion is a known real-world 

phenomenon. It is well-known that 

animals will avoid unpleasant stimuli, 

such as very high received levels of 

sound. A large and growing literature 

has demonstrated behavioral aversion in 

a number of contexts for many marine 

mammal species in increasingly 

controlled and well-documented 

contexts. While considerable species, 

individual, and context-dependencies 

exist in terms of received noise levels 

associated with behavioral aversion, 

clear patterns of behavioral aversion 

have been demonstrated empirically 

within odontocetes and mysticetes (e.g., 

Miller et al., 2012, 2014; DeRuiter et al., 

2013; Southall et al., 2019b). This is 

particularly true for exposure scenarios 

in which animals occur relatively close 

to sources and at the high levels that 

would be required for even TTS (much 

less PTS) to occur. In some instances, in 

these and other studies, behavioral 

avoidance has been measured at 

received levels many orders of 

magnitude below those required for 

predicted PTS onset and even below the 

nominal, 50 percent behavioral response 

probability at 160 dB rms that NMFS 

has applied historically. 

However, accounting for aversion 

quantitatively in an acoustic exposure 

modeling process is a significantly dataVerDate Sep<11>2014 19:33 Jan 17, 2021 Jkt 253001 PO 00000 Frm 00033 Fmt 4701 Sfmt 4700 E:\FR\FM\19JAR2.SGM 19JAR2

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heavy endeavor and, as we noted, 

despite the growing body of evidence 

there is at this time still not sufficient 

data regarding the specific degree of 

aversion and level of onset on a speciesspecific basis. That is, in order to 

account for aversion within the 

modeling process, one must program 

individual animats representing 

different species to respond at a specific 

received level by changing their 

direction of travel by a specific degree 

and assuming a specific rate of speed. 

Through a test scenario evaluation 

(discussed in the notice of proposed 

rulemaking), we determined that while 

this is possible to do, the specific values 

that must be used in programming the 

animat response could not be 

adequately derived. Instead, a nominal 

offset factor was applied to the modeled 

injurious exposures based on published 

model result evaluation to account for 

aversion. 

Ellison et al. (2016) modeled 

scenarios using animal movement 

models to evaluate predicted PTS in 

which no aversion was assumed relative 

to scenarios where reasonable 

assumptions were made about aversion, 

in line with historical response 

probability assumptions and that 

existing scientific literature suggest are 

appropriate. Scenarios where no 

aversion probability was used 

overestimated the potential for high 

levels of exposure required for PTS by 

about five times. Accordingly, total 

modeled injurious exposures calculated 

without accounting for behavioral 

aversion (for low- and high-frequency 

species) were multiplied by 0.2 as part 

of the EWG risk analysis. NMFS 

consulted the EWG in selecting the 

specific offset factor, and discussed that 

selection again in context of the public 

comments received. The EWG—which 

is composed of some of the foremost 

scientists in the field of marine mammal 

behavioral response study, and includes 

the lead author of the Ellison et al. 

(2016) study—agreed that the approach 

and specific offset factor was a 

reasonable and likely conservative 

approach to addressing the issue of 

aversion. 

The commenters do not dispute that 

aversion is a meaningful real-world 

phenomenon that is significantly 

influential on actual occurrence of Level 

A harassment. As NRDC acknowledges, 

‘‘it is certainly true that some marine 

mammals will flee the sound.’’ Yet the 

commenters would have us ignore this 

phenomenon and assume unrealistically 

high amounts of auditory injury for 

marine mammals in the GOM. NMFS 

does not agree that this would be 

appropriate. As described above, there 

is extensive information supporting the 

aversion concept in marine mammals, 

but limited quantitative data with which 

to develop precise, species-specific 

offset factors. Accordingly, utilizing the 

available data and expert input, NMFS 

applied its professional judgement in 

order to account for this meaningful 

phenomenon. 

Comment: NRDC disagrees with 

NMFS’ conclusion that Level A 

harassment is not likely to occur for 

mid-frequency (MF) cetaceans and 

states that this ‘‘problem [. . .] must be 

addressed.’’ 

Response: As was explained in the 

notice of proposed rulemaking, the 

number of modeled incidents of Level A 

harassment for MF cetacean species is 

not realistic. The modeled isopleth 

distance to the relevant Level A 

harassment threshold, i.e., the 

predominant MF peak pressure 

threshold, is only 18 m. As we 

explained in the notice of proposed 

rulemaking, it is understandable that 

even such a small assumed area could 

lead to the results given when a realworld density value is sufficiently high 

to lead to non-zero scaled 24-hr 

modeled exposure results, which are 

then multiplied by large numbers of 

notional survey days. We explain in 

greater detail below why relatively 

small zones, i.e., zones contained within 

the near-field of an airgun array, should 

not be expected to result in actual 

injurious exposure. NRDC also appears 

to be under the impression that the 

conclusion was based on what they refer 

to as ‘‘shorter injurious take distances 

assumed in the Gulf of Mexico modeling 

than in modeling for seismic in other 

regions, such as the Atlantic,’’ an 

apparent misunderstanding on the part 

of the commenter that they refer to as 

a ‘‘discrepancy’’ that is ‘‘never 

explained’’ and ‘‘appears arbitrary.’’ 

Given the lack of detail provided, NMFS 

cannot be sure what NRDC is referring 

to. However, we do know that state-ofscience propagation modeling 

performed for a notional array here 

provided the 18 m result described 

above. For five different, real-world 

arrays evaluated for use in the Atlantic 

Ocean (83 FR 63268; December 7, 2018), 

the calculated isopleth distance to the 

230 dB peak sound pressure level (SPL) 

MF Level A harassment threshold was 

an average 27 m (range 14–63 m), in 

keeping with the value calculated here. 

For MF cetaceans, the only potential 

injury zones will be based on the peak 

pressure metric, as such zones will be 

larger than those calculated on the basis 

of the cumulative sound exposure level 

(SEL) metric (which are essentially nonexistent for MF and HF cetaceans). As 

noted, the estimated zone size for the 

230 dB peak threshold for MF cetaceans 

is only 18 m. In a theoretical modeling 

scenario, it is possible for animats to 

engage with such a small assumed zone 

around a notional point source and, 

subsequently, for these interactions to 

scale to predictions of real-world 

exposures given a sufficient number of 

predicted 24-hr survey days in 

confluence with sufficiently high 

predicted real-world animal densities— 

i.e., the modeling process that resulted 

in the predicted exposure estimates for 

MF cetaceans in the modeling report. 

However, this is not a realistic outcome. 

The source level of the array is a 

theoretical definition assuming a point 

source and measurement in the far-field 

of the source (MacGillivray, 2006). As 

described by Caldwell and Dragoset 

(2000), an array is not a point source, 

but one that spans a small area. In the 

far-field, individual elements in arrays 

will effectively work as one source 

because individual pressure peaks will 

have coalesced into one relatively broad 

pulse. The array can then be considered 

a ‘‘point source.’’ For distances within 

the near-field, i.e., approximately 2–3 

times the array dimensions, pressure 

peaks from individual elements do not 

arrive simultaneously because the 

observation point is not equidistant 

from each element. The effect is 

destructive interference of the outputs 

of each element, so that peak pressures 

in the near-field will be significantly 

lower than the output of the largest 

individual element. Here, the 230 dB 

peak isopleth distances would be 

expected to be within the near-field of 

the arrays where the definition of source 

level breaks down. Therefore, actual 

locations within this distance (i.e., 

within 18 m) of the array center where 

the sound level exceeds 230 dB peak 

SPL would not necessarily exist. In 

general, Caldwell and Dragoset (2000) 

suggest that the near-field for airgun 

arrays is considered to extend out to 

approximately 250 m. 

In order to provide quantitative 

support for this theoretical argument, 

we calculated expected maximum 

distances at which the near-field would 

transition to the far-field for five 

specific, real-world arrays proposed for 

use in the Atlantic Ocean (83 FR 63268). 

The average distance to the near-field 

calculated for the five arrays, following 

the process described below, was 203 m 

(range 80–417 m). 

For a specific array one can estimate 

the distance at which the near-field 

transitions to the far-field by: 


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with the condition that D >> l, and 

where D is the distance, L is the longest 

dimension of the array, and l is the 

wavelength of the signal (Lurton, 2002). 

Given that l can be defined by: 

where f is the frequency of the sound 

signal and v is the speed of the sound 

in the medium of interest, one can 

rewrite the equation for D as: 

and calculate D directly given a 

particular frequency and known speed 

of sound (here assumed to be 1,500 

meters per second in water, although 

this varies with environmental 

conditions). 

To determine the closest distance to 

the array at which the modeled source 

level prediction is valid (i.e., maximum 

extent of the near-field), we calculated 

D based on an assumed frequency of 1 

kHz. A frequency of 1 kHz is commonly 

used in near-field/far-field calculations 

for airgun arrays (Zykov and Carr, 2014; 

MacGillivray, 2006; NSF and USGS, 

2011), and based on representative 

airgun spectrum data and field 

measurements of an airgun array used 

on the R/V Marcus G. Langseth, nearly 

all (greater than 95 percent) of the 

energy from airgun arrays is below 1 

kHz (Tolstoy et al., 2009). Thus, using 

1 kHz as the upper cut-off for 

calculating the maximum extent of the 

near-field should reasonably represent 

the near-field extent in field conditions. 

If the largest distance to the peak 

sound pressure level threshold was 

equal to or less than the longest 

dimension of the array (i.e., under the 

array), or within the near-field, then 

received levels that meet or exceed the 

threshold in most cases are not expected 

to occur. This is because within the 

near-field and within the dimensions of 

the array, the specified source level is 

overestimated and not applicable. In 

fact, until one reaches a distance of 

approximately three or four times the 

near-field distance, the average intensity 

of sound at any given distance from the 

array is still less than that based on 

calculations that assume a directional 

point source (Lurton, 2002). For 

example, an airgun array used on the R/ 

V Marcus G. Langseth has an 

approximate diagonal of 29 m, resulting 

in a near-field distance of 140 m at 1 

kHz (NSF and USGS, 2011). Field 

measurements of this array indicate that 

the source behaves like multiple 

discrete sources, rather than a 

directional point source, beginning at 

approximately 400 m (deep site) to 1 km 

(shallow site) from the center of the 

array (Tolstoy et al., 2009), distances 

that are actually greater than four times 

the calculated 140-m near-field 

distance. Within these distances, the 

recorded received levels were always 

lower than would be predicted based on 

calculations that assume a directional 

point source, and increasingly so as one 

moves closer towards the array (Tolstoy 

et al., 2009). Given this, relying on the 

calculated distances as the distances at 

which we expect to be in the near-field 

is a conservative approach because even 

beyond this distance the acoustic 

modeling still overestimates the actual 

received level. 

Within the near-field, in order to 

explicitly evaluate the likelihood of 

exceeding any particular acoustic 

threshold, one would need to consider 

the exact position of the animal, its 

relationship to individual array 

elements, and how the individual 

acoustic sources propagate and their 

acoustic fields interact. Given that 

within the near-field and dimensions of 

the array source levels would be below 

the modeled notional source level, we 

believe exceedance of the peak pressure 

threshold would only be possible under 

highly unlikely circumstances. 

Therefore, we expect the potential for 

Level A harassment of MF cetaceans to 

be de minimis, even before the likely 

moderating effects of aversion and/or 

other compensatory behaviors (e.g., 

Nachtigall et al., 2018) are considered. 

We do not believe that Level A 

harassment is a likely outcome for any 

MF cetacean. 

Comment: The MMC comments that 

the estimated numbers of Level B 

harassment must be increased to 

account for the incidents of acoustic 

exposure that were modeled as injurious 

but subsequently discounted due to 

aversion. NRDC commented similarly. 

Response: NMFS agrees that animals 

that avoid Level A harassment through 

aversive behavior should be considered 

as having been subject to Level B 

harassment and increased the Level B 

harassment estimates accordingly. 

However, these estimates have been 

superseded by the revised estimates 

submitted by BOEM in support of their 

revised scope of activity. 

Marine Mammal Protection Act— 

General 

Comment: The MMC recommended 

that any ‘‘formal interpretation’’ by 

NMFS of MMPA standards, such as the 

least practicable adverse impact 

standard and small numbers standard, 

be issued in stand-alone, generally 

applicable rulemakings (e.g., in 

amendments to 50 CFR 216.103 or 

216.105) or in a separate policy 

directive, rather than in the preambles 

to individual proposed rules. 

Response: We appreciate the 

recommendation and may consider the 

recommended approaches in the future. 

However, providing directly relevant 

explanations of programmatic 

approaches or interpretations related to 

the incidental take provisions of the 

MMPA in a proposed incidental take 

authorization is an effective and 

efficient way to provide information to 

and solicit focused input from the 

public. Further, this approach 

ultimately affords the same 


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opportunities for public comment as a 

stand-alone rulemaking would. 

Regarding the least practicable 

adverse impact standard, NMFS has 

provided similar explanations in other 

recent section 101(a)(5)(A) rules. See, 

e.g., 83 FR 66846 (December 27, 2018) 

(U.S. Navy Training and Testing 

Activities for Hawaii-Southern 

California Study Area). 

Least Practicable Adverse Impact 

Comment: NRDC believes NMFS 

relies on a ‘‘flawed interpretation’’ of 

the least practicable adverse impact 

standard. They state that NMFS (1) 

wrongly imports a population-level 

focus into the standard, contrary to the 

‘‘clear’’ holding of the Ninth Circuit in 

NRDC v. Pritzker, 828 F.3d 1125 (9th 

Cir. 2016); and (2) inappropriately 

‘‘balances’’ or weighs effectiveness 

against practicability without sufficient 

analysis, counter to Pritzker. 

Response: NMFS carefully evaluated 

the Ninth Circuit’s opinion in Pritzker 

and believe we have fully addressed the 

court’s concerns. NMFS’ discussion of 

the least practicable adverse impact 

standard in the Mitigation section 

explains why we believe a population 

focus is a reasonable interpretation of 

the standard. 

With regard to the second point, 

NMFS disagrees that the analysis is 

insufficient. NMFS’ interpretation of the 

LPAI standard is a reasonable 

interpretation that gives effect to the 

language in the statute and the 

underlying legislative intent. Congress 

intended the agencies administering 

section 101(a)(5)(A) to consider 

practicability when determining 

appropriate mitigation, and we do not 

believe the analysis must be conducted 

in a rigid sequential fashion. There is a 

tension inherent in the phrase ‘‘least 

practicable adverse impact’’ in that 

‘‘least [. . .] adverse impact’’ pulls in 

favor of one direction (i.e., expanding 

mitigation) while ‘‘practicable’’ pulls in 

favor of the other direction (i.e., limiting 

mitigation), and weighing the relative 

costs and benefits is, in NMFS’ view, a 

meaningful way to address and resolve 

this tension. Further, as described in the 

proposed rule and augmented in this 

final rule in both the Mitigation section 

and the response to comments, NMFS 

considered all recommended mitigation 

in the context of both the reduction of 

impacts on marine mammal species and 

stocks and their habitat and the 

practicability of such mitigation in 

reaching the required set of measures 

that we believe satisfy the least 

practicable adverse impact standard. 

Comment: The Associations assert 

that NMFS failed to provide sufficient 

practicability analyses for the proposed 

mitigation requirements. 

Response: No guidance is provided by 

the MMPA or NMFS’ implementing 

regulations as to what constitutes 

‘‘practicability’’ for the non-military 

readiness activities considered here, or 

how to ascertain whether a proposed 

measure is practicable. Neither the term 

‘‘practicable’’ nor the phrase ‘‘least 

practicable adverse impact’’ is defined 

by the MMPA or in NMFS’ 

implementing regulations. (See 

Mitigation, later in this document, for 

extensive discussion on NMFS’ 

interpretation of the meaning of ‘‘least 

practicable adverse impact.’’) Therefore, 

while the MMPA’s requirement to 

prescribe mitigation achieving the ‘‘least 

practicable adverse impact’’ demands 

consideration of practicability, the need 

for additional ‘‘analysis’’ of unspecified 

scope, detail, or methodology, as 

demanded by the Associations, cannot 

be found in the statute, legislative 

history, regulations, or case law. 

However, NMFS does not start from 

scratch. Our implementing regulations 

at 50 CFR 216.104(a)(11) require 

applications for incidental take 

authorizations to include information 

about the availability and feasibility 

(economic and technological) of 

equipment, methods, and manner of 

conducting such activity or other means 

of effecting the least practicable adverse 

impact upon the affected species or 

stocks, their habitat, and on their 

availability for subsistence uses, paying 

particular attention to rookeries, mating 

grounds, and areas of similar 

significance. This often provides the 

foundation of NMFS’ proposed 

mitigation, after consideration of the 

objectives of those and other possible 

measures and how they may achieve 

those objectives as well as, when 

possible, what we know about the 

practicability of the proposed measures. 

As a general matter, where an 

applicant proposes measures that are 

likely to reduce impacts to marine 

mammals, the fact that they are 

included in the proposal and 

application indicates that the measures 

are practicable, and it is not necessary 

for NMFS to conduct a detailed analysis 

of the measures the applicant proposed 

(rather, they are simply included). 

However, it is incumbent on NMFS to 

consider whether there are other 

practicable measures that would 

contribute to the reduction of risk or 

severity of adverse effects on the species 

or stocks. 

We then seek public comment on the 

proposal and, if contradictory 

information is presented by members of 

the public (including prospective 

applicants), the information is 

considered in making a decision 

regarding whether to retain, modify, or 

eliminate a proposed measure. 

Our notice of proposed rulemaking 

presented specific discussion of 

practicability considerations, including 

both the monetized direct costs of 

proposed measures as well as what we 

understand about potential indirect 

costs, and provided detailed discussion 

relating to certain measures. While 

much of this analysis was conducted 

under a regulatory impact analysis (RIA) 

conducted pursuant to Executive Order 

12866, as stated by the Associations, the 

utility of the analysis is not limited to 

use there. For example, while the 

Associations claim that NMFS fails to 

‘‘consider impacts beyond immediate 

operational impacts,’’ the RIA provides 

a detailed analysis of the sort of 

speculative indirect costs of concern to 

industry, and the RIA’s analysis is 

incorporated into NMFS’ consideration 

of practicability. Overall, we note that 

the Associations’ comments are 

peppered with reference to cost 

increases, both vague (‘‘resulting in 

millions of dollars of added cost’’) and 

specific (‘‘increase costs an estimated 

5% to 20%’’), but without sufficient 

supporting data. 

NMFS interprets ‘‘practicable’’ simply 

as capable of being put into practice or 

of being done or accomplished. 

Practicability of the standard 

operational protocols was reasonably 

assumed in consideration of the fact that 

they are included in many incidental 

take authorizations and that we did not 

receive any specific public comments to 

the contrary. Moreover, many of these 

measures were proposed by the 

applicant (BOEM) in their petition for 

regulations, including ramp-up and 

shutdown requirements and a 

requirement to observe a time-area 

restriction in coastal waters to protect 

bottlenose dolphins during the time of 

their reproductive activity peak. The 

Associations claim that our proposal 

applies these standard measures in such 

a way as to extend their ‘‘geographic 

and temporal scope or to circumstances 

where they are unnecessary or 

impossible to implement,’’ but provide 

no specific information as to what 

measures they specifically refer to, in 

what circumstances they believe 

specific measures are unnecessary, or in 

what circumstances specific measures 

are impossible to implement. The 

Associations assert that NMFS’ 

considerations of practicability ‘‘fail to 

adequately estimate levels of current 

and future geophysical work or consider 

costs and impacts beyond the 

immediate survey work,’’ but their 


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comments provide no specific 

information to enable NMFS to assess 

its consideration of practicability. 

NMFS’ consideration of practicability 

was sufficient and in accordance with 

law, and the Associations provided no 

specific contradictory information for 

NMFS’ evaluation. 

Comment: The MMC recommended 

that NMFS rework its evaluation criteria 

for applying the least practicable 

adverse impact standard to separate the 

factors used to determine whether a 

potential impact on marine mammal 

species or stocks or their habitat is 

adverse and whether possible mitigation 

measures would be effective. In this 

regard, the MMC asserted that it seems 

as though the proposed ‘‘effectiveness’’ 

criterion more appropriately fits as an 

element of practicability and should be 

addressed under that prong of the 

analysis. In other words, a measure not 

expected to be effective should not be 

considered a practicable means of 

reducing impacts. 

Response: In the Mitigation section, 

NMFS has explained in detail its 

interpretation of the least practicable 

adverse impact standard, the rationale 

for the interpretation, and our approach 

for implementing the interpretation. The 

ability of a measure to reduce effects on 

marine mammals is entirely related to 

its ‘‘effectiveness’’ as a measure, 

whereas the effectiveness of a measure 

is not connected to its practicability. 

The MMC did not support its argument 

with scientific information, and NMFS 

has not implemented the suggestion. 

Comment: The MMC recommended 

that NMFS address the habitat 

component of the least practicable 

adverse impact provision in greater 

detail. It asserted that NMFS’ discussion 

of critical habitat, marine sanctuaries, 

and biologically important areas (BIA) 

in the proposed rule is not integrated 

with the discussion of the least 

practicable adverse impact standard. As 

stated by the MMC, it would seem that, 

under the least practicable adverse 

impact provision, adverse impacts on 

important habitat should be avoided 

whenever practicable. Therefore, to the 

extent that activities would be allowed 

to proceed in these areas, NMFS should 

explain why it is not practicable to 

constrain them further. The MMC also 

suggests that NMFS intends to defer 

consideration of measures to protect 

habitat to individual LOAs, rather than 

addressing such measures in the 

regulations, as the MMC contends is 

required. 

Response: Marine mammal habitat 

value is informed by marine mammal 

presence and use and, in some cases, 

there may be overlap in mitigation 

measures for the species or stock 

directly and for use of habitat. In this 

rule, NMFS has identified one time-area 

restriction (carried forward from the 

proposed rule) based on a combination 

of factors that include higher densities 

and observations of specific important 

behaviors of marine mammals 

themselves, but also that clearly reflect 

preferred habitat. In addition to being 

delineated based on physical features 

that drive habitat function (e.g., 

bathymetric features, among others for 

some BIAs), the high densities and 

concentration of certain important 

behaviors (e.g., feeding) in these 

particular areas indicate the presence of 

preferred habitat. The MMC seems to 

suggest that NMFS must always 

consider separate measures aimed at 

marine mammal habitat. However, the 

MMPA does not specify that effects to 

habitat must be mitigated in separate 

measures, and NMFS has identified 

measures that provide significant 

reduction of impacts to both ‘‘marine 

mammal species and stocks and their 

habitat,’’ as required by the statute. 

Finally, we clarify here that all 

measures to reduce impacts to both 

marine mammal species and stocks and 

their habitat are included in the 

regulations and then implemented 

through activity-specific LOAs. 

Negligible Impact 

Comment: The Associations and 

Chevron concur with NMFS’ finding 

that the incidental taking that may be 

authorized under the ITR will have a 

negligible impact on the affected marine 

mammal stocks. The Associations 

additionally specify their agreement 

with NMFS’ conclusions that Level A 

harassment will not play a meaningful 

role in the overall degree of impact 

experienced by marine mammal 

populations as a result of the projected 

survey activity and that mid-frequency 

cetaceans are unlikely to incur Level A 

harassment, as well as with NMFS’ use 

of the Wood et al. (2012) probabilistic 

risk function. 

Response: NMFS appreciates the 

comments. 

Comment: NRDC claims that NMFS 

did not define the total amount of take 

it evaluated in making the negligible 

impact determination and asserts that 

the proposed rule is unclear about the 

data and calculations that informed the 

basis of the negligible impact finding. 

Response: NMFS disagrees with these 

comments. NMFS explicitly defined the 

basis, as well as the process, for the 

negligible impact analysis. Although the 

negligible impact analysis was built 

upon relatively sophisticated acoustic 

exposure modeling, and incorporated 

advances in the science of risk 

assessment, the informational inputs to 

the analysis and the analytical 

framework were clearly elucidated and 

the supporting documentation 

identified and provided as companion 

documents to the public for review in 

association with our negligible impact 

analysis. The notice of proposed 

rulemaking identified a point of contact 

available to provide further information 

or answer questions if necessary. 

NMFS stated that the ‘‘specified 

activity’’ for the proposed regulations is 

a broad program of geophysical survey 

activity that could occur at any time of 

year in U.S. waters of the GOM. This 

conceptual program, as defined by 

BOEM through projected levels of 

survey effort, was described and shown 

in Table 1 of the notice of proposed 

rulemaking. These annual survey 

projections aligned generally with 

‘‘low,’’ ‘‘moderate,’’ and ‘‘high’’ effort 

years (83 FR 29224). These projected 

levels of survey effort informed the 

acoustic modeling report (Zeddies et al. 

2015, 2017a), which was extensively 

and clearly summarized in the notice of 

proposed rulemaking, while the report 

itself was made available for public 

review concurrently with the notice of 

proposed rulemaking. In order to 

reasonably estimate the actual effort that 

might occur over the five-year 

timeframe of the proposed ITR, NMFS 

determined for the proposed rule 

analysis that it would be appropriate to 

assume that one high-effort year, two 

moderate-effort years, and two loweffort years (and, therefore, associated 

acoustic exposure estimates) would 

occur. NMFS then selected and 

identified the specific effort scenarios 

that formed the basis for the analysis in 

association with Table 9 of the notice of 

proposed rulemaking, titled ‘‘ScenarioSpecific Expected Take Numbers and 

Mean Annual Take Level.’’ Table 9 of 

the notice identified the annual and 

total amounts of take that NMFS 

expected to occur under the ITR. The 

preliminary negligible impact analysis 

then referred back to Table 9 as the basis 

for the analytical process and discussion 

provided therein (See 83 FR 29290– 

29291). 

NRDC complains that ‘‘NMFS never 

defines the total amount of take it 

proposes to authorize.’’ However, as is 

typical for a programmatic analysis, the 

ITR and its associated analysis 

(including negligible impact) do not 

propose to authorize take per se, but 

rather to provide a description of the 

upper bound within which take may be 

authorized via LOAs. The upper bounds 

of the instances of take that may be 

authorized under this rule are indicated 


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in Table 9 in this final rule. The actual 

amount of take authorized through 

LOAs under the ITR will be determined 

by applicant interest (subject to the 

upper bound). 

NMFS also identified the Expert 

Working Group (EWG) report (Southall 

et al., 2017) as an essential companion 

to the notice of proposed rulemaking 

and, similar to the acoustic modeling 

report, provided the document for 

concurrent public review. The EWG 

report describes the systematic risk 

assessment framework that, in part, 

forms the basis for the negligible impact 

analysis. We concisely described the 

analytical framework in the notice and 

provided the results of that analysis. 

Ultimately, the EWG report provides 

overall evaluated relative risk for each 

of the three effort scenarios (low, 

moderate, high) for each species in each 

of seven different zones. As stated in the 

notice, the severity and vulnerability 

ratings (facets of the analytical 

framework that are also clearly 

explained both in the EWG report and 

the notice) are integrated to provide 

relative impact ratings of overall risk. 

These zone-specific relative impact 

ratings for each species were then 

integrated using basic calculations to 

produce species-specific, GOM-wide 

overall evaluated relative risk ratings for 

each of the three effort scenarios. 

Overall vulnerability scores for each 

species were produced by summing the 

zone-specific vulnerability scores, as 

scaled to the zone-specific population. 

For example, the Zone 1 vulnerability 

score is multiplied by the ratio of the 

Zone 1 population to the total 

population. These zone-specific 

products are then summed. Overall 

severity scoring is calculated as the 

proportion of the sum of scenariospecific takes to the total population. 

These two factors are then integrated as 

described in the EWG report. 

NRDC also states that the ‘‘actual 

percentages of populations affected by 

takes’’ are not provided. NMFS 

disagrees, as this information can be 

replicated using information that was 

provided to the public via the acoustic 

modeling report. Additional underlying 

data are necessary to replicate zonespecific findings. Excel workbooks 

containing these data were made 

publicly available by BOEM during 

review of their PEIS. NMFS did not 

view these additional data as essential 

to understanding the modeling report or 

the proposed ITR and did not publish 

these data on its website. Members of 

the public interested in further 

exploration of the information provided 

in the modeling report, or in need of 

assistance regarding their independent 

analysis of the modeling report, could 

have contacted the NMFS point of 

contact identified in the notice of 

proposed rulemaking. 

In sum, NMFS provided sufficient 

information in support of its negligible 

impact analysis affording the public 

meaningful opportunity to comment. 

Further, consistent with a potential 

alternative scope identified in the 

proposed rule that would remove the 

Eastern Planning Area (EPA), the scope 

of this final rule has been modified to 

remove the GOMESA area, which 

includes most of the EPA (and a small 

portion of the Central Planning Area), 

based on BOEM’s update to its action. 

This has resulted in a reduction in the 

upper bounds of the instances of take 

that may be authorized for all species 

pursuant to this final rule (see Tables 8 

and 9). 

Comment: The MMC commented 

similarly to NRDC, expressing some 

concern regarding the risk assessment 

framework and asserting ‘‘apparent 

inconsistencies,’’ while recommending 

that NMFS (1) provide the final risk 

assessment framework, underlying 

results, and its interpretation of those 

results to the public and (2) allow for an 

additional 30-day comment period to 

review the findings sufficiently in 

advance of issuing the final rule. 

Response: NMFS disagrees with the 

MMC comments. They state that the 

EWG report and analysis ‘‘has some 

apparent inconsistencies’’ as compared 

against the preamble to the proposed 

rule because the scenario-specific high, 

moderate, and low values presented in 

Table 3 of the EWG report do not align 

with the summary minimum, 

maximum, and mean values given in 

Table 2 of the notice of proposed 

rulemaking. We note that the MMC 

provided clarifying questions to NMFS 

during the public comment period in 

advance of submitting a formal 

comment letter and expressed some 

confusion regarding Table 2 of that 

notice at that time. As was explained to 

the MMC then, Table 2 of the preamble 

was provided for illustrative purposes 

only, as a way of providing a more 

concise look at the information given in 

Table 1 of the preamble. As was 

explained, the values given in Table 2 

were not consequential with regard to 

anything that followed in the preamble. 

NMFS regrets any confusion caused by 

inclusion of Table 2 in the notice of 

proposed rulemaking but explained 

clearly to the MMC that the table was 

not related to the analysis. It has been 

removed from this final rule. 

Separately, the MMC states that 

‘‘neither NMFS nor BOEM stipulated 

why only certain years were selected for 

analysis,’’ claiming that NMFS 

indicated that years 1, 4, and 9 were 

used in the analysis ‘‘upon further 

inquiry.’’ This is incorrect. In the notice 

of proposed rulemaking, we stated that 

‘‘Year 1 provides an example of what 

might be a high-effort year in the GOM, 

while Year 9 is representative of a loweffort year. A moderate level of effort in 

the GOM, according to these 

projections, would be similar to the 

level of effort projected for Year 4.’’ (83 

FR 29224.) NMFS provided explanation 

of its choices in the notice of proposed 

rulemaking (see, e.g., 83 FR 29261– 

29262, 29290). 

This portion of the MMC’s 

recommendation regarding 

representative years is no longer 

relevant to this final rule. As discussed 

previously, BOEM revised the scope of 

the activity and provided revised effort 

projections and resulting take estimates 

accordingly. The revised take estimates 

provided by BOEM reflect years 1–5 of 

their original level of effort projections 

and, therefore, the question of rationale 

behind the selection of years 1, 4, and 

9 is no longer relevant. 

Regarding the notice of proposed 

rulemaking, the MMC also states that 

supposed discrepancies between zonespecific risk ratings and risk derived per 

year across the GOM are 

‘‘inconsistencies.’’ Zone-specific risk 

ratings for any given effort scenario are 

driven by the actual effort within that 

zone for that scenario, while the overall 

level of effort GOM-wide underlies the 

labeling of scenarios as ‘‘high,’’ 

‘‘moderate,’’ and ‘‘low.’’ For example, 

although year 1 was designated as the 

‘‘high’’ effort scenario and year 4 the 

‘‘moderate’’ effort scenario on the basis 

of the total projected GOM-wide survey 

days (2,286 and 1,902, respectively), the 

‘‘high’’ effort scenario actually includes 

significantly less projected effort in 

zones 2 and 4 than does the ‘‘moderate’’ 

effort scenario. Therefore, risk ratings 

for certain species were higher in those 

specific zones for the ‘‘moderate’’ effort 

scenario than they were for the ‘‘high’’ 

effort scenario. This was explained in 

our notice of proposed rulemaking: 

‘‘[P]er-zone ranges can provide a 

different outlook than does an 

assessment of total year projected effort 

across zones. For example, in the ‘‘high’’ 

effort annual scenario (Year 1; 

considering total projected survey days 

across zones), there are 263 projected 

survey days in Zone 2, while the 

‘‘moderate’’ effort annual scenario (Year 

4) projects 446 survey days in Zone 2.’’ 

This was explained directly to the MMC 

upon its informal inquiry during the 

public comment period. The MMC also 

stated to NMFS at that time that ‘‘the 


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relative risk scores for certain species 

[. . .] do not make sense, presumably 

because they are based on the incorrect 

number of estimated survey days,’’ 

giving as an example that ‘‘roughtoothed dolphins in Zone 5 have an 

overall Moderate risk in the High and 

Low scenario years, but a Low risk in 

the Moderate scenario year.’’ We 

reiterated to the MMC at that time that 

what the MMC viewed as illogical and 

erroneous did not in fact reflect errors, 

but rather the confluence of zonespecific activity levels and species 

presence for a given year. The effort 

scenarios used as the basis for the 

analysis were clearly identified, and 

there were no inconsistencies in terms 

of risk ratings in consideration of the 

zone-specific information underlying 

those ratings (which was explained in 

the notice of proposed rulemaking). 

Separately, the MMC stated its view 

that ‘‘the basis for determining the 

relative risk thresholds, relative rating 

thresholds, species-specific biological 

risk factors, and environmental risk 

factors was not provided’’ and that 

‘‘many of the quantitative aspects have 

not been substantiated.’’ While NMFS 

disagrees with this statement and refers 

the reader to the EWG report (Southall 

et al., 2017), we also point out that, in 

the absence of precise quantitative 

information on these aspects of the risk 

assessment framework (on a speciesand zone-specific basis), the application 

of the framework necessarily requires 

the application of professional 

judgment. As NMFS acknowledged, 

‘‘[e]lements of this approach are 

subjective and relative within the 

context of this program of projected 

actions and, overall, the analysis 

necessarily requires the application of 

professional judgment.’’ (83 FR 29290.) 

The MMC comments do not find fault 

with any specific element or attribute of 

the framework or with any specific 

value chosen to represent a particular 

risk threshold or a particular species’ 

vulnerability. NMFS does not agree that 

the MMC’s recommendation to allow for 

an additional 30-day comment period 

for the public to review the risk 

assessment framework findings in 

advance of issuing the final rule is 

warranted and has not implemented the 

suggestion. 

Comment: NRDC asserts that NMFS 

has erroneously used the relativistic 

assessment presented in the EWG report 

as the basis for the negligible impact 

determination, incorrectly applying it as 

though it evaluated absolute risk. A 

private citizen offers similar comments. 

Response: NMFS disagrees with the 

comment. The EWG analysis is an 

important component of the negligible 

impact analysis, but is not the sole basis 

for our determination. While the EWG 

analysis comprehensively considered 

the spatial and temporal overlay of the 

activities and the marine mammals in 

the GOM, as well as the number of takes 

predicted by the described modeling, 

there are details about the nature of any 

‘‘take’’ anticipated to result from these 

activities that were not considered 

directly in the EWG analysis and which 

warrant explicit consideration in the 

negligible impact analysis. Accordingly, 

NMFS’ analysis considers the results of 

the EWG analysis, the effects of the 

required mitigation, and the nature and 

context of the takes that are predicted to 

occur. NMFS’ analysis also explicitly 

considers the effects of predicted Level 

A harassment and impacts to marine 

mammal habitat, which were, 

respectively, not integrated into or 

included in the EWG risk ratings. These 

components of the full analysis, along 

with any germane species or stockspecific information, are integrated and 

summarized for each species or stock in 

the Species and Stock-specific 

Negligible Impact Analysis Summaries 

section of the negligible impact analysis. 

In addition, while the EWG 

framework comprehensively considers 

the aggregate impacts to marine 

mammal populations from the activities 

addressed in this rule in the context of 

both the severity of the impacts and the 

vulnerability of the affected species, it 

does not fully consider the absence of 

survey activity in the eastern GOM 

(within the GOMESA moratorium area), 

following BOEM’s update to the scope 

of activity. While this is to some degree 

reflected in the updated take estimates, 

and thereby incorporated into the EWG 

framework’s risk ratings, the absence of 

survey activities within areas of 

increased biological importance for 

certain species benefits those species 

GOM-wide beyond what is simply 

reflected in the updated take numbers. 

The negligible impact analysis considers 

the reduction of both acute and chronic 

effects afforded through the revised 

scope of the rule. 

Also, we note that while the EWG 

framework produces relativistic risk 

ratings, its components consist of 

absolute concepts, some of which are 

also absolutely quantified (e.g., whether 

the specified activity area contains 

greater than 30 percent of total regionwide estimated population, between 30 

and 15 percent, between 15 and 5 

percent, or less than 5 percent). Further, 

NMFS provided substantive input into 

the scoring used in implementing the 

EWG framework for the GOM, to ensure 

that the categories associated with 

different scores, the scores themselves, 

and the weight of the scores within the 

overall risk rating all reflected 

meaningful biological, activity, or 

environmental distinctions that would 

appropriately inform the negligible 

impact analysis. Accordingly, and as 

intended, we used our understanding of 

the framework and best professional 

judgment to interpret the relativistic 

results of the EWG analysis 

appropriately into the larger negligible 

impact analysis, with the other factors 

discussed above, to make the necessary 

findings specific to the effects of the 

total taking on the affected species and 

stocks. 

Comment: NRDC asserts that the 

vulnerability ratings used in the EWG 

framework fail to account for several 

factors appropriately, which undermine 

the framework’s ability to contribute 

accurately to the overall evaluation of 

relative risk. NRDC cites the following 

as problematic factors: Application of 

vulnerability ratings on a zone-by-zone 

basis, which they state negatively biases 

the habitat use and temporal overlap 

factors; unaccountably low ratings for 

non-seismic stressors (specifically citing 

the DWH oil spill); relatedly, failure to 

account appropriately for all other 

stressors; and failure to fully account for 

stock structure and status. 

Response: NMFS first notes that the 

application of the EWG framework, and 

specifically the development of 

appropriate vulnerability ratings, 

necessarily involves the use of 

professional judgment, here on the part 

of a group of experts in the fields of 

marine mammal biology, ocean 

acoustics, and the effects of noise on 

marine mammals, among other things 

(and in consultation with NMFS and 

BOEM). Reasonable people may 

disagree about the specific numerical 

values assigned to any one of the 11 

different factors contributing to the 

overall species-specific vulnerability 

score generated for each of the seven 

zones (with seven factors that are static 

GOM-wide and four that vary spatially, 

scoring for 18 taxa and seven zones 

means that 630 individual numerical 

value selections underlie the 

vulnerability scores); but this does not 

imply that any of the specific values 

selected are unreasonable. All relevant 

factors were considered in generating 

the species- and zone-specific 

vulnerability scores. 

NRDC misapprehends one of the 

fundamental values of the analytical 

framework, in that it is structured in a 

spatially explicit way that can be 

applied at multiple scales, based on the 

scope of the action and the information 

available to inform an assessment of the 

risk associated with the activity (or suite 


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of activities). This allows one to 

generate overall risk ratings while also 

evaluating risk on finer scales. In this 

case, severity ratings were generated on 

the basis of seven different GOM zones, 

allowing an understanding not only of 

the relative scenario-specific risk across 

the entire GOM, as is demanded for this 

analysis, but also to better understand 

the particular zones where risk may be 

high (depending on actual future survey 

effort) and what part of the stock’s range 

may be subject to relatively high risk. 

The framework recognizes, 

fundamentally, that the spatial, 

temporal, and spectral overlaps between 

noise-generating activities and animal 

distribution are the primary factors that 

drive the type, magnitude, and overall 

evaluated risk of potential noise effects 

on marine mammals. These 

considerations are inherent and 

fundamental in both the severity and 

vulnerability ratings and are 

deliberately integrated into both the 

vulnerability and severity assessments; 

in fact, key features of the analytical 

framework include explicit recognition 

of the importance of species distribution 

relative to activity spatial distribution 

and temporal and contextual differences 

in exposure scenarios. If the spatially 

explicit nature of the framework were 

removed, as it seems NRDC is 

suggesting, there would be no value in 

generating a ‘‘habitat use’’ factor (i.e., 

the spatial scale would be the GOM, and 

it would necessarily contain 100 percent 

of the estimated population). Spatial 

overlap is a central consideration for the 

extent of physical overlap between 

species and other environmental 

stressors, with consideration of species 

distribution across all zones, as well as 

the extent of population concentration 

and habitat specialization (as expressed 

through zone-specific vulnerability 

assessment). Regarding the temporal 

overlap factor referenced by NRDC, 

overall activity duration is a limited 

consideration within the vulnerability 

assessment rating but is expressed as a 

central consideration within magnitudeduration functions used to evaluate 

severity. 

Despite the explanations provided in 

the EWG report, NRDC characterizes 

certain aspects of the vulnerability 

scoring as ‘‘unaccountably low.’’ 

However, NRDC does not provide 

specific recommendations for revisions 

to the assigned numerical values, or 

justification for their contention that 

scoring is too low. All relevant stressors 

were accounted for in the vulnerability 

scoring and specific scores were 

reasonably made on the basis of expert 

professional judgment. Contrary to 

NRDC’s assertion, the effects of the 

DWH oil spill were considered in the 

vulnerability scoring (as well as in our 

development of mitigation in 

consideration of the MMPA’s least 

practicable adverse impact standard). 

Overall, NRDC seems to provide a 

blanket suggestion, without adequate 

justification or evidence, that for all 

species, impacts should be considered 

to be higher than we have determined. 

We believe that we have satisfied the 

statutory standards after careful 

consideration of the available science. 

Regarding stock structure, NRDC 

criticizes the treatment of bottlenose 

dolphins in the vulnerability scoring. 

Overall, species-level take and 

abundance estimates are used to support 

findings for bottlenose dolphins out of 

necessity. The best available 

information (Roberts et al., 2016) was 

used to inform combined species values 

and did not support further quantitative 

apportionment of estimated take or 

abundances to stocks. However, NRDC’s 

specific criticism of the ‘‘population’’ 

vulnerability scoring for bottlenose 

dolphins is unwarranted. The 

population score comprises three 

components: Status, i.e., is the stock 

listed under the ESA and/or designated 

as depleted under the MMPA; trend, i.e., 

does information over the available time 

series of abundance estimates indicate a 

trend; and size, i.e., is the population 

defined as small (less than 2,500). None 

of the five designated stocks of 

bottlenose dolphin in Federal waters of 

the GOM are listed under the ESA or 

designated as depleted under the 

MMPA, and none would be classed as 

small. Regarding trend, multiple SAR 

abundance estimates are available for 

three of the five stocks (oceanic stock 

and northern and western coastal 

stocks); and available information does 

show an increasing trend for these 

stocks. We recognize that the effects of 

the DWH oil spill included likely 

population reductions for all GOM 

marine mammal stocks (other than the 

eastern coastal stock of bottlenose 

dolphins, which was not impacted by 

the spill); however, the best available 

information indicates that these 

reductions were likely modest for all 

bottlenose dolphin stocks other than the 

northern coastal stock (Table 5), and no 

more recent population abundance 

estimates that might reflect any 

potential reduction are yet available. 

While the likely decline in population 

abundance for northern coastal 

bottlenose dolphins is subsumed within 

the population score assigned for 

bottlenose dolphins at the species level, 

vulnerability scoring is necessarily 

performed at the species level such that 

it may appropriately be integrated with 

the take-based severity scoring and used 

to generate an overall risk rating. As 

mentioned above, the best available 

scientific information does not allow for 

stock-specific parsing of take for 

bottlenose dolphins. Moreover, the 

trend component of the population 

score is a relatively small contribution 

to the overall vulnerability scoring, 

accounting for a maximum of two out of 

30 potential points. The likely decline 

in population abundance for northern 

coastal bottlenose dolphins, although 

not reflected in the existing 

vulnerability scoring, is insignificant as 

a contribution to the overall 

vulnerability score for bottlenose 

dolphins as a species. As noted above, 

the effects of the DWH oil spill are 

separately accounted for in the 

vulnerability scoring. Importantly, and 

also not accounted for in the EWG 

framework, we include significant 

mitigation (time-area restriction) 

intended to alleviate impacts to 

northern coastal bottlenose dolphins 

during periods of greatest importance 

for their reproductive behavior. 

Comment: NRDC states that NMFS’ 

use of daily exposure durations ‘‘to 

justify its negligible impact 

determination’’ is arbitrary and 

capricious. They state that we 

incorrectly used exposure times above 

the 160-dB threshold (rather than the 

lower threshold associated with the 

multi-step probabilistic risk function); 

assumed low severity for certain 

exposure durations; and disregarded 

repeated exposures. A private citizen 

offers similar comments. 

Response: As an initial matter, while 

it is true that NMFS evaluated exposure 

durations for the negligible impact 

analysis, it is not the only factor that we 

considered ‘‘to justify’’ the 

determination, as described fully in the 

Negligible Impact Analysis and 

Determinations section. Moreover, the 

consideration of exposure duration is 

entirely appropriate in assessing the 

severity of a likely exposure, which is 

critical to understanding how the 

authorized takes are likely to impact 

individual marine mammals. This was 

not addressed in the EWG assessment 

but was incorporated into the negligible 

impact analysis. 

NMFS appreciates NRDC’s comments 

regarding use of exposure times above 

the 160-dB threshold, and we have reevaluated the exposure duration 

information and better integrated 

discussion of this information into the 

negligible impact analysis (see 

Negligible Impact Analysis and 

Determinations and Table 16 for more 


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information). However, it is incorrect 

that ‘‘NMFS’ time-exposure analysis is 

predicated on its use of 160 dB as the 

operative threshold of harm’’ and that 

our use of exposure information above 

the 160-dB threshold is a ‘‘back-door 

return’’ of the ‘‘outdated 160 dB 

threshold.’’ Inherent in the concept of a 

multi-step probabilistic risk function is 

the assumption that varying proportions 

of an exposed population will be 

harassed upon exposure at the different 

steps of the function. We presented the 

160-dB exposure durations in the notice 

of proposed rulemaking because 

exposure above this step represents the 

50 percent midpoint of the function (for 

all species other than beaked whales) 

and, therefore, was deemed an 

appropriate representation of durations 

where a significant proportion of 

exposed animals would be expected to 

experience harassment (versus 10 

percent of the population exposed to 

received sound levels between 140 and 

160 dB). In Table 16 of this final rule, 

we present these durations for both the 

160-dB and 140-dB steps of the 

function. It is important to keep in mind 

that, of the animals exposed above the 

160-dB threshold for the indicated 

species-specific durations, not all are 

considered harassed. The risk function 

assumes 50 percent of animals exposed 

between 160-dB and 180-dB will be 

harassed. For the longer exposure 

durations associated with the 140-dB 

threshold, only 10 percent are expected 

to be harassed. 

As we indicate in the Negligible 

Impact Analysis and Determinations 

discussion of this final rule, to put the 

predicted amount of take into 

meaningful context, it is useful to 

understand the duration of exposure at 

or above a given level of received sound 

(as well as the likely number of repeated 

exposures across days). While a 

momentary exposure above the criteria 

for Level B harassment counts as an 

instance of take, that accounting does 

not make any distinction between 

fleeting exposures and more severe 

encounters in which an animal may be 

exposed to that received level of sound 

for a longer period of time. This 

information is meaningful to an 

understanding of the likely severity of 

the exposure, which is relevant to the 

negligible impact evaluation. For 

example, for bottlenose dolphin 

exposed to noise from 3D WAZ surveys 

in Zone 6, the modeling report shows 

that approximately 72 takes (Level B 

harassment) would be expected to occur 

in a 24-hr period. However, each animat 

modeled has a record or time history of 

received levels of sound over the course 

of the modeled 24-hr period. The 50th 

percentile of the cumulative distribution 

function indicates that the time spent 

exposed to levels of sound above 160 dB 

rms SPL (i.e., the 50 percent midpoint 

for Level B harassment) would be only 

1.8 minutes—a minimal amount of 

exposure carrying little potential for 

significant disruption of behavioral 

activity. 

The Species and Stock-specific 

Negligible Impact Analysis Summaries 

discussion considers the relative impact 

ratings in conjunction with required 

mitigation and other relevant contextual 

information—including exposure 

durations at the various thresholds—to 

produce an assessment of impact to the 

stock or species, i.e., the negligible 

impact determinations. For beaked 

whales, take is estimated on the basis of 

a risk function shifted down such that 

90 percent of the animals exposed to 

received levels above 140 dB and 50 

percent exposed to received levels 

above 120 dB are expected to be 

harassed. We used this approach based 

on the documented behavioral 

sensitivity of beaked whales. However, 

as NRDC acknowledges, context is 

important when assessing behavioral 

responses to sound. The exposures 

above 120 dB here occur at significant 

distance from the source (i.e., greater 

than 50 km). It is generally accepted that 

an animal’s distance from the sound 

source plays an important role in the 

animal’s behavioral response to a 

received sound level (e.g., Gomez et al., 

2016). NMFS believes that exposures to 

the relevant harassment thresholds at 

significant modeled distances from the 

actual sound source, although included 

in the take estimates based on the risk 

function, will not carry significant 

consequences for the potentially 

exposed animals. Rather, these 

exposures are likely to result in 

significantly less severe responses (if 

any). Examples provided by NRDC 

purporting to demonstrate greater 

severity of response than we have 

assumed include irrelevant examples— 

beaked whales are known to respond 

with greater severity to mid-frequency 

active military sonar than to other 

sources, as discussed in greater detail in 

a previous comment response—and 

examples of ‘‘responses’’ entailing 

changes to vocalization patterns over 

longer durations, but these responses do 

not necessarily rise to the level of a take, 

much less a take event of significant 

severity. 

Regarding repeated exposures, despite 

the figures cited by NRDC concerning 

potential days of activity, it is unlikely 

that any given individual animal would 

in fact experience repeated take events 

of the magnitude suggested. Each of the 

seven GOM zones is an extremely large 

area (average zone size approximately 

100,000 km2), and the likely harassment 

‘‘footprint’’ of any given survey would 

be relatively small. Modeled isopleth 

distances to the 160-dB threshold are 

approximately 12 km for low-frequency 

cetaceans (i.e., the Bryde’s whale), 7 km 

for mid-frequency cetaceans (i.e., sperm 

whales, beaked whales, dolphins), and 6 

km for high-frequency cetaceans (i.e., 

Kogia spp.). Distances to the 140-dB 

isopleths are substantially larger, but we 

again emphasize that only ten percent of 

the animals exposed at that level would 

be expected to incur harassment, while 

50 percent of the animals exposed at the 

160-dB level would be expected to incur 

harassment. It is clear that, in reality, 

there is a relatively low chance of any 

given individual marine mammal being 

repeatedly taken within relatively short 

timeframes, much less that such events 

would result in fitness consequences for 

those individuals. Additionally, NRDC 

suggests that NMFS fails to consider 

repeated takes at all, when in fact this 

likelihood is inherently addressed 

through the severity rating of the EWG 

assessment. 

NRDC concludes their comment by 

claiming that NMFS failed to undertake 

sufficient analysis in support of the 

negligible impact determinations. We 

disagree with this assertion, and refer to 

the Negligible Impact Analysis and 

Determinations section in support of 

this final rule. NRDC focuses in 

particular on sperm whales, implying 

that they are likely to incur impacts to 

reproductive fitness and stating that 

NMFS cannot make a negligible impact 

finding for sperm whales without 

additional mitigation requirements. 

NMFS agrees that the bioenergetics 

simulations of Farmer et al. (2018a)— 

cited by NRDC in support of their 

argument—show that frequent 

disruptions in foraging can have 

potentially severe fitness consequences 

for individual sperm whales. However, 

a follow-up study (Farmer et al., 2018b), 

which additionally accounted for the 

population-level effects of the DWH oil 

spill on GOM sperm whales, modeled 

the potential population level 

consequences of the specific 

disturbance events underlying this 

analysis (i.e., the acoustic exposure 

modeling of Zeddies et al., 2015, 2017a). 

This follow-up study found that, under 

realistic modeled scenarios, no sperm 

whales were projected to reach terminal 

starvation and no fetal abortions were 

predicted as a result of long-term 

disturbance effects (i.e., over ten years 

of projected survey activity). Similarly, 


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predicted declines in relative body 

condition (expressed as the percentage 

of available reserves for a disturbed 

individual whale relative to an 

undisturbed whale with identical 

characteristics) as a result of long-term 

disturbance effects were not significant 

under realistic modeled scenarios. 

When evaluating the additional effects 

of modeled disturbance on the DWH oil 

spill-impacted trajectory, the modeling 

did not predict any significant 

additional stock declines (Farmer et al., 

2018b). We believe the administrative 

record for this final rule amply 

demonstrates that NMFS used the best 

available science during our 

administrative process to inform our 

analyses and satisfy the standards under 

section 101(a)(5)(A). Of note, and as 

indicated in Changes from the Proposed 

Rule, as a result of BOEM’s updated 

scope of the activities and the associated 

revisions to the levels of effort, both the 

maximum allowable amount of take and 

the maximum annual take under the 

rule have decreased (significantly in 

some cases, including for Bryde’s 

whales and sperm whales) for all except 

two species/stocks. For the two 

exceptions these figures increased only 

slightly, and the severity of many of the 

impacts has been lessened via the 

removal and/or reduction of take in 

areas of greater biological importance 

previously considered as mitigation 

areas. 

Comment: Chevron comments that 

NMFS should make the final version of 

the EWG report available to the public 

for review and suggests expanding the 

description of the inputs of the analysis. 

Chevron states that the ‘‘vulnerability’’ 

assessment, in particular, would benefit 

from additional discussion to explain 

how professional judgments led to 

specific rankings for each species. 

Chevron also comments that NMFS 

should provide an additional plain 

language discussion of the risk analysis 

process, including background on the 

development of the risk analysis 

framework, including any relevant 

analogues in other ecosystems or 

regulatory contexts, the ways in which 

species may be considered 

‘‘vulnerable,’’ and the meaning of the 

‘‘risk’’ discussed. 

Response: NMFS appreciates the 

comment. The final report is available to 

the public online at: 

www.fisheries.noaa.gov/action/ 

incidental-take-authorization-oil-andgas-industry-geophysical-surveyactivity-gulf-mexico. The content of the 

final report was determined by NMFS 

and BOEM in conjunction with the 

EWG. We believe that we have provided 

sufficient plain language discussion of 

the EWG framework. 

Comment: NRDC claims that NMFS’ 

negligible impact analysis is 

inappropriately reliant upon the 

prescribed mitigation and, further, that 

the mitigation will be ineffective. 

Response: First, NMFS did not rely 

solely on the mitigation in order to 

reach its findings under the negligible 

impact standard. As is stated in the 

analysis, consideration of the 

implementation of prescribed mitigation 

is one factor in the analysis but is not 

determinative in any case. In certain 

circumstances, mitigation is more 

important in reaching the negligible 

impact determination, e.g., when 

mitigation helps to alleviate the likely 

significance of taking by avoiding or 

reducing impacts in important areas. 

Second, while NRDC dismisses the 

importance of the prescribed mitigation 

by stating (mistakenly) that it is 

‘‘unsupported by evidence,’’ NRDC 

offers no support for their conclusions. 

NRDC misunderstands the degree to 

which NMFS relies on shutdowns for 

sensitive or vulnerable species, 

including beaked whales, at extended 

distances. We agree that these measures 

in and of themselves will have limited 

benefit for cryptic species such as 

beaked whales that are unlikely to be 

observed. However, we believe that it 

makes sense to minimize the duration 

and intensity of disturbance for these 

species when they are observed, and 

because they are practicable we include 

them in the suite of prescribed measures 

and discuss them where appropriate. 

For more readily detected species, such 

as the sperm whale, which is easily 

detected when at the surface and which 

vocalizes frequently while underwater, 

the extended distance shutdowns (for 

both visual and acoustic detections) 

should appropriately be considered 

influential in our assessment of impacts 

to affected individuals and, therefore, 

ultimately on the stock. Despite NRDC’s 

dismissal of these requirements, we 

presume they would agree that the 

duration and intensity of disturbance of 

sensitive species should be minimized 

where practicable. 

In summary, we consider these 

measures appropriately as mitigating 

factors when considering context as part 

of our negligible impact analysis. 

Comment: The Associations state that 

the Expert Working Group framework 

was applied without following all of the 

recommended steps, such as conducting 

expert elicitation to derive risk 

functions for species that do not have 

parameterized Population Consequences 

of Disturbance (PCOD) models. The 

Associations recommend that NMFS 

seek input and advice on the framework 

and its conclusions from independent 

experts. 

Response: There is extensive 

scientific interest in forecasting how 

short-term behavioral responses by 

individual animals may aggregate and 

result in population-level consequences. 

The concept was introduced by the 

National Research Council (2005) as 

Population Consequences of Acoustic 

Disturbance. However, given the lack of 

data on acoustic responses, research 

studies have generalized the issue to 

look at environmental and 

anthropogenic stressors in general and 

renamed the concept Population 

Consequences of Disturbance. New et al. 

(2014) presented a modified conceptual 

framework to help forecast long-term 

impacts. Conceptually, a series of 

transfer functions connect increasingly 

broader impacts from the initial 

disturbance to effects on individual 

health, individual vital rates, and finally 

population dynamics. The concept has 

been demonstrated with a few species 

for which there are extensive data from 

tagged or photo-identified animals so 

that effects on individuals can be 

quantified. Northern elephant seals 

were the first study species for which 

the data from time-depth recorders were 

able to be linked to an individual 

animal’s body fat condition (Aoki et al., 

2011; Adachi et al., 2014), which 

provided insight into foraging success 

and ultimately individual health and 

vital rates (Robinson et al., 2010). 

Rolland et al. (2016) used photographic 

data of North Atlantic right whales to 

evaluate individual health and link it to 

demographic groups and population 

status. Additional studies exploring 

population consequences are ongoing, 

but a common theme is that extensive 

data documenting individual health and 

population vital rates are necessary for 

such analyses. These are considered the 

gold standards for future studies, but, at 

present, studies within the GOM have 

not occurred in sufficient detail for such 

analyses. 

For purposes of the analysis 

contained herein, the disturbance 

severity rating facet of the EWG 

framework involves a relativistic 

framework relating Level B harassment 

to the zone-specific population size and 

then evaluating this proportion to 

specified severity criteria common 

across species. In the idealized 

framework discussed by the EWG 

(Southall et al., 2017), the severity rating 

involves consideration of the magnitude 

of population affected and the duration 

of disturbance, i.e., by deriving 

magnitude-duration risk functions that 

describe the potential effects of 


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exposure to noise on affected 

populations. The EWG considered that 

a better approach would apply values 

obtained using software developed to 

implement the Interim PCOD approach 

(Harwood et al., 2014; King et al., 2015). 

While various models have been 

developed implementing the PCOD 

approach (e.g., New et al., 2013), the 

approach is problematic for general 

application because it is very dataheavy, and sufficient data specific to a 

taxon and/or disturbance context is not 

typically available. Few marine 

mammal populations have been as 

intensively studied as the PCOD case 

study populations, and the lack of 

appropriate datasets that link exposure 

to disturbance with behavioral change, 

and behavioral change with health, 

currently limits the general applicability 

of the full PCOD model. This difficulty 

led to development of the Interim PCOD 

approach, which uses results from an 

expert elicitation process, rather than 

empirical data, to predict the effects that 

a specific amount of disturbance will 

have on the vital rates of an individual 

marine mammal. In evaluating potential 

use of the Interim PCOD approach for 

developing magnitude-duration curves 

suitable for use in assessing risk 

associated with the projected survey 

activity considered here, the EWG used 

the results of an expert elicitation 

process that considered potential effects 

of pile driving noise associated with the 

construction of offshore wind farms on 

bottlenose dolphins, harbor porpoises, 

and minke whales in the North Sea. 

While this evaluation provided proof-ofconcept and highlighted areas for future 

improvement of the process, such 

evaluations are not appropriately 

extrapolated to a risk assessment 

involving dissimilar species, stressors, 

and locations. For example, 

demographic rates and population 

growth rates specific to those species in 

U.K. waters of the North Sea were used 

and, further, even in that expert 

elicitation the authors warned that the 

results for the minke whale were likely 

not reliable due to a lack of available 

data. The EWG recommended that the 

available elicitation results not be used 

towards the current analysis, and NMFS 

and BOEM concurred. Currently, results 

of these expert elicitation processes are 

additionally viewed as potentially 

unreliable because experts may 

misinterpret the questions they are 

asked (Booth et al., 2016). 

Overall, while we agree with the 

Associations that it would be ideal to 

evaluate the effects of the specified 

activity on the affected populations by 

incorporating a PCOD or Interim PCOD 

approach to the EWG framework, 

sufficient data are not available to 

conduct a PCOD approach, and 

sufficient resources were not available 

to NMFS to develop and implement an 

expert elicitation process specific to 

seismic and the affected GOM 

populations on a timeline amenable to 

this ITR. With regard to the 

Associations’ suggestion that outside 

experts review the EWG framework, we 

note that the EWG comprises experts 

outside NMFS and BOEM who were 

contracted for the express purpose of 

developing the framework. We do not 

believe it necessary to engage outside 

experts to review the work of other 

experts outside NMFS and BOEM, 

which is itself subject to review by 

experts within both NMFS and BOEM. 

Comment: The Associations object to 

the terminology used for the relative 

severity ratings in the EWG framework 

approach, stating their disagreement 

with the implications of rating 

descriptors such as ‘‘severe,’’ and 

reiterating their belief that the modeled 

exposure levels are incompatible with 

the available data. Relatedly, the 

Associations assert that there is ‘‘little 

scientific support’’ for the relative risk 

ratings for sperm and beaked whales. 

Response: Respectfully, NMFS 

believes this comment involves a 

semantic issue. The Associations do not 

suggest alternative terminology for the 

relative risk ratings. Regarding the risk 

ratings for sperm whales and beaked 

whales, these ratings are a product of a 

relatively straightforward analysis of 

severity (i.e., amount of predicted 

disturbance relative to population size) 

and vulnerability (i.e., consideration of 

factors inherent to the population that 

make it more or less vulnerable to the 

disturbance considered via the severity 

rating). The Associations provide no 

specific critique of any of these aspects 

of the analysis. We have addressed the 

Associations’ criticism of the acoustic 

exposure modeling elsewhere in these 

comment responses. 

Comment: The Associations object to 

use of the potential biological removal 

(PBR) metric as the basis for evaluating 

severity of Level A harassment within 

the EWG framework, stating that its use 

in evaluating non-serious injury is 

inappropriate because the metric was 

developed for evaluation of the 

significance of serious injury and 

mortality. 

Response: We acknowledge that the 

PBR metric defines a level of removals 

from a population (i.e., mortality) that 

would allow that population to remain 

at its optimum sustainable population 

level or, if depleted, would not increase 

the population’s time to recovery by 

more than 10 percent, and therefore that 

it is inappropriate to make comparisons 

between Level B harassment takes and 

the PBR value for any stock. However, 

as discussed in the EWG report and in 

the notice of proposed rulemaking, 

while NMFS does not expect PTS (Level 

A harassment) that might be accrued 

through noise exposure to result in 

mortality of marine mammals, PBR can 

serve as a good surrogate for population 

vulnerability/health. Accordingly, PBR 

or a related metric can be used 

appropriately as a value against which 

to evaluate the potential severity to the 

population of a permanent impact such 

as PTS on a given number of 

individuals, and it is only in this sense 

that we use the PBR value. The 

Associations do not provide an 

alternative recommendation. 

Small Numbers 

Comment: The Associations and other 

industry commenters express agreement 

with NMFS’ interpretation of the small 

numbers requirement as allowing that 

the finding may be made at the 

individual LOA level. 

Response: We thank the Associations 

for their comment in support of the 

small numbers approach. NMFS’ 

analysis generally comports with many 

of the points they raise, as discussed in 

this preamble. 

Comment: NRDC states that the 

interpretation of ‘‘small numbers’’ 

presented by NMFS in the notice of 

proposed rulemaking is contrary to the 

plain meaning and purpose of the 

MMPA, in part because NMFS allegedly 

did not provide a reasoned basis for the 

take limit proposed (i.e., one-third of the 

best available species or stock 

abundance estimate). NRDC makes four 

specific claims. First, NRDC states that 

one-third cannot be considered a ‘‘small 

number.’’ Second, NRDC states that 

Congress intended that takes be limited 

to ‘‘infrequent, unavoidable’’ 

occurrences, and that NMFS has not 

explained why the taking would be 

infrequent or unavoidable. Third, NRDC 

contends that NMFS should define 

different small numbers thresholds on 

the basis of the conservation status of 

individual species. Finally, NRDC 

believes that NMFS must account for 

‘‘additive and adverse synergistic 

effects’’ that may occur due to multiple 

concurrent surveys in conducting a 

small numbers analysis. Industry 

commenters suggest that additional 

detail is necessary regarding the basis 

for NMFS’ small numbers threshold. 

Response: NMFS disagrees with 

NRDC’s arguments on this topic. 

Although there is limited legislative 

history available to guide NMFS and an 

apparent lack of biological 


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6Section 101(a)(5)(D) states in relevant part: 

(i) Upon request therefor by citizens of the United 

States who engage in a specified activity (other than 

commercial fishing) within a specific geographic 

region, the Secretary shall authorize, for periods of 

not more than 1 year, subject to such conditions as 

the Secretary may specify, the incidental, but not 

intentional, taking by harassment of small numbers 

of marine mammals of a species or population stock 

by such citizens while engaging in that activity 

within that region if the Secretary finds that such 

harassment during each period concerned— 

(I) will have a negligible impact on such species 

or stock, and 

(II) will not have an unmitigable adverse impact 

on the availability of such species or stock for 

taking for subsistence uses[.] 

underpinning to the concept, we have 

worked to develop a reasoned approach 

to small numbers. As discussed in the 

section of the notice of proposed 

rulemaking entitled Small Numbers, 

NMFS explains the concept of ‘‘small 

numbers’’ in recognition that there 

could also be quantities of individuals 

taken that would correspond with 

‘‘medium’’ and ‘‘large’’ numbers. As 

such, NMFS has established that onethird of the most appropriate population 

abundance number—as compared with 

the assumed number of individuals 

taken—is an appropriate limit with 

regard to ‘‘small numbers.’’ This relative 

approach is consistent with the 

statement from the legislative history 

that ‘‘[small numbers] is not capable of 

being expressed in absolute numerical 

limits’’ (H.R. Rep. No. 97–228, at 19 

(September 16, 1981)), and relevant case 

law (Center for Biological Diversity v. 

Salazar, 695 F.3d 893, 907 (9th Cir. 

2012) (holding that the U.S. Fish and 

Wildlife Service reasonably interpreted 

‘‘small numbers’’ by analyzing take in 

relative or proportional terms)). 

NRDC claims that a number may be 

considered small only if it is ‘‘little or 

close to zero’’ or ‘‘limited in degree.’’ 

We note that the comment selectively 

picks a definition in support of NRDC’s 

favored position. For example, the 

definition of ‘‘small’’ in Webster’s New 

Collegiate Dictionary (1981) included 

‘‘having little size, esp. as compared 

with other similar things.’’ See also 

www.merriam-webster.com/dictionary/ 

small (defining ‘‘small’’ as ‘‘having 

comparatively little size’’). These 

definitions comport with the small 

numbers interpretation developed by 

NMFS, which utilizes a proportionality 

approach. The comment also selectively 

quotes the relevant legislative history 

language, stating that Congress 

‘‘intended that the agency limit takes to 

‘infrequent, unavoidable’ occurrences.’’ 

The actual statement from the legislative 

history is that taking of marine 

mammals should be ‘‘infrequent, 

unavoidable, or accidental.’’ H.R. Rep. 

No. 97–228, at 19 (September 16, 1981) 

(emphasis added). This language 

suggests that taking that is unavoidable 

(or accidental) may qualify as small 

numbers, even if not infrequent. 

The argument to establish a small 

numbers threshold on the basis of stockspecific context is unnecessarily 

duplicative of the required negligible 

impact finding, in which relevant 

biological and contextual factors are 

considered in conjunction with the 

amount of take. Similarly, NRDC’s 

assertion that NMFS’ proposed 

approach fails to account for ‘‘additive 

and adverse synergistic effects’’ from 

multiple surveys is not required by 

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

it is unclear how NRDC defines this 

concept or how it may be related to the 

‘‘small numbers’’ concept. These 

suggestions are not founded in any 

relevant requirement of statute or 

regulation, discussed in relevant 

legislative history, or supported by 

relevant case law. 

A private citizen echoed certain of 

NRDC’s comments on this topic, adding 

that NMFS’ approach is ‘‘embarrassing 

and scientifically indefensible.’’ 

However, the commenter does not 

provide a more scientifically defensible 

interpretation of small numbers, 

suggesting only that ‘‘[o]ne could 

approach this in many ways.’’ 

Regarding the comment that 

additional explanation is needed for 

NMFS’ interpretation of the small 

numbers standard, we believe the 

proposed and final rule provide 

sufficient explanation for setting onethird as the upper limit for small 

numbers where reasonably reliable 

quantified take estimates are available. 

See the Small Numbers section later in 

this preamble. 

Comment: Several commenters 

suggest that the small numbers finding 

need not be based on a quantitative 

threshold. 

Response: NMFS agrees that a more 

qualitative small numbers finding may 

be permissible. See, e.g., Center for 

Biological Diversity v. Salazar, 695 F.3d 

at 906–908. However, in this case, 

where take estimates can be predicted 

with relative confidence, we have 

elected to set a quantitative threshold. 

Moreover, the commenters do not 

provide any specific recommendations 

for an appropriate qualitative approach 

in this case. 

Comment: The MMC recommended 

that any ‘‘formal interpretation’’ of the 

small numbers standard by NMFS be 

issued in a stand-alone, generally 

applicable rulemaking (e.g., in 

amendments to 50 CFR 216.103 or 

216.105) or in a separate policy 

directive, rather than in the preambles 

to individual proposed rules. 

Response: We appreciate the MMC’s 

recommendation and may consider the 

recommended approaches in the future. 

We note, however, that providing 

relevant explanations in a proposed ITR 

is an effective and efficient way to 

provide information to the reader and 

solicit focused input from the public, 

and ultimately affords the same 

opportunities for public comment as a 

stand-alone rulemaking would. 

Comment: NRDC asserts that NMFS’ 

interpretation of the MMPA’s small 

numbers requirement is contrary to law, 

stating their belief that NMFS must 

make a small numbers determination in 

the rule, rather than for issuance of 

individual LOAs; that NMFS must 

evaluate the same amount of take in 

order to separately determine that the 

total take will both meet the small 

numbers standard and have a negligible 

impact; and that NMFS’ approach 

impermissibly cuts the public out of the 

agency’s findings. 

Response: Based on NMFS’ analysis 

of the language and structure of section 

101(a)(5)(A) and the implementing 

regulations for that provision, NMFS 

disagrees that the small numbers finding 

must be based on the total of all take 

over the five-year (or less) period from 

all potential survey activity. The MMPA 

does not define small numbers or 

explain how to apply the term in either 

section 101(a)(5)(A) or the similar 

provision for incidental harassment 

authorizations (IHAs) in section 

101(a)(5)(D),6 including how to apply 

the term in a way that allows for 

consistency across those two provisions 

that are similar but allow for potentially 

different time and activity scales. (See 

Small Numbers below.) Especially when 

taken together with NMFS’ 

implementing regulations, our approach 

is consistent with the structure of 

section 101(a)(5)(A), which provides: 

(i) Upon request therefor by citizens 

of the United States who engage in a 

specified activity (other than 

commercial fishing) within a specified 

geographical region, the Secretary shall 

allow, during periods of not more than 

five consecutive years each, the 

incidental, but not intentional, taking by 

citizens while engaging in that activity 

within that region of small numbers of 

marine mammals of a species or 

population stock if the Secretary, after 

notice (in the Federal Register and in 

newspapers of general circulation, and 

through appropriate electronic media, in 

the coastal areas that may be affected by 

such activity) and opportunity for 

public comment— 

(I) finds that the total of such taking 

during each five-year (or less) period 


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concerned will have a negligible impact 

on such species or stock and will not 

have an unmitigable adverse impact on 

the availability of such species or stock 

for taking for subsistence uses [. . .]. 

(emphasis added). 

Section 101(a)(5)(A)(i)(I) is explicit 

that the ‘‘negligible impact’’ 

determination for a specified activity 

must take into account the ‘‘total of such 

taking’’ (i.e., all of the taking that the 

Secretary may conceivably allow (or 

authorize) under individual LOAs 

during the five year (or less) period 

considered for the rule). In contrast, the 

‘‘small numbers’’ language in 

101(a)(5)(A) is not subject to the same 

time period requirement of five years (or 

less in cases where the period being 

considered for a rule is less than five 

years). 

In our view, the statutory language for 

small numbers and the negligible 

impact finding indicates that the 

negligible impact finding is made based 

on consideration of an aggregation of 

potential authorizations (LOAs) for 

taking small numbers of marine 

mammals, and allows for different 

temporal periods in applying the two 

different standards. The statute 

contemplates that the Secretary shall 

allow taking during the five year (or 

less) period, which in our view also 

implies that there could be multiple 

allowances or authorizations (i.e., 

LOAs), so long as the maximum 

allowable total taking from all of those 

authorizations combined is considered 

in the upfront assessment of whether 

the negligible impact standard is met. 

As we have noted, the regulatory 

vehicle for authorizing (i.e., allowing) 

the take of marine mammals is the LOA, 

a creature of NMFS’ long-standing 

implementing regulations that is not in 

the statute. See 50 CFR 216.106. Those 

1989 implementing regulations 

requiring an LOA to effectuate an 

authorization were in effect when 

Congress amended the MMPA in 1994 

to add section 101(a)(5)(D) for issuance 

of one-year IHAs, and over the years 

when Congress amended section 

101(a)(5)(A) for various reasons 

(including most recently in 2018, to 

extend the maximum authorization 

period to seven years for military 

readiness activities, Pub. L. 115–232 

(John S. McCain National Defense 

Authorization Act for Fiscal Year 2019) 

(Aug. 13, 2018)). Presumably Congress 

was aware of these implementing 

regulations and the framework they 

created for authorizing take under 

section 101(a)(5)(A) and could have 

invalidated those regulations had it so 

desired. 

Under NMFS’ approach, the 

negligible impact analysis for the 

rulemaking is conducted for the time 

period covered by the rule (five years in 

this case, the maximum under the 

statute for a non-military readiness 

activity), but the small numbers analysis 

attaches to the instrument that actually 

‘‘allows’’ or authorizes taking, i.e., the 

LOA. The statute does not preclude 

NMFS from issuing an LOA that 

comports with the small numbers level 

set forth in the relevant rule for the 

specified activity. Consistent with the 

MMPA requirement, here the Secretary 

(through NMFS) has prescribed the 

necessary specified activity regulations 

after notice and comment. At that point, 

once the regulations are effective, NMFS 

thereafter may authorize incidental take 

through the issuance of LOAs, provided 

that they satisfy the requirements set 

forth in the rule and regulations, 

including the small numbers standard 

articulated in the rule. 

NRDC cites Conservation Council for 

Hawaii v. NMFS, 97 F. Supp. 3d 1210 

(D. Hawaii 2015), in stating that the 

MMPA ‘‘plainly requires that the agency 

evaluate both whether there will be 

small numbers of take and whether 

there will be a negligible impact’’ before 

issuing regulations, and that these 

determinations ‘‘must be based on the 

same amount of take.’’ We disagree. In 

NMFS’ view, Conservation Council for 

Hawaii stands for the proposition that 

NMFS cannot authorize more take than 

it has analyzed under the negligible 

impact standard. 97 F. Supp. 3d at 1221. 

There the court found that there were 

substantial differences between the 

anticipated take numbers, which were 

the basis for the negligible impact 

finding, and the amount of take that 

NMFS was prepared to authorize 

incidental to U.S. Navy military 

readiness activities. That case did not 

even involve the small numbers 

provision, which does not apply in the 

case of military readiness activities. 16 

U.S.C. 1371(a)(5)(F)(i). The court in 

Conservation Council for Hawaii did not 

consider or make any pronouncements 

about whether the small numbers 

provision must be applied to the total 

annual taking under the rule or whether 

it could be applied at the LOA stage. 

NRDC repeatedly states that the 

negligible impact and small numbers 

provisions must have separate meaning. 

NMFS agrees that the two provisions do 

have separate meanings, and this rule 

satisfies that requirement. Each LOA 

must meet the small numbers 

requirement as NMFS has interpreted it 

in this rule. In other words, it is not 

sufficient for the survey activity 

described in an LOA application to fall 

within the scope of the activity analyzed 

for the rule and NMFS’ negligible 

impact determination. The small 

numbers limitation also must be 

satisfied. For example, NMFS may 

receive an application for an LOA where 

the take estimates exceed the small 

numbers standard identified in the rule. 

In that case, the request would be 

denied, even if the amount of taking was 

considered in the negligible impact 

evaluation. Thus the negligible impact 

and small numbers inquiries are 

separate and have different meanings. 

To summarize, the MMPA is silent on 

how to apply ‘‘small numbers’’ in either 

section 101(a)(5)(A) or (D), including in 

a way that allows for consistency across 

those two very similar provisions. 

Moreover, NMFS’ implementing 

regulations for section 101(a)(5)(A) 

make it clear that LOAs are the 

instrument for authorizing take. Thus, 

the mere existence of regulations under 

101(a)(5)(A) for a specified activity is 

not sufficient to authorize take under 

that provision. An LOA is required. 

As we have previously stated, the 

small numbers standard has limited 

biological relevance (i.e., there is a lack 

of a biological underpinning for the 

concept), but NMFS’ application of the 

small numbers standard at the LOA 

stage does not rely on that view for the 

approach taken here (and moreover, 

NMFS did not receive any public 

comments offering an alternative 

definition that is rooted in biological 

concepts or is not conflated with 

negligible impact considerations). As 

the notice of proposed rulemaking 

explained, NMFS’ interpretation and 

approach are based on analysis of the 

governing section 101(a)(5)(A) and 

limited legislative history, as well as 

consideration of section 101(a)(5)(D), 

and our long-standing approach to 

implementing section 101(a)(5)(A) 

through separate LOAs. NMFS has 

determined that the statute is 

ambiguous in terms of what small 

numbers means and how ‘‘small 

numbers’’ must be applied, which 

affords the agency reasonable discretion 

in how to do so. After weighing various 

policy considerations, NMFS exercised 

its discretion to define small numbers 

and apply small numbers 

determinations at the LOA level. 

Importantly, the final rule, which was 

subject to notice and comment, sets the 

small numbers standard for future LOAs 

issued under the rule. Moreover, 

contrary to NRDC’s assertions, NMFS 

has set the total taking allowable for all 

LOAs issued under the rule for this 

specified activity—i.e., the taking that 

was analyzed for the negligible impact 

determination. If an LOA application for 


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7We further note that population biology often 

focuses on annual cycles. See, e.g., 50 CFR 216.103 

(negligible impact defined in terms of impacts on 

annual rates of recruitment or survival); 16 U.S.C. 

1386(a), (c) (requiring stock assessment reports to 

estimate the annual human-caused mortality and 

serious injury of the stock, and annual review of 

stock assessments when significant new 

information is available that may indicate the stock 

assessment should be revised); 16 U.S.C. 1362(26) 

(defining ‘‘net productivity rate’’ as the annual per 

capita rate of increase in a stock resulting from 

additions due to reproduction, less losses due to 

mortality); 16 U.S.C. 1383a(l)(ii) (requiring MMC’s 

recommended guidelines to govern the incidental 

taking of marine mammals in the course of 

commercial fishing operations, to the maximum 

extent practicable, to include as a factor to be 

considered and utilized in determining permissible 

levels of taking ‘‘the abundance and annual net 

recruitment of such stocks’’). 

8The one exception to date is NMFS’ regulation 

governing the incidental take from explosive 

removal of offshore structures in the GOM (EROS), 

promulgated at the request of the Minerals 

Management Service on behalf of multiple private 

removal companies that individually submitted 

LOA requests. NMFS’ rulemaking for the EROS 

regulations evaluated the estimated annual take 

based on MMS’ projections for the specified activity 

as a whole, i.e., for all operators combined. Our rule 

here is consistent with the EROS rulemaking as it 

relates to the approach for the negligible impact 

evaluation. However, the EROS rule also concluded 

the total annual taking (by species) for all operators 

combined met the small numbers requirement. 

Thus NMFS did not have occasion before now to 

consider whether it could apply the small numbers 

provision at an individual LOA level where there 

are multiple concurrent LOA holders. Having now 

considered the question, NMFS believes the MMPA 

affords the discretion to do so. 

a survey provides take estimates that are 

within the small numbers threshold set 

in this rule, then the LOA for that 

survey will be deemed to satisfy the 

small numbers requirement. 

As NRDC correctly points out, NMFS’ 

implementing regulations require 

issuance of LOAs to be consistent with 

the ‘‘total taking allowable’’ under the 

activity-specific regulations. The 

regulations for the specified activity also 

reflect this. The rulemaking for these 

regulations evaluated the level of 

activity projected in BOEM’s update for 

its petition, and NMFS’ negligible 

impact determination is based on 

consideration of that level (as are the 

corresponding take estimates). Any LOA 

must be within the amount analyzed for 

the scope of the rule, and the total 

amount of take under all issued LOAs 

combined cannot exceed the amount 

analyzed and ‘‘allowable’’ under the 

rule for this activity. 

Regarding the differences between the 

processes under sections 101(a)(5)(A) 

and (D), we did not mean to suggest that 

section 101(a)(5)(A) is necessarily or 

always more protective than and 

preferable to 101(a)(5)(D). Rather, 

section 101(a)(5)(A), which can span a 

longer period of time and cover multiple 

applicants through issuance of LOAs, 

allows for a more comprehensive/ 

holistic analysis by the agency (one 

negligible impact analysis for all 

activities over the five-year (or less) 

period and consideration of mitigation 

appropriate for the full suite of 

activities). Such an approach has the 

potential to be more protective because 

it allows for a more comprehensive 

understanding of impacts, as well as a 

mechanism to include holistic 

mitigation that can more effectively 

address both acute and chronic effects 

resulting from multiple activities 

covered under a rule. Section 

101(a)(5)(A) also focuses public 

attention on one rulemaking (rather 

than—as would be the case for these 

survey activities—potentially dozens of 

IHA actions per year, each with separate 

notice and comment), and allows for 

other administrative efficiencies. We 

note that BOEM applied for the 

regulations in support of the oil and gas 

industry, and prepared an EIS in 

support of its own program related to 

the permitting of the survey activities 

that are the subject of this MMPA 

application and rulemaking. 

NRDC claims that the approach ‘‘is a 

novel interpretation of the MMPA.’’ 

However, the rule cited in support of 

their argument (81 FR 47240; July 20, 

2016) is consistent with one aspect of 

our approach here, in that the small 

numbers determinations in both 

contexts are based on annual take 

estimates, not total take over the fiveyear period of the regulations.7 We 

acknowledge that we have not 

previously determined that small 

numbers could be applied at the 

individual LOA stage where more than 

one LOA applicant may apply under the 

activity-specific regulations. However, 

that is simply because the issue had not 

previously presented itself. In nearly all 

cases to date,8 there has been a single 

operator who is the sole applicant for 

both the LOA (or LOAs if they cover less 

than the five-year period) and the 

governing specified activity regulations. 

As a result, in such a scenario, the small 

numbers determination by default 

corresponds to the maximum annual 

taking covered by the regulation (and 

the LOA). But even when there is only 

one applicant for LOAs under a 

regulation, NMFS does not tally take 

across the five-year period for purposes 

of assessing small numbers. Rather, 

NMFS assesses annual levels of take. 

(This also promotes consistency 

between 101(a)(5)(A) and 101(a)(5)(D) to 

avoid incentivizing IHAs at the expense 

of LOAs issued under more 

comprehensive rules.) 

Finally, NRDC’s statement that the 

public is impermissibly cut out of the 

agency’s findings is incorrect. The 

proposed rule set forth the maximum 

total taking and annual taking that 

would be allowable (via the issuance of 

LOAs) for the five-year period that the 

regulations will be effective, which was 

based on information contained in 

BOEM’s publicly available application 

and PEIS. Those figures decreased for 

all but two species. For the two species 

where the figures increased, we 

evaluated those changes and determined 

they do not represent a meaningful 

change for our analyses. See Changes 

From the Proposed Rule. 

The proposed rule included a 60-day 

public comment period. We also believe 

that our rulemaking afforded a full and 

focused opportunity for public review of 

and comment on the full scope of 

survey activities and proposed 

mitigation, rather than through dozens 

of individual IHAs, each with 30-day 

public comment periods and shorter 

timeframes for NMFS to consider the 

public comments. Thus the public had 

a meaningful opportunity to comment. 

Comment: Citing their interpretation 

of the statute and multiple judicial 

decisions, the MMC suggests that 

NMFS’ interpretation and 

implementation of the small numbers 

standard is contrary to law and further 

recommends that NMFS adopt a policy 

interpreting the small numbers 

requirement of section 101(a)(5)(A) such 

that it: 

• Requires determinations be made 

when issuing incidental take regulations 

(as opposed to when LOAs are issued); 

• makes such determinations based 

on the total take authorized incidental 

to the specified activity and for the full 

duration covered by those regulations 

(as opposed to for each LOA and on an 

annual basis); and 

• provides an opportunity for public 

notice and comment on all small 

numbers determinations. 

Response: As explained in the 

responses above and discussion under 

the Small Numbers section of this 

preamble, NMFS disagrees, based on 

our analysis of the statute, the 

legislative history, the implementing 

regulations, and relevant case law. 

NMFS issues incidental take 

authorizations under section 

101(a)(5)(A) through LOAs, provided 

that we satisfy the relevant statutory 

standards. Analysis of that statutory 

provision and relevant legislative 

history, including when read in 

conjunction with section 101(a)(5)(D), 

leads NMFS to conclude that the small 

numbers limitation may be applied at 

the LOA stage, provided that we make 

the negligible impact finding for the 

total taking allowable under the 

regulations for the specified activity and 


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set the small numbers standard for 

future LOAs in the notice and comment 

rulemaking. 

As noted above, the term ‘‘small 

numbers’’ is not defined in the statute. 

Over the years NMFS has grappled with 

how to define the term, particularly 

given the limited legislative history (i.e., 

‘‘accidental, infrequent, or 

unavoidable’’; ‘‘not capable of being 

expressed in absolute numerical 

terms’’). Recent court decisions lend 

support for NMFS’ proportional 

approach to the concept. See Center for 

Biological Diversity v. Salazar, 695 F.3d 

893 (9th Cir. 2012). In terms of what 

proportion may constitute ‘‘small 

numbers’’ for purposes of what the 

Secretary may authorize, NMFS has 

determined that small numbers means 

up to one-third of a species or stock. 

NMFS has further determined that this 

limit can be applied at the LOA level, 

subject to a finding that the total taking 

allowable (through any and all LOAs 

issued under the activity-specific rule 

and corresponding regulations) satisfies 

the negligible impact standard. 

The MMC inaccurately states that the 

‘‘interpretation of the small numbers 

requirement proposed by NMFS in 

many ways seeks to maximize the 

numbers of takes of marine mammals 

that may be authorized under a single 

rulemaking.’’ With one exception, the 

points raised by the MMC reflect NMFS’ 

existing practice. The decision to make 

small numbers findings on an LOAspecific basis is the only new 

development and, as explained in the 

response to the previous comment, 

came about only when the issue arose 

for the first time in the context of this 

rulemaking. NMFS considered the 

specific issue, determined that section 

101(a)(5)(A) does not unambiguously 

speak to it, and reasonably exercised its 

discretion in determining that small 

numbers findings could apply at the 

LOA stage, provided that the standard is 

set forth in the rule itself, which it is. 

We acknowledge that section 

101(a)(5)(A) does not expressly 

contemplate the issuance of LOAs, 

which are a creature of NMFS and U.S. 

Fish and Wildlife Service (FWS) joint 

implementing regulations for section 

101(a)(5)(A). (See 50 CFR 216 subpart I 

(NMFS regulations); 50 CFR 18.27 (FWS 

regulations)). Those implementing 

regulations, in effect since 1989, 

established LOAs as the regulatory 

instrument to authorize lawful 

incidental take under section 

101(a)(5)(A), after the promulgation of 

activity-specific regulations that 

undergo notice and comment 

rulemaking. 

Although not the typical scenario, 

NMFS’ implementing regulations allow 

for the issuance of LOAs to more than 

one ‘‘U.S. citizen’’ taking marine 

mammals under a specified activity 

regulation, see, e.g., 50 CFR 216.105(a); 

216.106(e); (54 FR 40338 (September 29, 

1989)), provided that the negligible 

impact finding is made for the total 

taking for the specified activity as a 

whole, by all entities conducting that 

activity. 

NMFS also administers section 

101(a)(5)(D), a very similar provision 

enacted in 1994 that established an 

expedited process for the issuance of 

one-year incidental take authorizations 

for the taking of small numbers of 

marine mammals by harassment only 

when the taking from the specified 

activity is found to have a negligible 

impact on the affected species or stocks 

of marine mammals (referred to as 

incidental harassment authorizations, or 

‘‘IHAs’’). See the Small Numbers section 

later in this Notice. The small numbers 

standard in section 101(a)(5)(D) applies 

to each individual one-year IHA, yet the 

same small numbers language also 

appears in section 101(a)(5)(A). In 

NMFS’ view, the statute is silent on how 

to apply the same small numbers 

limitation in these two provisions across 

potentially different scales and 

timeframes. In the case such as here, 

where serious injury or mortality is not 

expected from the activity (and would 

not be authorized in any LOA), each 

prospective LOA applicant could 

instead opt to apply for an IHA under 

section 101(a)(5)(D). It would be an 

absurd result to deny an LOA for a 

single geophysical survey on the sole 

basis that small numbers is not satisfied 

because the take numbers from that 

survey must be aggregated with the 

takes from other surveys occurring 

under the same regulations, only to turn 

around and issue an IHA for the same 

survey, simply because the applicant 

has decided to avail itself of section 

101(a)(5)(D) instead. But that would be 

the result under the MMC’s approach. 

Given NMFS’ implementing regulations 

for section 101(a)(5)(A), which are 

authorized under 16 U.S.C. 1382(a), and 

when viewed in light of section 

101(a)(5)(D) and applying our 

administrative experience, NMFS has 

determined our approach is a reasonable 

interpretation of how to carry out 

section 101(a)(5)(A) and the 

implementing regulations in the context 

of these two statutory provisions. This 

is a reasoned approach that draws on 

NMFS’ expertise. 

Further, authorization of take 

incidental to geophysical survey activity 

within the covered regions of the GOM 

under this ITR allows for the more 

comprehensive evaluation and 

management of take of marine mammals 

than if NMFS were to authorize take for 

those same activities under IHAs. NMFS 

worked with BOEM and its predecessor 

agency over many years to ensure a 

process that holistically analyzed the 

impacts from expected geophysical 

surveys in the GOM. This is preferable 

first and foremost for its greater 

likelihood of achieving the best 

substantive impact analysis and 

comprehensive management (including 

mitigation and monitoring) scheme, but 

the process is also efficient for 

stakeholders (regulated industry and 

interested members of the public) and 

results in more efficient use of 

administrative agency resources. 

The MMC argues that NMFS’ 

implementing regulations support the 

MMC’s view of the application of small 

numbers, because ‘‘whereas the 

regulatory section governing the 

issuance of incidental take regulations 

(50 CFR 216.105) includes a reference to 

the small numbers requirement, the 

section governing LOAs (50 CFR 

216.106) omits any reference to that 

requirement.’’ However, the 

implementing regulations originally 

defined small numbers as synonymous 

with negligible impact. NMFS no longer 

interprets small numbers in that way, 

but as a result of that original approach, 

the MMC’s particular citations do not 

shed light on the permissible approach 

for making a small numbers 

determination as that term is now 

interpreted. 

NMFS agrees with the MMC that 

workload alone would not be a 

sufficient basis for our interpretation, 

and it is not what we rely on. Rather, 

the analysis we presented leads us to 

conclude that NMFS has discretion to 

apply small numbers at the LOA level 

and, in this case, policy considerations 

supported that approach. 

Comment: NRDC states that NMFS’ 

interpretation of small numbers ‘‘leads 

to absurd results and permits excessive 

take.’’ 

Response: NMFS’ negligible impact 

assessment evaluated the risk to the 

affected species and stocks of marine 

mammals, taking into account the 

amount and severity of anticipated take 

(and take the agency is prepared to 

authorize) as well as the status of the 

species and mitigation/monitoring. Of 

note, and as indicated in Changes from 

the Proposed Rule, as a result of 

BOEM’s updated scope of the activities 

and the associated revisions to the 

levels of effort, both the maximum 

allowable amount of take under the rule, 

as well as the maximum annual take, 


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has decreased (significantly in some 

cases) for all species and stocks except 

two, for which maximum allowable take 

and/or maximum annual take increased 

slightly, and the severity of many of the 

impacts has been lessened via the 

elimination and/or reduction of take in 

areas of greater biological importance 

previously considered as mitigation 

areas. 

The numbers of potential incidents of 

take or animals taken are only part of an 

assessment and are not, alone, 

decisively indicative of the degree of 

impact. In order to adequately evaluate 

the effects of noise exposure at the 

population level, the total number of 

take incidents must be further 

interpreted in context of relevant 

biological and population parameters 

and other biological, environmental, 

and anthropogenic factors and in a 

spatially and temporally explicit 

manner. The effects to individuals of a 

‘‘take’’ are not necessarily equal. Some 

take events represent exposures that 

only just exceed a Level B harassment 

threshold, which would be expected to 

result in lower-level impacts, while 

other exposures (fewer, as the exposure 

modeling effort illustrates) occur at 

higher received levels and would 

typically be expected to have 

comparatively greater potential impacts 

on an individual. Further, responses to 

similar received levels may result in 

significantly different impacts on an 

individual dependent upon the context 

of the exposure or the status of the 

individuals (e.g., if it occurred in an 

area and time where concentrated 

feeding was occurring, or to individuals 

weakened by other effects). Last, 

impacts of a similar degree on a 

proportion of the individuals in a stock 

may have differing impacts to the stock 

based on its status, i.e., smaller stocks 

may be less able to absorb deaths or 

reproductive suppression and maintain 

similar growth rates as larger stocks. 

Comment: The MMC recommended 

that if such determinations are made 

based on a proportion of a species’ or 

stock’s abundance, NMFS adopt a 

policy interpreting the small numbers 

requirement of section 101(a)(5)(A) such 

that it: (1) Include a sliding scale, such 

that a lower proportion is allowed as 

stock size increases, and (2) include an 

evaluation of the relative risk that the 

established threshold would be 

exceeded if the best available 

population estimate or some other 

metric, such as a minimum or 

intermediate population, is used. 

Response: NMFS disagrees with these 

recommendations. Under the ‘‘onethird’’ interpretation offered here, and 

on which we will base our small 

numbers analyses when evaluating LOA 

applications under this rule, take 

equating to greater than one-third of the 

predicted individuals in the population 

would generally not be considered small 

numbers. The MMC presents an 

example from a very large population, 

asserting that an amount of take that 

would meet NMFS’ proportional small 

numbers standard would not 

appropriately be considered ‘‘small’’ 

because it is large in terms of absolute 

magnitude. The MMC does not present 

a rationale for why its proposed sliding 

scale approach is more appropriate, nor 

does it provide an explanation of what 

the drawbacks are (biological or 

otherwise) of authorizing takes of large 

numbers of marine mammals (in the 

absolute sense) from a significantly large 

(and arguably healthier and more 

robust) population (even where still less 

than one-third of the population under 

NMFS’ proportional approach). We have 

determined that a proportional 

approach is the appropriate way to 

interpret small numbers, not an absolute 

‘‘on its face’’ numeric standard. 

Accordingly, absolute numbers would 

not be relevant to our small numbers 

determinations. There is no meaningful 

way to define what should be 

considered as a ‘‘small’’ number on the 

basis of absolute magnitude, and the 

MMC offers no such recommendation. 

Mitigation, Monitoring, and Reporting 

Comment: NRDC states that NMFS 

should include a year-round area 

closure for Bryde’s whales. Specifically, 

NRDC states that this should include the 

following: (1) Excluding airgun surveys 

year-round from the whales’ occupied 

habitat; (2) excluding airgun surveys 

from areas identified, through modeling, 

as most likely to propagate lowfrequency sound into the Bryde’s 

whales’ habitat; and (3) establishing 

mitigation to reduce noise in the 

whales’ unoccupied habitat, i.e., areas 

they are likely to have inhabited 

according to the whaling records and 

have habitat characteristics similar to 

those of the De Soto canyon. The MMC 

also recommends that NMFS include a 

year-round area closure for Bryde’s 

whales, while agreeing that the area 

defined by NMFS in the proposed rule 

is appropriate. In addition, a private 

citizen commented that a year-round 

closure is more appropriate than a 

seasonal closure, because Bryde’s 

whales use the area year-round. The 

Associations and other industry 

commenters argue to the contrary, 

stating that there should be no 

restriction within the Bryde’s whale 

area and that, if a restriction is required, 

it should be seasonal rather than yearround. The Associations also state that 

if implemented, the restriction area 

should be smaller. With regard to the 

other alternative offered by NMFS for 

comment—no restriction but a 

requirement to conduct real-time whale 

detection through use of a moored 

listening array—the Associations state, 

‘‘the final ITR should not impose a 

moored array requirement because the 

limits inherent in such data are 

outweighed by the impracticability of 

such arrays.’’ The CRE also comments, 

with no supporting information, that 

there should be no restriction on survey 

effort in the Bryde’s whale core habitat 

area. 

Response: As described in the 

proposed rule, NMFS agrees with NRDC 

and the MMC that the status (e.g., small 

population size, restricted distribution, 

anthropogenic effects, small population 

effects) of the recently ESA-listed GOM 

Bryde’s whale warranted the 

consideration of a year-round closure to 

airgun surveys within the area described 

as core habitat for the whale (Area #3). 

We disagree with the Associations’ 

arguments that no requirement is 

warranted. However, the comments 

specifically relating to the need (or lack 

thereof) to impose a restriction on 

survey effort in Bryde’s whale core 

habitat, the duration of any such 

restriction, or any additional 

requirements in the core habitat area, 

are no longer relevant following BOEM’s 

updated scope of activity. This update 

means that no survey effort within 

Bryde’s whale core habitat is considered 

through this rulemaking and the vast 

majority of any anticipated or 

authorized impacts to this species have 

been eliminated. Please see Table 1 and 

Figure 2, earlier in this notice. 

Regarding NRDC’s recommendations 

for establishing Bryde’s whale 

mitigation measures beyond the core 

habitat area identified in the notice of 

proposed rulemaking, NMFS does not 

believe these are warranted. We initially 

note that the comment uses the terms 

‘‘occupied and ‘‘unoccupied’’ to 

describe habitat. These are terms of art 

in the Endangered Species Act and 

implementing regulations for 

designation of ‘‘critical habitat.’’ For this 

MMPA rulemaking, the correct standard 

is measures to effect the ‘‘least 

practicable adverse impact’’ on the 

affected species or stocks and their 

habitat. NMFS has now determined that 

additional geographic-based mitigation 

for Bryde’s whales is not warranted. 

Following BOEM’s update to the scope 

of their specified activity, expected 

takes of Bryde’s whales are significantly 

reduced in the remaining area where the 

specified activity will occur under this 


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rule (i.e., there are now no more than 10 

anticipated instances of take annually; 

see Table 9). 

Regarding NRDC’s comments that 

additional protections are needed in 

areas that are ‘‘unoccupied’’ by the 

Bryde’s whale, we disagree. NMFS’ 

objective in requiring a closure would 

be to minimize the effects of airgun 

surveys on Bryde’s whales while in 

important habitat. In areas where 

modeling and/or observational data 

show a species or stock is unlikely to 

occur during the period of the rule, it is 

generally unlikely that a geographic or 

other mitigative restriction would 

reduce impacts from the specified 

activities on the species or stock and its 

habitat, and therefore is not justifiable 

absent some other compelling basis. 

Finally, we are unsure of what NRDC 

might mean in recommending exclusion 

of surveys from areas identified as most 

likely to propagate low-frequency sound 

into Bryde’s whale habitat, or whether 

such areas are still covered by the rule 

given BOEM’s updated scope, and 

NRDC provides no meaningful 

justification for the recommendation, 

nor any useful recommendations for 

how such areas could be identified. 

Comment: In reference to NMFS’ 

statement that the agency does not 

consider towed passive acoustic 

monitoring (PAM) to be a useful tool 

with regard to detection of Bryde’s 

whales, the Associations state that they 

do believe more typical real-time 

detection-based mitigation, such as use 

of towed PAM, should provide 

sufficient protection for Bryde’s whales, 

and assert that we did not provide 

sufficient information to meaningfully 

comment on the conclusion. 

Response: It is generally wellaccepted fact that, even in the absence 

of a firing airgun, using a towed passive 

acoustic sensor to detect baleen whales 

(including Bryde’s whales) is not 

typically effective because the noise 

from the vessel, the flow noise, and the 

cable noise are in the same frequency 

band and will mask the vast majority of 

baleen whale calls. Further, Bryde’s 

whales have relatively short calls, 

further exacerbating the problem. As 

background, airguns produce loud, 

broadband, impulsive signals at low 

frequencies (e.g., Hildebrand, 2004). 

Source characteristics are variable but 

typically peak pressures are in the 5– 

300 Hz frequency range, with source 

levels as high as 260 dB peak re 1 mPa 

at 1 m output pressure (Hildebrand, 

2009). Pulse rates are typically one per 

10–20 s (Hildebrand, 2009). Seismic 

survey noise can raise background noise 

levels by 20 dB or more over large areas 

while present. Because the seismic 

pulse and the whale’s call are within the 

same frequency range, and the seismic 

pulse is much louder than the whale’s 

call (see below), it is extremely unlikely 

that a baleen whale can be detected 

during the pulse. In addition to the 

actual seismic pulse (approximately 

every 10–20 s), the background noise 

level is expected to be significantly 

increased as a result of the reverberant 

field generated from seismic pulses 

(Guerra et al., 2011; Guan et al., 2015), 

i.e., during the inter-pulse interval. The 

level of elevated inter-pulse noise levels 

can be as high as 30–45 dB within 1 km 

of an active 3,147 in3 airgun array 

(Guerra et al., 2011). Given that towing 

hydrophones for PAM used for marine 

mammal monitoring would be within 1 

km from the airgun source, the received 

noise spectral density during the interpulse interval is expected to be very 

high. 

Vessels also produce low-frequency 

noise, primarily through propeller 

cavitation, with main energy also in the 

5–300 Hz frequency range. Source levels 

range from about 140 to 195 dB re 1 mPa 

at 1 m (NRC, 2003; Hildebrand, 2009), 

depending on factors such as ship type, 

load, and speed, and ship hull and 

propeller design. Studies of vessel noise 

show that it appears to increase 

background noise levels in the 71–224 

Hz range by 10–13 dB (Hatch et al., 

2012; McKenna et al., 2012; Rolland et 

al., 2012). PAM systems employ 

hydrophones towed in streamer cables 

approximately 500 m behind a vessel. 

Noise from water flow around the cables 

and from strumming of the cables 

themselves is also low-frequency and 

typically masks signals in the same 

range. 

GOM Bryde’s whale calls have 

relatively low source levels (155 dB re 

1mPa) and frequency ranges (78–110 Hz; 

Sˇirovic ́ et al., 2014) that overlap the 

sounds described above. In addition, 

GOM Bryde’s whales call only 

infrequently (i.e., a 3.5 hour research 

encounter with 4 whales resulted in 

detections of 14 calls). The chances of 

acoustically detecting these whales is 

low under ideal research circumstances, 

is much lower with elevated 

background noise from the ship and 

towing cable, and essentially impossible 

with an airgun array shooting. Whales 

are routinely detected acoustically using 

moored systems and sonobuoys, or 

using autonomous gliders. However, 

these platforms are all quiet. A leading 

provider of observer services for the 

seismic industry, including PAM, 

reports that they have never detected a 

baleen whale (other than rare detections 

of humpback whales, which have 

significantly higher frequency content 

in their call) using PAM aboard a 

working seismic vessel (S. Milne, RPS 

Group, pers. comm.). Experienced PAM 

operators participating in a recent 

workshop (Thode et al., 2017) 

emphasized that a PAM operation could 

easily report no acoustic encounters, 

depending on species present, simply 

because background noise levels 

rendered any acoustic detection 

impossible. The same workshop report 

stated that a typical eight-element array 

towed 500 m behind a seismic vessel 

could be expected to detect delphinids, 

sperm whales, and beaked whales at the 

required range, but not baleen whales, 

due to expected background noise levels 

(including seismic noise, vessel noise, 

and flow noise). 

Comment: The Associations provided 

comments regarding NMFS’ proposed 

power-down exception to the general 

shutdown requirements for certain 

species of dolphin, as well as the related 

alternative of no shutdown or powerdown requirement. The Associations 

stated that no shutdowns for dolphins 

are warranted, and added that an 

exception should not be limited to small 

dolphins but rather should be expanded 

to all delphinid species. The MMC 

recommended that NMFS not require a 

shutdown or power-down when small 

delphinids enter the exclusion zone, 

and relatedly suggested that NMFS 

should provide clarification as to the 

basis for exempting only small 

delphinids from shutdowns. The MMC 

stated their agreement with NMFS that 

shutting down when small delphinids 

enter the exclusion zone is not 

warranted and may result in additional 

survey activity. Furthermore, as 

indicated in the MMC comments, 

power-down may not be effective. The 

MMC stated that, given the variation in 

array characteristics and configuration, 

a requirement to ‘‘power-down’’ does 

not provide sufficient assurance that the 

resulting received levels would be 

below the Level B harassment threshold. 

CGG provided a detailed analysis of the 

potential operational costs associated 

with dolphin shutdowns or powerdowns, supporting their comment that 

these costs would be substantial and 

that shutdown or power-down should 

not be required. NRDC provided 

multiple objections to NMFS’ proposals, 

stating that of the two proposals they 

favor power-down. 

Response: Following review of the 

available information and public 

comments, NMFS agrees that a general 

exception to the standard shutdown 

requirement is warranted for small 

delphinids, and that the alternative 

power-down requirement may not be 

effective and yet could impose costs on 


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operators. (Here we refer to ‘‘large 

delphinids’’ and ‘‘small delphinids’’ as 

shorthand for generally deep-diving 

versus surface-dwelling/bow-riding 

groups, respectively, as the important 

distinction is their dive behavior rather 

than their size.) As NMFS discussed in 

the notice of proposed rulemaking, midand high-frequency cetaceans are 

relatively insensitive to the frequencies 

where the most energy in an airgun 

signal is found. In order to demonstrate 

this quantitatively, a ‘‘spectral ratio’’ 

may be calculated for each hearing 

group. This ratio essentially compares 

the energy in a group-specific weighted 

airgun source spectrum with the energy 

in an unweighted airgun source 

spectrum, providing a representation of 

the proportion of total energy from the 

unweighted airgun spectrum that is 

available for animals to hear based on 

their group-specific general auditory 

filter shapes, which presumably 

influences the probability of behavioral 

response. Using M-weighting (i.e., Type 

I filters), spectral ratios for the three 

hearing groups are as follows: LF, 0.71; 

MF, 0.03; HF, 0.02. 

However, NMFS does not agree that 

the available evidence supports certain 

commenters’ assertions that seismic 

surveys do not have any adverse effects 

on dolphin species. As discussed in 

Mitigation, auditory injury is not 

expected for dolphins, but the reason for 

dolphin behavior around vessels (when 

they are attracted) is not understood and 

cannot be assumed to be harmless. In 

fact, the analyses of Barkaszi et al. 

(2012), Stone (2015a), Stone et al. 

(2017), and Barkaszi and Kelly (2018) 

show that dolphins do avoid working 

vessels. That said, the available 

information does not suggest that such 

reactions are likely to have meaningful 

energetic effects to individuals such that 

the effectiveness of such measures 

outweighs the practicability concerns 

raised by commenters, in terms of the 

operational costs as well as the 

difficulty of implementation. 

As noted above, the proposed rule 

included an alternative in which a 

power-down requirement would be 

required. However, following review of 

public comments, NMFS believes that a 

power-down requirement would 

potentially lead to the need for 

termination of survey lines and infill of 

the line where data were not acquired 

if a power-down was performed 

according to accepted practice, in which 

the power-down condition would last 

until the dolphin(s) are no longer 

observed within the exclusion zone. The 

need to revisit missed track line to 

reacquire data is likely to result in an 

overall increase in the total sound 

energy input to the marine environment 

and an increase in the total duration 

over which the survey is active in a 

given area. 

NMFS disagrees with comments that 

no shutdown requirements should 

apply to any delphinid species 

regardless of behavior. As noted above, 

industry commenters have asserted that 

no shutdown requirements are 

warranted for any delphinid species, 

stating that the best available science 

does not support imposing such 

requirements. The industry comments 

acknowledge that small delphinids are 

more likely to approach survey vessels 

than large delphinids, but claim without 

supporting data that there is no 

evidence that large delphinids will 

benefit from a shutdown requirement. In 

contrast to the typical behaviors of (and 

observed effects on) the small delphinid 

species group, the typical deep diving 

behavior of the relatively rarely 

occurring large delphinid group of 

species makes these animals potentially 

susceptible to interrupted/delayed 

feeding dives, which can cause 

energetic losses that can accrue to affect 

fitness. As described in greater detail in 

the notice of proposed rulemaking, there 

are ample data illustrating the responses 

of deeper diving odontocetes (including 

large delphinids) to loud sound sources 

(including seismic) to include 

interrupted foraging dives, as well as 

avoidance with increased speed and 

stroke rate, both of which may 

contribute to energetic costs through 

lost feeding opportunities and/or 

increased energy demands. Significant 

advances in study of the population 

consequences of disturbance are 

informing our understanding of how 

disturbances accrue to effects on 

individual fitness (reproduction and 

survival) and ultimately to populations 

via the use of energetic models, where 

data are available for a species, and 

expert elicitation when data are still 

limited. The link between behavioral 

disturbance, reduced energy budgets, 

and impacts on reproduction and 

survival is clear, as is the value in 

reducing the probability or severity of 

these behavioral disturbances where 

possible. Therefore, NMFS finds that 

there is support for the effectiveness of 

the standard shutdown requirement as 

applied to the large delphinid species 

group. 

Further, the claim that shutdowns for 

these deep-diving species would be 

impracticable was not accompanied by 

supporting data. The data available to 

NMFS demonstrates that this 

requirement is practicable. For example, 

recent synthesis of observer data in the 

GOM shows that large delphinids were 

sighted only rarely, and that of these 

sightings, almost half were not within 

the 500-meter exclusion zone. We note 

that the Associations provided a 

quantitative analysis of ‘‘historical PSO 

and PAM data from over 32,000 survey 

activity hours conducted in the GOM 

between 2007 and 2017,’’ but provide 

no citation for these data (nor the data 

itself). Therefore, we cannot verify or 

meaningfully evaluate the industrysupplied analysis. Nevertheless, as 

detailed herein, NMFS agrees in 

substantial part with the comments 

received and accordingly do not require 

shutdown or power-down for small 

delphinids detected within the 

exclusion zone. 

Comment: Several commenters 

criticized our proposal to require 

shutdowns upon detection of certain 

species or circumstances (e.g., beaked 

whales, Bryde’s whales) at any distance. 

The Associations suggest that such 

requirements are ‘‘arbitrary and 

unlawful’’ because they require 

shutdowns in ‘‘circumstances in which 

no disturbance or harassment will 

occur.’’ The Associations contend that 

PSOs are likely to make frequent 

‘‘precautionary’’ shutdown calls for 

uncertain observations ‘‘at any 

distance,’’ and that these measures will 

have negative impacts on the 

effectiveness of visual PSOs. CGG makes 

similar claims, stating that ‘‘there is no 

proven or likely efficacy to initiate a 

shutdown for cetaceans that are well 

outside of incidental take range’’ and 

concluding that the standard 500-m 

exclusion zone should be applied in 

these circumstances. The MMC 

commented that, in reference to the two 

proposals of ‘‘at any distance’’ or 

‘‘within 1 km,’’ they support the 

implementation of shutdowns for 

detections at any distance (rather than 

within 1 km of the airgun array), based 

on the status of the applicable species, 

their small population sizes, and their 

sensitivity to seismic sound. 

Response: As discussed below and in 

Mitigation, an extended shutdown 

distance of 1.5 km is included in the 

final rule, in lieu of the ‘‘at any 

distance’’ shutdown included in the 

proposed rule. We first note that the 

industry comments against proposed 

shutdowns for certain species, in their 

view beyond the range at which 

harassment may occur, appears to 

reflect an assumption that the singlestep 160-dB threshold is the relevant 

metric for harassment. Even if this were 

the case, the minimum distance to the 

160-dB isopleth, based on 60 different 

propagation modeling scenarios, would 

be beyond the likely detection distance 

for visual observers. The smallest 


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threshold radius to the 160-dB isopleth 

is more than 7 km. However, the multistep probabilistic risk function used 

here assumes that 10 percent of the 

population exposed above 140 dB 

would experience harassment; isopleth 

distances to 140 dB, based on the same 

modeling exercise, are typically greater 

than 50 km (minimum of approximately 

29 km). Even the 90 percent harassment 

isopleth (i.e., 180 dB) has a mean 

distance of 1.6 km. Therefore, the claims 

that shutdowns upon detection ‘‘at any 

distance’’ would occur in circumstances 

where there is no harassment are 

incorrect. The Associations’ comments 

are also inconsistent in that they imply 

both that marine mammals are likely to 

be detected at ranges significantly 

distant from the vessel, where 

shutdowns would be effected on 

detection of animals not subject to 

harassment, and that marine mammals 

cannot be adequately identified beyond 

close distances, resulting in unnecessary 

‘‘precautionary’’ shutdowns. NMFS 

agrees that visual monitoring under 

typical circumstances is unlikely to be 

effective at ranges much beyond the 

extended distance shutdown of 1.5 km, 

while under ideal circumstances 

acoustic detectability will also be 

limited to within the exclusion zone 

distance. (NMFS presented a detailed 

analysis in the notice of proposed 

rulemaking demonstrating that acoustic 

detections of sperm whales during 

active firing of an airgun array are not 

likely beyond approximately 500 m). 

Moreover, we specify in these 

regulations that shutdowns are required 

on positive identification of relevant 

species (as determined through 

professional judgment), meaning that 

there is no real likelihood that there 

would be numerous shutdowns based 

on false positive detections. Overall, it 

is unlikely that there will be 

‘‘unnecessary’’ shutdowns to any 

significant degree. 

The MMC provided the following 

supporting rationale to their comment: 

‘‘Bryde’s whales are LF cetaceans with 

particular sensitivity to the 

predominantly low-frequency energy 

output of airguns. Beaked whales are 

well-documented to react behaviorally 

to sound levels well below those 

thought to cause injury, and larger 

exclusion zones have been 

recommended for beaked whales and 

other deep-diving whales (such as Kogia 

spp. and sperm whales) as they are more 

likely to exhibit a stress response when 

disturbed (Wright et al., 2011).’’ NMFS 

agrees with these comments. In these 

cases, we have identified species or 

circumstances with particular 

sensitivities for which we determined it 

appropriate to minimize the duration 

and intensity of the behavioral 

disruption, as well as to minimize the 

potential for auditory injury (for lowand high-frequency cetaceans). 

NMFS disagrees with industry 

comments regarding the likelihood that 

trained, experienced professional PSOs 

would misunderstand the intent of a 

requirement to shut down upon 

detection ‘‘at any distance’’ and would 

therefore spend undue time focusing 

observational effort at distances beyond 

approximately 1,000 m from the 

acoustic source (i.e., the zone within 

which we assume that monitoring is 

typically focused, though not 

necessarily exclusively). Nevertheless, 

in order to ensure that this potential is 

minimized, and to address commenters’ 

concerns regarding the potential costs 

associated with shutdowns at any 

distance, especially in light of the 

diminished benefits of the measure 

beyond 1.5 km, we limit these 

shutdowns to within 1.5 km (versus at 

any distance). The rationale for this 

distance is explained later in this 

document in Mitigation. 

Comment: NRDC states that NMFS 

should require that ramp-up occur over 

several stages in order to minimize 

exposure. 

Response: NMFS agrees with NRDC 

on this point, which appears to restate 

the ramp-up procedures described by 

NMFS in the notice of proposed 

rulemaking. NMFS believes this 

approach is consistent with the 

Australian study referenced by NRDC. 

Comment: NRDC states that the 

standard 500-m exclusion zone is ‘‘not 

conservative,’’ asserting that NMFS did 

not explain why the proposed zone 

achieves the least practicable adverse 

impact and stating that NMFS must 

consider other exclusion zone distances. 

Response: NMFS has acknowledged 

that some limited occurrence of 

auditory injury is likely, for low- and 

high-frequency cetaceans. However, we 

disagree that a larger standard exclusion 

zone is warranted. As explained in the 

notice of proposed rulemaking, NMFS’ 

intent in prescribing a standard 

exclusion zone distance is to (1) 

encompass zones for most species 

within which auditory injury could 

occur on the basis of instantaneous 

exposure; (2) provide additional 

protection from the potential for more 

severe behavioral reactions (e.g., panic, 

antipredator response) for marine 

mammals at relatively close range to the 

acoustic source; (3) provide consistency 

and ease of implementation for PSOs, 

who need to monitor and implement the 

exclusion zone; and (4) to define a 

distance within which detection 

probabilities are reasonably high for 

most species under typical conditions. 

The use of 500 m as the zone is not 

based directly on any quantitative 

understanding of the range at which 

auditory injury would be entirely 

precluded or any range specifically 

related to disruption of behavioral 

patterns. Rather, NMFS believes it is 

based on a reasonable combination of 

factors. In summary, a practicable 

criterion such as this has the advantage 

of familiarity and simplicity while still 

providing in most cases a zone larger 

than relevant auditory injury zones, 

given realistic movement of source and 

receiver. Increased shutdowns, without 

a firm idea of the outcome the measure 

seeks to avoid, simply displace survey 

activity in time and increase the total 

duration of acoustic influence as well as 

total sound energy in the water, which 

NMFS seeks to avoid. 

NMFS agrees that, when practicable, 

the exclusion zone should encompass 

distances within which auditory injury 

is expected to occur on the basis of 

instantaneous exposure. For highfrequency cetaceans, this distance was 

modeled as 457 m (though we 

acknowledged that the actual distance 

would be dependent on the specific 

airgun array and could be larger). 

However, we require an extended 

exclusion zone of 1.5 km for certain 

sensitive species, including Kogia spp. 

Potential auditory injury for lowfrequency cetaceans is based on the 

accumulation of energy, and is therefore 

not a straightforward consideration. 

However, the extended exclusion zone 

is required for the only low-frequency 

cetacean in the GOM (Bryde’s whale). In 

keeping with the four broad goals 

outlined above, and in context of the 

information given here, the standard 

500-m exclusion zone is appropriate. 

NRDC does not provide any substantive 

reasoning for a larger zone. 

Comment: Several industry 

commenters criticized the requirement 

for use of buffer zones in addition to the 

standard exclusion zones, claiming in 

part that there is no scientific basis for 

monitoring a zone larger than the 

exclusion zones. 

Response: NMFS disagrees with the 

suggestion that there is no scientific 

basis for this requirement. It is 

important to implement a larger zone 

during pre-clearance, when naı ̈ve 

animals may be present and potentially 

subject to severe behavioral reactions if 

airguns begin firing at close range. 

While the delineation of zones is 

typically associated with shutdown, the 

period during which use of the acoustic 

source is being initiated is critical, and 


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in order to avoid more severe behavioral 

reactions it is important to be cautionary 

regarding marine mammal presence in 

the vicinity when the source is turned 

on. This requirement has broad 

acceptance in other required protocols: 

The Brazilian Institute of the 

Environment and Natural Resources 

previously required a 1,000-m preclearance zone before recently 

extending the exclusion zone to 

encompass the entire 1,000-m zone 

(IBAMA, 2005, 2018), the New Zealand 

Department of Conservation requires 

that a 1,000-m zone be monitored as 

both a pre-clearance and a shutdown 

zone for most species (DOC, 2013), and 

the Australian Department of the 

Environment, Water, Heritage and the 

Arts requires an even more protective 

scheme, in which a 2,000-m ‘‘power 

down’’ zone is maintained for higherpower surveys (DEWHA, 2008). Broker 

et al. (2015) describe the use of a 

precautionary 2-km exclusion zone in 

the absence of sound source verification 

(SSV), with a minimum zone radius of 

1 km (regardless of SSV results). We 

believe that the simple doubling of the 

exclusion zone required here is 

appropriate for use as a pre-clearance 

zone. 

Comment: CGG comments that 

shutdowns based on acoustic detections 

should be required only when the 

acoustic PSO is confident that the 

vocalization is from a non-delphinid 

species within the exclusion zone, as 

opposed to when the PSO is confident 

that the animal is outside of the 

exclusion zone. 

Response: We are unclear as to the 

practical impact of what appears to be 

a fairly nuanced difference, but clarify 

that shutdown upon acoustic detection 

of non-delphinids within the exclusion 

zone is required when the animal is 

detected acoustically and localized 

within the exclusion zone. However, we 

also note that PSO decision-making 

regarding shutdown implementation 

shall be informed to a reasonable extent 

by professional judgment. 

Comment: NRDC suggests that NMFS 

is remiss in not limiting the amount of 

activity that can occur overall (to a 

lesser amount than analyzed in the 

rule). Relatedly, NRDC suggests that 

NMFS must consider ‘‘placing a cap on 

the amount of allowable seismic 

activity.’’ 

Response: Such a requirement is not 

within NMFS’ authority under the 

MMPA, assuming that the requisite 

findings are made. NMFS’ responsibility 

is to evaluate the potential effects of the 

specified activity as presented by the 

applicant (BOEM in this case, acting on 

behalf of future industry applicants) and 

to determine whether the total taking 

will have a negligible impact on the 

affected species or stocks (among other 

things). If NMFS is unable to make the 

necessary finding, the applicant may 

then consider a revision to the specified 

activity that could lead to NMFS being 

able to make the necessary finding of 

negligible impact (or in some cases 

additional mitigation may enable a 

negligible impact finding). However, in 

this case, NMFS has made a finding of 

negligible impact, and it is not within 

NMFS’ authority to unilaterally impose 

a reduction in activity levels to some 

degree (NRDC does not specify the 

degree or distribution of reduction in 

time or space that they would find 

acceptable). 

Comment: NRDC expressed concern 

regarding the efficacy of the prescribed 

visual and acoustic monitoring 

methods, stating that species could go 

undetected. 

Response: While NMFS disagrees 

with some specific comments regarding 

efficacy, we generally agree with the 

overall point that there are limitations 

on what may reasonably be expected of 

either visual or acoustic monitoring. 

While visual and acoustic monitoring 

effectively complement each other, and 

acoustic monitoring is the more 

effective monitoring method (for certain 

species) during periods of impaired 

visibility, there is no expectation that 

these methods will detect all marine 

mammals present. In general, NRDC 

appears to misunderstand what NMFS 

claims with regard to what such 

monitoring may reasonably be expected 

to accomplish and/or the extent to 

which we rely on assumptions regarding 

the efficacy of monitoring in reaching 

the necessary findings. We acknowledge 

these limitations in prescribing these 

monitoring requirements, while stating 

why NMFS believes that visual and 

acoustic monitoring, and the related 

protocols we have prescribed, are an 

appropriate part of the suite of 

mitigation measures here that satisfy the 

MMPA’s least practicable adverse 

impact standard. However, the 

negligible impact finding is not 

conditioned on the presumption of a 

specific degree of monitoring efficacy. 

Comment: The MMC recommends 

that NMFS expand its shutdown 

requirement for sperm whales to 

include both visual and acoustic 

detections at extended distance, stating 

that vital functions of sperm whales, 

including both foraging and resting, 

should be afforded the additional 

protection of the extended shutdown 

zone. NRDC asserts that acoustic 

shutdowns for sperm whales, which 

they believe are not required under the 

ITR, would not be effective. The CRE 

comments that they ‘‘agree with [NMFS] 

that sperm whale shutdowns are not 

warranted.’’ 

Response: NMFS agrees with the 

MMC’s recommendation and has made 

the recommended change (albeit within 

a revised extended distance shutdown 

zone of 1.5 km; see Mitigation). 

However, we note the MMC’s statement 

that ‘‘[t]he requirement for 

implementing shut-down procedures 

upon acoustic detection of a sperm 

whale was inadvertently omitted from 

the proposed regulatory text.’’ NMFS 

disagrees with this statement. The 

proper interpretation of the proposed 

regulatory text was that such shutdowns 

would be required. Nevertheless, the 

revised, final regulatory text makes this 

requirement clearer, in addition to 

making the change to be inclusive of 

visual detections at the greater distance. 

Regarding the CRE’s comment, NMFS 

did not determine that ‘‘sperm whale 

shutdowns are not warranted.’’ 

Shutdowns for sperm whales have been 

required in the GOM for over a decade, 

and NMFS does not make any findings 

that this should change. 

With regard to NRDC, we reference 

this comment only to provide necessary 

clarification. Because NRDC mistakenly 

claims that ‘‘NMFS hasn’t included an 

acoustic shutdown requirement for 

sperm whales in its proposed 

regulation,’’ we refer the reader to the 

notice of proposed rulemaking, in 

which we state that shutdown of the 

acoustic source is required upon 

acoustic detection of a sperm whale 

(29274–29275). (‘‘We are proposing that 

shutdown of the acoustic source should 

also be required in the event of certain 

other observations [. . .]. Circumstances 

[. . .] include [. . .] acoustic detection 

of a sperm whale.’’) This requirement is 

carried forward in this final ITR, as 

modified (see Mitigation). 

With regard to the efficacy of the 

measure, we are confused as to NRDC’s 

comments. NRDC first asserts that 

sperm whales are the only species for 

which acoustic detection may 

reasonably be assumed, but then 

seemingly states that implementation of 

the measure is not sufficiently effective 

as to be considered in context of 

reducing impacts to sperm whales. As 

discussed in greater detail elsewhere, 

NMFS believes that shutdowns for 

sperm whales at an extended distance, 

on the basis of both acoustic and visual 

detections (the latter added in this final 

ITR), will meaningfully reduce impacts 

to the species. 

Comment: NRDC asserts that NMFS 

does not fulfill the MMPA’s requirement 

to prescribe mitigation achieving the 


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9The Associations also apparently misunderstand 

some discussion of stranding events (which have 

occurred primarily as a result of military use of 

mid-frequency active sonar) provided in the notice 

of proposed rulemaking, interpreting this 

discussion as NMFS’ ‘‘suggestion that seismic 

surveys are similar to mid-frequency sonar (which 

has been implicated in strandings) simply because 

seismic signatures include a mid-frequency 

component.’’ We suggested no such thing and agree 

with the Associations that airguns and sonar are 

very different sound sources with very different 

potential to cause strandings. 

‘‘least practicable adverse impact’’ to 

marine mammal habitat, and 

specifically notes that NMFS does not 

separately consider mitigation aimed at 

reducing impacts to marine mammal 

habitat, as the MMPA requires. 

Response: NMFS disagrees with this 

comment. Our discussion of least 

practicable adverse impact points out 

that because habitat value is informed 

by marine mammal presence and use, in 

some cases there may be overlap in 

measures for the species or stock and for 

use of habitat. In the notice of proposed 

rulemaking, NMFS identified time-area 

restrictions based on a combination of 

factors that include higher densities and 

observations of specific important 

behaviors of the animals themselves, but 

also clearly reflect preferred habitat. In 

addition to being delineated based on 

physical features that drive habitat 

function (e.g., bathymetric features, 

among others), the high densities and 

concentration of certain important 

behaviors (e.g., feeding) in these 

particular areas clearly indicates the 

presence of preferred habitat. Also, 

NRDC asserts that NMFS must 

‘‘separately’’ consider measures aimed 

at marine mammal habitat. The MMPA 

does not specify that effects to habitat 

must be mitigated in separate measures, 

and the notice of proposed rulemaking 

clearly identified measures that provide 

significant reduction of impacts to both 

‘‘marine mammal species and stocks 

and their habitat,’’ as required by the 

statute. Last, we note that NRDC 

acknowledges that the measures 

identified in the notice of proposed 

rulemaking measures would reduce 

impacts on ‘‘acoustic habitat.’’ 

Following BOEM’s update to the scope 

of activity, two of the three time-area 

restrictions identified and proposed by 

NMFS now fall outside the area in 

which survey activity may be 

considered under this rule. 

Comment: NRDC recommends that 

NMFS should consider a year-round 

restriction on geophysical survey 

activity within coastal waters in the 

footprint of the DWH oil spill, and that 

NMFS must expand its proposed GOMwide coastal restriction temporally to 

include the month of January. 

Conversely, the Associations state that 

no coastal restriction should be 

required. The MMC recommends that 

the proposed coastal closure be 

expanded temporally such that the 

timeframe is from January through 

August. 

Response: NMFS finds aspects of both 

NRDC’s and the Associations’ 

statements with which we agree and 

disagree and, as discussed in Mitigation, 

have revised the time-area restriction. 

This restriction on airgun survey 

activity (‘‘Area 1’’) was proposed as 

including all GOM waters inside the 20- 

m isobath, from February through May. 

The revised restriction is limited to 

those waters inside the 20-m isobath 

from 90 ° to 84 ° W. Temporally, the 

restriction is expanded to be in effect 

from January through May. 

The Associations provide extensive 

comments relating to the impacts on 

practicability presented by the proposed 

restriction. The potential economic 

consequences of the measure are 

addressed in greater detail in the 

regulatory impact analysis (RIA), which 

analysis we adopt as a portion of our 

practicability assessment for the revised 

measure. NMFS agrees that there will 

likely be negative economic and 

operational consequences of the 

restriction, though these consequences 

are difficult to assess (and cannot 

reasonably be assessed quantitatively) 

(see the RIA for full analysis). While the 

Associations express concerns regarding 

the practicability analysis as being too 

vague, they fail to provide additional 

specific information that would help to 

improve the analysis. For example, the 

Associations state that data from the 

area contained within the restriction are 

outdated and that the restriction will 

impede industry’s ability to identify 

prospects in coastal areas, but provide 

no specific information to support these 

claims, such as information about the 

data that do exist or the areas where 

industry anticipates having interest in 

identifying prospects. Despite the lack 

of information provided in support of 

the practicability concerns, NMFS takes 

seriously the Associations’ concerns, 

and therefore did consider eliminating 

the restriction. 

The Associations also assert that the 

restriction would not result in any 

meaningful benefit to coastal bottlenose 

dolphin populations. NMFS disagrees 

that this is the case. Although dolphins 

are less sensitive to the frequencies at 

which the greatest energy in an airgun 

signal is found, we have described the 

large body of evidence of adverse or 

aversive behavior by various dolphin 

species during airgun firing (e.g., Goold 

and Fish, 1998; Stone and Tasker, 2006; 

Barkaszi et al., 2012; Stone, 2015a; 

Barkaszi and Kelly, 2018). Considered 

in context of a generic dolphin 

population with no notable issues 

affecting the population as part of the 

environmental baseline, it may be 

reasonable to assume that such effects 

are not indicative of any response of a 

severity such that the need to avoid it 

outweighs the impact on practicability 

for the industry and operators. However, 

as was described in the notice of 

proposed rulemaking, and as discussed 

in NRDC’s comment, coastal bottlenose 

dolphins in the GOM—particularly the 

northern coastal stock of bottlenose 

dolphins—were severely impacted by 

the DWH oil spill. 

As explained in the notice of 

proposed rulemaking, while none of the 

dolphin strandings or deaths have been 

attributed to airgun survey activities, 

stocks in the area are stressed and the 

northern coastal stock in particular is in 

extremely poor health. The 

Associations’ discussion of NMFS’ 

analysis—claiming that our justification 

for the restriction was premised merely 

on ‘‘the broad understanding that 

‘marine mammals react to underwater 

noise’ ’’—is factually mistaken. As we 

stated, behavioral disturbance or stress 

may reduce fitness for individual 

animals and/or may exacerbate existing 

declines in reproductive health and 

survivorship. For example, stressors 

such as noise and pollutants may be 

expected to induce responses involving 

the neuroendocrine system, which 

controls reactions to stress and regulates 

many body processes (NAS, 2017), and 

there is strong evidence that petroleumassociated chemicals can adversely 

affect the endocrine system, providing a 

potential pathway for interactions with 

other stressors (Mohr et al., 2008, 2010). 

Romano et al. (2004) found that upon 

exposure to noise from a seismic 

watergun, bottlenose dolphins had 

significantly elevated levels of a stressrelated hormone and, correspondingly, a 

decrease in immune cells. As we stated, 

the restriction is intended specifically to 

avoid additional stressors to these 

coastal bottlenose dolphin populations 

during the time period believed to be of 

greatest importance as a reproductive 

period. The Associations do not 

contradict this information, instead 

weakly relating the concern to the 

potential for dolphins to experience 

damage to auditory structures (which 

NMFS agrees is unlikely) or to the idea 

that ‘‘reactions’’ to noise are 

innocuous.9

Population-level impacts related to 

energetic effects or other impacts of 

noise are difficult to determine, but the 

addition of other stressors can add 


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10However, we note that NRDC mischaracterizes 

sperm whale buzz rates as ‘‘a measure of foraging 

success,’’ as opposed to a measure of foraging effort. 

The study referenced by NRDC did not find that 

sperm whale foraging success ‘‘declined 

substantially’’ on exposure to airgun noise. 

Moreover, the measured decline in foraging effort 

was not a statistically significant result and, 

therefore, cannot appropriately be referred to as a 

substantial decline. See Miller et al. (2009). 

considerable complexity due to the 

potential for interaction between the 

stressors or their effects (NAS, 2017). 

When a population is at risk, NAS 

(2017) recommends identifying those 

stressors that may feasibly be mitigated. 

We cannot undo the effects of the DWH 

oil spill, but the potentially synergistic 

effects of noise due to the activities that 

are the subject of this rule may be 

mitigated. However, NMFS does 

acknowledge that the two populations 

of greatest concern—the western and 

northern coastal stocks of bottlenose 

dolphin—do not have the same status. 

As identified in the notice of proposed 

rulemaking, while both stocks were 

impacted by the DWH oil spill, the 

northern coastal stock in particular was 

perhaps the single most heavily 

impacted stock, with 82 percent of 

animals belonging to the stock expected 

to have been exposed to oil, resulting in 

a possible population reduction of 50 

percent (this latter figure was only five 

percent for the western stock). The 

northern coastal stock was also subject 

to a recent Unusual Mortality Event 

(UME), described later in this notice 

(see Description of Marine Mammals in 

the Area of the Specified Activity). 

NMFS acknowledges the uncertainty 

associated with predicting the ways in 

which different stressors may interact, 

or how the effects of a stressor might be 

exacerbated in an unhealthy population. 

However, as an example, Schwacke et 

al. (2014a) described findings indicating 

that a significant proportion of the 

population is expected to exhibit 

adrenal insufficiency as a result of oil 

exposure. Adrenal insufficiency can 

lead to adrenal crisis and death in 

animals that are challenged with other 

stressors (Venn-Watson et al., 2015b). 

NMFS agrees that the potential 

practicability concerns warrant 

consideration and, in light of the 

differential baselines for the potentially 

affected coastal stocks, has determined 

it appropriate to contract the restriction. 

However, the post-DWH oil spill 

baseline condition of the northern 

coastal stock, as exacerbated by the 

recent UME, requires caution. This 

restriction may reasonably be 

anticipated to provide additional 

protection to these populations during 

their peak reproductive activity. We 

note that NRDC’s proposed focus area 

for heightened restriction aligns 

generally with this area of concern, but 

that in aligning with the footprint of the 

spill rather than with the stock 

boundaries, this recommendation would 

not necessarily encompass the animals 

of greatest concern and which we 

assume are the population targeted by 

the proposal. 

With regard to the timing of the 

closure, there is no definitive definition 

of the ‘‘peak reproductive activity’’ 

associated with the stock and, 

additionally, there is some uncertainty 

as to whether the more important focus 

is on effects to pregnant mothers or on 

the post-partum period when energetic 

or stress effects would lead to greater 

risk for lactating mothers and/or 

disruption of mother-calf bonding and 

ultimate effects on rates of neonate and/ 

or calf survivorship. We acknowledged 

this uncertainty in discussing the 

recommendations of NMFS’ subject 

matter experts and describing the 

proposed temporal extent of February 

through May in the notice of proposed 

rulemaking. Upon review of the 

information presented in the comments 

of NRDC (e.g., reference to the data 

presented by, e.g., Carmichael et al., 

2012; Mattson et al., 2006; Urian et al., 

1996), which supported NRDC’s 

assertion that, in summary, inclusion of 

January would cover the remainder of 

the dolphins’ peak calving and late 

gestation periods as well as the 

beginning of the period of highest 

reproductive failure, NMFS agrees that 

this temporal expansion is appropriate 

(within the contracted region of our 

revised restriction area). In contrast, the 

MMC does not provide compelling 

information in support of the 

recommendation to expand the 

restriction by an additional three 

months (through August), stating only 

that ‘‘calves can be born at any time of 

the year’’ and referencing a bimodal 

peak in neonate strandings from the 

Sarasota Bay area. Given the 

exacerbation of practicability concerns 

that this expansion would entail and the 

lack of information to support it, NMFS 

does not believe it appropriate to 

expand the restriction through August. 

We do note that one concern of the 

Associations, which is that the 

restriction may result in an inability to 

complete surveys within one year, may 

be alleviated to some degree by the 

ability under this ITR to issue LOAs for 

any term up to five years. The 

Associations recommend that, if the 

restriction is included in the ITR, NMFS 

allow for multi-year LOAs, which we 

have done. 

Comment: The Associations state that 

the proposed time-area restriction in the 

Dry Tortugas region of the eastern GOM 

should not be required. However, the 

MMC concurs with NMFS’ proposal, 

stating that the imposition of this 

restriction is appropriate. 

Response: NMFS appreciates the 

comments. The proposed time-area 

restriction referenced here is no longer 

relevant following BOEM’s update to 

the geographic scope of activity, as no 

survey activity within this area can be 

considered through this rule. 

Comment: NRDC comments that 

NMFS must consider restrictions and 

limitations on survey activity in the 

Central Planning Area (CPA) restriction 

area analyzed in the proposed rule. 

NRDC states that NMFS’ practicability 

analysis must focus on (1) how much oil 

and gas development is projected to 

occur within the proposed areas over 

the next five years; (2) what effect the 

proposed mitigation area would have on 

that projected development; and (3) 

whether that projected development 

would be offset by exploration in other 

parts of the GOM. 

Response: NRDC accurately 

characterizes the area as being 

important for sperm whales 10 and 

beaked whales, as was described by 

NMFS in the notice of proposed 

rulemaking, and accurately describes 

that this area is projected to be subject 

to significant survey effort. NMFS 

acknowledges these issues. However, 

NRDC provides no serious rebuttal of 

NMFS’ practicability analysis, which 

includes incorporation by reference of 

the findings of the RIA for this rule, 

instead providing only a cursory 

rejection of the analysis as inadequate. 

We also note that the third prong of 

NRDC’s suggested analysis is not 

reasonable: Development foregone due 

to a lack of survey data in the closure 

areas cannot be ‘‘offset by exploration’’ 

elsewhere. 

As discussed in detail in the RIA, 

there are significant uncertainties 

associated with assessing the indirect 

costs of restricting survey effort within 

the described area. Notable areas of 

uncertainty include the demand for and 

timing of oil and gas production in the 

GOM over the next five years, the 

suitability of existing data to direct oil 

and gas production in the closure areas, 

and the most likely substitute sites for 

oil and gas production. These 

uncertainties foreclose the possibility of 

the analysis demanded by NRDC. 

However, what information is available 

strongly suggests that the economic 

impacts of the evaluated CPA 

restrictions would be significant. A 

mitigation requirement that could lead 


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11Leases within the closure areas considered 

within the Central Planning Area accounted for 

approximately 50 percent of total oil production in 

the GOM between 2012 and 2016 and 24 percent 

of total gas production. Existing reserves within the 

closure areas represent 57 percent of estimated oil 

reserves and 37 percent of estimated gas reserves in 

the GOM. 

to regional- to national-scale economic 

impacts is not practicable. 

The impacts of year-round area 

closures are highly dependent on 

volatile oil and gas market conditions 

over the next five years, which dictate 

the demand for activities in the GOM. 

The greater the demand for oil and gas, 

the greater the expected impacts of the 

restrictions. The extent to which oil and 

gas production is delayed because of the 

need for newer, better data is a key 

source of uncertainty. Some sites may 

be able to employ existing data from 

recent surveys. However, even for 

relatively recent data, the inability to 

collect new seismic data could affect oil 

and gas development given that oil 

companies typically use targeted 

seismic data to refine their geologic 

analysis before drilling a well. 

It is possible that some fraction of 

reductions in production from the 

closure areas may be made up for with 

production in other areas in the GOM, 

mitigating potential regional economic 

impacts. However, uncertainty with 

regard to the location of ‘‘substitute’’ 

production has potentially critical 

impacts on the ultimate economic 

impacts of the closure. If a closure 

requirement reduces exploration and 

development activity in the GOM, the 

displaced capital expenditures would 

likely shift to the next-lowest-cost 

opportunities promising the greatest 

development potential. Given that oil is 

produced and sold in a global market, 

the next-lowest-cost areas may be 

elsewhere within the GOM, but also 

may be international locations. To the 

extent that substitute areas are outside 

of the GOM but within the United 

States, national-level impacts of the 

closure areas would likely be limited. 

However, to the extent that industry 

moves displaced activities outside of the 

United States, national-level impacts 

associated with industry income and 

employment could be substantial. 

Recent levels of leasing and drilling 

activity in the CPA indicate that the 

closure areas considered are among the 

most productive in the entire GOM.11

Given this, it is less likely that other 

GOM areas will offer equivalent 

alternative opportunities. As a result, 

the analyzed area closures have greater 

potential to reduce domestic oil and gas 

production, industry income, and 

related regional employment 

opportunities. 

NRDC asks NMFS to conduct analyses 

that cannot be supported by existing 

data. Further, NRDC asks NMFS to 

speculate as to the impacts of restricting 

exploration activity outside the 

development of existing leases. 

However, such a restriction, while less 

impactful than a complete area-wide 

restriction, would necessarily foreclose 

the ability of both the government and 

industry to assess fair market value of 

leases already planned for sale. While 

NMFS believes that the evaluated 

restriction area would be beneficial for 

sperm whales and beaked whales, such 

restrictions are at this time not 

practicable. NRDC does not provide any 

information contradicting this 

conclusion, and provides no specific, 

viable alternatives for NMFS’ 

evaluation. 

Comment: NRDC states that NMFS 

should consider time-area closures for 

additional species. 

Response: NMFS did consider habitatbased protections for species additional 

to those discussed in the time-area 

restrictions section of Mitigation. For all 

affected species, NMFS evaluated the 

environmental baseline (i.e., other 

population-level stressors), the nature 

and degree of effects likely to be the 

result of the specified activities, and the 

information available to support the 

development of appropriate time-area 

restrictions. NMFS determined that the 

available information supported 

development of the measures described 

in the notice of proposed rulemaking for 

the Bryde’s whale, sperm whales, and 

beaked whales. For other species, 

context does not justify additional 

protections and/or the available 

information does not support the 

designation of any specific area for 

protection, when considered in 

combination with practicability 

concerns. 

NRDC asserts that ‘‘marine mammal 

populations in the northern Gulf of 

Mexico can no longer be considered by 

the agency to be too ‘data poor’ or 

broadly distributed to justify specific 

mitigation measures for their protection, 

including time-area closures.’’ This is 

not a representation NMFS made in the 

notice of proposed rulemaking. NRDC 

then erroneously claims that NMFS 

‘‘limits its analysis to two deep-diving 

species, sperm whales and beaked 

whales [. . .]. In doing so, however, it 

omitted other populations whose 

conservation status or modeled impacts 

pose particular concern.’’ First, NMFS 

did conduct core abundance analyses 

for all GOM stocks. Second, NRDC 

declines to elaborate on which stocks 

they believe ‘‘pose particular concern,’’ 

other than noting that Kogia spp. may be 

subject to Level A harassment. However, 

despite NRDC’s statement that species 

can no longer be considered to be too 

broadly distributed to justify specific 

time-area mitigation measures, our core 

abundance analysis for Kogia spp. 

shows exactly that. Based on the Roberts 

et al. (2016) models, the two species are 

broadly distributed in shelf-break waters 

essentially throughout the GOM, and 

there is no identified biologically 

important area or specific bathymetric 

feature that would allow us a more 

refined understanding of an area 

suitable for protection (if it were 

warranted). NRDC does not suggest any 

specific area for protection of Kogia spp. 

NRDC also suggests that NMFS 

should prohibit seismic activity in the 

Flower Garden Banks National Marine 

Sanctuary (FGBNMS) but offers no 

strong justification other than stating 

that marine mammals occur there. In 

addition, BOEM and/or BSEE will 

consult with NOAA’s Office of National 

Marine Sanctuaries when they receive 

an application that indicates that survey 

activity may occur within or near the 

FGBNMS. 

Overall, NRDC offers no useful 

recommendation as to the designation of 

protections for additional species. 

NMFS’ consideration of habitat-based 

protections was conducted 

appropriately in light of relevant 

information regarding the 

environmental baseline, expected effects 

of the specified activities, and 

information regarding species use of the 

GOM. 

Comment: Several commenters 

recommended establishing wider buffer 

zones around the proposed time-area 

closures. The Associations state that no 

buffers should be required around any 

time-area restriction (if required; the 

Associations also disagree that any 

restrictions should be required, as 

discussed previously). 

Response: NRDC indicates that 

NMFS’ stated objective in establishing 

the proposed buffer zones around timearea restrictions was unclear in terms of 

evaluating the proposed buffer zone 

relative to the objective. The stated 

objective was to exclude noise that is 

likely to result in harassment, which 

NMFS interpreted to mean site-specific 

modeled distances to the 160-dB 

isopleth (i.e., 50 percent midpoint of the 

Level B harassment risk probability 

function). Following review of public 

comments, NMFS provides further 

context here regarding the multi-step 

Level B harassment risk function 

employed for purposes of evaluating 

modeled noise exposures. 


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With regard to the establishment of a 

buffer zone, NMFS agrees with certain 

commenters that it is generally 

appropriate to buffer an area to be 

avoided by some degree, as discussed in 

the notice of proposed rulemaking. 

However, we disagree that a buffer must 

be developed to fully eliminate the 

potential for Level B harassment, as 

some commenters may have inferred 

from our use of the distance to the 160- 

dB isopleth (i.e., historically used as a 

100 percent single-step function for 

evaluation of Level B harassment; here 

the 50 percent midpoint of the Level B 

harassment risk function). Rather, the 

buffer concept, as described in the 

notice of proposed rulemaking, serves to 

reasonably minimize the extent and 

severity of what limited harassment may 

occur as a result of acoustic exposure to 

relatively low received levels of noise. 

The Associations asserted that NMFS 

did not consider the use of buffer areas 

in the practicability analyses and 

provides no biological basis for 

including buffers. We disagree. As noted 

earlier, the RIA analysis (which forms a 

substantial part of the practicability 

analysis for these measures) includes 

analysis of the economic impacts of the 

time-area restrictions inclusive of the 

buffer. As noted above, the logical 

biological rationale is to provide a buffer 

around an area determined to be of 

particular biological importance such 

that the effects of noise from outside the 

restriction area intruding within the 

area is minimized. 

However, BOEM’s update of the 

geographic scope for this rule eliminates 

the need for proposed time-area 

restrictions #3 and 4 (i.e., the Bryde’s 

whale core habitat area and the ‘‘Dry 

Tortugas area’’ designed for protection 

of beaked whales and sperm whales). 

Therefore, comments addressing the 

proposed buffers for those areas are no 

longer relevant. Regarding the coastal 

bottlenose dolphin restriction (Area #1), 

NMFS has determined that the addition 

of a buffer to this area is not warranted, 

based on the objectives of the restriction 

(described in detail in a previous 

response to comment) and on the 

manner in which the area was 

delineated. Areas #3 and 4 were 

delineated based on NMFS’ review of 

the available scientific information and 

expert opinion and in order to denote 

areas expected to be of particular 

biological importance for particular 

species. In contrast, the coastal dolphin 

restriction area was based simply on the 

stock boundaries for coastal bottlenose 

dolphins (i.e., the seaward extent of the 

area is set at the 20-m isobath). As this 

boundary does not mark an area of 

specific biological importance or high 

density for the stock, but is rather an 

approximation of stock presence, NMFS 

has determined following review of 

public comments, in which valid 

practicability concerns were raised, that 

the inclusion of a buffer to this area is 

not warranted. 

Comment: Noting that the proposed 

ITR included requirements to conduct 

visual monitoring following conclusion 

of active shooting, the MMC 

recommends that NMFS require 

operators to also continue conducting 

acoustic monitoring following 

conclusion of active shooting. 

Response: The proposed ITR stated 

that acoustic monitoring must occur for 

30 minutes prior to and during all active 

firing of airguns for deep penetration 

surveys, but was silent on the issue of 

acoustic monitoring following the 

survey. However, visual monitoring is 

required to continue for 60 minutes 

following cessation of survey activity 

during good visibility. NMFS agrees 

with the MMC that ‘‘both visual and 

acoustic monitoring should occur 

concurrently, as acoustic detections can 

provide additional information not 

readily available via visual detections 

alone regarding changes in foraging and 

social behavior during survey activities 

and after activities cease.’’ Accordingly, 

acoustic monitoring is also required to 

continue following cessation of survey 

activity for a period of 60 minutes. 

Comment: BP comments that they 

welcome use of industry standard PAM/ 

operator software such as PAMGuard. 

Noting the operational challenges 

associated with accommodating 

increased numbers of PSOs on survey 

vessels, BP also comments that they 

would welcome the inclusion of an 

option to implement PAM during 

survey activities using remote shorebased operators. 

Response: NMFS agrees that this may 

be appropriate, depending on various 

factors. While we are not currently 

aware of the state of existing technology 

towards achieving this end, NMFS 

would consider the use of remote PAM 

monitoring, assuming reliability and the 

ability to achieve the same performance 

as shipboard PAM monitoring. NMFS 

believes the adaptive management 

process will be an appropriate venue for 

further consideration of this approach. 

Comment: BP comments that, while 

they recognize the value of prospective 

formal standards for PAM operations 

(e.g., hardware, software, training), the 

standards have not yet been finalized. 

BP requests that the standards be 

considered for use only after an initial 

draft has been circulated via relevant 

standards development and issuance 

processes. 

Response: NMFS may adopt elements 

of the prospective standards, as it deems 

appropriate (as discussed in Monitoring 

and Reporting). However, we agree that 

wholesale adoption of the standards 

would not be appropriate until 

appropriate review and other necessary 

processes are complete. 

Comment: Industry commenters state 

that non-airgun high-resolution 

geophysical (HRG) surveys should not 

be subject to pre-clearance and 

shutdown requirements. Relatedly, BP 

and Chevron comment that exclusion 

zones should not be required for HRG 

surveys, as these surveys typically 

operate using acoustic sources deployed 

on an automated underwater vehicle 

(AUV) running 40 m above the seafloor. 

Therefore, they state that there is no 

environmental benefit to a requirement 

for a surface exclusion zone. 

Response: The Associations note that 

the acoustic footprint of sources 

typically used in non-airgun HRG 

surveys are too small to warrant the 

proposed exclusion and buffer zone 

distances and that, more importantly, 

due to the typically highly directional 

nature of these acoustic sources, 

animals observed at the surface will 

generally not be exposed to the signal. 

NMFS agrees with these comments, and 

notes that the proposed shutdown and 

exclusion zone requirements were 

offered in accordance with BOEM’s 

HRG survey protocols (Appendix B of 

BOEM, 2017). Following review of these 

comments, as well as the available 

scientific information regarding the 

typical interaction of these signals with 

the environment and likely lack of 

efficacy of typical standard operational 

protocols developed for omnidirectional 

sources, NMFS has eliminated these 

requirements. However, we also clarify 

that certain electromechanical sources 

may be subject to the pre-clearance and 

shutdown requirements associated with 

shallow penetration surveys. In 

addition, the exclusion and buffer zone 

distances for shallow penetration 

surveys have been reduced (while 

adding an extended distance shutdown 

zone for certain circumstances) in 

recognition of the typically smaller 

harassment zones associated with use of 

the acoustic sources considered here to 

be used in shallow penetration surveys. 

As noted here, NMFS has eliminated 

the requirement for implementation of 

an exclusion zone during HRG surveys. 

We also agree with BP’s comment that 

exclusion zones should not be required 

for surveys using an AUV-deployed 

acoustic source running at short 

distances above the seafloor. 

Comment: NRDC states that NMFS 

fails to prescribe adequate mitigation for 


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HRG surveys and, relatedly, that NMFS 

must not issue LOAs for use of lowerfrequency multibeam echosounders 

(MBES). 

Response: As evidenced by the 

previous comment response, in which 

describing elimination of certain 

mitigation measures that were proposed 

for HRG surveys, NMFS disagrees with 

NRDC. NRDC provides no reasonable 

justification for the recommendation to 

consider additional mitigation 

requirements. They reference the 2008 

Madagascar stranding of melon-headed 

whales, implying that a similar 

occurrence may be a reasonably 

anticipated outcome of HRG survey 

work in the GOM. Although it is correct 

that an investigation of the event 

indicated that use of a high-frequency 

mapping system (12-kHz MBES) was the 

most plausible and likely initial 

behavioral trigger of the event (with the 

caveat that there was no unequivocal 

and easily identifiable single cause), the 

panel also noted several site- and 

situation-specific secondary factors that 

may have contributed to the avoidance 

responses that led to the eventual 

entrapment and mortality of the whales 

(Southall et al., 2013). Specifically, 

regarding survey patterns prior to the 

event and in relation to bathymetry, the 

vessel transited in a north-south 

direction on the shelf break parallel to 

the shore, ensonifying deep-water 

habitat prior to operating intermittently 

in a concentrated area offshore from the 

stranding site. This may have trapped 

the animals between the sound source 

and the shore, thus driving them 

towards the lagoon system. Shorewarddirected surface currents and elevated 

chlorophyll levels in the area preceding 

the event may also have played a role. 

The relatively lower output 

frequency, higher output power, and 

complex nature of the system 

implicated in this event, in context of 

the other factors noted here, likely 

produced a fairly unusual set of 

circumstances that indicate that such 

events would likely remain rare and are 

not necessarily relevant to use of more 

commonly used lower-power, higherfrequency systems such as those 

evaluated for this analysis. The risk of 

similar events recurring is expected to 

be very low, given the extensive use of 

active acoustic systems used for 

scientific and navigational purposes 

worldwide on a daily basis and the lack 

of direct evidence of such responses 

previously reported. The only report of 

a stranding that may be associated with 

this type of sound source is the one 

reported in Madagascar. 

NRDC also references Cholewiak et al. 

(2017), stating that virtually no beaked 

whale vocalizations were detected 

acoustically during the time that the 

shipboard echosounder was operational. 

NRDC mischaracterizes the literature, 

including a speculative description of 

what they imagine the beaked whales 

were doing while not vocalizing 

(‘‘suggesting that the whales broke off 

their foraging behavior and engaged in 

[. . .] silent flight’’). Cholewiak et al. 

(2017) do describe finding that beaked 

whales were significantly less likely to 

be detected acoustically while 

echosounders were active. However, it 

is not clear that this response should be 

considered as Level B harassment when 

considered in the context of what is 

likely a brief, transient effect, given the 

mobile nature of the surveys and the 

fact that some beaked whale 

populations are known to have high site 

fidelity. In support of this conclusion, 

Quick et al. (2017) describe an 

experimental approach to assess 

potential changes in short-finned pilot 

whale behavior during exposure to an 

echosounder. Tags attached to the 

animals recorded both received levels of 

noise as well as orientation of the 

animal. Results did not show an overt 

response to the echosounder or a change 

to foraging behavior of tagged whales, 

but the whales did increase heading 

variance during exposure. The authors 

suggest that this response was not a 

directed avoidance response but was 

more likely a vigilance response, with 

animals maintaining awareness of the 

location of the echosounder through 

increased changes in heading variance 

(Quick et al., 2017). Visual observations 

of behavior did not indicate any 

dramatic response, unusual behaviors, 

or changes in heading, and cessation of 

biologically important behavior such as 

feeding was not observed. More 

recently, Varghese et al. (2020) reported 

the results of an investigation of the 

effects of a 12-kHz MBES system on 

beaked whale foraging behavior off of 

California. Echolocation clicks from 

Cuvier’s beaked whales were detected 

and classified into foraging events 

called group vocal periods (GVP), and 

compared across exposure periods 

before, during, and after MBES activity. 

Of the metrics used to assess beaked 

whale foraging behavior, only the 

number of GVPs per hour was 

statistically different during MBES 

activity versus a non-MBES period. 

GVPs per hour increased during MBES 

activity compared with before MBES 

activity, demonstrating that beaked 

whales did not stop foraging and were 

not displaced by the activity. These 

results suggest that there was not a 

negative impact of MBES activity on 

foraging behavior of this sensitive 

species (Varghese et al., 2020). 

Finally, NRDC references the work of 

Deng et al. (2014) and Hastie et al. 

(2014) in describing ‘‘leakage’’ of 

‘‘substantial noise’’ at frequencies 

within marine mammal hearing range 

during use of active acoustic systems 

that are operated at higher frequencies. 

The referenced studies reported some 

behavioral reaction by marine mammals 

to acoustic systems operating at userselected frequencies above 200 kHz. 

This work was discussed in the notice 

of proposed rulemaking. In general, the 

referenced literature indicates only that 

sub-harmonics could be detectable by 

certain species at distances up to several 

hundred meters. As NMFS has noted 

elsewhere, behavioral response to a 

stimulus does not necessarily indicate 

that Level B harassment, as defined by 

the MMPA, has occurred. Source levels 

of the secondary peaks considered in 

these studies—those within the hearing 

range of some marine mammals—mean 

that these sub-harmonics would either 

be below the threshold for Level B 

harassment or would attenuate to such 

a level within a few meters. The work 

cited by the commenters is consistent 

with previously observed occurrences of 

sub-harmonics. Essentially, the first subharmonic’s source level (e.g., if the 

primary frequency is 200 kHz, the first 

sub-harmonic is 200/2 or 100 kHz, the 

second is 200/3 or 66.7 kHz) is at least 

20–30 dB less than the primary 

frequency’s source level, with each 

subsequent sub-harmonic’s source level 

decreasing rapidly from there. These 

sub-harmonics are typically so reduced 

in source level that, for most side-scan 

and multi-beam sonar systems, they are 

not strong enough to produce impacts 

beyond tens of meters from the source 

(distances at which reactions to the 

vessel itself are likely to supersede 

reactions to an acoustic signal). 

Additionally, for any potential impacts 

to occur, an animal must be within this 

range and within the very narrow beams 

produced by the systems (for these subharmonic frequencies). 

In addition, recent sound source 

verification testing of these and other 

similar systems did not observe any subharmonics in any of the systems tested 

under controlled conditions (Crocker 

and Fratantonio, 2016). While this can 

occur during actual operations, the 

phenomenon may be the result of issues 

with the system or its installation on a 

vessel rather than an issue that is 

inherent to the output of the system. As 

concluded in the notice of proposed 

rulemaking, there is no evidence to 

suggest that Level B harassment of 

marine mammals should be expected in 


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relation to use of active acoustic sources 

at frequencies exceeding 180 kHz. 

NRDC’s comments did not address 

NMFS’ prior statements regarding this 

topic. 

NRDC fails to adequately support the 

claims of harm to marine mammals that 

are reasonably likely to occur as a result 

of HRG surveys and, thus, fails to justify 

their recommendation for enhanced 

mitigation. The recommended measures 

include ‘‘extended safety zone and 

monitoring requirements’’ and a ‘‘bar on 

nighttime operations.’’ Even when 

animals are receiving echosounder 

signals, they may not be harassed, as 

described above. However, given the 

directional nature of these sources, 

animals observed at the surface will 

almost certainly not be within the 

acoustic beam, thus negating the benefit 

of detection-based measures such as 

shutdowns. Any exposure to the 

echosounder would likely be only in the 

ensonified cone below the vessel, and 

responses to the vessel itself at such 

close ranges would influence likelihood 

of acoustic exposure. The package of 

active acoustic systems modeled as 

representative of a typical HRG survey 

included a 200-kHz echosounder. 

Regarding the suggestion that this bars 

use of any system with a lower 

frequency output, NMFS disagrees. 

NMFS’ analysis also includes use of 

different lower-frequency sources (i.e., 

single airguns and boomers). Moreover, 

the specific sources selected for analysis 

do not limit the actual sources that may 

be used, assuming the actual sources are 

reasonably similar to the full suite of 

analyzed sources, as is the case here. 

Comment: The Associations and other 

industry commenters claim that the 

proposed PSO staffing requirements 

compromise personnel safety, cannot be 

effectively implemented, and are 

unnecessary and unsupported. 

Response: In the notice of proposed 

rulemaking, NMFS described in detail 

the importance of detection-based 

mitigation as a component of standard 

operational mitigation protocols. 

Detection-based mitigation cannot occur 

effectively without both visual and 

acoustic monitoring, with the latter 

being the only effective method of 

detection during periods of poor 

visibility or at any time for cryptic 

species (e.g., beaked whales) or species 

with high availability bias (e.g., sperm 

whales). Therefore, visual monitoring is 

required during daylight hours and 

acoustic monitoring is required 

throughout the period of survey 

operations. When these monitoring 

techniques are required, two visual 

PSOs must be on duty in order to 

effectively monitor 360 degrees around 

the vessel, communicate with the 

operator as necessary, and record data, 

and an acoustic PSO must be on duty to 

monitor the PAM system. In order to 

effectively carry out monitoring duties, 

PSOs must have sufficient periods of 

rest to minimize fatigue that would 

compromise their performance. Based 

on these considerations, and in 

consideration of the literature relating to 

mitigation and monitoring requirements 

and standard practice for scientific 

surveys, NMFS proposed minimum 

duty requirements. 

While NMFS agrees that there is 

likely to be some increased logistical 

burden associated with these 

requirements, which are expanded to 

some degree from current practice in the 

GOM in the absence of compliance with 

the MMPA, the Associations do not 

demonstrate that this burden is so large 

as to be impracticable. Similarly, they 

do not provide information supporting 

claims that these requirements would 

compromise personnel safety (and 

certainly do not support the claim that 

the requirements are ‘‘unnecessary and 

unsupported’’). The Associations’ 

comment states that survey vessels are 

typically at maximum capacity. NMFS 

acknowledges that in some cases, 

increased PSO staffing may result in a 

need for operators to balance staffing in 

other areas, such as in the seismic crew 

(25 to 30) or the three to seven client 

representatives that the Associations 

state are typically aboard a survey 

vessel, in order to accommodate 

necessary PSO staffing while not 

exceeding a vessel’s maximum capacity. 

However, assuming that a vessel’s 

maximum capacity is not exceeded, the 

claim that increasing the number of 

people aboard necessarily increases ‘‘the 

risk of injuries, illnesses, and 

evacuation for medical reasons’’ is 

unsupported. The comment is 

inconsistent regarding the number of 

PSO staff that the requirements would 

add, at various places stating that the 

requirements would result in the 

addition of six to eight or three to five 

PSO staff. Overall, the Associations state 

that only three (and possibly up to four) 

PSOs should be allowed, without 

explaining how this may achieve the 

objective of the proposed detectionbased mitigation requirements. 

However, in recognition of the likely 

increase in logistical burden and the 

possibility that individual LOA 

applicants may be able to demonstrate 

legitimate practicability issues, NMFS 

allows for the potential that an 

exception may be obtained specifically 

for the requirement that PSOs may be on 

duty for a maximum period of two 

hours, followed by a minimum period of 

one hour off. If an exception is granted 

based on practicability, the historical 

practice of a maximum on-duty period 

of four hours, followed by a minimum 

period of two hours off, would be 

substituted. 

Comment: The Associations and other 

industry commenters comment that the 

proposed requirement for visual 

observation before and during nighttime 

ramp-ups would be ineffective and 

potentially present safety concerns. 

Response: NMFS agrees that reduced 

efficacy should be expected for visual 

monitoring at night and, in 

consideration of comments asserting 

that this may present a safety concern, 

we have eliminated this requirement 

(noting that passive acoustic monitoring 

is still required for all nighttime 

operations of large airgun arrays). NMFS 

also agrees with the Associations’ 

comment that employment of a PSO for 

the dedicated purpose of documenting 

entanglements with ocean-bottom node 

(OBN) cables is unnecessary and has 

eliminated this requirement. 

Elimination of these requirements is 

expected to help somewhat in 

alleviating the logistical concerns 

expressed by the Associations. 

Comment: The Associations suggest 

that entanglement avoidance 

requirements should be removed from 

the ITR. The MMC comments that they 

support these requirements, and that the 

requirements are consistent with best 

management practices developed for 

avoiding entanglements. 

Response: The Associations’ 

comment, offered only in a footnote, is 

unclear as to whether the Associations’ 

suggestion is to remove all entanglement 

avoidance requirements or only the 

requirement to use negatively buoyant 

coated wire-core tether cable. (Note that 

NMFS does agree with the suggested 

elimination of a requirement for use of 

a dedicated PSO for purposes of 

documenting entanglement.) Regardless, 

the Associations’ suggestion that this 

requirement should be removed is 

keyed only to concern regarding 

practicability. NMFS disagrees that this 

requirement is impracticable, and the 

Associations offer no information to the 

contrary. Moreover, this measure is 

designed to prevent serious injury or 

mortality, which cannot be authorized 

under this rule. 

Here, no mortality was requested or 

proposed for authorization and, 

therefore, potential for death by 

entanglement must be avoided. There is 

demonstrated potential for 

entanglement of protected species in 

association with OBN survey 

operations. As described in the notice of 

proposed rulemaking, a GOM OBN 


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operator remarkably entangled three 

different protected species within a 

year—including an Atlantic spotted 

dolphin, as well as an ESA-listed turtle 

and a manta ray. BSEE subsequently 

issued two enforcement actions against 

the operator for incidents of noncompliance, indicating that it is 

appropriate to be stringent regarding 

requirements relating to entanglement 

avoidance. Specific appropriate 

measures were determined in 

consultation between NMFS, BOEM, 

and BSEE, including consultation with 

NMFS’ gear engineering experts, and 

were subsequently included in permits 

issued by BOEM (e.g., OCS Permit L17– 

009, issued July 11, 2017). NMFS 

proposed these specific measures for 

this ITR and no comments offering 

useful suggestions regarding potential 

modifications to the measures were 

received. A generic suggestion that no 

entanglement avoidance requirements 

are necessary is not credible. 

Comment: NRDC claims that NMFS 

fails to consider mitigation to reduce 

ship strike, particularly within Bryde’s 

whale habitat. Separately, NRDC states 

that NMFS should consider extending 

ship-speed requirements to all project 

vessels. The Associations state that 

vessel strike avoidance measures should 

not be required, or that there should be 

modifications and/or exemptions to the 

measures. 

Response: NMFS disagrees with 

NRDC’s contention. NMFS’ required 

vessel strike avoidance protocol is 

expected to further minimize any 

potential interactions between marine 

mammals and survey vessels, relative to 

the already low likelihood of vessel 

strike in relation to the activities 

considered herein. Please see ‘‘Vessel 

Strike Avoidance’’ for a full description 

of requirements, which include: Vessel 

operators and crews must maintain a 

vigilant watch for all marine mammals 

and must take necessary actions to 

avoid striking a marine mammal; vessels 

must reduce speeds to 10 kn or less 

when mother/calf pairs, pods, or large 

assemblages of cetaceans are observed 

near a vessel; and vessels must maintain 

minimum separation distances. 

We also note that NRDC’s comment 

that ‘‘vessels supporting the seismic 

operation are not similarly constrained’’ 

is in error. All project vessels are 

required to adhere to vessel strike 

avoidance requirements, including 

speed requirements in certain 

circumstances. As stated clearly in the 

proposed and final regulatory text, 

‘‘[v]essel operators and crews must 

maintain a vigilant watch for all marine 

mammals and slow down or stop their 

vessel or alter course, as appropriate 

and regardless of vessel size, to avoid 

striking any marine mammal [. . .].’’ 

Regarding whether ship speed 

requirements are warranted for all 

project vessels in the Bryde’s whale core 

habitat area to minimize risk of strike 

for Bryde’s whales, the consideration is 

no longer relevant to this rule, as 

activity within the Bryde’s whale core 

habitat area referenced by NRDC can no 

longer be considered through this rule 

following BOEM’s update to the scope 

of action. Further, we disagree that 

similar risk exists for sperm whales and 

beaked whales, as would be necessary to 

warrant vessel speed restrictions in the 

Mississippi Canyon area. There are very 

few records of vessel strikes for sperm 

whales, as compared with mysticete 

whales in general, and Bryde’s whales’ 

dive behavior in particular makes them 

potentially more susceptible to vessel 

strike. 

The Associations’ comments state that 

they are not aware of any incidence of 

ship strike associated with a 

geophysical survey, implying that no 

strike avoidance measures are 

necessary. The lack of recorded 

incidents of strike does not mean that 

none have occurred and, more 

importantly, does not mean that none 

will occur. Therefore, it is NMFS’ 

responsibility to prescribe measures that 

will achieve the least practicable 

adverse impact via avoidance of vessel 

strike. The comments go on to assert 

that there is ‘‘no evidence’’ that strike 

avoidance measures benefit marine 

mammals, despite the wealth of 

scientific evidence described in the 

notice of proposed rulemaking that 

slower vessel speeds result in fewer 

strikes and, if a strike does occur, a 

significantly lower likelihood of 

mortality. Separation requirements are 

common sense—a moving vessel should 

maintain some minimum distance from 

a whale to avoid striking it—and are 

similar to generic strike avoidance 

guidelines found elsewhere. The 

comments implying that these 

requirements are unwarranted and 

burdensome are unpersuasive, 

particularly given that BOEM has 

required essentially identical strike 

avoidance measures in the GOM via 

notices to lessees for many years 

(currently, via BOEM NTL No. 2016– 

G01). 

Nevertheless, NMFS recognizes that 

there are legitimate concerns regarding 

vessels towing gear and human safety 

issues. We have clarified in the strike 

avoidance measures that vessel strike 

avoidance requirements do not apply in 

any case where compliance would 

create an imminent and serious threat to 

a person or vessel or to the extent that 

a vessel is restricted in its ability to 

maneuver and, because of the 

restriction, cannot comply. 

Comment: The Associations and other 

industry commenters raise concerns 

regarding the PSO requirements, 

including that NMFS’ requirements for 

PSOs will result in labor shortages, and 

make an accompanying 

recommendation that these be 

‘‘preferred’’ training requirements that 

LOA-holders would not have to meet. 

Response: NMFS disagrees with the 

comments. The Associations’ statement 

that requirements for PSOs to have 

bachelor’s degrees or to satisfy a 

positive experience requirement are 

‘‘difficult, if not impossible, to achieve’’ 

is not persuasive. As explained in the 

notice of proposed rulemaking, NMFS 

discussed these PSO requirements with 

BSEE and with third-party observer 

providers. Both parties indicated that 

the requirements should not be 

expected to result in any labor shortage. 

We pointed out that during a period 

when a significantly greater amount of 

survey activity was occurring in the 

GOM than at present (i.e., with as many 

as 30 source vessels), requirements 

similar to those proposed did not result 

in any labor shortage. Moreover, NMFS 

specifically requested comment on the 

assumption that the requirements would 

not result in any labor shortage. The 

Associations’ expressed concern 

regarding the potential for a labor 

shortage, but do not provide any 

specific information to support the 

claims. We also clarify that not all PSOs 

must have a minimum of 90 days at-sea 

experience, with no more than 18 

months elapsed since the conclusion of 

the most recent relevant experience. As 

described in the notice of proposed 

rulemaking and herein, a minimum of 

one visual PSO and two acoustic PSOs 

must have such experience (rather than 

all PSOs). 

Comment: The Associations provide a 

list of specific proposed monitoring and 

reporting requirements that they assert 

are unreasonable or otherwise 

problematic. Some of these comments 

are echoed by other industry 

commenters. 

Response: We address the specific 

issues raised by the Associations in 

turn. 

1. The Associations state that bigeye 

binoculars should not be required, 

because they are expensive, require 

installation on the vessel, and are not 

appropriate for monitoring of the 

exclusion zone. 

NMFS disagrees with this comment. 

While it is correct that procurement of 

bigeye binoculars will incur costs, these 

costs were analyzed in NMFS’ RIA. 


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While bigeye binoculars may not be an 

individual PSO’s tool of choice for 

observing marine mammals at close 

range to the vessel, they are an 

indispensable tool for observing marine 

mammals at greater distance upon 

initial detection, are a standard 

component of marine mammal 

observation (for scientific purposes, but 

also as a part of standard mitigation 

monitoring conducted aboard surveys 

for which incidental take authorizations 

are issued), and will be helpful in more 

accurately identifying animals at greater 

distances, such that the precautionary 

shutdowns of concern to the 

Associations are avoided. 

2. The Associations state that PSOs 

should not report on factors that may be 

contributing to impaired observations, 

as such reporting may be speculative, 

unverifiable, and/or incorrect. 

NMFS disagrees with this comment. 

Reporting on such conditions is not 

connected to any requirement for action, 

but it is important to understand 

whether visual observation is able to be 

conducted in an effective fashion, 

whether it be due to weather conditions 

or to conditions on the vessel. 

3. The Associations suggest that the 

reporting requirement to estimate 

numbers of animals observed by cohort 

is overly complicated, and that the rule 

should require only recording of 

juveniles and adults. 

NMFS agrees with this comment and 

has made corresponding edits to the 

regulatory text. 

4. The Associations express some 

confusion regarding language 

addressing the information that visual 

PSOs should be compiling on a daily 

basis and whether these daily ‘‘reports’’ 

include estimates of actual animals 

taken. 

NMFS clarifies that the language cited 

by the Associations was not intended to 

mean that PSOs should be estimating 

‘‘takes’’ on a daily basis, and confirm 

that the Associations’ statement that 

such information should be included 

only in annual reporting is correct. 

5. Regarding NMFS’ consideration of 

an approach recommended by the MMC 

to produce estimates of actual take from 

observations of animals during survey 

effort, the Associations express concern 

about the appropriate application of this 

process, and suggest that the protocol be 

applied at the end of a period long 

enough to accumulate sufficient data to 

adequately evaluate the appropriateness 

and proper application of the process as 

part of the adaptive management 

process. 

NMFS shares many of the 

Associations’ concerns on this subject 

and regarding the specific methodology 

proposed by the MMC. NMFS looks 

forward to working with the 

Associations (as well as BOEM and 

BSEE) towards the development of 

appropriate methods through the 

adaptive management process. 

6. In reference to the requirement for 

the lead PSO to submit to NMFS a 

statement concerning mitigation and 

monitoring implementation and 

effectiveness, CGG adds that, because 

there is a lead PSO on each offshore 

rotation, the LOA-holder should submit 

collated statements. 

NMFS agrees that this may be a more 

practical approach. 

Comment: The MMC recommends 

that NMFS require LOA-holders to 

implement electronic reporting systems 

for field-based PSO data entry and 

expedited reporting. 

Response: NMFS agrees that this 

would be appropriate and would better 

ensure expedited field entry and quality 

control checking of PSO data, as well as 

facilitate data transfer, quality control, 

data analysis, and automated report 

generation. Overall, such a requirement 

is helpful to ensure the efficient 

synthesis of data, as required by the 

comprehensive reporting process. 

Comment: The Associations express 

support for NMFS’ proposed approach 

to comprehensive monitoring and 

development of a structured adaptive 

management process, and highlight 

their support for efforts that improve the 

quantity and quality of information 

related to determining the nature and 

magnitude of the potential effects of 

offshore geophysical activities on 

marine mammals, including industrysupported independent third-party 

research. 

Response: NMFS appreciates the 

comments and looks forward to 

continued engagement with the 

regulated community, as well as BOEM 

and BSEE, to improve the collection and 

use of the best available science 

consistent with the requirements and 

limits of the MMPA. 

Comment: The MMC comments that 

they support an annual adaptive 

management process for the issuance of 

LOAs in the GOM and recommend that 

they be included in the process along 

with representatives from BOEM, BSEE, 

and industry. 

Response: NMFS appreciates the 

comments and will ensure that the 

adaptive management process includes 

participation of the parties noted, where 

appropriate. 

Comment: NRDC asserts that NMFS 

fails to prescribe requirements sufficient 

to monitor and report takings of marine 

mammals. The MMC recommends that 

NMFS and BOEM work together to 

develop a coordinated long-term 

monitoring and research plan, and 

further recommends that, to facilitate 

the completion of the plan, NMFS and 

BOEM establish a GOM scientific 

advisory group, composed of agency 

and industry representatives and 

independent scientists, to assist in the 

identification and prioritization of 

monitoring needs and hypothesis-driven 

research projects to better understand 

the short- and long-term effects of 

geophysical surveys on marine 

mammals in the GOM. Commenters also 

noted that there are many research gaps 

that need to be filled and suggested that 

NMFS should include monitoring 

requirements that fill those gaps. 

Response: Section 101(a)(5)(A) of the 

MMPA indicates that any regulations 

NMFS issues shall include 

‘‘requirements pertaining to the 

monitoring and reporting of such 

taking.’’ This broad requirement allows 

for a high degree of flexibility in what 

NMFS may accept or include as a 

monitoring requirement, but is not 

specific in identifying a threshold of 

what should be considered adequate 

monitoring. Contrary to NRDC’s 

comments, except for IHAs in Arctic 

waters, NMFS’ implementing 

regulations do not provide a specific 

standard regarding what required 

monitoring and reporting measures 

‘‘must’’ accomplish. However, NMFS’ 

implementing regulations require 

incidental take applications to include 

suggested means of accomplishing the 

necessary monitoring and reporting that 

will result in increased knowledge of 

the species, the level of taking, or 

impacts on populations of marine 

mammals that are expected to be 

present while conducting activities, as 

well as suggested means of minimizing 

burdens by coordinating such reporting 

requirements with other schemes 

already applicable to persons 

conducting such activity. 50 CFR 

216.104(a)(13). The comment extracts 

pieces of this language to suggest that 

future LOA applicants are required to 

coordinate with each other’s monitoring 

efforts, ignoring the fact that the 

relevant regulation points to this 

coordination only in support of 

minimizing the burden on the applicant 

and that it refers to coordination with 

‘‘schemes already applicable to persons 

conducting such activity.’’ 50 CFR 

216.104(a)(13). NRDC attempts to 

further the argument that coordination 

across projects is required by statute by 

referencing a monitoring plan that they 

state is in development by BOEM. The 

MMC also references development of a 

‘‘long-term monitoring plan’’ that they 


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attribute to BOEM. NMFS is not aware 

that any such monitoring plan has been 

developed and, therefore, such a plan is 

not ‘‘already applicable to persons 

conducting such activity.’’ 

NRDC discusses a litigation 

settlement agreement related to the 

activities that are the subject of this rule, 

stating that ‘‘BOEM must analyze ‘the 

development of a long-term adaptive 

monitoring plan that addresse[s] 

cumulative and chronic impacts from 

seismic surveys on marine mammal 

populations in the Gulf of Mexico.’ ’’ 

NRDC et al. v. Bernhardt et al., 2:10–cv– 

1882, ECF No. 118 (E.D. La. June 18, 

2013). NRDC also cites BOEM’s PEIS in 

discussing this plan. That requirement 

in the settlement agreement does not 

pertain to NMFS’ statutory authority 

under the MMPA, which does not 

provide authority for NMFS to require 

the development of a ‘‘long-term 

monitoring plan’’ via the promulgation 

of ITRs or as a condition of an 

incidental take authorization. As noted 

above, NMFS’ statutory authority is to 

prescribe ‘‘requirements pertaining to 

the monitoring and reporting of such 

taking.’’ Although applicants that 

anticipate the need for consecutive 

periods of five-year regulations to cover 

ongoing activities may develop 

monitoring and reporting plans that 

extend past the five-year effectiveness 

period of a rule, section 101(a)(5)(A) 

requires only monitoring and reporting 

to cover the specified activities 

undertaken during the period of the 

rule. Were a long-term monitoring plan 

to be developed by BOEM, it would 

therefore be a voluntary undertaking on 

the part of participants, rather than a 

requirement under the MMPA. While 

certainly an exemplar of what a strong 

comprehensive monitoring plan can 

look like, the U.S. Navy’s Integrated 

Comprehensive Monitoring Program 

(ICMP), which NRDC references as a 

relevant analogue to the monitoring 

plan that they assert is required in the 

GOM to satisfy the requirements of the 

MMPA, should not be hailed as a model 

that should always be copied or a 

standard that must be achieved for all 

MMPA ITRs. The Navy’s ICMP was 

developed in close coordination with 

NMFS and reflects several factors that 

are not present for all ITRs (including 

these regulations) and that lay the 

groundwork for what is an exceptionally 

comprehensive program. Specifically, as 

the single entity for which take is 

authorized and that has the 

responsibility for implementing a 

monitoring program, the Navy has an 

existing organizational and funding 

structure that can support a truly 

integrated and comprehensive plan that 

would be far more difficult under a rule 

allowing for authorization of take by 

disparate applicants with varying 

activity levels, resource availability, and 

familiarity with regulatory requirements 

and marine mammal issues. Also, the 

Navy has an independent 

environmental stewardship mandate 

that influences their monitoring 

approach and supports a robust program 

intended to work in concert with the 

work funded through their Office of 

Naval Research and Living Marine 

Resources programs to create essentially 

full coverage of the science necessary to 

support vigorous environmental 

assessment and compliance across all 

Navy actions. Last, Navy training and 

testing utilize a large variety and 

number of platforms and sound sources, 

many of which can result in the take of 

marine mammals but cannot be 

monitored at the source. Accordingly, 

the Navy employs the robust, problembased, often off-site monitoring program 

currently in place in order to answer 

targeted questions with controlled 

studies. 

Although NMFS’ authority with 

regard to the prescription of monitoring 

requirements does not include 

mandating long term monitoring, the 

MMPA does require an assessment of 

impacts from the total taking by all 

persons conducting the activity. Thus, 

meaningful monitoring and reporting for 

a specified activity under section 

101(a)(5)(A) should be designed to help 

us better understand the total taking that 

is considered for authorization under 

the regulations for all persons 

conducting the specified activities 

under the five-year regulations. This 

necessitates coordination across 

applicants with regard to 

comprehensive analysis and reporting of 

information collected in relation to ‘‘the 

level of taking or impacts on 

populations of marine mammals that are 

expected to be present while conducting 

activities.’’ 50 CFR 216.104(a)(13). We 

discuss these comprehensive reporting 

requirements in greater detail in 

Monitoring and Reporting. These 

requirements are appropriate to the 

necessary function of informing the 

assessment of the overall impact of the 

incidental take allowable under the 

regulations and acknowledge the need 

to conduct aggregation and analysis of 

the data in a manner that directly 

informs the question of whether and the 

degree to which marine mammal 

populations addressed may be affected 

by the incidental take authorized by 

LOAs. 

We appreciate the MMC’s 

acknowledgement of the investments 

made by BOEM and industry (via the 

E&P Sound and Marine Life Joint 

Industry Program) towards better 

understanding of marine mammal 

abundance and distribution, the 

characterization of anthropogenic sound 

sources in the GOM, and the effects of 

sound on marine mammal hearing and 

behavior, among other initiatives. We 

also note that much of the research 

recommended by NRDC has been 

conducted via the BOEM-sponsored 

Gulf of Mexico Marine Assessment 

Program for Protected Species initiative. 

However, while these voluntary efforts 

are commendable, section 101(a)(5)(A) 

does not require hypothesis-driven, 

focused research pertaining to the 

impact and mitigation of chronic noise 

exposure on populations of special 

concern, nor does it require a 

‘‘coordinated long-term monitoring and 

research plan,’’ as expressed by the 

commenters. 

Regarding the MMC’s 

recommendation that NMFS establish a 

GOM ‘‘scientific advisory group, 

composed of agency and industry 

representatives and independent 

scientists, to assist in the identification 

and prioritization of monitoring needs 

and hypothesis-driven research 

projects,’’ NMFS would be willing to 

explore with the MMC the appropriate 

mechanisms for convening such a 

group, including consideration of the 

MMC’s authorities under the MMPA. 

The monitoring approach described in 

this preamble includes LOA-specific 

monitoring and reporting set forth in the 

regulations and, separately, outlines a 

framework for potential data collection, 

analysis, research, or collaborative 

efforts that are not specified in these 

regulations but which work towards 

satisfying the information elements 

identified in our implementing 

regulations. NMFS is committed to 

working with industry and BOEM 

through the adaptive management 

process to ensure that LOA-specific 

monitoring and reporting will be used 

appropriately to help better understand 

the impacts of the total taking from the 

specified activity contemplated in this 

ITR on the affected populations, as well 

as how the more overarching voluntary 

efforts will be identified and carried out. 

Comment: The Associations reiterate 

their belief that NMFS, as the regulating 

agency, has the responsibility to collect, 

organize, and assess all of the data 

reported to NMFS under the terms of 

issued LOAs. 

Response: NMFS disagrees with this 

comment. The MMPA requires NMFS to 

prescribe regulations setting forth 

requirements pertaining to the 

monitoring and reporting of ‘‘such 


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taking.’’ 16 U.S.C. 

1371(a)(5)(A)(i)(II)(bb). (In contrast, the 

other required component of activityspecific regulations, relating to 

mitigation requirements, refers to 

‘‘taking pursuant to such activity.’’ 16 

U.S.C. 1371(a)(5)(A)(i)(II)(aa). In NMFS’ 

view, these monitoring and reporting 

requirements in our activity-specific 

regulations refer to the total taking from 

the specified activity as a whole, and 

they are requirements that can be 

imposed on those entities availing 

themselves of LOAs issued under the 

activity specific regulations. Therefore, 

it is incumbent upon LOA-holders, 

collectively, to provide this information 

to NMFS in a reasonably synthesized 

form such that NMFS may adequately 

assess the effects of the specified 

activity on an ongoing basis. This 

information may in some cases be 

essential to NMFS’ ability to carry out 

50 CFR 216.105(e) (‘‘Letters of 

Authorization shall be withdrawn or 

suspended, either on an individual or 

class basis, as appropriate, if, after 

notice and opportunity for public 

comment, the Assistant Administrator 

determines that: (1) The regulations 

prescribed are not being substantially 

complied with; or (2) The taking 

allowed is having, or may have, more 

than a negligible impact on the species 

or stock or, where relevant, an 

unmitigable adverse impact on the 

availability of the species or stock for 

subsistence uses’’ (emphasis added).) 

While NMFS recognizes that the 

Associations are not subject to the ITR 

(including any reporting requirements 

in the ITR or related LOAs), LOAholders (many of which are likely to be 

Association members) will collectively 

be responsible for the comprehensive 

reporting requirements described 

herein. The Associations in their 

comment commit to participate in the 

annual assessment process, and NMFS 

welcomes that participation. 

Comment: The MMC recommends 

that NMFS require industry operators to 

measure and report the horizontal 

leakage of their various airgun arrays 

and investigate options to minimize 

horizontal sound leakage from those 

array configurations. 

Response: As stated in the notice of 

proposed rulemaking, NMFS encourages 

the minimization of unnecessary 

horizontal propagation. However, while 

the MMC’s recommendation would 

likely lead to a better understanding of 

actual horizontal propagation (or 

‘‘leakage’’) that does occur, it is not clear 

that the product of such measurements 

(termed ‘‘waste ratios’’ by the MMC) 

would necessarily lead to a viable path 

to reducing such leakage. In addition, 

the MMC does not specify what it 

recommends as a sufficient amount of 

data concerning waste ratios to allow 

consideration of a potential threshold. 

Thus, the comment implies that all 

operators would be required to conduct 

field measurements of the acoustic 

output of airgun arrays under this 

recommendation, which NMFS believes 

would not be practicable. NMFS 

appreciates the comment and will 

further consider the utility of the 

recommendation, and methods of 

implementation, through the adaptive 

management process. 

We do note that BOEM currently 

requires operators to confirm through 

the permitting process that the airgun 

arrays used have been calibrated or 

tuned to maximize subsurface 

illumination and to minimize, to the 

extent practicable, horizontal 

propagation of noise. 

Comment: NRDC suggests that NMFS 

should consider requiring use of 

thermal detection as a supplement to 

visual monitoring. 

Response: NMFS appreciates the 

suggestion and agrees that relatively 

new thermal detection platforms have 

shown promising results. Following 

review of NRDC’s letter, we considered 

these and other supplemental platforms 

as suggested. However, to our 

knowledge, there is no clear guidance 

available for operators regarding 

characteristics of effective systems, and 

the detection systems cited by NRDC are 

typically extremely expensive, and are 

therefore considered impracticable for 

use in most surveys. For example, one 

system cited by NRDC (Zitterbart et al., 

2013)—a spinning infrared camera and 

an algorithm that detects whale blows 

on the basis of their thermal signature— 

was tested through funding provided by 

the German government and, according 

to the author at a 2015 workshop 

concerning mitigation and monitoring 

for seismic surveys, the system costs 

hundreds of thousands of dollars. We 

are not aware of its use in any 

commercial application. Further, these 

systems have limitations, as 

performance may be limited by 

conditions such as fog, precipitation, 

sea state, glare, water- and airtemperatures and ambient brightness, 

and the successful results obtained to 

date reflect a limited range of 

environmental conditions and species. 

NRDC acknowledges certain of these 

limitations in their comment, including 

that the systems have lesser utility in 

warmer temperatures. The GOM, 

however, is a warm environment. NRDC 

does not provide specific suggestions 

with regard to recommended systems or 

characteristics of systems. NMFS does 

not consider requirements to use 

systems such as those recommended by 

NRDC to currently be practicable. 

Comment: NRDC states that NMFS 

should prescribe requirements for use of 

‘‘noise-quieting’’ technology. NRDC 

elaborates that in addition to requiring 

noise-quieting technology (or setting a 

standard for ‘‘noise output’’), NMFS 

should ‘‘prescribe targets to drive 

research, development, and adoption of 

alternatives to conventional airguns.’’ 

Response: NMFS agrees with NRDC 

that development and use of quieting 

technologies, or technologies that 

otherwise reduce the environmental 

impact of geophysical surveys, is a 

laudable objective and may be 

warranted in some cases. However, here 

the recommended requirements either 

are not practicable or are not within 

NMFS’ authority to require. To some 

degree, NRDC misunderstands the 

discussion of this issue as presented in 

the notice of proposed rulemaking. 

NMFS recognizes, for example, that 

certain technologies, including the Bolt 

eSource airgun, are commercially 

available, and that certain techniques 

such as operation of the array in 

‘‘popcorn’’ mode may reduce impacts 

when viable, depending on survey 

design and objectives. However, a 

requirement to use different technology 

from that planned or specified by an 

applicant—for example, a requirement 

to use the Bolt eSource airgun—would 

require an impracticable expenditure to 

replace the airguns planned for use. 

NRDC offers no explanation for why 

such a large cost imposition (in the 

millions of dollars) should be 

considered practicable. 

Separately, NRDC appears to suggest 

that NMFS must require or otherwise 

incentivize the development of wholly 

new or currently experimental 

technologies. We note that BOEM’s PEIS 

concluded that alternative technologies 

are in various stages of development, 

and that none of the systems with the 

potential to replace airguns as a seismic 

source are currently commercially 

available for use on a scale of activity 

such as that considered herein. 

Although some alternative technologies 

are available now, or will be in the next 

several years, for select uses, none are, 

or will likely be in the next five years, 

at a stage where they can replace airgun 

arrays outright. However, some may be 

used in select environments when 

commercially available. According to 

BOEM, the suggestion in this comment 

would not provide the oil and gas 

industry or the government with 

sufficiently accurate data on the 

location, extent, and properties of 

hydrocarbon resources or the character 


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of formation fluids or gases, or 

information on shallow geologic hazards 

and seafloor geotechnical properties, in 

order to explore, develop, produce, and 

transport hydrocarbons safely and 

economically. Such technologies may be 

evaluated in the future as they become 

commercially available and on a scale 

commensurate to the need. In summary, 

while NMFS agrees that noise quieting 

technology is beneficial, the suggestions 

put forward by NRDC are either 

impracticable or outside the authority 

provided to NMFS by the MMPA. 

However, NMFS would consider 

participating in or learning about related 

efforts by parties interested in 

investigating these technologies. We 

note that NMFS has described a process 

by which new and unusual technologies 

may be considered for use under this 

rule (see Letters of Authorization). 

Comment: NRDC recommended that 

NMFS consider compensatory 

mitigation for the adverse impacts of the 

specified activity on marine mammals 

and their habitat that cannot be 

prevented or mitigated. 

Response: NMFS has prescribed a 

robust comprehensive suite of measures 

that are expected to reduce the amount 

of Level A and Level B harassment take, 

as well as the severity of any incurred 

impacts on the species or stock and 

their habitat. Compensatory mitigation 

is not required under the MMPA. 

Importantly, NRDC did not recommend 

any specific measure(s), rendering it 

impossible to evaluate their 

recommendation. In addition, many of 

the methods of compensatory mitigation 

that have proven successful in terrestrial 

settings (e.g., purchasing or preserving 

land with important habitat, improving 

habitat through plantings) are not 

applicable in a marine setting with such 

far-ranging species. NMFS concludes 

that the concept is too speculative at 

this time to warrant specific action. 

Letters of Authorization 

Comment: The Associations assert 

that it is ‘‘arbitrary and inappropriate’’ 

for NMFS to provide an opportunity for 

public notice and comment in the event 

that an LOA applicant wishes to deviate 

from the modeling approach used 

herein (which was subject to public 

review and comment). The Associations 

state that such a requirement is contrary 

to the legal requirement to base the 

authorization of incidental take under 

the MMPA on the best available science, 

as better information may become 

available during the period of 

effectiveness for the ITR. 

Response: LOAs issued under the 

authority of section 101(a)(5)(A) and 

NMFS’ implementing regulations must 

be preceded by both substantive 

findings (including a negligible impact 

finding) and a process that includes 

rulemaking after notice and comment. 

In the case of LOA applications whose 

take estimates are not based on the 

modeling used for the rulemaking, 

NMFS has determined that it may be 

appropriate to subject those to notice 

and comment in certain circumstances. 

Such a process requirement does not 

impede or contradict the requirement to 

use the best available information. 

Comment: The Associations and other 

industry commenters assert that there is 

no legal justification for NMFS to use 

the ITR as a mechanism to limit the 

number of activities that may occur in 

the GOM, stating that authorization of 

the activities themselves are subject to 

BOEM’s jurisdiction. 

Response: NMFS clarifies that we do 

not intend to use the ITR in the manner 

suggested by the Associations, and that 

the language cited in the Associations’ 

comment (‘‘cap on the number of 

authorizations that could be issued’’) 

was inartful. We also acknowledge 

BOEM’s jurisdiction regarding the 

authorization of the subject activities 

themselves. However, the total taking 

analyzed in the negligible impact 

analysis necessarily bounds the taking 

that may be authorized under these 

activity-specific regulations, as 

described in the Estimated Take section. 

Comment: Referencing a cap on the 

number of authorizations that could be 

issued, the MMC recommends that 

NMFS (1) provide details to the public 

on how NMFS plans to implement the 

proposed cap and the basis for it; and 

(2) allow for an additional 30-day 

comment period to review such details 

sufficiently in advance of issuing the 

final rule. 

Response: As discussed in the 

preceding comment response, the 

language referenced by the MMC was 

meant only to affirm what is inherent in 

the regulations, i.e., that the amount of 

take analyzed for making a finding of 

negligible impact necessarily bounds 

the amount of take that may be 

authorized through LOAs issued under 

this rule (provided they also satisfy the 

small numbers requirement). The MMC 

places undue emphasis on this aspect of 

rule implementation. In claiming a 

‘‘lack of transparency,’’ the MMC 

assigns complexity that does not exist, 

and no additional details exist to give. 

Therefore, we do not implement the 

MMC’s recommendation for additional 

public comment. 

Comment: The Associations and other 

industry commenters express concern 

regarding the implementation of the 

ITR, including the evaluation and 

processing of LOA requests. The 

Associations recommend that the final 

ITR clearly address how NMFS plans to 

process LOA applications in a timely 

and efficient manner, and encourage 

NMFS to retain flexibility in the final 

ITR for the development of efficient and 

effective LOA processes through 

workshops or other engagement with 

BOEM and the regulated community. 

Response: NMFS appreciates the 

concerns expressed by the commenters. 

We believe we have addressed these 

issues in the updated preamble to this 

ITR (see Letters of Authorization) and 

are committed to ongoing, proactive 

engagement with BOEM, BSEE, and the 

regulated community towards efficient 

implementation of the ITR. 

Comment: BP comments that a lowfrequency geophysical survey source 

they refer to as ‘‘Wolfspar’’ should be 

considered to be within the range of 

potential impacts modeled in the ITR 

and, therefore, able to be used under an 

LOA issued pursuant to the ITR. 

Response: NMFS will look forward to 

evaluating the Wolfspar source 

according to the ‘‘New and Unusual 

Technology’’ review process detailed in 

the Letters of Authorization section of 

this preamble. Only upon review of 

additional information regarding the 

source can NMFS make a determination 

in this regard. 

Regulatory Impact Analysis 

Comment: The Associations provide a 

bulleted list of criticisms of the RIA. We 

summarize these here and provide brief 

responses below. For full detail, we 

refer the reader to the final RIA, 

available online at: 

www.fisheries.noaa.gov/action/ 

incidental-take-authorization-oil-andgas-industry-geophysical-surveyactivity-gulf-mexico. The Associations’ 

critiques of the RIA are not 

accompanied by any specific 

recommendations regarding potential 

changes to the analysis or additional 

data. 

• The Associations assert that the RIA 

assumes that the only indirect costs of 

closures are delays, and state that such 

measures ‘‘may render some survey 

proposals economically unattractive to 

the point at which prospects will not be 

explored.’’ The Associations also state 

that closures may be assumed to be 

permanent, thereby having an 

additional dampening impact on 

exploration activity. 

Response: The RIA accompanying the 

proposed rule did not assume that the 

costs of closures are simply delays. The 

RIA stated that the ‘‘closures have the 

potential to affect the overall levels of 

G&G [geological and geophysical] 


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activities that occur in the GOM over 

the five-year timeframe of the analysis. 

In the case that the closures delay or 

reduce the ability of industry to collect 

the necessary data to identify and 

recover oil and gas resources, the overall 

level of oil and gas production in the 

GOM may in turn be delayed or 

reduced.’’ The RIA for the proposed rule 

discussed the possibility of both delays 

and reductions in activity due to the 

uncertainty surrounding rule impacts. 

In addition, NMFS reiterates that 

closures and any other measures are in 

effect only during the five-year period of 

effectiveness of the ITR. It is unclear 

why closures may be ‘‘assumed to be 

permanent’’ if the regulations requiring 

them are effective only for five years. 

We note here that two of the closure 

areas included in the proposed rule and 

evaluated in the RIA are no longer in the 

final rule because they fall outside the 

area considered for this rule, following 

BOEM’s update of the rule’s scope. 

• The Associations assert that the RIA 

‘‘incorrectly assumes that the costs of 

closures are highly uncertain or even 

low because geologic potential of some 

areas is low,’’ stating that geophysical 

surveys are essential to understanding 

the geologic potential of the areas. 

Response: There is significant 

uncertainty regarding the development 

potential of the areas considered for 

closure, and the RIA did not simply 

assume that it is ‘‘low.’’ The RIA 

accompanying the proposed rule 

provided the best available information 

regarding lease activity and reserves in 

the proposed closure areas and 

characterized the associated 

uncertainty. 

• The Associations assert that the RIA 

‘‘wrongly assumes that the GOMESA 

moratorium prevents exploration of the 

Eastern GOM,’’ when in fact the 

moratorium is currently set to expire in 

2022. The Associations go on to state 

that ‘‘the RIA seriously misleads readers 

about the costs of closure and increased 

restrictions in the Eastern GOM,’’ and 

that the potential cost of the closure 

should be considered equivalent to that 

of the closure considered for the Central 

GOM because ‘‘high-potential resources 

may underlie’’ the Eastern GOM closure. 

Response: The RIA made no such 

assumption, and in fact acknowledged 

that the moratorium does not restrict 

exploration per se. However, the Eastern 

GOM closure referenced by the 

commenter is no longer part of the rule, 

as BOEM’s update to the scope of the 

rule has removed the area from 

consideration. 

• The Associations state that the RIA 

fails to account for the environmental 

benefit associated with avoiding 

unnecessary drilling via use of 

geophysical surveys. Chevron echoes 

this comment. Neither commenter 

provides any specific recommendation 

as to how they believe it should be 

considered. 

Response: The RIA does acknowledge 

the benefit of geophysical technology. 

However, we note that the magnitude of 

this benefit depends on the extent to 

which exploration and development 

companies move forward with drilling 

in cases where they have less seismic 

data than they otherwise would because 

of the requirements of the ITR. 

• The Associations assert that the RIA 

for the proposed rule incorrectly 

assumes current geophysical data in the 

Eastern GOM is suitable, stating that 

‘‘there is high demand for state-of-theart new data for Eastern GOM frontier 

areas where older data is considered 

unsuitable to support new investment.’’ 

Response: The RIA did not state that 

current geophysical data for the Eastern 

GOM is ‘‘suitable.’’ Rather, the RIA 

stated that ‘‘the suitability of existing 

G&G data to direct oil and gas 

production in the closure areas is 

unknown.’’ As noted herein, the area of 

concern to the commenter is no longer 

considered through this rule. 

• The Associations assert that the RIA 

‘‘fails to account for possible increased 

industry interest in Eastern GOM 

geophysical surveys’’ and, therefore, 

that the RIA inappropriately relies on 

old statistics on survey interest for 

estimating costs. 

Response: The RIA acknowledged that 

industry interest in Eastern GOM 

geophysical surveys is likely to increase 

leading up to the expiration of the 

moratorium. As noted herein, the area of 

concern to the commenter is no longer 

considered through this rule. 

Comment: Chevron comments that 

NMFS should ensure in the final ITRs 

that all costs are evaluated, including 

the cost of reduced environmental 

benefits from effective geophysical 

surveys. The Associations echo these 

concerns. 

Response: NMFS has appropriately 

evaluated the regulatory impacts of the 

ITR according to the requirements of 

E.O. 12866. See section 5.3 of the Final 

RIA, which describes this benefit of 

geophysical technology. The magnitude 

of this benefit depends on the extent to 

which exploration and development 

companies move forward with drilling 

in cases where they have less seismic 

data than they otherwise would because 

of the rule. 

National Environmental Policy Act 

Comment: NRDC reiterates (and 

resubmitted) comments that it 

submitted on BOEM’s draft PEIS, stating 

that as it relates to marine mammals, the 

PEIS is deficient on its face due to the 

range of alternatives and mitigation 

considered, significance criteria, take 

and impact estimates, and cumulative 

impacts analysis. 

Response: As a cooperating agency, 

NMFS reviewed all responses to 

comments on the draft PEIS that were 

relevant to its management authorities 

and provided input where we deemed it 

appropriate. See Appendix M of the 

Final PEIS. 

Comment: NRDC also states that 

NMFS cannot rely on the PEIS because 

it ‘‘does not adequately address NMFS’ 

own actions and responsibilities under 

the MMPA,’’ given that BOEM’s PEIS is 

‘‘framed around a fundamentally 

different purpose and need’’ relating to 

its mandates under the Outer 

Continental Shelf Lands Act (OCSLA) 

that is ‘‘incongruent with NMFS 

obligations under the MMPA.’’ 

Response: The proposed action at 

issue is BOEM’s issuance of permits or 

authorizations for G&G activities in the 

GOM. PEIS Chapter 1.1.1. The PEIS also 

recognizes that NMFS’ proposed action 

is a decision on whether to approve 

BOEM’s petition for incidental take 

regulations. NOAA is a cooperating 

agency on BOEM’s PEIS, as NOAA has 

jurisdiction by law and special expertise 

over marine resources impacted by the 

proposed action, including marine 

mammals and federally listed 

threatened and endangered species. The 

PEIS explicitly recognizes that the PEIS 

would be used in support of NMFS’ 

decision on BOEM’s petition for 

incidental take regulations. See PEIS 

Appendix B. 


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Consistent with the Council on 

Environmental Quality’s (CEQ’s) 

regulations, it is accepted NEPA 

practice for NOAA to adopt a lead 

agency’s NEPA analysis when, after 

independent review, NOAA determines 

the document to be sufficient in 

accordance with 40 CFR 1506.3. 

Specifically here, NOAA is satisfied that 

BOEM’s PEIS adequately addresses the 

impacts of issuing the MMPA incidental 

take authorization and that NOAA’s 

comments and concerns have been 

adequately addressed. There is no 

requirement in CEQ regulations that 

NMFS, as a cooperating agency, issue a 

separate purpose and need statement in 

order to ensure adequacy and 

sufficiency for adoption. Nevertheless, 

the statement of Purpose and Need in 

the PEIS explicitly acknowledges 

NMFS’ own separate action of issuing 

an MMPA incidental take authorization, 

and the PEIS is replete with discussion 

of issues relating to the issuance of an 

MMPA authorization, including 

discussion of marine mammal impacts, 

mitigation, and take estimates. NMFS’ 

early participation in the NEPA process 

and the agency’s continuing role in 

shaping and informing analyses using 

its special expertise ensured that the 

analysis in the PEIS is sufficient for 

purposes of NMFS’ own NEPA 

obligations related to its issuance of an 

incidental take authorization under the 

MMPA. 

Regarding the alternatives, NMFS’ 

early involvement in the development 

of the PEIS and role in evaluating the 

effects of incidental take under the 

MMPA ensured that the PEIS would 

include adequate analysis of a 

reasonable range of alternatives. The 

PEIS includes a no action alternative 

specifically to address what could 

happen if NMFS did not issue an 

MMPA authorization. Some of the 

alternatives explicitly reference marine 

mammals or mitigation designed for 

marine mammals in their title. More 

importantly, these alternatives fully 

analyze a comprehensive variety of 

mitigation measures for marine 

mammals. This mitigation analysis 

supported NMFS’ evaluation of our 

options in potentially issuing an MMPA 

authorization. This approach to 

evaluating a reasonable range of 

alternatives is consistent with NMFS’ 

policy and practice for issuing MMPA 

incidental take authorizations. NOAA 

independently reviewed and evaluated 

the PEIS, including the purpose and 

need statement and range of 

alternatives, and determined that the 

PEIS fully satisfies NMFS’ NEPA 

obligations related to its decision to 

issue the MMPA final rule and 

associated Letters of Authorization. 

Accordingly, NMFS has adopted the 

PEIS. 

Finally, we disagree with the notion 

that the district court’s decision in 

Conservation Council for Hawaii v. 

NMFS somehow would preclude NMFS 

from adopting the PEIS here. In 

Conservation Council, the court 

concluded that the FEIS NMFS adopted 

was deficient because it did not 

consider a true ‘‘no action’’ alternative 

from NMFS’ perspective, in that the ‘‘no 

action’’ alternative assumed 

continuation of Navy’s baseline 

activities, and therefore avoided the task 

facing NMFS, i.e., whether to authorize 

the requested take. 97 F. Supp. 3d at 

1236. In contrast, the PEIS here for 

NMFS’ rule for GOM geophysical 

surveys includes a ‘‘no action’’ 

alternative from the perspectives of both 

NMFS and BOEM. See PEIS, Chapter 

2.9.1, pp. 2–20 to 2–22. 

Information Quality Act 

Comment: The CRE states that NMFS’ 

Technical Guidance violates 

Information Quality Act (IQA) 

requirements, because it (1) does not 

include an IQA Pre-dissemination 

Review Certification; (2) relies heavily 

on models that have not been peer 

reviewed to determine whether they are 

validated and comply with the 

Environmental Protection Agency’s 

Council for Regulatory Environmental 

Modeling (CREM) guidance; and (3) 

relies heavily on models that were not 

peer reviewed in compliance with the 

Office of Management and Budget’s 

(OMB) Final Information Quality 

Bulletin for Peer Review (70 FR 2664; 

January 14, 2005). 

Response: The CRE is incorrect. 

NMFS performed appropriate predissemination review and 

documentation according to relevant 

agency guidance (NMFS Policy 

Directive PD 04–108, Policy on the Data 

Quality Act; NMFS Instruction 04–108– 

03, Section 515 Pre-Dissemination 

Review and Documentation Guidelines). 

All aspects of development of the 2016 

Technical Guidance were peer reviewed 

(www.cio.noaa.gov/services_programs/ 

prplans/ID43.html). Also of note, the 

same information and methodology that 

supported development of NMFS’ 

Technical Guidance (NMFS, 2016, 2018) 

were more recently published in a peerreviewed journal (Southall et al., 

2019a). 

Comment: CRE states that NMFS’ use 

of models in the acoustic exposure 

modeling process for this rule violates 

the IQA because ‘‘they are incomplete, 

unfinished, inaccurate, unreliable, have 

never been validated, and have never 

been peer reviewed.’’ CRE also asserts 

that NMFS has not conducted predissemination review and 

documentation as required by the IQA 

and implies that, because NMFS did not 

address the IQA in the notice of 

proposed rulemaking, we must be in 

violation of it. 

Response: CRE is incorrect; NMFS is 

in compliance with the requirements of 

the IQA. NMFS conducted the required 

pre-dissemination review at both the 

proposed and final stages of this 

rulemaking and appropriate 

documentation is included in the 

administrative record for this action. 

CRE asserts that the models used in 

NMFS’ rulemaking process are not 

properly evaluated or validated. CRE 

asserts that as a result, NMFS ‘‘grossly 

overestimate[s] exposures and takes.’’ 

According to the CRE, the supposed 

failings of the modeling necessarily lead 

to the overestimation of takes, as 

opposed to error in potentially different 

directions and of different magnitude in 

association with the various 

components of the modeling process. 

CRE comments at length that NMFS 

should use only the relatively simple 

approach of ‘‘Line Transect,’’ which 

they believe will result in lower 

numbers of estimated takes (see more 

detailed response to these suggestions 

earlier in Comments and Responses). 

In asserting that the models used in 

support of this rule have not been 

adequately validated or peer reviewed, 

CRE refers to a similarly sophisticated, 

proprietary modeling package (Marine 

Acoustics, Inc.’s Acoustic Integration 

Model (‘‘AIM’’)) that underwent a 

dedicated external peer review, stating 

that AIM is ‘‘therefore properly 

validated and acceptable for regulatory 

use.’’ However, the AIM package 

functions virtually the same as the 

models used for this analysis, and was 

used for an essentially identical 

modeling process developed in support 

of BOEM’s 2014 PEIS for geological and 

geophysical survey activities on the 

Mid- and South Atlantic Outer 

Continental Shelf. 

The IQA concerns expressed in the 

comment are unfounded. As stated in 

the NOAA Information Quality 

Guidelines, information quality is 

composed of three elements: Utility, 

integrity, and objectivity. 

Utility means that disseminated 

information is useful to its intended 

users. The disseminated information at 

issue here—modeled exposures of 

marine mammals to underwater noise— 

is useful to NMFS in that it forms the 

basis for subsequent analysis allowing 

NMFS to make determinations 


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necessary under the MMPA. It is useful 

to the public in that it enables 

appropriate review of NMFS’ action and 

supporting determinations. It is useful 

to the regulated entities in that it will 

allow for an efficient regulatory regime, 

in which potential LOA applicants may 

make use of the existing modeling effort 

(while being afforded the opportunity to 

engage in different modeling if desired) 

in service of a streamlined LOA 

application process. 

Integrity refers to security, i.e., the 

protection of information from 

unauthorized access or revision, to 

ensure that the information is not 

compromised through corruption or 

falsification. The integrity of the 

information disseminated herein was 

not questioned, but it meets all relevant 

standards for integrity (as demonstrated 

in the administrative record for this 

action). 

Finally, objectivity ensures that 

information is accurate, reliable, and 

unbiased, and that information products 

are presented in an accurate, clear, 

complete, and unbiased manner. 

Objectivity consists of two distinct 

elements: Presentation and substance. 

The presentation element includes 

whether disseminated information is 

presented in an accurate, clear, 

complete, and unbiased manner and in 

a proper context. NMFS has 

appropriately presented the 

disseminated information, and CRE 

does not assert otherwise. The substance 

element involves a focus on ensuring 

accurate, reliable, and unbiased 

information. Disseminated information 

reflects the inherent uncertainty of the 

scientific process, which is inseparable 

from the concept of statistical variation. 

In assessing information for accuracy, 

the information is considered accurate if 

it is within an acceptable degree of 

imprecision or error appropriate to the 

particular kind of information at issue 

and otherwise meets commonly 

accepted scientific and statistical 

standards, as applicable. This concept is 

inherent in the definition of 

‘‘reproducibility,’’ as used in the OMB 

IQA Guidelines and adopted by NOAA. 

Therefore, original and supporting data 

that are within an acceptable degree of 

imprecision, or an analytic result that is 

within an acceptable degree of 

imprecision or error, are by definition 

within the agency standard and are 

therefore considered correct. CRE does 

not assert that the modeling results 

disseminated by NMFS are outside the 

bounds of an acceptable degree of 

imprecision or error. 

The modeling report goes into great 

detail regarding potential error 

associated with different facets of the 

modeling process, and provides specific 

analysis of uncertainty in both the 

acoustic and animal phases of the 

modeling process (discussed in detail in 

the notice of proposed rulemaking and 

in the modeling report). Uncertainty 

associated with all aspects of the 

modeling was clearly identified and 

evaluated as to the effect on the overall 

modeling results. In order to best 

represent the overall uncertainty 

associated with the modeling, the report 

presents the exposure estimates as a 

distribution. The exposure estimate 

distribution provides the public with an 

understanding of the probability of 

certain events occurring, including the 

probability that an operation would not 

result in any animals being exposed 

above a defined threshold. 

Regarding reproducibility and 

transparency, the NOAA Information 

Quality guidelines state that 

‘‘reproducibility means that the 

information is capable of being 

substantially reproduced, subject to an 

acceptable degree of imprecision [. . .] 

With respect to analytic results, ‘capable 

of being substantially reproduced’ 

means that independent analysis of the 

original or supporting data using 

identical methods would generate 

similar analytic results, subject to an 

acceptable degree of imprecision or 

error.’’ We have no reason to believe 

that similar modeling (for example, 

using the AIM modeling package) using 

the same data inputs would not return 

similar analytic results, and CRE 

provides none. Transparency is not 

defined in the OMB Guidelines, but is 

at the heart of the reproducibility 

standard. At its most basic, 

transparency—and ultimately 

reproducibility—is a matter of showing 

how you got the results you got. NMFS 

has produced a painstakingly detailed 

accounting of the modeling process and 

decisions made, such that an 

independent party using a different set 

of models would be able to perform a 

similar modeling effort in order to 

evaluate the similarity of the results. 

The modeling report includes a full 

description of all assumptions and 

reference material used for both sound 

sources and species of interest. CRE 

provides no meaningful argument to the 

contrary. 

The NOAA Information Quality 

guidelines expressly address and allow 

for the use of proprietary models and 

other supporting information which 

cannot be disclosed. In such cases, the 

guidelines call for ‘‘especially rigorous 

robustness checks.’’ As summarized 

below and described in detail in the 

notice of proposed rulemaking and 

modeling report, NMFS has conducted 

rigorous robustness checks of the 

proprietary models used in support of 

this rule. 

The models used in estimating the 

acoustic exposures described herein 

have been appropriately validated and 

reviewed. As described in detail in the 

notice of proposed rulemaking and in 

the modeling report, the acoustic 

exposure modeling effort requires the 

use of a package of models. Acoustic 

exposure modeling in general is not 

novel, controversial, or precedentsetting, and similar modeling has been 

performed for various applications for 

over 15 years. This type of modeling 

requires modeling of the acoustic output 

of a source, in this case a specified 

airgun array (as well as a single airgun 

and certain electromechanical sources 

that were modeled separately). The 

output of the source model is an input 

to a model or models used to model 

underwater sound propagation as a 

function of range from the source. The 

output of this process is a 3D sound 

field. Subsequently, an animal 

movement model is used to simulate the 

behavior of virtual animats in relation to 

the modeled sound field. Each animat 

acts as a virtual dosimeter, producing 

individual records of exposure history. 

There were many animats in the 

simulations, and together their received 

levels represent the probability, or risk, 

of exposure for each survey. 

In this case, the source model used 

was JASCO Applied Sciences’ 

proprietary Airgun Array Source Model 

(AASM). The AASM accepts airgun 

volume, pressure, and depth and has 

internal parameters that must be fit to 

real signature data. The model was 

originally fit to a large library of 

empirical airgun data spanning a range 

of airgun volumes and operating depths. 

Subsequently, the model was improved 

to better predict airgun radiation at 

frequencies above 1 kHz. Development 

and validation of this improved version 

were made possible by high quality 

airgun source signature data from field 

studies conducted under the industrysponsored Joint Industry Program on 

Sound and Marine Life. Desktop 

evaluation and validation of AASM 

have been conducted against 

commercial geophysical source models 

such as Gundalf and Nucleus. 

JASCO’s proprietary Marine 

Operations Noise Model (MONM) was 

used to generate the 3D sound fields 

necessary for sound exposure estimates. 

MONM is based on standard and proven 

acoustic propagation models. In this 

case, propagation at frequencies less 

than 2 kHz was computed using a 

version of the U.S. Naval Research 

Laboratory’s Range-dependent Acoustic 


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Model (RAM), which is based on a 

parabolic equation (PE) solution to the 

wave equation and extensively verified 

and validated under the Navy Ocean 

and Atmospheric Master Library 

process. The PE method has been 

extensively benchmarked and is widely 

employed in the underwater acoustics 

community (Collins et al., 1996), and 

RAM’s predictions (as generated within 

the MONM infrastructure) have been 

validated against experimental data in 

several underwater acoustic 

measurement programs conducted by 

JASCO (e.g., Aerts et al., 2008; Funk et 

al., 2008; Ireland et al., 2009; Blees et 

al., 2010; Warner et al., 2010). At 

frequencies greater than 2 kHz, 

increased sound attenuation due to 

volume absorption at higher frequencies 

is accounted for with the widely-used 

BELLHOP Gaussian beam ray-trace 

propagation model (Porter and Liu, 

1994). Both of these complementary, 

non-proprietary propagation models 

(RAM and BELLHOP) have been 

extensively tested over many years and 

are accepted by the acoustics 

community. Implementation of these 

codes within the MONM infrastructure 

has been evaluated and validated 

against other PE codes including RAMS, 

RAM-Geo and original RAM, and 

against normal mode or wavenumber 

integration (fast field) methods in 

standard codes. Finally, JASCO has 

conducted end-to-end validation of 

source and propagation modeling 

against field data collected in sound 

source verification experiments, 

demonstrating that the results of the 

acoustic field modeling are in agreement 

with field data. The comparison of 

model results and measurements show 

that MONM can produce reliable results 

in challenging acoustic propagation 

conditions (Hannay and Racca, 2005). 

The non-proprietary, peer-reviewed 

Marine Mammal Movement and 

Behavior (3MB) model (Houser, 2006) 

was used to generate realistic paths of 

simulated animals (animats) in the 

modeled area. JASCO’s Exposure 

Modeling System (JEMS) was used to 

combine animal movement data (i.e., 

the output from 3MB), with precomputed acoustic fields (i.e., the 

output from MONM described above). 

The JEMS is a relatively simple piece of 

software that acts as an indexer that 

finds the sound level from the 

computed fields for the location of each 

animat through time. The numerous, 

rigorous robustness checks described for 

the multiple modeling components are 

sufficient to comply with the IQA 

requirements, and no additional peer 

review is required. 

While certain components of the 

modeling process (AASM, MONM, and 

JEMS) are proprietary in the sense that 

JASCO does not make the code publicly 

available, they are all based on standard 

physics or mathematical models 

generally accepted in the field and 

based on peer-reviewed models (e.g., 

3MB). In addition, ample opportunity 

has been provided for public input and 

review of the underlying scientific 

information and modeling efforts 

contained herein (including by 

scientists, peer experts at other agencies, 

and non-governmental organizations). 

Relevant data is provided such that an 

entity using similar models could 

reproduce or challenge the results. 

While the modeling results 

disseminated here may reasonably be 

considered to be influential for purposes 

of the OMB Peer Review Bulletin— 

meaning that the information may 

reasonably be considered to have a clear 

and substantial impact on important 

public policies, such as this ITR—the 

modeling is not a ‘‘highly influential 

scientific assessment,’’ (HISA) which is 

defined as a scientific assessment that: 

(i) Could have a potential impact of 

more than $500 million in any year, or 

(ii) is novel, controversial, or precedentsetting or has significant interagency 

interest. As described above, similar 

approaches to acoustic exposure 

modeling have been performed by 

numerous disparate entities for multiple 

applications. In 2014, during the 

aforementioned modeling workshop cosponsored by the American Petroleum 

Institute and International Association 

of Geophysical Contractors, at least a 

half-dozen expert presenters 

(representing private and governmental 

entities from both the United States and 

Europe) discussed various available 

packages that function much the same 

way as what is described here. There is 

nothing novel, controversial, or 

precedent-setting about the modeling 

described here, and the additional peer 

review requirements associated with 

HISAs are not applicable. 

Miscellaneous 

Comment: NRDC contends that NMFS 

must consider a standard requiring 

analysis and selection of minimum 

source levels. In furtherance of this 

overall quieting goal, NRDC also states 

that NMFS should consider requiring 

that all vessels employed in the survey 

activities undergo regular maintenance 

to minimize propeller cavitation and be 

required to employ the best shipquieting designs and technologies 

available for their class of ship, and that 

NMFS should require these vessels to 

undergo measurement for their 

underwater noise output. 

Response: An expert panel, convened 

by BOEM to determine whether it 

would be feasible to develop standards 

to determine a lowest practicable source 

level, determined that it would not be 

reasonable or practicable to develop 

such metrics (see Appendix L in BOEM, 

2017). NMFS does not believe it 

appropriate to address disagreements 

with these conclusions to us. NRDC 

further claims that NMFS’ deference to 

the findings of an expert panel 

convened specifically to consider this 

issue is ‘‘arbitrary under the MMPA.’’ 

The bulk of NRDC’s comment appears to 

be addressed to BOEM, and NMFS 

encourages NRDC to engage with BOEM 

regarding these alleged shortcomings of 

the panel’s findings. The subject matter 

is outside NMFS’ expertise, and we 

have no basis upon which to doubt the 

panel’s published findings. 

With regard to the recommended 

requirements to measure or control 

vessel noise, or to make some minimum 

requirements regarding the design of 

vessels used in the surveys, NMFS 

disagrees that these requirements would 

be practicable. While NMFS agrees that 

vessel noise is of concern in a 

cumulative and chronic sense, it is not 

of substantial concern in relation to the 

MMPA’s least practicable adverse 

impact standard for this specified 

activity, given the few vessels used in 

any given survey and relative to 

commercial shipping. NMFS looks 

forward to continued collaboration with 

NRDC and others towards ship quieting. 

Comment: NRDC states that NMFS 

must consider mitigation that limits and 

reduces the amount of survey activity, 

including ‘‘prohibit[ing]’’ duplicative 

surveys, and should consider 

‘‘consolidating’’ surveys. Similarly, the 

MMC recommends that NMFS ‘‘work 

with BOEM’’ to require industry 

operators to increase collaboration on 

seismic surveys whenever possible. 

Response: NRDC states that NMFS 

should ‘‘require and enforce a cap’’ on 

surveys, without explaining how they 

believe this is within NMFS’ statutory 

authority or suggesting ways to 

appropriately apportion the amount of 

effort that might be allowed. NMFS 

cannot arbitrarily limit planned effort 

and has no legitimate means of changing 

the specified activity absent a 

conclusion that the activity would have 

more than a negligible impact. However, 

NMFS has made the necessary findings 

under the MMPA for issuance of this 

rule. NRDC goes on to state that NMFS 

should ‘‘require BOEM to eliminate 

unnecessary duplication of survey 

effort’’ but does not explain how they 


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believe that this suggestion is within 

NMFS’ statutory authority. As the 

permitting agency, BOEM has the 

authority to require permit applicants to 

submit statements indicating that 

existing data are not available to meet 

the data needs identified for the 

applicant’s survey (i.e., non-duplicative 

survey statement), but such 

requirements are not within NMFS’ 

purview. NMFS may not demand that 

BOEM discharge its authority under 

OCSLA in any particular manner. As 

stated previously, NMFS considers the 

specified activity described by an 

applicant in reviewing a request for an 

incidental take authorization. Nothing 

in the statute provides authority to 

direct consolidation or removal of 

activities based on some presumption of 

duplication that NMFS is not qualified 

to judge. NRDC claims erroneously that 

NMFS ‘‘has authority under the 

mitigation provision of the MMPA to 

consider directing the companies to 

consolidate their surveys,’’ placing such 

a requirement under the auspices of 

practicability. Leaving aside that 

directing any given applicant to 

abandon their survey plans would not 

in fact be practicable, it is inappropriate 

to consider this suggested requirement 

through that lens. 

The MMC specifically cites a number 

of collaborative surveys conducted in 

foreign waters and recommends that 

NMFS ‘‘work with BOEM’’ to require 

such collaboration. However, the MMC 

provides no useful recommendations as 

to how such collaboration might be 

achieved. Given the absence of 

appropriate statutory authority, NMFS 

is willing to explore with the MMC 

possible mechanisms for fostering such 

collaboration between geophysical data 

acquisition companies and relevant 

Federal agencies, within the context of 

our respective authorities. 

NMFS also notes that, although 

surveys may be perceived as 

‘‘duplicative’’ simply because other 

surveys have also occurred in the same 

location, they are in fact designed 

specifically to produce proprietary data 

that satisfies the needs of survey 

funders. As noted by NRDC, BOEM 

convened an expert panel to study the 

issue of duplicative surveys (see 

Appendix L in BOEM, 2017) and 

developed standards for consideration 

of what surveys are duplicative. NRDC 

provides extensive discussion of their 

thoughts regarding the insufficiency of 

BOEM’s duplicative survey standard 

and its implementation. We respectfully 

suggest that these comments are more 

appropriately directed at BOEM. 

Comment: Chevron states that NMFS 

‘‘must be mindful of the mandates 

under OCSLA to assess and then 

balance the costs and benefits of 

alternative restrictions on geophysical 

activities against a requirement for 

‘expeditious and orderly development’ 

of GOM resources.’’ 

Response: NMFS’ statutory 

obligations arise under the Marine 

Mammal Protection Act (with associated 

requirements under the Endangered 

Species Act, National Environmental 

Policy Act, and Administrative 

Procedure Act, among others). NMFS 

has no statutory obligation relative to 

OCSLA. 

Comment: CRE provides several 

comments relating to E.O. 12866. CRE 

reiterates their view that there is ‘‘no 

harm from seismic,’’ and therefore, that 

it is not surprising that NMFS has not 

produced a quantitative statement of 

benefits. They also conclude that 

‘‘[s]ince the benefits of the proposed 

rule are minimal at best, the resultant 

benefit-cost ratio is less than one, 

making the proposed rule noncompliant’’ with E.O. 12866. 

Response: NMFS disagrees with the 

commenter’s premise that there is no 

potential for harm, and accordingly 

evaluated the impacts of the specified 

activity and prescribed appropriate 

mitigation in the ITR, as required under 

the MMPA. With respect to E.O. 12866, 

the RIA provides a qualitative 

description of potential ecological 

benefits and their economic 

implications due to uncertainty 

preventing quantification. Similar to the 

qualitative evaluation of costs 

associated with the proposed area 

closures, the qualitative treatment of 

benefits does not indicate a lesser 

magnitude, but rather more data 

limitations or uncertainty. 

Comment: Regarding E.O. 13211, 

Chevron comments that NMFS has 

provided inconsistent statements that 

should be resolved. 

Response: NMFS has clarified its 

discussion regarding E.O. 13211. 

Overall, within the five-year timeframe 

of the analysis, the ITR is not expected 

to constitute a significant adverse effect 

on energy supply, distribution or use, 

according to the thresholds described by 

E.O. 13211, given that the direct 

compliance costs represent a small 

fraction (on the order of less than one 

percent) of the total costs of exploration 

and development in the GOM. 

Comment: Chevron notes that E.O. 

13795 required evaluation of NMFS’ 

2016 Technical Guidance (review of 

which was ongoing at the time of 

publication of the notice of proposed 

rulemaking). Chevron also asserts that 

assumptions of the 2016 Technical 

Guidance ‘‘are multiplied with those in 

other elements of the modeling to reach 

‘unrealistic’ conclusions.’’ Because the 

2016 Technical Guidance was used in 

the modeling, Chevron asserts that the 

modeling is inconsistent with the 

requirements of E.O. 13795. The CRE 

also claims that use of the 2016 

Technical Guidance is in violation of 

E.O. 13795 and that the guidance should 

be rescinded or substantially revised. 

CRE also states that NMFS must 

emphasize that use of the Technical 

Guidance is not required. 

Response: Review of the Technical 

Guidance under E.O. 13795 was 

completed in 2018. In response to the 

feedback received during the public 

comment period and the Interagency 

Consultation meeting, the Secretary of 

Commerce approved NMFS to issue a 

2018 Revised Technical Guidance for 

Assessing the Effects of Anthropogenic 

Sound on Marine Mammal Hearing: 

Acoustic Thresholds for Onset of 

Permanent and Temporary Threshold 

Shifts (2018 Revised Technical 

Guidance) (NOAA Technical 

Memorandum NMFS–OPR–59) (June 21, 

2018). NMFS’ use of the guidance is, 

therefore, in compliance with E.O. 

13795. 

The 2018 Revised Technical Guidance 

retains the thresholds and weighting 

functions presented in the original 2016 

Technical Guidance. Chevron’s 

comment that the Technical Guidance 

somehow contributes to what they 

characterize as ‘‘unrealistic’’ 

conclusions is, in context of industry’s 

overall comments on the modeling 

effort, unpersuasive. The industryfunded supplementary modeling 

variable analysis (Zeddies et al., 2017b) 

found that use of the Technical 

Guidance was the single most 

influential factor in reducing the 

modeled exposures (for Level A 

harassment). 

We acknowledge that the Technical 

Guidance is indeed guidance, and its 

use is voluntary (as stated in the 

Executive Summary of the Technical 

Guidance). The Technical Guidance 

provides more detail on if/when an 

alternative approach may be used. 

Description of Marine Mammals in the 

Area of the Specified Activities 

Sections 3 and 4 of the petition 

summarize available information 

regarding status and trends, distribution 

and habitat preferences, and behavior 

and life history of the potentially 

affected species. NMFS refers the reader 

to those descriptions, descriptions of the 

affected environment in Appendix E of 

BOEM’s PEIS, as well as NMFS’ Stock 

Assessment Reports (SAR; 

www.fisheries.noaa.gov/national/ 


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marine-mammal-protection/marinemammal-stock-assessments), 

incorporated here by reference, instead 

of reprinting the information. 

Additional general information about 

these species (e.g., physical and 

behavioral descriptions) may be found 

on NMFS’ website 

(www.fisheries.noaa.gov/find-species). 

Table 4 lists all species with expected 

potential for occurrence in the GOM and 

summarizes information related to the 

population or stock, including potential 

biological removal (PBR). For taxonomy, 

we follow Committee on Taxonomy 

(2020). PBR, defined by the MMPA as 

the maximum number of animals, not 

including natural mortalities, that may 

be removed from a marine mammal 

stock while allowing that stock to reach 

or maintain its optimum sustainable 

population, is considered in concert 

with known sources of ongoing 

anthropogenic mortality (as described in 

NMFS’ SARs). For status of species, we 

provide information regarding U.S. 

regulatory status under the MMPA and 

ESA. 

Marine mammal abundance estimates 

presented in this document represent 

the total number of individuals that 

make up a given stock or the total 

number estimated within a particular 

study area. NMFS’ stock abundance 

estimates for most species represent the 

total estimate of individuals within the 

geographic area, if known, that 

comprises that stock. For some species, 

this geographic area may extend beyond 

U.S. waters. Survey abundance (as 

compared to stock or species 

abundance) is the total number of 

individuals estimated within the survey 

area, which may or may not align 

completely with a stock’s geographic 

range as defined in the SARs. These 

surveys may also extend beyond U.S. 

waters. For many GOM stocks, 

information regarding distribution and 

range-wide abundance is limited, as 

available data are generally limited to 

U.S. waters of the northern GOM. 

Abundance and distribution for GOM 

stocks occurring in the Mexican EEZ or 

the high seas are poorly understood. As 

discussed in additional detail below, 

U.S. waters only comprise about 40 

percent of the entire GOM, and 65 

percent of GOM oceanic waters are 

south of the U.S. EEZ. Studies based on 

abundance and distribution surveys 

restricted to U.S. waters are unable to 

detect temporal shifts in distribution 

beyond U.S. waters that might account 

for any changes in abundance within 

U.S. waters. 

In some cases, species are treated as 

guilds. In general ecological terms, a 

guild is a group of species that have 

similar requirements and play a similar 

role within a community. However, for 

purposes of stock assessment or 

abundance prediction, certain species 

may be treated together as a guild 

because they are difficult to distinguish 

visually and many observations are 

ambiguous. For example, NMFS’ GOM 

SARs assess stocks of Mesoplodon spp. 

and Kogia spp. as guilds. Here, we 

consider beaked whales and Kogia spp. 

as guilds. In the following discussion, 

reference to ‘‘beaked whales’’ includes 

the Cuvier’s, Blainville’s, and Gervais 

beaked whales, and reference to ‘‘Kogia 

spp.’’ includes both the dwarf and 

pygmy sperm whale. 

Twenty-one species (with 24 managed 

stocks) have the potential to co-occur 

with the prospective survey activities. 

Extralimital species or stocks unlikely to 

co-occur with survey activity include 31 

estuarine bottlenose dolphin stocks, the 

blue whale (Balaenoptera musculus), fin 

whale (B. physalus), sei whale (B. 

borealis), minke whale (B. 

acutorostrata), humpback whale 

(Megaptera novaeangliae), North 

Atlantic right whale (Eubalaena 

glacialis), and the Sowerby’s beaked 

whale (Mesoplodon bidens). All 

mysticete species listed here (as well as 

Sowerby’s beaked whale) are considered 

only of accidental occurrence in GOM 

and are generally historically known 

only from a very small number of 

strandings and/or sightings (Wu ̈rsig et 

al., 2000; Wu ̈rsig, 2017). In addition, 

following BOEM’s update to the scope 

of activity considered through this rule, 

the eastern coastal stock of bottlenose 

dolphin, which was considered in the 

notice of proposed rulemaking, would 

no longer be potentially impacted by 

activities that may be authorized under 

this rule. For detailed discussion of 

these species, please see the notice of 

proposed rulemaking (83 FR 29212; 

June 22, 2018). In addition, the West 

Indian manatee (Trichechus manatus 

latirostris) may be found in coastal 

waters of the GOM. However, manatees 

are managed by the U.S. Fish and 

Wildlife Service and are not considered 

further in this document. All managed 

stocks in this region are assessed in 

NMFS’ U.S. Atlantic SARs. 

All values presented in Table 4, 

which are available in the most recent 

final SARs (Hayes et al., 2020) and have 

not changed since the proposed rule 

was published, are the most recent 

available at the time the analyses for 

this final rule were completed. We also 

reviewed new information for many 

GOM stocks in unpublished draft 2020 

SARs. The unpublished draft SARs 

include updates to most GOM stocks, 

including to abundance estimates, PBR 

values, and annual mortality and 

serious injury (M/SI) estimates. The 

most notable change is that, through the 

introduction of M/SI estimates related to 

the Deepwater Horizon (DWH) oil spill, 

M/SI values are generally larger than in 

past SARs and in some cases are larger 

than the PBR values. NMFS has 

considered this information and 

determined that it is previously 

accounted for as part of the baseline, 

through our existing analysis of the 

effects of the DWH oil spill. We have 

fully considered the underlying 

information in our analysis and have 

determined that the unpublished draft 

SAR updates do not impact our 

conclusions. 

TABLE 4—MARINE MAMMALS POTENTIALLY PRESENT IN THE SPECIFIED GEOGRAPHICAL REGION

Common name Scientific name Stock 

ESA/ 

MMPA 

status; 

Strategic 

(Y/N) 1

NMFS stock abundance 

(CV, Nmin, most recent 

abundance survey)2,7

Predicted 

mean (CV)/ 

maximum 

abundance 3

PBR 

Annual 

M/SI 

(CV) 4

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales) 

Family Balaenopteridae 

(rorquals): 

Bryde’s whale ........... Balaenoptera edeni ......... Gulf of Mexico ................. E/D; Y 33 (1.07; 16; 2009) ......... 44 (0.27)/n/a ... 0.03 0.8 

Superfamily Odontoceti (toothed whales, dolphins, and porpoises) 

Family Physeteridae: 

Sperm whale ............. Physeter macrocephalus GOM ................................ E/D; Y 763 (0.38; 560; 2009) ..... 2,128 (0.08)/ 

2,234.

1.1 0 


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TABLE 4—MARINE MAMMALS POTENTIALLY PRESENT IN THE SPECIFIED GEOGRAPHICAL REGION—Continued 

Common name Scientific name Stock 

ESA/ 

MMPA 

status; 

Strategic 

(Y/N) 1

NMFS stock abundance 

(CV, Nmin, most recent 

abundance survey)2,7

Predicted 

mean (CV)/ 

maximum 

abundance 3

PBR 

Annual 

M/SI 

(CV) 4

Family Kogiidae: 

Pygmy sperm whale Kogia breviceps .............. GOM ................................ -; N 186 (1.04; 90; 2009) 5 ..... 2,234 (0.19)/ 

6,117 5.

0.9 0.3 (1.0) 

Dwarf sperm whale ... K. sima ............................ GOM ................................ -; N 

Family Ziphiidae (beaked 

whales): 

Cuvier’s beaked 

whale:.

Ziphius cavirostris ........... GOM ................................ -; N 74 (1.04; 36; 2009) ......... 2,910 (0.16)/ 

3,958 5.

0.4 0 

Gervais beaked 

whale.

Mesoplodon europaeus .. GOM ................................ -; N 149 (0.91; 77; 2009) 5 ..... ......................... 0.8 0 

Blainville’s beaked 

whale.

M. densirostris ................. GOM ................................ -; N 

Family Delphinidae: 

Rough-toothed dolphin.Steno bredanensis .......... GOM ................................ -; N 624 (0.99; 311; 2009) ..... 4,853 (0.19)/n/ 

a.

2.5 0.8 (1.0) 

Common bottlenose 

dolphin.

Tursiops truncatus 

truncatus.

GOM Oceanic .................

GOM Continental Shelf ...

-; N 

-; N 

5,806 (0.39; 4,230; 2009) 

51,192 (0.10; 46,926; 

2011–12).

138,602 (0.06)/ 

192,176 5.

42 

469 

6.5 (0.65) 

0.8 

GOM Coastal, Northern .. -; N 7,185 (0.21; 6,044; 2011– 

12).

60 0.4 

GOM Coastal, Western ... -; N 20,161 (0.17; 17,491; 

2011–12).

175 0.6 

Clymene dolphin .............. Stenella clymene ............. GOM ................................ -; N 129 (1.00; 64; 2009) ....... 11,000 (0.16)/ 

12,115.

0.6 0 

Atlantic spotted dolphin .... S. frontalis ....................... GOM ................................ -; N 37,611 (0.28; 29,844; 

2000–01)6.

47,488 (0.13)/ 

85,108.

Undet. 42 (0.45) 

Pantropical spotted dolphin.S. attenuata attenuata .... GOM ................................ -; N 50,880 (0.27; 40,699; 

2009).

84,014 (0.06)/ 

108,764.

407 4.4 

Spinner dolphin ................ S. longirostris longirostris GOM ................................ -; N 11,441 (0.83; 6,221; 

2009).

13,485 (0.24)/ 

31,341.

62 0 

Striped dolphin ................. S. coeruleoalba ............... GOM ................................ -; N 1,849 (0.77; 1,041; 2009) 4,914 (0.17)/ 

5,323.

10 0 

Fraser’s dolphin ............... Lagenodelphis hosei ....... GOM ................................ -; N 726 (0.7; 427; 1996– 

2001)6.

1,665 (0.73)/n/ 

a.

Undet. 0 

Risso’s dolphin ................. Grampus griseus ............. GOM ................................ -; N 2,442 (0.57; 1,563; 2009) 3,137 (0.10)/ 

4,153.

16 7.9 (0.85) 

Melon-headed whale ....... Peponocephala electra ... GOM ................................ -; N 2,235 (0.75; 1,274; 2009) 6,733 (0.30)/ 

7,105.

13 0 

Pygmy killer whale ........... Feresa attenuata ............. GOM ................................ -; N 152 (1.02; 75; 2009) ....... 2,126 (0.30)/n/ 

a.

0.8 0 

False killer whale ............. Pseudorca crassidens ..... GOM ................................ -; N 777 (0.56; 501; 2003– 

04)6.

3,204 (0.36)/n/ 

a.

Undet. 0 

Killer whale ...................... Orcinus orca .................... GOM ................................ -; N 28 (1.02; 14; 2009) ......... 185 (0.41)/n/a 0.1 0 

Short-finned pilot whale ... Globicephala 

macrorhynchus.

GOM ................................ -; N 2,415 (0.66; 1,456; 2009) 1,981 (0.18)/n/ 

a.

15 0.5 (1.0) 

1ESA status: Endangered (E)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the 

MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely 

to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as 

a strategic stock. 2 NMFS marine mammal stock assessment reports online at: www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments. CV is 

coefficient of variation; Nmin is the minimum estimate of stock abundance. 3This information represents species- or guild-specific abundance predicted by habitat-based cetacean density models (Roberts et al., 2016). These models provide 

the best available scientific information regarding predicted density patterns of cetaceans in the U.S. Gulf of Mexico, and we provide the corresponding abundance 

predictions as a point of reference. Total abundance estimates were produced by computing the mean density of all pixels in the modeled area and multiplying by its 

area. 4These values, found in NMFS’ SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined (e.g., commercial fisheries, 

ship strike). A CV associated with estimated mortality due to commercial fisheries is presented in some cases. 5Abundance estimates are in some cases reported for a guild or group of species when those species are difficult to differentiate at sea. Similarly, the habitatbased cetacean density models produced by Roberts et al. (2016) are based in part on available observational data which, in some cases, is limited to genus or guild 

in terms of taxonomic definition. NMFS’ SARs present pooled abundance estimates for Kogia spp. and Mesoplodon spp., while Roberts et al. (2016) produced density 

models to genus level for Kogia spp. and as a guild for beaked whales (Ziphius cavirostris and Mesoplodon spp.). Finally, Roberts et al. (2016) produced a density 

model for bottlenose dolphins that does not differentiate between oceanic, shelf, and coastal stocks. The modeled abundance estimate provided here for all 

bottlenose dolphins includes abundance that may be attributed to the eastern coastal stock. 6 NMFS’ abundance estimates for these species are not considered current. PBR is therefore considered undetermined, as there is no current minimum abundance 

estimate for use in calculation. We nevertheless present the most recent abundance estimate. 7We note that Dias and Garrison (2016) present abundance estimates for oceanic stocks that were calculated for use in DWH oil spill injury quantification. For 

most stocks, these estimates are based on pooled observations from shipboard surveys conducted in 2003, 2004, and 2009 and corrected for detection bias. Estimates for beaked whales and Kogia spp. were based on density estimates derived from passive acoustic data collection (Hildebrand et al., 2012). The abundance estimate for Bryde’s whales incorporated the results of additional shipboard surveys conducted in 2007, 2010, and 2012. Here we retain NMFS’ official SAR information 

for comparison with model-predicted abundance (Roberts et al., 2016). 

For the majority of species potentially 

present in the specified geographical 

region, NMFS has designated only a 

single generic stock (i.e., ‘‘Gulf of 

Mexico’’) for management purposes, 

although there is currently no 

information to differentiate the stock 

from the Atlantic Ocean stock of the 

same species, nor information on 

whether more than one stock may exist 

in the GOM (Hayes et al., 2020). 

For the bottlenose dolphin, NMFS 

defines an oceanic stock, a continental 

shelf stock, and three coastal stocks. As 

in the northwestern Atlantic Ocean, 

there are two general bottlenose dolphin 

ecotypes: ‘‘coastal’’ and ‘‘offshore.’’ 


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These ecotypes are genetically and 

morphologically distinct (Hoelzel et al., 

1998; Waring et al., 2016), though 

ecotype distribution is not clearly 

defined and the stocks are delineated 

primarily on the basis of management 

rather than ecological boundaries. The 

offshore ecotype is assumed to 

correspond to the oceanic stock, with 

the stock boundary (and thus the de 

facto delineation of offshore and coastal 

ecotypes) defined as the 200-m isobath. 

The continental shelf stock is defined as 

between two typical survey strata: The 

20- and 200-m isobaths. While the shelf 

stock is assumed to consist primarily of 

coastal ecotype dolphins, offshore 

ecotype dolphins may also be present. 

There is expected to be some overlap 

with the three coastal stocks as well, 

though the degree is unknown and it is 

not thought that significant mixing or 

interbreeding occurs between them 

(Waring et al., 2016). The coastal stocks 

are defined as being in waters between 

the shore, barrier islands, or presumed 

outer bay boundaries out to the 20-m 

isobath and, as a working hypothesis, 

NMFS has assumed that dolphins 

occupying habitats with dissimilar 

climatic, coastal, and oceanographic 

characteristics might be restricted in 

their movements between habitats, thus 

constituting separate stocks (Waring et 

al., 2016). Shoreward of the 20-m 

isobath, the eastern coastal stock 

extends from Key West, FL to 84° W 

longitude; the northern coastal stock 

from 84° W longitude to the Mississippi 

River delta; and the western coastal 

stock from the Mississippi River delta to 

the Mexican border. The latter is 

assumed to be a trans-boundary stock, 

though no information is available 

regarding abundance in Mexican waters. 

As noted above, the eastern coastal 

stock will not be affected by activities 

considered through this rule. 

At the time of publication of the 

notice of proposed rulemaking, the 

GOM Bryde’s whale was proposed for 

listing as an endangered species under 

the ESA (81 FR 88639; December 8, 

2016). Since that time, NMFS has listed 

the GOM Bryde’s whale as endangered 

under the ESA, effective on May 15, 

2019 (84 FR 15446; April 15, 2019). The 

proposed listing was based largely on 

NMFS’ status review of Bryde’s whales 

in the GOM (Rosel et al., 2016), and no 

significant new information has become 

available since that time. No critical 

habitat has yet been designated for the 

species, and no recovery plan has yet 

been developed. NMFS’ analysis related 

to the GOM Bryde’s whale in the notice 

of proposed rulemaking was conducted 

in context of the same information that 

informed the proposal to list the GOM 

Bryde’s whale and, therefore, the final 

listing decision itself does not introduce 

new information for consideration in 

the analysis for this final rulemaking. 

In Table 4 above, NMFS reports two 

sets of abundance estimates: Those from 

NMFS’ SARs and those predicted by 

Roberts et al. (2016)—for the latter, we 

provide both the annual mean and the 

monthly maximum (where applicable). 

Please see footnotes 2–3 of Table 4 for 

more detail. NMFS’ SAR estimates are 

typically generated from the most recent 

shipboard and/or aerial surveys 

conducted. GOM oceanography is 

dynamic, and the spatial scale of the 

GOM is small relative to the ability of 

most cetacean species to travel. As an 

example, no groups of Fraser’s dolphins 

were observed during dedicated 

cetacean abundance surveys during 

2003–2004 or 2009, yet the SAR states 

that it is probable that Fraser’s dolphins 

were present in the northern GOM but 

simply not encountered, and therefore 

declines to present an abundance 

estimate of zero (Waring et al., 2013). 

U.S. waters only comprise about 40 

percent of the entire GOM, and 65 

percent of GOM oceanic waters are 

south of the U.S. EEZ. Studies based on 

abundance and distribution surveys 

restricted to U.S. waters are unable to 

detect temporal shifts in distribution 

beyond U.S. waters that might account 

for any changes in abundance within 

U.S. waters. NMFS’ SAR estimates also 

typically do not incorporate correction 

for detection bias. Therefore, they 

should generally be considered 

underestimates, especially for cryptic or 

long-diving species (e.g., beaked whales, 

Kogia spp., sperm whales). Dias and 

Garrison (2016) state, for example, that 

current abundance estimates for Kogia 

spp. may be considerably 

underestimated due to the cryptic 

behavior of these species and difficulty 

of detection in Beaufort sea state greater 

than one, and density estimates for 

certain species derived from long-term 

passive acoustic monitoring are much 

higher than are estimates derived from 

visual observations (Mullin and Fulling, 

2004; Mullin, 2007; Hildebrand et al., 

2012). 

The Roberts et al. (2016) abundance 

estimates represent the output of 

predictive models derived from multiyear observations and associated 

environmental parameters and which 

incorporate corrections for detection 

bias. Incorporating more data over 

multiple years of observation can yield 

different results in either direction, as 

the result is not as readily influenced by 

fine-scale shifts in species habitat 

preferences or by the absence of a 

species in the study area during a given 

year. NMFS’ abundance estimates show 

substantial year-to-year variability in 

some cases. For example, NMFSreported estimates for the Clymene 

dolphin vary by a maximum factor of 

more than 100 (2009 estimate of 129 

versus 1996–2001 estimate of 17,355), 

indicating that it may be more 

appropriate to use the model prediction 

versus a point estimate, as the model 

incorporates all available data (from 

1992–2009). The latter factor— 

incorporation of correction for detection 

bias—should systematically result in 

greater abundance predictions. For these 

reasons, the Roberts et al. (2016) 

estimates are generally more realistic 

and, for these purposes, represent the 

best available information. For purposes 

of assessing estimated exposures 

relative to abundance—used in this case 

to understand the scale of the predicted 

takes compared to the population— 

NMFS generally believes that the 

Roberts et al. (2016) abundance 

predictions are most appropriate 

because they were used to generate the 

exposure estimates and therefore 

provide the most relevant comparison. 

Roberts et al. (2016) represents the best 

available scientific information 

regarding marine mammal occurrence 

and distribution in the Gulf of Mexico. 

As a further illustration of the 

distinction between the SARs and 

model-predicted abundance estimates, 

the current NMFS stock abundance 

estimates for most GOM species are 

based on direct observations from 

shipboard surveys conducted in 2009 

(from the 200-m isobath to the edge of 

the U.S. EEZ) and not corrected for 

detection bias, whereas the exposure 

estimates presented herein for those 

species are based on the abundance 

predicted by a density surface model 

informed by observations from surveys 

conducted over approximately 20 years 

and covariates associated at the 

observation level. To directly compare 

the estimated exposures predicted by 

the outputs of the Roberts et al. (2016) 

model to NMFS’ SAR abundance would 

therefore not be meaningful. 

Biologically Important Areas (BIA)— 

As part of our description of the 

environmental baseline, we discuss any 

known areas of importance as marine 

mammal habitat. These areas may 

include designated critical habitat for 

ESA-listed species (as defined by 

section 3 of the ESA) or other known 

areas not formally designated pursuant 

to any statute or other law. Important 

areas may include areas of known 

importance for reproduction, feeding, or 

migration, or areas where small and 


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resident populations are known to 

occur. 

Although there is no designated 

critical habitat for marine mammal 

species in the specified geographical 

region, BIAs for marine mammals are 

recognized. For example, the GOM 

Bryde’s whale is a very small 

population that is genetically distinct 

from other Bryde’s whales and not 

genetically diverse within the GOM 

(Rosel and Wilcox, 2014). Further, the 

species is typically observed only 

within a narrowly circumscribed area 

within the eastern GOM. Therefore, this 

area is described as a year-round BIA by 

LaBrecque et al. (2015). Although 

survey effort has covered all oceanic 

waters of the U.S. GOM, whales were 

observed only between approximately 

the 100- and 300-m isobaths in the 

eastern GOM from the head of the De 

Soto Canyon (south of Pensacola, 

Florida) to northwest of Tampa Bay, 

Florida (Maze-Foley and Mullin, 2006; 

Waring et al., 2016; Rosel and Wilcox, 

2014; Rosel et al., 2016). NOAA 

subsequently conducted a status review 

of the GOM Bryde’s whale (Rosel et al., 

2016). The review expanded this 

description by stating that, due to the 

depth of some sightings, the area is 

more appropriately defined to the 400- 

m isobath and westward to Mobile Bay, 

Alabama, in order to provide some 

buffer around the deeper sightings and 

to include all sightings in the 

northeastern GOM. However, the 

recorded Bryde’s whale shipboard and 

aerial survey sightings between 1989 

and 2015 have mainly fallen within the 

BIA described by LaBreque et al. (2015). 

The entirety of this area is now 

excluded from the scope of this rule 

following BOEM’s update to that scope. 

LaBrecque et al. (2015) also described 

eleven year-round BIAs for small and 

resident BSE bottlenose dolphin 

populations in the GOM. Additional 

study would likely allow for 

identification of additional BIAs 

associated with other GOM BSE dolphin 

stocks. 

Deepwater Horizon Oil Spill—In 2010 

the Macondo well blowout and 

explosion aboard the Deepwater 

Horizon drilling rig (also known as the 

Deepwater Horizon explosion, oil spill, 

and response; hereafter referred to as the 

DWH oil spill) caused oil, natural gas, 

and other substances to flow into the 

GOM for 87 days before the well was 

sealed. Total oil discharge was 

estimated at 3.19 million barrels (134 

million gallons), resulting in the largest 

marine oil spill in history (DWH NRDA 

Trustees, 2016). In addition, the 

response effort involved extensive 

application of dispersants at the seafloor 

and at the surface, and controlled 

burning of oil at the surface was also 

used extensively as a response 

technique. The oil, dispersant, and burn 

residue compounds present ecological 

challenges in the region. NMFS 

discussed the impacts of the DWH oil 

spill on marine mammals in detail in 

the notice of proposed rulemaking (83 

FR 29212; June 22, 2018) and we refer 

the reader to that document for 

additional detail. 

At its maximum extent, oil covered 

over 40,000 km2 of ocean. Cumulatively, 

over the course of the spill, oil was 

detected on over 112,000 km2 of ocean. 

Currents, winds, and tides carried these 

surface oil slicks to shore, fouling more 

than 2,100 km of shoreline, including 

beaches, bays, estuaries, and marshes 

from eastern Texas to the Florida 

Panhandle. In addition, some lighter oil 

compounds evaporated from the slicks, 

exposing air-breathing organisms like 

marine mammals to noxious fumes at 

the sea surface. 

The Oil Pollution Act requires that a 

natural resource damage assessment 

(NRDA) be conducted following oil 

pollution incidents. An injury 

assessment undertaken as part of the 

NRDA first requires a determination of 

whether an incident injured natural 

resources. Trustees assessing natural 

resource injuries must establish that a 

pathway existed from the oil discharge 

to the resource, confirm that resources 

were exposed to the discharge, and 

evaluate the adverse effects that 

occurred as a result of the exposure (or 

response activities). Subsequently, the 

assessment requires injury 

quantification (including degree and 

spatiotemporal extent), essentially by 

comparing the post-event conditions 

with the pre-event baseline. For a fuller 

overview of the injury assessment 

process in this case, please see 

Takeshita et al. (2017). Critical 

pathways of exposure for marine 

mammals included the contaminated 

water column, where they swim and 

capture prey; the surface slick at the air 

to water interface, where they breathe, 

rest, and swim; and contaminated 

sediment, where they forage and capture 

prey. 

DWH oil was found to cause problems 

with the regulation of stress hormone 

secretion from adrenal cells and kidney 

cells, which will affect an animal’s 

ability to regulate body functions and 

respond appropriately to stressful 

situations, thus leading to reduced 

fitness. Bottlenose dolphins living in 

habitats contaminated with DWH oil 

showed signs of adrenal dysfunction, 

and dead, stranded dolphins from areas 

contaminated with DWH oil had smaller 

adrenal glands (Schwacke et al., 2014a; 

Venn-Watson et al., 2015b). Other 

factors were ruled out as a primary 

cause for the high prevalence of adverse 

health effects, reproductive failures, and 

disease in stranded animals. When all of 

the data were considered together, the 

DWH oil spill was determined to be the 

only reasonable cause for the full suite 

of observed adverse health effects. 

Due to the difficulty of investigating 

marine mammals in pelagic 

environments and across the entire 

region impacted by the event, the injury 

assessment focused on health 

assessments conducted on bottlenose 

dolphins in nearshore habitats and used 

these populations as case studies for 

extrapolating to coastal and oceanic 

populations that received similar or 

worse exposure to DWH oil, with 

appropriate adjustments made for 

differences in behavior, anatomy, 

physiology, life histories, and 

population dynamics among species. 

Investigators then used a population 

modeling approach to capture the 

overlapping and synergistic 

relationships among the metrics for 

injury, and to quantify the entire scope 

of DWH marine mammal injury to 

populations into the future, expressed 

as ‘‘lost cetacean years’’ due to the DWH 

oil spill (which represents years lost due 

to premature mortality as well as the 

resultant loss of reproductive output). 

This approach allowed for consideration 

of long-term impacts resulting from 

immediate losses and reproductive 

failures in the few years following the 

spill, as well as expected persistent 

impacts on survival and reproduction 

for exposed animals well into the future 

(Takeshita et al., 2017). For a more 

detailed overview of the injury 

quantification for these stocks and their 

post-DWH population trajectory, please 

see Schwacke et al. (2017), and for full 

details of the overall injury 

quantification, see DWH MMIQT (2015). 

The results of the quantification 

exercise for each affected shelf and 

oceanic stock, and for northern and 

western coastal stocks of bottlenose 

dolphin, are presented in Table 5. This 

is likely a conservative estimate of 

impacts, because: (1) Shelf and oceanic 

species experienced long exposures (up 

to 90 days) to very high concentrations 

of fresh oil and a diverse suite of 

response activities, while estuarine 

dolphins were not exposed until later in 

the spill period and to weathered oil 

products at lower water concentrations; 

(2) oceanic cetaceans dive longer and to 

deeper depths, and it is possible that the 

types of lung injuries observed in 

estuarine dolphins may be more severe 

for oceanic cetaceans; and (3) cetaceans 


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in deeper waters were exposed to very 

high concentrations of volatile gas 

compounds at the water’s surface near 

the wellhead. No analysis was 

performed for Fraser’s dolphins or killer 

whales; although they are present in the 

GOM, sightings are rare and there were 

no historical sightings in the oil spill 

footprint during the surveys used in the 

quantification process. These stocks 

were likely injured, but no information 

is available on which to base a 

quantification effort. 

TABLE 5—SUMMARY OF MODELED EFFECTS OF DWH OIL SPILL

Common name 

% Population 

exposed to 

oil (95% CI) 

% Population 

killed 

(95% CI) 

% Females 

with 

reproductive 

failure 

(95% CI) 

% Population 

with adverse 

health effects 

(95% CI) 

% Maximum 

population 

reduction 

(95% CI) 

Years to 

recovery 

(95% CI) b

Bryde’s whale ........................................... 48 (23¥100) 17 (7¥24) 22 (10¥31) 18 (7¥28) ¥22 69 

Sperm whale ............................................ 16 (11¥23) 6 (2¥8) 7 (3¥10) 6 (2¥9) ¥7 21 

Kogia spp. ................................................ 15 (8¥29) 5 (2¥7) 7 (3¥10) 6 (2¥9) ¥6 11 

Beaked whales ......................................... 12 (7¥22) 4 (2¥6) 5 (3¥8) 4 (2¥7) ¥6 10 

Rough-toothed dolphin ............................. 41 (16¥100) 14 (6¥20) 19 (9¥26) 15 (6¥23) ¥17 54 

Bottlenose dolphin, oceanic ..................... 10 (5¥10) 3 (1¥5) 5 (2¥6) 4 (1¥6) ¥4 n/a 

Bottlenose dolphin, northern coastal ....... 82 (55¥100) 38 (26¥58) 37 (17¥53) 30 (11¥47) ¥50 (32¥73) 39 (23¥76) 

Bottlenose dolphin, western coastal ........ 23 (16¥32) 1 (1¥2) 10 (5¥15) 8 (3¥13) ¥5 (3¥9) n/a 

Shelf dolphins a ........................................ 13 (9¥19) 4 (2¥6) 6 (3¥8) 5 (2¥7) ¥3 n/a 

Clymene dolphin ...................................... 7 (3¥15) 2 (1¥4) 3 (2¥5) 3 (1¥4) ¥3 n/a 

Pantropical spotted dolphin ..................... 20 (15¥26) 7 (3¥10) 9 (4¥13) 7 (3¥11) ¥9 39 

Spinner dolphin ........................................ 47 (24¥91) 16 (7¥23) 21 (10¥30) 17 (6¥27) ¥23 105 

Striped dolphin ......................................... 13 (8¥22) 5 (2¥7) 6 (3¥9) 5 (2¥8) ¥6 14 

Risso’s dolphin ......................................... 8 (5¥13) 3 (1¥4) 3 (2¥5) 3 (1¥4) ¥3 n/a 

Melon-headed whale ................................ 15 (6¥36) 5 (2¥7) 7 (3¥10) 6 (2¥9) ¥7 29 

Pygmy killer whale ................................... 15 (7¥33) 5 (2¥8) 7 (3¥10) 6 (2¥9) ¥7 29 

False killer whale ..................................... 18 (7¥48) 6 (3¥9) 8 (4¥12) 7 (3¥11) ¥9 42 

Short-finned pilot whale ........................... 6 (4¥9) 2 (1¥3) 3 (1¥4) 2 (1¥3) ¥3 n/a 

Modified from DWH NRDA Trustees (2016). 

CI = confidence interval. No CI was calculated for population reduction or years to recovery for shelf or oceanic stocks. 

a ‘‘Shelf dolphins’’ includes Atlantic spotted dolphins and the shelf stock of bottlenose dolphins (20–200 m water depth). These two species 

were combined because the abundance estimate used in population modeling was derived from aerial surveys and the species could not generally be distinguished from the air. b It is not possible to calculate YTR for stocks with maximum population reductions of less than or equal to 5 percent. 

Coastal and oceanic marine mammals 

were injured by exposure to oil from the 

DWH spill. Nearly all of the stocks that 

overlap with the oil spill footprint have 

demonstrable, quantifiable injuries, and 

the remaining stocks (for which there is 

no quantifiable injury) were also likely 

injured, though there is not currently 

enough information to make a 

determination. Injuries included 

elevated mortality rates, reduced 

reproduction, and disease. Due to these 

effects, affected populations may require 

decades to recover absent successful 

efforts at restoration (e.g., DWH NRDA 

Trustees, 2017). The ability of the stocks 

to recover and the length of time 

required for that recovery are tied to the 

carrying capacity of the habitat, and to 

the degree of other population 

pressures. NMFS treats the effects of the 

DWH oil spill as part of the baseline in 

considering the likely resilience of these 

populations to the effects of the 

activities considered in this regulatory 

framework. 

Unusual Mortality Events (UME)—A 

UME is defined under Section 410(6) of 

the MMPA as ‘‘a stranding that is 

unexpected; involves a significant dieoff of any marine mammal population; 

and demands immediate response.’’ 

From 1991 to the present, there have 

been fourteen formally recognized 

UMEs affecting marine mammals in the 

region and involving species under 

NMFS’ jurisdiction. These have 

primarily impacted coastal bottlenose 

dolphins, with multiple UMEs 

determined to have resulted from 

biotoxins and one from infectious 

disease. One relevant UME was declared 

since publication of the notice of 

proposed rulemaking and is discussed 

below. 

Most significantly, a UME affecting 

multiple cetacean species in the 

northern GOM occurred from 2010– 

2014. NMFS discussed this UME in the 

notice of proposed rulemaking (83 FR 

29212; June 22, 2018). Please see that 

document for additional information 

regarding the 2010–2014 UME. 

Additional information on the UME is 

also available online at: 

www.fisheries.noaa.gov/national/ 

marine-life-distress/2010-2014- 

cetacean-unusual-mortality-eventnorthern-gulf-mexico. In summary, the 

event included all cetaceans stranded 

during this time in Alabama, 

Mississippi, and Louisiana and all 

cetaceans other than bottlenose 

dolphins stranded in the Florida 

Panhandle (Franklin County through 

Escambia County), with a total of 1,141 

cetaceans stranded or reported dead 

offshore. For reference, the same area 

experienced a normal average of 75 

strandings per year from 2002–09 (Litz 

et al., 2014). The majority of stranded 

animals were bottlenose dolphins, 

though at least ten additional species 

were reported as well. Since not all 

cetaceans that die wash ashore where 

they may be found, the number reported 

stranded is likely a fraction of the total 

number of cetaceans that died during 

the UME. There was also an increase in 

strandings of stillborn and newborn 

dolphins (Colegrove et al., 2016). The 

UME investigation and the Deepwater 

Horizon Natural Resource Damage 

Assessment determined that the DWH 

oil spill (discussed above) is the most 

likely explanation of the persistent, 

elevated stranding numbers in the 

northern GOM after the 2010 spill. The 

evidence to date supports that exposure 

to hydrocarbons released during the 

DWH oil spill was the most likely 

explanation of adrenal and lung disease 

in dolphins, which has contributed to 

increased deaths of dolphins living 

within the oil spill footprint and 

increased fetal loss. The longest and 


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most prolonged stranding cluster was in 

Barataria Bay, Louisiana in 2010–11, 

followed by Mississippi and Alabama in 

2011, consistent with timing and spatial 

distribution of oil, while the number of 

deaths was not elevated for areas that 

were not as heavily oiled. Subsequent 

health assessments of live dolphins 

from Barataria Bay and comparison to a 

reference population found significantly 

increased adrenal disease, lung disease, 

and poor health, while histological 

evaluations of samples from dead 

stranded animals from within and 

outside the UME area found that UME 

animals were more likely to have lung 

and adrenal lesions and to have primary 

bacterial pneumonia, which caused or 

contributed significantly to death 

(Schwacke et al., 2014a, 2014b; VennWatson et al., 2015b). The chronic 

adrenal gland and lung diseases 

identified in stranded UME dolphins are 

consistent with exposure to petroleum 

compounds (Venn-Watson et al., 

2015b). Colegrove et al. (2016) found 

that the increase in perinatal strandings 

resulted from late-term pregnancy 

failures and development of in utero 

infections likely caused by chronic 

illnesses in mothers who were exposed 

to oil. 

While the number of dolphin 

mortalities in the area decreased after 

the peak from March 2010-July 2014, it 

does not indicate that the effects of the 

oil spill on these populations have 

ended. Researchers still saw evidence of 

chronic lung disease and adrenal 

impairment four years after the spill (in 

July 2014) and saw evidence of failed 

pregnancies in 2015 (Smith et al., 2017). 

These follow-up studies found a yearly 

mortality rate for Barataria Bay dolphins 

of roughly 13 percent (as compared to 

annual mortality rates of 5 percent or 

less that have been previously reported 

for other dolphin populations) and 

found that only 20 percent of pregnant 

dolphins produced viable calves 

(compared with 83 percent in a 

reference population) (Lane et al., 2015; 

McDonald et al., 2017). In addition, 

compromised health may make 

dolphins more susceptible to additional 

environmental stressors. 

Since the publication of the proposed 

rule, another UME involving bottlenose 

dolphins in the northern GOM was 

declared. Elevated bottlenose dolphin 

strandings occurred in Louisiana, 

Mississippi, Alabama, and the 

panhandle of Florida (Alabama border 

through Taylor County) from February 

1, 2019, through November 30, 2019. A 

total of 337 confirmed strandings were 

documented, with a majority occurring 

from February through May. Excluding 

prior UMEs, the annual average for 

February through May in the affected 

area is 57 dolphins; at least 260 

standings were documented during this 

period in 2019. The cause of the UME 

was determined to be environmentally 

driven by exposure to low salinity 

waters resulting from extreme 

freshwater discharge from watersheds 

that drain into the GOM, including 

rivers in Florida, Alabama, Mississippi 

and Louisiana. This unprecedented 

amount of freshwater discharge during 

the winter, spring, and summer months 

of 2019 resulted in a drop in salinity 

levels across the coastally associated 

waters in the region. Prolonged 

exposure to low salinity water has been 

documented to have harmful health 

impacts on bottlenose dolphins, ranging 

from skin lesions and serum electrolyte 

abnormalities to acute mortality. The 

location of the UME and the dolphin 

stocks affected, including the western 

and northern coastal stocks of 

bottlenose dolphin, are the same as 

those impacted by the 2010–2014 UME. 

For additional information, please visit 

www.fisheries.noaa.gov/national/ 

marine-life-distress/2019-bottlenosedolphin-unusual-mortality-event-alongnorthern-gulf. 

Marine Mammal Hearing 

Hearing is the most important sensory 

modality for marine mammals 

underwater, and exposure to 

anthropogenic sound can have 

deleterious effects. To appropriately 

assess the potential effects of exposure 

to sound, it is necessary to understand 

the frequency ranges that marine 

mammals are able to hear. Current data 

indicate that not all marine mammal 

species have equal hearing capabilities 

(e.g., Richardson et al., 1995; Wartzok 

and Ketten, 1999; Au and Hastings, 

2008). To reflect this, Southall et al. 

(2007) recommended that marine 

mammals be divided into functional 

hearing groups based on directly 

measured or estimated hearing ranges 

on the basis of available behavioral 

response data, audiograms derived 

using auditory evoked potential 

techniques, anatomical modeling, and 

other data. Note that no direct 

measurements of hearing ability have 

been successfully completed for 

mysticetes (i.e., low-frequency 

cetaceans). NMFS (2018) describes 

generalized hearing ranges for these 

marine mammal hearing groups. 

Generalized hearing ranges were chosen 

based on the approximately 65 dB 

threshold from the normalized 

composite audiograms, with the 

exception for lower limits for lowfrequency cetaceans where the lower 

bound was deemed to be biologically 

implausible and the lower bound from 

Southall et al. (2007) retained. The 

functional groups and the associated 

frequencies are indicated below (note 

that these frequency ranges correspond 

to the range for the composite group, 

with the entire range not necessarily 

reflecting the capabilities of every 

species within that group): 

• Low-frequency cetaceans

(mysticetes): Generalized hearing is 

estimated to occur between 

approximately 7 Hz and 35 kHz; 

• Mid-frequency cetaceans (larger

toothed whales, beaked whales, and 

most delphinids): Generalized hearing is 

estimated to occur between 

approximately 150 Hz and 160 kHz; 

• High-frequency cetaceans

(porpoises, river dolphins, and members 

of the genera Kogia and 

Cephalorhynchus; including two 

members of the genus Lagenorhynchus, 

on the basis of recent echolocation data 

and genetic data): Generalized hearing is 

estimated to occur between 

approximately 275 Hz and 160 kHz. 

For more detail concerning these 

groups and associated frequency ranges, 

please see NMFS (2018) for a review of 

available information. Twenty-one 

species of cetacean have the reasonable 

potential to co-occur with the proposed 

survey activities. Please refer to Table 4. 

Of the cetacean species that may be 

present, one is classified as a lowfrequency cetacean (i.e., the Bryde’s 

whale), 18 are classified as midfrequency cetaceans (i.e., all delphinid 

and ziphiid species and the sperm 

whale), and two are classified as highfrequency cetaceans (i.e., Kogia spp.). 

Potential Effects of the Specified 

Activities on Marine Mammals and 

Their Habitat 

In NMFS’ notice of proposed 

rulemaking (83 FR 29212; June 22, 

2018), this section included a 

comprehensive summary and 

discussion of the ways that components 

of the specified activity may impact 

marine mammals and their habitat, 

including general background 

information on sound and specific 

discussion of potential effects to marine 

mammals from noise produced through 

use of airgun arrays. We incorporate by 

reference that information and do not 

repeat that discussion here, instead 

referring the reader to the notice of 

proposed rulemaking. 

The Estimated Take section later in 

this document includes a quantitative 

analysis of the number of individuals 

that are expected to be taken by the 

specified activity. The Negligible Impact 

Analysis and Determinations section 

includes an analysis of how these 


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activities will impact marine mammals 

and considers the content of this 

section, the Estimated Take section, and 

the Mitigation section, to draw 

conclusions regarding the likely impacts 

of these activities on the reproductive 

success or survivorship of individuals 

and from that on the affected marine 

mammal populations. 

Description of Active Acoustic Sound 

Sources 

In the notice of proposed rulemaking, 

this section contained a brief technical 

background on sound, the 

characteristics of certain sound types, 

and on metrics used in the proposal 

inasmuch as the information is relevant 

to the specified activity and to a 

discussion of the potential effects of the 

specified activity on marine mammals 

found later in this document. Here, we 

summarize key information relating to 

terminology used in this notice. 

Amplitude (or ‘‘loudness’’) of sound 

is typically described using the relative 

unit of the decibel (dB). A sound 

pressure level (SPL) in dB is described 

as the ratio between a measured 

pressure and a reference pressure (for 

underwater sound, this is 1 microPascal 

(mPa)). The source level (SL) represents 

the SPL referenced at a distance of 1 m 

from the source (referenced to 1 mPa), 

while the received level is the SPL at 

the listener’s position (referenced to 1 

mPa). 

Root mean square (rms) is the 

quadratic mean sound pressure over the 

duration of an impulse. This 

measurement is often used in the 

context of discussing behavioral effects, 

in part because behavioral effects, 

which often result from auditory cues, 

may be better expressed through 

averaged units than by peak pressures. 

Sound exposure level (SEL; represented 

as dB re 1 mPa2¥s) represents the total 

energy contained within a pulse, and 

considers both intensity and duration of 

exposure. Peak sound pressure (also 

referred to as zero-to-peak sound 

pressure or 0–p) is the maximum 

instantaneous sound pressure 

measurable in the water at a specified 

distance from the source, and is 

represented in the same units as the rms 

sound pressure. Another common 

metric is peak-to-peak sound pressure 

(pk-pk), which is the algebraic 

difference between the peak positive 

and peak negative sound pressures. 

Peak-to-peak pressure is typically 

approximately 6 dB higher than peak 

pressure (Southall et al., 2007). 

As described in more detail in the 

notice of proposed rulemaking, airgun 

arrays are in a general sense considered 

to be omnidirectional sources of pulsed 

noise. Pulsed sound sources (as 

compared with non-pulsed sources) 

produce signals that are brief (typically 

considered to be less than one second), 

broadband, atonal transients (ANSI, 

1986, 2005; Harris, 1998; NIOSH, 1998; 

ISO, 2003) and occur either as isolated 

events or repeated in some succession. 

Pulsed sounds are all characterized by 

a relatively rapid rise from ambient 

pressure to a maximal pressure value 

followed by a rapid decay period that 

may include a period of diminishing, 

oscillating maximal and minimal 

pressures, and generally have an 

increased capacity to induce physical 

injury as compared with sounds that 

lack these features. Airguns produce 

sound with energy in a frequency range 

from about 10–2,000 Hz, with most 

energy radiated at frequencies below 

200 Hz. Although the amplitude of the 

acoustic wave emitted from the source 

is equal in all directions (i.e., 

omnidirectional), airgun arrays do 

possess some directionality due to 

different 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. 

Acoustic sources used for highresolution geophysical (HRG) surveys 

generally produce higher frequency 

signals with highly directional beam 

patterns. These sources are generally 

considered to be intermittent, with 

typically brief signal durations. 

Boomers, considered to be impulsive 

sources, generate a high-amplitude 

broadband (100 Hz-10 kHz) acoustic 

pulse with high downward directivity, 

though may be considered 

omnidirectional at frequencies below 1 

kHz. Other typical HRG sources are 

considered non-impulsive. Sub-bottom 

profiler systems generally project a 

chirp pulse spanning an operatorselectable frequency band, usually 

between 1 to 20 kHz, with a single beam 

directed vertically down. Multibeam 

echosounders use an array of 

transducers that project a highfrequency, fan-shaped beam under the 

hull of a survey ship and perpendicular 

to the direction of motion. Side-scan 

sonars use two transducers to project 

high-frequency beams that are usually 

wide in the vertical plane (50°–70°) and 

very narrow in the horizontal plane (less 

than a few degrees). Other, similar 

impulsive or non-impulsive sources 

may be used in conducting shallow 

penetration or HRG surveys. 

Acoustic Habitat 

NMFS also included a detailed 

discussion and analysis of potential 

impacts to acoustic habitat. Acoustic 

habitat is the soundscape—which 

encompasses all of the sound present in 

a particular location and time, as a 

whole—when considered from the 

perspective of the animals experiencing 

it. Animals listen for sounds produced 

by conspecifics (communication during 

feeding, mating, and other social 

activities), other animals (finding prey 

or avoiding predators), and the physical 

environment (finding suitable habitats, 

navigating). Together, sounds made by 

animals and the geophysical 

environment (e.g., produced by 

earthquakes, lightning, wind, rain, 

waves) make up the natural 

contributions to the total acoustics of a 

place. These acoustic conditions, 

termed acoustic habitat, are one 

attribute of an animal’s total habitat. 

That discussion summarized a report 

titled ‘‘Cumulative and Chronic Effects 

in the Gulf of Mexico: Estimating 

Reduction of Listening Area and 

Communication Space due to Seismic 

Activities,’’ (‘‘Cumulative and Chronic 

Effects report’’) as well as a subsequent 

addendum to the report presenting 

additional analysis relating to sperm 

whales. The initial report (originally 

presented as Appendix K in BOEM 

(2017)) as well as the addendum 

((hereafter, ‘‘the CCE report’’), are 

available online at 

www.fisheries.noaa.gov/action/ 

incidental-take-authorization-oil-andgas-industry-geophysical-surveyactivity-gulf-mexico. The CCE report 

presented a first-order cumulative and 

chronic effects assessment for noise 

produced by oil and gas exploration 

activities in the U.S. GOM. 

The term ‘‘listening area’’ refers to the 

region of ocean over which sources of 

sound can be detected by an animal at 

the center of the space. Loss of 

communication space concerns the area 

over which a specific animal signal, 

used to communicate with conspecifics 

in biologically-important contexts (e.g., 

foraging, mating), can be heard, in 

noisier relative to quieter conditions 

(Clark et al., 2009). Lost listening area 

concerns the more generalized 

contraction of the range over which 

animals would be able to detect a 

variety of signals of biological 

importance, including eavesdropping on 

predators and prey (Barber et al., 2009). 

Implications for acoustic masking (i.e., 

when a sound interferes with or masks 

the ability of an animal to detect a signal 

of interest that is above the absolute 

hearing threshold; see notice of 


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proposed rulemaking at 29239 for 

explanation of masking) and reduced 

communication space resulting from 

noise produced by airgun surveys in the 

GOM are expected to be particularly 

heightened for animals that actively 

produce low-frequency sounds or whose 

hearing is attuned to lower frequencies 

(i.e., Bryde’s whales). 

Acoustic modeling was conducted for 

ten locations (‘‘receiver sites’’) within 

the study area to examine aggregate 

noise produced over a full, generic year. 

The locations of the receiver sites were 

chosen to reflect areas of biological 

importance to cetaceans, areas of high 

densities of cetaceans, and areas of key 

biological diversity. The CCE report 

analyzed multiple scenarios, including a 

baseline scenario in which no 

geophysical surveys are conducted and 

noise consists of natural sounds and a 

minimum estimate of commercial vessel 

noise; a survey activity scenario in 

which projected activities were 

uniformly distributed throughout the 

study area, with the exception of coastal 

waters from February to May; and a 

closure scenario in which no activities 

are conducted in certain restriction 

areas, 25 percent of the activity that 

would have occurred in the restriction 

areas is redistributed into nonrestriction areas of the same activity 

zone, and 75 percent of the activities 

that would have occurred in the 

restriction areas are not conducted at 

all. For additional methodological 

details, see discussion in the notice of 

proposed rulemaking or the CCE report. 

Regarding sperm whales, the analysis 

shows that the survey activities do not 

significantly contribute to the 

soundscape in the frequency band 

relevant for their lower-frequency slowclicks, and that there will be no 

significant change in communication 

space for sperm whales. Because other 

sperm whale calls are higher-frequency, 

they would not be expected to be 

affected. Please see the CCE report for 

further discussion of the findings for 

sperm whales. The remaining 

discussion that follows is in reference to 

the findings for Bryde’s whales and to 

general findings for other hearing 

groups. 

The methods used in the CCE report 

were meant to average the conditions 

generated by low-frequency dominant 

noise sources throughout a full year, 

during which animals of key 

management interest rely on habitats 

within the study area. Considered as a 

complement to assessments of the acute 

effects of the same types of noise 

sources in the same region (discussed 

below in the Estimated Take section), 

the CCE assessment estimates noise 

produced by the same sources over 

much larger spatial scales, and 

considers how the summation of noise 

from these sources relates to levels 

without the proposed activity (ambient). 

The lost listening area method 

calculates a fractional reduction in 

listening area due to the addition of 

anthropogenic noise to ambient noise. 

Results are presented as a percentage of 

the original listening area remaining due 

to the increase in noise levels relative to 

no activity and between activity 

scenarios. The communication space 

assessment provides relative losses of 

communication space (in both areas and 

percentages) between the activity 

scenarios. 

At most sites, lost listening area was 

greater for deeper waters than for 

shallower waters, which is attributed to 

the downward-refracting sound speed 

profile near the surface, caused by the 

thermocline, which steers sound to 

deeper depths. Shallow water noise 

levels were reduced due to surface 

interactions that increase transmission 

loss, particularly for low frequencies. 

Listening area reductions were also 

generally most severe when weighted 

for low-frequency hearing cetaceans. 

Both low- and mid-frequency weighted 

losses were high in the Mississippi 

Canyon, while only low-frequency 

weighted values were high for the De 

Soto Canyon. Both of these sites are 

considered important to sperm whales 

as well as other deep-diving 

odontocetes. These modeling results 

suggest that accumulations of noise 

from survey activities below 5 kHz and 

often heightened at depth could be 

degrading the ability of animals that 

forage at great depths in the GOM to use 

acoustic cues to find prey as well as to 

maintain conspecific contact. 

Comparison between results provided 

for the two metrics applied in the CCE 

report highlights important interpretive 

differences for evaluating the biological 

implications of background noise. The 

strength of the communication space 

approach is that it evaluates potential 

contractions in the availability of a 

signal of documented importance to a 

population of animals of key 

management interest in the region. In 

this case, losses of communication 

space for Bryde’s whales were estimated 

to be higher in eastern and central GOM 

canyons and shelf break areas. In 

contrast, relative maintenance of 

listening area and communication space 

was seen within the Bryde’s whale core 

habitat area in the eastern GOM (an area 

that has since been removed from 

consideration through this rule). In 

areas where larger amounts of survey 

activity were projected, significant loss 

of low-frequency listening area and 

communication space for Bryde’s whale 

calls was estimated, though we 

emphasize that these are not areas 

where Bryde’s whales are expected to 

occur. 

The CCE report is described here in 

order to summarize information 

presented in the proposed rule 

regarding potential longer-term and 

wider-range noise effects from sources 

such as airguns. Please see the notice of 

proposed rulemaking, as well as the 

CCE report and addendum, for 

additional information. 

Estimated Take 

This section provides an estimate of 

the number and type of incidental takes 

that may be expected to occur under the 

specified activity (as it has been revised 

in scope), which informed NMFS’ 

negligible impact determination. 

Realized incidental takes would be 

determined by the actual levels of 

activity at specific times and places that 

occur under any issued LOAs. 

Except with respect to certain 

activities not pertinent here, section 

3(18) of 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). 

Harassment is the only type of take 

expected to result from these activities. 

Anticipated takes would primarily be 

by Level B harassment, as use of the 

described acoustic sources, particularly 

airgun arrays, is likely to disrupt 

behavioral patterns of marine mammals. 

There is also some potential for auditory 

injury (Level A harassment) to result for 

low- and high-frequency species due to 

the size of the predicted auditory injury 

zones for those species. NMFS does not 

expect auditory injury to occur for midfrequency species, as discussed in 

greater detail on the notice of proposed 

rulemaking (83 FR 29212; June 22, 2018) 

and in responses to public comments. 

The required mitigation and monitoring 

measures are expected to minimize the 

severity of such taking to the extent 

practicable. It is unlikely that lethal 

takes would occur even in the absence 

of the mitigation and monitoring 

measures, and no such takes are 

anticipated or will be authorized. Below 

we summarize how the take that may be 

authorized was estimated using acoustic 

thresholds, sound field modeling, and 


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marine mammal density data. Detailed 

discussion of all facets of the take 

estimation process was provided in the 

notice of proposed rulemaking (83 FR 

29212; June 22, 2018), and nothing has 

changed since that time. Therefore, that 

full discussion is not repeated. Please 

see that notice, and associated 

companion documents available online, 

for additional detail. 

Acoustic Thresholds 

NMFS uses acoustic thresholds that 

identify the received level of 

underwater sound above which exposed 

marine mammals generally would be 

reasonably expected to exhibit 

disruption of behavioral patterns (Level 

B harassment) or to incur permanent 

threshold shift (PTS) of some degree 

(Level A harassment). 

Level B Harassment—Although 

available data are consistent with the 

basic concept that louder sounds evoke 

more significant behavioral responses 

than softer sounds, defining precise 

sound levels that will potentially 

disrupt behavioral patterns is difficult 

because responses depend on the 

context in which the animal receives the 

sound, including an animal’s behavioral 

mode when it hears sounds (e.g., 

feeding, resting, or migrating), prior 

experience, and biological factors (e.g., 

age and sex). Some species, such as 

beaked whales, are known to be more 

highly sensitive to certain 

anthropogenic sounds than other 

species. Other contextual factors, such 

as signal characteristics, distance from 

the source, duration of exposure, and 

signal to noise ratio, may also help 

determine response to a given received 

level of sound. Therefore, levels at 

which responses occur are not 

necessarily consistent and can be 

difficult to predict (Southall et al., 2007; 

Ellison et al., 2012; Bain and Williams, 

2006). Typically, and especially in cases 

where PTS is predicted, NMFS 

anticipates that some number of 

individuals may incur temporary 

threshold shift (TTS) (considered Level 

B harassment). However, it is not 

necessary to separately quantify those 

takes, as it is unlikely that an individual 

marine mammal would be exposed at 

the levels and duration necessary to 

incur TTS without also being exposed to 

the levels associated with behavioral 

harassment and, therefore, NMFS 

expects any potential TTS takes to be 

captured by the estimated takes by 

behavioral harassment. 

Based on the practical need to use a 

relatively simple threshold based on 

available information that is both 

predictable and measurable for most 

activities, NMFS has historically used a 

generalized acoustic threshold based on 

received level to estimate the onset of 

Level B harassment. These thresholds 

are 160 dB rms (intermittent sources, 

which include impulsive sources) and 

120 dB rms (continuous sources). 

Airguns are impulsive sound sources 

and electromechanical sources used for 

HRG surveys are intermittent sources. 

Therefore, the 160 dB rms threshold has 

typically been used in evaluating effects 

from the sources planned for use in the 

specified activities. However, in the 

notice of proposed rulemaking, NMFS 

identified a more complex probabilistic 

risk function for use in evaluating the 

potential effects of the specified activity 

considered herein. That function, 

described in Wood et al. (2012), is better 

reflective of available scientific 

information (as discussed in detail in 

the notice of proposed rulemaking, as 

well as in comment responses provided 

earlier in this preamble). Such an 

approach takes the fundamental step of 

acknowledging the potential for Level B 

harassment at exposures to received 

levels below 160 dB rms (as well as the 

potential that animals exposed to 

received levels above 160 dB rms will 

not respond in ways constituting Level 

B harassment). The approach described 

by Wood et al. (2012) also accounts for 

differential hearing sensitivity by 

incorporating frequency-weighting 

functions. The analysis of Gomez et al. 

(2016) indicates that behavioral 

responses in cetaceans are best 

explained by the interaction between 

sound source type and functional 

hearing group. Southall et al. (2007) 

proposed auditory weighting functions 

for species groups based on known and 

assumed hearing ranges (Type I). 

Although newer filters are better 

designed to predict the onset of auditory 

injury (as discussed below and used for 

evaluation of potential Level A 

harassment), the broader Type I filters 

were retained for use in evaluating 

potential behavioral disturbance in 

conjunction with the Wood et al. (2012) 

probabilistic response function. 

NMFS received public comments on 

this topic, including some criticizing the 

proposed use of the Wood et al. (2012) 

risk function. We responded to all 

comments received on this topic and, in 

addition to the more detailed discussion 

provided in the Estimated Take section 

of the notice of proposed rulemaking, 

we provide detailed discussion of these 

concerns in the responses to comments, 

provided earlier in this preamble. NMFS 

retains use of the Wood et al. (2012) 

approach as the basis for estimating take 

and considering the effects of the 

specified activity on marine mammal 

behavior. The Level B harassment 

criteria upon which the analysis 

presented herein is based are presented 

in Table 6. 

TABLE 6—BEHAVIORAL EXPOSURE CRITERIA

Group 

Probability of response to frequency-weighted rms SPL 

120 

(%) 

140 

(%) 

160 

(%) 

180 

(%) 

Beaked whales ................................................................................................ 50 90 n/a n/a 

All other species .............................................................................................. n/a 10 50 90 

Level A Harassment—NMFS’ 

Technical Guidance for Assessing the 

Effects of Anthropogenic Sound on 

Marine Mammal Hearing (NMFS, 2018) 

(2018 Revised Technical Guidance) 

identifies dual criteria to assess the 

potential for auditory injury (Level A 

harassment) to occur for different 

marine mammal groups (based on 

hearing sensitivity) as a result of 

exposure to noise. The 2018 Revised 

Technical Guidance identifies the 

received levels, or thresholds, above 

which individual marine mammals are 

predicted to experience changes in their 

hearing sensitivity for all underwater 

anthropogenic sound sources and 

reflects the best available science on the 

potential for noise to affect auditory 

sensitivity by: 

• Dividing sound sources into two 

groups (i.e., impulsive and nonimpulsive) based on their potential to 

affect hearing sensitivity; 

• Choosing metrics that best address 

the impacts of noise on hearing 

sensitivity, i.e., peak sound pressure 

level (peak SPL) (reflects the physical 

properties of impulsive sound sources 

to affect hearing sensitivity) and 


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cumulative sound exposure level (cSEL) 

(accounts for not only level of exposure 

but also duration of exposure); and 

• Dividing marine mammals into 

hearing groups and developing auditory 

weighting functions based on the 

science that indicates that not all marine 

mammals hear and use sound in the 

same manner. 

The premise of the dual criteria 

approach is that, while there is no 

definitive answer to the question of 

which acoustic metric is most 

appropriate for assessing the potential 

for injury, both the received level and 

duration of received signals are 

important to an understanding of the 

potential for auditory injury. Therefore, 

peak SPL is used to define a pressure 

criterion above which auditory injury is 

predicted to occur, regardless of 

exposure duration (i.e., any single 

exposure at or above this level is 

considered to cause auditory injury), 

and cSEL is used to account for the total 

energy received over the duration of 

sound exposure (i.e., both received level 

and duration of exposure) (Southall et 

al., 2007, 2019a; NMFS, 2018). As a 

general principle, whichever criterion is 

exceeded first (i.e., results in the largest 

isopleth) would be used as the effective 

injury criterion (i.e., the more 

precautionary of the criteria). Note that 

cSEL acoustic threshold levels 

incorporate marine mammal auditory 

weighting functions, while peak 

pressure thresholds do not (i.e., flat or 

unweighted). Weighting functions for 

each hearing group (e.g., low-, mid-, and 

high-frequency cetaceans) are described 

in NMFS (2018). 

The 2018 Revised Technical Guidance 

recommends 24 hours as a maximum 

accumulation period relative to cSEL 

thresholds. These thresholds were 

developed by compiling and 

synthesizing the best available science, 

and are provided in Table 7 below. The 

references, analysis, and methodology 

used in the development of the 

thresholds are described in NMFS 

(2018), and more information is 

available online at: 

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/marinemammal-acoustic-technical-guidance. 

TABLE 7—EXPOSURE CRITERIA FOR AUDITORY INJURY

Hearing group 

Peak 

pressure 1

(dB) 

Cumulative sound exposure 

level 2

Impulsive 

(dB) 

Non-impulsive 

(dB) 

Low-frequency cetaceans ............................................................................................................ 219 183 199 

Mid-frequency cetaceans ............................................................................................................. 230 185 198 

High-frequency cetaceans ........................................................................................................... 202 155 173 

1 Referenced to 1 μPa; unweighted within generalized hearing range. 2 Referenced to 1 μPa2-s; weighted according to appropriate auditory weighting function. Airguns and the boomer are treated as impulsive 

sources; other HRG sources are treated as non-impulsive. 

NMFS considers these updated 

thresholds and associated weighting 

functions to be the best available 

information for assessing whether 

exposure to specific activities is likely 

to result in changes in marine mammal 

hearing sensitivity. 

Modeling Overview 

Zeddies et al. (2015, 2017a) (i.e., ‘‘the 

modeling report’’) provides estimates of 

the annual marine mammal acoustic 

exposure caused by sounds from 

geophysical survey activity in the GOM 

for ten years of notional activity levels. 

Here we provide a brief overview of key 

modeling elements, with more detail 

provided in the notice of proposed 

rulemaking (83 FR 29212; June 22, 

2018). For full details of the modeling 

effort, the interested reader should see 

the report (available online at: 

www.fisheries.noaa.gov/action/ 

incidental-take-authorization-oil-andgas-industry-geophysical-surveyactivity-gulf-mexico). 

Initial phases of the modeling effort 

involved preliminary modeling of a 

typical 3D WAZ survey, which was 

simulated at two locations in order to 

establish the basic methodological 

approach and to provide results used to 

evaluate test scenarios that could 

influence exposure estimates. We 

discussed each of the six evaluated test 

scenarios in the notice of proposed 

rulemaking. Please see that discussion 

and the modeling report for full details. 

The modeling effort produced 

exposure estimates computed from 

modeled sound levels as received by 

simulated animals (animats) in a 

specific modeling area. The GOM was 

divided into seven modeling zones with 

six survey types simulated within each 

zone to estimate the potential effects of 

each survey. The zones were designed 

as described previously (Description of 

the Specified Activity; Figure 3)—shelf 

and slope waters were divided into 

eastern, central, and western zones, plus 

a single deep-water zone—to account for 

both the geospatial dependence of 

acoustic fields and the geographic 

variations of animal distributions. The 

selected boundaries considered sound 

propagation conditions and species 

distribution to create regions of 

optimized uniformity in both acoustic 

environment and animal density. 

Survey types included deep penetration 

surveys using a large airgun array (2D, 

3D NAZ, 3D WAZ, and coil survey 

types), shallow penetration surveys 

using a single airgun (which were 

assumed to be a reasonable proxy for 

surveys conducted using a boomer), and 

high resolution surveys concurrently 

using a CHIRP sub-bottom profiler, sidescan sonar, and multibeam 

echosounder. The results from each 

zone were summed to provide GOMwide estimates of take for each marine 

mammal species for each survey type 

for each notional year. To get these 

annual aggregate exposure estimates, 24- 

hr average exposure estimates from each 

survey type were multiplied by the 

number of expected survey days from 

BOEM’s effort projections. Because 

these projections are not seasonspecific, surveys were assumed to be 

equally likely to occur at any time of the 

year and at any location within a given 

zone. 

Acoustic source emission levels and 

directivity of a single airgun and an 

airgun array were modeled using JASCO 

Applied Sciences’ Airgun Array Source 

Model (AASM). AASM is capable of 

predicting airgun source levels at 

frequencies up to 25 kHz, and produces 

a set of notional signatures for each 

array element based on array layout; 

volume, tow depth, and firing pressure 

for each element; and interactions 

between different elements in the array. 

The signatures are summed to obtain the 

far-field source signature of the entire 

array in the horizontal plane, which is 

then filtered into one third-octave 

frequency bands to compute the source 


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levels of the array as a function of 

frequency band and azimuthal angle in 

the horizontal plane (at the source 

depth), after which it is considered to be 

an azimuth-dependent directional point 

source in the far field. Source levels for 

high-resolution sources were obtained 

from manufacturer’s specifications for 

representative sources. 

Electromechanical sources were 

modeled on the basis of transducer 

beam theory, which is often used to 

estimate beam pattern of the source in 

the absence of field measurements, and 

which is described in detail in the 

modeling report. 

Underwater sound propagation (i.e., 

transmission loss) as a function of range 

from each source was modeled using 

JASCO’s Marine Operations Noise 

Model (MONM) for multiple 

propagation radials centered at the 

source to yield 3D transmission loss 

fields in the surrounding area. The 

MONM computes received per-pulse 

SEL for directional sources at specified 

depths. MONM uses two separate 

models to estimate transmission loss. At 

frequencies less than 2 kHz, MONM 

computes acoustic propagation via a 

wide-angle parabolic equation (PE) 

solution to the acoustic wave equation 

(Collins, 1993), based on a version of the 

U.S. Naval Research Laboratory’s Rangedependent Acoustic Model (RAM) 

modified to account for an elastic 

seabed (Zhang and Tindle, 1995). 

MONM–RAM incorporates bathymetry, 

underwater sound speed as a function of 

depth, and a geoacoustic profile based 

on seafloor composition, and accounts 

for source horizontal directivity. At 

frequencies greater than 2 kHz, MONM 

accounts for increased sound 

attenuation due to volume absorption at 

higher frequencies (Fisher and 

Simmons, 1977) with the widely-used 

BELLHOP Gaussian beam ray-trace 

propagation model (Porter and Liu, 

1994). This component incorporates 

bathymetry and underwater sound 

speed as a function of depth with a 

simplified representation of the sea 

bottom, as sub-bottom layers have a 

negligible influence on the propagation 

of acoustic waves with frequencies 

above 1 kHz. MONM–BELLHOP 

accounts for horizontal directivity of the 

source and vertical variation of the 

source beam pattern. Both propagation 

models account for full exposure from a 

direct acoustic wave, as well as 

exposure from acoustic wave reflections 

and refractions (i.e., multi-path arrivals 

at the receiver). 

In order to accurately estimate 

exposure, a simulation must adequately 

cover the various location- and seasonspecific environments. The surveys may 

be conducted at any location within the 

planning area and occur at any time of 

the year, so simulations must 

adequately cover each area and time 

period. The seven zones within which 

potential exposures were modeled, 

corresponding with shelf and slope 

environments subdivided into western, 

central, and eastern areas, as well as a 

single deep zone, were previously 

introduced (Figure 3). The subdivision 

depth definitions are: Shelf, 0–200 m; 

slope, 200–2,000 m; and deep, greater 

than 2,000 m. Within each of the seven 

zones, a set of representative surveysimulation rectangles for each of the 

survey types was defined, with larger 

areas for the ‘‘large-area’’ surveys (i.e., 

deep penetration airgun) and smaller 

areas for the ‘‘small-area’’ surveys (i.e., 

shallow penetration airgun and HRG). In 

Figure 3, the smaller numbered boxes 

represent the survey area extents for the 

different survey types. The stars 

represent acoustic modeling sites along 

western, central, and eastern transects 

(Figure 3). 

A set of 30 sites was selected to 

calculate acoustic propagation loss grids 

as functions of source, range from the 

source, azimuth from the source, and 

receiver depth. These were then used as 

inputs to the acoustic exposure model. 

The environmental parameters and 

acoustic propagation conditions 

represented by these 30 modeling sites 

were chosen to be representative of the 

prevalent acoustic propagation 

conditions within the survey extents. To 

account for seasonal variation in 

propagation, winter (most conservative) 

and summer (least conservative) were 

both used to calculate exposure 

estimates. Propagation during spring 

and fall was found to be almost 

identical to the results for summer, so 

those seasons were represented with the 

summer results. The primary seasonal 

influence on transmission loss is the 

presence of a sound channel, or duct, 

near the surface in winter. 

Marine Mammal Density Information 

The best available scientific 

information was considered in 

conducting marine mammal exposure 

estimates (the basis for estimating take). 

Roberts et al. (2016) provided several 

key improvements over information 

previously available for the GOM, by 

incorporating NMFS aerial and 

shipboard survey data collected over the 

period 1992–2009; controlling for the 

influence of sea state, group size, 

availability bias, and perception bias on 

the probability of making a sighting; and 

modeling density from an expanded set 

of eight physiographic and 16 dynamic 

oceanographic and biological covariates. 

There are multiple reasons why marine 

mammals may be undetected by 

observers. Animals are missed because 

they are underwater (availability bias) or 

because they are available to be seen, 

but are missed by observers (perception 

and detection biases) (e.g., Marsh and 

Sinclair, 1989). Negative bias on 

perception or detection of an available 

animal may result from environmental 

conditions, limitations inherent to the 

observation platform, or observer 

ability. Therefore, failure to correct for 

these biases may lead to underestimates 

of cetacean abundance (as is the case for 

NMFS’ SAR abundance estimates for the 

GOM). Additional data was used to 

improve detection functions for taxa 

that were rarely sighted in specific 

survey platform configurations. The 

degree of underestimation would likely 

be particularly high for species that 

exhibit long dive times or are cryptic, 

such as sperm whales, beaked whales, 

or Kogia spp. In summary, consideration 

of additional survey data and an 

improved modeling strategy allowed for 

an increased number of taxa modeled 

and better spatiotemporal resolutions of 

the resulting predictions. More 

information concerning the Roberts et 

al. (2016) models, including the model 

results and supplementary information 

for each model, is available online at 

seamap.env.duke.edu/models/Duke-ECGOM-2015/. 

Description of Exposure Estimates 

The sound received by an animal 

when near a sound source is a function 

of the animal’s position relative to the 

source, and both source and animals 

may be moving. To a reasonable 

approximation, we know, predict, or 

specify the location of the sound source, 

a 3D sound field around the source, and 

the expected occurrence of animals 

within 100 km2 grid cells (Roberts et al., 

2016). However, because the specific 

location of animals within the modeled 

sound field is unknown, agent-based 

animal movement modeling is necessary 

to complete the assessment of potential 

acoustic exposure. Realistic animal 

movement within the sound field can be 

simulated, and repeated random 

sampling (Monte Carlo)—achieved by 

simulating many animals within the 

operations area—used to estimate the 

sound exposure history of animals 

during the operation. Animats are 

randomly placed, or seeded, within the 

simulation boundary at a specified 

density, and the probability of an 

event’s occurrence is determined by the 

frequency with which it occurs in the 

simulation. Higher densities provide a 

finer resolution for an estimate of the 

probability distribution function (PDF), 


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but require greater computational 

resources. To ensure good 

representation of the PDF, the animat 

density is set as high as is practical, 

with the resulting PDF then scaled using 

the real-world animal density (Roberts 

et al., 2016) to obtain the real-world 

number of modeled acoustic exposures. 

Several models for marine mammal 

movement have been developed (e.g., 

Frankel et al., 2002, Gisiner et al., 2006; 

Donovan et al., 2013). Animats 

transition from one state to another, 

with user-specified parameters 

representing simple states, such as the 

speed or heading of the animal, or 

complex states, such as likelihood of an 

animal foraging, playing, resting, or 

traveling. This analysis uses the Marine 

Mammal Movement and Behavior 

(3MB) model (Houser, 2006). Parameter 

values to control animat movement are 

typically determined using available 

species-specific behavioral studies, but 

the amount and quality of available data 

varies by species. While available data 

often provides a detailed description of 

the proximate behavior expected for real 

individual animals, species with more 

available information must be used as 

surrogates for those without sufficient 

available information. In this study, 

pantropical spotted dolphins are used as 

a surrogate for Clymene, spinner, and 

striped dolphins; short-finned pilot 

whales are surrogates for Fraser’s 

dolphins, Kogia spp., and melon-headed 

whales; and rough-toothed dolphins are 

surrogates for false killer whales and 

pygmy killer whales. Observational data 

for all remaining species in the study 

were sufficient to determine animat 

movement. 

Species-specific animats were created 

with programmed behavioral parameters 

describing dive depth, surfacing and 

dive durations, swimming speed, course 

change, and behavioral aversions (e.g., 

water too shallow). The programmed 

animats were then randomly distributed 

over a given bounded simulation area. 

Because the exact positions of sound 

sources and animals are not known in 

advance for proposed activities, 

multiple runs of realistic predictions are 

used to provide statistical validity to the 

simulated scenarios. Each speciesspecific simulation was seeded with 

approximately 0.1 animats/km2 which, 

in most cases, represents a higher 

density of animats in the simulation 

than occurs in the real environment. A 

separate simulation was created and run 

for each combination of location, survey 

movement pattern, and marine mammal 

species. Animats were only allowed to 

be ‘taken’ once during a 24-hour 

evaluation period. That is, an animat 

whose received level exceeds the peak 

SPL threshold more than once during an 

evaluation period was only counted 

once. Energy accumulation for SEL 

occurred throughout the 24-hour 

integration period and was reset at the 

beginning of each period. Similarly, the 

maximum received rms SPL was 

determined for the entirety of the 

evaluation period and reset at the 

beginning of each period. 

The JASCO Exposure Modeling 

System (JEMS) combined animal 

movement data (i.e., the output from 

3MB), with pre-computed acoustic 

fields. The JEMS output was the timehistory of received levels and slant 

ranges (the three-dimensional distance 

between the animat and the source) for 

all animats of the 3MB simulation. 

Animat received levels and slant ranges 

are used to determine the risk of 

acoustic exposure. There were many 

animats in the simulations and together 

their received levels represent the 

probability, or risk, of exposure for each 

survey. 

All survey simulations were for 7 

days and a sliding 4-hr window 

approach was used to get the average 

24-hr exposure. In this sliding-window 

approach, 42 exposure estimate samples 

are obtained for each seven-day 

simulation, with the mean value then 

used as the 24-hr exposure estimate for 

that survey. The 24-hr exposure levels 

were then scaled by the projected level 

of effort for each survey type (i.e., 

multiplied by the number of days) to 

calculate associated annual exposure 

levels. The number of individual 

animals expected to exceed threshold 

during the 24-hr window is the number 

of animats exposed to levels exceeding 

threshold multiplied by the ratio of realworld animal density to model animat 

density. 

Injury—To evaluate the likelihood an 

animal might experience auditory injury 

as a result of accumulated sound energy, 

the cSEL for each animat in the 

simulation was calculated. To obtain 

that animat’s cSEL, the SEL an animat 

received from each source over the 24- 

hr integration window was summed, 

and the number of animats whose cSEL 

exceeded the specified thresholds 

(Table 7) during the integration window 

was counted. To evaluate the likelihood 

an animal might be injured via exposure 

to peak SPL, the range at which the 

specific peak SPL threshold (Table 7) 

occurs for each source based on the 

broadband peak SPL source level was 

estimated. For each 24-hr integration 

window, the number of animats that 

came within this range of the source 

was counted. 

Behavior—To evaluate the likelihood 

an animal might experience disruption 

of behavioral patterns (i.e., a ‘‘take’’), the 

number of animats that received a 

maximum rms SPL exposure within the 

specified step ranges (Table 6) was 

calculated. The number of animats with 

a maximum rms SPL received level 

categorized into each bin of the step 

function was multiplied by the 

probability of the behavioral response 

specific to that range (Table 6). 

Specifically, 10 percent of animals 

exposed to received levels from 140–159 

dB rms would be assumed as ‘‘takes,’’ 

while 50 percent exposed to levels 

between 160–179 dB rms and 90 percent 

exposed to levels of 180 dB rms and 

above would be. The totals within each 

bin were then summed as the total 

estimated number of exposures above 

Level B harassment thresholds. This 

process was repeated for each 24-hr 

integration window. For beaked whales, 

for which lower behavioral harassment 

thresholds are designated, 50 percent of 

animals exposed to received levels from 

120–149 dB rms would be assumed as 

‘‘takes,’’ while 90 percent exposed to 

levels of 140 dB rms and above would 

be. 

Take Estimates 

In summary, BOEM provided 

estimated levels of effort for geophysical 

survey activity in the GOM for a 

notional ten-year period. Exposure 

estimates were then computed from 

modeled sound levels received by 

animats for several representative types 

of geophysical surveying. Because 

animals and acoustic sources move 

relative to the environment and each 

other, and the sound fields generated by 

the sources are shaped by various 

physical parameters, the sound levels 

received by an animal are a complex 

function of location and time. The basic 

modeling approach was to use acoustic 

models to compute the 3D sound fields 

and their variations in time. Animats 

were modeled moving through these 

fields to sample the sound levels in a 

manner similar to how real animals 

would experience these sounds. From 

the time histories of the received sound 

levels of all animats, the numbers of 

animals exposed to levels exceeding 

effects threshold criteria were 

determined and then adjusted by the 

number of animals expected in the area, 

based on density information, to 

estimate the potential number of realworld marine mammal exposures to 

levels above the defined criteria. The 

acoustic exposure history of many 

simulated animals (animats) allows for 

the estimation of potential exposures 

due to operations. These modeled 

exposures are summed and represent 

the aggregate exposures that may result 


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from future surveys given the specified 

levels of effort for each survey type in 

each year and may vary according to the 

statistical distribution associated with 

these mean annual exposures. 

Exposure estimates above Level A and 

Level B harassment criteria, developed 

by Zeddies et al. (2015, 2017a) in 

association with the activity projections 

for the various annual effort scenarios, 

were generated based on the specific 

modeling scenarios (including source 

and survey geometry), i.e., 2D survey (1 

× 8,000 in3 array), 3D NAZ survey (2 × 

8,000 in3 array), 3D WAZ survey (4 × 

8,000 in3 array), coil survey (4 × 8,000 

in3 array), shallow penetration survey 

(either single 90 in3 airgun or boomer), 

and HRG surveys (side-scan sonar, 

multibeam echosounder, and subbottom profiler). Annual effort scenariobased pooled exposure estimates are 

therefore available by species. 

NMFS presented BOEM’s original 10- 

year activity projections in Table 1 of 

the notice of proposed rulemaking 

under ‘‘Detailed Description of 

Activities.’’ For purposes of analysis in 

the notice of proposed rulemaking, 

NMFS identified representative ‘‘high,’’ 

‘‘moderate,’’ and ‘‘low’’ effort years. 

Because the duration of these 

regulations are limited to five years, 

NMFS needed to determine a reasonable 

basis for evaluating acoustic exposures 

that might occur during that timeframe 

(rather than ten years). Therefore, for the 

proposed rule, in recognition of 

relatively low recent levels of 

geophysical survey activity, from the ten 

notional years of projected survey effort 

provided by BOEM, NMFS selected five 

representative years representing three 

different potential levels of survey effort 

as the basis for the assessment. These 

included one ‘‘high-activity’’ year, two 

separate ‘‘moderate-activity’’ years, and 

two separate ‘‘low-activity’’ years. 

Because the first 5 years of BOEM’s 

original effort projections were 

relatively high-effort years, NMFS’ 

level-of-effort selections for the 

proposed rule corresponded with the 

detailed per-survey type effort 

projections given for Years 1, 4, 5, 8, 

and 9, respectively. Exposure estimates 

resulting from the process summarized 

here and corresponding with those 

activity scenarios were shown in Table 

8 of the notice of proposed rulemaking. 

These exposure estimates were then 

further evaluated to provide an estimate 

of takes of marine mammals that could 

occur as a result of a reasonably 

expected level of geophysical survey 

activity in the GOM over the course of 

five years. Take estimates associated 

with those scenarios, which informed 

the analysis in the proposed rule, are 

shown in Table 8 of this document for 

reference. These values have been 

updated from those shown in Table 8 of 

the notice of proposed rulemaking by 

correctly incorporating discounted 

estimates of Level A harassment into the 

estimates of Level B harassment (as 

pointed out by public commenters). 

Level A Harassment 

As we explain here, the modeled 

exposure estimates for onset of 

permanent threshold shift (i.e., Level A 

harassment), are not expected to 

represent realistic results for any 

species. Overall, there is a low 

likelihood of take by Level A 

harassment for any species, though the 

degree of this low likelihood is 

primarily influenced by the specific 

hearing group. For mid- and highfrequency cetaceans, potential auditory 

injury would be expected to occur on 

the basis of instantaneous exposure to 

peak pressure output from an airgun 

array while, for low-frequency 

cetaceans, potential auditory injury 

would occur on the basis of the 

accumulation of energy output over 

time by an airgun array. Importantly, the 

modeled exposure estimates do not 

account for either aversion or the 

beneficial impacts of the required 

mitigation measures. 

Of even greater import for midfrequency cetaceans is that the small 

calculated Level A harassment zone size 

in conjunction with the properties of 

sound fields produced by arrays in the 

near field versus far field leads to a 

logical conclusion that Level A 

harassment is so unlikely for species in 

this hearing group as to be discountable. 

As stated in the notice of proposed 

rulemaking, for all mid-frequency 

cetaceans, following evaluation of the 

available scientific literature regarding 

the auditory sensitivity of midfrequency cetaceans and the properties 

of airgun array sound fields, NMFS does 

not expect any reasonable potential for 

Level A harassment to occur. We 

discussed this issue in detail earlier in 

the response to public comments. NMFS 

expects the potential for Level A 

harassment of mid-frequency cetaceans 

to be discountable, even before the 

likely moderating effects of aversion are 

considered. When considering potential 

for aversion, NMFS does not believe 

that Level A harassment is a likely 

outcome for any mid-frequency cetacean 

(as reflected in Table 9). 

As discussed in greater detail in the 

notice of proposed rulemaking, NMFS 

and BOEM considered the possibility of 

incorporating quantitative adjustments 

within the modeling process to account 

for the effects of mitigation and/or 

aversion, as both of these factors would 

lead to a reduction in likely injurious 

exposure. However, these factors were 

ultimately not quantified in the 

modeling because, in summary, there is 

too much inherent uncertainty regarding 

the effectiveness of detection-based 

mitigation to support any reasonable 

quantification of its effect in reducing 

injurious exposure and there is too little 

information regarding the likely level of 

onset and degree of aversion to quantify 

this behavior in the modeling process. 

This does not mean that mitigation is 

not effective (to some degree) in 

avoiding incidents of Level A 

harassment, nor does it mean that 

aversion is not a meaningful real-world 

effect of noise exposure that should be 

expected to reduce the number of 

incidents of Level A harassment. 

However, certain public commenters 

misconstrued statements in the notice of 

proposed rulemaking regarding the 

strictly modeling-related investigations 

of aversion (i.e., that there is not 

sufficient quantitative data to inform 

decisions regarding the programming of 

animats as far as received levels of noise 

that provoke aversive response, and the 

degree of response, for relevant species) 

as meaning that there is not sufficient 

information to support that aversion 

happens at all. To the contrary, there is 

ample evidence in the literature that 

aversion is one of the most common 

responses to noise exposure across 

varied species, though the onset and 

degree may be expected to vary across 

individuals and in different contexts. 

Therefore, NMFS proposed to 

incorporate a reasonable adjustment to 

modeled Level A harassment exposure 

estimates to account for aversion for 

low- and high-frequency species. That 

adjustment is retained here, as 

discussed in greater detail in the 

responses to public comments. 

Specifically, NMFS assumes here that 

an eighty percent reduction in modeled 

exposure estimates for Level A 

harassment for low- and high-frequency 

cetaceans is reasonable and likely 

conservative in terms of the overall 

numbers of actual incidents of Level A 

harassment for these species, as the 

adjustment does not explicitly account 

for the effects of mitigation. 

As discussed previously, BOEM 

provided an update to the scope of their 

proposed action through removal of 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, 


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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. The 

revised levels of effort are shown in 

Table 2. Associated revised take 

estimates, which were generated 

utilizing the methods described above 

and in the proposed rule and inform the 

analysis in this final rule, are shown in 

Table 9. These estimates have been 

modified from the values provided by 

BOEM (available online; ‘‘Revised 

Modeled Exposure Estimates’’) in that 

we have correctly accounted for the type 

of taking expected, i.e., for midfrequency cetaceans, Level A 

harassment is not expected to occur and 

the calculated takes have been shifted 

into the totals for Level B harassment. 

No incidents of Level A harassment for 

Bryde’s whales were predicted under 

the revised effort scenarios, which 

exclude the area where most Bryde’s 

whales would be expected to be found. 

For Kogia spp., estimates of Level A 

harassment were adjusted as discussed 

previously to account for likely 

aversion, and the portion of estimated 

Level A harassment events not expected 

to occur were shifted into the totals for 

Level B harassment for these species. 

Estimated instances of take, i.e., 

scenario-specific acoustic exposure 

estimates incorporating the adjustments 

to Level A harassment exposure 

estimates discussed here, are shown in 

Table 9. This information regarding total 

number of takes (with Level A 

harassment takes based on assumptions 

relating to mid-frequency cetaceans in 

general as well as aversion), on an 

annual basis for five years, provides the 

bounds within which incidental take 

authorizations may be issued in 

association with this regulatory 

framework. 

Typically, and especially in cases 

where PTS is predicted, NMFS 

anticipates that some number of 

individuals may incur TTS. However, it 

is not necessary to separately quantify 

those takes, as it is unlikely that an 

individual marine mammal would be 

exposed at the levels and duration 

necessary to incur TTS without also 

being exposed to the levels associated 

with behavioral disruption and, 

therefore, NMFS expects any potential 

TTS takes to be captured by the 

estimated takes by behavioral disruption 

(discussed below). 


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TABLE 8—SCENARIO-SPECIFIC INSTANCES OF

TAKE (BY

LEVEL A AND

LEVEL B HARASSMENT) AND

MEAN

ANNUAL

TAKE

LEVELS

EVALUATED IN THE

PROPOSED

RULE 1

Species 

Survey effort scenario 2

High Moderate #1 Moderate #2 Low #1 Low #2 Mean annual take 

A B A B A B A B A B A B 

Bryde’s whale ............................................................. 3 572 2 422 2 510 2 395 2 411 2 462 Sperm whale ............................................................... 0 43,549 0 27,300 0 33,378 0 26,681 0 27,689 0 31,719Kogia spp. ................................................................... 728 19,101 475 13,328 636 16,188 472 12,629 562 13,414 575 14,932 Beaked whale ............................................................. 0 235,667 0 162,172 0 190,824 0 151,745 0 156,622 0 179,406 Rough-toothed dolphin ............................................... 0 37,816 0 30,306 0 31,231 0 28,775 0 26,420 0 30,910 Bottlenose dolphin ...................................................... 0 655,345 0 979,905 0 598,607 0 941,001 0 581,121 0 751,196 Clymene dolphin ......................................................... 0 111,211 0 73,225 0 87,995 0 69,913 0 73,051 0 83,079 Atlantic spotted dolphin .............................................. 0 133,758 0 175,128 0 116,988 0 165,221 0 110,126 0 140,244 Pantropical spotted dolphin ........................................ 0 609,653 0 421,786 0 513,572 0 401,568 0 421,856 0 473,687 Spinner dolphin ........................................................... 0 83,041 0 59,818 0 73,259 0 56,735 0 59,448 0 66,460Striped dolphin ............................................................ 0 44,232 0 30,069 0 36,431 0 28,652 0 30,023 0 33,881 Fraser’s dolphin .......................................................... 0 13,910 0 9,690 0 11,438 0 9,162 0 9,426 0 10,725 Risso’s dolphin ............................................................ 0 27,165 0 18,197 0 22,005 0 17,380 0 18,166 0 20,583 Melon-headed whale .................................................. 0 69,152 0 47,719 0 57,004 0 45,011 0 46,801 0 53,137 Pygmy killer whale ...................................................... 0 18,112 0 12,335 0 14,859 0 11,733 0 12,198 0 13,847 False killer whale ........................................................ 0 25,622 0 17,708 0 20,922 0 16,849 0 17,239 0 19,668Killer whale ................................................................. 0 1,498 0 1,034 0 1,262 0 987 0 1,039 0 1,164 Short-finned pilot whale .............................................. 0 19,326 0 12,198 0 14,214 0 11,565 0 11,942 0 13,849 

1A and B refer to expected scenario-based instances of take by Level A and Level B harassment, respectively. For the Bryde’s whale and Kogia spp., expected takes by Level A harassment represent modeled exposures adjusted to account for aversion. For Kogia spp., exposures above Level A harassment criteria were predicted by the peak SPL metric. For the Bryde’s whale, exposures above Level A harassment criteria 

were predicted by the cSEL metric. 2 High survey effort scenario corresponds with level of effort projections given previously for Year 1 (see Table 1 of the notice of proposed rulemaking). Moderate #1 and #2 and Low #1 and #2 correspond with 

Years 4, 5, 8, and 9, respectively. 

TABLE 9—REVISED INSTANCES OF

TAKE (BY

LEVEL A AND

LEVEL B HARASSMENT) (YEARS 1–5) AND

MEAN

ANNUAL

TAKE

LEVELS 1

Species 

Year 1 Year 2 Year 3 Year 4 Year 5 Mean annual take 

A B A B A B A B A B A B 

Bryde’s whale ............................................................. 0 10 0 8 0 8 0 6 0 7 0 8 Sperm whale ............................................................... 0 16,405 0 14,205 0 13,603 0 9,496 0 12,388 0 13,219 Kogia spp. ................................................................... 371 10,383 337 9,313 310 8,542 209 6,238 314 8,318 308 8,559 Beaked whale ............................................................. 0 191,566 0 162,301 0 158,328 0 111,415 0 142,929 0 153,308 Rough-toothed dolphin ............................................... 0 30,640 0 27,024 0 25,880 0 19,620 0 23,219 0 25,277 Bottlenose dolphin ...................................................... 0 603,649 0 973,371 0 567,962 0 1,001,256 0 567,446 0 742,737 Clymene dolphin ......................................................... 0 85,828 0 67,915 0 73,522 0 47,332 0 60,379 0 66,995 Atlantic spotted dolphin .............................................. 0 128,299 0 183,717 0 112,120 0 191,495 0 111,305 0 145,387 Pantropical spotted dolphin ........................................ 0 478,490 0 436,047 0 391,363 0 311,316 0 395,987 0 402,641 Spinner dolphin ........................................................... 0 75,953 0 71,873 0 61,098 0 48,775 0 64,357 0 64,411Striped dolphin ............................................................ 0 33,573 0 29,275 0 27,837 0 20,136 0 26,056 0 27,375 Fraser’s dolphin .......................................................... 0 4,522 0 3,843 0 3,792 0 2,726 0 3,455 0 3,668 Risso’s dolphin ............................................................ 0 21,859 0 18,767 0 18,218 0 12,738 0 16,634 0 17,643 Melon-headed whale .................................................. 0 55,813 0 47,784 0 46,584 0 32,581 0 42,224 0 44,997 Pygmy killer whale ...................................................... 0 8,079 0 6,964 0 6,764 0 4,970 0 6,277 0 6,611 False killer whale ........................................................ 0 16,165 0 13,710 0 13,604 0 9,664 0 12,269 0 13,082 Killer whale ................................................................. 0 60 0 56 0 50 0 42 0 52 0 52 Short-finned pilot whale .............................................. 0 15,045 0 9,824 0 13,645 0 7,459 0 8,959 0 10,986 

1A and B refer to expected instances of take by Level A and Level B harassment, respectively, for Years 1–5. For Kogia spp., expected takes by Level A harassment represent modeled exposures adjusted to account for aversion. For the Bryde’s whale, no takes by Level A harassment are predicted to occur. Therefore, no adjustment to modeled exposures to account for aversion was necessary. For Kogia spp., exposures 

above Level A harassment criteria were predicted by the peak SPL metric. For the Bryde’s whale, the cSEL metric is used to evaluate the potential for Level A harassment. 


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Level B Harassment 

NMFS has determined the estimated 

values shown in Table 9 are a 

reasonable representation of the 

potential instances of take that may 

occur (more specifically, each of these 

‘‘takes’’ representing a day in which one 

individual is exposed above the Level B 

harassment criteria, even if only for 

seconds). However, these take numbers 

do not represent the number of 

individuals expected to be taken, given 

they are higher than the estimated 

abundance for all species. Accordingly, 

as described in the notice of proposed 

rulemaking, NMFS references Test 

Scenario 1 in the modeling report 

(‘‘Long-Duration Surveys and Scaling 

Methods’’) to inform two important 

parts of the analyses. Comparing the 

results of modeling simulations that 

more closely match longer survey 

durations (30 days) to the results of 24- 

hour take estimates scaled up to 30 days 

(as the instances of take in Table 9 were 

calculated) provides the comparative 

ratios of number of individuals taken/ 

calculated (within a 30-day survey) and 

instances of take, in order to better 

understand the comparative distribution 

of exposures across individuals of 

different species. First, in NMFS’ 

analyses in this rule, the ratio and its 

inverse are used to inform a better 

understanding of the nature in which 

individuals are taken across the 

multiple days of a longer duration 

survey given the different behaviors that 

are represented in the animat modeling, 

i.e., looking at the ratio of (number of 

individuals taken in 30-day modeling 

scenario)/(number of instances of take 

when 1-day average multiplied by 30 

days), if all else is equal within one 

survey, for the species with a smaller 

ratio (larger inverse), fewer individuals 

will be taken but each will be exposed 

above the threshold on a higher number 

of days (see Table 16). Second, this ratio 

may be appropriately be used in 

combination with the calculated 

instances of take to predict the number 

of individuals taken for surveys of 

similar duration (noting that for surveys 

of notably longer than 30-day duration, 

it will still likely result in some degree 

of overestimate of individuals), in order 

to support evaluation of take estimates 

in requests for Letters of Authorization, 

given the need to meet the ‘‘small 

numbers of marine mammals’’ standard, 

which is based on the number of 

individuals taken. A summary of this, 

which was included in the notice of 

proposed rulemaking along with a 

description of the other Test Scenarios 

and how they inform this analysis, is 

included below. 

Although some survey operations may 

continue for months, survey simulations 

were conducted for seven days in order 

to derive mean 24-hr exposure averages, 

with these averages then used to scale 

according to the total number of survey 

days projected by BOEM. This approach 

was necessary due to the more 

computationally-intensive modeling 

required to model more realistic 

durations (i.e., 30 days). As summarized 

above and discussed in detail in the 

notice of proposed rulemaking, a test 

scenario was used to evaluate methods 

for scaling results from shorter-duration 

simulations to longer duration 

operations. Results from test modeling 

conducted for a suite of six 

representative species over 30-day 

simulations of a hypothetical 3D WAZ 

survey were compared to the results of 

a shorter 5-day simulation, i.e., the 

number of animats exposed to levels 

exceeding threshold for 24-hr time 

periods multiplied by the number of 

days in the simulations was compared 

to the number of animats exposed to 

levels exceeding threshold for the entire 

duration of the simulations. The results 

of the test scenario indicated that 

undesired systematic biases in the 

modeling procedure, if present, were 

small relative to the survey design and 

would not affect scaling up the results 

in time (i.e., the shorter 7-day 

simulations ultimately used in the 

modeling would provide unbiased 

results). However, the results also 

indicated that scaling up the 24-hr 

average SPL exposure estimates to 30 

days greatly overestimates the number 

of notional marine mammals (i.e., 

animats) exposed to levels exceeding 

threshold when determined over the 

entire simulation (although the 

estimated instances of exposure are 

reasonably accurate). This occurs 

because animats were commonly 

exposed to levels exceeding these 

thresholds, and the relatively short reset 

period of 24 hours means that 

individual animats were, in effect, 

counted several times during the scaleup (i.e., on multiple days) whereas they 

would only have been counted once 

when evaluating over the entire 

simulation. When a real-world survey 

extends over longer durations within 

the same region, it is most likely that the 

same individuals are repeatedly 

exposed to survey noise. However, the 

modeling assumption that populations 

of animals were reset for each 24-hr 

period is equivalent to an assumption 

that each survey day is a completely 

independent event, i.e., that new 

individuals are impacted on each 

subsequent day. 

In order to determine more realistic 

exposure probabilities for individuals 

across multiple days, modeled results 

were compared for a 30-day period 

versus the aggregation of 24-hr 

population reset intervals (the 

investigation described above) to 

determine a species-typical offset of 

modeled daily exposures. When 

conducting computationally-intensive 

modeling over the full assumed 30-day 

survey period (versus aggregating the 

smaller 24-hr periods for 30 days), 

results showed about 10–45 percent of 

the total number of takes calculated 

using a 24-hr reset of the population, 

with differences relating to speciestypical movement and residency 

patterns. Given that many of the 

evaluated survey activities occur for 30- 

day or longer periods, particularly some 

of the larger surveys for which the 

majority of the modeled exposures 

occur, using such a scaling process is 

appropriate in order to evaluate the 

likely severity of the predicted 

exposures. This approach is also 

discussed in more detail in the EWG 

report (Southall et al., 2017), available 

online at: www.fisheries.noaa.gov/ 

action/incidental-take-authorization-oiland-gas-industry-geophysical-surveyactivity-gulf-mexico. 

The test scenario modeled six 

representative GOM species/guilds: 

Bryde’s whale, sperm whale, beaked 

whales, bottlenose dolphin, Kogia spp., 

and short-finned pilot whale. For 

purposes of this analysis, bottlenose 

dolphin was used as a proxy for other 

small dolphin species, and short-finned 

pilot whale was used as a proxy for 

other large delphinids. Tables 22–23 in 

the modeling report provide information 

regarding the number of modeled 

animals receiving exposure above 

criteria for average 24-hr sliding 

windows scaled to the full 30-day 

duration and percent change in 

comparison to the same number 

evaluated when modeling the full 30- 

day duration. This information was 

used to derive 30-day scalar ratios 

which, when applied to the total 

instances of take given in Table 9, 

captures repeated takes of individuals at 

a 30-day sampling level. Scalar ratios 

are as follows: Bryde’s whale, 0.189; 

sperm whale, 0.423; beaked whales, 

0.101; bottlenose dolphin, 0.287; Kogia 

spp., 0.321; and short-finned pilot 

whale, 0.295. Application of the rescaling method reduced the overall 

magnitude of modeled takes for all 

species by slightly more than double to 

up to ten-fold (Table 10). 

These adjusted take numbers (shown 

in Table 10) provide a more realistic 

basis upon which to evaluate severity of 


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the expected taking. Please see the 

Negligible Impact Analysis and 

Determinations section, later in this 

document, for additional detail. It is 

important to recognize that while these 

scaled numbers better reflect the 

number of individuals likely to be taken 

within a single 30-day survey than the 

number of instances in Table 9, they 

will still overestimate the number of 

individuals taken across the aggregated 

GOM activities, because they do not 

correct for (i.e., further reduce take to 

account for) individuals exposed to 

multiple surveys or fully correct for 

individuals exposed to surveys 

significantly longer than 30 days. 

As noted in the beginning of this 

section and in the Small Numbers 

section, using modeled instances of take 

(Table 9) and the method described here 

to scale those numbers (based on Test 

Scenario 1) allows one to more 

accurately predict the number of 

individuals that will be taken as a result 

of exposure to one survey and, 

therefore, these scaled predictions 

should be considered in requests for 

LOAs to assess whether a resulting LOA 

would meet the small numbers 

standard. However, for the purposes of 

ensuring that the take authorized 

pursuant to all issued LOAs is within 

the scope of the analysis conducted to 

support the negligible impact finding in 

this rule, authorized instances of take 

(which are the building blocks of the 

analysis) also must be assessed. 

Specifically, reflecting Table 9 and what 

has been analyzed, the total take 

authorized for any given species or 

stock over the course of the five years 

covered under these regulations should 

not exceed the sum of the five years of 

take indicated for the five scenarios in 

that table, and in any given year, the 

take of any species should not exceed 

the highest annual take listed for any of 

the five scenarios. 

TABLE 10—EXPECTED TOTAL TAKE NUMBERS, SCALED 1

Species Year 1 Year 2 Year 3 Year 4 Year 5 

Bryde’s whale ....................................................................... 2 2 2 1 1 

Sperm whale ........................................................................ 6,939 6,009 5,754 4,017 5,240 

Kogia spp. ............................................................................ 3,452 3,098 2,841 2,069 2,771 

Beaked whale ...................................................................... 19,348 16,392 15,991 11,253 14,436 

Rough-toothed dolphin ......................................................... 8,794 7,756 7,428 5,631 6,664 

Bottlenose dolphin ............................................................... 173,247 279,357 163,005 287,360 162,857 

Clymene dolphin .................................................................. 24,633 19,492 21,101 13,584 17,329 

Atlantic spotted dolphin ........................................................ 36,822 52,727 32,178 54,959 31,945 

Pantropical spotted dolphin ................................................. 137,327 125,145 112,321 89,348 113,648 

Spinner dolphin .................................................................... 21,799 20,628 17,535 13,998 18,470 

Striped dolphin ..................................................................... 9,635 8,402 7,989 5,779 7,478 

Fraser’s dolphin ................................................................... 1,298 1,103 1,088 782 992 

Risso’s dolphin ..................................................................... 6,448 5,536 5,374 3,758 4,907 

Melon-headed whale ............................................................ 16,465 14,096 13,742 9,611 12,456 

Pygmy killer whale ............................................................... 2,383 2,054 1,995 1,466 1,852 

False killer whale ................................................................. 4,769 4,044 4,013 2,851 3,619 

Killer whale ........................................................................... 18 17 15 12 15 

Short-finned pilot whale ....................................................... 4,438 2,898 4,025 2,200 2,643 

1Scalar ratios were applied to values in Table 9 as described in preceding text to derive scaled take numbers shown here. 

Mitigation 

‘‘Least Practicable Adverse Impact’’ 

Standard 

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

MMPA, NMFS must set forth the 

permissible methods of taking pursuant 

to such activity, and other means of 

effecting the least practicable adverse 

impact on such species or stock and its 

habitat, paying particular attention to 

rookeries, mating grounds, and areas of 

similar significance, and on the 

availability of such species or stock for 

subsistence uses (hereinafter referred to 

as ‘‘LPAI’’ or ‘‘least practicable adverse 

impact’’). NMFS does not have a 

regulatory definition for least 

practicable adverse impact. However, 

NMFS’ implementing regulations 

require applicants for incidental take 

authorizations to include information 

about the availability and feasibility 

(economic and technological) of 

equipment, methods, and manner of 

conducting such activity or other means 

of effecting the least practicable adverse 

impact upon the affected species or 

stocks and their habitat (50 CFR 

216.104(a)(11)). We note that in some 

cases, certain mitigation may be 

necessary in order to make a ‘‘negligible 

impact’’ finding for an affected species 

or stock, which is a fundamental 

requirement of issuing an 

authorization—in these cases, 

consideration of practicability may be a 

lower priority for decision-making if 

impacts to marine mammal species or 

stocks would not be negligible in the 

measure’s absence. 

In Conservation Council for Hawaii v. 

NMFS, 97 F. Supp. 3d 1210, 1229 (D. 

Haw. 2015), the district court stated that 

NMFS ‘‘appear[s] to think [it satisfies] 

the statutory ‘least practicable adverse 

impact’ requirement with a ‘negligible 

impact’ finding.’’ Later, expressing 

similar concerns in a challenge to an 

incidental take rule for U.S. Navy 

Operation of Surveillance Towed Array 

Sensor System Low Frequency Active 

(SURTASS LFA) Sonar (77 FR 50290, 

August 20, 2012), the Ninth Circuit in 

Natural Resources Defense Council 

(NRDC) v. Pritzker, 828 F.3d 1125, 1134 

(9th Cir. 2016), stated, ‘‘[c]ompliance 

with the ‘negligible impact’ requirement 

does not mean there [is] compliance 

with the ‘least practicable adverse 

impact’ standard.’’ NMFS is in full 

agreement that the ‘‘negligible impact’’ 

and ‘‘least practicable adverse impact’’ 

requirements are distinct, even though 

both statutory standards refer to species 

and stocks. With that in mind, we 

provide further explanation of NMFS’ 

interpretation of least practicable 

adverse impact and explain what 

distinguishes it from the negligible 

impact standard. This discussion is 

consistent with, and expands upon, 

previous rules issued by NMFS, such as 

the Navy Gulf of Alaska rule (82 FR 

19530; April 27, 2017); the Navy 

Atlantic Fleet Testing and Training rule 

(83 FR 57076; November 14, 2018); the 

Navy Hawaii-Southern California 

Training and Testing rule (83 FR 66846; 

December 27, 2018); and the SURTASS 


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12A growth rate can be positive, negative, or flat. 

13For purposes of this discussion, we omit 

reference to the language in the standard for least 

practicable adverse impact that says that NMFS also 

must mitigate for subsistence impacts, because 

subsistence impacts are not at issue in this action. 

14Mitigation may also be appropriate to ensure 

separate compliance with the ‘‘small numbers’’ 

language and negligible impact standard in MMPA 

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

LFA sonar rule (84 FR 40132; August 

13, 2019). 

Before NMFS can issue incidental 

take regulations under section 

101(a)(5)(A) of the MMPA, it must make 

a finding that the total taking will have 

a ‘‘negligible impact’’ on the affected 

‘‘species or stocks’’ of marine mammals. 

NMFS’ and the U.S. Fish and Wildlife 

Service’s implementing regulations for 

section 101(a)(5) both define ‘‘negligible 

impact’’ as an impact resulting from the 

specified activity that cannot be 

reasonably expected to, and is not 

reasonably likely to, adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival 

(50 CFR 216.103 and 50 CFR 18.27(c)). 

Recruitment (i.e., reproduction) and 

survival rates are used to determine 

population growth rates 12 and, 

therefore, are considered in evaluating 

population level impacts. 

As NMFS stated in the preamble to 

the final rule for the incidental take 

implementing regulations, not every 

population-level impact violates the 

negligible impact requirement. The 

negligible impact standard does not 

require a finding that the anticipated 

take will have ‘‘no effect’’ on population 

numbers or growth rates: ‘‘The statutory 

standard does not require that the same 

recovery rate be maintained, rather that 

no significant effect on annual rates of 

recruitment or survival occurs. [T]he 

key factor is the significance of the level 

of impact on rates of recruitment or 

survival.’’ (54 FR 40338, 40341–42; 

September 29, 1989). 

While some level of impact on 

population numbers or growth rates of 

a species or stock may occur and may 

still satisfy the negligible impact 

requirement—even without 

consideration of mitigation—the least 

practicable adverse impact provision 

separately requires NMFS to prescribe 

means of effecting the least practicable 

adverse impact on such species or stock 

and its habitat, paying particular 

attention to rookeries, mating grounds, 

and areas of similar significance, 50 CFR 

216.102(b), which are typically 

identified as mitigation measures.13

The negligible impact and least 

practicable adverse impact standards in 

the MMPA both call for evaluation at 

the level of the ‘‘species or stock.’’ The 

MMPA does not define the term 

‘‘species.’’ However, Webster’s New 

Collegiate Dictionary (1981) defines 

‘‘species’’ to include ‘‘a group of 

intimately related and physically 

similar organisms that actually or 

potentially interbreed [. . .], that 

ordinarily comprise differentiated 

populations limited geographically 

[. . .] or ecologically [. . .]’’ (emphasis 

added). See also Merriam-Webster 

Dictionary, which defines ‘‘species’’ to 

include ‘‘related organisms or 

populations potentially capable of 

interbreeding.’’ www.merriamwebster.com/dictionary/species 

(emphasis added). The MMPA defines 

‘‘stock’’ as a group of marine mammals 

of the same species or smaller taxa in a 

common spatial arrangement that 

interbreed when mature (16 U.S.C. 

1362(11)). The definition of 

‘‘population’’ includes ‘‘a group of 

interbreeding biotypes that represents 

the level of organization at which 

speciation begins.’’ Webster’s New 

Collegiate Dictionary (1981). See also 

www.merriam-webster.com/dictionary/ 

population, which defines population as 

‘‘a group of interbreeding organisms that 

represents the level of organization at 

which speciation begins.’’ The 

definition of ‘‘population’’ is strikingly 

similar to the MMPA’s definition of 

‘‘stock,’’ with both involving groups of 

individuals that belong to the same 

species and are located in a manner that 

allows for interbreeding. In fact, the 

term ‘‘stock’’ in the MMPA is 

interchangeable with the statutory term 

‘‘population stock.’’ (16 U.S.C. 

1362(11)). Both the negligible impact 

standard and the least practicable 

adverse impact standard call for 

evaluation at the level of the species or 

stock, and the terms ‘‘species’’ and 

‘‘stock’’ both relate to populations. 

Therefore, it is appropriate to view both 

the negligible impact standard and the 

least practicable adverse impact 

standard as having a population-level 

focus. 

This interpretation is consistent with 

Congress’s statutory findings for 

enacting the MMPA, nearly all of which 

are most applicable at the species or 

stock (i.e., population) level. See 16 

U.S.C. 1361 (finding that it is species 

and population stocks that are or may be 

in danger of extinction or depletion; that 

it is species and population stocks that 

should not diminish beyond being 

significant functioning elements of their 

ecosystems; and that it is species and 

population stocks that should not be 

permitted to diminish below their 

optimum sustainable population level). 

Annual rates of recruitment (i.e., 

reproduction) and survival are the key 

biological metrics used in the evaluation 

of population-level impacts, and 

accordingly these same metrics are also 

used in the evaluation of populationlevel impacts for the least practicable 

adverse impact standard. 

Recognizing this common focus of the 

least practicable adverse impact and 

negligible impact provisions on the 

‘‘species or stock’’ does not mean that 

NMFS conflates the two standards; 

despite some common statutory 

language, we recognize the two 

provisions are different and have 

different functions. 

First, a negligible impact finding is 

required before NMFS can issue an 

incidental take authorization. Although 

it is acceptable to use mitigation 

measures to reach a negligible impact 

finding (see 50 CFR 216.104(c)), no 

amount of mitigation can enable NMFS 

to issue an incidental take authorization 

for an activity that would not meet the 

negligible impact standard. 

Second, even where NMFS can reach 

a negligible impact finding—which we 

emphasize does allow for the possibility 

of some ‘‘negligible’’ population-level 

impact—the agency must still prescribe 

measures that will effect the least 

practicable amount of adverse impact 

upon the affected species or stock. 

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

NMFS to issue, in conjunction with its 

authorization, binding—and 

enforceable—restrictions (in the form of 

regulations) setting forth how the 

activity must be conducted, thus 

ensuring the activity has the ‘‘least 

practicable adverse impact’’ on the 

affected species or stocks and their 

habitat. In situations where mitigation is 

specifically needed to reach a negligible 

impact determination, section 

101(a)(5)(A)(i)(II) also provides a 

mechanism for ensuring compliance 

with the ‘‘negligible impact’’ 

requirement. 

Finally, as noted above, the least 

practicable adverse impact standard 

requires consideration of measures for 

marine mammal habitat, with particular 

attention to rookeries; mating grounds; 

and other areas of similar significance, 

and for subsistence impacts. By 

contrast, the negligible impact standard 

is concerned solely with conclusions 

about the impact of an activity on 

annual rates of recruitment and 

survival.14

In NRDC v. Pritzker, the Ninth Circuit 

stated, ‘‘[t]he statute is properly read to 

mean that even if population levels are 

not threatened significantly, still the 

agency must adopt mitigation measures 

aimed at protecting marine mammals to 


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15NMFS recognizes the least practicable adverse 

impact standard requires consideration of measures 

that will address minimizing impacts on the 

availability of the species or stocks for subsistence 

uses where relevant. Because subsistence uses are 

not implicated for this action, we do not discuss 

them. However, a similar framework would apply 

Continued 

the greatest extent practicable in light of 

military readiness needs.’’ Pritzker, 828 

F.3d at 1134 (emphases added). This 

statement is consistent with our 

understanding stated above that even 

when the effects of an action satisfy the 

negligible impact standard (i.e., in the 

court’s words, ‘‘population levels are 

not threatened significantly’’), still the 

agency must prescribe mitigation under 

the least practicable adverse impact 

standard. However, as the statute 

indicates, the focus of both standards is 

ultimately the impact on the affected 

‘‘species or stock’’; the standards are not 

solely focused on or directed at the 

impact on individual marine mammals. 

NMFS has carefully considered the 

Ninth Circuit’s opinion in NRDC v. 

Pritzker in its entirety. While the court’s 

reference to ‘‘marine mammals’’ rather 

than ‘‘marine mammal species or 

stocks’’ in the italicized language above 

might be construed as a holding that the 

least practicable adverse impact 

standard applies at the individual 

‘‘marine mammal’’ level, i.e., that NMFS 

must require mitigation to minimize 

impacts to each individual marine 

mammal unless impracticable, we 

believe that such an interpretation 

reflects an incomplete appreciation of 

the court’s decision. In NMFS’ view, the 

decision as a whole turned on the 

court’s determination that the agency 

had not given separate and independent 

meaning to the least practicable adverse 

impact standard apart from the 

negligible impact standard. NMFS 

further believes that the court’s use of 

the term ‘‘marine mammals’’ was not 

addressing the question of whether the 

standard applies to individual animals 

as opposed to the species or stock as a 

whole. We recognize that while 

consideration of mitigation can play a 

role in a negligible impact 

determination, consideration of 

mitigation measures extends beyond 

that analysis. In evaluating what 

mitigation measures are appropriate, 

NMFS considers the potential impacts 

of the specified activity, the availability 

of measures to minimize those potential 

impacts, and the practicability of 

implementing those measures, as 

described below. 

Implementation of Least Practicable 

Adverse Impact Standard 

In light of the NRDC v. Pritzker 

decision, we discuss here how NMFS 

determines whether a measure or set of 

measures meets the ‘‘least practicable 

adverse impact’’ standard. Our separate 

analysis of whether the take anticipated 

to result from the specified activities 

meets the ‘‘negligible impact’’ standard 

appears in the Negligible Impact 

Analysis and Determinations section 

below. 

NMFS’ evaluation of potential 

mitigation measures includes 

consideration of two primary factors: 

(1) The manner in which, and the 

degree to which, implementation of the 

potential measure(s) is expected to 

reduce adverse impacts to marine 

mammal species or stocks, their habitat, 

and their availability for subsistence 

uses (where relevant). This analysis 

considers such things as the nature of 

the potential adverse impact (such as 

likelihood, scope, and range), the 

likelihood that the measure will be 

effective if implemented, and the 

likelihood of successful 

implementation. 

(2) The practicability of the measures 

for applicant implementation. 

Practicability of implementation may 

consider such things as cost, impact on 

activities, personnel safety, and 

practicality of implementation. 

While the language of the least 

practicable adverse impact standard 

calls for minimizing impacts to affected 

species or stocks and their habitat, 

NMFS recognizes that the reduction of 

impacts to those species or stocks 

accrues through the application of 

mitigation measures that limit impacts 

to individual animals. Accordingly, 

NMFS’ analysis focuses on measures 

that are designed to avoid or minimize 

impacts on individual marine mammals 

that are likely to increase the probability 

or severity of population-level effects. 

While direct evidence of impacts to 

species or stocks from a specified 

activity is rarely available, and 

additional study is still needed to 

understand how specific disturbance 

events affect the fitness of individuals of 

certain species, there have been 

improvements in understanding the 

process by which disturbance effects are 

translated to the population. With 

recent scientific advancements (both 

marine mammal energetic research and 

the development of energetic 

frameworks), the relative likelihood or 

degree of impacts on species or stocks 

may often be inferred given a detailed 

understanding of the activity, the 

environment, and the affected species or 

stocks. This same information is used in 

the development of mitigation measures 

and helps us understand how mitigation 

measures contribute to lessening effects 

(or the risk thereof) to species or stocks. 

NMFS also acknowledges that there is 

always the potential that new 

information, or a new recommendation 

that had not previously been 

considered, becomes available and 

necessitates re-evaluation of mitigation 

measures (which may be addressed 

through adaptive management) to see if 

further reductions of population 

impacts are possible and practicable. 

In the evaluation of specific measures, 

the details of the specified activity will 

necessarily inform each of the two 

primary factors discussed above 

(expected reduction of impacts and 

practicability) and are carefully 

considered to determine the types of 

mitigation that are appropriate under 

the least practicable adverse impact 

standard. Analysis of how a potential 

mitigation measure may reduce adverse 

impacts on a marine mammal stock or 

species and practicability of 

implementation are not issues that can 

be meaningfully evaluated through a 

yes/no lens. The manner in which, and 

the degree to which, implementation of 

a measure is expected to reduce 

impacts, as well as its practicability, can 

vary widely. For example, a time-area 

restriction could be of very high value 

for reducing the potential for, or severity 

of, population-level impacts (e.g., 

avoiding disturbance of feeding females 

in an area of established biological 

importance) or it could be of lower 

value (e.g., decreased disturbance in an 

area of high productivity but of less 

firmly established biological 

importance). Regarding practicability, a 

measure might involve restrictions in an 

area or time that impede the operator’s 

ability to acquire necessary data (higher 

impact), or it could mean incremental 

delays that increase operational costs 

but still allow the activity to be 

conducted (lower impact). A 

responsible evaluation of ‘‘least 

practicable adverse impact’’ will 

consider the factors along these realistic 

scales. Expected effects of the activity 

and of the mitigation as well as status 

of the stock all weigh into these 

considerations. Accordingly, the greater 

the likelihood that a measure will 

contribute to reducing the probability or 

severity of adverse impacts to the 

species or stock or their habitat, the 

greater the weight that measure is given 

when considered in combination with 

practicability to determine the 

appropriateness of the mitigation 

measure, and vice versa. Consideration 

of these factors is discussed in greater 

detail below. 

1. Reduction of adverse impacts to 

marine mammal species or stocks and 

their habitat.15


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for evaluating those measures, taking into account 

both the MMPA’s directive that we make a finding 

of no unmitigable adverse impact on the availability 

of the species or stocks for taking for subsistence, 

and the relevant implementing regulations. 

The emphasis given to a measure’s 

ability to reduce the impacts on a 

species or stock considers the degree, 

likelihood, and context of the 

anticipated reduction of impacts to 

individuals (and how many individuals) 

as well as the status of the species or 

stock. 

The ultimate impact on any 

individual from a disturbance event 

(which informs the likelihood of 

adverse species- or stock-level effects) is 

dependent on the circumstances and 

associated contextual factors, such as 

duration of exposure to stressors. 

Though any proposed mitigation needs 

to be evaluated in the context of the 

specific activity and the species or 

stocks affected, measures with the 

following types of effects have greater 

value in reducing the likelihood or 

severity of adverse species- or stocklevel impacts: Avoiding or minimizing 

injury or mortality; limiting interruption 

of known feeding, breeding, mother/ 

young, or resting behaviors; minimizing 

the abandonment of important habitat 

(temporally and spatially); minimizing 

the number of individuals subjected to 

these types of disruptions; and limiting 

degradation of habitat. Mitigating these 

types of effects is intended to reduce the 

likelihood that the activity will result in 

energetic or other types of impacts that 

are more likely to result in reduced 

reproductive success or survivorship. It 

is also important to consider the degree 

of impacts that are expected in the 

absence of mitigation in order to assess 

the added value of any potential 

measures. Finally, because the least 

practicable adverse impact standard 

gives NMFS discretion to weigh a 

variety of factors when determining 

appropriate mitigation measures and 

because the focus of the standard is on 

reducing impacts at the species or stock 

level, the least practicable adverse 

impact standard does not compel 

mitigation for every kind of take, or 

every individual taken, if that mitigation 

is unlikely to meaningfully contribute to 

the reduction of adverse impacts on the 

species or stock and its habitat, even 

when practicable for implementation by 

the applicant. 

The status of the species or stock is 

also relevant in evaluating the 

appropriateness of potential mitigation 

measures in the context of least 

practicable adverse impact. The 

following are examples of factors that 

may (either alone, or in combination) 

result in greater emphasis on the 

importance of a mitigation measure in 

reducing impacts on a species or stock: 

the stock is known to be decreasing or 

status is unknown, but believed to be 

declining; the known annual mortality 

(from any source) is approaching or 

exceeding the PBR level; the affected 

species or stock is a small, resident 

population; or the stock is involved in 

a UME or has other known 

vulnerabilities, such as recovering from 

an oil spill. 

Habitat mitigation, particularly as it 

relates to rookeries, mating grounds, and 

areas of similar significance, is also 

relevant to achieving the standard and 

can include measures such as reducing 

impacts of the activity on known prey 

utilized in the activity area or reducing 

impacts on physical habitat. As with 

species- or stock-related mitigation, the 

emphasis given to a measure’s ability to 

reduce impacts on a species or stock’s 

habitat considers the degree, likelihood, 

and context of the anticipated reduction 

of impacts to habitat. Because habitat 

value is informed by marine mammal 

presence and use, in some cases there 

may be overlap in measures for the 

species or stock and for use of habitat. 

NMFS considers available 

information indicating the likelihood of 

any measure to accomplish its objective. 

If evidence shows that a measure has 

not typically been effective nor 

successful, then either that measure 

should be modified or the potential 

value of the measure to reduce effects 

should be lowered. 

2. Practicability. 

Factors considered may include those 

costs, impact on activities, personnel 

safety, and practicality of 

implementation. 

In carrying out the MMPA’s mandate 

for this action, NMFS applies the 

previously described context-specific 

balance between the manner in which 

and the degree to which measures are 

expected to reduce impacts to the 

affected species or stocks and their 

habitat and practicability for operators. 

The effects of concern (i.e., those with 

the potential to adversely impact 

species or stocks and their habitat), 

addressed previously in the Potential 

Effects of the Specified Activity on 

Marine Mammals and Their Habitat 

section of the notice of proposed 

rulemaking, include auditory injury, 

severe behavioral reactions, disruptions 

of critical behaviors, and to a lesser 

degree, masking and impacts on 

acoustic habitat (see discussion of this 

concept in the ‘‘Anticipated Effects on 

Marine Mammal Habitat’’ section in the 

notice of proposed rulemaking). Here, 

we focus on measures with proven or 

reasonably presumed ability to avoid or 

reduce the intensity of acute exposures 

that have potential to result in these 

anticipated effects with an 

understanding of the drawbacks or costs 

of these requirements, as well as timearea restrictions that would avoid or 

reduce both acute and chronic impacts. 

To the extent of the information 

available to NMFS, we considered 

practicability concerns, as well as 

potential undesired consequences of the 

measures, e.g., extended periods using 

the acoustic source due to the need to 

reshoot lines. NMFS also recognizes that 

instantaneous protocols, such as 

shutdown requirements, are not capable 

of avoiding all acute effects, and are not 

suitable for avoiding many cumulative 

or chronic effects and do not provide 

targeted protection in areas of greatest 

importance for marine mammals. 

Therefore, in addition to a basic suite of 

seismic mitigation protocols, we also 

consider measures that may or may not 

be appropriate for other activities (e.g., 

time-area restrictions specific to the 

surveys discussed herein), but that are 

warranted here given the spatial scope 

of these specified activities, potential for 

population-level effects and/or high 

magnitude of take for certain species in 

the absence of such mitigation (see 

Negligible Impact Analysis and 

Determinations), and the information 

we have regarding habitat for certain 

species. 

In order to satisfy the MMPA’s least 

practicable adverse impact standard, 

NMFS evaluated a suite of basic 

mitigation protocols that are required 

regardless of the status of a stock. 

Additional or enhanced protections are 

required for species whose stocks are in 

particularly poor health and/or are 

subject to some significant additional 

stressor that lessens that stock’s ability 

to weather the effects of the specified 

activities without worsening its status. 

NMFS reviewed the mitigation 

measures proposed in the petition, the 

requirements specified in BOEM’s PEIS, 

seismic mitigation protocols required or 

recommended elsewhere (e.g., HESS, 

1999; DOC, 2013; IBAMA, 2018; Kyhn 

et al., 2011; JNCC, 2017; DEWHA, 2008; 

BOEM, 2016; DFO, 2008; GHFS, 2015; 

MMOA, 2016; Nowacek et al., 2013; 

Nowacek and Southall, 2016), 

recommendations received during the 

public comment period, and the 

available scientific literature. NMFS 

also considered recommendations given 

in a number of review articles (e.g., Weir 

and Dolman, 2007; Compton et al., 

2008; Parsons et al., 2009; Wright and 

Cosentino, 2015; Stone, 2015b). Certain 

changes from the mitigation measures 

described in the notice of proposed 


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rulemaking were made on the basis of 

additional information and following 

review of public comments. The 

required suite of mitigation measures 

differs in some cases from the measures 

proposed in the petition and/or those 

specified by BOEM in the preferred 

alternative identified in their PEIS in 

order to reflect what NMFS believes to 

be the most appropriate suite of 

measures to satisfy the requirements of 

the MMPA. Additionally, two 

geographic mitigation measures 

discussed in the proposed rule are no 

longer applicable because of the change 

in the scope of the rule. 

For purposes of defining mitigation 

requirements, we differentiate here 

between requirements for two classes of 

airgun survey activity: Deep penetration 

and shallow penetration, with surveys 

using arrays greater than 1,500 in3 total 

airgun volume considered deep 

penetration. This delineation is 

discussed further below, under 

‘‘Changes from the Proposed 

Regulations.’’ Shallow penetration 

surveys also include those using single 

airguns, boomers, or equivalent sources. 

A third general class of surveys is also 

considered, referred to here as highresolution geophysical (HRG) surveys 

and including those surveys using the 

other electromechanical sources 

described previously. HRG surveys are 

treated differentially on the basis of 

water depth, with 200 m as the divider 

between shallow and deep HRG. Water 

depth is used as an indicator for surveys 

(shallow) that should be expected to 

have less potential for impacts to marine 

mammals, because HRG sources used in 

shallow waters are typically higherfrequency, lower power, and/or having 

some significant directionality to the 

beam pattern. Finally, HRG surveys 

using only sources operating at 

frequencies greater than or equal to 180 

kHz are exempt from the mitigation 

requirements described herein, with the 

exception of adherence to vessel strike 

avoidance protocols. (Note that this has 

been changed from 200 kHz to reflect 

the best available scientific information 

regarding generalized hearing ranges for 

affected marine mammal hearing groups 

(NMFS, 2018).) No distinction in 

standard required mitigations is made 

on the basis of BOEM’s planning areas 

(i.e., Western Planning Area (WPA), 

Central Planning Area (CPA), Eastern 

Planning Area (EPA)). 

First, we summarize notable changes 

made to the mitigation requirements as 

a result of review of public comments 

and/or new information and then 

describe mitigation prescribed in the 

regulations. For additional detail 

regarding mitigation considerations, 

including expected efficacy and/or 

practicability, or descriptions of 

mitigation considered but not required, 

please see the notice of proposed 

rulemaking. Where the practicability 

analysis was described in the notice of 

proposed rulemaking and nothing has 

changed, we do not repeat the 

description. 

Changes to Mitigation From the 

Proposed Regulations 

Here we summarize substantive 

changes to mitigation requirements from 

the proposed regulations. All changes 

were made on the basis of review of 

public comments received and/or 

review of new information. 

Delineation of Airgun Activity Tiers 

In the notice of proposed rulemaking, 

for purposes of prescribing mitigation, 

NMFS proposed to define ‘‘deep 

penetration’’ surveys as those using 

arrays greater than 400 in3 total volume. 

As stated in that notice, NMFS had little 

information upon which to base such a 

delineation for purposes of defining 

appropriate mitigation, but considered 

400 in3 as a reasonable cutoff based on 

descriptions of airgun surveys provided 

in BOEM’s petition. We also noted that 

the Associations stated in their 

comments on the petition that deep 

penetration array volumes used in the 

GOM range from approximately 2,000 to 

8,400 in3. BOEM has subsequently 

provided information to NMFS 

supporting a cutoff at 1,500 in3. In 

support of section 3(c) of E.O. 13795, 

BOEM analyzed available data for single 

airguns and airgun arrays, including 

arrays with known characteristics used 

by the National Science Foundation and 

U.S. Geological Survey and arrays 

evaluated through BOEM NEPA 

analyses. See e.g., Richardson et al. 

(1995); NSF and USGS (2011). These 

data suggest that the output of an array, 

in terms of peak source level, increases 

at a greater rate at volumes above 

approximately 1,500 in3. No public 

comments addressing this issue were 

received. Therefore, NMFS has elected 

to redefine the transition from ‘‘shallow 

penetration’’ to ‘‘deep penetration’’ from 

400 to 1,500 in3 total volume of the 

array. 

Time-Area Restrictions 

Bryde’s Whale Core Habitat Area: The 

proposed regulatory text included a 

seasonal restriction within an area we 

termed Bryde’s whale core habitat, and 

the preamble for the proposed rule 

presented several alternatives to the 

seasonal restriction for consideration by 

the public (83 FR 29281; 29302) 

including a year-round closure for this 

area, which was considered in the 

analysis for the preliminary 

determination of negligible impact. See 

83 FR 29280–29281; 83 FR 29297. 

However, the entirety of this area is 

now excluded from consideration 

through this rule following BOEM’s 

update to the scope of activity (i.e., 

removal of the GOMESA moratorium 

area from the geographic scope of the 

rulemaking). Therefore, consideration of 

a time-area restriction for the Bryde’s 

whale core habitat area (including the 

alternatives described above) is moot, 

and no restriction is included in this 

final rule. 

Dry Tortugas Area: As with the 

Bryde’s whale core habitat area, the 

entirety of the Dry Tortugas area is now 

excluded from consideration through 

this rule following BOEM’s update to 

the scope of activity (i.e., removal of the 

GOMESA moratorium area from the 

geographic scope of the rulemaking). 

Therefore, consideration of a time-area 

restriction for the biologically important 

area for sperm whales and beaked 

whales in the EPA is moot, and no 

restriction is included in this final rule. 

Coastal Restriction: NMFS proposed a 

GOM-wide restriction within coastal 

waters inside the 20-m isobath, to be in 

effect from February through May. For 

this final rule, NMFS contracted the 

proposed coastal time-area restriction 

spatially and expanded it temporally. 

The restriction has been reduced to 

cover the same coastal waters (20-m 

isobath) but between 90° W and the 

eastern extent of the coastal waters 

portion of BOEM’s updated specified 

geographic region, while expanding 

temporally to include the month of 

January. NMFS received informative 

public comment on both sides of this 

issue. Some commenters provided 

information indicating practicability 

concerns regarding the proposed 

restriction, while other commenters 

supported the importance of the 

restriction and provided information 

supporting the temporal expansion of 

the restriction to include January. As 

described in the notice of proposed 

rulemaking, the stock most heavily 

impacted by the DWH oil spill (of those 

that may be affected by the specified 

activities) was the northern coastal stock 

of bottlenose dolphin. Since publication 

of the proposed regulations, an 

additional UME occurred in the area 

largely overlapping the range of this 

stock. Therefore, while NMFS 

appreciates the practicability concerns 

raised by commenters, we contracted 

the restriction spatially but did not 

eliminate the restriction, while 

expanding it temporally to encompass 

January through May. The change is 


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described in more detail under 

Comments and Responses as well as 

later in this section where the details of 

the specific closure area is discussed. 

Restriction Area Buffer Zones: The 

proposed regulations included buffer 

zones specific to each time-area 

restriction that corresponded with 

modeled distances to the 160-dB 

isopleth (i.e., the midpoint of the Level 

B harassment risk function). These 

distances were 6 km around the EPA 

Bryde’s whale core habitat area (Area 

#2), 13 km around the coastal waters 

restriction (Area #1), and 9 km around 

the southern EPA area (Area #3). 

Following BOEM’s update to the 

geographic scope of activity considered 

through this rule, Areas 2 and 3 are 

excluded from consideration. Therefore, 

consideration of buffer zone size around 

these areas is not relevant. Upon review 

of public comment, in which 

commenters raised concerns about 

practicability among others, and reevaluation of the nature and extent of 

mitigation Area #1 as it relates to the 

necessity of an additional buffer area, 

NMFS determined it appropriate to not 

include a buffer for this area. The 

rationale for the change is described in 

more detail under Comments and 

Responses. 

Shutdown Requirements 

Delphinid Exception: NMFS does not 

require shutdown or power-down for 

certain delphinid species. In the notice 

of proposed rulemaking, we 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. While we are careful to note 

that the reasons for and potential effects 

of dolphin interaction with vessels, 

including working survey vessels, are 

not fully understood, we also 

understand that dolphins are unlikely to 

incur any degree of threshold shift due 

to their relative lack of sensitivity to the 

frequency content in an airgun signal (as 

well as because of potential coping 

mechanisms). NMFS also recognizes 

that, although dolphins do in fact react 

to airgun noise in ways that may be 

considered take (Barkaszi et al., 2012; 

Barkaszi and Kelly, 2018), there is a lack 

of notable adverse dolphin reactions to 

airgun noise despite a large body of 

observational data. Therefore, the 

removal of the power-down measure for 

small delphinids, in favor of the noshutdown or power-down alternative, is 

warranted in consideration of the 

available information regarding the 

effectiveness of such measures in 

mitigating impacts to small delphinids 

and the practicability of such measures. 

No shutdown or power-down is 

required for these species. 

Distance of Extended Shutdowns: 

NMFS limits extended distance 

shutdowns to within 1,500 m. We 

proposed a number of shutdown 

requirements on the basis of detections 

of certain species deemed particularly 

sensitive (e.g., beaked whales) or of 

particular circumstances deemed to 

warrant particular caution (e.g., whales 

with calves). These 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 extended distance 

shutdown requirements. We received 

several comments challenging the value 

of extended distance shutdown 

requirements at all and, while NMFS 

disagrees with these comments, we 

agree that some reasonable distance 

limit should be placed on these 

requirements in order to better focus the 

observational effort of protected species 

observers (PSO) and to avoid the 

potential for numerous shutdowns 

based on uncertain detections at great 

distance. Therefore, as described in 

greater detail later in this section, NMFS 

determined that a limit on such 

extended distance shutdown zones for 

relevant species or circumstances was 

appropriate. However, upon 

consideration of additional information 

(discussed later in this section), NMFS 

determined it appropriate to limit 

extended distance shutdown zones to 

1,500 m, rather than 1,000 m. 

Sperm Whale Shutdowns: The 

proposed regulatory text included an 

extended distance shutdown upon 

acoustic detection of sperm whales, and 

this final ITR explicitly expands that 

requirement to include any detection of 

sperm whales (i.e., including visual 

detection) at extended distance (i.e., 

within 1,500 m). As discussed in 

Comments and Responses, NMFS 

received some comments showing that 

there was a lack of clarity regarding the 

extended distance shutdowns for 

acoustic detections of sperm whales. 

NMFS also received comments 

indicating that the proposed division 

(i.e., extended distance shutdown upon 

acoustic detection of sperm whales but 

not visual detection) did not make sense 

given the available information 

regarding both the status of the GOM 

sperm whale population and the 

potential impacts of airgun noise on 

sperm whale foraging activity. While 

this measure does not avoid such 

impacts—the observed impacts on 

foraging behavior were at even greater 

distances (Miller et al., 2009)—it may be 

expected to practicably reduce the 

occurrence and severity of impacts on 

foraging behavior. 

Shallow Penetration Surveys: NMFS 

has reduced the standard exclusion 

zone from 200 m to 100 m, and included 

an extended distance shutdown 

requirement that mirrors the 

requirements for deep penetration 

surveys but out to a distance of 500 m. 

The 200-m shutdown distance was 

proposed on the basis of BOEM’s HRG 

survey protocol (Appendix B of BOEM, 

2017). However, practicability concerns 

were raised by public commenters and 

100-m shutdown zones have been 

effectively applied in the past to afford 

protection from potential Level A 

harassment and more severe behavioral 

responses from these types of activities. 

Therefore, rather than defer to BOEM’s 

HRG survey protocol, NMFS reevaluated the same information 

informing development of the proposed 

rule, as well as public comment, and 

determined that the 200-m shutdown 

distance is not warranted and we reduce 

the distance accordingly. Regarding the 

extended distance shutdown in special 

circumstances, NMFS proposed this 

mitigation concept in context of deep 

penetration surveys in the notice of 

proposed rulemaking. Airgun (and 

equivalent) surveys are considered to 

have similar effects on exposed marine 

mammals, and the sensitive species for 

which the extended distance shutdown 

measure was proposed are similarly 

susceptible to disturbance from shallow 

penetration surveys, if exposed. 

Therefore, NMFS expands the extended 

distance shutdown measure to shallow 

penetration surveys in addition to deep 

penetration surveys. 

HRG Surveys: 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. As discussed above for shallow 

penetration surveys, this proposal was 


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16Note that, although we discuss requirements 

related only to observation of marine mammals, we 

use the generic term ‘‘protected species observer.’’ 

17 Deep penetration surveys are defined as those 

surveys using airgun arrays with total volume 

greater than 1,500 in3. 

18The coordination of PSO duty schedules and 

roles may alternatively be performed by a thirdparty, shore-based Monitoring Coordinator. 

modeled after BOEM’s HRG survey 

protocol. However, NMFS re-evaluated 

the available information, as well as 

public comment, and has determined 

the requirement to not be warranted. 

These sources are typically higherfrequency and lower-power, and have 

highly directional beam patterns. Effects 

to marine mammals due to use of these 

sources, if any, are expected to be of 

very low severity and, therefore, the 

benefits of the proposed shutdown 

requirement would be minimal 

(especially given that animals observed 

at the surface are necessarily not 

ensonified by the downward-directed 

beams from the source at the time they 

are observed). 

Monitoring 

Nighttime Ramp-Up: NMFS 

eliminates the requirement for visual 

observation during nighttime ramp-up 

and pre-clearance. Public commenters 

indicated that this measure is not likely 

to be effective, and that there are safety 

concerns associated with PSOs working 

on deck at night. NMFS concurs with 

this assessment, as described in detail in 

Comments and Responses. 

PSOs for Node Retrieval: The 

proposed requirement for third-party 

PSOs aboard node retrieval vessels is 

eliminated due to practicability 

concerns expressed through public 

comment. NMFS concurs with this 

assessment, as described in detail in 

Comments and Responses. 

Below, mitigation requirements are 

described in detail. 

Mitigation-Related Monitoring 

Monitoring by dedicated, trained 

marine mammal observers is required in 

all water depths and, for certain 

surveys, observers must be independent. 

Additionally, for some surveys, NMFS 

requires that some PSOs 16 have prior 

experience in the role. Independent 

observers are employed by a third-party 

observer provider; vessel crew may not 

serve as PSOs when independent 

observers are required. Dedicated 

observers are those who have no tasks 

other than to conduct observational 

effort, record observational data, and 

communicate with and instruct the 

survey operator (i.e., vessel captain and 

crew) with regard to the presence of 

marine mammals and mitigation 

requirements. Communication with the 

operator may include brief alerts 

regarding maritime hazards. Trained 

PSOs have successfully completed an 

approved PSO training course (see 

Monitoring and Reporting), and 

experienced PSOs have additionally 

gained a minimum of 90 days at-sea 

experience working as a PSO during a 

deep penetration seismic survey, with 

no more than 18 months having elapsed 

since the conclusion of the relevant atsea experience. Training and experience 

is specific to either visual or acoustic 

PSO duties (where required). An 

experienced visual PSO must have 

completed approved, relevant training 

and must have gained the requisite 

experience working as a visual PSO. An 

experienced acoustic PSO must have 

completed a passive acoustic 

monitoring (PAM) operator training 

course and must have gained the 

requisite experience working as an 

acoustic PSO. Hereafter, we also refer to 

acoustic PSOs as PAM operators, 

whereas when we use ‘‘PSO’’ without a 

qualifier, the term refers to either visual 

PSOs or PAM operators (acoustic PSOs). 

NMFS does not formally administer 

any PSO training program or endorse 

specific providers but will approve 

PSOs that have successfully completed 

courses that meet the curriculum and 

trainer requirements specified herein 

(see Monitoring and Reporting). NMFS 

will provide PSO approvals in the 

context of the need to ensure that PSOs 

have the necessary training to carry out 

their duties competently while also 

approving applicant staffing plans 

quickly. In order for PSOs to be 

approved, NMFS must review and 

approve PSO resumes indicating 

successful completion of an acceptable 

training course. Although PSOs must be 

approved by NMFS, third-party observer 

providers and/or companies seeking 

PSO staffing should expect that 

observers having satisfactorily 

completed acceptable training and with 

the requisite experience (if required) 

will be quickly approved and, if NMFS 

does not respond within one week of 

having received the required 

information, such PSOs shall be 

considered to have received de facto 

approval. A PSO may be trained and/or 

experienced as both a visual PSO and 

PAM operator and may perform either 

duty, pursuant to scheduling 

requirements. Where multiple PSOs are 

required and/or PAM operators are 

required, PSO watch schedules shall be 

devised in consideration of the 

following restrictions: (1) A maximum 

of two consecutive hours on watch 

followed by a break of at least one hour 

between watches for visual PSOs 

(periods typical of observation for 

research purposes and as used for 

airgun surveys in certain circumstances 

(Broker et al., 2015)); (2) a maximum of 

four consecutive hours on watch 

followed by a break of at least two 

consecutive hours between watches for 

PAM operators; and (3) a maximum of 

12 hours observation per 24-hour 

period. NMFS may grant an exception 

for the requirement that visual PSOs be 

limited to a maximum of two 

consecutive hours on watch followed by 

a break of at least one hour between 

watches if requested on the basis of 

practicability concerns by LOA 

applicants. If an exception is granted, 

visual PSOs would instead be limited to 

a maximum of four consecutive hours 

on watch followed by a break of at least 

two hours between watches. Further 

information regarding PSO requirements 

may be found in the Monitoring and 

Reporting section, later in this 

document. 

Deep Penetration Surveys—During 

deep penetration survey 17 operations 

(e.g., any day on which use of the 

acoustic source is planned to occur; 

whenever the acoustic source is in the 

water, whether activated or not), a 

minimum of two independent PSOs 

must be on duty and conducting visual 

observations at all times during daylight 

hours (i.e., from 30 minutes prior to 

sunrise through 30 minutes following 

sunset). PSOs should use NOAA’s solar 

calculator (www.esrl.noaa.gov/gmd/ 

grad/solcalc/) to determine sunrise and 

sunset times at their specific location. 

NMFS recognizes that certain daytime 

conditions (e.g., fog, heavy rain) may 

reduce or eliminate effectiveness of 

visual observations. However, on-duty 

PSOs shall remain alert for marine 

mammal observational cues and/or a 

change in conditions. 

All source vessels must carry a 

minimum of one experienced visual 

PSO, who shall be designated as the 

lead PSO, coordinate duty schedules 

and roles,18 and serve as the primary 

point of contact for the operator. 

However, while it is desirable for all 

PSOs to be qualified through 

experience, NMFS is also mindful of the 

need to expand the workforce by 

allowing opportunity for newly trained 

PSOs to gain experience. Therefore, the 

lead PSO shall devise the duty schedule 

such that experienced PSOs are on duty 

with trained PSOs (i.e., those PSOs with 

appropriate training but who have not 

yet gained relevant experience) to the 

maximum extent practicable in order to 

provide necessary mentorship. 


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19Shallow penetration surveys are defined as 

those using airgun arrays with total volume less 

than or equal to 1,500 in3, single airguns, boomers, 

or equivalent sources. 

With regard to specific observational 

protocols, NMFS largely follows those 

described in Appendix B of BOEM’s 

PEIS (BOEM, 2017). The lead PSO shall 

determine the most appropriate 

observation posts that will not interfere 

with navigation or operation of the 

vessel while affording an optimal, 

elevated view of the sea surface. These 

should be the highest elevation 

available on each vessel, with the 

maximum viewable range from the bow 

to 90 degrees to port or starboard of the 

vessel. PSOs shall coordinate to ensure 

360° visual coverage around the vessel, 

and shall conduct visual observations 

using binoculars and the naked eye 

while free from distractions and in a 

consistent, systematic, and diligent 

manner. All source vessels must be 

equipped with pedestal-mounted 

‘‘bigeye’’ binoculars that will be 

available for PSO use. Within these 

broad outlines, the lead PSO and PSO 

team will have discretion to determine 

the most appropriate vessel- and surveyspecific system for implementing 

effective marine mammal observational 

effort. Any observations of marine 

mammals by crew members aboard any 

vessel associated with the survey, 

including receiver or chase vessels, 

should be relayed to the source vessel(s) 

and to the PSO team. 

All source vessels must use a towed 

PAM system for potential detection of 

marine mammals at all times when 

operating the sound source in waters 

deeper than 100 m. The term ‘‘towed 

PAM system’’ refers to any combination 

of hardware and software that uses a 

towed array for operations. The array 

can be physically separate from other 

in-water hardware, or embedded into 

other equipment, such as seismic 

streamers. The system must be 

monitored at all times during use of the 

acoustic source, and acoustic 

monitoring must begin at least 30 

minutes prior to ramp-up. PAM 

operators must be independent, and all 

source vessels shall carry a minimum of 

two experienced PAM operators. PAM 

operators shall communicate all 

detections to visual PSOs, when visual 

PSOs are on duty, including any 

determination by the PSO regarding 

species identification, distance and 

bearing, and the degree of confidence in 

the determination. Further detail 

regarding PAM system requirements 

may be found in the Monitoring and 

Reporting section, later in this 

document. The effectiveness of PAM 

depends to a certain extent on the 

equipment and methods used and 

competency of the PAM operator, but no 

formal standards are currently in place 

regarding PAM system hardware/ 

software requirements, or regarding 

PAM operator training. 

Visual monitoring must begin at least 

30 minutes prior to ramp-up (described 

below) and must continue until one 

hour after use of the acoustic source 

ceases or until 30 minutes past sunset. 

If any marine mammal is observed at 

any distance from the vessel, a PSO 

would record the observation and 

monitor the animal’s position (including 

latitude/longitude of the vessel and 

relative bearing and estimated distance 

to the animal) until the animal dives or 

moves out of visual range of the 

observer. A PSO would continue to 

observe the area to watch for the animal 

to resurface or for additional animals 

that may surface in the area. Visual 

PSOs shall communicate all 

observations to PAM operators, 

including any determination by the PSO 

regarding species identification, 

distance, and bearing and the degree of 

confidence in the determination. 

As noted previously, all source 

vessels must carry a minimum of one 

experienced visual PSO and two 

experienced PAM operators. The 

observer designated as lead PSO 

(including the full team of visual PSOs 

and PAM operators) must have 

experience as a visual PSO. The 

applicant may determine how many 

additional PSOs are required to 

adequately fulfill the requirements 

specified here. To summarize, these 

requirements are: (1) 24-hour acoustic 

monitoring during use of the acoustic 

source in waters deeper than 100 m; (2) 

visual monitoring during use of the 

acoustic source by two PSOs during all 

daylight hours; (3) maximum of two 

consecutive hours on watch followed by 

a minimum of one hour off watch for 

visual PSOs and a maximum of four 

consecutive hours on watch followed by 

a minimum of two consecutive hours off 

watch for PAM operators; and (4) 

maximum of 12 hours of observational 

effort per 24-hour period for any PSO, 

regardless of duties. 

Shallow Penetration Surveys—During 

shallow penetration surveys,19 operators 

must follow the same requirements 

described above for deep penetration 

surveys, with one notable exception. 

The use of PAM is not required. 

HRG Surveys—HRG survey protocols 

differ from the previously described 

protocols for deep and shallow 

penetration surveys, and we 

differentiate between deep-water 

(greater than 100 m) and shallow-water 

HRG surveys. Water depth in the GOM 

provides a reliable indicator of the 

marine mammal fauna that may be 

encountered and, therefore, the 

complexity of likely observations and 

concern related to potential effects on 

deep-diving and/or sensitive species. 

Deep-water HRG surveys are required 

to employ a minimum of one 

independent visual PSO during all 

daylight operations, in the same manner 

as was described for deep and shallow 

penetration surveys. Shallow-water 

HRG surveys are required to employ a 

minimum of one visual PSO, which may 

be a crew member. PSOs employed 

during shallow-water HRG surveys are 

only required during a pre-clearance 

period. PAM is not required for any 

HRG survey. 

PAM Malfunction—Emulating 

sensible protocols described by the New 

Zealand Department of Conservation for 

airgun surveys conducted in New 

Zealand waters (DOC, 2013), survey 

activity may continue for brief periods 

of time when the PAM system 

malfunctions or is damaged. Activity 

may continue for 30 minutes without 

PAM while the PAM operator diagnoses 

the issue. If the diagnosis indicates that 

the PAM system must be repaired to 

solve the problem, operations may 

continue for an additional two hours 

without acoustic monitoring under the 

following conditions: 

• Daylight hours and sea state is less 

than or equal to Beaufort sea state (BSS) 

4; 

• No marine mammals (excluding 

delphinids; see below) detected solely 

by PAM in the exclusion zone (see 

below) in the previous two hours; 

• NMFS is notified via email as soon 

as practicable with the time and 

location in which operations began 

without an active PAM system; and 

• Operations with an active acoustic 

source, but without an operating PAM 

system, do not exceed a cumulative total 

of four hours in any 24-hour period. 

Exclusion Zone and Buffer Zone 

An exclusion zone is a defined area 

within which occurrence of a marine 

mammal triggers mitigation action 

intended to reduce the potential for 

certain outcomes such as auditory 

injury or more severe disruption of 

behavioral patterns. For deep 

penetration surveys, the PSOs shall 

establish and monitor a 500-m exclusion 

zone and additional 500-m buffer zone 

(total 1,000 m) during the pre-clearance 

period (see below) and a 500-m 

exclusion zone during the ramp-up and 

operational periods (see below for 

description of extended 1,500-m zone in 


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special circumstances). PSOs should 

generally focus their observational effort 

within a 1.5-km zone, to the extent 

possible, with animals observed at 

greater distances recorded and 

mitigation action taken as necessary (see 

below). For shallow penetration 

surveys, the PSOs shall establish and 

monitor a 100-m exclusion zone with 

additional 100-m buffer (total 200-m 

zone) during the pre-clearance period 

and a 100-m exclusion zone during the 

ramp-up (for small arrays only, versus 

single airguns) and operational periods 

(see below for description of extended 

500-m zone in special circumstances). 

PSOs should generally focus their 

observational effort within a 500-m 

zone, to the extent possible, with 

animals observed at greater distances 

recorded and mitigation action taken as 

necessary (see below). These zones shall 

be based upon radial distance from any 

element of the airgun array (rather than 

being based on the center of the array 

or around the vessel itself). During use 

of the acoustic source, occurrence of 

marine mammals within the buffer zone 

(but outside the exclusion zone) should 

be communicated to the operator to 

prepare for the potential shutdown of 

the acoustic source. Use of the buffer 

zone in relation to ramp-up is discussed 

below under ‘‘Ramp-up.’’ Further detail 

regarding the exclusion zone and 

shutdown requirements is given under 

‘‘Exclusion Zone and Shutdown 

Requirements.’’ 

Ramp-Up 

Ramp-up of an acoustic source is 

intended to provide a gradual increase 

in sound levels, enabling animals to 

move away from the source if the signal 

is sufficiently aversive prior to its 

reaching full intensity. We infer on the 

basis of behavioral avoidance studies 

and observations that this measure 

results in some reduced potential for 

auditory injury and/or more severe 

behavioral reactions. Although this 

measure is not proven and some 

arguments have been made that use of 

ramp-up may not have the desired effect 

of aversion (which is itself a potentially 

negative impact but assumed to be 

better than the alternative), ramp-up 

remains a relatively low-cost, commonsense component of standard mitigation 

for surveys using airgun arrays. Rampup is most likely to be effective for more 

sensitive species (e.g., beaked whales) 

with known behavioral responses at 

greater distances from an acoustic 

source (e.g., Tyack et al., 2011; DeRuiter 

et al., 2013; Miller et al., 2015). Rampup is required for all surveys using 

airgun arrays. While non-airgun 

acoustic sources are not typically 

amenable to ‘‘ramping up’’ the acoustic 

output in the way that multi-element 

airgun arrays are, power to these sources 

should be increased as feasible in order 

to effect a ramp-up. 

The ramp-up procedure involves a 

step-wise increase in the number of 

airguns firing and total array volume 

until all operational airguns are 

activated and the full volume is 

achieved. Ramp-up is required at all 

times as part of the activation of the 

acoustic source (including source tests; 

see ‘‘Miscellaneous Protocols’’ for more 

detail) and may occur at times of poor 

visibility, assuming appropriate acoustic 

monitoring with no detections in the 30 

minutes prior to beginning ramp-up. 

Acoustic source activation may only 

occur at night where operational 

planning cannot reasonably avoid such 

circumstances. For example, a nighttime 

initial ramp-up following port departure 

is reasonably avoidable and may not 

occur. Ramp-up must occur at night 

following acoustic source deactivation 

due to line turn or mechanical 

difficulty. The operator must notify a 

designated PSO of the planned start of 

ramp-up as agreed-upon with the lead 

PSO; the notification time should be at 

least 60 minutes prior to the planned 

ramp-up. A designated PSO must be 

notified again immediately prior to 

initiating ramp-up procedures and the 

operator must receive confirmation from 

the PSO to proceed. 

Ramp-up procedures follow the 

recommendations of IAGC (2015). 

Ramp-up begins by activating a single 

airgun (i.e., array element) of the 

smallest volume in the array. Ramp-up 

continues in stages by doubling the 

number of active elements at the 

commencement of each stage, with each 

stage of approximately the same 

duration. Total duration should not be 

less than approximately 20 minutes but 

maximum duration is not prescribed 

and will vary depending on the total 

number of stages. Von Benda-Beckmann 

et al. (2013), in a study of the 

effectiveness of ramp-up for sonar, 

found that extending the duration of 

ramp-up did not have a corresponding 

effect on mitigation benefit. There will 

generally be one stage in which 

doubling the number of elements is not 

possible because the total number is not 

even. This should be the last stage of the 

ramp-up sequence. The operator must 

provide information to the PSO 

documenting that appropriate 

procedures were followed. Ramp-ups 

should be scheduled so as to minimize 

the time spent with the source activated 

prior to reaching the designated run-in. 

This approach is intended to ensure a 

perceptible increase in sound output per 

increment while employing increments 

that produce similar degrees of increase 

at each step. 

For deep penetration surveys, PSOs 

must monitor a 1,000-m zone (or to the 

distance visible if less than 1,000 m) for 

a minimum of 30 minutes prior to rampup (i.e., pre-clearance). For shallow 

penetration surveys, PSOs must monitor 

a 200-m zone (or to the distance visible 

if less than 200 m) for a minimum of 30 

minutes prior to ramp-up or start-up (for 

single airgun or non-airgun surveys). 

(Note that extended distance 

shutdowns, discussed below, may be 

required if certain species or 

circumstances are detected within 

greater distances: 1.5 km for deep 

penetration surveys and 500 m for 

shallow penetration surveys). The preclearance period may occur during any 

vessel activity (i.e., transit, line turn). 

Ramp-up must be planned to occur 

during periods of good visibility when 

possible; operators may not target the 

period just after visual PSOs have gone 

off duty. Following deactivation of the 

source for reasons other than mitigation, 

the operator must communicate the 

near-term operational plan to the lead 

PSO with justification for any planned 

nighttime ramp-up. Any suspected 

patterns of abuse by the operator must 

be reported by the lead PSO to be 

investigated by NMFS. Ramp-up may 

not be initiated if any marine mammal 

is within the designated zone. If a 

marine mammal is observed within the 

zone during the pre-clearance period, 

ramp-up may not begin until the 

animal(s) has been observed exiting the 

zone or until an additional time period 

has elapsed with no further sightings 

(i.e., 15 minutes for small delphinids 

and 30 minutes for all other species). 

PSOs will monitor the exclusion zone 

during ramp-up, and ramp-up must 

cease and the source shut down upon 

observation of marine mammals within 

or approaching the zone. 

Exclusion Zone and Shutdown 

Requirements 

Deep Penetration Surveys—The PSOs 

must establish a minimum exclusion 

zone with a 500-m radius as a perimeter 

around the outer extent of the airgun 

array (rather than being delineated 

around the center of the array or the 

vessel itself). If a marine mammal (other 

than the small delphinid species 

discussed below) appears within or 

enters this zone, the acoustic source 

must be shut down (i.e., power to the 

acoustic source must be immediately 

turned off). If a marine mammal is 

detected acoustically, the acoustic 

source must be shut down, unless the 

PAM operator is confident that the 


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5414 Federal Register / Vol. 86, No. 11 / Tuesday, January 19, 2021 / Rules and Regulations 

animal detected is outside the exclusion 

zone or that the detected species is not 

subject to the shutdown requirement 

(see below). 

The 500-m radial distance of the 

standard exclusion zone is expected to 

contain sound levels exceeding peak 

pressure injury criteria for all hearing 

groups other than, potentially, highfrequency cetaceans, while also 

providing a consistent, reasonably 

observable zone within which PSOs 

would typically be able to conduct 

effective observational effort. Although 

significantly greater distances may be 

observed from an elevated platform 

under good conditions, NMFS believes 

that 500 m is likely regularly attainable 

for PSOs using the naked eye during 

typical conditions. In addition, an 

exclusion zone is expected to be helpful 

in avoiding more severe behavioral 

responses. Behavioral response to an 

acoustic stimulus is determined not 

only by received level but by context 

(e.g., activity state) including, 

importantly, proximity to the source 

(e.g., Southall et al., 2007; Ellison et al., 

2012; DeRuiter et al., 2013). In 

prescribing an exclusion zone, NMFS 

seeks not only to avoid most potential 

auditory injury but also to reduce the 

likely severity of the behavioral 

response at a given received level of 

sound. 

As discussed in the notice of 

proposed rulemaking, use of monitoring 

and shutdown measures within defined 

exclusion zone distances is inherently 

an essentially instantaneous 

proposition—a rule or set of rules that 

requires mitigation action upon 

detection of an animal. This indicates 

that defining an exclusion zone on the 

basis of thresholds related to the 

accumulation of energy (i.e., cumulative 

SEL), which require that an animal 

accumulate some level of sound energy 

exposure over some period of time (e.g., 

24 hours), has questionable relevance as 

a standard protocol for mobile sources, 

given the relative motion of the source 

and the animals. A PSO aboard a mobile 

source will typically have no ability to 

monitor an animal’s position relative to 

the acoustic source over relevant time 

periods for purposes of understanding 

whether auditory injury is likely to 

occur on the basis of cumulative sound 

exposure and, therefore, whether action 

should be taken to avoid such potential. 

Cumulative SEL (cSEL) thresholds are 

more relevant for purposes of modeling 

the potential for auditory injury than 

they are for dictating real-time 

mitigation, though they can be 

informative (especially in a relative 

sense). NMFS recognizes the importance 

of the accumulation of sound energy to 

an understanding of the potential for 

auditory injury and that it is likely that, 

at least for low-frequency cetaceans, 

some potential auditory injury may be 

impossible to fully avoid, depending on 

survey location in relation to the areas 

where these species occur, and should 

be considered for authorization. 

Considering both the dual-metric 

thresholds described previously (and 

shown in Table 7) and hearing groupspecific marine mammal auditory 

weighting functions in the context of 

airgun sources, auditory injury zones 

indicated by the peak pressure metric 

are expected to be predominant for both 

mid- and high-frequency cetaceans, 

while zones indicated by cSEL criteria 

are expected to be predominant for lowfrequency cetaceans. Assuming a source 

level of 255.2 dB 0-pk SPL for the 

notional 8,000 in3 array and spherical 

spreading propagation, distances for 

exceedance of group-specific peak 

injury thresholds are as follows: 65 m 

(LF), 18 m (MF), and 457 m (HF) (for 

high-frequency cetaceans, although the 

notional source parameters indicate a 

zone less than 500 m, we recognize that 

actual isopleth distances will vary based 

on specific array characteristics and 

site-specific propagation characteristics, 

and that it is therefore possible that a 

real-world distance to the injury 

threshold could exceed 500 m). 

Assuming a source level of 227.7 dB 

0-pk SPL for the notional 90 in3 single 

airgun and spherical spreading 

propagation, these distances would be 

3 m (LF) and 19 m (HF) (the source level 

is lower than the threshold criterion 

value for mid-frequency cetaceans). 

These specific modeled source level 

values were discussed in the notice of 

proposed rulemaking, and additional 

information may be found in the 

modeling report. 

Consideration of auditory injury 

zones based on cSEL criteria is 

dependent on the animal’s generalized 

hearing range and how it overlaps with 

the frequencies produced by the sound 

source of interest in relation to marine 

mammal auditory weighting functions 

(NMFS, 2018). As noted above, zones 

based on the cSEL threshold are 

expected to be predominant for lowfrequency cetaceans because their most 

susceptible hearing range overlaps the 

low frequencies produced by airguns, 

while the modeling indicates that zones 

based on peak pressure criteria 

dominate for mid- and high-frequency 

cetaceans. As described in detail in the 

notice of proposed rulemaking, NMFS 

obtained unweighted spectrum data 

(modeled in 1 Hz bands) for a 

reasonably equivalent acoustic source 

(i.e., a 36-airgun array with total volume 

of 6,600 in3) in order to evaluate 

notional zone sizes and to incorporate 

NMFS’ Technical Guidance weighting 

functions over an airgun array’s full 

acoustic band. Using NMFS’ associated 

User Spreadsheet with hearing groupspecific weighted source levels, and 

inputs assuming a 231.8 dB SEL source 

level for the notional 8,000 in3 array, 

spherical spreading propagation, a 

source velocity of 4.5 kn, pulse duration 

of 100 ms, and a 25-m shot interval 

(shot intervals may vary, with longer 

shot intervals resulting in smaller 

calculated zones), distances for groupspecific threshold criteria are as follows: 

574 m (LF), 0 m (MF), and 1 m (HF). 

NMFS also assessed the potential for 

injury based on the accumulation of 

energy resulting from use of the single 

airgun and, assuming a source level of 

207.8 dB SEL, there would be no 

realistic zone within which injury 

would occur. 

Therefore, the 500-m exclusion zone 

contains the entirety of any potential 

injury zone for mid-frequency cetaceans 

(realistically, there is no such zone, as 

discussed above in Estimated Take and 

in Comments and Responses), while the 

zones within which injury could occur 

may be larger for high-frequency 

cetaceans (on the basis of peak pressure 

and depending on the specific array) 

and for low-frequency cetaceans (on the 

basis of cumulative sound exposure). 

In summary, NMFS’ goal in 

prescribing a standard exclusion zone 

distance is to (1) encompass zones for 

most species within which auditory 

injury could occur on the basis of 

instantaneous exposure; (2) provide 

protection from the potential for more 

severe behavioral reactions (e.g., panic, 

antipredator response) for marine 

mammals at relatively close range to the 

acoustic source; (3) enable more 

effective implementation of required 

mitigation by providing consistency and 

ease of implementation for PSOs, who 

need to monitor and implement the 

exclusion zone; and (4) define a 

distance within which detection 

probabilities are reasonably high for 

most species under typical conditions. 

NMFS’ use of 500 m as the zone is not 

based directly on any quantitative 

understanding of the range at which 

auditory injury would be entirely 

precluded or any range specifically 

related to disruption of behavioral 

patterns. Rather, we believe it is a 

reasonable combination of factors. This 

zone has been proven as a feasible 

measure through past implementation 

by operators in the GOM. In summary, 

a practicable criterion such as this has 

the advantage of familiarity and 

simplicity while still providing in most 


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cases a zone larger than relevant 

auditory injury zones, given realistic 

movement of source and receiver. 

Increased shutdowns, without a firm 

idea of the outcome the measure seeks 

to avoid, simply displace survey activity 

in time and increase the total duration 

of acoustic influence as well as total 

sound energy in the water (due to 

additional ramp-up and overlap where 

data acquisition was interrupted). The 

shutdown requirement described here 

would be required for most marine 

mammals, with certain differences. 

Small delphinids are excepted from the 

shutdown requirement, as described in 

the following section. Certain species 

are subject to an extended distance 

shutdown zone, as described in the 

subsequent section entitled ‘‘Other 

Shutdown Requirements.’’ 

Dolphin Exception—The shutdown 

requirement described above is in place 

for all marine mammals, with the 

exception of small delphinids. As 

defined here, the small delphinid group 

is intended to encompass those 

members of the Family Delphinidae 

most likely to voluntarily approach the 

source vessel for purposes of interacting 

with the vessel and/or airgun array (e.g., 

bow-riding). (Here we refer to ‘‘large 

delphinids’’ and ‘‘small delphinids’’ as 

shorthand for generally deep-diving 

versus surface-dwelling/bow-riding 

groups, respectively, as the important 

distinction is their dive behavior rather 

than their size.) This exception to the 

shutdown requirement applies solely to 

specific genera of dolphins—Steno, 

Tursiops, Stenella, and Lagenodelphis 

(see Table 4)—and applies under all 

circumstances, regardless of what the 

perception of the animal(s) behavior or 

intent may be. The proposed regulations 

included a requirement to conduct a 

power-down upon detection of these 

species within the exclusion zone. 

However, in the preamble to the 

proposed regulations, NMFS also 

included an alternative proposal for 

public review and comment in which 

no shutdown or power-down would be 

required. We requested comment on 

both proposals and other variations of 

those proposals, including NMFS’ 

interpretation of the data and any other 

data that support the necessary findings 

regarding dolphins for no shutdown and 

no power-down or no shutdown but a 

power-down. Upon review of the public 

comments received, as well as the 

scientific information summarized 

below, NMFS has determined that the 

alternative proposal of no shutdown or 

power-down is appropriate, and 

satisfies the least practicable adverse 

impact requirement. 

Variations of this measure that 

include exceptions based on animal 

behavior—e.g., ‘‘bow-riding’’ dolphins, 

or only ‘‘traveling’’ dolphins, meaning 

that the intersection of the animal and 

exclusion zone may be due to the 

animal rather than the vessel—have 

been proposed by both NMFS and 

BOEM and have been criticized, in part 

due to the subjective on-the-spot 

decision-making this scheme would 

require of PSOs. If the mitigation 

requirements are not sufficiently clear 

and objective, the outcome may be 

differential implementation across 

surveys as informed by individual 

PSOs’ experience, background, and/or 

training. The exception described here 

is based on several factors: The lack of 

evidence of or presumed potential for 

the types of effects to these species of 

small delphinid that our shutdown 

requirement for other species seeks to 

avoid, the uncertainty and subjectivity 

introduced by such a decision 

framework, and the practicability 

concern presented by the operational 

impacts. Despite a large volume of 

observational effort during airgun 

surveys, including in locations where 

dolphin shutdowns have not previously 

been required (i.e., the U.S. GOM and 

United Kingdom (UK) waters), we are 

not aware of accounts of notable adverse 

dolphin reactions to airgun noise 

(Stone, 2015a; Barkaszi et al., 2012; 

Barkaszi and Kelly, 2018) other than one 

isolated incident (Gray and Van 

Waerebeek, 2011). Dolphins have a 

relatively high threshold for the onset of 

auditory injury (i.e., PTS) and more 

severe adverse behavioral responses 

seem less likely given the evidence of 

purposeful approach and/or 

maintenance of proximity to vessels 

with operating airguns. 

The best available scientific evidence 

indicates that auditory injury as a result 

of airgun sources is extremely unlikely 

for mid-frequency cetaceans, primarily 

due to a relative lack of sensitivity and 

susceptibility to noise-induced hearing 

loss at the frequency range output by 

airguns (i.e., most sound below 500 Hz) 

as shown by the mid-frequency cetacean 

auditory weighting function (NMFS, 

2018). Criteria for TTS in mid-frequency 

cetaceans for impulsive sounds were 

derived by experimental measurement 

of TTS in beluga whales exposed to 

pulses from a seismic watergun. 

Dolphins exposed to the same stimuli in 

this study did not display TTS 

(Finneran et al., 2002). Moreover, when 

the experimental watergun signal was 

weighted appropriately for midfrequency cetaceans, less energy was 

filtered than would be the case for an 

airgun signal. More recently, Finneran 

et al. (2015) exposed bottlenose 

dolphins to repeated pulses from an 

airgun and measured no TTS. 

NMFS cautions that, while dolphins 

are observed voluntarily approaching 

source vessels (e.g., bow-riding or 

interacting with towed gear), the reasons 

for the behavior are unknown. In 

context of an active airgun array, the 

behavior cannot be assumed to be 

harmless. Although bow-riding 

comprises approximately 30 percent of 

behavioral observations in the GOM, 

there is a much lower incidence of the 

behavior when the acoustic source is 

active (Barkaszi et al., 2012), and this 

finding was replicated by Stone (2015a) 

for surveys occurring in UK waters. 

Some studies have found evidence of 

aversive behavior by dolphins during 

firing of airguns. Barkaszi et al. (2012) 

found that the median closest distance 

of approach to the acoustic source was 

at significantly greater distances during 

times of full-power source operation 

when compared to silence, while Stone 

(2015a) and Stone and Tasker (2006) 

reported that behavioral responses, 

including avoidance and changes in 

swimming or surfacing behavior, were 

evident for dolphins during firing of 

large arrays. Goold and Fish (1998) 

described a ‘‘general pattern of localized 

disturbance’’ for dolphins in the vicinity 

of an airgun survey. However, while 

these general findings—typically, 

dolphins will display increased distance 

from the acoustic source, decreased 

prevalence of ‘‘bow-riding’’ activities, 

and increases in surface-active 

behaviors—are indicative of adverse or 

aversive responses that may rise to the 

level of ‘‘take’’ (as defined by the 

MMPA), they are not indicative of any 

response of a severity such that the need 

to avoid it outweighs the impact on 

practicability for the industry and 

operators. 

Additionally, increased shutdowns 

resulting from such a measure would 

require source vessels to revisit the 

missed track line to reacquire data, 

resulting in an overall increase in the 

total sound energy input to the marine 

environment and an increase in the total 

duration over which the survey is active 

in a given area. Therefore, the removal 

of such measures for small delphinids is 

warranted in consideration of the 

available information regarding the 

effectiveness of such measures in 

mitigating impacts to small delphinids 

and the practicability of such measures. 

Although other mid-frequency 

hearing specialists (e.g., large 

delphinids) are considered no more 

likely to incur auditory injury than are 

small delphinids, they are more 


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typically deep divers, meaning that 

there is some increased potential for 

more severe effects from a behavioral 

reaction, as discussed in greater detail 

in Comments and Responses. Therefore, 

NMFS anticipates benefit from a 

shutdown requirement for large 

delphinids, in that it is likely to 

preclude more severe behavioral 

reactions for any such animals in close 

proximity to the source vessel as well as 

any potential for physiological effects. 

At the same time, large delphinids are 

much less likely to approach vessels. 

Therefore, a shutdown requirement for 

large delphinids would not have similar 

impacts as a small delphinid shutdown 

in terms of either practicability for the 

applicant or corollary increase in sound 

energy output and time on the water. 

Other Surveys—Shutdown protocols 

for shallow penetration surveys are 

similar to those described for deep 

penetration surveys, except that the 

exclusion zone is defined as a 100-m 

radial distance around the perimeter of 

the acoustic source. The dolphin 

exception described above for deep 

penetration surveys would apply. As 

described previously, no shutdowns 

would be required for HRG surveys. 

Extended Shutdown Requirements for 

Special Circumstances—Shutdown of 

the acoustic source is also required in 

the event of certain other detections 

beyond the standard exclusion zones. In 

the proposed regulatory text, NMFS 

conditioned these shutdowns upon 

detection of the relevant species or 

circumstances at any distance. However, 

in the preamble to the proposed 

regulations, we also included an 

alternative proposal for public review 

and comment in which shutdown of the 

acoustic source would occur in the 

circumstances listed below, but only 

within 1 km of the source (for deep 

penetration surveys). We requested 

comment on both proposals and other 

variations of those proposals, including 

NMFS’ interpretation of the data and 

any other data that support the 

necessary findings regarding initiating 

shutdown for certain circumstances at 

any distance or within 1 km. Following 

review of public comments and the 

relevant scientific information, NMFS 

determined that it is appropriate to limit 

such shutdown requirements. However, 

as discussed in the next paragraph, we 

also determined that the relevant 

scientific information better supports 

1.5 km as a reasonable detection radius 

(versus 1 km). Placement of a distance 

limit on these requirements maintains 

the intent of the measures as originally 

proposed, i.e., to provide for additional 

real-time protection by limiting the 

intensity and duration of acoustic 

exposures for certain species or in 

certain circumstances, while reducing 

the area over which PSOs must 

maintain observational effort. As for 

normal shutdowns within the standard 

exclusion zone, shutdowns at extended 

distance should be made on the basis of 

confirmed detections (visual or 

acoustic) within the zone. 

For deep penetration surveys, NMFS 

determined an appropriate distance on 

the basis of available information 

regarding detection functions for 

relevant species, but notes that, while 

based on quantitative data, the distance 

is an approximate limit that is merely 

intended to encompass the region 

within which we would expect a 

relatively high degree of success in 

sighting certain species while also 

improving PSO efficacy by removing the 

potential that a PSO might interpret 

these requirements as demanding a 

focus on areas further from the vessel. 

The appropriate distance limit may vary 

for different regions, depending on the 

species to which it may apply. For each 

modeled taxon, Roberts et al. (2016) 

fitted detection functions that modeled 

the detectability of the taxon according 

to distance from the trackline and other 

covariates (i.e., the probability of 

detecting an animal given its distance 

from the transect). These functions were 

based on nearly 1.1 million linear km of 

line-transect survey effort conducted 

from 1992–2014, with surveys arranged 

in aerial and shipboard hierarchies and 

further grouped according to similarity 

of observation protocol and platform. 

Where a taxon was sighted infrequently, 

a detection function was fit to pooled 

sightings of suitable proxy species. For 

example, for the Bryde’s whale and 

shipboard binocular surveys (i.e., the 

relevant combination of platform and 

protocol), a detection function was fit 

using pooled sightings of Bryde’s 

whales and other mysticete species 

(Roberts et al., 2015c). The resulting 

detection function shows a slightly 

more than 20 percent probability of 

detecting whales at 2 km, with a mean 

effective strip half-width (ESHW) 

(which provides a measure of how far 

animals are seen from the transect line; 

Buckland et al., 2001) of 1,309 m 

(Roberts et al., 2015c). Similarly, Barlow 

et al. (2011) reported mean ESHWs for 

various mysticete species ranging from 

approximately 1.5–2 km. The detection 

function used in modeling density for 

beaked whales provided mean ESHWs 

of 1,462 m and 2,258 m for two NOAA 

vessels on which visual surveys have 

historically been conducted (Roberts et 

al., 2015b). Therefore, NMFS set the 

shutdown radius for special 

circumstances (described below) at 1.5 

km for deep penetration surveys. The 

shutdown radius for special 

circumstances is set at 500 m for 

shallow penetration surveys. 

Comments disagreeing with the 

proposal to require shutdowns upon 

certain detections at any distance also 

suggested that the measures did not 

have commensurate benefit for the 

relevant species. However, it must be 

noted that any such observations would 

still be within range of where behavioral 

disturbance of some form and degree 

would be likely to occur. While visual 

PSOs should focus observational effort 

within the vicinity of the acoustic 

source and vessel, this does not 

preclude them from periodic scanning 

of the remainder of the visible area or 

from noting observations at greater 

distances, and there is no reason to 

believe that such periodic scans by 

professional PSOs would hamper the 

ability to maintain observation of areas 

closer to the source and vessel. 

Circumstances justifying shutdown at 

extended distance (e.g., within 1.5 km) 

include: 

• Upon detection of a Bryde’s whale. 

On the basis of the findings of NMFS’ 

status review (Rosel et al., 2016), NMFS 

has listed the GOM Bryde’s whale as an 

endangered species pursuant to the ESA 

(April 15, 2019; 84 FR 15446). These 

whales form a small and resident 

population in the northeastern GOM, 

with a highly restricted geographic 

range and a very small population 

abundance (fewer than 100)—recently 

determined by a status review team to 

be ‘‘at or below the near-extinction 

population level’’ (Rosel et al., 2016). 

The review team stated that, aside from 

the restricted distribution and small 

population, the whales face a significant 

suite of anthropogenic threats, one of 

which is noise produced by geophysical 

surveys. NMFS believes it appropriate 

to eliminate potential effects to 

individual Bryde’s whales to the extent 

practicable. There may be rare sightings 

of vagrant baleen whales of other 

species in the GOM, and the PSO may 

order a shutdown when observed in the 

applicable exclusion zone. 

• Upon detection of a sperm whale. 

NMFS provided an expanded 

discussion of the available evidence that 

supports this measure in the notice of 

proposed rulemaking. In summary, the 

sperm whale’s primary means of 

locating prey is echolocation (Miller et 

al., 2004), and multiple studies have 

shown that noise can disrupt feeding 

behavior and/or significantly reduce 

foraging success for sperm whales at 

relatively low levels of exposure (e.g., 

Miller et al., 2009, 2012; Isojunno et al., 


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2016; Sivle et al., 2012; Cure et al., 

2016). Effects on energy intake with no 

immediate compensation, as is 

suggested by disruption of foraging 

behavior without corollary movements 

to new locations, would be expected to 

result in bioenergetics consequences to 

individual whales. Farmer et al. (2018a) 

developed a stochastic life-stage 

structured bioenergetic model to 

evaluate the consequences of reduced 

foraging efficiency in sperm whales, 

finding that individual resilience to 

foraging disruptions is primarily a 

function of size (i.e., reserve capacity) 

and daily energetic demands, and that 

the ultimate effects on reproductive 

success and individual fitness are 

largely dependent on the duration and 

frequency of disturbance. The 

bioenergetic simulations of Farmer et al. 

(2018a) show that frequent disruptions 

in foraging, as might be expected when 

large amounts of survey activity overlap 

with areas of importance for sperm 

whales, can have potentially severe 

fitness consequences. In addition, the 

GOM sperm whale population was 

heavily impacted by the DWH oil spill. 

Therefore, in consideration of the 

potential energetic impacts of survey 

activity on individual sperm whales and 

the environmental baseline for the GOM 

sperm whale population, NMFS 

determined that meaningful measures 

must be taken to minimize disruption of 

foraging behavior. As described earlier 

in this section, the proposed regulations 

limited this extended distance 

shutdown requirement to acoustic 

detections of sperm whales. However, 

while stating that NMFS preliminarily 

did not believe the addition of 

shutdowns for sperm whales based on 

visual detections at any distance were 

warranted, we also requested any 

information from the public that would 

be relevant to that determination. 

NMFS’ review of the comments and 

information provided by the public 

indicates that expansion of this 

requirement to include all sperm whale 

detections, rather than only acoustic 

detections (as was proposed), is 

warranted. Please see Comments and 

Responses for further discussion. 

• Upon detection of a beaked whale 

or Kogia spp. These species are 

behaviorally sensitive deep divers and it 

is possible that disturbance could 

provoke a severe behavioral response 

leading to fitness consequences (e.g., 

Wursig et al., 1998; Cox et al., 2006). 

NMFS recognizes that there are 

generally low detection probabilities for 

beaked whales and Kogia spp., meaning 

that many animals of these species may 

go undetected. Barlow (1999) estimates 

such probabilities at 0.23 to 0.45 for 

Cuvier’s and Mesoplodont beaked 

whales, respectively. However, Barlow 

and Gisiner (2006) predict a roughly 24– 

48 percent reduction in the probability 

of detecting beaked whales during 

seismic mitigation monitoring efforts as 

compared with typical research survey 

efforts, and Moore and Barlow (2013) 

noted a decrease in g(0) for Cuvier’s 

beaked whales from 0.23 at BSS 0 (calm) 

to 0.024 at BSS 5. Similar detection 

probabilities have been noted for Kogia 

spp., though they typically travel in 

smaller groups and are less vocal, thus 

making detection more difficult (Barlow 

and Forney, 2007). As discussed 

previously in this document (see the 

Estimated Take section), there are high 

levels of predicted exposures for beaked 

whales in particular. Because it is likely 

that only a small proportion of beaked 

whales and Kogia spp. potentially 

affected by the proposed surveys would 

actually be detected, it is important to 

avoid potential impacts when 

practicable. Additionally for Kogia 

spp.—the one species of high-frequency 

cetacean likely to be encountered— 

auditory injury zones relative to peak 

pressure thresholds are significantly 

greater than for other cetaceans— 

approximately 500 m from the acoustic 

source, depending on the specific real 

world array characteristics (NMFS, 

2018). 

Shutdown Implementation 

Protocols—Any PSO on duty has the 

authority to delay the start of survey 

operations or to call for shutdown of the 

acoustic source. When shutdown is 

called for by a PSO, the acoustic source 

must be immediately deactivated and 

any dispute resolved only following 

deactivation. The operator must 

establish and maintain clear lines of 

communication directly between PSOs 

on duty and crew controlling the 

acoustic source to ensure that shutdown 

commands are conveyed swiftly while 

allowing PSOs to maintain watch; handheld UHF radios are recommended. 

When both visual PSOs and PAM 

operators are on duty, all detections 

must be immediately communicated to 

the remainder of the on-duty team for 

potential verification of visual 

observations by the PAM operator or of 

acoustic detections by visual PSOs and 

initiation of dialogue as necessary. 

When there is certainty regarding the 

need for mitigation action on the basis 

of either visual or acoustic detection 

alone, the relevant PSO(s) must call for 

such action immediately. 

Upon implementation of shutdown, 

the source may be reactivated after the 

animal(s) has been observed exiting the 

exclusion zone or following a 30-minute 

clearance period with no further 

detection of the animal(s). 

If the acoustic source is shut down for 

reasons other than mitigation (e.g., 

mechanical difficulty) for brief periods 

(i.e., less than 30 minutes), it may be 

activated again without ramp-up if PSOs 

have maintained constant observation 

(including acoustic observation, where 

required) and no visual detections of 

any marine mammal have occurred 

within the exclusion zone and no 

acoustic detections have occurred 

(when required). NMFS defines ‘‘brief 

periods’’ in keeping with other 

clearance watch periods and to avoid 

unnecessary complexity in protocols for 

PSOs. For any longer shutdown (e.g., 

during line turns), pre-clearance watch 

and ramp-up are required. For any 

shutdown at night or in periods of poor 

visibility (e.g., BSS 4 or greater), rampup is required but if the shutdown 

period was brief and constant 

observation maintained, pre-clearance 

watch is not required. 

Miscellaneous Protocols 

The acoustic source must be 

deactivated when not acquiring data or 

preparing to acquire data, except as 

necessary for testing. Unnecessary use 

of the acoustic source should be 

avoided. Firing of the acoustic source at 

any volume above the stated production 

volume would not be authorized. The 

operator must provide information to 

the lead PSO at regular intervals 

confirming the firing volume. Notified 

operational capacity (not including 

redundant backup airguns) must not be 

exceeded during the survey, except 

where unavoidable for source testing 

and calibration purposes. All occasions 

where activated source volume exceeds 

notified operational capacity must be 

noticed to the PSO(s) on duty and fully 

documented for reporting. The lead PSO 

must be granted access to relevant 

instrumentation documenting acoustic 

source power and/or operational 

volume. 

Testing of the acoustic source 

involving all elements requires normal 

mitigation protocols (e.g., ramp-up). 

Testing limited to individual source 

elements or strings does not require 

ramp-up but does require pre-clearance. 

Restriction Areas 

Discussion of various time-area 

restrictions was provided in the notice 

of proposed rulemaking. NMFS 

proposed two time-area restrictions 

located within the area covered by the 

current GOMESA moratorium. As 

discussed previously, BOEM 

subsequently updated the scope of the 

specified activity that was the subject of 


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the petition for the ITR, removing the 

area subject to the current GOMESA 

moratorium from consideration through 

this rule. Therefore, consideration of 

those two proposed restrictions (Areas 

2–3 in Figure 4 below), and any 

alternatives, is no longer relevant. 

Figure 4 depicts the time-area 

restrictions, absent consideration of 

BOEM’s removal of the GOMESA 

moratorium area. Areas 2 and 3 are 

entirely within that area, and the eastern 

extent of Area 1 is functionally reduced 

through the removal of the GOMESA 

moratorium area. 

BILLING CODE 3510–22–P 

BILLING CODE 3510–22–C 

Coastal Restriction—No airgun 

surveys may occur from 90–84° W (as 

truncated through removal of the 

GOMESA moratorium area) and 

shoreward of a line indicated by the 

20-m isobath, during the months of 

January through May (Area 1; Figure 4). 

Waters shoreward of the 

20-m isobath, where coastal dolphin 

stocks occur, represent the areas of 

greatest abundance for bottlenose 

dolphins (Roberts et al., 2016). As 

discussed above, and in greater detail in 

Comments and Responses, this 

requirement was modified from the 

proposed regulations by contracting the 

area spatially while expanding the 

restriction temporally by one month, in 

order to more practicably minimize 

potential impacts on the potentially 

affected stock most heavily impacted by 

the DWH oil spill (i.e., the northern 

coastal stock of bottlenose dolphins). 

The restriction is intended 

specifically to avoid additional stressors 

to the northern coastal stock of 

bottlenose dolphins during the time 

period believed to be of greatest 

importance as a reproductive period. As 

described previously, NOAA estimates 

that potentially 82 percent of northern 

coastal dolphins were exposed to DWH 

oil, resulting in an array of long-term 

health impacts (including reproductive 

failure) and possible population 

reductions of 50 percent for the stock 

(DWH MMIQT, 2015). The same 

analysis estimated that these 

population-level impacts could require 

39 years to recovery, in the absence of 

other additional stressors. More 

recently, the stock has been subject to 

another declared UME; further 

discussion of this UME is provided 

under Description of Marine Mammals 

in the Area of the Specified Activity. 

The January–May timeframe is 

intended to best encompass the most 

important reproductive period for 

bottlenose dolphins in these coastal 

waters, when additional stress is most 

likely to have serious impacts on 

pregnancy and/or survival of neonates. 

Expert interpretation of the long-term 

data for neonate strandings is that 

February–April are the primary months 

that animals are born in the northern 

GOM, and that fewer but similar 

numbers are born in January and May. 

This refers to long-term averages and in 

any particular year the peak 

reproductive period can shift earlier or 

later. 

Bryde’s Whale—The ‘‘Bryde’s whale 

core habitat area’’ considered in the 

notice of proposed rulemaking was 

designated as between the 100- and 

400-m isobaths, from 87.5° W to 27.5° N 

(Area 2; Figure 4). As summarized at the 

beginning of this section, and discussed 

in greater detail in Comments and 

Responses, the proposed regulatory text 

included a seasonal restriction within 

the same area. The preamble to the 

proposed regulations also included 

alternative proposals for public review 

and comment. This area is entirely 


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located in the GOMESA moratorium 

area, which is now removed from 

consideration through this rule. 

As described previously, NOAA’s 

status review team determined the 

status of the GOM Bryde’s whale to be 

precarious (Rosel et al., 2016). These 

findings formed, in part, the basis for 

the analysis presented in the preamble 

to the proposed regulations and 

subsequently supported NMFS’ listing 

of the GOM Bryde’s whale as an 

endangered species pursuant to the ESA 

(84 FR 15446; April 15, 2019). These 

whales form a small and resident 

population in the northeastern GOM, 

with a highly restricted geographic 

range and a very small population 

abundance—determined by the status 

review team to be ‘‘at or below the nearextinction population level’’ (Rosel et 

al., 2016). Aside from the restricted 

distribution and small population, the 

whales face a significant suite of 

anthropogenic threats, one of which is 

noise produced by airgun surveys. 

While various population abundance 

estimates are available (e.g., Waring et 

al., 2016; Roberts et al., 2016; Dias and 

Garrison, 2016), the population 

abundance was almost certainly less 

than 100 prior to the DWH oil spill. 

NOAA estimated that, as a result of that 

event, 48 percent of the population may 

have been exposed to DWH oil, with 17 

percent killed and 22 percent of females 

experiencing reproductive failure. The 

best estimate for maximum population 

reduction was 22 percent, with an 

estimated 69 years to recovery (to the 

precarious status prior to the DWH oil 

spill) (DWH MMIQT, 2015). It is 

considered likely that Bryde’s whale 

habitat previously extended to shelf and 

slope areas of the western and central 

GOM similar to where they are found 

now in the eastern GOM, and that 

anthropogenic activity—largely energy 

exploration and production— 

concentrated in those areas could have 

resulted in habitat abandonment 

(Reeves et al., 2011; Rosel and Wilcox, 

2014). Further, the population exhibits 

very low levels of genetic diversity and 

significant genetic mitochondrial DNA 

divergence from other Bryde’s whales 

worldwide (Rosel and Wilcox, 2014). 

The small population size, restricted 

range, and low genetic diversity alone 

place these whales at significant risk of 

extinction (IWC, 2017), which has been 

exacerbated by the effects of the DWH 

oil spill. Additionally, Bryde’s whale 

dive and foraging behavior places them 

at heightened risk of being struck by 

vessels and/or entangled in fishing gear 

(Soldevilla et al., 2017). NMFS 

considered a restriction in this core 

habitat area to protect Bryde’s whales 

because of their hearing sensitivity in 

the lower frequency range (which makes 

them generally more susceptible to 

incurring effects from airgun noise than 

other taxa in the GOM); the potential 

impacts to important behavioral 

functions such as feeding, breeding, and 

raising young; their dangerously low 

population size; and other issues 

discussed previously. The absence of 

survey activity in the area would be 

expected to protect Bryde’s whales and 

their habitat through the alleviation or 

minimization of a range of airgun 

effects, both acute and chronic, that 

could otherwise accrue to impact the 

reproduction or survival of individuals 

in the core habitat area. The absence of 

survey activity in the area would not 

only largely avoid Level B harassment of 

Bryde’s whales, but also very 

importantly minimize other acoustic 

effects such as masking and loss of 

communication space. Based on Roberts 

et al., 2016, this core habitat area is 

expected to encompass approximately 

92 percent of Bryde’s whales in the Gulf 

of Mexico. The update of the scope of 

the rule eliminates this core area and 

the corresponding impacts of concern 

from consideration in the analysis. 

Although this area is no longer 

relevant under the updated geographic 

scope of the specified activity and this 

rule, the discussion above is still 

important to provide a picture of the 

species’ distribution in the GOM and 

NMFS’ work to identify appropriate 

mitigation in this rulemaking. Because 

NMFS acknowledges that some whales 

may be present at locations other than 

within this core habitat area, we 

considered additional information in 

order to evaluate whether a different 

closure area may be warranted. For 

example, a NOAA survey reported 

observation of a Bryde’s whale in the 

western GOM in 2017 (NMFS, 2018). 

There had not previously been a verified 

sighting of a Bryde’s whale in the 

western GOM and, given the importance 

of this observation, additional survey 

effort was conducted in an attempt to 

increase effort in the area. However, no 

additional sightings were recorded. 

Overall, Bryde’s whales observations 

have been consistently located within 

the eastern GOM core habitat area, with 

few whales sighted elsewhere despite a 

large amount of dedicated cetacean 

survey effort that covered both 

continental shelf and oceanic waters. 

Whales have been sighted in the core 

habitat area in all seasons, and all 

indications are that the whales inhabit 

this area year-round as a resident 

population. A tagged whale remained 

within the area for 38 days, the entire 

time the tag was active. Therefore, while 

it is possible that Bryde’s whales occur 

outside the core habitat area, or that 

whales from the eastern GOM 

occasionally travel outside the area, the 

few existing observations outside the 

eastern GOM do not affect NMFS’ 

determination that the area considered 

in the proposed rule represents core 

habitat, or identify any additional 

important habitat that may 

appropriately be subject to a restriction 

on survey activity. 

Entanglement Avoidance 

The use of ocean-bottom nodes (OBN) 

or similar equipment requiring the use 

of tethers or connecting lines poses an 

entanglement risk. In order to avoid 

incidents of entanglement, NMFS 

requires the same measures included for 

the same purpose in permits issued by 

BOEM. These measures apply to 

operators conducting OBN surveys (or 

surveys using similar equipment), and 

include: (1) Use negatively buoyant 

coated wire-core tether cable (e.g., 3⁄4’’ 

polyurethane-coated cable with 1⁄2’’ 

wire core); (2) retrieve all lines 

immediately following completion of 

the survey; and (3) attach acoustic 

pingers directly to the coated tether 

cable. Acoustic releases should not be 

used. No unnecessary release lines or 

lanyards may be used and nylon rope 

may not be used for any component of 

the system. Pingers must be attached 

directly to the nodal tether cable via 

shackle, with cables retrieved via 

grapnel. If a lanyard is required it must 

be as short as possible and made as stiff 

as possible, e.g., by placing inside a 

hose sleeve. The notice of proposed 

rulemaking also included a proposed 

requirement to require operators to 

employ a third-party PSO aboard the 

node retrieval vessel in order to 

document any unexpected marine 

mammal entanglement. In consideration 

of the information provided by public 

commenters, NMFS has determined that 

this measure is unnecessary and 

eliminates it from the final ITR. Use of 

a third-party PSO in this capacity would 

not help to avoid entanglement events, 

and operators would be required to 

report any such events to BSEE. 

Therefore, the requirement provides 

little benefit while imposing costs on 

operators. 

Vessel Strike Avoidance 

These measures apply to all vessels 

associated with any survey activity (e.g., 

source vessels, streamer vessels, chase 

vessels, supply vessels). However, 

NMFS notes that these requirements do 

not apply in any case where compliance 

would create an imminent and serious 


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threat to a person or vessel or to the 

extent that a vessel is restricted in its 

ability to maneuver and, because of the 

restriction, cannot comply. These 

measures include the following: 

1. Vessel operators and crews must 

maintain a vigilant watch for all marine 

mammals and must slow down, stop 

their vessel, or alter course, as 

appropriate and regardless of vessel 

size, to avoid striking any marine 

mammal. A visual observer aboard the 

vessel must monitor a vessel strike 

avoidance zone around the vessel 

(distances stated below). Visual 

observers monitoring the vessel strike 

avoidance zone may be third-party 

observers (i.e., PSOs) or crew members, 

but crew members responsible for these 

duties must be provided sufficient 

training to (1) distinguish protected 

species from other phenomena and (2) 

broadly to identify a marine mammal as 

a baleen whale, sperm whale, or other 

marine mammal; 

2. Vessel speeds must be reduced to 

10 kn or less when mother/calf pairs, 

pods, or large assemblages of any 

marine mammal are observed near a 

vessel; 

3. All vessels must maintain a 

minimum separation distance of 500 m 

from baleen whales; 

4. All vessels must maintain a 

minimum separation distance of 100 m 

from sperm whales; 

5. All vessels must, to the maximum 

extent practicable, attempt to maintain a 

minimum separation distance of 50 m 

from all other marine mammals, with an 

understanding that at times this may not 

be possible (e.g., for animals that 

approach the vessel); and 

6. When marine mammals are sighted 

while a vessel is underway, the vessel 

shall take action as necessary to avoid 

violating the relevant separation 

distance (e.g., attempt to remain parallel 

to the animal’s course, avoid excessive 

speed or abrupt changes in direction 

until the animal has left the area). If 

marine mammals are sighted within the 

relevant separation distance, the vessel 

must reduce speed and shift the engine 

to neutral, not engaging the engines 

until animals are clear of the area. This 

does not apply to any vessel towing gear 

or any vessel that is navigationally 

constrained. 

NMFS has carefully evaluated the 

suite of mitigation measures described 

here and considered a range of other 

measures in the context of ensuring that 

we prescribe the means of effecting the 

least practicable adverse impact on the 

affected marine mammal species and 

stocks and their habitat. Based on our 

evaluation of these measures, we have 

determined that the required mitigation 

measures provide the means of effecting 

the least practicable adverse impact on 

marine mammal species or stocks and 

their habitat, paying particular attention 

to rookeries, mating grounds, and areas 

of similar significance. 

Monitoring and Reporting 

In order to issue an LOA for an 

activity, Section 101(a)(5)(A) of the 

MMPA states that NMFS must set forth 

requirements pertaining to the 

monitoring and reporting of the 

authorized taking. NMFS’ MMPA 

implementing regulations further 

describe the information that an 

applicant should provide when 

requesting an authorization (50 CFR 

216.104(a)(13)), including the means of 

accomplishing the necessary monitoring 

and reporting that will result in 

increased knowledge of the species and 

the level of taking or impacts on 

populations of marine mammals. 

Effective reporting is critical both to 

compliance as well as ensuring that the 

most value is obtained from the required 

monitoring. 

Section 101(a)(5)(A) allows that 

incidental taking may be authorized 

only if the total of such taking 

contemplated over the course of five 

years will have a negligible impact on 

affected species or stocks (a finding 

based on impacts to annual rates of 

recruitment and survival) and, further, 

section 101(a)(5)(B) requires that 

authorizations issued pursuant to 

101(a)(5)(A) be withdrawn or suspended 

if the total taking is having, or may 

have, more than a negligible impact (or 

such information may inform decisions 

on requests for LOAs under the specific 

regulations). Therefore, the necessary 

requirements pertaining to monitoring 

and reporting must address the total 

annual impacts to marine mammal 

species or stocks. Effective reporting is 

critical both to compliance as well as 

ensuring that the most value is obtained 

from the required monitoring. 

These requirements are described 

below under ‘‘Data Collection’’ and 

‘‘LOA Reporting.’’ Additional 

comprehensive reporting, across LOAholders on an annual basis, is also 

required and is described below under 

‘‘Comprehensive Reporting.’’ 

More specifically, monitoring and 

reporting requirements prescribed by 

NMFS should contribute to improved 

understanding of one or more of the 

following: 

• Occurrence of marine mammal 

species in action area (e.g., presence, 

abundance, distribution, density); 

• Nature, scope, or context of likely 

marine mammal exposure to potential 

stressors/impacts (individual or 

cumulative, acute or chronic), through 

better understanding of: (1) Action or 

environment (e.g., source 

characterization, propagation, ambient 

noise); (2) affected species (e.g., life 

history, dive patterns); (3) co-occurrence 

of marine mammal species with the 

action; or (4) biological or behavioral 

context of exposure (e.g., age, calving or 

feeding areas); 

• Individual marine mammal 

responses (behavioral or physiological) 

to acoustic stressors (acute, chronic, or 

cumulative), other stressors, or 

cumulative impacts from multiple 

stressors; 

• How anticipated responses to 

stressors impact either: (1) Long-term 

fitness and survival of individual 

marine mammals; or (2) populations, 

species, or stocks; 

• Effects on marine mammal habitat 

(e.g., marine mammal prey species, 

acoustic habitat, or important physical 

components of marine mammal habitat); 

and 

• Mitigation and monitoring 

effectiveness. 

Changes To Monitoring and Reporting 

From the Notice of Proposed 

Rulemaking 

Here we summarize substantive 

changes to monitoring and reporting 

requirements from the notice of 

proposed rulemaking. All changes were 

made on the basis of review of public 

comments received and/or review of 

new information. 

• Although NMFS recognizes the 

importance of producing the most 

accurate estimates of actual take 

possible, we agree that the specific 

approach described in the proposed rule 

for correcting observations to produce 

estimates of actual takes is novel in that 

it has not been previously required of 

applicants conducting similar activities 

and, therefore, its appropriateness for 

application to observations conducted 

from working source vessels (versus 

research vessels) is unknown. As 

suggested through public comment, 

NMFS will continue to evaluate the best 

method for producing accurate 

estimates of actual take, based on 

marine mammal detections, through the 

adaptive management process, 

including consideration of the Marine 

Mammal Commission-recommended 

method included in the proposed 

regulations. 

• 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 


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certain circumstances, in order to reflect 

current best practice. 

PSO Eligibility and Qualifications 

All PSO resumes must be submitted 

to NMFS and PSOs must be approved 

by NMFS after a review of their 

qualifications. These qualifications 

include whether the individual has 

successfully completed the necessary 

training (see ‘‘Training,’’ below) and, if 

relevant, whether the individual has the 

requisite experience (and is in good 

standing). PSOs should provide a 

current resume and information 

indicating successful completion of an 

acceptable PSO training course; 

submitted resumes should not include 

superfluous information. In order for a 

PSO training course to be deemed 

acceptable by NMFS (in consultation 

with BOEM/BSEE), the agencies must, 

at minimum, review a course 

information packet that includes the 

name and qualifications (e.g., 

experience, training, or education) of 

the instructor(s), the course outline or 

syllabus, and course reference material. 

Absent a waiver (discussed below), 

PSOs must be trained biologists, with 

the following minimum qualifications: 

• A bachelor’s degree from an 

accredited college or university with a 

major in one of the natural sciences and 

a minimum of 30 semester hours or 

equivalent in the biological sciences and 

at least one undergraduate course in 

math or statistics; and 

• Successful completion of relevant 

training (described below), including 

completion of all required coursework 

and passing (80 percent or greater) a 

written and/or oral examination 

developed for the training program. 

In addition, it is recommended that 

PSOs meet the following requirements: 

• Experience and ability to conduct 

field observations and collect data 

according to assigned protocols (may 

include academic experience) and 

experience with data entry on 

computers; 

• Visual acuity in both eyes (vision 

correction is permissible) sufficient for 

discernment of moving targets at the 

water’s surface with ability to estimate 

target size and distance; use of 

binoculars may be necessary to correctly 

identify the target (required for visual 

PSOs only); 

• Experience or training in the field 

identification of marine mammals, 

including the identification of behaviors 

(required for visual PSOs only); 

• Sufficient training, orientation, or 

experience with the survey operation to 

ensure personal safety during 

observations; 

• Writing skills sufficient to prepare a 

report of observations (e.g., description, 

summary, interpretation, analysis) 

including but not limited to the number 

and species of marine mammals 

observed; marine mammal behavior; 

and descriptions of activity conducted 

and implementation of mitigation; and 

• Ability to communicate orally, by 

radio or in person, with survey 

personnel to provide real-time 

information on marine mammals 

detected in the area as necessary. 

The educational requirements may be 

waived if the PSO has acquired the 

relevant skills through alternate 

experience. Requests for such a waiver 

must include written justification, and 

prospective PSOs granted waivers must 

satisfy training requirements described 

below. Alternate experience that may be 

considered includes, but is not limited 

to, the following: 

• Secondary education and/or 

experience comparable to PSO duties; 

• Previous work experience 

conducting academic, commercial, or 

government-sponsored marine mammal 

surveys; and 

• Previous work experience as a PSO; 

the PSO should demonstrate good 

standing and consistently good 

performance of PSO duties. 

Training—NMFS does not formally 

administer any PSO training program or 

endorse specific providers but will 

approve PSOs that have successfully 

completed courses that meet the 

curriculum and trainer requirements 

specified herein and, therefore, are 

deemed acceptable. To be deemed 

acceptable, training should adhere 

generally to the recommendations 

provided by ‘‘National Standards for a 

Protected Species Observer and Data 

Management Program: A Model Using 

Geological and Geophysical Surveys’’ 

(Baker et al., 2013). Those 

recommendations include the following 

topics for training programs: 

• Life at sea, duties, and authorities; 

• Ethics, conflicts of interest, 

standards of conduct, and data 

confidentiality; 

• Offshore survival and safety 

training; 

• Overview of oil and gas activities 

(including geophysical data acquisition 

operations, theory, and principles) and 

types of relevant sound source 

technology and equipment; 

• Overview of the MMPA and ESA as 

they relate to protection of marine 

mammals; 

• Mitigation, monitoring, and 

reporting requirements as they pertain 

to geophysical surveys; 

• Marine mammal identification, 

biology and behavior; 

• Background on underwater sound; 

• Visual surveying protocols, distance 

calculations and determination, cues, 

and search methods for locating and 

tracking different marine mammal 

species (visual PSOs only); 

• Optimized deployment and 

configuration of PAM equipment to 

ensure effective detections of cetaceans 

for mitigation purposes (PAM operators 

only); 

• Detection and identification of 

vocalizing species or cetacean groups 

(PAM operators only); 

• Measuring distance and bearing of 

vocalizing cetaceans while accounting 

for vessel movement (PAM operators 

only); 

• Data recording and protocols, 

including standard forms and reports, 

determining range, distance, direction, 

and bearing of marine mammals and 

vessels; recording GPS location 

coordinates, weather conditions, 

Beaufort wind force and sea state, etc.; 

• Proficiency with relevant software 

tools; 

• Field communication/support with 

appropriate personnel, and using 

communication devices (e.g., two-way 

radios, satellite phones, internet, email, 

facsimile); 

• Reporting of violations, 

noncompliance, and coercion; and 

• Conflict resolution. 

PAM operators should regularly 

refresh their detection skills through 

practice with simulation-modeling 

software and should keep up to date 

with training on the latest software/ 

hardware advances. 

Visual Monitoring 

The lead PSO is responsible for 

establishing and maintaining clear lines 

of communication with vessel crew. The 

vessel operator shall work with the lead 

PSO to accomplish this and shall ensure 

any necessary briefings are provided for 

vessel crew to understand mitigation 

requirements and protocols. While on 

duty, PSOs will continually scan the 

water surface in all directions around 

the acoustic source and vessel for 

presence of marine mammals, using a 

combination of the naked eye and highquality binoculars, from optimum 

vantage points for unimpaired visual 

observations with minimum 

distractions. PSOs will collect 

observational data for all marine 

mammals observed, regardless of 

distance from the vessel, including 

species, group size, presence of calves, 

distance from vessel and direction of 

travel, and any observed behavior 

(including an assessment of behavioral 

responses to survey activity). Upon 

observation of marine mammal(s), a 


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PSO will record the observation and 

monitor the animal’s position (including 

latitude/longitude of the vessel and 

relative bearing and estimated distance 

to the animal) until the animal dives or 

moves out of visual range of the 

observer, and a PSO will continue to 

observe the area to watch for the animal 

to resurface or for additional animals 

that may surface in the area. PSOs will 

also record environmental conditions at 

the beginning and end of the 

observation period and at the time of 

any observations, as well as whenever 

conditions change significantly in the 

judgment of the PSO on duty. 

For all deep penetration surveys, the 

vessel operator must provide bigeye 

binoculars of appropriate quality (e.g., 

25 x 150; 2.7 view angle; individual 

ocular focus; height control) solely for 

PSO use. These should be pedestalmounted on the deck at the most 

appropriate vantage point that provides 

for optimal sea surface observation, PSO 

safety, and safe operation of the vessel. 

Other required equipment, which 

should be made available to PSOs by the 

third-party observer provider, includes 

reticle binoculars of appropriate quality 

(e.g., 7 x 50), GPS, digital camera with 

a telephoto lens (the camera or lens 

should also have an image stabilization 

system) that is at least 300 mm or 

equivalent on a full-frame single-lens 

reflex, compass, and any other tools 

necessary to adequately perform the 

tasks described above, including 

accurate determination of distance and 

bearing to observed marine mammals. 

Individuals implementing the 

monitoring protocol will assess its 

effectiveness using an adaptive 

approach. Monitoring biologists will use 

their best professional judgment 

throughout implementation and seek 

improvements to these methods when 

deemed appropriate. Specifically, 

implementation of shutdown 

requirements will be made on the basis 

of the PSO’s best professional judgment. 

While PSOs should not insert undue 

precaution into decision-making, it is 

expected that PSOs may call for 

mitigation action on the basis of 

reasonable certainty regarding the need 

for such action, as informed by 

professional judgment. Any 

modifications to protocol will be 

coordinated between NMFS and the 

applicant. 

Acoustic Monitoring 

Use of towed PAM is required for 

deep penetration surveys. Monitoring of 

a towed PAM system is required at all 

times for these surveys, from 30 minutes 

prior to ramp-up, throughout all use of 

the acoustic source, and for 60 minutes 

following cessation of survey activity. 

Towed PAM systems should consist of 

hardware (e.g., hydrophone array, 

recorder, cables) and software (e.g., data 

processing program and algorithm). 

Some type of automated detection 

software must be used. Acoustic signals 

are processed for output to the PAM 

operator with software designed to 

detect marine mammal vocalizations. 

Current PAM technology has some 

limitations (e.g., limited directional 

capabilities and detection range, 

detection of signals due to vessel and 

flow noise, low accuracy in localization) 

and there are no formal guidelines 

currently in place regarding 

specifications for hardware, software, or 

operator training requirements. 

NMFS’ requirement to use PAM refers 

to the use of calibrated hydrophone 

arrays with full system redundancy to 

detect, identify, and estimate distance 

and bearing to vocalizing cetaceans, to 

the extent possible. With regard to 

calibration, the PAM system should 

have at least one calibrated hydrophone, 

sufficient for determining whether 

background noise levels on the towed 

PAM system are sufficiently low to meet 

performance expectations. Additionally, 

if multiple hydrophone types occur in a 

system (i.e., monitor different 

bandwidths), then one hydrophone from 

each such type shall be calibrated, and 

whenever sets of hydrophones (of the 

same type) are sufficiently spatially 

separated such that they would be 

expected to experience ambient noise 

environments that differ by 6 dB or 

more across any integrated species 

cluster bandwidth, then at least one 

hydrophone from each set should be 

calibrated. In terms of calibrating the 

rest of the system, the signal route to the 

data recorder and monitoring software 

shall be calibrated so that the binary 

amplitude data written to hard disk can 

be converted into units of acoustic 

pressure. The configuration of hardware 

should be coupled with appropriate 

software to aid monitoring and listening 

by a PAM operator skilled in 

bioacoustics analysis and computer 

system specifications capable of running 

appropriate software. GPS data 

acquisition is recommended for all PAM 

operations. If the PAM plan (see below) 

claims an ability to localize, every 

localization estimate obtained from a 

PAM system must be accompanied by 

some estimate of uncertainty and 

ambiguity. 

In the absence of formal standards 

addressing any of these three facets of 

PAM technology, all applicants must 

provide a PAM plan including 

description of the hardware and 

software proposed for use prior to 

proceeding with any survey where PAM 

is required. Following the survey, a 

validation document must be submitted 

as part of required reporting (see below). 

The purpose of the PAM plan is to 

demonstrate that the PAM system being 

proposed for use is adequate for 

addressing the mitigation goals. The 

plan shall include methodology and 

documentation requirements for all 

stages of the project. As recommended 

by Thode et al. (2017), PAM plans 

should, at minimum, adequately 

address and describe (1) the hardware 

and software planned for use, including 

a hardware performance diagram 

demonstrating that the sensitivity and 

dynamic range of the hardware is 

appropriate for the operation; (2) 

deployment methodology, including 

target depth/tow distance; (3) 

definitions of expected operational 

conditions, used to summarize 

background noise statistics; (4) 

proposed detection-classificationlocalization methodology, including 

anticipated species clusters (using a 

cluster definition table), target 

minimum detection range for each 

cluster, and the proposed localization 

method for each cluster; (5) operation 

plans, including the background noise 

sampling schedule; (6) array design 

considerations for noise abatement; and 

(7) cluster-specific details regarding 

which real-time displays and automated 

detectors the operator would monitor. 

Where relevant, the plan should address 

the potential for PAM deployment on a 

receiver vessel or other associated vessel 

separate from the acoustic source. 

Species clusters—The plan shall list 

the species of concern during the 

upcoming operation. While some 

species may be listed individually for 

special attention, in many 

circumstances it is expected that for the 

purposes of a PAM operation multiple 

species can be grouped together in a 

‘‘cluster’’ that shares similar acoustic 

and behavioral characteristics (e.g., 

sperm whale, beaked whales). The plan 

must specify a target minimum 

detection (and possibly localization) 

range for each species cluster used in 

the document. Different ranges can be 

defined for different operational 

conditions. The PAM system may 

exceed this detection range, but shall 

always be capable of achieving this 

minimum detection range. 

Hardware and software 

specifications—The plan shall have a 

section dedicated to demonstrating that 

the PAM hardware is sensitive enough 

to detect signals from the species 

clusters of concern at the target 

minimum detection ranges specified. 

The plan should include a hardware 


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specification table and hardware 

performance diagram. The diagram will 

show the sensitivity and bandwidth of 

the combined array hardware and 

recording system, as well as the 

received levels required for a given 

species cluster to be detectable at the 

target minimum detection range. The 

overall goal of the diagram is to visually 

demonstrate that the planned PAM 

array/recording system would have the 

capability of detecting various species 

clusters at required target ranges, 

provided that background noise levels 

are not an issue. 

Operational conditions—The 

validation document should 

demonstrate whether the PAM system 

has been compromised by excessive 

background noise, whether that noise is 

electronic interference, flow, platform, 

or environmental noise. Therefore, the 

plan shall define a set of ‘‘operational 

conditions’’ under which detection 

statistics (background noise profiles) 

will be categorized during the project. 

Operational conditions consist of three 

categories: Platform activity and status, 

mitigation (activity) status, and 

environmental status. 

Operating procedures—The plan shall 

describe the level of effort that is 

reasonably expected to occur for the 

monitoring requirements. For every 

species cluster, the plan should detail 

which part of the PAM display would 

be used for detecting that cluster. For 

example, if a scrolling spectrogram 

display is being used for a species 

cluster, then the spectrogram’s fast 

Fourier transform sample size, 

frequency bandwidth, and their refresh 

rate shall be specified. Similar details 

would be provided for other software 

tools, such as click detectors and other 

automated detectors and classifiers. The 

plan shall also provide a screenshot of 

the expected monitor display. 

In coordination with vessel crew, the 

lead PAM operator will be responsible 

for deployment, retrieval, and testing 

and optimization of the hydrophone 

array. While on duty, the PAM operator 

must diligently listen to received signals 

and/or monitoring display screens in 

order to detect vocalizing cetaceans, 

except as required to attend to PAM 

equipment. The PAM operator must use 

appropriate sample analysis and 

filtering techniques and must report all 

cetacean detections. While not required 

prior to development of formal 

standards for PAM use, NMFS 

recommends that vessel self-noise 

assessments be undertaken during 

mobilization in order to optimize PAM 

array configuration according to the 

specific noise characteristics of the 

vessel and equipment involved, and to 

refine expectations for distance/bearing 

estimations for cetacean species during 

the survey. Copies of any vessel selfnoise assessment reports must be 

included with the summary trip report. 

Data Collection 

PSOs must use standardized 

electronic data forms. PSOs will record 

detailed information about any 

implementation of mitigation 

requirements, including the distance of 

animals to the acoustic source and 

description of specific actions that 

ensued, the behavior of the animal(s), 

any observed changes in behavior before 

and after implementation of mitigation, 

and if shutdown was implemented, the 

length of time before any subsequent 

ramp-up of the acoustic source to 

resume survey. If required mitigation 

was not implemented, PSOs should 

submit a description of the 

circumstances. NMFS requires that, at a 

minimum, the following information be 

reported: 

• Vessel names (source vessel and 

other vessels associated with survey), 

vessel size and type, maximum speed 

capability of vessel, port of origin, and 

call signs; 

• PSO names and affiliations; 

• Dates of departures and returns to 

port with port name; 

• Dates and participants of PSO 

briefings; 

• Dates and times (Greenwich Mean 

Time) of survey effort and times 

corresponding with PSO effort; 

• Vessel location (latitude/longitude) 

when survey effort begins and ends and 

vessel location at beginning and end of 

visual PSO duty shifts; 

• Vessel location at 30 second 

intervals (if software capability allows) 

or 5 minute intervals (if location must 

be manually recorded); 

• Vessel heading and speed at 

beginning and end of visual PSO duty 

shifts and upon any line change; 

• Environmental conditions while on 

visual survey (at beginning and end of 

PSO shift and whenever conditions 

change significantly), including 

Beaufort scale and any other relevant 

weather conditions including cloud 

cover, fog, sun glare, night, and overall 

visibility to the horizon; 

• Vessel location when 

environmental conditions change 

significantly; 

• Factors that may have contributed 

to impaired observations during each 

PSO shift change or as needed as 

environmental conditions change (e.g., 

vessel traffic, equipment malfunctions); 

• Survey activity information, such as 

acoustic source power output while in 

operation, number and volume of 

airguns operating in an array, tow depth 

of an acoustic source, and any other 

notes of significance (i.e., pre-clearance, 

ramp-up, shutdown, testing, shooting, 

ramp-up completion, end of operations, 

streamers, etc.); 

• If a marine mammal is sighted, the 

following information should be 

recorded: 

Æ Watch status (sighting made by 

PSO on/off effort, opportunistic, crew, 

alternate vessel/platform); 

Æ PSO who sighted the animal and 

PSO location (including height above 

water) at time of sighting; 

Æ Time of sighting; 

Æ Vessel location at time of sighting; 

Æ Water depth; 

Æ Direction of vessel’s travel 

(compass direction); 

Æ Direction of animal’s travel relative 

to the vessel; 

Æ Pace of the animal; 

Æ Estimated distance to the animal 

(and method of estimating distance) and 

its heading relative to vessel at initial 

sighting; 

Æ Identification of the animal (e.g., 

genus/species, lowest possible 

taxonomic level, or unidentified) and 

PSO confidence in identification; also 

note the composition of the group if 

there is a mix of species; 

Æ Estimated number of animals (high/ 

low/best); 

Æ Estimated number of animals by 

cohort (adults, yearlings, juveniles, 

calves, group composition, etc.); 

Æ Description (as many 

distinguishing features as possible of 

each individual seen, including length, 

shape, color, pattern, scars or markings, 

shape and size of dorsal fin, shape of 

head, and blow characteristics); 

Æ Detailed behavior observations 

(e.g., number of blows, number of 

surfaces, breaching, spyhopping, diving, 

feeding, traveling; as explicit and 

detailed as possible; note any observed 

changes in behavior); 

Æ Animal’s closest point of approach 

(CPA) and/or closest distance from the 

acoustic source; 

Æ Platform activity at time of sighting 

(e.g., deploying, recovering, testing, 

shooting, data acquisition, other); and 

Æ Description of any actions 

implemented in response to the sighting 

(e.g., delays, shutdown, ramp-up); time 

and location of the action should also be 

recorded; 

• If a marine mammal is detected 

while using the PAM system, the 

following information should be 

recorded: 

Æ An acoustic encounter 

identification number, and whether the 

detection was linked with a visual 

sighting; 


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Æ Time when first and last heard; 

Æ Types and nature of sounds heard 

(e.g., clicks, whistles, creaks, burst 

pulses, continuous, sporadic, strength of 

signal, etc.); and 

Æ Any additional information 

recorded such as water depth of the 

hydrophone array, bearing of the animal 

to the vessel (if determinable), species 

or taxonomic group (if determinable), 

spectrogram screenshot, and any other 

notable information. 

LOA Reporting 

PSO effort, survey details, and 

sightings data should be recorded 

continuously during surveys. Reports 

must include all information described 

above under ‘‘Data Collection,’’ 

including amount and location of linekms surveyed and all marine mammal 

observations with closest approach 

distance. Reports must be submitted to 

NMFS within 90 days of survey 

completion or following expiration of an 

issued LOA. In the event that an LOA 

is issued for a period exceeding one 

year, annual reports must be submitted 

during the period of validity. The draft 

report must be accompanied by a 

certification from lead PSOs as to the 

accuracy of the report. A final report 

must be submitted within 30 days 

following resolution of any comments 

on the draft report. 

The report must describe the 

operations conducted and sightings of 

marine mammals near the operations; 

provide full documentation of methods, 

results, and interpretation pertaining to 

all monitoring; summarize the dates and 

locations of survey operations, and all 

marine mammal sightings (dates, times, 

locations, activities, associated survey 

activities); and provide information 

regarding locations where the acoustic 

source was used. The LOA-holder shall 

provide geo-referenced time-stamped 

vessel tracklines for all time periods in 

which airguns (full array or single) were 

operating. Tracklines should include 

points recording any change in airgun 

status (e.g., when the airguns began 

operating, when they were turned off). 

GIS files shall be provided in ESRI 

shapefile format and include the UTC 

date and time, latitude in decimal 

degrees, and longitude in decimal 

degrees. All coordinates should be 

referenced to the WGS84 geographic 

coordinate system. In addition to the 

report, all raw observational data shall 

be made available to NMFS. 

This report must also include a 

validation document concerning the use 

of PAM (if PAM was required), which 

should include necessary noise 

validation diagrams (NVD) and 

demonstrate whether background noise 

levels on the PAM deployment limited 

achievement of the planned detection 

goals. A separate diagram shall be 

produced for every background noise 

percentile chosen for analysis. 

Background noise percentiles, rather 

than a simple average of the data, are 

required because the highly nonstationary characteristics of many 

background noise profiles cannot be 

described by a simple mean. For 

example, data collected during a seismic 

survey will have short periods of time 

containing high-intensity pulses and 

longer periods of time dominated by 

lower levels of reverberation. Taking a 

simple mean of these noise data would 

imply background noise levels 

substantially higher than what may 

actually have been present between 

seismic pulses. A validation report 

would typically contain between three 

to five diagrams, depending on the 

number of percentiles analyzed. At a 

minimum, the validation report should 

contain three diagrams that include the 

50th percentile (median), 5th percentile, 

and 95th percentile. The 25th percentile 

and 75th percentile may also be 

included. In each percentile diagram, a 

separate background noise curve shall 

be drawn for each defined operational 

condition. In general, the NVD should 

be generated from the data stream that 

is used for detecting the presence of 

marine mammal signals. For example, if 

beamforming or some other form of 

array gain has been applied before 

invoking signal detection, then the NVD 

should be generated using the 

beamformed data, and not 

omnidirectional data. The complete set 

of NVDs, one for each percentile of 

interest, combined with a table that lists 

the fraction of time the activity was in 

each operational state, provides a means 

of reviewing the background noiselimitations encountered by the PAM 

system during various operational 

conditions. Actual marine mammal 

detections should be plotted on this 

diagram for a reasonableness check on 

the expected received levels. Overall, 

the validation document should 

reiterate all the goals and parameters 

stated in the planning document and 

verify that goals were/were not met, 

why, changes, etc. Also, the validation 

document should state whether the 

planning was suited to the needs of the 

survey and met the required mitigation 

standards. 

There are multiple reasons why 

marine mammals may be present and 

yet be undetected by observers. Animals 

are missed because they are underwater 

(availability bias) or because they are 

available to be seen, but are missed by 

observers (perception and detection 

biases) (e.g., Marsh and Sinclair, 1989). 

Negative bias on perception or detection 

of an available animal may result from 

environmental conditions, limitations 

inherent to the observation platform, or 

observer ability. In this case, we do not 

have prior knowledge of any potential 

negative bias on detection probability 

due to observation platform or observer 

ability. Therefore, it may be appropriate 

to make observational data corrections 

with respect to assumed species-specific 

detection probability as evaluated 

through consideration of environmental 

factors (e.g., f(0)). Appropriate methods 

will be considered through the adaptive 

management process. 

The report must include a post-survey 

estimate of the instances of take of each 

species utilizing the line miles of survey 

actually conducted and the same 

methods used to initially predict the 

estimated take in the LOA application. 

Depending on the length and dates of 

the survey, LOA-holders may be 

required to segment take estimates into 

specific years to support the 

administration of the rule. 

Comprehensive Reporting 

Individual LOA-holders will be 

responsible for collecting and 

submitting monitoring data to NMFS, as 

described above. In addition, on an 

annual basis, LOA-holders will also 

collectively be responsible for 

compilation and analysis of those data 

for inclusion in subsequent annual 

synthesis reports. Individual LOAholders may collaborate to produce this 

report or may elect to have their trade 

associations support the production of 

such a report. These reports would 

summarize the data presented in the 

individual LOA-holder reports, provide 

analysis of these synthesized results, 

discuss the implementation of required 

mitigation, and present any 

recommendations. This comprehensive 

annual report would be the basis of an 

annual adaptive management process 

(described below in Adaptive 

Management). The following topics will 

be described in comprehensive 

reporting: 

• Summary of geophysical survey 

activity by survey type, geographic zone 

(i.e., the seven zones described in the 

modeling report), month, and acoustic 

source status (e.g., inactive, ramp-up, 

full-power, power-down); 

• Summary of monitoring effort (oneffort hours and/or distance) by acoustic 

source status, location, and visibility 

conditions (for both visual and acoustic 

monitoring); 

• Summary of mitigation measures 

implemented (e.g., delayed ramp-ups, 


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shutdowns, course alterations for vessel 

strike avoidance) by survey type and 

location; 

• Sighting rates of marine mammals 

during periods with and without 

acoustic source activities and other 

variables that could affect detectability 

of marine mammals, such as: 

Æ Initial sighting distances of marine 

mammals relative to source status; 

Æ Closest point of approach of marine 

mammals relative to source status; 

Æ Observed behaviors and types of 

movements of marine mammals relative 

to source status; 

Æ Distribution/presence of marine 

mammals around the survey vessel 

relative to source status; and 

Æ Analysis of the effects of various 

factors influencing the detectability of 

marine mammals (e.g., wind speed, sea 

state, swell height, presence of glare or 

fog). 

• Estimates of total take across all 

activities for which take is authorized 

based on actual survey effort and 

original estimation method; 

• Summary and conclusions from 

monitoring in previous year; and 

• Recommendations for adaptive 

management. 

Each annual comprehensive report 

should cover one full year of monitoring 

effort and must be submitted for review 

each year. Each report should analyze 

survey and monitoring effort described 

in reports submitted by individual LOAholders during a given one-year period, 

beginning from the date of effectiveness 

of these regulations. Each annual 

comprehensive report must be 

submitted for review 90 days following 

conclusion of the annual reporting 

period. 

Reporting Injured or Dead Marine 

Mammals 

Discovery of Injured or Dead Marine 

Mammal—In the event that personnel 

involved in the survey activities covered 

by the authorization discover an injured 

or dead marine mammal, the LOAholder shall report the incident to the 

Office of Protected Resources (OPR), 

NMFS and to the regional stranding 

network as soon as feasible. The report 

must include the following information: 

• Time, date, and location (latitude/ 

longitude) of the first discovery (and 

updated location information if known 

and applicable); 

• Species identification (if known) or 

description of the animal(s) involved; 

• Condition of the animal(s) 

(including carcass condition if the 

animal is dead); 

• Observed behaviors of the 

animal(s), if alive; 

• If available, photographs or video 

footage of the animal(s); and 

• General circumstances under which 

the animal was discovered. 

Vessel Strike—In the event of a ship 

strike of a marine mammal by any vessel 

involved in the activities covered by the 

authorization, the LOA-holder shall 

report the incident to OPR, NMFS and 

to the regional stranding network as 

soon as feasible. The report must 

include the following information: 

• Time, date, and location (latitude/ 

longitude) of the incident; 

• Species identification (if known) or 

description of the animal(s) involved; 

• Vessel’s speed during and leading 

up to the incident; 

• Vessel’s course/heading and what 

operations were being conducted (if 

applicable); 

• Status of all sound sources in use; 

• Description of avoidance measures/ 

requirements that were in place at the 

time of the strike and what additional 

measures were taken, if any, to avoid 

strike; 

• Environmental conditions (e.g., 

wind speed and direction, Beaufort sea 

state, cloud cover, visibility) 

immediately preceding the strike; 

• Estimated size and length of animal 

that was struck; 

• Description of the behavior of the 

marine mammal immediately preceding 

and following the strike; 

• If available, description of the 

presence and behavior of any other 

marine mammals immediately 

preceding the strike; 

• Estimated fate of the animal (e.g., 

dead, injured but alive, injured and 

moving, blood or tissue observed in the 

water, status unknown, disappeared); 

and 

• To the extent practicable, 

photographs or video footage of the 

animal(s). 

Actions To Minimize Additional Harm 

to Live-Stranded (or Milling) Marine 

Mammals 

For deep penetration surveys, in the 

event of a live stranding (or near-shore 

atypical milling) event within 50 km of 

the survey operations, where the NMFS 

stranding network is engaged in herding 

or other interventions to return animals 

to the water, the Director of OPR, NMFS 

(or designee) will advise the LOAholder of the need to implement 

shutdown procedures for all active 

acoustic sources operating within 50 km 

of the stranding. Shutdown procedures 

for live stranding or milling marine 

mammals include the following: 

• If at any time, the marine mammals 

die or are euthanized, or if herding/ 

intervention efforts are stopped, the 

Director of OPR, NMFS (or designee) 

will advise the LOA-holder that the 

shutdown around the animals’ location 

is no longer needed. 

• Otherwise, shutdown procedures 

will remain in effect until the Director 

of OPR, NMFS (or designee) determines 

and advises the LOA-holder that all live 

animals involved have left the area 

(either of their own volition or following 

an intervention). 

• If further observations of the marine 

mammals indicate the potential for restranding, additional coordination with 

the LOA-holder will be required to 

determine what measures are necessary 

to minimize that likelihood (e.g., 

extending the shutdown or moving 

operations farther away) and to 

implement those measures as 

appropriate. 

Shutdown procedures are not related 

to the investigation of the cause of the 

stranding and their implementation is 

not intended to imply that the specified 

activity is the cause of the stranding. 

Rather, shutdown procedures are 

intended to protect marine mammals 

exhibiting indicators of distress by 

minimizing their exposure to possible 

additional stressors, regardless of the 

factors that contributed to the stranding. 

Additional Information Requests—If 

NMFS determines that the 

circumstances of any marine mammal 

stranding found in the vicinity of the 

activity suggest investigation of the 

association with survey activities is 

warranted (example circumstances 

noted below), and an investigation into 

the stranding is being pursued, NMFS 

will submit a written request to the 

LOA-holder indicating that the 

following initial available information 

must be provided as soon as possible, 

but no later than 7 business days after 

the request for information. 

• Status of all sound source use in the 

48 hours preceding the estimated time 

of stranding and within 50 km of the 

discovery/notification of the stranding 

by NMFS; and 

• If available, description of the 

behavior of any marine mammal(s) 

observed preceding (i.e., within 48 

hours and 50 km) and immediately after 

the discovery of the stranding. 

Examples of circumstances that could 

trigger the additional information 

request include, but are not limited to, 

the following: 

• Atypical nearshore milling events 

of live cetaceans; 

• Mass strandings of cetaceans (two 

or more individuals, not including cow/ 

calf pairs); 

• Beaked whale strandings; or, 

• Necropsies with findings of 

pathologies that are unusual for the 

species or area. 


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In the event that the investigation is 

still inconclusive, the investigation of 

the association of the survey activities is 

still warranted, and the investigation is 

still being pursued, NMFS may provide 

additional information requests, in 

writing, regarding the nature and 

location of survey operations prior to 

the time period above. 

Negligible Impact Analysis and 

Determinations 

NMFS has defined negligible impact 

as an impact resulting from the 

specified activity that cannot be 

reasonably expected to, and is not 

reasonably likely to, adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival 

(50 CFR 216.103). A negligible impact 

finding is based on the lack of likely 

adverse effects on annual rates of 

recruitment or survival (i.e., populationlevel effects). An estimate of the number 

of takes alone is not enough information 

on which to base a negligible impact 

determination. In addition to 

considering estimates of the number of 

marine mammals that might be ‘‘taken’’ 

by mortality, serious injury, and Level A 

or Level B harassment, we consider 

other factors, such as the type of take, 

the likely nature of any behavioral 

responses (e.g., intensity, duration), the 

context of any such responses (e.g., 

critical reproductive time or location, 

migration), as well as effects on habitat, 

and the likely effectiveness of 

mitigation. We also assess the number, 

intensity, and context of estimated takes 

by evaluating this information relative 

to population status. Consistent with the 

1989 preamble for NMFS’ implementing 

regulations (54 FR 40338; September 29, 

1989), the impacts from other past and 

ongoing anthropogenic activities are 

incorporated into these analyses via 

their impacts on the baseline (e.g., as 

reflected in the regulatory status of the 

species, population size and growth rate 

where known, ongoing sources of 

human-caused mortality). 

For each potential activity-related 

stressor, NMFS considers the potential 

effects to marine mammals and the 

likely significance of those effects to the 

species or stock as a whole. Potential 

risk due to vessel collision and related 

mitigation measures, as well as potential 

risk due to entanglement and 

contaminant spills, was addressed 

under Mitigation and in the Potential 

Effects of the Specified Activity on 

Marine Mammals section of this notice 

and the notice of proposed rulemaking 

and are not discussed further, as there 

are minimal risks expected from these 

potential stressors. 

The ‘‘specified activity’’ for these 

regulations is a broad program of 

geophysical survey activity that could 

occur at any time of year in U.S. waters 

of the GOM, within the specified 

geographical region as updated by 

BOEM (i.e., excluding the GOMESA 

leasing moratorium area). In recognition 

of the broad scale of this activity in 

terms of geographic and temporal scales, 

we use a new analytical methodology— 

first described by Ellison et al. (2015) 

and proposed for use and discussed in 

detail in the notice of proposed 

rulemaking—through which an explicit, 

systematic risk assessment framework is 

applied to evaluate potential effects of 

aggregated discrete acoustic exposure 

events (i.e., proposed geophysical 

survey activities) on marine mammals. 

This risk assessment framework is one 

component of the overall negligible 

impact analysis. Development of the 

approach was supported collaboratively 

by BOEM and NMFS, which together 

provided guidance to an expert working 

group (EWG) in terms of application to 

relevant regulatory processes. The risk 

assessment framework (or EWG 

framework) is described by Southall et 

al. (2017), which is available online at: 

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/incidentaltake-authorizations-oil-and-gas. That 

document is a companion to this 

analysis, and is referred to hereafter as 

the ‘‘EWG report.’’ The risk assessment 

framework is also described below. It 

was developed and implemented by the 

EWG in relation to the specified activity 

described in the proposed rule, 

provided for public review in 

association with the notice of proposed 

rulemaking (Southall et al., 2017), and 

subsequently refined in response to 

public comment and in consideration of 

the updated scope of the activity. We 

incorporate the framework and its 

results into this analysis. 

The EWG framework described below 

comprehensively considers the 

aggregate impacts to marine mammal 

populations from the activities 

addressed in this rule in the context of 

both (1) the severity of the impacts and 

(2) the vulnerability of the affected 

species. However, it does not consider 

the effects of the mitigation required 

through these regulations in identifying 

risk ratings for the affected species. In 

addition, while the EWG framework 

comprehensively considers the spatial 

and temporal overlay of the activities 

and the marine mammals in the GOM, 

as well as the number of takes predicted 

by the described modeling (both in the 

proposed rule, and as updated in this 

final rule), there are details about the 

nature of any ‘‘take’’ anticipated to 

result from these activities that were not 

considered directly in the EWG 

framework analysis that warrant explicit 

consideration in the negligible impact 

determination. Last, the EWG 

framework analysis addresses impacts 

to guilds in some cases where there is 

not specific information to further 

support species-specific findings. 

Accordingly, following the description 

of the EWG framework below, NMFS 

highlights a few factors regarding the 

nature of the predicted ‘‘takes’’ and then 

brings together the results of 

implementation of the EWG framework, 

these additional factors, and the 

anticipated effects of the mitigation to 

summarize the negligible impact 

analysis for each of the affected species 

or stocks. 

EWG Risk Assessment 

The acoustic exposure modeling 

(Zeddies et al., 2015, 2017a) provided 

marine mammal noise exposure 

estimates based on BOEM-provided 

projections of future survey effort and 

best available modeling of sound 

propagation, animal distribution, and 

animal movement. This provided a 

conservative but reasonable best 

estimate of potential acute noise 

exposure events that may result from 

the described suite of activities, and 

formed the basis for the analysis in the 

proposed rule. BOEM subsequently 

updated the scope of its activity, which 

reduced the amount of activity overall 

through removal of projected activity in 

the eastern GOM (see Table 1 and Figure 

2). Acoustic exposure estimates were 

updated by BOEM accordingly (based 

on the same modeling presented in the 

proposed rule) and these revised 

estimates form the basis for this updated 

analysis. 

The primary goal of this new 

analytical effort was to develop a 

systematic risk assessment framework 

that would use the modeling results to 

put into biologically-relevant context 

the level of potential risk of injury and/ 

or disturbance to marine mammals. The 

risk assessment framework considers 

both the aggregation of acute effects and 

the broad temporal and spatial scales 

over which chronic effects may occur. 

Previously, Wood et al. (2012) 

conducted an analysis of a proposed 

airgun survey, in which the authors 

derived a qualitative risk assessment 

method of considering the biological 

significance of exposures predicted to 

be consistent with the onset of physical 

injury and behavioral disturbance. 

Subsequently, Ellison et al. (2015) 

described development of a more 

systematic and (in some cases) 


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quantitative basis for a risk assessment 

approach to assess the biological 

significance and potential population 

consequences of predicted noise 

exposures. The approach for this final 

rule, which incorporates the revised 

acoustic exposure modeling results as 

an input, includes certain modifications 

to and departures from the conceptual 

approach described by Ellison et al. 

(2015). These are described in greater 

detail in the EWG report. 

Generally, this approach is a 

relativistic risk assessment that provides 

an interpretation of the exposure 

estimates within the context of key 

biological and population parameters 

(e.g., population size, life history 

factors, compensatory ability of the 

species, animal behavioral state, 

aversion), as well as other biological, 

environmental, and anthropogenic 

factors. This analysis as updated since 

BOEM revised the scope of its action 

was performed on a species-specific 

basis within each modeling zone (Figure 

3) for a high-effort scenario (represented 

by Year 1 of BOEM’s revised effort 

projections) and a moderate-effort 

scenario (represented by Year 4 of 

BOEM’s revised effort projections). (For 

most species, the maximum annual take 

occurs under the Year 1 scenario. The 

two exceptions are the bottlenose 

dolphin and Atlantic spotted dolphin, 

for which the maximum annual take 

occurs under the Year 4 scenario.) The 

end result provides an indication of the 

biological significance of these exposure 

numbers for each affected marine 

mammal stock (i.e., yielding the severity 

of impact and vulnerability of stock/ 

population information), and forecasts 

the likelihood of any such impact. This 

result is expressed as relative impact 

ratings of overall risk that couple 

potential severity of effect on a stock 

and likely vulnerability of the 

population to the consequences of those 

effects, given biologically relevant 

information (e.g., compensatory ability). 

Spectral, temporal, and spatial 

overlaps between survey activities and 

animal distribution are the primary 

factors that drive the type, magnitude, 

and severity of potential effects on 

marine mammals, and these 

considerations are integrated into both 

the severity and vulnerability 

assessments. In discussion with BOEM 

and NMFS, the EWG developed a 

strategic approach to balance the weight 

of these considerations between the two 

assessments, specifying and clarifying 

where and how the interactions between 

potential disturbance and species 

within these dimensions are evaluated. 

Overall ratings are then considered in 

conjunction with the required 

mitigation (and any additional relevant 

contextual information) to ultimately 

inform our determinations. Elements of 

this approach are subjective and relative 

within the context of this program of 

projected actions and, overall, the 

analysis necessarily requires the 

application of professional judgment. 

Severity of Effect 

Level A Harassment—In order to 

evaluate the potential severity of the 

expected potential takes by Level A 

harassment (accounting for aversion) 

(Table 9) on the species or stock, the 

EWG framework uses a potential 

biological removal (PBR)-equivalent 

metric. As described previously, PBR is 

defined by the MMPA as the maximum 

number of animals, not including 

natural mortalities, that may be removed 

from a marine mammal stock while 

allowing that stock to reach or maintain 

its optimum sustainable population. To 

be clear, NMFS does not expect any of 

the potential occurrences of injury (i.e., 

permanent threshold shift (PTS)) that 

may be authorized under this rule to 

result in mortality of marine mammals, 

nor should Level A harassment be 

considered a ‘‘removal’’ in the context 

of PBR when used to inform a negligible 

impact determination. PTS is not 

appropriately considered equivalent to 

serious injury. However, PBR can serve 

as a gross indicator of the status of the 

species and a good surrogate for 

population vulnerability/health and, 

accordingly, PBR or a related metric can 

be used appropriately to inform a 

separate analysis to evaluate the 

potential relative severity to the 

population of a permanent impact such 

as PTS on a given number of 

individuals. This analysis is used to 

assess relative risks to populations as a 

result of PTS; NMFS does not expect 

that Level A harassment could directly 

result in mortality and our use of the 

PBR metric in this context should not be 

interpreted as such. 

However, exposure estimates 

generated using habitat-based density 

models (Roberts et al., 2016) cannot 

appropriately be directly related to the 

PBR values found in NMFS’ SARs. 

Therefore, a modified PBR value was 

derived on the basis of the typical 

pattern for NMFS’ PBR values, where 

the value varies between approximately 

0.6–0.9 percent of the minimum 

population abundance depending upon 

population confidence limits (higher 

with increasing confidence). For 

endangered species, PBR values are 

typically 1⁄5 of the values for nonendangered species due to assumption 

of a lower recovery factor—endangered 

species are typically assigned recovery 

factors of 0.1, while species of unknown 

status relative to the optimum 

sustainable population level (i.e., most 

species) are typically assigned factors of 

0.5. This basic relationship of 

population size relative to PBR was 

used to define the following relative risk 

levels due to Level A harassment. 

• Very high—Level A harassment 

greater than 1.5 or 0.3 percent (the latter 

figure is used for endangered species) of 

zone-specific estimated population 

abundance. 

• High—0.75–1.5 or 0.15–0.3 percent 

of zone-specific population. 

• Moderate—0.375–0.75 or 0.075– 

0.15 percent of zone-specific 

population. 

• Low—0.075–0.375 or 0.015–0.075 

percent of zone-specific population. 

• Very low—less than 0.075 or less 

than 0.015 percent of zone-specific 

population. 

Relative severity scores by zone 

(Figure 3) and species were determined 

for high and moderate annual effort 

scenarios. As described previously, we 

do not believe that Level A harassment 

is likely to actually occur for midfrequency cetaceans and therefore do 

not predict (nor will we authorize) any 

take by Level A harassment for these 

species (i.e., most species in the GOM). 

Bryde’s whales (a low-frequency 

cetacean species) are expected to be 

present primarily in Zones 1 and 4 

(though may be present to a lesser 

extent in Zones 2 and 5). BOEM’s 

update to the geographic scope of its 

action removed the entirety of Zone 1 

and the majority of Zone 4 from 

consideration in this rule. Altogether, 

no incidents of Level A harassment are 

predicted for Bryde’s whales. 

Kogia spp. (high-frequency cetacean 

species) are primarily present in Zones 

4–7. We assess the relative severity 

resulting from injury for Kogia spp. to 

be ‘‘very high’’ in Zones 5–7 under both 

evaluated activity scenarios. In Zone 4, 

relative severity is ‘‘high’’ under the 

moderate effort scenario, and no activity 

is projected in Zone 4 under the high 

effort scenario. 

In summary, we assess that there is no 

risk of Level A harassment for any midfrequency cetacean species. Overall 

severity associated with take by Level A 

harassment is expected to be very high 

for Kogia spp. and very low for Bryde’s 

whales, as no incidents of Level A 

harassment are predicted for the stock. 

We note that regardless of the relative 

risk assessed in this framework, because 

of the anticipated received levels and 

duration of sound exposure expected for 

any marine mammals exposed above 

Level A harassment criteria, no 

individuals of any species or stock are 


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expected to receive more than a 

relatively minor degree of PTS, which 

would not be expected to meaningfully 

increase the likelihood or severity of 

any potential population-level effects. 

See ‘‘Loss of Hearing Sensitivity,’’ 

below, for additional discussion. 

Level B Harassment—As described 

above in Estimated Take, a significant 

model assumption was that populations 

of animals were reset for each 24-hr 

period. Exposure estimates for the 24-hr 

period were then aggregated across all 

assumed survey days as completely 

independent events, assuming 

populations turn over completely 

within each large zone on a daily basis. 

In order to evaluate modeled daily 

exposures and determine more realistic 

exposure probabilities for individuals 

across multiple days, we used 

information on species-typical 

movement behavior to determine a 

species-typical offset of modeled daily 

exposures, using the exploratory 

analysis discussed under Estimated 

Take (i.e., Test Scenario 1). In this test 

scenario, modeled results were 

compared for a 30-day period versus the 

aggregation of 24-hr population reset 

intervals. When conducting 

computationally-intensive modeling 

over the full assumed 30-day survey 

period (versus aggregating the smaller 

24-hr periods for 30 days), results 

showed about 10–45 percent of the total 

number of takes calculated using a 24- 

hr reset of the population, with 

differences relating to species-typical 

movement and residency patterns. 

Given that many of the evaluated survey 

activities occur for 30-day or longer 

periods, particularly some of the larger 

surveys for which the majority of the 

modeled exposures occur, using such a 

scaling process is appropriate in order 

to evaluate the likely severity of the 

predicted exposures and to estimate 

take for the purposes of LOA 

applications and predicting the number 

of individual marine mammals taken 

during the course of a single survey 

(although, as noted previously, for 

surveys significantly longer than 30 

days, the take numbers with this scaling 

applied would still be expected to 

overestimate the number of individuals, 

given the greater degree of repeat 

exposures that would be expected the 

longer the survey goes on). This output 

was used in a severity assessment. This 

approach is also discussed in more 

detail in the EWG report. 

Similar to the evaluation of severity 

for Level A harassment, the scaled Level 

B harassment takes were rated through 

a population-dependent binning system. 

For each species, scaled takes were 

divided by the zone-specific predicted 

abundance, and these proportions were 

used to evaluate the relative severity of 

modeled exposures based on the 

distribution of values across species to 

evaluate risk associated with behavioral 

disruption across species—a simple, 

logical means of evaluating relative risk 

across species and areas. Relative risk 

ratings using percent of area population 

size were defined as follows: 

• Very high—Adjusted Level B 

harassment takes greater than 800 

percent of zone-specific population; 

• High—Adjusted Level B harassment 

takes 401–800 percent of zone-specific 

population; 

• Moderate—Adjusted Level B 

harassment takes 201–400 percent of 

zone-specific population; 

• Low—Adjusted Level B harassment 

takes 100–200 percent of zone-specific 

population; and 

• Very low—Adjusted Level B 

harassment takes less than 100 percent 

of zone-specific population. 

Vulnerability of Affected Population 

Vulnerability rating seeks to evaluate 

the relative risk of a predicted effect 

given species-typical and populationspecific parameters (e.g., speciesspecific life history, population factors) 

and other relevant interacting factors 

(e.g., human or other environmental 

stressors). The assessment includes 

consideration of four categories within 

two overarching risk factors (speciesspecific biological and environmental 

risk factors). These values were selected 

to capture key aspects of the importance 

of spatial (geographic), spectral 

(frequency content of noise in relation 

to species-typical hearing and sound 

communications), and temporal 

relationships between sound and 

receivers. Explicit numerical criteria for 

identifying scores were specified where 

possible, but in some cases qualitative 

judgments based on a reasonable 

interpretation of given aspects of the 

proposed activity and how it relates to 

the species in question and the 

environment within the specified area 

were required. Factors considered in the 

vulnerability assessment were detailed 

in Southall et al. (2017) and are 

reproduced here (Table 11). Note that 

the effects of the Deepwater Horizon oil 

spill are accounted for through the nonnoise chronic anthropogenic risk factor 

identified below, while the effects to 

acoustic habitat and on individual 

animal behavior via masking 

(summarized in Potential Effects of the 

Specified Activity on Marine Mammals 

and Their Habitat and described in 

detail in that section of the notice of 

proposed rulemaking) are accounted for 

through the masking and chronic 

anthropogenic noise risk factors. 

Species-specific vulnerability scoring 

according to this scheme is shown in 

Table 12. Zone-specific vulnerability 

ratings corresponding with the scores 

given in Table 12 below are provided in 

Tables 8–10 of the EWG report. 

TABLE 11—VULNERABILITY ASSESSMENT FACTORS

Score 

Masking: Degree of spectral overlap between biologically important acoustic signals 

and predominant noise source of proposed activity (max: 7 out of 30): 

Communication masking: Predominant noise energy directly/partially overlaps 1 species-specific signals utilized for communication.+3/+1 

Foraging masking: Predominant noise energy directly/partially overlaps1 species-specific signals utilized in foraging (including echolocation and other foraging coordination signals).+2/+1 

Navigation/Orientation signal masking: Predominant noise energy directly/partially overlaps1 signals likely utilized in spatial orientation to which species is well capable of hearing.+2/+1 

Species population: Stock status, trend, and size (max: 7 out of 30): 

Population status: Endangered (ESA) and/or depleted (MMPA) (Y/N) .................................................................................... +3/0 

Trend rating: Decreasing/unknown or data deficient/stable (i.e., within 5 percent)/increasing (last three SARs for which 

new population estimates were updated).

+2/+1/0/¥1 

Population size: Small (less than 2,500) ................................................................................................................................... +2 

Species habitat use and compensatory abilities: Degree to which activity within a specified area 2 overlaps with species habitat and distribution (max: 7 out of 30): 

Habitat use: Survey area contains greater than 30/15–30/5–15/less than 5 percent of total region-wide estimated population (during defined survey period).+4/+2/+1/0 


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TABLE 11—VULNERABILITY ASSESSMENT FACTORS—Continued 

Score 

Temporal sensitivity: Survey overlaps temporally with well-defined species-specific biologically-important period (e.g., 

calving).

Up to +3 

Other (chronic) noise and non-noise stressors: Magnitude of other potential sources of disturbance or other stressors that 

may influence a species response to additional noise and disturbance of the proposed activity (max: 9 out of 30): 

Chronic anthropogenic noise: Species subject to high/moderate degree of current or known future (overlapping activity) 

chronic anthropogenic noise.

+2/+1 

Chronic anthropogenic risk factors (non-noise): Species subject to high/moderate degree of current or known future risk 

from other chronic, non-noise anthropogenic activities (e.g., fisheries interactions, ship strike).

Up to +4/+2 

Chronic biological risk factors (non-noise): Known presence of disease, parasites, prey limitation, or high predation pressure.Up to +3 

1 Direct or partial overlap means that the predominant spectral content of received noise exposure from activity specific sources is expected to 

occur at identical frequencies as signals of interest, or that secondary (lower-level) spectral content of received noise exposure from activity specific sources is expected to occur at identical frequencies as signals of interest. 2This is the area over which an activity is evaluated and a local population is determined, in this case the seven modeling zones. 

TABLE 12—VULNERABILITY ASSESSMENT SCORING 1

Species Communication Foraging Navigation Status Trend Size Habitat Time Chronic 

noise 

Chronic 

other 

Biological 

risk 

Total 

score 

range 

Bryde’s whale 3 2 2 3 2 2 0–4 0–1 1–2 0–3 0 16–23 

Sperm whale 1 1 2 3 2 2 0–4 0–1 1–2 0–3 0 14–18 

Kogia spp. ..... 0 0 1 0 2 2 0–4 0–1 1–2 0–3 0 8–13 

Beaked whale 0 0 1 0 1 0 0–4 0–1 1–2 0–3 1 6–13 

Rough-toothed 

dolphin ....... 0 0 1 0 2 0 1–4 0–1 1–2 0–3 0 6–10 

Bottlenose 

dolphin ....... 1 0 1 0 ¥1 0 0–4 0–1 1–2 0–3 0 2–10 

Clymene dolphin ............ 0 0 1 0 2 0 0–4 0–1 1–2 0–3 0 6–10 

Atlantic spotted dolphin 1 0 1 0 1 0 0–4 0–1 1–2 0–3 2 6–14 

Pantropical 

spotted dolphin ............ 0 0 1 0 2 0 0–4 0–1 1–2 0–3 0 6–10 

Spinner dolphin ............ 0 0 1 0 0 0 0–4 0–1 1–2 0–3 0 3–9 

Striped dolphin ............ 0 0 1 0 2 0 0–4 0–1 1–2 0–3 0 6–10 

Fraser’s dolphin ............ 0 0 1 0 1 2 0–4 0–1 1–2 0–3 0 7–11 

Risso’s dolphin ............ 0 0 1 0 ¥1 0 0–4 0–1 1–2 0–3 1 4–9 

Melon-headed 

whale ......... 0 0 1 0 2 0 0–4 0–1 1–2 0–3 0 6–10 

Pygmy killer 

whale ......... 0 0 1 0 2 2 0–4 0–1 1–2 0–3 0 8–12 

False killer 

whale ......... 0 0 1 0 ¥1 0 0–4 0–1 1–2 0–3 0 3–7 

Killer whale .... 1 0 1 0 2 2 0–4 0–1 1–2 0–3 0 9–12 

Short-finned 

pilot whale 1 0 1 0 0 2 0–4 0–1 1–2 0–3 1 7–13 

1Factors with a single value presented are those that remain constant across zones; other factors vary based on zone and a range of values is presented. 

TABLE 13—VULNERABILITY RATING SCHEME

Total score 

Risk 

probability 

(% of total) 

Vulnerability rating 

24–30 ......................................................................................................................................... 80–100 Very high. 

18–23 ......................................................................................................................................... 60–79 High. 

12–17 ......................................................................................................................................... 40–59 Moderate. 

6–11 ........................................................................................................................................... 20–39 Low. 

0–5 ............................................................................................................................................. 0–19 Very low. 

Risk 

In the final step of the framework, 

severity and vulnerability ratings are 

integrated to provide relative impact 

ratings of overall risk. Severity and 

vulnerability assessments each produce 

a numerical rating (1–5) corresponding 

with the qualitative rating (i.e., very 

low, low, moderate, high, very high). A 

matrix is then used to integrate these 

two scores to provide an overall risk 

assessment. The matrix is shown in 

Table 2 of Southall et al. (2017). 

The likely severity of effect was 

assessed as the percentage of total 

population affected based on scaled 

modeled Level B harassment takes 

relative to zone population size. There 

is no risk due to the effects of survey 

activity when there is no survey activity 

in a given zone for a given effort 

scenario. However, a stock’s inherent 

zone-specific vulnerability score drives 

the risk rating in those zones (Zone 1 

under any activity scenario and Zone 4 

under the high effort scenario), and risk 

ratings for all zones are considered 


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together in generating scenario-specific 

GOM-wide risk ratings for each species. 

Also, zones predicted to contain 

abundance of less than 0.05 percent of 

the GOM-wide population for a species 

were considered to have de minimis risk 

and are not included in derivation of the 

stock-specific GOM-wide rating. 

Table 14 provides relative impact 

ratings by zone, and Table 15 provides 

GOM-wide relative impact ratings, for 

overall risk associated with predicted 

takes by Level B harassment, for 

representative high and moderate effort 

scenarios. 

TABLE 14—OVERALL EVALUATED RISK BY ZONE AND ACTIVITY SCENARIO

Species 

Zone 1 1 Zone 2 Zone 3 Zone 4 1 Zone 5 Zone 6 Zone 7 

H M H M H M H M H M H M H M 

Bryde’s whale ....................... L L L L n/a n/a L L L L n/a n/a n/a n/a 

Sperm whale ......................... n/a n/a n/a n/a n/a n/a L L VH VH M L L L 

Kogia spp. ............................. VL VL n/a n/a n/a n/a L L H M L VL VL VL 

Beaked whale ....................... n/a n/a n/a n/a n/a n/a VL VL VH VH H M M L 

Rough-toothed dolphin ......... VL VL L M VL VL VL VL H M M L VL VL 

Bottlenose dolphin ................ VL VL H H VL VL VL VL VL VL n/a n/a n/a n/a 

Clymene dolphin ................... n/a n/a n/a n/a n/a n/a VL VL H M M L VL VL 

Atlantic spotted dolphin ........ L L H VH VL VL VL VL M L n/a n/a n/a n/a 

Pantropical spotted dolphin .. VL VL n/a n/a n/a n/a VL VL H M L VL L L 

Spinner dolphin ..................... VL VL n/a n/a n/a n/a VL VL H M n/a n/a VL VL 

Striped dolphin ...................... n/a n/a n/a n/a n/a n/a VL VL H M L VL L VL 

Fraser’s dolphin .................... VL VL VL VL VL VL VL VL M L L VL VL VL 

Risso’s dolphin ..................... VL VL n/a n/a n/a n/a VL VL H M M VL VL VL 

Melon-headed whale ............ VL VL n/a n/a n/a n/a VL VL H M M VL VL VL 

Pygmy killer whale ................ VL VL n/a n/a n/a n/a VL VL M L L VL VL VL 

False killer whale .................. VL VL VL VL VL VL VL VL H M L VL VL VL 

Killer whale ........................... VL VL VL VL VL VL VL VL L L VL VL L L 

Short-finned pilot whale ........ n/a n/a n/a n/a n/a n/a VL VL M M M VL VL VL 

H = Year 1 (representative high effort scenario); M = Year 4 (representative moderate effort scenario). 

n/a = less than 0.05% of GOM-wide population predicted in zone. 

VL = very low; L = low; M = moderate; H = high; VH = very high. 

1 No activity would occur in Zone 1, and no activity is projected in Zone 4 under the high effort scenario. 

TABLE 15—OVERALL EVALUATED RISK BY ACTIVITY SCENARIO, GOM-WIDE

Species High effort scenario 

(Year 1) 

Moderate effort scenario 

(Year 4) 

Bryde’s whale ................................................................................................................ Low ..................................... Low. 

Sperm whale .................................................................................................................. Moderate 1 .......................... Low. 

Kogia spp. ...................................................................................................................... Low ..................................... Very low. 

Beaked whales .............................................................................................................. High 1 .................................. Moderate.1

Rough-toothed dolphin .................................................................................................. Very low ............................. Very low. 

Bottlenose dolphin (shelf/coastal) .................................................................................. Very low ............................. Very low. 

Bottlenose dolphin (oceanic) ......................................................................................... Very low ............................. Very low. 

Clymene dolphin ............................................................................................................ Low ..................................... Low.1

Atlantic spotted dolphin ................................................................................................. Low ..................................... Low. 

Pantropical spotted dolphin ........................................................................................... Low ..................................... Very low. 

Spinner dolphin .............................................................................................................. Very low ............................. Very low. 

Striped dolphin ............................................................................................................... Low ..................................... Very low. 

Fraser’s dolphin ............................................................................................................. Very low ............................. Very low. 

Risso’s dolphin ............................................................................................................... Very low ............................. Very low. 

Melon-headed whale ..................................................................................................... Very low ............................. Very low. 

Pygmy killer whale ......................................................................................................... Very low ............................. Very low. 

False killer whale ........................................................................................................... Very low ............................. Very low. 

Killer whale .................................................................................................................... Very low ............................. Very low. 

Short-finned pilot whale ................................................................................................. Low ..................................... Low.1

1For these ratings, the median value across zones for the scenario fell between two ratings, and the higher rating is presented.

In order to characterize the relative 

risk for each species across their entire 

range in the GOM, the EWG analysis 

used the median of the seven zonespecific risk ratings for each activity 

scenario (high and moderate effort), not 

counting those in which less than 0.05 

percent of the GOM-wide abundance 

occurred, to describe a GOM-wide risk 

rating for each of the representative 

activity scenarios (Table 15). 

Overall, the results of the risk 

assessment show that (as expected), risk 

is highly correlated with effort and 

density. Areas where little or no survey 

activity is predicted to occur or areas 

within which few or no animals of a 

particular species are believed to occur 

have very low or no potential risk of 

negatively affecting marine mammals, as 

seen across activity scenarios in Zones 

1, 3, and 4. Areas with consistently high 

levels of effort (Zones 2, 5, 6, and 7) are 

generally predicted to have higher 

overall evaluated risk across all species. 

However, fewer species of animals are 

expected to be present in Zone 2, where 

we primarily expect shelf species such 

as bottlenose and Atlantic spotted 

dolphins. In Zone 7, animals are 

expected to be subject to less other 

chronic noise and non-noise stressors, 

which is reflected in the vulnerability 

scoring for that zone. Therefore, despite 

consistently high levels of projected 

effort, overall rankings for that zone are 

lower than for Zones 5 and 6. 

Zones 2 and 5 were the only zones 

with ‘‘very high’’ levels of risk due to 

behavioral disturbance, identified for 

two species of particular concern in 

Zone 5 (beaked and sperm whales) and 

for Atlantic spotted dolphins in Zone 2 

(moderate effort scenario only). As 

particularly sensitive species, beaked 

whales and sperm whales consistently 

receive relatively high severity scores. 

For sperm whales, this sensitivity is 

manifest through typically higher 

vulnerability scoring, whereas the 

assumed sensitivity of beaked whales to 


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noise exposure is expressed through the 

application of behavioral harassment 

criteria (Table 6) and, therefore, 

relatively high assumed take numbers. 

Bottlenose dolphins and Atlantic 

spotted dolphin are generally the only 

species expected to commonly occur in 

relatively shallow waters of the 

continental shelf (Zones 1–3) and 

relatively high risk is assessed for these 

species in Zone 2, across activity 

scenarios. Relatively moderate levels of 

risk were also identified for other 

species in some contexts, and these are 

generally explained by the interaction of 

specific factors related to survey effort 

concentration and areas of heightened 

geographic distribution or specific 

factors related to population trends or 

zone-related differences in 

vulnerability. Overall, following 

BOEM’s update to the geographic scope 

of activity (with the entirety of Zone 1, 

most of Zone 4, and one-third of Zone 

7 removed from consideration here; see 

Table 1) the greatest relative risk across 

species is generally seen in Zones 5 and 

6. 

When considered across both 

representative activity scenarios (Table 

15), only beaked whales are considered 

to have relatively high risk (under the 

high effort scenario only). Relatively 

moderate risk is assessed for beaked 

whales under the moderate effort 

scenario. Relatively moderate risk is 

also assessed for sperm whales under 

the high effort scenario. The rest of the 

species have no more than low to very 

low risk under either scenario. Shelf/ 

coastal and oceanic bottlenose dolphin 

stocks, rough-toothed dolphins, spinner 

dolphins, Fraser’s dolphins, Risso’s 

dolphins, melon-headed whales, pygmy 

killer whales, false killer whales, and 

killer whales are assessed as having no 

greater than very low relative risk under 

any scenario. 

Although the scores generated by the 

EWG framework and further aggregated 

across zones (as described above) are 

species-specific, additional stockspecific information can be gleaned 

through the zone-specific nature of the 

analysis. For example, with some 

bottlenose dolphin stocks, the zones 

align with stock range edges. The 

oceanic stock of bottlenose dolphins 

occurs within Zones 4–7, while coastal 

and shelf stocks occur within Zones 1– 

3 (sufficient information is not available 

to attribute takes on a stock-specific 

basis in Zones 1–3). These speciesspecific risk ratings are broadly applied 

in NMFS’ negligible impact analysis to 

all of the multiple stocks that are 

analyzed in this rule (Table 4). 

However, NMFS is also considering 

additional stock-specific information in 

our analysis, where appropriate, as 

indicated in our Description of Marine 

Mammals in the Area of the Specified 

Activity, Potential Effects of the 

Specified Activity on Marine Mammals 

and Their Habitat, and Mitigation 

sections (e.g., coastal bottlenose 

dolphins were heavily impacted by the 

DWH oil spill, and we have therefore 

required a time/area restriction to 

reduce impacts). 

Duration of Level B Harassment 

Exposures 

In order to more fully place the 

predicted amount of take into 

meaningful context, it is useful to 

understand the duration of exposure at 

or above a given level of received sound, 

as well as the likely number of repeated 

exposures across days. While a 

momentary exposure above the criteria 

for Level B harassment counts as an 

instance of take, that accounting does 

not make any distinction between 

fleeting exposures and more severe 

encounters in which an animal may be 

exposed to that received level of sound 

for a longer period of time. Yet this 

information is meaningful to an 

understanding of the likely severity of 

the exposure, which is relevant to the 

negligible impact evaluation and not 

directly incorporated into the risk 

assessment framework described above. 

For example, for bottlenose dolphins 

exposed to noise from 3D WAZ surveys 

in Zone 6, the modeling report shows 

that approximately 72 takes (Level B 

harassment) would be expected to occur 

in a 24-hr period. However, each animat 

modeled has a record or time history of 

received levels of sound over the course 

of the modeled 24-hr period. The 50th 

percentile of the cumulative distribution 

function indicates that the time spent 

exposed to levels of sound above 160 dB 

rms SPL (i.e., the 50 percent midpoint 

for Level B harassment) would be only 

1.8 minutes—a minimal amount of 

exposure carrying little potential for 

significant disruption of behavioral 

activity. We provide summary 

information regarding the total average 

time in a 24-hr period that an animal 

would spend with received levels above 

160 dB and between 140 and 160 dB in 

Table 16. 

Additionally, as we discussed in the 

Estimated Take section of the notice of 

proposed rulemaking for Test Scenario 

1 (and summarized above), by 

comparing exposure estimates generated 

by multiplying 24-hr exposure estimates 

by the total number of survey days 

versus modeling for a full 30-day survey 

duration for six representative species, 

we were able to refine the exposure 

estimates to better reflect the number of 

individuals exposed above threshold 

within a single survey. Using this same 

comparison and scalar ratios described 

above, we are able to predict an average 

number of days each of the 

representative species modeled in the 

test scenario were exposed above the 

Level B harassment thresholds within a 

single survey. As with the duration of 

exposures discussed above, the number 

of repeated exposures is important to an 

understanding of the severity of effects. 

For example, the ratio for beaked whales 

indicates that the 30-day modeling 

showed that approximately 10 percent 

as many individual beaked whales 

(compared to the results produced by 

multiplying average 24-hr exposure 

results by the 30-day survey duration) 

could be expected to be exposed above 

harassment thresholds. However, the 

approach of scaling up the 24-hour 

exposure estimates appropriately 

reflects the instances of exposure above 

threshold (which cannot be more than 1 

in 24 hours), so the inverse of the scalar 

ratio suggests the average number of 

days in the 30-day modeling period that 

beaked whales are exposed above 

threshold is approximately ten. It is 

important to remember that this is an 

average and that it is likely some 

individuals would be exposed on fewer 

days and some on more. Table 16 

reflects the average days exposed above 

threshold for the indicated species 

having applied the scalar ratios 

described previously. 

TABLE 16—TIME IN MINUTES (PER DAY) SPENT ABOVE THRESHOLDS (50TH PERCENTILE) AND AVERAGE NUMBER OF

DAYS INDIVIDUALS TAKEN DURING 30-DAY SURVEY

Species 

Survey type and time (min/day) above 

160 dB rms 

(50% take) 

Survey type and time (min/day) above 

140 dB rms 

(10% take) 

Average 

number of 

days ‘‘taken’’ 

during 30-day 

2D 3D NAZ 3D WAZ Coil 2D 3D NAZ 3D WAZ Coil survey 

Bryde’s whale ........................................................................ 7.6 18.2 6.8 21.4 61.7 163.5 55.4 401.1 5.3 

Sperm whale ......................................................................... 5.2 10.3 4.0 20.7 12.0 31.8 10.7 25.2 2.4 


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TABLE 16—TIME IN MINUTES (PER DAY) SPENT ABOVE THRESHOLDS (50TH PERCENTILE) AND AVERAGE NUMBER OF

DAYS INDIVIDUALS TAKEN DURING 30-DAY SURVEY—Continued 

Species 

Survey type and time (min/day) above 

160 dB rms 

(50% take) 

Survey type and time (min/day) above 

140 dB rms 

(10% take) 

Average 

number of 

days ‘‘taken’’ 

during 30-day 

2D 3D NAZ 3D WAZ Coil 2D 3D NAZ 3D WAZ Coil survey 

Kogia spp. ............................................................................. 3.2 7.9 2.8 15.3 7.6 19.0 6.7 13.9 3.1 

Beaked whale 1 ..................................................................... 6.0 12.4 4.4 24.0 16.2 39.7 14.1 31.1 9.9 

Rough-toothed dolphin .......................................................... 3.0 6.3 2.5 11.4 11.2 27.6 10.2 20.9 3.5 

Bottlenose dolphin ................................................................. 4.5 11.7 4.0 16.8 22.0 54.6 19.7 53.2 3.5 

Clymene dolphin ................................................................... 1.8 3.9 1.6 8.7 8.0 21.1 7.2 20.4 3.5 

Atlantic spotted dolphin ......................................................... 7.0 16.0 6.5 25.7 23.4 58.1 20.9 49.3 3.5 

Pantropical spotted dolphin ................................................... 1.8 4.1 1.6 8.7 8.1 21.0 7.1 22.2 3.5 

Spinner dolphin ..................................................................... 3.2 8.5 2.7 16.4 12.4 31.0 10.8 22.8 3.5 

Striped dolphin ...................................................................... 1.8 4.0 1.6 8.5 8.0 21.0 7.2 21.3 3.5 

Fraser’s dolphin ..................................................................... 2.8 6.4 2.4 13.8 9.4 24.2 8.4 24.0 3.5 

Risso’s dolphin ...................................................................... 3.4 8.4 2.9 15.3 13.8 37.7 12.2 31.5 3.5 

Melon-headed whale ............................................................. 2.6 5.9 2.2 13.1 9.3 24.2 8.3 24.0 3.4 

Pygmy killer whale ................................................................ 1.8 3.6 1.4 7.1 7.3 18.5 6.6 17.3 3.4 

False killer whale .................................................................. 2.4 4.9 1.9 9.3 8.8 22.0 8.0 17.8 3.4 

Killer whale ............................................................................ 2.7 6.1 3.3 12.0 16.8 46.1 14.9 73.6 3.4 

Short-finned pilot whale ........................................................ 3.3 8.1 2.9 17.5 10.9 27.4 9.8 20.8 3.4 

1Beaked whales are evaluated according to a different scale where 90% of the population exposed above 140 dB rms is considered taken and 50% of the population exposed above 120 dB rms is considered taken. 

Loss of Hearing Sensitivity 

In general, NMFS expects that noiseinduced hearing loss, whether 

temporary (temporary threshold shift, 

equivalent to Level B harassment) or 

permanent (PTS, the only form of Level 

A harassment that may result from this 

action), is only possible as a result of 

airgun survey activity for low-frequency 

and high-frequency cetaceans. The best 

available scientific information 

indicates that low-frequency cetacean 

species (i.e., mysticete whales, 

including the Bryde’s whale) have 

heightened sensitivity to frequencies in 

the range output by airguns, as shown 

by their auditory weighting function, 

whereas high-frequency cetacean 

species (including Kogia spp.) have 

heightened sensitivity to noise in 

general (as shown by their lower 

threshold for the onset of PTS) (NMFS, 

2018). However, no instances of Level A 

harassment are predicted to occur for 

Bryde’s whales, and Level A harassment 

of Bryde’s whales will not be authorized 

under this rule. 

Level A harassment is predicted to 

occur for Kogia spp. (as indicated in 

Table 9 and evaluated in the ‘‘Level A 

harassment’’ subsection above). 

However, the degree of injury (hearing 

impairment) is expected to be mild. If 

permanent hearing impairment occurs, 

it is most likely that the affected animal 

would lose a few dB in its hearing 

sensitivity, which in most cases would 

not be expected to affect its ability to 

survive and reproduce. Hearing 

impairment that occurs for these 

individual animals would be limited to 

at or slightly above the dominant 

frequency of the noise sources. In 

particular, the predicted PTS resulting 

from airgun exposure is not likely to 

affect their echolocation performance or 

communication, as Kogia spp. likely 

produce acoustic signals at frequencies 

above 100 kHz (Merkens et al., 2018), 

well above the frequency range of airgun 

noise. Further, modeled exceedance of 

Level A harassment criteria typically 

resulted from being near an individual 

source once, rather than accumulating 

energy from multiple sources. Overall, 

the modeling indicated that exceeding 

the SEL threshold is a rare event, and 

having four vessels close to each other 

(350 m between tracks) did not cause 

appreciable accumulation of energy at 

the ranges relevant for injury exposures. 

Accumulation of energy from 

independent surveys is expected to be 

negligible. This is relevant for Kogia 

spp. because based on their expected 

sensitivity, we expect that aversion may 

play a stronger role in avoiding 

exposures above the peak pressure PTS 

threshold than we have accounted for. 

For both Bryde’s whales and Kogia 

spp., some subset of the individual 

marine mammals predicted to be taken 

by Level B harassment may incur some 

TTS in addition to being behaviorally 

harassed. For Bryde’s whales, TTS is 

more likely to occur at frequencies 

important for communication. However, 

any TTS incurred would be expected to 

be of a relatively small degree and short 

duration. This is due to the low 

likelihood of sound source approaches 

of the proximity or duration necessary 

to cause more severe TTS, given the fact 

that both sound source and marine 

mammals are continuously moving, the 

anticipated effectiveness of shutdowns, 

and general avoidance by marine 

mammals of louder sources. 

For these reasons, and in conjunction 

with the required mitigation, NMFS 

does not believe that Level A 

harassment (here, PTS) or Level B 

harassment in the form of TTS will play 

a meaningful role in the overall degree 

of impact experienced by marine 

mammal populations as a result of the 

projected survey activity. Further, the 

impacts of any TTS incurred are 

addressed along with behavioral 

disruption through the broader analysis 

of Level B harassment. 

Impacts to Habitat 

Potential impacts to marine mammal 

habitat, including to marine mammal 

prey, were discussed in detail in the 

notice of proposed rulemaking and 

summarized herein (see Potential Effects 

of the Specified Activities on Marine 

Mammals and Their Habitat as well as 

responses to comments concerning 

these issues). 

Regarding impacts to prey species 

such as fish and invertebrates, NMFS’ 

review of the available information 

leads to a conclusion that the most 

likely impact of survey activity 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. 

Therefore, the specified activities 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 longterm consequences for individual 

marine mammals, or to contribute to 

adverse impacts on their populations. 

Regarding potential impacts to 

acoustic habitat, NMFS previously 

summarized a detailed analysis of 


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potential cumulative and chronic effects 

to marine mammals (found in the CCE 

report available online at 

www.fisheries.noaa.gov/action/ 

incidental-take-authorization-oil-andgas-industry-geophysical-surveyactivity-gulf-mexico). That analysis 

focused on potential effects to sperm 

whales (which also provides a 

conservative proxy regarding potential 

effects to other mid- and high-frequency 

cetacean species) and to Bryde’s whales. 

Regarding sperm whales, the analysis 

shows that the survey activities do not 

significantly contribute to the 

soundscape in the frequency band 

relevant for their lower-frequency slowclicks, and that there will be no 

significant change in communication 

space for sperm whales. Similar 

conclusions may be assumed for other 

mid- and high-frequency cetacean 

species. 

Implications for acoustic masking and 

reduced communication space resulting 

from noise produced by airgun surveys 

in the GOM are expected to be 

particularly heightened for animals that 

actively produce low-frequency sounds 

or whose hearing is attuned to lower 

frequencies (i.e., Bryde’s whales). The 

strength of the communication space 

approach used here is that it evaluates 

potential contractions in the availability 

of a signal of documented importance to 

a population of animals of key 

management interest in the region. In 

this case, losses of communication 

space for Bryde’s whales were estimated 

to be higher in eastern and central GOM 

canyons and shelf break areas. In 

contrast, relative maintenance of 

listening area and communication space 

was seen within the Bryde’s whale core 

habitat area in the eastern GOM. The 

result was heavily influenced by the 

projected lack of survey activity in that 

region, which underscores the 

importance of maintaining this 

important habitat for the Bryde’s whale. 

Following BOEM’s update to the scope 

of activity considered herein, no survey 

activity will occur under this rule 

within Bryde’s whale core habitat, or 

within the broader eastern GOM. In 

areas where larger amounts of survey 

activity were projected, significant loss 

of low-frequency listening area and 

communication space for Bryde’s whale 

calls was estimated. However, these are 

areas where Bryde’s whales are unlikely 

to occur (i.e., deeper waters of the 

central and western GOM). 

Species and Stock-Specific Negligible 

Impact Analysis Summaries 

In this section, we consider the 

relative impact ratings described above 

in conjunction with the required 

mitigation and other relevant contextual 

information in order to produce a final 

assessment of impact to the stock or 

species, i.e., the negligible impact 

determinations. The effects of the DWH 

oil spill are accounted for through the 

vulnerability scoring (Table 12). NMFS 

developed mitigation requirements for 

consideration in the proposed rule, 

including time-area restrictions, 

designed specifically to provide benefit 

to certain populations for which a 

relatively high amount of risk is 

predicted in relation to exposure to 

survey noise. The required time-area 

restrictions, described in detail in 

Proposed Mitigation in the notice of 

proposed rulemaking and depicted in 

Figure 4, were designed specifically to 

provide benefit to the bottlenose 

dolphin, Bryde’s whale, and beaked and 

sperm whales, with additional benefits 

to Kogia spp., which are often found in 

higher densities in the same locations of 

greater abundance for beaked and sperm 

whales. Two of the three time-area 

restrictions in the proposed rule—the 

Bryde’s whale core habitat area and the 

Dry Tortugas area (Areas #2 and 3; 

Figure 4)—are eliminated from 

consideration as a result of BOEM’s 

update to the geographic scope of 

action, as these two areas are entirely 

within the portion of the GOM removed 

from consideration. The bottlenose 

dolphin area, as revised herein (see 

Mitigation), is included in this final 

rule. 

Although the Bryde’s whale core 

habitat and Dry Tortugas areas are not 

the subject of restrictions on survey 

activity, as the updated scope of activity 

considered here does not include those 

two areas, the beneficial effect for 

animals in those areas, and the stocks of 

which they are a part, remains the same. 

No survey activity in those areas can be 

considered for LOAs issued under this 

rule. In addition, we expect the lack of 

survey activity in those areas to provide 

some subsidiary benefit to additional 

species that may be present, as 

indicated in the sections below and 

reflected in the updated take estimates. 

The absence of survey activity in 

those two areas benefits both the 

primary species for which they were 

designed and species that may benefit 

secondarily by likely reducing the 

portion of a stock likely exposed to 

survey noise and avoiding impacts to 

certain species in areas of importance 

for them. These areas are discussed 

more specifically in the context of the 

species and stocks they were designed 

to protect in the Proposed Mitigation 

section of the notice of proposed 

rulemaking, and are summarized in the 

sections below. 

Bryde’s Whale 

First, we note that the estimated (and 

allowable) take of Bryde’s whales has 

been reduced as compared to the 

proposed rule as a result of the change 

in scope. Specifically, both the 

maximum annual take and the average 

annual take decreased by approximately 

98 percent. The EWG analysis, which 

evaluated the relative significance of the 

aggregated impacts of the survey 

activities across seven GOM zones in 

the context of the vulnerability of each 

species, concluded that the GOM-wide 

risk ratings for Bryde’s whales are low, 

regardless of activity scenario. We note 

that, although the evaluated severity of 

take for Bryde’s whales is very low in 

all zones where take could occur, 

vulnerability for the species is assessed 

as high in all zones where the species 

occurs. When integrated through the 

risk framework as described above, 

overall risk for the species is therefore 

assessed as low for both the high and 

moderate effort scenarios. Evaluated risk 

is lower than what was considered in 

the proposed rule, where analysis of the 

prior take estimates resulted in a risk 

rating of moderate for both scenarios. 

We further consider the likely severity 

of any predicted behavioral disruption 

of Bryde’s whales in the context of the 

likely duration of exposure above Level 

B harassment thresholds. Specifically, 

the average modeled time per day spent 

at received levels above 160 dB rms 

(where 50 percent of the exposed 

population is considered taken) ranges 

from 6.8–21.4 minutes for deep 

penetration survey types. The average 

time spent exposed to received levels 

between 140 and 160 dB rms (where 10 

percent of the exposed population is 

considered taken) ranges from 55–164 

minutes for 2D, 3D NAZ, and 3D WAZ 

surveys, and 401 minutes for coil 

surveys (which comprise approximately 

10 percent of the total activity days). 

Importantly, no survey activity will 

occur within the Bryde’s whale core 

habitat area pursuant to this rule. The 

absence of survey activity in the area is 

expected to benefit Bryde’s whales and 

their habitat by minimizing a range of 

potential effects of airgun noise, both 

acute and chronic, that could otherwise 

accrue to impact the reproduction or 

survival of individuals in this area. 

Absence of survey activity in this area 

will minimize disturbance of the species 

in the place most important to them for 

critical behaviors such as foraging and 

socialization. Based on Roberts et al. 

(2016), the area encompasses 

approximately 92 percent of the 

predicted abundance of Bryde’s whales 

in the GOM. Intensive survey effort in 


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the region has not resulted in any 

confirmed Bryde’s whale sightings 

outside this core habitat area (aside from 

a single anomalous sighting in the 

western GOM). Although some sound 

from airguns may still propagate into 

the Bryde’s whale core habitat area from 

surveys that may occur outside of the 

area (in certain locations where 

separation distance between the core 

habitat area and the area considered for 

survey activity through this rule is less; 

see Figure 2), exposure of Bryde’s 

whales to sound levels that may be 

expected to result in Level B harassment 

will be eliminated or reduced for 

animals within the Bryde’s whale core 

area. The absence of survey activity in 

this area and significant reduction in 

associated exposure of Bryde’s whales 

to seismic airgun noise is expected to 

eliminate the likelihood of auditory 

injury of Bryde’s whales. Finally, the 

absence of survey activity in the eastern 

GOM will reduce chronic exposure of 

Bryde’s whales to higher levels of 

anthropogenic sound and the associated 

effects including masking, disruption of 

acoustic habitat, long-term changes in 

behavior such as vocalization, and 

stress. 

As described in the preceding ‘‘Loss 

of Hearing Sensitivity’’ section, we have 

analyzed the likely impacts of potential 

temporary hearing impairment and do 

not expect that they would result in 

impacts on reproduction or survival of 

any individuals. The extended 

shutdown zone for Bryde’s whales 

(1,500 m)—to be implemented in the 

unlikely event that a Bryde’s whale is 

encountered outside of the core habitat 

area—is expected to further minimize 

the severity of any hearing impairment 

incurred as well as reducing the 

likelihood of more severe behavioral 

responses. Similarly, application of this 

extended distance shutdown 

requirement when calves are present 

will minimize the potential for and 

degree of disturbance during this 

sensitive life stage. 

No mortality of Bryde’s whales is 

anticipated or authorized. It is possible 

that Bryde’s whale individuals in this 

stock, if encountered in areas not 

typically considered to be Bryde’s whale 

habitat, will be impacted briefly on one 

or more days during a year of activity 

by one type of survey or another and 

some subset of those exposures above 

thresholds may be of comparatively long 

duration within a day. However, the 

significant and critical protection 

afforded through the absence of survey 

activity in the core habitat area and the 

associated reduction in estimated take 

ensures that the impacts of the expected 

takes from these activities are not likely 

to adversely affect the GOM stock of 

Bryde’s whales through impacts on 

annual rates of recruitment or survival. 

Sperm Whale 

First, we note that the estimated (and 

allowable) take of sperm whales has 

been reduced as compared to the 

proposed rule as a result of the change 

in scope. Specifically, the maximum 

annual take decreased by approximately 

62 percent and the average annual take 

decreased by approximately 58 percent. 

The EWG analysis, which evaluated the 

relative significance of the aggregated 

impacts of the survey activities across 

seven GOM zones in the context of the 

vulnerability of each species, concluded 

that the GOM-wide risk ratings for 

sperm whales were between moderate 

and low (equivalent to a 2.5 on a 5-point 

scale, with a 3 equating to ‘‘moderate’’) 

(for the high effort scenario) or low (for 

the moderate effort scenario). Evaluated 

risk is reduced from the proposed rule, 

where the high effort scenario resulted 

in a very high risk rating and the 

moderate effort scenario resulted in a 

high risk rating. We further consider the 

likely severity of any predicted 

behavioral disruption of sperm whales 

in the context of the likely duration of 

exposure above Level B harassment 

thresholds. Specifically, the average 

modeled time per day spent at received 

levels above 160 dB rms (where 50 

percent of the exposed population is 

considered taken) ranges from 4–10.3 

minutes for 2D, 3D NAZ, and 3D WAZ 

surveys and up to 20.7 minutes for coil 

surveys (which comprise less than 10 

percent of the total projected activity 

days) and the average time spent 

between 140 and 160 dB rms (where 10 

percent of the exposed population is 

considered taken) is 12–31.8 minutes. 

Odontocetes echolocate to find prey, 

and while there are many different 

strategies for hunting, one common 

pattern, especially for deeper-diving 

species, is to conduct multiple repeated 

deep dives within a feeding bout, and 

multiple bouts within a day, to find and 

catch prey. While exposures of the short 

durations noted above could potentially 

interrupt a dive or cause an individual 

to relocate to feed, such a short-duration 

interruption would typically be unlikely 

to have significant impacts on an 

individual’s energy budget. However, 

the moderate risk rating for the high 

effort scenario reflects the higher 

number of total days across which these 

singularly more minor impacts may 

occur, as well as other factors, and 

points to the need for the consideration 

of additional reduction of impacts 

where possible. In years when less effort 

occurs, as represented by the moderate 

effort scenario, risk will be less. 

Importantly, no survey activity is 

expected within the Dry Tortugas 

Mitigation Area, which was analyzed 

and proposed for implementation in the 

proposed rule. The area provides 

preferred habitat for comparatively high 

densities of sperm whales and is 

thought to be used as a calving area. The 

absence of survey activity in the area is 

expected to alleviate some of the 

previous impacts of concern to sperm 

whales (as well as beaked whales and 

Kogia spp.) and their habitat by 

minimizing a range of potential effects 

of airgun noise, both acute and chronic, 

that could otherwise accrue to impact 

the reproduction or survival of 

individuals in this area. Absence of 

survey activity in this area will 

minimize disturbance of the species in 

a place of importance for critical 

behaviors such as foraging and 

socialization and, overall, helps to 

reduce evaluated risk to the stock as a 

whole. 

Additionally, we note that the 

extended distance shutdown zone for 

sperm whales (1,500 m) is expected to 

further reduce the likelihood and 

minimize the severity of more severe 

behavioral responses. Similarly, 

application of this extended distance 

shutdown requirement when calves are 

present will minimize the potential for 

and degree of disturbance during this 

sensitive life stage. 

No mortality or Level A harassment of 

sperm whales is anticipated or 

authorized. While it is likely that the 

majority of the individual sperm whales 

will be impacted briefly on one or more 

days during a year of activity by one 

type of survey or another, based on the 

nature of the individual exposures 

(shorter duration) and takes, as well as 

the aggregated scale of the impacts 

across the GOM in consideration of the 

mitigation discussed here, the impacts 

of the expected takes from these 

activities are not likely to adversely 

affect the GOM stock of sperm whales 

through adverse impacts on annual rates 

of recruitment or survival. 

Beaked Whales 

In consideration of the similarities in 

the nature and scale of impacts, we 

consider the GOM stocks of Cuvier’s, 

Gervais’, and Blainville’s beaked whales 

together in this section. First, we note 

that the estimated (and allowable) take 

of beaked whales has been reduced as 

compared to the proposed rule as a 

result of the change in scope. 

Specifically, the maximum annual take 

decreased by approximately 19 percent 

and the average annual take decreased 


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by approximately 15 percent. The EWG 

analysis, which evaluated the relative 

significance of the aggregated impacts of 

the survey activities across seven GOM 

zones in the context of the vulnerability 

of each species, concluded that the 

GOM-wide risk ratings for beaked 

whales were between high and 

moderate (equivalent to a 3.5 on a 5- 

point scale, with a 4 equating to ‘‘high’’) 

for the high effort scenario and between 

moderate and low (equivalent to a 2.5 

on a 5-point scale, with a 3 equating to 

‘‘moderate’’) for the moderate effort 

scenario. Evaluated risk is reduced from 

the proposed rule, where the high effort 

scenario resulted in a very high risk 

rating and the moderate effort scenario 

resulted in a high risk rating. We further 

consider the likely severity of any 

predicted behavioral disruption of 

beaked whales in the context of the 

likely duration of exposure above Level 

B harassment thresholds. Beaked whales 

are considered more behaviorally 

sensitive to sound than most other 

species, and therefore we utilize 

different thresholds to predict 

behavioral disturbance. However, this 

means that beaked whales are evaluated 

as ‘‘taken’’ upon exposure to received 

sound levels as low as 120 dB (where 50 

percent of the exposed beaked whale 

population is considered taken). These 

received levels are typically reached at 

extreme distance from the acoustic 

source (i.e., greater than 50 km from the 

source). Behavioral responses to noise 

are significantly correlated with 

distance from the source (e.g., Gomez et 

al., 2016); and potential responses to 

these relatively low received levels at 

such great distances, while 

conservatively evaluated here as take 

under the MMPA, are unlikely to result 

in any response of such a severity as to 

carry any cost to the animal. 

(Additionally, in certain circumstances, 

noise from the surveys at these 

distances may be indistinguishable from 

other low-frequency background noise). 

Therefore, as for other species, we 

consider only the average modeled time 

per day spent at received levels above 

140 dB rms (where 90 percent of the 

exposed beaked whale populations are 

considered taken) and 160 dB rms 

(where, potentially, all exposed beaked 

whales are taken). The average time 

spent in a state of exposure above 160 

dB rms is only 6–12.4 minutes for 2D, 

3D NAZ, and 3D WAZ surveys and 24 

minutes for coil surveys. The average 

time spent in a state of exposure above 

140 dB rms is 14.1 minutes for 3D WAZ 

surveys, 16.2 minutes for 2D surveys, 

31.1 minutes for coil surveys, and 39.7 

minutes for 3D NAZ surveys. 

Odontocetes echolocate to find prey, 

and while there are many different 

strategies for hunting, one common 

pattern, especially for deeper-diving 

species, is to conduct multiple repeated 

deep dives within a feeding bout, and 

multiple bouts within a day, to find and 

catch prey. As we noted, while some of 

the exposures of the durations noted 

above could interrupt a dive or cause an 

individual to relocate to feed because of 

the lower thresholds combined with the 

way exposures are distributed across 

received levels, a higher proportion of 

the total takes (as compared to other 

taxa) are at the lower end of the received 

levels at which take would be expected 

to occur and at great distance from the 

acoustic source, where responses (if 

any) should be assumed to be minor. All 

else being equal, exposures to lower 

received levels and, separately, at 

greater distances might be expected to 

result in less severe responses, even 

given longer durations (e.g., DeRuiter et 

al., 2013). Considered individually or 

infrequently, these sorts of feeding 

interruptions would be unlikely to have 

significant impacts on an individual’s 

energy budget, especially given the 

likely availability of adequate alternate 

feeding areas relatively nearby. 

However, the high risk rating for the 

high effort scenario reflects the higher 

number of total days across which these 

singularly more minor impacts may 

occur, as well as other factors, and 

points to the need for the consideration 

of additional reduction of impacts 

where possible. In years when less effort 

occurs, as represented by the moderate 

effort scenario, risk will be less. 

Importantly, no survey activity is 

expected within the Dry Tortugas 

Mitigation Area, which was analyzed 

and proposed for implementation in the 

proposed rule. The area provides 

preferred habitat for comparatively high 

densities of beaked whales. The absence 

of survey activity in this important area 

is expected to alleviate some of the 

previous impacts of concern to beaked 

whales (as well as sperm whales and 

Kogia spp.) and their habitat by 

minimizing a range of potential effects 

of airgun noise, both acute and chronic, 

that could otherwise accrue to impact 

the reproduction or survival of 

individuals in this area. Absence of 

survey activity in this area will 

minimize disturbance of the species in 

a place of importance for critical 

behaviors such as foraging and 

socialization and, overall, helps to 

reduce evaluated risk to the stocks as a 

whole. 

Additionally, we note that the 

extended distance shutdown zone for 

beaked whales (1,500 m) is expected to 

further reduce the likelihood of, and 

minimize the severity of, more severe 

behavioral responses. 

Despite the nature and duration of the 

exposures anticipated, which at a 

smaller scale might not be expected to 

meaningfully impact individual fitness, 

given the high to moderate EWG risk 

rating and the relatively high number of 

predicted beaked whale takes 

(increasing the likelihood of some 

subset of individuals accruing a fair 

number of repeated takes over 

sequential days—albeit assuming takes 

at low received levels and at distances 

from the source where responses, if any, 

should be expected to be minor), it is 

more likely that a small number of 

individuals could be interrupted during 

foraging in a manner and amount such 

that impacts to the energy budgets of 

females (from either losing feeding 

opportunities or expending energy to 

find alternative feeding options) could 

cause them to forego reproduction for a 

year. Energetic impacts to males are 

generally meaningless to population 

rates unless they cause death, and 

extreme energy deficits (beyond what 

could be considered reasonably likely to 

result from these activities) are required 

to cause the death of an adult marine 

mammal. As noted previously, however, 

foregone reproduction (especially for 

one year, which is the maximum 

predicted because the relatively small 

number anticipated in any one year 

makes the probability that any 

individual would be impacted in this 

way twice in five years very low) has far 

less of an impact on population rates 

than mortality. And a small number of 

instances of foregone reproduction 

would not be expected to adversely 

affect these stocks through effects on 

annual rates of recruitment or survival. 

It is worth noting that in similar 

situations, i.e., where individual beaked 

whales may be exposed to noise above 

harassment thresholds regularly, 

populations appear to be stable based on 

multiple studies and lines of evidence 

(e.g., Falcone and Schorr, 2014; 

DiMarzio et al., 2018). In research done 

at the Navy’s fixed tracking range in the 

Bahamas, animals were observed to 

leave the immediate area of an antisubmarine warfare training exercise but 

return within a few days after the event 

ended (Claridge and Durban, 2009; 

McCarthy et al., 2011; Moretti et al., 

2009, 2010; Tyack et al., 2010, 2011). It 

is important to note that in these 

contexts, beaked whales were exposed 

to noise stimuli to which they are 

significantly more acoustically sensitive 

(i.e., mid-frequency active sonar versus 

low-frequency airgun noise). 


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Of note, due to their pelagic 

distribution, typical high availability 

bias due to deep-diving behavior and 

cryptic nature when at the surface, 

beaked whales are rarely sighted during 

at-sea surveys and difficult to 

distinguish between species when 

visually observed in the field. 

Accordingly, abundance estimates in 

NMFS SARs are recorded for 

Mesoplodon spp. Available sightings 

data, including often unresolved 

sightings of beaked whales, must be 

combined in order to develop habitatbased density models for beaked 

whales, as were used to inform our 

acoustic exposure modeling effort. 

Therefore, density and take estimates in 

this rule are similarly lumped for the 

three species of beaked whales, and 

there is no additional information by 

which NMFS could appropriately 

apportion impacts other than equally/ 

proportionally across the three species. 

No mortality or Level A harassment of 

any of these three species of beaked 

whales is anticipated or authorized. It is 

likely that the majority of the individual 

beaked whales will be impacted on one 

or more days during a year of activity 

by one type of survey or another. It is 

possible that some small number of 

female beaked whales may experience a 

year of foregone reproduction. However, 

based on the nature of the majority of 

the individual exposures and the overall 

scale of the aggregate impacts and risk 

rating in consideration of the mitigation 

discussed here, and noting the 

continued presence of beaked whales in 

the GOM given the many years of high 

activity levels and the evidence that 

beaked whales maintain stable or 

increasing populations in other areas 

with high levels of acoustic activity, the 

impacts of the expected takes from these 

activities are not likely to adversely 

affect the GOM stocks of Cuvier’s, 

Gervais’, or Blainville’s beaked whales 

through adverse impacts on annual rates 

of recruitment or survival. 

Kogia spp. 

First, we note that the estimated (and 

allowable) take of Kogia spp. has been 

reduced as compared to the proposed 

rule as a result of the change in scope. 

Specifically, the maximum annual take 

by Level B harassment decreased by 

approximately 46 percent and the 

average annual take decreased by 

approximately 43 percent. (These 

reductions are 49 and 46 percent, 

respectively, for Level A harassment.) 

The EWG analysis, which evaluated the 

relative significance of the aggregated 

impacts of the survey activities across 

seven GOM zones in the context of the 

vulnerability of each species, concluded 

that the GOM-wide risk ratings for Kogia 

spp. were low (for the high effort 

scenario) and very low (for the moderate 

effort scenario). Evaluated risk is 

reduced from the proposed rule, where 

the high effort scenario resulted in a 

moderate risk rating and the moderate 

effort scenario resulted in a low risk 

rating. We further consider the likely 

severity of any predicted behavioral 

disruption of Kogia spp. in the context 

of the likely duration of exposure above 

Level B harassment thresholds. 

Specifically, the average modeled time 

per day spent at received levels above 

160 dB rms (where 50 percent of the 

exposed population is considered taken) 

ranges from 2.8–7.9 minutes for 2D, 3D 

NAZ, and 3D WAZ surveys and up to 

15.3 minutes for coil surveys (which 

comprise less than 10 percent of the 

total projected activity days), and the 

average time spent between 140 and 160 

dB rms (where 10 percent of the 

exposed population is considered taken) 

is 6.7–19 minutes. 

Odontocetes echolocate to find prey, 

and while there are many different 

strategies for hunting, one common 

pattern, especially for deeper diving 

species, is to conduct multiple repeated 

deep dives within a feeding bout, and 

multiple bouts within a day, to find and 

catch prey. While exposures of the short 

durations noted above could potentially 

interrupt a dive or cause an individual 

to relocate to feed, such a short-duration 

interruption would be unlikely to have 

significant impacts on an individual’s 

energy budget and, further, for these 

species and this open-ocean area, there 

are no specific known reasons (i.e., 

these species range GOM-wide beyond 

the continental slope and there are no 

known biologically important areas) to 

expect that there would not be adequate 

alternate feeding areas relatively nearby, 

especially considering the anticipated 

absence of survey activity in the eastern 

GOM. 

As described above, no survey activity 

is expected within the Dry Tortugas 

Mitigation Area, which was analyzed 

and proposed for implementation in the 

proposed rule. The absence of survey 

activity in the area is expected to afford 

additional reduction of impacts to Kogia 

spp., in addition to sperm and beaked 

whales, given their relatively high 

density in that area. Importantly, the 

absence of survey activity in the area 

will reduce disturbance of these species 

in places of importance to them for 

critical behaviors such as foraging and 

socialization and, overall, help to 

reduce evaluated risk to the stocks as a 

whole. 

NMFS has analyzed the likely impacts 

of potential hearing impairment, 

including the estimated upper bounds 

of permanent threshold shift (Level A 

harassment) that could be authorized 

under the rule, and do not expect that 

they would result in impacts on 

reproduction or survival of any 

individuals. As described in the 

previous section, the degree of injury for 

individuals would be expected to be 

mild, and the predicted PTS resulting 

from airgun exposure is not likely to 

affect echolocation performance or 

communication for Kogia spp. 

Additionally, the extended distance 

shutdown zone for Kogia spp. (1,500 m) 

is expected to further minimize the 

severity of any hearing impairment 

incurred and also to further reduce the 

likelihood of, and minimize the severity 

of, more severe behavioral responses. 

Of note, due to their pelagic 

distribution, small size, and cryptic 

behavior, pygmy sperm whales and 

dwarf sperm whales are rarely sighted 

during at-sea surveys and difficult to 

distinguish between when visually 

observed in the field. Accordingly, 

abundance estimates in NMFS SARs are 

recorded for Kogia spp. only, density 

and take estimates in this rule are 

similarly lumped for the two species, 

and there is no additional information 

by which NMFS could appropriately 

apportion impacts other than equally/ 

proportionally across the two species. 

No mortality of Kogia spp. is 

anticipated or authorized. While it is 

likely that the majority of the 

individuals of these two species will be 

impacted briefly on one or more days 

during a year of activity by one type of 

survey or another, based on the nature 

of the individual exposures and takes, 

as well as the aggregated scale of the 

impacts across the GOM, and in 

consideration of the mitigation 

discussed here, the impacts of the 

expected takes from these activities are 

not likely to adversely impact the GOM 

stocks of dwarf or pygmy sperm whales 

through adverse impacts on annual rates 

of recruitment or survival. 

Bottlenose Dolphins 

The change in scope did not result in 

any appreciable change to estimated 

(and allowable) take of bottlenose 

dolphins compared to the proposed 

rule. Specifically, the maximum annual 

take increased slightly (by 

approximately 2 percent), while the 

average annual take decreased slightly 

(by approximately 1 percent). The EWG 

analysis, which evaluated the relative 

significance of the aggregated impacts of 

the survey activities across seven GOM 

zones in the context of the vulnerability 

of each species, concluded that the 

GOM-wide risk ratings for both oceanic 


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bottlenose dolphins and coastal/shelf 

bottlenose dolphins are very low for 

both scenarios. In the proposed rule, 

risk was evaluated for bottlenose 

dolphins GOM-wide (here we have 

refined the risk evaluation to 

differentiate between oceanic and 

coastal/shelf stocks). Evaluated risk is 

reduced from the proposed rule, where 

the high effort scenario resulted in a low 

risk rating and the moderate effort 

scenario resulted in a moderate risk 

rating. We further considered the likely 

severity of any predicted behavioral 

disruption of bottlenose dolphins in the 

context of the likely duration of 

exposure above Level B harassment 

thresholds. Specifically, the average 

modeled time per day spent at received 

levels above 160 dB rms (where 50 

percent of the exposed population is 

considered taken) ranges from 4–11.7 

minutes for 2D, 3D NAZ, and 3D WAZ 

surveys and up to 16.8 minutes for coil 

surveys (which comprise less than 10 

percent of the total projected activity 

days) and the average time spent 

between 140 and 160 dB rms is 19.7– 

54.6 minutes. While exposures of the 

short durations noted above could 

potentially interrupt a dive or cause an 

individual to relocate to feed, among 

other impacts, such a short-duration 

interruption would be unlikely to have 

significant impacts on an individual’s 

energy budget or otherwise impact 

reproduction or survival. 

As described earlier in this preamble, 

the northern coastal stock of bottlenose 

dolphin was particularly severely 

impacted by the DWH oil spill, and was 

additionally affected by a recent UME. 

Importantly, as described in Mitigation, 

NMFS is requiring a seasonal time-area 

restriction on airgun survey activity 

within the coastal waters where this 

stock is likely to be found. The closure 

area is expected to protect coastal 

bottlenose dolphins and their habitat 

through the alleviation or minimization 

of a range of potential effects of airgun 

noise, both acute and chronic, that 

could otherwise accrue to impact the 

reproduction or survival of individuals 

in this area. The timing of the restriction 

provides protection during the times of 

year thought to be most important for 

bottlenose dolphin calving and nursing 

of young. Although some sound from 

airguns may still propagate into the area 

from surveys that may occur outside of 

the area, exposure of bottlenose 

dolphins to sound levels that would 

result in Level B harassment will be 

alleviated or reduced for animals within 

the closure area. Any exposure to noise 

that may increase stress levels and 

exacerbate health problems in 

bottlenose dolphins still recovering 

from the effects of the DWH spill will 

be minimized during this important 

reproductive period. This important 

mitigation results in a reduction in the 

scale of aggregate effects (which, among 

other things, suggests the comparative 

number of days across which individual 

bottlenose dolphins might be taken 

within a year) and associated risk 

assessment. 

Of note, bottlenose dolphins cannot 

be identified to stock when visually 

observed in the field. Abundance 

estimates in NMFS SARs are based 

strictly on the location where animals 

are observed, and available sightings 

data must be combined in order to 

develop habitat-based density models 

for bottlenose dolphins, as were used to 

inform our acoustic exposure modeling 

effort. Therefore, density and take 

estimates in this rule are provided for 

bottlenose dolphins as a GOM-wide 

species. However, based on NMFS’ 

stock delineations, we can reasonably 

assume that dolphins occurring within 

Zones 4–7 would be from the oceanic 

stock, while dolphins occurring within 

Zones 1–3 would be from the shelf stock 

and/or coastal stocks. Therefore, for the 

oceanic stock, we are able to draw stockspecific conclusions in this analysis. For 

coastal/shelf stocks, there is no 

additional information by which NMFS 

could appropriately apportion impacts 

other than equally/proportionally across 

the stocks, with the exception of 

predicting reduced impacts to the 

northern coastal stock as described 

above. We note that, as a result of 

BOEM’s update to the scope of activity, 

the eastern coastal stock will not 

experience any impacts and is 

accordingly no longer considered in this 

rule. 

No mortality or Level A harassment of 

bottlenose dolphins is anticipated or 

authorized. While it is likely that the 

majority of individual dolphins may be 

impacted briefly on one or more days 

during a year of activity by one type of 

survey or another, based on the nature 

of the individual exposures (shorter 

duration) and takes, as well as the 

aggregated scale of the impacts across 

the GOM in consideration of the 

mitigation discussed here, the impacts 

of the expected takes from these 

activities are not likely to adversely 

affect any affected GOM stock of 

bottlenose dolphins through adverse 

impacts on annual rates of recruitment 

or survival. 

All Other Stocks 

In consideration of the similarities in 

the nature and scale of impacts, we 

consider the GOM stocks of the 

following species together in this 

section: Rough-toothed dolphin, 

Clymene dolphin, Atlantic spotted 

dolphin, pantropical spotted dolphin, 

striped dolphin, spinner dolphin, 

Fraser’s dolphin, Risso’s dolphin, 

melon-headed whale, pygmy killer 

whale, false killer whale, killer whale, 

and short-finned pilot whale. Estimated 

(and allowable) take of these stocks 

(including both the maximum annual 

take and the average annual take) has 

been reduced as compared to the 

proposed rule as a result of the change 

in scope (with the exception of the 

Atlantic spotted dolphin). For the 

Atlantic spotted dolphin, the change in 

scope resulted in increases compared to 

the proposed rule. Specifically, the 

maximum annual take increased by 

approximately 9 percent, while the 

average annual take increased by 

approximately 4 percent. These slight 

increases do not impact our analysis for 

the stock. 

The EWG analysis, which evaluated 

the relative significance of the 

aggregated impacts of the survey 

activities across seven GOM zones in 

the context of the vulnerability of each 

species, concluded that the GOM-wide 

risk ratings for high and moderate effort 

scenarios ranged from very low to low 

for these species. For all stocks, there 

was a trend of decreased or static risk 

ratings compared to the proposed rule, 

where the GOM-wide risk ratings for 

high and moderate effort scenarios 

ranged from low to moderate. 

We further considered the likely 

severity of any predicted behavioral 

disruption of the individuals of these 

species in the context of the likely 

duration of exposure above Level B 

harassment thresholds. Specifically, the 

average modeled time per day spent at 

received levels above 160 dB rms 

(where 50 percent of the exposed 

population is considered taken) ranges 

from 1.4–11.7 minutes for 2D, 3D NAZ, 

and 3D WAZ surveys and up to 25.7 

minutes for coil surveys (which 

comprise less than 10 percent of the 

total projected activity days). The 

average time per day spent between 140 

and 160 dB rms for individuals that are 

taken is from 8–58.1 minutes, with the 

one exception of killer whales exposed 

to noise from coil surveys, which 

average 73.6 minutes (though we note 

that the overall risk rating for the 

species is very low). 

Odontocetes echolocate to find prey, 

and there are many different strategies 

for hunting. One common pattern for 

deeper-diving species is to conduct 

multiple repeated deep dives within a 

feeding bout, and multiple bouts within 

a day, to find and catch prey. While 


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exposures of the shorter durations noted 

above could potentially interrupt a dive 

or cause an individual to relocate to 

feed, such a short-duration interruption 

would be unlikely to have significant 

impacts on an individual’s energy 

budget and, further, for these species 

and this open-ocean area, there are no 

specific known reasons (i.e., these 

species range GOM-wide beyond the 

continental slope and there are no 

known biologically important areas) to 

expect that there would not be adequate 

alternate feeding areas relatively nearby, 

especially considering the anticipated 

absence of survey activity in the eastern 

GOM. For those species that are more 

shallow feeding species, it is unlikely 

that the noise exposure considered 

herein would result in minimal 

significant disruption of foraging 

behavior and, therefore, the concomitant 

energetic effects would similarly be 

minimal. 

Of note, the Atlantic spotted dolphin 

would benefit (via lessening of both 

number and severity of takes) from the 

coastal waters time-area restriction 

developed to benefit bottlenose 

dolphins and several additional species 

experience notably reduced effects from 

the absence of survey activity in 

important eastern GOM habitat. 

Specifically, multiple shelf-break 

associated and pelagic species (such as 

Risso’s dolphin, melon-headed whales, 

and rough-toothed dolphins) experience 

a reduction estimated take from the 

absence of survey activity in both the 

Bryde’s whale core habitat and Dry 

Tortugas Areas. Maximum annual and 

average annual take decreased for these 

species compared with the proposed 

rule by 20 and 14 percent, 19 and 15 

percent, and 19 and 18 percent, 

respectively. Numerous other species 

would be expected to be present in 

varying numbers at various times. 

No mortality or Level A harassment of 

these species is anticipated or 

authorized. It is likely that the majority 

of the individuals of these 13 species 

will be impacted briefly on one or more 

days during a year of activity by one 

type of survey or another. Based on the 

nature of the individual exposures and 

takes, as well as the very low to low 

aggregated scale of the impacts across 

the GOM and considering the mitigation 

discussed here, the impacts of the 

expected takes from these activities are 

not likely to adversely impact the GOM 

stocks of any of these 13 GOM stocks of 

these species through adverse impacts 

on annual rates of recruitment or 

survival. 

Determination 

Based on the analysis contained 

herein of the likely effects of the 

specified activities on marine mammals 

and their habitat, and taking into 

consideration the implementation of the 

monitoring and mitigation measures, 

NMFS finds that the total marine 

mammal take from the specified 

activities will have a negligible impact 

on all affected marine mammal species 

and stocks. 

Small Numbers 

The sections below provide an 

explanation of how NMFS interprets 

and applies the small numbers standard 

and remain substantively unchanged 

from the discussion provided in the 

notice of proposed rulemaking. 

Additional discussion appears in 

Comments and Responses to address 

specific comments, questions, or 

recommendations received from the 

public. 

What are small numbers? 

The term ‘‘small numbers’’ appears in 

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

follows: 

(5)(A)(i) Upon request therefor by 

citizens of the United States who engage 

in a specified activity (other than 

commercial fishing) within a specified 

geographical region, the Secretary shall 

allow, during periods of not more than 

five consecutive years each, the 

incidental, but not intentional, taking by 

citizens while engaging in that activity 

within that region of small numbers of 

marine mammals of a species or 

population stock if the Secretary, after 

notice (in the Federal Register and in 

newspapers of general circulation, and 

through appropriate electronic media, in 

the coastal areas that may be affected by 

such activity) and opportunity for 

public comment— 

(I) finds that the total of such taking 

during each five-year (or less) period 

concerned will have a negligible impact 

on such species or stock and will not 

have an unmitigable adverse impact on 

the availability of such species or stock 

for taking for subsistence uses [ . . . ] 

and 

(II) prescribes regulations setting 

forth— 

(aa) permissible methods of taking 

pursuant to such activity, and other 

means of effecting the least practicable 

adverse impact on such species or stock 

and its habitat, paying particular 

attention to rookeries, mating grounds, 

and areas of similar significance, and on 

the availability of such species or stock 

for subsistence uses; and 

(bb) requirements pertaining to the 

monitoring and reporting of such taking. 

(Emphasis added.) 

In addition to section 101(a)(5)(A), the 

MMPA as amended in 1994 includes a 

similar provision in section 101(a)(5)(D), 

which provides for the issuance of 

incidental take authorizations for small 

numbers of marine mammals without 

the need for regulations, effective for up 

to one year, where the taking is limited 

to harassment: 

(5)(D)(i) Upon request therefor by 

citizens of the United States who engage 

in a specified activity (other than 

commercial fishing) within a specific 

geographic region, the Secretary shall 

authorize, for periods of not more than 

1 year, subject to such conditions as the 

Secretary may specify, the incidental, 

but not intentional, taking by 

harassment of small numbers of marine 

mammals of a species or population 

stock by such citizens while engaging in 

that activity within that region if the 

Secretary finds that such harassment 

during each period concerned— 

(I) will have a negligible impact on 

such species or stock, and 

(II) will not have an unmitigable 

adverse impact on the availability of 

such species or stock for taking for 

subsistence uses[.] 

(Emphasis added.) 

The MMPA does not define ‘‘small 

numbers.’’ NMFS’ and the U.S. Fish and 

Wildlife Service’s 1989 implementing 

regulations defined small numbers as a 

portion of a marine mammal species or 

stock whose taking would have a 

negligible impact on that species or 

stock. This definition was invalidated in 

Natural Resources Defense Council v. 

Evans, 279 F.Supp.2d 1129 (2003) (N.D. 

Cal. 2003), based on the court’s 

determination that the regulatory 

definition of small numbers was 

improperly conflated with the 

regulatory definition of ‘‘negligible 

impact,’’ which rendered the small 

numbers standard superfluous. As the 

court observed, ‘‘the plain language 

indicates that small numbers is a 

separate requirement from negligible 

impact.’’ Since that time, NMFS has not 

applied the definition found in its 

regulations. Rather, consistent with 

Congress’ pronouncement that small 

numbers is not a concept that can be 

expressed in absolute terms (House 

Committee on Merchant Marine and 

Fisheries Report No. 97–228 (September 

16, 1981)), NMFS makes its small 

numbers findings based on an analysis 

of whether the number of individuals 

authorized to be taken annually from a 

specified activity is small relative to the 

stock or population size. The Ninth 

Circuit has upheld a similar approach. 

See Center for Biological Diversity v. 

Salazar, 695 F.3d 893 (9th Cir. 2012). 


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20We note that although NMFS’ implementing 

regulations require applications for incidental take 

to include an estimate of the marine mammals to 

be taken, there is nothing in section 101(a)(5)(A) (or 

(D)) that requires NMFS to quantify or estimate 

numbers of marine mammals to be taken for 

purposes of evaluating whether the number is 

small. (See CBD v. Salazar.) 

21As the court observed in Native Village of 

Chickaloon v. NMFS, 947 F. Supp. 2d 1031, 1049 

n.123 (D. Alaska 2013) ‘‘the same statutory 

standards apply’’ to incidental take authorization 

under both provisions. 

However, NMFS has not historically 

indicated what the agency believes to be 

the upper limit of small numbers. 

To maintain an interpretation of small 

numbers as a proportion of a species or 

stock that does not conflate with 

negligible impact, NMFS uses a simple 

approach that establishes equal bins 

corresponding to small, medium, and 

large proportions of the population 

abundance. NMFS then compares the 

number of individuals estimated and 

authorized to be taken against the best 

available abundance estimate for that 

species or stock. 

It can be challenging to predict the 

numbers of individual marine mammals 

that will be taken by an activity. Many 

models calculate instances of take but 

are unable to account for repeated 

exposures of individual marine 

mammals, though the instances of take 

necessarily represent the upper bound 

of the number of individuals. In some of 

those cases, such as for this rule (see 

Estimated Take), we are able to generate 

a more refined estimate of the numbers 

of individuals predicted to be taken 

utilizing a combination of quantitative 

tools and qualitative information. When 

an acceptable estimate of the individual 

marine mammals taken is available,20

the small numbers determination is 

based directly upon whether these 

estimates exceed one-third of the stock 

abundance. In other words, consistent 

with past practice, when the estimated 

number of individual animals taken 

(which may or may not be assumed as 

equal to the total number of takes, 

depending on the available information) 

is up to, but not greater than, one-third 

of the most appropriate species or stock 

abundance, NMFS will determine that 

the numbers of marine mammals taken 

of a species or stock are small. 

Another circumstance in which 

NMFS considers it appropriate to make 

a small numbers finding is in the case 

of a species or stock that may 

potentially be taken but is either rarely 

encountered or only expected to be 

taken on rare occasions. In that 

circumstance, one or two assumed 

encounters with a group of animals 

(meaning a group that is traveling 

together or aggregated, and thus exposed 

to a stressor at the same approximate 

time) should reasonably be considered 

small numbers, regardless of 

consideration of the proportion of the 

stock, as infrequent or rare encounters 

resulting in take of one or two groups 

should be considered small relative to 

the range and distribution of any stock. 

In summary, when quantitative take 

estimates of individual marine 

mammals are available or inferable 

through consideration of additional 

factors, and the number of animals 

taken is one-third or less of the best 

available abundance estimate for the 

species or stock, NMFS considers it to 

be of small numbers. NMFS may also 

appropriately find that one or two 

predicted group encounters will result 

in small numbers of take relative to the 

range and distribution of a species, 

regardless of the estimated proportion of 

the abundance. 

Is the small numbers standard 

evaluated based on total take under 

incidental take regulations or within the 

context of an individual letter of 

authorization? 

Neither the MMPA nor NMFS’ 

implementing regulations address 

whether the small numbers 

determination should be based upon the 

total annual taking for (1) all activities 

occurring under specific incidental take 

regulation or (2) to individual LOAs 

issued thereunder. The MMPA does not 

define small numbers or explain how to 

apply the term in either paragraph (A) 

or (D) of section 101(a)(5), including 

how to apply the term in a way that 

allows for consistency between those 

two very similar provisions in the 

statute. Whether to apply the small 

numbers finding to each individual 

LOA under regulations that cover 

multiple concurrent LOA holders is a 

matter of first impression for NMFS. 

Specifically, section 101(a)(5)(A)(i)(I) 

explicitly states that the negligible 

impact determination for a specified 

activity must take into account the total 

taking over the five-year period, but the 

small numbers language is not tied 

explicitly to the same language. Rather, 

the small numbers provision appears in 

section 101(a)(5)(A)(i) as a limitation on 

what the Secretary may allow. The 

regulatory vehicle for authorizing (i.e., 

‘‘allowing’’) the take of marine 

mammals is the LOA. 

Given NMFS’ discretion in light of the 

ambiguities in the statute regarding how 

to apply the small numbers standard, 

we have determined that the small 

numbers finding should be applied to 

the annual take authorized per 

individual LOA, rather than to the total 

annual taking for all activities 

potentially occurring under the 

incidental take regulations. This perLOA approach harmonizes section 

101(a)(5)(A) with the per-IHA 

application in section 101(a)(5)(D) of the 

MMPA.21 This per-LOA approach is not 

only permissible but also preferable to 

the total annual taking approach 

because NMFS’ per-LOA approach to 

small numbers in section 101(a)(5)(A) 

affords greater regulatory flexibility to 

utilize section 101(a)(5)(A) when there 

are benefits to doing so for the resource 

(marine mammals), the public, 

prospective applicants, and 

administrative efficiency: 

• From a resource protection 

standpoint, it is better to conduct a 

comprehensive negligible impact 

analysis that considers all of the 

activities covered under the rule (versus 

considering them independently 

pursuant to individual IHAs) and 

ensures that the total combined taking 

from those activities will have a 

negligible impact on the affected marine 

mammal species or stocks and no 

unmitigable adverse impact on 

subsistence uses. Furthermore, 

mitigation and monitoring are more 

effective when considered across all 

activity and years covered under 

regulations. 

• From an agency resource 

standpoint, it ultimately will save 

significant time and effort to cover 

multi-year activities under a rule 

instead of multiple incidental 

harassment authorizations (IHAs). 

While regulations require more analysis 

up front, additional public comment 

and internal review, and additional time 

to promulgate compared to a single IHA, 

they are effective for up to five years (for 

non-military readiness activities) and 

can cover multiple actors within a year. 

The process of issuing individual LOAs 

under incidental take regulations 

utilizes the analysis, public comment, 

and review that was conducted for the 

regulations, and takes significantly less 

time than it takes to issue independent 

IHAs. 

• From an applicant standpoint, 

incidental take regulations offer more 

regulatory certainty than IHAs (five 

years versus one year) and significant 

cost savings, both in time and 

environmental compliance analysis and 

documentation. This is especially true 

for situations like here, where multiple 

applicants will be applying for 

individual LOAs under regulations. In 

the case of this rule, the certainty 

afforded by the promulgation of a 

regulatory framework (e.g., by using 

previously established take estimates, 

mitigation and monitoring 


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requirements, and procedures for 

requesting and obtaining an LOA) is a 

significant benefit for prospective 

applicants. 

NMFS’ evaluation of past IHAs 

suggests that bundling together the 

activities covered by two or three IHAs 

that might be ideal subjects for a 

combined incidental take regulation 

(e.g., for ongoing maintenance 

construction activities, or seismic 

surveys in the Arctic by different 

entities) may exceed the taking of small 

numbers of a species if NMFS were to 

apply the small numbers standard 

across all taking contemplated by the 

regulation in a year. In other words, if 

the small numbers standard is applied 

to the total annual taking under a rule, 

NMFS may not be able to make the 

necessary small numbers finding, which 

would preclude the use of section 

101(a)(5)(A) for multiple activities, 

thereby eliminating the opportunity to 

derive the resource and streamlining 

benefits outlined above. Also, 

application of the small numbers 

standard across the total annual taking 

covered by an incidental take 

regulation, inasmuch as prospective 

applicants can see that the total annual 

take may exceed one-third of species or 

stock abundance, would create an 

incentive for applicants to pursue 

individual IHAs (again, precluding the 

ability to gain the benefits outlined 

above). 

Our conclusion is that NMFS can 

appropriately elect to make a ‘‘small 

numbers’’ finding based on the 

estimated annual take in individual 

LOAs issued under the rule. This 

approach does not affect the negligible 

impact analysis for a rule, which is the 

biologically relevant inquiry and based 

on the total annual estimated taking for 

all activities the regulations will govern. 

Making the small numbers finding 

based on the estimated annual take in 

individual LOAs allows NMFS to take 

advantage of the associated 

administrative and environmental 

benefits of utilizing section 101(a)(5)(A) 

that would be precluded in many cases 

if small numbers were required to be 

applied to the total annual taking under 

the regulations. NMFS finds this 

method of making a small numbers 

determination to be a permissible 

interpretation of the relevant MMPA 

provisions. 

Although this application of small 

numbers may be argued as being less 

protective of marine mammals, NMFS 

disagrees. As noted previously, the 

small numbers standard has less 

biological significance as compared to 

the substantive and contextuallyspecific analysis necessary to support 

the negligible impact determination. 

The negligible impact determination is 

still controlling, and the maximum total 

annual taking that may be authorized 

across all LOAs under an incidental take 

regulation still could not exceed the 

overall amount analyzed for the 

negligible impact determination. Thus, 

under this option, the negligible impact 

analysis for the rulemaking still would 

have to be conducted for the time period 

explicitly specified in the statute (i.e., 

up to five years), but the small numbers 

analysis would attach to the instrument 

itself that authorizes the taking, i.e., the 

LOA. 

How will small numbers be evaluated 

under this GOM rule? 

In this rule, up-to-date species 

information is available, and 

sophisticated models have been used to 

estimate take in a manner that will 

allow for quantitative comparison of the 

take of individuals versus the best 

available abundance estimates for the 

species or stocks. Specifically, while the 

modeling effort utilized in the rule 

enumerates the estimated instances of 

takes that will occur across days as the 

result of the operation of certain survey 

types in certain areas, the modeling 

report also includes the evaluation of a 

test scenario that allows for a reasonable 

modification of those generalized take 

estimates to better estimate the number 

of individuals that will be taken within 

one survey. LOA applicants using 

modeling results from the rule to inform 

their applications will be able to 

reasonably estimate the number of 

marine mammal individuals taken by 

their activities. LOA applications that 

do not use the modeling provided in the 

rule to estimate take for their activities 

will need to be reviewed, and applicants 

will be required to ensure that their 

estimates adequately inform the small 

numbers finding. If applicants use the 

modeling provided by this rule to 

estimate take, additional review will not 

be deemed necessary (unless other 

conditions necessitating review exist, as 

described in the Letters of Authorization 

section). If applicants do not use the 

modeling provided by the rule, 

however, NMFS may publish a notice in 

the Federal Register soliciting public 

comment, if the model or inputs differ 

substantively from those that have been 

reviewed by NMFS and the public 

previously, if the model or inputs differ 

substantively from those that have been 

reviewed by NMFS and the public 

previously. The estimated take of 

marine mammals for each species will 

then be compared against the best 

available scientific information on 

species or stock abundance estimate as 

determined by NMFS, and estimates 

that do not exceed one-third of that 

estimate will be considered small 

numbers. 

Adaptive Management 

The regulations governing the take of 

marine mammals incidental to 

geophysical survey activities contain an 

adaptive management component. The 

comprehensive reporting requirements 

associated with this rule (see the 

Monitoring and Reporting section) are 

designed to provide NMFS with 

monitoring data from the previous year 

to allow consideration of whether any 

changes are appropriate. The use of 

adaptive management allows NMFS to 

consider new information from different 

sources to determine (with input from 

the LOA-holders regarding 

practicability) on a regular (e.g., annual 

or biennial) basis if mitigation or 

monitoring measures should be 

modified (including additions or 

deletions). Mitigation measures could be 

modified if new data suggests that such 

modifications would have a reasonable 

likelihood of reducing adverse effects to 

marine mammal species or stocks or 

their habitat and if the measures are 

practicable. The adaptive management 

process and associated reporting 

requirements would serve as the basis 

for evaluating performance and 

compliance. 

The following are some of the 

possible sources of applicable data to be 

considered through the adaptive 

management process: (1) Results from 

monitoring reports, as required by 

MMPA authorizations; (2) results from 

general marine mammal and sound 

research; and (3) any information which 

reveals that marine mammals may have 

been taken in a manner, extent, or 

number not authorized through these 

regulations and subsequent LOAs or 

that the specified activity may be having 

more than a negligible impact on 

affected stocks. 

Under this rule, NMFS plans to 

implement an annual adaptive 

management process including BOEM, 

BSEE, industry operators (including 

geophysical companies as well as 

exploration and production companies), 

and others as appropriate. Industry 

operators may elect to be represented in 

this process by their respective trade 

associations. NMFS, BOEM, and BSEE 

(i.e., the regulatory agencies) and 

industry operators who have conducted 

or contracted for survey operations in 

the GOM in the prior year (or their 

representatives) will provide an agreedupon description of roles and 

responsibilities, as well as points of 

contact, in advance of each year’s 


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adaptive management process. The 

foundation of the adaptive management 

process will be the annual 

comprehensive reports produced by 

LOA-holders (or their representatives), 

as well as the results of any relevant 

research activities, including research 

supported voluntarily by the oil and gas 

industry and research supported by the 

Federal government. Please see the 

Monitoring Contribution Through Other 

Research section in the notice of 

proposed rulemaking for a description 

of representative past research efforts. 

The outcome of the annual adaptive 

management process would be an 

assessment of effects to marine mammal 

populations in the GOM relative to 

NMFS’ determinations under the 

MMPA and ESA, recommendations 

related to mitigation, monitoring, and 

reporting, and recommendations for 

future research (whether supported by 

industry or the regulatory agencies). 

Data collection and reporting by 

individual LOA-holders will occur on 

an ongoing basis, per the terms of issued 

LOAs. In a given annual cycle, the 

comprehensive annual report will 

summarize and synthesize all LOAspecific reports received, with report 

development (supported through 

collaboration of individual LOA-holders 

or by their representatives) occurring for 

90 days following the end of a given 

one-year period. Review and revision of 

the report, followed by a joint meeting 

of the parties, will occur within 90 days 

following receipt of the annual report. 

Any agreed-upon modifications will 

occur through the process for 

modifications and/or adaptive 

management described in the regulatory 

text following this preamble. 

Monitoring Contribution Through Other 

Research 

NMFS’ MMPA implementing 

regulations require that applicants for 

incidental take authorizations describe 

the suggested means of coordinating 

research opportunities, plans, and 

activities relating to reducing incidental 

taking and evaluating its effects (50 CFR 

216.104(a)(14)). Such coordination can 

serve as an effective supplement to the 

monitoring and reporting required 

pursuant to issued LOAs and/or 

incidental take regulations. NMFS 

expects that relevant research efforts 

will inform the annual adaptive 

management process described above, 

and that levels and types of research 

efforts will change from year to year in 

response to identified needs and 

evolutions in knowledge, emerging 

trends in the economy and available 

funding, and available scientific and 

technological resources. In the notice of 

proposed rulemaking, NMFS described 

examples of relevant research efforts (83 

FR 29300–29301). We do not repeat that 

information here, but refer the reader to 

that notice for more information. The 

described efforts may not be predictive 

of any future levels and types of 

research efforts. Research occurring in 

locations other than the GOM may be 

relevant to understanding the effects of 

geophysical surveys on marine 

mammals or marine mammal 

populations or the effectiveness of 

mitigation. NMFS also refers the reader 

to the industry Joint Industry Program 

(JIP) website 

(www.soundandmarinelife.org), which 

hosts a database of available products 

funded partially or fully through the JIP, 

and to BOEM’s Environmental Studies 

Program (ESP), which develops, funds, 

and manages scientific research to 

inform policy decisions regarding outer 

continental shelf resource development 

(www.boem.gov/studies). 

Impact on Availability of Affected 

Species for Taking for Subsistence Uses 

There are no relevant subsistence uses 

of marine mammals implicated by these 

actions. Therefore, NMFS has 

determined that the total taking of 

affected species or stocks will not have 

an unmitigable adverse impact on the 

availability of such species or stocks for 

taking for subsistence purposes. 

Endangered Species Act (ESA) 

Section 7 of the ESA requires Federal 

agencies to insure that their actions are 

not likely to jeopardize the continued 

existence of endangered or threatened 

species or adversely modify or destroy 

their designated critical habitat. Federal 

agencies must consult with NMFS for 

actions that may affect such species 

under NMFS’ jurisdiction or critical 

habitat designated for such species. 

At the conclusion of consultation, the 

consulting agency provides an opinion 

stating whether the Federal agency’s 

action is likely to jeopardize the 

continued existence of ESA-listed 

species or destroy or adversely modify 

designated critical habitat. 

NMFS’s issuance of this final rule, 

and any subsequent LOAs, is subject to 

the requirements of Section 7 of the 

ESA. Therefore, NMFS’ Office of 

Protected Resources (OPR), Permits and 

Conservation Division requested 

initiation of a formal consultation with 

the NMFS OPR, ESA Interagency 

Cooperation Division on the proposed 

issuance of the rule and subsequent 

LOAs on July 19, 2018. The formal 

consultation concluded and a final 

Biological Opinion (BiOp) was issued 

on March 13, 2020. The BiOp concluded 

that the Permits and Conservation 

Division’s proposed action is not likely 

to jeopardize the continued existence of 

sperm whales or the GOM Bryde’s 

whale. 

National Environmental Policy Act 

In 2017, BOEM produced a final 

Programmatic Environmental Impact 

Statement (PEIS) to evaluate the direct, 

indirect, and cumulative impacts of 

geological and geophysical survey 

activities on the GOM OCS, pursuant to 

requirements of NEPA. These activities 

include geophysical surveys in support 

of hydrocarbon exploration, as are 

described in the MMPA petition before 

NMFS. The PEIS is available online at: 

www.boem.gov/Gulf-of-MexicoGeological-and-Geophysical-ActivitiesProgrammatic-EIS/. NOAA, through 

NMFS, participated in preparation of 

the PEIS as a cooperating agency due to 

its legal jurisdiction and special 

expertise in conservation and 

management of marine mammals, 

including its responsibility to authorize 

incidental take of marine mammals 

under the MMPA. 

NEPA, Council on Environmental 

Quality (CEQ) regulations, and NOAA’s 

NEPA implementing procedures (NOAA 

Administrative Order (NAO) 216–6A) 

encourage the use of programmatic 

NEPA documents to streamline 

decision-making. NMFS reviewed the 

Final PEIS and determined that it meets 

the requirements of the CEQ regulations 

(40 CFR part 1500–1508) and NAO 216– 

6A. NMFS further determined, after 

independent review, that the Final PEIS 

satisfied NMFS’ comments and 

suggestions in the NEPA process. In the 

notice of proposed rulemaking, NMFS 

stated its intention to adopt BOEM’s 

analysis in order to assess the impacts 

to the human environment of issuance 

of the subject ITR, and that we would 

review all comments submitted in 

response to the notice as we completed 

the NEPA process, including a final 

decision of whether to adopt BOEM’s 

PEIS and sign a Record of Decision 

related to issuance of the ITR and 

subsequent LOAs. Following review of 

public comments received, NMFS 

confirmed that it would be appropriate 

to adopt BOEM’s analysis in order to 

support assessment of the impacts to the 

human environment of issuance of the 

subject ITR and subsequent LOAs. 

Therefore NMFS prepared a Record of 

Decision for the following purposes: (1) 

To adopt the Final PEIS to support 

NMFS’ analysis associated with 

issuance of incidental take 

authorizations pursuant to section 

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

regulations governing the taking and 


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importing of marine mammals (50 CFR 

part 216); and (2) in accordance with 40 

CFR 1505.2, to announce and explain 

the basis for NMFS’ decision to review 

and potentially issue incidental take 

authorizations under the MMPA on a 

case-by-case basis, if appropriate. 

Letters of Authorization 

Under these incidental take 

regulations, industry operators may 

apply for and obtain LOAs, as described 

in NMFS’ MMPA implementing 

regulations (50 CFR 216.106). LOAs may 

be issued for any time period that does 

not exceed the effective duration of the 

final rule, provided the description of 

the activity in the request includes a 

sufficient degree of specificity with 

which to evaluate whether the activity 

falls within the scope of the rule. 

Because the specified activity described 

herein does not provide actual specifics 

of the timing, location, and survey 

design for activities that would be the 

subject of issued LOAs, such requests 

must include, at minimum, the 

information described at 50 CFR 

216.104(a)(1) and (2), and should 

include an affirmation of intent to 

adhere to the mitigation, monitoring, 

and reporting requirements described in 

the regulations. The level of effort 

proposed by an operator would be used 

to develop an LOA-specific take 

estimate based on the results of Zeddies 

et al. (2015, 2017a). 

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 

(Zeddies et al., 2015, 2017a) would be 

published for public comment prior to 

the issuance of an LOA. However, upon 

further consideration of the ‘‘Gulf of 

Mexico Acoustic Exposure Model 

Variable Analysis’’ (Zeddies et al., 

2017b; ‘‘Acoustic Exposure Model 

Variable Analysis’’) provided by IAGC 

and API to NMFS prior to the 

publication of the proposed rule and 

made available to the public with the 

proposed rule and the Associations’ 

public comments, which extensively 

referenced the Acoustic Exposure Model 

Variable Analysis, the final rule more 

flexibly provides that if applicants do 

not use the modeling provided by the 

rule, NMFS may publish a notice in the 

Federal Register soliciting public 

comment, if the model or inputs differ 

substantively from those that have been 

reviewed by NMFS and the public 

previously. Specifically, the Acoustic 

Exposure Model Variable Analysis 

includes the results (i.e., take estimates) 

of a supplemental analysis of the same 

modeling effort used in Zeddies et al. 

(2015, 2017a) to support the proposed 

rule, but evaluating the effects on the 

modeling results of different variables. 

One analyzed variable of particular 

utility was the use of a smaller airgun 

array that could serve as a reasonable 

representative for some of the smaller 

arrays that are commonly used in the 

GOM. This specific applicable example, 

in which the model and inputs of this 

Acoustic Exposure Model Variable 

Analysis have been reviewed by NMFS 

and the public previously (both in that 

they mirror Zeddies et al. (2015, 2017a) 

and in that NMFS also explicitly made 

the Acoustic Exposure Model Variable 

Analysis available to the public during 

the comment period), illustrates the 

need to provide flexibility and make 

efficient use of previous public and 

agency review. NMFS has, therefore, 

determined it appropriate to allow that 

additional public review is not needed 

unless the model or inputs differ 

substantively from those that have been 

reviewed by NMFS and the public 

previously. Further, we explicitly note 

the utility of the modeling and results 

presented in the Acoustic Exposure 

Model Variable Analysis report for 

representing smaller airgun arrays that 

are commonly used in the GOM and 

affirm that further public comment on 

that report should not be necessary prior 

to the use of its results to support the 

issuance of LOAs. 

Technologies continue to evolve to 

meet the technical, environmental, and 

economic challenges of oil and gas 

development. The use of ‘‘new and 

unusual technologies’’ (NUT), i.e., 

technologies other than those described 

herein, will be evaluated on a case-bycase basis and may require public 

review. Some seemingly new 

technologies proposed for use by 

operators are often extended 

applications of existing technologies 

and interface with the environment in 

essentially the same way as well-known 

or conventional technologies. For such 

evaluations, NMFS will follow the 

existing process used by BOEM, by 

using the following considerations: 

• Has the technology or hardware 

been used previously or extensively in 

the U.S. GOM under operating 

conditions similar to those anticipated 

for the activities proposed by the 

operator? If so, the technology would 

not be considered a NUT; 

• Does the technology function in a 

manner that potentially causes different 

impacts to the environment than similar 

equipment or procedures did in the 

past? If so, the technology would be 

considered a NUT; 

• Does the technology have a 

significantly different interface with the 

environment than similar equipment or 

procedures did in the past? If so, the 

technology would be considered a NUT; 

and 

• Does the technology include 

operating characteristics that are outside 

established performance parameters? If 

so, the technology would be considered 

a NUT. 

NMFS will consult with BOEM as 

well as with NMFS’ ESA Interagency 

Cooperation Division regarding the level 

of review necessary for issuance of an 

LOA in which a NUT is proposed for 

use. 

Classification 

Pursuant to the procedures 

established to implement Executive 

Order 12866, the Office of Management 

and Budget (OMB) has determined that 

this rule is economically significant. 

Accordingly, a regulatory impact 

analysis (RIA) was prepared and made 

available for review by the public. 

Following review of public comments, a 

final RIA has been prepared and is 

available online at: 

www.fisheries.noaa.gov/action/ 

incidental-take-authorization-oil-andgas-industry-geophysical-surveyactivity-gulf-mexico. Appendix B of the 

RIA provides a final regulatory 

flexibility analysis (FRFA, discussed 

below), while Appendix C addresses 

other compliance requirements. 

The RIA evaluates the potential costs 

and benefits of these incidental take 

regulations against two baselines, a 

baseline corresponding with regulatory 

conditions in place since 2013 pursuant 

to a settlement agreement, as amended 

through stipulated agreement, involving 

a stay of litigation (NRDC et al. v. 

Bernhardt et al., Civil Action No. 2:10 

cv–01882 (E.D. La.)), and a baseline 

corresponding to conditions prior to the 

2013 settlement agreement. Under the 

settlement agreement that is in effect, 

industry trade groups representing 

operators agreed to include certain 

mitigation requirements for geophysical 

surveys in the GOM. 

OMB Circular A–4 provides that 

agencies may present multiple baselines 

where this would provide additional 

useful information to the public on the 

projected effects of the regulation. 

NMFS presented both baselines for 

public information and comment, 

consistent with the Circular A–4 

provision allowing agencies to present 

multiple baselines. No information or 

comments regarding the economic 

baselines were received. 

These regulations require new 

mitigation measures relative to the 

settlement baseline and, thus, new costs 

for survey operators. However, the rule 


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also alleviates the burden of 

implementing minimum separation 

distance requirements for deep 

penetration airgun surveys, as required 

under the settlement agreement. The 

rule also results in certain indirect (but 

non-monetized) costs. However, the RIA 

analysis demonstrates that these costs 

are not likely to be significant. 

Moreover, as described in the RIA, total 

costs related to compliance for survey 

activities are small compared with 

expenditures on other aspects of oil and 

gas industry operations, and direct 

compliance costs of the regulatory 

requirements are unlikely to result in 

materially reduced oil and gas activities 

in the GOM. 

The rule also results in certain nonmonetized benefits. The protection of 

marine mammals afforded by this rule 

(pursuant to the requirements of the 

MMPA) benefits the regional economic 

value of marine mammals via tourism 

and recreation to some extent, as 

mitigation measures applied to 

geophysical survey activities in the 

GOM region are expected to benefit the 

marine mammal populations that 

support this economic activity in the 

GOM. In addition, some degree of 

benefits can be expected to accrue solely 

via ecological benefits to marine 

mammals and other wildlife as a result 

of the regulatory requirements. The 

published literature (described in the 

RIA) is clear that healthy populations of 

marine mammals and other co-existing 

species benefit regional economies and 

provide social welfare benefits to 

people. However, the literature does not 

provide a basis for quantitatively 

valuing the cost of anticipated 

incremental changes in environmental 

disturbance and marine mammal 

harassment associated with the rule. 

Notably, the rule also affords 

significant benefit to the regulated 

industry by providing regulatory 

certainty through an efficient framework 

within which to achieve compliance 

with the MMPA. In particular, cost 

savings may be generated by the 

reduced administrative effort required 

to obtain an LOA under the framework 

established by a rule compared to what 

would be required to obtain an 

incidental harassment authorization 

(IHA) under section 101(a)(5)(D). Absent 

the rule, to attain equivalent compliance 

with the MMPA, survey operators in the 

GOM would need to apply for an IHA. 

Although not monetized in the RIA, 

NMFS’ analysis indicates that the 

upfront work associated with the rule 

(e.g., analyses, modeling, process for 

obtaining LOA) likely saves significant 

time and money for operators. A 

conservative cost savings calculation, 

based on estimates of the costs for IHA 

applications relative to LOA application 

costs and an assumption of the number 

of likely authorizations based on total 

annual survey days and survey 

estimates included in the RIA, ranges 

from $500,000 to $1.5 million annually. 

In terms of timing, NMFS recommends 

that IHA applicants contact the agency 

six to nine months in advance of the 

planned activity, whereas NMFS 

anticipates a timeframe of three months 

or less (depending upon the content of 

the request and the activities covered) 

for LOA applications under this rule. 

Details regarding cost estimation are 

available in the RIA. A qualitative 

evaluation of indirect costs related to 

the regulations is also provided in the 

RIA. Note that these costs would be 

diffused across all operators receiving 

LOAs. 

NMFS prepared a FRFA, as required 

by Section 603 of the Regulatory 

Flexibility Act (RFA), for this rule. The 

FRFA describes the economic effects 

this rule will have on small entities. A 

description of this action, why it is 

being considered, the objectives of the 

action, and the legal basis for the action 

are contained in the preamble of this 

rule. A copy of the full analysis is 

available as an appendix to the RIA. The 

MMPA provides the statutory basis for 

this rule. No duplicative, overlapping, 

or conflicting Federal rules have been 

identified. A detailed summary of the 

initial regulatory flexibility analysis was 

provided at the proposed rule stage. No 

comments or information regarding this 

analysis were received. 

This final rule is expected to directly 

regulate businesses that conduct 

geophysical surveys in the GOM with 

the potential to incidentally take marine 

mammals. Some of these businesses 

may be defined as small entities. The 

FRFA is summarized below. 

The FRFA focuses on identifying 

small businesses that would bear the 

incremental survey costs associated 

with the rule. These may include 

entities undertaking, commissioning, or 

purchasing surveys. In order to estimate 

the number of small entities to which 

the rule will apply, permit applications 

between 2006 and 2015 were analyzed 

to understand what industries were 

involved in permit applications for 

geophysical surveys in the Gulf of 

Mexico and to identify U.S.-based 

permit applicants that would be 

classified as small according to Small 

Business Administration definitions and 

the most recent revenue or employment 

data available. In total, 34 U.S.-based 

small businesses applied for 

geophysical survey permits in the Gulf 

of Mexico between 2006 and 2015. By 

assuming that the same proportion of 

international, large, and small 

companies will undertake the surveys 

over the next five years as occurred 

during 2006 to 2015, the likely number 

of future surveys that will include small 

entity applicants may be estimated. 

Accordingly, NMFS estimates that small 

entities would apply for approximately 

32 to 53 surveys over the next five years, 

or approximately six to 11 surveys 

annually. Historically, there was a ratio 

of approximately 2.2 surveys applied for 

per small entity. Using this ratio, NMFS 

estimates that approximately 15 to 24 

small companies will likely apply for 

permits over the next five years, or 

approximately 3 to 5 small companies 

each year. The future distribution of 

small survey companies by industry is 

not known, but the historical pattern of 

surveys suggests that companies 

involved in oil and gas extraction 

(NAICS 2111) and support activities for 

oil and gas (213112) will account for the 

majority of the survey applications by 

small companies. 

A review of the reported annual 

revenues for the 34 small entities that 

applied for survey permits between 

2006 and 2015 reveals a wide range, 

with the lowest revenues reported to be 

$0.04 million and the highest revenues 

reported to be $1.9 billion. Average 

revenues for the small entities who 

applied for permits were $232 million, 

with median revenues of $12.26 million. 

We note, however, that the revenues 

and numbers of employees reported for 

many of these small companies 

appeared to be erroneous, in multiple 

instances reporting annual revenues 

significantly less than the costs of 

conducting even the lowest cost 

surveys. As a result, these revenue 

estimates are likely to be inaccurate or, 

alternatively, permit applicants must 

pass survey costs on to the companies 

that purchase or commission the 

seismic data. Given that the oil and gas 

extraction companies are generally the 

entities purchasing the survey data, we 

expect that it is most likely that survey 

costs are ultimately borne by NAICS 

2111 (oil and gas extraction), either as 

the permittees for the survey permit or 

because the other, smaller businesses 

pass these costs along in the data 

purchase price. 

In summary, the FRFA finds the 

following: First, in the majority of cases 

(88 percent), survey permit applicants 

are large businesses. Second, when the 

permit applicants are small businesses, 

the majority of the time (63 percent) 

they are oil and gas extractors (NAICS 

2111). Third, together, these permits (for 

large businesses and small businesses 

with high annual revenues for which 


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rule costs are a small fraction) account 

for 96 percent of the survey permits. 

Fourth, while small entities in other 

industries occasionally apply for 

permits (four percent historically), these 

businesses are quite small, with average 

annual revenues in the millions or even 

less. Given their size, it is unlikely that 

these permit applicants bear survey 

costs; otherwise it would be reflected in 

their annual revenues (i.e., their 

revenues on average would reflect that 

they recover their costs). Accordingly, 

NMFS expects it is most likely that 

survey costs are passed on to oil and gas 

extraction companies who commission 

the surveys or purchase the data. And 

fifth, overall, up to five small businesses 

(NAICS 2111) per year may experience 

increased costs of between 0.1 and 0.7 

percent of average annual revenues. 

The draft version of the RIA and the 

Initial Regulatory Flexibility Analysis 

considered effects of a more stringent 

alternative than the proposed rule. The 

more stringent alternative included 

additional shutdown requirements and 

area closures for surveys, generating 

costs up to 20 percent greater than the 

proposed rule. NMFS did not elect to 

proceed with these elements of the more 

stringent alternative in the final rule, 

which reduces the potential for impacts 

to small businesses. NMFS determined 

that the final rule achieves the statutory 

objectives with a lower regulatory 

burden. As described above, a relatively 

small portion of total survey activities 

are undertaken by small entities and the 

FRFA determines that it is unlikely that 

small entities will bear the compliance 

costs described in the RIA. 

This final rule revises the information 

collection request (ICR) requirement 

associated with OMB Control Number 

0648–0151 to allow for the expected 

increase in applicants/respondents due 

to this final action. This revision is 

subject to review and approval by OMB 

under the Paperwork Reduction Act 

(PRA) and has been submitted to OMB. 

NMFS published a 30-day Federal 

Register notice (85 FR 60765; September 

28, 2020) that provided for an additional 

comment period. Details on the new 

information collection requirements can 

be found in the RIA Appendix C.2. 

NMFS anticipates that 95 to 151 

geophysical surveys will take place 

annually on average over the five years 

of the regulations in the GOM that 

would be subject to potential 

information collection requirements. 

Due to this final rule, NMFS estimates 

at least 95 new LOA applications 

annually. Because the existing OMB 

Control Number 0648–0151 expires less 

than a year (June 30, 2021) after this 

final rule publishes, there will be less 

than a year for respondents to carry out 

work under these regulations before this 

OMB Control Number expires. Thus, 

NMFS estimates no more than onequarter of respondents (24) will 

complete work to the point of 

developing an annual report prior to 

when 0648–0151 must be renewed. 

We invite the general public and other 

Federal agencies to comment on 

proposed and continuing information 

collections, which helps us assess the 

impact of our information collection 

requirements and minimize the public’s 

reporting burden. Written comments 

and recommendations for this 

information collection should be 

submitted at the following website: 

www.reginfo.gov/public/do/PRAMain. 

Find this particular information 

collection by using the search function 

and entering either the title of the 

collection or the OMB Control Number 

0648–0151. 

Notwithstanding any other provision 

of the law, no person is required to 

respond to, nor shall any person be 

subject to a penalty for failure to comply 

with, a collection of information subject 

to the requirements of the PRA, unless 

that collection of information displays a 

currently valid OMB Control Number. 

List of Subjects in 50 CFR Part 217 

Exports, Fish, Imports, Indians, 

Labeling, Marine mammals, Penalties, 

Reporting and recordkeeping 

requirements, Seafood, Transportation. 

Dated: December 7, 2020. 

Samuel D. Rauch III, 

Deputy Assistant Administrator for 

Regulatory Programs, National Marine 

Fisheries Service. 

For reasons set forth in the preamble, 

50 CFR part 217 is amended as follows: 

PART 217—REGULATIONS 

GOVERNING THE TAKING AND 

IMPORTING OF MARINE MAMMALS 

■ 1. The authority citation for part 217 

continues to read as follows: 

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

■ 2. Add Subpart S, consisting of 

§§ 217.180 through 217.189, to read as 

follows: 

Subpart S—Taking Marine Mammals 

Incidental to Geophysical Survey Activities 

in the Gulf of Mexico 

Sec. 

217.180 Specified activity and specified 

geographical region. 

217.181 Effective dates. 

217.182 Permissible methods of taking. 

217.183 Prohibitions. 

217.184 Mitigation requirements. 

217.185 Requirements for monitoring and 

reporting. 

217.186 Letters of Authorization. 

217.187 Renewals and modifications of 

Letters of Authorization. 

217.188 [Reserved] 

217.189 [Reserved] 

Subpart S—Taking Marine Mammals 

Incidental to Geophysical Survey 

Activities in the Gulf of Mexico 

§ 217.180 Specified activity and specified 

geographical region. 

(a) Regulations in this subpart apply 

only to oil and gas industry operators 

(LOA-holders), and those persons 

authorized to conduct activities on their 

behalf, for the taking of marine 

mammals that occurs in the area 

outlined in paragraph (b) of this section 

and that occurs incidental to 

geophysical survey activities. 

(b) The taking of marine mammals by 

oil and gas industry operators may be 

authorized in a Letter of Authorization 

(LOA) only if it occurs within U.S. 

waters in the Gulf of Mexico, outside 

the area subject to a Congressional 

leasing moratorium under the Gulf of 

Mexico Energy Security Act (GOMESA) 

(Pub L. 109–432, § 104) as of the 

effective date of these regulations. 

§ 217.181 Effective dates. 

Regulations in this subpart are 

effective from April 19, 2021 through 

April 19, 2026. 

§ 217.182 Permissible methods of taking. 

Under LOAs issued pursuant to 

§§ 216.106 of this chapter and 217.186, 

LOA-holders may incidentally, but not 

intentionally, take marine mammals 

within the area described in 

§ 217.180(b) by Level A and Level B 

harassment associated with geophysical 

survey activities, provided the activity 

is in compliance with all terms, 

conditions, and requirements of the 

regulations in this subpart and the 

appropriate LOA. 

§ 217.183 Prohibitions. 

Notwithstanding takings 

contemplated in §§ 217.180 and 

217.182, and authorized by a LOA 

issued under §§ 216.106 of this chapter 

and 217.186, no person in connection 

with the activities described in 

§ 217.180 may: 

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

terms, conditions, and requirements of 

this subpart or a LOA issued under 

§§ 216.106 of this chapter and 217.186; 

(b) Take any marine mammal not 

specified in such LOAs; 

(c) Take any marine mammal 

specified in such LOAs in any manner 

other than as specified; or 

(d) Take a marine mammal specified 

in such LOAs if NMFS determines such 


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taking results in more than a negligible 

impact on the species or stocks of such 

marine mammal. 

§ 217.184 Mitigation requirements. 

When conducting the activities 

identified in § 217.180, the mitigation 

measures contained in any LOA issued 

under §§ 216.106 of this chapter and 

217.186 must be implemented. These 

mitigation measures shall include but 

are not limited to: 

(a) General conditions. (1) A copy of 

any issued LOA must be in the 

possession of the LOA-holder, vessel 

operator, other relevant personnel, the 

lead protected species observer (PSO), 

and any other relevant designees 

operating under the authority of the 

LOA. 

(2) The LOA-holder must instruct 

relevant vessel personnel with regard to 

the authority of the protected species 

monitoring team (PSO team), and must 

ensure that relevant vessel personnel 

and PSO team participate in a joint 

onboard briefing, led by the vessel 

operator and lead PSO, prior to 

beginning work to ensure that 

responsibilities, communication 

procedures, protected species 

monitoring protocols, operational 

procedures, and LOA requirements are 

clearly understood. This briefing must 

be repeated when relevant new 

personnel join the survey operations 

before work involving those personnel 

commences. 

(3) The acoustic source must be 

deactivated when not acquiring data or 

preparing to acquire data, except as 

necessary for testing. Unnecessary use 

of the acoustic source must be avoided. 

For surveys using airgun arrays as the 

acoustic source, notified operational 

capacity (i.e., total array volume) (not 

including redundant backup airguns) 

must not be exceeded during the survey, 

except where unavoidable for source 

testing and calibration purposes. All 

occasions where activated source 

volume exceeds notified operational 

capacity must be communicated to the 

PSO(s) on duty and fully documented. 

The lead PSO must be granted access to 

relevant instrumentation documenting 

acoustic source power and/or 

operational volume. 

(4) PSOs must be used as specified in 

this paragraph (a)(4). 

(i) LOA-holders must use 

independent, dedicated, qualified PSOs, 

meaning that the PSOs must be 

employed by a third-party observer 

provider, must have no tasks other than 

to conduct observational effort, collect 

data, and communicate with and 

instruct relevant vessel crew with regard 

to the presence of protected species and 

mitigation requirements (including brief 

alerts regarding maritime hazards), and 

must be qualified pursuant to 

§ 217.185(a) (except as specified at 

§ 217.184(d)(2)(iii–iv)). Acoustic PSOs 

are required to complete specialized 

training for operating passive acoustic 

monitoring (PAM) systems and are 

encouraged to have familiarity with the 

vessel on which they will be working. 

PSOs may act as both acoustic and 

visual observers (but not 

simultaneously), so long as they 

demonstrate that their training and 

experience are sufficient to perform 

each task. 

(ii) The LOA-holder must submit PSO 

resumes for NMFS review and approval 

prior to commencement of the survey 

(except as specified at 

§ 217.184(d)(2)(iii)). Resumes should 

include dates of training and any prior 

NMFS approval, as well as dates and 

description of last experience, and must 

be accompanied by information 

documenting successful completion of 

an acceptable training course. NMFS is 

allowed one week to approve PSOs from 

the time that the necessary information 

is received by NMFS, after which PSOs 

meeting the minimum requirements will 

automatically be considered approved. 

(iii) At least one visual PSO and two 

acoustic PSOs (when required) aboard 

each acoustic source vessel must have a 

minimum of 90 days at-sea experience 

working in those roles, respectively, 

with no more than eighteen months 

elapsed since the conclusion of the atsea experience (except as specified at 

§ 217.184(d)(2)(iii)). One visual PSO 

with such experience must be 

designated as the lead for the entire PSO 

team. The lead must coordinate duty 

schedules and roles for the PSO team 

and serve as the primary point of 

contact for the vessel operator. (Note 

that the responsibility of coordinating 

duty schedules and roles may instead be 

assigned to a shore-based, third-party 

monitoring coordinator.) To the 

maximum extent practicable, the lead 

PSO must devise the duty schedule 

such that experienced PSOs are on duty 

with those PSOs with appropriate 

training but who have not yet gained 

relevant experience. 

(b) Deep penetration surveys. (1) Deep 

penetration surveys are defined as 

surveys using airgun arrays with total 

volume greater than 1,500 in3. 

(2) Visual monitoring must be 

conducted as specified in this paragraph 

(b)(2). 

(i) During survey operations (i.e., any 

day on which use of the acoustic source 

is planned to occur, and whenever the 

acoustic source is in the water, whether 

activated or not), a minimum of two 

PSOs must be on duty and conducting 

visual observations at all times during 

daylight hours (i.e., from 30 minutes 

prior to sunrise through 30 minutes 

following sunset). 

(ii) Visual monitoring must begin not 

less than 30 minutes prior to ramp-up 

and must continue until one hour after 

use of the acoustic source ceases or until 

30 minutes past sunset. 

(iii) Visual PSOs must coordinate to 

ensure 360° visual coverage around the 

vessel from the most appropriate 

observation posts, and must conduct 

visual observations using binoculars 

and the naked eye while free from 

distractions and in a consistent, 

systematic, and diligent manner. 

(iv) Visual PSOs must immediately 

communicate all observations of marine 

mammals to the on-duty acoustic PSO, 

including any determination by the PSO 

regarding species identification, 

distance, and bearing and the degree of 

confidence in the determination. 

(v) Any observations of marine 

mammals by crew members aboard any 

vessel associated with the survey must 

be relayed to the PSO team. 

(vi) During good conditions (e.g., 

daylight hours; Beaufort sea state (BSS) 

3 or less), visual PSOs must conduct 

observations when the acoustic source 

is not operating for comparison of 

sighting rates and behavior with and 

without use of the acoustic source and 

between acquisition periods, to the 

maximum extent practicable. 

(vii) Visual PSOs may be on watch for 

a maximum of two consecutive hours 

followed by a break of at least one hour 

between watches and may conduct a 

maximum of 12 hours of observation per 

24-hour period. NMFS may grant an 

exception for LOA applications that 

demonstrate such a ‘‘two hours on/one 

hour off’’ duty cycle is not practicable, 

in which case visual PSOs will be 

subject to a maximum of four 

consecutive hours on watch followed by 

a break of at least two hours between 

watches. Combined observational duties 

(visual and acoustic but not at the same 

time) must not exceed 12 hours per 24- 

hour period for any individual PSO. 

(3) Acoustic monitoring must be 

conducted as specified in this paragraph 

(b)(3). 

(i) All source vessels must use a 

towed PAM system at all times when 

operating in waters deeper than 100 m, 

which must be monitored by a 

minimum of one acoustic PSO 

beginning at least 30 minutes prior to 

ramp-up, at all times during use of the 

acoustic source, and until one hour after 

use of the acoustic source ceases. ‘‘PAM 

system’’ refers to calibrated hydrophone 

arrays with full system redundancy to 


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detect, identify, and estimate distance 

and bearing to vocalizing cetaceans, 

coupled with appropriate software to 

aid monitoring and listening by a PAM 

operator skilled in bioacoustics analysis 

and computer system specifications 

capable of running appropriate software. 

The PAM system must have at least one 

calibrated hydrophone (per each 

deployed hydrophone type and/or set) 

sufficient for determining whether 

background noise levels on the towed 

PAM system are sufficiently low to meet 

performance expectations. Applicants 

must provide a PAM plan including 

description of the hardware and 

software proposed for use prior to 

proceeding with any survey where PAM 

is required. 

(ii) Acoustic PSOs must immediately 

communicate all detections of marine 

mammals to visual PSOs (when visual 

PSOs are on duty), including any 

determination by the PSO regarding 

species identification, distance, and 

bearing, and the degree of confidence in 

the determination. 

(iii) Acoustic PSOs may be on watch 

for a maximum of four consecutive 

hours followed by a break of at least two 

hours between watches, and may 

conduct a maximum of 12 hours of 

observation per 24-hour period. 

Combined observational duties (visual 

and acoustic but not at the same time) 

must not exceed 12 hours per 24-hour 

period for any individual PSO. 

(iv) Survey activity may continue for 

30 minutes when the PAM system 

malfunctions or is damaged, while the 

PAM operator diagnoses the issue. If the 

diagnosis indicates that the PAM system 

must be repaired to solve the problem, 

operations may continue for an 

additional two hours without acoustic 

monitoring during daylight hours only 

under the following conditions: 

(A) Sea state is less than or equal to 

BSS 4; 

(B) No marine mammals (excluding 

delphinids) detected solely by PAM in 

the applicable exclusion zone in the 

previous two hours; 

(C) NMFS is notified via email as soon 

as practicable with the time and 

location in which operations began 

occurring without an active PAM 

system; and 

(D) Operations with an active acoustic 

source, but without an operating PAM 

system, do not exceed a cumulative total 

of four hours in any 24-hour period. 

(4) PSOs must establish and monitor 

applicable exclusion and buffer zones. 

These zones must be based upon the 

radial distance from the edges of the 

airgun array (rather than being based on 

the center of the array or around the 

vessel itself). During use of the acoustic 

source (i.e., anytime the acoustic source 

is active, including ramp-up), 

occurrence of marine mammals within 

the relevant buffer zone (but outside the 

exclusion zone) should be 

communicated to the operator to 

prepare for the potential shutdown of 

the acoustic source. 

(i) Two exclusion zones are defined, 

depending on the species and context. 

A standard exclusion zone 

encompassing the area at and below the 

sea surface out to a radius of 500 meters 

from the edges of the airgun array (0– 

500 m) is defined. For special 

circumstances (defined at 

§ 217.184(b)(9)(v)), the exclusion zone 

encompasses an extended distance of 

1,500 meters (0–1,500 m). 

(ii) During pre-start clearance 

monitoring (i.e., before ramp-up begins), 

the buffer zone acts as an extension of 

the exclusion zone in that observations 

of marine mammals within the buffer 

zone would also preclude airgun 

operations from beginning (i.e., rampup). For all marine mammals (except 

where superseded by the extended 

1,500-m exclusion zone), the buffer zone 

encompasses the area at and below the 

sea surface from the edge of the 0–500 

meter exclusion zone out to a radius of 

1,000 meters from the edges of the 

airgun array (500–1,000 m). The buffer 

zone is not applicable when the 

exclusion zone is greater than 500 

meters, i.e., the observational focal zone 

is not increased beyond 1,500 meters. 

(5) A ramp-up procedure, involving a 

step-wise increase in the number of 

airguns firing and total active array 

volume until all operational airguns are 

activated and the full volume is 

achieved, is required at all times as part 

of the activation of the acoustic source. 

A 30-minute pre-start clearance 

observation period must occur prior to 

the start of ramp-up. The LOA-holder 

must adhere to the following pre-start 

clearance and ramp-up requirements: 

(i) The operator must notify a 

designated PSO of the planned start of 

ramp-up as agreed upon with the lead 

PSO; the notification time should not be 

less than 60 minutes prior to the 

planned ramp-up. 

(ii) Ramp-ups must be scheduled so as 

to minimize the time spent with source 

activated prior to reaching the 

designated run-in. 

(iii) A designated PSO must be 

notified again immediately prior to 

initiating ramp-up procedures and the 

operator must receive confirmation from 

the PSO to proceed. 

(iv) Ramp-up must not be initiated if 

any marine mammal is within the 

applicable exclusion or buffer zone. If a 

marine mammal is observed within the 

exclusion zone or the buffer zone during 

the 30-minute pre-start clearance 

period, ramp-up must not begin until 

the animal(s) has been observed exiting 

the zones or until an additional time 

period has elapsed with no further 

sightings (15 minutes for small 

delphinids and 30 minutes for all other 

species). 

(v) Ramp-up must begin by activating 

a single airgun of the smallest volume 

in the array and shall continue in stages 

by doubling the number of active 

elements at the commencement of each 

stage, with each stage of approximately 

the same duration. Total duration must 

not be less than 20 minutes. The 

operator must provide information to 

the PSO documenting that appropriate 

procedures were followed. 

(vi) Ramp-up must cease and the 

source shut down upon observation of 

marine mammals within the applicable 

exclusion zone. Once ramp-up has 

begun, observations of marine mammals 

within the buffer zone do not require 

shutdown. 

(vii) Ramp-up may occur at times of 

poor visibility, including nighttime, if 

appropriate acoustic monitoring has 

occurred with no detections of a marine 

mammal other than delphinids in the 30 

minutes prior to beginning ramp-up. 

Acoustic source activation may only 

occur at night where operational 

planning cannot reasonably avoid such 

circumstances. 

(viii) If the acoustic source is shut 

down for brief periods (i.e., less than 30 

minutes) for reasons other than 

implementation of prescribed mitigation 

(e.g., mechanical difficulty), it may be 

activated again without ramp-up if PSOs 

have maintained constant visual and/or 

acoustic observation and no visual or 

acoustic detections of any marine 

mammal have occurred within the 

applicable exclusion zone. For any 

longer shutdown, pre-start clearance 

observation and ramp-up are required. 

For any shutdown at night or in periods 

of poor visibility (e.g., BSS 4 or greater), 

ramp-up is required, but if the 

shutdown period was brief and constant 

observation maintained, pre-start 

clearance watch is not required. 

(ix) Testing of the acoustic source 

involving all elements requires rampup. Testing limited to individual source 

elements or strings does not require 

ramp-up but does require the pre-start 

clearance observation period. 

(6) Shutdowns must be implemented 

as specified in this paragraph (b)(6). 

(i) Any PSO on duty has the authority 

to delay the start of survey operations or 

to call for shutdown of the acoustic 

source pursuant to the requirements of 

this subpart. 


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(ii) The operator must establish and 

maintain clear lines of communication 

directly between PSOs on duty and 

crew controlling the acoustic source to 

ensure that shutdown commands are 

conveyed swiftly while allowing PSOs 

to maintain watch. 

(iii) When both visual and acoustic 

PSOs are on duty, all detections must be 

immediately communicated to the 

remainder of the on-duty PSO team for 

potential verification of visual 

observations by the acoustic PSO or of 

acoustic detections by visual PSOs. 

(iv) When the airgun array is active 

(i.e., anytime one or more airguns is 

active, including during ramp-up) and 

(1) a marine mammal appears within or 

enters the applicable exclusion zone 

and/or (2) a marine mammal (excluding 

delphinids) is detected acoustically and 

localized within the applicable 

exclusion zone, the acoustic source 

must be shut down. When shutdown is 

called for by a PSO, the acoustic source 

must be immediately deactivated and 

any dispute resolved only following 

deactivation. 

(v) The extended 1,500-m exclusion 

zone must be applied upon detection 

(visual or acoustic) of a baleen whale, 

sperm whale, beaked whale, or Kogia 

spp. within the zone. 

(vi) Shutdown requirements are 

waived for dolphins of the following 

genera: Tursiops, Stenella, Steno, and 

Lagenodelphis. If a delphinid is visually 

detected within the exclusion zone, no 

shutdown is required unless the PSO 

confirms the individual to be of a genus 

other than those listed above, in which 

case a shutdown is required. Acoustic 

detection of delphinids does not require 

shutdown. 

(vii) If there is uncertainty regarding 

identification or localization, PSOs may 

use best professional judgment in 

making the decision to call for a 

shutdown. 

(viii) Upon implementation of 

shutdown, the source may be 

reactivated after the marine mammal(s) 

has been observed exiting the applicable 

exclusion zone or following a 30-minute 

clearance period with no further 

detection of the marine mammal(s). 

(c) Shallow penetration surveys. (1) 

Shallow penetration surveys are defined 

as surveys using airgun arrays with total 

volume equal to or less than 1,500 in3, 

single airguns, boomers, or equivalent 

sources. 

(2) LOA-holders conducting shallow 

penetration surveys must follow the 

requirements defined for deep 

penetration surveys at § 217.184(b), with 

the following exceptions: 

(i) Acoustic monitoring is not 

required for shallow penetration 

surveys. 

(ii) Ramp-up for small airgun arrays 

must follow the procedure described 

above for large airgun arrays, but may 

occur over an abbreviated period of 

time. Ramp-up is not required for 

surveys using only a single airgun. For 

non-airgun sources, power should be 

increased as feasible to effect a ramp-up. 

(iii) Two exclusion zones are defined, 

depending on the species and context. 

A standard exclusion zone 

encompassing the area at and below the 

sea surface out to a radius of 100 meters 

from the edges of the airgun array (if 

used) or from the acoustic source (0–100 

m) is defined. For special circumstances 

(§ 217.184(b)(6)(v)), the exclusion zone 

encompasses an extended distance of 

500 meters (0–500 m). 

(iv) The buffer zone encompasses the 

area at and below the sea surface from 

the edge of the 0–100 meter exclusion 

zone out to a radius of 200 meters from 

the edges of the airgun array (if used) or 

from the acoustic source (100–200 

meters). The buffer zone is not 

applicable when the exclusion zone is 

greater than 100 meters. 

(d) High-resolution geophysical (HRG) 

surveys. (1) HRG surveys are defined as 

surveys using an electromechanical 

source that operates at frequencies less 

than 180 kHz, other than those defined 

at § 217.184(c)(1) (e.g., side-scan sonar, 

multibeam echosounder, or chirp subbottom profiler). 

(2) LOA-holders conducting HRG 

surveys must follow the requirements 

defined for shallow penetration surveys 

at § 217.184(c), with the following 

exceptions: 

(i) No shutdowns are required for 

HRG surveys. Pre-start clearance watch 

is required as defined at § 217.184(c), 

i.e., for a period of 30 minutes and over 

a 200-m radius from the acoustic source. 

(ii) During survey operations (e.g., any 

day on which use of the acoustic source 

is planned to occur, and whenever the 

acoustic source is in the water, whether 

activated or not), a minimum of one 

trained and experienced independent 

PSO must be on duty and conducting 

visual observations at all times during 

daylight hours (i.e., from 30 minutes 

prior to sunrise through 30 minutes 

following sunset) when operating in 

waters deeper than 100 m. 

(iii) When operating in waters 

shallower than 100 m, LOA-holders 

must employ one trained visual PSO, 

who may be a crew member, only for 

purposes of conducting pre-start 

clearance monitoring. If PSOs are crew 

members, i.e., are not independent 

PSOs, the PSOs are not subject to 

NMFS’ approval. In these 

circumstances, LOA requests must 

describe the training that will be 

provided to crew members filling the 

role of PSO. 

(iv) PSOs are not required during 

survey operations in which the active 

acoustic source(s) are deployed on an 

autonomous underwater vehicle. 

(e) Time-area closure. From January 1 

through May 31, no use of airguns may 

occur shoreward of the 20-m isobath 

and between 90–84° W. 

(f) Entanglement avoidance. To avoid 

the risk of entanglement, LOA-holders 

conducting surveys using ocean-bottom 

nodes or similar gear must: 

(1) Use negatively buoyant coated 

wire-core tether cable; 

(2) Retrieve all lines immediately 

following completion of the survey; and 

(3) Attach acoustic pingers directly to 

the coated tether cable; acoustic releases 

should not be used. 

(g) Vessel strike avoidance. LOAholders must adhere to the following 

requirements: 

(1) Vessel operators and crews must 

maintain a vigilant watch for all marine 

mammals and must slow down, stop 

their vessel, or alter course, as 

appropriate and regardless of vessel 

size, to avoid striking any marine 

mammal. A visual observer aboard the 

vessel must monitor a vessel strike 

avoidance zone around the vessel, 

which shall be defined according to the 

parameters stated in this subsection. 

Visual observers monitoring the vessel 

strike avoidance zone may be thirdparty observers (i.e., PSOs) or crew 

members, but crew members 

responsible for these duties must be 

provided sufficient training to 

distinguish marine mammals from other 

phenomena and broadly to identify a 

marine mammal as a baleen whale, 

sperm whale, or other marine mammal; 

(2) Vessel speeds must be reduced to 

10 kn or less when mother/calf pairs, 

pods, or large assemblages of marine 

mammals are observed near a vessel; 

(3) All vessels must maintain a 

minimum separation distance of 500 m 

from baleen whales; 

(4) All vessels must maintain a 

minimum separation distance of 100 m 

from sperm whales; 

(5) All vessels must, to the maximum 

extent practicable, attempt to maintain a 

minimum separation distance of 50 m 

from all other marine mammals, with an 

exception made for those animals that 

approach the vessel; and 

(6) When marine mammals are 

sighted while a vessel is underway, the 

vessel must take action as necessary to 

avoid violating the relevant separation 

distance, e.g., attempt to remain parallel 


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to the animal’s course, avoid excessive 

speed or abrupt changes in direction 

until the animal has left the area. If 

marine mammals are sighted within the 

relevant separation distance, the vessel 

must reduce speed and shift the engine 

to neutral, not engaging the engines 

until animals are clear of the area. This 

does not apply to any vessel towing gear 

or any vessel that is navigationally 

constrained. 

(7) These requirements do not apply 

in any case where compliance would 

create an imminent and serious threat to 

a person or vessel or to the extent that 

a vessel is restricted in its ability to 

maneuver and, because of the 

restriction, cannot comply. 

§ 217.185 Requirements for monitoring 

and reporting. 

(a) PSO qualifications. (1) PSOs must 

successfully complete relevant, 

acceptable training, including 

completion of all required coursework 

and passing (80 percent or greater) a 

written and/or oral examination 

developed for the training program. 

(2) PSOs must have successfully 

attained a bachelor’s degree from an 

accredited college or university with a 

major in one of the natural sciences, a 

minimum of 30 semester hours or 

equivalent in the biological sciences, 

and at least one undergraduate course in 

math or statistics. The educational 

requirements may be waived if the PSO 

has acquired the relevant skills through 

alternate experience. Requests for such 

a waiver must be submitted to NMFS 

and shall include written justification. 

Requests will be granted or denied (with 

justification) by NMFS within one week 

of receipt of submitted information. 

Alternate experience that may be 

considered includes, but is not limited 

to: 

(i) Secondary education and/or 

experience comparable to PSO duties; 

(ii) Previous work experience 

conducting academic, commercial, or 

government-sponsored marine mammal 

surveys; or 

(iii) Previous work experience as a 

PSO; the PSO should demonstrate good 

standing and consistently good 

performance of PSO duties. 

(b) Equipment. LOA-holders are 

required to: 

(i) Provide PSOs with bigeye 

binoculars (e.g., 25 x 150; 2.7 view 

angle; individual ocular focus; height 

control) of appropriate quality solely for 

PSO use. These must be pedestalmounted on the deck at the most 

appropriate vantage point that provides 

for optimal sea surface observation, PSO 

safety, and safe operation of the vessel. 

(ii) For each vessel required to use a 

PAM system, provide a PAM system 

that has been verified and tested by an 

experienced acoustic PSO who will be 

using it during the trip for which 

monitoring is required; 

(iii) Work with the selected thirdparty observer provider to ensure PSOs 

have all equipment (including backup 

equipment) needed to adequately 

perform necessary tasks, including 

accurate determination of distance and 

bearing to observed marine mammals. 

(Equipment specified in A. through G. 

below may be provided by an individual 

PSO, the third-party observer provider, 

or the LOA-holder, but the LOA-holder 

is responsible for ensuring PSOs have 

the proper equipment required to 

perform the duties specified herein.) 

Such equipment, at a minimum, must 

include: 

(A) Reticle binoculars (e.g., 7 x 50) of 

appropriate quality (at least one per 

PSO, plus backups); 

(B) Global Positioning Unit (GPS) 

(plus backup); 

(C) Digital camera with a telephoto 

lens (the camera or lens should also 

have an image stabilization system) that 

is at least 300 mm or equivalent on a 

full-frame single lens reflex (SLR) (plus 

backup); 

(D) Compass (plus backup); 

(E) Radios for communication among 

vessel crew and PSOs (at least one per 

PSO, plus backups); and 

(F) Any other tools necessary to 

adequately perform necessary PSO 

tasks. 

(c) Data collection. PSOs must use 

standardized electronic data forms. 

PSOs must record detailed information 

about any implementation of mitigation 

requirements, including the distance of 

marine mammals to the acoustic source 

and description of specific actions that 

ensued, the behavior of the animal(s), 

any observed changes in behavior before 

and after implementation of mitigation, 

and if shutdown was implemented, the 

length of time before any subsequent 

ramp-up or activation of the acoustic 

source. If required mitigation was not 

implemented, PSOs must record a 

description of the circumstances. At a 

minimum, the following information 

should be recorded: 

(1) Vessel names (source vessel and 

other vessels associated with survey), 

vessel size and type, maximum speed 

capability of vessel, port of origin, and 

call signs; 

(2) PSO names and affiliations; 

(3) Dates of departures and returns to 

port with port name; 

(4) Dates of and participants in PSO 

briefings; 

(5) Dates and times (Greenwich Mean 

Time) of survey effort and times 

corresponding with PSO effort; 

(6) Vessel location (latitude/ 

longitude) when survey effort began and 

ended and vessel location at beginning 

and end of visual PSO duty shifts; 

(7) Vessel location at 30-second 

intervals (if software capability allows) 

or 5-minute intervals (if location must 

be manually recorded); 

(8) Vessel heading and speed at 

beginning and end of visual PSO duty 

shifts and upon any line change; 

(9) Environmental conditions while 

on visual survey (at beginning and end 

of PSO shift and whenever conditions 

changed significantly), including 

Beaufort sea state and any other relevant 

weather conditions including cloud 

cover, fog, sun glare, and overall 

visibility to the horizon; 

(10) Vessel location when 

environmental conditions change 

significantly; 

(11) Factors that may have 

contributed to impaired observations 

during each PSO shift change or as 

needed as environmental conditions 

change (e.g., vessel traffic, equipment 

malfunctions); 

(12) Survey activity information, such 

as acoustic source power output while 

in operation, number and volume of 

airguns operating in an array, tow depth 

of an acoustic source, and any other 

notes of significance (i.e., pre-start 

clearance, ramp-up, shutdown, testing, 

shooting, ramp-up completion, end of 

operations, streamers, etc.); and 

(13) Upon visual observation of a 

marine mammal, the following 

information: 

(i) Watch status (sighting made by 

PSO on/off effort, opportunistic, crew, 

alternate vessel/platform); 

(ii) PSO who sighted the animal and 

PSO location (including height above 

water) at time of sighting; 

(iii) Time of sighting; 

(iv) Vessel coordinates at time of 

sighting; 

(v) Water depth; 

(vi) Direction of vessel’s travel 

(compass direction); 

(vii) Speed of the vessel(s) from which 

the observation was made; 

(viii) Direction of animal’s travel 

relative to the vessel; 

(ix) Pace of the animal; 

(x) Estimated distance to the animal 

(and method of estimating distance) and 

its heading relative to vessel at initial 

sighting; 

(xi) Identification of the animal (e.g., 

genus/species, lowest possible 

taxonomic level, or unidentified), PSO 

confidence in identification, and the 

composition of the group if there is a 

mix of species; 


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(xii) Estimated number of animals 

(high/low/best); 

(xiii) Estimated number of animals by 

cohort (adults, juveniles, group 

composition, etc.); 

(xiv) Description (as many 

distinguishing features as possible of 

each individual seen, including length, 

shape, color, pattern, scars or markings, 

shape and size of dorsal fin, shape of 

head, and blow characteristics); 

(xv) Detailed behavior observations 

(e.g., number of blows/breaths, number 

of surfaces, breaching, spyhopping, 

diving, feeding, traveling; as explicit 

and detailed as possible; note any 

observed changes in behavior), 

including an assessment of behavioral 

responses to survey activity; 

(xvi) Animal’s closest point of 

approach (CPA) and/or closest distance 

from any element of the acoustic source; 

(xvii) Platform activity at time of 

sighting (e.g., deploying, recovering, 

testing, shooting, data acquisition, 

other); and 

(xviii) Description of any actions 

implemented in response to the sighting 

(e.g., delays, shutdown, ramp-up) and 

time and location of the action. 

(12) Upon acoustic detection of a 

marine mammal using a PAM system, 

the following information: 

(i) An acoustic encounter 

identification number, and whether the 

detection was linked with a visual 

sighting; 

(ii) Date and time when first and last 

heard; 

(iii) Types and nature of sounds heard 

(e.g., clicks, whistles, creaks, burst 

pulses, continuous, sporadic, strength of 

signal); and 

(iv) Any additional information 

recorded such as water depth of the 

hydrophone array, bearing of the animal 

to the vessel (if determinable), species 

or taxonomic group (if determinable), 

spectrogram screenshot, and any other 

notable information. 

(d) Reporting. (1) Annual reporting 

must be submitted as specified in this 

paragraph. 

(i) LOA-holders must submit a 

summary report to NMFS on all 

activities and monitoring results within 

90 days of the completion of the survey 

or expiration of the LOA, whichever 

comes sooner, and must include all 

information described above under 

§ 217.185(c). If an issued LOA is valid 

for greater than one year, the summary 

report must be submitted on an annual 

basis. 

(ii) The report must describe activities 

conducted and sightings of marine 

mammals, must provide full 

documentation of methods, results, and 

interpretation pertaining to all 

monitoring, and must summarize the 

dates and locations of survey operations 

and all marine mammal sightings (dates, 

times, locations, activities, associated 

survey activities, and information 

regarding locations where the acoustic 

source was used). In addition to the 

report, all raw observational data must 

be made available to NMFS. 

(iii) For operations requiring the use 

of PAM, the report must include a 

validation document concerning the use 

of PAM, which should include 

necessary noise validation diagrams and 

demonstrate whether background noise 

levels on the PAM deployment limited 

achievement of the planned detection 

goals. Copies of any vessel self-noise 

assessment reports must be included 

with the report. 

(iv) The LOA-holder must provide 

geo-referenced time-stamped vessel 

tracklines for all time periods in which 

airguns (full array or single) were 

operating. Tracklines must include 

points recording any change in airgun 

status (e.g., when the airguns began 

operating, when they were turned off). 

GIS files must be provided in ESRI 

shapefile format and include the UTC 

date and time, latitude in decimal 

degrees, and longitude in decimal 

degrees. All coordinates must be 

referenced to the WGS84 geographic 

coordinate system. 

(v) The draft report must be 

accompanied by a certification from the 

lead PSO as to the accuracy of the 

report, and the lead PSO may submit 

directly to NMFS a statement 

concerning implementation and 

effectiveness of the required mitigation 

and monitoring. 

(vi) A final report must be submitted 

within 30 days following resolution of 

any comments on the draft report. 

(2) Comprehensive reporting must be 

submitted as specified in this paragraph. 

LOA-holders must contribute to the 

compilation and analysis of data for 

inclusion in an annual synthesis report 

addressing all data collected and 

reported through annual reporting in 

each calendar year. The synthesis 

period shall include all annual reports 

deemed to be final by NMFS in a given 

one-year reporting period. The report 

must be submitted to NMFS within 90 

days following the end of a given oneyear reporting period. 

(e) Reporting of injured or dead 

marine mammals. (1) In the event that 

personnel involved in the survey 

activities discover an injured or dead 

marine mammal, the LOA-holder must 

report the incident to the Office of 

Protected Resources (OPR), NMFS and 

to the Southeast Regional Stranding 

Network as soon as feasible. The report 

must include the following information: 

(i) Time, date, and location (latitude/ 

longitude) of the first discovery (and 

updated location information if known 

and applicable); 

(ii) Species identification (if known) 

or description of the animal(s) involved; 

(iii) Condition of the animal(s) 

(including carcass condition if the 

animal is dead); 

(iv) Observed behaviors of the 

animal(s), if alive; 

(v) If available, photographs or video 

footage of the animal(s); and 

(vi) General circumstances under 

which the animal was discovered. 

(2) In the event of a ship strike of a 

marine mammal by any vessel involved 

in the survey activities, the LOA-holder 

must report the incident to OPR, NMFS 

and to the Southeast Regional Stranding 

Network as soon as feasible. The report 

must include the following information: 

(i) Time, date, and location (latitude/ 

longitude) of the incident; 

(ii) Species identification (if known) 

or description of the animal(s) involved; 

(iii) Vessel’s speed during and leading 

up to the incident; 

(iv) Vessel’s course/heading and what 

operations were being conducted (if 

applicable); 

(v) Status of all sound sources in use; 

(vi) Description of avoidance 

measures/requirements that were in 

place at the time of the strike and what 

additional measures were taken, if any, 

to avoid strike; 

(vii) Environmental conditions (e.g., 

wind speed and direction, Beaufort sea 

state, cloud cover, visibility) 

immediately preceding the strike; 

(viii) Estimated size and length of 

animal that was struck; 

(ix) Description of the behavior of the 

marine mammal immediately preceding 

and following the strike; 

(x) If available, description of the 

presence and behavior of any other 

marine mammals immediately 

preceding the strike; 

(xi) Estimated fate of the animal (e.g., 

dead, injured but alive, injured and 

moving, blood or tissue observed in the 

water, status unknown, disappeared); 

and 

(xii) To the extent practicable, 

photographs or video footage of the 

animal(s). 

(3) For deep penetration surveys, in 

the event of a live stranding (or nearshore atypical milling) event within 50 

km of the survey operations, where the 

NMFS stranding network is engaged in 

herding or other interventions to return 

animals to the water, the Director of 

OPR, NMFS (or designee) will advise 

the LOA-holder of the need to 


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implement shutdown procedures for all 

active acoustic sources operating within 

50 km of the stranding. Shutdown 

procedures for live stranding or milling 

marine mammals include the following: 

(i) If at any time, the marine 

mammal(s) die or are euthanized, or if 

herding/intervention efforts are stopped, 

the Director of OPR, NMFS (or designee) 

will advise the LOA-holder that the 

shutdown around the animals’ location 

is no longer needed. 

(ii) Otherwise, shutdown procedures 

will remain in effect until the Director 

of OPR, NMFS (or designee) determines 

and advises the LOA-holder that all live 

animals involved have left the area 

(either of their own volition or following 

an intervention). 

(iii) If further observations of the 

marine mammals indicate the potential 

for re-stranding, additional coordination 

with the LOA-holder will be required to 

determine what measures are necessary 

to minimize that likelihood (e.g., 

extending the shutdown or moving 

operations farther away) and to 

implement those measures as 

appropriate. 

(4) If NMFS determines that the 

circumstances of any marine mammal 

stranding found in the vicinity of the 

activity suggest investigation of the 

association with survey activities is 

warranted, and an investigation into the 

stranding is being pursued, NMFS will 

submit a written request to the LOAholder indicating that the following 

initial available information must be 

provided as soon as possible, but no 

later than 7 business days after the 

request for information. In the event that 

the investigation is still inconclusive, 

the investigation of the association of 

the survey activities is still warranted, 

and the investigation is still being 

pursued, NMFS may provide additional 

information requests, in writing, 

regarding the nature and location of 

survey operations prior to the time 

period above. 

(i) Status of all sound source use in 

the 48 hours preceding the estimated 

time of stranding and within 50 km of 

the discovery/notification of the 

stranding by NMFS; and 

(ii) If available, description of the 

behavior of any marine mammal(s) 

observed preceding (i.e., within 48 

hours and 50 km) and immediately after 

the discovery of the stranding. 

§ 217.186 Letters of Authorization. 

(a) To incidentally take marine 

mammals pursuant to these regulations, 

prospective LOA-holders must apply for 

and obtain an LOA. 

(b) An LOA, unless suspended or 

revoked, may be effective for a period 

not to exceed the expiration date of 

these regulations. 

(c) In the event of projected changes 

to the activity or to mitigation and 

monitoring measures required by an 

LOA, the LOA-holder must apply for 

and obtain a modification of the LOA as 

described in § 217.187. 

(d) The LOA shall set forth: 

(1) Permissible methods of incidental 

taking; 

(2) Means of effecting the least 

practicable adverse impact (i.e., 

mitigation) on the species or stock and 

its habitat; and 

(3) Requirements for monitoring and 

reporting. 

(e) Issuance of the LOA shall be based 

on a determination that the level of 

taking will be consistent with the 

findings made for the total taking 

allowable under these regulations and a 

determination that the amount of take 

authorized under the LOA is of no more 

than small numbers. 

(f) For LOA issuance, where either (1) 

the conclusions put forth in an 

application (e.g., take estimates) are 

based on analytical methods that differ 

substantively from those used in the 

development of the rule, or (2) the 

proposed activity or anticipated impacts 

vary substantively in scope or nature 

from those analyzed for the rule, NMFS 

may publish a notice of proposed LOA 

in the Federal Register, including the 

associated analysis of the differences, 

and solicit public comment before 

making a decision regarding issuance of 

the LOA. 

(g) Notice of issuance or denial of an 

LOA shall be published in the Federal 

Register within thirty days of a 

determination. 

§ 217.187 Renewals and modifications of 

Letters of Authorization (LOA). 

(a) An LOA issued under § 216.106 of 

this chapter and § 217.186 for the 

activity identified in § 217.180 shall be 

modified upon request by the applicant, 

provided that: 

(1) The proposed specified activity 

and mitigation, monitoring, and 

reporting measures, as well as the 

anticipated impacts, are the same as 

those described and analyzed for these 

regulations (excluding changes made 

pursuant to the adaptive management 

provision in paragraph (c)(1) of this 

section); and 

(2) NMFS determines that the 

mitigation, monitoring, and reporting 

measures required by the previous LOA 

under these regulations were 

implemented. 

(b) For LOA modification requests by 

the applicant that include changes to 

the activity or the mitigation, 

monitoring, or reporting (excluding 

changes made pursuant to the adaptive 

management provision in paragraph 

(c)(1) of this section) that result in more 

than a minor change in the total 

estimated number of takes (or 

distribution by species or years), NMFS 

may publish a notice of proposed LOA 

in the Federal Register, including the 

associated analysis of the change, and 

solicit public comment before issuing 

the LOA. 

(c) An LOA issued under § 216.106 of 

this chapter and § 217.186 for the 

activity identified in § 217.180 may be 

modified by NMFS under the following 

circumstances: 

(1) NMFS may modify (including 

adding or removing measures) the 

existing mitigation, monitoring, or 

reporting measures (after consulting 

with the LOA-holder regarding the 

practicability of the modifications) if 

doing so is practicable and creates a 

reasonable likelihood of more 

effectively accomplishing the goals of 

the mitigation and monitoring set forth 

in the preamble for these regulations; 

(i) Possible sources of data that could 

contribute to the decision to modify the 

mitigation, monitoring, or reporting 

measures in an LOA: 

(A) Results from monitoring from 

previous years; 

(B) Results from other marine 

mammal and/or sound research or 

studies; and 

(C) Any information that reveals 

marine mammals may have been taken 

in a manner, extent or number not 

authorized by these regulations or 

subsequent LOAs. 

(ii) If, through adaptive management, 

the modifications to the mitigation, 

monitoring, or reporting measures are 

substantial, NMFS will publish a notice 

of proposed LOA in the Federal 

Register and solicit public comment. 

(2) If NMFS determines that an 

emergency exists that poses a significant 

risk to the well-being of the species or 

stocks of marine mammals specified in 

an LOA issued pursuant to § 216.106 of 

this chapter and § 217.186, an LOA may 

be modified without prior notice or 

opportunity for public comment. Notice 

would be published in the Federal 

Register within thirty days of the action. 

§§ 217.188–217.189 [Reserved] 

[FR Doc. 2020–27252 Filed 1–15–21; 8:45 am] 

BILLING CODE 3510–22–P 


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