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

Federal RegisterJun 22, 2018

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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/incidental-take-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

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-Mexico-Geological-and-Geophysical-Activities-Programmatic-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/incidental-take-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) high-resolution surveys, which may use a variety of acoustic sources. Generally speaking, these surveys may occur within Federal territorial waters and waters of the U.S. Exclusive Economic Zone (EEZ) (

i.e.,

to 200 nautical miles (nmi)) within the GOM, and corresponding with BOEM's 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

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

Deep penetration seismic surveys using airgun arrays as an acoustic source (sound sources are described in the “Detailed Description of Activities” section) are a primary method of obtaining geophysical data used to characterize subsurface structure. These surveys are designed to illuminate deeper subsurface structures and formations that may be of economic interest as a reservoir for oil and gas exploitation. A deep penetration survey uses an acoustic source suited to provide data on geological formations that may be thousands of meters (m) beneath the seafloor, as compared with a shallow penetration or high resolution geophysical (HRG) survey that may be intended to evaluate shallow subsurface formations or the seafloor itself (

e.g.,

for hazards).

Deep penetration surveys may be two-dimensional (2D) or three-dimensional (3D) (see Figure 1-2 of the petition), and there are a variety of survey methodologies designed to provide the specific data of interest. 2D surveys are designed to acquire data over large areas (thousands of square miles) in order to screen for potential hydrocarbon prospectivity, and provide a cross-sectional image of the structure. In contrast, 3D surveys may use similar acoustic sources but are designed to cover smaller areas with greater resolution (

e.g.,

with closer survey line spacing), providing a volumetric image of underlying geological structures. Repeated 3D surveys are referred to as four-dimensional (4D), or time-lapse, surveys that assess the depletion of a reservoir.

Shallow penetration and high-resolution surveys are designed to highlight seabed and near-surface potential obstructions, archaeology, and geohazards that may have safety implications during rig installation or well and development facility siting. Shallow penetration surveys may use a small airgun array, single airgun, or subbottom profiler, while high-resolution 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 non-operational downtime due to a variety of factors, including technical or mechanical problems, standby for weather or other interferences, and implementation of mitigation measures.

Specified Geographical Region

The 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 (km

). 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.

EP22JN18.000

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/m

/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, mini-basins, 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

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

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 in

. However, BOEM's permitting records show that during one recent year, over one-third of arrays in use had volumes greater than 8,000 in

. The output of an airgun array is directly proportional to airgun firing pressure or to the number of airguns, and is expressed as the cube root of the total volume of the array.

Airguns are considered to be low-frequency acoustic sources, producing sound with energy in a frequency range from less than 10 Hz to 2 kHz (though there may be energy 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, back-calculated source levels are not typically considered to be accurate indicators of the true maximum amplitude of the output in the far field, which is what is typically of concern in assessing potential impacts to marine mammals. In addition, the effective source level for sound propagating in near-horizontal directions (

i.e.,

directions likely to impact most marine mammals in the vicinity of an array) is likely to be substantially lower (

e.g.,

15-24 dB; Caldwell and Dragoset, 2000) than the nominal source level applicable to downward propagation because of the directional nature of the sound from the airgun array. The horizontal propagation of sound is reduced by noise cancellation effects created when sound from neighboring airguns on the same horizontal plane partially cancel each other out.

Survey protocols generally involve a predetermined set of survey, or track, lines. The seismic acquisition vessel(s) (source vessel) will travel down a linear track for some distance until a line of data is acquired, then turn and acquire data on a different track. In some cases, data is acquired as the source vessel(s) turns continuously rather than moving on a linear track (

i.e.,

coil surveys). The spacing between track lines and the length of track lines can vary greatly, depending on the objectives of a survey.

In addition to the line over which data acquisition is desired, full-power operation may include run-in and run-out. Run-in is approximately 1 km of full-power source operation before starting a new line to ensure equipment is functioning properly, and run-out is additional full-power operation beyond the conclusion of a trackline (

e.g.,

half the distance of the acquisition streamer behind the source vessel, when used) to ensure that all data along the trackline are collected by the streamer. Line turns can require two to six hours when towed hydrophones are used, due to the long trailing streamers, but may be much faster when streamers are not used. Spacing and length of tracks varies by survey. Survey operations often involve the source vessel(s), supported by a chase vessel. Chase vessels typically support the source vessel(s) by protecting the long hydrophone streamer 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 four-component survey data (

i.e.,

including pressure and 3D linear acceleration collected via geophone). For OBS surveys, one or two vessels usually are needed to lay out and pick up cables, one ship is needed to record data, one ship tows an airgun array, and two smaller utility boats support survey operations. 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, single-vessel 3D surveys are referred to as narrow azimuth (NAZ) surveys. Other 3D survey techniques include wide-azimuth (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-to-noise 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

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-to-receiver 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 towed-streamer 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) Zero-offset 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 zero-offset 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 in

, 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

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 fan-shaped 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 across-track 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 mi

(2,590 km

) and include 2D, 3D NAZ, 3D WAZ, and coil types. Geotechnical study surveys are assumed to cover an area less than 100 mi

(259 km

) and use small airguns and/or high-frequency electromechanical sources installed on an AUV. VSP surveys, assuming a single source vessel with one 8,000 in

array, were also modeled.

The nominal airgun sources used for analysis of the proposed action include a small single airgun (90 in

Sercel airgun) towed at 4 m depth and a large airgun array (8,000 in

) 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 in

. 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/incidental-take-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 km

. 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 km

2D surveys were simulated by assuming use of a single 8,000 in

array,

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 fill-in 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 high-resolution 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 side-mounted 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 km

. 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, pre-leasing, 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

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.

EP22JN18.001

Table 1—Projected Levels of Effort in 24-Hr Survey Days for Ten Years, by Zone and Survey Type

Year

Zone

3D NAZ

3D WAZ

Coil

VSP

Total

(deep)

Shallow

hazards

Boomer

HRG

Total

(shallow)

243

389

192

721

186

256

515

248

106

940

Total

125

1,363

489

209

2,190

364

426

389

192

665

502

241

103

878

Total

1,354

476

204

2,101

243

342

160

573

186

256

456

208

755

Total

1,227

417

179

1,827

101

364

426

157

247

414

380

140

676

Total

188

1,181

300

129

1,802

243

295

192

571

467

241

103

814

Total

1,196

433

185

1,819

103

364

426

247

160

478

186

256

421

208

721

Total

1,310

460

198

1,973

104

243

124

247

160

506

380

220

761

Total

125

1,060

401

172

1,763

107

364

426

247

128

441

380

160

633

Total

1,151

331

143

1,671

113

243

200

192

476

321

241

103

668

Total

924

433

185

1,547

115

364

426

200

160

431

321

200

615

Total

1,075

403

174

1,667

116

Projected levels of effort in 24-hr survey days.

Zones follow the zones depicted in Figure 2.

Deep penetration survey types include 2D, which uses one source vessel with one large array (8,000 in

); 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.

Shallow penetration/HRG survey types include shallow hazards surveys, assumed to use a single 90 in

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 low-effort 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

Min

Mean

Max

Shallow penetration/HRG surveys

Min

Mean

Max

1 (Shelf east)

2 (Shelf central)

243

304

426

3 (Shelf west)

4 (Slope east)

157

5 (Slope central)

414

480

721

6 (Slope west)

133

256

7 (Deep)

615

678

940

Total

1,547

1,669

2,190

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/marine-mammal-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 Würsig (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

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/draft-marine-mammal-stock-assessment-reports

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 (Würsig

et al.,

2000; Würsig, 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 (Würsig, 2017). Although North Atlantic right whales are well known from the east coast of Florida, that area represents the southern limit of their range; Würsig (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 northward-migrating whales from the Caribbean becoming disoriented (Würsig

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 (Würsig

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 Würsig, 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.

Table 3—Marine Mammals Potentially Present in the Specified Geographical Region

Common name

Scientific name

Stock

ESA/

MMPA

status;

strategic

(Y/N)

NMFS stock abundance (CV, N

min

, most recent abundance survey)

2 8

Predicted mean

(CV)/maximum

abundance

PBR

Annual

M/SI (CV)

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)

Family Balaenopteridae (rorquals):

Bryde's whale

Balaenoptera edeni

Gulf of Mexico

; 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

Family Kogiidae:

Pygmy sperm whale

Kogia breviceps

GOM

-; N

186 (1.04; 90; 2009)

2,234 (0.19)/6,117

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

0.4

Gervais beaked whale

Mesoplodon europaeus

GOM

-; N

149 (0.91; 77; 2009)

0.8

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

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

6.5 (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)

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

Atlantic spotted dolphin

S. frontalis

GOM

-; N

37,611 (0.28; 29,844; 2000-01)

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

Striped dolphin

S. coeruleoalba

GOM

-; N

1,849 (0.77; 1,041; 2009)

4,914 (0.17)/5,323

Fraser's dolphin

Lagenodelphis hosei

GOM

-; N

726 (0.7; 427; 1996-2001)

1,665 (0.73)/n/a

Undet.

Risso's dolphin

Grampus griseus

GOM

-; N

2,442 (0.57; 1,563; 2009)

3,137 (0.10)/4,153

7.9 (0.85)

Melon-headed whale

Peponocephala electra

GOM

-; N

2,235 (0.75; 1,274; 2009)

6,733 (0.30)/7,105

Pygmy killer whale

Feresa attenuata

GOM

-; N

152 (1.02; 75; 2009)

2,126 (0.30)/n/a

0.8

False killer whale

Pseudorca crassidens

GOM

-; N

777 (0.56; 501; 2003-04)

3,204 (0.36)/n/a

Undet.

Killer whale

Orcinus orca

GOM

-; N

28 (1.02; 14; 2009)

185 (0.41)/n/a

0.1

Short-finned pilot whale

Globicephala macrorhynchus

GOM

-; N

2,415 (0.66; 1,456; 2009)

1,981 (0.18)/n/a

0.5 (1.0)

ESA 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.

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; N

min

is the minimum estimate of stock abundance.

This 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.

These 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.

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

Abundance estimates are in some cases reported for a guild or group of species when those species are difficult to differentiate at sea. Similarly, the habitat-based 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.

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.

We 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).

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, Maze-Foley 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 multi-year 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, NMFS-reported 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

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 die-off 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; Venn-Watson

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

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_gulfofmexico.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-mammal-unusual-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.deepwaterhorizoneconomicsettlement.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 km

of ocean. Cumulatively, over the course of the spill, oil was detected on over 112,000 km

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

which bacteria degrade the oil in order to prevent oil slicks from fouling sensitive shoreline habitats. The large-scale 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.

EP22JN18.002

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 km

of ocean surface; 2,100 km of shoreline; and between 1,000-1,900 km

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)

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

failures, and adverse health effects due to the DWH oil spill. The number of years predicted for the DWH oil-impacted 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)

Bryde's whale

48 (23-100)

17 (7-24)

22 (10-31)

18 (7-28)

−22

Sperm whale

16 (11-23)

6 (2-8)

7 (3-10)

6 (2-9)

−7

Kogia

spp.

15 (8-29)

5 (2-7)

7 (3-10)

6 (2-9)

−6

Beaked whales

12 (7-22)

4 (2-6)

5 (3-8)

4 (2-7)

−6

Rough-toothed dolphin

41 (16-100)

14 (6-20)

19 (9-26)

15 (6-23)

−17

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

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

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

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

Pygmy killer whale

15 (7-33)

5 (2-8)

7 (3-10)

6 (2-9)

−7

False killer whale

18 (7-48)

6 (3-9)

8 (4-12)

7 (3-11)

−9

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.

“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.

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

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 low-frequency 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 low-frequency cetacean (

i.e.,

the Bryde's whale), 18 are classified as mid-frequency cetaceans (

i.e.,

all delphinid and ziphiid species and the sperm whale), and two are classified as high-frequency 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

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 (μPa)), 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 μPa), while the received level is the SPL at the listener's position (referenced to 1 μPa).

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 non-pulsed 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

) is the measure of the average amount of energy carried by a time-dependent pressure wave over a period of time. The

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

reflects the average SPL of an acoustic signal over tens of seconds or longer.

Sound exposure level (SEL; represented as dB re 1 μPa

-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

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 high-amplitude 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 high-frequency, 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 noise-induced 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; Götz

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 mid-frequency 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

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 in

(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

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