# Takes of Marine Mammals Incidental to Specified Activities; Low-Energy Marine Geophysical Survey in the Scotia Sea and South Atlantic Ocean, September to October 2014 > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2014-18396 ## Record - **Collection:** Federal Register - **Document type:** Notice - **Published:** August 5, 2014 - **Citation:** 79 FR 45592 ## Text DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration RIN 0648-XD256 Takes of Marine Mammals Incidental to Specified Activities; Low-Energy Marine Geophysical Survey in the Scotia Sea and South Atlantic Ocean, September to October 2014 AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Notice; proposed Incidental Harassment Authorization; request for comments. SUMMARY: NMFS has received an application from the National Science Foundation (NSF) Division of Polar Programs, and Antarctic Support Contract (ASC) on behalf of two research institutions, University of Texas at Austin and University of Memphis, for an Incidental Harassment Authorization (IHA) to take marine mammals, by harassment, incidental to conducting a low-energy marine geophysical (seismic) survey in the Scotia Sea and South Atlantic Ocean, September to October 2014. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an IHA to NSF and ASC to incidentally harass, by Level B harassment only, 26 species of marine mammals during the specified activity. DATES: Comments and information must be received no later than September 4, 2014. ADDRESSES: Comments on the application should be addressed to Jolie Harrison, Incidental Take Program, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910. The mailbox address for providing email comments is ITP.Goldstein@noaa.gov. NMFS is not responsible for email comments sent to addresses other than the one provided here. Comments sent via email, including all attachments, must not exceed a 25-megabyte file size. Instructions: All comments received are a part of the public record and will generally be posted to: http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications without change. All Personal Identifying Information (for example, name, address, etc.) voluntarily submitted by the commenter may be publicly accessible. Do not submit Confidential Business Information or otherwise sensitive or protected information. A copy of the application may be obtained by writing to the address specified above, telephoning the contact listed here (see FOR FURTHER INFORMATION CONTACT ) or visiting the Internet at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications. Documents cited in this notice may also be viewed by appointment, during regular business hours, at the aforementioned address. NSF and ASC have prepared a “Draft Initial Environmental Evaluation/Environmental Assessment to Conduct a Study of the Role of the Central Scotia Sea and North Scotia Ridge in the Onset and Development of the Antarctic Circumpolar Current” (IEE/EA) in accordance with the National Environmental Policy Act (NEPA) and the regulations published by the Council of Environmental Quality (CEQ). It is posted at the foregoing site. NMFS will independently evaluate the IEE/EA and determine whether or not to adopt it. NMFS may prepare a separate NEPA analysis and incorporate relevant portions of the NSF and ASC's draft IEE/EA by reference. Information in the NSF and ASC's IHA application, EA and this notice collectively provide the environmental information related to proposed issuance of the IHA for public review and comment. NMFS will review all comments submitted in response to this notice as we complete the NEPA process, including a decision of whether to sign a Finding of No Significant Impact (FONSI), prior to a final decision on the IHA request. FOR FURTHER INFORMATION CONTACT: Howard Goldstein or Jolie Harrison, Office of Protected Resources, NMFS, 301-427-8401. SUPPLEMENTARY INFORMATION: Background Sections 101(a)(5)(A) and (D) of the MMPA, (16 U.S.C. 1361 et seq. ) direct the Secretary of Commerce (Secretary) to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by United States 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 authorization is provided to the public for review. An authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such takings are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as “. . . an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.” Section 101(a)(5)(D) of the MMPA established an expedited process by which citizens of the United States can apply for an authorization to incidentally take small numbers of marine mammals by harassment. Section 101(a)(5)(D) of the MMPA establishes a 45-day time limit for NMFS's review of an application, followed by a 30-day public notice and comment period on any proposed authorizations for the incidental harassment of small numbers of marine mammals. Within 45 days of the close of the public comment period, NMFS must either issue or deny the authorization. Except with respect to certain activities not pertinent here, the MMPA defines “harassment” as: Any act of pursuit, torment, or annoyance which (i) has the potential to injure a marine mammal or marine mammal stock in the wild [Level A harassment]; or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering [Level B harassment]. Summary of Request On April 15, 2014, NMFS received an application from NSF and ASC requesting that NMFS issue an IHA for the take, by Level B harassment only, of small numbers of marine mammals incidental to conducting a low-energy marine seismic survey in the Exclusive Economic Zone (EEZ) of the South Georgia and South Sandwich Islands and International Waters (i.e., high seas) in the Scotia Sea and southern Atlantic Ocean during September to October 2014. The research would be conducted by two research institutions: University of Texas at Austin and University of Memphis. NSF and ASC plan to use one source vessel, the R/VIB Nathaniel B. Palmer ( Palmer ), and a seismic airgun array and hydrophone streamer to collect seismic data in the Scotia Sea and southern Atlantic Ocean. The vessel would be operated by ASC, which operates the United States Antarctic Program (USAP) under contract with NSF. In support of the USAP, NSF and ASC plan to use conventional low-energy, seismic methodology to perform marine-based studies in the Scotia Sea, including evaluation of lithosphere adjacent to and beneath the Scotia Sea and southern Atlantic Ocean in two areas, the South Georgia micro-continent and the seafloor of the eastern portion of the central Scotia Sea (see Figures 1 and 2 of the IHA application). In addition to the proposed operations of the seismic airgun array and hydrophone streamer, NSF and ASC intend to operate a single-beam echosounder, multi-beam echosounder, acoustic Doppler current profiler (ADCP), and sub-bottom profiler continuously throughout the survey. Acoustic stimuli (i.e., increased underwater sound) generated during the operation of the seismic airgun array may have the potential to cause behavioral disturbance for marine mammals in the proposed survey area. This is the principal means of marine mammal taking associated with these activities, and NSF and ASC have requested an authorization to take 26 species of marine mammals by Level B harassment. Take is not expected to result from the use of the single-beam echosounder, multi-beam echosounder, ADCP, and sub-bottom profiler, as the brief exposure of marine mammals to one pulse, or small numbers of signals, to be generated by these instruments in this particular case is not likely to result in the harassment of marine mammals. Also, NMFS does not expect take to result from collision with the source vessel because it is a single vessel moving at a relatively slow, constant cruise speed of 5 knots ([kts]; 9.3 kilometers per hour [km/hr]; 5.8 miles per hour [mph]) during seismic acquisition within the survey, for a relatively short period of time (approximately 30 operational days). It is likely that any marine mammal would be able to avoid the vessel. Description of the Proposed Specified Activity Overview NSF and ASC proposes to use one source vessel, the Palmer, a two GI airgun array and one hydrophone streamer to conduct the conventional seismic survey as part of the NSF-funded research project “Role of Central Scotia Sea Floor and North Scotia Ridge in the Onset and Development of the Antarctic Circumpolar Current.” In addition to the airguns, NSF and ASC intend to conduct a bathymetric survey, dredge sampling, and geodetic measurements from the Palmer during the proposed low-energy seismic survey. Dates and Duration The Palmer is expected to depart from Punta Arenas, Chile on approximately September 20, 2014 and arrive at Punta Arenas, Chile on approximately October 20, 2014. Research operations would be conducted over a span of 30 days, including to and from port. Some minor deviation from this schedule is possible, depending on logistics and weather (e.g., the cruise may depart earlier or be extended due to poor weather; or there could be additional days of seismic operations if collected data are deemed to be of substandard quality). Specified Geographic Region The proposed project and survey sites are located in selected regions of the Scotia Sea (located northeast of the Antarctic Peninsula) and the southern Atlantic Ocean and focus on two areas: (1) Between the central rise of the Scotia Sea and the East Scotia Sea, and (2) the far southern Atlantic Ocean immediately northeast of South Georgia towards the northeastern Georgia Rise (both encompassing the region between 53 to 58° South, and between 33 to 40° West) (see Figure 2 of the IHA application). The majority of the proposed seismic survey would be within the EEZ of the Government of the South Georgia and South Sandwich Islands (United Kingdom) and a limited portion of the seismic survey would be conducted in International Waters. Figure 3 of the IHA application illustrates the general bathymetry of the proposed study area and the border of the existing South Georgia Maritime Zone. Water depths in the survey area exceed 1,000 m. There is limited information on the depths in the study area and therefore more detailed information on bathymetry is not available. The proposed seismic survey would be within an area of approximately 3,953 km 2 (1,152.5 nmi 2 ). This estimate is based on the maximum number of kilometers for the seismic survey (2,950 km) multiplied by the predicted rms radii (m) based on modeling and empirical measurements (assuming 100% use of the two 105 in 3 GI airguns in greater than 1,000 m water depths), which was calculated to be 675 m (2,214.6 ft). Detailed Description of the Proposed Specified Activity NSF and ASC propose to conduct a low-energy seismic survey in the Scotia Sea and the southern Atlantic Ocean from September to October 2014. In addition to the low-energy seismic survey, scientific activities would include conducting a bathymetric profile survey of the seafloor using transducer-based instruments such as a multi-beam echosounder and sub-bottom profiler; collecting global positioning system (GPS) information through the temporary installation of three continuous Global Navigation Satellite Systems (cGNSS) on the South Georgia micro-continent; and collecting dredge sampling around the edges of seamounts or ocean floor with significant magnetic anomalies to determine the nature and age of bathymetric highs near the eastern edge of the central Scotia Sea. Water depths in the survey area are greater than 1,000 meters (m) (3,280.1 feet [ft]). The seismic survey is scheduled to occur for a total of approximately 325 hours over the course of the entire cruise, which would be for approximately 30 operational days in September to October 2014. The proposed seismic survey would be conducted during the day and night, and for up to 40 hours of continuous operations at a time. The operation hours and survey length would include equipment testing, ramp-up, line changes, and repeat coverage. The long transit time between port and the study site constrains how long the ship can be in the study area and effectively limits the maximum amount of time the airguns can operate. Some minor deviation from these dates would be possible, depending on logistics and weather. The proposed survey of the Scotia Sea and southern Atlantic Ocean would involve conducting single channel seismic reflection profiling across the northern central Scotia Sea along two lines that cross the seismically active and apparently compressive boundary between the South Georgia micro-continent and the Northeast Georgia Rise. The targeted seismic survey would occur in the unexplored zones of elevated crust in the eastern central Scotia Sea and is designed to address several critical questions with respect to the tectonic nature of the northern and southern boundaries of the South Georgia micro-continent. Opening of deep Southern Ocean gateways between Antarctica and South America and between Antarctica and Australia permitted complete circum-Antarctic circulation. This Antarctic Circumpolar Current is not well understood. The Antarctic Circumpolar Current may have been critical in the transition from a warm Earth in the early Cenozoic to the subsequent much cooler conditions that persist to the present day. Opening of Drake Passage and the west Scotia Sea likely broke the final barrier formed by the Andes of Tierra del Fuego and the “Antarctandes” of the Antarctic Peninsula. Once this deep gateway, usually referred to as the Drake Passage gateway, was created, the strong and persistent mid-latitude winds could generate one of the largest deep currents on Earth, at approximately 135 Sverdrup (a Sverdrup [Sv] is a measure of average flow rate in million cubic meters of water per second). This event is widely believed to be closely associated in time with a major, abrupt drop in global temperatures and the rapid expansion of the Antarctic ice sheets at 33 to 34 Million Annus (Ma, i.e., million years from the present/before the current date), the Eocene-Oligocene boundary. The events leading to the complete opening of the Drake Passage gateway are very poorly known. The uncertainty is due to the complex tectonic history of the Scotia Sea and its enclosing Scotia Ridge, the eastward-closing, locally emergent submarine ridge that joins the southernmost Andes to the Antarctic Peninsula and deflects the Antarctic Circumpolar Current through gaps in its northern limb. The critical keys to this problem are the enigmatic floor of the central Scotia Sea between the high relief South Georgia (approximately 3,000 m [9,842.5 ft]) and the lower South Orkney islands (approximately 1,200 m [3,937 ft]), emergent parts of micro-continental blocks on the North and South Scotia ridges respectively, and the North Scotia Ridge itself. In 2008, an International Polar Year research program was conducted using the RVIB Nathaniel B. Palmer ( Palmer ) (Cruise NBP 0805) that was designed to elucidate the structure and history of this area to help provide the constraints necessary for understanding of the initiation of the critical Drake Passage—Scotia Sea gateway. Underway data and dredged samples produced unexpected results that led to a structurally different view of the central Scotia Sea and highlighted factors bearing on initiation of the Antarctic Circumpolar Current that had not been previously considered. The results of this study of the central Scotia Sea are fragmentary due to the limited time available during Cruise NBP 0805. Therefore, the extent, geometry, and physiography of a submerged volcanic arc that may have delayed formation of a complete Antarctic Circumpolar Current until after the initiation of Antarctic glaciation are poorly defined, with direct dating limited to a few sites. To remedy these deficiencies, thereby further elucidating the role of the central Scotia Sea in the onset and development of the Antarctic Circumpolar Current, the proposed targeted surveying and dredging would determine likely arc constructs in the eastern central Scotia Sea. These would be combined with a survey of the margins of the South Georgia micro-continent and installation of three continuous GPS stations on South Georgia that would test the hypothesis regarding the evolution of the North Scotia Ridge, also an impediment to the present Antarctic Circumpolar Current. The Principal Investigators are Dr. Ian Dalziel and Dr. Lawrence Lawver of the University of Texas at Austin, and Dr. Robert Smalley of the University of Memphis. The procedures to be used for the survey would be similar to those used during previous low-energy seismic surveys by NSF and would use conventional seismic methodology. The proposed survey would involve one source vessel, the Palmer. NSF and ASC would deploy a two Sercel Generator Injector (GI) airgun array (each with a discharge volume of 105 in 3 [1,720 cm 3 ], in one string, with a total volume of 210 in 3 [3,441.3 cm 3 ]) as an energy source, at a tow depth of up to 3 to 4 m (9.8 to 13.1 ft) below the surface (more information on the airguns can be found in Appendix B of the IHA application). A third airgun would serve as a “hot spare” to be used as a back-up in the event that one of the two operating airguns malfunctions. The airguns in the array would be spaced approximately 3 m (9.8 ft) apart and 15 to 40 m (49.2 to 131.2 ft) astern of the vessel. The receiving system would consist of one or two 100 m (328.1 ft) long, 24-channel, solid-state hydrophone streamer(s) towed behind the vessel. Data acquisition is planned along a series of predetermined lines, all of which would be in water depths greater than 1,000 m. As the GI airguns are towed along the survey lines, the hydrophone streamer(s) would receive the returning acoustic signals and transfer the data to the onboard processing system. All planned seismic data acquisition activities would be conducted by technicians provided by NSF and ASC, with onboard assistance by the scientists who have proposed the study. The vessel would be self-contained, and the crew would live aboard the vessel for the entire cruise. The weather and sea conditions would be closely monitored, including for conditions that could limit visibility. Pack ice is not anticipated to be encountered during the proposed cruise; therefore, no icebreaking activities are expected. If situations are encountered which pose a risk to the equipment, impede data collection, or require the vessel to stop forward progress, the equipment would be shut-down and retrieved until conditions improve. In general, the airgun array and streamer(s) could be retrieved in less than 30 minutes. The planned seismic survey (including equipment testing, start-up, line changes, repeat coverage of any areas, and equipment recovery) would consist of approximately 2,950 kilometers (km) (1,592.9 nautical miles [nmi]) of transect lines (including turns) in the survey area in the Scotia Sea and southern Atlantic Ocean (see Figures 1, 2, and 3 of the IHA application). In addition to the operation of the airgun array, a single-beam and multi-beam echosounder, ADCP, and a sub-bottom profiler would also likely be operated from the Palmer continuously throughout the cruise. There would be additional seismic operations associated with equipment testing, ramp-up, and possible line changes or repeat coverage of any areas where initial data quality is sub-standard. In NSF and ASC's estimated take calculations, 25% has been added for those additional operations. Table 1—Proposed Low-Energy Seismic Survey Activities in the Scotia Sea and the Southern Atlantic Ocean Survey length (km) Cumulative duration (hr) 1 Airgun array total volume Time between airgun shots (distance) Streamer length (m) 2,950 (1,592.9 nmi) ~325 2 × 105 in 3 (2 × 1,720 cm 3 ) 5 to 10 seconds (12.5 to 25 m or 41 to 82 ft) 100 (328.1 ft). 1 Airgun operations are planned for no more than 40 continuous hours at a time. Vessel Specifications The Palmer, a research vessel owned by Edison Chouest Offshore, Inc. and operated by NSF and ACS (under a long-term charter with Edison Chouest Offshore, Inc.), would tow the two GI airgun array, as well as the hydrophone streamer. When the Palmer is towing the airgun array and the relatively short hydrophone streamer, the turning rate of the vessel while the gear is deployed is approximately 20 degrees per minute, which is much higher than the limit of 5 degrees per minute for a seismic vessel towing a streamer of more typical length (much greater than 1 km [0.5 nmi]). Thus, the maneuverability of the vessel is not limited much during operations with the streamer. The U.S.-flagged vessel, built in 1992, has a length of 94 m (308.5 ft); a beam of 18.3 m (60 ft); a maximum draft of 6.8 m (22.5 ft); and a gross tonnage of 6,174. The ship is powered by four Caterpillar 3608 diesel engines (3,300 brake horsepower [hp] at 900 rotations per minute [rpm]) and a 1,400 hp flush-mounted, water jet azimuthing bowthruster. Electrical power is provided by four Caterpillar 3512, 1,050 kiloWatt (kW) diesel generators. The GI airgun compressor onboard the vessel is manufactured by Borsig-LMF Seismic Air Compressor. The Palmer' s operation speed during seismic acquisition is typically approximately 9.3 km/hr (5 kts) (varying between 7.4 to 11.1 km/hr [4 to 6 kts]). When not towing seismic survey gear, the Palmer typically cruises at 18.7 km/hr (10.1 kts) and has a maximum speed of 26.9 km/hr (14.5 kts). The Palmer has an operating range of approximately 27,780 km (15,000 nmi) (the distance the vessel can travel without refueling), which is approximately 70 to 75 days. The vessel can accommodate 37 scientists and 22 crew members. The vessel also has two locations as likely observation stations from which Protected Species Observers (PSO) would watch for marine mammals before and during the proposed airgun operations. Observing stations would be at the bridge level, with a PSO's eye level approximately 16.5 m (54.1 ft) above sea level and an approximately 270° view around the vessel, and an aloft observation tower that is approximately 24.4 m (80.1 ft) above sea level, is protected from the weather and has an approximately 360° view around the vessel. More details of the Palmer can be found in the IHA application and online at: http://www.nsf.gov/geo/plr/support/nathpalm.jsp and http://www.usap.gov/vesselScienceAndOperations/contentHandler.cfm?id=1561. Acoustic Source Specifications—Seismic Airguns The Palmer would deploy an airgun array, consisting of two 105 in 3 Sercel GI airguns as the primary energy source and a 100 m streamer containing hydrophones. The airgun array would have a supply firing pressure of 2,000 pounds per square inch (psi) and 2,200 psi when at high pressure stand-by (i.e., shut-down). The regulator is adjusted to ensure that the maximum pressure to the GI airguns is 2,000 psi, but there are times when the GI airguns may be operated at pressures as low as 1,750 to 1,800 psi. Seismic pulses for the GI airguns would be emitted at intervals of approximately 5 seconds. At vessel speeds of approximately 9.3 km/hr, the shot intervals correspond to spacing of approximately 12.5 m (41 ft) during the study. During firing, a brief (approximately 0.03 second) pulse sound is emitted; the airguns would be silent during the intervening periods. The dominant frequency components range from two to 188 Hertz (Hz). The GI airguns would be used in harmonic mode, that is, the volume of the injector chamber (I) of each GI airgun is equal to that of its generator chamber (G): 105 in 3 (1,721 cm 3 ) for each airgun. The generator chamber of each GI airgun in the primary source is the one responsible for introducing the sound pulse into the ocean. The injector chamber injects air into the previously-generated bubble to maintain its shape, and does not introduce more sound into the water. The airguns would fire the compressed air volume in unison in a harmonic mode. In harmonic mode, the injector volume is designed to destructively interfere with the reverberations of the generator (source component). Firing the airguns in harmonic mode maximizes resolution in the data and minimizes any excess noise in the water column or data caused by the reverberations (or bubble pulses). The two GI airguns would be spaced approximately 3 m (9.8 ft) apart, side-by-side, between 15 and 40 m (49.2 and 131.2 ft) behind the Palmer, at a depth of up to 3 to 4 m during the survey. The Nucleus modeling software used at Lamont-Doherty Earth Observatory of Columbia University (L-DEO) does not include GI airguns as part of its airgun library, however signatures and mitigation models have been obtained for two 105 in 3 G airguns at 3 m tow depth that are close approximations. For the two 105 in 3 airgun array, the source output (downward) is 234.4 dB re 1 μPam 0-to-peak and 239.8 dB re 1 μPam for peak-to-peak. These numbers were determined applying the aforementioned G-airgun approximation to the GI airgun and using signatures filtered with DFS V out-256 Hz 72 dB/octave. The dominant frequency range would be 20 to 160 Hz for a pair of GI airguns towed at 3 m depth and 35 to 230 Hz for a pair of GI airguns towed at 2 m depth. During the low-energy seismic survey, the vessel would attempt to maintain a constant cruise speed of approximately 5 knots. The airguns would operate continuously for no more than 40 hours at a time. The cumulative duration of the airgun operations would not exceed 325 hrs. The relatively short, 24-channel hydrophone streamer would provide operational flexibility to allow the seismic survey to proceed along the designated cruise track. The design of the seismic equipment is to achieve high-resolution images with the ability to correlate to the ultra-high frequency sub-bottom profiling data and provide cross-sectional views to pair with the seafloor bathymetry. Metrics Used in This Document This section includes a brief explanation of the sound measurements frequently used in the discussions of acoustic effects in this document. Sound pressure is the sound force per unit area, and is usually measured in micropascals (μPa), where 1 pascal (Pa) is the pressure resulting from a force of one newton exerted over an area of one square meter. Sound pressure level (SPL) is expressed as the ratio of a measured sound pressure and a reference level. The commonly used reference pressure level in underwater acoustics is 1 μPa, and the units for SPLs are dB re 1 μPa. SPL (in decibels [dB]) = 20 log (pressure/reference pressure). SPL is an instantaneous measurement and can be expressed as the peak, the peak-to-peak (p-p), or the root mean square (rms). Root mean square, which is the square root of the arithmetic average of the squared instantaneous pressure values, is typically used in discussions of the effects of sounds on vertebrates and all references to SPL in this document refer to the root mean square unless otherwise noted. SPL does not take the duration of a sound into account. Characteristics of the Airgun Pulses Airguns function by venting high-pressure air into the water, which creates an air bubble. The pressure signature of an individual airgun consists of a sharp rise and then fall in pressure, followed by several positive and negative pressure excursions caused by the oscillation of the resulting air bubble. The oscillation of the air bubble transmits sounds downward through the seafloor, and the amount of sound transmitted in the near horizontal directions is reduced. However, the airgun array also emits sounds that travel horizontally toward non-target areas. The nominal downward-directed source levels of the airgun arrays used by NSF and ASC on the Palmer do not represent actual sound levels that can be measured at any location in the water. Rather, they represent the level that would be found 1 m (3.3 ft) from a hypothetical point source emitting the same total amount of sound as is emitted by the combined GI airguns. The actual received level at any location in the water near the GI airguns would not exceed the source level of the strongest individual source. In this case, that would be about 228.2 dB re 1 µPam peak or 233.5 dB re 1 µPam peak-to-peak for the two 105 in 3 airgun array. However, the difference between rms and peak or peak-to-peak values for a given pulse depends on the frequency content and duration of the pulse, among other factors. Actual levels experienced by any organism more than 1 m from either GI airgun would be significantly lower. Accordingly, L-DEO has predicted and modeled the received sound levels in relation to distance and direction from the two GI airgun array. A detailed description of L-DEO's modeling for this survey's marine seismic source arrays for protected species mitigation is provided in the NSF/USGS PEIS. These are the nominal source levels applicable to downward propagation. The NSF/USGS PEIS discusses the characteristics of the airgun pulses. NMFS refers the reviewers to that document for additional information. Predicted Sound Levels for the Airguns To determine buffer and exclusion zones for the airgun array to be used, received sound levels have been modeled by L-DEO for a number of airgun configurations, including two 105 in 3 G airguns, in relation to distance and direction from the airguns (see Figure 2 in Attachment A of the IEE/EA). The model does not allow for bottom interactions, and is most directly applicable to deep water. Because the model results are for G airguns, which have more energy than GI airguns of the same size, those distances overestimate (by approximately 10%) the distances for the two 105 in 3 GI airguns. Although the distances are overestimated, no adjustments for this have been made to the radii distances in Table 2 (below). Based on the modeling, estimates of the maximum distances from the GI airguns where sound levels of 190, 180, and 160 dB re 1 μPa (rms) are predicted to be received in deep water are shown in Table 2 (see Table 1 of Attachment A of the IEE/EA). Empirical data concerning the 190, 180, and 160 dB (rms) distances were acquired for various airgun arrays based on measurements during the acoustic verification studies conducted by L-DEO in the northern GOM in 2003 (Tolstoy et al., 2004) and 2007 to 2008 (Tolstoy et al., 2009; Diebold et al., 2010). Results of the 18 and 36 airgun array are not relevant for the two GI airguns to be used in the proposed survey because the airgun arrays are not the same size or volume. The empirical data for the 6, 10, 12, and 20 airgun arrays indicate that, for deep water, the L-DEO model tends to overestimate the received sound levels at a given distance (Tolstoy et al., 2004). Measurements were not made for a two GI airgun array in deep water; however, NSF and ASC proposes to use the buffer and exclusion zones predicted by L-DEO's model for the proposed GI airgun operations in deep water, although they are likely conservative given the empirical results for the other arrays. Using the L-DEO model, Table 2 (below) shows the distances at which three rms sound levels are expected to be received from the two GI airguns. The 160 dB re 1 μPam (rms) is the threshold specified by NMFS for potential Level B (behavioral) harassment from impulsive noise for both cetaceans and pinnipeds. The 180 and 190 dB re 1 μPam (rms) distances are the safety criteria for potential Level A harassment as specified by NMFS (2000) and are applicable to cetaceans and pinnipeds, respectively. If marine mammals are detected within or about to enter the appropriate exclusion zone, the airguns would be shut-down immediately. Table 2 summarizes the predicted distances at which sound levels (160, 180, and 190 dB [rms]) are expected to be received from the two airgun array (each 105 in 3 ) operating in deep water (greater than 1,000 m [3,280 ft]) depths. Table 2—Predicted and Modeled (Two 105 in 3 GI Airgun Array) Distances to Which Sound Levels ≥160, 180, and 190 d B re 1 μP a (rms) Could Be Received in Deep Water During the Proposed Low-Energy Seismic Survey in the Scotia Sea and the Southern Atlantic Ocean, September to October 2014 Source and total volume Tow depth (m) Water depth (m) Predicted RMS radii distances (m) for 2 GI airgun array 160 dB 180 dB 190 dB Two GI Airguns (105 in 3 ) 3 to 4 Deep (>1,000) 670 (2,198.2 ft) 100 (328.1 ft) 20 * (65.6 ft) * 100 would be used for pinnipeds as well as cetaceans. NMFS expects that acoustic stimuli resulting from the proposed operation of the two GI airgun array has the potential to harass marine mammals. NMFS does not expect that the movement of the Palmer, during the conduct of the low-energy seismic survey, has the potential to harass marine mammals because the relatively slow operation speed of the vessel (approximately 5 kts; 9.3 km/hr; 5.8 mph) during seismic acquisition should allow marine mammals to avoid the vessel. Bathymetric Survey Along with the low-energy airgun operations, other additional geophysical measurements would be made using swath bathymetry, backscatter sonar imagery, high-resolution sub-bottom profiling (“CHIRP”), imaging, and magnetometer instruments. In addition, several other transducer-based instruments onboard the vessel would be operated continuously during the cruise for operational and navigational purposes. During operations, when the vessel is not towing seismic equipment, its average speed would be approximately 10.1 kts (18.8 km/hr). Operating characteristics for the instruments to be used are described below. Single-Beam Echosounder (Knudsen 3260)—The hull-mounted CHIRP sonar would be operated continuously during all phases of the cruise. This instrument is operated at 12 kHz for bottom-tracking purposes or at 3.5 kHz in the sub-bottom profiling mode. The sonar emits energy in a 30° beam from the bottom of the ship. Single-Beam Echosounder (Bathy 2000)—The hull-mounted sonar characteristics of the Bathy 2000 are similar to the Knudsen 3260. Only one hull-mounted echosounder can be operated at a time, and this source would be operated instead of the Knudsen 3260 only if needed (i.e., only one would be in continuous operation during the cruise). The specific model to be used is expected to be selected by the scientific researchers. Multi-Beam Sonar (Simrad EM120)—The hull-mounted multi-beam sonar would be operated continuously during the cruise. This instrument operates at a frequency of 12 kHz, has an estimated maximum source energy level of 242 dB re 1μPa (rms), and emits a very narrow (<2°) beam fore to aft and 150° in cross-track. The multi-beam system emits a series of nine consecutive 15 ms pulses. Acoustic Doppler Current Profiler (ADCP Teledyne RDI VM-150)—The hull-mounted ADCP would be operated continuously throughout the cruise. The ADCP operates at a frequency of 150 kHz with an estimated acoustic output level at the source of 223.6 dB re 1μPa (rms). Sound energy from the ADCP is emitted as a 30° conically-shaped beam. Acoustic Doppler Current Profiler (ADCP Ocean Surveyor OS-38)—The characteristics of this backup hull-mounted ADCP unit are similar to the Teledyne VM-150 and would be continuously operated. Passive Instruments—During the seismic survey in the Scotia Sea and southern Atlantic Ocean, a precession magnetometer and Air-Sea gravity meter would be deployed. In addition, numerous (approximately 60) expendable bathythermograph (XBTs) probes would also be released (and none would be recovered) over the course of the cruise to obtain temperature data necessary to calculate sound velocity profiles used by the multi-beam sonar. Dredge Sampling The primary sampling goals involve the acquisition of in situ rock samples from deep marine rises (escarpments) at 3,000 to 4,000 m (9,842.5 to 13,123.4 ft) depths to determine the composition and age of the seafloor. Underway multi-beam and seismic data would be used to locate submarine outcrops. Dredging would be conducted upslope on escarpments. No dredging would be undertaken across the top of any seamounts, and final selection of dredge sites would include review to ensure that the tops of seamounts and corals in the area are avoided. It is anticipated that researchers would survey and dredge two deep marine rises and one topographic high (see areas A and B in Figure 2 of the IHA application). There will be only six deployments of the dredge. The dredge buckets would be less than 1 m (3.28 ft) across and each sample area to be dredged would be no longer than approximately 1,000 m. Approximately 1,000 m 2 (10,763.9 ft 2 ) of seafloor would be disturbed by each deployment of the dredge at two different sites (resulting in a total of approximately 6,000 m 2 [64,583.46 ft 2 ] of affected seafloor for the proposed project). Six samples would be taken, with each dredge effort being 1,000 m 2 in length. Two samples would be collected from each of two locations (seamount sides) at Box A and two samples would be collected from one location at Box B (see Figure 2 of the IHA application). Table 3—Proposed Dredging Activities in the Scotia Sea and Southern Atlantic Ocean Sampling device Area (see Figure 2 of the IHA application) Number of deployments Scripps Institution of Oceanography (SIO)-style Deep Sea Rock Dredge A and B 3 The Government of South Georgia and South Sandwich Islands has established a large sustainable use Marine Protected Area covering over 1 million km 2 (291,553.35 nmi 2 ) of the South Georgia and South Sandwich Islands Maritime Zone. Activities within the Marine Protected Area are subject to the requirements of the current Management Plan (see Attachment C of the IHA application). The area was designated as a Marine Protected Area to ensure the protection and conservation of the resources and biodiversity and support important ecosystem roles, such as feeding areas for marine mammals, and penguins and other seabirds. Research activities, including trawling and sampling the seafloor, require application for a permit issued by the Government of South Georgia and South Sandwich Islands. The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has adopted Conservation Measures 22-06, 22-07, and 22-09 to protect vulnerable marine ecosystems, which include seamounts, hydrothermal vents, cold water corals, and sponge fields. These measures apply to the entire proposed study area. Additionally, the area surrounding South Georgia Island was designated by CCAMLR as an Integrated Study Area to assist with the collection and management of information relating to the CCAMLR Ecosystem Monitoring Program. The Conservation Measure 22-07 includes mitigation and reporting requirements if vulnerable marine ecosystems are encountered. The science team would follow these requirements (see Attachment C of the IHA application) if vulnerable marine ecosystems are encountered while sampling the sea bottom; however, the specific intent of the proposed dredging activities is to avoid obtaining material from the tops of seamounts. Geodetic Measurements Researchers would install three continuous Global Navigation Satellite System (cGNSS) stations on the South Georgia micro-continent (see Figure 3 of the IHA application). The cGNSS systems would collect GPS and meteorological data with daily data recovery using IRIDIUM-based communications. These stations would complement the cGNSS station installed at King Edward Point in Cumberland Bay on the northeastern side of the island (see the “red star” in Figure 3 of the IHA application). One station would be installed near Cooper Bay on the southeastern extremity of the island, the second station would be installed on a reef or islet between Cooper Bay and Annenkov Island, and the third station would be installed on Bird Island. The stations would be removed after three years of operation. Description of the Marine Mammals in the Area of the Proposed Specified Activity Various national Antarctic research programs (e.g., British Antarctic Survey, Australian Antarctic Division, and NMFS National Marine Mammal Laboratory), academic institutions (e.g., Duke University, University of St. Andrews, and Woods Hole Oceanographic Institution), and other organizations (e.g., South Georgia Museum, Fundacion Cethus, Whale and Dolphin Conservation, and New England Aquarium) have conducted scientific cruises and/or examined data on marine mammal sightings along the coast of Antarctica, south Atlantic Ocean, Scotia Sea, and around South Georgia and South Sandwich islands, and these data were considered in evaluating potential marine mammals in the proposed action area. Records from the International Whaling Commission's International Decade of Cetacean Research (IDCR), Southern Ocean Collaboration Program (SOC), and Southern Ocean Whale and Ecosystem Research (IWC-SOWER) circumpolar cruises were also considered. The marine mammals that generally occur in the proposed action area belong to three taxonomic groups: Mysticetes (baleen whales), odontocetes (toothed whales), and pinnipeds (seals and sea lions). The marine mammal species that could potentially occur within the southern Atlantic Ocean in proximity to the proposed action area in the Scotia Sea include 32 species of cetaceans and 7 species of pinnipeds. The waters of the Scotia Sea and southern Atlantic Ocean, especially those near South Georgia Island, are characterized by high biomass and productivity of phytoplankton, zooplankton, and vertebrate predators, and may be a feeding ground for many of these marine mammals (Richardson, 2012). In general, many of the species present in the sub-Antarctic study area may be present or migrating through the Scotia Sea during the proposed low-energy seismic survey. Many of the species that may be potentially present in the study area seasonally migrate to higher latitudes near Antarctica. In general, most large whale species (except for the killer whale) migrate north in the middle of the austral winter and return to Antarctica in the early austral summer. The six species of pinnipeds that are found in the southern Atlantic Ocean and Southern Ocean and may be present in the proposed study area include the crabeater ( Lebodon carcinophagus ), leopard ( Hydrurga leptonyx ), Weddell ( Leptonychotes weddellii ), southern elephant ( Mirounga leonina ), Antarctic fur ( Arctocephalus gazella ), and Subantarctic fur ( Arctocephalus tropicalis ) seal. Many of these pinniped species breed on either the pack ice or subantarctic islands. The southern elephant seal and Antarctic fur seal have haul-outs and rookeries that are located on subantarctic islands and prefer beaches. The Ross seal ( Ommatophoca rossii ) is generally found in dense consolidated pack ice and on ice floes, but may migrate into open water to forage. This species' preferred habitat is not in the proposed study area, and thus it is not considered further in this document. Marine mammal species likely to be encountered in the proposed study area that are listed as endangered under the U.S. Endangered Species Act of 1973 (ESA; 16 U.S.C. 1531 et seq. ), includes the southern right ( Eubalaena australis ), humpback ( Megaptera novaeangliae ), sei ( Balaenoptera borealis ), fin ( Balaenoptera physalus ), blue ( Balaenoptera musculus ), and sperm ( Physeter macrocephalus ) whale. In addition to the 26 species known to occur in the Scotia Sea and the southern Atlantic Ocean, there are 14 cetacean species with ranges that are known to potentially occur in the waters of the study area: Pygmy right ( Caperea marginata ), Bryde's ( Balaenoptera brydei ), dwarf minke ( Balaenoptera acutorostrata spp.), pygmy blue ( Balaenoptera musculus brevicauda ), pygmy sperm ( Kogia breviceps ), dwarf sperm ( Kogia sima ), Andrew's beaked ( Mesoplodon bowdoini ), Blainville's beaked ( Mesoplodon densirostris ), Hector's beaked ( Mesoplodon hectori ), and spade-toothed beaked ( Mesoplodon traversii ) whale, and Commerson's ( Cephalorhynchus commersonii ), Dusky ( Lagenorhynchus obscurus ), bottlenose ( Tursiops truncatus ), and Risso's ( Grampus griseus ) dolphin. However, these species have not been sighted and are not expected to occur where the proposed activities would take place. These species are not considered further in this document. Table 4 (below) presents information on the habitat, occurrence, distribution, abundance, population status, and conservation status of the species of marine mammals that may occur in the proposed study area during September to October 2014. Table 4—The Habitat, Occurrence, Range, Regional Abundance, and Conservation Status of Marine Mammals That May Occur in or Near the Proposed Low-Energy Seismic Survey Area in the Scotia Sea and Southern Atlantic Ocean [See text and Tables 6 and 7 in NSF and ASC's IHA application for further details] Species Habitat Occurrence Range Population estimate ESA 1 MMPA 2 Mysticetes: Southern right whale ( Eubalaena australis ) Coastal, pelagic Common Circumpolar 20 to 55° South 8,000 3 to 15,000 4 EN D Pygmy right whale ( Caperea marginata ) Coastal, pelagic Rare 30 to 55° South NA NL NC Humpback whale ( Megaptera novaeangliae ) Pelagic, nearshore waters, and banks Common Cosmopolitan 35,000 to 40,000 3 —Worldwide 9,484 5 —Scotia Sea and Antarctica Peninsula EN D Minke whale ( Balaenoptera acutorostrata including dwarf sub-species) Pelagic and coastal Common Circumpolar—Southern Hemisphere to 65° South NA NL NC Antarctic minke whale ( Balaenoptera bonaerensis ) Pelagic, ice floes Common 7° South to ice edge (usually 20 to 65° South) Several 100,000 3 —Worldwide 18,125 5 —Scotia Sea and Antarctica Peninsula NL NC Bryde's whale ( Balaenoptera brydei ) Pelagic and coastal Rare Circumglobal 40° North to 40° South NA NL NC Sei whale ( Balaenoptera borealis ) Primarily offshore, pelagic Uncommon Migratory, Feeding Concentration 40 to 50° South 80,000 3 —Worldwide EN D Fin whale ( Balaenoptera physalus ) Continental slope, pelagic Common Cosmopolitan, Migratory 140,000 3 —Worldwide 4,672 5 —Scotia Sea and Antarctica Peninsula EN D Blue whale ( Balaenoptera musculus; including pygmy blue whale [ Balaenoptera musculus brevicauda ]) Pelagic, shelf, coastal Uncommon Migratory Pygmy blue whale—North of Antarctic Convergence 55° South 8,000 to 9,000 3 —Worldwide 1,700 6 —Southern Ocean EN D Odontocetes: Sperm whale ( Physeter macrocephalus ) Pelagic, deep sea Common Cosmopolitan, Migratory 360,000 3 —Worldwide 9,500 3 —Antarctic EN D Pygmy sperm whale ( Kogia breviceps ) Pelagic, slope Rare Widely distributed in tropical and temperate zones NA NL NC Dwarf sperm whale ( Kogia sima ) Pelagic, slope Rare Widely distributed in tropical and temperate zones NA NL NC Arnoux's beaked whale ( Berardius arnuxii ) Pelagic Common Circumpolar in Southern Hemisphere, 24 to 78° South NA NL NC Cuvier's beaked whale ( Ziphius cavirostris ) Pelagic Uncommon Cosmopolitan NA NL NC Shepherd's beaked whale ( Tasmacetus shepherdi ) Pelagic Common Circumpolar—south of 30° South NA NL NC Southern bottlenose whale ( Hyperoodon planifrons ) Pelagic Common Circumpolar—30° South to ice edge 500,000 3 —South of Antarctic Convergence NL NC Andrew's beaked whale ( Mesoplodon bowdoini ) Pelagic Rare 32 to 55° South NA NL NC Blainville's beaked whale ( Mesoplodon densirostris ) Pelagic Rare Temperate and tropical waters worldwide NA NL NC Gray's beaked whale ( Mesoplodon grayi ) Pelagic Common 30° South to Antarctic waters NA NL NC Hector's beaked whale ( Mesoplodon hectori ) Pelagic Rare Circumpolar—cool temperate waters of Southern Hemisphere NA NL NC Spade-toothed beaked whale ( Mesoplodon traversii ) Pelagic Rare Circumantarctic NA NL NC Strap-toothed beaked whale ( Mesoplodon layardii ) Pelagic Common 30° South to Antarctic Convergence NA NL NC Killer whale ( Orcinus orca ) Pelagic, shelf, coastal, pack ice Common Cosmopolitan 80,000 3 —South of Antarctic Convergence 25,000 7 —Southern Ocean NL NC Long-finned pilot whale ( Globicephala melas ) Pelagic, shelf, coastal Common Circumpolar—19 to 68° South in Southern Hemisphere 200,000 3 8 —South of Antarctic Convergence NL NC Risso's dolphin ( Grampus griseus ) Shelf, slope, seamounts Rare 60° North to 60° South NA NL NC Bottlenose dolphin ( Tursiops truncatus ) Offshore, inshore, coastal, estuaries Rare 45° North to 45° South >625,500 3 —Worldwide NL NC Southern right whale dolphin ( Lissodelphis peronii ) Pelagic Uncommon 12 to 65° South NA NL NC Peale's dolphin ( Lagenorhynchus australis ) Coastal, continental shelf, islands Uncommon 33 to 60° South NA 200—southern Chile 3 NL NC Commerson's dolphin (Cephalorhynchus commersonii) Coastal, continental shelf, islands Rare South America Falkland Islands Kerguelen Islands 3,200—Strait of Magellan 3 NL NC Dusky dolphin ( Lagenorhynchus obscurus ) Coastal, continental shelf and slope Rare Widespread in Southern Hemisphere NA NL NC Hourglass dolphin ( Lagenorhynchus cruciger ) Pelagic, ice edge Common 33° South to pack ice 144,000 3 —South of Antarctic Convergence NL NC Spectacled porpoise ( Phocoena dioptrica ) Coastal, pelagic Uncommon Circumpolar—Southern Hemisphere NA NL NC Pinnipeds: Crabeater seal ( Lobodon carcinophaga ) Coastal, pack ice Common Circumpolar—Antarctic 5,000,000 to 15,000,000 3 9 NL NC Leopard seal ( Hydrurga leptonyx ) Pack ice, sub-Antarctic islands Common Sub-Antarctic islands to pack ice 220,000 to 440,000 3 10 NL NC Ross seal ( Ommatophoca rossii ) Pack ice, smooth ice floes, pelagic Rare Circumpolar—Antarctic 130,000 3 , 20,000 to 220,000 14 NL NC Weddell seal ( Leptonychotes weddellii ) Fast ice, pack ice, sub-Antarctic islands Uncommon Circumpolar—Southern Hemisphere 500,000 to 1,000,000 3 11 NL NC Southern elephant seal ( Mirounga leonina ) Coastal, pelagic, sub-Antarctic waters Common Circumpolar—Antarctic Convergence to pack ice 640,000 12 to 650,000 3 , 470,000—South Georgia Island 14 NL NC Antarctic fur seal ( Arctocephalus gazella ) Shelf, rocky habitats Common Sub-Antarctic islands to pack ice edge 1,600,000 13 to 3,000,000 3 NL NC Subantarctic fur seal ( Arctocephalus tropicalis ) Shelf, rocky habitats Uncommon Subtropical front to sub-Antarctic islands and Antarctica Greater than 310,000 3 NL NC NA = Not available or not assessed. 1 U.S. Endangered Species Act: EN = Endangered, T = Threatened, DL = Delisted, NL = Not listed. 2 U.S. Marine Mammal Protection Act: D = Depleted, S = Strategic, NC = Not Classified. 3 Jefferson et al., 2008. 4 Kenney, 2009. 5 Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) survey area (Reilly et al., 2004). 6 Sears and Perrin, 2009. 7 Ford, 2009. 8 Olson, 2009. 9 Bengston, 2009. 10 Rogers, 2009. 11 Thomas and Terhune, 2009. 12 Hindell and Perrin, 2009. 13 Arnould, 2009. 14 Academic Press, 2009. Refer to sections 3 and 4 of NSF and ASC's IHA application for detailed information regarding the abundance and distribution, population status, and life history and behavior of these other marine mammal species and their occurrence in the proposed project area. The IHA application also presents how NSF and ASC calculated the estimated densities for the marine mammals in the proposed survey area. NMFS has reviewed these data and determined them to be the best available scientific information for the purposes of the proposed IHA. Potential Effects of the Proposed Specified Activity on Marine Mammals This section includes a summary and discussion of the ways that the types of stressors associated with the specified activity (e.g., seismic airgun operation, vessel movement, gear deployment) have been observed to impact marine mammals. This discussion may also include reactions that we consider to rise to the level of a take and those that we do not consider to rise to the level of take (for example, with acoustics, we may include a discussion of studies that showed animals not reacting at all to sound or exhibiting barely measureable avoidance). This section is intended as a background of potential effects and does not consider either the specific manner in which this activity would be carried out or the mitigation that would be implemented, and how either of those would shape the anticipated impacts from this specific activity. The “Estimated Take by Incidental Harassment” section later in this document would include a quantitative analysis of the number of individuals that are expected to be taken by this activity. The “Negligible Impact Analysis” section will include the analysis of how this specific activity will impact marine mammals and will consider the content of this section, the “Estimated Take by Incidental Harassment” section, the “Proposed Mitigation” section, and the “Anticipated Effects on Marine Mammal Habitat” section to draw conclusions regarding the likely impacts of this activity on the reproductive success or survivorship of individuals and from that on the affected marine mammal populations or stocks. When considering the influence of various kinds of sound on the marine environment, it is necessary to understand that different kinds of marine life are sensitive to different frequencies of sound. Based on available behavioral data, audiograms have been derived using auditory evoked potentials, anatomical modeling, and other data; Southall et al. (2007) designate “functional hearing groups” for marine mammals and estimate the lower and upper frequencies of functional hearing of the groups. The functional groups and the associated frequencies are indicated below (though animals are less sensitive to sounds at the outer edge of their functional range and most sensitive to sounds of frequencies within a smaller range somewhere in the middle of their functional hearing range): • Low-frequency cetaceans (13 species of mysticetes): Functional hearing is estimated to occur between approximately 7 Hz and 30 kHz; • Mid-frequency cetaceans (32 species of dolphins, six species of larger toothed whales, and 19 species of beaked and bottlenose whales): Functional hearing is estimated to occur between approximately 150 Hz and 160 kHz; • High-frequency cetaceans (eight species of true porpoises, six species of river dolphins, Kogia spp., the franciscana [ Pontoporia blainvillei ], and four species of cephalorhynchids): Functional hearing is estimated to occur between approximately 200 Hz and 180 kHz; and • Phocid pinnipeds in water: Functional hearing is estimated to occur between approximately 75 Hz and 100 kHz; • Otariid pinnipeds in water: Functional hearing is estimated to occur between approximately 100 Hz and 40 kHz. As mentioned previously in this document, 26 marine mammal species (20 cetacean and 6 pinniped species) are likely to occur in the proposed seismic survey area. Of the 20 cetacean species likely to occur in NSF and ASC's proposed action area, 7 are classified as low-frequency cetaceans (southern right, humpback, minke, Antarctic minke, sei, fin, and blue whale), 12 are classified as mid-frequency cetaceans (sperm, Arnoux's beaked, Cuvier's beaked, Shepherd's beaked, southern bottlenose, Gray's beaked, strap-toothed beaked, killer, and long-finned pilot whale, and southern right whale, Peale's, and hourglass dolphin), and 1 is classified as a high-frequency cetacean (spectacled porpoise) (Southall et al., 2007). Of the 6 pinniped species likely to occur in NSF and ASC's proposed action area, 4 are classified as phocid pinnipeds (crabeater, leopard, Weddell, and southern elephant seal), and 2 are classified as otariid pinnipeds (Antarctic and Subantarctic fur seal) (Southall et al., 2007). A species functional hearing group is a consideration when we analyze the effects of exposure to sound on marine mammals. Acoustic stimuli generated by the operation of the airguns, which introduce sound into the marine environment, may have the potential to cause Level B harassment of marine mammals in the proposed survey area. The effects of sounds from airgun operations might include one or more of the following: Tolerance, masking of natural sounds, behavioral disturbance, temporary or permanent hearing impairment, or non-auditory physical or physiological effects (Richardson et al., 1995; Gordon et al., 2004; Nowacek et al., 2007; Southall et al., 2007). Permanent hearing impairment, in the unlikely event that it occurred, would constitute injury, but temporary threshold shift (TTS) is not an injury (Southall et al., 2007). Although the possibility cannot be entirely excluded, it is unlikely that the proposed project would result in any cases of temporary or permanent hearing impairment, or any significant non-auditory physical or physiological effects. Based on the available data and studies described here, some behavioral disturbance is expected. A more comprehensive review of these issues can be found in the “Programmatic Environmental Impact Statement/Overseas Environmental Impact Statement prepared for Marine Seismic Research that is funded by the National Science Foundation and conducted by the U.S. Geological Survey” (NSF/USGS, 2011). Tolerance Richardson et al. (1995) defines tolerance as the occurrence of marine mammals in areas where they are exposed to human activities or man-made noise. In many cases, tolerance develops by the animal habituating to the stimulus (i.e., the gradual waning of responses to a repeated or ongoing stimulus) (Richardson, et al., 1995; Thorpe, 1963), but because of ecological or physiological requirements, many marine animals may need to remain in areas where they are exposed to chronic stimuli (Richardson, et al., 1995). Numerous studies have shown that pulsed sounds from airguns are often readily detectable in the water at distances of many kilometers. Several studies have shown that marine mammals at distances more than a few kilometers from operating seismic vessels often show no apparent response. That is often true even in cases when the pulsed sounds must be readily audible to the animals based on measured received levels and the hearing sensitivity of the marine mammal group. Although various baleen whales and toothed whales, and (less frequently) pinnipeds have been shown to react behaviorally to airgun pulses under some conditions, at other times marine mammals of all three types have shown no overt reactions. The relative responsiveness of baleen and toothed whales are quite variable. Masking The term masking refers to the inability of a subject to recognize the occurrence of an acoustic stimulus as a result of the interference of another acoustic stimulus (Clark et al., 2009). Introduced underwater sound may, through masking, reduce the effective communication distance of a marine mammal species if the frequency of the source is close to that used as a signal by the marine mammal, and if the anthropogenic sound is present for a significant fraction of the time (Richardson et al., 1995). The airguns for the proposed low-energy seismic survey have dominant frequency components of 2 to 188 Hz. This frequency range fully overlaps the lower part of the frequency range of odontocete calls and/or functional hearing (full range about 150 Hz to 180 kHz). Airguns also produce a small portion of their sound at mid and high frequencies that overlap most, if not all, frequencies produced by odontocetes. While it is assumed that mysticetes can detect acoustic impulses from airguns and vessel sounds (Richardson et al., 1995a), sub-bottom profilers, and most of the multi-beam echosounders would likely be detectable by some mysticetes based on presumed mysticete hearing sensitivity. Odontocetes are presumably more sensitive to mid to high frequencies produced by the multi-beam echosounders and sub-bottom profilers than to the dominant low frequencies produced by the airguns and vessel. A more comprehensive review of the relevant background information for odontocetes appears in Section 3.6.4.3, Section 3.7.4.3 and Appendix E of the NSF/USGS PEIS (2011). Masking effects of pulsed sounds (even from large arrays of airguns) on marine mammal calls and other natural sounds are expected to be limited. Because of the intermittent nature and low duty cycle of seismic airgun pulses, animals can emit and receive sounds in the relatively quiet intervals between pulses. However, in some situations, reverberation occurs for much or the entire interval between pulses (e.g., Simard et al., 2005; Clark and Gagnon, 2006) which could mask calls. Some baleen and toothed whales are known to continue calling in the presence of seismic pulses, and their calls can usually be heard between the seismic pulses (e.g., Richardson et al., 1986; McDonald et al., 1995; Greene et al., 1999; Nieukirk et al., 2004; Smultea et al., 2004; Holst et al., 2005a,b, 2006; and Dunn and Hernandez, 2009). However, Clark and Gagnon (2006) reported that fin whales in the North Atlantic Ocean went silent for an extended period starting soon after the onset of a seismic survey in the area. Similarly, there has been one report that sperm whales ceased calling when exposed to pulses from a very distant seismic ship (Bowles et al., 1994). However, more recent studies found that they continued calling in the presence of seismic pulses (Madsen et al., 2002; Tyack et al., 2003; Smultea et al., 2004; Holst et al., 2006; and Jochens et al., 2008). Dilorio and Clark (2009) found evidence of increased calling by blue whales during operations by a lower-energy seismic source (i.e., sparker). Dolphins and porpoises commonly are heard calling while airguns are operating (e.g., Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a, b; and Potter et al., 2007). The sounds important to small odontocetes are predominantly at much higher frequencies than are the dominant components of airgun sounds, thus limiting the potential for masking. Pinnipeds have the most sensitive hearing and/or produce most of their sounds in frequencies higher than the dominant components of airgun sound, but there is some overlap in the frequencies of the airgun pulses and the calls. However, the intermittent nature of airgun pules presumably reduces the potential for masking. Marine mammals are thought to be able to compensate for masking by adjusting their acoustic behavior through shifting call frequencies, increasing call volume, and increasing vocalization rates. For example blue whales are found to increase call rates when exposed to noise from seismic surveys in the St. Lawrence Estuary (Dilorio and Clark, 2009). The North Atlantic right whales ( Eubalaena glacialis ) exposed to high shipping noise increased call frequency (Parks et al., 2007), while some humpback whales respond to low-frequency active sonar playbacks by increasing song length (Miller et al., 2000). In general, NMFS expects the masking effects of seismic pulses to be minor, given the normally intermittent nature of seismic pulses. Behavioral Disturbance Marine mammals may behaviorally react to sound when exposed to anthropogenic noise. Disturbance includes a variety of effects, including subtle to conspicuous changes in behavior, movement, and displacement. Reactions to sound, if any, depend on species, state of maturity, experience, current activity, reproductive state, time of day, and many other factors (Richardson et al., 1995; Wartzok et al., 2004; Southall et al., 2007; Weilgart, 2007). These behavioral reactions are often shown as: Changing durations of surfacing and dives, number of blows per surfacing, or moving direction and/or speed; reduced/increased vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); visible startle response or aggressive behavior (such as tail/fluke slapping or jaw clapping); avoidance of areas where noise sources are located; and/or flight responses (e.g., pinnipeds flushing into the water from haul-outs or rookeries). If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007). The biological significance of many of these behavioral disturbances is difficult to predict, especially if the detected disturbances appear minor. However, the consequences of behavioral modification could be expected to be biologically significant if the change affects growth, survival, and/or reproduction. Some of these significant behavioral modifications include: • Change in diving/surfacing patterns (such as those thought to be causing beaked whale stranding due to exposure to military mid-frequency tactical sonar); • Habitat abandonment due to loss of desirable acoustic environment; and • Cessation of feeding or social interaction. The onset of behavioral disturbance from anthropogenic noise depends on both external factors (characteristics of noise sources and their paths) and the receiving animals (hearing, motivation, experience, demography) and is also difficult to predict (Richardson et al., 1995; Southall et al., 2007). Given the many uncertainties in predicting the quantity and types of impacts of noise on marine mammals, it is common practice to estimate how many mammals would be present within a particular distance of industrial activities and/or exposed to a particular level of sound. In most cases, this approach likely overestimates the numbers of marine mammals that would be affected in some biologically-important manner. Baleen Whales —Baleen whales generally tend to avoid operating airguns, but avoidance radii are quite variable (reviewed in Richardson et al., 1995; Gordon et al., 2004). Whales are often reported to show no overt reactions to pulses from large arrays of airguns at distances beyond a few kilometers, even though the airgun pulses remain well above ambient noise levels out to much longer distances. However, baleen whales exposed to strong noise pulses from airguns often react by deviating from their normal migration route and/or interrupting their feeding and moving away. In the cases of migrating gray ( Eschrichtius robustus ) and bowhead ( Balaena mysticetus ) whales, the observed changes in behavior appeared to be of little or no biological consequence to the animals (Richardson, et al., 1995). They simply avoided the sound source by displacing their migration route to varying degrees, but within the natural boundaries of the migration corridors. Studies of gray, bowhead, and humpback whales have shown that seismic pulses with received levels of 160 to 170 dB re 1 μPa (rms) seem to cause obvious avoidance behavior in a substantial fraction of the animals exposed (Malme et al., 1986, 1988; Richardson et al., 1995). In many areas, seismic pulses from large arrays of airguns diminish to those levels at distances ranging from 4 to 15 km (2.2 to 8.1 nmi) from the source. A substantial proportion of the baleen whales within those distances may show avoidance or other strong behavioral reactions to the airgun array. Subtle behavioral changes sometimes become evident at somewhat lower received levels, and studies have shown that some species of baleen whales, notably bowhead, gray, and humpback whales, at times, show strong avoidance at received levels lower than 160 to 170 dB re 1 μPa (rms). Researchers have studied the responses of humpback whales to seismic surveys during migration, feeding during the summer months, breeding while offshore from Angola, and wintering offshore from Brazil. McCauley et al. (1998, 2000a) studied the responses of humpback whales off western Australia to a full-scale seismic survey with a 16 airgun array (2,678 in 3 ) and to a single airgun (20 in 3 ) with source level of 227 dB re 1 µPa (p-p). In the 1998 study, they documented that avoidance reactions began at 5 to 8 km (2.7 to 4.3 nmi) from the array, and that those reactions kept most pods approximately 3 to 4 km (1.6 to 2.2 nmi) from the operating seismic boat. In the 2000 study, they noted localized displacement during migration of 4 to 5 km (2.2 to 2.7 nmi) by traveling pods and 7 to 12 km (3.8 to 6.5 nmi) by more sensitive resting pods of cow-calf pairs. Avoidance distances with respect to the single airgun were smaller but consistent with the results from the full array in terms of the received sound levels. The mean received level for initial avoidance of an approaching airgun was 140 dB re 1 μPa (rms) for humpback pods containing females, and at the mean closest point of approach distance the received level was 143 dB re 1 μPa (rms). The initial avoidance response generally occurred at distances of 5 to 8 km (2.7 to 4.3 nmi) from the airgun array and 2 km (1.1 nmi) from the single airgun. However, some individual humpback whales, especially males, approached within distances of 100 to 400 m (328 to 1,312 ft), where the maximum received level was 179 dB re 1 μPa (rms). Data collected by observers during several seismic surveys in the Northwest Atlantic showed that sighting rates of humpback whales were significantly greater during non-seismic periods compared with periods when a full array was operating (Moulton and Holst, 2010). In addition, humpback whales were more likely to swim away and less likely to swim towards a vessel during seismic vs. non-seismic periods (Moulton and Holst, 2010). Humpback whales on their summer feeding grounds in southeast Alaska did not exhibit persistent avoidance when exposed to seismic pulses from a 1.64-L (100 in 3 ) airgun (Malme et al., 1985). Some humpbacks seemed “startled” at received levels of 150 to 169 dB re 1 μPa. Malme et al. (1985) concluded that there was no clear evidence of avoidance, despite the possibility of subtle effects, at received levels up to 172 dB re 1 μPa (rms). However, Moulton and Holst (2010) reported that humpback whales monitored during seismic surveys in the Northwest Atlantic had lower sighting rates and were most often seen swimming away from the vessel during seismic periods compared with periods when airguns were silent. Studies have suggested that South Atlantic humpback whales wintering off Brazil may be displaced or even strand upon exposure to seismic surveys (Engel et al., 2004). The evidence for this was circumstantial and subject to alternative explanations (IAGC, 2004). Also, the evidence was not consistent with subsequent results from the same area of Brazil (Parente et al., 2006), or with direct studies of humpbacks exposed to seismic surveys in other areas and seasons. After allowance for data from subsequent years, there was “no observable direct correlation” between strandings and seismic surveys (IWC, 2007: 236). Reactions of migrating and feeding (but not wintering) gray whales to seismic surveys have been studied. Malme et al. (1986, 1988) studied the responses of feeding eastern Pacific gray whales to pulses from a single 100 in 3 airgun off St. Lawrence Island in the northern Bering Sea. They estimated, based on small sample sizes, that 50 percent of feeding gray whales stopped feeding at an average received pressure level of 173 dB re 1 μPa on an (approximate) rms basis, and that 10 percent of feeding whales interrupted feeding at received levels of 163 dB re 1 µPa (rms). Those findings were generally consistent with the results of experiments conducted on larger numbers of gray whales that were migrating along the California coast (Malme et al., 1984; Malme and Miles, 1985), and western Pacific gray whales feeding off Sakhalin Island, Russia (Wursig et al., 1999; Gailey et al., 2007; Johnson et al., 2007; Yazvenko et al., 2007a, b), along with data on gray whales off British Columbia (Bain and Williams, 2006). Various species of Balaenoptera (blue, sei, fin, and minke whales) have occasionally been seen in areas ensonified by airgun pulses (Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006), and calls from blue and fin whales have been localized in areas with airgun operations (e.g., McDonald et al., 1995; Dunn and Hernandez, 2009; Castellote et al., 2010). Sightings by observers on seismic vessels off the United Kingdom from 1997 to 2000 suggest that, during times of good sightability, sighting rates for mysticetes (mainly fin and sei whales) were similar when large arrays of airguns were shooting versus silent (Stone, 2003; Stone and Tasker, 2006). However, these whales tended to exhibit localized avoidance, remaining significantly further (on average) from the airgun array during seismic operations compared with non-seismic periods (Stone and Tasker, 2006). Castellote et al. (2010) reported that singing fin whales in the Mediterranean moved away from an operating airgun array. Ship-based monitoring studies of baleen whales (including blue, fin, sei, minke, and humpback whales) in the Northwest Atlantic found that overall, this group had lower sighting rates during seismic vs. non-seismic periods (Moulton and Holst, 2010). Baleen whales as a group were also seen significantly farther from the vessel during seismic compared with non-seismic periods, and they were more often seen to be swimming away from the operating seismic vessel (Moulton and Holst, 2010). Blue and minke whales were initially sighted significantly farther from the vessel during seismic operations compared to non-seismic periods; the same trend was observed for fin whales (Moulton and Holst, 2010). Minke whales were most often observed to be swimming away from the vessel when seismic operations were underway (Moulton and Holst, 2010). Data on short-term reactions by cetaceans to impulsive noises are not necessarily indicative of long-term or biologically significant effects. It is not known whether impulsive sounds affect reproductive rate or distribution and habitat use in subsequent days or years. However, gray whales have continued to migrate annually along the west coast of North America with substantial increases in the population over recent years, despite intermittent seismic exploration (and much ship traffic) in that area for decades (Appendix A in Malme et al., 1984; Richardson et al., 1995; Allen and Angliss, 2010). The western Pacific gray whale population did not seem affected by a seismic survey in its feeding ground during a previous year (Johnson et al., 2007). Similarly, bowhead whales have continued to travel to the eastern Beaufort Sea each summer, and their numbers have increased notably, despite seismic exploration in their summer and autumn range for many years (Richardson et al., 1987; Allen and Angliss, 2010). The history of coexistence between seismic surveys and baleen whales suggests that brief exposures to sound pulses from any single seismic survey are unlikely to result in prolonged effects. Toothed Whales —Little systematic information is available about reactions of toothed whales to noise pulses. Few studies similar to the more extensive baleen whale/seismic pulse work summarized above have been reported for toothed whales. However, there are recent systematic studies on sperm whales (e.g., Gordon et al., 2006; Madsen et al., 2006; Winsor and Mate, 2006; Jochens et al., 2008; Miller et al., 2009). There is an increasing amount of information about responses of various odontocetes to seismic surveys based on monitoring studies (e.g., Stone, 2003; Smultea et al., 2004; Moulton and Miller, 2005; Bain and Williams, 2006; Holst et al., 2006; Stone and Tasker, 2006; Potter et al., 2007; Hauser et al., 2008; Holst and Smultea, 2008; Weir, 2008; Barkaszi et al., 2009; Richardson et al., 2009; Moulton and Holst, 2010). Seismic operators and PSOs on seismic vessels regularly see dolphins and other small toothed whales near operating airgun arrays, but in general there is a tendency for most delphinids to show some avoidance of operating seismic vessels (e.g., Goold, 1996a,b,c; Calambokidis and Osmek, 1998; Stone, 2003; Moulton and Miller, 2005; Holst et al., 2006; Stone and Tasker, 2006; Weir, 2008; Richardson et al., 2009; Barkaszi et al., 2009; Moulton and Holst, 2010). Some dolphins seem to be attracted to the seismic vessel and floats, and some ride the bow wave of the seismic vessel even when large arrays of airguns are firing (e.g., Moulton and Miller, 2005). Nonetheless, small toothed whales more often tend to head away, or to maintain a somewhat greater distance from the vessel, when a large array of airguns is operating than when it is silent (e.g., Stone and Tasker, 2006; Weir, 2008; Barry et al., 2010; Moulton and Holst, 2010). In most cases, the avoidance radii for delphinids appear to be small, on the order of one km or less, and some individuals show no apparent avoidance. Captive bottlenose dolphins and beluga whales ( Delphinapterus leucas ) exhibited changes in behavior when exposed to strong pulsed sounds similar in duration to those typically used in seismic surveys (Finneran et al., 2000, 2002, 2005). However, the animals tolerated high received levels of sound before exhibiting aversive behaviors. Results of porpoises depend on species. The limited available data suggest that harbor porpoises ( Phocoena phocoena ) show stronger avoidance of seismic operations than do Dall's porpoises ( Phocoenoides dalli ) (Stone, 2003; MacLean and Koski, 2005; Bain and Williams, 2006; Stone and Tasker, 2006). Dall's porpoises seem relatively tolerant of airgun operations (MacLean and Koski, 2005; Bain and Williams, 2006), although they too have been observed to avoid large arrays of operating airguns (Calambokidis and Osmek, 1998; Bain and Williams, 2006). This apparent difference in responsiveness of these two porpoise species is consistent with their relative responsiveness to boat traffic and some other acoustic sources (Richardson et al., 1995; Southall et al., 2007). Most studies of sperm whales exposed to airgun sounds indicate that the sperm whale shows considerable tolerance of airgun pulses (e.g., Stone, 2003; Moulton et al., 2005, 2006a; Stone and Tasker, 2006; Weir, 2008). In most cases the whales do not show strong avoidance, and they continue to call. However, controlled exposure experiments in the Gulf of Mexico indicate that foraging behavior was altered upon exposure to airgun sound (Jochens et al., 2008; Miller et al., 2009; Tyack, 2009). There are almost no specific data on the behavioral reactions of beaked whales to seismic surveys. However, some northern bottlenose whales ( Hyperoodon ampullatus ) remained in the general area and continued to produce high-frequency clicks when exposed to sound pulses from distant seismic surveys (Gosselin and Lawson, 2004; Laurinolli and Cochrane, 2005; Simard et al., 2005). Most beaked whales tend to avoid approaching vessels of other types (e.g., Wursig et al., 1998). They may also dive for an extended period when approached by a vessel (e.g., Kasuya, 1986), although it is uncertain how much longer such dives may be as compared to dives by undisturbed beaked whales, which also are often quite long (Baird et al., 2006; Tyack et al., 2006). Based on a single observation, Aguilar-Soto et al. (2006) suggested that foraging efficiency of Cuvier's beaked whales may be reduced by close approach of vessels. In any event, it is likely that most beaked whales would also show strong avoidance of an approaching seismic vessel, although this has not been documented explicitly. In fact, Moulton and Holst (2010) reported 15 sightings of beaked whales during seismic studies in the Northwest Atlantic; seven of those sightings were made at times when at least one airgun was operating. There was little evidence to indicate that beaked whale behavior was affected by airgun operations; sighting rates and distances were similar during seismic and non-seismic periods (Moulton and Holst, 2010). There are increasing indications that some beaked whales tend to strand when naval exercises involving mid-frequency sonar operation are ongoing nearby (e.g., Simmonds and Lopez-Jurado, 1991; Frantzis, 1998; NOAA and USN, 2001; Jepson et al., 2003; Hildebrand, 2005; Barlow and Gisiner, 2006; see also the “Stranding and Mortality” section in this notice). These strandings are apparently a disturbance response, although auditory or other injuries or other physiological effects may also be involved. Whether beaked whales would ever react similarly to seismic surveys is unknown. Seismic survey sounds are quite different from those of the sonar in operation during the above-cited incidents. Odontocete reactions to large arrays of airguns are variable and, at least for delphinids, seem to be confined to a smaller radius than has been observed for the more responsive of some mysticetes. However, other data suggest that some odontocete species, including harbor porpoises, may be more responsive than might be expected given their poor low-frequency hearing. Reactions at longer distances may be particularly likely when sound propagation conditions are conducive to transmission of the higher frequency components of airgun sound to the animals' location (DeRuiter et al., 2006; Goold and Coates, 2006; Tyack et al., 2006; Potter et al., 2007). Pinnipeds —Pinnipeds are not likely to show a strong avoidance reaction to the airgun array. Visual monitoring from seismic vessels has shown only slight (if any) avoidance of airguns by pinnipeds, and only slight (if any) changes in behavior. In the Beaufort Sea, some ringed seals avoided an area of 100 m to (at most) a few hundred meters around seismic vessels, but many seals remained within 100 to 200 m (328 to 656 ft) of the trackline as the operating airgun array passed by (e.g., Harris et al., 2001; Moulton and Lawson, 2002; Miller et al., 2005.). Ringed seal ( Pusa hispida ) sightings averaged somewhat farther away from the seismic vessel when the airguns were operating than when they were not, but the difference was small (Moulton and Lawson, 2002). Similarly, in Puget Sound, sighting distances for harbor seals ( Phoca vitulina ) and California sea lions ( Zalophus californianus ) tended to be larger when airguns were operating (Calambokidis and Osmek, 1998). Previous telemetry work suggests that avoidance and other behavioral reactions may be stronger than evident to date from visual studies (Thompson et al., 1998). During seismic exploration off Nova Scotia, gray seals ( Halichoerus grypus ) exposed to noise from airguns and linear explosive charges did not react strongly (J. Parsons in Greene et al., 1985). Pinnipeds in both water and air, sometimes tolerate strong noise pulses from non-explosive and explosive scaring devices, especially if attracted to the area for feeding and reproduction (Mate and Harvey, 1987; Reeves et al., 1996). Thus pinnipeds are expected to be rather tolerant of, or habituate to, repeated underwater sounds from distant seismic sources, at least when the animals are strongly attracted to the area. Hearing Impairment and Other Physical Effects Exposure to high intensity sound for a sufficient duration may result in auditory effects such as a noise-induced threshold shift—an increase in the auditory threshold after exposure to noise (Finneran, Carder, Schlundt, and Ridgway, 2005). Factors that influence the amount of threshold shift include the amplitude, duration, frequency content, temporal pattern, and energy distribution of noise exposure. The magnitude of hearing threshold shift normally decreases over time following cessation of the noise exposure. The amount of threshold shift just after exposure is called the initial threshold shift. If the threshold shift eventually returns to zero (i.e., the threshold returns to the pre-exposure value), it is called temporary threshold shift (TTS) (Southall et al., 2007). Researchers have studied TTS in certain captive odontocetes and pinnipeds exposed to strong sounds (reviewed in Southall et al., 2007). However, there has been no specific documentation of TTS let alone permanent hearing damage, i.e., permanent threshold shift (PTS), in free-ranging marine mammals exposed to sequences of airgun pulses during realistic field conditions. Temporary Threshold Shift —TTS is the mildest form of hearing impairment that can occur during exposure to a strong sound (Kryter, 1985). While experiencing TTS, the hearing threshold rises and a sound must be stronger in order to be heard. At least in terrestrial mammals, TTS can last from minutes or hours to (in cases of strong TTS) days. For sound exposures at or somewhat above the TTS threshold, hearing sensitivity in both terrestrial and marine mammals recovers rapidly after exposure to the noise ends. Few data on sound levels and durations necessary to elicit mild TTS have been obtained for marine mammals, and none of the published data concern TTS elicited by exposure to multiple pulses of sound. Available data on TTS in marine mammals are summarized in Southall et al. (2007). Table 2 (above) presents the estimated distances from the Palmer' s airguns at which the received energy level (per pulse, flat-weighted) would be expected to be greater than or equal to 180 and 190 dB re 1 µPa (rms). To avoid the potential for injury, NMFS (1995, 2000) concluded that cetaceans and pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding 180 and 190 dB re 1 μPa (rms). NMFS believes that to avoid the potential for Level A harassment, cetaceans and pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding 180 and 190 dB re 1 μPa (rms), respectively. The established 180 and 190 dB (rms) criteria are not considered to be the levels above which TTS might occur. Rather, they are the received levels above which, in the view of a panel of bioacoustics specialists convened by NMFS before TTS measurements for marine mammals started to become available, one could not be certain that there would be no injurious effects, auditory or otherwise, to marine mammals. NMFS also assumes that cetaceans and pinnipeds exposed to levels exceeding 160 dB re 1 μPa (rms) may experience Level B harassment. For toothed whales, researchers have derived TTS information for odontocetes from studies on the bottlenose dolphin and beluga. The experiments show that exposure to a single impulse at a received level of 207 kPa (or 30 psi, p-p), which is equivalent to 228 dB re 1 Pa (p-p), resulted in a 7 and 6 dB TTS in the beluga whale at 0.4 and 30 kHz, respectively. Thresholds returned to within 2 dB of the pre-exposure level within 4 minutes of the exposure (Finneran et al., 2002). For the one harbor porpoise tested, the received level of airgun sound that elicited onset of TTS was lower (Lucke et al., 2009). If these results from a single animal are representative, it is inappropriate to assume that onset of TTS occurs at similar received levels in all odontocetes ( cf. Southall et al., 2007). Some cetaceans apparently can incur TTS at considerably lower sound exposures than are necessary to elicit TTS in the beluga or bottlenose dolphin. For baleen whales, there are no data, direct or indirect, on levels or properties of sound that are required to induce TTS. The frequencies to which baleen whales are most sensitive are assumed to be lower than those to which odontocetes are most sensitive, and natural background noise levels at those low frequencies tend to be higher. As a result, auditory thresholds of baleen whales within their frequency band of best hearing are believed to be higher (less sensitive) than are those of odontocetes at their best frequencies (Clark and Ellison, 2004). From this, it is suspected that received levels causing TTS onset may also be higher in baleen whales than those of odontocetes (Southall et al., 2007). In pinnipeds, researchers have not measured TTS thresholds associated with exposure to brief pulses (single or multiple) of underwater sound. Initial evidence from more prolonged (non-pulse) exposures suggested that some pinnipeds (harbor seals in particular) incur TTS at somewhat lower received levels than do small odontocetes exposed for similar durations (Kastak et al., 1999, 2005; Ketten et al., 2001). The TTS threshold for pulsed sounds has been indirectly estimated as being an SEL of approximately 171 dB re 1 µPa 2 ·s (Southall et al., 2007) which would be equivalent to a single pulse with a received level of approximately 181 to 186 dB re 1 µPa (rms), or a series of pulses for which the highest rms values are a few dB lower. Corresponding values for California sea lions and northern elephant seals ( Mirounga angustirostris ) are likely to be higher (Kastak et al., 2005). Permanent Threshold Shift —When PTS occurs, there is physical damage to the sound receptors in the ear. In severe cases, there can be total or partial deafness, whereas in other cases, the animal has an impaired ability to hear sounds in specific frequency ranges (Kryter, 1985). There is no specific evidence that exposure to pulses of airgun sound can cause PTS in any marine mammal, even with large arrays of airguns. However, given the possibility that mammals close to an airgun array might incur at least mild TTS, there has been further speculation about the possibility that some individuals occurring very close to airguns might incur PTS (e.g., Richardson et al., 1995, p. 372 ff; Gedamke et al., 2008). Single or occasional occurrences of mild TTS are not indicative of permanent auditory damage, but repeated or (in some cases) single exposures to a level well above that causing TTS onset might elicit PTS. Relationships between TTS and PTS thresholds have not been studied in marine mammals but are assumed to be similar to those in humans and other terrestrial mammals (Southall et al., 2007). PTS might occur at a received sound level at least several dBs above that inducing mild TTS if the animal were exposed to strong sound pulses with rapid rise times. Based on data from terrestrial mammals, a precautionary assumption is that the PTS threshold for impulse sounds (such as airgun pulses as received close to the source) is at least 6 dB higher than the TTS threshold on a peak-pressure basis, and probably greater than 6 dB (Southall et al., 2007). Given the higher level of sound necessary to cause PTS as compared with TTS, it is considerably less likely that PTS would occur. Baleen whales generally avoid the immediate area around operating seismic vessels, as do some other marine mammals. Non-auditory Physiological Effects —Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to strong underwater sound include stress, neurological effects, bubble formation, resonance, and other types of organ or tissue damage (Cox et al., 2006; Southall et al., 2007). Studies examining such effects are limited. However, resonance effects (Gentry, 2002) and direct noise-induced bubble formations (Crum et al., 2005) are implausible in the case of exposure to an impulsive broadband source like an airgun array. If seismic surveys disrupt diving patterns of deep-diving species, this might perhaps result in bubble formation and a form of the bends, as speculated to occur in beaked whales exposed to sonar. However, there is no specific evidence of this upon exposure to airgun pulses. In general, very little is known about the potential for seismic survey sounds (or other types of strong underwater sounds) to cause non-auditory physical effects in marine mammals. Such effects, if they occur at all, would presumably be limited to short distances and to activities that extend over a prolonged period. The available data do not allow identification of a specific exposure level above which non-auditory effects can be expected (Southall et al., 2007), or any meaningful quantitative predictions of the numbers (if any) of marine mammals that might be affected in those ways. Marine mammals that show behavioral avoidance of seismic vessels, including most baleen whales, some odontocetes, and some pinnipeds, are especially unlikely to incur non-auditory physical effects. Stranding and Mortality —When a living or dead marine mammal swims or floats onto shore and becomes “beached” or incapable of returning to sea, the event is termed a “stranding” (Geraci et al., 1999; Perrin and Geraci, 2002; Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a stranding under the MMPA is that “(A) a marine mammal is dead and is (i) on a beach or shore of the United States; or (ii) in waters under the jurisdiction of the United States (including any navigable waters); or (B) a marine mammal is alive and is (i) on a beach or shore of the United States and is unable to return to the water; (ii) on a beach or shore of the United States and, although able to return to the water is in need of apparent medical attention; or (iii) in the waters under the jurisdiction of the United States (including any navigable waters), but is unable to return to its natural habitat under its own power or without assistance.” Marine mammals are known to strand for a variety of reasons, such as infectious agents, biotoxicosis, starvation, fishery interaction, ship strike, unusual oceanographic or weather events, sound exposure, or combinations of these stressors sustained concurrently or in series. However, the cause or causes of most strandings are unknown (Geraci et al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous studies suggest that the physiology, behavior, habitat relationships, age, or condition of cetaceans may cause them to strand or might pre-dispose them to strand when exposed to another phenomenon. These suggestions are consistent with the conclusions of numerous other studies that have demonstrated that combinations of dissimilar stressors commonly combine to kill an animal or dramatically reduce its fitness, even though one exposure without the other does not produce the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a, 2005b; Romero, 2004; Sih et al., 2004). Strandings Associated with Military Active Sonar —Several sources have published lists of mass stranding events of cetaceans in an attempt to identify relationships between those stranding events and military active sonar (Hildebrand, 2004; IWC, 2005; Taylor et al., 2004). For example, based on a review of stranding records between 1960 and 1995, the International Whaling Commission (2005) identified ten mass stranding events and concluded that, out of eight stranding events reported from the mid-1980s to the summer of 2003, seven had been coincident with the use of mid-frequency active sonar and most involved beaked whales. Over the past 12 years, there have been five stranding events coincident with military mid-frequency active sonar use in which exposure to sonar is believed to have been a contributing factor to strandings: Greece (1996); the Bahamas (2000); Madeira (2000); Canary Islands (2002); and Spain (2006). Refer to Cox et al. (2006) for a summary of common features shared by the strandings events in Greece (1996), Bahamas (2000), Madeira (2000), and Canary Islands (2002); and Fernandez et al., (2005) for an additional summary of the Canary Islands 2002 stranding event. Potential for Stranding from Seismic Surveys —Marine mammals close to underwater detonations of high explosives can be killed or severely injured, and the auditory organs are especially susceptible to injury (Ketten et al., 1993; Ketten, 1995). However, explosives are no longer used in marine waters for commercial seismic surveys or (with rare exceptions) for seismic research. These methods have been replaced entirely by airguns or related non-explosive pulse generators. Airgun pulses are less energetic and have slower rise times, and there is no specific evidence that they can cause serious injury, death, or stranding even in the case of large airgun arrays. However, the association of strandings of beaked whales with naval exercises involving mid-frequency active sonar (non-pulse sound) and, in one case, the co-occurrence of an L-DEO seismic survey (Malakoff, 2002; Cox et al., 2006), has raised the possibility that beaked whales exposed to strong “pulsed” sounds could also be susceptible to injury and/or behavioral reactions that can lead to stranding (e.g., Hildebrand, 2005; Southall et al., 2007). Specific sound-related processes that lead to strandings and mortality are not well documented, but may include: (1) Swimming in avoidance of a sound into shallow water; (2) A change in behavior (such as a change in diving behavior) that might contribute to tissue damage, gas bubble formation, hypoxia, cardiac arrhythmia, hypertensive hemorrhage or other forms of trauma; (3) A physiological change such as a vestibular response leading to a behavioral change or stress-induced hemorrhagic diathesis, leading in turn to tissue damage; and (4) Tissue damage directly from sound exposure, such as through acoustically-mediated bubble formation and growth or acoustic resonance of tissues. Some of these mechanisms are unlikely to apply in the case of impulse sounds. However, there are indications that gas-bubble disease (analogous to “the bends”), induced in supersaturated tissue by a behavioral response to acoustic exposure, could be a pathologic mechanism for the strandings and mortality of some deep-diving cetaceans exposed to sonar. The evidence for this remains circumstantial and associated with exposure to naval mid-frequency sonar, not seismic surveys (Cox et al., 2006; Southall et al., 2007). Seismic pulses and mid-frequency sonar signals are quite different, and some mechanisms by which sonar sounds have been hypothesized to affect beaked whales are unlikely to apply to airgun pulses. Sounds produced by airgun arrays are broadband impulses with most of the energy below one kHz. Typical military mid-frequency sonar emits non-impulse sounds at frequencies of 2 to 10 kHz, generally with a relatively narrow bandwidth at any one time. A further difference between seismic surveys and naval exercises is that naval exercises can involve sound sources on more than one vessel. Thus, it is not appropriate to expect that the same effects to marine mammals would result from military sonar and seismic surveys. However, evidence that sonar signals can, in special circumstances, lead (at least indirectly) to physical damage and mortality (e.g., Balcomb and Claridge, 2001; NOAA and USN, 2001; Jepson et al., 2003; Fernández et al., 2004, 2005; Hildebrand 2005; Cox et al., 2006) suggests that caution is warranted when dealing with exposure of marine mammals to any high-intensity sound. There is no conclusive evidence of cetacean strandings or deaths at sea as a result of exposure to seismic surveys, but a few cases of strandings in the general area where a seismic survey was ongoing have led to speculation concerning a possible link between seismic surveys and strandings. Suggestions that there was a link between seismic surveys and strandings of humpback whales in Brazil (Engel et al., 2004) were not well founded (IAGC, 2004; IWC, 2007). In September 2002, there was a stranding of two Cuvier's beaked whales in the Gulf of California, Mexico, when the L-DEO vessel R/V Maurice Ewing was operating a 20 airgun (8,490 in 3 ) array in the general area. The link between the stranding and the seismic surveys was inconclusive and not based on any physical evidence (Hogarth, 2002; Yoder, 2002). Nonetheless, the Gulf of California incident plus the beaked whale strandings near naval exercises involving use of mid-frequency sonar suggests a need for caution in conducting seismic surveys in areas occupied by beaked whales until more is known about effects of seismic surveys on those species (Hildebrand, 2005). No injuries of beaked whales are anticipated during the proposed study because of: (1) The high likelihood that any beaked whales nearby would avoid the approaching vessel before being exposed to high sound levels, and (2) Differences between the sound sources to be used in the proposed study and operated by NSF and ASC and those involved in the naval exercises associated with strandings. Potential Effects of Other Acoustic Devices and Sources Multi-Beam Echosounder NSF and ASC would operate the Simrad EM120 multi-beam echosounder from the source vessel during the planned study. Sounds from the multi-beam echosounder are very short pulses, occurring for approximately 15 ms, depending on water depth. Most of the energy in the sound pulses emitted by the multi-beam echosounder is at frequencies near 12 kHz, and the maximum source level is 242 dB re 1 μPa (rms). The beam is narrow (1 to 2°) in fore-aft extent and wide (150°) in the cross-track extent. Each ping consists of nine (in water greater than 1,000 m deep) consecutive successive fan-shaped transmissions (segments) at different cross-track angles. Any given mammal at depth near the trackline would be in the main beam for only one or two of the nine segments. Also, marine mammals that encounter the Simrad EM120 are unlikely to be subjected to repeated pulses because of the narrow fore-aft width of the beam and would receive only limited amounts of pulse energy because of the short pulses. Animals close to the ship (where the beam is narrowest) are especially unlikely to be ensonified for more than one 15 ms pulse (or two pulses if in the overlap area). Similarly, Kremser et al. (2005) noted that the probability of a cetacean swimming through the area of exposure when a multi-beam echosounder emits a pulse is small. The animal would have to pass the transducer at close range and be swimming at speeds similar to the vessel in order to receive the multiple pulses that might result in sufficient exposure to cause TTS. Navy sonars that have been linked to avoidance reactions and stranding of cetaceans: (1) Generally have longer pulse duration than the Simrad EM120; and (2) are often directed close to horizontally, as well as omnidirectional, versus more downward and narrowly for the multi-beam echosounder. The area of possible influence of the multi-beam echosounder is much smaller—a narrow band below the source vessel. Also, the duration of exposure for a given marine mammal can be much longer for naval sonar. During NSF and ASC's operations, the individual pulses would be very short, and a given mammal would not receive many of the downward-directed pulses as the vessel passes by. Possible effects of a multi-beam echosounder on marine mammals are described below. In 2013, an International Scientific Review Panel investigated a 2008 mass stranding of approximately 100 melon-headed whales in a Madagascar lagoon system (Southall et al., 2013) associated with the use of a high-frequency mapping system. The report indicated that the use of a 12 kHz multi-beam echosounder was the most plausible and likely initial behavioral trigger of the mass stranding event. This was the first time that a relatively high-frequency mapping sonar system has been associated with a stranding event. However, the report also notes that there were several site- and situation-specific secondary factors that may have contributed to the avoidance responses that lead to the eventual entrapment and mortality of the whales within the Loza Lagoon system (e.g., the survey vessel transiting in a north-south direction on the shelf break parallel to the shore may have trapped the animals between the sound source and the shore driving them towards the Loza Lagoon). The report concluded that for odontocete cetaceans that hear well in the 10 to 50 kHz range, where ambient noise is typically quite low, high-power active sonars operating in this range may be more easily audible and have potential effects over larger areas than low-frequency systems that have more typically been considered in terms of anthropogenic noise impacts (Southall et al., 2013). However, the risk may be very low given the extensive use of these systems worldwide on a daily basis and the lack of direct evidence of such responses previously (Southall et al., 2013). Masking —Marine mammal communications would not be masked appreciably by the multi-beam echosounder signals, given the low duty cycle of the echosounder and the brief period when an individual mammal is likely to be within its beam. Furthermore, in the case of baleen whales, the multi-beam echosounder signals (12 kHz) generally do not overlap with the predominant frequencies in the calls (16 Hz to less than 12 kHz), which would avoid any significant masking (Richardson et al., 1995). Behavioral Responses —Behavioral reactions of free-ranging marine mammals to sonars, echosounders, and other sound sources appear to vary by species and circumstance. Observed reactions have included silencing and dispersal by sperm whales (Watkins et al., 1985), increased vocalizations and no dispersal by pilot whales (Rendell and Gordon, 1999), and the previously-mentioned beachings by beaked whales. During exposure to a 21 to 25 kHz “whale-finding” sonar with a source level of 215 dB re 1 µPa, gray whales reacted by orienting slightly away from the source and being deflected from their course by approximately 200 m (656.2 ft) (Frankel, 2005). When a 38 kHz echosounder and a 150 kHz acoustic Doppler current profiler were transmitting during studies in the Eastern Tropical Pacific, baleen whales showed no significant responses, while spotted and spinner dolphins were detected slightly more often and beaked whales less often during visual surveys (Gerrodette and Pettis, 2005). Captive bottlenose dolphins and a beluga whale exhibited changes in behavior when exposed to 1 second tonal signals at frequencies similar to those that would be emitted by the multi-beam echosounder used by NSF and ASC, and to shorter broadband pulsed signals. Behavioral changes typically involved what appeared to be deliberate attempts to avoid the sound exposure (Schlundt et al., 2000; Finneran et al., 2002; Finneran and Schlundt, 2004). The relevance of those data to free-ranging odontocetes is uncertain, and in any case, the test sounds were quite different in duration as compared with those from a multi-beam echosounder. Hearing Impairment and Other Physical Effects —Given several stranding events that have been associated with the operation of naval sonar in specific circumstances, there is concern that mid-frequency sonar sounds can cause serious impacts to marine mammals (see above). However, the multi-beam echosounder proposed for use by NSF and ASC is quite different than sonar used for Navy operations. Pulse duration of the multi-beam echosounder is very short relative to the naval sonar. Also, at any given location, an individual marine mammal would be in the beam of the multi-beam echosounder for much less time, given the generally downward orientation of the beam and its narrow fore-aft beamwidth; Navy sonar often uses near-horizontally-directed sound. Those factors would all reduce the sound energy received from the multi-beam echosounder rather drastically relative to that from naval sonar. NMFS believes that the brief exposure of marine mammals to one pulse, or small numbers of signals, from the multi-beam echosounder in this particular case is not likely to result in the harassment of marine mammals. Single-Beam Echosounder NSF and ASC would operate the Knudsen 3260 and Bathy 2000 single-beam echosounders from the source vessel during the planned study. Sounds from the single-beam echosounder are very short pulses, depending on water depth. Most of the energy in the sound pulses emitted by the singlebeam echosounder is at frequencies near 12 kHz for bottom-tracking purposes or at 3.5 kHz in the sub-bottom profiling mode. The sonar emits energy in a 30° beam from the bottom of the ship. Marine mammals that encounter the Knudsen 3260 or Bathy 2000 are unlikely to be subjected to repeated pulses because of the relatively narrow fore-aft width of the beam and would receive only limited amounts of pulse energy because of the short pulses. Animals close to the ship (where the beam is narrowest) are especially unlikely to be ensonified for more than one pulse (or two pulses if in the overlap area). Similarly, Kremser et al. (2005) noted that the probability of a cetacean swimming through the area of exposure when a single-beam echosounder emits a pulse is small. The animal would have to pass the transducer at close range and be swimming at speeds similar to the vessel in order to receive the multiple pulses that might result in sufficient exposure to cause TTS. Navy sonars that have been linked to avoidance reactions and stranding of cetaceans: (1) Generally have longer pulse duration than the Knudsen 3260 or Bathy 2000; and (2) are often directed close to horizontally versus more downward for the echosounder. The area of possible influence of the single-beam echosounder is much smaller—a narrow band below the source vessel. Also, the duration of exposure for a given marine mammal can be much longer for naval sonar. During NSF and ASC's operations, the individual pulses would be very short, and a given mammal would not receive many of the downward-directed pulses as the vessel passes by. Possible effects of a single-beam echosounder on marine mammals are described below. Masking —Marine mammal communications would not be masked appreciably by the single-beam echosounder signals given the low duty cycle of the echosounder and the brief period when an individual mammal is likely to be within its beam. Furthermore, in the case of baleen whales, the single-beam echosounder signals (12 or 3.5 kHz) do not overlap with the predominant frequencies in the calls (16 Hz to less than 12 kHz), which would avoid any significant masking (Richardson et al., 1995). Behavioral Responses —Behavioral reactions of free-ranging marine mammals to sonars, echosounders, and other sound sources appear to vary by species and circumstance. Observed reactions have included silencing and dispersal by sperm whales (Watkins et al., 1985), increased vocalizations and no dispersal by pilot whales (Rendell and Gordon, 1999), and the previously-mentioned beachings by beaked whales. During exposure to a 21 to 25 kHz “whale-finding” sonar with a source level of 215 dB re 1 μPa, gray whales reacted by orienting slightly away from the source and being deflected from their course by approximately 200 m (656.2 ft) (Frankel, 2005). When a 38 kHz echosounder and a 150 kHz ADCP were transmitting during studies in the Eastern Tropical Pacific, baleen whales showed no significant responses, while spotted and spinner dolphins were detected slightly more often and beaked whales less often during visual surveys (Gerrodette and Pettis, 2005). Captive bottlenose dolphins and a beluga whale exhibited changes in behavior when exposed to 1 second tonal signals at frequencies similar to those that would be emitted by the single-beam echosounder used by NSF and ASC, and to shorter broadband pulsed signals. Behavioral changes typically involved what appeared to be deliberate attempts to avoid the sound exposure (Schlundt et al., 2000; Finneran et al., 2002; Finneran and Schlundt, 2004). The relevance of those data to free-ranging odontocetes is uncertain, and in any case, the test sounds were quite different in duration as compared with those from a single-beam echosounder. Hearing Impairment and Other Physical Effects —Given recent stranding events that have been associated with the operation of naval sonar, there is concern that mid-frequency sonar sounds can cause serious impacts to marine mammals (see above). However, the single-beam echosounder proposed for use by NSF and ASC is quite different than sonar used for Navy operations. Pulse duration of the single-beam echosounder is very short relative to the naval sonar. Also, at any given location, an individual marine mammal would be in the beam of the single-beam echosounder for much less time given the generally downward orientation of the beam and its narrow fore-aft beamwidth; Navy sonar often uses near-horizontally-directed sound. Those factors would all reduce the sound energy received from the single-beam echosounder rather drastically relative to that from naval sonar. NMFS believes that the brief exposure of marine mammals to one pulse, or small numbers of signals, from the single-beam echosounder in this particular case is not likely to result in the harassment of marine mammals. Acoustic Doppler Current Profilers NSF and ASC would operate the ADCP Teledyne RDI VM-150 and ADCP Ocean Surveyor OS-38 from the source vessel during the planned study. Most of the energy in the sound pulses emitted by the ADCPs operate at frequencies near 150 kHz, and the maximum source level is 223.6 dB re 1 μPa (rms). Sound energy from the ADCP is emitted as a 30° conically-shaped beam. Marine mammals that encounter the ADCPs are unlikely to be subjected to repeated pulses because of the relatively narrow fore-aft width of the beam and would receive only limited amounts of pulse energy because of the short pulses. Animals close to the ship (where the beam is narrowest) are especially unlikely to be ensonified for more than one 15 ms pulse (or two pulses if in the overlap area). Similarly, Kremser et al. (2005) noted that the probability of a cetacean swimming through the area of exposure when the ADCPs emit a pulse is small. The animal would have to pass the transducer at close range and be swimming at speeds similar to the vessel in order to receive the multiple pulses that might result in sufficient exposure to cause TTS. Navy sonars that have been linked to avoidance reactions and stranding of cetaceans: (1) Generally have longer pulse duration than the ADCPs; and (2) are often directed close to horizontally versus more downward for the ADCPs. The area of possible influence of the ADCPs is much smaller—a narrow band below the source vessel. Also, the duration of exposure for a given marine mammal can be much longer for naval sonar. During NSF and ASC's operations, the individual pulses would be very short, and a given mammal would not receive many of the downward-directed pulses as the vessel passes by. Possible effects of the ADCPs on marine mammals are described below. Masking —Marine mammal communications would not be masked appreciably by the ADCP signals, given the low duty cycle of the ADCPs and the brief period when an individual mammal is likely to be within its beam. Furthermore, in the case of baleen whales, the ADCP signals (150 kHz) do not overlap with the predominant frequencies in the calls (16 Hz to less than 12 kHz), which would avoid any significant masking (Richardson et al., 1995). Behavioral Responses —Behavioral reactions of free-ranging marine mammals to sonars, echosounders, and other sound sources appear to vary by species and circumstance. Observed reactions have included silencing and dispersal by sperm whales (Watkins et al., 1985), increased vocalizations and no dispersal by pilot whales (Rendell and Gordon, 1999), and the previously-mentioned beachings by beaked whales. During exposure to a 21 to 25 kHz “whale-finding” sonar with a source level of 215 dB re 1 μPa, gray whales reacted by orienting slightly away from the source and being deflected from their course by approximately 200 m (656.2 ft) (Frankel, 2005). When a 38 kHz echosounder and a 150 kHz ADCP were transmitting during studies in the Eastern Tropical Pacific, baleen whales showed no significant responses, while spotted and spinner dolphins were detected slightly more often and beaked whales less often during visual surveys (Gerrodette and Pettis, 2005). Captive bottlenose dolphins and a beluga whale exhibited changes in behavior when exposed to 1 second tonal signals at frequencies similar to those that would be emitted by the ADCPs used by NSF and ASC, and to shorter broadband pulsed signals. Behavioral changes typically involved what appeared to be deliberate attempts to avoid the sound exposure (Schlundt et al., 2000; Finneran et al., 2002; Finneran and Schlundt, 2004). The relevance of those data to free-ranging odontocetes is uncertain, and in any case, the test sounds were quite different in duration as compared with those from an ADCP. Hearing Impairment and Other Physical Effects —Given recent stranding events that have been associated with the operation of naval sonar, there is concern that mid-frequency sonar sounds can cause serious impacts to marine mammals (see above). However, the ADCPs proposed for use by NSF and ASC is quite different than sonar used for Navy operations. Pulse duration of the ADCPs is very short relative to the naval sonar. Also, at any given location, an individual marine mammal would be in the beam of the ADCPs for much less time given the generally downward orientation of the beam and its narrow fore-aft beamwidth; Navy sonar often uses near-horizontally-directed sound. Those factors would all reduce the sound energy received from the ADCPs rather drastically relative to that from naval sonar. NMFS believes that the brief exposure of marine mammals to one pulse, or small numbers of signals, from the ADCPs in this particular case is not likely to result in the harassment of marine mammals. Dredging Activities During dredging, the noise created by the mechanical action of the devices on the seafloor is expected to be perceived by nearby fish and other marine organisms and deter them from swimming toward the source. Dredging activities would be highly localized and short-term in duration and would not be expected to significantly interfere with marine mammal behavior. The potential direct effects include temporary localized disturbance or displacement from associated sounds and/or physical movement/actions of the operations. Additionally, the potential indirect effects may consist of very localized and transitory/short-term disturbance of bottom habitat and associated prey in shallow-water areas as a result of dredging (NSF/USGS PEIS, 2011). NMFS believes that the brief exposure of marine mammals to noise created from the mechanical action of the devices for dredging is not likely to result in the harassment of marine mammals. The dredge would be attached to the main winch cable using a chain bridle. To dredge a rocky bottom, the dredge would be lowered slowly to [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2014-18396. Public record. Not legal advice.