Small Takes of Marine Mammals Incidental to Specified Activities; Low-Energy Marine Seismic Survey in the Northeast Pacific Ocean, September 2007

AGENCY:

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

ACTION:

Notice; proposed incidental take authorization; request for comments.

SUMMARY:

NMFS has received an application from Scripps Institute of Oceanography (SIO) for an Incidental Harassment Authorization (IHA) to take marine mammals incidental to conducting a low-energy marine seismic survey in the northeastern Pacific Ocean during September, 2007. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an IHA to SIO to incidentally take, by Level B harassment only, several species of marine mammals during the aforementioned activity.

DATES:

Comments and information must be received no later than August 31, 2007.

ADDRESSES:

Comments on the application should be addressed to P. Michael Payne, Chief, Permits, Conservation and Education Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910-3225. The mailbox address for providing email comments is PR1.0648XB70@noaa.gov. NMFS is not responsible for e-mail comments sent to addresses other than the one provided here. Comments sent via e-mail, including all attachments, must not exceed a 10-megabyte file size.

A copy of the application containing a list of the references used in this document may be obtained by writing to the address specified above, telephoning the contact listed below (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 be viewed, by appointment, during regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT:

Candace Nachman or Jolie Harrison, Office of Protected Resources, NMFS, (301) 713-2289.

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 to allow, upon request, the incidental, but not intentional, taking of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and 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.

Authorization shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring, and reporting of such 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 U.S. can apply for an authorization to incidentally take small numbers of marine mammals by harassment. Except with respect to certain activities not pertinent here, the MMPA defines “harassment” as:

any act of pursuit, torment, or annoyance which (i) has the potential to injure a marine mammal or marine mammal stock in the wild [Level A harassment]; or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering [Level B harassment].

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

Summary of Request

On May 4, 2007, NMFS received an application from SIO for the taking, by Level B harassment only, of 32 species of marine mammals incidental to conducting, with research funding from the National Science Foundation (NSF), an ocean-bottom seismograph (OBS) deployment and a magnetic, bathymetric, and seismic survey program off the Oregon coast in the northeastern Pacific Ocean during September, 2007. The purpose of the research program is to record microearthquakes in the forearc to determine whether seismicity on the plate boundary is characteristic of a locked or a freely slipping fault plane. OBSs will be deployed and left in place for a year, and a seismic survey will be used to locate the instruments accurately and precisely on the seafloor and to characterize the shallow sediment structure around the instrument. Seismometers measure movement in the Earth's crust. About 90 percent of all natural earthquakes occur under water, where great pressure and cold make measurements difficult. The OBS was developed for this task. Scientists use seismometer data to calculate the energy released by earthquakes. Also included in the research is the use of a magnetometer and sub-bottom profiler.

Description of the Activity

The seismic surveys will involve one vessel, the R/V Wecoma (Wecoma), which is scheduled to depart from Newport, Oregon on September 5, 2007 and return on September 11, 2007. The exact dates of the activities may vary by a few days because of weather conditions, repositioning, OBS and streamer operations and adjustments, GI-gun deployment, or the need to repeat some lines if data quality is substandard. The seismic surveys will take place off the Oregon coast in the northeastern Pacific Ocean. The overall area within which the seismic surveys will occur is located between approximately 44° and 45° N. and 124.5° and 126° W. (Figure 1 in the application). The surveys will occur approximately 25-110 km (15.5-68.4 mi) offshore from Oregon in water depths between approximately 110 and 3,050 m (361 and 10,007 ft), entirely within the Exclusive Economic Zone of the U.S.

The Wecoma will deploy a single low-energy Generator-Injector (GI) airgun as an energy source (with a discharge volume of 45 in³), 16 OBSs that will remain in place for a year, and a 300 m-long (984 ft-long), 16-channel, towed hydrophone streamer. The program will consist of approximately 21 km (13 mi) of surveys over each of the 16 OBSs. The GI gun will be operated on a small grid for approximately 2 hours at each of 16 OBS sites over an approximately 7-day period during September, 2007. There will be additional seismic operations associated with equipment testing, start-up, and repeat coverage of any areas where initial data quality is sub-standard. The OBSs are acoustically passive and do not emit any sounds into the ocean.

In addition to the operations of the GI gun, a 3.5-kHz sub-bottom profiler, a Knudsen 320BR sub-bottom profiler, and a magnetometer may be run on the transit between OBS locations.

Vessel Specifications

The Wecoma has a length of 56.4 m (185 ft), a beam of 10.1 m (33.1 ft), and a maximum draft of 5.6 m (18.4 ft). The ship is powered by a single 3,000-hp EMD diesel engine driving a single, controllable-pitch propeller through a clutch and reduction gear, and an electric, 350-hp azimuthing bow thruster. An operation speed of 11.1 km/h (6 knots) is used during seismic acquisition. When not towing seismic survey gear, the Wecoma cruises at 22.2 km/h (12 knots) and has a maximum speed of 26 km/h (14 knots). It has a normal operating range of approximately 13,300 km (8,264 mi).

Acoustic Source Specifications

Seismic Airguns

The vessel Wecoma will tow a GI gun and an 300 m-long (984-ft) streamer containing hydrophones along predetermined lines. Seismic pulses will be emitted at intervals of 10 s, which corresponds to a shot interval of approximately 31 m (102 ft) at a speed of 6 knots (11.1 km/h). The generator chamber of the GI gun, the one responsible for introducing the sound pulse into the ocean, is 45 in³. The larger (105 in³) injector chamber injects air into the previously-generated bubble to maintain its shape and does not introduce more sound into the water. The 45 in³ GI gun will be towed 21 m (69 ft) behind the Wecoma, at a depth of 4 m (13 ft). The dominant frequency components are 0-188 Hz.

The sound pressure field of the GI gun variation at a tow depth of 2.5 m (8.2 ft) has been modeled by the Lamont-Doherty Earth Observatory (L-DEO) in relation to distance and direction from the airgun. This source, which is directed downward, was found to have an output (0-peak) of 225.3 dB re 1 μPa m.

The rms (root mean square) received levels that are used as impact criteria for marine mammals are not directly comparable to the peak or peak to peak values normally used to characterize source levels of airgun arrays. The measurement units used to describe airgun sources, peak or peak-to-peak decibels, are always higher than the rms decibels referred to in biological literature. A measured received level of 160 dB rms in the far field would typically correspond to a peak measurement of approximately 170 to 172 dB, and to a peak-to-peak measurement of approximately 176 to 178 dB, as measured for the same pulse received at the same location (Greene 1997; McCauley et al., 1998, 2000). The precise difference between rms and peak or peak-to-peak values depends on the frequency content and duration of the pulse, among other factors. However, the rms level is always lower than the peak or peak-to-peak level for an airgun-type source.

Sub-bottom Profiler

The Wecoma will utilize the Knudsen Engineering Model 320BR sub-bottom profiler, which is a dual-frequency transceiver designed to operate at 3.5 and/or 12 kHz. It is used to provide data about the sedimentary features that occur below the sea floor. The energy from the sub-bottom profiler is directed downward (in an 80-degree cone) via a 12-kHz transducer (EDO 323B) or a 3.5-kHz array of 16 ORE 137D transducers in a 4 x 4 arrangement. The maximum power output of the 320BR is 10 kilowatts for the 3.5-kHz section and 2 kilowatts for the 12-kHz section.

The pulse length for the 3.5 kHz section of the 320BR is 0.8-24 ms, controlled by the system operator in regards to water depth and reflectivity of the bottom sediments, and will usually be 12 or 24 ms in this survey. The system produces one sound pulse and then waits for its return before transmitting again. Thus, the pulse interval is directly dependent upon water depth, and in this survey is 4.5-8 sec. Using the Sonar Equations and assuming 100 percent efficiency in the system (impractical in real world applications), the source level for the 320BR is calculated to be 211 dB re 1 mPa-m. In practice, the system is rarely operated above 80 percent power level.

Safety Radii

NMFS has determined that for acoustic effects, using acoustic thresholds in combination with corresponding safety radii is the most effective way to consistently apply measures to avoid or minimize the impacts of an action, and to quantitatively estimate the effects of an action. Thresholds are used in two ways: (1) to establish a mitigation shut-down or power down zone, i.e., if an animal enters an area calculated to be ensonified above the level of an established threshold, a sound source is powered down or shut down; and (2) to calculate take, in that a model may be used to calculate the area around the sound source that will be ensonified to that level or above, then, based on the estimated density of animals and the distance that the sound source moves, NMFS can estimate the number of marine mammals that may be “taken”. NMFS believes that to avoid permanent physiological damage (Level A Harassment), cetaceans and pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding, respectively, 180 and 190 dB re 1 μPa (rms). NMFS also assumes that cetaceans or pinnipeds exposed to levels exceeding 160 dB re 1 μPa (rms) may experience Level B Harassment.

Received sound levels have been modeled by L-DEO for a number of airgun configurations, including one 45-in³ GI gun, in relation to distance and direction from the airgun(s). The model does not allow for bottom interactions and is most directly applicable to deep water. Based on the modeling, estimates of the maximum distances from the GI gun where sound levels of 190, 180, and 160 dB re 1 μPa (rms) are predicted to be received in deep (>1000-m, 3280-ft) water are 8, 23, and 220 m (26.2, 75.5, and 721.8 ft), respectively and 12, 35, and 330 m (39.4, 115, and 1,082.7 ft), respectively for intermediate water depths (100-1000m, 328-3,280 ft). Because the model results are for a 2.5-m (8.2-ft) tow depth, the above distances slightly underestimate the distances for the 45-in³ GI gun towed at 4-m (13-ft) depth.

Empirical data concerning the 180- and 160- dB distances have been acquired based on measurements during the acoustic verification study conducted by L-DEO in the northern Gulf of Mexico from 27 May to 3 June 2003 (Tolstoy et al., 2004). Although the results are limited, the data showed that radii around the airguns where the received level would be 180 dB re 1 mPa (rms) vary with water depth. Similar depth-related variation is likely in the 190-dB distances applicable to pinnipeds. Correction factors were developed for water depths 100-1,000 m (328-3,280 ft) and <100 m (328 ft). The proposed survey will occur in depths 110-3,050 m (361-10,007 ft), so the correction factors for the latter are not relevant here.

The empirical data indicate that, for deep water (>1,000 m, 3,280 ft), the L-DEO model tends to overestimate the received sound levels at a given distance (Tolstoy et al., 2004). However, to be precautionary pending acquisition of additional empirical data, it is proposed that safety radii during airgun operations in deep water will be the values predicted by L-DEO's model (above). Therefore, the assumed 180- and 190-dB radii are 23 m and 8 m (75.5 and 26.2 ft), respectively.

Empirical measurements were not conducted for intermediate depths (100-1,000 m, 328-3,280 ft). On the expectation that results will be intermediate between those from shallow and deep water, a 1.5x correction factor is applied to the estimates provided by the model for deep water situations. This is the same factor that was applied to the model estimates during L-DEO cruises in 2003. The assumed 180- and 190-dB radii in intermediate-depth water are 35 m and 12 m (115 and 39.4 ft), respectively.

The airgun will be shut down immediately when cetaceans or pinnipeds are detected within or about to enter the appropriate 180-dB (rms) or 190-dB (rms) radius, respectively.

Description of Marine Mammals in the Activity Area

Thirty-two marine mammal species, including 19 odontocete (dolphins and small and large toothed whales) species, seven mysticete (baleen whales) species, five pinniped species, and the sea otter, may occur or have been documented to occur in the marine waters off Oregon and Washington, excluding extralimital sightings or strandings (Table 1 here). Six of the species that may occur in the project area are listed under the U.S. Endangered Species Act (ESA) as Endangered, including sperm, humpback, blue, fin, sei, and North Pacific right whales. One other species listed as Threatened may occur in the project area: the Steller sea lion.

Gray whales and sea otters (which is under the jurisdiction of the U.S. Fish and Wildlife Service) are not expected in the project area because their occurrence off Oregon is limited to very shallow, coastal waters. The California sea lion, Steller sea lion, and harbor seal are also mainly coastal and would be rare at most at the OBS locations. Information on habitat and abundance of the species that may occur in the study area are given in Table 1 below. Vagrant ringed seals, hooded seals, and ribbon seals have been sighted or stranded on the coast of California (see Mead, 1981; Reeves et al., 2002) and presumably passed through Oregon waters. A vagrant beluga was seen off the coast of Washington (Reeves et al., 2002).

The six species of marine mammals expected to be most common in the deep pelagic or slope waters of the project area, where most of the survey sites are located, include the Pacific white-sided dolphin, northern right whale dolphin, Risso's dolphin, short-beaked common dolphin, Dall's porpoise, and northern fur seal (Green et al., 1992, 1993; Buchanan et al., 2001; Barlow, 2003; Carretta et al., 2006).

The sperm, pygmy sperm, mesoplodont species, Baird's beaked, and Cuvier's beaked whales and the northern elephant seal are considered pelagic species but are generally uncommon in the waters near the survey area.

Additional information regarding the distribution of these species expected to be found in the project area and how the estimated densities were calculated may be found in SIO's application.

Potential Effects on Marine Mammals

Potential Effects of Airguns

The effects of sounds from airguns might include one or more of the following: tolerance, masking of natural sounds, behavioral disturbance, and temporary or permanent hearing impairment or non-auditory physical or physiological effects (Richardson et al., 1995; Gordon et al., 2004). Given the small size of the GI gun planned for the present project, effects are anticipated to be considerably less than would be the case with a large array of airguns. It is very unlikely that there would be any cases of temporary or, especially, permanent hearing impairment or any significant non-auditory physical or physiological effects. Also, behavioral disturbance is expected to be limited to relatively short distances.

Tolerance

Numerous studies have shown that pulsed sounds from airguns are often readily detectable in the water at distances of many kilometers. For a summary of the characteristics of airgun pulses, see Appendix A of SIO's application. However, it should be noted that most of the measurements of airgun sounds that have been reported concerned sounds from larger arrays of airguns, whose sounds would be detectable considerably farther away than the GI gun planned for use in the present project.

Numerous other studies have shown that marine mammals at distances more than a few kilometers from operating seismic vessels often show no apparent response (see Appendix A (e) of SIO's application). That is often true even in cases when the pulsed sounds appear to be readily audible to the animals based on measured received levels and the hearing sensitivity of that mammal group. Although various baleen whales, toothed whales, and (less frequently) pinnipeds have been shown to react behaviorally to airgun pulses under some conditions, at other times mammals of all three types have shown no overt reactions. In general, pinnipeds and small odontocetes seem to be more tolerant of exposure to airgun pulses than are baleen whales. Given the relatively small and low-energy airgun source planned for use in this project, NMFS expects mammals (and sea turtles) to tolerate being closer to this source than for a larger airgun source typical of most seismic surveys.

Masking

Obscuring of sounds of interest by interfering sounds, generally at similar frequencies, is known as masking. Masking effects of pulsed sounds (even from large arrays of airguns) on marine mammal calls and other natural sounds are expected to be limited, although there are very few specific data on this matter. Some whales are known to continue calling in the presence of seismic pulses. Their calls can 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). Although there has been one report that sperm whales cease calling when exposed to pulses from a very distant seismic ship (Bowles et al., 1994), a recent study reports that sperm whales off northern Norway continued calling in the presence of seismic pulses (Madsen et al., 2002c). Similar reactions have also been shown during recent work in the Gulf of Mexico (Tyack et al., 2003; Smultea et al., 2004). Given the small source planned for use here, there is even less potential for masking of baleen or sperm whale calls during the present study than in most seismic surveys. Masking effects of seismic pulses are expected to be negligible in the case of the smaller odontocete cetaceans, given the intermittent nature of seismic pulses and the relatively low source level of the airgun to be used here. Dolphins and porpoises are commonly heard calling while airguns are operating (Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a,b). Also, the sounds important to small odontocetes are predominantly at much higher frequencies than are airgun sounds. Masking effects, in general, are discussed further in Appendix A (d) of SIO's application.

Disturbance Reactions

Disturbance includes a variety of effects, including subtle changes in behavior, more conspicuous changes in activities, 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. If a marine mammal responds to an underwater sound by changing its behavior or moving a small distance, the response may or may not rise to the level of harassment, let alone affect the stock or the species as a whole. Alternatively, if a sound source displaces marine mammals from an important feeding or breeding area, effects on the stock or species could potentially be more than negligible. 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 are likely to be present within a particular distance of industrial activities, or exposed to a particular level of industrial sound. This practice potentially overestimates the numbers of marine mammals that are affected in some biologically-important manner.

The sound criteria used to estimate how many marine mammals might be disturbed to some biologically-important degree by a seismic program are based on behavioral observations during studies of several species. However, information is lacking for many species. Detailed studies have been done on humpback, gray, and bowhead whales and ringed seals. Less detailed data are available for some other species of baleen whales, sperm whales, small toothed whales, and sea otters. Most of those studies have focused on the impacts resulting from the use of much larger airgun sources than those planned for use in the present project. Thus, effects are expected to be limited to considerably smaller distances and shorter periods of exposure in the present project than in most of the previous work concerning marine mammal reactions to airguns.

Baleen Whales - Baleen whales generally tend to avoid operating airguns, but avoidance radii are quite variable. 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, as reviewed in Appendix A (e) of SIO's application, baleen whales exposed to strong noise pulses from airguns often react by deviating from their normal migration route and/or interrupting their feeding activities and moving away from the sound source. In the case of the migrating gray and bowhead whales, the observed changes in behavior appeared to be of little or no biological consequence to the animals. 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 determined that received levels of pulses in the 160-170 dB re 1 μPa rms range seem to cause obvious avoidance behavior in a substantial fraction of the animals exposed. In many areas, seismic pulses from large arrays of airguns diminish to those levels at distances ranging from 4.5-14.5 km (2.8-9 mi) from the source. A substantial proportion of the baleen whales within those distances may show avoidance or other strong disturbance reactions to the airgun array. Subtle behavioral changes sometimes become evident at somewhat lower received levels, and recent studies, reviewed in Appendix A (e) of SIO's application, have shown that some species of baleen whales, notably bowheads and humpbacks, at times show strong avoidance at received levels lower than 160-170 dB re 1 μPa rms. Reaction distances would be considerably smaller during the present project, in which the 160-dB radius is predicted to be approximately 0.22 or 0.33 km (0.14 or 0.21 mi), as compared with several kilometers when a large array of airguns is operating.

McCauley et al. (1998, 2000) studied the responses of humpback whales off Western Australia to a full-scale seismic survey with a 16-airgun, 2,678-in³ array, and to a single 20-in³ airgun with a source level of 227 dB re 1 μPa m. McCauley et al. (1998) documented that avoidance reactions began at 5-8 km (3.1-5 mi) from the array, and that those reactions kept most pods approximately 3-4 km (1.9-2.5 mi) from the operating seismic boat. McCauley et al. (2000) noted localized displacement during migration of 4-5 km (2.5-3.1 mi) by traveling pods and 7-12 km (4.3-7.5 mi) by 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 received sound levels. Mean avoidance distance from the airgun corresponded to a received sound level of 140 dB re 1 μPa (rms); that was the level at which humpbacks started to show avoidance reactions to an approaching airgun. The standoff range, i.e., the closest point of approach of the whales to the airgun, corresponded to a received level of 143 dB re 1 μPa (rms). The initial avoidance response generally occurred at distances of 5-8 km (3.1-5 mi) from the airgun array and 2 km (1.2 mi) from the single airgun. However, some individual humpback whales, especially males, approached within distances of 100-400 m (328-1,312 ft), where the maximum received level was 179 dB re 1 μPa (rms).

Humpback whales summering in southeast Alaska did not exhibit persistent avoidance when exposed to seismic pulses from a 1.64-L (100 in³) airgun (Malme et al., 1985). Some humpbacks seemed “startled” at received levels of 150-169 dB re 1 μPa on an approximate rms basis. 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 re 1 μPa (approximately rms). Additional effects from seismic surveys to wintering humpback whales off Brazil can be found in Appendix A (e) of SIO's application.

Results from bowhead whales show that responsiveness of baleen whales to seismic surveys can be quite variable depending on the activity (migrating vs. feeding) of the whales. Bowhead whales migrating west across the Alaskan Beaufort Sea in autumn, in particular, are unusually responsive, with substantial avoidance occurring out to distances of 20 30 km (12.4-18.6 mi) from a medium-sized airgun source, where received sound levels were on the order of 130 dB re 1 μPa (rms) (Miller et al., 1999; Richardson et al., 1999). However, more recent research on bowhead whales (Miller et al., 2005a) corroborates earlier evidence that, during the summer feeding season, bowheads are not as sensitive to seismic sources. In summer, bowheads typically begin to show avoidance reactions at a received level of about 160 170 dB re 1 μPa (rms) (Richardson et al., 1986; Ljungblad et al., 1988; Miller et al., 1999). There are not data on reactions of wintering bowhead whales to seismic surveys. See Appendix A (e) of SIO's application for more information regarding bowhead whale reactions to airguns.

Malme et al. (1986, 1988) studied the responses of feeding Eastern Pacific gray whales to pulses from a single 100 in³ airgun off St. Lawrence Island in the northern Bering Sea. Malme et al. (1986, 1988) estimated, based on small sample sizes, that 50 percent of feeding gray whales ceased 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. Those findings were generally consistent with the results of experiments conducted on larger numbers of gray whales that were migrating along the California coast and on observations of Western Pacific gray whales feeding off Sakhalin Island, Russia (Johnson, 2002).

We are not aware of any information on reactions of Bryde's whales to seismic surveys. However, other species of Balaenoptera (blue, sei, fin, and minke whales) have occasionally been reported in areas ensonified by airgun pulses. Sightings by observers on seismic vessels off the U.K. from 1997 to 2000 suggest that, at times of good sightability, numbers of rorquals seen are similar when airguns are shooting and not shooting (Stone, 2003). Although individual species did not show any significant displacement in relation to seismic activity, all baleen whales combined were found to remain significantly further from the airguns during shooting compared with periods without shooting (Stone, 2003; Stone and Tasker, 2006). In a study off Nova Scotia, Moulton and Miller (in press) found only a little or no difference in sighting rates and initial sighting distances of balaenopterid whales when airguns were operating vs. silent. However, there were indications that these whales were more likely to be moving away when seen during airgun operations.

Data on short-term reactions (or lack of reactions) of cetaceans to impulsive noises do not necessarily provide information about long-term effects. It is not known whether impulsive noises affect reproductive rate or distribution and habitat use in subsequent days or years. However, gray whales continued to migrate annually along the west coast of North America despite intermittent seismic exploration and much ship traffic in that area for decades (Appendix A in Malme et al., 1984). Bowhead whales continued to travel to the eastern Beaufort Sea each summer despite seismic exploration in their summer and autumn range for many years (Richardson et al., 1987). In any event, the brief exposures to sound pulses from the present small airgun source are highly 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, a systematic study on sperm whales has been done (Jochens and Biggs, 2003; Tyack et al., 2003; Miller et al., 2006), and there is an increasing amount of information about responses of various odontocetes to seismic surveys based on monitoring studies (Stone, 2003; Smultea et al., 2004; Bain and Williams, 2006; Holst et al., 2006; Stone and Tasker, 2006; Moulton and Miller, in press).

Seismic operators sometimes see dolphins and other small toothed whales near operating airgun arrays, but in general there seems to be a tendency for most delphinids to show some limited avoidance of seismic vessels operating large airgun systems. However, 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. Nonetheless, there have been indications that small toothed whales sometimes 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 (Goold, 1996; Calambokidis and Osmek, 1998; Stone, 2003). In most cases, the avoidance radii for delphinids appear to be small, on the order of 1 km (0.62 mi) or less.

The beluga may be a species that (at least at times) shows long-distance avoidance of seismic vessels. Aerial surveys during seismic operations in the southeastern Beaufort Sea recorded much lower sighting rates of beluga whales within 10-20 km (6.2-12.4 mi) of an active seismic vessel. These results were consistent with the low number of beluga sightings reported by observers aboard the seismic vessel, suggesting that some belugas might be avoiding the seismic operations at distances of 10-20 km (6.2-12.4 mi) (Miller et al., 2005a). Similarly, captive bottlenose dolphins and beluga whales exhibit 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; Finneran and Schlundt, 2004). However, the animals tolerated high received levels of sound (pk-pk level >200 dB re 1 μPa) before exhibiting aversive behaviors.

Results for porpoises depend on species. Dall's porpoises seem relatively tolerant of airgun operations (MacLean and Koski, 2005; Bain and Williams, 2006), whereas the limited available data suggest that harbor porpoises show stronger avoidance (Stone, 2003; Bain and Williams, 2006). This apparent difference in responsiveness of these two porpoise species is consistent with their relative responsiveness to boat traffic in general (Richardson et al., 1995).

Most studies of sperm whales exposed to airgun sounds indicate that this species shows considerable tolerance of airgun pulses. In most cases, the whales do not show strong avoidance, and they continue to call (see Appendix A (e) of SIO's application for review). However, controlled exposure experiments in the Gulf of Mexico indicate that foraging effort is apparently somewhat reduced upon exposure to airgun pulses from a seismic vessel operating in the area, and there may be a delay in diving to foraging depth.

There are no specific data on the behavioral reactions of beaked whales to seismic surveys. Most beaked whales tend to avoid approaching vessels of other types (Wursig et al., 1998). They may also dive for an extended period when approached by a vessel (Kasuya, 1986). It is likely that these beaked whales would normally show strong avoidance of an approaching seismic vessel, but this has not been documented explicitly.Odontocete reactions to large arrays of airguns are variable and, at least for delphinids and some porpoises, seem to be confined to a smaller radius than has been observed for mysticetes (see Appendix A of SIO's application for more information). Behavioral reactions of odontocetes to the small GI-gun source to be used here are expected to be very localized, probably to distances <0.4 km (0.25 mi).

Pinnipeds - Pinnipeds are not likely to show a strong avoidance reaction to the GI gun that will be used. Visual monitoring from seismic vessels, usually employing larger sources, has shown only slight (if any) avoidance of airguns by pinnipeds, and only slight (if any) changes in behavior (see Appendix A (e) of SIO's application). Ringed seals frequently do not avoid the area within a few hundred meters of operating airgun arrays (Harris et al., 2001; Moulton and Lawson, 2002; Miller et al., 2005a). However, initial telemetry work suggests that avoidance and other behavioral reactions by two other species of seals to small airgun sources may at times be stronger than evident to date from visual studies of pinniped reactions to airguns (Thompson et al., 1998). Even if reactions of any pinnipeds that might be encountered in the present study area are as strong as those evident in the telemetry study, reactions are expected to be confined to relatively small distances and durations, with no long-term effects on pinniped individuals or populations.

Additional details on the behavioral reactions (or the lack thereof) by all types of marine mammals to seismic vessels can be found in Appendix A (e) of SIO's application.

Hearing Impairment and Other Physical Effects

Temporary or permanent hearing impairment is a possibility when marine mammals are exposed to very strong sounds, but there has been no specific documentation of this for marine mammals exposed to sequences of airgun pulses. Current NMFS policy regarding exposure of marine mammals to high-level sounds is that cetaceans and pinnipeds should not be exposed to impulsive sounds of 180 and 190 dB re 1 μPa (rms), respectively. Those criteria have been used in defining the safety (shut-down) radii planned for the proposed seismic survey. The precautionary nature of these criteria is discussed in Appendix A (f) of SIO's application, including the fact that the minimum sound level necessary to cause permanent hearing impairment is higher, by a variable and generally unknown amount, than the level that induces barely-detectable temporary threshold shift (TTS) (which NMFS' criteria are based on) and the level associated with the onset of TTS is often considered to be a level below which there is no danger of permanent damage. NMFS is presently developing new noise exposure criteria for marine mammals that take account of the now-available scientific data on TTS, the expected offset between the TTS and permanent threshold shift (PTS) thresholds, differences in the acoustic frequencies to which different marine mammal groups are sensitive, and other relevant factors.

Because of the small size of the airgun source in this project (one 45-in3 GI gun), alongwith the planned monitoring and mitigation measures, there is little likelihood that any marine mammals will be exposed to sounds sufficiently strong to cause hearing impairment. Several aspects of the planned monitoring and mitigation measures for this project are designed to detect marine mammals occurring near the GI gun (and sub-bottom profiler), and to avoid exposing them to sound pulses that might, at least in theory, cause hearing impairment. In addition, many cetaceans are likely to show some avoidance of the area with high received levels of airgun sound (see above). In those cases, the avoidance responses of the animals themselves will reduce or (most likely) avoid any possibility of hearing impairment.

Non-auditory physical effects may also occur in marine mammals exposed to strong underwater pulsed sound. Possible types of non-auditory physiological effects or injuries that theoretically might occur in mammals close to a strong sound source include stress, neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage. It is possible that some marine mammal species (i.e., beaked whales) may be especially susceptible to injury and/or stranding when exposed to strong pulsed sounds. However, as discussed below, there is no definitive evidence that any of these effects occur even for marine mammals in close proximity to large arrays of airguns. It is especially unlikely that any effects of these types would occur during the present project given the small size of the source, the brief duration of exposure of any given mammal, and the planned monitoring and mitigation measures (see below). The following subsections discuss in somewhat more detail the possibilities of TTS, PTS, and non-auditory physical effects.

Temporary Threshold Shift (TTS) - 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. 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 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.

For toothed whales exposed to single short pulses, the TTS threshold appears to be, to a first approximation, a function of the energy content of the pulse (Finneran et al., 2002, 2005). Given the available data, the received level of a single seismic pulse (with no frequency weighting) might need to be approximately 186 dB re 1 μPa².s (i.e., 186 dB SEL or approximately 221-226 dB pk-pk) in order to produce brief, mild TTS. Exposure to several strong seismic pulses that each have received levels near 175-180 dB SEL might result in slight TTS in a small odontocete, assuming the TTS threshold is (to a first approximation) a function of the total received pulse energy. The distance from the Wecoma's GI gun at which the received energy level (per pulse) would be expected to be ≥175-180 dB SEL are the distances shown in the 190 dB re 1 μPa (rms) column in Table 1 of SIO's application (given that the rms level is approximately 10-15 dB higher than the SEL value for the same pulse). Seismic pulses with received energy levels ≥175-180 dB SEL (190 dB re 1 μPa (rms)) are expected to be restricted to radii no more than 23-35 m (75.5-115 ft) around the GI gun. The specific radius depends on the depth of the water. For an odontocete closer to the surface, the maximum radius with ≥175-180 dB SEL or ≥190 dB re 1 μPa (rms) would be smaller. Such levels would be limited to distances within a few meters of the small GI gun source to be used in this project.

For baleen whales, direct or indirect data do not exist on levels or properties of sound thatare required to induce TTS. The frequencies to which baleen whales are most sensitive are 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. In any event, no cases of TTS are expected given three considerations: (1) the low abundance of baleen whales expected in the planned study areas; (2) the strong likelihood that baleen whales would avoid the approaching airguns (or vessel) before being exposed to levels high enough for there to be any possibility of TTS; and (3) the mitigation measures that are planned.

In pinnipeds, TTS thresholds associated with exposure to brief pulses (single or multiple) of underwater sound have not been measured. Initial evidence from prolonged exposures suggested that some pinnipeds may incur TTS at somewhat lower received levels than do small odontocetes exposed for similar durations (Kastak et al., 1999, 2005; Ketten et al., 2001; cf. Au et al., 2000). However, more recent indications are that TTS onset in the most sensitive pinniped species studied (harbor seal) may occur at a similar sound exposure level as in odontocetes (Kastak et al., 2004).

To avoid injury, NMFS has determined that cetaceans and pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding, respectively, 180 and 190 dB re 1 μPa (rms). Those sound levels were not considered to be the levels above which TTS might occur. Rather, they were 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. As summarized above, data that are now available imply that TTS is unlikely to occur unless odontocetes (and probably mysticetes as well) are exposed to airgun pulses strong than 180 dB re 1 μPa (rms).

Permanent Threshold Shift (PTS) - When PTS occurs, there is physical damage to the sound receptors in the ear. In some cases, there can be total or partial deafness, while in other cases, the animal has an impaired ability to hear sounds in specific frequency ranges.

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 TTS, there has been further speculation about the possibility that some individuals occurring very close to airguns might incur PTS. Single or occasional occurrences of mild TTS are not indicative of permanent auditory damage in terrestrial mammals. 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. PTS might occur at a received sound level at least several decibels above that inducing mild TTS if the animal were exposed to strong sound pulses with rapid rise time (see Appendix A (f) of SIO's application). The specific difference between the PTS and TTS thresholds has not been measured for marine mammals exposed to any sound type. However, 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 more than 6 dB.

In the present project employing a single 45-in³ GI gun, marine mammals are highly unlikely to be exposed to received levels of seismic pulses strong enough to cause TTS, as they would probably need to be within a few meters of the GI gun for that to occur. Given the higher level of sound necessary to cause PTS, it is even less likely that PTS could occur. In fact, even the levels immediately adjacent to the GI gun may not be sufficient to induce PTS, especially since a mammal would not be exposed to more than one strong pulse unless it swam immediately alongside the GI gun for a period longer than the inter-pulse interval. Baleen whales generally avoid the immediate area around operating seismic vessels, as do some other marine mammals. The planned monitoring and mitigation measures, including visual monitoring and shut downs of the GI gun when mammals are seen within the “safety radii”, will minimize the already-minimal probability of exposure of marine mammals to sounds strong enough to induce PTS.

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 effects, and other types of organ or tissue damage. However, studies examining such effects are limited. If any such effects do occur, they would probably be limited to unusual situations when animals might be exposed at close range for unusually long periods. It is doubtful that any single marine mammal would be exposed to strong seismic sounds for time periods long enough to induce physiological stress.

Until recently, it was assumed that diving marine mammals are not subject to the bends or air embolism. This possibility was first explored at a workshop (Gentry [ed.], 2002) held to discuss whether the stranding of beaked whales in the Bahamas in 2000 (Balcomb and Claridge, 2001; NOAA and USN, 2001) might have been related to bubble formation in tissues caused by exposure to noise from naval sonar. However, this link could not be confirmed. Jepson et al. (2003) first suggested a possible link between mid-frequency sonar activity and acute chronic tissue damage that results from the formation in vivo of gas bubbles, based on the beaked whale stranding in the Canary Islands in 2002 during naval exercises. Fernandez et al. (2005a) showed those beaked whales did indeed have gas bubble-associated lesions, as well as fat embolisms. Fernandez et al. (2005b) also found evidence of fat embolism in three beaked whales that stranded 100 km (62 mi) north of the Canaries in 2004 during naval exercises. Examinations of several other stranded species have also revealed evidence of gas and fat embolisms (Arbelo et al., 2005; Jepson et al., 2005a; Mendez et al., 2005). Most of the afflicted species were deep divers. There is speculation that gas and fat embolisms may occur if cetaceans ascend unusually quickly when exposed to aversive sounds, or if sound in the environment causes the destablization of existing bubble nuclei (Potter, 2004; Arbelo et al., 2005; Fernandez et al. 2005a; Jepson et al., 2005b; Cox et al., 2006). Even if gas and fat embolisms can occur during exposure to mid-frequency sonar, there is no evidence that that type of effect occurs in response to airgun sounds.

In general, little is known about the potential for seismic survey sounds to cause auditory impairment or other physical effects in marine mammals. Available data suggest that such effects, if they occur at all, would be limited to short distances and probably to projects involving large arrays of airguns. However, the available data do not allow for 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 auditory impairment or other physical effects. Also, the planned mitigation measures, including shut downs of the GI gun, will reduce any such effects that might otherwise occur.

Strandings and Mortality

Marine mammals close to underwater detonations of high explosives can be killed or severely injured, and their auditory organs are especially susceptible to injury (Ketten et al., 1993; Ketten 1995). Airgun pulses are less energetic and have slower rise times, and there is no proof that they can cause serious injury, death, or stranding even in the case of large airgun arrays. However, the association of mass strandings of beaked whales with naval exercises and, in one case, an L-DEO seismic survey, has raised the possibility that beaked whales exposed to strong pulsed sounds may be especially susceptible to injury and/or behavioral reactions that can lead to stranding. Appendix A (g) of SIO's application provides additional details.

Seismic pulses and mid-frequency sonar pulses are quite different. Sounds produced by airgun arrays are broadband with most of the energy below 1 kHz. Typical military mid-frequency sonars operate at frequencies of 2-10 kHz, generally with a relatively narrow bandwidth at any one time. Thus, it is not appropriate to assume that there is a direct connection between the effects of military sonar and seismic surveys on marine mammals. However, evidence that sonar pulses can, in special circumstances, lead to physical damage and mortality (Balcomb and Claridge, 2001; NOAA and USN, 2001; Jepson et al., 2003; Fernandez et al., 2004, 2005a; Cox et al., 2006), even if only indirectly, suggests that caution is warranted when dealing with exposure of marine mammals to any high-intensity pulsed sound.

There is no conclusive evidence of cetacean strandings as a result of exposure to seismic surveys. Speculation concerning a possible link between seismic surveys and strandings of humpback whales in Brazil (Engel et al., 2004) was not well founded based on available data (IAGC, 2004; IWC, 2006). In September 2002, there was a stranding of two Cuvier's beaked whales in the Gulf of California, Mexico, when the L-DEO vessel Maurice Ewing was operating a 20-gun, 8,490-in³ array in the general area. The link between the stranding and the seismic survey was inconclusive and not based on any physical evidence (Hogarth, 2002; Yoder, 2002). Nonetheless, the preceding example plus the incidents involving beaked whale strandings near naval exercises suggests a need for caution in conducting seismic surveys in areas occupied by beaked whales. No injuries of beaked whales are anticipated during the proposed study because of the proposed monitoring and mitigation measures.

The present project will involve a much smaller sound source than used in typical seismic surveys. That, along with the monitoring and mitigation measures that are planned, are expected to minimize any possibility for strandings and mortality.

Potential Effects of Other Acoustic Devices

Sub-bottom Profiler Signals

A sub-bottom profiler will be operated from the source vessel at all times during the planned study. Sounds from the sub-bottom profiler are very short pulses, occurring for 12 or 24 ms once every 4.5-8 seconds. Most of the energy in the sound pulses emitted by this sub-bottom profiler is at mid frequencies, centered at 3.5 kHz. The beam width is approximately 80o (cone-shaped) and is directed downward.

The sub-bottom profiler on the Wecoma has a stated maximum source level of 211 dB re 1 μPa m (see section II of SIO's application). Thus, the received level would be expected to decrease to 180 dB and 160 dB approximately 35 m (115 ft) and 350 m (1,148.3 ft) below the transducer, respectively, assuming spherical spreading. Corresponding distances in the horizontal plane would be substantially lower, given the directionality of this source. Kremser et al. (2005) noted that the probability of a cetacean swimming through the area of exposure when a bottom profiler emits a pulse is small, and if the animal was in the area, it would have to pass the transducer at close range in order to be subjected to sound levels that could cause TTS.

Marine mammal communications will not be masked appreciably by the sub-bottom profiler signals given their directionality and the brief period when an individual mammal is likely to be within its beam. Furthermore, in the case of most odontocetes, the sonar signals do not overlap with the predominant frequencies in the calls, which would avoid significant masking.

Marine mammal behavioral reactions to other pulsed sound sources are discussed above, and responses to the sub-bottom profiler are likely to be similar to those for other pulsed sources if received at the same levels. Behavioral responses are not expected unless marine mammals are very close to the source.

Source levels of the sub-bottom profiler are much lower than those of the airguns and the multi-beam sonar, which are discussed above. Sounds from the sub-bottom profiler are estimated to decrease to 180 dB re 1 μPa (rms) at approximately 35 m (115 ft) downward from the source. Furthermore, received levels of pulsed sounds that are necessary to cause temporary or especially permanent hearing impairment in marine mammals appear to be higher than 180 dB (see earlier). Thus, it is unlikely that the sub-bottom profiler produces pulse levels strong enough to cause hearing impairment or other physical injuries even in an animal that is (briefly) in a position near the source.

The sub-bottom profiler is usually operated simultaneously with other higher-power acoustic sources. Many marine mammals will move away in response to the approaching higher-power sources or the vessel itself before the mammals would be close enough for there to be any possibility of effects from the less intense sounds from the sub-bottom profiler. In the case of mammals that do not avoid the approaching vessel and its various sound sources, mitigation measures that would be applied to minimize effects of the higher-power sources would further reduce or eliminate any minor effects of the sub-bottom profiler.

Estimated Take by Incidental Harassment

All anticipated takes would be “takes by harassment”, involving temporary changes in behavior. The proposed mitigation measures are expected to minimize the possibility of injurious takes. (However, as noted earlier, there is no specific information demonstrating that injurious “takes” would occur even in the absence of the planned mitigation measures.) In the sections below, we describe methods to estimate “take by harassment”, and present estimates of the numbers of marine mammals that might be affected during the proposed seismic survey in the northeast Pacific Ocean. The estimates are based on data concerning marine mammal densities (numbers per unit area) obtained during surveys off Oregon and Washington during 1996 and 2001 by NMFS Southwest Fisheries Science Center (SWFSC) and estimates of the size of the area where effects potentially could occur.

The following estimates are based on a consideration of the number of marine mammals that might be disturbed appreciably by operations with the GI gun to be used during approximately 340 line-km of surveys at 16 sites off the coast of Oregon in the northeastern Pacific Ocean. The anticipated radii of influence of the sub-bottom profiler are less than those for the GI gun. It is assumed that, during simultaneous operations of the GI gun and sub-bottom profiler, any marine mammals close enough to be affected by the sub-bottom profiler would already be affected by the airgun. No animals are expected to exhibit more than short-term and inconsequential responses to the sub-bottom profiler, given its characteristics (e.g., narrow downward-directed beam) and other considerations described previously. Therefore, no additional allowance is included for animals that might be affected by this source.

Extensive systematic aircraft- and ship-based surveys have been conducted for marine mammals offshore of Oregon and Washington (Bonnell et al., 1992; Green et al., 1992, 1993; Barlow, 1997, 2003; Barlow and Taylor, 2001; Calambokidis and Barlow, 2004). The most comprehensive and recent density data available for cetacean species off slope and offshore waters of Oregon are from the 1996 and 2001 NMFS SWFSC “ORCAWALE” ship surveys as synthesized by Barlow (2003). The surveys were conducted from late July to early November (1996) or early December (2001). They were conducted up to approximately 556 km (1,824 ft) offshore from Oregon and Washington.Systematic, offshore, at-sea survey data for pinnipeds are more limited. The most comprehensive such studies are reported by Bonnell et al. (1992) and Green et al. (1993) based on systematic aerial surveys conducted in 1989 1990 and 1992, primarily from coastal to slope waters with some offshore effort as well.

Oceanographic conditions, including occasional El Nino and La Nina events, influence the distribution and numbers of marine mammals present in the northeastern Pacific Ocean, including Oregon, resulting in considerable year-to-year variation in the distribution and abundance of many marine mammal species (Forney and Barlow, 1998; Buchanan et al., 2001; Escorza-Trevino, 2002; Ferrero et al., 2002; Philbrick et al., 2003). Thus, for some species the densities derived from recent surveys may not be representative of the densities that will be encountered during the proposed seismic survey.

Table 3 in SIO's application gives the average and maximum densities for each species or species group of marine mammals reported off Oregon and Washington (and used to calculate the take estimates in Table 1 here), corrected for effort, based on the densities reported for the 1996 and 2001 ORCAWALE surveys (Barlow, 2003). The densities from these studies had been corrected, by the original author, for both detectability bias and availability bias. Detectability bias is associated with diminishing sightability with increasing lateral distance from the trackline [f(0)]. Availability bias refers to the fact that there is less-than-100 percent probability of sighting an animal that is present along the survey trackline, and it is measured by g(0).

It should be noted that the following estimates of “takes by harassment” assume that the seismic surveys will be undertaken and completed; in fact, the planned number of line-kms has been increased by 25 percent to accommodate lines that may need to be repeated, equipment testing, etc. As is typical on offshore ship surveys, inclement weather, and equipment malfunctions may cause delays and may limit the number of useful line-kms of seismic operations that can be undertaken. Furthermore, any marine mammal sightings within or near the designated safety zones will result in the shut down of seismic operations as a mitigation measure. Thus, the following estimates of the numbers of marine mammals potentially exposed to 160-dB sounds are precautionary, and probably overestimate the actual numbers of marine mammals that might be involved. These estimates assume that there will be no weather, equipment, or mitigation delays, which is unlikely.

There is some uncertainty about the representativeness of the data and the assumptions used in the take calculations. However, the approach used here is believed to be the best available approach. Also, to provide some allowance for the uncertainties, “maximum estimates” as well as “best estimates” of the numbers potentially affected have been derived. Best and maximum estimates are based on the average and maximum estimates of densities reported by Barlow (2003) described above. SIO has requested authorization for the take of the maximum estimates and NMFS has analyzed the maximum estimate for it's effect on the species or stock.

The number of different individuals that may be exposed to GI-gun sounds with received levels ≥160 dB re 1 μPa (rms) on one or more occasions can be estimated by considering the total marine area that would be within the 160-dB radius around the operating GI gun on at least one occasion. The proposed seismic lines do not run parallel to each other in close proximity, which minimizes the number of times an individual mammal may be exposed during the survey. The best estimates in this section are based on the average of the densities from the 1996 and 2001 NMFS surveys, and maximum estimates are based on the higher estimate. Table 4 in SIO's application (and used to calculate the take estimates in Table 1 here) shows the best and maximum estimates of the number of marine mammals that could potentially be affected during the seismic survey.

The number of different individuals potentially exposed to received levels ≥160 dB re 1 μPa (rms) was calculated by multiplying:

• The expected species density, either “average” (i.e., best) or “maximum”, times
• The anticipated minimum area to be ensonified to that level during GI gun operations.

The area expected to be ensonified was determined by entering the planned survey lines into a MapInfo Geographic Information System (GIS), using the GIS to identify the relevant areas by “drawing” the applicable 160-dB around each seismic line and then calculating the total area within the buffers. Areas where overlap occurred (because of intersecting lines) were included only once to determine the minimum area expected to be ensonified.

Applying the approach described above, approximately 206 km² would be within the 160-dB isopleth on one or more occasions. This approach does not allow for turnover in the mammal populations in the study area during the course of the studies. That might underestimate actual numbers of individuals exposed, although the conservative distances used to calculate the area may offset this. In addition, the approach assumes that no cetaceans will move away or toward the trackline as the Wecoma approaches in response to increasing sound levels prior to the time the levels reach 160 dB. Another way of interpreting the estimates that follow is that they represent the number of individuals that are expected (in the absence of a seismic program) to occur in the waters that will be exposed to ≥160 dB re 1 μPa (rms).

The ‘best estimate’ of the number of individual cetaceans that might be exposed to seismic sounds with received levels ≥160 dB re 1 μPa (rms) during the surveys is 57 (Table 4 in SIO's application). The total does not include any endangered or beaked whales. Dall's porpoise and Pacific white-sided and northern right whale dolphins are estimated to be the most common species exposed; the best estimates for those species are 39, 6, and 5, respectively. Estimates for the two other dolphin species that could be exposed are lower (Table 4 in SIO's application).

The ‘maximum estimate’ column in Table 4 of SIO's application shows an estimated total of 109 cetaceans that might be exposed to seismic sounds ≥160 dB during the surveys. In most cases, those estimates are based on survey data, as described above. For endangered species, the ‘maximum estimate’ is the mean group size (from Barlow and Forney, in prep) in cases where the calculated maximum number of individuals exposed was between 0.05 and the mean group size (humpback, fin, blue, and sperm whales). The numbers for which take authorization is requested, given in the far right column of Table 4 in SIO's application and Table 1 here, are the best estimates. Based on the abundance numbers given in Table 2 of SIO's application and Table 1 here for non-listed cetacean species, NMFS believes that the estimated take numbers are small relative to the stock sizes for these species (i.e., no more than 0.4 percent of any species).

Only two of the five pinniped species discussed in Section III of SIO's application the northern fur seal and the northern elephant seal are likely to occur in the offshore and slope waters (where 12 of the 16 OBSs are located) in numbers greater than a few stray individuals. The other three species of pinnipeds known to occur regularly off Oregon and Washington the California sea lion, Steller sea lion, and harbor seal likely would not be found at the OBS locations, or could be found only at the inshore locations, because they are coastal, usually staying within approximately 20 km (12.4 mi) of the coast (see Section III of SIO's application). A best estimate of three northern fur seals, one harbor seal, and one Steller sea lion could be exposed to airgun sounds with received levels ≥160 dB re 1 μPa (rms). Numbers of sightings of the other two species that could occur in the study area were too low to warrant density estimates. The numbers for which “take authorization” is requested, given in the far right column of Table 4 of SIO's application and Table 1 here, are for the average or (for the northern fur seal) the maximum estimate. The estimated numbers of pinnipeds that may be exposed to received levels ≥160 dB are probably overestimates of the actual numbers that will be affected significantly. Less than 0.01 percent of northern fur seals and harbor seals are expected to be affected.

Potential Effects on Habitat

The proposed seismic surveys will not result in any permanent impact on habitats used by marine mammals or to the food sources they use. The main impact issue associated with the proposed activity will be temporarily elevated noise levels and the associated direct effects on marine mammals, as discussed above.

One of the reasons for the adoption of airguns as the standard energy source for marine seismic surveys was that, unlike explosives, they do not result in any appreciable fish kill. However, the existing body of information relating to the impacts of seismic surveys on marine fish (see Appendix B of SIO's application) and invertebrate species is very limited. The various types of potential effects of exposure to seismic on fish and invertebrates can be considered in three categories: (1) pathological, (2) physiological, and (3) behavioral. Pathological effects include lethal and sub-lethal damage to the animals, physiological effects include temporary primary and secondary stress responses, and behavioral effects refer to changes in exhibited behavior of the fish and invertebrates. The three categories are interrelated in complex ways. For example, it is possible that certain physiological and behavioral changes could potentially lead to the ultimate pathological effect on individual animals (i.e., mortality).

Available information on the impacts of seismic surveys on marine fish and invertebrates provides limited insight on the effects only at the individual level. Ultimately, the most important knowledge in this area relates to how significantly seismic affects animal populations.

The following sections provide an overview of the information that exists on the effects of seismic surveys on fish and invertebrates. The information comprises results from scientific studies of varying degrees of soundness and some anecdotal information.

Pathological Effects - In water, acute injury and death of organisms exposed to seismic energy depends primarily on two features of the sound source: (1) the received peak pressure, and (2) the time required for the pressure to rise and decay (Hubbs and Rechnitzer, 1952 in Wardle et al., 2001). Generally, the higher the received pressure and the less time it takes for the pressure to rise and decay, the greater the chance of acute pathological effects. Considering the peak pressure and rise/decay time characteristics of seismic airgun arrays used today, the pathological zone for fish and invertebrates would be expected to be within a few meters of the seismic source (Buchanan et al., 2004). For the proposed survey, any injurious effects on fish would be limited to very short distances, especially considering the small source planned for use in this project (one 45-in3 GI gun). Numerous other studies provide examples of no fish mortality upon exposure to seismic sources (Falk and Lawrence, 1973; Holliday et al., 1987; La Bella et al., 1996; Santulli et al., 1999; McCauley et al., 2000a, 2000b, 2003; Bjarti, 2002; Hassel et al., 2003; Popper et al., 2005).

Little is known about the mechanisms and characteristics of damage to fish that may be inflicted by exposure to seismic survey sounds. Few data have been presented in the peer-reviewed scientific literature. There are two valid papers with proper experimental methods, controls, and careful pathological investigation implicating sounds produced by actual seismic survey airguns with adverse anatomical effects. One such study indicated anatomical damage and the second indicated TTS in fish hearing. McCauley et al. (2003) found that exposure to airgun sound caused observable anatomical damage to the auditory maculae of “pink snapper” (Pagrus auratus). This damage in the ears had not been repaired in fish sacrificed and examined almost two months after exposure. On the other hand, Popper et al. (2005) documented only TTS (as determined by auditory brainstem response) in two of three fishes from the Mackenzie River Delta. This study found that broad whitefish (Coreogonus nasus) that received a sound exposure level of 177 dB re 1 μPa².s showed no hearing loss. During both studies, the repetitive exposure to sound was greater than would have occurred during a typical seismic survey. However, the substantial low-frequency energy produced by the airgun arrays [less than approximately 400 Hz in the study by McCauley et al. (2003) and less than approximately 200 Hz in Popper et al. (2005)] likely did not propagate to the fish because the water in the study areas was very shallow (approximately 9 m, 29.5 ft, in the former case and <2 m, 6.6 ft, in the latter). Water depth sets a lower limit on the lowest sound frequency that will propagate (the “cutoff frequency”) at about one-quarter wavelength (Urick, 1983; Rogers and Cox, 1988).

Except for these two studies, at least with airgun-generated sound treatments, most contributions rely on rather subjective assays such as fish “alarm” or “startle response” or changes in catch rates by fishers. These observations are important in that they attempt to use the levels of exposures that are likely to be encountered by most free-ranging fish in actual survey areas. However, the associated sound stimuli are often poorly described, and the biological assays are varied (Hastings and Popper, 2005).

Some studies have reported that mortality of fish, fish eggs, or larvae can occur close to seismic sources (Kostyuchenko, 1973; Dalen and Knutsen, 1986; Booman et al., 1996; Dalen et al., 1996). Some of the reports claimed seismic effects from treatments quite different from actual seismic survey sounds or even reasonable surrogates. Saetre and Ona (1996) applied a ‘worst-case scenario’ mathematical model to investigate the effects of seismic energy on fish eggs and larvae and concluded that mortality rates caused by exposure to seismic are so low compared to natural mortality that the impact of seismic surveying on recruitment to a fish stock must be regarded as insignificant.

For the single GI gun planned for the proposed program, the pathological (mortality) zone for crustaceans and cephalopods is expected to be within a few meters of the seismic source; however, very few specific data are available on levels of seismic signals that might damage these animals. This premise is based on the peak pressure and rise/decay time characteristics of seismic airgun arrays currently in use around the world.

Some studies have suggested that seismic survey sound has a limited pathological impact on early developmental stages of crustaceans (Pearson et al., 1994; Christian et al., 2003; DFO, 2004). However, the impacts appear to be either temporary or insignificant compared to what occurs under natural conditions. Controlled field experiments on adult crustaceans (Christian et al., 2003, 2004; DFO, 2004) and adult cephalopods (McCauley et al., 2000a,b) exposed to seismic survey sound have not resulted in any significant pathological impacts on the animals. It has been suggested that exposure to commercial seismic survey activities has injured giant squid (Guerra et al., 2004), but there is no evidence to support such claims.

Physiological Effects - Biochemical responses by marine fish and invertebrates to acoustic stress have also been studied, although in a limited way. Studying the variations in the biochemical parameters influenced by acoustic stress might give some indication of the extent of the stress and perhaps forecast eventual detrimental effects. Such stress could potentially affect animal populations by reducing reproductive capacity and adult abundance and increasing mortality.

Stress indicators in the haemolymph of adult male snow crabs were monitored after exposure of the animals to seismic energy (Christian et al., 2003, 2004) and at various intervals after exposure. No significant acute or chronic differences between exposed and unexposed animals were found in the stress indicators (e.g., proteins, enzymes, cell type count).

Primary and secondary stress responses of fish after exposure to seismic energy all appear to be temporary in any studies done to date (Sverdrup et al., 1994; McCauley et al., 2000a,b). The periods necessary for these biochemical changes to return to normal are variable depending on numerous aspects of the biology of the species and of the sound stimulus. See Appendix B of SIO's application for more information on the effects of airgun sounds on marine fish.

Summary of Physical (Pathological and Physiological) Effects - As indicated in the preceding general discussion, there is a relative lack of knowledge about the potential physical (pathological and physiological) effects of seismic energy on marine fish and invertebrates. Available data suggest that there may be physical impacts on egg, larval, juvenile, and adult stages at very close range. Considering typical source levels associated with commercial seismic arrays, close proximity to the source would result in exposure to very high energy levels. Again, this study will employ a sound source that will generate low energy levels. Whereas egg and larval stages are not able to escape such exposures, juveniles and adults most likely would avoid it. In the case of eggs and larvae, it is likely that the numbers adversely affected by such exposure would not be that different from those succumbing to natural mortality. Limited data regarding physiological impacts on fish and invertebrates indicate that these impacts are short term and are most apparent after exposure at close range.

The proposed seismic program for 2007 is predicted to have negligible to low physical effects on the various life stages of fish and invertebrates for its short duration (approximately 2 hours at each of 16 sites off the coast of Oregon) and approximately 21-km (13-mi) extent. Therefore, physical effects of the proposed program on the fish and invertebrates would be not significant.

Behavioral Effects - Because of the apparent lack of serious pathological and physiological effects of seismic energy on marine fish and invertebrates, most concern now centers on the possible effects of exposure to seismic surveys on the distribution, migration patterns, mating, and catchability of fish. There is a need for more information on exactly what effects such sound sources might have on the detailed behavior patterns of fish and invertebrates at different ranges.

Studies investigating the possible effects of seismic energy on fish and invertebrate behavior have been conducted on both uncaged and caged animals (Chapman and Hawkins, 1969; Pearson et al., 1992; Santulli et al., 1999; Wardle et al., 2001; Hassel et al., 2003). Typically, in these studies fish exhibited a sharp “startle” response at the onset of a sound followed by habituation and a return to normal behavior after the sound ceased.

There is general concern about potential adverse effects of seismic operations on fisheries, namely a potential reduction in the “catchability” of fish involved in fisheries. Although reduced catch rates have been observed in some marine fisheries during seismic testing, in a number of cases the findings are confounded by other sources of disturbance (Dalen and Raknes, 1985; Dalen and Knutsen, 1986; Lokkeborg, 1991; Skalski et al., 1992; Engas et al., 1996). In other airgun experiments, there was no change in catch per unit effort of fish when airgun pulses were emitted, particularly in the immediate vicinity of the seismic survey (Pickett et al., 1994; La Bella et al., 1996). For some species, reductions in catch may have resulted from a change in behavior of the fish (e.g., a change in vertical or horizontal distribution) as reported in Slotte et al. (2004).

In general, any adverse effects on fish behavior or fisheries attributable to seismic testing may depend on the species in question and the nature of the fishery (season, duration, fishing method). They may also depend on the age of the fish, its motivational state, its size, and numerous other factors that are difficult, if not impossible, to quantify at this point, given such limited data on effects of airguns on fish, particularly under realistic at-sea conditions.

For marine invertebrates, behavioral changes could potentially affect such aspects as reproductive success, distribution, susceptibility to predation, and catchability by fisheries. Studies of squid indicated startle responses (McCauley et al., 2000a,b). In other cases, no behavioral impacts were noted (e.g., crustaceans in Christian et al., 2003, 2004; DFO, 2004). There have been anecdotal reports of reduced catch rates of shrimp shortly after exposure to seismic surveys; however, other studies have not observed any significant changes in shrimp catch rate (Andriguetto-Filho et al., 2005). Any adverse effects on crustacean and cephalopod behavior or fisheries attributable to seismic survey sound depend on the species in question and the nature of the fishery (season, duration, fishing method). Additional information regarding the behavioral effects of seismic on invertebrates is contained in Appendix C of SIO's application.

Summary of Behavioral Effects - As is the case with pathological and physiological effects of seismic on fish and invertebrates, available information is relatively scant and often contradictory. There have been well-documented observations of fish and invertebrates exhibiting behaviors that appeared to be responses to exposure to seismic energy (i.e., startle response, change in swimming direction and speed, and change in vertical distribution), but the ultimate importance of those behaviors is unclear. Some studies indicate that such behavioral changes are very temporary, whereas others imply that fish might not resume pre-seismic behaviors or distributions for a number of days. There appears to be a great deal of inter- and intra-specific variability. In the case of finfish, three general types of behavioral responses have been identified: startle, alarm, and avoidance. The type of behavioral reaction appears to depend on many factors, including the type of behavior being exhibited before exposure, and proximity and energy level of sound source.

During the proposed study, only a small fraction of the available habitat would be ensonified at any given time, and fish species would return to their pre-disturbance behavior once the seismic activity ceased. The proposed seismic program is predicted to have negligible to low behavioral effects on the various life stages of the fish and invertebrates during its short duration (approximately 2 hours at each of 16 sites off the coast of Oregon) and 21-km (31-mi) extent.Because of the reasons noted above and the nature of the proposed activities (small airgun and limited duration), the proposed operations are not expected to have any habitat-related effects that could cause significant or long-term consequences for individual marine mammals or their populations or stocks. Similarly, any effects to food sources are expected to be negligible.

Monitoring

Vessel-based marine mammal visual observers (MMVOs) will be based aboard the seismic source vessel and will watch for marine mammals and turtles near the vessel during all daytime GI gun operations and during start-ups of the gun at night. MMVOs will also watch for marine mammals and turtles near the seismic vessel for at least 30 minutes prior to the start of GI gun operations. When feasible, MMVOs will also make observations during daytime periods when the seismic system is not operating for comparison of animal abundance and behavior. Based on MMVO observations, the airgun will be shut down when marine mammals are observed within or about to enter a designated exclusion zone (EZ; safety radius). The EZ is a region in which a possibility exists of adverse effects on animal hearing or other physical effects.

MMVOs will be appointed by the academic institution conducting the research cruise, with NMFS Office of Protected Resources concurrence. At least one MMVO will monitor the EZ during daytime GI gun operations and any nighttime startups. MMVOs will normally work in shifts of 4 hours duration or less. The vessel crew will also be instructed to assist in detecting marine mammals and turtles.

The Wecoma is a suitable platform for marine mammal observations. Observing stations will be on the bridge wings, with observers' eyes approximately 6.5 m (21.3 ft) above the water line and a 180° view outboard from either side, on the whaleback deck in front of the bridge, with observers' eyes approximately 7.5 m (24.6 ft) above the waterline and an approximate 200° view forward, and on the aft control station, with observers' eyes approximately 5.5 m (18 ft) above the waterline and an approximate 180° view aft that includes the 40-m (131-ft; 180-dB) radius area around the GI gun. The eyes of the bridge watch will be at a height of approximately 6.5 m (21.3 ft). MMVOs will repair to the enclosed bridge during any inclement weather.

Standard equipment for MMVOs will be 7 x 50 reticule binoculars and optical range finders. At night, night-vision equipment will be available. Observers will be in wireless communication with ship officers on the bridge and scientists in the ship's operations laboratory, so they can advise promptly of the need for avoidance maneuvers or GI gun shut down.

MMVOs will record data to estimate the numbers of marine mammals exposed to various received sound levels and to document any apparent disturbance reactions. Data will be used to estimate the numbers of mammals potentially “taken” by harassment. It will also provide the information needed to order a shutdown of the GI gun when a marine mammal is within or near the EZ. When a mammal sighting is made, the following information about the sighting will be recorded:

(1) Species, group size, age/size/sex categories (if determinable), behavior when first sighted and after initial sighting, heading (if consistent), bearing and distance from seismic vessel, sighting cue, apparent reaction to the GI gun or seismic vessel (e.g., none, avoidance, approach, paralleling, etc.), and behavioral pace.

(2) Time, location, heading, speed, activity of the vessel (shooting or not), sea state, visibility, cloud cover, and sun glare.

The data listed under (2) will also be recorded at the start and end of each observation watch and during a watch, whenever there is a change in one or more of the variables.

All mammal observations and airgun shutdowns will be recorded in a standardized format. Data accuracy will be verified by the MMVOs at sea, and preliminary reports will be prepared during the field program and summaries forwarded to the operating institution's shore facility and to NSF weekly or more frequently. MMVO observations will provide the following information:

(1) The basis for decisions about shutting down the GI gun.

(2) Information needed to estimate the number of marine mammals potentially “taken” by harassment, which must be reported to NMFS.

(3) Data on the occurrence, distribution, and activities of marine mammals in the area where the seismic study is conducted.

(4) Data on the behavior and movement patterns of marine mammals seen at times with and without seismic activity.

Mitigation

Mitigation and monitoring measures proposed to be implemented for the proposed seismic survey have been developed and refined during previous SIO and L-DEO seismic studies and associated EAs, IHA applications, and IHAs. The mitigation and monitoring measures described herein represent a combination of the procedures required by past IHAs for other SIO and L-DEO projects. The measures are described in detail below.

The number of individual animals expected to be approached closely during the proposed activity will be small in relation to regional population sizes. With the proposed monitoring and shut-down provisions (see below), any effects on individuals are expected to be limited to behavioral disturbance and will have only negligible impacts on the species and stocks.

Mitigation measures that will be adopted will include (1) vessel speed or course alteration, provided that doing so will not compromise operational safety requirements, (2) GI gun shut down, and (3) minimizing approach to slopes and submarine canyons, if possible, because of sensitivity of beaked whales. Two other standard mitigation measures airgun array power down and airgun array ramp up are not possible because only one, low-volume GI gun will be used for the surveys.

Speed or Course Alteration - If a marine mammal is detected outside the EZ but is likely to enter it based on relative movement of the vessel and the animal, then if safety and scientific objectives allow, the vessel speed and/or direct course will be adjusted to minimize the likelihood of the animal entering the EZ. Major course and speed adjustments are often impractical when towing long seismic streamers and large source arrays, but are possible in this case because only one GI gun and a short (300-m, 984-ft) streamer will be used. If the animal appears likely to enter the EZ, further mitigative actions will be taken, i.e. either further course alterations or shut down of the airgun.

Shut-down Procedures - If a marine mammal is within or about to enter the EZ for the single GI gun, it will be shut down immediately. Following a shut down, GI gun activity will not resume until the marine mammal is outside the EZ for the full array. The animal will be considered to have cleared the EZ if it: (1) visually observed to have left the EZ; (2) has not been seen within the EZ for 15 minutes in the case of small odontocetes and pinnipeds; or (3) has not been seen within the EZ for 30 minutes in the case of mysticetes and large odontocetes, including sperm, pygmy sperm, dwarf sperm, and beaked whales.

Minimize Approach to Slopes and Submarine Canyons - Although sensitivity of beaked whales to airguns is not known, they appear to be sensitive to other sound sources (mid-frequency sonar; see section IV of SIO's application). Beaked whales tend to concentrate in continental slope areas and in areas where there are submarine canyons. Avoidance of airgun operations over or near submarine canyons has become a standard mitigation measure, but there are none within or near the study area. Four of the 16 OBS locations are on the continental slope, but the GI gun is low volume (45 in³), and it will operate only a short time (approximately 2 hours) at each location.

Reporting

A report will be submitted to NMFS within 90 days after the end of the cruise. The report will describe the operations that were conducted and the marine mammals that were detected near the operations. The report will be submitted to NMFS, providing full documentation of methods, results, and interpretation pertaining to all monitoring. The 90-day report will summarize the dates and locations of seismic operations, all marine mammal sightings (dates, times, locations, activities, associated seismic survey activities), and estimates of the amount and nature of potential “take” of marine mammals by harassment or in other ways.

ESA

Under section 7 of the ESA, the NSF has begun informal consultation on this proposed seismic survey. NMFS will also consult informally on the issuance of an IHA under section 101(a)(5)(D) of the MMPA for this activity. Consultation will be concluded prior to a determination on the issuance of the IHA.

National Environmental Policy Act (NEPA)

NSF prepared an Environmental Assessment of a Planned Low-Energy Marine Seismic Survey by the Scripps Institution of Oceanography in the Northeast Pacific Ocean, September 2007. NMFS will either adopt NSF's EA or conduct a separate NEPA analysis, as necessary, prior to making a determination on the issuance of the IHA.

Preliminary Determinations

NMFS has preliminarily determined that the impact of conducting the seismic survey in the northeast Pacific Ocean may result, at worst, in a temporary modification in behavior (Level B Harassment) of small numbers of eight species of marine mammals. Further, this activity is expected to result in a negligible impact on the affected species or stocks. The provision requiring that the activity not have an unmitigable adverse impact on the availability of the affected species or stock for subsistence uses does not apply for this proposed action.

For reasons stated previously in this document, this determination is supported by: (1) the likelihood that, given sufficient notice through relatively slow ship speed, marine mammals are expected to move away from a noise source that is annoying prior to its becoming potentially injurious; (2) the fact that marine mammals would have to be closer than either 35 m (115 ft) in intermediate depths or 23 m (75.5 ft) in deep water from the vessel to be exposed to levels of sound (180 dB) believed to have even a minimal chance of causing TTS; and (3) the likelihood that marine mammal detection ability by trained observers is high at that short distance from the vessel. As a result, no take by injury or death is anticipated and the potential for temporary or permanent hearing impairment is very low and will be avoided through the incorporation of the proposed mitigation measures.

While the number of potential incidental harassment takes will depend on the distribution and abundance of marine mammals in the vicinity of the survey activity, the number of potential harassment takings is estimated to be small, less than a few percent of any of the estimated population sizes, and has been mitigated to the lowest level practicable through incorporation of the measures mentioned previously in this document.

Proposed Authorization

As a result of these preliminary determinations, NMFS proposes to issue an IHA to SIO for conducting a low-energy seismic survey in the Pacific Ocean during September, 2007, provided the previously mentioned mitigation, monitoring, and reporting requirements are incorporated.