29212 Federal Register / Vol. 83, No. 121 / Friday, June 22, 2018 / Proposed Rules 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric 

Administration 

50 CFR Part 217 

[Docket No. 110811494–7925–01] 

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: Proposed rule; request for 

comments. 

SUMMARY: NMFS has received a petition 

for an incidental take regulation (ITR) 

from the Bureau of Ocean Energy 

Management (BOEM). The requested 

ITR would govern the authorization of 

take of small numbers of marine 

mammals over the course of five years 

incidental to geophysical survey 

activities conducted by industry 

operators in Federal waters of the U.S. 

Gulf of Mexico (GOM). BOEM submitted 

the petition in support of oil and gas 

industry operators, who would conduct 

the activities. A final ITR would allow 

for the issuance of Letters of 

Authorization (LOA) to the 

aforementioned industry operators over 

a five-year period. As required by the 

Marine Mammal Protection Act 

(MMPA), NMFS requests comments on 

its proposed rule, including the 

following; the proposed regulations, 

several alternatives to the proposed 

regulations described in the ‘‘Proposed 

Mitigation’’ and ‘‘Alternatives for 

Consideration’’ sections of the 

preamble, two baselines against which 

to evaluate the incremental economic 

impacts of the proposed regulations 

(addressed in the ‘‘Economic Baseline’’ 

section), and, two sections with broader 

implications: A clarification of NMFS’s 

interpretation and application of the 

‘‘small numbers’’ standard (see the 

‘‘Small Numbers’’ section of the 

preamble); and an alternative method 

for assessing Level B harassment from 

exposure to anthropogenic noise (see 

the ‘‘Estimated Take’’ section of the 

preamble). 

DATES: Comments and information must 

be received no later than August 21, 

2018. 

ADDRESSES: You may submit comments 

on this document, identified by NOAA– 

NMFS–2018–0043, by any of the 

following methods: 

• Electronic submission: Submit all 

electronic public comments via the 

Federal e-Rulemaking Portal. Go to 

www.regulations.gov/ 

#!docketDetail;D=NOAA-NMFS-2018- 

0043, click the ‘‘Comment Now!’’ icon, 

complete the required fields, and enter 

or attach your comments. 

• Mail: Submit written comments to 

Jolie Harrison, Chief, Permits and 

Conservation Division, Office of 

Protected Resources, National Marine 

Fisheries Service, 1315 East West 

Highway, Silver Spring, MD 20910. 

Comments regarding any aspect of the 

collection of information requirement 

contained in this proposed rule should 

be sent to NMFS via one of the means 

provided here and to the Office of 

Information and Regulatory Affairs, 

NEOB–10202, Office of Management 

and Budget, Attn: Desk Officer, 

Washington, DC 20503, OIRA@

omb.eop.gov. 

Instructions: Comments sent by any 

other method, to any other address or 

individual, or received after the end of 

the comment period, may not be 

considered by NMFS. All comments 

received are a part of the public record 

and will generally be posted for public 

viewing on www.regulations.gov 

without change. All personal identifying 

information (e.g., name, address), 

confidential business information, or 

otherwise sensitive information 

submitted voluntarily by the sender will 

be publicly accessible. NMFS will 

accept anonymous comments (enter ‘‘N/ 

A’’ in the required fields if you wish to 

remain anonymous). Attachments to 

electronic comments will be accepted in 

Microsoft Word, Excel, or Adobe PDF 

file formats only. 

FOR FURTHER INFORMATION CONTACT: Ben 

Laws, Office of Protected Resources, 

NMFS, (301) 427–8401. 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/national/ 

marine-mammal-protection/incidentaltake-authorizations-oil-and-gas. In case 

of problems accessing these documents, 

please call the contact listed above. 

SUPPLEMENTARY INFORMATION: 

Purpose and Need for Regulatory 

Action 

This proposed rule would 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 five-year 

regulations. Subsequent LOAs would be 

requested by industry operators. Take 

would 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 Proposed 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 ‘‘Proposed 

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 proposed rule 

containing five-year regulations, and for 

any subsequent LOAs. As directed by 

this legal authority, this proposed rule 

contains mitigation, monitoring, and 

reporting requirements. 

Summary of Major Provisions Within 

the Proposed Rule 

Following is a summary of the major 

provisions of this proposed rule 

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; 

• Time-area restrictions designed to 

avoid effects to certain species of marine 

mammals in times and/or places 

believed to be of greatest importance; 

• Vessel strike avoidance measures; 

and 

• Monitoring and reporting 

requirements. 

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 


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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 

takings shall be granted if NMFS finds 

that the taking will have a negligible 

impact on the species or stock(s), will 

not have an unmitigable adverse impact 

on the availability of the species or 

stock(s) for subsistence uses (where 

relevant), and if the permissible 

methods of taking and requirements 

pertaining to the mitigation, monitoring 

and reporting of such takings are set 

forth. 

NMFS has defined ‘‘negligible 

impact’’ in 50 CFR 216.103 as an impact 

resulting from the specified activity that 

cannot be reasonably expected to, and is 

not reasonably likely to, adversely affect 

the species or stock through effects on 

annual rates of recruitment or survival. 

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). 

National Environmental Policy Act 

To comply with the National 

Environmental Policy Act of 1969 

(NEPA; 42 U.S.C. 4321 et seq.) and 

NOAA Administrative Order (NAO) 

216–6A, NMFS must evaluate the 

proposed action (i.e., the promulgation 

of regulations and subsequent issuance 

of incidental take authorizations) and 

alternatives with respect to potential 

impacts on the human environment. 

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 requirements of NEPA. 

These activities include geophysical 

surveys in support of hydrocarbon 

exploration and development, as are 

described in the petition for ITR before 

NMFS. The PEIS is available online at: 

www.boem.gov/Gulf-of-MexicoGeological-and-Geophysical-ActivitiesProgrammatic-EIS/. NMFS participated 

in development of the PEIS as a 

cooperating agency and believes it is 

appropriate to adopt the analysis in 

order to assess the impacts to the human 

environment of issuance of the subject 

ITR and any subsequent LOAs. 

Information in the petition, BOEM’s 

PEIS, and this document collectively 

provide the environmental information 

related to proposed issuance of this ITR 

for public review and comment. 

Summary of Request 

BOEM was formerly known as the 

Minerals Management Service (MMS) 

and, later, the Bureau of Ocean Energy 

Management, Regulation, and 

Enforcement (BOEMRE). On December 

20, 2002, MMS petitioned NMFS for 

rulemaking under Section 101(a)(5)(A) 

of the MMPA to authorize take of sperm 

whales (Physeter macrocephalus) 

incidental to conducting geophysical 

surveys during hydrocarbon exploration 

and development activities in the GOM. 

On March 3, 2003, NMFS published a 

notice of receipt of MMS’s application 

and requested comments and 

information from the public (68 FR 

9991). MMS subsequently submitted a 

revised petition on September 30, 2004, 

to include a request for incidental take 

authorization of additional species of 

marine mammals. On April 18, 2011, 

BOEMRE submitted a revision to the 

petition, which incorporated updated 

information and analyses. NMFS 

published a notice of receipt of this 

revised petition on June 14, 2011 (76 FR 

34656). In order to incorporate the best 

available information, BOEM submitted 

another revision to the petition on 

March 28, 2016, which was followed on 

October 17, 2016, by a revised version 

that was deemed adequate and complete 

based on NMFS’s implementing 

regulations at 50 CFR 216.104. In the 

interim period, BOEM, with NMFS 

representing NOAA as a cooperating 

agency, prepared a PEIS for the GOM 

OCS Proposed G&G Activities. 

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 discussed in this document, and all 

comments received are available online 

at www.fisheries.noaa.gov/national/ 

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

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 subbottom profiler as 

the acoustic source, and (3) highresolution 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 Western, 

Central, and Eastern GOM OCS 

planning areas. 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. 

This proposed rule would establish a 

framework under the authority of the 

MMPA (16 U.S.C. 1361 et seq.) and 

NMFS’s 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 

requested regulations would be valid 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) are the high-end estimates. 

Actual total amounts of effort by survey 

type and location would not be known 

in advance of receiving LOA requests 

from industry operators. 

Geophysical surveys are conducted to 

obtain information on marine seabed 


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and subsurface geology for a variety of 

reasons, including to: (1) Obtain data for 

hydrocarbon and mineral exploration 

and production; (2) aid in siting of oil 

and gas structures, facilities, and 

pipelines; (3) identify possible seafloor 

or shallow depth geologic hazards; and 

(4) locate potential archaeological 

resources and benthic habitats that 

should be avoided. In addition, 

geophysical survey data inform Federal 

government decisions. For example, 

BOEM uses such data for resource 

estimation and bid evaluation to ensure 

that the government receives a fair 

market value for OCS leases, as well as 

to help to evaluate worst-case discharge 

for potential oil-spill analysis and to 

evaluate sites for potential hazards prior 

to drilling. 

Deep penetration seismic surveys 

using airgun arrays as an acoustic 

source (sound sources are described in 

the ‘‘Detailed Description of Activities’’ 

section) are a primary method of 

obtaining geophysical data used to 

characterize subsurface structure. These 

surveys are designed to illuminate 

deeper subsurface structures and 

formations that may be of economic 

interest as a reservoir for oil and gas 

exploitation. A deep penetration survey 

uses an acoustic source suited to 

provide data on geological formations 

that may be thousands of meters (m) 

beneath the seafloor, as compared with 

a shallow penetration or high resolution 

geophysical (HRG) survey that may be 

intended to evaluate shallow subsurface 

formations or the seafloor itself (e.g., for 

hazards). 

Deep penetration surveys may be 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 

subbottom profiler, while highresolution surveys (which are limited to 

imaging the seafloor itself) may use 

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 the proposed 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 experiences 

approximately 20 to 30 percent of nonoperational 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 proposed survey activities would 

occur off the Gulf of Mexico coast of the 

United States, within BOEM’s Western, 

Central, and Eastern GOM OCS 

planning areas (approximately within 

the U.S. EEZ; Figure 1). U.S. waters of 

the GOM include only the northern 

GOM. 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. 

In addition to general knowledge and 

other citations contained herein, this 

section relies upon the descriptions 

found in Sherman and Hempel (2009), 

Wilkinson et al. (2009), and BOEM 

(2017). 

The GOM is a deep marginal sea—the 

largest semi-enclosed coastal sea of the 

western Atlantic—bordered by Cuba, 

Mexico, and the United States and 

encompassing more than 1.5 million 

square kilometers (km2). The GOM is 

distinctive in physical oceanography 

and freshwater influx, with major, 

persistent currents and a high nutrient 

load. Oceanic water enters from the 

Yucatan Channel and exits through the 

Straits of Florida, creating the Loop 

Current. The Loop Current—the GOM’s 

most dominant oceanographic feature— 

flows clockwise between Cuba and the 

Yucatan Peninsula, Mexico, and 

circulates into the eastern GOM before 

exiting as the Florida Current, where it 

ultimately joins the Gulf Stream in the 

Atlantic. Small-scale, ephemeral 

currents known as eddies form off the 

Loop Current and may enter the western 

GOM. The eastern edge of the Loop 

Current interacts with the shallow shelf 

to create zones of upwelling and 

onshore currents—nutrient-rich events 

promoting high phytoplankton growth 

and supporting high productivity. 

The distribution of plankton in the 

deeper waters of the GOM, especially 

the northern and eastern parts of the 

Gulf, is controlled by the Loop Current 

(Mullin and Fulling, 2004). The 

temporal movement of all organisms, 

including marine mammals and their 

prey, may be affected by upwelling of 

nutrient rich cold water eddies (Davis et 

al., 2002). However, habitat use appears 

to be more directly correlated with static 

features such as water depth, bottom 

gradient, and longitude (Mullin and 

Fulling, 2004). Temporal fluctuation 

near the surface can cause changes in 

diurnal movement patterns in squid, 

which prefer colder water, but does not 

substantially affect cetaceans feeding on 

squid in deeper waters. 


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The northern GOM is characterized as 

semi-tropical, with a seasonal 

temperature regime influenced mainly 

by tropical currents in the summer and 

continental influences during the 

winter. The GOM is topographically 

diverse, with an extensive continental 

shelf (comprising about 30 percent of 

the total area), a steep continental slope, 

and distinctive bathymetric and 

morphologic processes and features. 

These include the Flower Garden Banks, 

which are surface expressions of salt 

domes that host the northernmost coral 

reefs in the U.S. The northern GOM also 

has a small section of the larger abyssal 

plain of the greater GOM. The GOM has 

about 60 percent of U.S. tidal marshes, 

hosting significant nursery habitat for 

fish and other marine species. A major 

climatological feature is tropical storm 

activity, including hurricanes. Sea 

surface temperature ranges from 14–24 

°C in the winter and 28–30 °C in the 

summer. The area is considered to be of 

moderately high productivity (referring 

to fixated carbon (i.e., g C/m2/yr), which 

relates to the carrying capacity of an 

ecosystem). 

Muddy clay-silts and muddy sands 

dominate bottom substrates of the 

region offshore Texas and Louisiana, 

transitioning to sand, gravel, and shell 

from Alabama to Florida. The shelf off 

Florida is a carbonate limestone 

substrate overlain with sand and silt, 

supporting extensive seagrass beds, and 

interspersed with gravel-rock and coral 

reefs. The continental shelf in the 

western GOM is broadest (up to 135 

miles) off Houston, Texas, and east to 

offshore the Atchafalaya Delta, 

Louisiana. It reaches its narrowest point 

(approximately 12 miles) near the 

mouth of the Mississippi River 

southeast of New Orleans, Louisiana. 

The continental shelf is narrow offshore 

Mobile Bay, Alabama, but broadens 

significantly offshore Florida to almost 

200 miles wide. 

Topography of the continental slope 

off the Florida panhandle is relatively 

smooth and featureless aside from the 

De Soto Canyon, whereas the slope off 

western Florida is distinguished by 

steep gradients and irregular 

topography. In the central and western 

GOM, the continental slope is 

characterized by canyons, troughs, minibasins, and salt structures (e.g., small 

diapiric domes) with higher relief than 

surrounding areas. The Sigsbee 

Escarpment defines the southern limit 

of the Texas-Louisiana slope and was 

formed by a large system of salt ridges 

that underlie the region. In addition to 

De Soto Canyon off the coast of Florida, 

the northern GOM contains four 

significant canyons on or near the 

Texas-Louisiana continental slope: 

Mississippi Canyon, located southwest 

of the Mississippi River Delta; Alaminos 

Canyon, located on the western end of 

the Sigsbee Escarpment; Keathley 

Canyon, also located on the western end 

of the Sigsbee Escarpment; and Rio 

Perdido Canyon, located between the 

Texas-Louisiana continental slope and 

the East Mexico continental slope. 

The GOM is strongly influenced by 

freshwater input from several rivers, 

most importantly the Mississippi River 

and its tributary, the Atchafalaya River. 

The Mississippi River and its tributaries 

drain a large portion of the continental 

United States and carry large amounts of 

freshwater into the GOM along with 

sediment and a variety of nutrients and 

pollutants. The highest volume of 


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freshwater from the Mississippi River 

flows into the GOM from May through 

November, when large volumes of 

turbid water become entrained in a 

westward-flowing longshore current. 

The delivery and deposition of 

increased loads of terrestrial organic 

material, including significant industrial 

and agricultural discharge, have often 

resulted in severe oxygen depletions in 

bottom waters and the appearance of a 

so-called ‘‘dead zone,’’ where large 

numbers of benthic fauna die. This is 

the largest zone of coastal hypoxia in 

the western hemisphere. 

Wetlands in the GOM have 

experienced severe loss and 

degradation, due in part to interference 

with normal erosional/depositional 

processes, sea level rise, and coastal 

subsidence. Wetlands are converted to 

open water when accretion is 

insufficient to compensate for natural 

subsidence, while large areas of 

wetlands have been drained for 

industrial, urban, and agricultural 

development. Increasing salinity due to 

saltwater intrusion accompanies these 

changes, which further exacerbates the 

loss of coastal flora. This loss of 

wetlands ultimately increases erosion 

due to waves and tides, with the whole 

issue exacerbated by sea level rise. 

The northern GOM hosts a vigorous 

complex of offshore hydrocarbon 

exploration, extraction, shipping, 

service, construction, and refining 

industries, resulting in additional 

impacts to coastal wetlands as well as 

large- and small-scale petroleum 

discharges and oil spills. Of particular 

note, in 2010 the Macondo discovery 

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 

concerns in the region. We discuss the 

impacts of the DWH oil spill on marine 

mammals in greater detail later in our 

‘‘Description of Marine Mammals in the 

Area of the Specified Activity’’ section. 

The GOM is also known for having 

many natural hydrocarbon seeps that 

contribute to a background level of 

chemicals in the environment. 

Chemosynthetic communities with 

aerobic bacterial components typically 

are associated with natural oil seeps. 

These naturally occurring seeps are 

common in deep slope waters, and there 

are hundreds of known, constant seeps 

that produce perennial slicks of oil at 

consistent locations (Kvenvolden and 

Cooper, 2003). DWH NRDA Trustees 

(2016) provided an estimate of the total 

amount of natural oil seepage in the 

GOM of between 9 and 23 million 

gallons per year. Although there is 

much uncertainty in attempting to 

estimate seepage rates (Kvenvolden and 

Cooper, 2003), it is clear that natural 

seepage is not comparable to the DWH 

oil spill release; about six to 15 times 

more oil was released from a single 

location in 87 days as is typically slowly 

released in a year from thousands of 

seeps across the entire GOM. 

In addition to being a major area for 

activities associated with the oil and gas 

industry, the GOM hosts significant 

amounts of commercial fishing and 

tourism activities and has two of the 

world’s busiest shipping fairways and 

top-ranking ports for container and 

passenger vessel traffic, all of which are 

noise-producing activities. The 

underwater environment is typically 

loud due to ambient sound, which is 

defined as environmental background 

sound levels lacking a single source or 

point (Richardson et al., 1995). The 

sound level of a region is defined by the 

total acoustical energy being generated 

by known and unknown sources. These 

sources may include physical (e.g., 

wind and waves, earthquakes, ice, 

atmospheric sound), biological (e.g., 

sounds produced by marine mammals, 

fish, and invertebrates), and 

anthropogenic (e.g., vessels, dredging, 

construction) sound. A number of 

sources contribute to ambient sound, 

including wind and waves, which are a 

main source of naturally occurring 

ambient sound for frequencies between 

200 hertz (Hz) and 50 kilohertz (kHz) 

(Mitson, 1995) (for description of 

metrics related to underwater sound, 

please see the ‘‘Description of Sound 

Sources’’ section later in this 

document). In general, ambient sound 

levels tend to increase with increasing 

wind speed and wave height. 

Precipitation can become an important 

component of total sound at frequencies 

above 500 Hz, and possibly down to 100 

Hz during quiet times. Marine mammals 

can contribute significantly to ambient 

sound levels, as can some fish and 

snapping shrimp. The frequency band 

for biological contributions is from 

approximately 12 Hz to over 100 kHz. 

Sources of ambient sound related to 

human activity include transportation 

(surface vessels), dredging and 

construction, oil and gas drilling and 

production, geophysical surveys, sonar, 

and explosions. Vessel noise typically 

dominates the total ambient sound for 

frequencies between 20 and 300 Hz. In 

general, the frequencies of 

anthropogenic sounds are below 1 kHz 

and, if higher frequency sound levels 

are created, they attenuate rapidly. 

The sum of the various natural and 

anthropogenic sound sources that 

comprise ambient sound at any given 

location and time depends not only on 

the source levels (as determined by 

current weather conditions and levels of 

biological and human activity) but also 

on the ability of sound to propagate 

through the environment. In turn, sound 

propagation is dependent on the 

spatially and temporally varying 

properties of the water column and sea 

floor, and is frequency-dependent. As a 

result of the dependence on a large 

number of varying factors, ambient 

sound levels can be expected to vary 

widely over both coarse and fine spatial 

and temporal scales. Sound levels at a 

given frequency and location can vary 

by 10–20 decibels (dB) from day to day 

(Richardson et al., 1995). 

Estabrook et al. (2016) measured 

underwater noise at seven sites in the 

northern GOM, within three frequency 

bands (10–500 Hz (LF); 500–1,000 Hz 

(MF); 1,000–3,150 Hz (HF)). The authors 

found that the GOM is a spectrally, 

temporally, and spatially dynamic 

ambient noise environment, and that, 

while abiotic and other anthropogenic 

noise sources contributed significantly 

to the ambient noise environment, noise 

from geophysical surveys dominated the 

noise environment during the study 

period (2010–2012) and chronically 

elevated noise levels across several 

marine habitats. Specifically, although 

wind was a significant noise source at 

higher frequencies (i.e., 500–3,550 Hz), 

these levels were relatively low 

compared to those of anthropogenic 

noise in the low-frequency band (10– 

500 Hz). Previous studies had identified 

anthropogenic sound as a major noise 

contributor in the GOM (e.g., Newcomb 

et al., 2003); however, Estabrook et al. 

(2016) found that sound levels from 

shipping activity were not nearly as 

pronounced as those from geophysical 

surveys, which, in many cases, persisted 

for months. As described below, typical 

airgun surveys fire pulses 

approximately every 10–20 seconds but, 

in addition, the resulting multipath 

propagation and reverberation from 

airgun pulses can exceed ambient levels 

during the interpulse interval (Guerra et 


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al., 2011; Guan et al., 2015). Estabrook 

et al. (2016) found that, in some 

instances, there were near-continuous 

elevated noise levels and that airgun 

noise propagated over large spatial 

scales of several hundred kilometers. 

Background noise, considered to be the 

noise level that is present in the absence 

of notable anthropogenic, biological, 

and meteorological sound sources, was 

measured across all sites as follows: 102 

dB (LF), 84 dB (MF), and 85 dB (HF). 

The median equivalent continuous 

sound pressure level across all sites 

was: 112 dB (LF), 90 dB (MF), and 93 

dB (HF). Finally, the median equivalent 

continuous sound pressure level for a 

five-day interval when airgun pulses 

were present was: 124 dB (LF), 91 dB 

(MF), and 92 dB (HF). 

Wiggins et al. (2016) also monitored 

the northern GOM soundscape over a 

comparable time period (2010–2013), 

conducting measurements at five 

locations and monitoring frequencies 

from 10–1,000 Hz. The authors made 

similar findings, i.e., that average 

ambient noise levels at low frequencies 

in the northern GOM are among the 

highest measured in the world’s oceans, 

and geophysical surveys dominate these 

high noise levels. In fact, Wiggins et al. 

(2016) found that during passage of a 

hurricane, low frequency sound 

pressure levels actually decreased due 

to the absence of survey activity. 

Although shipping noise was observed, 

the duration was typically shorter 

(approximately one hour versus more 

than 12 hours), and was masked by 

airgun noise at lower frequencies. 

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. 

However, BOEM’s permitting records 

show that during one recent year, over 

one-third of arrays in use had volumes 

greater than 8,000 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 in the signal at 

frequencies up to 5 kHz), 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 s (or 25–50 

m, depending on vessel speed). The 

return signal is recorded by a listening 

device, and later analyzed with 

computer interpretation and mapping 

systems used to depict the subsurface. 

There must be enough time between 

shots for the sound signals to propagate 

down to and reflect from the feature of 

interest, and then to propagate upward 

to be received on hydrophones or 

geophones. Reverberation of sound from 

previous shots must also be given time 

to dissipate. The receiving hydrophones 

can be towed behind or in front of the 

airgun array (may be towed from the 

source vessel or from a separate receiver 

vessel), or geophone receivers can be 

deployed on the seabed. Receivers may 

be displaced several kilometers 

horizontally away from the source, so 

horizontal propagation time is also 

considered in setting the interval 

between shots. 

Sound levels for airgun arrays are 

typically modeled or measured at some 

distance from the source and a nominal 

source level then back-calculated. 

Because these arrays constitute a 

distributed acoustic source rather than a 

single point source (i.e., the ‘‘source’’ is 

actually comprised of multiple sources 

with some pre-determined 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 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. 


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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 from damage (e.g., 

from other vessels) (when used) 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 

are described below (summarized from 

the petition); for full detail please refer 

to sections 1.2 and 1.3 of the petition. 

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 proposed regulations. NMFS will 

evaluate any such developments on a 

case-specific basis to determine whether 

expected impacts on marine mammals 

are consistent with those described or 

referenced in this document and, 

therefore, whether any anticipated take 

incidental to use of those new 

technologies or practices is 

appropriately authorized under what 

would be 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. Operators should 

be aware that there may be some 

activities previously unpermitted by 

BOEM, such as certain ancillary 

activities, that would appropriately be 

subject to the requirements of this 

proposed rule and they should consult 

NMFS regarding the need to obtain a 

LOA under this rule prior to conducting 

such activities. Unauthorized taking of 

marine mammals is a violation of the 

MMPA. 

2D and 3D Surveys (Deep Penetration 

Surveys)—As discussed, deep 

penetration surveys use an airgun 

array(s) as the acoustic source and may 

be 2D or 3D (with repeated 3D surveys 

termed 4D). 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. The size of the OBS receiver 

grid is usually limited by the amount of 

equipment available; however, to 

efficiently conduct a survey, 

approximately 500 nodes or 100 km of 

cable are needed. 

We described previously the basic 

differences between 2D and 3D surveys. 

A typical 2D survey deploys a single 

array covering an area approximately 

12.5–18 m long and 16–36 m wide 

behind the source vessel, whereas a 3D 

vessel may deploy multiple source 

arrays and/or streamers, with a 

potentially much larger width behind 

the vessel. A 3D vessel usually will tow 

8–14 streamers (but as many as 24), each 

3–8 km long. For example, an array 

containing ten streamers could have a 

total swath width behind the vessel of 

675–1,350 m. Among 3D surveys in 

particular, there are a variety of survey 

designs employed to acquire the specific 

data of interest. These survey types may 

differ in the number of vessels used (for 

source or receiver), sound sources 

deployed, and the location or type of 

hydrophones. Conventional, singlevessel 3D surveys are referred to as 

narrow azimuth (NAZ) surveys. Other 

3D survey techniques include wideazimuth (WAZ), multi-azimuth (MAZ), 

rich-azimuth (RAZ), and full-azimuth 

(FAZ) surveys. Please see Figures 1–10 

and 1–11 in the petition for depictions 

of these survey geometries. 

In conventional 3D seismic surveys 

involving a single source vessel, only a 

subset of the reflected wave field can be 

obtained because of the narrow range of 

source-receiver azimuths (thus called 

NAZ surveys). Newer survey 

techniques, as well as improvements in 

data processing, provide better data 

quality than that achievable using 

traditional NAZ surveys, including 

better illumination, higher signal-tonoise ratios, and higher resolution. This 

is useful in imaging subsurface areas 

containing complex geologic structures, 

particularly those beneath salt bodies 

with irregular geometries. 

Offset refers to the distance between 

a source and a particular receiver, while 

azimuth refers to the angles covered by 

the various directions between a source 

and individual receiving sensors. With 

NAZ surveys, the width (crossline 

dimension) of the nominal area imaged 

when the source is fired one time will 

be less than half the length (inline 

dimension). The aspect ratio (crossline 

divided by inline) of this nominal area 

is much less than 0.5 (see Figure 1–10 

of the petition). 

To achieve wider azimuthal coverage, 

multiple source vessels are deployed in 

order to achieve greater crossline 

dimension of the nominal area imaged. 

Different WAZ methods using multiple 

source vessels and, in some cases, 

multiple receiver vessels, are depicted 

in Figure 1–11 of the petition. A basic 

method used to acquire MAZ data 

involves a single source and streamer 

vessel, using conventional 3D survey 

methodology, covering transects on the 

same area multiple times along different 

azimuthal directions (Figure 1–11D of 


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the petition). A combination of WAZ 

and MAZ geometries provides either 

RAZ or FAZ results. Acquisition of RAZ 

data requires using multiple passes of 

one source-and-streamer vessel and two 

source-only vessels. Making two passes 

at right angles to each other with a 

specific WAZ configuration would 

produce 180° azimuth (i.e., FAZ) 

coverage. New survey designs will 

likely continue to be tested as the 

industry works to make WAZ, MAZ, 

RAZ, and FAZ shooting more efficient 

and less costly. Another development is 

synchronized discharge of airgun arrays 

being towed by different vessels 

(advances in data processing can 

separate the energy from synchronized 

sources using differences in source-toreceiver offset distances). While this 

increases the level of sound in the 

ensonified water volume, it also reduces 

the length of time that the water volume 

is ensonified. 

In summary, 3D survey design 

involves a vessel with one or more 

acoustic sources covering an area of 

interest with relatively tight spatial 

configuration. 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. The time required to 

complete one pass of a trackline for a 

single NAZ vessel and the time required 

for one pass by a multi-vessel entourage 

conducting a WAZ survey will be 

essentially the same. Turn times will be 

somewhat longer during multi-vessel 

surveys to ensure that all vessels are 

properly aligned prior to beginning the 

next trackline. Turn times depend 

mostly on the vessels and the 

equipment they are towing (as in 

conventional 3D surveys); however, the 

number of vessels towing streamers in 

the entire entourage is the main 

determinant of the turn time. The MAZ 

technique, where multiple passes are 

made, increases the time needed for a 

survey in proportion to the number of 

passes that will be made within an area. 

The reduction in the number of passes 

is one of the most significant driving 

factors in continued efforts to design 

more efficient surveys. Coil surveys, 

described previously, reduce the total 

survey time due to elimination of the 

trackline-turn methodology. 

Borehole Seismic Surveys—The 

placement of seismic sensors in a 

drilled well or borehole is another way 

data can be acquired. These surveys, 

typically referred to as vertical seismic 

profiles (VSP), provide information 

about geologic structure, lithology, and 

fluids that is intermediate between that 

obtained from sea surface surveys and 

well-log scale information (well logging 

is the process of recording various 

physical, chemical, electrical, or other 

properties of the rock/fluid mixtures 

penetrated by drilling a borehole). VSP 

surveying is conducted by placing 

receivers such as geophones at many 

(50–200) depths in a wellbore and 

recording both direct-arriving and 

reflection energy from an acoustic 

source. The acoustic source usually is a 

single airgun or small airgun array hung 

from a platform or deployed from a 

source vessel. The airguns used for 

VSPs may be the same or similar to 

those used for 2D and 3D towedstreamer surveys; however, the number 

of airguns and the total volume of an 

array used are less than those used for 

towed-streamer surveys. Less sound 

energy is required for VSP surveys 

because the seismic sensors are in a 

borehole, which is a much quieter 

environment than that for sensors in a 

towed streamer, and because the VSP 

sensors are located nearer to the targeted 

reflecting horizons. Some VSP surveys 

take less than a day, and most are 

completed in a few days. Borehole 

seismic surveys include 2D VSPs, 3D 

VSPs, checkshot surveys, and seismic 

while drilling (SWD). 

Types of 2D VSPs are defined by 

source location, as follows: (1) Zerooffset VSPs involve a single source 

position that is close to the well (often 

deployed from a platform) compared to 

the depths where the sensors are placed 

(thereby causing the sensors to receive 

mostly vertically propagating energy); 

(2) offset VSPs involve a stationary 

vessel-based source position (or 

multiple positions) that is far enough 

away from the well that the recorded 

waveforms have a significant amount of 

horizontally-propagating energy; (3) 

walkaway VSPs involve a moving vessel 

and multiple source positions along a 

line away from the well; and (4) 

deviated-well VSPs involve source 

positions placed vertically above a well 

path. See Figure 1–12 of the petition for 

depictions. 

3D VSPs involve use of multi-level 

sensor strings, allowing 1,500 to 3,000 

m to be instrumented within a well. As 

with 2D VSPs, individual airguns and 

arrays used are generally similar to 

those used in towed-streamer surveys. 

The data acquisition design could 

involve typical 3D rectangular survey 

vessel track patterns, or spiral track 

patterns with the source vessel moving 

away from the well. For 3D VSPs, the 

distance from the well covered by the 

source vessel will approximately equal 

the depth of the well (see Figure 1–13 

in the petition). 

Checkshot surveys are similar to zerooffset VSPs but are less complex. The 

purpose of a checkshot survey is to 

estimate the velocity of sound in rocks 

penetrated by the well, and these 

surveys are typically conducted quickly. 

These surveys involve a single source 

typically hung from a platform and a 

sensor placed at a few depths in the 

well, where only the first energy arrival 

is recorded. 

SWD refers to the acquisition of 

borehole data, using an airgun array as 

an acoustic source, while there is 

downtime from the actual drilling 

operation. SWD surveys are run 

intermittently for weeks up until the 

well completion depth. 

Shallow Penetration/HRG Surveys— 

These 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. In most cases, 

conventional 2D and 3D deep 

penetration surveys do not have the 

correct resolution to provide the 

required information. Although HRG 

surveys may use a single airgun source, 

they generally use electromechanical 

sources such as side-scan sonars, 

shallow- and medium-penetration 

subbottom profilers, and single-beam 

echosounders or multibeam 

echosounders. Non-airgun HRG sources 

are often used in combination in order 

to acquire necessary data during a single 

deployment. HRG surveys are 

sometimes conducted using 

autonomous underwater vehicles (AUV) 

equipped with multiple acoustic 

sources. 

HRG surveys may be conducted using 

airguns as the acoustic source. These 

typically use one or two airguns that are 

the same as those described for use in 

arrays during deep penetration surveys. 

However, the total volume is typically 

only approximately 40–400 in3, the 

streamers are shorter, and the shot 

intervals are shorter. The intent is 

typically to image the shallow 

subsurface (less than 1,000 m below the 

seafloor). Including vessel turns at the 

end of lines, the time required to survey 

one OCS lease block is approximately 

36 hours. These surveys are sometimes 

conducted using 3D techniques, e.g., 

multiple sources and/or streamers. 

Electromechanical sources are 

generally considered to be relatively 


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mid- to high-frequency sources, and 

produce acoustic signals by creating an 

oscillatory overpressure through rapid 

vibration of a surface, using either 

electromagnetic forces or the 

piezoelectric effect of some materials. A 

vibratory source based on the 

piezoelectric effect is commonly 

referred to as a transducer, which may 

be designed to excite an acoustic wave 

of a specific frequency, often in a highly 

directive beam. The directional 

capability increases with increasing 

operating frequency. 

Subbottom profiling surveys are 

typically used for high-resolution 

imaging of the shallow subsurface. 

These surveys may use a variety of 

acoustic sources, commonly referred to 

as ‘‘boomers,’’ ‘‘sparkers,’’ or ‘‘chirps.’’ 

A sparker uses electricity to vaporize 

water, creating collapsing bubbles that 

produce a broadband (50 Hz to 4 kHz), 

omnidirectional pulse of sound that can 

penetrate a few hundred meters into the 

subsurface. Short hydrophone arrays 

towed near the sparker receive the 

return signal; typically, the sparker is 

towed on one side of the vessel and the 

hydrophone array is towed on the other 

side. A boomer consists of a circular 

piston moved by electromagnetic force, 

generating a broadband acoustic pulse 

(300 Hz to 3 kHz, though adjustments to 

the applied electrical impulse may 

increase the frequency). Boomer systems 

can penetrate as deep as 200 m in soft 

sediments, though a more typical 

penetration may be 25–50 m. Boomer 

sources show some directionality, 

which increases with the acoustic 

frequency; at frequencies below 1 kHz 

they can usually be considered 

omnidirectional. Boomers are typically 

sled-mounted and towed behind the 

vessel, with short hydrophone arrays 

used to receive the return signal. The 

characteristics of the acoustic wave 

emitted by the boomer source are 

comparable to those emitted by the 

sparker source. 

Chirp (Compressed High-Intensity 

Radiated Pulse) sources operate 

differently, sending a continuous sweep 

of frequencies (e.g., 500 Hz to 24 kHz) 

approximately every 0.5 to 1 seconds. 

Some chirp systems work in multiple 

frequency bands simultaneously (e.g., 

3.5/12/200 kHz). Beamwidth will vary 

depending on the frequency, but is 

approximately 10–30°. Because this 

continuous sweep of frequencies 

provides a much wider range of 

information, chirp systems are able to 

create a much clearer, higher-resolution 

image while achieving the same or 

better depth of penetration. Chirps are 

typically towed behind the vessel or 

deployed on an AUV. 

Side-scan sonars and echosounders 

do not penetrate the surface of the 

seabed, using reflections of sound 

pulses to locate, image, and aid in the 

identification of objects in the water 

column and on the seafloor, and to 

determine water depth. Echosounders 

typically emit short, single-frequency 

signals, with frequency decreasing as 

water depth increases. A deep-water 

system might operate at approximately 

3–12 kHz, while a shallow-water system 

might operate at 200 kHz or greater. 

Multibeam echosounder systems use an 

array of transducers that project a fanshaped beam under the hull of a vessel 

and perpendicular to the direction of 

motion, producing a swath of depth 

measurements to ensure full coverage of 

an area. Echosounders are typically 

hull-mounted or deployed on AUVs. 

Side-scan sonar systems produce 

shaded relief images of the ocean 

bottom by recording the intensity and 

timing of signals reflected off the 

seafloor, and consist of two transducers 

on the sides of the towed sonar body 

that are oriented perpendicularly to the 

towing direction. The signals are 

typically single-frequency, with a highly 

directional beam that is wide acrosstrack and narrow in the direction of 

travel. Due to the transducer placement, 

side-scan sonars may not effectively 

image the area directly beneath the 

vessel and are often used in conjunction 

with echosounders. Side-scan sonars are 

typically high-frequency sources and 

therefore have a limited range (50–200 

m). In deeper water, the source may be 

towed at greater depth or deployed on 

an AUV. 

Representative Sound Sources 

Because the specifics of acoustic 

sources to be used would not be known 

in advance of receiving LOA requests 

from industry operators, it is necessary 

to define representative acoustic source 

parameters, as well as representative 

survey patterns. BOEM determined 

realistic representative proxy sound 

sources and survey patterns, which are 

used in the modeling and more broadly 

to support the analysis, after discussions 

with individual geophysical companies. 

Representative sources include a 

single airgun, an airgun array, and 

multiple electromechanical sources: 

Boomer, chirp, multibeam echosounder, 

and side-scan sonar. Two major survey 

types were considered: Large-area 

seismic and small-area, high-resolution 

geotechnical. Large-area seismic surveys 

are assumed to cover more than 1,000 

mi2 (2,590 km2) and include 2D, 3D 

NAZ, 3D WAZ, and coil types. 

Geotechnical study surveys are assumed 

to cover an area less than 100 mi2 (259 

km2) and use small airguns and/or highfrequency electromechanical sources 

installed on an AUV. VSP surveys, 

assuming a single source vessel with 

one 8,000 in3 array, were also modeled. 

The nominal airgun sources used for 

analysis of the proposed action include 

a small single airgun (90 in3 Sercel 

airgun) towed at 4 m depth and a large 

airgun array (8,000 in3) towed at 8 m 

depth. Airguns are assumed to fire 

simultaneously at 2,000 psi. The airgun 

array was assumed to consist of 72 

elements (Bolt 1900 LLXT airguns) 

arranged in six sub-arrays of 12 airguns 

each with 9 m in-line separations. 

Individual elements range from 40 to 

250 in3. The layout of the modeled array 

(i.e., airgun distribution in the 

horizontal plane) is shown in Figure 11 

of Zeddies et al. (2015). For the single 

airgun, modeled source levels were 

227.7 dB 0-peak (pk) sound pressure 

level (SPL) and 207.8 dB sound 

exposure level (SEL) (for description of 

metrics related to underwater sound, 

please see ‘‘Description of Sound 

Sources,’’ later in this document). 

Modeled source levels for the array 

range from 248.1 (broadside, i.e., 

perpendicular to the tow direction) to 

255.2 (endfire; i.e., parallel to the tow 

direction) dB 0-pk SPL and from 225.7 

(broadside) to 231.8 (endfire) dB SEL. 

Zeddies et al. (2015, 2017a), ‘‘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,’’ are hereafter referred to as 

‘‘the modeling report.’’ The reports are 

available online at: 

www.fisheries.noaa.gov/national/ 

marine-mammal-protection/incidentaltake-authorizations-oil-and-gas. Below, 

we outline the 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. 

Source vessels are assumed to travel 

at an average speed of 4.5–5 kn (i.e., 

200–220 linear km per day), and airgun 

arrays were assumed to be off during 

turns. The run-in and run-out sections 

were 1 km long. Each large-area survey 

(excluding coil surveys) was assumed to 

cover an area of 10 x 30 lease blocks, 

equivalent to 48 x 145 km or 

approximately 6,960 km2. Coil surveys 

are assumed to cover a smaller area of 

12 x 12 lease blocks, equivalent to 58 x 

58 km or approximately 3,364 km2. 

2D surveys were simulated by 

assuming use of a single 8,000 in3 array, 


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with transect lines offset laterally by 4.8 

km. The production lines were filled in 

with a racetrack fill-in method, skipping 

two tracks on the left side turn (15 km 

wide turn) and transitioning onto the 

adjacent line on the right side turn (5 

km wide turn) (see Figure 105 of the 

modeling report). The vessel speed was 

4.5 kts and the shot interval was 21.6 s 

(approximately every 50 m). 

3D NAZ surveys were simulated by 

assuming use of two source vessels 

towing identical arrays. Sources at each 

vessel produce seismic pulses 

simultaneously. Both vessels follow the 

same track, but were separated along the 

track by 6 km. The production lines 

were laterally spaced by 1 km (see 

Figure 106 of the modeling report). The 

production lines were filled via a 

racetrack fill-in method with eight loops 

in each racetrack (7–8 km wide turn). 

Forty-nine lines were required to fully 

cover the survey area. The vessel speed 

was 4.9 kn and the shot interval was 15 

s (approximately every 37.5 m) for each 

vessel. 

3D WAZ surveys were simulated by 

assuming use of four source vessels 

towing identical arrays. Sources at each 

vessel produce seismic pulses 

sequentially. The tracks of each vessel 

had the same geometry and had 1.2 km 

lateral offset. The vessels also had 500 

m offset along the track (see Figure 107 

of the modeling report). The production 

lines were filled in with a racetrack fillin method with two loops in each 

racetrack (9.6 km wide turn). Forty lines 

were required to fully cover the survey 

area. The vessel speed was 4.5 kn, with 

individual vessel shot interval of 86.4 s 

(approximately every 200 m)— 

equivalent to 21.6 s for the group. 

Coil surveys are performed by 

multiple vessels that sail a series of 

circular tracks with some angular 

separation while towing acoustic 

sources. These surveys were simulated 

by assuming use of four source vessels 

towing identical arrays. Sources at each 

vessel produce seismic pulses 

simultaneously. Tracks consist of a 

series of circles with 12.5 km diameter 

(see Figure 108 of the modeling report). 

Once each vessel completes a full circle, 

it advances to the next one along a 

tangential connection segment. The 

offset between the center of one circle 

and the next, either along-swath or 

between swaths, was 5 km. The full 

survey geometry consisted of two tracks 

with identical configuration with 1.2 km 

and 600 m offsets along X and Y 

directions, respectively. Two of the four 

vessels followed the first track with 180° 

separation; the other two vessels 

followed the second track with 180 ° 

separation relative to each other and 90 ° 

separation relative to the first pair. One 

hundred circles per vessel pair were 

required to fully cover the survey area. 

The vessel speed was 4.9 kn and the 

shot interval was 20 s (approximately 

every 50 m) for each vessel. 

For small-area, high-resolution 

geotechnical surveys, we described the 

proxy single airgun source above. The 

representative boomer system was the 

Applied Acoustics AA301, based on a 

single plate with approximately 40 cm 

baffle diameter. The input energy for the 

AA301 boomer plate was up to 350 

joules (J) per pulse or 1,000 J per 

second. The width of the pulse was 

0.15–0.4 milliseconds (ms). A source 

verification study performed on a 

similar system by Martin et al., (2012) 

showed that the broadband source level 

for the system was 203.3 dB root mean 

square (rms) SPL over a 0.2 ms window 

length and 172.6 dB SEL. These data 

were used for modeling the boomer 

source with a ¥4.6 dB correction 

applied to account for differences in 

input energy between the two systems. 

As noted above, certain highresolution acoustic sources may be 

deployed together and used 

concurrently. Here, the modeling 

assumes that a multibeam echosounder, 

side-scan sonar, and chirp subbottom 

profiler are operated concurrently and 

deployed on an AUV. Towing depth of 

the AUV was assumed to be 4 m below 

the sea surface when the water depth 

was less than 100 m and 40 m above the 

seafloor where water depth was more 

than 100 m. The representative 

multibeam echosounder (MBES) system 

was the Simrad EM2000 (manufactured 

by Kongsberg Maritime AS). According 

to manufacturer specifications, this 

device operates at 200 kHz and is 

equipped with a transducer head that 

produces a single beam 17 ° x 88 ° wide. 

The nominal source level was 203 dB 

rms SPL, with per-pulse SEL dependent 

on the pulse length (160–175 dB). Pulse 

width is 0.04–1.3 ms. The representative 

side-scan sonar is the EdgeTech 2200 

IM, which works at two frequencies 

simultaneously (120 and 410 kHz). The 

beam angle produced by two sidemounted transducers was 70 ° x 0.8 ° at 

120 kHz and 70 ° x 0.5 ° at 410 kHz. At 

120 kHz, the estimated peak source 

level is 210 dB with pulse length of 8.3 

ms; at 410 kHz these values are 216 dB 

and 2.4 ms. The chirp subbottom 

profiler uses the same side-scan sonar 

system, which is designed as a modular 

system for installation on an AUV, and 

adds the DW–424, a full spectrum chirp 

subbottom profiler that produces a 

sweep signal in the frequency range 

from 4 to 24 kHz. The projected 

beamwidth varies from 15 ° to 25 ° 

depending on the emitted frequency, 

with estimated source level of 200 dB 

and pulse length of 10 ms. 

For these HRG surveys, the same 

survey pattern was assumed regardless 

of the source. Total survey area was 

assumed to be an area of 1 x 3 lease 

blocks, equivalent to 5 x 14.5 km or 

approximately 72.5 km2. A single source 

vessel towing the appropriate source 

(i.e., single airgun, boomer, or AUV with 

concurrently operated MBES, side-scan 

sonar, and chirp) was assumed. 

Production lines were laterally spaced 

30 m (see Figure 109 of the modeling 

report) then filled in with a racetrack 

fill-in method where each racetrack has 

20 loops (1.2 km wide turn). One 

hundred and sixty lines were required 

to fully cover the survey area. The 

vessel speed was 4 kn and, for surveys 

using the single airgun, the shot interval 

was 10 seconds(s) (approximately every 

20 m). 

Estimated Levels of Effort 

As noted previously, actual total 

amounts of effort by survey type and 

location would not be known in 

advance of receiving LOA requests from 

industry operators. Therefore, BOEM 

provided projections of survey level of 

effort for the different survey types for 

a 10-year period (note that this proposed 

rule covers only a 5-year period). In 

order to construct a realistic scenario for 

future geophysical survey effort, BOEM 

evaluated recent trends in permit 

applications as well as industry 

estimates of future survey activity. 

BOEM also accounted for restrictions 

under the Gulf of Mexico Energy 

Security Act (GOMESA; Pub. L. 109– 

432), which precludes leasing, preleasing, or any related activity (though 

not geophysical surveys that have been 

permitted) 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, 

which will to some degree influence 

geophysical survey effort, are in place 

until June 30, 2022. 

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 


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approximately 150 km). The slope starts 

where the seabed relief is steeper and 

extends into deeper water; in the GOM 

water deepens from 100–200 m to 

1,500–2,500 m over as little as a 50 km 

horizontal distance. As the slope ends, 

water depths become more consistent, 

though depths can vary from 2,000– 

3,300 m. Three primary bathymetric 

areas were defined as shelf (0–200 m 

water depth), slope (200–2,000 m), and 

deep (>2,000 m). 

Available information regarding 

cetacean density in the GOM (e.g., 

Roberts et al., 2016) shows that, in 

addition to water depth, animal 

distribution tends to vary from east to 

west in the GOM and appears correlated 

with the width of shelf and slope areas 

from east to west. The western region is 

characterized by a relatively narrow 

shelf and moderate-width slope. The 

central region has a moderate-width 

shelf and moderate-width slope, and the 

eastern region has a wide shelf and a 

very narrow slope. Therefore, BOEM’s 

western, central, and eastern planning 

area divisions provide appropriate 

longitudinal separations for the shelf 

and slope areas. Due to relative 

consistency in both physical properties 

and predicted animal distribution, the 

deep area was not subdivided. As 

shown in Figure 2, 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 

(note that other features of Figure 2 are 

described in the ‘‘Estimated Take’’ 

section). Table 1 displays BOEM’s 10- 

year estimated levels of effort, estimated 

as 24-hr survey days, including annual 

totals by survey type and by zone for 

deep penetration and shallow 

penetration surveys, respectively. 

TABLE 1—PROJECTED LEVELS OF EFFORT IN 24-HR SURVEY DAYS FOR TEN 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 ................ 0 243 0 0 0 243 2 0 19 21 

3 ................ 0 30 0 0 0 30 0 0 4 4 

4 ................ 0 0 0 0 0 0 0 0 0 0 

5 ................ 56 389 192 82 2 721 0 0 26 26 

6 ................ 0 186 49 21 0 256 0 0 10 10 

7 ................ 69 515 248 106 2 940 0 0 34 34 

Total ........ ................... 125 1,363 489 209 4 2,190 2 0 94 96 

2 ..................... 1 ................ 0 0 0 0 0 0 0 0 1 1 

2 ................ 0 364 43 19 0 426 2 0 19 21 

3 ................ 0 0 0 0 0 0 0 0 4 4 

4 ................ 33 0 0 0 0 33 0 0 0 0 

5 ................ 0 389 192 82 2 665 0 0 26 26 

6 ................ 0 99 0 0 0 99 0 0 11 11 

7 ................ 30 502 241 103 2 878 0 0 34 34 

Total ........ ................... 63 1,354 476 204 4 2,101 2 0 95 96 


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TABLE 1—PROJECTED LEVELS OF EFFORT IN 24-HR SURVEY DAYS FOR TEN YEARS, BY ZONE AND SURVEY TYPE 1— 

Continued 

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

3 ..................... 1 ................ 0 0 0 0 0 0 0 0 1 1 

2 ................ 0 243 0 0 0 243 2 0 18 20 

3 ................ 0 0 0 0 0 0 0 0 4 4 

4 ................ 0 0 0 0 0 0 0 0 1 1 

5 ................ 0 342 160 69 2 573 0 0 27 27 

6 ................ 0 186 49 21 0 256 0 0 12 12 

7 ................ 0 456 208 89 2 755 0 0 36 36 

Total ........ ................... 0 1,227 417 179 4 1,827 2 0 99 101 

4 ..................... 1 ................ 0 0 0 0 0 0 0 0 0 0 

2 ................ 0 364 43 19 0 426 2 1 16 19 

3 ................ 0 30 0 0 0 30 0 0 3 3 

4 ................ 66 61 21 9 0 157 0 0 1 1 

5 ................ 28 247 96 41 2 414 0 0 27 27 

6 ................ 0 99 0 0 0 99 0 0 12 12 

7 ........ 94 380 140 60 2 676 0 0 36 36 

Total ........ ................... 188 1,181 300 129 4 1,802 2 1 95 98 

5 ..................... 1 ................ 0 0 0 0 0 0 0 0 0 0 

2 ................ 0 243 0 0 0 243 0 0 20 20 

3 ................ 0 0 0 0 0 0 0 0 3 3 

4 ................ 0 92 0 0 0 92 0 0 0 0 

5 ................ 0 295 192 82 2 571 2 1 25 28 

6 ................ 0 99 0 0 0 99 0 0 13 13 

7 ................ 0 467 241 103 3 814 3 2 34 39 

Total ........ ................... 0 1,196 433 185 5 1,819 5 3 95 103 

6 ..................... 1 ................ 0 0 0 0 0 0 0 0 0 0 

2 ................ 0 364 43 19 0 426 0 0 18 18 

3 ................ 0 0 0 0 0 0 0 0 2 2 

4 ................ 0 92 0 0 0 92 0 0 1 1 

5 ................ 0 247 160 69 2 478 0 0 30 30 

6 ................ 0 186 49 21 0 256 0 0 13 13 

7 ................ 0 421 208 89 3 721 0 0 40 40 

Total ........ ................... 0 1,310 460 198 5 1,973 0 0 104 104 

7 ..................... 1 ................ 0 0 0 0 0 0 0 0 0 0 

2 ................ 0 243 0 0 0 243 0 0 16 16 

3 ................ 0 30 0 0 0 30 0 0 2 2 

4 ................ 33 61 21 9 0 124 0 0 1 1 

5 ................ 28 247 160 69 2 506 0 0 32 32 

6 ................ 0 99 0 0 0 99 0 0 13 13 

7 ................ 64 380 220 94 3 761 0 0 43 43 

Total ........ ................... 125 1,060 401 172 5 1,763 0 0 107 107 

8 ..................... 1 ................ 0 0 0 0 0 0 0 0 0 0 

2 ................ 0 364 43 19 0 426 0 0 16 16 

3 ................ 0 0 0 0 0 0 0 0 2 2 

4 ................ 11 61 0 0 0 72 0 0 1 1 

5 ................ 9 247 128 55 2 441 0 0 35 35 

6 ................ 0 99 0 0 0 99 0 0 13 13 

7 ................ 21 380 160 69 3 633 0 0 46 46 

Total ........ ................... 41 1,151 331 143 5 1,671 0 0 113 113 

9 ..................... 1 ................ 0 0 0 0 0 0 0 0 0 0 

2 ................ 0 243 0 0 0 243 0 0 16 16 

3 ................ 0 0 0 0 0 0 0 0 2 2 

4 ................ 0 61 0 0 0 61 0 0 1 1 

5 ................ 0 200 192 82 2 476 0 0 35 35 

6 ................ 0 99 0 0 0 99 0 0 14 14 

7 ................ 0 321 241 103 3 668 0 0 47 47 

Total ........ ................... 0 924 433 185 5 1,547 0 0 115 115 

10 ................... 1 ................ 0 0 0 0 0 0 0 0 0 0 

2 ................ 0 364 43 19 0 426 0 0 13 13 

3 ................ 0 30 0 0 0 30 0 0 2 2 

4 ................ 5 61 0 0 0 66 0 0 1 1 

5 ................ 0 200 160 69 2 431 0 0 37 37 

6 ................ 0 99 0 0 0 99 0 0 14 14 

7 ................ 5 321 200 86 3 615 0 0 49 49 


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TABLE 1—PROJECTED LEVELS OF EFFORT IN 24-HR SURVEY DAYS FOR TEN YEARS, BY ZONE AND SURVEY TYPE 1— 

Continued 

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

Total ........ ................... 10 1,075 403 174 5 1,667 0 0 116 116 

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

2Zones follow the zones depicted in Figure 2. 

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, subbottom profiling using a boomer, and high-resolution surveys using the MBES, side-scan sonar, and chirp systems concurrently. ‘‘Shallow’’ refers to survey type, not to water depth. 

Table 2 provides a summary of the 

projected levels of effort. Very little 

effort is predicted in the EPA, with no 

deep penetration surveys expected in 

Zone 1 and an annual average of 63 

survey days predicted in Zone 4. 

Similarly, very little overall effort is 

expected in western shelf waters. The 

vast majority of effort is expected to 

occur in the CPA, in all water depths. 

For deep penetration surveys, 3D NAZ 

is expected to be the most common 

survey type (in terms of total survey 

says) with approximately 65 percent of 

the total. 3D WAZ surveys represent 

approximately 22 percent of total survey 

days. Shallow penetration surveys 

overall represent an insignificant 

addition to the projected deep 

penetration effort, reflecting the smaller 

amount of effort associated with these 

survey types. 

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. 

However, per-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. 

Projected levels of effort presented here 

represent expected maxima, and it is 

possible that actual levels of effort will 

be lower, whether due to effects of the 

economy on industry activities or other 

reasons. Please see Figure 3.2–1 of 

BOEM’s PEIS (BOEM, 2017) for 

projected potential ranges of survey 

activity. The ranges of projected activity 

level include an upper bound based on 

industry capacity in the GOM and a 

lower bound that accounts for a number 

of things that could affect these 

activities (e.g., marketplace changes, 

adjustment of schedules for closures). 

TABLE 2—SUMMARY OF PROJECTED LEVELS OF EFFORT IN 24-HR SURVEY DAYS

Zone/region 

Deep penetration surveys Shallow penetration/HRG surveys 

Min Mean Max Min Mean Max 

1 (Shelf east) ................................................................... 0 0 0 0 0 1 

2 (Shelf central) ............................................................... 243 304 426 13 18 21 

3 (Shelf west) ................................................................... 0 11 30 2 3 4 

4 (Slope east) .................................................................. 0 63 157 0 1 1 

5 (Slope central) .............................................................. 414 480 721 26 30 37 

6 (Slope west) .................................................................. 99 133 256 10 13 14 

7 (Deep) ........................................................................... 615 678 940 34 40 49 

Total .......................................................................... 1,547 1,669 2,190 96 105 116 

Proposed mitigation, monitoring, and 

reporting measures are described in 

detail later in this document (please see 

‘‘Proposed Mitigation’’ and ‘‘Proposed 

Monitoring and Reporting’’). 

Description of Marine Mammals in the 

Area of the Specified Activity 

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. We refer the reader to 

these descriptions, to descriptions of the 

affected environment in Appendix E of 

BOEM’s PEIS, as well as to NMFS’s 

Stock Assessment Reports (SAR; 

www.fisheries.noaa.gov/national/ 

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’s website 

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

the U.S. Navy’s Marine Resource 

Assessment for the GOM (DoN, 2007a) 

(available online at: 

www.navfac.navy.mil/products_and_

services/ev/products_and_services/ 

marine_resources/marine_resource_

assessments.html), or Wu ̈rsig (2017). 

Table 3 lists all species with expected 

potential for occurrence in the Gulf of 

Mexico and summarizes information 

related to the population or stock. For 

taxonomy, we follow Committee on 

Taxonomy (2017). While no mortality or 

serious injury is anticipated or proposed 

for authorization, potential biological 

removal (PBR; defined in 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) and annual serious injury 

and mortality from anthropogenic 

sources are included here as gross 

indicators of the status of the species 

and other threats (as described in 

NMFS’s SARs). 

Species that could potentially occur 

in the proposed survey areas, but are not 

reasonably expected to have potential to 


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be affected by the specified activity, are 

described briefly but omitted from 

further analysis. These include 

extralimital species, which are species 

that do not normally occur in a given 

area but for which there are one or more 

occurrence records that are considered 

beyond the normal range of the species. 

For status of species, we provide 

information regarding U.S. regulatory 

status under the MMPA and Endangered 

Species Act (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’s stock abundance 

estimates for most species represent the 

total estimate of individuals within the 

geographic area, if known, that 

comprises that stock. All managed 

stocks in this region are assessed in 

NMFS’s U.S. Atlantic SARs (e.g., Hayes 

et al., 2017). All values presented in 

Table 3 are the most recent available at 

the time of publication and are available 

in the 2016 SARs (Hayes et al., 2017) or 

draft 2017 SARs 

(www.fisheries.noaa.gov/national/ 

marine-mammal-protection/draftmarine-mammal-stock-assessmentreports). 

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’s 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 25 managed 

stocks) have the potential to co-occur 

with the proposed survey activities. 

Extralimital species or stocks unlikely to 

co-occur with survey activity include 31 

estuarine bottlenose dolphin stocks 

(discussed below), 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 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). The blue whale is known from 

two stranding records, the fin whale 

from five strandings and rare sightings, 

and the sei whale from five strandings 

(Wu ̈rsig, 2017). Although North Atlantic 

right whales are well known from the 

east coast of Florida, that area represents 

the southern limit of their range; Wu ̈rsig 

(2017) reports one stranding and one 

sighting of two whales in the GOM. 

Occasional minke whale strandings and 

rare sightings near the Florida Keys 

show a winter-spring pattern, which 

may be indicative of northwardmigrating whales from the Caribbean 

becoming disoriented (Wu ̈rsig et al., 

2000). In 1997, a single group of six 

humpback whales was observed 

approximately 250 km east of the 

Mississippi River delta in deep water; 

however, this sighting as well as other 

occasional strandings and rare sighting 

records are believed to represent 

vagrants from the Caribbean (Wu ̈rsig et 

al., 2000). A Sowerby’s beaked whale 

was found stranded in western Florida 

in 1984, a record representing the 

lowest known latitude for the species 

(Bonde and O’Shea, 1989). We also note 

here that Hildebrand et al. (2015) report 

acoustic detections of an ‘‘as yet 

unidentified species of beaked whale’’ 

from three sites. At the three sites— 

Mississippi Canyon, Green Canyon, and 

Dry Tortugas—vocal encounters of the 

unknown species represented four, 

three, and 0.1 percent of total beaked 

whale vocal encounters. The same 

acoustic echolocation signature was 

previously reported near Hawaii (but 

without simultaneous visual and 

acoustic detection), and would 

presumably be a species with tropical 

distribution (Hildebrand et al., 2012; 

McDonald et al., 2009). Nothing else is 

known of this potential new species. 

Roberts et al. (2016) developed a 

stratified density model for the fin 

whale in the GOM, on the basis of one 

observation during an aerial survey in 

the early 1990s. None of the other 

extralimital species listed here were 

observed during NMFS shipboard or 

aerial survey effort from 1992–2009. The 

fin whale is the second-most frequently 

reported mysticete in the GOM (after the 

Bryde’s whale), though with only a 

handful of stranding and sighting 

records, and is considered here as a rare 

and likely accidental migrant. As noted 

by the model authors, while the 

probability of a chance encounter is not 

zero, the single sighting during NMFS 

survey effort should be considered 

extralimital (Roberts et al., 2015a). 

Estuarine stocks of bottlenose dolphin 

primarily inhabit inshore waters of bays, 

sounds, and estuaries (BSE), and stocks 

are defined throughout waters adjacent 

to the specified geographical region. 

However, estuarine stock ranges are 

generally described as including coastal 

waters (i.e., waters adjacent to shore, 

barrier islands, or presumed outer bay 

boundaries and outside of typical 

inshore ranges) to approximately 1–3 

km. For example, bottlenose dolphins 

that were captured in Texas and 

outfitted with radio transmitters largely 

remained within the bays, with three 

individuals tracked to 1 km offshore 

(Lynn and Wu ̈rsig, 2002). Radio-tracking 

of dolphins in the St. Joseph Bay, 

Florida area showed that most dolphins 

stayed within the bay and that, although 

some individuals ranged more than 40 

km along the coastline from the study 

site, they never ventured outside of 

immediate nearshore waters (Balmer et 

al., 2008). More recently, dolphins 

captured in Barataria Bay, Louisiana 

were fitted with satellite-linked 

transmitters, showing that most 

dolphins remained within the bay, 

while those that entered nearshore 

coastal waters remained within 1.75 km 

(Wells et al., 2017). Therefore, these 

stocks would not generally be expected 

to be impacted by the described 

geophysical surveys. If a deep 

penetration seismic survey were 

occurring in nearshore Federal waters 

(i.e., at least 3 miles from shore but 9 

miles from shore off Texas and Florida), 

it is possible that a dolphin belonging to 

a BSE stock could be affected. However, 

such surveys are expected to be rare in 

such shallow waters, and given the fact 

that BSE dolphins in sheltered inshore 

waters would largely not be impacted by 

noise generated offshore, we believe that 

impacts from the described activities 

that could potentially be considered as 

a ‘‘take’’ (as defined by the MMPA) 

should be considered discountable. 

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. 


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TABLE 3—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 8

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 ................ - 5; Y 33 (1.07; 16; 2009) ......... 44 (0.27)/n/a ........... 0.03 0.7 

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 

Family Kogiidae: 

Pygmy sperm whale Kogia breviceps .............. GOM ............................... -; N 186 (1.04; 90; 2009) 6 ..... 2,234 (0.19)/6,117 6 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 6 0.4 0 

Gervais beaked 

whale.

Mesoplodon europaeus .. GOM ............................... -; N 149 (0.91; 77; 2009) 6 ..... ................................. 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 ...... 3 0.8 (1.0) 

Common bottlenose 

dolphin.

Tursiops truncatus 

truncatus.

GOM Oceanic ................. -; N 5,806 (0.39; 4,230; 2009) 138,602 (0.06)/ 

192,176 6.

42 6.5 (0.65) 

GOM Continental Shelf .. -; N 51,192 (0.10; 46,926; 

2011–12).

................................. 469 0.8 

GOM Coastal, Eastern ... -; N 12,388 (0.13; 11,110; 

2011–12).

................................. 111 1.6 

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) 7.

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) 7.

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) 7.

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’s 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. 5 NMFS has proposed to list the GOM Bryde’s whale as an endangered species under the ESA (81 FR 88639; December 8, 2016). 

6Abundance 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’s 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. 7 NMFS’s abundance estimates for these species are greater than eight years old and 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. 8We 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’s official SARs information for comparison with model-predicted abundance (Roberts et al., 2016). 


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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., 2017). 

During aerial and ship-based cetacean 

surveys, the most commonly sighted 

species in the GOM are bottlenose 

dolphins, pantropical spotted dolphins, 

Atlantic spotted dolphins, Risso’s 

dolphins, sperm whales, and Kogia spp. 

(Baumgartner et al., 2001; Mullin and 

Fulling, 2004; Mullin et al., 2004, MazeFoley and Mullin, 2006; Mullin, 2007; 

Dias and Garrison, 2016). Short-finned 

pilot whales, striped dolphins, Clymene 

dolphins, spinner dolphins, and beaked 

whales are somewhat commonly 

observed during surveys and have 

different rates of detection (Mullin et al., 

2004; Mullin and Fulling, 2004; Dias 

and Garrison, 2016). Rarely recorded 

species include melon-headed whales, 

false killer whales, killer whales, and 

pygmy killer whales (Dias and Garrison, 

2016). Bryde’s whales are also 

infrequently seen and are the only 

species of baleen whale recurrently seen 

in the GOM (Baumgartner et al., 2001; 

Mullin and Fulling, 2004; Mullin et al., 

2004, Maze-Foley and Mullin, 2006; 

Mullin, 2007; Dias and Garrison, 2016). 

Fraser’s dolphins are present in the 

GOM, but there are very few detections 

during marine mammal surveys (Mullin 

and Fulling, 2004; Dias and Garrison, 

2016). 

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.’’ 

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. 

All genetic samples collected during 

1994–2008 in waters greater than 200 m 

were of the offshore ecotype (Waring et 

al., 2016). 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. 

Genetic studies have shown significant 

differentiation between inshore stocks 

and the adjacent coastal stock (Sellas et 

al., 2005) and among dolphins living in 

coastal and shelf waters (Waring et al., 

2016), suggesting that despite spatial 

overlap there may be mechanisms 

reducing interbreeding among coastal 

stocks and between coastal stocks and 

BSE stocks (Waring et al., 2016). 

Continued studies are necessary to 

examine the current stock boundaries 

delineated in coastal, shelf, and oceanic 

waters (Waring et al., 2016). 

In Table 3 above, we report two sets 

of abundance estimates: those from 

NMFS’s 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 for more detail. 

NMFS’s 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 NMFS 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’s SAR estimates also 

typically do not incorporate correction 

for detection bias. Therefore, they 

should generally be considered as 

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’s 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 data from 1992–2009. The 

latter factor—incorporation of correction 

for detection bias—should 

systematically result in greater 

abundance predictions. For these 

reasons, we expect that 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—we generally believe that 

the Roberts et al. (2016) abundance 

predictions are most appropriate 

because they were used to generate the 

exposure estimates and therefore 


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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’s 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 

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. The review, 

described in a technical memorandum 

(Rosel et al. (2016)), 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). 

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. 

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 twelve formally recognized UMEs 

affecting marine mammals in the region 

and involving species under NMFS’s 

jurisdiction. These have primarily 

impacted coastal bottlenose dolphins, 

with multiple UMEs determined to have 

resulted from biotoxins and one from 

infectious disease. None of these 

involve ongoing investigation. Most 

significantly, a UME affecting multiple 

cetacean species in the northern GOM 

occurred from 2010–2014. 

The northern GOM UME was 

determined to have begun in March 

2010 and extended through July 2014. 

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 (described below) 

determined that the DWH oil spill 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 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. 

However, increased dolphin 

strandings occurred in Louisiana and 

Mississippi before the DWH oil spill, 

and identified stranding clusters within 

the UME suggest that the event may 

involve different additional contributing 

factors varying by location, time, and 

population (Venn-Watson et al., 2015a). 

Some previous GOM cetacean UMEs 

had included environmental influences 

(e.g., low salinity due to heavy rainfall 

and associated runoff of land-based 

pesticides, low temperatures) as 

possible contributing factors (Litz et al., 

2014). Low air and water temperatures 

occurred in the spring of 2010 

throughout the GOM prior to and during 

the start of the UME, and a portion of 

the pre-spill atypical strandings 

occurred in Lake Pontchartrain, 

Louisiana, concurrent with lower than 

average salinity (Mullin et al., 2015). 

Therefore, a large part of the pre-spill 

increased dolphin strandings may have 

been due to a combination of cold 

temperatures and low salinity (Litz et 

al., 2014). 

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). In order to 

diagnose health, dolphin capture-release 

health assessments were conducted in 

Barataria Bay, during which physical 

examinations, including weighing and 

morphometric measurements, were 

conducted, routine biological samples 

(e.g., blood, tissue) were obtained, and 

animals were examined with 

ultrasound. Veterinarians then reviewed 


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the findings and determined an overall 

prognosis for each animal (e.g., 

favorable outcome expected, outcome 

uncertain, unfavorable outcome 

expected). Almost half of the examined 

animals were given a guarded or worse 

prognosis, and 17 percent were not 

expected to survive (Schwacke et al., 

2014a). 

The prevalence of brucellosis and 

morbillivirus infections was low and 

biotoxin levels were low or below the 

detection limit, meaning that these were 

not likely primary causes of the UME 

(Venn-Watson et al., 2015b; Fauquier et 

al., 2017). Subsequent study found that 

persistent organic pollutants (e.g., 

polychlorinated biphenyls), which are 

associated with endocrine disruption 

and immune suppression when present 

in high levels, are likely not a primary 

contributor to the poor health 

conditions and increased mortality 

observed in these GOM populations 

(Balmer et al., 2015). 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). Research into 

the long-term health effects of the spill 

on marine mammal populations is 

ongoing. For more information on the 

UME, please visit www.nmfs.noaa.gov/ 

pr/health/mmume/cetacean_gulfof

mexico.htm. 

Prior UMEs averaged six months in 

duration and involved significantly 

fewer mortalities. In most of these 

relatively localized events, dolphin 

morbillivirus or brevetoxicosis was 

confirmed or suspected as a causal 

factor (Litz et al., 2014). One other 

recent UME occurred during 2011–12 

for bottlenose dolphins in Texas. 

Investigators were not able to determine 

a cause for the UME, though findings 

included lung infection, poor body 

condition, and discoloring of teeth. No 

connection has been identified between 

this event and the 2010–14 event 

described above. For more information 

on UMEs, please visit: 

www.fisheries.noaa.gov/national/ 

marine-life-distress/marine-mammalunusual-mortality-events. 

Deepwater Horizon Oil Spill 

We introduced the DWH oil spill— 

which includes the impacts of the spill 

as well as the response efforts— 

previously in our description of the 

‘‘Specified Geographical Region.’’ Here 

we provide additional description of the 

potential effects of the spill on the 

marine mammals that may be affected 

by the activities that are the subject of 

this proposed rule. The summary 

provided below is an incorporation by 

reference of relevant information from 

DWH NRDA Trustees (2016) and DWH 

MMIQT (2015); more detail on the DWH 

oil spill and its effects on marine 

mammals is available in these 

documents. Additional technical reports 

relating to the assessment of marine 

mammal injury due to the DWH oil spill 

are available online at: www.doi.gov/ 

deepwaterhorizon/adminrecord. A brief 

overview of injury assessment activities 

and associated findings is provided by 

Wallace et al., (2017). 

On April 20, 2010, the Deepwater 

Horizon offshore drilling platform, a 

semi-submersible exploratory drilling 

rig operating on the exploratory 

Macondo well (within BOEM’s 

Mississippi Canyon lease block), 

exploded and subsequently sank in 

1,522 m of water in the GOM, 

approximately 81 km off the coast of 

Louisiana. This incident resulted in the 

release of an estimated 3.19 million 

barrels (134 million gallons) of oil from 

the compromised well. In addition, 

approximately 1.84 million gallons of 

chemical dispersants were applied to 

the waters of the spill area. The release 

of oil continued for 87 days, with an 

average of more than 1.5 million gallons 

of fresh oil entering the ocean per day— 

essentially creating a new major oil spill 

every day for nearly 3 months, 

equivalent to the 1989 Exxon Valdez oil 

spill re-occurring in the same location 

every week for the duration. Response 

techniques included deployment of 

containment booms, physical removal of 

oil, controlled burning of oil on the 

surface, major releases of fresh water to 

keep the oil offshore, beach and fishery 

closures, construction of berms, wildlife 

rehabilitation and relocation (e.g., 

Wilkin et al., 2017), and application of 

chemical dispersants on the surface and 

at the wellhead on the seafloor (with the 

goal of breaking the oil into small 

droplets). For more information about 

the DWH oil spill, please visit 

response.restoration.noaa.gov/ 

deepwater-horizon-oil-spill and 

www.deepwaterhorizoneconomic

settlement.com/docs.php. 

An estimated 7.7 billion standard 

cubic feet of natural gas was released in 

association with the oil; bacteria 

proliferated, consumed the gas, and 

died. Mucus produced by bacteria, as 

well as some of the bacterial mass itself, 

agglomerated with brown-colored oil 

droplets and settled through the water 

column—this phenomenon is referred to 

as ‘‘marine oil snow.’’ Oil, released from 

the well-head approximately 1,500 m 

deep, moved with currents, creating a 

plume of oil within the deep sea; oil and 

associated ‘‘marine oil snow’’ also 

settled on the sea floor. More buoyant 

oil traveled up through the water 

column and formed large surface slicks; 

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. Figure 3 

shows the cumulative area of detectable 

surface oil slick during the DWH oil 

spill. 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. Air 

pollution resulted from compounds in 

the oil that evaporated into the air and 

from fires purposely started to burn off 

oil at the ocean surface. The oil released 

during the event was a complex mixture 

containing thousands of individual 

chemical compounds—many of which 

are known to be toxic to biota—which 

then changed as they were subject to 

natural processes such as mixing with 

air and water, microbial degradation, 

and exposure to sunlight. DWH oil has 

a specific chemical signature that, 

together with other lines of evidence, 

allowed investigators to determine 

which oil-derived contaminants found 

in the environment originated from the 

spill. 

Dispersants are chemicals that reduce 

the tension between oil and water, 

leading to the formation of oil droplets 

that more readily disperse within the 

water column. A main purpose of using 

dispersants is to enhance the rate at 


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which bacteria degrade the oil in order 

to prevent oil slicks from fouling 

sensitive shoreline habitats. The largescale use of dispersants raised concerns 

about the potential for toxic effects of 

dispersed oil in the water column, as 

well as the potential for hypoxia due to 

bacterial consumption of dispersed oil. 

The surface application of dispersants 

increased exposure of near-surface 

biota, such as marine mammals, to oil 

that re-entered the water column. 

The DWH oil spill was subject to the 

provisions of the Oil Pollution Act 

(OPA) of 1990 (33 U.S.C. 2701 et seq.), 

which addresses prevention, response, 

and compensation for oil pollution 

incidents in navigable waters, adjoining 

shorelines, and the U.S. EEZ. Under the 

authority of OPA, a council of Federal 

and state trustees was established, on 

behalf of the public, to assess natural 

resource injuries resulting from the 

incident and work to make the 

environment and public whole for those 

injuries. As required under OPA, the 

trustees conducted a natural resource 

damage assessment (NRDA), finding 

that the injuries resulting from the DWH 

oil spill affected such a wide array of 

linked resources over such an enormous 

area that the effects must be described 

as constituting an ecosystem-level 

injury. OPA regulations (15 CFR part 

990) establish a process for conducting 

a NRDA that require, in part, the 

assessment of potential injuries to 

relevant resources, here including 

marine mammals and habitats they rely 

upon. OPA regulations define injury as 

an observable or measurable adverse 

change in a natural resource that may 

occur directly or indirectly. Types of 

injuries include adverse changes in 

survival, growth, and reproduction; 

health, physiology and biological 

condition; behavior; community 

composition; ecological processes and 

functions; and physical and chemical 

habitat quality or structure. 

The injury assessment first requires a 

determination of whether an incident 

injured natural resources. Trustees 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). Because of the 

vast scale of the incident, the trustees 

evaluated injuries to a set of 

representative habitats, communities, 

species, and ecological processes, with 

studies conducted at many scales. Key 

findings are as follows: (1) Oil flowed 

within deep ocean water currents 

hundreds of miles away from the well 

and moved upwards and across a very 

large area of the ocean surface, affecting 

vast areas overall (e.g., approximately 

112,000 km2 of ocean surface; 2,100 km 

of shoreline; and between 1,000–1,900 

km2 of seafloor), including every type of 

habitat occupied by marine mammals in 

the northern GOM as well as habitat for 

all stocks of marine mammals in the 

northern GOM; (2) the oil that was 

released was toxic to a wide range of 

organisms, including marine mammals; 

(3) oil came into contact with and 

injured a wide range of organisms, 

including marine mammals; (4) 


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response activities had collateral 

impacts on the environment; and (5) 

exposure to oil and response activities 

resulted in extensive injuries to 

multiple habitats, species, and 

ecological functions, across broad 

geographic regions. 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. Response 

workers and scientists witnessed 85 

instances of marine mammals (with a 

total of 1,394 individuals) swimming in 

surface oil or with oil on their bodies; 

these instances represented a minimum 

of 11 species, including dolphins, sperm 

whales, Kogia spp., and a beaked whale. 

The marine mammal injury 

assessment synthesized data from 

NRDA field studies, stranded carcasses 

collected by the Southeast Marine 

Mammal Stranding Network, historical 

data on marine mammal populations, 

NRDA toxicity testing studies, and the 

published literature. 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). Limited 

cetacean exposure studies have 

demonstrated that bottlenose dolphins 

may sustain liver damage and that 

bottlenose dolphins and sperm whales 

may develop skin lesions (Engelhardt, 

1983). Field and laboratory studies and 

other data analysis were designed to 

explicitly examine other potential 

explanations for marine mammal 

injuries, including biotoxins, infectious 

diseases, human and fishery 

interactions, and other unrelated 

potential contaminants. Each of these 

other factors was 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 are considered together, the 

DWH oil spill is the only reasonable 

cause for the full suite of observed 

adverse health effects. 

Findings related to bottlenose 

dolphins living in heavily oiled 

nearshore habitats were described 

previously in the UME discussion. 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 (i.e., Barataria Bay and 

Mississippi Sound) 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. 

Based on direct observation, injuries 

were quantified for four BSE stocks of 

bottlenose dolphin, e.g., for the 

Barataria Bay stock, the DWH oil spill 

caused 35 percent (CI 15–49) excess 

mortality, 46 percent (CI 21–65) excess 

failed pregnancies, and a 37 percent (CI 

14–57) higher likelihood that animals 

would have adverse health effects. The 

process for assigning a health prognosis 

(Schwacke et al., 2014a) was described 

previously in the UME discussion. Two 

dolphins having received the lowest 

grade died within 6 months, and the 

percentage of the population with the 

two lowest prognoses (17 percent poor 

and grave) essentially predicted the 

percentage of dolphins that disappeared 

and presumably died the following year 

based on photo-identification surveys. 

Investigators then used a population 

modeling approach to capture the 

overlapping and synergistic 

relationships among the three 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 example, 

lost cetacean years were estimated for 

the Barataria Bay stock of bottlenose 

dolphins, leading to an estimated 51 

percent (CI 32–72) maximum reduction 

in population size and a time to 

recovery of 39 years (CI 24–80) in the 

absence of potential benefits of 

restoration activities. 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). 

To calculate the increase in percent 

mortality for the shelf and oceanic 

marine mammal stocks, the Barataria 

Bay percent mortality was applied to the 

percentage of animals in each stock that 

was exposed to oil. This percentage was 

calculated assuming that animals 

experiencing a level of cumulative 

surface oiling similar to or greater than 

that in Barataria Bay would have been 

likely to suffer a similar or greater 

degree and magnitude of injury. 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 

in deeper waters were exposed to very 

high concentrations of volatile gas 

compounds at the water’s surface near 

the wellhead. 

As an example of the calculation, 47 

percent of the spinner dolphin stock 

range in the northern GOM experienced 

oiling equal to or greater than Barataria 

Bay, and, therefore, was assumed to 

have experienced a rate of mortality 

increase equal to that calculated for 

Barataria Bay (35 percent). Thus, the 

entire northern GOM spinner dolphin 

stock is assumed to have experienced a 

16 percent mortality increase (0.35 × 

0.47 = 0.16). Similarly, the percentage of 

females with reproductive failure in 

Barataria Bay and Mississippi Sound (46 

percent; stocks pooled for sample size 

considerations) is considered to be the 

best estimate of excess failed 

pregnancies for other marine mammals 

in the oil spill footprint, and the 

percentage of the population with a 

guarded or worse health prognosis— 

compared with dolphins sampled in a 

healthy reference population—from 

Barataria Bay (37 percent) was applied 

to other stocks. 

The population modeling approach 

used in the injury quantification allows 

consideration of long-term impacts 

resulting from individual losses, adverse 

reproductive effects, and persistent 

impacts on survival for exposed 

animals. The model was run using 

baseline mortality and reproductive 

parameters to determine what the 

population trajectory of each stock 

would have been if the DWH spill had 

not happened. The same model was 

then run a second time, with estimates 

for excess mortality, reproductive 


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failures, and adverse health effects due 

to the DWH oil spill. The number of 

years predicted for the DWH oilimpacted population to recover (without 

active restoration) is the number of 

years until the DWH oil-injured 

population trajectory reaches 95 percent 

of the baseline population trajectory, 

reported as years to recovery. The 

output from the population model also 

predicts the largest proportional 

decrease in population size (i.e., the 

difference between the two population 

trajectories when the DWH oil-impacted 

trajectory is at its lowest point). A 

separate population model is run for 

each stock, with inputs for the models 

restricted to the available data for each 

stock. For inputs without empirical 

data, the values are extrapolated from 

other stocks or incorporate additional 

modeling efforts. For bottlenose 

dolphins, uncertainty in model output 

was evaluated by drawing from the 

distributions for model input 

parameters to execute 10,000 

simulations, producing distributions for 

each of the model outputs. For other 

species, because there was insufficient 

information to construct informed input 

parameter distributions, only a single 

model scenario was run using point 

estimates for input parameter values 

and simulations were not conducted to 

explore the effects of uncertainty in the 

model parameters. 

The results of these calculations for 

each affected shelf and oceanic stock, 

and for northern and western coastal 

stocks of bottlenose dolphin, are 

presented in Table 4. The eastern 

coastal stock of bottlenose dolphin was 

considered to be not affected by the 

DWH oil spill, as the cumulative 

footprint of oil did not overlap the 

stock’s range. Results for BSE dolphin 

stocks are not presented here. 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 4—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). Tens of thousands of 

marine mammals were exposed to the 

DWH surface slick, where they inhaled, 

aspirated, ingested, and came into 

contact with oil components (Dias et al., 

2017). The oil’s physical and toxic 

effects damaged tissues and organs, 

leading to a constellation of adverse 

health effects, including reproductive 

failure, adrenal disease, lung disease, 

and poor body condition, as observed in 

bottlenose dolphins (De Guise et al., 

2017; Kellar et al., 2017). Coastal and 

estuarine bottlenose dolphin 

populations were some of the most 

severely injured (Hohn et al., 2017; 

Rosel et al., 2017; Thomas et al., 2017), 

as described previously in relation to 

the UME, but oceanic species were also 

exposed and experienced increased 

mortality, increased reproductive 

failure, and a higher likelihood of other 

adverse health effects. 

Due to the scope of the spill, the 

magnitude of potentially injured 

populations, and the difficulties and 

limitations of working with marine 

mammals, it is impossible to quantify 

injury without uncertainty. Wherever 

possible, the quantification results 

represent ranges of values that 

encapsulate the uncertainty inherent in 

the underlying datasets. The population 

model outputs shown in Table 4 best 

represent the temporal magnitude of the 

injury and the potential recovery time 

from the injury. 

Aside from the heavily impacted 

stocks of bottlenose dolphin, two 

species of particular concern are the 

sperm whale and Bryde’s whale. For the 

Bryde’s whale, it was estimated that 48 

percent of the population was impacted 

by DWH oil, resulting in an estimated 

22 percent maximum decline in 

population size that will require 69 

years to recovery. However, small 

populations are highly susceptible to 


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stochastic, or unpredictable, processes 

and genetic effects that can reduce 

productivity and resiliency to 

perturbations. The population models 

do not account for these effects, and, 

therefore, the capability of the Bryde’s 

whale population to recover from this 

injury is unknown. For the sperm 

whale, a 7 percent maximum decline in 

population size requiring 21 years to 

recovery was predicted. However, little 

is known about the fate and transport of 

DWH deep-sea oil plumes in relation to 

deep-diving marine mammals, such as 

sperm whales, and the results should be 

viewed with caution. Other stocks with 

particularly concerning results include 

the rough-toothed dolphin and spinner 

dolphin (Table 4). 

In the absence of active (and effective) 

restoration, marine mammal stocks 

across the northern GOM will take many 

years to recover (Table 4). Marine 

mammals are slow to reach reproductive 

maturity, only give birth to a single 

offspring every 3 to 5 years, and are 

generally long lived (with lifespans up 

to 80 years). Two populations of killer 

whales suffered losses of 33 and 41 

percent in the year following the Exxon 

Valdez oil spill in Alaska, and recovery 

of both populations has been 

unexpectedly slow (Matkin et al., 2008). 

Persistent pollutant exposure (Ylitalo et 

al., 2001), decline of a primary prey 

source (Ver Hoef and Frost, 2003), and 

disruption of social groups (Matkin et 

al., 2008; Wade et al., 2012) may be 

contributing factors. Populations of 

dolphins depleted as the result of tuna 

fishery bycatch in the eastern tropical 

Pacific also demonstrated slower than 

expected rates of recovery, which may 

be due in part to the continued effects 

of stressful interactions with the fishery 

(Gerrodette and Forcada, 2005). 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. We treat the 

effects of the DWH oil spill as part of the 

environmental baseline in considering 

the likely resilience of these populations 

to the effects of the activities considered 

in this proposed regulatory framework. 

In addition to injuries from direct 

exposure to DWH oil, marine mammal 

habitat was degraded. Exposure to oil at 

or near the surface occurred in an area 

of high biological abundance and high 

productivity during a time of year 

(spring and summer) that corresponds 

with peaks in seasonal productivity in 

the northern GOM. Developing fish 

larvae exposed to the surface slick 

suffered almost 100 percent mortality, 

and oil concentrations at different levels 

in the water column exceeded levels 

known to cause mortality and sub-lethal 

effects to fish—this is expected to have 

caused the loss of millions to billions of 

fish that would have reached one year 

of age. However, though damage to fish 

and invertebrate populations was likely 

significant during the time oil was 

present, populations of directly affected 

fish and invertebrate species appear not 

to have suffered a lasting impact. 

Although marine mammals were 

harmed through the effects of DWH oil 

on plankton, fish, and invertebrate 

populations, it is difficult to interpret 

any long-term impacts on marine 

mammal populations resulting from 

significant short-term impacts on prey 

populations. Prey reductions, when they 

occur, can have cascading effects on 

larger species. Animals in the wild live 

in a dynamic relationship with their 

environment and available resources, 

balancing energy expenditures and 

nutritional uptake in order to survive, 

remain healthy, and reproduce. Any 

impact that shifts that balance by 

diminishing food resources or requiring 

unusual expenditures of energy— 

whether to acquire prey, avoid 

predators, fight disease and infection, or 

successfully reproduce—is inherently 

harmful to the species. Additionally, as 

noted previously, injury due to the 

DWH oil spill is considered an 

ecosystem-level event, which will 

impact marine mammals in particular 

due to their long lives and position as 

apex predators reliant upon a healthy 

ecosystem (e.g., Moore, 2008; Bossart, 

2011). 

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 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). Subsequently, NMFS (2016) 

described 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 an 

exception for lower limits for lowfrequency cetaceans where the result 

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, with 

best hearing estimated to be from 100 

Hz to 8 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, 

with best hearing from 10 to less than 

100 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 (2016) 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 3. 

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 

Activity on Marine Mammals and Their 

Habitat 

This section includes a summary and 

discussion of the ways that components 

of the specified activity may impact 

marine mammals and their habitat. The 

‘‘Estimated Take’’ section later in this 

document includes a quantitative 

analysis of the number of individuals 

that are expected to be taken by this 

activity. The ‘‘Negligible Impact 

Analysis and Determination’’ section 

considers the content of this section and 


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the material it references, the 

‘‘Estimated Take’’ section, and the 

‘‘Proposed Mitigation’’ section, to draw 

conclusions regarding the likely impacts 

of these activities on the reproductive 

success or survivorship of individuals 

and how those impacts on individuals 

are likely to impact marine mammal 

species or stocks. In the following 

discussion, we provide general 

background information on sound 

before considering potential effects to 

marine mammals from the specified 

activities (i.e., sound, ship strike, and 

contaminants). 

Background on Sound and Acoustic 

Metrics 

This section contains a brief technical 

background on sound, on the 

characteristics of certain sound types, 

and on metrics used in this proposal 

inasmuch as the information is relevant 

to other sections of this document. For 

general information on sound and its 

interaction with the marine 

environment, please see, e.g., Au and 

Hastings (2008); Richardson et al. 

(1995); Urick (1983). 

Sound travels in waves, the basic 

components of which are frequency, 

wavelength, velocity, and amplitude. 

Frequency is the number of pressure 

waves that pass by a reference point per 

unit of time and is measured in Hz or 

cycles per second. Wavelength is the 

distance between two peaks or 

corresponding points of a sound wave 

(length of one cycle). Higher frequency 

sounds have shorter wavelengths than 

lower frequency sounds, and typically 

attenuate (decrease) more rapidly, 

except in certain cases in shallower 

water. Amplitude is the height of the 

sound pressure wave or the ‘‘loudness’’ 

of a sound and is typically described 

using the relative unit of the 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)), and is a 

logarithmic unit that accounts for large 

variations in amplitude; therefore, a 

relatively small change in dB 

corresponds to large changes in sound 

pressure. 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). 

When underwater objects vibrate or 

activity occurs, sound-pressure waves 

are created. These waves alternately 

compress and decompress the water as 

the sound wave travels. Underwater 

sound waves radiate in a manner similar 

to ripples on the surface of a pond and 

may be either directed in a beam or 

beams or may radiate in all directions 

(omnidirectional sources), as is 

nominally the case for sound produced 

by airguns (though when grouped in 

arrays there is some directionality). The 

compressions and decompressions 

associated with sound waves are 

detected as changes in pressure by 

aquatic life and man-made sound 

receptors such as hydrophones. 

Sounds are often considered to fall 

into one of two general types: Pulsed 

and non-pulsed (defined in the 

following). The distinction between 

these two sound types is important 

because they have differing potential to 

cause physical effects, particularly with 

regard to hearing (e.g., Ward, 1997 in 

Southall et al., 2007). Please see 

Southall et al. (2007) for an in-depth 

discussion of these concepts. The 

distinction between these two sound 

types is not always obvious, as certain 

signals share properties of both pulsed 

and non-pulsed sounds. A signal near a 

source could be categorized as a pulse, 

but due to propagation effects as it 

moves farther from the source, the 

signal duration becomes longer (e.g., 

Greene and Richardson, 1988). 

Pulsed sound sources (e.g., airguns, 

explosions, gunshots, sonic booms, 

impact pile driving) 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. 

Non-pulsed sounds can be tonal, 

narrowband, or broadband, brief or 

prolonged, and may be either 

continuous or intermittent (ANSI, 1995; 

NIOSH, 1998). Some of these nonpulsed sounds can be transient signals 

of short duration but without the 

essential properties of pulses (e.g., rapid 

rise time). Examples of non-pulsed 

sounds include those produced by 

vessels, aircraft, machinery operations 

such as drilling or dredging, vibratory 

pile driving, and active sonar systems. 

The duration of such sounds, as 

received at a distance, can be greatly 

extended in a highly reverberant 

environment. 

Root mean square (rms) is the 

quadratic mean sound pressure over the 

duration of an impulse. Root mean 

square is calculated by squaring all of 

the sound amplitudes, averaging the 

squares, and then taking the square root 

of the average (Urick, 1983). Root mean 

square accounts for both positive and 

negative values; squaring the pressures 

makes all values positive so that they 

may be accounted for in the summation 

of pressure levels (Hastings and Popper, 

2005). The length of the time window 

used for the purpose of the rms SPL 

calculation can be selected using 

different approaches. This value is 

commonly defined as the 90 percent 

energy pulse duration, containing the 

central 90 percent (from 5 to 95 percent 

of the total) of the cumulative square 

pressure (or sound exposure level) of 

the pulse. However, as was the case in 

the modeling performed for this effort, 

a fixed time window may be used. Here, 

a sliding window was used to calculate 

rms SPL values for a series of fixed 

window lengths within the pulse. The 

maximum value of rms SPL over all 

time window positions is taken to 

represent the rms SPL of the pulse. 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. 

Energy equivalent SPL (denoted Leq) is 

the measure of the average amount of 

energy carried by a time-dependent 

pressure wave over a period of time. 

The Leq is numerically equal to the rms 

SPL of a steady sound that has the same 

total energy as the sound measured over 

the given time window. Conceptually, 

the difference between the two metrics 

is that the rms SPL is computed over 

short time periods, usually one second 

or less, and tracks the fluctuations of a 

non-steady acoustic signal, whereas the 

Leq reflects the average SPL of an 

acoustic signal over tens of seconds or 

longer. 

Sound exposure level (SEL; 

represented as dB re 1 mPa2-s) represents 

the total energy in a stated frequency 

band over a stated time interval or 

event, and considers both intensity and 

duration of exposure. The per-pulse SEL 

is calculated over the time window 

containing the entire pulse (i.e., 100 

percent of the acoustic energy). SEL is 

a cumulative metric; it can be 

accumulated over a single pulse, or 

calculated over periods containing 

multiple pulses. Cumulative SEL 

represents the total energy accumulated 

by a receiver over a defined time 

window or during an event. 

Peak sound pressure (also referred to 

as zero-to-peak sound pressure or 0-pk) 

is the maximum instantaneous sound 


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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). 

Airguns produce pulsed signals, with 

energy in a frequency range from about 

10–2,000 Hz, and most energy radiated 

at frequencies below 200 Hz. Larger 

airguns, with larger internal air volume, 

produce higher broadband sound levels 

with sound energy spectrum shifted 

toward the lower frequencies. The 

amplitude of the acoustic wave emitted 

from the source is equal in all directions 

(i.e., omnidirectional), but when used in 

arrays, airguns 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 

more sound energy is focused 

downwardly than horizontally, and 

sound transmitted in horizontal 

directions and at higher frequencies is 

minimized to the extent possible. 

Acoustic sources used for 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, and temporal characteristics 

that more closely resemble those of 

impulsive sounds than non-impulsive 

sounds. Boomers generate a highamplitude broadband (100 Hz–10 kHz) 

acoustic pulse with high downward 

directivity, though may be considered 

omnidirectional at frequencies below 1 

kHz. Subbottom profiler systems 

generally project a chirp pulse spanning 

an operator-selectable 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). 

Vessel noise, produced largely by 

cavitation of propellers and by 

machinery inside the hull, is considered 

a non-pulsed sound. Sounds emitted by 

survey vessels are low frequency and 

continuous, but would be widely 

dispersed in both space and time. 

Survey vessel traffic is of low density 

compared to traffic associated with 

commercial shipping, industry support 

vessels, or commercial fishing vessels, 

and would therefore be expected to 

represent an insignificant incremental 

increase in the total amount of 

anthropogenic sound input to the 

marine environment. For these reasons, 

we do not consider vessel traffic noise 

further in this analysis. 

Potential Effects of Underwater Sound 

Note that, in the following discussion, 

we refer in many cases to a review 

article concerning studies of noiseinduced hearing loss conducted from 

1996–2015 (i.e., Finneran, 2015). For 

study-specific citations, please see that 

work. Anthropogenic sounds cover a 

broad range of frequencies and sound 

levels and can have a range of highly 

variable impacts on marine life, from 

none or minor to potentially severe 

responses, depending on received 

levels, duration of exposure, behavioral 

context, and various other factors. The 

potential effects of underwater sound 

from active acoustic sources can 

potentially result in one or more of the 

following: Temporary or permanent 

hearing impairment, non-auditory 

physical or physiological effects, 

behavioral disturbance, stress, and 

masking (Richardson et al., 1995; 

Gordon et al., 2004; Nowacek et al., 

2007; Southall et al., 2007; Go ̈tz et al., 

2009). The degree of effect is 

intrinsically related to the signal 

characteristics, received level, distance 

from the source, and duration of the 

sound exposure. In general, sudden, 

high level sounds can cause hearing 

loss, as can longer exposures to lower 

level sounds. Temporary or permanent 

loss of hearing will occur almost 

exclusively for noise within an animal’s 

hearing range. We first describe specific 

manifestations of acoustic effects before 

providing discussion specific to the use 

of airgun arrays. 

Richardson et al. (1995) described 

zones of increasing intensity of effect 

that might be expected to occur, in 

relation to distance from a source and 

assuming that the signal is within an 

animal’s hearing range. First is the area 

within which the acoustic signal would 

be audible (potentially perceived) to the 

animal, but not strong enough to elicit 

any overt behavioral or physiological 

response. The next zone corresponds 

with the area where the signal is audible 

to the animal and of sufficient intensity 

to elicit behavioral or physiological 

responsiveness. Third is a zone within 

which, for signals of high intensity, the 

received level is sufficient to potentially 

cause discomfort or tissue damage to 

auditory or other systems. Overlaying 

these zones to a certain extent is the 

area within which 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) may occur; the 

masking zone may be highly variable in 

size. 

We describe more severe effects (i.e., 

certain non-auditory physical or 

physiological effects) only briefly as we 

do not expect that use of airgun arrays 

are reasonably likely to result in such 

effects (see below for further 

discussion). Potential effects from 

impulsive sound sources can range in 

severity from effects such as behavioral 

disturbance or tactile perception to 

physical discomfort, slight injury of the 

internal organs and the auditory system, 

or mortality (Yelverton et al., 1973). 

Non-auditory physiological effects or 

injuries that theoretically might occur in 

marine mammals exposed to high level 

underwater sound or as a secondary 

effect of extreme behavioral reactions 

(e.g., change in dive profile as a result 

of an avoidance reaction) caused by 

exposure to sound include neurological 

effects, bubble formation, resonance 

effects, and other types of organ or 

tissue damage (Cox et al., 2006; Southall 

et al., 2007; Zimmer and Tyack, 2007; 

Tal et al., 2015). The survey activities 

considered here do not involve the use 

of devices such as explosives or midfrequency tactical sonar that are 

associated with these types of effects. 

When a live or dead marine mammal 

swims or floats onto shore and is 

incapable of returning to sea, the event 

is termed a ‘‘stranding’’ (16 U.S.C. 

1421h(3)). Marine mammals are known 

to strand for a variety of reasons, such 

as infectious agents, biotoxicosis, 

starvation, fishery interaction, ship 

strike, unusual oceanographic or 

weather events, sound exposure, or 

combinations of these stressors 

sustained concurrently or in series (e.g., 

Geraci et al., 1999). However, the cause 

or causes of most strandings are 

unknown (e.g., Best, 1982). 

Combinations of dissimilar stressors 

may combine to kill an animal or 

dramatically reduce its fitness, even 

though one exposure without the other 

would not be expected to produce the 

same outcome (e.g., Sih et al., 2004). For 

further description of specific stranding 

events see, e.g., Southall et al., 2006, 

2013; Jepson et al., 2013; Wright et al., 

2013. 

Use of military tactical sonar has been 

implicated in multiple investigated 

stranding events, although one 

stranding event was contemporaneous 

with and reasonably associated spatially 


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with the use of seismic airguns. This 

event occurred in the Gulf of California, 

coincident with seismic reflection 

profiling by the R/V Maurice Ewing 

operated by Columbia University’s 

Lamont-Doherty Earth Observatory and 

involved two Cuvier’s beaked whales 

(Hildebrand, 2004). The vessel had been 

firing an array of 20 airguns with a total 

volume of 8,500 in3 (Hildebrand, 2004; 

Taylor et al., 2004). Most known 

stranding events have involved beaked 

whales, though a small number have 

involved deep-diving delphinids or 

sperm whales (e.g., Mazzariol et al., 

2010; Southall et al., 2013). In general, 

long duration (∼1 second) and highintensity sounds (235 dB SPL) have 

been implicated in stranding events 

(Hildebrand, 2004). With regard to 

beaked whales, mid-frequency sound is 

typically implicated (when causation 

can be determined) (Hildebrand, 2004). 

Although seismic airguns create 

predominantly low-frequency energy, 

the signal does include a mid-frequency 

component. 

Threshold Shift—Marine mammals 

exposed to high-intensity sound, or to 

lower-intensity sound for prolonged 

periods, can experience hearing 

threshold shift (TS), which is the loss of 

hearing sensitivity at certain frequency 

ranges (Finneran, 2015). TS can be 

permanent (PTS), in which case the loss 

of hearing sensitivity is not fully 

recoverable, or temporary (TTS), in 

which case the animal’s hearing 

threshold would recover over time 

(Southall et al.,, 2007). Repeated sound 

exposure that leads to TTS could cause 

PTS. In severe cases of PTS, there can 

be total or partial deafness, while in 

most cases the animal has an impaired 

ability to hear sounds in specific 

frequency ranges (Kryter, 1985). 

When PTS occurs, there is physical 

damage to the sound receptors in the ear 

(i.e., tissue damage), whereas TTS 

represents primarily tissue fatigue and 

is reversible (Southall et al., 2007). In 

addition, other investigators have 

suggested that TTS is within the normal 

bounds of physiological variability and 

tolerance and does not represent 

physical injury (e.g., Ward, 1997). 

Therefore, NMFS does not consider TTS 

to constitute auditory injury. 

Relationships between TTS and PTS 

thresholds have not been studied in 

marine mammals, and there is no PTS 

data for cetaceans, but such 

relationships are assumed to be similar 

to those in humans and other terrestrial 

mammals. PTS typically occurs at 

exposure levels at least several decibels 

above (a 40-dB threshold shift 

approximates PTS onset; e.g., Kryter et 

al., 1966; Miller, 1974) that inducing 

mild TTS (a 6-dB threshold shift 

approximates TTS onset; e.g., Southall 

et al. 2007). Based on data from 

terrestrial mammals, a precautionary 

assumption is that the PTS thresholds 

for impulse sounds (such as airgun 

pulses as received close to the source) 

are at least 6 dB higher than the TTS 

threshold on a peak-pressure basis and 

PTS cumulative sound exposure level 

thresholds are 15 to 20 dB higher than 

TTS cumulative sound exposure level 

thresholds (Southall et al., 2007). Given 

the higher level of sound or longer 

exposure duration necessary to cause 

PTS as compared with TTS, it is 

considerably less likely that PTS could 

occur. 

For mid-frequency cetaceans in 

particular, potential protective 

mechanisms may help limit onset of 

TTS or prevent onset of PTS. Such 

mechanisms include dampening of 

hearing, auditory adaptation, or 

behavioral amelioration (e.g., Nachtigall 

and Supin, 2013; Miller et al., 2012; 

Finneran et al., 2015; Popov et al., 2016; 

Nachtigall et al., 2017). 

TTS is the mildest form of hearing 

impairment that can occur during 

exposure to sound (Kryter, 1985). While 

experiencing TTS, the hearing threshold 

rises, and a sound must be at a higher 

level in order to be heard. In terrestrial 

and marine mammals, TTS can last from 

minutes or hours to days (in cases of 

strong TTS). In many cases, hearing 

sensitivity recovers rapidly after 

exposure to the sound ends. Few data 

on sound levels and durations necessary 

to elicit mild TTS have been obtained 

for marine mammals. 

Marine mammal hearing plays a 

critical role in communication with 

conspecifics, and interpretation of 

environmental cues for purposes such 

as predator avoidance and prey capture. 

Depending on the degree (elevation of 

threshold in dB), duration (i.e., recovery 

time), and frequency range of TTS, and 

the context in which it is experienced, 

TTS can have effects on marine 

mammals ranging from discountable to 

serious. For example, a marine mammal 

may be able to readily compensate for 

a brief, relatively small amount of TTS 

in a non-critical frequency range that 

occurs during a time where ambient 

noise is lower and there are not as many 

competing sounds present. 

Alternatively, a larger amount and 

longer duration of TTS sustained during 

time when communication is critical for 

successful mother/calf interactions 

could have more serious impacts. 

Finneran et al. (2015) measured 

hearing thresholds in three captive 

bottlenose dolphins before and after 

exposure to ten pulses produced by a 

seismic airgun in order to study TTS 

induced after exposure to multiple 

pulses. Exposures began at relatively 

low levels and gradually increased over 

a period of several months, with the 

highest exposures at peak SPLs from 

196 to 210 dB and cumulative 

(unweighted) SELs from 193–195 dB. 

No substantial TTS was observed. In 

addition, behavioral reactions were 

observed that indicated that animals can 

learn behaviors that effectively mitigate 

noise exposures (although exposure 

patterns must be learned, which is less 

likely in wild animals than for the 

captive animals considered in the 

study). The authors note that the failure 

to induce more significant auditory 

effects was likely due to the intermittent 

nature of exposure, the relatively low 

peak pressure produced by the acoustic 

source, and the low-frequency energy in 

airgun pulses as compared with the 

frequency range of best sensitivity for 

dolphins and other mid-frequency 

cetaceans. 

Currently, TTS data only exist for four 

species of cetaceans (bottlenose 

dolphin, beluga whale (Delphinapterus 

leucas), harbor porpoise (Phocoena 

phocoena), and Yangtze finless porpoise 

(Neophocoena asiaeorientalis)) exposed 

to a limited number of sound sources 

(i.e., mostly tones and octave-band 

noise) in laboratory settings (Finneran, 

2015). In general, harbor porpoises have 

a lower TTS onset than other measured 

cetacean species (Finneran, 2015). 

Additionally, the existing marine 

mammal TTS data come from a limited 

number of individuals within these 

species. There are no data available on 

noise-induced hearing loss for 

mysticetes. 

Critical questions remain regarding 

the rate of TTS growth and recovery 

after exposure to intermittent noise and 

the effects of single and multiple pulses. 

Data at present are also insufficient to 

construct generalized models for 

recovery and determine the time 

necessary to treat subsequent exposures 

as independent events. More 

information is needed on the 

relationship between auditory evoked 

potential and behavioral measures of 

TTS for various stimuli. For summaries 

of data on TTS in marine mammals or 

for further discussion of TTS onset 

thresholds, please see Southall et al. 

(2007), Finneran and Jenkins (2012), 

Finneran (2015), and NMFS (2016). 

Behavioral Effects—Behavioral 

disturbance may include a variety of 

effects, including subtle changes in 

behavior (e.g., minor or brief avoidance 

of an area or changes in vocalizations), 

more conspicuous changes in similar 

behavioral activities, and more 


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sustained and/or potentially severe 

reactions, such as displacement from or 

abandonment of high-quality habitat. 

Behavioral responses to sound are 

highly variable and context-specific and 

any reactions depend on numerous 

intrinsic and extrinsic factors (e.g., 

species, state of maturity, experience, 

current activity, reproductive state, 

auditory sensitivity, time of day), as 

well as the interplay between factors 

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

al., 2003; Southall et al., 2007; Weilgart, 

2007; Archer et al., 2010). Behavioral 

reactions can vary not only among 

individuals but also within an 

individual, depending on previous 

experience with a sound source, 

context, and numerous other factors 

(Ellison et al., 2012), and can vary 

depending on characteristics associated 

with the sound source (e.g., whether it 

is moving or stationary, number of 

sources, distance from the source). 

Please see Appendices B–C of Southall 

et al. (2007) for a review of studies 

involving marine mammal behavioral 

responses to sound. 

Habituation can occur when an 

animal’s response to a stimulus wanes 

with repeated exposure, usually in the 

absence of unpleasant associated events 

(Wartzok et al., 2003). Animals are most 

likely to habituate to sounds that are 

predictable and unvarying. It is 

important to note that habituation is 

appropriately considered as a 

‘‘progressive reduction in response to 

stimuli that are perceived as neither 

aversive nor beneficial,’’ rather than as, 

more generally, moderation in response 

to human disturbance (Bejder et al., 

2009). The opposite process is 

sensitization, when an unpleasant 

experience leads to subsequent 

responses, often in the form of 

avoidance, at a lower level of exposure. 

As noted, behavioral state may affect the 

type of response. For example, animals 

that are resting may show greater 

behavioral change in response to 

disturbing sound levels than animals 

that are highly motivated to remain in 

an area for feeding (Richardson et al., 

1995; NRC, 2003; Wartzok et al., 2003). 

Controlled experiments with captive 

marine mammals have showed 

pronounced behavioral reactions, 

including avoidance of loud sound 

sources (Ridgway et al., 1997). Observed 

responses of wild marine mammals to 

loud pulsed sound sources (typically 

airguns or acoustic harassment devices) 

have been varied but often consist of 

avoidance behavior or other behavioral 

changes suggesting discomfort (Morton 

and Symonds, 2002; see also Richardson 

et al., 1995; Nowacek et al., 2007). 

However, many delphinids approach 

acoustic source vessels with no 

apparent discomfort or obvious 

behavioral change (e.g., Barkaszi et al., 

2012). 

Available studies show wide variation 

in response to underwater sound; 

therefore, it is difficult to predict 

specifically how any given sound in a 

particular instance might affect marine 

mammals perceiving the signal. If a 

marine mammal does react briefly to an 

underwater sound by changing its 

behavior or moving a small distance, the 

impacts of the change are unlikely to be 

significant to the individual, let alone 

the stock or population. However, if a 

sound source displaces marine 

mammals from an important feeding or 

breeding area for a prolonged period, 

impacts on individuals and populations 

could be significant (e.g., Lusseau and 

Bejder, 2007; Weilgart, 2007; NRC, 

2005). However, there are broad 

categories of potential response, which 

we describe in greater detail here, that 

include alteration of dive behavior, 

alteration of foraging behavior, effects to 

breathing, interference with or alteration 

of vocalization, avoidance, and flight. 

Changes in dive behavior can vary 

widely, and may consist of increased or 

decreased dive times and surface 

intervals as well as changes in the rates 

of ascent and descent during a dive (e.g., 

Frankel and Clark, 2000; Ng and Leung, 

2003; Nowacek et al.; 2004; Goldbogen 

et al., 2013a, 2013b). Variations in dive 

behavior may reflect interruptions in 

biologically significant activities (e.g., 

foraging) or they may be of little 

biological significance. The impact of an 

alteration to dive behavior resulting 

from an acoustic exposure depends on 

what the animal is doing at the time of 

the exposure and the type and 

magnitude of the response. 

Disruption of feeding behavior can be 

difficult to correlate with anthropogenic 

sound exposure (but see discussion of 

impacts to sperm whale foraging 

behavior below and in ‘‘Proposed 

Mitigation’’), so it is usually inferred by 

observed displacement from known 

foraging areas, the appearance of 

secondary indicators (e.g., bubble nets 

or sediment plumes), or changes in dive 

behavior. As for other types of 

behavioral response, the frequency, 

duration, and temporal pattern of signal 

presentation, as well as differences in 

species sensitivity, are likely 

contributing factors to differences in 

response in any given circumstance 

(e.g., Croll et al., 2001; Nowacek et al.; 

2004; Madsen et al., 2006a; Yazvenko et 

al., 2007). A determination of whether 

foraging disruptions incur fitness 

consequences would require 

information on or estimates of the 

energetic requirements of the affected 

individuals and the relationship 

between prey availability, foraging effort 

and success, and the life history stage of 

the animal. 

Visual tracking, passive acoustic 

monitoring, and movement recording 

tags were used to quantify sperm whale 

behavior prior to, during, and following 

exposure to airgun arrays at received 

levels in the range 140–160 dB at 

distances of 7–13 km, following a phasein of sound intensity and full array 

exposures at 1–13 km (Madsen et al., 

2006a; Miller et al., 2009). Sperm 

whales did not exhibit horizontal 

avoidance behavior at the surface. 

However, foraging behavior may have 

been affected. The sperm whales 

exhibited 19 percent less vocal (buzz) 

rate during full exposure relative to post 

exposure, and the whale that was 

approached most closely had an 

extended resting period and did not 

resume foraging until the airguns had 

ceased firing. The remaining whales 

continued to execute foraging dives 

throughout exposure; however, 

swimming movements during foraging 

dives were 6 percent lower during 

exposure than control periods (Miller et 

al., 2009). These data raise concerns that 

airgun surveys may impact foraging 

behavior in sperm whales, although 

more data are required to understand 

whether the differences were due to 

exposure or natural variation in sperm 

whale behavior (Miller et al., 2009). We 

discuss these findings in greater detail 

under ‘‘Proposed Mitigation.’’ 

Variations in respiration naturally 

vary with different behaviors and 

alterations to breathing rate as a 

function of acoustic exposure can be 

expected to co-occur with other 

behavioral reactions, such as a flight 

response or an alteration in diving. 

However, respiration rates in and of 

themselves may be representative of 

annoyance or an acute stress response. 

Various studies have shown that 

respiration rates may either be 

unaffected or could increase, depending 

on the species and signal characteristics, 

again highlighting the importance in 

understanding species differences in the 

tolerance of underwater noise when 

determining the potential for impacts 

resulting from anthropogenic sound 

exposure (e.g., Kastelein et al., 2001, 

2005, 2006; Gailey et al., 2007; Gailey et 

al., 2016). 

Marine mammals vocalize for 

different purposes and across multiple 

modes, such as whistling, echolocation 

click production, calling, and singing. 

Changes in vocalization behavior in 

response to anthropogenic noise can 


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occur for any of these modes and may 

result from a need to compete with an 

increase in background noise or may 

reflect increased vigilance or a startle 

response. For example, in the presence 

of potentially masking signals, 

humpback whales and killer whales 

have been observed to increase the 

length of their songs (Miller et al., 2000; 

Fristrup et al., 2003; Foote et al., 2004), 

while right whales have been observed 

to shift the frequency content of their 

calls upward while reducing the rate of 

calling in areas of increased 

anthropogenic noise (Parks et al., 2007). 

In some cases, animals may cease sound 

production during production of 

aversive signals (Bowles et al., 1994). 

Cerchio et al. (2014) used passive 

acoustic monitoring to document the 

presence of singing humpback whales 

off the coast of northern Angola and to 

opportunistically test for the effect of 

seismic survey activity on the number of 

singing whales. Two recording units 

were deployed between March and 

December 2008 in the offshore 

environment; numbers of singers were 

counted every hour. Generalized 

Additive Mixed Models were used to 

assess the effect of survey day 

(seasonality), hour (diel variation), 

moon phase, and received levels of 

noise (measured from a single pulse 

during each ten minute sampled period) 

on singer number. The number of 

singers significantly decreased with 

increasing received level of noise, 

suggesting that humpback whale 

communication was disrupted to some 

extent by the survey activity. 

Castellote et al. (2012) reported 

acoustic and behavioral changes by fin 

whales in response to shipping and 

airgun noise. Acoustic features of fin 

whale song notes recorded in the 

Mediterranean Sea and northeast 

Atlantic Ocean were compared for areas 

with different shipping noise levels and 

traffic intensities and during an airgun 

survey. During the first 72 hours of the 

survey, a steady decrease in song 

received levels and bearings to singers 

indicated that whales moved away from 

the acoustic source and out of the study 

area. This displacement persisted for a 

time period well beyond the 10-day 

duration of airgun activity, providing 

evidence that fin whales may avoid an 

area for an extended period in the 

presence of increased noise. The authors 

hypothesize that fin whale acoustic 

communication is modified to 

compensate for increased background 

noise and that a sensitization process 

may play a role in the observed 

temporary displacement. 

Seismic pulses at average received 

levels of 131 dB re 1 mPa2-s caused blue 

whales to increase call production (Di 

Iorio and Clark, 2010). In contrast, 

McDonald et al. (1995) tracked a blue 

whale with seafloor seismometers and 

reported that it stopped vocalizing and 

changed its travel direction at a range of 

10 km from the acoustic source vessel 

(estimated received level 143 dB pk-pk). 

Blackwell et al. (2013) found that 

bowhead whale call rates dropped 

significantly at onset of airgun use at 

sites with a median distance of 41–45 

km from the survey. Blackwell et al. 

(2015) expanded this analysis to show 

that whales actually increased calling 

rates as soon as airgun signals were 

detectable before ultimately decreasing 

calling rates at higher received levels 

(i.e., 10-minute cumulative sound 

exposure level (cSEL) of ∼127 dB). 

Overall, these results suggest that 

bowhead whales may adjust their vocal 

output in an effort to compensate for 

noise before ceasing vocalization effort 

and ultimately deflecting from the 

acoustic source (Blackwell et al., 2013, 

2015). These studies demonstrate that 

even low levels of noise received far 

from the source can induce changes in 

vocalization and/or behavior for 

mysticetes. 

Avoidance is the displacement of an 

individual from an area or migration 

path as a result of the presence of a 

sound or other stressors, and is one of 

the most obvious manifestations of 

disturbance in marine mammals 

(Richardson et al., 1995). For example, 

gray whales are known to change 

direction—deflecting from customary 

migratory paths—in order to avoid noise 

from airgun surveys (Malme et al., 

1984). Humpback whales showed 

avoidance behavior in the presence of 

an active airgun array during 

observational studies and controlled 

exposure experiments in western 

Australia (McCauley et al., 2000a). 

Avoidance may be short-term, with 

animals returning to the area once the 

noise has ceased (e.g., Bowles et al., 

1994; Goold, 1996; Stone et al., 2000; 

Morton and Symonds, 2002; Gailey et 

al., 2007). Longer-term displacement is 

possible, however, which may lead to 

changes in abundance or distribution 

patterns of the affected species in the 

affected region if habituation to the 

presence of the sound does not occur 

(e.g., Bejder et al., 2006; Teilmann et al., 

2006). 

Forney et al. (2017) detail the 

potential effects of noise on marine 

mammal populations with high site 

fidelity, including displacement and 

auditory masking, noting that a lack of 

observed response does not imply 

absence of fitness costs and that 

apparent tolerance of disturbance may 

have population-level impacts that are 

less obvious and difficult to document. 

As we discuss in describing our 

proposed mitigation later in this 

document, avoidance of overlap 

between disturbing noise and areas and/ 

or times of particular importance for 

sensitive species may be critical to 

avoiding population-level impacts 

because (particularly for animals with 

high site fidelity) there may be a strong 

motivation to remain in the area despite 

negative impacts. Forney et al. (2017) 

state that, for these animals, remaining 

in a disturbed area may reflect a lack of 

alternatives rather than a lack of effects. 

The authors discuss several case 

studies, including western Pacific gray 

whales, which are a small population of 

mysticetes believed to be adversely 

affected by oil and gas development off 

Sakhalin Island, Russia (Weller et al., 

2002; Reeves et al., 2005). Western gray 

whales display a high degree of 

interannual site fidelity to the area for 

foraging purposes, and observations in 

the area during airgun surveys has 

shown the potential for harm caused by 

displacement from such an important 

area (Weller et al., 2006; Johnson et al., 

2007). As we discuss below in 

‘‘Proposed Mitigation,’’ similar concerns 

exist in relation to the potential for 

survey activity in the resident habitat of 

the GOM’s small population of Bryde’s 

whales. Forney et al. (2017) also discuss 

beaked whales, noting that 

anthropogenic effects in areas where 

they are resident could cause severe 

biological consequences, in part because 

displacement may adversely affect 

foraging rates, reproduction, or health, 

while an overriding instinct to remain 

could lead to more severe acute effects. 

A flight response is a dramatic change 

in normal movement to a directed and 

rapid movement away from the 

perceived location of a sound source. 

The flight response differs from other 

avoidance responses in the intensity of 

the response (e.g., directed movement, 

rate of travel). Relatively little 

information on flight responses of 

marine mammals to anthropogenic 

signals exist, although observations of 

flight responses to the presence of 

predators have occurred (Connor and 

Heithaus, 1996). The result of a flight 

response could range from brief, 

temporary exertion and displacement 

from the area where the signal provokes 

flight to, in extreme cases, marine 

mammal strandings (Evans and 

England, 2001). However, it should be 

noted that response to a perceived 

predator does not necessarily invoke 

flight (Ford and Reeves, 2008), and 


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whether individuals are solitary or in 

groups may influence the response. 

Behavioral disturbance can also 

impact marine mammals in more subtle 

ways. Increased vigilance may result in 

costs related to diversion of focus and 

attention (i.e., when a response consists 

of increased vigilance, it may come at 

the cost of decreased attention to other 

critical behaviors such as foraging or 

resting). These effects have generally not 

been demonstrated for marine 

mammals, but studies involving fish 

and terrestrial animals have shown that 

increased vigilance may substantially 

reduce feeding rates (e.g., Beauchamp 

and Livoreil, 1997; Fritz et al., 2002; 

Purser and Radford, 2011). In addition, 

chronic disturbance can cause 

population declines through reduction 

of fitness (e.g., decline in body 

condition) and subsequent reduction in 

reproductive success, survival, or both 

(e.g., Harrington and Veitch, 1992; Daan 

et al., 1996; Bradshaw et al., 1998). 

However, Ridgway et al. (2006) reported 

that increased vigilance in bottlenose 

dolphins exposed to sound over a fiveday period did not cause any sleep 

deprivation or stress effects. 

Many animals perform vital functions, 

such as feeding, resting, traveling, and 

socializing, on a diel cycle (24-hour 

cycle). Disruption of such functions 

resulting from reactions to stressors 

such as sound exposure are more likely 

to be significant if they last more than 

one diel cycle or recur on subsequent 

days (Southall et al., 2007). 

Consequently, a behavioral response 

lasting less than one day and not 

recurring on subsequent days is not 

considered particularly severe unless it 

could directly affect reproduction or 

survival (Southall et al., 2007). Note that 

there is a difference between multi-day 

substantive behavioral reactions and 

multi-day anthropogenic activities. For 

example, just because an activity lasts 

for multiple days does not necessarily 

mean that individual animals are either 

exposed to activity-related stressors for 

multiple days or, further, exposed in a 

manner resulting in sustained multi-day 

substantive behavioral responses. 

Stone (2015a) reported data from atsea observations during 1,196 airgun 

surveys from 1994 to 2010. When large 

arrays of airguns (considered to be 500 

in3 or more) were firing, lateral 

displacement, more localized 

avoidance, or other changes in behavior 

were evident for most odontocetes. 

However, significant responses to large 

arrays were found only for the minke 

whale and fin whale. Behavioral 

responses observed included changes in 

swimming or surfacing behavior, with 

indications that cetaceans remained 

near the water surface at these times. 

Cetaceans were recorded as feeding less 

often when large arrays were active. 

Behavioral observations of gray whales 

during an airgun survey monitored 

whale movements and respirations 

pre-, during-, and post-seismic survey 

(Gailey et al., 2016). Behavioral state 

and water depth were the best ‘natural’ 

predictors of whale movements and 

respiration and, after considering 

natural variation, none of the response 

variables were significantly associated 

with survey or vessel sounds. 

Stress Responses—An animal’s 

perception of a threat may be sufficient 

to trigger stress responses consisting of 

some combination of behavioral 

responses, autonomic nervous system 

responses, neuroendocrine responses, or 

immune responses (e.g., Seyle, 1950; 

Moberg, 2000). In many cases, an 

animal’s first and sometimes most 

economical (in terms of energetic costs) 

response is behavioral avoidance of the 

potential stressor. Autonomic nervous 

system responses to stress typically 

involve changes in heart rate, blood 

pressure, and gastrointestinal activity. 

These responses have a relatively short 

duration and may or may not have a 

significant long-term effect on an 

animal’s fitness. 

Neuroendocrine stress responses often 

involve the hypothalamus-pituitaryadrenal system. Virtually all 

neuroendocrine functions that are 

affected by stress—including immune 

competence, reproduction, metabolism, 

and behavior—are regulated by pituitary 

hormones. Stress-induced changes in 

the secretion of pituitary hormones have 

been implicated in failed reproduction, 

altered metabolism, reduced immune 

competence, and behavioral disturbance 

(e.g., Moberg, 1987; Blecha, 2000). 

Increases in the circulation of 

glucocorticoids are also equated with 

stress (Romano et al., 2004). 

The primary distinction between 

stress (which is adaptive and does not 

normally place an animal at risk) and 

‘‘distress’’ is the cost of the response. 

During a stress response, an animal uses 

glycogen stores that can be quickly 

replenished once the stress is alleviated. 

In such circumstances, the cost of the 

stress response would not pose serious 

fitness consequences. However, when 

an animal does not have sufficient 

energy reserves to satisfy the energetic 

costs of a stress response, energy 

resources must be diverted from other 

functions. This state of distress will last 

until the animal replenishes its 

energetic reserves sufficiently to restore 

normal function. 

Relationships between these 

physiological mechanisms, animal 

behavior, and the costs of stress 

responses are well-studied through 

controlled experiments and for both 

laboratory and free-ranging animals 

(e.g., Holberton et al., 1996; Hood et al., 

1998; Jessop et al., 2003; Krausman et 

al., 2004; Lankford et al., 2005). Stress 

responses due to exposure to 

anthropogenic sounds or other stressors 

and their effects on marine mammals 

have also been reviewed (Fair and 

Becker, 2000; Romano et al., 2002b) 

and, more rarely, studied in wild 

populations (e.g., Romano et al., 2002a). 

For example, Rolland et al. (2012) found 

that noise reduction from reduced ship 

traffic in the Bay of Fundy was 

associated with decreased stress in 

North Atlantic right whales. These and 

other studies lead to a reasonable 

expectation that some marine mammals 

will experience physiological stress 

responses upon exposure to acoustic 

stressors and that it is possible that 

some of these would be classified as 

‘‘distress.’’ In addition, any animal 

experiencing TTS would likely also 

experience stress responses (NRC, 

2003). 

Auditory Masking—Sound can 

disrupt behavior through masking, or 

interfering with, an animal’s ability to 

detect, recognize, or discriminate 

between acoustic signals of interest (e.g., 

those used for intraspecific 

communication and social interactions, 

prey detection, predator avoidance, 

navigation) (Richardson et al., 1995; 

Erbe et al., 2016). Masking occurs when 

the receipt of a sound is interfered with 

by another coincident sound at similar 

frequencies and at similar or higher 

intensity, and may occur whether the 

sound is natural (e.g., snapping shrimp, 

wind, waves, precipitation) or 

anthropogenic (e.g., shipping, sonar, 

seismic exploration) in origin. The 

ability of a noise source to mask 

biologically important sounds depends 

on the characteristics of both the noise 

source and the signal of interest (e.g., 

signal-to-noise ratio, temporal 

variability, direction), in relation to each 

other and to an animal’s hearing 

abilities (e.g., sensitivity, frequency 

range, critical ratios, frequency 

discrimination, directional 

discrimination, age or TTS hearing loss), 

and existing ambient noise and 

propagation conditions. 

Under certain circumstances, marine 

mammals experiencing significant 

masking could also be impaired from 

maximizing their performance fitness in 

survival and reproduction. Therefore, 

when the coincident (masking) sound is 

man-made, it may be considered 

harassment when disrupting or altering 

critical behaviors. It is important to 


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distinguish TTS and PTS, which persist 

after the sound exposure, from masking, 

which occurs during the sound 

exposure. Because masking (without 

resulting in TS) is not associated with 

abnormal physiological function, it is 

not considered a physiological effect, 

but rather a potential behavioral effect. 

The frequency range of the potentially 

masking sound is important in 

determining any potential behavioral 

impacts. For example, low-frequency 

signals may have less effect on highfrequency echolocation sounds 

produced by odontocetes but are more 

likely to affect detection of mysticete 

communication calls and other 

potentially important natural sounds 

such as those produced by surf and 

some prey species. The masking of 

communication signals by 

anthropogenic noise may be considered 

as a reduction in the communication 

space of animals (e.g., Clark et al., 2009; 

Matthews et al., 2016) and may result in 

energetic or other costs as animals 

change their vocalization behavior (e.g., 

Miller et al., 2000; Foote et al., 2004; 

Parks et al., 2007; Di Iorio and Clark, 

2009; Holt et al., 2009). Masking can be 

reduced in situations where the signal 

and noise come from different 

directions (Richardson et al., 1995), 

through amplitude modulation of the 

signal, or through other compensatory 

behaviors (Houser and Moore, 2014). 

Masking can be tested directly in 

captive species (e.g., Erbe, 2008), but in 

wild populations it must be either 

modeled or inferred from evidence of 

masking compensation. There are few 

studies addressing real-world masking 

sounds likely to be experienced by 

marine mammals in the wild (e.g., 

Branstetter et al., 2013). 

Masking affects both senders and 

receivers of acoustic signals and can 

potentially have long-term chronic 

effects on marine mammals at the 

population level as well as at the 

individual level. Low-frequency 

ambient sound levels have increased by 

as much as 20 dB (more than three times 

in terms of SPL) in the world’s ocean 

from pre-industrial periods, with most 

of the increase from distant commercial 

shipping (Hildebrand, 2009). All 

anthropogenic sound sources, but 

especially chronic and lower-frequency 

signals (e.g., from vessel traffic), 

contribute to elevated ambient sound 

levels, thus intensifying masking. 

Ship Strike 

Vessel collisions with marine 

mammals, or ship strikes, can result in 

death or serious injury of the animal. 

Wounds resulting from ship strike may 

include massive trauma, hemorrhaging, 

broken bones, or propeller lacerations 

(Knowlton and Kraus, 2001). An animal 

at the surface may be struck directly by 

a vessel, a surfacing animal may hit the 

bottom of a vessel, or an animal just 

below the surface may be cut by a 

vessel’s propeller. Superficial strikes 

may not kill or result in the death of the 

animal. These interactions are typically 

associated with large whales, which are 

occasionally found draped across the 

bulbous bow of large commercial ships 

upon arrival in port. Although smaller 

cetaceans are more maneuverable in 

relation to large vessels than are large 

whales, they may also be susceptible to 

strike. The severity of injuries typically 

depends on the size and speed of the 

vessel, with the probability of death or 

serious injury increasing as vessel speed 

increases (Knowlton and Kraus, 2001; 

Laist et al., 2001; Vanderlaan and 

Taggart, 2007; Conn and Silber, 2013). 

Impact forces increase with speed, as 

does the probability of a strike at a given 

distance (Silber et al., 2010; Gende et 

al., 2011). 

Pace and Silber (2005) also found that 

the probability of death or serious injury 

increased rapidly with increasing vessel 

speed. Specifically, the predicted 

probability of serious injury or death 

increased from 45 to 75 percent as 

vessel speed increased from 10 to 14 kn, 

and exceeded 90 percent at 17 kn. 

Higher speeds during collisions result in 

greater force of impact, but higher 

speeds also appear to increase the 

chance of severe injuries or death 

through increased likelihood of 

collision by pulling whales toward the 

vessel (Clyne, 1999; Knowlton et al., 

1995). In a separate study, Vanderlaan 

and Taggart (2007) analyzed the 

probability of lethal mortality of large 

whales at a given speed, showing that 

the greatest rate of change in the 

probability of a lethal injury to a large 

whale as a function of vessel speed 

occurs between 8.6 and 15 kn. The 

chances of a lethal injury decline from 

approximately 80 percent at 15 kn to 

approximately 20 percent at 8.6 kn. At 

speeds below 11.8 kn, the chances of 

lethal injury drop below 50 percent, 

while the probability asymptotically 

increases toward 100 percent above 

15 kn. 

In an effort to reduce the number and 

severity of strikes of the endangered 

North Atlantic right whale, NMFS 

implemented speed restrictions in 2008 

(73 FR 60173; October 10, 2008). These 

restrictions require that vessels greater 

than or equal to 65 ft (19.8 m) in length 

travel at less than or equal to 10 kn near 

key port entrances and in certain areas 

of right whale aggregation along the U.S. 

eastern seaboard. Conn and Silber 

(2013) estimated that these restrictions 

reduced total ship strike mortality risk 

levels by 80 to 90 percent. 

For vessels used in geophysical 

survey activities, vessel speed while 

towing gear is typically only 4–5 kn. At 

these speeds, both the possibility of 

striking a marine mammal and the 

possibility of a strike resulting in 

serious injury or mortality are 

discountable. At average transit speed, 

the probability of serious injury or 

mortality resulting from a strike is less 

than 50 percent. However, the 

likelihood of a strike actually happening 

is again unlikely. Ship strikes, as 

analyzed in the studies cited above, 

generally involve commercial shipping, 

which is much more common in both 

space and time than is geophysical 

survey activity. Jensen and Silber (2004) 

summarized ship strikes of large whales 

worldwide from 1975–2003 and found 

that most collisions occurred in the 

open ocean and involved large vessels 

(e.g., commercial shipping). Commercial 

fishing vessels were responsible for 

three percent of recorded collisions, 

while no such incidents were reported 

for geophysical survey vessels during 

that time period. 

It is possible for ship strikes to occur 

while traveling at slow speeds. For 

example, a hydrographic survey vessel 

traveling at low speed (5.5 kn) while 

conducting mapping surveys off the 

central California coast struck and killed 

a blue whale in 2009. The State of 

California determined that the whale 

had suddenly and unexpectedly 

surfaced beneath the hull, with the 

result that the propeller severed the 

whale’s vertebrae, and that this was an 

unavoidable event. The strike 

represented the only such incident in 

approximately 540,000 hours of similar 

coastal mapping activity (p = 1.9 × 10¥6; 

95% CI = 0¥5.5 × 10¥6; NMFS, 2013). 

In addition, a research vessel reported a 

fatal strike in 2011 of a dolphin in the 

Atlantic, demonstrating that it is 

possible for strikes involving smaller 

cetaceans to occur. In that case, the 

incident report indicated that an animal 

apparently was struck by the vessel’s 

propeller as it was intentionally 

swimming near the vessel. While 

indicative of the type of unusual events 

that cannot be ruled out, neither of these 

instances represents a circumstance that 

would be considered reasonably 

foreseeable or that would be considered 

preventable. 

Although the likelihood of vessels 

associated with geophysical surveys 

striking a marine mammal are low, we 

require a robust ship strike avoidance 

protocol (see ‘‘Proposed Mitigation’’), 

which we believe eliminates any 


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foreseeable risk of ship strike. We 

anticipate that vessel collisions 

involving seismic data acquisition 

vessels towing gear, while not 

impossible, represent unlikely, 

unpredictable events for which there are 

no preventive measures. Given the 

required mitigation measures, the 

relatively slow speeds of vessels towing 

gear, the presence of bridge crew 

watching for obstacles at all times 

(including marine mammals), the 

presence of marine mammal observers, 

and the small number of seismic survey 

cruises relative to commercial ship 

traffic, we believe that the possibility of 

ship strike is discountable and, further, 

that were a strike of a large whale to 

occur, it would be unlikely to result in 

serious injury or mortality. No 

incidental take resulting from ship 

strike is anticipated or proposed for 

authorization, and this potential effect 

of the specified activity will not be 

discussed further in the following 

analysis. 

Other Potential Impacts 

Here, we briefly address the potential 

risks due to entanglement and 

contaminant spills. We are not aware of 

any records of marine mammal 

entanglement in towed arrays such as 

those considered here, and we address 

measures designed to eliminate the 

potential for entanglement in gear used 

by OBS surveys in ‘‘proposed 

Mitigation.’’ The discharge of trash and 

debris is prohibited (33 CFR 151.51–77) 

unless it is passed through a machine 

that breaks up solids such that they can 

pass through a 25-mm mesh screen. All 

other trash and debris must be returned 

to shore for proper disposal with 

municipal and solid waste. Some 

personal items may be accidentally lost 

overboard. However, U.S. Coast Guard 

and Environmental Protection Act 

regulations require operators to become 

proactive in avoiding accidental loss of 

solid waste items by developing waste 

management plans, posting 

informational placards, manifesting 

trash sent to shore, and using special 

precautions such as covering outside 

trash bins to prevent accidental loss of 

solid waste. Any permits issued by 

BOEM would include guidance for the 

handling and disposal of marine trash 

and debris, similar to BSEE’s Notice to 

Lessees 2015–G03 (‘‘Marine Trash and 

Debris Awareness and Elimination’’) 

(BSEE, 2015; BOEM, 2017). We believe 

entanglement risks are essentially 

eliminated by the proposed 

requirements, and entanglement risks 

are not discussed further in this 

document. 

Marine mammals could be affected by 

accidentally spilled diesel fuel from a 

vessel associated with proposed survey 

activities. Quantities of diesel fuel on 

the sea surface may affect marine 

mammals through various pathways: 

Surface contact of the fuel with skin and 

other mucous membranes, inhalation of 

concentrated petroleum vapors, or 

ingestion of the fuel (direct ingestion or 

by the ingestion of contaminated prey) 

(e.g., Geraci and St. Aubin, 1980, 1985, 

1990). However, the likelihood of a fuel 

spill during any particular geophysical 

survey is considered to be remote, and 

the potential for impacts to marine 

mammals would depend greatly on the 

size and location of a spill and 

meteorological conditions at the time of 

the spill. Spilled fuel would rapidly 

spread to a layer of varying thickness 

and break up into narrow bands or 

windrows parallel to the wind direction. 

The rate at which the fuel spreads 

would be determined by the prevailing 

conditions such as temperature, water 

currents, tidal streams, and wind 

speeds. Lighter, volatile components of 

the fuel would evaporate to the 

atmosphere almost completely in a few 

days. Evaporation rate may increase as 

the fuel spreads because of the 

increased surface area of the slick. 

Rougher seas, high wind speeds, and 

high temperatures also tend to increase 

the rate of evaporation and the 

proportion of fuel lost by this process 

(Scholz et al., 1999). We do not 

anticipate potentially meaningful effects 

to marine mammals as a result of any 

contaminant spill resulting from the 

proposed survey activities, and 

contaminant spills resulting from the 

specified activity are not discussed 

further in this document. 

Anticipated Effects on Marine Mammal 

Habitat 

Physical Disturbance—Sources of 

seafloor disturbance related to 

geophysical surveys that may impact 

marine mammal habitat include 

placement of anchors, nodes, cables, 

sensors, or other equipment on or in the 

seafloor for various activities. 

Equipment deployed on the seafloor has 

the potential to cause direct physical 

damage and could affect bottomassociated fish resources. Several NTLs 

detail the mitigation measures used to 

prevent adverse impacts (‘‘Biologicallysensitive Underwater Features and 

Areas’’ (NTL 2009–G39), ‘‘Deepwater 

Benthic Communities’’ (NTL 2009– 

G40), and ‘‘Shallow Hazards Program’’ 

(NTL 2008–G05) (MMS, 2008; 2009a; 

2009b)). 

Placement of equipment, such as 

nodes, on the seafloor could damage 

areas of hard bottom where direct 

contact with the seafloor occurs and 

could crush epifauna (organisms that 

live on the seafloor or surface of other 

organisms). Damage to unknown or 

unseen hard bottom could occur, but 

because of the small area covered by 

most bottom-founded equipment, the 

patchy distribution of hard bottom 

habitat, BOEM’s review process, and 

BOEM’s application of avoidance 

conditions of approval, contact with 

unknown hard bottom is expected to be 

rare and impacts minor. Seafloor 

disturbance in areas of soft bottom can 

cause loss of small patches of epifauna 

and infauna due to burial or crushing, 

and bottom-feeding fishes could be 

temporarily displaced from feeding 

areas. Overall, any effects of physical 

damage to habitat are expected to be 

minor and temporary. 

Effects to Prey—Sound may affect 

marine mammals through impacts on 

the abundance, behavior, or distribution 

of prey species (e.g., crustaceans, 

cephalopods, fish, zooplankton). Marine 

mammal prey varies by species, season, 

and location and, for some, is not well 

documented. Here, we describe studies 

regarding the effects of noise on known 

marine mammal prey. 

Fish utilize the soundscape and 

components of sound in their 

environment to perform important 

functions such as foraging, predator 

avoidance, mating, and spawning (e.g., 

Zelick et al., 1999; Fay, 2009). 

Depending on their hearing anatomy 

and peripheral sensory structures, 

which vary among species, fishes hear 

sounds using pressure and particle 

motion sensitivity capabilities and 

detect the motion of surrounding water 

(Fay et al., 2008). The potential effects 

of airgun noise on fishes depends on the 

overlapping frequency range, distance 

from the sound source, water depth of 

exposure, and species-specific hearing 

sensitivity, anatomy, and physiology. 

Key impacts to fishes may include 

behavioral responses, hearing damage, 

barotrauma (pressure-related injuries), 

and mortality. 

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. Short 

duration, sharp sounds can cause overt 

or subtle changes in fish behavior and 

local distribution. 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. Hastings and Popper (2005) 

identified several studies that suggest 

fish may relocate to avoid certain areas 


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of sound energy. Several 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). However, some 

studies have shown no or slight reaction 

to airgun sounds (e.g., Pena et al., 2013; 

Wardle et al., 2001; Jorgenson and 

Gyselman, 2009; Cott et al., 2012). More 

commonly, though, the impacts of noise 

on fish are temporary. Investigators 

reported significant, short-term declines 

in commercial fishing catch rate of 

gadid fishes during and for up to five 

days after survey operations, but the 

catch rate subsequently returned to 

normal (Engas et al, 1996; Engas and 

Lokkeborg, 2002); other studies have 

reported similar findings (Hassel et al., 

2004). However, even temporary effects 

to fish distribution patterns can impact 

their ability to carry out important lifehistory functions (Paxton et al., 2017). 

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. 

(2012a) showed that a 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. No mortality occurred 

to fish in any of these studies. 

Injury caused by barotrauma can 

range from slight to severe and can 

cause death, and is most likely for fish 

with swim bladders. Barotrauma 

injuries have been documented during 

controlled exposure to impact pile 

driving (an impulsive noise source, as 

are airguns) (Halvorsen et al., 2012b; 

Casper et al., 2013). For geophysical 

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. 

Invertebrates appear to be able to 

detect sounds (Pumphrey, 1950; Frings 

and Frings, 1967) and are most sensitive 

to low-frequency sounds (Packard et al., 

1990; Budelmann and Williamson, 

1994; Lovell et al., 2005; Mooney et al., 

2010). 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). Cephalopods 

have a specialized sensory organ inside 

the head called a statocyst that may help 

an animal determine its position in 

space (orientation) and maintain 

balance (Budelmann, 1992). Packard et 

al. (1990) showed that cephalopods 

were sensitive to particle motion, not 

sound pressure, and Mooney et al. 

(2010) demonstrated that squid 

statocysts act as an accelerometer 

through which particle motion of the 

sound field can be detected. 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). 

Impacts to benthic communities from 

impulsive sound generated by active 

acoustic sound sources are not well 

documented. There are no published 

data that indicate whether threshold 

shift injuries or effects of auditory 

masking occur in benthic invertebrates, 

and there are little data to suggest 

whether sounds from seismic surveys 

would have any substantial impact on 

invertebrate behavior (Hawkins et al., 

2014), though some studies have 

indicated showed no short-term or longterm effects of airgun exposure (e.g., 

Andriguetto-Filho et al., 2005; Payne et 

al., 2007; 2008; Boudreau et al., 2009). 

Exposure to airgun signals was found to 

significantly increase mortality in 

scallops, in addition to causing 

significant changes in behavioral 

patterns during exposure (Day et al., 

2017). However, the implications of this 

finding are not straightforward, as the 

authors state that the observed levels of 

mortality were not beyond naturally 

occurring rates. 

There is little information concerning 

potential impacts of noise on 

zooplankton populations. However, one 

recent study (McCauley et al., 2017) 

investigated zooplankton abundance, 

diversity, and mortality before and after 

exposure to airgun noise, finding that 

the exposure 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. The majority of taxa present 

were copepods and cladocerans; for 

these taxa, the range within which 

effects on abundance were detected was 

up to approximately 1.2 km. In order to 

have significant impacts on r-selected 

species such as plankton, the spatial or 

temporal scale of impact must be large 

in comparison with the ecosystem 

concerned (McCauley et al., 2017). 

Therefore, the large scale of effect 

observed here is of concern— 

particularly where repeated noise 

exposure is expected—and further study 

is warranted. 

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 

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 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. 

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 

produce sound for, or 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. 


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Soundscapes are also defined by, and 

acoustic habitat influenced by, the total 

contribution of anthropogenic sound. 

This may include incidental emissions 

from sources such as vessel traffic, or 

may be intentionally introduced to the 

marine environment for data acquisition 

purposes (as in the use of airgun arrays). 

Anthropogenic noise varies widely in its 

frequency content, duration, and 

loudness and these characteristics 

greatly influence the potential habitatmediated effects to marine mammals 

(please also see the previous discussion 

on masking in the ‘‘Acoustic Effects’’ 

subsection), which may range from local 

effects for brief periods of time to 

chronic effects over large areas and for 

long durations. Depending on the extent 

of effects to habitat, animals may alter 

their communications signals (thereby 

potentially expending additional 

energy) or miss acoustic cues (either 

conspecific or adventitious). Problems 

arising from a failure to detect cues are 

more likely to occur when noise stimuli 

are chronic and overlap with 

biologically relevant cues used for 

communication, orientation, and 

predator/prey detection (Francis and 

Barber, 2013). For more detail on these 

concepts see, e.g., Barber et al., 2009; 

Pijanowski et al., 2011; Francis and 

Barber, 2013; Lillis et al., 2014. 

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). 

Such metrics do not, in and of 

themselves, document fitness 

consequences for the marine animals 

that live in chronically noisy 

environments. Long-term populationlevel consequences mediated through 

changes in the ultimate survival and 

reproductive success of individuals are 

difficult to study, and particularly so 

underwater. However, it is increasingly 

well documented that aquatic species 

rely on qualities of natural acoustic 

habitats, with researchers quantifying 

reduced detection of important 

ecological cues (e.g., Francis and Barber, 

2013; Slabbekoorn et al., 2010) as well 

as survivorship consequences in several 

species (e.g., Simpson et al., 2014; 

Nedelec et al., 2015). 

Specific to the GOM and the activities 

considered here, Matthews et al. (2016, 

2017) developed a first-order 

cumulative and chronic effects 

assessment for noise produced by oil 

and gas exploration activities in the U.S. 

GOM. The 2016 report was originally 

presented as Appendix K in BOEM 

(2017), with an addendum to the report 

produce in 2017; both are available 

online at: www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

incidental-take-authorizations-oil-andgas. Here, we summarize the study and 

its findings (referred to here as ‘‘the CCE 

report’’). For full methodological details 

and results, please see the report. 

As discussed previously in this 

section, direct exposure to the pulses 

produced by airguns can result in acute 

impacts at close ranges. However, lowfrequency dominant airgun noise 

undergoes multiple reflections at the 

ocean bottom and surface and refraction 

through the water column, both of 

which cause prolonged decay time of 

the original acoustic signals (Urick, 

1984). Extended decay time can lead to 

high sound levels lasting from one 

impulse to the onset of the next, 

elevating ambient noise levels (Guan et 

al., 2015). In addition, low-frequency 

energy from airgun surveys, with access 

to conductive propagation conditions 

(e.g., deeper waters), has been 

documented to travel long distances, 

contributing to increased background 

noise over very large areas (Nieukirk et 

al., 2012). Implications for acoustic 

masking and reduced communication 

space resulting from noise produced by 

airgun surveys are expected to be 

particularly heightened for animals that 

actively produce low frequency sounds 

or whose hearing is attuned to lower 

frequencies. Bryde’s whales are the only 

GOM species classified within the lowfrequency hearing group, producing 

calls that span a low frequency range 

that directly overlaps the dominant 

energies produced by airguns. However, 

impacts associated with cumulative 

noise within the frequencies of the 

Matthews et al. (2016) study (10–5,000 

Hz), are relevant to the majority of 

cetacean species in the GOM. In the 

addendum to the CCE report (Matthews 

et al., 2017), the same methods for 

calculating changes in communication 

space were applied to sperm whales 

(based on male sperm whale slowclicks; Madsen et al., 2002b). 

Acoustic modeling was conducted for 

ten locations (‘‘receiver sites’’) within 

the study area to examine aggregate 

noise produced over a full year. The 

locations of the receiver sites are given 

in Table 5 and shown in the map of 

Figure 4. These sites were chosen to 

reflect areas of biological importance to 

cetaceans, (e.g., LaBrecque et al., 2015), 

areas of high densities of cetaceans 

(Roberts et al., 2016), and areas of key 

biological diversity (e.g., National 

Marine Sanctuaries). The study area was 

divided into six ‘‘activity zones’’ (Figure 

4) (note that these zones are different 

from those used for acoustic exposure 

modeling and described below in the 

‘‘Estimated Take’’ section). 

TABLE 5—MODELED RECEIVER SITE LOCATIONS, WATER DEPTHS, AND SELECTION BASIS

Site Receiver site Latitude Longitude Water depth 

(m) Selection basis 

1 .................... Western GOM ................................ 27.01606° N ..... 95.7405° W ...... 842 Higher density cryptic deep diving 

and social pelagic cetaceans. 

2 .................... Florida Escarpment ........................ 25.95807° N ..... 84.6956° W ...... 693 Higher density multiple cetacean 

species shelf break and slope. 

3 .................... Midwestern GOM ........................... 27.43300° N ..... 92.1200° W ...... 830 Higher density multiple cetacean 

species shelf break and slope. 

4 .................... Sperm whale site ........................... 24.34771° N ..... 83.7727° W ...... 1,053 Higher density sperm whales and 

cryptic deep diving cetaceans. 

5 .................... Deep offshore ................................ 27.64026° N ..... 87.0285° W ...... 3,050 Location of NOAA noise reference 

station. 

6 .................... Mississippi Canyon ........................ 28.15455° N ..... 89.3971° W ...... 1,106 Higher density sperm whales and 

cryptic deep diving cetaceans. 

7 .................... Bryde’s whale site .......................... 28.74043° N ..... 85.7302° W ...... 212 Bryde’s whale biologically important area. 


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TABLE 5—MODELED RECEIVER SITE LOCATIONS, WATER DEPTHS, AND SELECTION BASIS—Continued 

Site Receiver site Latitude Longitude Water depth 

(m) Selection basis 

8 .................... De Soto Canyon ............................ 29.14145° N ..... 87.1762° W ...... 919 Higher density sperm whales and 

cryptic deep diving cetaceans. 

9 .................... Flower Garden Banks National 

Marine Sanctuary.

27.86713° N ..... 93.8259° W ...... 88 National Marine Sanctuary. 

10 .................. Bottlenose dolphin site ................... 29.40526° N ..... 93.3247° W ...... 12 Bottlenose dolphin biologically important area. 

Note that ‘‘closure areas’’ depicted in 

Figure 4 represent those described in 

Chapter 2.8 of BOEM (2017), which are 

in some cases different from those 

described in this document (see the 

‘‘Proposed Mitigation’’ section). 

Matthews et al. (2016, 2017) analyzed 

multiple scenarios, including a baseline 

scenario (referred to in the CCE report 

as ‘‘Alternative A’’) 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 

(referred to in the CCE report as 

‘‘Alternative C’’) in which projected 

activities were uniformly distributed 

throughout the study area, with the 

exception of the coastal waters 

restriction from February to May (as 

described below in the ‘‘Proposed 

Mitigation’’ section); and a closure 

scenario (referred to in the CCE report 

as ‘‘Alternative F1’’) in which no 

activities are conducted in the 

restriction areas, 25 percent of the 

activity that would have occurred in the 

restriction areas is redistributed into 

non-restriction areas of the same activity 

zone (Figure 4), and 75 percent of the 

activities that would have occurred in 

the restriction areas are not conducted 

at all. Matthews et al. (2016, 2017) also 

assessed additional scenarios not 

relevant to this proposed rulemaking; 

these are not discussed here. 

Several simplifying assumptions were 

necessary. Changes in the distribution of 

survey activities would result in 

differences in the relative amount of 

noise accumulating at different receiver 

sites, and that variance was not 

examined. Instead, results associated 

with zone-varying densities of activity 

types but homogenous distributions of 

activities of each type within zones 

were presented. The approach applied 

accounts for spatial variance in resulting 

cumulative noise due to factors affecting 

sound propagation (e.g., topography, 

bottom type) among locations of key 

management interest in the region. 

However, it does not produce results for 

additional locations (e.g., a uniform 

map). 

The average of the projected annual 

amounts of survey activities for ten 


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years in each zone (Table 1) was 

calculated from the total survey line 

length within the respective zones. 

These average activity levels were 

modified by implementing area 

restrictions. Two representative acoustic 

sources were modeled and applied to 

five total activity types: Various 

configurations of one or more 8,000 in3

airgun arrays were used to simulate 2D, 

3D NAZ, 3D WAZ, and coil surveys, and 

a single 90 in3 airgun was used to 

simulate boomer and sparker type 

sources used for geotechnical surveys 

(see Table 2 in the CCE report for full 

details of these assumptions). Since the 

specific location of each type of activity 

was unknown, the survey source pulses 

were uniformly distributed throughout 

the activity zones according to the 

projected amount of each type of survey 

activity. In order to account for the 

seasonal closure of coastal waters, 

Zones 1, 3, and 5 were separated into 

waters occurring within coastal vs. 

deeper waters at the 20-m isobath. The 

numbers of pulses occurring annually 

within the coastal versus deeper 

portions of the zone were titrated to 

account for only eight months per year 

of survey activity within the coastal 

portion. 

The acoustic fields at the receiver 

sites were modeled at frequencies from 

10 Hz to 5 kHz, for sources up to 500 

km away. Results are provided for three 

depths as available at each receiver 

location: 5, 30, and 500 m. Annual 

cumulative SELs and time-averaged 

equivalent SPLs (Leq) at the selected 

receiver sites were calculated for all 

survey activity. A feature of underwater 

sound propagation is that nearby 

sources contribute substantially more 

SEL than more distant sources, since the 

exposure levels decay approximately 

with the square of distance from the 

source. This causes cumulative SEL 

received from spatially distributed and 

moving sources to be dominated by the 

sources closest to a receiver. However, 

the duration of exposures from very 

close sources is typically quite short. 

While exposures from nearby sources 

are important for assessing acute effects, 

their inclusion in a chronic effects 

assessment can be misleading. To 

overcome this issue, this approach 

excluded the highest shot exposures 

received during a fraction (10 percent) 

of the total study time period. Thus, the 

effective accumulation period was 90 

percent of a year. The cumulative levels 

estimated using the approach applied in 

the study are accurate when the cell 

dimensions are small, relative to the 

source-receiver separation. This 

approach could have led to errors when 

survey lines approached within a few 

kilometers from the receiver locations; 

however, the close range cells where 

this could have been a problem were 

automatically excluded by the removal 

of the top 10 percent of pulse noise 

contributions. Marine mammal hearing 

frequency weighting filter coefficients 

were applied to the received levels, and 

results are presented both with and 

without weighting. Results relevant to 

this proposed rule for cumulative SEL 

(Tables 8 and 10 in the CCE report) and 

Leq (Tables 12 and 16 in the CCE report) 

calculations are presented in the CCE 

report. 

A baseline ambient noise level must 

be assumed to estimate lost listening 

area and changes in communication 

space for various levels of activity. Here, 

ambient noise levels were defined as 

some contribution of commercial 

shipping noise in the 50–800 Hz band 

and noise from natural sounds 

(produced mainly by wind and waves). 

The commercial shipping noise levels 

were obtained from products available 

at cetsound.noaa.gov/sound-index, 

which provide commercial shipping 

noise levels over the GOM region in one 

third-octave frequency bands between 

50–800 Hz (shipping noise was 

neglected outside this range). Natural 

ambient noise levels were calculated 

from the formulas of Wenz (1962) and 

Cato (2008) for a wind speed of 8.5 kn. 

The natural noise levels were added to 

the vessel noise levels to generate 

composite one third-octave band 

ambient levels between 10 Hz and 5 

kHz. Broadband ambient levels varied 

between 94.3 and 102.3 dB, depending 

on the receiver location and depth 

(Table 7 in the CCE report). Estimates 

were assigned to each receiver site 

based on proximity and matched by 

water depth. Tables 13 and 17 in the 

CCE report present relevant results for 

modeled Leq above ambient at each 

receiver site with and without frequency 

weighting. 

The lost listening area assessment 

method has been applied to in-air noise 

(Barber et al., 2009) and in soundscape 

management contexts (NPS, 2010). 

Sound sources considered by this 

method can be from the same species (as 

discussed for communication space), a 

different species (e.g., predator or prey), 

natural sounds, or anthropogenic 

sounds. The lost listening area method 

applied by Barber et al. (2009) 

calculates a fractional reduction in 

listening area due to the addition of 

anthropogenic noise to ambient noise. It 

does not provide absolute areas or 

volumes of space; however, a benefit of 

the listening area method is that it does 

not rely on source levels of the sounds 

of interest. Instead, the method depends 

on the rate of sound transmission loss. 

Such results can be considered with 

frequency weightings, which represent 

the hearing sensitivity variations of 

three marine mammal species groups 

and transmission loss variations with 

range, or more generally without 

weighting. 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. Relevant 

results are presented in Tables 20, 22, 

and 25 of the CCE report. 

The communication space assessment 

was performed for Bryde’s whales and 

sperm whales using methods previously 

implemented for examining 

anthropogenic noise effects on whales 

(Clark et al., 2009; Hatch et al., 2012). 

Communication space represents the 

area within which whales can detect 

calls from other whales. For Bryde’s 

whales, all calculations were performed 

in the single one third-octave frequency 

band centered at 100 Hz, representing 

the highest received sound levels for the 

calls attributed to Bryde’s whales in the 

GOM (Rice et al., 2014; Sirovic et al., 

2014). A one third-octave band sound 

level of 152 dB at 1 m was specified. An 

estimate of 12.36 dB signal processing 

gain (which accounts for the animal’s 

ability to not only detect but recognize 

a signal from an animal of the same 

species) was applied. The areas of 

communication space at each receiver 

for the Bryde’s whale calls under 

ambient conditions and under each 

relevant activity scenario are presented 

in Tables 28, 29, and 31 of the CCE 

report. Relative losses of 

communication space (in both areas and 

percentages) between the activity 

scenarios are presented in Table 34 of 

the CCE report. 

For sperm whales, calculations were 

performed in the third-octave frequency 

band centered at 3,150 Hz, with a 

specified sound level of 181 dB at 1 m 

(Madsen et al., 2002b). Sperm whales 

produce at least four types of clicks: 

Usual clicks, buzzes (also called creaks), 

codas (patterns of 3–20 clicks), and 

slow-clicks (or clangs). Sperm whales 

on feeding grounds emit slow-clicks in 

seemingly repetitive temporal patterns 

(Oliveira et al., 2013), supporting the 

hypothesis that their function is long 

range communication between males, 

possibly relaying information about 

individual identity or behavioral states. 

These calls were chosen for the analysis 

since they have a lower frequency 

emphasis and longer duration than 

other sperm whale clicks (the center 

frequency of usual clicks and buzzes is 

15 kHz; Madsen et al., 2002b). Since the 


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frequency band of slow-clicks is closest 

to that of the airgun activity, these calls 

are the most affected in the context of 

the study. In addition, low-frequency 

sounds generally propagate farther than 

high-frequency ones. Thus, lowfrequency communication is generally 

more affected by distant noise sources 

than high-frequency communication. 

The signal processing gain was 

estimated at 3.0 dB, based on a median 

frequency bandwidth of 4 kHz and call 

length of 500 ms (Madsen et al., 2002b). 

Results for sperm whales are shown in 

Table 2 of the CCE report addendum. 

In the 3,150 Hz band, noise 

contribution from airgun survey 

activities in the GOM was estimated 

between 82.0 and 82.1 dB for all sites 

and all alternatives, levels similar to the 

estimated baseline levels of 82.0 dB at 

all sites. Therefore, the analysis shows 

that the survey activities do not 

significantly contribute to the 

soundscape in the 3,150 Hz band, and 

that there will be no significant change 

in communication space for sperm 

whales under the modeled alternatives. 

Because other sperm whale calls are 

higher-frequency, they would not be 

expected to be affected. However, we 

must be clear that this analysis is in 

reference to potential chronic effects 

resulting from changes to effective 

communication space, and that acute 

expects, as discussed elsewhere in this 

preamble, remain of concern 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 lost listening area and 

communication space metrics do not 

reflect variance in an individual 

animal’s experience of the noise 

produced by the modeled activities from 

one moment to the next. With both 

sources of noise and animals moving, 

the time-series of an individual’s noise 

exposure will show considerable 

variation. The methods used by 

Matthews et al. (2016, 2017) 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). Approaches such as 

the communication space estimation 

include approximation for the evolved 

ability of many acoustically active 

animals, such as Bryde’s whales, to hear 

the calls of conspecifics in the presence 

of some overlapping noise. 

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. The winter sound speed 

profile applied in the CCE modeling 

(February) was considered to be 

conservative relative to summer, as it 

includes a surface sound channel at 

certain sites that are conducive to sound 

propagation from shallow sound 

sources. 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. 

Filters that more heavily weighted the 

mid-frequencies modeled in this study 

(150 Hz–5 kHz) often reduced estimates 

of lost listening area. Canyon areas in 

the central and eastern GOM saw 

significant loss of listening area. 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. Other areas relevant to 

sperm whales, including site 4 off the 

Dry Tortugas, also saw heavy reductions 

in listening area. Additional heavily 

affected sites were those chosen to 

represent locations with predicted high 

densities of cryptic deep divers (e.g., 

site 1 in the far western GOM). Though 

most of these species are classified as 

having mid-frequency hearing 

sensitivity, many have shown 

sensitivity to airgun noise, with sperm 

whales the most well documented in the 

GOM. These modeling results suggest 

that accumulations of noise from survey 

activities below 5 kHz and often 

heightened at depth could be degrading 

the availability of animals that forage at 

great depths in the GOM to use acoustic 

cues 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. The 

maintenance of listening area and 

communication space at site 7 is of 

particular interest because the location 

is within the area of designated 

biological importance to the Bryde’s 

whale. The apparent protection of 

listening area and communication space 

within the calling frequencies utilized 

by the Bryde’s whale appears to take 

advantage of both local propagation 

conditions and the predicted lower 

levels of survey activity in the shallower 

portions of the Eastern Planning Area, 

which more strongly affect noise levels 

at this site. However, the significant loss 

of low-frequency listening area and 

communication space for their calls 

estimated for in additional locations, 

including just off the shelf in the eastern 

GOM, is of concern for this population. 

The effectiveness of time-area 

restrictions for maintaining 

communication space or listening area 

were highly variable among locations. 

This assessment evaluated the 

implications of displacing a portion (25 

percent) of the activity that would have 

taken place within a restriction area to 

within the remaining area outside the 

restriction. Thus, sites that were within 

large restriction areas (sites 6 and 8) 

experienced reduced cumulative noise 

levels and improved listening and 

communication conditions when those 

restrictions were in effect. Conditions at 

sites within restrictions designed 

around biologically important areas 

(sites 7 and 10) were not improved 

solely because they were not degraded 

under non-restriction conditions. In 

contrast, some sites outside restrictions, 

particularly those located in deeper 

water zones that correspond with denser 

projected levels of survey activity (sites 

1, 3, and 5) experienced higher noise 

levels with time-area restrictions, due to 

activity that was displaced to within 

their propagation vicinity. Finally, the 

methods used in this assessment to 

remove 10 percent of shots from survey 

activity closest to the receiver locations 

are likely to have reduced the relative 

difference between accumulated energy 

resulting from smaller restrictions 

(which further eliminated shots that 

would have taken place within the 160 

dB buffered restriction areas). This loss 

of resolution between restriction and 

non-restriction results does not 

adequately capture the reduction in 

acute noise exposure that could be 

experienced by animals through 

implementation of a restriction. 


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The CCE report is described here in 

order to present information regarding 

potential longer-term and wider-range 

noise effects from sources such as 

airguns. The metrics applied in this 

study do not, in and of themselves, 

document the consequences of lost 

listening area or communication space 

for the survivorship or reproductive 

success of individual animals. However, 

they do translate a growing body of 

scientific evidence for concern 

regarding the degradation of the quality 

of high-value acoustic habitats into 

quantifiable attributes that can related to 

baseline conditions, including those to 

which animals have evolved. 

In general, losses of broadband 

listening area far exceeded losses of 

communication space when evaluated 

at the same locations and under the 

same activity levels. This is appropriate 

to the interpretive role of the lost 

listening space calculation, which is to 

provide a more conservative estimate of 

the areas over which animals have 

access to a variety of acoustic cues of 

importance to their survival and 

reproductive success. Acoustic cues 

provide particularly important 

information in areas where other 

sensory cues are diminished (e.g., dark) 

and where navigation is challenging 

(e.g., complex coastlines and 

topography). Documentation of such 

cues (e.g., Barber et al., 2009; 

Slabbekoorn et al., 2010) indicate that 

they can be well outside of the 

frequencies that animals use to 

communicate with conspecifics, are 

often of lower source levels than 

conspecific calls and in many cases 

cannot benefit from evolved capacity to 

compensate for noise (e.g., gain applied 

to communication space calculations), 

due to the absence of a mechanism for 

natural selection to act (e.g., most 

eavesdropping contexts). The results of 

the CCE study highlight the need for 

further long-term monitoring in the 

GOM. 

Estimated Take 

This section provides an estimate of 

the number and type of incidental takes 

that may be expected to occur under the 

proposed activity, which will inform 

NMFS’s 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. 

Harassment is the only type of take 

expected to result from these activities. 

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). 

Incidental takes would primarily be 

expected to be by Level B harassment, 

as use of the described acoustic sources 

has the potential to result in disruption 

of behavioral patterns for individual 

marine mammals. There is also some 

potential for auditory injury (Level A 

harassment) to result for mysticetes and 

high frequency species due to the size 

of the predicted auditory injury zones 

for those species. Auditory injury is less 

likely to occur for mid-frequency 

species, due to their relative lack of 

sensitivity to the frequencies at which 

the primary energy of an airgun signal 

is found, as well as such species’ 

general lower sensitivity to auditory 

injury as compared to high-frequency 

cetaceans. As discussed in further detail 

below, we do not expect auditory injury 

for mid-frequency cetaceans. The 

proposed mitigation and monitoring 

measures are expected to minimize the 

severity of such taking to the extent 

practicable. No mortality is anticipated 

as a result of these activities. 

Acoustic Thresholds 

Using the best available science, 

NMFS has developed acoustic 

thresholds that identify the received 

level of underwater sound above which 

exposed marine mammals would be 

reasonably expected to exhibit 

behavioral disruptions (equated to Level 

B harassment) or to incur PTS of some 

degree (equated to 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 sound 

levels that 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, 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). 

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. This approach was 

developed based on the 1997 HighEnergy Seismic Survey Workshop 

(HESS, 1999) and a 1998 NMFS 

workshop on acoustic criteria, and 

assumed a step-function threshold. A 

step-function threshold assumes that 

animals receiving SPLs that exceed the 

threshold will always respond in a way 

that constitutes behavioral harassment, 

while those receiving SPLs below the 

threshold will not. This approach 

assumes that the responses of marine 

mammals would not be affected by 

differences in acoustic conditions; 

differences between species and 

populations; differences in gender, age, 

reproductive status, or social behavior; 

or the prior experience of the 

individuals (or any other contextual 

factor). For impulsive sources, such as 

airguns, a threshold of 160 dB rms SPL 

was selected on the basis of measured 

avoidance responses observed in 

whales. Specifically, the threshold was 

initially derived from data for mothercalf pairs of migrating gray whales 

(Malme et al., 1983, 1984) and bowhead 

whales (Richardson et al., 1985, 1986) 

responding when exposed to airguns. 

Subsequent data collection has not 

suggested that the 160-dB value is 

generally unrepresentative, inasmuch as 

a single-value threshold used to predict 

behavioral responses across multiple 

taxa and contexts can be adequately 

representative. This threshold was 

historically unweighted, meaning that 

the assessment of potential for 

behavioral disturbance does not account 

for differential hearing sensitivity across 

species. 

However, most marine mammals 

exposed to impulse noise demonstrate 

responses of varying magnitude in the 

140-180 dB rms exposure range 

(Southall et al., 2007), including the 

whales studied by Malme et al. (1983, 

1984), and potential disturbance levels 

at SPLs above 140 dB rms were also 

highlighted by HESS (1999). Studies of 

marine mammals in the wild and in 

experimental settings do not support the 

assumptions described above for the 

single step approach—different species 

of marine mammals and different 

individuals of the same species respond 

differently to noise exposure. Further, 


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studies of animal physiology suggest 

that gender, age, reproductive status, 

and social behavior, among other 

variables, probably affect how marine 

mammals respond to noise exposures 

(e.g., Wartzok et al., 2003; Southall et 

al., 2007; Ellison et al., 2012). 

Southall et al. (2007) did not suggest 

any specific new criteria due to lack of 

convergence in the data, instead 

proposing a severity scale that increases 

with sound level as a qualitative scaling 

paradigm. Lack of controls, precise 

measurements, appropriate metrics, and 

context dependency of responses all 

contribute to variability. Subsequently, 

Wood et al. (2012) proposed a 

probabilistic response function at which 

10 percent, 50 percent, and 90 percent 

of individuals exposed are assumed to 

produce a behavioral response at 

exposures of 140, 160, and 180 dB rms, 

respectively. It is important to note that 

the probabilities associated with the 

steps identify the proportion of an 

exposed population that is likely to 

respond to an exposure, rather than an 

individual’s probability of responding. 

This function is shifted for species (or 

contexts) assumed to be more 

behaviorally sensitive, e.g., for beaked 

whales, 50 percent and 90 percent 

response probabilities were assumed to 

occur at 120 and 140 dB rms, 

respectively. 

In assessing the potential for 

behavioral response as a result of sonar 

exposure, the U.S. Navy has developed, 

with NMFS, acoustic risk functions (or 

‘‘dose-response’’ functions) that relate 

an exposure to the probability of 

response. These assume that the 

probability of a response depends first 

on the ‘‘dose’’ (in this case, the received 

level of sound) and that the probability 

of a response increases as the ‘‘dose’’ 

increases (e.g., Dunlop et al., 2017). 

Based on observations of various 

animals, including humans, the 

relationship represented by an acoustic 

risk function is a more robust predictor 

of the probable behavioral responses of 

marine mammals to noise exposure. 

Similar approaches are commonly used 

for assessing the effects of other 

‘‘pollutants’’. However, no such 

function has yet been developed for 

exposure to noise from acoustic sources 

other than military sonar. Defining such 

a function is difficult due to the 

complexity resulting from the array of 

potential social, environmental, and 

other contextual effects described 

briefly above, as well as because it 

requires definition of a ‘‘significant’’ 

response (i.e., one rising to the level of 

‘‘harassment’’), which is not welldefined. 

NMFS acknowledges that the 160-dB 

rms step-function approach is 

simplistic, and that an approach 

reflecting a more complex probabilistic 

function is better reflective of available 

scientific information. 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 

behavioral harassment). Zeddies et al. 

(2015) assessed the potential for 

behavioral disturbance of marine 

mammals as a result of the specified 

activities described herein against both 

the 160 dB rms step-function and the 

Wood et al. (2012) approach described 

above. Although Wood et al. (2012) also 

used a modified risk function for 

migrating baleen whales due to assumed 

heightened sensitivity when in that 

behavioral state, this approach was 

deemed not relevant for the GOM as the 

only baleen whale present is resident. 

The modified risk function for sensitive 

species was used for beaked whales. 

While there has been no direct 

evaluation of beaked whale sensitivity 

to noise from airguns, there is 

significant evidence of sensitivity by 

beaked whales to mid-frequency sonar 

(Tyack et al., 2011; DeRuiter et al., 2013; 

Stimpert et al., 2014; Miller et al., 2015), 

as well as to vessel noise (Aguilar Soto 

et al., 2006; Pirotta et al., 2012). 

The approach described by Wood et 

al. (2012), which we are using here, also 

accounts for differential hearing 

sensitivity by incorporating frequencyweighting 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). Finneran and Jenkins (2012) 

developed newer weighting functions 

based on perceptual measure of 

subjective loudness, which better match 

the onset of hearing impairment than 

the original functions (Type II). 

However, because data for the equalloudness contours do not cover the full 

frequency range of the Type I filters, a 

hybrid approach was proposed. 

Subsequently, Finneran (2016) 

recommended new auditory weighting 

functions (Type III) which were adopted 

by NMFS (2016). While Type III filters 

are better designed to predict the onset 

of auditory injury, as a conservative 

measure Type I filters were retained for 

use in evaluating potential behavioral 

disturbance in conjunction with the 

Wood et al. (2012) probabilistic 

response function. 

NMFS is currently evaluating 

available information towards 

development of guidance for assessing 

the effects of anthropogenic sound on 

marine mammal behavior. For this 

specified activity we have determined it 

appropriate to use the Zeddies et al. 

(2015) exposure estimates produced 

using the Wood et al. (2012) approach 

as our basis for estimating take and 

considering the effects of the specified 

activity on marine mammal behavior. 

While we believe that the general 

approach of Wood et al. (2012)—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, distance 

from the source, and particularly 

sensitive species—is appropriate, we 

acknowledge that there is some element 

of professional judgment involved in 

defining the particular steps at which 

specific response probabilities are 

assumed to occur and that this remains 

a relatively simplistic approach to a 

very complex matter. However, we 

believe that the Wood et al. (2012) 

function is consistent with the best 

available science, and is therefore an 

appropriate approach. We are aware of 

the recommendations of Nowacek et al. 

(2015)—i.e., a similar scheme, but 

shifted downward with the 50 percent 

response probability midpoint at 140 dB 

rms—but disagree that these 

recommendations are justified by the 

available scientific evidence. In fact, our 

preliminary analysis of data presented 

in available studies describing 

behavioral response to intermittent 

sound sources (including airguns and 

sonar) (e.g., Malme et al., 1984, 1988; 

Houser et al., 2013; Antunes et al., 2014; 

Moretti et al., 2014), conducted using a 

non-parametric regression method, 

indicates that the 50 percent midpoint 

is very close to 160 dB rms (i.e., 159 dB 

rms). While there may be other 

recommended iterations of this basic 

approach, we address the differences 

between Wood et al. (2012) and 

Nowacek et al. (2015) below. 

Both the Wood et al. (2012) and 

Nowacek et al. (2015) functions 

acknowledge that Level B harassment is 

not a simple one-step function and 

responses can occur at received levels 

below 160 dB rms. The relevant series 

of step functions provided within Wood 

et al. (2012) for beaked whales (50 

percent at 120 dB; 90 percent at 140 dB) 

and all other species (10 percent at 140 

dB; 50 percent at 160 dB; 90 percent at 


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180 dB) attempt to provide a more 

realistic behavioral paradigm, which is 

probabilistic and acknowledges that not 

all exposures are expected to yield 

similar responses for every species and/ 

or behavioral context, as described 

above. The differences between Wood et 

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

stem from how probabilities at 

corresponding received level are 

assigned, with both methodologies 

seemingly relying upon professional 

judgment in interpreting available data 

to make these decisions. 

Regarding mysticetes, changes in 

vocalization associated with exposure to 

airgun surveys within migratory and 

non-migratory contexts have been 

observed (e.g., Castellote et al., 2012; 

Blackwell et al., 2013; Cerchio et al., 

2014). The potential for anthropogenic 

sound to have impacts over large spatial 

scales is not surprising for species with 

large communication spaces, like 

mysticetes (e.g., Clark et al., 2009), 

although not every change in a 

vocalization would necessarily rise to 

the level of a take. Additionally, because 

of existing acoustic monitoring 

techniques, detecting changes in 

vocalizations at further distances from 

the source is more likely, as opposed to 

observing other types of responses (e.g., 

visible changes in behavior) at these 

distances. However, the consideration of 

these observed vocal responses is not 

contrary to Wood et al. (2012). 

Specifically, Blackwell et al. (2013) 

report the onset of changes in vocal 

behavior for migratory bowhead whales 

at received levels that are consistent 

with those provided in the Wood et al. 

(2012) function for migrating mysticete 

species (which are not present in the 

GOM). Cerchio et al. (2014) observed 

the number of singing humpback whales 

in a breeding habitat decrease in the 

presence of increasing background 

received levels during airgun surveys. 

However, because the study was 

opportunistic, specific information on 

distances between singers and source 

vessels, as well as received levels at the 

singing whales, could not be obtained. 

Nevertheless, some probability of these 

vocal responses would likely be 

captured by the Wood et al. (2012) 

function for all other species/behaviors. 

Moreover, a decision about the 

appropriateness of a particular function 

should be based on how well it reflects 

the best available information, rather 

than on how it affects the resulting 

number of takes. 

We also acknowledge concern 

regarding the differences between sperm 

whales and other cetaceans in the midfrequency group, i.e., sperm whales are 

believed to be somewhat more sensitive 

to low-frequency sound, and Miller et 

al. (2009) conclude that exposure to 

noise from airguns may impact sperm 

whale foraging behavior. While the 

available information provides a basis 

for concern regarding the effects of 

airguns on sperm whales, the onset of 

changes in buzz rates (i.e., indicators of 

foraging behavior) occur at received 

levels that are consistent with the 

probabilities predicted by the Wood et 

al. (2012) function for all other species/ 

behaviors. Moreover, the probabilistic 

function recommended by Nowacek et 

al. (2015) likewise does not make 

distinctions between any species or 

species groups, including sperm whales 

(i.e., Nowacek et al. (2015) offers a 

single function for all species and 

contexts). Therefore, Nowacek et al. 

(2015) offers no advantage in this 

regard. 

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 

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. 

Finally, other than providing the 50 

percent midpoint, Nowacek et al. (2015) 

offer minimal detail on how their 

recommended probabilistic function 

should be derived and/or implemented, 

and provide no quantitative 

recommendations for acknowledging 

that behavioral responses can vary by 

species group and/or behavioral context. 

For example, relying upon Nowacek et 

al. (2015), in comparison with Wood et 

al. (2012), does not adequately 

acknowledge that beaked whales are 

known to be particularly sensitive and 

behavioral impacts would be 

underestimated. The behavioral 

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’s 

Technical Guidance for Assessing the 

Effects of Anthropogenic Sound on 

Marine Mammal Hearing (NMFS, 2016) 

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 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 

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 


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science supporting 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; NMFS, 2016). 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 (2016). 

NMFS (2016) 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 (2016), which is 

available online at: www.nmfs.noaa.gov/ 

pr/acoustics/guidelines.htm. 

TABLE 7—EXPOSURE CRITERIA FOR

AUDITORY INJURY FOR IMPULSIVE

SOURCES

Hearing group 

Peak 

pressure 1

Cumulative 

sound exposure level 2

Impulsive 

Nonimpulsive 

Low-frequency 

cetaceans.

219 dB 183 dB 199 dB 

Mid-frequency 

cetaceans.

230 dB 185 dB 198 dB 

High-frequency 

cetaceans.

202 dB 155 dB 173 dB 

1 Referenced to 1 μPa; unweighted within 

generalized hearing range. 

2 Referenced to 1 μPa2-s; weighted according to appropriate auditory weighting function. 

All airguns and the boomer are treated as impulsive sources; other HRG sources are treated as non-impulsive. 

The 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. Details of each peer review are 

included within the technical guidance, 

and specific peer reviewer comments 

and NMFS’s responses are available 

online at: www.nmfs.noaa.gov/pr/ 

acoustics/guidelines.htm. In addition, 

there were three separate public 

comment periods. Responses to public 

comments were provided in a previous 

Federal Register notice (81 FR 51694; 

August 4, 2016). At this time, NMFS 

considers the technical guidance to 

represent the best available scientific 

information. Therefore, we are not 

soliciting and will not respond to 

comments concerning the contents of 

the technical guidance, as such 

comments are outside the scope of this 

proposed rule. NMFS recently provided 

a fourth opportunity for review of the 

technical guidance (82 FR 24950; May 

31, 2017) for the specific purpose of 

soliciting input to assist in review of the 

technical guidance pursuant to 

Executive Order 13795. 

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 

(Table 1). Here we provide a brief 

overview of key modeling elements, 

with more detail provided in the 

following sections. Significant portions 

of the following discussion represent 

incorporation by reference of Zeddies et 

al. (2015) and, for full details of the 

modeling effort, the interested reader 

should see the report (available online 

at: www.fisheries.noaa.gov/national/ 

marine-mammal-protection/incidentaltake-authorizations-oil-and-gas). The 

original modeling report (Zeddies et al., 

2015) evaluated the potential for 

auditory injury using criteria described 

by Southall et al. (2007) and Finneran 

and Jenkins (2012), with some 

appropriate modifications. Following 

completion of NMFS’s technical 

guidance (NMFS, 2016), the original 

exposure modeling results for auditory 

injury were updated using the 

frequency-weighting functions and 

associated thresholds described in 

NMFS (2016) (Zeddies et al., 2017a). 

A modeling workshop was 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 objectives of the 

workshop were to identify: (1) Gaps in 

modeling sound fields from airgun 

arrays and other active acoustic sources, 

including data requirements and 

performance in various contexts, (2) 

gaps in approaches to integration of 

modeled sound fields with biological 

data to estimate marine mammal 

exposures, and (3) assumptions and 

uncertainties in approaches and 

resultant effects on exposure estimates. 

This workshop aided BOEM and 

NMFS’s development of a Request for 

Proposals, Statement of Work, and, 

ultimately, the methodologies 

undertaken in the modeling project. 

The project was divided into two 

phases. Each phase produced exposure 

estimates computed from modeled 

sound levels as received by simulated 

animals (animats) in a specific modeling 

area. In Phase I (described below under 

‘‘Test Scenarios;’’ all other discussion 

here refers to Phase II), a typical 3D 

WAZ survey 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. 

Results from the test scenarios were 

then used to guide the main modeling 

effort of Phase II. In Phase II, 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 2)—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), shallow 

penetration surveys using a single 

airgun, and high resolution surveys 

concurrently using side-scan sonar, 

subbottom profiler, 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 


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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. 

Sound Field Modeling 

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). Source levels for highresolution sources were obtained from 

manufacturer’s specifications for 

representative sources. The AASM 

accounts for the physics of oscillation 

and radiation of airgun bubbles 

(Ziolkowski, 1970) and nonlinear 

pressure interactions between airguns, 

port throttling, bubble damping, and 

generator-injector gun behavior 

(Dragoset, 1984; Laws et al., 1990; 

Landro, 1992). The model was originally 

fit to a large library of empirical airgun 

data, consisting of measured signatures 

of Bolt 600/B airguns ranging in volume 

from 5 to 185 in3. Airgun signatures 

have a random component at higher 

frequencies that cannot be predicted 

using a deterministic model; therefore, 

AASM uses a stochastic simulation to 

predict the high-frequency components 

based on a statistical analysis of a large 

collection of airgun source signature 

data (maintained by the International 

Association of Oil and Gas Producers’ 

Joint Industry Programme). 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 thirdoctave frequency bands to compute the 

source 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. 

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. 

It should be noted that source 

modeling for the boomer source was 

compared to that for the single airgun. 

Results of the comparison indicate that 

the acoustic field modeling results for 

the airgun adequately approximate the 

ones for the boomer. Considering the 

negligible fraction of total surveys 

conducted using boomers and that the 

estimated impact from the single airgun 

is always greater than for the boomer, 

the single airgun results were used as a 

conservative substitute for the boomer. 

Underwater sound propagation (i.e., 

transmission loss) as a function of range 

from each source was modeled using 

JASCO Applied Sciences’ 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. The PE 

method has been extensively 

benchmarked and is widely employed 

in the underwater acoustics community 

(Collins et al., 1996), and MONM– 

RAM’s predictions 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, 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 

Lui, 1994). This component 

incorporates bathymetry and 

underwater sound speed as a function of 

depth with a simplified representation 

of the sea bottom, as subbottom 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). 

These propagation models effectively 

assume a continuous wave source, 

which is an acceptable assumption for 

a pulse in the case of the SEL metric 

because the energy in the various multipath arrivals is summed. When 

significant multi-path arrivals cause 

broadening of the pulse, the continuous 

wave assumption breaks down for 

pressure metrics such as rms SPL. 

Multipath arrivals can have very 

different temporal and spectral 

properties when received by marine 

mammals (Madsen et al., 2006b). 

Models are more efficient at 

estimating SEL than rms SPL. Therefore, 

conversions may be necessary to derive 

the corresponding rms SPL. Propagation 

was modeled for a subset of sites using 

a full-wave RAM PE model (FWRAM), 

from which broadband SEL to SPL 

conversion factors were calculated using 

a sliding 100 ms integration window. 

This window was selected to represent 

the shortest expected temporal 

integration time for the mammalian ear 

(Plomp and Bouman, 1959; 

MacGillivray et al., 2014). The FWRAM 

required intensive calculation for each 

site, thus a representative subset of 

modeling sites were used to develop 

azimuth-, range-, and depth-dependent 

conversion factors. These conversion 

factors were used to calculate the 

broadband rms SPL from the broadband 

SEL prediction at all the modeling sites. 

Conversion factors were calculated for 

each modeling location. 

For electromechanical source and 

single airgun propagation modeling, a 

fixed conversion difference of +10 dB 

from SEL to rms SPL was applied at all 

receiver positions, because there was 

little variability over the range of 

propagation for these sources. This 

approach is accurate at distances where 

the pulse duration is less than 100 ms, 

and conservative for longer distances. 

Most of the effects of these sources 

occur at relatively short distances where 

the pulse durations are short so this 

approach is not expected to be overly 

conservative even for lower-level 

effects. This is a conservative but 

reasonable approximation to simplify 

the variability across all HRG sources, 

effectively assuming that an HRG 

transmission is on for only 1/10 of a 

second for any given second. 

As described below, in order to 

accurately estimate exposure a 

simulation must adequately cover the 

various location- and season-specific 

environments. The surveys may be 

conducted at any location within the 

planning area and occur at any time of 


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the year, so simulations must 

adequately cover each area and time 

period. We previously introduced 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 and 

deep zone (Figure 2). 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 2, 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 2). 

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. 

Geographic coordinates and water 

column depth of each acoustic modeling 

site are listed in Table 48 of the 

modeling report. 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. Inputs are as follows: 

• Water depths throughout the 

modeled area were obtained from the 

National Geophysical Data Center’s U.S. 

Coastal Relief Model l. Bathymetry data 

have a horizontal resolution of 

approximately 80 x 90 m. 

• The top sections of the sediment 

cover in the GOM are represented by 

layers of unconsolidated sediments at 

least several hundred meters thick, with 

grain size of the surficial sediments 

following the general trend for 

sedimentary basins (decreasing with the 

distance from the shore). For the shelf 

zone, the general surficial bottom type 

was assumed to be sand, for the slope 

zone silt, and for the deep zone clay. In 

constructing a geoacoustic model for 

input to MONM, a median grain size 

value was generally selected. Assumed 

geoacoustic properties for each zone as 

a function of depth are presented in 

Tables 52–55 of the modeling report. 

• The sound speed profiles for the 

modeled sites were derived from 

temperature and salinity profiles from 

the U.S. Naval Oceanographic Office’s 

Generalized Digital Environmental 

Model V 3.0 (GDEM). GDEM provides an 

ocean climatology of temperature and 

salinity for the world’s oceans on a 

latitude-longitude grid with 0.25° 

resolution, with a temporal resolution of 

one month, based on global historical 

observations from the U.S. Navy’s 

Master Oceanographic Observational 

Data Set. The GDEM temperaturesalinity profiles were converted to 

sound speed profiles. 

Variation in the sound speed profile 

throughout the year was investigated 

and a set of 12 sound speed profiles 

produced, each representing one month 

in the shelf, slope, and deep zones. The 

set was divided into four seasons and, 

for each zone, one month was selected 

to represent the propagation conditions 

in the water column in each season. 

Acoustic fields were modeled using 

sound speed profiles for winter 

(January–March) and summer (July– 

September). Profiles for Season 1 

(February) provided the most 

conservative propagation environment 

because a surface duct, caused by 

upward refraction in the top 50–75 m 

(of sound above 500 and 250 Hz, 

respectively), was present. Ducting of 

the sound above the relevant frequency 

cutoffs is important as most marine 

mammals are sensitive to these sounds 

and the horizontal far-field acoustic 

projection from the airgun array sources 

do have significant energy in this part 

of the spectrum. Profiles for Season 3 

(August or September) provided the 

least conservative results because they 

have weak to no sound channels at the 

surface and are strongly downward 

refracting in the top 200 m. Only the top 

100 m of the water column are affected 

by the seasonal variation in the sound 

speed. 

Many assumptions are necessary in 

modeling complex scenarios. When 

possible, the most representative data or 

methods were used. When necessary, 

the choices were made to be 

conservative so as not to ultimately 

underestimate potential marine 

mammal exposures to noise. 

Assumptions related to acoustic 

modeling include: 

• The environmental input parameters 

used for transmission loss modeling were 

from databases that provide averaged values 

with limited spatial and temporal resolution. 

Sound speed profiles are averaged seasonal 

values taken from many sample locations. 

Geoacoustic parameters (including sediment 

type, thickness, and reflectivity coefficients) 

and bathymetric grids are smoothed and 

averaged to characterize large regions of the 

seafloor. Local variability, which can be 

affected by weather, daily temperature 

cycles, and small-scale surface and sediment 

details, generally increases signal 

transmission loss, but was removed by these 

averaging processes. As a result, the 

transmission loss could in some cases be 

underestimated and, therefore, the received 

levels would be overestimated. 

• The acoustic propagation model, 

MONM, used the horizontal-direction source 

level for all vertical angles. This may slightly 

underestimate the true sound levels in the 

vertical directional beam of the array that 

ensonifies a zone directly under the array. 

This is expected to be a minor effect given 

the small volume over which the reduction 

occurs. Additionally, there is a steep angle 

limitation in the PE model used in MONM 

that also leads to slightly reduced levels 

directly under the array. The wide-angle PE 

that is used in MONM is accurate to at least 

70 degrees. The reduced-level zone is a cone 

within a few degrees of vertical, which 

represents a relatively small water volume 

that should not significantly affect results. 

• Seasons modeled: 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). 

Historically, distance sampling 

methodology (Buckland et al., 2001) has 

been applied to visual line-transect 

survey data to estimate abundance 

within large geographic strata (e.g., 

Fulling et al., 2003; Mullin and Fulling, 

2004). Design-based surveys that apply 

such sampling techniques produce 

stratified abundance estimates and do 

not provide information at appropriate 

spatiotemporal scales for assessing 

environmental risk of a planned survey. 

To address this issue of scale, efforts 

were developed to relate animal 

observations and environmental 

correlates such as sea surface 

temperature in order to develop 

predictive models used to produce finescale maps of habitat suitability (e.g., 

Waring et al., 2001; Hamazaki, 2002; 

Best et al., 2012). However, these 

studies generally produce relative 

estimates that cannot be directly used to 

quantify potential exposures of marine 

mammals to sound, for example. A more 

recent approach known as density 

surface modeling couples traditional 

distance sampling with multivariate 

regression modeling to produce density 

maps predicted from fine-scale 

environmental covariates (e.g., DoN, 

2007b; Becker et al., 2014; Roberts et al., 

2016). 


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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’s SARs 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/. 

In the GOM, there are clear 

differences in marine mammal 

distribution by water depth, i.e., from 

shelf to slope and from slope to deep. 

Division of the modeling area into zones 

was chosen so that nominal marine 

mammal densities remain relatively 

constant over the resulting depth 

intervals. Density of several species 

varies within the shelf and slope areas, 

seemingly correlated with the 

orientation and differences in the 

widths of these areas over the east-west 

extent of the project area. Therefore, 

shelf and slope zones were divided in 

western, central, and eastern areas 

according to BOEM’s planning area 

boundaries (Figure 2). The minimum, 

maximum, and mean (and standard 

deviation of the mean) zone-specific 

marine mammal density estimates, 

derived from Roberts et al. (2016), are 

shown in Tables 62–68 of the modeling 

report (with density seeding 

adjustments). Although sperm whales 

are sometimes encountered in shallower 

water, they were depth restricted in the 

model to waters greater than 1,000 m. 

Females are rarely seen in waters less 

than 1,000 m (Taylor et al., 2008), and 

Wursig (2017) reports a mean encounter 

depth of 1,732 m, so this is a reasonable 

restriction. It is important to note that 

the Zone 6 densities for Bryde’s whales 

(Table 67 in the modeling report) reflect 

the output of an earlier iteration of the 

Bryde’s whale density model. This 

earlier iteration predicted the presence 

of Bryde’s whales in Zone 6 (western 

GOM slope), an area where they are not 

currently believed to occur, on the basis 

of two ambiguous Balaenoptera spp. 

sightings from 1992. Subsequently, 

Roberts et al. (2016) revised the model 

by changing the modeling period from 

1992–2009 to 1994–2009 so that those 

sightings were not included, and also 

added a bivariate smooth of XY to the 

model, to concentrate density where 

sightings were reported (Roberts et al., 

2015c). Based on the results of this 

revised model, Bryde’s whales would 

not be expected to occur in Zone 6 and, 

on this basis, we have discounted the 

predicted exposures of Bryde’s whales 

in that zone. 

Animal Movement Modeling and 

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), 

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 individuals affected. 

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). 3MB 

controls animat movement in horizontal 

and vertical directions using submodels. Travel sub-models determine 

horizontal movement, including submodels for the animats’ travel direction 

and the travel rate (speed of horizontal 

movement). Dive sub-models determine 

vertical movement. Diving behavior submodels include ascent and descent 

rates, maximum dive depth, bottom 

following, reversals, and surface 

interval. Bottom following describes the 

animat’s behavior when it reaches the 

seafloor, for example during a foraging 

dive. Reversals simulate foraging 

behavior by defining the number of 

vertical excursions the animat makes 

after it reaches its maximum dive depth. 

The surface interval is the amount of 

time an animat spends at the surface 

before diving again. 3MB allows a user 

to define multiple behavioral states, 

which distinguish between specific 

subsets of behaviors like shallow and 

deep dives, or more general behavioral 

states such as foraging, resting, and 

socializing. The transition probability 

between these states can be defined as 

a probability value and related to the 

time of day. The level of detail included 

depends on the amount of data available 

for the species, and on the temporal and 

spatial framework of the simulation. 

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 


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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. The use of surrogate species 

is a reasonable assumption for the 

simulation of proximate or observable 

behavior, and it is unlikely that this 

choice adds more uncertainty about 

location preference. Species-specific 

parameter values are given in Tables D– 

1 to D–18 of the modeling report. 

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; 

boundaries extend at least one degree of 

latitude or longitude beyond the extent 

of the vessel track to ensure an adequate 

number of animats in all directions, and 

to ensure that the simulation areas 

extend beyond the area where 

substantial behavioral reactions might 

be anticipated. 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 species-specific 

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. Representative survey patterns 

were described under ‘‘Detailed 

Description of Activities.’’ 

During all simulations in this 

modeling effort, any animat that left the 

simulation area as it crossed the 

simulation boundary was replaced by a 

new animat traveling in the same 

direction and entering at the opposite 

boundary. For example, an animat 

heading north and crossing the northern 

boundary of the simulation was 

replaced by a new animat heading north 

and entering at the southern boundary. 

By replacing animats in this manner, the 

animat modeling density remained 

constant. Animats were only allowed to 

be ‘taken’ once during a 24-hr 

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-hr 

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. 

In Figure 2, the large transparent 

boxes represent the seven defined 

modeling areas (animal simulation 

extents) within the seven zones. During 

the survey simulations, the source was 

moved within the smaller survey area 

extents, but the sound output would 

ensonify a larger area (represented by 

the animal simulation extents). These 

animat simulation boxes set the 

geographic limits of the 3MB 

simulation. 

For the large-area surveys, injury 

simulation boxes extend outward 

(north, south, east, and west) by 10 km 

from the survey limits, a distance over 

which the unweighted received levels 

drop below 160 dB SEL for a single shot. 

The behavior simulation boxes, on the 

other hand, extend outward by 50 km 

from the survey limits, a distance 

necessary to ensure that the animat 

movement modeling extends out to 

where the weighted received levels drop 

to 120 dB rms SPL or lower, and below 

160 dB SEL for unweighted received 

levels. Geographic extent of the boxes is 

shown in Tables 59–60 of the modeling 

report. 

The received levels for the single 

airgun and electromechanical sources 

drop off much more quickly with range 

than for the airgun array sources 

discussed above. Consequently, the 

3MB simulation boxes for the small-area 

surveys were extended to 10 km from 

the center of the survey in each cardinal 

direction, a much larger distance than 

that required for the received level 

conditions, but one that supports more 

realistic animal movements. Geographic 

extent of the boxes is shown in Table 61 

of the modeling report. 

The JASCO Exposure Modeling 

System (JEMS) combines 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. JEMS can use any 

acoustic field data provided as a 3D 

radial grid. Source movement and 

shooting patterns can be defined, and 

multiple sources and sound fields used. 

For impulsive sources, a shooting 

pattern based on movement can be 

defined for each source, with shots 

distributed along the vessel track by 

location (or time). Because the acoustic 

environment varies with location, 

acoustic fields are pre-computed at 

selected sites in the simulation area and 

JEMS chooses the closest modeled site 

to the source at each time step. 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-windows 

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. 

As described above for acoustic 

modeling, assumptions and choices 

must be made when modeling complex 

scenarios: 

• Social grouping: Marine mammals often 

form social groups, or pods, that may number 

in the hundreds of animals. Although it was 

found that group size affects the distribution 

of the exposure estimates (see Test Scenario 

2, below), the mean value of the exposure 

estimate was, generally, unchanged. Because 

the annual exposure estimates are meant to 

represent the aggregate of many surveys 

conducted in many locations at various times 

throughout the year, it is the mean exposure 

estimates that are most relevant. For this 

reason, social group size was not included in 

the exposure estimates. 

• Mitigation procedures, such as shutting 

down an airgun array when animals are 

detected within an established exclusion 

zone, can reduce the injury exposure 

estimates. Mitigation effectiveness was found 

to be influenced by several factors, most 

importantly the ability to detect the animals 

within the exclusion zone. Some species are 

more easily detected than others, and 

detection probability varies with weather and 

observational set-up. Weather during any 

seismic survey is unknown beforehand and 

detection probabilities are difficult to predict, 

so the effects of mitigation were not included 

in the exposure estimates (see Test Scenario 

3, below). 

• Aversion is a context-dependent 

behavioral response affected by biological 

factors, including energetic and reproductive 

state, sociality, and health status of 

individual animals. Animals may avoid loud 

or annoying sounds, which could reduce 

exposure levels. The effect of aversion itself 


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can be considered as a take (Level B 

harassment) that results in avoidance of 

potential for more serious take (Level A 

harassment). Currently, too little is known 

about the factors that lead to avoidance (or 

attraction) of sounds to quantify aversive 

behavior for these activities when modeling 

marine mammal exposure to sound (see Test 

Scenario 4, below). However, we include an 

aversion factor in defining the level of take 

that may occur, as compared with the 

modeled exposure estimates. 

Injury—To evaluate the likelihood an 

animal might be injured 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 occurs (Table 7) 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 

behavioral harassment thresholds. This 

process was repeated for each 24-hr 

integration window. 

Potential for disruption of behavioral 

patterns was also evaluated using 

NMFS’s standard 160 dB rms criterion. 

To evaluate this likelihood, the 

exposure simulation was set to use 

unweighted rms SPL acoustic fields. 

The number of animats that received an 

exposure greater than 160 dB was 

counted as the number of behavioral 

responses. However, note that the 

modeling report also separately 

evaluated exposures at received levels 

exceeding 180 dB rms; therefore, the 

true number of exposures greater than 

160 dB rms would be the sum of 

separately calculated exposures between 

160 and 180 dB and greater than 180 dB. 

As with the other criteria, the animat 

received level was reset at the beginning 

of each 24-hr integration window. 

Please see Zeddies et al. (2015) for 

exposure results relating to the 160-dB 

rms criterion. The methods did not 

account for potential habituation, 

whereby severity of behavioral reactions 

to a stimulus may be reduced due to 

reduced sensitivity in individual 

animals from repeated exposure over 

time. However, we are not aware of any 

literature suggesting that marine 

mammals in the wild and away from 

areas with consistent industrial activity 

(e.g., ports) become habituated to noise 

or of any method by which such 

theoretical habituation could be 

modeled. 

Test Scenarios 

As described above, Phase I of the 

modeling effort involved preliminary 

modeling of a typical 3D WAZ survey 

(all survey parameters were described 

under ‘‘Detailed Description of 

Activities’’), 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 provide a summary of 

each of the six evaluated test scenarios 

below. For all test scenarios, please see 

the modeling report for full details. 

Locations considered were both near 

the Mississippi Canyon, including a site 

centered on the slope of the continental 

shelf break and a site centered on the 

deep ocean plain (please see Figure 10 

in Zeddies et al. (2015)). A reduced 

suite of six representative species were 

included in the Phase I effort: Bryde’s 

whale, sperm whale, Cuvier’s beaked 

whale, bottlenose dolphin, dwarf sperm 

whale, and short-finned pilot whale. 

Bryde’s whales and dwarf sperm whales 

were chosen as the only low-frequency 

species in the GOM and as the 

representative high-frequency species, 

respectively. The four mid-frequency 

species were chosen to represent 

various other aspects of diving and 

hearing sensitivity. Cuvier’s beaked 

whales are deep-diving and behaviorally 

sensitive to sound, while sperm whales 

are also deep-diving and are a unique 

species in the GOM behaviorally. Shortfinned pilot whales and bottlenose 

dolphins both represent the swimming 

behavior of smaller cetaceans with 

different preferred water depths. Note 

that, for this preliminary modeled 

scenario, density estimates were 

obtained from DoN (2007b), as Roberts 

et al. (2016) was not yet available. Full 

details of the preliminary modeling are 

available in the modeling report. 

To evaluate potential behavioral 

response, 30-day simulations of the 

hypothetical 3D WAZ survey were run 

at both sites for each of the species 

evaluated. The boundaries of the 

simulation were determined from 

transmission loss calculations, and were 

set at 50 km from the source. 

Test Scenario 1 (Long-duration 

Surveys and Scaling Methods)—Some 

surveys operate (nearly) continuously 

for months. Evaluating the potential 

impacts due to underwater sound 

exposures from these extended 

operations is challenging because 

assumptions about parameters that are 

valid for short-duration simulations may 

become less valid, or more varied, as the 

time period increases. Treating 

parameters such as sound velocity 

profile or large-scale animal movement 

as constant over longer durations, as is 

typically done in shorter duration 

simulations, could lead to errors. 

However, there is no information 

indicating that species migrate regularly 

on a large-scale in the GOM; thus, largescale movement was not integrated into 

the animal movement model. Therefore, 

a test scenario was used to evaluate 

possible systematic bias in the modeling 

process, and methods for scaling results 

from shorter-duration simulations to 

longer duration operations were 

suggested. 

Exposure estimates from 30-day and 

5-day simulations, using different 

animat seeding values (0.1 and 2.0 

animats/km2, respectively), were 

determined in subsets using a ‘sliding 

window’ to find the number of 

exposures as a function of time. The 30- 

day simulation was used to evaluate 

exposures against the rms SPL criteria, 

and the 5-day simulation was used to 

evaluate exposures against the peak SPL 

and cSEL criteria. The length of the 

sliding window was 24 hr, advanced by 

4 hr, resulting in 174 samples from the 

30-day simulation and 25 samples from 

the 5-day simulation. A sliding window 

of 7 days advancing by 1 day for the 30- 

day simulation was also evaluated. Bias 

in the model was expected to manifest 

itself as a trend in the exposure levels 

as a function of time. 

To investigate potential systematic, 

and possibly unknown, biases in the 

modeling procedure, behavioral 

exposure estimates were determined for 

subsets of the simulations. Behavioral 

exposure estimates were determined as 

a function of time by finding the 

number of exposures occurring in 24-hr 

subsets using a sliding window that 

advanced in 4-hr increments. Trends 


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were evident, particularly at the slope 

site, but the trends appeared to be the 

consequence of survey design, such as 

changing sound fields as the vessels 

move into different acoustic zones. For 

sperm whales, there was an additional 

bias due to their general avoidance of 

water depths less than 1000 m. The area 

of the slope site began at a location with 

water depth approximately 1,500 m, but 

proceeds to depths less than 200 m. 

Therefore, fewer sperm whale animats 

were within exposure range of the 

source later in the simulation. To 

determine if undesired, and unknown, 

systematic biases exist in the modeling 

procedure, simulations were run with 

the source stationary and with no 

limiting bathymetric constraints. No 

clear trends were found, indicating 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, if applied. 

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. Given that an animat 

represents an individual marine 

mammal, scaling up the 24-hr average 

SPL exposure estimates to 30 days 

greatly overestimates the number of 

individual marine mammals 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-hr means that individual 

animats were, in effect, counted several 

times during the scale-up (i.e., on 

multiple days) that would only have 

been counted once when evaluating 

over the entire simulation. Comparison 

between the full-duration estimate 

(obtained through modeling the full 

survey duration) and the estimate 

developed through ‘‘scaling’’ the 24-hr 

exposure estimate allows for better 

interpretation of the exposure estimates, 

e.g., through a refined estimate of the 

number of individuals exposed above 

behavioral harassment criteria (versus 

instances of exposure) and the average 

number of days on which those 

exposures occur (described below in 

‘‘Description of Exposure Estimates’’). 

Because SEL is an accumulation of 

energy, evaluating over a longer period 

(e.g., summing accumulation over 30 

days) could result in more animats 

exposed to levels exceeding SEL 

thresholds than when evaluated over a 

shorter period (unlike as described 

above for SPL metrics). 

The systematic trends evident in the 

modeling procedure indicated that 

survey design can affect exposure 

estimates when scaling is used. 

Therefore, the minimum duration of a 

simulation should include all of the 

acoustic environments likely to be 

encountered during the operation. The 

test scenario produced the following 

recommendations, which were 

employed during the Phase II modeling 

effort: (1) Identify the shortest largescale animal movement time-period 

(e.g., seasonal migration); (2) Identify 

acoustic environments over which the 

survey will occur (e.g., shallow, slope, 

deep, and associated geoacoustic 

parameters); (3) Identify the minimum 

period of validity for the acoustic model 

(e.g., month due to changing sound 

velocity profile); (4) Break the survey 

into parts that are shorter in duration 

than both large-scale animal movement 

times and the period of acoustic model 

validity; (5) Create animal movement 

simulations for acoustic exposure with 

adequate duration to meaningfully 

sample the exposure-estimating 

parameter (e.g., for a 24-hr reset period, 

enough samples should be obtained to 

get a reliable mean value given the 

various acoustic environments); (6) If 

the simulation time is less than the 

duration of the survey parts determined 

in Step 4, then scale the results by the 

ratio of survey duration to simulation 

time (e.g., if the simulation time is one 

week, but the survey division is 28 days, 

then multiply the simulation exposure 

results by four); and (7) Sum, or 

aggregate, the results from the survey 

parts to calculate exposures for the 

entire survey. 

This test scenario also illustrated that 

knowing the amount of time that 

animals are exposed to levels exceeding 

the threshold criteria can provide 

additional information about the 

potential impacts of the activity. For 

example, the amounts of time that 

animats were exposed to levels 

exceeding 160 dB rms SPL over the 30- 

day duration were approximately twice 

as long as the average times in a 24-hr 

window, as it was common for the 

threshold to be exceeded on multiple 

separate occasions. Two factors 

contributed to the total time thresholds 

were exceeded—the amount of time per 

occasion (i.e., how long an animat was 

near the source) and the number of 

occasions that occur (i.e., how many 

times an animat was near a source). The 

number of occasions was, essentially, 

the same item determined when finding 

the number of animats with exposures 

exceeding threshold criteria (the typical 

use of the threshold criteria). The 

number of occasions scales with the 

duration of the evaluation period, but 

the time per occasion does not, and is 

specific to how an individual animat 

interacted with a source. Information 

provided through this investigation was 

used to derive scaler values (described 

below in ‘‘Description of Exposure 

Estimates’’) for use in determining the 

expected number of individuals 

represented by a sum total of exposures 

generated through the scaling of 24-hr 

exposures up to match the total duration 

of a modeled survey. 

Test Scenario 2 (Sources and Effects 

of Uncertainty)—The modeling process 

requires the use of simplifying 

assumptions about oceanographic 

parameters, seabed parameters, and 

animal behaviors. 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. For example, 

acoustic propagation models assume a 

specific shape of the sound speed 

profile in the ocean (speed of sound 

versus depth) for each season. We know, 

however, that the real sound speed 

profile regularly changes and that 

substantial variation within a season is 

possible. The assumption that a single 

profile represents the environment 

through a full season approximates realworld cases but can, to some degree, 

cause errors. The uncertainty in model 

outputs caused by approximations like 

this can be investigated by examining 

how much the outputs change when the 

inputs are purposely offset. ‘‘Parametric 

uncertainty analysis’’ provides a means 

to characterize the accuracy, or 

uncertainty, of the model results in light 

of errors in model inputs and can also 

be used to characterize the expected 

variability in model results due to 

natural variations in some of the input 

parameters. Use of resampling 

techniques can quantify the effects of 

uncertainty in exposure estimates due to 

uncertainty in acoustic and animal 

movement models. Uncertainty related 

to acoustic modeling can be introduced 

through source characterization 

modeling; acoustic propagation 

modeling; and selection of inputs for 

sound speed profiles, geoacoustic 

parameters, bathymetry, and sea state. 

Uncertainty in animal modeling can be 

introduced through incomplete 

knowledge regarding animal locations 

and behavioral/motivational states. Both 

the uncertainty in acoustic modeling 

and uncertainty in the animal modeling 


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contribute to overall uncertainty in the 

exposure estimates. Please see the 

modeling report for full details of these 

investigations. 

Zeddies et al. (2015) describe 

uncertainties in the acoustic field as 

representing a multi-dimensional 

envelope that can be wrapped around 

the main modeling results. This 

envelope is meant to enclose the 

modeled acoustic field and the real 

world acoustic field. The uncertainties 

in the different dimensions of this 

envelope (sound speed profile, 

geoacoustics, bathymetry, and sea state) 

cannot be summed to yield a ‘‘total’’ 

uncertainty as this would be a 

meaningless quantity. The overall 

uncertainty is measured for the volume 

of the multi-dimensional uncertainty 

envelope, but this is a difficult concept 

to use in operational planning. The best 

way to visualize the overall uncertainty 

is in terms of the different dimensions 

of the uncertainty envelope, which 

range from inconsequential (e.g., effects 

of sea state) to greater than 10 dB 

between median and maximum 

propagation scenarios in the shelf zone 

due to uncertainty in the sound speed 

profile. 

With regard to uncertainty relating to 

animal movement parameters, 

comparisons between animals generally 

resulted in similar exposure estimates 

when the same filtering and thresholds 

were applied. The exposure estimates 

for bottlenose dolphins, short-finned 

pilot whales and, to some extent, sperm 

whales were similar. For sperm whales, 

however, the behavioral depth 

restriction for this species (animats do 

not enter water depths less than 1,000 

m) resulted in differences. Sperm 

whales also showed greater potential of 

behavioral response to noise exposure 

than other species with the same 

auditory thresholds. Sperm whales are 

deep divers; in this downward 

refracting environment they appear to 

receive consistently greater exposures 

relative to shallow diving species. 

In order to address overall uncertainty 

in the exposure estimates resulting from 

combined uncertainty due to both 

acoustic and animal modeling, a 

‘‘bootstrap’’ resampling process was 

used in which relevant uncertainty 

could be added to animats’ received 

levels. For example, for potential 

auditory injury, the primary acoustic 

uncertainty was the source level 

variance. Airguns are designed to have 

low inter-shot variability and predicted 

source levels within 3 dB. A 

conservative estimate of ±3 dB standard 

deviation was used to investigate the 

effects of source level variance on SEL 

injury exposure estimates. While the 

mean number of animats above SEL 

threshold increased relative to the 

expected value, the exposure estimate 

distributions did not change much. For 

potential behavioral disturbance, 

propagation uncertainty (due to the 

greater ranges involved) also contributes 

to the uncertainty in the acoustic 

modeling predictions; therefore, 6 dB 

was chosen as a test to include both the 

source variance plus uncertainty due to 

propagation. The mean behavioral 

disruption estimates and the 

distribution ranges stayed 

approximately the same when ± 6dB of 

acoustic variability was included. 

During resampling, acoustic uncertainty 

can be combined with real-world 

density (mean ± standard deviation) and 

social group size (mean ± standard 

deviation). In general, the uncertainty 

associated with the animals (density 

and group size) does not change the 

mean exposure estimate, but can affect 

the exposure estimate distribution. 

Test Scenario 3 (Mitigation 

Effectiveness)—With reference to 

detection-based mitigation, effectiveness 

at reducing marine mammal exposure to 

potentially injurious sound levels is 

unknown. Mitigation effectiveness 

corresponds with the ability to detect an 

animal in the relevant zone. 

Detectability, and consequently 

mitigation efficacy, depends on the 

species, potentially individual animal 

characteristics, survey configuration, 

and environmental conditions. 

Mitigation effectiveness was evaluated 

using a modeling approach to quantify 

the potential reduction in the numbers 

of exposures at or above Level A 

harassment thresholds for selected 

species by comparing acoustic exposure 

estimates with and without mitigation 

(array shutdown). For each of the six 

species considered in the preliminary 

modeling, a range of detection 

probabilities (i.e., g(0)) was considered. 

The positions of animats in the 

simulation are known and reported in 

short time steps. The detection 

probability, however, is the probability 

of detecting an animal along the 

trackline as the survey passes through 

an area, rather than for an individual 

time step. For this evaluation, g(0) is 

used as estimate of the detection 

probability for animats near the surface 

and close to the vessel. 

Level A harassment exposure 

estimates associated with the 5-day 

survey simulation were calculated with 

and without a mitigation procedure. 

Exposure estimates were computed 

relative to SEL and peak SPL exposure 

criteria. Airgun shutdown was modeled 

by zeroing all animat received levels 

when an animat was detected within an 

exclusion zone, with detection 

registered when the horizontal range of 

an animat from the source was less than 

500 m, its depth was less than 50 m, and 

a random draw from a uniform 

distribution between 0 and 1 indicated 

detection. If the random value was less 

than the assumed g(0), the detection was 

registered, the time of the closest point 

of approach (CPA) was found, and the 

received levels for all animats were 

zeroed for 30 minutes before and after 

the CPA. For the purposes of the 

simulation, it was assumed that portions 

of the survey line missed during 

shutdown were re-surveyed (i.e., 

shutdowns result in an increase in the 

overall survey duration in order to keep 

the distance surveyed the same as the 

unmitigated case). Shutdown was 

assumed to occur only for the source 

array around which the animat was 

detected. Other sources present in the 

simulation continued operating. Model 

simulations were run for detection 

probabilities of 0.05 to 0.45 (increments 

of 0.05) and 0.5 to 0.9 (increments of 

0.1) to simulate a reasonable range of 

probabilities for cryptic species and 

other species, respectively. 

The inclusion of mitigation 

procedures in the simulations reduced 

the numbers of exposures based on peak 

SPL criteria for five out of six species 

and detection probabilities considered, 

even though an extension in the survey 

period due to line re-shoot was taken 

into account. The exception was Bryde’s 

whales, due to low real-world density 

values. Mitigation effectiveness, 

expressed as the reduction in the 

number of individual animals exposed, 

was generally related to animal 

densities; species with higher densities 

were more often exposed and the 

reduction in the number of exposures 

from mitigation was greater. As 

expected, the percentage reduction in 

exposures for species with relatively 

high detection probability was higher 

than the percentage reduction for 

species with relatively low detection 

probability. 

The usefulness of mitigation depends 

on species characteristics and 

environmental conditions, meaning that 

there is a high degree of inherent 

variability (and potential error) involved 

in attempting to predict some reduction 

in potential exposures resulting from 

mitigation effectiveness. Reductions due 

to mitigation for easily-detected species 

with large populations may be large in 

terms of percentage decrease (assuming 

shutdown is a required measure) while, 

for low-density species that are difficult 

to detect in rough seas, there may be 

little realistic mitigation effect. Further, 

for deep-diving species with unreliable 


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vocal rates, a very conservative estimate 

of mitigation effectiveness should be 

used. Ultimately, on the basis of these 

findings, quantification of mitigation 

effectiveness was not incorporated into 

the Phase II modeling effort (i.e., is not 

reflected in the modeled exposure 

estimates). 

Test Scenario 4 (Effects of Aversion)— 

Animal behavior in response to sound 

exposure may vary widely, but if sounds 

are perceived as a threat or an 

annoyance, animals might temporarily 

or permanently avoid the area near the 

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

Ellison et al., 2012)—a phenomenon 

referred to as aversion. Aversive 

responses to sounds are of particular 

interest here because such behavior 

could decrease the number of injuries 

that result from acoustic exposure in the 

real world. If aversion occurs at a 

received level lower than that 

considered an injurious exposure, a 

decrease in the corresponding number 

of estimated exposures above Level A 

harassment criteria can be assumed. The 

degree of aversion and level of onset for 

aversion, however, are poorly 

understood. 

As for mitigation effectiveness, a test 

scenario was investigated using a 

modeling approach to quantify the 

potential reduction in injury exposure 

estimates due to aversion. Aversion is 

simulated as a reduction in received 

levels and, because little is known about 

the received levels at which animals 

begin to avert, the sound levels and 

probabilities used to evaluate potential 

behavioral disturbance are used to 

approximate aversion. However, it is 

possible that aversion could occur at 

greater or lesser received sound levels, 

depending on the context and/or 

motivation of the animal. It is important 

to note that, as considered here, 

aversion itself can represent a 

behavioral disruption; therefore, 

aversion is only meaningful in reducing 

the potential for injury, i.e., those 

animals that avert may have avoided 

Level A harassment, but would have 

nevertheless experienced Level B 

harassment. 

Injury exposure estimates associated 

with the 5-day 3D WAZ simulation were 

determined with and without aversion. 

The difference in the mean value of the 

exposure estimate distributions with 

and without aversion indicates the 

effect of aversion on the injury exposure 

estimates. Each animat sampled during 

the bootstrap resampling process has an 

associated exposure history, i.e., a time 

series of received sound levels arising 

from relative motion of the source and 

animat. These exposure histories were 

computed assuming the animats’ 

behaviors were otherwise unaffected by 

their received sound levels. Each 

exposure history was then modified 

based on received-level dependent 

probabilities of averting: 

• Step 1: For each bootstrap sample, the 

occurrence of aversion was determined 

probabilistically based on the exposure level 

and the probability of aversion defined 

according to the function described 

previously (Table 6) for both SEL and peak 

SPL. An iteration-specific aversion efficacy 

was also chosen randomly from a uniform 

distribution in the range of 2–10 dB. 

• Step 2: Animats for which aversion 

occurred in Step 1 had their received levels 

adjusted as described in the following steps. 

The received levels were unchanged for 

animats that did not avert. 

• Step 3: For an animat entering an averted 

state, the aversion level excesses (the levels 

above the threshold that prompted aversion) 

until the end of the aversion episode were 

calculated from the difference between the 

received level at the start of aversion and the 

threshold level at which aversion began up 

to a maximum of 5 dB. 

• Step 4: The adjusted received level 

during aversion was set to the greater of two 

quantities: (1) The received level minus the 

aversion efficacy (from Step 1), or (2) the 

threshold level plus the aversion level excess 

at the start of aversion (from Step 3). 

Adjusted exposure histories were 

computed separately for each source, 

animat, and episode of aversion; each 

occurrence of aversive behavior was 

thus independent. Although the 

probability of aversion was defined in 

terms of the rms SPL, exposure histories 

were recorded in terms of the per-pulse 

SEL. A nominal conversion offset of +10 

dB from SEL to rms SPL was used so the 

two metrics could be compared. 

Cumulative SELs over the 5-day 

simulation, were weighted using Type I 

filters for Bryde’s whales and Type II 

filters for mid- and high-frequency 

cetaceans, but behavioral effects were 

estimated using Type I filters for all 

species, with appropriate adjustments 

made to the 5-day SEL exposure 

histories. The mean time spent in an 

averted state for four of six species were 

approximately 18 and 4 min for the 

slope and deep sites, respectively. For 

beaked whales, the means were 41 and 

19 min. Too few Bryde’s whale animats 

exceeded threshold to obtain a reliable 

statistical measure. 

Aversion in the simulations reduced 

the numbers of exposures based on peak 

SPL criteria for most species. Aversion 

effectiveness, as measured by the 

percentage reduction in the exposure 

estimates, could be high: Approximately 

85 percent for bottlenose dolphins, 

Cuvier’s beaked whales, short-finned 

pilot whales, and sperm whales, and 40 

percent for dwarf sperm whales. Bryde’s 

whales, whose real-world densities were 

so low that no exposures were modeled 

even in the absence of aversion, were 

the exception. The numbers of 

exposures based on SEL criteria were 

near zero for most species even without 

aversion. The reduction in exposures 

was influenced by the criteria used to 

estimate exposures and by the 

assumptions made with respect to 

aversion probability. For example, 

although the real-world densities of 

dwarf sperm whales (a high-frequency 

cetacean) are similar to those for 

Cuvier’s beaked whales (a midfrequency cetacean), exposure estimates 

and the decrease in number of exposure 

estimates arising from aversion were 

different. The differences in aversion 

effectiveness reflect differences in injury 

threshold criteria and aversion 

probability. Ultimately, the effects of 

aversion were not quantified in the 

Phase II modeling due to lack of 

information regarding species-specific 

degree of aversion and level of onset. 

Test Scenarios 5–6 (Separation 

Distance and Simultaneous Source 

Firing)—Geophysical surveys using 

airgun arrays may use survey designs 

that involve multiple source vessels 

separated by tens of meters to several 

kilometers, while newer technology has 

allowed for different surveys to be 

performed closer together than 

previously. Due to the possibility that 

the combined sound pressure levels of 

multiple airgun arrays operated close to 

one another could lead to increased 

noise effects than would occur with a 

single source, these scenarios were 

designed to address the issue of the 

aggregate noise produced by multiple 

airgun arrays and the potential for those 

signals to combine and lead to larger 

effects. 

The investigations found that while 

SEL increases for overlapping surveys, 

injury due to accumulated energy is a 

rare event, and threshold exceedance 

resulted from a few high-level exposures 

near a source rather than an 

accumulation of many lower-level 

exposures. The range to injury assessed 

by peak SPL is up to a few hundred 

meters and does not accumulate. Injury 

in typical airgun surveys, therefore, 

occurs mainly because of a close 

encounter with a single airgun array. 

There are practical limits to how close 

two acquisition lines can be without one 

survey source interfering with the other 

survey’s recordings. Depending on the 

survey type and the propagation 

environment of the area, the stand-off 

distance between fully concurrent 

surveys operating independently may be 

several tens of kilometers. If two surveys 

are conducted in closer proximity, then 

the operators will generally agree to 


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‘‘time-sharing’’ strategies whereby, for 

example, one survey acquires a line 

while the other completes a line turn 

with the source inactive, or similar ways 

of minimizing the amount of missed 

effort. Effects of overlapping surveys on 

injury exposure estimates are unlikely. 

For potential behavioral disturbance, 

overlapping surveys may affect 

exposure estimates, but the effect is 

either small or potentially negative 

(reducing the overall number of 

estimated exposures). Because 

coincident reception in which the 

sound level increases appreciably 

occurs only in small portions of the 

ensonified volume, overlapping survey 

sound fields do not generally result in 

higher maximum received sound 

pressure levels. And, because animals 

may only be ‘‘taken’’ once within a 24- 

hr window, animals exposed in more 

than one survey are only counted once 

in the aggregate of the surveys. This 

does not preclude possible behavioral 

effects of animals spending more time 

above threshold, but such effects are not 

addressed by existing criteria. 

From an energetic perspective, the 

relative firing pattern of different arrays 

does not matter. The same SEL will be 

registered when two arrays are 

alternated or fired simultaneously. For 

the pressure-based metrics, peak SPL 

and rms SPL, simultaneous firing can 

increase the received levels, but in only 

a small portion of the ensonified 

volume. Because the maximum received 

levels are rarely increased, the exposure 

estimates based on SPL are rarely 

increased. The most likely place for 

meaningful summation to occur is very 

near the source, and in that case the 

firing pattern would be included in the 

simulation and therefore in the 

exposure estimates. 

In summary, neither separation 

distance nor simultaneous firing is of 

significant concern when estimating 

exposures using the current criteria. 

Modeling Issues 

NMFS is aware of criticism that the 

modeling results are unrealistic or 

overly conservative (e.g., ‘‘biased 

modeling based on flawed 

assumptions’’). For example, we 

received public comment in response to 

our Federal Register notice of receipt of 

the petition from the IAGC, API, 

National Ocean Industries Association, 

and Offshore Operators Committee 

(hereafter referred to as ‘‘the 

Associations’’). The Associations quote 

certain statements made by BOEM in its 

draft Programmatic EIS (e.g., ‘‘an overly 

conservative upper limit,’’ exposure 

estimates are ‘‘higher than BOEM 

expects would actually occur in a real 

world environment,’’ modeling results 

represent a ‘‘worst-case scenario’’). 

NMFS strongly disagrees with these 

characterizations. While the modeling 

required that a number of assumptions 

and choices be made by subject matter 

experts, some of these are purposely 

conservative to minimize the likelihood 

of underestimating the potential impacts 

on marine mammals represented by the 

level of effort specified by the applicant. 

The modeling effort incorporated 

representative sound sources and 

projected survey scenarios (both based 

on the best available information 

obtained through BOEM’s consultation 

with members of industry as well as 

historical permit application data), 

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. 

NMFS’s position is that the results of 

the modeling effort represent a 

conservative but reasonable best 

estimate, not a ‘‘worst-case scenario.’’ 

We call attention to our own public 

comments submitted to BOEM 

following review of the draft PEIS: 

‘‘[NMFS] disagrees that the PEIS 

analysis is based on the ‘upper limit’ of 

potential marine mammal exposures to 

sound produced by [survey] activities. 

The PEIS provides no reasonable 

justification as to why the exposure 

estimates [. . .] should be considered as 

‘conservative upper limits’, represent an 

‘overestimate,’ or are ‘unrealistically 

high.’ [NMFS] believes that the 

exposure estimates represent a 

conservative but reasonable best 

estimate [. . . .] [NMFS] disagrees that 

‘each of the inputs into the models is 

purposely developed to be 

conservative.’ Although it may be 

correct that conservativeness 

accumulates throughout the analysis, 

BOEM has not adequately described the 

nature of conservativeness associated 

with model inputs or to what degree 

(either quantitatively or qualitatively) 

such conservativeness ‘accumulates.’ 

While exposure modeling is inherently 

complex, complexity does not 

inherently result in overestimation of 

exposures [. . . .] [NMFS] strongly 

disagrees that the exposure estimates are 

‘overly conservative,’ are ‘upper limits,’ 

or that these estimates are in some way 

differentiated from what might actually 

be expected to occur.’’ Finally, we note 

that BOEM’s final PEIS removed 

erroneous statements and provided 

additional clarification regarding 

descriptions of the modeling results to 

more accurately describe the nature of 

the results as a conservative but 

reasonable best estimate, consistent 

with NMFS’s comments on the draft 

PEIS. 

IAGC and API contracted with JASCO 

Applied Sciences, who performed the 

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 

(‘‘Gulf of Mexico Acoustic Exposure 

Model Variable Analysis;’’ Zeddies et 

al., 2017b). The results of this analysis 

were not made available to NMFS in 

time to fully consider them in preparing 

these proposed regulations. However, 

the report is available online for public 

review (www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

incidental-take-authorizations-oil-andgas) and we expect to consider these 

results as appropriate in developing a 

final rule. The primary finding of 

Zeddies et al. (2017b) is that use of 

appropriate acoustic injury criteria (i.e., 

NMFS, 2016) and quantitative 

consideration of animal aversion and 

mitigation effectiveness decrease 

predictions of injurious exposure. As 

described herein, we have used acoustic 

criteria for both Level A and Level B 

harassment that reflect the best available 

science, and have incorporated 

reasonable correction for animal 

aversion. 

Here, we address some specific issues 

regarding the modeling assumptions 

and briefly address the results provided 

by Zeddies et al. (2017b): 

• Representative large array. 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 creates a smaller ensonified area 

resulting in fewer numbers of animals 

expected to exceed exposure thresholds. 

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 


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arrays currently used in the GOM, 

which are roughly 4,000–8,400 in3

(BOEM, 2017). According to BOEM’s 

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

were 8,000 in3 or greater. More 

importantly, the horizontal modeling of 

the 8,000-in3 array should give sound 

pressure results similar to other 

configurations. The output of an airgun 

array is directly proportional to the 

firing pressure and to the number of 

elements. However, the sound pressure 

(peak amplitude) generated by the array 

is not linear but instead is proportional 

to the cube root of the volume of that 

array. For example, doubling the size of 

the airgun array from 4,000 to 8,000 in3

would be expected to add 

approximately 3 dB to the source 

pressure level. Thus, an 8,000 in3 array 

produces only about twice the loudness 

of a 1,000 in3 array, assuming similar 

parameters such as the number of 

elements and the spatial dimensions of 

the array. This volume to loudness ratio 

holds for the sizes of single elements as 

well, e.g., a 240-in3 element only 

generates twice the peak pressure level 

of a 30-in3 element (not eight times the 

level). It is primarily the frequency 

components of the source signals that 

differ with size, i.e., larger elements 

produce more low-frequency sound. It 

should also be noted that airgun arrays 

are configured geometrically so as to 

direct energy downward into the 

seafloor (known as tuning the array); the 

model fully recognizes this 

directionality and accounts for the 

lower sound energy radiated at 

shallower angles and at specific 

bearings in computing the exposure 

levels. 

The exact configuration of the 4,130 

in3 array evaluated by Zeddies et al. 

(2017b) is not provided. Assuming that 

it is roughly symmetrical to the 8,000 

in3 array modeled by Zeddies et al. 

(2015, 2017a), and using the scaling 

laws where only total volume applies, 

the larger array would be expected to be 

about 2 dB louder. Contrary to this 

estimate, Zeddies et al. (2017b) report a 

7.3 dB difference in source levels, a 

result that cannot be completely 

understood given the information 

provided by Zeddies et al. (2017b). One 

identified issue is that the source level 

for the smaller array (247.9 dB) is for a 

broadside prediction, while the source 

level for the larger array (255.2 dB) is for 

the endfire prediction. The broadside 

source level for the larger array is 

predicted to be 248.1 dB, which is 

reasonably close to that of the smaller 

array (i.e., within 2 dB difference). The 

broadside value may be a better 

representation of source level for the 

main beams which are directed 

downward, while the endfire is 

applicable for a smaller range of 

horizontal bearing from the array. 

Ultimately, differences in the array 

geometry may be significant, and the 

lack of transparency in disclosing this 

information for the smaller array 

problematic to a meaningful comparison 

of results. Overall, the 8,000-in3 array 

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

remains a reasonable representation of 

the arrays that may be used in the 

future, without being overly 

conservative. 

• Sound propagation modeling. 

Acoustic propagation in the GOM is 

complex and routinely changing due to 

variations in the Loop Current (and its 

eddies) and weather (including 

hurricanes). Additionally, propagation 

modeling needs to address a wide range 

of water depths (i.e., shelf, slope, and 

deep waters) as well as strong 

freshwater runoff from the Mississippi 

River and other rivers. In order to 

capture this variability, the acoustic 

propagation modeling examined the 

historic sound velocity profiles (SVP) 

for the entire U.S. GOM throughout the 

entire year. As summarized earlier, 

these SVPs were analyzed for 

similarities and ultimately grouped into 

seven zones or areas with SVPs of 

similar structure or characteristics. 

These seven zones also included 

consideration of bathymetric, 

oceanographic, and biological factors in 

their definition. The SVP analysis also 

identified the need to capture seasonal 

variations by modeling the summer and 

winter seasons, which represent the 

bounds of reasonable environmental 

variability, rather than ‘‘extremes.’’ The 

profiles selected to model each of these 

seven zones are reasonable 

representatives of the family of SVPs for 

that zone and reflect an average of 

feasible conditions. Within each of the 

geographic boundaries for each modeled 

zone, multiple sites were selected to 

serve as the actual acoustic location for 

a modeled source, in order to capture 

the propagation for that zone. The sites 

selected for these locations included 

consideration of the overall 

characteristic of the zone (i.e., it should 

be representative of the zone and not an 

extreme case), the proximity of the 

adjacent zones, the location of 

important bathymetric or oceanographic 

features, and, if possible, any important 

information on biologically important 

factors (e.g., migratory routes, animal 

concentrations). Finally, the 3D 

propagation fields for each of the zones 

were examined by modeling multiple 

azimuthal planes radiating out from the 

source location. For additional detail, 

see the modeling report. 

• Mitigation and aversion. As 

discussed in further detail above, the 

effects of mitigation and aversion on 

exposure estimates were investigated 

via Test Scenarios. We acknowledge 

that both of these factors would lead to 

a reduction in likely injurious exposure 

to some degree. 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 justify 

its use in the modeling. 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 rerunning simulations is evident. While 

aversion and mitigation implementation 

would be expected to reduce somewhat 

the modeled levels of injurious 

exposure, they would not be expected to 

result in any meaningful reduction in 

assumed exposures resulting in 

behavioral disturbance. However, we 

incorporated a reasonable adjustment to 

modeled Level A exposure estimates to 

account for aversion for low- and highfrequency species and, as described 

below, we do not believe that Level A 

harassment is likely to occur for midfrequency cetaceans. 

In conclusion, and as stated by BOEM 

(2017), the results of the modeling are 

expected to incorporate a reasonable 

margin of conservatism, and they 

represent use of the most credible, 

science-based methodologies and 

information available at this time. We 

believe it appropriate to incorporate 

conservatism to a reasonable extent in 

order to produce take estimates that 

would be sufficient to address the likely 

impacts of the activity and to allow for 

issuance of authorizations that would 

cover the expected requests by operators 

over the course of 5 years. 

Take Estimates 

In order 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 

5 years, we evaluated BOEM’s 10-year 

level of effort predictions and the 


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associated modeled exposures provided 

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

acoustic exposure history of many 

simulated animals (animats) allows for 

the estimation of takes due to 

operations. These modeled takes are 

summed and represent the aggregate 

takes expected to result 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. We use the scaling 

factors derived from the results of Test 

Scenario 1 to differentiate between the 

total number of predicted instances of 

take and the likely number of individual 

marine mammals to which the takes 

occur. This information—total number 

of takes (with Level A harassment takes 

based on assumptions relating to midfrequency cetaceans in general as well 

as aversion, as described below) and 

individuals, on an annual basis for five 

hypothetical years representing three 

different potential levels of survey 

effort—provide a partial basis for our 

negligible impact analysis, as well as the 

bounds within which incidental take 

authorizations would be issued in 

association with this proposed 

regulatory framework. 

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. 

With the overall modeling goal to 

estimate exposure levels from future 

survey activity whose individual details 

such as exact location and duration are 

unknown, a primary concern was how 

to account for different survey types, 

locations and spatial extents, and 

durations. In Test Scenario 1, issues 

arising when estimating impacts during 

long-duration surveys were investigated 

and a method was suggested. The 

defined 24-hr integration window, or 

reset period, creates a scaling time-basis 

for impact analysis, and 24 hours is 

short relative to most surveys. Test 

Scenario 1 demonstrated that while 

scaling (multiplying) the average 24-hr 

exposure estimate by the number of 

days of a survey is appropriate for 

estimating the number of instances of 

exposure above threshold, this same 

number is likely an overestimate of the 

number of individual marine mammals 

exposed above threshold during that 

time period. The associated 30-day 

model runs resulted in lower numbers 

of animats exposed to levels exceeding 

the threshold because individual 

animats were only counted once in the 

30-day period even when exposed above 

the threshold across multiple days, 

which allows for a more refined 

consideration of individual animal 

takes, i.e., comparison between the 

results of these two methods (24-hr 

exposure estimate scaled to 30 days 

versus 30-day exposure estimate) allows 

for a more realistic understanding of the 

likely numbers of individuals exposed 

within a 30-day period (as well as a 

better understanding of which species 

are likely taken across more days). 

However, while this correction helps 

account for the difference in estimates 

of individuals taken between the 

primary modeling method (24-hr 

modeled exposures multiplied by total 

number of survey days) and a 30-day 

modeled event, these remain somewhat 

of an overestimate, as evidenced by the 

total predicted takes versus the 

population abundance. Reasons include 

that many of the surveys will likely be 

significantly longer than 30 days, and 

that this correction does not address the 

fact that individuals could be taken by 

multiple surveys within a given year. In 

conclusion, while the exposure 

estimates presented in the modeling 

report identify instances of anticipated 

take, the ‘‘corrected’’ take numbers 

identify a closer approximation, and 

relative comparison, of the numbers of 

individuals affected. However, this 

method of correction still overestimates 

the numbers of individuals affected 

across the year, as it does not consider 

the additional repeated takes of 

individuals during surveys that are 

longer than 30 days or by multiple 

surveys. 

The parameters governing animal 

movement were obtained from shortduration events, such as several dives, 

and for this modeling effort did not 

include long-duration behavior like 

migration or periodically revisiting an 

area as part of a circulation pattern. 

These behaviors could be modeled, but 

there are no data available currently to 

support detailed modeling of this type 

of behavior in the GOM. Seven-day 

simulations were chosen to ensure 

differing environments would be 

sampled. 

With any modeling exercise, 

uncertainty in the input parameters 

results in uncertainty in the output. 

Sources of uncertainty and their effects 

on exposure estimates were investigated 

in Test Scenario 2. The primary source 

of uncertainty in this project was the 

location of the animals at the times of 

the surveys, which drives the choice of 

using an agent-based modeling 

approach and Monte Carlo sampling. 

Density estimates assume a uniform, 

static distribution of animals over a 

survey area, although real world animal 

densities can fluctuate significantly. 

However, assuming many surveys will 

be conducted in many locations, the 

variations in density are expected to 

average toward the mean. Sources of 

uncertainty in the other modeling 

parameters were found to affect the 

variance of the modeling results, as 

opposed to their mean, and the use of 

mean input parameters is therefore 

justified by the same argument as using 

mean animal densities: With many 

surveys occurring over many locations, 

variations are expected to average 

toward the mean. The effects of the 

variability in many of the modeling 

parameters on exposure estimates were 

quantified using a resampling 

technique. It was found that uncertainty 

in parameters such as animal density 

and social group size had a profound 

effect on the distribution of the 

exposure estimates, but not on the mean 

exposure. That is, the distribution shape 

and range of the number of animals 

above threshold changed, but the mean 

number of animals above threshold 

remained the same. 

We previously presented BOEM’s 10- 

year activity projections under 

‘‘Detailed Description of Activities’’ 

(Table 1), and identified representative 

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

years. Level of effort is currently 

significantly reduced in the GOM. A 

decrease in permit applications was 

seen over the 2016 calendar year and 

the trend in reduced exploration activity 

continued in 2017. However, BOEM 

states that they assume that future levels 

will return to previous levels. Therefore, 

the existing scenario levels, which 

contain projections based on BOEM’s 


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analysis by subject matter experts of 

past activity levels and trends as well as 

industry-projected activity levels, 

remain valid (BOEM, 2017). BOEM’s 

projected activity levels must be viewed 

as notional years. While they are based 

on expert professional judgment as 

informed by historical data and the best 

available information, it would be 

inappropriate to view them as literal 

representations of what would 

definitively happen in a given year. 

Therefore, in order to provide the best 

reasonable basis for conducting a 

negligible impact analysis, and in 

recognition of the current economic 

downturn as it relates to oil and gas 

industry exploratory activity, we select 

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

‘‘moderate-activity’’ years, and two 

separate ‘‘low-activity’’ years as the 

basis for our assessment (corresponding 

with the detailed per-survey type effort 

projections given in Table 1 for Years 1, 

4, 5, 8, and 9, respectively). Exposure 

estimates above Level A and Level B 

harassment criteria, developed by 

Zeddies et al. (2015, 2017a) in 

association with the activity projections 

for these year scenarios, are presented 

here (Table 8). Exposure estimates 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). Here, we present scenariobased pooled exposure estimates by 

species. 

TABLE 8—ESTIMATED EXPOSURES BY SURVEY SCENARIO

[Zeddies et al., 2015, 2017a] 1

Species 

Survey effort scenario 2

High Moderate #1 Moderate #2 Low #1 Low #2 

A B A B A B A B A B 

Bryde’s whale ............................................ 15 560 11 413 14 498 11 386 11 402 

Sperm whale ............................................. 45 43,504 29 27,271 38 33,340 30 26,651 32 27,657 

Kogia spp .................................................. 3,640 16,189 2,375 11,428 3,180 13,644 2,358 10,743 2,811 11,165 

Beaked whale ............................................ 52 235,615 38 162,134 47 190,777 37 151,708 38 156,584 

Rough-toothed dolphin .............................. 150 37,666 114 30,192 128 31,103 112 28,663 105 26,315 

Bottlenose dolphin ..................................... 1,940 653,405 2,797 977,108 1,783 596,824 2,679 938,322 1,718 579,403 

Clymene dolphin ....................................... 469 110,742 312 72,913 380 87,615 304 69,609 310 72,741 

Atlantic spotted dolphin ............................. 331 133,427 423 174,705 290 116,698 397 164,824 269 109,857 

Pantropical spotted dolphin ....................... 2,924 606,729 2,048 419,738 2,535 511,037 1,987 399,581 2,032 419,824 

Spinner dolphin ......................................... 262 82,779 195 59,623 246 73,013 189 56,546 195 59,253 

Striped dolphin .......................................... 194 44,038 133 29,936 164 36,267 130 28,522 133 29,890 

Fraser’s dolphin ......................................... 52 13,858 36 9,654 44 11,394 35 9,127 35 9,391 

Risso’s dolphin .......................................... 103 27,062 73 18,124 91 21,914 71 17,309 74 18,092 

Melon-headed whale ................................. 252 68,900 171 47,548 213 56,791 169 44,842 170 46,631 

Pygmy killer whale .................................... 83 18,029 57 12,278 71 14,788 56 11,677 57 12,141 

False killer whale ...................................... 111 25,511 77 17,631 94 20,828 75 16,774 76 17,163 

Killer whale ................................................ 5 1,493 3 1,031 4 1,258 3 984 3 1,036 

Short-finned pilot whale ............................ 68 19,258 43 12,155 51 14,163 42 11,523 42 11,900 

1A and B refer to estimated exposures above Level A and Level B harassment criteria, respectively. For all species other than the Bryde’s whale, 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 (Table 1). Moderate #1 and #2 and Low #1 and #2 correspond 

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

For all mid-frequency cetaceans, i.e., 

all species other than the Bryde’s whale 

and Kogia spp., we do not expect Level 

A harassment to actually occur. For all 

species other than low-frequency 

cetaceans (i.e., Bryde’s whale), the 

estimates of exposure above Level A 

harassment criteria are based on the 

peak pressure metric and, for midfrequency cetaceans, no exposures 

above Level A harassment criteria were 

predicted for airgun surveys on the basis 

of the cSEL metric. However, the 

estimated zone size for the 230 dB peak 

threshold for mid-frequency cetaceans is 

only 18 m and, while in a theoretical 

modeling scenario it is possible for 

animats to engage with a zone of 18 m 

radius 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, 

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. The 230 dB isopleth was within 

the near field of the array where the 

definition of source level breaks down, 

so actual locations within the 18 m of 

the array center where the sound level 

exceeds 230 dB peak SPL would not 

necessarily exist. Further, our proposed 

mitigation (see discussion in ‘‘Proposed 

Mitigation’’ would require a powerdown for small dolphins within a 500- 

m exclusion zone (and a shutdown for 

other mid-frequency cetaceans). During 

the power-down procedure, a single 

airgun would remain firing. The output 

of a single airgun would not be expected 

to exceed the peak pressure injury 

threshold for mid-frequency cetaceans. 

Therefore, we expect the potential for 

Level A harassment of mid-frequency 

cetaceans to be de minimis, even before 

the likely moderating effects of aversion 

are considered. When considering 

potential for aversion, we do not believe 

that Level A harassment is a likely 

outcome for any mid-frequency 

cetacean. 

For other species (i.e., Bryde’s whales 

and Kogia spp.), we believe that while 

some amount of Level A harassment is 

likely, the lack of aversion within the 

animal movement modeling process 

results in overestimates of potential 

injurious exposure. Although there was 

not sufficient information to inform a 

precise quantification of aversion within 

the modeling (Test Scenario 4), we 

believe that sufficient information exists 

to inform a reasonable, conservative 

approximation of aversion and apply an 

offset method accordingly (Southall et 

al., 2017). Ellison et al. (2016) 

demonstrated that animal movement 

models where no aversion probability 

was used overestimated the potential for 

high levels of exposure required for PTS 

by about five times. Accordingly, total 


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estimated exposures above Level A 

harassment criteria (without accounting 

for behavioral aversion) were multiplied 

by 0.2 to reasonably obtain a more 

realistic estimate of potential injurious 

exposure. Adjusted total scenariospecific and mean annual take estimates 

are given in Table 9. 

TABLE 9—SCENARIO-SPECIFIC EXPECTED TAKE NUMBERS AND MEAN ANNUAL TAKE LEVEL 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 ............................ 3 560 2 413 2 498 2 386 2 402 2 452 

Sperm whale ............................. 0 43,504 0 27,271 0 33,340 0 26,651 0 27,657 0 31,685 

Kogia spp .................................. 728 16,189 475 11,428 636 13,644 472 10,743 562 11,165 575 12,634 

Beaked whale ............................ 0 235,615 0 162,134 0 190,777 0 151,708 0 156,584 0 179,364 

Rough-toothed dolphin .............. 0 37,666 0 30,192 0 31,103 0 28,663 0 26,315 0 30,788 

Bottlenose dolphin ..................... 0 653,405 0 977,108 0 596,824 0 938,322 0 579,403 0 749,012 

Clymene dolphin ....................... 0 110,742 0 72,913 0 87,615 0 69,609 0 72,741 0 82,724 

Atlantic spotted dolphin ............. 0 133,427 0 174,705 0 116,698 0 164,824 0 109,857 0 139,902 

Pantropical spotted dolphin ....... 0 606,729 0 419,738 0 511,037 0 399,581 0 419,824 0 471,382 

Spinner dolphin ......................... 0 82,779 0 59,623 0 73,013 0 56,546 0 59,253 0 66,243 

Striped dolphin .......................... 0 44,038 0 29,936 0 36,267 0 28,522 0 29,890 0 33,731 

Fraser’s dolphin ......................... 0 13,858 0 9,654 0 11,394 0 9,127 0 9,391 0 10,685 

Risso’s dolphin .......................... 0 27,062 0 18,124 0 21,914 0 17,309 0 18,092 0 20,500 

Melon-headed whale ................. 0 68,900 0 47,548 0 56,791 0 44,842 0 46,631 0 52,942 

Pygmy killer whale .................... 0 18,029 0 12,278 0 14,788 0 11,677 0 12,141 0 13,783 

False killer whale ...................... 0 25,511 0 17,631 0 20,828 0 16,774 0 17,163 0 19,581 

Killer whale ................................ 0 1,493 0 1,031 0 1,258 0 984 0 1,036 0 1,160 

Short-finned pilot whale ............ 0 19,258 0 12,155 0 14,163 0 11,523 0 11,900 0 13,800 

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 

Level A takes represent modeled exposures adjusted to account for aversion. 2 High survey effort scenario correspond level of effort projections given previously for Year 1 (Table 1). Moderate #1 and #2 and Low #1 and #2 correspond with 

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

Economic Baseline 

This proposed rule has been 

designated as significant under 

Executive Order 12866. Accordingly, a 

draft regulatory impact analysis (RIA) 

has been prepared and is available for 

review online at: 

www.fisheries.noaa.gov/national/ 

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

RIA evaluates the potential costs and 

benefits of these proposed incidental 

take regulations, as well as a more 

stringent alternative, against two 

baselines. The two baselines correspond 

with: (1) Regulatory requirements 

associated with management of 

geophysical survey activity in the GOM 

prior to 2013 pursuant to permits that 

were issued by BOEM under its 

authorities in the Outer Continental 

Shelf Lands Act but that did not address 

statutory requirements of the MMPA 

administered by NOAA; and (2) 

conditions in place since 2013 pursuant 

to a settlement agreement, as amended 

through stipulated agreement, involving 

a stay of litigation (NRDC et al. v. Zinke 

et al., Civil Action No. 2:10 cv-01882 

(E.D. La.)). Under the settlement 

agreement (which expires in November 

2018), industry trade groups 

representing operators agreed to include 

certain mitigation requirements for 

geophysical surveys in the GOM. 

Appendix B of the RIA provides an 

initial regulatory flexibility analysis 

(IRFA), while Appendix C addresses 

other compliance requirements. 

Office of Management and Budget 

(OMB) Circular A–4 directs that the 

baseline for regulatory analysis should 

be the agency’s best assessment of the 

state of the world in the absence of the 

proposed action. A–4 also provides that 

agencies may present multiple baselines 

where this would provide additional 

useful information to the public on the 

projected effects of the regulation. We 

are presenting two baselines for public 

information and comment, consistent 

with the A–4 provision allowing 

agencies to present multiple baselines. 

Thus, in addition to a baseline that 

reflects current assumed industry 

practices as agreed upon in the 2013 

settlement agreement, NMFS is also 

presenting a baseline corresponding 

with geophysical activities in the GOM 

as carried out prior to the 2013 

settlement agreement but without 

authorization from NMFS under the 

MMPA. 

Estimated direct costs of the measures 

in the proposed regulations, relative to 

both baselines, are presented in Table 

10. Details regarding cost estimation are 

available in the RIA. A qualitative 

evaluation of indirect costs related to 

the proposed regulations is also 

provided in the RIA. Note that these 

costs would be diffused across all 

operators receiving LOAs. 

TABLE 10—QUANTIFIED DIRECT COMPLIANCE COSTS BY BASELINE

Mitigation measure 

Annualized costs, millions 1

Pre-stay agreement 

baseline 

(prior to 2013) 

Stay agreement 

baseline 

(2013–present) 

Mitigation requirements for dolphins: Shutdowns for large dolphins in the exclusion zone and power 

downs for small dolphins in the exclusion zone .................................................................................. $3.9–$49.7 $3.9–$49.7 

Expanded observer requirements and mitigation in shallow waters: Shutdowns for all ‘‘whale’’ species in the exclusion zone for airgun surveys in water depths less than 200 m in the Central and 

Western Planning Areas ...................................................................................................................... $0.02–$2.1 $0 

Additional mitigation requirements: Shutdowns for Bryde’s/beaked/Kogia whales outside of exclusion 

zone for deep penetration airgun surveys ........................................................................................... $1.1–$3.0 $1.1–$3.0 


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TABLE 10—QUANTIFIED DIRECT COMPLIANCE COSTS BY BASELINE—Continued 

Mitigation measure 

Annualized costs, millions 1

Pre-stay agreement 

baseline 

(prior to 2013) 

Stay agreement 

baseline 

(2013–present) 

Acoustic monitoring and associated mitigation: Shutdowns for all non-delphinid detections for deep 

penetration airgun surveys ................................................................................................................... $43.9–$127 $21.9–$65.8 

Observer requirements for non-airgun HRG surveys and associated mitigation: Shutdowns for whale 

and large dolphin observations in the exclusion zone ........................................................................ $0.12–$0.39 $0.12–$0.39 

Remove minimum separation distance requirements for deep penetration airgun surveys: The stay 

agreement baseline includes minimum separation distances. Costs reflect the downtime associated with maintaining the minimum separation distance from other surveys. This mitigation measure is not included in the proposed rule, thus creating a benefit (negative cost) of the proposed 

rule relative to the stay agreement baseline ....................................................................................... n/a ($37.9)–($266) 

Proposed Rule Total Direct Compliance Costs ............................................................................... $49–$182 2 ($10.8)–($147) 

1 Costs are presented in terms of 2016 U.S. dollars and are annualized over the five-year timeframe applying a 7% discount rate. Annualized 

costs applying a 3% discount rate are provided in Appendix D of the RIA. 2Estimates within parentheses indicate negative costs, or cost savings. The proposed rule total direct compliance costs relative to the stay 

agreement baseline reflect new costs of $27–$119 less cost savings of $38–$266. 

Proposed Mitigation 

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 

taking for certain subsistence uses 

(‘‘least practicable adverse impact’’). 

Consideration of the availability of 

marine mammal species or stocks for 

taking for subsistence uses pertains only 

to Alaska, and is therefore not relevant 

here. NMFS does not have a regulatory 

definition for ‘‘least practicable adverse 

impact.’’ However, NMFS’s 

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)). It is important to note 

that in some cases, certain mitigation 

may be necessary in order to ensure a 

‘‘negligible impact’’ on 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 be greater than negligible 

in the measure’s absence. 

In evaluating how mitigation may or 

may not be appropriate to ensure the 

least practicable adverse impact on 

species or stocks and their habitat, we 

carefully consider two primary factors: 

(1) The manner in which, and the 

degree to which, implementation of the 

measure(s) is expected to reduce 

impacts to marine mammal species or 

stocks, their habitat, and their 

availability for subsistence uses (when 

relevant). This analysis will consider 

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 measure 

for applicant implementation. 

Practicability of implementation may 

consider such things as cost, impact on 

operations, 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, we recognize that the 

reduction of impacts to those species or 

stocks accrues through the application 

of mitigation measures that limit 

impacts to individual animals. 

Accordingly, our analysis focuses on 

measures designed to avoid or minimize 

impacts on marine mammals from 

activities that are likely to increase the 

probability or severity of populationlevel effects, including auditory injury 

or disruption of important behaviors, 

such as foraging, breeding, or mother/ 

calf interactions. See also 82 FR 19460 

(April 27, 2017) and 83 FR 10954 

(March 13, 2018) (discussion of least 

practicable adverse impact standard in 

proposed incidental take rule for Navy’s 

Surveillance Towed Array Sensor 

System Low Frequency Sonar activities 

and Atlantic Fleet Testing and Training 

activities, respectively). 

NMFS is aware of public statements 

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. For example, 

BOEM stated publicly that ‘‘there has 

been no documented scientific evidence 

of noise from airguns . . . adversely 

affecting marine animal populations’’ 

(BOEM, 2014; www.boem.gov/BOEMScience-Note-August-2014/). On their 

face, these carefully worded statements 

are not incorrect; however, they are 

easily misconstrued and, as used in 

arguments against certain proposed 

mitigation measures, represent a 

common logical fallacy (i.e., that a 

proposition is false because it has not 

yet been proven true). In reality, 

conclusive statements regarding 

population-level consequences of 

acoustic stressors cannot be made due to 

insufficient investigation, as such 

studies are exceedingly difficult to carry 

out and no appropriate study and 

reference populations have yet been 

established. For example, a recent report 

from the National Academy of Sciences 

noted that, while a commonly-cited 

statement from the National Research 

Council (‘‘[n]o scientific studies have 

conclusively demonstrated a link 

between exposure to sound and adverse 

effects on a marine mammal 

population’’) remains true, it is largely 

because such impacts are very difficult 

to demonstrate (NRC, 2005; NAS, 2017). 

Population-level effects are inherently 

difficult to assess because of high 

variability, migrations, and multiple 

factors affecting the populations. 


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The MMPA defines ‘‘take’’ to include 

Level B (behavioral) harassment, which 

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), as well as 

auditory injury (Level A harassment), 

for which there is also evidence from 

loud sound sources (e.g., Southall et al., 

2007). Further, there is growing 

scientific evidence demonstrating the 

connections between sub-lethal effects, 

such as behavioral disturbance, and 

population-level effects on marine 

mammals (e.g., Lusseau and Bedjer, 

2007; New et al., 2014). 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 is 

compromised), which in turn can 

adversely affect populations depending 

on their health, abundance, and growth 

trends. As BOEM stated in a follow-up 

to the above-referenced Science Note, 

‘‘[we] should not assume that lack of 

evidence for adverse population-level 

effects of airgun surveys means that 

those effects may not occur.’’ (BOEM, 

2015; www.boem.gov/BOEM-ScienceNote-March-2015/). 

While direct evidence of impacts to 

species or stocks from a specified 

activity is rarely available, and 

additional study is still needed to 

describe 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. 

We also acknowledge that there is 

always the potential that new 

information, or a new recommendation 

that we had not previously considered, 

becomes available and necessitates 

reevaluation of mitigation measures 

(which may be addressed through 

adaptive management) to see if further 

reduction 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 will be 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 in 

terms of these considerations, can vary 

widely. For example, a time/area 

restriction could be of very high value 

for decreasing population-level impacts 

(e.g., avoiding disturbance of feeding 

females in an area of established 

biological importance) or it could be of 

lower value (e.g., decreased disturbance 

in an area of high productivity but of 

less firmly established biological 

importance). Regarding practicability, a 

measure might involve operational 

restrictions that completely impede the 

operator’s ability to acquire necessary 

data (higher impact), or it could mean 

additional 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, 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. We 

discuss consideration of these factors in 

greater detail below. 

1. Reduction of Adverse Impacts to 

Marine Mammal Species and Stocks and 

Their Habitat 

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 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 goals are often 

applied to reduce the likelihood or 

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

injury or mortality; limiting interruption 

of known feeding, breeding, mother/ 

calf, 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 were 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 

authorizes NMFS to weigh a variety of 

factors when evaluating appropriate 

mitigation measures, it does not compel 

mitigation for every kind of individual 

take, even when practicable for 

implementation by the applicant. 

The status of the species or stock is 

also relevant in evaluating the 

appropriateness of certain 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, 


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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. 

We consider available information 

indicating the likelihood of any measure 

to accomplish its objective. If evidence 

shows that a measure has not typically 

been effective or successful, then either 

that measure should be modified or the 

potential value of the measure to reduce 

effects is lowered. 

2. Practicability 

Factors considered may include those 

such as cost, impact on operations, 

personnel safety, and practicality of 

implementation. In carrying out the 

MMPA’s mandate, we apply 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 the 

applicant. The effects of concern, 

addressed previously in the ‘‘Potential 

Effects of the Specified Activity on 

Marine Mammals and Their Habitat’’ 

section, include auditory injury, severe 

behavioral reactions, disruptions of 

critical behaviors, and potentially 

detrimental chronic and/or cumulative 

effects to acoustic habitat (see 

discussion of this concept in the 

‘‘Anticipated Effects on Marine Mammal 

Habitat’’ section). Here, we focus on 

measures with proven or reasonably 

presumed ability to avoid or reduce the 

intensity of acute exposures that may 

potentially result in these effects with 

an understanding of the drawbacks of 

these requirements, while also 

evaluating time-area restrictions that 

would avoid or reduce both acute and 

chronic impacts. To the extent of the 

information available to us, we consider 

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. We also recognize 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 not be 

appropriate for other activities (e.g., 

time-area restrictions specific to the 

proposed surveys discussed here) but 

that are warranted here given the scope 

of these specified activities and 

associated higher potential for 

population-level effects and/or a large 

magnitude of take of individuals of 

certain species, in the absence of such 

mitigation. 

In order to satisfy the MMPA’s least 

practicable adverse impact standard, we 

propose a suite of basic mitigation 

protocols that are required regardless of 

the status of a stock. Additional or 

enhanced protections are proposed for 

species whose stocks are in poor health 

and/or are subject to some significant 

additional stressor that lessens that 

stock’s ability to weather the effects of 

the specified activity without worsening 

its status. We 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, 2005; Kyhn 

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

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

MMOA, 2015; Nowacek et al., 2013; 

Nowacek and Southall, 2016), and the 

available scientific literature. We 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). The 

suite of mitigation measures proposed 

here 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 we believe 

to be the most appropriate suite of 

measures to satisfy the requirements of 

the MMPA. 

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 400 in3 total 

airgun volume considered deep 

penetration. We consider this a 

reasonable cutoff as most arrays or 

single airguns of this size or smaller will 

typically be purposed for shallow 

penetration surveys—BOEM states in 

the petition that airgun sources used for 

shallow penetration surveys typically 

range from 40–400 in3, while the 

Associations state in their comments on 

the petition that deep penetration array 

volumes used in the GOM range from 

approximately 2,000 to 8,400 in3. We 

also consider a third general class of 

surveys, referred to here as HRG surveys 

and including those surveys using the 

non-airgun 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. We use 

this 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 200 

kHz would be exempt from the 

mitigation requirements described 

herein, with the exception of adherence 

to vessel strike avoidance protocols. We 

do not make any distinction in standard 

required mitigations on the basis of 

BOEM’s planning areas (i.e., Western 

Planning Area (WPA), CPA, EPA). 

As described previously in the 

‘‘Marine Mammal Hearing’’ section, the 

upper limit of hearing for marine 

mammals is approximately 160 kHz; 

therefore, they would not be expected to 

detect signals from systems operating at 

frequencies of 200 kHz and greater. 

Sounds that are above the functional 

hearing range of marine animals may be 

audible if sufficiently loud (e.g., M<hl, 

1968). However, the typical relative 

output levels of these sources mean that 

they would potentially be detectable to 

marine mammals at maximum distances 

of only a few meters, and are highly 

unlikely to be of sufficient intensity to 

result in Level B harassment. Sources 

operating at high frequencies also 

generally have short duration signals 

and highly directional beam patterns, 

meaning that any individual marine 

mammal would be unlikely to even 

receive a signal that would almost 

certainly be inaudible. 

We are aware of two studies (Deng et 

al., 2014; Hastie et al., 2014) 

demonstrating some behavioral reaction 

by marine mammals to acoustic systems 

operating at user-selected frequencies 

above 200 kHz. These studies generally 

indicate only that sub-harmonics could 

be detectable by certain species at 

distances up to several hundred meters. 

However, this detectability is in 

reference to ambient noise, not to 

thresholds for assessing the potential for 

incidental take for these sources. Source 

levels of the secondary peaks 

considered in these studies—those 

within the hearing range of some marine 

mammals—range from 135–166 dB, 

meaning that these sub-harmonics 

would either be below levels likely to 

result in Level B harassment or would 

attenuate to such a level within a few 

meters. Therefore, acoustic sources 

operating at frequencies greater than or 

equal to 200 kHz are not expected to 

have any effect on marine mammals. 

Further, recent sound source 

verification testing of these and other 

similar systems did not observe any subVerDate Sep<11>2014 23:28 Jun 21, 2018 Jkt 244001 PO 00000 Frm 00056 Fmt 4701 Sfmt 4702 E:\FR\FM\22JNP2.SGM 22JNP2

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harmonics 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. We 

do not discuss these surveys further and 

none of the requirements described 

below (other than vessel strike 

avoidance procedures) would apply to 

these surveys. 

Our consideration of the two major 

points described above (i.e., ability of 

the measure to reduce the probability or 

severity of adverse impacts on marine 

mammal species or stocks and their 

habitat and practicability for the 

applicant) points to the need for a basic 

system of mitigation protocols that 

reasonably may be expected to achieve 

the following outcomes: (1) Avoid or 

minimize effects of concern that 

otherwise could accrue in a way that 

could cause or appreciably increase the 

risk of population-level impacts; (2) be 

easily implemented in the field; (3) 

reduce subjective decision-making for 

observers to the extent possible; and, (4) 

appropriately weigh a range of potential 

outcomes from sound exposure in 

determining what should be avoided or 

minimized where possible. 

Subsequently, we describe measures 

specific to the GOM in relation to 

specific contextual concerns. 

Mitigation-Related Monitoring 

Avoidance or minimization of acute 

exposure is first and foremost 

dependent upon detection of animals 

present in the vicinity of the survey 

activity. Requirements necessary to 

adequately detect marine mammals 

incur costs, which we consider in 

scaling mitigation-related monitoring 

requirements relative to the expected 

effects of the specific activity (as 

described above, we bin activity types 

and detail below the proposed 

monitoring requirements associated 

with each). Visual monitoring is a 

critical component of any detection 

system, as evidenced by the inclusion of 

visual monitoring requirements in every 

set of protocols and recommendations 

we reviewed, and has long been 

accepted as such. However, visual 

monitoring is only effective during 

periods of good visibility and when 

animals are available for detection (i.e., 

at the surface). 

Acoustic monitoring is an equally 

critical component of an effective 

detection system, supplanting visual 

monitoring during periods of poor 

visibility and supplementing during 

periods of good visibility. There are 

multiple explanations of how marine 

mammals could be in a shutdown zone 

and yet go 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. Species vary widely in the 

inherent characteristics that inform 

expected bias on their availability for 

detection or the extent to which 

availability bias is convolved with 

detection bias (e.g., Barlow and Forney 

(2007) estimate probabilities of 

detecting an animal directly on a 

transect line (g(0)), ranging from 0.23 for 

small groups of Cuvier’s beaked whales 

to 0.97 for large groups of dolphins). 

Typical dive times range widely, from 

just a few minutes for Bryde’s whales 

(Alves et al., 2010) to more than 45 

minutes for sperm whales (Jochens et 

al., 2008; Watwood et al., 2006), while 

g(0) for cryptic species such as Kogia 

spp. declines more rapidly with 

increasing Beaufort sea state than it does 

for other species (Barlow, 2015). Barlow 

and Gisiner (2006) estimated that when 

weather and daylight considerations 

were taken into account, visual 

monitoring would detect fewer than two 

percent of beaked whales that were 

directly in the path of the ship. PAM 

can be expected to improve on that 

performance, and has been used 

effectively as a mitigation tool by 

operators in the GOM since at least 

2012. BOEM highlighted the importance 

of PAM to detection-based mitigation 

protocols in the petition for rulemaking, 

submitted to NMFS in support of 

industry, and we agree. However, we do 

not agree that use of 24-hr PAM should 

be limited to the Mississippi Canyon 

and De Soto Canyon lease blocks (as 

proposed by BOEM). Species that are 

difficult to detect but vocally active are 

present in significant numbers outside 

those areas, and PAM should be a 

standard component of detection-based 

mitigation anywhere such species are 

expected to be present. 

PAM does have limitations, e.g., 

animals may only be detected when 

vocalizing, species making directional 

vocalizations must vocalize towards the 

array to be detected, and species 

identification and localization may be 

difficult. However, for certain species 

and in appropriate environmental 

conditions it is an indispensable 

complement to visual monitoring during 

good sighting conditions and it is the 

only meaningful monitoring technique 

during periods of poor visibility; 

without PAM, there can be no 

expectation that any animal would be 

detected at night, and even during good 

conditions many deep-diving and/or 

cryptic species would go undetected 

much of the time. In the GOM, beaked 

whales and sperm whales (both vocally 

active) are two taxa of greatest concern; 

beaked whales would rarely be detected 

by visual means alone (an analysis of six 

years of GOM survey data found only 11 

records for beaked whales; Barkaszi et 

al., 2012), and, while commonly 

observed when they are at the surface, 

sperm whales spend significant 

amounts of time in locations where they 

are unavailable for visual detection. 

However, acoustic monitoring imposes 

additional costs on operators and, as 

discussed by Nowacek et al. (2013), we 

consider this in relation to the 

anticipated effects of the survey type. 

Thus, while PAM should be required 

during the deep penetration airgun 

surveys of greatest concern, we do not 

propose to require it for other survey 

types. 

Note that, although we propose 

requirements related only to observation 

of marine mammals, we hereafter use 

the generic term ‘‘protected species 

observer’’ (PSO). 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, we propose to require that 

some PSOs 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 geophysical 

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. We are 

proposing to define trained PSOs as 

having successfully completed an 

approved PSO training course (see the 

‘‘Proposed Monitoring and Reporting’’ 

section), and experienced PSOs as 

having additionally gained a minimum 

of 90 days at-sea experience working as 

a PSO, with no more than 18 months 

having elapsed since the conclusion of 

the relevant at-sea experience. Training 

and experience is specific to either 

visual or acoustic PSO duties (where 


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required). Furthermore, we propose that 

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 expects to provide informal 

approval for specific training courses in 

consultation with BOEM and the Bureau 

of Safety and Environmental 

Enforcement (BSEE) as needed to 

approve PSO staffing plans. NMFS does 

not propose to formally administer any 

training program or to sanction any 

specific provider, but will approve 

courses that meet the curriculum and 

trainer requirements specified herein 

(see the ‘‘Proposed Monitoring and 

Reporting’’ section). We propose this in 

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, we propose that NMFS must 

review and approve PSO resumes 

accompanied by a relevant training 

course information packet that includes 

the name and qualifications (i.e., 

experience, training completed, or 

educational background) of the 

instructor(s), the course outline or 

syllabus, and course reference material 

as well as a document stating the PSO’s 

successful completion of the course. 

Although we are proposing that NMFS 

must affirm PSO approvals, third-party 

observer providers and/or companies 

seeking PSO staffing should expect that 

observers having satisfactorily 

completed approved 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, we propose that such PSOs 

shall be considered to be approved. 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, we propose that 

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. Further information regarding 

PSO requirements may be found in the 

‘‘Proposed Monitoring and Reporting’’ 

section, later in this document. NMFS 

has discussed the PSO requirements 

specified herein with BSEE and with 

third-party observer providers; these 

parties have indicated that the 

requirements should not be expected to 

result in any labor shortage. For 

example, a significantly greater amount 

of survey activity was occurring in the 

GOM during 2013–2015 than at present 

(i.e., as many as 30 source vessels) with 

requirements similar to those described 

here. No labor shortage was 

experienced. We request comment on 

this assumption. We also invite 

comment on the proposed definitions of 

trained and experienced PSOs, 

requirements for PSO approval by 

NMFS, and watch schedule for visual 

PSO and PAM operators. 

Deep Penetration Airgun—During 

deep penetration airgun survey 

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), 

we propose the additional requirement 

that 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) and 30 minutes prior 

to and during nighttime ramp-ups of the 

airgun array (see ‘‘Ramp-ups’’ below). 

PSOs should use NOAA’s solar 

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

grad/solcalc/) to determine sunrise and 

sunset times at their specific location. 

We recognize 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. 

We propose that 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, and serve as 

primary point of contact for the 

operator. Experience is critical to best 

performance of the PSO team (e.g., 

Stone, 2015b), e.g., Mori et al. (2003) 

found that observers classed as having 

limited experience were significantly 

less successful in detecting animals than 

were experienced observers. A survey of 

professional PSOs and other experts 

(GHFS, 2015) highlighted the 

importance of experience as a best 

practice in selecting PSOs, both for 

improved performance in detecting 

animals but also due to the unique 

challenges a PSO faces while charged 

with implementing required mitigations 

onboard a working survey vessel. 

Experience breeds the confidence and 

professionalism necessary to maintain 

positive relations with the vessel 

operator while making sometimes 

difficult decisions regarding 

implementation of mitigation. However, 

while it is desirable for all PSOs to be 

qualified through experience, we are 

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. 

With regard to specific observational 

protocols, we are proposing to largely 

follow 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 

and to the PSO team. 

We are proposing that 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. In shallower waters, only two 


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species are typically present (bottlenose 

and Atlantic spotted dolphin; roughtoothed dolphins are the only other 

species potentially encountered in shelf 

waters but are typically found in deep 

water (Davis et al., 1998; Fulling et al., 

2003; Maze-Foley and Mullin, 2006)). 

While dolphins may be detected using 

PAM, we are not proposing to require 

shutdowns of the source for dolphin 

presence (described below); therefore, 

the mitigation would be of low value 

relative to the estimated cost of 

equipment and additional personnel. 

We are proposing that 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. Because 

the role of PAM operator is more 

technically complex than is the role of 

visual PSO, experience is more 

important (D. Epperson, BSEE, pers. 

comm.) and we are proposing that all 

source vessels shall carry a minimum of 

two experienced PAM operators, which 

is a stricter requirement than for visual 

PSOs. 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 

‘‘Proposed 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 established 

standards are currently in place. We do 

offer some specifications later in this 

document and would require that 

applicants follow any standards that are 

established in the future. 

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, with one visual PSO onduty during nighttime ramp-ups; (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. 

We invite comment on the mitigationrelated monitoring requirements 

proposed for deep penetration airgun 

survey operations. 

Shallow Penetration Airgun—We are 

proposing that shallow penetration 

airgun surveys (those using a total 

volume of airguns less than or equal to 

400 in3) follow the same requirements 

described above for deep penetration 

surveys, with one notable exception. 

The use of PAM is not required, except 

to begin use of the airgun(s) at night in 

waters deeper than 100 m. A nighttime 

start-up must follow the same protocol 

described above for deep-penetration 

surveys: Monitoring of the PAM system 

during a 30-minute pre-clearance period 

and during the ramp-up period (if 

applicable). If a PAM system is used 

during a shallow penetration survey, the 

PAM operator must have prior 

experience and training but may be a 

crew member, and the PAM system does 

not need to be monitored during fullpower firing. 

Non-Airgun HRG Surveys—HRG 

surveys would differ from the 

previously described protocols for 

airgun surveys and, as described 

previously, we differentiate between 

deep-water (greater than 200 m) and 

shallow-water HRG. 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. 

We are proposing to generally follow the 

HRG protocol described in Appendix B 

of BOEM’s PEIS (BOEM, 2017), with 

some differences. 

Deep-water HRG surveys would be 

required to employ a minimum of one 

independent visual PSO during all 

daylight operations, in the same manner 

as was described for airgun surveys. 

Shallow-water HRG surveys would be 

required to employ a minimum of one 

visual PSO, which may be a crew 

member. PSOs employed during 

shallow-water HRG surveys would only 

be required during a pre-clearance 

period. PAM would not be 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), we are 

proposing that 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) 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. 

Practicability—As discussed above, 

both visual and acoustic monitoring 

capabilities are critical components of 

any detection-based mitigation plan, 

and are routine requirements around the 

world. Without the use of acoustic 

monitoring, even during periods of good 

visibility, species projected to bear the 

greatest consequences of effects from the 

specified activity (e.g., beaked whales 

and sperm whales; see ‘‘Negligible 

Impact Analysis and Preliminary 

Determination’’) would go undetected 

much of the time. In addition, the data 

collected through both visual and 

acoustic monitoring comprises a 

majority of the separate monitoring 

requirements proposed here to satisfy 

the requirements of the MMPA (see 

‘‘Proposed Monitoring and Reporting’’). 


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The use of visual observers has 

historically been required by BOEM; 

therefore, the RIA does not assess the 

costs associated with our proposal to 

continue this requirement. The use of 

PAM came into use in the GOM via an 

incentive scheme introduced in MMS’s 

2007 Notice to Lessees concerning 

‘‘Implementation of Seismic Survey 

Mitigation Measures and Protected 

Species Observer Program’’ (NTL No. 

2007–G02), which allowed nighttime 

start-ups conditional upon use of PAM. 

More recently, use of PAM in the GOM 

was expanded pursuant to the terms of 

the 2013 settlement agreement (as 

amended and extended through 

stipulated agreements) referenced 

above, in which industry parties agreed 

to use PAM in water depths greater than 

100 m during times of reduced 

visibility. The RIA considers the likely 

incremental costs of our proposal to 

require the use of PAM at all times in 

waters greater than 100 meters in depth 

and associated shutdowns for detections 

of ‘‘whales’’ (i.e., sperm whales, baleen 

whales, beaked whales, and Kogia spp.), 

reflecting the increased costs associated 

with hardware, software, personnel, and 

additional shutdowns due to acoustic 

detections relative to both pre-2013 

settlement agreement and post-2013 

settlement agreement. The range of costs 

shown in Table 10 reflects the range of 

projected activity levels provided by 

BOEM. Please see the RIA for full 

details. Operationally, use of PAM 

should not present meaningful difficulty 

to operators because PAM has been used 

in some form in the GOM for many 

years. 

In consideration of the expected 

benefits of the expanded PAM 

requirements in reducing the probability 

or severity of impacts to marine 

mammals species or stocks and the 

practicability for applicant 

implementation (e.g., in light of the 

costs and historical use), we 

preliminarily determine these measures 

are warranted. We invite comment on 

the costs for the additional observer and 

monitoring requirements and our 

interpretation of the analysis for 

determining what measures are 

warranted. 

Exclusion Zone and Buffer Zone 

For deep penetration airgun surveys, 

we are proposing that the PSOs shall 

establish and monitor a 500-m exclusion 

zone and additional 500-m buffer zone 

(total 1 km) during the pre-clearance 

period and a 500-m exclusion zone 

during the ramp-up and operational 

periods. PSOs should focus their 

observational effort within this 1-km 

zone, although animals observed at 

greater distances should be recorded 

and mitigation action taken as necessary 

(see below). For shallow penetration 

airgun surveys, we are proposing that 

the PSO shall establish and monitor a 

200-m exclusion zone with additional 

200-m buffer (total 400 m zone) during 

the pre-clearance period and a 200-m 

exclusion zone during the ramp-up (for 

small arrays only, versus single airguns) 

and operational periods. These zones 

would be based upon radial distance 

from any element of the airgun array or 

from a single airgun (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) would 

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 

under ‘‘Ramp-up.’’ Further detail 

regarding the exclusion zone and 

shutdown requirements is given under 

‘‘Exclusion Zone and Shutdown 

Requirements.’’ 

For deep-water non-airgun HRG 

surveys, the PSO would establish and 

monitor a 400-m zone during the preclearance period and a 200-m exclusion 

zone during the operational periods (the 

latter as required under BOEM’s HRG 

protocol). For shallow-water non-airgun 

HRG surveys, the PSO would establish 

and monitor and 200-m pre-clearance 

zone (no shutdowns required during 

operational periods). 

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 are 

proposing that ramp-up is required for 

all airgun surveys (unless using only 

one airgun), but is not required for nonairgun HRG surveys, as the types of 

acoustic sources used in such surveys 

are not typically amenable to ‘‘ramping 

up’’ the acoustic output in the way that 

multi-element airgun surveys are. 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. Stone 

(2015a) reported on behavioral 

observations during airgun surveys from 

1994–2010, stating that detection rates 

of cetaceans during ramp-up were 

significantly lower than when the 

airguns were not firing and on surveys 

with large arrays (defined in that study 

as greater than 500 in3), more cetaceans 

were observed avoiding or traveling 

away from the survey vessel during the 

ramp-up than at any other time. Dunlop 

et al. (2016) studied the effect of rampup during an airgun survey on migrating 

humpback whales, comparing ramp-up 

versus use of a constant source level 

operating at a higher level than the 

initial ramp-up stage but lower than at 

full power. Although behavioral 

response indicating potential avoidance 

was observed, there was no evidence 

that audibly increasing levels during 

ramp-up was more effective in this 

experimental context at causing 

aversion than was a constant source. 

Regardless, the majority of whale groups 

did avoid the source vessel at distances 

greater than the radius of most 

mitigation zones (Dunlop et al., 2016). 

Von Benda-Beckmann et al. (2013), in a 

study of the effectiveness of ramp-up for 

sonar, found that ramp-up procedures 

reduced the risk of auditory injury for 

killer whales, and that extending the 

duration of ramp-up did not have a 

corresponding effect on mitigation 

benefit. 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 

assumed to be better than the 

alternative), ramp-up remains a 

relatively low-cost, common-sense 

component of standard mitigation for 

airgun surveys. Ramp-up is most likely 

to be effective for more sensitive species 

(e.g., beaked whales) (e.g., Tyack et al., 

2011; DeRuiter et al., 2013; Miller et al., 

2015). 

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 would be 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 

should 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 may 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 not be less than 60 minutes prior 

to the planned ramp-up. A designated 


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PSO must be notified again immediately 

prior to initiating ramp-up procedures 

and the operator must receive 

confirmation from the PSO to proceed. 

We are proposing that ramp-up 

procedures follow the recommendations 

of IAGC (2015). Ramp-up would begin 

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 be 

not less than approximately 20 minutes 

but is not prescribed and will vary 

depending on the total number of stages. 

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. We are 

proposing that the operator would be 

required to provide information to the 

PSO documenting that appropriate 

procedures were followed, and request 

comment on how this information 

would best be documented. Ramp-ups 

should be scheduled so as to minimize 

the time spent with source activated 

prior to reaching the designated run-in. 

We are proposing to adopt this approach 

to ramp-up (increments of array 

elements) because we believe it is 

relatively simple to implement for the 

operator as compared with more 

complex schemes involving activation 

by increments of array volume, or 

activation on the basis of element 

location or size. Such approaches may 

also be more likely to result in irregular 

leaps in sound output due to variations 

in size between individual elements 

within an array and their geometric 

interaction as more elements are 

recruited. It may be argued whether 

smooth incremental increase is 

necessary, but stronger aversion than is 

necessary should be avoided. The 

approach proposed here is intended to 

ensure a perceptible increase in sound 

output per increment while employing 

increments that produce similar degrees 

of increase at each step. We request 

comment on the proposed ramp-up 

procedures and requirements. 

During deep penetration airgun 

surveys, we are proposing that 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) or start-up (for 

single airgun or non-airgun surveys). 

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 

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 

requires a 1,000-m pre-clearance zone 

(IBAMA, 2005), 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 

proposed exclusion zone described here 

is appropriate for use as a pre-clearance 

zone. Thus, the pre-clearance zone 

would be 1,000 m for deep penetration 

airgun surveys, 400 m for shallow 

penetration airgun surveys or deepwater HRG surveys, and 200 m for 

shallow-water HRG surveys. We request 

comment on this interpretation of a preclearance zone which would provide 

the appropriate protections for the 

different survey types. 

The pre-clearance 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 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 1,000-m 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. 

We suggest an appropriate elapsed time 

period should be 15 minutes for small 

odontocetes and 30 minutes for all other 

species, and request comment on this 

proposal. PSOs will monitor the 500-m 

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 Airgun—An 

exclusion zone is a defined area within 

which occurrence of a marine mammal 

triggers mitigation action intended to 

reduce potential for certain outcomes, 

e.g., auditory injury, more severe 

disruption of behavioral patterns. For 

deep penetration airgun surveys, we 

propose that 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 appears within or enters this 

zone, the acoustic source would be shut 

down (i.e., power to the acoustic source 

must be immediately turned off). If a 

non-delphinid marine mammal is 

detected acoustically, the acoustic 

source would be shut down, unless the 

PAM operator is confident that the 

animal detected is outside the exclusion 

zone or that the detected species is not 

subject to the shutdown requirement. 

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, we believe 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). Ellison et 

al. (2012) describe a qualitative, 10-step 

index for the severity of behavioral 

response on the basis of the observed 

physical magnitude of the response 

(e.g., minor change in orientation, 

change in respiration rate, fleeing the 

area) and its potential biological 

significance (e.g., cessation of 

vocalizations, abandonment of feeding, 

separation of mother and offspring). In 

prescribing an exclusion zone, we seek 

not only to avoid most potential 

auditory injury but also to reduce the 

likely severity of the behavioral 


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response at a given received level of 

sound. 

Use of monitoring and shutdown or 

power-down 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 definition of an exclusion zone on 

the basis of cumulative sound exposure 

level (cSEL) thresholds, 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. 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 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). We 

recognize 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 is likely 

impossible to mitigate 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 the 

airgun sources considered here, 

auditory injury zones indicated by the 

peak pressure metric are expected to be 

predominant for both mid- and highfrequency cetaceans, while zones 

indicated by cSEL criteria are expected 

to be predominant for low-frequency 

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). 

Consideration of auditory injury 

zones based on cSEL criteria are 

dependent on the animal’s applied 

hearing range and how that overlaps 

with the frequencies produced by the 

sound source of interest in relation to 

marine mammal auditory weighting 

functions (NMFS, 2016). As noted 

above, these are expected to be 

predominant for low-frequency 

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. In 

order to evaluate notional zone sizes 

and to incorporate the technical 

guidance’s weighting functions over a 

seismic array’s full acoustic band, we 

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). Using these data, we made 

adjustments (dB) to the unweighted 

spectrum levels, by frequency, 

according to the weighting functions for 

each relevant marine mammal hearing 

group. We then converted these 

adjusted/weighted spectrum levels to 

pressures (micropascals) in order to 

integrate them over the entire 

broadband spectrum, resulting in 

broadband weighted source levels by 

hearing group that could be directly 

incorporated within NMFS’s User 

Spreadsheet (i.e., override the 

spreadsheet’s more simple weighting 

factor adjustment). Using the User 

Spreadsheet’s ‘‘safe distance’’ 

methodology for mobile sources 

(described by Sivle et al., 2014) with 

appropriate dB adjustments derived 

from the methodology described above, 

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). 

We 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. On the basis of this 

finding as well as the potential zone 

sizes based on the peak pressure criteria 

described above, we do not expect any 

reasonable potential for auditory injury 

resulting from use of the single airgun. 

No potential injurious exposures were 

predicted for single airgun surveys 

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

We expect that the proposed 500-m 

exclusion zone would typically contain 

the entirety of any potential injury zone 

for mid-frequency cetaceans 

(realistically, there is no such zone), 

while the zones within which injury 

could occur may be larger for highfrequency 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). These findings 

indicate that auditory injury is unlikely 

for mid-frequency cetaceans. 

In summary, our 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. 

Our 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 

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 the exception of small 

delphinoids, described in the following 

section; and Bryde’s whales, any large 

whale observed with calf, sperm whales, 

beaked whales, and Kogia spp., 


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described in the subsequent section 

entitled ‘‘Other Shutdown 

Requirements.’’ We request comment on 

our interpretation of the data, proposed 

standard exclusion zone, and shutdown 

requirements for most species (see 

subsequent proposed exceptions) during 

deep penetration airgun surveys. 

Dolphin Exception—As defined here, 

the small delphinoid 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). This exception to the shutdown 

requirement applies solely to specific 

genera of small dolphins—Steno, 

Tursiops, Stenella, and Lagenodelphis 

(see Table 3)—and applies under all 

circumstances, regardless of what the 

perception of the animal(s) behavior or 

intent may be. 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 proposal here is based on 

several factors: The lack of evidence of 

or presumed potential for the types of 

effects to these species of small 

delphinoid that our shutdown proposal 

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. While there may be 

some potential for adverse impacts to 

dolphins—Gray and Van Waerebeek 

(2011) report an observation of a 

pantropical spotted dolphin exhibiting 

severe distress in close proximity to an 

airgun survey, examine other potential 

causes for the display, and ultimately 

suggest a cause-effect relationship—we 

are not aware of other such incidents 

despite a large volume of observational 

effort during airgun surveys in the 

GOM, where dolphin shutdowns have 

not previously been required. Dolphins 

have a relatively high threshold for the 

onset of auditory injury (i.e., permanent 

threshold shift) 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, 

2016). Criteria for temporary threshold 

shift (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 mid-frequency 

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. 

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 bowriding 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 United Kingdom waters. There 

appears to be strong 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 significant 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 ‘‘bowriding’’ activities, and increases in 

surface-active behaviors—are indicative 

of adverse or aversive responses that 

may be construed as ‘‘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. 

Instead of shutdown, if a dolphin of 

the indicated genera (Steno, Tursiops, 

Stenella, and Lagenodelphis) appears 

within or enters the 500-m exclusion 

zone, or is acoustically detected and 

localized within the zone, we present 

two alternatives. 

• Proposal 1: The acoustic source 

would be powered down to the smallest 

single element of the array. The powerdown is intended to minimize potential 

disturbance to dolphins in a practicable 

way, by reducing the acoustic output 

while maintaining what should be an 

aversive stimulus. 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. A source vessel traveling at a 

typical speed of approximately 4.5 kn 

would transit approximately 2 km 

during this period. We expect that the 

resulting gap in data acquisition would 

be sufficiently small as to not require 

reshooting for infill; therefore, increased 

time over which acoustic energy is 

output, as well as significant operational 

impacts, would be avoided while 

maintaining reasonable protections for 

dolphins. 

• Proposal 2: No shutdown or powerdown would be required. We described 

above the information that supports our 

preliminary decision that an exception 

to the general shutdown requirement is 

warranted for small dolphins, as well as 

the information that we believe 

indicates that a power-down 

requirement is warranted in lieu of 

shutdown. However, members of the 

public may interpret this information as 

supporting an exception to the 

shutdown requirement with no powerdown requirement. 

We request comment on both 

proposals and other variations of these 

proposals, including our interpretation 

of the data and any other data that 

support the necessary findings regarding 

small dolphins for no shutdown and no 

power-down or no shutdown but a 

power-down. 


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Although other mid-frequency 

hearing specialists (e.g., large 

delphinoids) are considered no more 

likely to incur auditory injury than are 

small delphinoids, they are much less 

likely to approach vessels. Therefore, 

we have evaluated that retaining a 

shutdown requirement for large 

delphinoids would not have similar 

impacts in terms of either practicability 

for the applicant or corollary increase in 

sound energy output and time on the 

water. We do anticipate some benefit for 

a shutdown requirement for large 

delphinoids in that it simplifies 

somewhat the total array of decisionmaking for PSOs and may preclude any 

potential for physiological effects other 

than to the auditory system as well as 

some more severe behavioral reactions 

for any such animals in close proximity 

to the source vessel. The variations in 

regulatory text for these proposals can 

be found in ‘‘Alternative Regulatory 

Text,’’ later in this preamble, and in the 

regulatory text at the end of the 

document. 

Practicability—The requirement to 

use a generalized 500-m exclusion zone 

and to require shutdown upon 

observation of whales within that zone 

has historically been required by BOEM. 

Here, we assess practicability for 

possible dolphin shutdowns (described 

in full in the RIA). The IAGC provided 

information in response to a 2014 

survey regarding the costs of survey 

activities including, by survey type, 

average survey duration, mobilization 

and pre-mobilization costs, and vessel 

operating costs per day, allowing for 

estimates of total average survey costs. 

IAGC also provided information relating 

to estimated average shutdown time 

following marine mammal observations 

in the exclusion zone and typical 

additional hours required to reshoot the 

areas missed during the shutdown 

period. For the latter, estimates ranged 

from 1–2 additional hours up to 12 

hours (for 3D WAZ surveys). Barkaszi et 

al. (2012) found that small dolphins 

were observed within the exclusion 

zone on 5.7 percent of days, and that 

large dolphins were observed in the 

exclusion zone on 1.2 percent of days 

(unidentified delphinid species were 

observed on an additional 1.2 percent of 

days). The cost of shutdowns for 

dolphins in the exclusion zone is a 

function of the total number of days 

added to a survey, which accrue via (1) 

total time from shutdown until 

resuming data acquisition (1.6–2 hours) 

and (2) time required to reshoot an 

interrupted survey line (1–12 hours, 

depending on the survey type). To 

quantify this cost, the total number of 

added days is multiplied by the daily 

vessel operating cost for each survey 

type that uses airguns, with resulting 

annualized costs for shutdowns due to 

dolphins in the exclusion zone 

depending on actual level of activity 

(see RIA for cost estimates). In 

consideration of the preceding 

discussion of expected benefit from 

shutdowns for dolphins in context with 

these impacts on operations, we do not 

consider full shutdown for small 

dolphins in the exclusion zone to be 

warranted. The alternative presented 

requiring power-down for small 

dolphins in the exclusion zone is 

expected to cost less because of the 

ability to start back up without a rampup and the potentially reduced need to 

reshoot lines. The same would hold true 

for the alternative presented requiring 

no power-down based on there being no 

need to modify the survey at all. 

Operationally, we have attempted to 

minimize the potential for subjective 

and potentially inconsistent decisionmaking by PSOs. NMFS expects that 

large delphinoids (e.g., false killer 

whales, melon-headed whales) in 

general are easily distinguished from 

small delphinoids (e.g., spotted 

dolphins, Clymene dolphins) in general 

by trained, experienced observers on the 

basis of differences in size, color, and 

cranial/dorsal morphology, and requests 

any information relating to this 

assumption. Based on the protective 

value of the described measure and the 

understanding of practicability, we 

preliminarily determine the powerdown measures are warranted. 

Other Shutdown Requirements—We 

are proposing that shutdown of the 

acoustic source should also be required 

in the event of certain other 

observations regardless of the defined 

exclusion zone. It must be noted up 

front that any such observations would 

still be within range of where behavioral 

disturbance of some form and degree 

would be likely to occur, e.g., Zeddies 

et al. (2015) estimated unweighted mean 

95 percent range to 160 dB rms 

threshold (i.e., the 50 percent midpoint 

for behavioral disturbance) levels across 

water depths and seasons at 

approximately 13 km (range 7.7–21.8 

km) for the 8,000 in3 array (Zeddies et 

al., 2015). Thus, for the species or 

situations listed below, we present two 

alternatives: 

• Proposal 1: Shutdown of the 

acoustic source would occur in the 

circumstances listed below, with no 

distance limit (i.e., at any distance from 

the source). While visual PSOs would 

focus observational effort within the 

vicinity of the acoustic source and 

vessel (i.e., approximately 1 km radius), 

this does not preclude them from 

periodic scanning of the remainder of 

the visible area, and we do not have a 

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. 

• Proposal 2: Shutdown of the 

acoustic source would occur in the 

circumstances listed below, only within 

1 km of the source (measured as the 

radial distance from any element of the 

airgun array). 

We request comment on both 

proposals and other variations of these 

proposals, including our 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. The variations in regulatory text 

for these proposals can be found in 

‘‘Alternative Regulatory Text,’’ later in 

this preamble, and in the regulatory text 

at the end of the document. 

Circumstances triggering Proposal 1 

or Proposal 2 include: 

• Upon detection (visual or acoustic) 

of a Bryde’s whale. On the basis of the 

findings of NMFS’s status review 

(described in a NOAA technical 

memorandum; Rosel et al., 2016), NMFS 

has proposed to list the GOM Bryde’s 

whale as an endangered species 

pursuant to the ESA (81 FR 88639; 

December 8, 2016). 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 nearextinction 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. We believe it 

appropriate to eliminate potential 

effects to individual Bryde’s whales to 

the extent practicable. As described 

previously, there may be rare sightings 

of vagrant baleen whales of other 

species in the GOM; if identification of 

the observed whale is inconclusive the 

shutdown must be implemented. 

• Upon observation of a large whale 

(i.e., sperm whale or any baleen whale) 

with calf, with ‘‘calf’’ defined as an 

animal less than two-thirds the body 

size of an adult observed to be in close 

association with an adult. Groups of 

whales are likely to be more susceptible 

to disturbance when calves are present 

(e.g., Bauer et al., 1993), and 

disturbance of cow-calf pairs could 

potentially result in separation of 


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vulnerable calves from adults. 

McCauley et al. (2000a) found that 

groups of humpback whale females with 

calves consistently avoided a single 

operating airgun, while male 

humpbacks were attracted to it, 

concluding that cow-calf pairs are more 

likely to exhibit avoidance responses to 

unfamiliar sounds and that such 

responses should be a focus of 

management. Behavioral disturbance 

has been implicated in mother-calf 

separations for odontocete species as 

well (Noren and Edwards, 2007; Wade 

et al., 2012). Separation, if it occurred, 

could be exacerbated by airgun signals 

masking communication between adults 

and the separated calf (Videsen et al., 

2017). Absent separation, airgun signals 

can disrupt or mask vocalizations 

essential to mother-calf interactions. 

Given the status of large whales in the 

GOM, the consequences of potential loss 

of calves, as well as the functional 

sensitivity of the mysticete whales to 

frequencies associated with the subject 

geophysical survey activity, we believe 

this measure is warranted by the 

MMPA’s least practicable adverse 

impact standard. 

• Upon acoustic detection of a sperm 

whale. Sperm whales are not necessarily 

expected to display physical avoidance 

of sound sources (e.g., Madsen et al., 

2002a; Jochens et al., 2008; Winsor et 

al., 2017). Although Winsor et al. (2017) 

report that distances and orientations 

between tagged whales and active 

airgun arrays appeared to be randomly 

distributed with no evidence of 

horizontal avoidance, it must be noted 

that their study was to some degree 

precipitated by an earlier observation of 

significantly decreased sperm whale 

density in the presence of airgun 

surveys (Mate et al., 1994). However, 

effects on vocal behavior are common 

(e.g., Watkins and Schevill, 1975; 

Watkins et al., 1985). In response to a 

low-frequency tone, sperm whales were 

observed to cease vocalizing 

(vocalizations detected during 24 

percent of a baseline period and not 

detected during transmission; 

vocalizations resumed at most 36 hours 

post-transmission). Although the signal 

characteristics in this study were 

dissimilar to airgun signals, the authors 

also note that an airgun survey was 

being conducted simultaneously with 

signals exceeding background noise by 

10–15 dB (Bowles et al., 1994). 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., 

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. (2018) 

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. 

Sperm whales in the GOM spend the 

majority of their time foraging, engaging 

in dive cycles consisting of deep dives 

of approximately 45 minutes followed 

by shorter surface intervals (resting 

bouts) of approximately 10 minutes 

(Watwood et al., 2006). Sperm whales 

alternate between shallow and deep 

dives over periods of several hours, 

targeting predominantly epipelagic prey 

during shallow dives and benthopelagic 

prey during deep dives (Fais et al., 

2015). During the search phase of their 

dive, whales emit regular clicks with 

high directionality, high source levels, 

and frequencies around 15 kHz, suitable 

for long-range sonar (M<hl et al., 2003). 

During the capture phase, interclick 

interval, amplitude, and signal duration 

decrease dramatically, providing rapid 

updates on the location of prey during 

capture, creating a sound termed as 

either a creak or a buzz (Madsen et al., 

2002b; Miller et al., 2004). On the basis 

of observed echolocation during the 

ascent phase, Fais et al. (2015) 

concluded that sperm whale decisions 

about where to forage during subsequent 

dives may be based on both prior 

foraging success and information 

gathered during ascent, suggesting that 

sperm whales can perform auditory 

stream segregation of multiple targets 

when echolocating, simultaneously 

tracking several targets for sequential 

capture and perceptually organizing a 

multi-target auditory scene. As stated by 

Farmer et al. (2018), this complex 

information-gathering allows sperm 

whales to efficiently locate and access 

prey resources in a dark, patchy, and 

vast environment while leaving whales 

vulnerable to reduction in sensory 

volume and/or interference with 

complex auditory stream signal 

processing (Fais et al., 2015). Such 

effects, which may result from increased 

noise in the environment, can increase 

search effort required to locate resources 

and ultimately reduce foraging 

efficiency (e.g., Zollner and Lima, 1999). 

As deep-diving animals, sperm whales 

may be expected to be more consistently 

exposed to elevated sound levels in the 

downward-refracting acoustic 

environment. 

Miller et al. (2009) showed that GOM 

sperm whales are susceptible to 

disruption of foraging behavior upon 

exposure to relatively moderate sound 

levels at distances greater than 

contemplated for our proposed general 

exclusion zone. Although tagged whales 

did not change behavioral state during 

exposure or show horizontal avoidance, 

they increased energy put into 

swimming and their buzz rates (a proxy 

for attempts to capture prey) were 

approximately 20 percent lower (though 

not a statistically significant result). One 

whale, despite not showing avoidance 

behavior, engaged in an unusually long 

resting bout of 265 minutes (compared 

with typical duration of approximately 

10 min), representing a significant delay 

in foraging effort (Miller et al., 2008, 

2009). This finding is of particular 

importance, as it indicates that sperm 

whales may not be as likely to show 

avoidance of active sound sources 

which would then leave them more 

vulnerable to subsequent foraging 

disruption—an effect of greater 

significance. Analysis conducted by 

Jochens et al. (2008) suggested that, for 

these whales, a 20 percent decrease in 

foraging activity was more likely than 

no change in foraging activity, with one 

whale showing a statistically significant 

decrease of 60 percent. 

The income breeding strategy used by 

sperm whales requires stable or 

predictable environments that enable 

continuous energy acquisition 

throughout the year, at rates of up to 

thousands of kilograms of prey per day 

(Irvine et al., 2017; Clarke et al., 1993; 

Farmer et al., 2018). On days when 

sperm whale foraging is impaired, 

whales would likely compensate for the 

caloric deficit by depleting carbohydrate 

reserves and, secondarily, lipid and 

protein reserves (Lockyer, 1991; 

Castellini and Rea, 1992; Farmer et al., 

2018). Energy reserves are available 

from carbohydrates in the blubber and 

muscle; lipids in the blubber, muscle, 

and viscera; and proteins in the muscle 

and viscera. However, physiological 

evidence suggests that sperm whales are 

poorly adapted to handle periods of 

food shortage, as the energy density of 

sperm whale blubber is much lower 

than that of baleen whales; sperm 

whales do not exhibit appreciable 


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changes in blubber thickness relative to 

body length, even during lactation; and 

the vast majority of blubber lipids are 

stored in a form that helps to conserve 

oxygen during metabolism but is less 

accessible as a source of energy 

(Lockyer, 1981; Koopman, 2007; Farmer 

et al., 2018). If total energy reserves are 

depleted below critical levels, an 

individual’s body condition would be 

expected to decline over time and, for 

pregnant or lactating females, fetus 

abortion or calf abandonment could 

occur (e.g., New et al., 2013). In this 

way, responses to airgun survey noise 

can accrue towards population-level 

impacts (e.g., New et al., 2014; King et 

al., 2015; Fleishman et al., 2016). 

Sperm whales in the northern GOM 

have a relatively small population 

abundance, and with a relatively narrow 

distribution that overlaps almost 

completely with areas of current and 

future geophysical survey activity and 

other oil and gas industry activity. 

Further, most resident female sperm 

whale movements in the GOM range 

within smaller areas—approximately 

200 km around a core home range— 

although larger individual and group 

movements were also observed (Jochens 

et al., 2008). The bioenergetic 

simulations of Farmer et al. (2018) 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. 

Even partial disturbances of foraging, if 

sufficiently frequent, may lead to lower 

body condition, with potential indirect 

effects of delayed sexual maturation or 

reduced reproductive fitness (Farmer et 

al., 2018). It is also unlikely that any 

‘‘hunger response’’ following disruption 

of foraging would result in increases in 

daily growth rate that could be expected 

to offset the effects of sustained foraging 

disruption (Farmer et al., 2018). While 

the modeling exercise conducted by 

Farmer et al. (2018) shows that terminal 

starvation is an unlikely outcome— 

though possible in mature whales 

repeatedly exposed to sound levels that 

result in reduced foraging ability over 

periods of weeks to months—minor 

disruptions can cause substantial 

reductions in available reserves over 

time. 

Multiple lines of evidence indicate 

that sperm whales in the northern GOM 

are somewhat isolated from global 

sperm whale populations (Jochens et al., 

2008). The estimated annual rate of 

increase from reproduction for GOM 

sperm whales is less than one percent 

per year, while Chiquet et al. (2013) 

found that reducing the survivorship 

rate of mature female sperm whales by 

as little as 2.2 percent or the 

survivorship rate of mothers by as little 

as 4.8 percent would drop the 

asymptotic growth rate of the northern 

GOM sperm whale population below 

one, i.e., a declining population. NOAA 

estimates that the DWH oil spill may 

have caused reproductive failure in 7 

percent of female sperm whales (DWH 

MMIQT, 2015). Separately, NOAA 

estimates that 16 percent of the sperm 

whale population was exposed to high 

concentrations of oil both at the surface 

and sub-surface, high concentrations of 

volatile gases that could be inhaled at 

the surface, and response activities 

including increased vessel operations, 

dispersant applications, and oil burns 

(DWH MMIQT, 2015). Independent of 

other factors, the DWH oil spill may 

have a long-term impact of reducing the 

GOM sperm whale population by up to 

7 percent, with an estimated time to 

recovery of 21 years (DWH MMIQT, 

2015). Therefore, even in the absence of 

other future stressors, the environmental 

baseline for the GOM sperm whale 

population requires that meaningful 

measures be taken to minimize 

disruption of foraging behavior. Such 

measures are all the more important, as 

we have considered but eliminated a 

time-area restriction for sperm whales 

(described below). 

We also considered requirement of 

shutdown upon visual detection of 

sperm whales. Here, we assume that 

acoustic detections of sperm whales 

would most likely be representative of 

the foraging behavior we intend to 

minimize disruption of, while visual 

observations of sperm whales would 

represent resting between bouts of such 

behavior. Occurrence of resting sperm 

whales at distances beyond the 

exclusion zone may not indicate a need 

to implement shutdown. We consider 

these assumptions in conjunction with 

an assessment of the costs and 

operational feasibility of these measures 

in ‘‘Practicability,’’ below. 

• Upon observation (visual or 

acoustic) 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 injury 

(e.g., Wursig et al., 1998; Cox et al., 

2006). Unlike the sperm whale, we 

recognize 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 highfrequency 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, 2016). 

Practicability—In the bulleted 

subsections above, we evaluated the 

importance of offering expanded 

protections via shutdown for these 

species/circumstances and, as 

discussed, we find that avoidance to 

extent practicable of acute impacts for 

Bryde’s whales, sperm whales, beaked 

whales, and Kogia spp., as well as for 

large whales with calves, is important to 

a reduction of effects for these species. 

In the RIA, we evaluate the annualized 

incremental costs of these expanded 

measures (note that the costs of 

additional shutdowns based on acoustic 

detections is included in our previous 

discussion of costs associated with 

expanded use of PAM). Additional 

requirements for shutdowns based on 

visual detections outside the exclusion 

zone result in a small cost relative to the 

benefits afforded by the measures. 

Additionally, due to the rarity of visual 

observations of these species groups, we 

do not believe that the expanded 

shutdowns would cause any undue 

operational burden. 

In the GOM, we expect that the 

optimum detection range of sperm 

whales in low-noise conditions is likely 

to be approximately 2–3 km. This 

relatively short detection range is likely 

due to the propagation conditions 

resulting when a relatively warmer 

mixed surface layer provides a strong 

negative sound velocity profile, causing 

strong downward refraction of acoustic 

rays. While the maximum detection 


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range of vocalizing marine mammals 

continues to be a challenging area in use 

of PAM for mitigation monitoring, basic 

signal detection theory dictates that 

received levels have to exceed certain 

noise levels in order for the signal to be 

detected. We consider the following 

sonar equations: 

EL = SL¥TL (1) 

SNR = EL¥NR (2) 

SE = SNR¥DT (3) 

where EL is the received level, SL the 

source level, TL the transmission loss, 

SNR the signal-to-noise ratio, NR the 

received noise spectral density, SE the 

signal excess, and DT the detection 

threshold. 

As the signal (in this case, a sperm 

whale click) propagates from its source 

(the whale) through the environment to 

a receiver (a hydrophone), its intensity 

(acoustic power within a unit area) is 

reduced due to acoustic energy 

divergence and attenuation (absorption 

and scattering). By the time the whale 

click reaches the hydrophone, its 

received intensity level is greatly 

reduced from its original source level. In 

addition, for the received level to be 

detected by the hydrophone, the signalto-noise ratio (received level minus the 

background noise spectral density) must 

be above a certain detection threshold, 

i.e., there must be a positive signal 

excess. 

Based on various studies (Madsen and 

Mohl, 2000; Mohl et al., 2000; Thode et 

al., 2002; Zimmer et al., 2005), the 

source levels of sperm whale clicks fall 

between 202 and 223 dB re 1 mPa, with 

a pronounced directionality and 

significant energy above 10 kHz. 

However, these values are selected from 

the most intense clicks from each 

sequence so they are likely to have been 

recorded close to the acoustic axis 

(Mohl et al., 2000). Considering all 

recordings, Mohl et al. (2000) suggest 

that sperm whale click maximum source 

levels are in the range of 175 to 200 dB 

re 1 mPa. By using a middle range of the 

maximum source level of 188 dB re 1 

mPa with a 50 percent detection range at 

4 km, and assume an ambient noise 

spectral density at 75 dB with a 

detection threshold of 6 dB, the 

transmission loss at this range would be 

107 dB. By simply applying a geometric 

spreading model, it can be shown that 

the transmission loss (TL) follows TL = 

29.7log10(R), where R is the distance 

from the source in meters. Please note 

that this approximation is based on a 

very low ambient noise spectrum 

density (Wenz, 1962). 

In the presence of an airgun survey, 

the background noise level is expected 

to be significantly increased as a result 

of the reverberant field generated from 

intense pulses (Guerra et al., 2011; Guan 

et al., 2015). It has been shown that the 

level of elevated inter-pulse noise levels 

can be as high as 20 dB within 1 km of 

an active firing airgun array of 640 in3

(Guan et al., 2015) to 30–45 dB for a 

3,147 cu3 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 is expected to be very 

high. Using a relatively low 25 dB 

increase from the inter-pulse noise level 

to compute detection with the otherwise 

the same parameters from the above 

example in the quiet environment, one 

would find that a 50 percent detection 

probability is quickly reduced to 576 m. 

If, given the unfavorable signal 

propagation conduction in the GOM in 

comparison to the more favorable 

conditions in the North Pacific (Barlow 

and Taylor, 2005), a 50 percent 

detection probability at 3 km in quiet 

conditions would be reduced to 462 m 

during the active airgun survey. A 50 

percent detection probability at 2 km in 

quiet conditions would further reduce 

the detection range to 339 m. 

However, we recognize that the 

addition of sperm whale shutdowns 

based on visual detections beyond the 

exclusion zone would result in a larger 

estimated additional cost per year. 

Based on these costs, and our previous 

discussion of assumptions related to 

acoustic versus visual detections of 

sperm whales, we preliminarily do not 

believe the addition of shutdowns for 

sperm whales based on visual 

detections at any distance to be 

warranted, and request any information 

from the public that would be relevant 

to this determination. For this proposed 

rule, we preliminarily determine that 

the addition of the proposed shutdown 

measures described above are warranted 

when their likely ability to reduce the 

probability or severity of impacts on 

species or stocks and their habitat is 

considered along with their 

practicability. 

Other Surveys—Shutdowns for 

shallow penetration airgun surveys or 

deep-water non-airgun HRG surveys 

would be similar to those described for 

deep penetration airgun surveys, except 

that the exclusion zone would be 

defined as a 200-m radial distance 

around the perimeter of the acoustic 

source, in keeping with BOEM’s 

exclusion zone requirements for their 

‘‘HRG survey protocol.’’ The special 

circumstance shutdowns described 

above for deep penetration airgun 

surveys would not be required. The 

dolphin exception described for deep 

penetration airgun surveys would apply; 

if the survey is using a small airgun 

array (i.e., less than or equal to 400 in 3, 

versus a single airgun), then powerdown should be implemented as 

described for deep penetration airgun 

surveys. As described previously, no 

shutdowns would be required for 

shallow-water non-airgun HRG surveys. 

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 

observation of the animal(s). Where 

there is no relevant zone (e.g., 

shutdowns at any distance), a 30-minute 

clearance period must be observed 

following the last 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 visual and 

acoustic observation and no visual 

detections of any marine mammal have 

occurred within the exclusion zone and 

no acoustic detections have occurred. 

We define ‘‘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), preclearance watch 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 


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constant observation maintained, preclearance watch is not required. 

Power-Down 

Power-down, as defined here, refers to 

reducing the array to a single element as 

a substitute for full shutdown. We 

address use of a single airgun as a 

‘‘mitigation source’’ below. In a powerdown scenario, it is assumed that 

reducing the size of the array to a single 

element reduces the ensonified area 

such that an observed animal is outside 

of any area within which injury or more 

severe behavioral reactions could occur. 

Zeddies et al. (2015) modeled the 95 

percent ranges for a single airgun as 360 

m to the 160-dB rms SPL threshold and 

42 m to the 180-dB rms SPL threshold. 

As proposed here, power-down to the 

single smallest array element is required 

when a small dolphin enters the defined 

EZ, but is not allowed for any other 

reason (e.g., to avoid pre-clearance and/ 

or ramp-up). Our rationale is that this is 

a necessary corollary to the dolphin 

exception described previously. As 

described previously, use of the acoustic 

source at full power may resume 

following visual observation of the 

animal(s) exiting the exclusion zone or 

15 minutes following the last 

observation of the animal. If ramp-up 

were required, it is likely that infill of 

the missed line would be necessary, 

thereby reducing the benefit of the 

dolphin exception. 

Mitigation Source 

Mitigation sources may be separate 

individual airguns or may be an airgun 

of the smallest volume in the array, and 

have historically been used when the 

full array is not being used (e.g., during 

line turns) in order to allow ramp-up 

during poor visibility. The difference 

between use of a single airgun in a 

power-down scenario and as a 

‘‘mitigation source’’ is that the powerdown scenario is conditional upon the 

presence of animals in the exclusion 

zone, whereas the mitigation source was 

historically used during times when the 

array would otherwise not be in use at 

all. The general premise is that this 

lower-intensity source, if operated 

continuously, would be sufficiently 

aversive to marine mammals to ensure 

that they are not within an exclusion 

zone, and therefore, ramp-up may occur 

at times when pre-clearance visual 

watch is minimally effective. There is 

no information to suggest that this is an 

effective protective strategy, yet we are 

certain that this technique involves 

input of extraneous sound energy into 

the marine environment, even when use 

of the mitigation source is limited to 

some maximum time period. For these 

reasons, we do not believe use of the 

mitigation source is appropriate and 

propose not to allow its use. However, 

as noted above, ramp-up may occur 

under periods of poor visibility 

assuming that no acoustic or visual 

detections are made during a 30-minute 

pre-clearance period. This is a change 

from how mitigation sources have been 

considered in the past in that the visual 

pre-clearance period was typically 

assumed to be highly effective during 

good visibility conditions and viewed as 

critical to avoiding auditory injury and, 

therefore, maintaining some likelihood 

of aversion through use of mitigation 

sources during poor visibility 

conditions was deemed valuable. 

In light of the available information, 

we think it more appropriate to 

acknowledge the limitations of visual 

observations—even under good 

conditions, not all animals will be 

observed and cryptic species may not be 

observed at all—and recognize that 

while visual observation is a common 

sense measure it should not be 

determinative of when survey effort may 

occur. Given the lack of proven efficacy 

of visual observation in preventing 

auditory injury, we do not believe that 

its absence should imply such 

potentially detrimental impacts on 

marine mammals. Therefore, use of a 

mitigation source is not a sensible 

substitute component of seismic 

mitigation protocols. We also believe 

that consideration of mitigation sources 

in the past has reflected an outdated 

balance, in which the possible 

prevention of relatively few instances of 

auditory injury is outweighed by many 

more instances of unnecessary 

behavioral disturbance of animals and 

degradation of acoustic habitat. 

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. 

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. 

We encourage the applicant 

companies and operators to pursue the 

following objectives in designing, 

tuning, and operating acoustic sources: 

(1) Use the minimum amount of energy 

necessary to achieve operational 

objectives (i.e., lowest practicable 

source level); (2) minimize horizontal 

propagation of sound energy; and (3) 

minimize the amount of energy at 

frequencies above those necessary for 

the purpose of the survey. However, we 

are not aware of available specific 

measures by which to achieve such 

certifications. In fact, an expert panel 

convened by BOEM to determine 

whether it would be feasible to develop 

standards to determine a lowest 

practicable source level has determined 

that it would not be reasonable or 

practicable to develop such metrics (see 

Appendix L in BOEM, 2017). 

Minimizing production of sound at 

frequencies higher than are necessary 

would likely require design, testing, and 

use of wholly different airguns than are 

proposed for use by the applicants. At 

minimum, 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. BOEM currently requires 

applicants for permits to conduct 

geophysical surveys 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) 

and that the operations are using the 

minimal source array size/power 

necessary to meet the survey goals and 

that the array is tuned to maximize 

radiation of the emitted energy toward 

the seafloor. 

Restriction Areas 

Below we provide discussion of 

various restriction areas that were 

considered during development of the 

proposed regulations. Because the 

purpose of these areas is to reduce the 

likelihood of exposing animals within 

the designated areas to noise from 

airgun surveys that is likely to result in 

harassment (i.e., 50 percent midpoint of 

the Level B harassment risk probability 

function), we are proposing to require 

that source vessels maintain minimum 

standoff distances (i.e., buffers) from the 

areas. Sound propagation modeling 

results for a notional large airgun array 

were provided by Matthews et al. 

(2016), specific to each of the potential 

time-area restrictions evaluated therein, 

in order to exclude SPLs exceeding 160 


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dB rms from those areas. Those 

distances are proposed for use here and 

are described in each section below. 

Coastal Restriction—We are 

proposing that no airgun surveys may 

occur shoreward of a line indicated by 

the 20-m isobath, buffered by 13 km 

(Matthews et al., 2016), during the 

months of February through May (Area 

1; Figure 5). 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). 

The restriction is intended 

specifically to avoid additional stressors 

to bottlenose dolphin populations 

during the time period believed to be of 

greatest importance as a reproductive 

period. BOEM proposed a similar 

coastal restriction on airgun survey 

effort in the petition submitted in 

support of industry, and NMFS agrees 

that this is appropriate. Coastal dolphin 

stocks, particularly the northern coastal 

stock, were heavily impacted by the 

DWH oil spill. As described previously, 

NOAA estimates that potentially 23 

percent of western coastal dolphins and 

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 5 

percent and 50 percent for the western 

and northern stocks, respectively (DWH 

MMIQT, 2015). For the northern coastal 

stock, it is estimated that these 

population-level impacts could require 

39 years to recovery, in the absence of 

other additional stressors. 

NMFS’s subject matter experts 

identified a reasonable range that in 

their professional judgment 

encompasses an important reproductive 

period for bottlenose dolphins in these 

coastal waters. 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. While pregnant mothers may be 

susceptible to the impacts of noise, we 

believe that neonates and/or calves are 

likely most susceptible, because 

behavioral disruption could have more 

severe energetic effects for lactating 

mothers and/or lead to disruption of 

mother-calf bonding and ultimate effects 

on rates of neonate and/or calf 

survivorship. Therefore, we believe that 

February through May represents a 

reasonable best estimate of the time 

period of most sensitivity for bottlenose 

dolphins in coastal waters. 

While none of the dolphin strandings 

or deaths have been attributed to airgun 

survey activities, stocks in the area are 

stressed, and studies have shown that 

marine mammals react to underwater 

noise. 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 can 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. Populationlevel impacts related to energetic effects 

or other impacts of noise are difficult to 

determine, but the addition of other 

stressors can add considerable 

complexity due to the potential for 

interaction between the stressors or 

their effects (NAS, 2017). When a 

population is at risk, as is the case for 

these bottlenose dolphin populations, 

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 

proposed rule may be mitigated. The 

post-DWH oil spill baseline condition of 

these populations requires caution, and 

this restriction may reasonably be 

anticipated to provide additional 

protection to these populations during 

their peak reproductive activity. Note 

that, in reference to the findings of 

Matthews et al., (2016), this proposed 

time-area restriction would also reduce 

impacts to stocks of marine mammals 

occurring within the restriction area 

through reducing effects to listening 

area. We request comment on our 

proposed seasonal closure in Area 1. 

Practicability—Given survey 

operators’ ability to plan around these 

seasonal restrictions, we believe it is 

unlikely that the restrictions will affect 

oil and gas productivity in the GOM. 

Therefore, when this practicability 

factor is considered in light of the 

expected ability of these measures to 

reduce the probability or severity of 

impacts on species or stocks and their 

habitat, we preliminarily determine 

these restrictions are warranted. We 

request comment on our interpretation 

of the impact of the proposed seasonal 

closure for Area 1. 


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Bryde’s Whale—We examined the 

appropriateness of restricting survey 

effort such that particular areas of 

expected importance for Bryde’s whales 

are not ensonified by levels of sound 

above 160 dB rms SPL (the 50 percent 

midpoint for behavioral harassment) 

(Area 3; Figure 5). We analyzed a yearround closure of the area described 

herein; we request comment on this and 

several other alternatives. The variations 

in regulatory text for these proposals 

can be found in ‘‘Alternative Regulatory 

Text,’’ later in this preamble, and in the 

regulatory text at the end of the 

document. Matthews et al. (2016) 

specified a buffer distance of 5.4 km for 

the De Soto Canyon area, which we 

round to 6 km. As described previously, 

NOAA’s status review team determined 

the status of the GOM Bryde’s whale is 

considered to be precarious (described 

in the status review technical 

memorandum (Rosel et al. (2016)). On 

the basis of these findings, NMFS has 

proposed to list the GOM Bryde’s whale 

as an endangered species pursuant to 

the ESA (81 FR 88639; December 8, 

2016). These whales form a small and 

resident population in the northeastern 

GOM, with a highly restricted 

geographic range and a very small 

population abundance—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. 

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). 

Based on this review and further 

consultation with the Society for Marine 

Mammalogy’s Committee on Taxonomy, 

NMFS has proposed to list the GOM 

Bryde’s whale as an endangered species 

pursuant to the ESA (81 FR 88639; 

December 8, 2016). 

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). It is in 

consideration of this environmental 

baseline and risk profile that we 

analyzed a year-round restriction. 

LaBrecque et al. (2015) described a 

biologically important area for GOM 

Bryde’s whales as between the 100- and 


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300-m isobaths in the eastern GOM, 

from the head of De Soto Canyon to an 

area northwest of Tampa Bay. The 

recorded Bryde’s whale shipboard and 

aerial survey sightings between 1989 

and 2015 have mainly fallen within this 

area (see the NOAA’s status review 

technical memorandum (Rosel et al. 

(2016)). We are proposing to expand this 

area for protection of Bryde’s whales 

following the recommendations of 

NOAA’s status review (described in the 

status review technical memorandum 

(Rosel et al. (2016)), which stated that 

due to the depth of some sightings, the 

BIA for Bryde’s whales in the GOM 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. The average depth of 

Bryde’s whale sightings is 226 m (SE = 

7.9; range 199–302 m; Maze-Foley & 

Mullin 2006). Rice et al. (2014) detected 

sounds associated with Bryde’s whales 

in waters south of Panama City, FL, and 

there are sightings of Bryde’s whales 

along the shelf break to Tampa Bay 

(about 28.0° N). Bryde’s whales were 

also detected acoustically in this area by 

Hildebrand et al. (2012). Additionally, 

because of past survey design, survey 

effort in waters less than 200 m water 

depth has not been as thorough as that 

for waters greater than 200 m; therefore, 

Bryde’s whales may use water depths 

between 100–200m more regularly than 

we currently know. The Bryde’s whale 

restriction is designated as the area 

between the 100- and 400-m isobaths, 

from 87.5° W to 27.5° N (Area 3; Figure 

5). This area largely covers the home 

range (i.e., 95 percent of predicted 

abundance) predicted by Roberts et al. 

(2016). The designated area would then 

be buffered by 6 km. The restriction area 

would also provide benefit to any other 

marine mammals present there— 

primarily Atlantic spotted dolphins and 

bottlenose dolphins, but possibly also 

including other species that may occur 

there in slope waters. Reporting 

preliminary results from a passive 

acoustic monitoring study, Hildebrand 

et al. (2012) found a significantly higher 

detection rate and a more steady 

presence for delphinids at this site than 

at four other sites (three deep-water and 

one shallow). Note that, in reference to 

the findings of Matthews et al. (2016), 

a time-area restriction would also 

reduce impacts to stocks of marine 

mammals occurring within the 

restriction area through reducing effects 

to communication space and listening 

area. 

Given the likely condition of this 

population, and in the absence of a full 

habitat characterization and more 

knowledge about why Bryde’s whales 

occur where they do, we analyzed a 

year-round restriction that covered the 

full area of Bryde’s whale sightings. We 

request comment on our interpretation 

of the data and our evaluated alternative 

of year-round restrictions on airgun 

surveys in Area 3 (Figure 5). In addition, 

we present three less-restrictive 

alternatives, including seasonal 

restrictions and no restrictions for Area 

3 with differing requirements for 

monitoring. We request comment on all 

proposals and other variations of these 

proposals, including our interpretation 

of the data and any other data that 

support the necessary findings regarding 

time-area restrictions for Bryde’s 

whales. 

• Proposal 1: A year-round restriction 

on airgun surveys in Area 3, as 

described above. 

• Proposal 2: A three-month seasonal 

restriction on airgun surveys in Area 3. 

In addition to public comment on the 

proposal and information that may 

support the necessary findings in 

consideration of this proposal, we 

request information regarding the 

proposed duration and/or timing of 

such a seasonal closure, if sufficient. We 

note that this proposal is reflected in 

our proposed regulatory text, at the end 

of this document. 

• Proposal 3: A three-month seasonal 

restriction, such as what is described 

just previously, but with the addition of 

a requirement for BOEM and/or 

members or representatives of the oil 

and gas industry to ensure real-time 

detection of Bryde’s whales across the 

area of potential impact including realtime communication of detections to 

survey operators. This real-time 

detection would be used to initiate 

shutdowns to ensure that survey 

operations do not take place when a 

Bryde’s whale is within 6 km of the 

acoustic source. We do not consider 

towed passive acoustic monitoring to be 

sufficient to ensure detection of the 

Bryde’s whale and, for the three-month 

restriction, we propose use of a moored 

listening array. In addition to public 

comment on the proposal and 

information that may support the 

necessary findings in consideration of 

this proposal, as well as on the 

appropriate timing and/or duration of a 

seasonal restriction, we request 

information regarding appropriate 

alternative technologies for real-time 

detection of Bryde’s whales. 

• Proposal 4: No restriction, but with 

the addition of a requirement for BOEM 

and/or members or representatives of 

the oil and gas industry to ensure realtime detection of Bryde’s whales across 

the area of potential impact including 

real-time communication of detections 

to survey operators. As with the 

previous seasonal closure with 

monitoring proposal, we do not 

consider towed passive acoustic 

monitoring to be sufficient to ensure 

detection of the Bryde’s whale and seek 

comment on appropriate technologies 

for real-time detection. We request 

public comment on the proposal and 

information that may support the 

necessary findings in consideration of 

this proposal, as well as regarding 

appropriate alternative technologies for 

real-time detection of Bryde’s whales. 

The variations in regulatory text for 

these proposals can be found in 

‘‘Alternative Regulatory Text,’’ later in 

this preamble, and in the regulatory text 

at the end of the document. 

Practicability—There is a moratorium 

on leasing pursuant to GOMESA 

(through June 2022, or almost the 

entirety of the period of validity for 

these proposed regulations). Further, 

BOEM has projected very low activity 

levels in this area over the next 10 years 

(Table 1). There are two active leases in 

this proposed restriction area (though 

no platforms), and an exception to the 

year-round restriction requirements 

would be made in accordance with 

existing rights associated with those 

active leases. The RIA indicates that 

there is potential for effects on oil and 

gas productivity given delays in the 

ability to conduct exploratory surveys in 

advance of the end of the existing 

GOMESA moratorium (if not continued) 

and a year-round restriction may be 

warranted. As described just previously, 

we invite the public to evaluate and 

comment on the presented alternatives. 

Dry Tortugas—This proposed 

restriction area is expected to benefit 

resident sperm and beaked whales. 

Beaked whales are acoustically 

sensitive, with a correspondingly high 

magnitude of predicted exposures, 

while noise from airgun surveys may 

have an outsize impact on sperm whale 

populations due to disruption of 

foraging behavior (as detailed 

previously). While the predicted 

impacts on these species are based on 

projected levels of activity elsewhere in 

the GOM, we acknowledge the potential 

importance of this area to these species 

and propose the restriction to ensure 

that this habitat is not impacted. 

Sightings of both beaked whales and 

sperm whales are very dense in this 

area, and it is possible—based on 

unpublished observations of calves 

here—that sperm whales use this area as 

a calving area (K. Mullin, pers. comm.). 


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Hildebrand et al. (2012, 2015) 

conducted passive acoustic monitoring 

over more than 3 years (2010–2013) at 

three deep-water sites on the GOM 

slope, including within this area. In 

contrast with reported visual 

observations of sperm whales in the 

area, preliminary results reported by 

Hildebrand et al. (2012) showed 

relatively low rates of acoustic detection 

for sperm whales, and corresponding 

density estimates were lower at the Dry 

Tortugas site than at the other sites (i.e., 

Mississippi Canyon and Green Canyon). 

However, four species of beaked whale, 

including an unidentified species, were 

detected. As reported by Hildebrand et 

al. (2015), Cuvier’s beaked whale was 

the dominant species presence (61 

percent of vocal encounters), but 

Gervais’ beaked whales also appear to 

be present in significant numbers (39 

percent). No Blainville’s beaked whales 

were detected. Average densities for 

Cuvier’s and Gervais’ beaked whales 

were derived from vocal click counting. 

Combined density for the two species 

was very high at the Dry Tortugas site 

(approximately 29 whales/1,000 km2). 

At two other sites where beaked whales 

are expected to be present in significant 

numbers and were detected (Mississippi 

Canyon and Green Canyon), the 

combined density value was 

approximately 4 whales/1,000 km2, at 

both locations. Both species had a 

strong and consistent presence 

throughout the monitoring period 

(Hildebrand et al., 2015). 

The area aligns well with a portion of 

the predicted 25 percent core 

abundance area for beaked whales in the 

GOM, and overlaps with portions of the 

sperm whale 25 percent core abundance 

area (Roberts et al., 2016; core 

abundance areas are explained in 

greater detail below in ‘‘Central 

Planning Area’’). The restriction area 

would also provide benefit to any other 

marine mammals present there— 

including other species expected to 

occur in deep slope waters. Hildebrand 

et al. (2012) estimated the density of 

Kogia spp. in this area at 5.9 animals/ 

1,000 km2. The proposed year-round 

restriction area includes waters 

bounded by the 200- to 2,000-m isobaths 

from the northern border of BOEM’s 

Howell Hook leasing area to 81.5° W 

(Area 4; Figure 5). The defined area 

would be buffered by 9 km (rounded up 

from the 8.4 km distance provided by 

Matthews et al. (2016) for the Dry 

Tortugas area). Note that, in reference to 

the findings of Matthews et al. (2016), 

this proposed time-area restriction 

would also reduce impacts to stocks of 

marine mammals occurring within the 

restriction area through reducing effects 

to listening area. We invite the public to 

comment on our interpretation of the 

data and proposal of year-round 

restrictions on airgun surveys in Area 4 

(Figure 5). We are interested in public 

comment on this proposal, including 

any data that may support the necessary 

findings regarding this proposal, 

including modifications that could vary 

the length of closure from what we 

proposed. 

Practicability—BOEM has projected 

no survey activity in this area over the 

next 10 years. There are no active leases, 

and the area is subject to the GOMESA 

moratorium, so we do not expect that 

there would be any impact on industry 

operators. We seek comment on this 

assumption. 

Central Planning Area (CPA)—We 

evaluated the possibility of 

implementing a restriction area in this 

portion of the GOM for sperm whales 

and for beaked whales (Area 2; Figure 

5). Sperm whales, an endangered 

species, are considered to be 

acoustically sensitive and potentially 

subject to significant disturbance of 

important foraging behavior as detailed 

earlier in this document. Beaked whales 

are also considered to be behaviorally 

sensitive to noise exposure and are 

predicted to sustain a high magnitude of 

exposures to noise above criteria for 

Level B harassment. A potential CPA 

restriction had already been identified 

in BOEM (2017) on the basis of sightings 

data and animal telemetry studies (for 

sperm whales). 

Based on satellite tracking studies 

conducted by Jochens et al. (2008), the 

home range of tagged sperm whales 

within the northern GOM is broad, 

comprising nearly the entire GOM in 

waters deeper than 500 m. Home range 

is defined as an area over which an 

animal or group of animals regularly 

travels in search of food or mates that 

may overlap with those of neighboring 

animals or groups of the same species. 

By contrast, the composite core area 

(defined as a section of the home range 

that is utilized more thoroughly and 

frequently as primary locales for 

activities such as feeding) of GOM 

sperm whales generally includes the 

Mississippi Canyon, Mississippi River 

Delta, and, to a lesser extent, the Rio 

Grande Slope (Jochens et al., 2008). 

These data support the fact that sperm 

whales aggregate in the Mississippi 

Canyon area, but regularly move across 

the northern GOM continental slope. 

Reporting preliminary data from a 

passive acoustic monitoring study, 

Hildebrand et al. (2012) found that 

among three deep-water sites in the 

GOM, the Mississippi Canyon area was 

home to the greatest density of sperm 

whales. 

Beaked whales are typically deep 

divers, foraging for mesopelagic squid 

and fish, and are often found in deep 

water near high-relief bathymetric 

features, such as slopes, canyons, and 

escarpments where these prey are found 

(e.g., Madsen et al., 2014; MacLeod and 

D’Amico, 2006; Moors-Murphy, 2014). 

In the GOM, all reported sightings have 

occurred over the continental slope or 

the abyss (Roberts et al., 2015b). 

Movements or seasonal migrations of 

beaked whales are not known, though it 

is likely that their distributional 

patterns depend on the movement of 

mesoscale hydrographic features. The 

CPA, including waters from the slope to 

2,000 m and approximately between 

BOEM’s Atwater Valley and De Soto 

Canyon leasing areas, is believed to 

support relatively high densities of 

sperm whales and beaked whales (K. 

Mullin, pers. comm.). 

In order to quantitatively evaluate this 

large area and produce a more refined 

prospective restriction area, we 

considered the outputs of habitat-based 

predictive density models (Roberts et 

al., 2016) by creating core abundance 

areas, i.e., an area that contains some 

percentage of predicted abundance for a 

given species or species group. Please 

see ‘‘Marine Mammal Density 

Information,’’ previously in this 

document, for a full description of the 

density models. The purpose of a core 

abundance area is to represent the 

smallest area containing some 

percentage of the predicted abundance 

of each species. Summing all the cells 

(pixels) in the species distribution 

product gives the total predicted 

abundance. Core area is calculated by 

ranking cells by their abundance value 

from greatest to least, then summing 

cells with the highest abundance values 

until the total is equal to or greater than 

the specified percentage of the total 

predicted abundance. For example, if a 

50 percent core abundance area is 

produced, half of the predicted 

abundance falls within the identified 

core area, and half occurs outside of it. 

To determine core abundance areas, 

we follow a three-step process: 

• Determine the predicted total abundance 

of a species/time period by adding up all 

cells of the density raster (grid) for the 

species/time period. For the Roberts et al. 

(2016) density rasters, density is specified as 

the number of animals per 100 km2 cell. 

• Sort the cells of the species/time period 

density raster from highest density to the 

lowest. 

• Sum and select the raster cells from 

highest to lowest until a certain percentage 

of the total abundance is reached. 


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The selected cells represent the 

smallest area that represents a given 

percentage of abundance. We created a 

range of core abundance areas for sperm 

and beaked whales, and found that there 

was good agreement between the 

outputs of the two models at a range of 

approximately 15 to 20 percent core 

abundance for sperm whales in concert 

with a 25 percent core abundance 

threshold for beaked whales. On this 

basis, we defined a restriction area for 

evaluation as follows, in two adjacent 

but distinct areas (which would likely 

be joined from an operational 

perspective): (1) An area bounded by 

90° W and 88° W (E–W) and the 500- 

and 1,000-fathom isobaths (N–S), and 

(2) an area bounded by five sets of 

coordinates (Area 2, Figure 5). 

Practicability—We provided a 

description of this area for evaluation in 

the RIA associated with this rule. This 

analysis found that our proposed CPA 

restriction area overlaid approximately 

21 percent of active GOM leases 

(including 95 active production 

platforms) and that a significant number 

of wells have been spudded in the CPA 

restriction area in the past five years. 

These leases accounted for 

approximately 50 and 24 percent of total 

GOM production of oil and gas, 

respectively, from 2012–2016. A 

significant amount of the projected 

survey activity considered herein would 

be conducted in the potential CPA 

restriction area. Compliance costs, in 

terms of operational mitigation 

protocols such as shutdown 

requirements, generally would not be 

expected to reduce the level of oil and 

gas development in the GOM, given that 

the costs of survey activities are 

relatively minor compared to 

expenditures on drilling, engineering, 

installation of platforms, and 

production operations. However, in 

contrast to the findings related to 

operational mitigation protocols, area 

restrictions may lead to reductions in 

leasing and exploration activity. The 

length of time associated with the 

restriction is a key concern; the longer 

the restriction period, the more difficult 

for operators to plan surveys to comply 

and increasing the likelihood that some 

portion of planned surveys are delayed 

to future years. There is no information 

available in the GOM on which to base 

a definition of seasonality for the CPA 

restriction area that we evaluated. The 

analysis suggests the possibility that 

closing the CPA area could affect the 

broader contribution of the GOM to U.S. 

oil and gas activity, with shifts in effort 

potentially reducing domestic oil and 

gas production, industry income, and 

employment, ultimately concluding that 

the economic impact on the regional 

economy could be significant. Given 

that the evaluated area restrictions 

account for an estimated 57 percent of 

oil reserves and 37 percent of gas 

reserves, these areas account for a 

sizable contribution to regional 

economic productivity and 

employment. On the basis of this 

analysis, and in consideration of other 

mitigation required with regard to 

sperm whales (i.e., expanded shutdown 

requirements), we preliminarily find 

that implementation of this restriction 

area is not warranted when the potential 

benefits to marine mammals species or 

stocks and their habitat are weighed 

against the significant costs and 

impracticality. We request comment on 

this, preliminary determination, 

including our interpretation of the data, 

our preliminary finding that inclusion 

of this measure is not warranted due to 

the significant costs and impracticality, 

and any other data that may support the 

necessary findings. 

Entanglement Avoidance 

We are not aware of any records of 

marine mammal entanglement in towed 

arrays, streamers, or other towed 

acoustic sources. Therefore, we do not 

believe there is evidence to indicate that 

there is any meaningful entanglement 

risk posed by those activities. However, 

the use of OBNs or similar equipment 

requiring the use of tethers or 

connecting lines does pose a meaningful 

entanglement risk. Multiple marine taxa 

are susceptible to entanglement in 

underwater lines and, in 2014, an 

Atlantic spotted dolphin was entangled 

in a nylon nodal tether line and killed 

during a GOM OBN survey. 

In order to avoid the reasonable 

potential for entanglement in such lines, 

one must generally seek to apply 

common sense, including use of stiffer 

lines that are taut and are not positivelybuoyant, and are therefore less likely to 

wrap or loop around animals, and 

secure bottom lines. Specifically, we 

propose that operators conducting OBN 

surveys adhere to the following 

requirements: (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; (3) attach acoustic pingers 

directly to the coated tether cable; 

acoustic releases should not be used; 

and (4) employ a third-party PSO aboard 

the node retrieval vessel in order to 

document any unexpected marine 

mammal entanglement. No unnecessary 

release lines or lanyards may be used 

and nylon rope may not be used for any 

component of the OBN 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. Similar 

measures, including the commonly 

referred to ‘‘orange coated rope,’’ have 

been required by BOEM as permit 

conditions and have proven successful 

in preventing further entanglements. 

Vessel Strike Avoidance 

These proposed measures generally 

follow those described in BOEM’s PEIS 

(BOEM, 2017). These measures apply to 

all vessels associated with any proposed 

survey activity (e.g., source vessels, 

streamer vessels, chase vessels, supply 

vessels); however, we note that 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. The proposed measures include 

the following: 

1. Vessel 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. A visual 

observer aboard the vessel must monitor 

a vessel strike avoidance zone around 

the vessel, according to the parameters 

stated below, to ensure the potential for 

strike is minimized. Visual observers 

monitoring the vessel strike avoidance 

zone can be either third-party observers 

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. All vessels, regardless of size, must 

observe a 10 kn speed restriction within 

the EPA restriction area described 

previously. It is critically important to 

avoid vessel strike of a Bryde’s whale, 

as single mortalities over time can be 

devastating for such small populations. 

Further, Bryde’s whales engage in 

shallow nocturnal diving, spending 

significant amounts of time near the 

surface at night and increasing the risk 

of strike when vessels are transiting 

Bryde’s whale habitat (Soldevilla et al., 

2017). 

3. Vessel speeds must also be reduced 

to 10 kn or less when mother/calf pairs, 

pods, or large assemblages of cetaceans 

are observed near a vessel. A single 

cetacean at the surface may indicate the 

presence of submerged animals in the 


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vicinity of the vessel; therefore, 

precautionary measures should be 

exercised when an animal is observed. 

4. All vessels must maintain a 

minimum separation distance of 500 

yards (yd) (457 m) from baleen whales. 

Our intention is to be precautionary in 

prescribing avoidance measures to avoid 

the potential for strike of Bryde’s 

whales—the only baleen whale that 

would be expected with any regularity 

in the GOM—but we do not expect that 

crew members standing watch would be 

able to reliably identify baleen whales to 

species in the GOM. The following 

avoidance measures should be taken if 

a baleen whale is within 500 yd of any 

vessel: 

a. While underway, the vessel 

operator should steer a course away 

from the whale at 10 kn or less until the 

minimum separation distance has been 

established. 

b. If a whale is spotted in the path of 

a vessel or within 500 yd of a vessel 

underway, the operator should reduce 

speed and shift engines to neutral. The 

operator should re-engage engines only 

after the whale has moved out of the 

path of the vessel and is more than 500 

yd away. If the whale is still within 500 

yd of the vessel, the vessel should select 

a course away from the whale’s course 

at a speed of 10 kn or less. The 

recommendation to shift engines to 

neutral does not apply to any vessel 

towing gear due to safety concerns. 

c. This procedure should also be 

followed if a whale is spotted while a 

vessel is stationary. Whenever possible, 

a vessel should remain parallel to the 

whale’s course while maintaining the 

500-yd distance as it travels, avoiding 

abrupt changes in direction until the 

whale is no longer in the area. 

5. All vessels must maintain a 

minimum separation distance of 100 yd 

(91 m) from sperm whales. The 

following avoidance measures should be 

taken if a sperm whale is within 100 yd 

of any vessel: 

a. The vessel underway should reduce 

speed and shift the engine to neutral, 

and should not engage the engines until 

the whale has moved outside of the 

vessel’s path and the minimum 

separation distance has been 

established. This does not apply to any 

vessel towing gear. 

b. If a vessel is stationary, the vessel 

should not engage engines until the 

whale has moved out of the vessel’s 

path and beyond 100 yd. 

6. All vessels must attempt to 

maintain a minimum separation 

distance of 50 yd (46 m) from all other 

marine mammals, with an exception 

made for those animals that approach 

the vessel. If an animal is encountered 

during transit, a vessel should attempt 

to remain parallel to the animal’s 

course, avoiding excessive speed or 

abrupt changes in course. 

Marine Debris 

Any permits issued by BOEM would 

include guidance for the handling and 

disposal of marine trash and debris, 

similar to BSEE NTL 2015–G03 

(‘‘Marine Trash and Debris Awareness 

and Elimination’’) (BSEE, 2015; BOEM, 

2017). If there were an LOA applicant 

for an activity not requiring a BOEM 

permit, NMFS would also require 

adherence to this guidance. 

TABLE 11—SUMMARY OF MITIGATION MEASURES WITH ALTERNATIVES FOR CONSIDERATION

Measure Proposal 

Proposal preliminarily determined to 

support ‘‘least practicable 

adverse impact’’ and ‘‘negligible 

impact’’ findings? 

Proposal 

included in 

proposed 

regulatory 

text? 

Dolphin shutdown exception ................... Power-down ........................................... Yes ......................................................... Yes. 

No power-down ...................................... No ........................................................... No. 

Extended distance shutdown in certain 

circumstances.

Shutdown for detections at any distance Yes ......................................................... Yes. 

Shutdown for detections within 1 km ..... No ........................................................... No. 

Time-area restriction for Bryde’s whales Year-round ............................................. Yes ......................................................... No. 

Seasonal ................................................ No ........................................................... Yes. 

Seasonal with real-time detection .......... No ........................................................... No. 

No restriction with real-time detection ... No ........................................................... No. 

Based on our evaluation of the 

mitigation measures described in this 

section, as well as other measures 

considered by NMFS, we have 

preliminarily determined those 

mitigation measures that provide the 

means of effecting the least practicable 

adverse impact on the affected species 

or stocks and their habitat, paying 

particular attention to rookeries, mating 

grounds, and areas of similar 

significance. We request comment on all 

proposals and other variations of these 

proposals, including our interpretation 

of the data and any other data that 

support the necessary findings. 

Proposed 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’s 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. 

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, it is clear that 

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 proposed requirements are 

described below under ‘‘Data 

Collection’’ and ‘‘LOA Reporting.’’ 

Additional comprehensive reporting, 

across LOA-holders on an annual basis, 


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is also proposed and is described below 

under ‘‘Comprehensive Reporting.’’ 

More specifically, monitoring and 

reporting requirements 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). 

• Mitigation and monitoring effectiveness. 

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. NMFS expects to 

maintain a list of approved PSOs, which 

will minimize review time for 

previously approved PSOs with current 

experience. 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 related to PSO training; 

submitted resumes should not include 

superfluous information. Information 

related to PSO training should include 

(1) 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; 

and (2) a document stating the PSO’s 

successful completion of the course. 

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; 

• Experience and ability to conduct field 

observations and collect data according to 

assigned protocols (may include academic 

experience; required for visual PSOs only) 

and experience with data entry on 

computers; 

• Visual acuity in both eyes (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; 

• Ability to communicate orally, by radio 

or in person, with survey personnel to 

provide real-time information on marine 

mammals observed in the area as necessary; 

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. 

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 governmentsponsored 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 expects to provide 

informal approval for specific training 

courses in consultation with BOEM and 

BSEE as needed to approve PSO staffing 

plans. NMFS does not propose to 

formally administer any training 

program or to sanction any specific 

provider, but will approve courses that 

meet the curriculum and trainer 

requirements specified herein. These 

requirements adhere generally to the 

recommendations provided by 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 (bigeye binoculars 

must be provided during deep 

penetration airgun surveys; see below), 

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, 


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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 

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 airgun 

surveys and deep-water surveys (i.e., 

water depths greater than 200 m) 

generally, the vessel operator must 

provide bigeye binoculars (e.g., 25 × 

150; 2.7 view angle; individual ocular 

focus; height control) of appropriate 

quality (i.e., Fujinon or equivalent) 

solely for PSO use. These should be 

pedestal-mounted on the deck at the 

most appropriate vantage point that 

provides for optimal sea surface 

observation, PSO safety, and safe 

operation of the vessel. The operator 

must also provide a night-vision device 

suited for the marine environment for 

use during nighttime ramp-up preclearance, at the discretion of the PSOs. 

NVDs may include night vision 

binoculars or monocular or forwardlooking infrared device (e.g., Exelis 

PVS–7 night vision goggles; Night 

Optics D–300 night vision monocular; 

FLIR M324XP thermal imaging camera 

or equivalents). At minimum, the device 

should feature automatic brightness and 

gain control, bright light protection, 

infrared illumination, and optics suited 

for low-light situations. This equipment 

is not required for shallow penetration 

airgun surveys or non-airgun HRG 

surveys that occur in shallow water. 

Other required equipment, which 

should be made available to PSOs by the 

third-party observer provider, includes 

reticle binoculars (e.g., 7 × 50) of 

appropriate quality (i.e., Fujinon or 

equivalent), GPS, digital single-lens 

reflex camera of appropriate quality 

(i.e., Canon or equivalent), 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. Any modifications 

to protocol will be coordinated through 

an adaptive management process. 

Acoustic Monitoring 

Use of PAM is required for deep 

penetration airgun surveys. Monitoring 

of a towed PAM system is required at all 

times, from 30 minutes prior to ramp-up 

and throughout all use of the acoustic 

source. Towed PAM systems generally 

consist of hardware (e.g., hydrophone 

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

processing and monitoring system). 

Some type of automated detection 

software must be used; while not 

required, we recommend use of industry 

standard software (e.g., PAMguard, 

which is open source). Hydrophone 

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, 

masking of signals due to noise from the 

vessel, source, and/or flow, localization) 

and there are no formal guidelines 

currently in place regarding 

specifications for hardware, software, or 

operator training requirements. 

However, a working group (led by A.M. 

Thode) is developing formal standards 

under the auspices of the Acoustical 

Society of America’s (ASA) Accredited 

Standards Committee on Animal 

Bioacoustics (ANSI S3/SC1/WG3; 

‘‘Towed Array Passive Acoustic 

Operations for Bioacoustics 

Applications’’). While no formal 

standards have yet been completed, a 

‘‘roadmap’’ was developed during a 

2016 workshop held for the express 

purpose of continuing development of 

such standards. A workshop report 

(Thode et al., 2017) provides a highly 

detailed preview of what the scope and 

structure of the standard would be, 

including operator training, planning, 

hardware, real-time operations, 

localization, and performance 

validation. NMFS expects that LOA 

applicants will incorporate these 

considerations in developing or refining 

PAM plans (described below), as 

appropriate. NMFS proposes to adopt 

such standards in governing the 

development of PAM plans following 

finalization. 

Our 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. Multi-hydrophone (i.e., 

more than four) arrays are required to 

allow for potential determination of 

bearing and range to detected animals. 

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 should 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. The arrays 

should incorporate appropriate 

hydrophone elements (1 Hz to 180 kHz 

range) and sound data acquisition card 

technology for sampling relevant 

frequencies (i.e., to 360 kHz). This 

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. 

In the absence of a formally defined 

set of prescriptions 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. As recommended by Thode 

et al. (2017), the 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 


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receiver vessel or other associated vessel 

separate from the acoustic source. 

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, as described 

below, must report all cetacean 

detections. While not required prior to 

development of formal standards for 

PAM use, we recommend that vessel 

self-noise assessments are 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 data 

forms, whether hard copy or electronic. 

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. We require that, at a 

minimum, the following information be 

reported: 

• Vessel names (source vessel and other 

vessels associated with survey) and call 

signs; 

• PSO names and affiliations; 

• Dates of departures and returns to port 

with port name; 

• 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; vessel 

location at beginning and end of visual PSO 

duty shifts; 

• 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 wind speed and 

direction, Beaufort sea state, Beaufort wind 

force, swell height, weather conditions, cloud 

cover, sun glare, and overall visibility to the 

horizon; 

• Factors that may be contributing 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 the array, tow depth of the array, 

and any other notes of significance (i.e., preramp-up survey, ramp-up, shutdown, testing, 

shooting, ramp-up completion, end of 

operations, streamers, etc.) (if the survey is a 

non-airgun survey, information relevant to 

the acoustic source used should be 

provided); 

• 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; 

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 its 

heading relative to vessel at initial sighting; 

Æ Identification of the animal (e.g., genus/ 

species, lowest possible taxonomic level, or 

unidentified); 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, speed or course 

alteration, etc.); time and location of the 

action should also be recorded; and 

• 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; 

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 and reports 

prepared each day during which survey 

effort is conducted. These reports would 

include amount and location of linekms surveyed, all marine mammal 

observations with closest approach 

distance, and corrected numbers of 

marine mammals ‘‘taken.’’ We propose 

submission of such reports 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 would be submitted during the 

period of validity. 

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, observational data 

corrections must be made with respect 

to assumed species-specific detection 

probability as evaluated through 

consideration of environmental factors 

(e.g., f(0)). In order to make these 

corrections, we propose a method 

recommended by the Marine Mammal 

Commission for estimating the number 

of cetaceans in the vicinity of 

geophysical surveys based on the 

number of groups detected. 

This method incorporates f(0) and 

BSS-specific g(0) values from Barlow 

(2015) that were derived using Distance 

sampling methods (Buckland et al., 

2001) and sightings data. If we know 

that we have detected n groups, and the 

probability of detecting each group is p, 

a standard way to estimate the total 

number of groups is n/p. We know n for 

each species from the data collected 

during each survey, so the problem is to 

find p for each species. During scientific 

marine mammal surveys, p is estimated 

from the data collected on each survey 

as part of a line-transect analysis. The 

probability p for each species depends 


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principally on the distance of the 

animals from the observer, but may also 

depend on other factors such as group 

size and sea state. 

In the absence of a line-transect 

analysis, the Commission suggests 

taking estimates of p from other studies 

which use ships of similar size and 

searching methods. For line-transect 

analysis, p is a product of the 

probability of detecting a group of 

animals directly on the trackline (g(0)) 

and the probability of detecting a group 

of animals within the half-strip width 

on each side of the trackline (μ/w, where 

w is the transect truncation distance 

beyond which data are not recorded and 

μ is the effective strip half-width). The 

effective strip half-width also may be 

expressed as μ = 1/f(0), where f(0) is the 

estimated probability density function 

of observed perpendicular distances y 

evaluated at y = 0. 

The species discussed in Barlow 

(2015) may be different from those 

observed during a geophysical survey, 

but data from similar species can be 

used. Since g(0) and f(0) values for each 

species or genera depend on group size, 

BSS, swell height and other factors, 

those factors should be taken into 

account if possible. 

The probability of detecting a group of 

cetaceans can therefore be expressed as: 

If there are n sightings of a species 

along a section of trackline, the 

estimated number of Groups for a given 

BSS, within a perpendicular distance w 

on each side of the trackline, and within 

the Level B harassment zone is: 

and the estimated number of individual 

animals in that given BSS then is: 

where S is the mean group size for the 

species. 

The number of animals seen within 

each BSS should be summed for each 

Level B harassment zone. That total 

number then must be scaled by the 

distance to the Level B harassment 

threshold relative to the truncation 

distance to estimate the total number of 

animals potentially taken during a given 

survey. Examples of the application of 

this process are given in the 

Commission’s letter, relevant portions of 

which are available online at: 

www.fisheries.noaa.gov/national/ 

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

As noted, a draft report must be 

submitted to NMFS within 90 days of 

the completion of survey effort or 

following expiration of the LOA 

(whichever comes first), or annually (if 

a multi-year LOA is issued), and must 

include all information described above 

under ‘‘Data Collection.’’ The report will 

describe the operations conducted and 

sightings of marine mammals near the 

operations. The report will provide full 

documentation of methods, results, and 

interpretation pertaining to all 

monitoring. The report will summarize 

the dates and locations of survey 

operations, and all marine mammal 

sightings (dates, times, locations, 

activities, associated survey activities); 

information regarding locations where 

the acoustic source was used must be 

provided. 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, or 

when they changed from full array to 

single gun or vice versa). 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 and 

demonstrate whether background noise 

levels on the PAM deployment limited 

achievement of the planned detection 

goals. 

The report will also include estimates 

of the number of takes based on the 

observations and in consideration of the 

detectability of the marine mammal 

species observed (as described above). 

Applicants must provide an estimate of 

the number (by species) of marine 

mammals that may have been exposed 

(based on observational data and 

accounting for animals present but 

unavailable for sighting) to the survey 

activity within areas associated with the 

relevant frequency-weighted sound 

fields (i.e., 140/160/180 dB rms). The 

draft report must be accompanied by a 

certification from the lead PSO 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. 

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 

should 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, powerdown); 

• Summary of monitoring effort (on-effort 

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, 

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; 

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); and 

Æ Estimates of the number of marine 

mammals taken by harassment, corrected for 

animals potentially missed by observers; 

• 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 

by October 1 of each year. Therefore, to 

allow for adequate preparation, each 


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report should analyze survey and 

monitoring effort described in reports 

submitted by individual LOA-holders 

from July 1 of one year through June 30 

of the next. Of necessity, the first annual 

report may cover a different period of 

time, e.g., from the date of issuance of 

a rule until October 1 of the next year. 

Reporting Injured or Dead Marine 

Mammals 

In the event that the specified activity 

clearly causes the take of a marine 

mammal in a manner not permitted by 

the authorization (if issued), such as a 

serious injury or mortality, the LOAholder shall immediately cease the 

specified activities and immediately 

report the take to NMFS. The report 

must include the following information: 

• Time, date, and location (latitude/ 

longitude) of the incident; 

• Name and type of vessel involved; 

• Vessel’s speed during and leading up to 

the incident; 

• Description of the incident; 

• Status of all sound source use in the 24 

hours preceding the incident; 

• Water depth; 

• Environmental conditions (e.g., wind 

speed and direction, Beaufort sea state, cloud 

cover, and visibility); 

• Description of all marine mammal 

observations in the 24 hours preceding the 

incident; 

• Species identification or description of 

the animal(s) involved; 

• Fate of the animal(s); and 

• Photographs or video footage of the 

animal(s) (if equipment is available). 

The LOA-holder shall not resume its 

activities until NMFS is able to review 

the circumstances of the prohibited 

take. NMFS would work with the LOAholder to determine what is necessary to 

minimize the likelihood of further 

prohibited take and ensure MMPA 

compliance. The LOA-holder may not 

resume their activities until notified by 

NMFS. 

In the event that the LOA-holder 

discovers an injured or dead marine 

mammal, and the lead PSO determines 

that the cause of the injury or death is 

unknown and the death is relatively 

recent (i.e., in less than a moderate state 

of decomposition as we describe in the 

next paragraph), the LOA-holder will 

immediately report the incident to 

NMFS. The report must include the 

same information identified in the 

paragraph above this section. Activities 

may continue while NMFS reviews the 

circumstances of the incident. NMFS 

would work with the LOA-holder to 

determine whether modifications to the 

activities are appropriate. 

In the event that the LOA-holder 

discovers an injured or dead marine 

mammal, and the lead PSO determines 

that the injury or death is not associated 

with or related to the specified activities 

(e.g., previously wounded animal, 

carcass with moderate to advanced 

decomposition, or scavenger damage), 

the LOA-holder would report the 

incident to NMFS within 24 hours of 

the discovery. The LOA-holder would 

provide photographs or video footage (if 

available) or other documentation of the 

animal to NMFS. 

Negligible Impact Analysis and 

Preliminary Determination 

NMFS has defined negligible impact 

as an impact resulting from the 

specified activity that cannot be 

reasonably expected to, and is not 

reasonably likely to, adversely affect the 

species or stock through effects on 

annual rates of recruitment or survival 

(50 CFR 216.103). A negligible impact 

finding is based on the lack of likely 

adverse effects on annual rates of 

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

of takes alone is not enough information 

on which to base an impact 

determination. In addition to 

considering estimates of the number of 

marine mammals that might be ‘‘taken,’’ 

NMFS considers other factors, such as 

the type of take (e.g., mortality, injury), 

the likely nature of any responses (e.g., 

intensity, duration), the context of any 

responses (e.g., critical reproductive 

time or location, migration), as well as 

effects on habitat, and the likely 

effectiveness of the mitigation. We also 

assess the number, intensity, and 

context of estimated takes by evaluating 

this information relative to population 

status. Consistent with the 1989 

preamble for NMFS’s implementing 

regulations (54 FR 40338; September 29, 

1989), the impacts from other past and 

ongoing anthropogenic activities are 

incorporated into this analysis via their 

impacts on the environmental baseline 

(e.g., as reflected in the regulatory status 

of the species, population size and 

growth rate where known, ongoing 

sources of human-caused mortality, or 

ambient noise levels). 

For each potential activity-related 

stressor, we consider the potential 

impacts on affected marine mammals 

and the likely significance of those 

impacts to the affected stock or 

population as a whole. Potential risk 

due to vessel collision and related 

mitigation measures as well as potential 

risk due to entanglement and 

contaminant spills were addressed 

under ‘‘Proposed Mitigation’’ and 

‘‘Potential Effects of the Specified 

Activity on Marine Mammals’’ 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. In recognition of the broad 

scale of this activity in terms of 

geographic and temporal scales, we 

propose use of a new analytical 

framework—first described by Ellison et 

al. (2015)—through which an explicit, 

systematic risk assessment methodology 

is applied to evaluate potential effects of 

aggregated discrete acoustic exposure 

events (i.e., proposed geophysical 

survey activities) on marine mammals. 

We believe the approach described here 

addresses the scope and scale of 

potential impacts to marine mammal 

populations from these activities. 

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 

framework and preliminary results are 

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 described below was 

developed and preliminarily 

implemented by Southall et al. (2017) in 

relation to the specified activity 

described herein; we incorporate the 

framework and its results into our 

analysis as appropriate. 

As described previously, Zeddies et 

al. (2015, 2017a) provided marine 

mammal noise exposure estimates based 

on BOEM-provided projections of future 

survey effort and based on 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. The primary goal in this new 

analytical effort was to develop a 

systematic framework that would use 

those modeling results to put into 

biologically-relevant context the level of 

potential risk of injury and/or 

disturbance to marine mammals. The 

framework considers both the 

aggregation of acute effects as well as 

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 they derived a 

qualitative risk assessment method of 


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considering the biological significance 

of exposures predicted to be consistent 

with the onset of physical injury and 

behavioral disturbance (the latter 

determined according to the same 

approach used here). Subsequently, 

Ellison et al. (2015) described 

development of a more systematic and 

(in some cases) quantitative basis for a 

risk-assessment approach to assess the 

biological significance and potential 

population consequences of predicted 

noise exposures. The approach here, 

which incorporated the results of 

Zeddies et al. (2015, 2017a) 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. The analysis is performed 

specifically on a species-specific basis 

for each effort scenario (‘‘high,’’ 

‘‘moderate,’’ and ‘‘low’’) within each 

modeling zone (Figure 2). 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), as well as 

forecasting 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 our proposed 

mitigation strategy (and any additional 

relevant contextual information) to 

ultimately inform our preliminary 

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 (Table 9) on the species or 

stock, the EWG report uses a PBRequivalent 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., 

PTS) that may be authorized under this 

rule to result in mortality of marine 

mammals, nor do we believe that Level 

A harassment should 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, because habitat-based 

density models (Roberts et al., 2016) 

were used to predict cetacean 

distribution and abundance in the GOM, 

exposure estimates cannot appropriately 

be directly related to the PBR values 

found in NMFS’s SARs. Therefore, a 

modified PBR value was derived on the 

basis of the typical pattern for NMFS’s 

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 non-endangered 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 (e.g., considered equivalent to 

estimated X percent of PBR) was used 

to define the following relative risk 

levels due to Level A harassment. 

• Very high—Level A takes 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 2) and species for high, 

moderate, and low annual activity 

scenarios are shown in Tables 4–7 of the 

EWG report. However, as described 

previously, we do not believe that Level 

A harassment is likely to actually occur 

for mid-frequency cetaceans and 

therefore do not predict any take by 

Level A harassment for these species. 

The risk presented by Level A 

harassment to mid-frequency species is 

therefore expected to be none to very 

low. 

Due to the combination of density 

estimates and effort projections, the 

predicted takes by Level A harassment 

(accounting for aversion) for both 

Bryde’s whale and Kogia spp. are 

expected to represent a ‘‘very high’’ risk 

for the moderate and low effort 

scenarios in Zone 4 (note that the 

‘‘high’’ effort scenario, while including 

the most survey days when aggregating 

across the entire GOM, includes no 

projected survey days in Zone 4). For 

Kogia spp. only, all three effort 

scenarios represent a ‘‘very high’’ risk in 

Zones 6 and 7. All other combinations 

of effort and zone result in overall 

evaluated risk of none to low for these 

species. 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 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. 

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 


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assumed survey days as completely 

independent events, assuming 

populations turn over completely 

within each large zone on a daily basis. 

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. In order to evaluate modeled 

daily exposures and determine more 

realistic exposure probabilities for 

individuals across multiple days, we 

use 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. However, as noted 

earlier, even with this correction factor 

the resulting number of predicted takes 

of individuals is still an overestimate 

because individuals are expected to be 

exposed to multiple surveys in a year 

and many surveys are longer than 30 

days. This approach is also discussed in 

more detail in the EWG report. 

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 exposure 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. This output was used in 

a severity assessment. 

TABLE 12—SCENARIO-SPECIFIC EXPECTED TAKE NUMBERS, INSTANCES AND INDIVIDUALS 1

Species 

Survey effort scenario 2

High Moderate #1 Moderate #2 Low #1 Low #2 

Ins. Ind. Ins. Ind. Ins. Ind. Ins. Ind. Ins. Ind. 

Bryde’s whale ............................................ 560 106 413 78 498 94 386 73 402 76 

Sperm whale ............................................. 43,504 18,395 27,271 11,531 33,340 14,097 26,651 11,269 27,657 11,694 

Kogia spp. ................................................. 16,189 5,189 11,428 3,663 13,644 4,373 10,743 3,443 11,165 3,579 

Beaked whale ............................................ 235,615 23,704 162,134 16,311 190,777 19,193 151,708 15,262 156,584 15,753 

Rough-toothed dolphin .............................. 37,666 10,793 30,192 8,651 31,103 8,912 28,663 8,213 26,315 7,540 

Bottlenose dolphin ..................................... 653,405 187,222 977,108 279,974 596,824 171,010 938,322 268,860 579,403 166,018 

Clymene dolphin ....................................... 110,742 31,731 72,913 20,892 87,615 25,105 69,609 19,945 72,741 20,843 

Atlantic spotted dolphin ............................. 133,427 38,231 174,705 50,059 116,698 33,438 164,824 47,228 109,857 31,478

Pantropical spotted dolphin ....................... 606,729 173,848 419,738 120,269 511,037 146,429 399,581 114,493 419,824 120,293 

Spinner dolphin ......................................... 82,779 23,719 59,623 17,084 73,013 20,921 56,546 16,202 59,253 16,978 

Striped dolphin .......................................... 44,038 12,618 29,936 8,578 36,267 10,392 28,522 8,172 29,890 8,564 

Fraser’s dolphin ......................................... 13,858 3,971 9,654 2,766 11,394 3,265 9,127 2,615 9,391 2,691 

Risso’s dolphin .......................................... 27,062 7,754 18,124 5,193 21,914 6,279 17,309 4,960 18,092 5,184 

Melon-headed whale ................................. 68,900 20,355 47,548 14,047 56,791 16,777 44,842 13,247 46,631 13,776 

Pygmy killer whale .................................... 18,029 5,326 12,278 3,627 14,788 4,369 11,677 3,450 12,141 3,587 

False killer whale ...................................... 25,511 7,536 17,631 5,209 20,828 6,153 16,774 4,955 17,163 5,070 

Killer whale ................................................ 1,493 441 1,031 305 1,258 372 984 291 1,036 306 

Short-finned pilot whale ............................ 19,258 5,689 12,155 3,591 14,163 4,184 11,523 3,404 11,900 3,516 

1 Instances of take (‘‘Ins.’’) reflects expected scenario-based takes by Level B harassment given previously in Table 9. Scalar ratios were applied as described in 

preceding text to derive expected numbers of individuals taken (‘‘Ind.’’). 2 High survey effort scenario correspond level of effort projections given previously for Year 1 (Table 1). Moderate #1 and #2 and Low #1 and #2 correspond with 

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

As was done in evaluating severity of 

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 behavioral risk 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 behavioral takes 

greater than 800 percent of zone-specific 

population; 

• High—Adjusted behavioral takes 400– 

800 percent of zone-specific population; 

• Moderate—Adjusted behavioral takes 

200–400 percent of zone-specific population; 

• Low—Adjusted behavioral takes 100– 

200 percent of zone-specific population; and 

• Very low—Adjusted behavioral takes 

less than 100 percent of zone-specific 

population. 

Results of severity ranking for Level B 

harassment are shown in Tables 8–10 of 

Southall et al. (2017). Note that these 

have been adjusted here to account for 


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the erroneous density value that 

underlies the exposure predictions 

given by Zeddies et al. (2015, 2017b) for 

Bryde’s whales in Zone 6. 

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 severity 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 13); note that the effects of the 

DWH oil spill are accounted for through 

the non-noise chronic anthropogenic 

risk factor identified below, while the 

effects to acoustic habitat and on 

individual animal behavior via masking 

described in ‘‘Potential Effects of the 

Specified Activity on Marine Mammals 

and Their Habitat’’ are accounted for 

through the masking chronic 

anthropogenic noise risk factors. 

Species-specific vulnerability scoring 

according to this scheme is shown in 

Table 14. Based on the range in 

vulnerability assessment scoring, an 

overall vulnerability rating was selected 

from the zone- and species-specific 

aggregate vulnerability score as shown 

in Table 15. 

TABLE 13—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 overlaps 1 species-specific signals utilized in foraging (including echolocation and other foraging coordination signals) ....................................................................................................... +2/+1 

Navigation/Orientation signal masking: Predominant noise energy directly/partially overlaps 1 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 

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 a specified activity is evaluated and a local population is determined, in this case the seven modeling zones. 

BILLING CODE 3510–22–P 


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BILLING CODE 3510–22–C 

TABLE 15—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. 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 when 

there is no survey activity in a given 

zone for a given effort scenario, and 

zones predicted to contain abundance of 

less of five or less individuals of a 

species were also considered to have de 

minimis 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). Please see Tables 

8–10 of the EWG report for species- and 

zone-specific severity and vulnerability 

ratings for each of three activity 

scenarios. Tables 16–17 provide relative 

impact ratings by zone, and Table 18 

provides GOM-wide relative impact 

ratings, for overall risk associated with 

predicted takes by Level B harassment, 

for each of three activity scenarios. 


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TABLE 16—OVERALL EVALUATED RISK BY ZONE AND ACTIVITY SCENARIO

[Zones 1–4] 

Species 

Zone 1 1 Zone 2 Zone 3 Zone 4 1

High High Moderate Low High Moderate Low Moderate Low 

Bryde’s whale .......................... Low ............ n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Moderate .... Moderate. 

Sperm whale ............................ n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Moderate ... Low. 

Kogia spp. ................................ Low ............ n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Low ............ Low. 

Beaked whale .......................... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. High ........... Low. 

Rough-toothed dolphin ............ Low ............ Moderate ... High ........... High ........... Very low ..... Very low ..... Very low ..... Low ............ Very low. 

Bottlenose dolphin ................... Low ............ Low ............ High ........... Moderate ... Very low ..... Very low ..... Very low ..... Very low ..... Very low. 

Clymene dolphin ...................... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Moderate ... Low. 

Atlantic spotted dolphin ........... Low ............ Moderate .... High ........... High ........... Very low ..... Very low ..... Very low ..... Very low ..... Very low. 

Pantropical spotted dolphin ..... Low ............ n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Very low ..... Very low. 

Spinner dolphin ........................ Very low ..... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Very low ..... Very low. 

Striped dolphin ......................... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Low ............ Very low. 

Fraser’s dolphin ....................... Low ............ Low ............ High ........... Moderate ... n/a .............. n/a .............. n/a .............. Low ............ Very low. 

Risso’s dolphin ......................... Low ............ n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Very low ..... Very low. 

Melon-headed whale ............... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Moderate .... Moderate. 

Pygmy killer whale ................... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Low ............ Very low. 

False killer whale ..................... Low ............ Low ............ Moderate ... Moderate .... Very low ..... Very low ..... Very low ..... Very low ..... Very low. 

Killer whale .............................. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Low ............ Very low. 

Short-finned pilot whale ........... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. Low ............ Very low. 

n/a = no activity projected for zone or five or less individuals predicted in zone. 

1 No activity is projected in Zone 1 under the moderate and low activity scenarios, and no activity is projected in Zone 4 under the high activity scenario. 

TABLE 17—OVERALL EVALUATED RISK BY ZONE AND ACTIVITY SCENARIO

[Zones 5–7] 

Species 

Zone 5 Zone 6 Zone 7 

High Moderate Low High Moderate Low High Moderate Low 

Bryde’s whale .......................... Very high ... Very high ... Very high ... n/a .............. n/a .............. n/a .............. n/a .............. n/a .............. n/a. 

Sperm whale ............................ Very high ... Very high ... Very high ... Very high ... Very high ... High ........... Moderate ... Moderate .... Moderate. 

Kogia spp. ................................ High ........... High ........... Moderate ... Moderate .... Moderate ... Low ............ Moderate .... Low ............ Low. 

Beaked whale .......................... Very high ... Very high ... Very high ... High ........... Moderate .... Moderate .... High ........... High ........... High. 

Rough-toothed dolphin ............ High ........... High ........... Moderate .... Moderate .... Low ............ Low ............ Low ............ Low ............ Low. 

Bottlenose dolphin ................... High ........... High ........... Moderate ... Low ............ Very low ..... Very low ..... Low ............ Very low ..... Very low. 

Clymene dolphin ...................... High ........... High ........... Moderate ... Moderate .... Low ............ Low ............ Low ............ Low ............ Low. 

Atlantic spotted dolphin ........... High ........... High ........... High ........... Moderate .... Low ............ Low ............ n/a .............. n/a .............. n/a. 

Pantropical spotted dolphin ..... High ........... High ........... Moderate ... Moderate .... Low ............ Low ............ Low ............ Low ............ Low. 

Spinner dolphin ........................ High ........... High ........... Moderate .... Low ............ Very low ..... Very low ..... Low ............ Very low ..... Very low. 

Striped dolphin ......................... High ........... High ........... Moderate ... Moderate .... Low ............ Low ............ Low ............ Low ............ Low. 

Fraser’s dolphin ....................... High ........... High ........... Moderate ... Moderate .... Low ............ Low ............ Low ............ Low ............ Low. 

Risso’s dolphin ......................... High ........... High ........... High ........... Low ............ Very low ..... Very low ..... Very low ..... Very low ..... Very low. 

Melon-headed whale ............... High ........... High ........... Moderate ... Moderate .... Low ............ Low ............ Moderate .... Low ............ Low. 

Pygmy killer whale ................... High ........... High ........... Moderate ... Moderate .... Low ............ Low ............ Low ............ Low ............ Low. 

False killer whale ..................... High ........... High ........... Moderate .... Low ............ Very low ..... Very low ..... Low ............ Low ............ Low. 

Killer whale .............................. High ........... High ........... High ........... Moderate .... Low ............ Low ............ Low ............ Low ............ Low. 

Short-finned pilot whale ........... High ........... High ........... Moderate .... Moderate ... Low ............ Moderate .... Moderate .... Low ............ Low. 

n/a = no activity projected for zone or five or less individuals predicted in zone. 

TABLE 18—OVERALL EVALUATED RISK BY ACTIVITY SCENARIO, GOM-WIDE

Species High activity scenario Moderate activity 

scenario Low activity scenario 

Bryde’s whale .............................................................................. Moderate ........................ Moderate ........................ Moderate. 

Sperm whale ............................................................................... Very high ....................... High ............................... High. 

Kogia spp. ................................................................................... Moderate ........................ Low ................................ Low. 

Beaked whale .............................................................................. Very high ....................... High ............................... High. 

Rough-toothed dolphin ................................................................ Moderate ........................ Low ................................ Low. 

Bottlenose dolphin ....................................................................... Low ................................ Moderate ........................ Low. 

Clymene dolphin ......................................................................... Moderate ........................ Low ................................ Low. 

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

Pantropical spotted dolphin ......................................................... Moderate ........................ Low ................................ Low. 

Spinner dolphin ........................................................................... Low ................................ Low ................................ Low. 

Striped dolphin ............................................................................ Moderate ........................ Low ................................ Low. 

Fraser’s dolphin ........................................................................... Moderate ........................ Low ................................ Low. 

Risso’s dolphin ............................................................................ Moderate ........................ Low ................................ Low. 

Melon-headed whale ................................................................... Moderate ........................ Moderate ........................ Moderate. 

Pygmy killer whale ...................................................................... Moderate ........................ Low ................................ Low. 

False killer whale ........................................................................ Moderate ........................ Low ................................ Low. 

Killer whale .................................................................................. Moderate ........................ Low ................................ Low. 

Short-finned pilot whale .............................................................. Moderate ........................ Low ................................ Low. 


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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 5 and 6 were the only zones 

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

behavioral disturbance, identified for 

three species of particular concern in 

Zone 5 (Bryde’s, beaked, and sperm 

whales) and two in Zone 6 (beaked and 

sperm whales). Projected effort levels 

were sufficiently high in Zone 5 that the 

rankings were not generally sensitive to 

activity scenario, while in Zone 6 the 

highest rankings were associated with 

the high activity scenario. As 

particularly sensitive species, beaked 

whales and sperm whales consistently 

receive relatively high severity scores. 

Bryde’s whales receive very high 

vulnerability scoring across zones, due 

in large part to the differential 

susceptibility to masking, while sperm 

whales were also typically ranked as 

being highly vulnerable. Relatively high 

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. When considered across 

the entire GOM and all activity 

scenarios, the only species considered 

to have relatively high risk are the 

sperm whale and beaked whales, while 

the Bryde’s whale and melon-headed 

whales have relatively moderate risk. 

Although the scores generated by the 

EWG framework, and further aggregated 

across zones as described by NMFS 

above, are species-specific, additional 

stock-specific information can be 

gleaned through the zone-specific 

nature of the analysis in that, for 

example with bottlenose dolphins, the 

zones align with stock range edges. 

These species-specific risk scores are 

broadly applied in NMFS’s negligible 

impact analysis to all of the multiple 

stocks that are analyzed in this rule 

(Table 3), 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 ‘‘Proposed Mitigation’’ 

sections (e.g., coastal bottlenose 

dolphins were heavily impacted by the 

DWH oil spill and we have therefore 

recommended a time/area restriction to 

reduce impacts). 

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. However, 

this information is meaningful to an 

understanding of the likely severity of 

the exposure, which is relevant to the 

negligible impact evaluation, and is not 

directly incorporated into the risk 

assessment framework described above. 

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 behavioral 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 time in 

a 24-hr period that an animal would 

spend in this received level condition in 

Table 19. 

Additionally, as we discussed in the 

‘‘Estimated Take’’ section for Test 

Scenario 1, 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. 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. As with 

the duration of exposures discussed 

above, the number of repeated 

exposures is important to our 

understanding of the severity of effects. 

Specifically, for example, the ratio for 

beaked whales indicates that the 30-day 

modeling showed that approximately 10 

percent as many individual beaked 

whales could be expected to be exposed 

above harassment thresholds as was 

reflected in the results given by 

multiplying average 24-hr exposure 

results by the survey duration (i.e., 30 

days). 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 19 reflects the average days 

exposed above threshold for the 

indicated species having applied the 

scalar ratios described previously. 


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TABLE 19—TIME IN MINUTES (PER DAY) SPENT ABOVE 160 DB RMS SPL (50TH PERCENTILE) AND AVERAGE NUMBER OF

DAYS INDIVIDUALS EXPOSED ABOVE THRESHOLD DURING 30-DAY SURVEY

Species 

Survey type and time (min/day) above 160 dB rms Average number of days 

exposed 

above threshold during 30- 

day survey 2D 3D NAZ 3D WAZ Coil 

5.3 

Bryde’s whale ....................................................................... 5.1 11.8 4.6 19.5 2.4 

Sperm whale ........................................................................ 4.7 9.5 4.0 17.2 3.1 

Kogia spp. ............................................................................ 3.3 8.0 3.0 16.3 9.9 

Beaked whale ...................................................................... 4.8 10.1 4.0 20.3 3.5 

Rough-toothed dolphin ......................................................... 3.6 7.8 3.1 14.2 3.5 

Bottlenose dolphin ............................................................... 3.3 8.4 2.9 15.1 3.5 

Clymene dolphin .................................................................. 3.2 7.9 2.9 13.7 3.5 

Atlantic spotted dolphin ........................................................ 5.5 12.8 5.0 23.6 3.5 

Pantropical spotted dolphin ................................................. 3.2 7.9 2.9 13.7 3.5 

Spinner dolphin .................................................................... 3.2 7.9 2.9 13.7 3.5 

Striped dolphin ..................................................................... 3.2 7.9 2.9 13.7 3.5 

Fraser’s dolphin ................................................................... 3.3 8.0 3.0 16.3 3.5 

Risso’s dolphin ..................................................................... 4.5 10.9 3.9 18.6 3.5 

Melon-headed whale ............................................................ 3.3 8.0 3.0 16.3 3.1 

Pygmy killer whale ............................................................... 3.6 7.7 3.1 14.2 3.1 

False killer whale ................................................................. 3.6 7.7 3.1 14.2 3.1 

Killer whale ........................................................................... 9.3 23.3 8.0 35.4 3.1 

Short-finned pilot whale ....................................................... 3.3 8.0 3.0 14.7 3.1 

We expect that Level A harassment 

could occur for low-frequency species 

(i.e., Bryde’s whale)—due to these 

species’ heightened sensitivity to 

frequencies in the range output by 

airguns, as shown by their auditory 

weighting function—and for highfrequency species, due to their 

heightened sensitivity to noise in 

general (as shown by their lower 

threshold for the onset of PTS) (NMFS, 

2016). However, to the extent that Level 

A harassment occurs it will be in the 

form of PTS, and the degree of injury is 

expected to be mild. If hearing 

impairment occurs, it is most likely that 

the affected animal would lose a few dB 

in its hearing sensitivity, which in most 

cases is not likely to affect its ability to 

survive and reproduce. Hearing 

impairment that occurs for these 

individual animals would be limited to 

at and slightly above the dominant 

frequency of the noise sources, i.e., in 

the low-frequency region below 2–4 

kHz. Therefore, the degree of PTS is not 

likely to affect the echolocation 

performance of the Kogia spp., which 

use frequencies between 60–120 kHz 

(Wartzok and Ketten, 1999). 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. For Kogia spp., because of 

expected sensitivity, we expect that 

aversion may play a stronger role in 

avoiding exposures above the peak 

pressure threshold than we have 

accounted for. For these reasons, and in 

conjunction with our proposed 

mitigation plan, we do not believe that 

Level A harassment will play a 

meaningful role in the overall degree of 

impact experienced by marine mammal 

populations as a result of the projected 

survey activity. 

We consider the relative impact 

ratings described above in conjunction 

with our proposed mitigation and other 

relevant contextual information in order 

to produce a final assessment of impact 

to the stock or species, i.e., our 

preliminary negligible impact 

determination. Annual levels of humancaused mortality are less than PBR for 

all GOM stocks aside from the Bryde’s 

whale and, for most species, are zero 

(Hayes et al., 2017). The effects of the 

DWH oil spill, which is not reflected in 

NMFS’s published values for annual 

human-caused mortality, are accounted 

for through our vulnerability scoring 

(Table 14). We developed mitigation 

requirements, including time-area 

restrictions, designed specifically to 

provide benefit to certain populations 

for which we predict a relatively high 

amount of risk in relation to exposure to 

survey noise. The proposed time-area 

restrictions, described in detail in 

‘‘Proposed Mitigation’’ and depicted in 

Figure 5, are 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. In addition, we expect these 

areas to provide some subsidiary benefit 

to additional species that may be 

present. The Atlantic spotted dolphin 

would also benefit from the coastal 

restriction proposed for bottlenose 

dolphins, and multiple shelf-break 

associated species would benefit from 

both the Bryde’s whale and Dry 

Tortugas restrictions. The output of the 

Roberts et al. (2016) models, as used in 

core abundance area analyses (described 

in detail in ‘‘Proposed Mitigation’’), 

provides information about species most 

likely to derive subsidiary benefit from 

the proposed restrictions. Notably, high 

densities of Kogia spp. are predicted in 

the area of the Dry Tortugas restriction. 

Other shelf-break/pelagic species that 

are abundant in the eastern GOM 

include the melon-headed whale, 

Risso’s dolphin, and rough-toothed 

dolphin, but numerous other species 

would be expected to be present in 

varying numbers at various times. 

These proposed measures benefit both 

the primary species for which they were 

designed and the species that may 

benefit secondarily by likely reducing 


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the number of individuals exposed to 

survey noise and, for resident species in 

areas where seasonal restrictions are 

proposed, reducing the numbers of 

times that individuals are exposed to 

survey noise. However, and perhaps of 

greater importance, we expect that these 

restrictions will reduce disturbance of 

these species in the places most 

important to them for critical behaviors 

such as foraging and socialization. The 

Bryde’s whale area is the only known 

habitat of the species in the GOM, while 

the Dry Tortugas area is assumed to be 

an area important for beaked whale 

foraging and sperm whale reproduction. 

The coastal restriction would provide 

protection for the bottlenose dolphin 

populations most severely impacted by 

the DWH oil spill during a time of 

importance for reproduction. Further 

detail regarding rationale for these 

restrictions is provided under 

‘‘Proposed Mitigation.’’ 

The endangered sperm whale and the 

Bryde’s whale received special 

consideration in our development of 

proposed mitigation. The alternative of 

a year-round closure alternative with a 

6-km buffer is designed to avoid impacts 

to the Bryde’s whale by completely 

avoiding known habitat. Survey 

activities must avoid all areas where the 

Bryde’s whale is found, and we propose 

to require shutdown of the acoustic 

source upon observation of any Bryde’s 

whale at any distance. The Bryde’s 

whale is proposed for listing as 

endangered, has a very low population 

size, is more sensitive to the low 

frequencies output by airguns, and faces 

significant additional stressors. 

Therefore, regardless of impact rating, 

we believe that the year-round closure 

alternative and 6-km buffer described 

previously would allow us to make the 

necessary negligible impact finding. We 

preliminarily find, were this alternative 

finalized, that the total potential marine 

mammal take from the projected survey 

activities will have a negligible impact 

on the Bryde’s whale. 

While the economic analysis 

accompanying this proposed rule 

indicates that a CPA restriction 

benefiting sperm whales would not be 

practicable, we propose to require a 

shutdown of the acoustic source upon 

any acoustic detection of sperm whales. 

We also propose shutdown 

requirements upon any detection of 

beaked whales or Kogia spp. (although 

these two species are rarely detected 

visually). If the observed animal is 

within the behavioral harassment zone, 

it would still be considered to have 

experienced harassment, but by 

immediately shutting down the acoustic 

source the duration and degree of 

disruption is minimized and the 

significance of the harassment event 

reduced as much as possible. Therefore, 

in consideration of the proposed 

mitigation, we preliminarily find that 

the total potential marine mammal take 

from the projected survey activities will 

have a negligible impact on the sperm 

whale, beaked whales, and Kogia spp. 

The risk assessment process rates 

impacts as moderate or less for all other 

affected species. Therefore, in 

consideration of the proposed 

mitigation, we preliminarily find that 

the total potential marine mammal take 

from the projected survey activities will 

have a negligible impact on all other 

affected species, including all affected 

stocks of bottlenose dolphin. 

In summary and as described above, 

the following factors primarily support 

our preliminary determination that the 

impacts resulting from this activity are 

not expected to adversely affect the 

affected species or stocks through effects 

on annual rates of recruitment or 

survival: 

• No mortality is anticipated or 

authorized; 

• Level A harassment not expected for 

species other than Bryde’s whale and Kogia 

spp., and not expected to be a meaningful 

source of harm for these species; 

• Risk assessment process rates impacts as 

moderate or less, for most species in most 

places and higher risk species have 

associated mitigation to lessen impacts; 

• Known habitat for Bryde’s whales 

protected; 

• Shutdown requirements for species of 

concern (Bryde’s whale, sperm whale, beaked 

whales, Kogia spp.); and 

• Modeling resulted in daily exposures 

totaling 3–35 minutes, which, in most 

situations, is likely insufficient time to result 

in disruptions of behavior that raise concerns 

about fitness consequences. 

Based on the analysis contained 

herein of the likely effects of the 

specified activity on marine mammals 

and their habitat, and taking into 

consideration the implementation of the 

proposed monitoring and mitigation 

measures, with a year-round closure in 

Bryde’s whale habitat (Area 3; Figure 5), 

we preliminarily find that the total 

marine mammal take from the proposed 

activity will have a negligible impact on 

all affected marine mammal species or 

stocks. 

Small Numbers 

What are small numbers? 

The MMPA does not define ‘‘small 

numbers.’’ NMFS’s and the U.S. Fish 

and Wildlife Service’s joint 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 now makes its small 

numbers findings based on an analysis 

of whether the number of individuals 

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, No. 

10–35123, 2012 WL 3570667 (9th Cir. 

Aug. 21, 2012). However, we have not 

previously indicated what we believe 

the upper limit of small numbers is. 

Here, we provide additional information 

and clarification regarding our 

consideration of small numbers 

pursuant to paragraphs (A) and (D) of 

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

To maintain an interpretation of small 

numbers as a proportion of a species or 

stock that does not conflate with 

negligible impact, we propose the 

following framework. A plain reading of 

‘‘small’’ implies as corollary that there 

also could be ‘‘medium’’ or ‘‘large’’ 

numbers of animals from the species or 

stock taken. We therefore propose a 

simple approach that establishes three 

equal bins corresponding to small, 

medium, and large numbers of animals: 

Small is comprised of 1–33 percent, 

medium 34–66 percent, and large 67– 

100 percent of the population 

abundance. 

NMFS’s practice for making small 

numbers determinations is to compare 

the number of individuals estimated to 

be taken against the best available 

abundance estimate for that species or 

stock. Although NMFS’s implementing 

regulations require applications for 

incidental take to include an estimate of 

the marine mammals to be taken, there 

is nothing in paragraphs (A) or (D) of 

section 101(a)(5) that requires NMFS to 

quantify or estimate numbers of marine 

mammals to be taken for purposes of 

evaluating whether the number is small. 


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While 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 and are unable to 

account for repeated exposures of 

individuals), in some cases we are able 

to generate a reasonable estimate 

utilizing a combination of quantitative 

tools and qualitative information. When 

it is possible to predict with relative 

confidence the number of individual 

marine mammals of each species or 

stock that are likely to be taken, we 

recommend the small numbers 

determination be based directly upon 

whether or not these estimates exceed 

one third of the stock abundance. In 

other words, as in past practice, when 

the estimated number of animals is up 

to, but generally not greater than, one 

third of the species or stock abundance, 

NMFS will determine that the numbers 

of marine mammals of a species or stock 

are small. 

When sufficient quantitative 

information is not available to estimate 

the number of individuals that might be 

taken (typically due to insufficient 

information about presence, density, or 

daily or seasonal movement patterns of 

the species in an area), we consider 

other factors, such as the spatial scale of 

the specified activity footprint as 

compared with the range of the affected 

species or stock and/or the duration of 

the activity in order to infer the relative 

proportion of the affected species or 

stock that might reasonably be expected 

to be taken by the activity. For example, 

an activity that is limited to a small 

spatial scale (e.g., a coastal construction 

project or HRG survey) and relatively 

short duration might not be expected to 

result in take of more than a small 

number of a comparatively widerranging species. Unlike direct 

quantitative modeling of a number of 

individuals taken, this comparison may 

necessitate the presentation of some 

additional information and logical 

inferences to make a small numbers 

determination. 

Another circumstance in which 

NMFS considers it appropriate to make 

a small numbers finding in the absence 

of a quantitative estimate 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) could reasonably be considered 

small numbers, regardless of 

consideration of the proportion of the 

stock (if known), as rare brief 

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 would consider 

it to be of small numbers. When 

quantitative take estimates are not 

available, NMFS will examine other 

factors, such as the spatial extent of the 

take zone compared to the species or 

stock range and/or the duration of the 

activity to determine if the take will 

likely be small relative to the abundance 

of the affected species or stocks. Last, 

NMFS may 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. 

How is the small numbers standard 

evaluated within the structure of the 

section 101(a)(5)(A) process? 

Neither the MMPA nor NMFS’s 

implementing regulations address 

whether the small numbers 

determination should be based upon the 

total annual taking for all activities 

occurring under incidental take 

regulations or 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. NMFS has 

not previously made a clear and 

deliberate policy choice or specifically 

explored applying the small numbers 

finding to each individual LOA under 

regulations that cover multiple 

concurrent LOA holders. Here we 

propose a reasonable interpretation of 

how to make a small numbers 

determination based on a permissible 

interpretation of the statute. 

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. As the 

provision is structured, the small 

numbers language is not framed as a 

standard for the issuance of the 

authorization, but rather appears in the 

chapeau 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’s discretion in light of 

the ambiguities in the statute regarding 

how to apply the small numbers 

standard, and the clear benefits of 

application as described here, we have 

determined that the small numbers 

finding should be applied to the annual 

take authorized in each LOA. To 

demonstrate why this approach is 

preferred, we first describe below why 

it is beneficial to NMFS, the public, and 

the resource (marine mammals) to 

utilize section 101(a)(5)(A) for multiple 

activities, where possible. 

• From a resource protection standpoint, it 

is more protective to conduct a 

comprehensive negligible impact analysis 

that considers all of the activities covered 

under the rule 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 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 an IHA. 

• 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, especially for situations 

like here, where multiple applicants will be 

applying for individual LOAs under 

regulations. In the case of this proposed rule, 

the certainty afforded by the promulgation of 

a regulatory framework (e.g., by using 

previously established take estimates, 

mitigation and monitoring requirements, and 

procedures for requesting and obtaining an 

LOA) is a significant benefit for prospective 

applicants. 

A review of IHAs we have issued 

suggests that bundling together 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) would 

very often result in greater than small 

numbers of one or more species being 

taken if we were to apply the small 

numbers standard across all activity 

contemplated by the regulation in a 


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year, thereby precluding the use of 

section 101(a)(5)(A) in many cases. 

Application of the small numbers 

standard across the total annual taking 

covered by regulations, inasmuch as 

potential applicants can see that the 

total take may exceed one third of 

species or stock abundance, creates an 

incentive for applicants to pursue 

individual IHAs, and will often 

preclude the ability to gain the benefits 

of regulations 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, 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. 

Although this application of small 

numbers may be argued as being less 

protective of marine mammals, NMFS 

disagrees. As specifically differentiated 

from the negligible impact finding, the 

small numbers standard has little 

biological relevance. The negligible 

impact determination, which does have 

biological significance, is still 

controlling, and the total annual taking 

authorized across all LOAs under an 

incidental take regulation still could not 

exceed the overall amount analyzed for 

the negligible impact determination. 

Moreover, to the extent that this process 

is perceived as less protective than 

applying the small numbers standard 

across all activity occurring annually 

under the regulations (in that the small 

numbers standard can be met more 

readily under our proposed approach), 

that perception ignores the fact that 

applicants could always opt to pursue 

an IHA to circumvent a more restrictive 

approach to applying small numbers 

under section 101(A)(5)(A) (in cases 

where there is no serious injury or 

mortality). 

How will small numbers be evaluated 

under this proposed GOM rule? 

In this proposed 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 proposed activities. LOA 

applications that do not use the 

modeling provided in the rule to 

estimate take for their activities will 

need to be independently reviewed, and 

applicants will be required to ensure 

that their estimates adequately inform 

the small numbers finding. 

Additionally, if applicants use the 

modeling provided by this rule to 

estimate take, additional public input 

will not be deemed necessary (unless 

other conditions necessitating public 

review exist, as described in the ‘‘Letters 

of Authorization’’ section); if they do 

not, however, NMFS will publish a 

notice in the Federal Register soliciting 

public comment. 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 would 

contain an adaptive management 

component. The comprehensive 

reporting requirements associated with 

this proposed rule (see the ‘‘Proposed 

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 an annual or biennial 

basis if mitigation or monitoring 

measures should be modified (including 

additions or deletions). Mitigation 

measures could be modified if new data 

suggests that such modifications would 

have a reasonable likelihood of 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 by these 

regulations or subsequent LOAs or that 

the specified activity may be having 

more than a negligible impact on 

affected stocks. 

Under this proposed rule, NMFS 

proposes an annual adaptive 

management process involving BOEM, 

BSEE, and industry operators (including 

geophysical companies as well as 

exploration and production companies). 

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 

agreed-upon description of roles and 

responsibilities, as well as points of 

contact, in advance of each year’s 

adaptive management process. The 

foundation of the adaptive management 

process would 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 below 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’s 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 would occur on 

an ongoing basis, per the terms of issued 

LOAs. In a given annual cycle, we 

propose that the comprehensive annual 

report would summarize and synthesize 

the LOA-specific reports received from 


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July 1 of one year through June 30 of the 

next, with report development 

(supported through collaboration of 

individual LOA-holders or by their 

representatives) occurring from July 1 

through September 30 of a given year. 

Review and revision of the report, 

followed by a joint meeting of the 

parties, would occur between October 1 

and December 31 of each year. Any 

agreed-upon modifications would occur 

through the process for modifications 

and/or adaptive management described 

in the proposed regulatory text 

following this preamble. 

Monitoring Contribution Through Other 

Research 

NMFS’s 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. We expect 

that relevant research efforts will inform 

the annual adaptive management 

process describe 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. Here, we describe examples 

of relevant research efforts, which 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. 

Industry—In 2006, several exploration 

and production (E&P) companies and 

industry associations began a multi-year 

research program known as the E&P 

Sound and Marine Life Joint Industry 

Program (JIP). The aim of the program 

was to advance scientific understanding 

of the effects of sound generated by 

offshore oil and gas industry operations 

on living marine resources, including 

marine mammals. Since its inception, 

the JIP, the largest nongovernmental 

funder of research on this topic, has 

allocated $55 million to fund a wide 

range of different projects. The JIP 

website (www.soundandmarinelife.org) 

hosts a database of available products 

funded partially or fully through the JIP. 

As of June 2017, this database contained 

records for 133 JIP data products, 

including 41 project reports and 83 

peer-reviewed publications, as well as 

the other notable products mentioned 

below. JIP policies stipulate that the 

research results be shared in public 

reports and submitted to peer-reviewed 

scientific journals to ensure maximum 

transparency and value to the wider 

research, stakeholder, and regulatory 

communities. JIP-funded projects and 

products are organized into six research 

categories: (1) Sound source 

characterization; (2) physical and 

physiological effects and hearing; (3) 

behavioral reactions and biologically 

significant effects; (4) mitigation and 

monitoring; (5) research tools; and (6) 

communication. Below, we summarize 

certain key studies as well as additional 

initiatives that are planned or underway 

(note that this is a small sample of 

studies and that not all of the initiatives 

described below have been funded 

through the JIP). 

• Analyses of existing PSO data: The GOM 

is one of three regions currently being 

reviewed under a JIP contract, initiated in 

2016, to assess the utility of existing PSO 

data. Visual PSO and PAM data through 2015 

are being examined for quality and 

consistency, and assessments will be made 

about the data’s utility in the validation of 

risk modeling, assessing behavioral 

responses, and the potential for deriving 

animal density and distribution information. 

This work will complement and reinforce 

similar efforts by BOEM (see below). An 

earlier JIP study resulted in standardizing the 

basic data recording formats used by vessel 

operators in the UK and other jurisdictions 

(jncc.defra.gov.uk/page-1534). 

• Acoustic measurements and modeling: 

The JIP has funded measurement of the 

acoustic output of both single airgun sources 

as well as airgun arrays that help increase 

confidence in the source and propagation 

models used in the GOM. These include 

extensive near-field, mid-field, and far-field 

in-water acoustic measurements (conducted 

in Norwegian waters in 2007–2010) of the 

most commonly used single-source and twoelement configurations over a range of 

volumes, depths, and pressures with the 

objective of measuring acoustic output at 

higher frequencies up to 50 kHz. More 

recently, measurements of the sound field 

from a fully operational airgun array in the 

GOM have been completed, with fully 

analyzed data products anticipated in 2018. 

Additionally, the JIP is funding work into the 

development of standard procedures for 

underwater noise measurements for activities 

related to offshore oil and gas exploration 

and production, to ensure that processing of 

selected acoustic metrics used to describe the 

characteristics of a sound signal propagating 

in water can be analyzed in a consistent and 

systematic manner, and is funding a review 

of available marine acoustic propagation 

models. 

• PAMGuard: Industry has funded ongoing 

development and at-sea testing of this nowstandard, open source real-time PAM 

software to improve mitigation capabilities 

during operations. More information and the 

software itself is available online at 

www.pamguard.org. 

• Alternative technology: Pursuant to the 

terms of a settlement agreement (as amended) 

concerning pending litigation between the 

Natural Resources Defense Council et al. and 

the Department of Interior (joined by 

industry as intervenor-defendants) (NRDC et 

al. v. Zinke et al., Civil Action No. 2:10 cv01882 (E.D. La.)), industry has conducted a 

study of vibroseis technology, including 

construction and testing of prototypes. 

Development of vibroseis technology is 

promising in terms of reducing potential 

harm to marine mammals because the system 

outputs lower peak amplitude, and 

consequently less high-frequency energy, 

while maintaining the main bandwidth 

necessary for seismic data acquisition. 

• Advanced dive behavior tag technology 

development: The JIP co-funded, with 

BOEM’s predecessor agency (MMS) and the 

U.S. Navy’s Office of Naval Research (ONR), 

initial development of advanced dive 

behavior tracking technology that has been 

used to study sperm whale diving and 

foraging behavior in the GOM. 

• Effects of sound on marine mammal 

hearing: The JIP funds multiple hearing 

research projects specifically focused on 

defining the impacts of seismic sound 

sources on the hearing systems of various 

marine mammal species, e.g., TTS, TTS 

growth, and masking in bottlenose dolphins 

and harbor porpoise. For example, the JIP 

funded research by the U.S. Navy’s Marine 

Mammal Program that specifically examined 

the physiological effect of airgun sound on 

hearing in bottlenose dolphins by measuring 

TTS after exposure to multiple seismic 

pulses (Finneran et al., 2015). New and 

ongoing studies are aimed at developing an 

understanding of the role of hearing recovery 

between exposures from intermittent sound 

sources, like airguns, in the process of TTS 

generation, as well as developing TTS growth 

functions to better refine TTS/PTS threshold 

relationships. The JIP has also funded 

research into modeling work to better 

estimate baleen whale hearing. 

• Behavioral response study: The JIP and 

BOEM jointly funded a study examining how 

humpback whales respond to airgun sound 

in general and to the ramp-up procedure 

specifically (Behavioral Response of 

Australian Humpback Whales to Seismic 

Surveys (BRAHSS)). The experimental design 

progressed from using a single airgun source 

to a fully operational commercial array with 

a ramp-up procedure, and involved treatment 

and control groups, a pre-trial statistical 

power analysis, a range of exposures, and a 

four-stage ramp-up design. For more details 

of the study and results, please see Cato et 

al. (2013) and Dunlop et al. (2013, 2015, 

2016, 2017). 

BOEM—BOEM’s Environmental 

Studies Program (ESP) develops, funds, 

and manages scientific research to 

inform policy decisions regarding OCS 

resource development. These 

environmental studies cover a broad 

range of disciplines, including physical 


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oceanography, biology, protected 

species, and the environmental impacts 

of energy development. Through the 

ESP, BOEM is a leading contributor to 

the growing body of scientific 

knowledge about the marine and coastal 

environment. BOEM and its predecessor 

agencies have funded more than $1 

billion in research since the studies 

program began in 1973. Technical 

summaries of more than 1,200 BOEMsponsored environmental research 

projects and more than 3,400 research 

reports are publicly available online 

through the Environmental Studies 

Program Information System (ESPIS). 

Below, we summarize certain key 

studies, as well as additional initiatives 

that are planned or underway. For the 

latest information on BOEM’s ongoing 

environmental studies work, please visit 

www.boem.gov/studies. 

• Analyses of existing PSO data: MMS 

previously funded an analysis of GOM PSO 

data from 2002–2008 (Barkaszi et al., 2012), 

and BOEM has currently contracted for 

additional analyses of PSO data from 2009– 

2015. 

• Development of PAM standards: As 

discussed in ‘‘Proposed Monitoring and 

Reporting,’’ BSEE is working with Scripps 

Institute of Oceanography to develop 

standards for towed PAM systems. 

• Passive acoustic monitoring: BOEM is 

funding a fixed PAM array for 5 years. 

Hydrophones will be deployed, maintained, 

and redeployed on a regular schedule 

throughout the GOM. Placement will include 

shelf, slope and deep water depths as well as 

all planning areas in order to gather a 

comprehensive data set representative of the 

entire GOM. This program is expected to 

establish a relative baseline for ambient noise 

in the GOM against which to evaluate 

potential future noise impacts from permitted 

activities as well as characterize the sound 

budget from other kinds of noise already 

occurring in the GOM (e.g., shipping). In 

addition, acoustic recorders will be able to 

detect vocalizing marine mammals, 

providing both spatial and temporal 

information about cetacean species in the 

GOM. 

• Sperm whale studies: The Sperm Whale 

Acoustic Monitoring Program (SWAMP) 

began in 2000 with joint support from MMS, 

ONR, and NMFS and laid the groundwork for 

future study by developing new methods for 

studying sperm whale behavior and their 

responses to sound. Subsequently, the Sperm 

Whale Seismic Study (SWSS) began in 2002 

to evaluate potential effects of geophysical 

exploration on sperm whales in the GOM 

(e.g., Jochens et al., 2008). SWSS included 

support from MMS, ONR, the National 

Science Foundation (NSF), and a coalition of 

industry funders. In 2009, MMS (through an 

interagency agreement with NMFS) began the 

Sperm Whale Acoustic Prey Study (SWAPS), 

which studied how airgun noise may affect 

sperm whale prey species (e.g., squid and 

small pelagic fish). 

• GoMMAPPS: BOEM is supporting a 

multi-year, multi-disciplinary study of 

marine protected species in the GOM (Gulf 

of Mexico Marine Assessment Program for 

Protected Species (GoMMAPPS)), which is 

patterned after the successful Atlantic Marine 

Assessment Program for Protected Species 

(AMAPPS) that began in 2010 and has 

provided valuable information on the 

seasonal distribution and abundance of 

protected species in U.S. waters of the 

Atlantic Ocean. The overall goals are to 

improve our understanding of living marine 

resource abundance, distribution, habitat use, 

and behavior in the GOM to facilitate 

appropriate mitigation and monitoring of 

potential impacts from human activities, 

including geophysical survey activities. The 

study will utilize a variety of methods, 

depending on target species, including aerial 

surveys, shipboard surveys, satellite tagging 

and tracking, and genetic analyses. 

GoMMAPPS is a joint partnership of BOEM, 

NMFS, the U.S. Fish and Wildlife Service, 

and the U.S. Geological Survey. More 

information is available online at 

(www.boem.gov/GOMMAPPS/). 

• Workshops: BOEM has funded various 

workshops, including a 2012 workshop 

focused on mitigation and monitoring 

associated with seismic surveys and a 2013 

workshop concerning quieting technologies 

for reducing noise during seismic surveying 

(BOEM, 2014). 

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, we have determined 

that the total taking of affected species 

or stocks would 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(a)(2) of the Endangered 

Species Act of 1973 (16 U.S.C. 1531 et 

seq.) requires that each Federal agency 

insure that any action it authorizes, 

funds, or carries out is not likely to 

jeopardize the continued existence of 

any endangered or threatened species or 

result in the destruction or adverse 

modification of designated critical 

habitat. To ensure ESA compliance for 

the promulgation of regulations and 

potential issuance of LOAs, NMFS 

consults internally whenever we 

propose to authorize take for ESA-listed 

marine mammal species. The sperm 

whale is listed as endangered under the 

ESA, and the GOM Bryde’s whale has 

been proposed to be listed as 

endangered. Consultation under section 

7 of the ESA will be concluded prior to 

issuance of any final incidental take 

regulations. 

Letters of Authorization 

Under issued incidental take 

regulations, industry operators would be 

able to apply for and obtain LOAs, as 

described in NMFS’s MMPA 

implementing regulations (50 CFR 

216.106). LOAs may be issued for 

multiple years, depending on the degree 

of specificity with which an operator 

can describe their planned survey 

activities. 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 annual 

estimated take, per zone and per 

species, would serve as a cap on the 

number of authorizations that could be 

issued. Applicants may choose to 

present additional information in a 

request for LOA, e.g., independent 

exposure estimates, description of 

proposed mitigation and monitoring (if 

more stringent than the requirements in 

issued regulations). However, such 

additional information would be subject 

to NMFS review and approval as well as 

public review via a 30-day comment 

period prior to issuance. Any 

substantive departure from the activity 

and exposure estimation parameters 

described here and which form the basis 

for our preliminary determinations 

would be subject to public review. 

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, would be evaluated on a caseby-case 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, we propose to 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 


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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. 

We would consult with BOEM as well as 

with NMFS’s Endangered Species Act 

Interagency Cooperation Division regarding 

the level of review necessary for issuance of 

an LOA in which a NUT is proposed for use. 

Alternative Regulatory Text 

Please see Table 11 for a summary of 

mitigation measures with alternatives 

for consideration, for which alternative 

regulatory text is presented here. 

Area Restriction 

• Based on our analyses-to-date 

(‘‘Proposed Mitigation’’ and ‘‘Negligible 

Impact Analysis and Preliminary 

Determination’’), we evaluated a year-round 

restriction on airgun surveys in Area 3 

(Figure 5), and our preliminary finding of 

negligible impact on the Gulf of Mexico stock 

of Bryde’s whale is based on a year-round 

restriction in this area. Alternative regulatory 

text at § 217.184(e)(2) for this proposal would 

read: ‘‘No use of airguns may occur within 

the area bounded by the 100- and 400-m 

isobaths, from 87.5° W to 27.5° N (buffered 

by 6 km).’’ 

For our proposals of no restriction or 

a seasonal restriction, but with the 

addition of a requirement for BOEM 

and/or members or representatives of 

the oil and gas industry to ensure realtime detection of Bryde’s whales across 

the area of potential impact including 

real-time communication of detections 

to survey operators, which would be 

used to initiate shutdowns to ensure 

that survey operations do not take place 

when a Bryde’s whale is within 6 km of 

the acoustic source, the proposed 

regulatory text would be the following. 

For the three-month restriction, we are 

proposing using a moored listening 

array and thus the alternative regulatory 

text at § 217.184(e)(2) would read: ‘‘No 

use of airguns may occur within the area 

bounded by the 100- and 400-m 

isobaths, from 87.5° W to 27.5° N 

(buffered by 6 km), during June through 

August. During September through May, 

LOA-holders conducting airgun surveys 

must monitor the area of potential 

impact using a moored passive listening 

array and may not use airguns when 

Bryde’s whales are detected within 6 km 

of the acoustic source.’’ For no 

restriction plus a requirement of realtime detection using the moored array 

in the area of impact alone, alternative 

regulatory text at § 217.184(e)(2) would 

read: ‘‘In the area bounded by the 100- 

and 400-m isobaths, from 87.5° W to 

27.5° N (buffered by 6 km), LOA-holders 

conducting airgun surveys must monitor 

a moored passive listening array and 

may not use airguns when a confirmed 

or potential Bryde’s whale is detected 

within 6 km of the acoustic source.’’ 

The proposal of a three-month 

seasonal restriction on airgun surveys in 

Area 3 with no additional monitoring 

requirement is included in the 

regulatory text at the end of this 

document, following the preamble. 

As mentioned in the ‘‘Proposed 

Mitigation’’ section, we are interested in 

public comment on these proposals, 

including any data that may support the 

necessary findings regarding potential 

impacts to the GOM Bryde’s whale for 

these proposals, as well as any 

additional alternative proposals that 

could vary the time period or length of 

seasonal closure from what NMFS has 

proposed. 

Shutdowns 

For the proposal requiring shutdown 

upon a confirmed acoustic detection of 

sperm whales within 1 km or upon a 

confirmed visual or acoustic detection 

of Bryde’s whales, large whales with 

calf, beaked whales, or Kogia spp. 

within 1 km, the regulatory text at 

§ 217.184(b)(6) would read: ‘‘Buffer 

Zone and Exclusion Zone—The PSOs 

shall establish and monitor a 500-m 

exclusion zone and additional 500-m 

buffer to the exclusion zone. For all 

confirmed detections of baleen whales, 

beaked whales, and Kogia spp., and for 

confirmed acoustic detections of sperm 

whales, the full 1,000-m zone shall 

function as an exclusion zone. 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) shall be communicated 

to the operator to prepare for the 

potential shutdown of the acoustic 

source. PSOs must monitor the 1,000-m 

zone for a minimum of 30 minutes prior 

to ramp-up (i.e., pre-clearance).’’ 

Regulatory text at § 217.184(b)(8)(ii) 

would read: ‘‘Upon completion of rampup, if a marine mammal appears within, 

enters, or appears on a course to enter 

the exclusion zone, the acoustic source 

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

acoustic source must be immediately 

turned off). If a marine mammal 

(excluding delphinids) is detected 

acoustically and is determined to be 

within 1 km of the acoustic source, the 

acoustic source must be shut down.’’ 

Regulatory text at § 217.184(b)(8)(iv) 

would read: ‘‘Shutdown of the acoustic 

source is required upon detection 

(visual or acoustic) of a baleen whale, 

beaked whale, or Kogia spp. within 1 

km.’’ 

For the proposal waiving the 

shutdown or power-down requirement 

upon detection of small dolphins within 

a 500-m exclusion zone, regulatory text 

at § 217.184(b)(8)(iii) would read: ‘‘This 

shutdown requirement is waived for 

dolphins of the following genera: 

Tursiops, Stenella, Steno, and 

Lagenodelphis. If there is uncertainty 

regarding identification (i.e., whether 

the observed animal(s) belongs to the 

group described above), shutdown must 

be implemented.’’ 

The other proposals discussed in the 

‘‘Proposed Mitigation’’ section for 

detection of Bryde’s whales, beaked 

whales, sperm whales, Kogia spp., and 

small dolphins are included in the 

regulatory text following the preamble. 

As mentioned in the ‘‘Proposed 

Mitigation’’ section, we are interested in 

public comment on these proposals. 

Scope of the Rule 

NMFS requests comment on the 

issuance of incidental take regulations 

that do not apply to BOEM’s Eastern 

Planning Area. In the regulatory text, 

217.180(b) would be replaced with the 

following text: ‘‘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 the Bureau of Ocean Energy 

Management’s Western or Central 

Planning Areas in the Gulf of Mexico.’’ 

Under this alternative scope, NMFS 

would continue working on a 

programmatic approach to the 

authorization of take incidental to 

geophysical survey operations in the 

Eastern Planning Area, but applicants 

could apply for individual permits 

(IHAs) until that process is completed. 

This revision of scope, if it occurred, 

would result in less impacts to affected 

species or stocks of marine mammals 

relative to what was considered in the 

analyses presented previously in this 

preamble. Based on the analysis 

included in the preceding sections, if no 

other changes are made to the scope of 

the rule or the required mitigation 

measures analyzed in the preceding 

sections (i.e., the measures are not 

modified as considered above in this 

Alternatives for Consideration section), 

we preliminarily find that the total 

marine mammal take from the proposed 

activity (reflecting the revised scope 

considered here) will have a negligible 

impact on all affected marine mammal 

species or stocks and the mitigation 


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measures included would effect the 

least practicable adverse impact on the 

affected species and stocks and their 

habitat. 

Request for Information 

NMFS requests interested persons to 

submit comments, information, and 

suggestions concerning 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 (www.fisheries.noaa.gov/ 

national/marine-mammal-protection/ 

incidental-take-authorizations-oil-andgas) (see ADDRESSES). All comments will 

be reviewed and evaluated as we 

prepare the final rule. This proposed 

rule and referenced documents provide 

all environmental information relating 

to our proposed action for public 

review. 

Classification 

Pursuant to the procedures 

established to implement Executive 

Order 12866, the Office of Management 

and Budget has determined that this 

proposed rule is significant. 

Accordingly, a regulatory impact 

analysis (RIA) has been prepared and is 

available for review online at: 

www.fisheries.noaa.gov/national/ 

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

RIA evaluates the potential costs and 

benefits of these proposed incidental 

take regulations, as well as a more 

stringent alternative, against two 

baselines. The baselines correspond 

with regulatory requirements associated 

with management of geophysical survey 

activity in the GOM prior to 2013 

(pursuant to BOEM’s authorities under 

the Outer Continental Shelf Lands Act) 

and conditions in place since 2013 

pursuant to a settlement agreement, as 

amended through stipulated agreement, 

involving a stay of litigation (NRDC et 

al. v. Zinke et al., Civil Action No. 2:10 

cv–01882 (E.D. La.)). 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. As described 

previously in this preamble (‘‘Economic 

Baseline’’), NMFS is seeking comment 

on the most appropriate baseline against 

which to measure the costs and benefits 

of the proposed regulatory action. 

The proposed rule would require new 

mitigation measures relative to the 

baseline and, thus, new costs for survey 

operators. However, the proposed rule 

would also alleviate the regulatory 

burden of implementing minimum 

separation distance requirements for 

deep penetration airgun surveys. The 

proposed rule also would result in 

indirect (but non-monetized) costs as a 

result of the proposed time-area 

restrictions. However, we do not believe 

that these would be significant, as 

described in the RIA and in the 

‘‘Proposed Mitigation’’ section. 

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 proposed rule would also result 

in certain non-monetized benefits. The 

protection of marine mammals afforded 

by this rule (pursuant to the 

requirements of the MMPA) would 

benefit 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 proposed 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, it 

does not provide a basis for 

quantitatively valuing the cost of 

anticipated incremental changes in 

environmental disturbance and marine 

mammal harassment associated with the 

proposed rule. 

Notably, the proposed rule would also 

afford significant benefit to the 

regulated industry by providing an 

efficient framework within which to 

achieve compliance with the MMPA, 

and the attendant regulatory certainty. 

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, survey 

operators in the GOM would likely be 

required to apply for an IHA. Although 

not monetized in the RIA, NMFS’s 

analysis indicates that the upfront work 

associated with the rule (e.g., analyses, 

modeling, process for obtaining LOA) 

would likely save significant time and 

money for operators. A conservative 

cost savings calculation, based on 

estimates of the costs for IHA 

applications (provided by a contractor 

providing such services) 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 just three months for LOA 

applications under a rule. 

We prepared an initial regulatory 

flexibility analysis (IRFA), as required 

by Section 603 of the Regulatory 

Flexibility Act (RFA), for this proposed 

rule. The IRFA describes the economic 

effects this proposed rule, if adopted, 

would have on small entities. A 

description of this action, why it is 

being considered, the objectives of, and 

legal basis for this proposed rule are 

contained in the preamble of this 

proposed rule. A copy of the full 

analysis is available online at 

www.fisheries.noaa.gov/national/ 

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

MMPA provides the statutory basis for 

this proposed rule. No duplicative, 

overlapping, or conflicting Federal rules 

have been identified. A summary of the 

IRFA follows. 

This proposed 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 IRFA identifies these 

businesses as well as potential indirect 

impacts to small business boat owners 

and operators, who would not be 

directly regulated by the rule, but who 

may be involved in the implementation 

of the survey activities. The IRFA found 

that, for ten years of relevant permit 

data (2006–2015), 62 U.S. basedcompanies applied for 284 permits for 

relevant surveys, in 15 different 

industry NAICS codes. The IRFA also 

found that, for the period 2012–2014, 33 

U.S.-flagged vessels operated under 

contract to permit applicants; the parent 

companies and primary NAICS codes 

under which those vessels operated 

were also identified where possible. 

Of the total number of relevant survey 

applications from 2006–2015, 12 

percent (75 applications) were put forth 

by small entities. In total, 34 U.S.-based 

small businesses applied for relevant 

permits in the GOM between 2006– 

2015, representing only 12 percent of 

permit applications during this period. 


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Foreign businesses and U.S.-based large 

businesses applied for more permits per 

business than did small businesses. 

Companies involved in crude petroleum 

and natural gas extraction (NAICS 

211111) and support activities for oil 

and gas (NAICS 213112) conducted the 

majority of the surveys by small 

companies (87 percent of companies). 

Historically, small entities undertook a 

larger percentage of HRG surveys 

(airgun and non-airgun) than did 

businesses as a whole (85 percent of 

surveys conducted by small businesses 

were HRG, compared to 57 percent of 

surveys by all entities). Small 

businesses did not undertake larger 

surveys (e.g., 3D WAZ), according to the 

permit database reviewed. 

Using this information, the IRFA finds 

that small entities would participate in 

approximately 33 to 57 surveys over the 

five years, or approximately 7 to 11 

surveys annually, and that 

approximately 15 to 26 small companies 

will likely apply for relevant permits 

over the five years (approximately 3 to 

5 small companies each year). The 

future distribution of small companies 

by industry is not known, but the 

historical pattern suggests that 

companies involved in crude petroleum 

and natural gas extraction (NAICS 

211111) and support activities for oil 

and gas (213112) will conduct the 

majority of the surveys by small 

companies. 

Annual median revenues for small 

entities who applied for relevant 

permits were $12.26 million. 

Incremental costs of the proposed rule 

for non-airgun surveys, which 

comprised most of the HRG surveys (95 

percent are forecast to be non-airgun, as 

opposed to airgun, surveys), are 

anticipated to range from $5,700 to 

$12,300 per survey. Airgun HRG survey 

costs are anticipated to range from 

$25,800 to $37,500 per survey. 

Approximately four small entities are 

anticipated to be involved in survey 

activities annually over the five years. 

As such, impacts would not be 

universally experienced by all small 

entities, and would depend on the 

specific survey types the companies 

engaged in. Incremental impacts for 

HRG surveys, which historically 

comprised most small business surveys, 

are anticipated to increase costs to small 

entities by one percent or less of annual 

revenues. For those entities engaged in 

other types of surveys, costs could 

comprise a larger portion of annual 

revenues. 

In summary, the IRFA finds: (1) In the 

majority of cases (88 percent), survey 

permit applicants are large businesses; 

(2) When the permit applicants are 

small businesses, the majority of the 

time (63 percent) they are oil and gas 

extractors (NAICS 211111); (3) Together 

these permits (for large businesses and 

small businesses with high annual 

revenues for which rule costs are a 

small fraction) account for 96 percent of 

the survey permits; (4) 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, we expect it is most 

likely the survey costs are passed on to 

oil and gas extraction companies who 

commission the surveys or purchase the 

data; and (5) Overall, up to five small 

businesses (NAICS 211111) per year 

may experience increased costs of 

between 0.1 and 1.1 percent of average 

annual revenues. 

NMFS’s RIA evaluates the 

incremental regulatory impact of the 

proposed rule, as well as the 

incremental regulatory impact of a more 

stringent alternative to the mitigation, 

monitoring, and reporting requirements 

of the proposed rule. NMFS is 

requesting comment on the costs of 

these proposed incidental take 

regulations on small entities, with the 

goal of ensuring a thorough 

consideration and discussion at the final 

rule stage. We request comments on the 

analysis of entities affected, as well as 

information on regulatory alternatives 

that would simultaneously reduce the 

burden on small entities and afford 

appropriate protections to affected 

marine mammal species and stocks. 

This proposed rule contains a 

collection-of-information requirement 

subject to the provisions of the 

Paperwork Reduction Act (PRA). 

Notwithstanding any other provision of 

law, no person is required to respond to 

nor shall a 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. 

These requirements have been approved 

by OMB under control number 0648– 

0151, currently under application for 

renewal, and include applications for 

regulations, subsequent LOAs, and 

reports. Send comments regarding any 

aspect of this data collection, including 

suggestions for reducing the burden, to 

NMFS and the OMB Desk Officer (see 

ADDRESSES). 

List of Subjects in 50 CFR Part 217 

Exports, Fish, Imports, Indians, 

Labeling, Marine mammals, Penalties, 

Reporting and recordkeeping 

requirements, Seafood, Transportation. 

Dated: June 12, 2018. 

Donna S. Wieting, 

Acting Deputy Assistant Administrator for 

Regulatory Programs, National Marine 

Fisheries Service. 

For reasons set forth in the preamble, 

50 CFR part 217 is proposed to be 

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. The heading of part 217 is revised 

to read as set forth above. 

■ 3. Add Subpart S 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 (LOA). 

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 the Gulf 

of Mexico. 

§ 217.181 Effective dates. 

Regulations in this subpart are 

effective from [EFFECTIVE DATE OF 

FINAL RULE] through [DATE 5 YEARS 

AFTER EFFECTIVE DATE OF FINAL 

RULE]. 


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§ 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; 

(d) Take a marine mammal specified 

in such LOAs if NMFS determines such 

taking results in more than a negligible 

impact on the species or stocks of such 

marine mammal; or 

(e) Take a marine mammal specified 

in such LOAs if NMFS determines such 

taking results in an unmitigable adverse 

impact on the species or stock of such 

marine mammal for taking for 

subsistence uses. 

§ 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, the 

vessel operator and other relevant 

personnel, the lead protected species 

observer (PSO), and any other relevant 

designees of the LOA-holder operating 

under the authority of the LOA. 

(2) The LOA-holder shall ensure that 

the vessel operator and other relevant 

vessel personnel are briefed on all 

responsibilities, communication 

procedures, marine mammal monitoring 

protocol, operational procedures, and 

LOA requirements prior to the start of 

survey activity, and when relevant new 

personnel join the survey operations. 

The LOA-holder shall instruct relevant 

vessel personnel with regard to the 

authority of the protected species 

monitoring team, and shall ensure that 

relevant vessel personnel and protected 

species monitoring team participate in a 

joint onboard briefing led by the vessel 

operator and lead PSO to ensure that 

responsibilities, communication 

procedures, marine mammal monitoring 

protocol, operational procedures, and 

LOA requirements are clearly 

understood. This briefing must be 

repeated when relevant new personnel 

join the survey operations. 

(b) Deep penetration airgun surveys: 

(1) Deep penetration airgun surveys 

are defined as surveys using airgun 

arrays with total volume greater than 

400 in3. 

(2) The LOA-holder must use 

independent, dedicated, trained PSOs, 

meaning that the PSOs must be 

employed by a third-party observer 

provider, may have no tasks other than 

to conduct observational effort, record 

observational data, and communicate 

with and instruct relevant vessel crew 

with regard to the presence of marine 

mammals and mitigation requirements 

(including brief alerts regarding 

maritime hazards), and must have 

successfully completed an approved 

PSO training course. NMFS will 

maintain a list of approved PSOs and, 

for PSOs not on the list, NMFS must 

review and approve PSO resumes 

accompanied by a relevant training 

course information packet that includes 

the name and qualifications (i.e., 

experience, training completed, and 

educational background) of the 

instructor(s), the course outline or 

syllabus, and course reference material 

as well as a document stating the PSO’s 

successful completion of the course. 

NMFS shall have one week to approve 

PSOs from the time that the necessary 

information is submitted, after which 

PSOs meeting the minimum 

requirements shall automatically be 

considered approved. 

(3) At least one visual PSO and two 

acoustic PSOs must have a minimum of 

90 days at-sea experience working in 

those roles, respectively, during a deep 

penetration seismic survey, with no 

more than eighteen months elapsed 

since the conclusion of the at-sea 

experience. One visual PSO with such 

experience shall be designated as the 

lead for the entire protected species 

observation team. The lead shall 

coordinate duty schedules and roles for 

the PSO team and serve as primary 

point of contact for the vessel operator. 

To the maximum extent practicable, the 

lead PSO shall 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. 

(4) Visual observation: 

(i) 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 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) and 30 minutes prior 

to and during nighttime ramp-ups of the 

airgun array. 

(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 shall coordinate to 

ensure 360° visual coverage around the 

vessel from the most appropriate 

observation posts, and shall conduct 

visual observations using binoculars 

and the naked eye while free from 

distractions and in a consistent, 

systematic, and diligent manner. 

(iv) Visual PSOs shall immediately 

communicate all observations to 

acoustic PSOs, including any 

determination by the PSO regarding 

species identification, distance, and 

bearing and the degree of confidence in 

the determination. 

(v) 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. 

(vi) Any observations of marine 

mammals by crew members aboard any 

vessel associated with the survey shall 

be relayed to the PSO team. 

(vii) During good conditions (e.g., 

daylight hours; Beaufort sea state (BSS) 

3 or less), visual PSOs shall 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. 

(5) Acoustic observation: 

(i) All surveys must use a towed 

passive acoustic monitoring (PAM) 

system at all times when operating in 

waters deeper than 100 m, which must 

be monitored beginning at least 30 

minutes prior to ramp-up and at all 

times during use of the acoustic source. 

(ii) Acoustic PSOs shall immediately 

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. 


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(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. 

(iv) 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: 

(A) Daylight hours and sea state is less 

than or equal to BSS 4; 

(B) No marine mammals (excluding 

delphinids) detected solely by PAM in 

the 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 

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. 

(6) Exclusion Zone and Buffer Zone— 

The PSOs shall establish and monitor a 

500-m exclusion zone and additional 

500-m buffer zone. 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) shall be 

communicated to the operator to 

prepare for the potential shutdown of 

the acoustic source. PSOs must monitor 

the 1,000-m zone for a minimum of 30 

minutes prior to ramp-up (i.e., preclearance). 

(7) Ramp-up—A ramp-up procedure, 

involving 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, is required at all times as part 

of the activation of the acoustic source. 

Ramp-up may not be initiated if any 

marine mammal is within the 

designated exclusion zone or buffer 

zone. If a marine mammal is observed 

within these zones during the preclearance period, ramp-up may not 

begin until the animal(s) has been 

observed exiting the 1,000-m zone or 

until an additional time period has 

elapsed with no further sightings (i.e., 

15 minutes for small odontocetes and 30 

minutes for all other species). PSOs 

shall monitor the exclusion zone during 

ramp-up, and ramp-up must cease and 

the source shut down upon observation 

of marine mammals within the zones. 

Ramp-up may occur at times of poor 

visibility if appropriate acoustic 

monitoring has occurred with no 

detections in the 30 minutes prior to 

beginning ramp-up. Acoustic source 

activation may only occur at times of 

poor visibility where operational 

planning cannot reasonably avoid such 

circumstances. 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. 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 shall 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. Duration should not be 

less than 20 minutes. The operator must 

provide information to the PSO 

documenting that appropriate 

procedures were followed. Ramp-ups 

shall be scheduled so as to minimize the 

time spent with source activated prior to 

reaching the designated run-in. 

(8) Shutdown requirements: 

(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. 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. 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. When there is 

uncertainty regarding the nature of the 

observation, all on duty PSOs must 

agree upon the mitigation action. When 

only the acoustic PSO is on duty and 

there is uncertainty regarding the need 

for mitigation action on the basis of a 

detection, the PSO may request that the 

acoustic source be shut down as a 

precaution. 

(ii) Upon completion of ramp-up, if a 

marine mammal appears within, enters, 

or is clearly on a course to enter the 

exclusion zone, the acoustic source 

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

acoustic source must be immediately 

turned off). If a marine mammal 

(excluding delphinids) is detected 

acoustically, the acoustic source must 

be shut down. 

(iii) This shutdown requirement is 

waived for dolphins of the following 

genera: Tursiops, Stenella, Steno, and 

Lagenodelphis. Instead of shutdown, the 

acoustic source must be powered down 

to the smallest single element of the 

array if a dolphin of the indicated 

genera appears within or enters the 500- 

m exclusion zone, or is acoustically 

detected and localized within the zone. 

Power-down conditions shall 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. 

(iv) Shutdown of the acoustic source 

is required upon detection (visual or 

acoustic) of a baleen whale, beaked 

whale, or Kogia spp. at any distance. 

(v) Shutdown of the acoustic source is 

required upon observation of a whale 

(i.e., sperm whale or any baleen whale) 

with calf at any distance, with ‘‘calf’’ 

defined as an animal less than twothirds the body size of an adult observed 

to be in close association with the calf. 

(vi) 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 observation of the 

animal(s). Where there is no relevant 

zone (e.g., shutdown due to observation 

of a baleen whale), a 30-minute 

clearance period must be observed 

following the last observation of the 

animal(s). 

(vii) 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 visual 

and acoustic observation and no visual 

detections of any marine mammal have 

occurred within the exclusion zone and 

no acoustic detections (excluding 

delphinids) have occurred. For any 

longer shutdown, 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. 

(9) Miscellaneous protocols: 

(i) The acoustic source must be 

deactivated when not acquiring data or 

preparing to acquire data, except as 


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necessary for testing. Unnecessary use 

of the acoustic source shall be avoided. 

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. The lead 

PSO must be granted access to relevant 

instrumentation documenting acoustic 

source power and/or operational 

volume. 

(ii) 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. 

(c) Shallow penetration surveys: 

(1) Shallow penetration surveys are 

defined as surveys using airgun arrays 

with total volume equal to or less than 

400 in3 or boomers. 

(2) LOA-holders shall follow the 

requirements defined for deep 

penetration airgun surveys at 

§ 217.184(b), with the following 

exceptions: 

(i) Use of a towed PAM system is not 

required except to begin use of the 

airgun(s) at night in waters deeper than 

100 m. Use of a PAM system is required 

for nighttime start-up, with monitoring 

by a trained and experienced acoustic 

PSO during a 30-minute pre-clearance 

period and during the ramp-up period 

(if applicable). The required acoustic 

PSO may be a crew member. 

(ii) Ramp-up is not required for 

shallow penetration surveys using only 

a single airgun or boomer. 

(iii) The exclusion zone shall be 

established at a distance of 200 m, with 

an additional 200-m buffer monitored 

during pre-clearance. 

(iv) No shutdown or power-down 

action is required upon detection of the 

dolphin genera described at 

§ 217.184(b)(8)(iii) for surveys using a 

single airgun or boomer. 

(v) Shutdowns are not required for 

observations beyond the exclusion zone 

under any circumstance. 

(d) Non-airgun surveys: 

(1) Non-airgun surveys are defined as 

surveys using an acoustic source other 

than an airgun(s) or boomer that 

operates at frequencies less than 200 

kHz (i.e., side-scan sonar, multibeam 

echosounder, or subbottom profiler). 

(2) LOA-holders conducting nonairgun surveys shall follow the 

requirements defined for shallow 

penetration surveys at § 217.184(c), with 

the following exceptions: 

(i) Use of a towed PAM system is not 

required under any circumstances; 

(ii) Ramp-up is not required under 

any circumstances; 

(iii) Non-airgun surveys shall employ 

a minimum of one trained and 

experienced independent visual PSO 

during all daylight operations (as 

described at § 217.184(b)) when 

operating in waters deeper than 200 m. 

In waters shallower than 200 m, nonairgun surveys shall employ one trained 

visual PSO, who may be a crew 

member, to monitor the exclusion zone 

and buffer during the pre-clearance 

period; and 

(iv) No shutdown or power-down 

action is required upon detection of the 

dolphin genera described at 

§ 217.184(b)(8)(iii). 

(e) Restriction areas: 

(1) From February 1 through May 31, 

no use of airguns may occur shoreward 

of the 20-m isobath (buffered by 13 km). 

(2) No use of airguns may occur 

within the area bounded by the 100- and 

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

(buffered by 6 km), during June through 

August. 

(3) No use of airguns may occur 

within the area bounded by the 200- and 

2,000-m isobaths from the northern 

border of BOEM’s Howell Hook leasing 

area to 81.5° W (buffered by 9 km). 

(f) 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; 

(3) Attach acoustic pingers directly to 

the coated tether cable; acoustic releases 

should not be used; and 

(4) Employ a third-party PSO aboard 

the node retrieval vessel in order to 

document any unexpected marine 

mammal entanglement. 

(g) To avoid the risk of vessel strike, 

LOA-holders must adhere to the 

following requirements: 

(1) Vessel 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. 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, to ensure the potential 

for strike is minimized. Visual observers 

monitoring the vessel strike avoidance 

zone can be either third-party observers 

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) All vessels, regardless of size, must 

observe a 10 kn speed restriction within 

the restriction area described previously 

at § 217.184(e)(2); 

(3) Vessel speeds must also be 

reduced to 10 kn or less when mother/ 

calf pairs, pods, or large assemblages of 

cetaceans are observed near a vessel; 

(4) All vessels must maintain a 

minimum separation distance of 500 yd 

(457 m) from baleen whales; 

(5) All vessels must maintain a 

minimum separation distance of 100 yd 

(91 m) from sperm whales; 

(6) All vessels must attempt to 

maintain a minimum separation 

distance of 50 yd (46 m) from all other 

marine mammals, with an exception 

made for those animals that approach 

the vessel; 

(7) When cetaceans are sighted while 

a vessel is underway, vessels shall 

attempt to remain parallel to the 

animal’s course, and shall avoid 

excessive speed or abrupt changes in 

direction until the animal has left the 

area; and 

(8) If cetaceans are sighted in a 

vessel’s path or in close proximity to a 

moving vessel, the vessel shall 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. 

§ 217.185 Requirements for monitoring 

and reporting. 

(a) LOA-holders must provide bigeye 

binoculars (e.g., 25 x 150; 2.7 view 

angle; individual ocular focus; height 

control) of appropriate quality (i.e., 

Fujinon or equivalent) solely for PSO 

use. These shall be pedestal-mounted on 

the deck at the most appropriate vantage 

point that provides for optimal sea 

surface observation, PSO safety, and 

safe operation of the vessel. The 

operator must also provide a nightvision device suited for the marine 

environment for use during nighttime 

ramp-up pre-clearance, at the discretion 

of the PSOs. At minimum, the device 

should feature automatic brightness and 

gain control, bright light protection, 

infrared illumination, and optics suited 

for low-light situations. 

(b) PSOs must also be equipped with 

reticle binoculars (e.g., 7 x 50) of 

appropriate quality (i.e., Fujinon or 

equivalent), GPS, a digital single-lens 

reflex camera of appropriate quality 

(i.e., Canon or equivalent), a compass, 

and any other tools necessary to 

adequately perform necessary tasks, 

including accurate determination of 


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distance and bearing to observed marine 

mammals. 

(c) PSO qualifications: 

(1) PSOs must successfully complete 

relevant 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 and 

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 by NMFS 

if the PSO has acquired the relevant 

skills through alternate experience. 

Requests for such a waiver shall be 

submitted to NMFS and must include 

written justification. Requests shall 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. 

(d) Data collection—PSOs must use 

standardized data forms, whether hard 

copy or electronic. PSOs shall 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 

record a description of the 

circumstances. We require that, at a 

minimum, the following information be 

recorded: 

(1) Vessel names (source vessel and 

other vessels associated with survey) 

and call signs; 

(2) PSO names and affiliations; 

(3) Dates of departures and returns to 

port with port name; 

(4) Dates and times (Greenwich Mean 

Time) of survey effort and times 

corresponding with PSO effort; 

(5) Vessel location (latitude/ 

longitude) when survey effort begins 

and ends; vessel location at beginning 

and end of visual PSO duty shifts; 

(6) Vessel heading and speed at 

beginning and end of visual PSO duty 

shifts and upon any line change; 

(7) Environmental conditions while 

on visual survey (at beginning and end 

of PSO shift and whenever conditions 

change significantly), including wind 

speed and direction, Beaufort sea state, 

Beaufort wind force, swell height, 

weather conditions, cloud cover, sun 

glare, and overall visibility to the 

horizon; 

(8) Factors that may be contributing to 

impaired observations during each PSO 

shift change or as needed as 

environmental conditions change (e.g., 

vessel traffic, equipment malfunctions); 

(9) Survey activity information, such 

as acoustic source power output while 

in operation, number and volume of 

airguns operating in the array, tow 

depth of the array, and any other notes 

of significance (i.e., pre-ramp-up survey, 

ramp-up, shutdown, testing, shooting, 

ramp-up completion, end of operations, 

streamers, etc.); and 

(10) If a marine mammal is sighted, 

the following information should be 

recorded: 

(i) Watch status (sighting made by 

PSO on/off effort, opportunistic, crew, 

alternate vessel/platform); 

(ii) PSO who sighted the animal; 

(iii) Time of sighting; 

(iv) Vessel location at time of sighting; 

(v) Water depth; 

(vi) Direction of vessel’s travel 

(compass direction); 

(vii) Direction of animal’s travel 

relative to the vessel; 

(viii) Pace of the animal; 

(ix) Estimated distance to the animal 

and its heading relative to vessel at 

initial sighting; 

(x) Identification of the animal (e.g., 

genus/species, lowest possible 

taxonomic level, or unidentified), also 

note the composition of the group if 

there is a mix of species; 

(xi) Estimated number of animals 

(high/low/best); 

(xii) Estimated number of animals by 

cohort (adults, yearlings, juveniles, 

calves, group composition, etc.); 

(xiii) 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); 

(xiv) 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); 

(xv) Animal’s closest point of 

approach (CPA) and/or closest distance 

from the center point of the acoustic 

source; 

(xvi) Platform activity at time of 

sighting (e.g., deploying, recovering, 

testing, shooting, data acquisition, 

other); and 

(xvii) Description of any actions 

implemented in response to the sighting 

(e.g., delays, shutdown, ramp-up, speed 

or course alteration, etc.); time and 

location of the action should also be 

recorded. 

(11) If a marine mammal is detected 

while using the PAM system, the 

following information should be 

recorded: 

(i) An acoustic encounter 

identification number, and whether the 

detection was linked with a visual 

sighting; 

(ii) 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, etc.); 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. 

(e) LOA-holders shall provide to 

NMFS within 90 days of survey 

conclusion geo-referenced time-stamped 

vessel tracklines for all time periods in 

which airguns were operating. 

Tracklines should include points 

recording any change in airgun status 

(e.g., when the airguns began operating, 

when they were turned off, or when 

they changed from full array to single 

gun or vice versa). 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 shall 

be referenced to the WGS84 geographic 

coordinate system. 

(f) Reporting: 

(1) Annual reporting: LOA-holders 

shall submit an annual 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. 

The report must describe all activities 

conducted and sightings of marine 

mammals near the activities, 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). Geospatial data 

regarding locations where the acoustic 

source was used, provided to NMFS 

under subparagraph § 217.185(e), must 


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be provided as an ESRI shapefile with 

all necessary files and appropriate 

metadata. The report must summarize 

the data collected as required under 

§ 217.185(d). In addition to the report, 

all raw observational data shall be made 

available to NMFS. 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. A final report must be 

submitted within 30 days following 

resolution of any comments on the draft 

report. 

(2) Comprehensive reporting: LOAholders shall 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 from July 

1 of one year through June 30 of the 

subsequent year. The report must be 

submitted to NMFS by October 1 of each 

year. 

(g) Reporting of injured or dead 

marine mammals: 

(1) In the unanticipated event that the 

activity defined in § 217.180 clearly 

causes the take of a marine mammal in 

a prohibited manner, the LOA-holder 

shall immediately cease such activity 

and report the incident to the Office of 

Protected Resources (OPR), NMFS, and 

to the Southeast Regional Stranding 

Coordinator, NMFS. Activities shall not 

resume until NMFS is able to review the 

circumstances of the prohibited take. 

NMFS will work with the LOA-holder 

to determine what measures are 

necessary to minimize the likelihood of 

further prohibited take and ensure 

MMPA compliance. The LOA-holder 

may not resume their activities until 

notified by NMFS. The report must 

include the following information: 

(i) Time, date, and location (latitude/ 

longitude) of the incident; 

(ii) Name and type of vessel involved; 

(iii) Vessel’s speed during and leading 

up to the incident; 

(iv) Description of the incident; 

(v) Status of all sound source use in 

the 24 hours preceding the incident; 

(vi) Water depth; 

(vii) Environmental conditions (e.g., 

wind speed and direction, Beaufort sea 

state, cloud cover, visibility); 

(viii) Description of all marine 

mammal observations in the 24 hours 

preceding the incident; 

(ix) Species identification or 

description of the animal(s) involved; 

(x) Fate of the animal(s); and 

(xii) Photographs or video footage of 

the animal(s). 

(2) In the event that the LOA-holder 

discovers an injured or dead marine 

mammal and determines that the cause 

of the injury or death is unknown and 

the death is relatively recent (e.g., in 

less than a moderate state of 

decomposition), the LOA-holder shall 

immediately report the incident to OPR 

and the Southeast Regional Stranding 

Coordinator, NMFS. The report must 

include the information identified in 

paragraph (f)(1) of this section. 

Activities may continue while NMFS 

reviews the circumstances of the 

incident. NMFS will work with the 

LOA-holder to determine whether 

additional mitigation measures or 

modifications to the activities are 

appropriate. 

(3) In the event that the LOA-holder 

discovers an injured or dead marine 

mammal and determines that the injury 

or death is not associated with or related 

to the activities defined in § 217.180 

(e.g., previously wounded animal, 

carcass with moderate to advanced 

decomposition, scavenger damage), the 

LOA-holder shall report the incident to 

OPR and the Southeast Regional 

Stranding Coordinator, NMFS, within 

24 hours of the discovery. The LOAholder shall provide photographs or 

video footage or other documentation of 

the stranded animal sighting to NMFS. 

§ 217.186 Letters of Authorization (LOA). 

(a) To incidentally take marine 

mammals pursuant to these regulations, 

prospective LOA-holders must apply for 

and obtain a LOA. 

(b) A 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 a 

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 

in the preamble to 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 a 

LOA shall be published in the Federal 

Register within thirty days of a 

determination. 

§ 217.187 Renewals and modifications of 

Letters of Authorization. 

(a) A 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) A 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) Adaptive Management—NMFS 

may modify (including augment) 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 


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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 a 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) Emergencies—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 a LOA issued pursuant to 

§ 216.106 of this chapter and § 217.186, 

a 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 [Reserved] 

§ 217.189 [Reserved] 

[FR Doc. 2018–12906 Filed 6–21–18; 8:45 am] 

BILLING CODE 3510–22–P 


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