Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey in the Northeast Pacific Ocean

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RTID 0648-XA144]

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey in the Northeast Pacific Ocean

AGENCY:

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

ACTION:

Notice; issuance of an incidental harassment authorization.

SUMMARY:

In accordance with the regulations implementing the Marine Mammal Protection Act (MMPA) as amended, notification is hereby given that NMFS has issued an incidental harassment authorization (IHA) to Lamont-Doherty Earth Observatory of Columbia University (L-DEO) to incidentally harass, by Level A and Level B harassment, marine mammals during a marine geophysical survey in the northeast Pacific Ocean.

DATES:

This Authorization is effective from May 19, 2021 through May 18, 2022.

FOR FURTHER INFORMATION CONTACT:

Amy Fowler, 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:

https://www.fisheries.noaa.gov/permit/incidental-take-authorizations-under-marine-mammal-protection-act.

In case of problems accessing these documents, please call the contact listed above.

SUPPLEMENTARY INFORMATION:

Background

The MMPA prohibits the “take” of marine mammals, with certain exceptions. Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361

et seq.

) direct 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 and either regulations are issued or, if the taking is limited to harassment, a notice of a proposed incidental take authorization may be provided to the public for review.

Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) and will not have an unmitigable adverse impact on the availability of the species or stock(s) for taking for subsistence uses (where relevant). Further, NMFS must prescribe the permissible methods of taking and other “means of effecting the least practicable adverse impact” on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of the species or stocks for taking for certain subsistence uses (referred to in shorthand as “mitigation”); and requirements pertaining to the mitigation, monitoring and reporting of the takings are set forth.

Summary of Request

On November 8, 2019, NMFS received a request from L-DEO for an IHA to take marine mammals incidental to a marine geophysical survey of the Cascadia Subduction Zone off the coasts of Washington, Oregon, and British Columbia, Canada. The application was deemed adequate and complete on March 6, 2020. L-DEO's request is for take of small numbers of 31 species of marine mammals by Level A and Level B harassment. NMFS published a notice of proposed IHA for public review and comment on April 7, 2020 (85 FR 19580). On May 29, 2020, L-DEO informed NMFS that the project had been delayed by one year and would begin in June 2021.

Description of Proposed Activity

Overview

Researchers from L-DEO, Woods Hole Oceanographic Institution (WHOI), and the University of Texas at Austin Institute of Geophysics (UTIG), with funding from the National Science Foundation (NSF), and in collaboration with researchers from Dalhousie University and Simon Fraser University (SFU) plan to conduct a high-energy seismic survey from the Research Vessel (R/V)

Marcus G Langseth

(

Langseth

) in the northeast Pacific Ocean beginning in June 2021. The seismic survey will be conducted at the Cascadia Subduction Zone off the coasts of Oregon, Washington, and British Columbia, Canada. The proposed two-dimensional (2-D) seismic survey will occur within the Exclusive Economic Zones (EEZs) of Canada and the United States, including U.S. state waters and Canadian territorial waters. The survey will use a 36-airgun towed array with a total discharge volume of ~6,600 cubic inches (in

3

) as an acoustic source, acquiring return signals using both a towed streamer as well ocean bottom seismometers (OBSs) and ocean bottom nodes (OBNs).

The planned study will use 2-D seismic surveying and OBSs and OBNs to investigate the Cascadia Subduction Zone and provide data necessary to illuminate the depth, geometry, and physical properties of the seismogenic portion and updip extent of the megathrust zone between the subducting Juan de Fuca plate and the overlying accretionary wedge/North American plate. These data will provide essential constraints for earthquake and tsunami hazard assessment in this heavily populated region of the Pacific Northwest. The primary objectives of the survey planned by researchers from L-DEO, WHOI, and UTIG is to characterize: (1) The deformation and topography of the incoming plate; (2) the depth, topography, and reflectivity of the megathrust; (3) sediment properties and amount of sediment subduction; and (4) the structure and evolution of the accretionary wedge, including geometry and reflectivity of fault networks, and how these properties vary along strike, spanning the full length of the margin and down dip across what may be the full width of the Cascadia Subduction Zone.

Dates and Duration

The survey is expected to last for 40 days, with 37 days of seismic operations, 2 days of equipment deployment, and 1 day of transit. R/V

Langseth

will likely leave out of and return to port in Newport, Oregon, during June-July 2021.

Specific Geographic Region

The survey will occur within ~42-51° N, ~124-130° W. Planned survey tracklines are shown in Figure 1. Some deviation in actual track lines, including the order of survey operations, could be necessary for reasons such as science drivers, poor data quality, inclement weather, or mechanical issues with the research vessel and/or equipment. The survey will occur within the EEZs of the United States and Canada, as well as in U.S. state waters and Canadian territorial waters, ranging in depth 60-4400 meters (m). A maximum of 6,540 kilometers (km) of transect lines will be surveyed. Most of the survey (69 percent) will occur in deep water (>1,000 m), 28 percent will occur in intermediate water (100-1,000 m deep), and 3 percent will take place in shallow water <100 m deep. Approximately 3.6 percent of the transect lines (234 km) will be undertaken in Canadian territorial waters (from 0-12 nautical miles (22.2 km) from shore), with most

effort in intermediate water depths. NMFS cannot authorize the incidental take of marine mammals in the territorial seas of foreign nations, as the MMPA does not apply in those waters. However, NMFS has still calculated the level of incidental take in the entire activity area (including Canadian territorial waters) as part of the analysis supporting our determination under the MMPA that the activity will have a negligible impact on the affected species.

BILLING CODE 3510-22-P

EN28MY21.012

BILLING CODE 3510-22-C

Detailed Description of Specific Activity

The procedures to be used for the planned survey will be similar to those used during previous seismic surveys by L-DEO and will use conventional seismic methodology. The surveys will involve one source vessel, R/V

Langseth.

R/V

Langseth

will deploy an array of 36 airguns as an energy source with a total volume of ~6,600 in

3

. The array consists of 20 Bolt 1500LL airguns with volumes of 180 to 360 in

3

and 16 Bolt 1900LLX airguns with volumes of 40 to 120 in

3

. The airgun array configuration is illustrated in Figure 2-11 of NSF and USGS's Programmatic Environmental Impact Statement (PEIS; NSF-USGS, 2011). The vessel speed during seismic operations will be approximately 4.2 knots (~7.8 km/hour) during the survey and the airgun array will be towed at a depth of 12 m. The receiving system will consist of one 15-km long hydrophone streamer, OBSs, and OBNs. R/V

Oceanus,

which is owned by NSF and operated by Oregon State University, will be used to deploy the OBSs and OBNs. As the airguns are towed along the survey lines, the hydrophone streamer will transfer the data to the on-board processing system, and the OBSs and OBNs will receive and store the returning acoustic signals internally for later analysis.

Long 15-km-offset multichannel seismic (MCS) data will be acquired along numerous 2-D profiles oriented perpendicular to the margin and located to provide coverage in areas inferred to be rupture patches during past earthquakes and their boundary zones. The survey will also include several strike lines including one continuous line along the continental shelf centered roughly over gravity-inferred fore-arc basins to investigate possible segmentation near the down-dip limit of the seismogenic zone. The margin normal lines will extend ~50 km seaward of the deformation front to image the region of subduction bend faulting in the incoming oceanic plate, and landward of the deformation front to as close to the shoreline as can be safely maneuvered. L-DEO plans to survey the southern transects off Oregon first, followed by the profiles off Washington and Vancouver Island, British Columbia.

The OBSs will consist of short-period multi-component OBSs from the Ocean Bottom Seismometer Instrument Center (OBSIC) and a large-N array of OBNs from a commercial provider to record shots along ~11 MCS margin-perpendicular profiles. OBSs will be deployed at 10-km spacing along ~10 profiles from Vancouver Island to Oregon, and OBNs will be deployed at a 500-m spacing along a portion of three profiles off Oregon. Two OBS deployments will occur with a total of 115 instrumented locations. 60 OBSs will be deployed to instrument seven profiles off Oregon, followed by a second deployment of 55 OBSs to instrument four profiles off Washington and Vancouver Island. The first deployment off Oregon will occur prior to the start of the planned survey, after which R/V

Langseth

will acquire data in the southern portion of the study area. R/V

Oceanus

will start recovering the OBSs from deployment 1, and then re-deploy 55 OBSs off Washington and Vancouver Island, so that R/V

Langseth

can acquire data in the northern portion of the survey area. The OBSs have a height and diameter of ~1 m, and an ~80 kilogram (kg) anchor. To retrieve OBSs, an acoustic release transponder (pinger) is used to interrogate the instrument at a frequency of 8-11 kilohertz (kHz), and a response is received at a frequency of 11.5-13 kHz. The burn-wire release assembly is then activated, and the instrument is released to float to the surface from the anchor, which is not retrieved.

A total of 350 OBNs will be deployed: 179 nodes along one transect off northern Oregon, 107 nodes along a second transect off central Oregon, and 64 nodes along a third transect off southern Oregon. The nodes are not connected to each other; each node is independent from each other, and there are no cables attached to them. Each node has internal batteries; all data is recorded and stored internally. The nodes weigh 21 kg in air (9.5 kg in water). As the OBNs are small (330 millimeters (mm) × 289 mm × 115 mm), compact, not buoyant, and lack an anchor-release mechanism, they cannot be deployed by free-fall as with the OBSs. The nodes will be deployed and retrieved using a remotely operated vehicle (ROV); the ROV will be deployed from R/V

Oceanus.

OBNs will be deployed approximately 17 days prior to the start of the R/V

Langseth

cruise. The ROV will be fitted with a skid with capacity for 32 units, lowered to the seafloor, and towed at a speed of 0.6 knots at 5-10 m above the seafloor between deployment sites. After the 32 units are deployed, the ROV will be retrieved, the skid will be reloaded with another 32 units, and sent back to the seafloor for deployment, and so on. The ROV will recover the nodes 3 days after the completion of the R/V

Langseth

cruise. The nodes will be recovered one by one by a suction mechanism. Take of marine mammals is not expected to occur incidental to L-DEO's use of OBSs and OBNs.

In addition to the operations of the airgun array, a multibeam echosounder (MBES), a sub-bottom profiler (SBP), and an Acoustic Doppler Current Profiler (ADCP) will be operated from R/V

Langseth

continuously during the seismic surveys, but not during transit to and from the survey area. All planned geophysical data acquisition activities will be conducted by L-DEO with on-board assistance by the scientists who have planned the studies. The vessel will be self-contained, and the crew will live aboard the vessel. Take of marine mammals is not expected to occur incidental to use of the MBES, SBP, or ADCP because they will be operated only during seismic acquisition, and it is assumed that, during simultaneous operations of the airgun array and the other sources, any marine mammals close enough to be affected by the MBES, SBP, and ADCP would already be affected by the airguns. However, whether or not the airguns are operating simultaneously with the other sources, given their characteristics (

e.g.,

narrow downward-directed beam), marine mammals would experience no more than one or two brief ping exposures, if any exposure were to occur. Mitigation, monitoring, and reporting measures are described in detail later in this document (please see Mitigation and Monitoring and Reporting).

Comments and Responses

A notice of NMFS's proposal to issue an IHA to L-DEO was published in the

Federal Register

on April 7, 2020 (85 FR 19580). During the public comment period, NMFS received comment letters from the Marine Mammal Commission (Commission), Ecojustice (on behalf of the David Suzuki Foundation, Georgia Strait Alliance, Raincoast Conservation Foundation, and World Wildlife Fund Canada), Deep Green Wilderness, and a group of environmental non-governmental organizations (ENGOs) including the Center for Biological Diversity (CBD), Natural Resources Defense Council, Orca Relief Citizens Alliance, Friends of the San Juans, Whale and Dolphin Conservation, Friends of the Earth, Oceana, and Orca Conservancy. NMFS has posted the comments online at:

https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.

Please see the letters for full details and rationale. A summary of the comments and our responses are provided here.

Comment 1:

Ecojustice requested NMFS deny L-DEO's request for an IHA

because the survey will affect Southern Resident killer whale critical habitat (

e.g.,

Swiftsure and La Perouse Banks) designated in Canada under the Canadian Species at Risk Act (SARA). The commenter asserts that noise production in these areas will both harm or harass individuals and constitute destruction of a portion of Canadian critical habitat.

Response:

This comment is beyond the scope of NMFS' proposed action, which is to authorize take of marine mammals incidental to the proposed survey. NMFS does not allow or deny the survey itself, and NMFS' action of authorizing incidental take does not cause effects to critical habitat (in Canada or the U.S.). However, as part of their consultation with Canada's Department of Fisheries and Oceans (DFO) under Canada's SARA, L-DEO has removed all survey tracklines with associated ensonified areas that overlap with Canadian designated killer whale critical habitat at Swiftsure and La Perouse Bank (see Figure 1); therefore, the Canadian critical habitat will not be subject to destruction.

Comment 2:

Ecojustice asserts that the critically endangered status of Southern Resident killer whales means there is no acceptable level of take for the species. Similarly, the ENGOs recommended NMFS not issue any take authorization until it has effectively reduced the take of Southern Resident killer whales to zero, citing concern that behavioral disturbance can interfere with reproduction and survival due to lost foraging time.

Response:

NMFS disagrees that there is no acceptable level of take for Southern Resident killer whales, and the commenters have not demonstrated that any level of taking of Southern Resident killer whales would result in greater than a negligible impact on the stock. However, we do agree that additional effort to reduce impacts to Southern Resident killer whales is warranted to minimize to the extent practicable the amount of taking as well as the impact of taking that is authorized. In addition to removing tracklines within Canadian designated Southern Resident killer whale critical habitat at Swiftsure and La Perouse Banks (discussed above), L-DEO has removed and modified tracklines between Tillamook Head, Oregon and Barkley Sound, British Columbia, the area in which Southern Resident killer whales have the highest estimated densities (U.S. Navy 2019) and high-use foraging areas (NMFS 2019). The effect of these modifications to the survey plan is that, between these landmarks, the estimated Level B harassment ensonified area will not extend into water shallower than the 100-m depth contour. As a result, the total estimated take of Southern Resident killer whales has been reduced from 43 takes by Level B harassment in the proposed IHA (with an additional two takes within Canadian territorial waters, outside NMFS' jurisdiction) to 10 takes by Level B harassment (plus one take by Level B harassment within Canadian territorial waters), which is less than the population of any pod in the Southern Resident stock. This estimated take represents either 10 individual Southern Resident killer whales taken by Level B harassment once over the course of the survey, or a smaller number of individuals taken multiple times (

e.g.,

a single matriline of five animals taken by Level B harassment on two separate days). By avoiding surveying in the areas with highest expected Southern Resident killer whale presence and foraging rates, the likelihood of survey activities resulting in interference in feeding and migration that could result in lost feeding opportunities or necessitate additional energy expenditure to find other good foraging opportunities or migration routes is greatly reduced. Procedural mitigations that avoid the likelihood of injury, such as shutdown measures, also further reduce the likelihood of more severe behavioral responses.

Comment 3:

The ENGOs assert that NMFS inadequately considered the impacts of the proposed action on prey availability for Southern Resident killer whales, citing studies showing responses of fish to sound from seismic surveys. The ENGOs also state that NMFS must also consider the fitness of salmon being indirectly affected by the survey's impacts on herring, a key prey species for Pacific salmon.

Response:

NMFS disagrees with the suggestion that we ignored effects to prey species. In fact, we considered relevant literature (including that cited by the ENGOs) in finding that the most likely impact of survey activity to prey species such as fish and invertebrates would be temporary avoidance of an area, with a rapid return to pre-survey distribution and behavior, and minimal impacts to recruitment or survival anticipated. While there is a lack of specific scientific information to allow an assessment of the duration, intensity, or distribution of effects to prey in specific locations at specific times and in response to specific surveys, NMFS' review of the available information does not indicate that such effects could be significant enough to impact marine mammal prey to the extent that marine mammal fitness would be affected. We agree that seismic surveys could affect certain marine mammal prey species, and addressed these potential effects, as well as the potential for those effects to impact marine mammal populations, in our notice of proposed IHA (85 FR 19580; April 7, 2020). As stated in the notice of proposed IHA, our review of the available information and the specific nature of the activities considered herein suggest that L-DEO's proposed survey activities are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species. Further, any impacts to prey species are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.

For additional information on the effects of L-DEO's proposed survey on salmon species present in the survey area, we refer the reader to the Biological Opinion issued by the NMFS Office of Protected Resources, Interagency Cooperation Division (available at

https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities

). In summary, fish react to sounds which are especially strong and/or intermittent low-frequency sounds, and behavioral responses such as flight or avoidance are the most likely effects. However, the reaction of fish to airguns depends on the physiological state of the fish, past exposures, motivation (

e.g.,

feeding, spawning, migration), and other environmental factors. While we agree that some studies have demonstrated that airgun sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs (

e.g.,

Fewtrell and McCauley, 2012; Pearson

et al.,

1992; Skalski

et al.,

1992; Santulli

et al.,

1999; Paxton

et al.,

2017), our review shows that the weight of evidence indicates either no or only a slight reaction to noise (

e.g.,

Miller and Cripps, 2013; Dalen and Knutsen, 1987; Pena

et al.,

2013; Chapman and Hawkins, 1969; Wardle

et al.,

2001; Sara

et al.,

2007; Jorgenson and Gyselman, 2009; Blaxter

et al.,

1981; Cott

et al.,

2012; Boeger

et al.,

2006), and that, most commonly, while there may be impacts to fish as a result of noise from nearby airguns, any effects will be temporary. For example, investigators reported significant, short-term declines in commercial fishing catch rate of gadid fishes during and for up to five days after seismic survey operations, but the catch rate subsequently returned to normal (Engas

et al.,

1996; Engas and Lokkeborg, 2002). Other studies have reported similar findings (

e.g.,

Hassel

et al.,

2004). Skalski

et al.

(1992) also found a reduction in catch rates—for rockfish (

Sebastes spp.

) in response to controlled airgun exposure—but suggested that the mechanism underlying the decline was not dispersal but rather decreased responsiveness to baited hooks associated with an alarm behavioral response. A companion study showed that alarm and startle responses were not sustained following the removal of the sound source (Pearson

et al.,

1992). Therefore, Skalski

et al.

(1992) suggested that the effects on fish abundance may be transitory, primarily occurring during the sound exposure itself. In some cases, effects on catch rates are variable within a study, which may be more broadly representative of temporary displacement of fish in response to airgun noise (

i.e.,

catch rates may increase in some locations and decrease in others) than any long-term damage to the fish themselves (Streever

et al.,

2016).

Sound pressure levels (SPLs) of sufficient strength have been known to cause injury to fish and fish mortality and, in some studies, fish auditory systems have been damaged by airgun noise (McCauley

et al.,

2003; Popper

et al.,

2005; Song

et al.,

2008). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen

et al.

(2012) showed that a temporary threshold shift (TTS) of 4-6 decibel (dB) was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long—both of which are conditions unlikely to occur for surveys that are necessarily transient in any given location and likely result in brief, infrequent noise exposure to prey species in any given area. For these surveys, the sound source is constantly moving, and most fish would likely avoid the sound source prior to receiving sound of sufficient intensity to cause physiological or anatomical damage. In addition, ramp-up may allow certain fish species the opportunity to move further away from the sound source.

NMFS considered the research referenced by the ENGOs and disagrees with the assertion that “[NMFS] irrationally discounts those impacts,” as well as with the commenters' interpretation of the literature. A recent comprehensive review (Carroll

et al.,

2017) found that results are mixed as to the effects of airgun noise on the prey of marine mammals. While some studies suggest a change in prey distribution and/or a reduction in prey abundance following the use of seismic airguns, others suggest no effects or even positive effects in prey abundance. Regarding Paxton

et al.

(2017), which describes findings related to the effects of a 2014 seismic survey on a reef off of North Carolina, while the study did show a 78 percent decrease in observed nighttime abundance for certain species, it is important to note that the evening hours during which the decline in fish habitat use was recorded (via video recording) occurred on the same day that the seismic survey passed, and no subsequent data is presented to support an inference that the response was long-lasting. Additionally, given that the finding is based on video images, the lack of recorded fish presence does not support a conclusion that the fish actually moved away from the site or suffered any serious impairment because fish may remain present yet not be recorded on video. In summary, this particular study corroborates prior studies demonstrating a startle response or short-term displacement.

The Carroll

et al.

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

et al.,

2017).

In summary, the scientific literature demonstrates that impacts of seismic surveys on marine mammal prey species will likely be limited to behavioral responses, the majority of prey species will be capable of moving out of the area during surveys, a rapid return to normal recruitment, distribution, and behavior for prey species is anticipated, and, overall, impacts to prey species, if any, will be minor and temporary. Prey species exposed to sound might move away from the sound source, experience TTS, experience masking of biologically relevant sounds, or show no obvious direct effects. Mortality from decompression injuries is possible in close proximity to a sound, but only limited data on mortality in response to airgun noise exposure are available (Hawkins

et al.,

2014). The most likely impacts for most prey species in a given survey area would be temporary avoidance of the area. Surveys using towed airgun arrays move through an area relatively quickly, limiting exposure to multiple impulsive sounds. In all cases, sound levels would return to ambient once a survey moves out of the area or ends and the noise source is shut down and, when exposure to sound ends, behavioral and/or physiological responses are expected to end relatively quickly (McCauley

et al.,

2000b). The duration of fish avoidance of a given area after survey effort stops is unknown, but a rapid return to normal recruitment, distribution, and behavior is anticipated. While the potential for disruption of spawning aggregations or schools of important prey species can be meaningful on a local scale, the mobile and temporary nature of most surveys and the likelihood of temporary avoidance behavior suggest that impacts would be minor.

NMFS believes that no evidence is presented to contradict our conclusions regarding likely impacts to marine mammals due to effects on prey species,

i.e.,

that impacts of the specified activity are not likely to have more than short-term adverse effects on any prey habitat or populations of prey species, and that any effects that do occur are not expected to result in significant or long-term consequences for individual marine mammals, or to contribute to adverse impacts on their populations.

Finally, we note that the National Science Foundation (NSF) is funding a study run by Oregon State University to assess the effects of L-DEO's survey activities on rockfish, Dungeness crab, and longnose skate. While the species chosen for this study do not represent important prey species for Southern Resident killer whales, which were the primary concern of the ENGOs, the study will provide important information on the effects of seismic surveys on nearshore species.

Comment 4:

The ENGOs commented that in making the negligible impact determination, NMFS underestimated the potential harm to the relevant stocks and distinct population segments (DPSs) of humpback whales, adding that the stock definitions for humpback whales are outdated and should match the DPSs as defined under the Endangered Species Act. The ENGOs assert that the takes proposed by NMFS are more than

negligible for the California/Oregon/Washington stock because the annual rate of serious injury and mortality (40.2 humpback whales per year) exceeds the potential biological removal (PBR; 33.4 humpbacks per year). Additionally, for both humpback and blue whales, the ENGOs assert that take by Level A harassment in the form of permanent hearing impairment amounts to serious injury, therefore the negligible impact determination overly relies on the assumption that there will be no serious injury or mortality from the seismic survey.

Response:

First, NMFS agrees that the alignment of MMPA stocks and Endangered Species Act (ESA) DPSs of humpback whales is important, and is actively working on rectifying the differences between stocks and DPSs. However, this issue is outside the scope of the action considered here. NMFS disagrees with the ENGOs' assertion that the authorized take of humpback or blue whales (or any species of marine mammal) by Level A harassment constitutes serious injury or has any relation to the PBR of the stock. PBR is defined in the MMPA (16 U.S.C. 1362(20)) 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 is a measure to be considered when evaluating the effects of mortality or serious injury on a marine mammal species or stock. There is no evidence that permanent threshold shift (PTS) can lead to mortality such that it should be considered “serious injury” or “removing” an individual from a stock. Therefore, it is not appropriate to use the PBR metric to directly evaluate the effects of Level A harassment (

e.g.,

PTS) on a stock in the manner suggested by the ENGOs. Given the short duration of exposure, only low levels of hearing impairment are likely to occur, and would not affect the fitness of individual marine mammals or populations.

As noted above, the PBR metric concerns levels of allowable removals from a population. Therefore, the PBR metric is not directly related to an assessment of negligible impact for this specified activity, which does not involve any expected potential for serious injury or mortality. PBR is not an appropriate metric with which to evaluate Level B harassment. However, we appropriately do consider levels of ongoing anthropogenic mortality from other sources, such as vessel strike, in relation to calculated PBR values as an important contextual factor in our negligible impact analysis, but a direct comparison of takes by harassment to the PBR value is not germane. While it is conceptually possible to link disturbance to potential fitness impacts to individuals over time (

e.g.,

population consequences of disturbance), we have no evidence that is the case here and the take authorized here is not expected to affect the reproduction or survivorship of any individual marine mammals.

Comment 5:

The ENGOs assert that the negligible impact determination also relies on an expectation that marine mammals would be likely to move away from the sound source, which contradicts other statements from the notice of proposed IHA that avoidance is not assumed to occur because “the extent to which marine mammals would move away from the sound source is difficult to quantify and is therefore not accounted for in the take estimates.” The commenters go on to state that animals avoiding the sound source still provokes an adverse behavioral reaction which displaces the animal from preferred habitat and potentially toward predators or shore with a risk of stranding.

Response:

NMFS does not rely on avoidance behaviors to make its negligible impact determination. NMFS agrees that avoidance of preferred habitat may temporarily limit optimal feeding or other biologically important behaviors. NMFS does not adjust take estimates based on the assumption that marine mammals would avoid the area, as the avoidance itself may constitute behavioral harassment. However, avoiding the sound source prevents the animal from exposure to the highest source levels, reducing the likelihood of temporary (Level B harassment) or permanent hearing impairment (Level A harassment), and reducing the intensity and/or duration of the harassment event. The avoidance is expected to be temporary, and animals are likely to return to the area after the survey vessel has passed through. In consideration of the likelihood of animals to independently avoid the sound source, and the mitigation requirements to shut down the airgun array if animals do approach within a certain distance, NMFS finds that the level of take expected to result from the survey is unlikely to have any impact on fitness or reproduction of individual animals, let alone populations.

Comment 6:

Citing studies suggesting that blue whales are especially sensitive to high intensity anthropogenic noise, such as mid-frequency sonar (

e.g.,

Goldbogen

et al.,

2013), the ENGOs suggest that NMFS' consideration of the impact of the proposed activities on blue whales may underestimate the adverse impacts on the stock.

Response:

As discussed in the notice of proposed IHA, Goldbogen

et al.

(2013) found blue whales feeding on highly concentrated prey in shallow depths were less likely to respond and cease foraging than whales feeding on deep, dispersed prey when exposed to simulated sonar sources, suggesting that the benefits of feeding for blue whales foraging on high-density prey may outweigh perceived harm from the acoustic stimulus, such as the seismic survey. Southall

et al.

(2019b) observed that after exposure to simulated and operational mid-frequency active sonar, more than 50 percent of blue whales in deep-diving states responded to the sonar, while no behavioral response was observed in shallow-feeding blue whales. Southall

et al.

(2019b) noted that the behavioral responses they observed were generally brief, of low to moderate severity, and highly dependent on exposure context (behavioral state, source-to-whale horizontal range, and prey availability). The proposed survey area does not represent a major feeding area for blue whales and any disruption of feeding is likely to be short-term and of low to sometimes moderate severity, with no anticipated effect on reproduction or survival for individual whales or the population as a whole.

Comment 7:

Deep Green Wilderness and the ENGOs noted that North Pacific right whales have been documented within the survey area, and recommended NMFS consider the potential effects of the survey on the species. Deep Green Wilderness referred to sightings of a North Pacific right whale at Swiftsure Bank in 2013, and the ENGOs noted an account of a sighting of a North Pacific right whale off northern Vancouver Island in May 2020.

Response:

We thank the organizations for providing information on recent observations of North Pacific right whales in the survey area. NMFS shares the commenters' concern regarding the status of this endangered species. Although sightings have been reported in the survey area, the rate of sightings is less than one per year and NMFS has determined the likelihood of the proposed 37-day survey encountering a North Pacific right whale is discountable. However, in the very unlikely event a North Pacific right whale is detected during the survey, at any distance, L-DEO must immediately shut down the airgun array to prevent exposure to potentially injurious sound levels and to minimize the intensity and

duration of any sound exposure, and must immediately report the observation to NMFS and Canada's DFO to further inform research on the distribution of the species.

Comment 8:

The ENGOs challenge NMFS' preliminary finding that the proposed take numbers are of no more than small numbers of marine mammals. The ENGOs reference a court decision that they assert supports a lower “small numbers” threshold, and highlight certain species for which the commenters deem the take to be too high.

Response:

The reference to a supposed take limit of 12 percent for small numbers comes from a 2003 district court opinion (

Natural Resources Defense Council

v.

Evans,

279 F. Supp. 2d 1129 (N.D. Cal. 2003)). However, given the particular administrative record and circumstances in that case, including the fact that our small numbers finding for the challenged incidental take rule was based on an invalid regulatory definition of small numbers, we view the district court's opinion regarding 12 percent as dicta. Moreover, since that time the Ninth Circuit Court of Appeals has upheld a small numbers finding that was not based on a quantitative calculation.

Center for Biological Diversity

v.

Salazar,

695 F.3d 893 (9th Cir. 2012). To maintain an interpretation of small numbers as a proportion of a species or stock that does not conflate with negligible impact, we use the following framework. A plain reading of “small” implies as corollary that there also could be “medium” or “large” numbers of animals from the species or stock taken. We therefore use a simple approach that establishes equal bins corresponding to small, medium, and large proportions of the population abundance.

NMFS's practice for making small numbers determinations is to compare the number of individuals estimated and authorized to be taken (often using estimates of total instances of take, without regard to whether individuals are exposed more than once) against the best available abundance estimate for that species or stock. We note, however, that although NMFS's implementing regulations require applications for incidental take to include an estimate of the marine mammals to be taken, there is nothing in paragraphs (A) or (D) of section 101(a)(5) that requires NMFS to quantify or estimate numbers of marine mammals to be taken for purposes of evaluating whether the number is small. (See

CBD

v.

Salazar.

) While it can be challenging to predict the numbers of individual marine mammals that will be taken by an activity (again, many models calculate instances of take and are unable to account for repeated exposures of individuals), in some cases we are able to generate a reasonable estimate utilizing a combination of quantitative tools and qualitative information. When it is possible to predict with relative confidence the number of individual marine mammals of each species or stock that are likely to be taken, the small numbers determination should be based directly upon whether or not these estimates exceed one third of the stock abundance. In other words, consistent with past practice, when the estimated number of individual animals taken (which may or may not be assumed as equal to the total number of takes, depending on the available information) is up to, but not greater than, one third of the species or stock abundance, NMFS will determine that the numbers of marine mammals taken of a species or stock are small.

Finally, regarding the species highlighted by the ENGOs with proposed take above 20 percent of the stock (Pacific white-sided dolphin, Risso's dolphin, pygmy and dwarf sperm whale, Dall's porpoise, harbor porpoise, northern fur seal and harbor seal), the revised take estimates for all of the aforementioned stocks aside from the California/Oregon/Washington stock of Dall's porpoise and Northern Oregon/Washington Coast stock of harbor porpoise represent under one-third of the stock. The analysis of these two stocks is discussed further in the Small Numbers section of this notice.

Comment 9:

The ENGOs further object to NMFS' small numbers determination for the Southern Resident killer whale, for which NMFS proposed to authorize take of more than 57 percent of the stock. Regarding the Southern Resident killer whale take estimate, the ENGOs disagree with NMFS' assumption that the number of individual Southern Resident killer whales taken by Level B harassment will be fewer than the total estimated instances of take due to the historical pattern of Southern Resident killer whales occupying the inland waters of the Salish Sea during the summer months. Additionally, because they travel in pods, the commenters assert that there is risk of exposure of an entire pod to airgun blasting, and state that they are unclear whether such aggregation has been considered.

Response:

The ENGO's objection to NMFS' small numbers threshold was addressed in the previous response, but we also note here that using the revised survey tracklines, the authorized take of Southern Resident killer whales represents only 13.7 percent of the stock, which falls under NMFS' threshold for small numbers, even if all takes represent different individuals taken by Level B harassment. The authorized take is less than the size of any pod of Southern Residents (J, K, or L pods), and is more likely to represent a single matriline (typically two to nine killer whales; Weiss

et al.,

2020) exposed to the survey on one or two days of the survey. NMFS agrees that the seasonal distribution of Southern Resident killer whales in recent years has deviated from the historical pattern of residency within the Salish Sea (

e.g.,

Shields

et al.,

2018), but note that our discussion of the distribution of Southern Resident killer whales was in the context of the U.S. Navy density models used to estimate take, which were created with the assumption that the entire population was either within the Salish Sea or outside the Salish Sea on the outer coast at any given time (U.S. Navy 2019). Southern Resident killer whales may be encountered during the survey along the coast, but the revised tracklines are expected to reduce the likelihood of whole pods being exposed to sound from the seismic survey by avoiding surveying in areas of expected high Southern Resident killer whale occurrence. Additionally, L-DEO is required to shut down the airgun array if killer whales (of any ecotype) are observed at any distance. Killer whales are highly visible animals, especially when traveling as large pods as the ENGOs suggest, and we expect PSOs will be able to detect killer whales at sufficient distances to implement shutdown procedures to avoid exposing large pods of killer whales to sounds from the survey.

Comment 10:

The ENGOs commented that NMFS must include estimated takes off Canada in making the small numbers determination, adding that since the take prohibition applies outside U.S. waters, the Service must make a small numbers determination that analyzes all of the estimated take. The commenters state that, accordingly, NMFS must demonstrate compliance with these standards and may not issue the authorization without fully analyzing and authorizing all take contemplated under this action. The commenters also state that it is unclear in the small numbers determination whether the takes in Canadian waters have been taken into consideration. The ENGOs also expressed concern that the small numbers determination was based on 1 year of activities and did not consider

the potential renewal of the authorization.

Response:

NMFS has not authorized any take of marine mammals within the territorial waters of Canada. An estimate of take that may occur within Canadian territorial waters is presented in Table 11, and the take has been considered in our negligible impact determination as part of the larger implications of the survey on the marine mammal populations and habitat in the survey area. However, our small numbers analysis applies only to the take we have authorized. NMFS has made the necessary small numbers and negligible impact determinations for this authorization.

The ENGOs appear to misunderstand the context in which a potential renewal IHA could be issued for this activity, as well as the requirements for issuing a renewal IHA. Although renewal IHAs in general may be issued in appropriate circumstances for up to another year of identical or nearly identical activities as were covered by the initial IHA, this context is not relevant to the proposed seismic survey. L-DEO would not conduct the survey as planned and then duplicate the survey activities in a subsequent year. Regardless, NMFS would not grant a renewal IHA in those circumstances. However, if the planned survey were unexpectedly delayed for another year, NMFS could consider a request for issuance of a renewal IHA. In order to do so, NMFS would need to review all relevant information, including the status of the affected species or stocks and any other pertinent information, such as information relevant to the small numbers determination. In short, potential consideration of a renewal in this context would necessarily be associated with the same activity associated with this IHA, in the event that it is not conducted during the period of effectiveness for this IHA, and would entail a review of all relevant information to ensure that the findings NMFS has made in support of issuance of this initial IHA remain valid.

Comment 11:

The ENGOs recommended NMFS analyze the effects of L-DEO's use of a multi-beam echosounder (MBES) associated with the survey, noting that the proposed equipment (the Kongsberg Simrad E122) is similar to another Kongsberg system that was closely associated with a 2008 mass stranding of melon-headed whales in Madagascar. The ENGOs recommended NMFS apply its take threshold for continuous noise sources (120 dB) rather than its threshold for intermittent sources (160 dB) to the proposed system and revise its take estimates accordingly. Further, NMFS should not assume, for purposes of making its negligible impact determinations, that the severity of impacts from an airgun array operating concurrently with such an echosounder system would be equivalent to that of an airgun array operating alone.

Response:

Although it is correct that an investigation of the stranding event referenced by the ENGOs indicated that use of a high-frequency mapping system (12-kilohertz (kHz) MBES) was the most plausible and likely initial behavioral trigger of the event (with the caveat that there was no unequivocal and easily identifiable single cause), the panel also noted several site- and situation-specific secondary factors that may have contributed to the avoidance responses that led to the eventual entrapment and mortality of the whales (Southall

et al.,

2013). Specifically, regarding survey patterns prior to the event and in relation to bathymetry, the vessel transited in a north-south direction on the shelf break parallel to the shore, ensonifying deep-water habitat prior to operating intermittently in a concentrated area offshore from the stranding site. This may have trapped the animals between the sound source and the shore, thus driving them towards the lagoon system. Shoreward-directed surface currents and elevated chlorophyll levels in the area preceding the event may also have played a role. The risk of similar events recurring is expected to be very low, given the extensive use of active acoustic systems used for scientific and navigational purposes worldwide on a daily basis and the lack of direct evidence of such responses previously reported. The only report of a stranding that may be associated with this type of sound source is the one reported in Madagascar.

NMFS disagrees with the recommendation that the 120 dB threshold should be applied to estimate takes incidental to use of the MBES. Sound sources can be divided into broad categories based on various criteria or for various purposes. As discussed by Richardson

et al.

(1995), source characteristics include strength of signal amplitude, distribution of sound frequency and, importantly in context of these thresholds, variability over time. With regard to temporal properties, sounds are generally considered to be either continuous or transient (

i.e.,

intermittent). Continuous sounds, which are produced by the industrial noise sources for which the 120-dB behavioral harassment threshold was selected, are simply those whose sound pressure level remains above ambient sound during the observation period (ANSI, 2005). Intermittent sounds are defined as sounds with interrupted levels of low or no sound (NIOSH, 1998). Simply put, a continuous noise source produces a signal that continues over time, while an intermittent source produces signals of relatively short duration having an obvious start and end with predictable patterns of bursts of sound and silent periods (

i.e.,

duty cycle) (Richardson and Malme, 1993). It is this fundamental temporal distinction that is most important for categorizing sound types in terms of their potential to cause a behavioral response. For example, Gomez

et al.

(2016) found a significant relationship between source type and marine mammal behavioral response when sources were split into continuous (

e.g.,

shipping, icebreaking, drilling) versus intermittent (

e.g.,

sonar, seismic, explosives) types. In addition, there have been various studies noting differences in responses to intermittent and continuous sound sources for other species (

e.g.,

Neo

et al.,

2014; Radford

et al.,

2016; Nichols

et al.,

2015).

Sound sources may also be categorized based on their potential to cause physical damage to auditory structures and/or result in threshold shifts. In contrast to the temporal distinction discussed above, the most important factor for understanding the differing potential for these outcomes across source types is simply whether the sound is impulsive or not. Impulsive sounds, such as those produced by airguns, are defined as sounds which are typically transient, brief (<1 second (sec)), broadband, and consist of a high peak pressure with rapid rise time and rapid decay (ANSI, 1986; NIOSH, 1998). These sounds are generally considered to have greater potential to cause auditory injury and/or result in threshold shifts. Non-impulsive sounds can be broadband, narrowband or tonal, brief or prolonged, continuous or intermittent, and typically do not have the high peak pressure with rapid rise/decay time that impulsive sounds do (ANSI, 1995; NIOSH, 1998). Because the selection of the 160-dB behavioral threshold was focused largely on airgun signals, it has historically been commonly referred to as the “impulse noise” threshold (including by NMFS). However, this longstanding confusion in terminology—

i.e.,

the erroneous impulsive/continuous dichotomy—presents a narrow view of the sound sources to which the thresholds apply, and inappropriately implies a limitation in scope of applicability for the 160-dB behavioral threshold in particular.

An impulsive sound is by definition intermittent; however, not all intermittent sounds are impulsive. Many sound sources for which it is generally appropriate to consider the authorization of incidental take are in fact either impulsive (and intermittent) (

e.g.,

impact pile driving) or continuous (and non-impulsive) (

e.g.,

vibratory pile driving). However, scientific sonars (such as MBESs) present a less common case where the sound produced is considered intermittent but non-impulsive. We note also the commenters' assertion that the system produces “virtually continuous noise output” in support of their recommendation to apply the continuous noise threshold to evaluation of this source. In context of marine mammal hearing, this would mean that the interval between signals would not be discernible to the animal, rendering them effectively continuous. However, echosounder signals are emitted in a similar fashion as odontocete echolocation click trains. Research indicates that marine mammals, in general, have extremely fine auditory temporal resolution and can detect each signal separately (

e.g.,

Au

et al.,

1988; Dolphin

et al.,

1995; Supin and Popov, 1995; Mooney

et al.,

2009), especially for species with echolocation capabilities. Therefore, it is highly unlikely that marine mammals would perceive echosounder signals as being continuous.

Given the existing paradigm—dichotomous thresholds appropriate for generic use in evaluating the potential for behavioral harassment resulting from exposure to continuous or intermittent sound sources—the ENGOs do not adequately explain why potential harassment from an intermittent sound source should be evaluated using a threshold developed for use with continuous sound sources. Therefore, we have not reevaluated L-DEO's use of the MBES using the 120 dB continuous noise threshold.

As discussed in the notice of proposed IHA, due to the lower source level of the MBES relative to the R/V

Langseth's

airgun array, sounds from the MBES are expected to be effectively subsumed by the sounds from the airgun array when both sources are operational. Thus, NMFS has determined that any marine mammal potentially exposed to sounds from the MBES would already have been exposed to sounds from the airgun array, which are expected to propagate further in the water, when both sources are operational. NMFS has determined that, given the movement and speed of the vessel and the intermittent and narrow downward-directed nature of the sounds emitted by the MBES (each ping emitted by the MBES consists of eight (in water >1,000 m deep) or four (<1,000 m) successive fan-shaped transmissions, each ensonifying a sector that extends 1° fore-aft), the MBES would result in no more than one or two brief ping exposures to any individual marine mammal, if any exposure were to occur. The ENGOs do not offer any evidence in support of their contention that potentially greater impacts than we have considered should be assumed likely in relation to use of this source.

Comment 12:

The ENGOs comment that NMFS has failed to implement “means of effecting the least practicable impact” on marine mammals and assert that NMFS relies on mitigation measures that are known to be ineffective (

e.g.,

real-time detection-based measures).

Response:

Under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking by harassment pursuant to such activity, and other means of effecting the least practicable impact on such species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of such species or stock for taking for subsistence uses (hereinafter referred to as least practicable adverse impact). NMFS does not have a regulatory definition for least practicable adverse impact.

NMFS disagrees with the assertion that we have failed to meet the least practicable adverse impact standard in this case. NMFS considered all recommended mitigation in the context of both the reduction of impacts on marine mammal species and stocks and their habitat and the practicability of such mitigation in reaching the required set of measures that we believe satisfy the least practicable adverse impact standard.

NMFS' evaluation of potential mitigation measures includes consideration of two primary factors:

(1) The manner in which, and the degree to which, implementation of the potential measure(s) is expected to reduce adverse impacts to marine mammal species or stocks, their habitat, and their availability for subsistence uses (where relevant). This analysis considers such things as the nature of the potential adverse impact (such as likelihood, scope, and range), the likelihood that the measure will be effective if implemented, and the likelihood of successful implementation.

(2) The practicability of the measures for applicant implementation. Practicability of implementation may consider such things as cost, impact on activities, personnel safety, and practicality of implementation.

While the language of the least practicable adverse impact standard calls for minimizing impacts to affected species or stocks and their habitat, NMFS recognizes that the reduction of impacts to those species or stocks accrues through the application of mitigation measures that limit impacts to individual animals. Accordingly, NMFS' analysis focuses on measures that are designed to avoid or minimize impacts on individual marine mammals that are likely to increase the probability or severity of population-level effects.

While direct evidence of impacts to species or stocks from a specified activity is rarely available, and additional study is still needed to understand how specific disturbance events affect the fitness of individuals of certain species, there have been improvements in understanding the process by which disturbance effects are translated to the population. With recent scientific advancements (both marine mammal energetic research and the development of energetic frameworks), the relative likelihood or degree of impacts on species or stocks may often be inferred given a detailed understanding of the activity, the environment, and the affected species or stocks. This same information is used in the development of mitigation measures and helps us understand how mitigation measures contribute to lessening effects (or the risk thereof) to species or stocks. NMFS also acknowledges that there is always the potential that new information, or a new recommendation that had not previously been considered, becomes available and necessitates re-evaluation of mitigation measures to see if further reductions of population impacts are possible and practicable.

In the evaluation of specific measures, the details of the specified activity will necessarily inform each of the two primary factors discussed above (expected reduction of impacts and practicability) and are carefully considered to determine the types of mitigation that are appropriate under the least practicable adverse impact standard. Analysis of how a potential mitigation measure may reduce adverse impacts on a marine mammal stock or species and practicability of implementation are not issues that can be meaningfully evaluated through a yes/no lens. The manner in which, and the degree to which, implementation of a measure is expected to reduce impacts, as well as its practicability, can

vary widely. For example, a time-area restriction could be of very high value for reducing the potential for, or severity of, population-level impacts (

e.g.,

avoiding disturbance of feeding females in an area of established biological importance) or it could be of lower value (

e.g.,

decreased disturbance in an area of high productivity but of less firmly established biological importance). Regarding practicability, a measure might involve restrictions in an area or time that impede the operator's ability to acquire necessary data (higher impact), or it could mean incremental delays that increase operational costs but still allow the activity to be conducted (lower impact). A responsible evaluation of “least practicable adverse impact” will consider the factors along these realistic scales. Expected effects of the activity and of the mitigation as well as status of the stock all weigh into these considerations. Accordingly, the greater the likelihood that a measure will contribute to reducing the probability or severity of adverse impacts to the species or stock or their habitat, the greater the weight that measure is given when considered in combination with practicability to determine the appropriateness of the mitigation measure, and vice versa. Consideration of these factors is discussed in greater detail below.

1. Reduction of Adverse Impacts to Marine Mammal Species or Stocks and Their Habitat

The emphasis given to a measure's ability to reduce the impacts on a species or stock considers the degree, likelihood, and context of the anticipated reduction of impacts to individuals (and how many individuals) as well as the status of the species or stock.

The ultimate impact on any individual from a disturbance event (which informs the likelihood of adverse species- or stock-level effects) is dependent on the circumstances and associated contextual factors, such as duration of exposure to stressors. Though any proposed mitigation needs to be evaluated in the context of the specific activity and the species or stocks affected, measures with the following types of effects have greater value in reducing the likelihood or severity of adverse species- or stock-level impacts: Avoiding or minimizing injury or mortality; limiting interruption of known feeding, breeding, mother/young, or resting behaviors; minimizing the abandonment of important habitat (temporally and spatially); minimizing the number of individuals subjected to these types of disruptions; and limiting degradation of habitat. Mitigating these types of effects is intended to reduce the likelihood that the activity will result in energetic or other types of impacts that are more likely to result in reduced reproductive success or survivorship. It is also important to consider the degree of impacts that are expected in the absence of mitigation in order to assess the added value of any potential measures. Finally, because the least practicable adverse impact standard gives NMFS discretion to weigh a variety of factors when determining appropriate mitigation measures and because the focus of the standard is on reducing impacts at the species or stock level, the least practicable adverse impact standard does not compel mitigation for every kind of take, or every individual taken, if that mitigation is unlikely to meaningfully contribute to the reduction of adverse impacts on the species or stock and its habitat, even when practicable for implementation by the applicant.

The status of the species or stock is also relevant in evaluating the appropriateness of potential mitigation measures in the context of least practicable adverse impact. The following are examples of factors that may (either alone, or in combination) result in greater emphasis on the importance of a mitigation measure in reducing impacts on a species or stock: The stock is known to be decreasing or status is unknown, but believed to be declining; the known annual mortality (from any source) is approaching or exceeding the PBR level; the affected species or stock is a small, resident population; or the stock is involved in a UME or has other known vulnerabilities, such as recovering from an oil spill.

Habitat mitigation, particularly as it relates to rookeries, mating grounds, and areas of similar significance, is also relevant to achieving the standard and can include measures such as reducing impacts of the activity on known prey utilized in the activity area or reducing impacts on physical habitat. As with species- or stock-related mitigation, the emphasis given to a measure's ability to reduce impacts on a species or stock's habitat considers the degree, likelihood, and context of the anticipated reduction of impacts to habitat. Because habitat value is informed by marine mammal presence and use, in some cases there may be overlap in measures for the species or stock and for use of habitat.

NMFS considers available information indicating the likelihood of any measure to accomplish its objective. If evidence shows that a measure has not typically been effective nor successful, then either that measure should be modified or the potential value of the measure to reduce effects should be lowered.

2. Practicability

Factors considered may include those costs, impact on activities, personnel safety, and practicality of implementation.

In carrying out the MMPA's mandate for this action, NMFS applies the previously described context-specific balance between the manner in which and the degree to which measures are expected to reduce impacts to the affected species or stocks and their habitat and practicability for operators. The effects of concern (

i.e.,

those with the potential to adversely impact species or stocks and their habitat), addressed previously in the Potential Effects of the Specified Activity on Marine Mammals and Their Habitat section of the notice of proposed IHA, include auditory injury, severe behavioral reactions, disruptions of critical behaviors, and to a lesser degree, masking and impacts on acoustic habitat. Here, we focus on measures with proven or reasonably presumed ability to avoid or reduce the intensity of acute exposures that have potential to result in these anticipated effects with an understanding of the drawbacks or costs of these requirements, as well as time-area restrictions that would avoid or reduce both acute and chronic impacts. To the extent of the information available to NMFS, we considered practicability concerns, as well as potential undesired consequences of the measures,

e.g.,

extended periods using the acoustic source due to the need to reshoot lines. NMFS also recognizes that instantaneous protocols, such as shutdown requirements, are not capable of avoiding all acute effects, and are not suitable for avoiding many cumulative or chronic effects and do not provide targeted protection in areas of greatest importance for marine mammals. Therefore, in addition to a basic suite of seismic mitigation protocols, we also consider measures that may or may not be appropriate for other activities (

e.g.,

survey plan modifications specific to the action discussed herein), but that are warranted here given the potential for impacts to a stock of particular concern (

i.e.,

Southern Resident killer whales) (see Negligible Impact Analysis and Determination), and the information we have regarding habitat for certain species.

We appreciate the ENGOs suggestions for additional mitigation and monitoring

requirements. However, we note that many of the recommendations require a scale of effort that is not commensurate to the scale of either the underlying activities or the anticipated impacts of the activities on marine mammals covered by this authorization. In other words, many of the recommended measures would necessitate complex and expensive survey designs and methods that are not reasonable in the context of an activity that consists of one mobile source moving across a large area and that will last for only 37 days. As described in the

Mitigation Measures Considered but Eliminated

section of this notice, out of concern for the status of Southern Resident killer whales and proposed critical habitat, NMFS considered implementing a closure area and prohibiting L-DEO from conducting survey operations between the 200-m isobath and the coastline. However, as the main goal of L-DEO's survey is to examine the geologic features of the Cascadia subduction zone along the coastal shelf, NMFS determined that this exclusion would not be practicable. NMFS did ultimately incorporate mitigation measures that are specific to this action and beyond that which is typically required for L-DEO's surveys. Specifically, we have required L-DEO to revise their proposed tracklines to avoid surveying in waters less than 100 m deep in areas with highest estimated Southern Resident killer whale occurrence. We have determined this measure, which will significantly reduce impacts to Southern Resident killer whales while allowing L-DEO to complete its survey objectives, to be practicable. Additionally, L-DEO must use a second vessel traveling ahead of the R/V

Langseth

with additional PSOs to increase the likelihood of detecting Southern Resident killer whales and, therefore, allowing for greater efficacy in implementing shutdown procedures to minimize impacts to animals that may be in the area. Regardless of whether other monitoring plans suggested by the ENGOs would also suffice, NMFS has determined that the mitigation and monitoring required as part of this authorization meets the MMPA requirement for least practicable adverse impact.

Comment 13:

The ENGOs suggested NMFS should work with L-DEO and explore ways to conduct the survey without ensonifying designated and proposed Southern Resident killer whale critical habitat, or at minimum, prohibit ramp-up in the proposed and designated critical habitat unless the location of all three pods of Southern Resident killer whales is known to be within the Salish Sea or in an area not impacted by survey activity on each day of the survey.

Response:

As discussed above, NMFS considered prohibiting L-DEO from operating within the proposed critical habitat for Southern Resident killer whales, but determined that the exclusion was not practicable, as it would prevent L-DEO from completing their survey objectives. NMFS has worked with L-DEO to revise the survey tracklines to avoid ensonifying waters less than 100 m deep above the Level B harassment threshold, between Tillamook Head, Oregon and Barkley Sound, British Columbia. As stated above, this area contains the highest estimated density of Southern Resident killer whales. NMFS has not required L-DEO to confirm the location of Southern Resident killer whales before beginning survey activities each day as the location of all three pods is often unknown and waiting for confirmation would not allow L-DEO to complete their research objectives. L-DEO is required to contact several entities (including NMFS, Canada's DFO, Orca Network, and the Whale Museum) on each day of the survey to obtain any recent reports of Southern Resident killer whales in the survey area.

Comment 14:

The ENGOs suggested NMFS should consider closures or limits on survey activity in proposed humpback whale critical habitat and biologically important areas for blue whales.

Response:

The revised tracklines mentioned above, while primarily intended to avoid areas of highest Southern Resident killer whale occurrence, also reduce survey tracklines in recently finalized humpback whale critical habitat (86 FR 21082; April 21, 2021) and BIAs for humpback whales and other marine mammals (we note that no BIAs for blue whales have been identified in the survey area). Eliminating all tracklines in humpback whale critical habitat would prevent L-DEO from completing their research objectives, as the proposed critical habitat occupies most of the continental shelf area off of the west coast of the U.S., the key area for L-DEO's research. Additionally, the ENGOs do not provide any substantive reasoning for why prohibiting L-DEO from operating within humpback whale critical habitat or BIAs is warranted. As discussed in the Negligible Impact Analysis and Determination section of this notice, L-DEO's activity is not expected to have a lasting physical impact on humpback whale critical habitat, prey within it, or overall humpback whale fitness.

Comment 15:

In addition to vessel-based passive acoustic monitoring (PAM), the ENGOs suggested NMFS should require the use of existing moored passive acoustic monitoring systems and installation of temporary hydrophones or sonabuoys in the survey area to monitor marine mammal presence.

Response:

NMFS appreciates the suggestions regarding increasing acoustic monitoring. However, the existing network of acoustic recorders along the Washington coast is comprised of archival recorders, which are not monitored in real-time. While the deployment of temporary hydrophones and sonabuoys in the survey area may aid in detection and monitoring of marine mammals, NMFS does not expect that any additional protection would outweigh the cost and practicability concerns associated with additional personnel required to monitor the systems and relay detections to the research vessel. The use of on-board PAM will adequately alert L-DEO of vocalizing marine mammals in the immediate vicinity of the survey activity.

Comment 16:

The ENGOs recommended NMFS should require the use of a support vessel traveling ahead of the R/V

Langseth

in proposed critical habitat for humpback whales and biologically important areas (BIAs) for other cetaceans.

Response:

The support vessel referenced by the ENGOs is required to travel approximately 5 km ahead of the R/V

Langseth

while surveying in waters 200 m or less between Tillamook Head, Oregon and Barkley Sound, British Columbia (see Mitigation section of this notice). This area encompasses much of the critical habitat for humpback whales and biologically important areas for other species (

e.g.,

gray whale BIA for migration). The area of the humpback whale critical habitat expected to be surveyed on a given day is only a small portion of the overall critical habitat along the coast. Any impacts to marine mammals in this area are expected to be minor and temporary, and any additional protection that may be provided by requiring L-DEO to use the support vessel outside of the 200-m isobath is not warranted in the context of the expected effects and practicability concerns.

Comment 17:

The ENGOs suggested NMFS should prohibit survey activity in low-visibility conditions.

Response:

NMFS disagrees that survey activity should be prohibited in low-visibility conditions. Any requirement to cease operations during low visibility conditions, including at

night, would not only be impracticable, it would also likely result in greater impacts to marine mammals, as such a measure would require operations to continue for significantly more time, to make up for lost operations during low-visibility times. Ramp-up of the acoustic source, when necessary, may occur at times of poor visibility (including nighttime), assuming that a pre-clearance period has been observed. If the pre-clearance period occurs at nighttime, the pre-clearance watch would be conducted only by the acoustic observer.

Comment 18:

The ENGOs suggested NMFS should consider whether aerial observations would have less impact (than the support vessel).

Response:

Similar to the suggestion of deploying additional PAM systems above, NMFS has determined it is not practicable to require L-DEO to use aerial monitoring systems. NMFS does not expect that any additional protection would outweigh the cost and practicability of additional personnel required to monitor the systems and relay detections to the research vessel.

Comment 19:

The ENGOs suggested the 1,500-meter exclusion zone, which is required for beaked whales, should apply for other marine mammal species that they suggest are particularly sensitive — such as harbor porpoises, Steller sea lions, baleen whales (except gray whales) and Southern Resident killer whales. The commenters suggest that the presence of Southern Residents should trigger a shut-down whenever they are detected, regardless of distance.

Response:

NMFS disagrees that a larger standard exclusion zone is warranted for the species and groups suggested by the ENGOs. The standard exclusion zone for all marine mammals included in the IHA is 500 m, with larger exclusion zones or shutdown requirements for certain species and/or scenarios. NMFS' intent in prescribing a standard exclusion zone distance is to (1) encompass zones for most species within which auditory injury could occur on the basis of instantaneous exposure; (2) provide additional protection from the potential for more severe behavioral reactions (

e.g.,

panic, antipredator response) for marine mammals at relatively close range to the acoustic source; (3) provide consistency and ease of implementation for protected species observers (PSOs), who need to monitor and implement the exclusion zone; and (4) define a distance within which detection probabilities are reasonably high for most species under typical conditions. The use of 500 m as the zone is not based directly on any quantitative understanding of the range at which auditory injury would be entirely precluded or any range specifically related to disruption of behavioral patterns. Rather, NMFS believes it is based on a reasonable combination of factors. In summary, a practicable criterion such as this has the advantage of familiarity and simplicity while still providing in most cases a zone larger than relevant auditory injury zones, given realistic movement of source and receiver. Increased shutdowns, without a firm idea of the outcome the measure seeks to avoid, simply displace survey activity in time and increase the total duration of acoustic influence as well as total sound energy in the water, which NMFS seeks to avoid. In keeping with the four broad goals outlined above, and in context of the information given here, the standard 500-m exclusion zone is appropriate. The ENGOs do not provide any substantive reasoning for a larger zone.

The proposed IHA included the requirement to shut down the airgun array if killer whales (of any ecotype) are visually or acoustically detected at any distance and NMFS has retained this requirement in the final authorization.

Comment 20:

The ENGOs suggested NMFS should require L-DEO to use the lowest practicable source level for airgun usage.

Response:

L-DEO has selected the equipment necessary to achieve their research objectives. We have evaluated the specified activity as defined by the applicant, including changes agreed-upon with NMFS in order to provide additional protection for Southern Resident killer whales, and made the necessary findings to authorize taking of marine mammals incidental to L-DEO's survey activities. We also note that an expert panel was convened by the Bureau of Ocean Energy Management to determine whether it would be feasible to develop standards to determine a lowest practicable source level. The panel determined that it would not be reasonable or practicable to develop such metrics (see Appendix L in BOEM, 2017).

Comment 21:

The ENGOs suggested NMFS should require in situ sound source verification to determine accurate exclusion zones. Similarly, the Commission recommended NMFS require L-DEO analyze the data recorded on the OBSs and OBNs to determine the extents of the Level B harassment zones in shallow-, intermediate-, and deep-water depths and specify how the in-situ zones compare to the Level B harassment zones specified in the final authorization.

Response:

As stated above, the exclusion zones are not necessarily based on specific acoustic parameters, thus sound source verification is not necessary in the context of exclusion zones. Regarding the Commission's recommendation to conduct analysis of OBS data, L-DEO has not previously undertaken the type of analysis suggested by the Commission, and indicated to NMFS that it does not have the expertise or capability to do so at this time. In addition, we note that the Commission's recommendation is vague; detailed direction would be needed from the Commission on how to accomplish the recommended effort. This would need to include agreement on the analytical approach in order to meet expectations and to ensure acceptance of results. The Commission's recommendation does not acknowledge the time it would take to perform the analysis or the level of effort and cost that would be involved,

e.g.,

experts needed to obtain and review data, performing detailed comparative analysis, preparation of a report. Based on these concerns, NMFS believes that the recommendation is not practicable.

Also, implementation of this recommendation would not provide any additional conservation value (

e.g.,

improvement in mitigation effectiveness) for the proposed survey. The analysis would be retrospective and could be used to help inform analysis of future surveys in the same area. NSF is considering funding a survey of the Queen Charlotte Fault, north of the planned survey area for this action, but the survey would be completed before the acoustic data from this survey suggested by the Commission could be analyzed. NMFS is not aware of any other NSF-proposed seismic surveys on the R/V

Langseth

for this region in the foreseeable future that could incorporate the in situ data, if analyzed.

Comment 22:

The ENGOs suggested NMFS should prohibit the use of the Kongsberg Simrad 122 MBES in shallow water because the system's lower frequencies were designed for use in deeper water.

Response:

The ENGOs provide no justification for prohibiting the use of the MBES in shallow water aside from describing its characteristics. As discussed in previous comment responses, NMFS has determined the MBES is not likely to result in take of marine mammals and has no reason to believe that the use of the Kongsberg Simrad 122 in shallow water is cause for concern. The ENGOs do not provide any substantive argument to the contrary.

Comment 23:

The ENGOs suggested NMFS should require L-DEO to immediately cease survey activities if any authorized take limits are exceeded or if a take of an unauthorized species occurs (

e.g.,

take of a North Pacific right whale).

Response:

NMFS agrees with the ENGOs that L-DEO must shut down the airgun array if a marine mammal species for which take was not authorized, or a species for which authorization was granted but the takes have been met, approaches the Level A or Level B harassment zones. This requirement was included in the notice of proposed IHA but was inadvertently omitted from the draft IHA. The final authorization includes this requirement.

Comment 24:

The ENGOs suggested NMFS should require L-DEO to immediately cease survey activities if a take of an unauthorized level or intensity occurs, (

e.g.,

serious injury or mortality of any species or take of a Southern Resident killer whale by Level A harassment). The ENGOs further suggest that if take is found to have been exceeded, then there should be an investigation and additional mitigation to avoid any additional take before activities can resume. Similarly, the Commission recommended NMFS include in all draft and final authorizations an explicit requirement to cease activities if a marine mammal is injured or killed during the specified activities, including by vessel strike, until NMFS reviews the circumstances involving any injury or death that is likely attributable to the activities and determines what additional measures are necessary to minimize additional injuries or death.

Response:

NMFS does not expect that the proposed activities have the potential to result in injury or mortality to marine mammals and therefore does not agree that a blanket requirement for project activities to cease would be warranted. NMFS does not agree that a requirement for a vessel that is operating on the open water to suddenly stop operating is practicable, and it is unclear what mitigation benefit would result from such a requirement in relation to vessel strike. The Commission does not suggest what measures other than those prescribed in this IHA would potentially prove more effective in reducing the risk of strike. Therefore, we have not included this requirement in the authorization. NMFS retains authority to modify the IHA and cease all activities immediately based on a vessel strike and will exercise that authority if warranted.

With respect to the Commission's recommendation that NMFS include these requirements in all proposed and final IHAs, NMFS determines the requirements for mitigation measures in each authorization based on numerous case-specific factors, including the practicability of the measures for applicant implementation, which may consider such things as cost, impact on operations, and, in the case of a military readiness activity, personnel safety, practicality of implementation, and impact on the effectiveness of the military readiness activity. As NMFS must make these determinations on a case by case basis, we therefore do not agree with this recommendation.

Comment 25:

The ENGOs suggested NMFS impose a ship speed limit of 10 knots or less at all times to reduce noise and prevent ship strikes, with an exception for rare emergency or safety necessities. While the vessel conducting the survey is likely to be traveling well under 10 knots, NMFS should make this a requirement of any crew-transfer vessels used in the project.

Response:

NMFS has analyzed the potential for ship strike resulting from L-DEO's planned activity and has determined that the mitigation measures specific to ship strike avoidance are sufficient to avoid the potential for ship strike. These include: A requirement that all vessel operators reduce vessel speed to 10 knots (18.5 km/hour) or less when any large whale, any mother/calf pairs, pods, or large assemblages of non-delphinoid cetaceans are observed within 100 m of an underway vessel; a requirement that all survey vessels maintain a separation distance of 100 m or greater from all large whales, and 500 m or greater from any sighted North Pacific right whale (if a whale is observed but cannot be confirmed as a species other than a right whale, the vessel operator must assume that it is a right whale and take appropriate action); a requirement that if protected species are sighted while a vessel is underway, the vessel must take action as necessary to avoid violating the relevant separation distance (

e.g.,

attempt to remain parallel to the animal's course, avoid excessive speed or abrupt changes in direction until the animal has left the area); and a requirement that if marine mammals are sighted within the relevant separation distance, the vessel must reduce speed and shift the engine to neutral, not engaging the engines until animals are clear of the area. Finally, we note that all crew will be aboard the R/V

Langseth

through the entire survey, and there will not be any crew transfer vessels. We have determined that the ship strike avoidance measures are sufficient to ensure the least practicable adverse impact on species or stocks and their habitat and therefore we do not include the 10 knot ship speed limit recommended by the ENGOs.

Comment 26:

The ENGOs recommended NMFS require L-DEO to minimize the use of lines and cables and ensure that they are not flexible to reduce entanglement risk.

Response:

As discussed in the notice of proposed IHA, no incidents of entanglement of marine mammals with seismic survey gear have been documented in over 54,000 nautical miles (nmi; 100,000 km) of previous NSF-funded seismic surveys when observers were aboard (

e.g.,

Holst and Smultea 2008; RPS 2019; RPS 2021). Although entanglement with the streamer is theoretically possible, it has not been documented during tens of thousands of miles of NSF-sponsored seismic cruises or, to our knowledge, during hundreds of thousands of miles of industrial seismic cruises. Entanglement in OBSs and OBNs is also not expected to occur. There are a relative few deployed devices, and no interaction between marine mammals and any such device has been recorded during prior NSF surveys using the devices. There are no meaningful entanglement risks posed by the proposed survey, and therefore although we encourage L-DEO to use lines and cables that minimize entanglement risk, NMFS has not included the recommended requirement as a condition in the final authorization.

Comment 27:

The ENGOs state that marine mammal strandings are most likely to result when a sound source is moving directly toward the shore. Therefore, the ENGOs suggested NMFS should require reconfigured tracklines to avoid these approaches when the airguns are firing.

Response:

There is no conclusive evidence that exposure to airgun noise results in behaviorally-mediated forms of injury (

i.e.,

mass stranding events). Behaviorally-mediated injury has been primarily associated with beaked whales exposed to mid-frequency active (MFA) naval sonar. As described in the notice of proposed IHA, tactical sonar is very different from the noise produced by airguns. One should therefore not expect the same reaction to airgun noise as to these other sources. The ENGOs reference a survey conducted by L-DEO in 2002 that was contemporaneous with and reasonably associated spatially with the stranding of two Cuvier's beaked whales. However, the event was not considered a “true atypical mass stranding” (according to Frantzis (1998)) as used in the analysis of Castellote and Llorens (2016). While we agree with the

authors that this lack of evidence should not be considered conclusive, it is clear that there is very little evidence that seismic surveys should be considered as posing a significant risk of acute harm to beaked whales or other mid-frequency cetaceans. Although NMFS does not expect that stranding is a potential outcome of this survey activity, we also note that certain tracklines closest to shore (

i.e.,

in waters less than 100 m deep in areas with highest estimated Southern Resident killer whale occurrence) have been eliminated, further reducing the risk of this outcome. We have considered the potential for the proposed surveys to result in marine mammal stranding and have concluded that, based on the best available information, stranding is not expected to occur. Therefore, we have not adopted the ENGOs recommendation to reconfigure the survey tracklines.

Comment 28:

Both the ENGOs and Commission object to NMFS' potential consideration of a renewal IHA for this action, and in general. The ENGOs assert that IHA renewals are not permissible under the MMPA and instead recommend that applicants request a multi-year permit and accordingly reevaluate the effects of the action based on multiple years of take. The Commission recommended NMFS refrain from issuing IHA renewals for any authorization and instead use an abbreviated

Federal Register

notice process, which is similarly expeditious and fulfills NMFS' intent to maximize efficiencies. If NMFS continues to propose to issue IHA renewals, the Commission recommends that NMFS (1) stipulate that a renewal is a one-time opportunity (a) in all

Federal Register

notices requesting comments on the possibility of a renewal, (b) on its web page detailing the renewal process, and (c) in all draft and final authorizations that include a term and condition for a renewal and (2) if NMFS declines to adopt this recommendation, explain fully its rationale for not doing so.

Response:

NMFS' IHA renewal process meets all statutory requirements. All IHAs issued, whether an initial IHA or a renewal IHA, are valid for a period of not more than one year. In addition, the public has at least 30 days to comment on all proposed IHAs, with a cumulative total of 45 days for IHA renewals. As noted above, the

Request for Public Comments

section of the notice of proposed IHA made clear that the agency was seeking comment on both the initial proposed IHA and the potential issuance of a renewal for this project. Because any renewal (as explained in the

Request for Public Comments

section of the notice of proposed IHA) is limited to another year of identical or nearly identical activities in the same location (as described in the Description of Proposed Activity section) or the same activities that were not completed within the 1 year period of the initial IHA, reviewers have the information needed to effectively comment on both the immediate proposed IHA and a possible 1 year renewal, should the IHA holder choose to request one in the coming months.

While there will be additional documents submitted with a renewal request, for a qualifying renewal these will be limited to documentation that NMFS will make available and use to verify that the activities are identical to those in the initial IHA, are nearly identical such that the changes would have either no effect on impacts to marine mammals or decrease those impacts, or are a subset of activities already analyzed and authorized but not completed under the initial IHA. NMFS will also confirm, among other things, that the activities will occur in the same location; involve the same species and stocks; provide for continuation of the same mitigation, monitoring, and reporting requirements; and that no new information has been received that would alter the prior analysis. The renewal request will also contain a preliminary monitoring report, but that is to verify that effects from the activities do not indicate impacts of a scale or nature not previously analyzed. The additional 15-day public comment period provides the public an opportunity to review these few documents, provide any additional pertinent information and comment on whether they think the criteria for a renewal have been met. Between the initial 30-day comment period on these same activities and the additional 15 days, the total comment period for a renewal is 45 days.

In addition to the IHA renewal process being consistent with all requirements under section 101(a)(5)(D), it is also consistent with Congress' intent for issuance of IHAs to the extent reflected in statements in the legislative history of the MMPA. Through the provision for renewals in the regulations, description of the process and express invitation to comment on specific potential renewals in the Request for Public Comments section of each proposed IHA, the description of the process on NMFS' website, further elaboration on the process through responses to comments such as these, posting of substantive documents on the agency's website, and provision of 30 or 45 days for public review and comment on all proposed initial IHAs and renewals respectively, NMFS has ensured that the public “is invited and encouraged to participate fully in the agency decision-making process.”

NMFS does not agree with the Commission and therefore does not adopt the Commission's recommendation that NMFS use an abbreviated

Federal Register

notice instead of IHA renewal. NMFS has previously provided responses to this specific recommendation in multiple notices, including 84 FR 52464 (October 2, 2019). NMFS does agree with the Commission's recommendation that NMFS specify that IHA renewals are a one-time opportunity in all

Federal Register

notices requesting comments on the possibility of an IHA renewal, in all associated proposed and final IHAs, and on our website. NMFS has specified this in the final IHA for L-DEO's activities and has been including this in

Federal Register

notices and proposed and final authorizations since last year.

Comment 29:

The ENGOs recommended NMFS and L-DEO explore whether the proposed research could be conducted using alternative technologies or approaches that are less harmful to marine mammals. More broadly, and beyond the scope of this action, the ENGOs recommended NMFS engage with NSF to invest in research that explores alternative technologies.

Response:

NMFS agrees with the ENGOs that development and use of technologies that reduce the environmental impact of geophysical surveys is a laudable objective and may be warranted in some cases. Alternative technologies are in various stages of development, and none of the systems with the potential to replace airguns as a seismic source are currently commercially available for use on a scale of activity such as that considered herein. Although some alternative technologies are available now, or will be in the next several years, for select uses, none are at a stage where they can replace airgun arrays outright. However, some may be used in select environments when commercially available. Such technologies may be evaluated in the future as they become commercially available and on a scale commensurate to the need. In summary, while we agree that alternative technologies may be beneficial, the ENGOs do not suggest any specific technologies or approaches and the suggestion that NMFS engage with NSF to research these methods is outside the authority provided to NMFS by the MMPA. However, NMFS would consider participating in related efforts

by the ENGOs or other entities interested in these technologies.

Comment 30:

The ENGOs and the Commission recommended NMFS require L-DEO to use the method proposed by the Commission to estimate take and apply relevant corrections for airgun activity in daylight vs nighttime (including dawn and dusk) to better estimate the numbers of marine mammals taken by Level A and B harassment. The Commission further recommends that NMFS require L-DEO to specify in the final monitoring report (1) the number of days on which the airgun array was active and (2) the percentage of time and total time the array was active during daylight vs nighttime hours (including dawn and dusk).

Response:

NMFS appreciates the Commission's development of a recommended approach to better estimate the numbers of marine mammals that may have been taken during geophysical survey activities, including marine mammals that were not detected. The “Commission's method” (see the Commission's letter for additional discussion and citation to a full description provided in an addendum to a May 1, 2019 Commission comment letter) involves correction of marine mammal sightings data through use of proxies for marine mammal detectability (

f

(0)) and platform/observer bias on marine mammal detection (

g

(0)), and extrapolation of corrected marine mammal sightings data based on the assumed extent of the Level B harassment zones.

However, NMFS does not concur with the recommendation to require L-DEO to implement this approach because we do not have confidence in the reliability of estimates of potential marine mammal take that would result from use of the approach. The Commission does not address the multiple assumptions that must be made in order to have confidence in the estimates that would be produced through application of the method. For example, the assumption that the application of proxy values for

g

(0) and

f

(0) is appropriate is not justified (including application of

f

(0) values to species for which no value is available and assuming that application of

f

(0) to species in a wholly different region is appropriate). Notably,

g

(0) values are typically derived on a platform-specific basis, and even for specific observers—not generalized across platforms, as the Commission's method would require.

Separately, the appropriate application of distance sampling methods requires that certain assumptions are valid, and the Commission does not explain why these assumptions should be assumed to be valid during a seismic survey, as compared with typical line-transect surveys operating without an active acoustic source. For example, a key underlying concept of distance sampling methodology is that the probability of detecting an animal decreases as its distance from the observer increases. This cannot be assumed true during an active seismic survey. NMFS believes it unlikely that the numerous assumptions inherent to application of the Commission's method would be accepted in a research context (where distance sampling approaches are typically applied).

Furthermore, the area over which observations are to be extrapolated through the Commission's method is a modeled ensonified area. We do not believe it appropriate to assume a modeled ensonified area is always accurate for purposes of estimating total take. In purporting to estimate total takes, the method ignores the fact that marine mammals exposed to a level of received sound assumed to cause take for analytical purposes may not in fact respond behaviorally in a way that equates to take, especially at great distance from the source.

NMFS believes it is important to focus on collection and reporting of empirical data that can directly inform an assessment of the effects of a specified activity on the affected species or stock. While there may be value in an assessment of potential unobserved take, we need to proceed cautiously in the development of derived values given our low confidence in multiple inputs. NMFS is currently more broadly evaluating monitoring requirements, including data collection, interpretation, and reporting, as well as the specific issue the Commission has raised, and is committed to developing improved approaches.

NMFS does concur with the Commission's recommendation that NMFS require L-DEO to specify in the final monitoring report (1) the number of days on which the airgun array was active and (2) the percentage of time and total time the array was active during daylight vs nighttime hours (including dawn and dusk). This requirement has been added to the final authorization.

Comment 31:

The Commission asserts that L-DEO and other NSF-affiliated entities have not complied with all of the requirements set forth in certain final IHAs, and recommends that, should the alleged shortcomings occur again, NMFS refrain from issuing any further authorizations to L-DEO and other NSF-affiliated entities until such time that the monitoring reports include all of the required information.

Response:

NMFS appreciates the Commission's concern and will consider any future requests for incidental take authorization from NSF-affiliated entities according to the requirements of the MMPA.

Comment 32:

Noting its disagreement with L-DEO's approach to estimating the size of various ensonified areas, the Commission recommends that NMFS require L-DEO to either (1) re-estimate the proposed Level A and B harassment zones and associated takes of marine mammals using (a) both operational and site-specific environmental parameters, (b) what the Commission believes to be a comprehensive source model and (c) what the Commission believes to be an appropriate sound propagation model for the proposed IHA or (2) collect or provide the relevant acoustic data to substantiate that its modeling approach is conservative for both deep- and intermediate-water depths beyond the Gulf of Mexico. In addition, the Commission recommends that NMFS (1) explain why sound channels with downward refraction, as well as seafloor reflections, are not likely to occur during the geophysical survey, (2) specify the degree to which both of those parameters would affect the estimation (or underestimation) of Level B harassment zones in deep- and intermediate- water depths, (3) explain why L-DEO's model and other modeling approaches provide more accurate, realistic, and appropriate Level A and B harassment zones than BELLHOP (a different propagation model favored by the Commission), particularly for deep- and intermediate-water depths, and (4) explain why, if L-DEO's model and other modeling approaches are considered best available science, other action proponents that conduct seismic surveys are not implementing similar methods, particularly given their simplicity.

Response:

As noted by the Commission, these comments reflect a longstanding disagreement between NMFS and the Commission regarding L-DEO's approach to modeling the output of their airgun array and its propagation through the water column. NMFS has previously responded to similar Commission comments on L-DEO's modeling approach. We refer the reader to previous

Federal Register

notices providing responses rather than repeat them here (

e.g.,

84 FR 60059, November 07, 2019; 84 FR 54849, October 11, 2019; 84 FR 35073, July 22, 2019). Regardless of the addition of

slightly different points or modifications to the language with which the Commission expresses these points, the gist of the Commission's disagreement with L-DEO's modeling approach remains the same. NMFS believes that its prior responses have adequately explained the rationale for not following the Commission's recommendations and, importantly, why L-DEO's modeling approach is adequate.

Comment 33:

The ENGOs asserted that NMFS must prepare an Environmental Impact Statement and cannot rely on the NSF's Environmental Assessment (EA) because they believe that there are significant environmental impacts. The CBD's comments on the NSF's draft EA were incorporated by reference in the ENGOs' comment letter on the proposed IHA. CBD's comments on NSF's draft EA primarily concerned Southern Resident killer whales, similar to the concerns addressed above.

Response:

The NSF's draft EA, which NMFS adopted, was revised in consideration of CBD's comments (and those of other public commenters) and adequately analyzes the effects of the action. The commenters do not provide any information to support their claim of significant environmental impacts under NEPA. NMFS has reviewed the NSF's final EA, determined it to be sufficient, and adopted that EA and signed a Finding of No Significant Impact (FONSI).

Comment 34:

The ENGOs expressed doubt that the proposed activities were permissible under the ESA because they would jeopardize the continued existence of Southern Resident killer whales, North Pacific right whales, humpback whales, and blue whales, among other protected species and adversely modify proposed critical habitat. The proposed action clearly affects listed species as well as proposed and designated critical habitat, and therefore both NMFS and the NSF must undergo consultation under the ESA. The ENGOs urged NMFS to fulfill our commitment to complete consultation before authorizing any take of marine mammals, and requested a public comment period on the products of the consultation. The ENGOs strongly believe that NMFS cannot authorize the specified activities because they will jeopardize the recovery and survival of Southern Resident killer whales and North Pacific right whales.

Response:

NMFS has completed consultation under the ESA on our proposal to authorize take of listed marine mammals incidental to L-DEO's survey activities. The NMFS Office of Protected Resources, Interagency Cooperation Division issued a Biological Opinion concluding that the proposed action is not likely to jeopardize the continued existence of ESA-listed blue whales, fin whales, sei whales, sperm whales, Central America DPS humpback whales, Mexico DPS humpback whales, Southern Resident killer whale DPS, and Guadalupe fur seals and is not likely to destroy or adversely modify Steller sea lion or humpback whale critical habitat. There is no designated critical habitat in the action area for the other listed species. The Interagency Cooperation Division determined that a public comment period on the Biological Opinion was not warranted. The final Biological Opinion is available on our website at:

https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-research-and-other-activities.

Comment 35:

The ENGOs asserted that NMFS cannot approve the proposed activity without first consulting with the states of Washington and Oregon under the Coastal Zone Management Act (CZMA). The CZMA authorizes states with federally approved coastal management programs to review applications for Federal licenses or permits to conduct activities in, or outside of, the coastal zone that affects land uses, water uses, or natural resources within the coastal zone to ensure the activity is fully consistent with the state's management plan.

Response:

The NSF submitted consistency determinations to Washington and Oregon. Both the Washington State Department of Ecology and Oregon Coastal Management Program, the respective CZMA authorities for Washington and Oregon, concurred with the NSF's determinations. NMFS' action of authorizing take of marine mammal is incidental to the NSF's action of conducting the survey, therefore NMFS is not required to independently submit consistency determinations under CZMA.

Comment 36:

The ENGOs and Deep Green Wilderness expressed concern that the proposed survey overlaps with Olympic Coast National Marine Sanctuary (OCNMS). The ENGOs reference the National Marine Sanctuaries Act (NMSA), which aims to maintain the natural biological communities in the national marine sanctuaries, and to protect, and, where appropriate, restore and enhance natural habitats, populations, and ecological processes. To achieve these purposes, the NMSA requires that Federal agency actions internal or external to a national marine sanctuary, including private activities authorized by licenses, leases, or permits that are likely to destroy, cause the loss of, or injure any sanctuary resource are subject to consultation with the Secretary. The ENGOs noted that the action agency must follow the recommendations of the Secretary to avoid injury to any sanctuary resource or otherwise act to prevent and mitigate damage to such resources.

Response:

NMFS satisfied our responsibilities under section 304(d) of the NMSA. NMFS and the NSF drafted a joint Sanctuary Resource Statement (SRS) to consult with the NOAA Office of National Marine Sanctuaries (ONMS) under the NMSA. ONMS provided two recommended alternatives to minimize injury and to protect sanctuary resources: (1) Limit operations in OCNMS to daylight hours only regardless of depth; and 2) use of the secondary support vessel aiding in marine mammal observations throughout the entire sanctuary. NMFS has included these recommendations in the final IHA.

Changes From the Proposed IHA to Final IHA

There are numerous changes from the proposed IHA, starting with the timing of the survey. The survey was initially proposed to occur in summer 2020 but was delayed until summer 2021. Since conclusion of the public comment period in May 2020, NMFS has reviewed newly available information, including recent draft Stock Assessment Reports, information on relevant Unusual Mortality Events, and other scientific literature, and incorporated this information into our analysis of impacts on marine mammals and their habitat.

In addition to the timing changes, the survey tracklines have been modified to avoid surveying in the areas with the highest expected occurrence of Southern Resident killer whales. Between Tillamook Head, Oregon and Barkley Sound, British Columbia, L-DEO's planned tracklines have been truncated or removed entirely such that the ensonified area does not extend within the 100-meter (m) depth contour (see Estimated Take section for description of the Level B harassment zones and ensonified area). In addition to removing tracklines in nearshore shallow waters along the coast, L-DEO also modified tracklines such that the ensonified area will not extend within Canadian designated Southern Resident and Northern Resident killer whale critical habitat. Additionally, under consultation with Canada DFO, L-DEO removed all tracklines in waters 100 m or less in Canadian waters. Thus north of Tillamook Head, Oregon, no surveys

will occur in waters 100 m or less (see Figure 1). Based on informal recommendations from the Commission, NMFS recalculated the densities of Steller sea lions by applying the appropriate pup and non-pup growth rates of the population in Washington and British Columbia. Takes of all species and stocks have been recalculated using the revised tracklines and resulting ensonified areas. Additionally, NMFS has revised the mitigation requirements regarding use of a second support vessel and daylight-only operations in waters 200 m or less. The proposed IHA required the use of the support vessel and limited operations to daylight only along the entire survey area in waters 200 m or less. In consideration of operational practicability, we have revised that requirement to apply only between Tillamook Head, Oregon and Barkley Sound, British Columbia. Based on consultation with the Olympic Coast National Marine Sanctuary (OCNMS), the final IHA requires L-DEO to use the support vessel and operate only during daylight hours within the OCNMS, regardless of water depth. OCNMS has also been added to the list of entities L-DEO must contact each day to obtain sightings reports of Southern Resident killer whales in the survey area and, in turn, report their own sightings of killer whales to the Sanctuary. Finally, as recommended by the Commission, we have clarified the required elements that must be included in L-DEO's monitoring report.

Description of Marine Mammals in the Area of Specified Activities

Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history, of the potentially affected species. Additional information regarding population trends and threats may be found in NMFS's Stock Assessment Reports (SARs;

https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments

) and more general information about these species (

e.g.,

physical and behavioral descriptions) may be found on NMFS's website (

https://www.fisheries.noaa.gov/find-species

).

Table 1 lists all species with expected potential for occurrence in the survey area and summarizes information related to the population or stock, including regulatory status under the MMPA and ESA and potential biological removal (PBR), where known. For taxonomy, we follow Committee on Taxonomy (2020). PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as described in NMFS's SARs). While no mortality is anticipated or authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species and other threats.

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 or survey 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. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS's U.S. Pacific and Alaska SARs. All MMPA stock information presented in Table 1 is the most recent available at the time of publication and is available in the 2019 SARs (Caretta

et al.,

2020; Muto

et al.,

2020) and draft 2020 SARs (available online at:

https://www.fisheries.noaa.gov/national/marine-mammal-protection/draft-marine-mammal-stock-assessment-reports

). Where available, abundance and status information is also presented for marine mammals in Canadian waters in British Columbia.

Table 1—Marine Mammals That Could Occur in the Survey Area

Common name

Scientific name

Stock

ESA/MMPA status; strategic

(Y/N)

1

Stock abundance

(CV, N

min

, most recent abundance

survey)

2

PBR

Annual M/SI

3

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)

Family Eschrichtiidae:

Gray whale

Eschrichtius robustus

Eastern North Pacific

-/-; N

26,960 (0.05, 25,849, 2016)

801

131

Family Balaenopteridae (rorquals):

Humpback whale

Megaptera novaeangliae

California/Oregon/Washington

-/-; Y

2,900 (0.05, 2,784, 2014)

16.7

>42.1

Central North Pacific

-/-; Y

10,103 (0.30, 7,891, 2006)

83

26

Minke whale

Balaenoptera acutorostrata

California/Oregon/Washington

-/-; N

636 (0.72, 369, 2014)

3.5

>1.3

Sei whale

Balaenoptera borealis

Eastern North Pacific

E/D; Y

519 (0.4, 374, 2014)

0.75

>0.2

Fin whale

Balaenoptera physalus

California/Oregon/Washington

E/D; Y

9,029 (0.12, 8,127, 2014)

81

>43.7

Northeast Pacific

E/D; Y

3,168 (0.26, 2,554, 2013)

5.1

0.6

Blue whale

Balaenoptera musculus

Eastern North Pacific

E/D; Y

1,496 (0.44, 1,050, 2014)

1.2

>19.4

Superfamily Odontoceti (toothed whales, dolphins, and porpoises)

Family Physeteridae:

Sperm whale

Physeter macrocephalus

California/Oregon/Washington

E/D; Y

1,997 (0.57, 1,270, 2014)

2.5

0.4

Family Kogiidae:

Pygmy sperm whale

Kogia breviceps

California/Oregon/Washington

-/-; N

4,111 (1.12, 1,924, 2014)

19

0

Dwarf sperm whale

Kogia sima

California/Oregon/Washington

-/-; N

Unknown (Unknown, Unknown, 2014)

Undetermined

0

Family Ziphiidae (beaked whales):

Cuvier's beaked whale

Ziphius cavirostris

California/Oregon/Washington

-/-; N

3,274 (0.67, 2,059, 2014)

21

<0.1

Baird's beaked whale

Berardius bairdii

California/Oregon/Washington

-/-; N

2,697 (0.6, 1,633, 2014)

16

0

Mesoplodont beaked whales

Mesoplodon spp.

California/Oregon/Washington

-/-; N

3,044 (0.54, 1,967, 2014)

20

0.1

Family Delphinidae:

Bottlenose dolphin

Tursiops truncatus

California/Oregon/Washington offshore

-/-; N

1,924 (0.54, 1,255, 2014)

11

>1.6

Striped dolphin

Stenella coeruleoalba

California/Oregon/Washington

-/-; N

29,211 (0.2, 24,782, 2014)

238

>0.8

Common dolphin

Delphinus delphis

California/Oregon/Washington

-/-; N

969,861 (0.17, 839,325, 2014)

8,393

>40

Pacific white-sided dolphin

Lagenorhynchus obliquidens

California/Oregon/Washington

-/-; N

26,814 (0.28, 21,195, 2014)

191

7.5

British Columbia

4

N/A

22,160 (unknown, 16,522, 2008)

Unknown

Unknown

Northern right whale dolphin

Lissodelphis borealis

California/Oregon/Washington

-/-; N

26,556 (0.44, 18,608, 2014)

179

3.8

Risso's dolphin

Grampus griseus

California/Oregon/Washington

-/-; N

6,336 (0.32, 4,817, 2014)

46

>3.7

False killer whale

Pseudorca crassidens

N/A

N/A

N/A

N/A

N/A

Killer whale

Orcinus orca

Offshore

-/-; N

300 (0.1, 276, 2012)

2.8

0

Southern Resident

E/D; Y

73 (N/A, 73, 2019)

0.13

>0.4

Northern Resident

-/-; N

302 (N/A, 302, 2018)

2.2

0.2

West Coast Transient

-/-; N

349 (N/A, 349, 2018)

3.5

0.4

Short-finned pilot whale

Globicephala macrorhynchus

California/Oregon/Washington

-/-; N

836 (0.79, 466, 2014)

4.5

1.2

Family Phocoenidae (porpoises):

Harbor porpoise

Phocoena phocoena

Northern Oregon/Washington Coast

-/-; N

21,487 (0.44, 15,123, 2011)

151

>3.0

Northern California/Southern Oregon

-/-; N

35,769 (0.52, 23,749, 2011)

475

>0.6

British Columbia

4

N/A

8,091 (unknown, 4,885, 2008)

Unknown

Unknown

Dall's porpoise

Phocoenoides dalli

California/Oregon/Washington

-/-; N

25,750 (0.45, 17,954, 2014)

172

0.3

British Columbia

4

N/A

5,303 (unknown, 4,638, 2008)

Unknown

Unknown

Order Carnivora—Superfamily Pinnipedia

Family Otariidae (eared seals and sea lions):

Northern fur seal

Callorhinus ursinus

Eastern Pacific

-/D; Y

608,143 (0.2, 514,738, 2018)

11,067

387

California

-/D; N

14,050 (N/A, 7,524, 2013)

451

1.8

California sea lion

Zalophus californianus

U.S.

-/-; N

257,606 (N/A, 233,515, 2014)

14,011

>321

Steller sea lion

Eumetopias jubatus

Eastern U.S.

-/-; N

43,201 (see SAR, 43,201, 2017)

2,592

113

British Columbia

4

N/A

4,037 (unknown, 1,100, 2008)

Unknown

Unknown

Guadalupe fur seal

Arctocephalus philippii townsendi

Mexico to California

T/D; Y

34,187 (N/A, 31,019, 2013)

1,062

>3.8

Family Phocidae (earless seals):

Harbor seal

Phoca vitulina

Oregon/Washington Coastal

-/-; N

Unknown (Unknown, Unknown, 1999)

Undetermined

10.6

British Columbia

4

N/A

24,916 (Unknown, 19,666, 2008)

Unknown

Unknown

Northern elephant seal

Mirounga angustirostris

California Breeding

-/-; N

179,000 (N/A, 81,368, 2010)

4,882

8.8

1—Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (-) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.

2—NMFS marine mammal stock assessment reports online at:

https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments.

CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable.

3—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). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases.

4—Best

et al.

(2015) total abundance estimates for animals in British Columbia based on surveys of the Strait of Georgia, Johnstone Strait, Queen Charlotte Sound, Hecate Strait, and Dixon Entrance. These rows represent British Columbia abundance estimates, where available, but do not represent additional stocks.

5—The California/Oregon/Washington stock of Mesoplodont beaked whales includes six species of beaked whales. Of the six species represented in this stock, only Blainville's beaked whales, Hubbs' beaked whales, and Stejneger's beaked whales are expected to be encountered or taken.

All species that could potentially occur in the planned survey areas are included in Table 1. However, additional species have been recorded in the specified geographic region but are considered sufficiently rare that take is not anticipated. The temporal and/or spatial occurrence of North Pacific right whales (

Eubalaena japonica

) is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here. Only 82 sightings of right whales in the entire eastern North Pacific were reported from 1962 to 1999, with the majority of these occurring in the Bering Sea and adjacent areas of the Aleutian Islands (Brownell

et al.,

2001). Most sightings in the past 20 years have occurred in the southeastern Bering Sea, with a few in the Gulf of Alaska (Wade

et al.,

2011). Despite many miles of systematic aerial and ship-based surveys for marine mammals off the coasts of Washington, Oregon and California over several years, only seven documented sightings of right whales were made from 1990 to 2000 (Waite

et al.,

2003), and NMFS only aware of two documented sightings in the area since then. Because of the small population size and the fact that North Pacific right whales spend the summer feeding in high latitudes, the likelihood that the planned survey would encounter a North Pacific right whale is discountable.

In addition, the Northern sea otter (

Enhydra lutris kenyoni

) may be found in coastal waters of the survey area. However, sea otters are managed by the U.S. Fish and Wildlife Service and are not considered further in this document.

A detailed description of the species likely to be affected by L-DEO's geophysical survey, including brief introductions to the species and relevant stocks as well as available information regarding population trends and threats, and information regarding local occurrence, were provided in the

Federal Register

notice of proposed IHA (85 FR 19580; April 7, 2020). Since that time, NMFS has published the draft 2020 SARs with updated abundance, PBR, and/or mortality information for the Eastern Pacific stock of northern fur seals, West Coast Transient stock of killer whales, Central North Pacific stock of humpback whales, Northeast Pacific and California/Oregon/Washington stocks of fin whale, Eastern North Pacific Southern Resident stock of killer whales, and Eastern North Pacific Stock and Pacific Coast Feeding Group of gray whales. The relevant information for these stocks has been updated in Table 1, however the status of these species and stocks has not changed; therefore detailed descriptions are not provided here. Please refer to the

Federal Register

notice of proposed IHA for these descriptions. Please also refer to NMFS' website (

https://www.fisheries.noaa.gov/find-species

) for generalized species accounts.

Biologically Important Areas and Critical Habitat

Biologically Important Areas (BIAs) for feeding gray whales along the coasts of Washington, Oregon, and California have been identified, including northern Puget Sound, Northwestern Washington, and Grays Harbor in Washington, Depoe Bay and Cape Blanco and Orford Reef in Oregon, and Point St. George in California; most of these areas are of importance from late spring through early fall (Calambokidis

et al.,

2015). BIAs have also been identified for migrating gray whales along the entire coasts of Washington, Oregon, and California; although most whales travel within 10 km from shore, the BIAs were extended out to 47 km from the coastline (Calambokidis

et al.,

2015). The planned survey will occur during the late spring/summer feeding season, when most individuals from the eastern North Pacific stock occur farther north. Nonetheless, individual gray whales, particularly those from the PCFG could be encountered in nearshore waters of the project area.

Prior to 2016, humpback whales were listed under the ESA as an endangered species worldwide. Following a 2015 global status review (Bettridge

et al.,

2015), NMFS delineated 14 distinct population segments (DPS) with different listing statuses (81 FR 62259; September 8, 2016) pursuant to the ESA. The DPSs that occur in U.S. waters do not necessarily equate to the existing stocks designated under the MMPA and shown in Table 1. Because MMPA stocks cannot be portioned,

i.e.,

parts managed as ESA-listed while other parts managed as not ESA-listed, until such time as the MMPA stock delineations are reviewed in light of the DPS designations, NMFS considers the existing humpback whale stocks under the MMPA to be endangered and depleted for MMPA management purposes (

e.g.,

selection of a recovery factor, stock status).

Within the survey area, three DPSs may occur: The Hawaii DPS (not listed), Mexico DPS (threatened), and Central America DPS (endangered). On April 21, 2021, NMFS issued a final rule to designate critical habitat in nearshore waters of the North Pacific Ocean for the endangered Central America DPS and the threatened Mexico DPS of humpback whale (86 FR 21082). Critical habitat for the Central America DPS and Mexico DPS was established within the California Current Ecosystem (CCE) off the coasts California, Oregon, and Washington, representing areas of key foraging habitat. Off Washington and northern Oregon, the critical habitat extends from the 50-m isobath out to the 1200-m isobath; off southern Oregon (south of 42°10′ N), it extends out to the 2000-m isobath. L-DEO's easternmost planned tracklines occur within designated humpback whale critical habitat along the coast.

Critical habitat for humpbacks has been designated under Canadian law in four locations in British Columbia (DFO 2013), including in the waters of the survey area off southwestern Vancouver Island. The other three locations are located north of the survey area at Haida Gwaii (Langara Island and Southeast Moresby Island) and at Gil Island (DFO 2013). These areas show persistent aggregations of humpback whales and have features such as prey availability, suitable acoustic environment, water quality, and physical space that allow for feeding, foraging, socializing, and resting (DFO 2013). A small portion of L-DEO's planned tracklines overlap with Canadian designated humpback whale critical habitat off southwest Vancouver Island.

BIAs for feeding humpbacks along the coasts of Oregon and Washington, which have been described from May to November, are all within approximately 80 km from shore, and include the waters off northern Washington, and Stonewall and Heceta Bank, Oregon (Calambokidis

et al.,

2015). Some segments of L-DEO's planned tracklines overlap with these BIAs.

The U.S. Southern Resident killer whale critical habitat designated under the ESA currently includes inland waters of Washington relative to a contiguous shoreline delimited by the line at a depth of 6.1 m relative to extreme high water (71 FR 69054; November 29, 2006). On September 19, 2019, NMFS published a proposed rule to revise designated Southern Resident killer whale critical habitat to include 40,472.7 km

2

of marine waters between the 6.1-m depth contour and the 200-m depth contour from the U.S. international border with Canada south to Point Sur, California (84 FR 49214; September 19, 2019). The planned survey tracklines overlap with NMFS' proposed expanded Southern Resident critical habitat.

In Canada, Southern Resident killer whales are listed as Endangered under the Species at Risk Act (SARA), and critical habitat has been designated in the trans-boundary waters in southern British Columbia, including the

southern Strait of Georgia, Haro Strait, and Strait of Juan de Fuca (SOR/2018-278, December 13, 2018; SOR/2009-68, February 19, 2009; DFO 2018). The continental shelf waters off southwestern Vancouver Island, including Swiftsure and La Pérouse Banks have also been designated as critical habitat for Southern Resident and Northern Resident killer whales (SOR/2018-278, December 13, 2018). As discussed above, L-DEO's initial proposed survey tracklines that overlapped with Canadian designated critical habitat for killer whales have been eliminated.

Federally designated critical habitat for Steller sea lions in Oregon and California includes all rookeries (NMFS 1993). Although the Eastern DPS was delisted from the ESA in 2013, the designated critical habitat remains valid (NOAA 2019e). The critical habitat in Oregon is located along the coast at Rogue Reef (Pyramid Rock) and Orford Reef (Long Brown Rock and Seal Rock). The critical habitat area includes aquatic zones that extend 0.9 km seaward and air zones extending 0.9 km above these terrestrial and aquatic zones (NMFS 1993). L-DEO's planned tracklines lie about 9 and 13 km away from the two Oregon units of Steller sea lion critical habitat.

Unusual Mortality Events

On May 30, 2019, NMFS declared an unusual mortality event (UME) for gray whales after elevated numbers of strandings occurred along the U.S. west coast. As of April 5, 2021, a total of 430 stranded gray whales have been reported, including 209 in the United States (93 in Alaska, 50 in Washington, 9 in Oregon, and 57 in California), 205 in Mexico, and 16 in Canada. Full or partial necropsy examinations were conducted on a subset of the whales. Preliminary findings in several of the whales have shown evidence of emaciation. These findings are not consistent across all of the whales examined, so more research is needed. The UME is ongoing, and NMFS continues to investigate the cause(s). Additional information about the UME is available at

https://www.fisheries.noaa.gov/national/marine-life-distress/2019-2020-gray-whale-unusual-mortality-event-along-west-coast.

Increased strandings of Guadalupe fur seals have occurred along the entire coast of California. Guadalupe fur seal strandings began in January 2015 and were eight times higher than the historical average. Strandings have continued since 2015 and have remained well above average through 2019. Strandings are seasonal and generally peak in April through June of each year. Strandings in Oregon and Washington became elevated starting in 2019 and have continued to present. Strandings in these two states in 2019 are five times higher than the historical average. Guadalupe fur seals have stranded alive and dead. Those stranding are mostly weaned pups and juveniles (1-2 years old). The majority of stranded animals showed signs of malnutrition with secondary bacterial and parasitic infections. NMFS has declared a UME for Guadalupe fur seals along the entire U.S. West Coast; the UME is ongoing and NMFS is continuing to investigate the cause(s). For additional information on the UME, see

https://www.fisheries.noaa.gov/national/marine-life-distress/2015-2020-guadalupe-fur-seal-unusual-mortality-event-california.

Elevated strandings of California sea lion pups occurred in Southern California between January 2013 and September 2016. As a result, NMFS declared a UME. The UME was confined to pup and yearling California sea lions, many of which were emaciated, dehydrated, and underweight for their age. A change in the availability of sea lion prey, especially sardines, a high value food source for nursing mothers, was a likely contributor to the large number of strandings. Sardine spawning grounds shifted further offshore in 2012 and 2013, and while other prey were available (market squid and rockfish), these may not have provided adequate nutrition in the milk of sea lion mothers supporting pups, or for newly-weaned pups foraging on their own. Although the pups showed signs of some viruses and infections, findings indicate that this event was not caused by disease, but rather by the lack of high quality, close-by food sources for nursing mothers. Current evidence does not indicate that this UME was caused by a single infectious agent, though a variety of disease-causing bacteria and viruses were found in samples from sea lion pups. The investigative team examined multiple potential explanations for the high numbers of malnourished California sea lion pups observed on the island rookeries and stranded on the mainland in 2013. For more information, see

https://www.fisheries.noaa.gov/national/marine-life-distress/2013-2017-california-sea-lion-unusual-mortality-event-california.

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 (2018) 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 the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall

et al.

(2007) retained. Marine mammal hearing groups and their associated hearing ranges are provided in Table 2.

Table 2—Marine Mammal Hearing Groups (NMFS, 2018)

Hearing group

Generalized hearing range *

Low-frequency (LF) cetaceans (baleen whales)

7 Hz to 35 kHz.

Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)

150 Hz to 160 kHz.

High-frequency (HF) cetaceans (true porpoises,

Kogia,

river dolphins, cephalorhynchid,

Lagenorhynchus cruciger

&

L. australis

)

275 Hz to 160 kHz.

Phocid pinnipeds (PW) (underwater) (true seals)

50 Hz to 86 kHz.

Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)

60 Hz to 39 kHz.

* Represents the generalized hearing range for the entire group as a composite (

i.e.,

all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65 dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall

et al.

2007) and PW pinniped (approximation).

The pinniped functional hearing group was modified from Southall

et al.

(2007) on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range (Hemilä

et al.,

2006; Kastelein

et al.,

2009; Reichmuth and Holt, 2013).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information. 31 marine mammal species (25 cetacean and six pinniped (four otariid and two phocid) species) have the reasonable potential to co-occur with the planned survey activities. Please refer to Table 1. Of the cetacean species that may be present, six are classified as low-frequency cetaceans (

i.e.,

all mysticete species), 15 are classified as mid-frequency cetaceans (

i.e.,

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

i.e.,

porpoises and

Kogia

spp.).

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

The effects of underwater noise from L-DEO's geophysical survey activities have the potential to result in behavioral harassment of marine mammals in the vicinity of the survey area. The notice of proposed IHA (85 FR 19580; April 7, 2020) included a discussion of the effects of anthropogenic noise on marine mammals and the potential effects of underwater noise from L-DEO's geophysical survey activities on marine mammals and their habitat. That information and analysis is incorporated by reference into this final IHA determination and is not repeated here; please refer to the notice of proposed IHA (85 FR 19580; April 7, 2020). The referenced information includes a summary and discussion of the ways that the specified activity may impact marine mammals and their habitat. Consistent with the analysis in our prior

Federal Register

notices for similar L-DEO surveys and after independently evaluating the analysis in L-DEO's application, we determine that the survey is likely to result in the takes described in the Estimated Take section of this document and that other forms of take are not expected to occur.

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, the Estimated Take section, and the Mitigation section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and how those impacts on individuals are likely to impact marine mammal species or stocks.

Description of Active Acoustic Sound Sources

The notice of proposed IHA provided a brief technical background on sound, on the characteristics of certain sound types, and on metrics used in the proposal inasmuch as the information was relevant to the specified activity and to a discussion of the potential effects of the specified activity on marine mammals found later in this document. Please see that document (85 FR 19580; April 7, 2020) for additional information. 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).

Estimated Take

This section provides an estimate of the number of incidental takes authorized through this IHA, which will inform both NMFS' consideration of “small numbers” and the negligible impact determination.

Harassment is the only type of take expected to result from these activities. Except with respect to certain activities not pertinent here, section 3(18) of the MMPA defines “harassment” as any act of pursuit, torment, or annoyance, which (i) has the potential to injure a marine mammal or marine mammal stock in the wild (Level A harassment); or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering (Level B harassment).

Authorized takes will primarily be by Level B harassment, as use of seismic airguns has the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury (Level A harassment) for mysticetes and high frequency cetaceans (

i.e.,

porpoises,

Kogia

spp.). The mitigation and monitoring measures are expected to minimize the severity of such taking to the extent practicable.

As described previously, no serious injury or mortality is anticipated or authorized for this activity. Below we describe how the take is estimated.

Generally speaking, we estimate take by considering: (1) Acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and, (4) and the number of days of activities. We note that while these basic factors can contribute to a basic calculation to provide an initial prediction of takes, additional information that can qualitatively inform take estimates is also sometimes available (

e.g.,

previous monitoring results or average group size). Below, we describe the factors considered here in more detail and present the take estimate.

Acoustic Thresholds

NMFS uses acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment).

Level B Harassment for non-explosive sources

—Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source (

e.g.,

frequency, predictability, duty cycle), the environment (

e.g.,

bathymetry), and the receiving animals (hearing, motivation, experience,

demography, behavioral context) and can be difficult to predict (Southall

et al.,

2007, Ellison

et al.,

2012). NMFS uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS predicts that marine mammals are likely to be behaviorally harassed in a manner we consider Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 dB re 1 microPascal (μPa) root mean square (rms) for continuous (

e.g.,

vibratory pile-driving, drilling) and above 160 dB re 1 μPa (rms) for non-explosive impulsive (

e.g.,

seismic airguns) or intermittent (

e.g.,

scientific sonar) sources. L-DEO's planned activity includes the use of impulsive seismic sources. Therefore, the 160 dB re 1 μPa (rms) criteria is applicable for analysis of Level B harassment.

Level A harassment for non-explosive sources

—NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (Version 2.0) (Technical Guidance, 2018) identifies dual criteria to assess auditory injury (Level A harassment) to five different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). L-DEO's planned seismic survey includes the use of impulsive (seismic airguns) sources.

These thresholds are provided in the table below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS 2018 Technical Guidance, which may be accessed at

https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-acoustic-technical-guidance.

Table 3—Thresholds Identifying the Onset of Permanent Threshold Shift

Hearing group

PTS onset acoustic thresholds

*

(received level)

Impulsive

Non-impulsive

Low-Frequency (LF) Cetaceans

Cell 1:

L

pk,flat

: 219 dB;

L

E,LF,24h

: 183 dB.

Cell 2:

L

E,LF,24h

: 199 dB.

Mid-Frequency (MF) Cetaceans

Cell 3:

L

pk,flat

: 230 dB;

L

E,MF,24h

: 185 dB

Cell 4:

L

E,MF,24h

: 198 dB.

High-Frequency (HF) Cetaceans

Cell 5:

L

pk,flat

: 202 dB;

L

E,HF,24h

: 155 dB

Cell 6:

L

E,HF,24h

: 173 dB.

Phocid Pinnipeds (PW) (Underwater)

Cell 7:

L

pk,flat

: 218 dB;

L

E,PW,24h

: 185 dB

Cell 8:

L

E,PW,24h

: 201 dB.

Otariid Pinnipeds (OW) (Underwater)

Cell 9:

L

pk,flat

: 232 dB;

L

E,OW,24h

: 203 dB

Cell 10:

L

E,OW,24h

: 219 dB.

* Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive sounds, these thresholds should also be considered.

Note:

Peak sound pressure (

L

pk

) has a reference value of 1 µPa, and cumulative sound exposure level (

L

E

) has a reference value of 1µPa

2

s. In this Table, thresholds are abbreviated to reflect American National Standards Institute standards (ANSI 2013). However, peak sound pressure is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript “flat” is being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function (LF, MF, and HF cetaceans, and PW and OW pinnipeds) and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude of ways (

i.e.,

varying exposure levels and durations, duty cycle). When possible, it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be exceeded.

Ensonified Area

Here, we describe operational and environmental parameters of the activity that will feed into identifying the area ensonified above the acoustic thresholds, which include source levels and acoustic propagation modeling.

L-DEO's modeling methodology is described in greater detail in the IHA application (LGL 2019). The planned 2D survey will acquire data using the 36-airgun array with a total discharge volume of 6,600 cubic inches (in

3

) at a maximum tow depth of 12 m. L-DEO model results are used to determine the 160-dBrms radius for the 36-airgun array in deep water (>1,000 m) down to a maximum water depth of 2,000 m. Water depths in the project area may be up to 4,400 m, but marine mammals are generally not anticipated to dive below 2,000 m (Costa and Williams 1999). Received sound levels were predicted by L-DEO's model (Diebold

et al.,

2010) which uses ray tracing for the direct wave traveling from the array to the receiver and its associated source ghost (reflection at the air-water interface in the vicinity of the array), in a constant-velocity half-space (infinite homogeneous ocean layer, unbounded by a seafloor). In addition, propagation measurements of pulses from the 36-airgun array at a tow depth of 6 m have been reported in deep water (approximately 1600 m), intermediate water depth on the slope (approximately 600-1100 m), and shallow water (approximately 50 m) in the Gulf of Mexico in 2007-2008 (Tolstoy

et al.

2009; Diebold

et al.

2010).

For deep and intermediate-water cases, the field measurements cannot be used readily to derive Level A and Level B harassment isopleths, as at those sites the calibration hydrophone was located at a roughly constant depth of 350-500 m, which may not intersect all the sound pressure level (SPL) isopleths at their widest point from the sea surface down to the maximum relevant water depth for marine mammals of ~2,000 m. At short ranges, where the direct arrivals dominate and the effects of seafloor interactions are minimal, the data recorded at the deep and slope sites are suitable for comparison with modeled levels at the depth of the calibration hydrophone. At longer ranges, the comparison with the model—constructed from the maximum SPL through the entire water column at varying distances from the airgun array—is the most relevant.

In deep and intermediate-water depths, comparisons at short ranges between sound levels for direct arrivals recorded by the calibration hydrophone and model results for the same array tow depth are in good agreement (Fig. 12 and 14 in Appendix H of NSF-USGS, 2011). Consequently, isopleths falling within this domain can be predicted reliably by the L-DEO model, although they may be imperfectly sampled by measurements recorded at a single depth. At greater distances, the calibration data show that seafloor-reflected and sub-seafloor-refracted arrivals dominate, whereas the direct arrivals become weak and/or incoherent. Aside from local topography effects, the region around the critical distance is where the observed levels rise closest to the model curve. However, the observed sound levels are found to fall almost entirely below the

model curve. Thus, analysis of the Gulf of Mexico calibration measurements demonstrates that although simple, the L-DEO model is a robust tool for conservatively estimating isopleths. For deep water (>1,000 m), L-DEO used the deep-water radii obtained from model results down to a maximum water depth of 2,000 m.

A recent retrospective analysis of acoustic propagation from use of the R/V

Langseth

sources during a 2012 survey off Washington (

i.e.,

in the same location) suggests that predicted (modeled) radii (using the same approach as that used here) were 2-3 times larger than the measured radii in shallow water. (Crone

et al.,

2014). Therefore, because the modeled shallow-water radii were specifically demonstrated to be overly conservative for the region in which the current survey is planned, L-DEO used the received levels from multichannel seismic data collected by the R/V

Langseth

during the 2012 survey to estimate Level B harassment radii in shallow (<100 m) and intermediate (100-1,000 m) depths (Crone

et al.,

2014). Streamer data in shallow water collected in 2012 have the advantage of including the effects of local and complex subsurface geology, seafloor topography, and water column properties, and thus allow determination of radii more confidently than using data from calibration experiments in the Gulf of Mexico.

The survey will acquire data with a four-string 6,600-in

3

airgun array at a tow depth of 12 m while the data collected in 2012 were acquired with the same airgun array at a tow depth of 9 m. To account for the differences in tow depth between the 2012 survey and the planned 2021 survey, L-DEO calculated a scaling factor using the deep water modeling (see Appendix D in L-DEO's IHA application). A scaling factor of 1.15 was applied to the measured radii from the airgun array towed at 9 m.

The estimated distances to the Level B harassment isopleth for the R/V

Langseth's

36-airgun array are shown in Table 4.

Table 4—Predicted Radial Distances to Isopleths Corresponding to Level B Harassment Threshold

Source and volume

Tow depth

(m)

Water depth

(m)

Level B

harassment

zone (m)

using L-DEO

model

36 airgun array, 6,600-in

3

12

>1000

a

6,733

100-1000

b

9,468

<100

b

12,650

a

Distance based on L-DEO model results.

b

Distance based on data from Crone

et al.

(2014).

Predicted distances to Level A harassment isopleths, which vary based on marine mammal hearing groups, were calculated based on modeling performed by L-DEO using the NUCLEUS source modeling software program and the NMFS User Spreadsheet, described below. The acoustic thresholds for impulsive sounds (

e.g.,

airguns) contained in the Technical Guidance were presented as dual metric acoustic thresholds using both cumulative sound exposure level (SEL

cum

) and peak sound pressure metrics (NMFS 2018). As dual metrics, NMFS considers onset of PTS (Level A harassment) to have occurred when either one of the two metrics is exceeded (

i.e.,

metric resulting in the largest isopleth). The SEL

cum

metric considers both level and duration of exposure, as well as auditory weighting functions by marine mammal hearing group. In recognition of the fact that the requirement to calculate Level A harassment ensonified areas could be more technically challenging to predict due to the duration component and the use of weighting functions in the new SEL

cum

thresholds, NMFS developed an optional User Spreadsheet that includes tools to help predict a simple isopleth that can be used in conjunction with marine mammal density or occurrence to facilitate the estimation of take numbers.

The values for SEL

cum

and peak SPL for the R/V

Langseth

airgun array were derived from calculating the modified far-field signature (Table 5). The farfield signature is often used as a theoretical representation of the source level. To compute the farfield signature, the source level is estimated at a large distance below the array (

e.g.,

9 km), and this level is back projected mathematically to a notional distance of 1 m from the array's geometrical center. However, when the source is an array of multiple airguns separated in space, the source level from the theoretical farfield signature is not necessarily the best measurement of the source level that is physically achieved at the source (Tolstoy

et al.

2009). Near the source (at short ranges, distances <1 km), the pulses of sound pressure from each individual airgun in the source array do not stack constructively, as they do for the theoretical farfield signature. The pulses from the different airguns spread out in time such that the source levels observed or modeled are the result of the summation of pulses from a few airguns, not the full array (Tolstoy

et al.

2009). At larger distances, away from the source array center, sound pressure of all the airguns in the array stack coherently, but not within one time sample, resulting in smaller source levels (a few dB) than the source level derived from the farfield signature. Because the farfield signature does not take into account the large array effect near the source and is calculated as a point source, the modified farfield signature is a more appropriate measure of the sound source level for distributed sound sources, such as airgun arrays. L-DEO used the acoustic modeling methodology as used for Level B harassment with a small grid step of 1 m in both the inline and depth directions. The propagation modeling takes into account all airgun interactions at short distances from the source, including interactions between subarrays, which are modeled using the NUCLEUS software to estimate the notional signature and MATLAB software to calculate the pressure signal at each mesh point of a grid.

For a more complete explanation of this modeling approach, please see “Appendix A: Determination of Mitigation Zones” in the IHA application.

Table 5—Modeled Source Levels Based on Modified Farfield Signature for the 6,600-in

3

Airgun Array

Low frequency cetaceans

(

L

pk,flat

: 219 dB;

L

E,LF,24h

: 183 dB)

Mid frequency cetaceans

(

L

pk,flat

: 230 dB;

L

E,MF,24h

: 185 dB

High

frequency

cetaceans

(

L

pk,flat

: 202 dB;

L

E,HF,24h

: 155 dB)

Phocid

pinnipeds

(underwater)

(

L

pk,flat

: 218 dB;

L

E,HF,24h

: 185 dB)

Otariid

pinnipeds

(underwater)

(

L

pk,flat

: 232 dB;

L

E,HF,24h

: 203 dB)

6,600 in

3

airgun array (Peak SPL

flat

)

252.06

252.65

253.24

252.25

252.52

6,600 in

3

airgun array (SEL

cum

)

232.98

232.84

233.10

232.84

232.08

In order to more realistically incorporate the Technical Guidance's weighting functions over the seismic array's full acoustic band, unweighted spectrum data for the R/V

Langseth's

airgun array (modeled in 1 Hz bands) was used to make adjustments (dB) to the unweighted spectrum levels, by frequency, acco

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