Daily Rules, Proposed Rules, and Notices of the Federal Government


National Oceanic and Atmospheric Administration

RIN 0648-XC091

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Marine Seismic Survey in the Beaufort and Chukchi Seas, Alaska

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; issuance of an incidental take authorization.
SUMMARY: In accordance with the Marine Mammal Protection Act (MMPA) regulations, notification is hereby given that NMFS has issued an Incidental Harassment Authorization (IHA) to ION Geophysical (ION) to take, by harassment, small numbers of nine species of marine mammals incidental to in-ice marine seismic surveys in the Beaufort and Chukchi Seas, Alaska, during the fall and winter of 2012.
DATES: Effective October 17, 2011, through December 15, 2012.
ADDRESSES: Requests for information on the incidental take authorization should be addressed to P. Michael Payne, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910. A copy of the application containing a list of the references used in this document, NMFS' Environmental Assessment (EA), Finding of No Significant Impact (FONSI), and the IHA may be obtained by writing to the address specified above or visiting the Internet at:

Documents cited in this notice may be viewed, by appointment, during regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Shane Guan, Office of Protected Resources, NMFS, (301) 427-8401 or Brad Smith, NMFS, Alaska Region, (907) 271-3023.

Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361et seq.) direct the Secretary of Commerce (Secretary) to allow, upon request, the incidental, but not intentional taking 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 regulations are issued or, if the taking is limited to harassment, a notice of a proposed authorization is provided to the public for review.

Authorization shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such taking are set forth.

NMFS has defined “negligible impact” in 50 CFR 216.103 as “* * * an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.”

Section 101(a)(5)(D) of the MMPA established an expedited process by which citizens of the U.S. can apply for an authorization to incidentally take small numbers of marine mammals by harassment. Except with respect to certain activities not pertinent here, the MMPA defines “harassment” as: any act of pursuit, torment, or annoyance which (i) has the potential to injure a marine mammal or marine mammal stock in the wild [Level A harassment]; or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering [Level B harassment].

Section 101(a)(5)(D) establishes a 45-day time limit for NMFS review of an application followed by a 30-day public notice and comment period on any proposed authorizations for the incidental harassment of marine mammals. Within 45 days of the close of the comment period, NMFS must either issue or deny issuance of the authorization.

Summary of Request

NMFS received an application on March 1, 2012, from ION for the taking, by harassment, of marine mammals incidental to a marine seismic survey in ice in the Beaufort and Chukchi Seas, Alaska, during October through December 15, 2012. After addressing comments from NMFS, ION modified its application and submitted a revised application on June 11, 2012.

Description of the Specified Activity

ION's activities consist of a geophysical in-ice (seismic reflection/refraction) survey and related vessel operations to be conducted primarily in the Alaskan Beaufort and Chukchi seas from October to December 15, 2012. The primary survey area extends from the U.S.-Canadian border in the east to Point Barrow in the west. Two survey lines extend west of Point Barrow into the northern Chukchi Sea, and three short tracks are proposed near the U.S.-Russian border (see Figure 1 of ION's IHA application). The bathymetry of the proposed survey area ranges from shallow (<20 m [66 ft]) to relatively deep (>3,500 m [11,483 ft]) water over the continental shelf, the continental slope, and the abyssal plain.

The survey will be conducted from the seismic vesselGeo Arcticescorted by thePolar Prince,a medium class (100A) icebreaker. The survey grid consists of ∼7,175 km (4,458 mi) of transect line, not including transits when the airguns are not operating. There may be small amounts of additional seismic operations associated with airgun testing, start up, and repeat coverage of any areas where initial data quality is sub-standard. The seismic source towed by theGeo Arcticwould be an airgun array consisting of 26 active Sercel G-gun airguns with a total volume of 4,450 in3. A single hydrophone streamer 4.5-9 km (2.8-5.6 mi) in length, depending on ice conditions, would be towed by theGeo Arcticto record the returning seismic signals.

The survey vessels arrived in the survey area from Canadian waters in early October and plan to begin data collection on or after October 15, 2012. After completion of the survey, or when ice and weather conditions dictate, the vessels will exit to the south, transiting through the Chukchi and Bering Seas. ThePolar Princemay be used to perform an at-sea refueling (bunkering) operation to supply as much as 500 metric tons of Arctic diesel to theGeo Arctic.ThePolar Princewill carry that fuel onboard at the start of the operation, and it will be transferred to theGeo Arcticif/when necessary. Depending on its own fuel consumption, thePolar Princemay then transit to Tuktoyuktuk, Canada to take on additional fuel for itself. Once thePolar Princereturns to theGeo Arcticthe survey would continue. The entire refueling operation will therefore involve one fuel transfer and potentially one transit to and from Tuktoyuktuk. The refueling operation will likely take place in late October, at which time the Geo Arcticwill likely be in the eastern or east-central Alaskan Beaufort Sea.

ION's geophysical survey has been designed and scheduled to minimize potential effects to marine mammals, bowhead whales in particular, and subsistence users. For mitigation and operational reasons, the survey area has been bisected by a line that runs from 70.5° N. 150.5° W. to 73° N. 148° W. (see Figure 1 of ION's IHA application). Weather and ice permitting, ION plans to begin survey operations east of the line described above (eastern survey area) and in offshore waters (>1,000 m [3,281 ft]) where bowheads are expected to be least abundant in early October. This operational plan is based on the fact that only ∼2% of bowhead whales observed by Bureau of Ocean Energy Management's (BOEM) aerial surveys from 1979-2007 occurred in areas of water depth >1,000 m (3,281 ft) (MMS, 2010), and on average ∼97% of bowheads have passed through the eastern U.S. Beaufort Sea by October 15 (Milleret al.,2002). The survey will then progress to shallower waters in the eastern survey area before moving to the western survey area in late October or early November 2012.

Ice conditions are expected to range from open water to 10/10 ice cover. However, the survey cannot take place in thick multi-year ice as both the icebreaker and seismic vessel must make continuous forward progress at 3-4 kts. In order for the survey to proceed, areas of high ice concentration can only consist of mostly newly forming juvenile first year ice or young first year ice less than 0.5 m (1.6 ft) thick. Sounds generated by the icebreaker and seismic vessel moving through these relatively light ice conditions are expected to be far below the high sound levels often attributed to icebreaking. These high sound levels (>200 dB re 1 μPa [rms]) have been recorded from icebreakers during backing and ramming operations in very heavy ice conditions and are created by cavitation of the propellers as the vessel is slowed by the ice or reverses direction (Erbe and Farmer, 1998; Roth and Schmidt, 2010).

Acoustic Sources (1) Seismic Airgun Array

The seismic source used during the project would be an airgun array consisting of 28 Sercel G-gun airguns, of which 26 would be active and have a total discharge volume of 4,450 in3. The 28 airguns would be distributed in two sub-arrays with 14 airguns per sub-array. Individual airgun sizes range from 70 to 380 in3. Airguns will be operated at 2,000 psi. The seismic array and a single hydrophone streamer 4.5-9 km (2.8-5.6 mi) in length would be towed behind theGeo Arctic.Additional specifications of the airgun array are provided in Appendix B of ION's IHA application.

(2) Echo Sounders

Both vessels will operate industry standard echo sounder/fathometer instruments for continuous measurements of water depth while underway. These instruments are used by all large vessels to provide routine water depth information to the vessel crew. Navigation echo sounders send a single, narrowly focused, high frequency acoustic signal directly downward to the sea floor. The sound energy reflected off the sea floor returns to the vessel where it is detected by the instrument, and the depth is calculated and displayed to the user. Source levels of navigational echo sounders of this type are typically in the 180-200 dB re 1 μPA-m (Richardsonet al.1995a).

TheGeo Arcticwill use one navigational echo sounder during the project. The downward facing single-beam Simrad EA600 operates at frequencies ranging from 38 to 200 kHz with an output power of 100-2000 Watts. Pulse durations are between 0.064 and 4.096 milliseconds, and the pulse repetition frequency (PRF or ping rate) depends on the depth range. The highest PRF at shallow depths is about 40 pings per second. It can be used for water depths up to 4,000 m (13,123 ft) and provides up to 1 cm (0.4 in) resolution.

ThePolar Princewill use one echo sounder, an ELAC LAZ-72. The LAZ-72 has an operating frequency of 30 kHz. The ping rate depends on the water depth and the fastest rate, which occurs in shallow depths, is about 5 pings per second.

Dates, Duration, and Region of Activity

The proposed geophysical survey would be conducted for ∼76 days from approximately October 15 to December 15, 2012. Both theGeo Arcticand thePolar Princeentered the Alaskan Beaufort Sea from Canadian waters in early October. The survey area will be bounded approximately by 138° to 169° W. longitude and 70° to 73° N. latitude in water depths ranging from <20 to >3,500 m (66 to 11,483 ft) (see Figure 1 of ION's IHA application). For mitigation and operational reasons the survey area has been bisected by a line that runs from 70.5° N, 150.5° W to 73° N, 148° W. Weather and ice permitting, ION plans to begin survey operations east of the line (eastern survey area) in offshore waters (>1,000 m [3,281 ft]) where bowheads are expected to be least abundant in early October. The survey will then progress to shallower waters in the eastern survey area before moving to the west survey area in late October or early November. The vessels will depart the region to the south via the Chukchi and Bering Seas and arrive in Dutch Harbor in mid- to late December.

Comments and Responses

A notice of NMFS' proposal to issue an IHA to ION was published in theFederal Registeron August 17, 2012 (77 FR 49922). That notice described, in detail, ION's proposed activity, the marine mammal species that may be affected by the activity, and the anticipated effects on marine mammals and the availability of marine mammals for subsistence uses. During the 30-day public comment period, NMFS received comments from the following organizations: the Marine Mammal Commission (Commission), the North Slope Borough (NSB), Oceana, Ocean Conservation Research, Ocean Conservancy, PEW Environment Group (PEW), and a group joined by the Alaska Wilderness League, Audubon Alaska, Center for Biological Diversity, EarthJustice, Natural Resources Defense Council, Northern Alaska Environmental Center, Ocean Conservation Research, Pacific Environment, Sierra Club, and World Wildlife Fund (AWLet al.).

Any comments specific to ION's application that address the statutory and regulatory requirements or findings NMFS must make to issue an IHA are addressed in this section of theFederal Registernotice.

General MMPA Issues and Impact Analyses

Comment 1:The Commission recommends that NMFS continue to include proposed incidental harassment authorization language, including the total number of estimated takes by Level A and Level B harassment, at the end ofFederal Registernotices but ensure that the language is consistent with that referenced in the main body of the corresponding notice.

Response:NMFS agrees with the Commission's recommendation and will, to the extent practicable, include proposed incidental harassment authorization language at the end ofFederal Registernotices. In addition, NMFS agrees that the language should be consistent with that referenced in the main body of the corresponding notice and will make every effort to ensure consistency. However, the total number of estimated takes by Level A and Level B harassment is presented in tableswithin the subsectionEstimated Takes by Harassmentof theFederal Registernotice, and it would be redundant to repeat this information within the proposed incidental harassment authorization language elsewhere in the sameFederal Registernotice.

Comment 2:The Commission recommends that NMFS propose to issue regulations under section 101(a)(5)(A) of the MMPA and a letter of authorization, rather than an incidental harassment authorization, for any proposed activities expected to cause a permanent threshold shift (PTS).

Response:The legal requirements and underlying analysis for the issuance of an IHA concerning take do not require the issuance of regulations and a letter of authorization in this particular case. In order to issue an authorization pursuant to Section 101(a)(5)(D) of the MMPA, NMFS must determine that the taking by harassment of small numbers of marine mammal species or stocks will have a negligible impact on affected species or stocks, and will not have an unmitigable adverse impact on the availability of affected species or stocks for taking for subsistence uses. If there were a potential for serious injury or mortality, NMFS could not issue an IHA. Instead, any incidental take authorization would need to be processed under Section 101(a)(5)(A) of the MMPA.

As described here and in previous FR notices, PTS is considered to be injury (Level A Harassment). However, an animal would need to stay very close to the sound source for an extended amount of time to incur a serious degree of PTS, which could increase the probability of mortality. In this case, it would be highly unlikely for this scenario to unfold given the nature of any anticipated acoustic exposures that could potentially result from a mobile marine mammal that is generally expected to avoid loud sounds swimming in the vicinity of an airgun array moving at 3-4 knots. Therefore, it is appropriate to issue an incidental take authorization under 101(a)(5)(D), as we have made the necessary findings (described elsewhere in this document) under that Section of the MMPA.

Comment 3:The Ocean Conservancy, Ocean Conservation Research, Oceana, and AWLet al.state the proposed seismic survey would result in harassment takes of a large number of marine mammals, specifically 250 bowhead whales, 4,300 beluga whales, and 60,000 ringed seals, all of which would be exposed to received levels above 160 dB (rms). Thus, the commenters assert that NMFS cannot satisfy MMPA's small number and negligible impact provisions.

Response:NMFS disagrees with the commenters' assessment. First, as mentioned in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012) and earlier in this document, the estimated takes of marine mammals are based on summer/fall marine mammal densities. With most marine mammals moving out of the proposed seismic area as winter approaches, the density would be lower and the actual numbers of takes would be far fewer than those calculated based on fall densities. As described in the Negligible Impact and Small Numbers Analysis and Determination section of this document, NMFS considers the number of authorized takes small.

As discussed in detail in the Negligible Impact and Small Numbers Analysis and Determination section of this document, most of the takes from ION's proposed in-ice seismic surveys are expected to be Level B behavioral harassment, in the form of startle behavior or vacating the area for the short duration of time when the seismic airgun is firing in the area. Animals could also change their behavior patterns during this short duration, butare expected to resume their normal activities and reoccupy the area as soon as the vessels move away. Additionally, since the proposed icebreaking seismic survey is planned outside the time when ice seals are giving birth and after approximately 97% of the bowhead population is expected to have moved through the area, no impacts on pups or calves are expected, and nor are there any orther areas of particular importance for reproduction or feeding that could be impacted. Therefore, any behavioral effects to ringed seals, bowheads, or other species are not expected to have significant impacts to individual fitness or the population. In addition, the mitigation and monitoring measures (described previously in this document) included in the IHA are expected to further reduce any potential disturbance to marine mammals. Last, a small number of takes in the form of PTS are being authorized, however, if incurred, they would be expected to be minor in degree (low intensity—a few dBs of loss at certain frequencies), and they are not expected because of a combination of mitigation and likely avoidance of high source levels. Mortality is neither authorized nor anticipated.

Therefore, NMFS believes that the take, by harassment, from ION's in-ice seismic survey will have a negligible impacton the affected species or stocks.

Comment 4:The Ocean Conservancy, Ocean Conservation Research, and AWLet that NMFS failed to consider cumulative impacts adequately. In addition, AWLet al.states that it is essential for NMFS to consider ION's proposed survey along with the impacts of Shell's exploratory drilling program in Beaufort and Chukchi Seas.

Response:Section 101(a)(5)(D) of the MMPA requires NMFS to make a determination that the harassment incidental to a specified activity will have a negligible impact on the affected species or stocks of marine mammals, and will not result in an unmitigable adverse impact on the availability of marine mammals for taking for subsistence uses. Neither the MMPA nor NMFS' implementing regulations specify how to consider other activities and their impacts on the same populations. However, consistent with the 1989 preamble for NMFS' implementing regulations (54 FR 40338, September 29, 1989), the impacts from other past and ongoing anthropogenic activities are incorporated into the negligible impact analysis via their impacts on the environmental baseline (e.g.,as reflected in the density/distribution and status of the species, population size and growth rate, and ambient noise).

In addition, cumulative effects were addressed in the Environmental Assessment and biological opinion prepared for this action, both of which NMFS indicated would be completed prior to the issuance of an IHA (77 FR 49922; August 17, 2012). The Environmental Assessment's cumulative effects analysis included consideration of (among other things): BP Exploration (Alasks), Inc.'s (BPXA) ocean-bottom-cable seismic surveys in the Simpson Lagoon area of the Beaufort Sea; BPXA's proposed Northstar oil production activity in the Beaufort Sea; and Shell Offshore Inc.'s (Shell) proposed exploratory drilling activities in the Beaufort and Chukchi Seas, Arctic warming, subsistence hunting, and noise contribution from vessel traffic.

These documents, as well as the Alaska Marine Stock Assessments and the most recent abundance estimates for the affected species, are part of NMFS' Administrative Record for this action, and provided the decision maker with information regarding other activities in the action area that affect marine mammals, an analysis of cumulative impacts, and other information relevant to the determination made under the MMPA.

Comment 5:AWLet al.states that in determining whether to proceed withION's request, NMFS must also consider the extent of missing information as to both the environmental baseline in the Arctic and marine mammal responses to noise in general.

Response:NMFS has been conducting such analyses in both aspects since 2010 when it first received ION's IHA application.

Regarding the environmental baseline, as described in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012), where the marine mammal distribution and density data for fall and winter seasons in the Beaufort and Chukchi Seas were not available, NMFS used the summer and fall density data. This data is an appropriate proxy for this analysis because it is for the same species and because we assume it is an overestimate since animals are known to move out of the area in the winter (Allen and Angliss 2011).

Separately, regarding marine mammal responses to noise in general and as described in thePotential Effects of the Specified Activity on Marine Mammalssection of the proposed IHA, while there are not data indicating the responses of every species to every specific sound source type, we believe that the large body of available information across multiple species and sound types allows us to reasonably anticipate likely responses to the proposed seismic airgun and icebreaking and make the findings necessary for issuance of this IHA.

Density Calculation and Take Estimate

Comment 6:PEW states that NMFS did not use the best available data for impact analysis, as most survey data NMFS were collected during the open water season that usually conclude by October.

Response:NMFS does not agree with PEW's statement that we did not use the best available data for impact analysis. As it was discussed in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012), the reason for using the fall marine mammal densities for take calculation is because the lack of marine mammal density data in the winter season. Nevertheless, the fall marine mammal density data NMFS and ION used are the best available data. In addition, during the initial impact analysis, NMFS Office of Protected Resources and ION consulted with NMFS National Marine Mammal Laboratory (NMML) to make sure that the marine mammal density data used for impact analysis are the best available data. Using marine mammal summer/fall density data results in over-estimates as the overwhelming majority marine mammals will have likely departed the Beaufort and Chukchi Seas by the start of winter (Mateet al.2000; Milleret al.2002; Frostet al.2004; Suydamet al.2005; Cameron and Boveng, 2009; Christieet al.2010; Allen and Angliss 2011).

Comment 7:AWLet al.states that using density is unsuited for determining bowhead take during the fall migration. AWLet al.further argues that the bowhead whales would pass through the Beaufort and Chukchi Sea in the fall during their migration within a migratory corridor. AWLet al.then points out that it was not clear NMFS has adequately considered the migration of beluga whales in the Beaufort Sea as well. AWLet al.predicts that when taking the bowhead migration into account could dramatically increase the estimate of harassed whales.

Response:NMFS does not agree AWLet al.'sassessment. ION's in-ice seismic survey would only occur after the majority of bowhead and beluga whales have migrated out of the Beaufort Sea. In addition, as noted in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012), ION would start its seismic survey from the east and proceed westward, thereby overlapping with the fewest possible number of marine mammals later in the season. Therefore, using summer/fall marine mammal density to calculate takes in the Arctic when most animals have left the area is a reasonable and scientifically supportable approach, although, as stated it will result in an over-estimate of takes.

Comment 8:The Commission requests NMFS require ION to (1) consult with NMFS National Marine Mammal Laboratory (NMML) and other researchers and revise its expected density estimates for gray whales and bearded seals to reflect new information from passive acoustic recordings, and (2) include, as appropriate, an estimate of takes by Level A harassment for those species. Citing Staffordet al.(2007), Wang and Overland (2009), Shelden and Mocklin (2012), the Commission points out that acoustic data show that these species are present throughout the winter months. The NSB also expresses its concern that bowhead and gray whales may remain in the area much longer than previously thought. Oceana is also concerned that there could be Level A takes of bearded seals, though it recognizes that much of the bearded seal population will have already migrated into the Bering Sea.

Response:NMFS' Office of Protected Resources and ION worked extensively with NMFS' NMML on density estimates for all marine mammals (gray whales and bearded seals included) that could occur in the proposed survey area. The approaches took into account the best available scientific data on the abundance of marine mammals (gray whales and bearded seals included) that could potentially occur through the winter season, as well as estimates erred on the overestimation. NMFS and ION conducted a thorough review of acoustic recordings data pertaining to overwintering marine mammals (e.g.,Staffordet al.2007; Roth 2008; MacIntyre and Stafford 2011; Shelden and Mocklin 2012). We concluded that although some marine mammals were detected in the Beaufort and Chukchi Seas during this time, none of the studies allowed us to identify specific density estimates. In addition, many studies show that marine mammal calling rates dropped significantly during the winter months (Roth 2008; MacIntyre and Stafford 2011), which is consistent with our prediction based on tagging research (Cameron and Boveng 2009; Harwoodet al.2012). The notion is also shared by Oceana as it stated in its comment that much of the population of bearded seals will have already migrated into the Bering Sea. These reviews support our initial analyses and the basis for marine mammal take estimates. Therefore, we do not believe it is necessary, nor is it feasible, to revise density estimates or to include gray whales and bearded seals in the Level A take estimates.

Finally, we acknowledge that bowhead and gray whales may remain in the Beaufort and Chukchi Seas during the timeframe of ION's proposed survey. To account for this possibility, NMFS relied on summer/fall data to estimate potential abundance of these species, which resulted in an over-estimate of take.

Comment 9:The Commission requests NMFS require ION to recalculate expected densities for bowhead whales based on (1) the corrected decrease in abundance of bowhead whales reported by Milleret al.(2002) for early and late October (i.e.,78 percent) and (2) any additional information from more recent surveys, including acoustical surveys, conducted by NMFS' NMML and other researchers to assess the distribution and relative abundance of bowhead whales in the survey area from October through December.

Response:Through the process of analyzing the potential impacts of ION's in-ice seismic survey in the Beaufort and Chukchi Seas, NMFS' Office of Protected Resources and ION worked extensively with NMFS' NMML on marine mammal density estimates, including distribution and densities ofbowhead whales. The early October (October 1-15) bowhead abundance of 0.55 bowheads/100 km and the late October (October 15-31) abundance of 0.12 bowheads/100 km reported in Milleret al.(2002) were both calculated as overall averages across the four survey regions and all water depth strata. The reference density to which the 90% decrease from early October to late October adjustment was applied was based only on bowhead sightings in less than 200 m of water. Thus, data in table Appendix 9.1 in Milleret al.(2002), which excludes water depths >200 m, were used for the calculation. In that table, the mean number of bowheads/100 km seen from October 1-15 was 0.618 and the mean for October 16-31 was 0.089. This represents an 86% decrease from early to late October, which was rounded to 90%.

If the percentage decrease were left unrounded the average density for water depths <200 m in the Eastern Beaufort Sea in Table 2 of the ION's IHA application would become 0.0132 bowheads/km2. Using this value the take calculations would be 282, instead of the 201 stated in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012).

NMFS and ION by focused on bowhead whale aerial surveys that were conducted in the spring of 2011 and 2012. We ultimately agreed that the aerial survey data being used for density calculations was the most appropriate and that any newer data (i.e.from 2011 surveys) was of no added value. More recent aerial survey data were not used for the direct calculation of densities in late October as there have been very few surveys conducted at that time of year in the eastern U.S. Beaufort in recent years. Although acoustic data can be useful in assessing distribution, and to a limited extent, relative abundance, however, as with acoustic data for other marine mammals, none of them provides a basis for density estimates.

Comment 10:The Commission requests NMFS provide stronger assurance that the actual number of takes would be negligible by (1) estimating the expected number of takes plus some measure of uncertainty in that estimate, (2) using maximum estimated densities of the marine mammals in the survey area to estimate takes, or (3) using some comparable approach that accounts for uncertainty and provides a high level of assurance that the actual taking would, in fact, be negligible. In addition, the Commission requests NMFS require ION to account for all sources of uncertainty in its estimation approach, including animals that may be present but not observed. Oceana and the NSB also express their concerns regarding the uncertainty of the impacts to marine mammals from ION's in-ice seismic survey during the winter season.

Response:NMFS believes that the analyses provided in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012) has already provided a well-founded assurance that the impacts from even the overestimated takes, which were based on summer-fall marine mammal density, would be negligible to marine mammal species and stocks in ION's in-ice seismic survey areas in the Beaufort and Chukchi Seas, and that the take would not have unmitigable impacts to subsistence use of these species and stocks. These analyses already took uncertainties of marine mammal winter distribution and densities into account and erred on the side of caution.

The determination regarding whether the total taking would have a negligible impact on the species or stocks is based on the species-specific average density, or based on allotted number from past chance occurrence, as described above and in the proposedFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012). More importantly, the negligible impact analysis is not simply an assessment of the number of takes, but rather includes consideration of the nature, context, and likely severity of the takes, as well as the anticipated effectiveness of the mitigation measures. As described later in this document, our analysis allowed us to determine that the total taking would have a negligible impact on the affected species.

Regarding the requirement for ION to account for all sources of uncertainty in its estimation approach, including animals that may be present but not observed, NMFS believes that all population survey studies, as well as density estimates, take into account for marine mammals not observed during the survey.

Acoustic Impacts

Comment 11:PEW states that NMFS needs to ensure that best science is used when considering permitting an IHA to authorize Level A harassment of marine mammals, since this is the first time Level A take is being proposed.

Response:NMFS has relied on the best available scientific information to support the issuance of ION's authorization. In the case of authorizing Level A harassment, NMFS has estimated that no more than 1 bowhead whale, 3 beluga whales, and 4 ringed seals could, although unlikely, experience minor permanent threshold shifts of hearing sensitivity (PTS). The available data and analyses, as described more fully in the proposed IHA, include extrapolation results of many studies on marine mammal noise-induced temporary threshold shifts of hearing sensitivities (TTS) (Kryter 1985; Richardsonet al.1995; Kastaket al.1999; Schlundtet al.2000; Finneranet al.2002; 2005; Nachtigallet al.2003; 2004; Kastaket al.2004; 2005; Southallet al.2007; Mooneyet al.2009a; 2009b; Finneranet al.2010a; 2010b). An extensive review of TTS studies and experiments prompted NMFS to conclude that possibility of minor PTS in the form of slight upward shift of hearing threshold at certain frequency bands by a few individuals of marine mammals is extremely low, but not unlikely.

Comment 12:Citing NMFS' 1995Federal Registernotice (60 FR 28379), AWLet al.argues that since the proposed seismic survey has the potential to cause permanent hearing loss in marine mammals, the impact must constitute “serious injury.” Ocean Conservancy also states that PTS equals “serious injury”. AWLet al.further states that marine mammals enter the 180/190 dB re 1 µPa exclusion zones have at least the potential to suffer serious injury, and thus AWLet al.assumes that at least 23 beluga whales, 6 bowhead whales, and 277 ringed seals could potentially suffer serious injury as a result of the survey. Oceana also expresses its concern that serious injury could occur to marine mammals.

Response:Our understanding of noise-induced impacts on marine mammals has evolved over the past two decades and we no longer believe, based on the best available data, that PTS equals “serious injury.” As described in detail in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012), the potential Level A takes would be limited to minor degrees of PTS by 1 bowhead whale, 3 beluga whales, and 4 ringed seals. This level of injury is different from “serious injury,” which is defined as “any injury that will likely result in mortality” (50 CFR 229.2).

Noise-induced threshold shifts (TS, include PTS) are defined as increases in the threshold of audibility (i.e.,the sound has to be louder to be detected) of the ear at a certain frequency or range of frequencies (ANSI 1995; Yost 2000). Several important factors relate to the magnitude of TS, such as level, duration, spectral content (frequency range), and temporal pattern (continuous, intermittent) of exposure (Yost 2000; Hendersonet al.2008). TS occurs in terms of frequency range(hertz [Hz] or kHz), hearing threshold level (dB), or both frequency and hearing threshold level (CDC 2004).

In addition, there are different degrees of PTS: Ranging from slight/mild to moderate and from severe to profound (Clark 1981). Profound PTS or the complete loss of the ability to hear in one or both ears is commonly referred to as deafness (CDC 2004; WHO 2006). High-frequency PTS, presumably as a normal process of aging that occurs in humans and other terrestrial mammals, has also been demonstrated in captive cetaceans (Ridgway and Carder 1997; Yuenet al.2005; Finneranet al.2005a; Houser and Finneran 2006; Finneranet al.2007a; Schlundtet al.2011) and in stranded individuals (Mannet al.2010).

In terms of what is analyzed for the potential PTS (Level A harassment) in marine mammals as a result of ION's in-ice seismic survey, if it occurs, NMFS has determined that the levels would be slight/mild because research shows that most cetaceans (and particularly Arctic cetaceans) show relatively high levels of avoidance when received sound pulse levels exceed 160 dB re 1 μPa (rms) (review in Richardsonet al.1995; Southallet al.2007), and it is uncommon to sight Arctic cetaceans within the 180 dB radius, especially for prolonged duration. Results from monitoring programs associated with seismic activities in the Arctic have shown significant responses by cetaceans at levels much lower than 180 dB. These results have been used by agencies to support monitoring requirements within distances where received levels fall below 160 dB and even 120 dB. Thus, very few animals would be exposed to sound levels of 180 dB re 1 μPa (rms) regardless of detectability by protected species observers. Avoidance varies among individuals and depends on their activities or reasons for being in the area, and occasionally a few individual Arctic cetaceans will tolerate sound levels above 160 dB. Tolerance of levels above 180 dB is infrequent, regardless of the circumstances. Therefore, a calculation of the number of cetaceans potentially exposed to >180 dB that is based simply on density would be a gross overestimate of the actual numbers exposed to 180 dB. Such calculations would be misleading unless avoidance response behaviors were taken into account to estimate what fraction of those originally present within the soon-to-be ensonified to >180 dB zone (as estimated from density) would still be there by the time levels reach 180 dB.

Comment 13:The Ocean Conservancy and AWLet al.state that NMFS' analysis underestimated the impact of stress and the effects of airguns on bowhead whales.

Response:NMFS does not agree with the assessment. TheFederal Registerfor the proposed IHA (77 FR 49922; August 17, 2012) provided an analysis of the potential stress response to marine mammals (bowhead included) that could result from ION's in-ice seismic survey. However, almost no information is available on sound-induced stress in marine mammals, or on its potential (alone or in combination with other stressors) to affect the long-term well-being or reproductive success of marine mammals (Fair and Becker 2000; Hildebrand 2005; Wrightet al.2007a, 2007b). Nevertheless, extrapolation of information regarding stress responses in other species is applicable because the responses are highly consistent among all species in which they have been examined to date, especially considering that marine mammals will likely respond in a manner consistent with other species studied (Wrightet al.2007a). In the section discussing non-auditory effects, NMFS summarized that a range of issues may arise from an extended stress response from noise exposure, which include suppression of reproduction (physiologically and behaviorally), accelerated aging and sickness-like symptoms. Such long-term effects, if they occur, would be mainly associated with chronic noise exposure, which is characteristic of some seismic surveys and exposure situations (McCauleyet al.2000b; Nieukirket al.2009) but not of some others. As described in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012), ION's in-ice seismic survey would be performed in a limited area for a short duration (a total 76 days). In addition, the source vessel would be in constant movement as it acquires seismic data and [would not overlap with individuals for a substantial period of time]. Therefore, we have concluded that marine mammals would not suffer from chronic and long-term, noise exposure.

In addition, NMFS provided more detailed analyses on noise-induced stress in its EA for the issuance of an IHA to ION (NMFS 2012), which also included three specific studies concerning marine mammals (Thomaset al.1990; Romanoet al.2004; Rollandet al.2012). These studies point out that short-term noise exposure, such as those animals being tested for TTS, only induced stress-immune system change during intense noise exposure (Romanoet al.2004), while during playbacks of recorded drilling noise to four captive beluga whales showed no changes in blood levels of stress-related hormones (Thomaset al.1990).

Comment 14:Citing Luckeet al.(2009) TTS experiment on a harbor porpoise, the AWLet al.points out that a harbor porpoise experienced TTS when exposed to airgun noise at 164 dB, a significantly lower level than what NMFS predicts.

Response:NMFS does not agree with AWLet al.'s assessment. AWLet al.erroneously interpreted the results of the TTS-induced sound exposure level (SEL) in Luckeet al.(2009) to be sound pressure level (SPL) that NMFS uses for the threshold of PTS. In their paper, Luckeet al.(2009) found a threshold shift (TS) of a harbor porpoise after exposing it to airgun noise with peak-to-peak (pk-pk) received SPL at 200.2 dBpk-pkre 1 μPa, which according to the authors, corresponds to SEL of 164.5 dB re 1 μPa2s after integrating exposure. It is important to understand that SPL and SEL are two very different ways to express the relative sound intensity. NMFS currently uses root-mean-square (rms) of received SPL at 180 dB and 190 dB re 1 μPa as the threshold above which PTS could occur for cetaceans and pinnipeds, respectively, and that TTS is thought to occur below these levels. However, TTS experiments so far have shown that in almost all cases TTS would occur at levels much higher than the 180 and 190 dB re 1 μPa thresholds. It is difficult to determine the equivalent of rms SPL from the reported pk-pk SPL in Luckeet al.(2009) because the airgun noise is a broadband impulse. Although it is a standard practice to subtract 9 dB from pk-pk SPL of a sinusoidal signal to convert it to rms SPL, for boardband signal from seismic surveys, the difference could be as large as 16 dB (Harriset al.2001; McCauleyet al.2000). If we applied the 16 dB difference and convert the pk-pk reported in Luckeet al.(2009), the rms SPL for harbor porpoise to experience TTS would be 184 dB re 1 μPa, and the received levels associated with PTS (Level A harassment) would be higher than that. This is still above NMFS 180 dBrmsre 1 μPa threshold for injury.

Nevertheless, NMFS recognizes that the TTS threshold of harbor porpoise is lower that other cetacean species (bottlenose dolphin and beluga whale) tested (e.g.,Finneranet al.2002), and is discussed in theFederal Registernotice of the proposed IHA (77 FR 49922; August 17, 2012), as well as the EA for the issuance of the IHA to ION (NMFS 2012).

Comment 15:Citing Kastaket al.(2008) and Jujawa and Liberman (2009), AWLet al.states that anthropogenic sound can induce PTS at lower levelsthan anticipated. In addition, AWL states that new data indicate that mid-frequency cetaceans, such as bottlenose dolphins and beluga whales have greater sensitivity to sounds within their best hearing range than was supposed at the time Southallet al.(2007) was published.

Response:NMFS agrees that PTS could occur at relatively lower levels, such as at levels normally would only cause TTS, if the animal experiences repeated exposures at very close distances to the sound source. These long term effects are well known in terrestrial mammals (Yost 2000; Hendersonet al.2008) and is acknowledged in theFederal Registernotice for the proposed IHA (77 FR 49922; August 17, 2012) that repeated exposure to elevated noise that causes TTS could eventually result in PTS. However, as mentioned in detailed in the proposed IHA, ION's in-ice seismic survey would be performed in a limited area for a short duration of a total 76 days. In addition, the source vessel would be in constant movement as it acquires seismic data and any overlap between the vessel and affected species would be minimal and short-lived. Therefore, NMFS considers it highly unlikely many animals would be repeatedly exposed to received levels that would cause TTS.

As far as the hearing sensitivity of mid-frequency cetaceans is concerned, it is well known that mid-frequency cetaceans have greater sensitivity to sounds within their best hearing ranges, which are typically between 10-100 kHz (Johnson 1967; Hall and Johnson 1972; Whiteet al.1978; Awbreyet al.1988; Johnsonet al.1989; Ridgwayet al.2001). Further TTS research on a bottlenose dolphin exposed to pure tones suggests that mid-frequency cetacean tends to be more vulnerable (in terms of TTS occurrence) at their most sensitive hearing range (Finneranet al.2010). However, the majority of acoustic energy from a seismic airgun, vessel and icebreaking noise is under 1 kHz (Richardsonet al.1995), which is expected to have less impact on the most sensitive hearing ranges of these cetaceans.

Comment 16:AWLet al.argues that NMFS' justifications for the use of a correction factor of only counting 10% marine mammals being exposure to received levels at Level A would show no avoidance and thus subject to PTS and that exposure will only be brief are both flawed and unsupported by survey data and scientific evidence. Citing Arctic seismic survey monitoring and mitigation reports from previous years, AWLet al.states that marine mammals, especially ice seals, do not always avoid loud noises, and that marine mammals routinely stray too close to the airguns, even during daylight hours. The Commission also requests NMFS require ION provide a scientific basis for any conclusions about the animals' responses to the airguns. The Commission further requests NMFS require ION to revise the estimated number of Level A harassment takes to include all marine mammals that may be exposed to source levels greater than or equal to 180 and 190 dB re 1 μPa for cetaceans and pinnipeds, respectively.

Response:NMFS does not agree with AWLet al.'sassessment. As discussed earlier in the response to Comment 13, NMFS' current Level A take threshold of 180 dB re 1 μPa for cetaceans is appropriate. Marine mammals found in these zones are not expected to experience TTS (a form of Level B Harassment), much less PTS (Level A Harassment) even if they are exposed to a few seismic impulses. On the other hand, almost all marine mammals that underwent TTS experiments showed strong aversive behavioral reactions when the received noise levels approached to levels that could cause TTS (e.g.,Nachtigallet al.2004; Fineran and Schlundt 2004; Luckeet al.2009), despite the fact that these animals are trained and food-reinforced to participate the studies. Simply because previous seismic survey monitoring reports reveal that marine mammals were observed in the exclusion zones does not mean the animals necessarily experienced TTS, much less PTS..

The 10% correction factor used by NMFS is appropriate for estimating likely Level A Harassment takes, since there is evidence suggesting that most, if not all, marine mammals would avoid the noise levels that could cause immediate PTS (as described in the Estimated Take section below.

NMFS does not agree with the Commission's recommendation. Again, there is a difference between potential TTS (Level B Harassment), potential PTS (Level A Harassment) and serious injury. As described in detail in the response to Comment 13, the 180/190 dB re 1 μPa are the current standards used to prevent marine mammals from experiencing injury, which is equated with PTS, not TTS, which occurs at substantively lower received levels than PTS. In fact, all studies on marine mammal TTS have pointed out that TTS occurs at a received levels higher than NMFS current 180/190 dB re 1 μPa threshold (e.g.,Finneranet al.2000; 2002; Luckeet al.2009). Even if the animal is exposed multiple times at levels higher than the 180/190 dB re 1 μPa threshold and receives TTS, it is not considered physical injury. TTS, which is also referred to as auditory fatigue, is a reversible hearing threshold shift and it often recovers within minutes to hours (Ward 1997; Finneranet al.2000; 2002). The numbers AWLet al.cited in their comment are the estimates of marine mammals that could occur within NMFS 180/190 dB re 1 μPa exclusion zones, which do not represent the number of animals that would receive TTS, not to mention PTS. In fact, NMFS considers in most cases all animals would avoid staying within the zones long enough to receive TTS. Therefore, most marine mammals will not experience TTS, which means the occurrence of PTS would be even lower.

Finally, even if the animal receives PTS, this does not equate to serious injury. As stated earlier in response to Comment 13, NMFS defines injury as “any injury that will likely result in mortality” (50 CFR 229.2), which, based on the best available science and NMFS' judgment, does not include PTS. .

Comment 17:The AWLet al.states that the current NMFS 160-dB re 1 μPa threshold for Level B harassment is arbitrary and non-conservative. Citing papers by Clark and Gagnon (2006), Rischet al.(2012), Bain and Williams (2006), Milleret al.(1999; 2005), the AWLet al.argues that in many cases marine mammals respond to much lower noise levels.

Response:NMFS does not agree with AWLet al.'s assessment, as the papers AWL cited do not necessarily indicate that the animals exposed under the certain received levels constitute a “take” as defined under the MMPA. Clark and Gagnon (2006) reported that fin whales (Balaenoptera physalus) in the northeast Pacific Ocean went silent for an extended period starting soon after the onset of a seismic survey in the area, and Rischet al.(2012) reported that humpback whale (Megaptera novaeangliae) song in the Stellwagen Bank National Marine Sanctuary was reduced, concurrent with transmissions of an Ocean Acoustic Waveguide Remote Sensing experiment that produced series of frequency modulated pulses approximately 200 km away in the Gulf of Maine. Although Milleret al.(1999) reported that bowhead whale deflection may occur about 35 km (21.7 mi) to the east of the seismic operations, no SPL measurement to that distance was provided, except noting that received levels at 30 km (18.6 mi) were about 107-126 dB re 1 μPa rms, depending on propagation. In addition, Milleret al.(2005) and Bain and Williams (2006) observed that marine mammal densities were generally lowerduring seismic surveys and were seen moving away from seismic sources, even in areas where received levels were far below 160 dB re 1 μPa. Nevertheless, Milleret al.(2005) noted that bowhead whales have been sighted within the “safety radius” without any observed behavioral responses.

To address these observations, it is important to understand that the vocal behaviors shown by fin and humpback whales, as reported by Clark and Gagnon (2006) and Rischet al.(2012), are considered to be related to mating activities, which do not apply to bowhead whales and other marine mammal species in the Beaufort and Chukchi Seas during ION's in-ice seismic survey. Second, as stated in the past, NMFS does not believe that minor course corrections during a migration or temporarily moving away from seismic source, as observed by Milleret al.(1999; 2005) and Bain and Williams (2005) equate to “take” under the MMPA. This conclusion is based on controlled exposure experiments conducted on migrating gray whales exposed to the U.S. Navy's low frequency sonar (LFA) sources (Tyack 2009). When the source was placed in the middle of the migratory corridor, the whales were observed deflecting around the source during their migration. However, such minor deflection is considered not to be biologically significant. To show the contextual nature of this minor behavioral modification, recent monitoring studies of Canadian seismic operations indicate that when not migrating, but involved in feeding, bowhead whales do not move away from a noise source at an SPL of 160 dB. Therefore, while bowheads may avoid an area of 20 km (12.4 mi) around a noise source, when that determination requires a post-survey computer analysis to find that bowheads have made a 1 or 2 degree course change, NMFS believes that does not rise to a level of a “take.” NMFS therefore continues to estimate “takings” under the MMPA from impulse noises, such as seismic, as being at a distance of 160 dB re 1 µPa. Although it is possible that marine mammals could react to any sound levels detectable above the ambient noise level within the animals' respective frequency response range, this does not mean that such animals would react in a biologically significant way. According to experts on marine mammal behavior, the degree of reaction which constitutes a “take,”i.e.,a reaction that could potentially disrupt the migration, breathing, nursing, breeding, feeding, or sheltering, etc., of a marine mammal is complex and context specific, and it depends on several variables in addition to the received level of the sound by the animals. These additional variables include, but are not limited to, other source characteristics (such as frequency range, duty cycle, continuous vs. impulse vs. intermittent sounds, duration, moving vs. stationary sources, etc.); specific species, populations, and/or stocks; prior experience of the animals (naive vs. previously exposed); habituation or sensitization of the sound by the animals; and behavior context (whether the animal perceives the sound as predatory or simply annoyance), etc. (Southallet al.2007).

Based on the information and data summarized in Southallet al.(2007), and on information from various studies, NMFS believes that the onset for behavioral harassment is largely context dependent, and there are many studies showing marine mammals do not show behavioral responses when exposed to multiple pulses at received levels above 160 dB re 1 µPa (e.g.,Malmeet al.1983; Malmeet al.1984; Richardsonet al.1986; Akamatsuet al.1993; Madsen and Møhl 2000; Harriset al.2001; Milleret al.2005). Therefore, although using a uniform SPL of 160-dB for the onset of behavioral harassment for impulse noises may not capture all of the nuances of different marine mammal reactions to sound, it is an appropriate way to manage and regulate anthropogenic noise impacts on marine mammals. Therefore, unless and until an improved approach is developed and peer-reviewed, NMFS will continue to use the 160-dB threshold for determining the level of take of marine mammals by Level B harassment for impulse noise (such as from airguns).

Comment 18:Citing the Expert Panel Review of Statoil and ION's 2011 monitoring plans, the AWLet al.states that the noise from seismic airgun arrays as “a mixed impulsive/continuous noise source” and that “NMFS should evaluate its impacts on that basis.”

Response:NMFS does not agree with the AWLet al.'s statement. First, nowhere in the Expert Panel's report did it states that airgun sound is “a mixed impulsive/continuous noise source”. It has been well understood that the source characteristics from a seismic airgun (or airgun array) are impulsive, with no continuous acoustic components (Richardsonet al.1995). What the Expert Panel stated in its report is that “seismic airgun signals should not be treated as truly impulsive when received at ranges where sound propagation is known to remove the impulsive nature of these signals”, which means that the signals become “stretched” at very large distance due to reverberation and multipath propagation. Furthermore, the Expert Panel stated that “[o]ver very short ranges where potential hearing loss (temporary or permanent) can occur, airgun impulses retain their impulsive features and should be considered as impulses.”

Although it has been known that at long distances an impulse acoustic signal will lose its pulse feature by stretching its duration due to multipath propagation, these signals (or noises) are still fundamentally different from other non-impulse noise sources such as those from vibratory pile driving, drilling, and dredging based on the following characteristics:

First, the elongated pulse signals from the airgun array at far distances are caused by multipath propagation in a reverberant environment (Greene and Richardson 1988; Richardsonet al.1995; Madsenet al.2002; Lurton 2002), which is different from other non-pulse signals at closer distances, which is composed of mostly direct sound. The reverberation part of the sound in the ocean behaves differently compared to the direct sound and early surface and bottom reflections from the perspective of the receiver. The direct sound and early reflections follow the inverse square law, with the addition of absorption effects in the case of early reflections, and so their amplitude varies with distance. However the reverberant part of the sound remains relatively constant up to a large distance with the position of the receiver. Therefore, as distance increases from the source, the component of reverberant sounds increases against the direct sound. In addition, the reverberant energy is less directional and is distributed more uniformly around the ambient environment of the animal. As shown in human psychoacoustics, these characteristics in a reverberant field provide distance cues to the listener as to how far away the source is located (Howard and Angus 2006). Therefore, at a distance where the airgun signals have been “stretched” to non-pulse, the receiving animals would be able to correctly perceive that these sounds are coming from far away, and would thus be less likely to be affected behaviorally as behavior responses are not solely dependent on received levels. Other factors such as distance to the source, movement of the source, source characteristics, and the receiver's (i.e.,animal's) age, sex, motivation states, and prior experience, etc. probably play more significant roles in determining the responses of the animals that arebeing exposed to lower levels of noises than solely the received sound level.

Second, even though during horizontal propagation, the initial short pulse could be “stretched” from milliseconds when emitted to about 0.25-0.5 second long at a few kilometers in shallow water (Richardsonet al.1995), the noise duration is still very short when compared to those “conventional” non-pulse noise sources (vibratory pile driving, drilling, and dredging, etc.) for which NMFS applies a 120 dB threshold for assessing behavioral harassment. The empirical measurements of a 3,000 in3 airgun array received signal characteristics showed that its pulse duration was stretched to 0.2 second at approximately 1.3 km (0.8 mi), to 0.5 second at approximately 10 km (6.2 mi), and to about 1.8 seconds at 80 km (50 mi) from the source (O'Neillet al.2011). Based on the airgun array's firing rate of 0.1 Hz (1 shot every 10 seconds), the duty cycle was only 18% for the signal at 80 km (50 mi) (1.8 seconds on for every 10 seconds). Conversely, the “conventional” non-pulse noises from vibratory pile driving, drilling, and dredging typically last much longer (minutes to hours) with very brief (seconds for vibratory pile driving) intervals.

Therefore, NMFS does not agree that it is appropriate to treat elongated airgun pulses at long distances as a “conventional” non-pulse signal and apply the 120 dB behavioral response threshold to that received sound.

Comment 19:Citing Madsen (2005), the AWLet al.states that “the threshold's basis in the root mean square (“RMS”) of sound pressure, rather than in peak pressure, is non-conservative.” The AWLet al.further claims that studies have criticized the use of RMS for seismic sound because of the degree to which pulsed sounds must be “stretched,” resulting in significant potential underestimates of marine mammal take. The AWLet al.predicts that if NMFS would modify its threshold estimates to use the peak pressure level instead of RMS, the estimated number of marine mammal takes could be significantly higher than the number of takes NMFS intends to authorize in for this survey.

Response:NMFS does not agree with the AWLet al.'s statement. First, there is no scientific basis that the use of root-mean-square (rms) for sound pressure is less conservative than using peak pressure (which includes zero-peak pressure and peak-peak pressure). All of these are valid terms to express acoustic pressure and other physical oscillations (e.g.,alternating electrical current). NMFS chooses to use rms because it was first established to regulate underwater noise impacts to marine mammals and that rms uses the product mean of acoustic pressures, which provides a more consistent result when dealing with multiple impulses such as pile driving. For a sinusoidal signal, the relationship between rms level