Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey off the Central Coast of California, November to December, 2012
Notice; Proposed Incidental Harassment Authorization; Request For Comments.
NMFS has received an application from the Lamont-Doherty Earth Observatory of Columbia University (L-DEO), in cooperation with the Pacific Gas and Electric Company (PG&E), for an Incidental Harassment Authorization (IHA) to take marine mammals, by harassment, incidental to conducting a marine geophysical (seismic) survey off the central coast of California, November to December, 2012. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an IHA to L-DEO and PG&E to incidentally harass, by Level B harassment only, 25 species of marine mammals during the specified activity.
Table of Contents Back to Top
- FOR FURTHER INFORMATION CONTACT:
- SUPPLEMENTARY INFORMATION:
- Summary of Request
- Description of the Proposed Specified Activity
- Project Purpose
- Survey Details
- Vessel Movements
- Mobilization and Demobilization
- Offshore Survey Operations
- Vessel Specifications
- Acoustic Source Specifications
- Seismic Airguns
- Hydrophone Streamer
- Metrics Used in This Document
- Characteristics of the Airgun Pulses
- Predicted Sound Levels for the Airguns
- Multibeam Echosounder
- Sub-Bottom Profiler
- Nearshore and Onshore Survey Operations
- Dates, Duration, and Specified Geographic Region
- Description of the Marine Mammals in the Area of the Proposed Specified Activity
- Potential Effects on Marine Mammals
- Behavioral Disturbance
- Hearing Impairment and Other Physical Effects
- Potential Effects of Other Acoustic Devices
- Multibeam Echosounder
- Sub-Bottom Profiler
- Vessel Movement and Collisions
- Anticipated Effects on Marine Mammal Habitat
- Anticipated Effects on Fish
- Anticipated Effects on Invertebrates
- Proposed Mitigation
- Use of a Small-Volume Airgun During Turns and Maintenance
- Nighttime Survey Areas
- Harbor Porpoise Mitigation, Monitoring, and Adaptive Management Plan
- Proposed Monitoring and Reporting
- Proposed Monitoring
- Aerial Surveys
- Vessel-Based Visual Monitoring
- Vessel-Based Passive Acoustic Monitoring
- PSO Data and Documentation
- Estimated Take by Incidental Harassment
- Encouraging and Coordinating Research
- Negligible Impact Determination
- Impact on Availability of Affected Species or Stock for Taking for Subsistence Uses
- Endangered Species Act
- National Environmental Policy Act
- Proposed Authorization
- Information Solicited
Tables Back to Top
- Table 3—Estimated Densities of Marine Mammal Species in the Proposed Survey Off the Central Coast of California, November to December, 2012
- Table 4—Survey Areas and Survey Areas With 160 d B Buffer Zone
- Table 5—Estimates of the Possible Numbers of Marine Mammals Exposed to Sound Levels ≥160 d B during L-DEO and PG&E's Proposed Seismic Surveys Off the Central Coast of California During November to December, 2012
DATES: Back to Top
Comments and information must be received no later than October 15, 2012.
ADDRESSES: Back to Top
Comments on the application should be addressed to P. Michael Payne, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910. The mailbox address for providing email comments is ITP.Goldstein@noaa.gov. NMFS is not responsible for email comments sent to addresses other than the one provided here. Comments sent via email, including all attachments, must not exceed a 10-megabyte file size.
All comments received are a part of the public record and will generally be posted to http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications without change. All Personal Identifying Information (for example, name, address, etc.) voluntarily submitted by the commenter may be publicly accessible. Do not submit confidential business information or otherwise sensitive or protected information.
A copy of the application containing a list of the references used in this document may be obtained by writing to the above address, telephoning the contact listed here (see FOR FURTHER INFORMATION CONTACT) or visiting the internet at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications.
The National Science Foundation (NSF), which owns the R/V Marcus G. Langseth, has prepared a draft “Environmental Assessment Pursuant to the National Environmental Policy Act, 42 U.S.C. 4321 et seq. Marine Seismic Survey in the Pacific Ocean off Central California, 2012” (EA). NSF's EA incorporates a draft “Environmental Assessment of Marine Geophysical Surveys by the R/V Marcus G. Langseth for the Central California Seismic Imaging Project,” prepared by Padre Associates, Inc., on behalf of NSF, PG&E, and L-DEO, which is also available at the same internet address. Documents cited in this notice may be viewed, by appointment, during regular business hours, at the aforementioned address.
FOR FURTHER INFORMATION CONTACT: Back to Top
Howard Goldstein or Jolie Harrison, Office of Protected Resources, NMFS, 301-427-8401.
SUPPLEMENTARY INFORMATION: Back to Top
Background Back to Top
Section 101(a)(5)(D) of the MMPA, as amended (16 U.S.C. 1371(a)(5)(D)), directs the Secretary of Commerce (Secretary) to authorize, upon request, the incidental, but not intentional, taking of small numbers of marine mammals of a species or population stock, by United States citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and, if the taking is limited to harassment, a notice of a proposed authorization is provided to the public for review.
Authorization for the incidental taking of small numbers of marine mammals shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), and will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant). The authorization must set forth the permissible methods of taking, other means of effecting the least practicable adverse impact on the species or stock and its habitat, and requirements pertaining to the mitigation, monitoring and reporting of such takings. NMFS has defined “negligible impact” in 50 CFR 216.103 as “* * * an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.”
Section 101(a)(5)(D) of the MMPA established an expedited process by which citizens of the United States can apply for an authorization to incidentally take small numbers of marine mammals by harassment. Section 101(a)(5)(D) of the MMPA establishes a 45-day time limit for NMFS's review of an application followed by a 30-day public notice and comment period on any proposed authorizations for the incidental harassment of small numbers of marine mammals. Within 45 days of the close of the public comment period, NMFS must either issue or deny the authorization.
Except with respect to certain activities not pertinent here, the MMPA defines “harassment” as: Any act of pursuit, torment, or annoyance which (i) has the potential to injure a marine mammal or marine mammal stock in the wild [Level A harassment]; or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering [Level B harassment].
Summary of Request Back to Top
On May 17, 2012, NMFS received an application from the L-DEO and PG&E requesting that NMFS issue an IHA for the take, by Level B harassment only, of small numbers of marine mammals incidental to conducting a marine seismic survey within the U.S. Exclusive Economic Zone off the central coast of California during November to December, 2012. NMFS received a revised application on August 31, 2012. The updated IHA application reflects revisions to the proposed project that have resulted from discussions between NMFS and the applicant during the MMPA consultation process, as well as other Federal and State regulatory requirements and include the elimination of portions of the originally planned survey area (specifically Survey Box 3) and the splitting of the proposed project into two years, and the shortening of the 2012 work window to November and December. Additionally, PG&E has agreed to operationally and financially support the design and implementation of a comprehensive monitoring, stranding response, and adaptive management plan that will support real-time decision making to reduce impacts to the Morro Bay stock of harbor porpoises (Phocoena phocoena). L-DEO and PG&E plan to use one source vessel, the R/V Marcus G. Langseth (Langseth) and a seismic airgun array to collect seismic data as part of the “Offshore Central Coastal California Seismic Imaging Project” located in the central area of San Luis Obispo County, California.
PG&E proposes to conduct a high energy seismic survey in the vicinity of the Diablo Canyon Power Plant and known offshore fault zones near the power plant. The observations will be interpreted in the context of global synthesis of observations bearing on earthquake rupture geometries, earthquake displacements, fault interactions, and fault evolution. Estimating the limits of future earthquake ruptures is becoming increasingly important as seismic hazard maps are based on geologists' maps of active faults and, locally, the Hosgri Fault strikes adjacent to one of California's major nuclear power plants. In addition to the proposed operations of the seismic airgun array and hydrophone streamer, L-DEO and PG&E intend to operate a multibeam echosounder and a sub-bottom profiler continuously throughout the survey.
Acoustic stimuli (i.e., increased underwater sound) generated during the operation of the seismic airgun array may have the potential to cause a behavioral disturbance for marine mammals in the survey area. This is the principal means of marine mammal taking associated with these activities and L-DEO and PG&E have requested an authorization to take 25 species of marine mammals by Level B harassment. Take is not expected to result from the use of the multibeam echosounder or sub-bottom profiler, for reasons discussed in this notice; nor is take expected to result from collision with the source vessel because it is a single vessel moving at a relatively slow speed (4.6 knots [kts]; 8.5 kilometers per hour [km/hr]; 5.3 miles per hour [mph]) during seismic acquisition within the survey, for a relatively short period of time (approximately 50 days). It is likely that any marine mammal would be able to avoid the vessel.
Description of the Proposed Specified Activity Back to Top
PG&E proposes to conduct a high energy seismic survey in the vicinity of the Diablo Canyon Power Plant and known offshore fault zones near the power plant (see Figure 1 of the IHA application). The project, as proposed by L-DEO and PG&E, consists of deploying seismic or sound sources and receivers at onshore and offshore locations to generate data that can be used to improve imaging of major geologic structures and fault zones in the vicinity of the Diablo Canyon Power Plant. The details of the proposed seismic studies are outlined in a Science Plan submitted to the National Science Foundation (NSF) by L-DEO, University of Nevada, and Scripps Institution of Oceanography. NSF, as owner of the Langseth will serve as the lead Federal agency and will ensure the approval of the proposed Science Plan is in compliance with the National Environmental Policy Act (NEPA) of 1969.
These seismic studies would provide additional insights of any relationships or connection between the known faults as well as enhance knowledge of offshore faults in proximity to the central coast of California and the Diablo Canyon Power Plant. The proposed deep penetrating (10 to 15 kilometers [km] or 6 to 9 miles [mi]), high energy seismic survey (energy greater than 2 kilo Joule) would complement a previously completed shallow (less than 1 km [0.6 mi]), low energy (less than 2 kilo Joule) three-dimensional (3D) seismic reflection survey.
The objectives of the proposed high energy 3D seismic survey are to:
- Record high resolution two-dimensional (2D) and 3D seismic reflection profiles of major geologic structures and fault zones in the vicinity of the central coast of California and Diablo Canyon Power Plant.
- Obtain high-resolution deep-imaging (greater than 1 km [0.6 mi]) of the Hosgri and Shoreline fault zones in the vicinity of the Diablo Canyon Power Plant to constrain fault geometry and slip rate (scheduled for the seismic survey activities in 2013).
- Obtain high-resolution, deep-imaging of the intersection of the Hosgri and Shoreline fault zones near Point Buchon.
- Obtain high-resolution, deep-imaging of the geometry and slip rate of the Los Osos fault, as well as the intersection of the Hosgri and Los Osos fault zones in Estero Bay.
- Augment the current regional seismic database for subsequent use and analysis through the provision of all data to the broader scientific and safety community.
The studies require the collection of data over a long period of time. However, the project timeframe is limited to fall and winter months to minimize environmental impacts to the greatest extent feasible. L-DEO and PG&E are proposing to conduct the studies 24 hours a day for 7 days a week. This schedule is designed to reduce overall air emissions, length of time for operation in the water thereby reducing impacts to marine wildlife, commercial fishing, and other area users. PG&E will work with environmental agencies to appropriately address the balancing of public health and safety and environmental concerns during the conduct of these studies.
The proposed survey involves both marine (offshore) and land (onshore) activities. The offshore components consist of operating a seismic survey vessel and support/monitoring vessels within the areas shown in Figure 1 of the IHA application and transiting between the four different survey box areas extending between the mouth of the Santa Maria River and Estero Bay. The seismic survey vessel would tow a series of sound-generating airguns and sound-recording hydrophones along pre-determined shore parallel and shore-perpendicular transects to conduct deep (10 to 15 km [6 to 9 mi]) seismic reflection profiling of major geologic structures and fault zones in the vicinity of the Diablo Canyon Power Plant.
The offshore part of the survey activities include the placement of a limited number of seafloor geophones (e.g., Fairfield Z700 nodal units) into nearshore waters.
The planned seismic survey (e.g., equipment testing, startup, line changes, repeat coverage of any areas, and equipment recovery) will consist of approximately 3,565.8 km (1,925.4 nmi) (1,417.6 km [765.4 nmi] for Survey Box 4 and 2,148.2 km [1,159.9 nmi] for Survey Box 2) of transect lines (including turns) in the survey area off the central coast of California (see Figure 2 of the IHA application). In addition to the operations of the airgun array, a Kongsberg EM 122 multibeam echosounder and Knudsen Chirp 3260 sub-bottom profiler will also be operated from the Langseth continuously throughout the cruise. There will be additional seismic operations associated with equipment testing, ramp-up, and possible line changes or repeat coverage of any areas where initial data quality is sub-standard. In L-DEO and PG&E's estimated take calculations, 25% has been added for those additional operations. Detailed descriptions of the proposed actions for each component are provided below in this document.
The tracklines for the 3D seismic survey will encompass an area of approximately 740.52 km  (215.9 square nautical miles [nmi  ]). The 2012 project area is divided into two “primary target areas” (Survey Boxes 2 and 4) are described below and shown in Figure 2 of the IHA application. The offshore (vessel) survey would be conducted in both Federal and State waters and water depths within the proposed survey areas ranging from 0 to over 400 m (1,300 ft). The State Three-Mile Limit is identified in Figure 1 of the IHA application. The Point Buchon Marine Protected Area lies within portions of the survey area. In addition, the Monterey Bay National Marine Sanctuary, a Federally-protected marine sanctuary that extends northward from Cambria to Marine County, is located to the north and outside of the proposed project area.
Survey Box 2 (Survey area from Estero Bay to offshore Santa Maria River Mouth):
- Area: 406.04 km  (118.4 nmi  );
- Total survey line length is 2,148.2 km (1,159.9 nmi); and
- Strike line surveys along the Hosgri fault zone and Shoreline, Hosgri, and Los Osos fault intersections.
Survey Box 4 (Estero Bay):
- Area: 334.48 km  (97.5 nmi  );
- Total survey line length is 1,417.6 km (765.4 nmi);
- Dip line survey across the Hosgri and Los Osos fault zones in Estero Bay.
Figure 2 of the IHA application depicts the proposed survey transit lines. These lines depict the survey lines as well as the turning legs. The full seismic array is firing during the straight portions of the track lines as well as the initial portions of the run-out (offshore) sections and later portions of the run-in (inshore) sections. During turns and most of the initial portion of the run-ins, there will only be one airgun firing (i.e., mitigation airgun). Assuming a daily survey rate of approximately 8.3 km/hour (km/hr) (4.5 knots [kts] for 24/7 operations), the Survey Box 2 is expected to take approximately 14 days and approximately 9.25 days for Survey Box 4. When considering mobilization, demobilization, refueling, equipment maintenance, weather, marine mammal activity, and other contingencies, the proposed survey is expected to be completed in 49.25 days.
Mobilization and Demobilization
The offshore equipment and vessels for the proposed 3D marine seismic survey are highly specialized and typically no seismic vessels are located in California. The proposed seismic survey vessel (R/V Marcus G. Langseth) is currently operating on the U.S. west coast and is available to conduct the proposed seismic survey work.
The Langseth would transit south prior to the start of survey operations (approximately October 15 through December 31, 2012, with active airgun survey operations starting approximately November 1, 2012). Once the vessel has arrived in the project area, the survey crew, any required equipment, and support provisions would be transferred to the vessel. Larger equipment, if required, would need to be loaded onboard the vessel at either Port of San Francisco/Oakland or Port Hueneme. The proposed survey vessel is supported by two chase/scout boats, each with three Protected Species Observers (PSOs) and a third support boat that will provide logistical support to the Langseth or chase boats. This support vessel will also serve as a relief vessel for either of the two chase boats as required or equivalent. Any additional scout/monitoring vessels required for the proposed project will be drawn from local vessel operators. Upon completion of the offshore survey operations, the survey crew would be transferred to shore and the survey vessel would transit out to the proposed project area.
Nearshore operations would be conducted using locally available vessels such as the M/V Michael Uhl (Michael Uhl) or equivalent vessel. Equipment, including the geophones and cables, would be loaded aboard the Michael Uhl in Morro Bay Harbor and transferred to the offshore deployment locations. Following deployment and recovery of the geophones and cables, they would be transferred back to Morro Bay Harbor for transport offsite.
During onshore operations, receiver line equipment would be deployed by foot-based crews supported by four-wheel drive vehicles or small vessel. Once the proposed project has been completed, the equipment would demobilize from the area by truck.
Offshore Survey Operations
The proposed offshore seismic survey would be conducted with vessels specifically designed and built to conduct such surveys. PG&E has selected the Langseth, which is operated by L-DEO. The following outlines the general specifications for the Langseth and the support vessels needed to complete the proposed offshore seismic survey.
In water depths from 30 to 305 m (100 to greater than 1,000 ft), the Langseth will tow four hydrophone streamers with a length of approximately 6 km (3.2 nmi). The intended tow depth of the streamers is approximately 9 m (29.5 ft). Flotation is provided on each streamer as well as streamer recovery devices. The streamer recovery devices are activated when the streamer sinks to a pre-determined depth (e.g., 50 m [164 ft]) to aid in recovery.
- Primary vessel—the Langseth is 71.5 m (235 ft) in length, and is outfitted to deploy/retrieve hydrophone streamers and airgun array, air compressors for the airgun array, and survey recording facilities.
- Two Chase/Scout boats—22.9 to 41.2 m (75 to 135 ft) in length and will be around the Langseth to observe potential obstructions, conduct additional marine mammal monitoring and support deployment of seismic equipment.
- Third support vessel-will be approximately 18.3 to 25.9 m (60 to 85 ft) in length and would act as a support boat for the Langseth and the two other chase/scout and would provide relief to either chase/scout boat as required.
- A nearshore work vessel (e.g., Michael Uhl) approximately 50 m (150 ft) in length would be used to deploy and retrieve seafloor geophones in the shallow water (0 to 20 m) zone.
- Monitoring aircraft—Partenavia P68-OBS “Observer,” a high-wing, twin-engine plane or equivalent aircraft is 9.5 m (31 ft) in length and has a wingspan of 12 m (39 ft) with a carrying capacity of six persons. The aircraft has two “bubble” observation windows, a glass nose for clear observation, and will be equipped with communication and safety equipment sufficient to support the proposed operations. The aircraft would be used to perform aerial surveys of marine mammals.
The Langseth, a seismic research vessel owned by the NSF, will tow the 36 airgun array, as well as the hydrophone streamer, along predetermined lines (see Figure 2 of the IHA application). When the Langseth is towing the airgun array and the hydrophone streamer, the turning rate of the vessel is limited to three degrees per minute (2.5 km [1.5 mi]). Thus, the maneuverability of the vessel is limited during operations with the streamer. The vessel would “fly” the appropriate U.S. Coast Guard-approved day shapes (mast head signals used to communicate with other vessels) and display the appropriate lighting to designate the vessel has limited maneuverability.
The vessel has a length of 71.5 m (235 ft); a beam of 17.0 m (56 ft); a maximum draft of 5.9 m (19 ft); and a gross tonnage of 3,834. The Langseth was designed as a seismic research vessel with a propulsion system designed to be as quiet as possible to avoid interference with the seismic signals emanating from the airgun array. The ship is powered by two 3,550 horsepower (hp) Bergen BRG-6 diesel engines which drive two propellers directly. Each propeller has four blades and the shaft typically rotates at 750 revolutions per minute. The vessel also has an 800 hp bowthruster, which is not used during seismic acquisition. The Langseth' s operation speed during seismic acquisition is typically 7.4 to 9.3 km per hour (hr) (km/hr) (4 to 5 knots [kts]). When not towing seismic survey gear, the Langseth typically cruises at 18.5 km/hr (10 kts). The Langseth has a range of 25,000 km (13,499 nmi) (the distance the vessel can travel without refueling).
The vessel also has an observation tower from which Protected Species Visual Observers (PSVO) will watch for marine mammals before and during the proposed airgun operations. When stationed on the observation platform, the PSVO's eye level will be approximately 21.5 m (71 ft) above sea level providing the PSVO an unobstructed view around the entire vessel. More details of the Langseth can be found in the IHA application.
Acoustic Source Specifications
The Langseth will deploy a 36-airgun array, consisting of two 18 airgun sub-arrays. Each sub-array will have a volume of approximately 3,300 cubic inches (in  ). The airgun array will consist of a mixture of Bolt 1500LL and Bolt 1900LLX airguns ranging in size from 40 to 360 in  , with a firing pressure of 1,900 pounds per square inch (psi). The 18 airgun sub-arrays will be configured as two identical linear arrays or “strings” (see Figure 3 and 4 of the IHA application). Each string will have 10 airguns, the first and last airguns in the strings are spaced 16 m (52.5 ft) apart. Of the 10 airguns, nine airguns in each string will be fired simultaneously (1,650 in  ), whereas the tenth is kept in reserve as a spare, to be turned on in case of failure of another airgun. The sub-arrays would be fired alternately during the survey. The two airgun sub-arrays will be distributed across an area of approximately 12 x 16 m (40 x 52.5 ft) behind the Langseth and will be towed approximately 140 m (459.3 ft) behind the vessel. Discharge intervals depend on both the ship's speed and Two Way Travel Time recording intervals. The shot interval will be 37.5 m (123) during the study. The shot interval will be relatively short, approximately 15 to 20 seconds (s) based on an assumed boat speed of 4.5 knots. During firing, a brief (approximately 0.1 s) pulse sound is emitted; the airguns will be silent during the intervening periods. The dominant frequency components range from two to 188 Hertz (Hz).
The tow depth of the airgun array will be 9 m (29.5 ft) during the surveys. Because the actual source is a distributed sound source (18 airguns) rather than a single point source, the highest sound measurable at any location in the water will be less than the nominal source level. In addition, the effective source level for sound propagating in near-horizontal directions will be substantially lower than the nominal omni-directional source level applicable to downward propagation because of the directional nature of the sound from the airgun array (i.e., sound is directed downward). Figure 3 of the IHA application shows one linear airgun array or “string” with ten airguns. Figure 4 of the IHA application diagrams the airgun array and streamer deployment from the Langseth.
Acoustic signals will be recorded using a system array of four hydrophone streamers, which would be towed behind the Langseth. Each streamer would consist of Sentry Solid Streamer Sercel cable approximately 6 km (3.2 nmi) long. The streamers are attached by floats to a diverter cable, which keeps the streamer spacing at approximately 100 to 150 m (328 to 492 ft) apart.
Seven hydrophones will be present along each streamer for acoustic measurement. The hydrophones will consist of a mixture of Sonardyne Transceivers. Each streamer will contain three groups of paired hydrophones, with each group approximately 2,375 m (7,800 ft) apart. The hydrophones within each group will be approximately 300 m (984 ft) apart. One additional hydrophone will be located on the tail buoy attached to the end of the streamer cable. In addition, one Sonardyne Transducer will be attached to the airgun array. Compass birds will be used to keep the streamer cables and hydrophones at a depth of approximately 10 m (32.8 ft). One compass bird will be placed at the front end of each streamer as well as periodically along the streamer. Figure 4 of the IHA application depicts the configuration of both the streamer and airgun array used by the Langseth. Details regarding the hydrophone streamer and acoustic recording equipment specifications are included in Table 1 of the IHA application.
Metrics Used in This Document
This section includes a brief explanation of the sound measurements frequently used in the discussions of acoustic effects in this document. Sound pressure is the sound force per unit area, and is usually measured in micropascals (μPa), where 1 pascal (Pa) is the pressure resulting from a force of one newton exerted over an area of one square meter. Sound pressure level (SPL) is expressed as the ratio of a measured sound pressure and a reference level. The commonly used reference pressure level in underwater acoustics is 1 μPa, and the units for SPLs are dB re: 1 μPa. SPL (in decibels [dB]) = 20 log (pressure/reference pressure).
SPL is an instantaneous measurement and can be expressed as the peak, the peak-peak (p-p), or the root mean square (rms). Root mean square, which is the square root of the arithmetic average of the squared instantaneous pressure values, is typically used in discussions of the effects of sounds on vertebrates and all references to SPL in this document refer to the root mean square unless otherwise noted. SPL does not take the duration of a sound into account.
Characteristics of the Airgun Pulses
Airguns function by venting high-pressure air into the water which creates an air bubble. The pressure signature of an individual airgun consists of a sharp rise and then fall in pressure, followed by several positive and negative pressure excursions caused by the oscillation of the resulting air bubble. The oscillation of the air bubble transmits sounds downward through the seafloor and the amount of sound transmitted in the near horizontal directions is reduced. However, the airgun array also emits sounds that travel horizontally toward non-target areas.
The nominal source levels of the airgun arrays used by L-DEO and PG&E on the Langseth are 236 to 265 dB re 1 μPa (p-p) and the rms value for a given airgun pulse is typically 16 dB re 1 μPa lower than the peak-to-peak value (Greene, 1997; McCauley et al., 1998, 2000a). The specific source output for the 18 airgun array is 252 dB (peak) and 259 dB (p-p). However, the difference between rms and peak or peak-to-peak values for a given pulse depends on the frequency content and duration of the pulse, among other factors.
Accordingly, L-DEO and PG&E have predicted the received sound levels in relation to distance and direction from the 18 airgun array and the single Bolt 1900LL 40 in  airgun, which will be used during power-downs. A detailed description of L-DEO and PG&E's modeling for this survey's marine seismic source arrays for protected species mitigation is provided in Appendix A of the IHA application and NSF's EA. Appendix A (GSI Technical Memorandum 470-3 and GSI Technical Memorandum 470-2RevB) of the IHA application and NSF's EA discusses the characteristics of the airgun pulses. NMFS refers the reviewers to the IHA application and EA documents for additional information.
Predicted Sound Levels for the Airguns
To determine exclusion zones for the airgun array to be used off the central coast of California, the noise modeling for the proposed 3D seismic survey is based on the results of mathematical modeling conducted by Greeneridge Sciences, Inc. (2011). The model results are based upon the airgun specifications provided for the Langseth and seafloor characteristics available for the project area. Specifically, L-DEO's predicted sound contours were used to estimate pulse sound level extrapolated to an effective distance of one meter, effectively reducing the multi-element array to a point source. Such a description is valid for descriptions of the far field sounds, i.e., at distances that are long compared to the dimensions of the array and the sound wavelength. Greeneridge Sciences, Inc. did not account for near-field effects. However, since the vast majority of acoustic energy radiated by an airgun array is below 500 Hz and the near field is small for the given airgun array at these frequencies (the radius of the near field around the array is 21 m [68.9 ft] or less for frequencies below 500 Hz), near-field effects are considered minimal.
The sound propagation from the airgun array was modeled in accordance with physical description of sound propagation and depends on waveguide characteristics, including water depth, water column sound velocity profile, and geoacoustic parameters of the ocean bottom. For the sound propagation model, Greeneridge Sciences, Inc. relied on variants of the U.S. Navy's range-dependent Acoustic Model. Greeneridge Sciences, Inc. modeled three 2D (range versus depth) propagation paths, each with range-dependent (i.e., range-varying) bathymetry and range-independent geoacoustic profiles. The resulting received sound levels at a receiver depth of 6 m (19.7 ft) and across range were then “smoothed” via least-squares regression. The monotonically-decreasing regression equations yielded the estimated safety radii.
The accuracy of the sound field predicted by the acoustic propagation model is limited by the quality and resolution of the available environmental data. Greeneridge Sciences, Inc. used environmental information provided by the client for the proposed survey area, specifically, bathymetry data, a series of measured water column sound speed profiles, and descriptive sediment and basement properties. Greeneridge Sciences, Inc. used two geoacoustic profiles for its three propagation paths: One for the upslope propagation path (sand overlaying sandstone) and one for the downslope and alongshore propagation paths (silt overlaying sandstone)
L-DEO and PG&E have used these calculated values to determine exclusion zones for the 18 airgun array and previously modeled measurements by L-DEO for the single airgun, to designate exclusion zones for purposes of mitigation, and to estimate take for marine mammals off the central coast of California. A detailed description of the modeling effort is provided in Appendix A of NSF's EA.
Using the model (airgun array and single airgun), Table 1 (below) shows the distances at which three rms sound levels are expected to be received from the 18 airgun array and a single airgun. To avoid the potential for injury or permanent physiological damage (Level A harassment), NMFS (1995, 2000) has concluded that cetaceans and pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding 180 dB re: 1 µPa and 190 dB re: 1 µPa, respectively. L-DEO and PG&E used these levels to establish the exclusion zones. If marine mammals are detected within or about to enter the appropriate exclusion zone, the airguns will be powered-down (or shut-down, if necessary) immediately. NMFS also assumes that marine mammals exposed to levels exceeding 160 dB re: 1 µPa may experience Level B harassment.
Table 1 summarizes the predicted distances at which sound levels (160, 180, and 190 dB [rms]) are expected to be received from the 18 airgun array and a single airgun operating in upslope (inshore), downslope (offshore), and alongshore depths. For the proposed project, L-DEO and PG&E plan to use the upslope distance (inshore) for the 160 dB (6,210 m [20,374 ft]) and 180 dB (1,010 m [3,313.7 ft], and alongshore distance for the 190 dB (320 m [1,049.9 ft]), for the determination of the buffer and exclusion zones since this represents the largest and therefore most conservative distances determined by the Greeneridge Sciences, Inc. modeling.
Table 1. Modeled (array) or predicted (single airgun) distances to which sound levels ≥ 190, 180, and 160 dB re: 1 μPa (rms) could be received in upslope, downslope, and alongshore propagation paths during the proposed survey off the central coast of California, November to December, 2012.
|Sound pressure level (SPL) (dB re 1 µPa)||Predicted RMS radii distances for 18 airgun array|
|Upslope distance (inshore)||Downslope distance (offshore)||Alongshore distance|
|190 dB||250 m (0.13 nmi)||280 m (0.15 nmi)||320 m (0.17 nmi)|
|180 dB||1,010 m (0.55 nmi)||700 m (0.38 nmi)||750 m (0.40 nmi)|
|160 dB||6,210 m (3.35 nmi)||4,450 m (2.40 nmi)||4,100 m (2.21 nmi)|
|Sound pressure level (SPL) (dB re 1 µPa)||Predicted RMS radii distances for single airgun|
|Shallow water (< 100 m)||Intermediate water (100 to 1,000 m)||Deep Water (> 1,000 m)|
|190 dB||150 m (0.08 nmi)||18 m (< 0.01 nmi)||12 m (< 0.01 nmi)|
|180 dB||296 m (0.16 nmi)||60 m (0.03 nmi)||40 m (0.02 nmi)|
|160 dB||1,050 m (0.57 nmi)||578 m (0.31 nmi)||385 m (0.21 nmi)|
Along with the airgun operations, two additional acoustical data acquisition systems will be operated from the Langseth continuously during the survey. The ocean floor will be mapped with the Kongsberg EM 122 multibeam echosounder and a Knudsen 320B sub-bottom profiler. These sound sources will be operated continuously from the Langseth throughout the cruise.
The Langseth will operate a Kongsberg EM 122 multibeam echosounder concurrently during airgun operations to map characteristics of the ocean floor. The hull-mounted multibeam echosounder emits brief pulses of sound (also called a ping) (10.5 to 13, usually 12 kHz) in a fan-shaped beam that extends downward and to the sides of the ship. The transmitting beamwidth is 1° or 2° fore-aft and 150° athwartship and the maximum source level is 242 dB re: 1 μPa.
Each ping consists of eight (in water greater than 1,000 m) or four (less than 1,000 m) successive, fan-shaped transmissions, each ensonifying a sector that extends 1° fore-aft. Continuous-wave pulses increase from 2 to 15 milliseconds (ms) long in water depths up to 2,600 m (8,350.2 ft), and frequency modulated (FM) chirp pulses up to 100 ms long are used in water greater than 2,600 m. The successive transmissions span an overall cross-track angular extent of about 150°, with 2 ms gaps between the pulses for successive sectors (see Table 2 of the IHA application).
The Langseth will also operate a Knudsen Chirp 320B sub-bottom continuously throughout the cruise simultaneously with the multibeam echosounder to map and provide information about the sedimentary features and bottom topography. The beam is transmitted as a 27° cone, which is directed downward by a 3.5 kHz transducer in the hull of the Langseth. The maximum output is 1 kilowatt (kW), but in practice, the output varies with water depth. The pulse interval is one second, but a common mode of operation is to broadcast five pulses at one second intervals followed by a 5-second pause.
Both the multibeam echosounder and sub-bottom profiler are operated continuously during survey operations. Given the relatively shallow water depths of the survey area (20 to 300 m [66 to 984 ft]), the number of pings or transmissions would be reduced from 8 to 4, and the pulse durations would be reduced from 100 ms to 2 to 15 ms for the multibeam echosounder. Power levels of both instruments would be reduced from maximum levels to account for water depth. Actual operating parameters will be established at the time of the survey.
NMFS expects that acoustic stimuli resulting from the proposed operation of the single airgun or the 18 airgun array has the potential to harass marine mammals. NMFS does not expect that the movement of the Langseth, during the conduct of the seismic survey, has the potential to harass marine mammals because of the relatively slow operation speed of the vessel (approximately 4.6 knots [kts]; 8.5 km/hr; 5.3 mph) during seismic acquisition.
The Langseth will employ a Bell Aerospace BGM-3 gravimeter system (see Figure 5 of the IHA application) to measure very tiny fractional changes within the Earth's gravity caused by nearby geologic structures, the shape of the Earth, and by temporal tidal variations. The gravimeter has been specifically designed to make precision measurements in a high motion environment. Precision gravity measurements are attained by the use of the highly accurate Bell Aerospace Model XI inertial grade accelerometer.
The Langseth will employ a Bell Aerospace BGM-3 geometer, which contains a model G-882 cesium-vapor marine magnetometer (see Figure 6 of the IHA application). Magnetometers measure the strength and/or direction of a magnetic field, generally in units of nanotesla in order to detect and map geologic formations. These data would enhance earlier marine magnetic mapping conducted by the U.S. Geologic Survey (Sliter et al., 2009).
The G-882 is designed for operation from small vessels for shallow water surveys as well as for the large survey vessels for deep tow applications. Power may be supplied from a 24 to 30 VDC battery power or a 110/220 VAC power supply. The standard G-882 tow cable includes a Vectran strength member and can be built to up to 700 m (2,297 ft) (no telemetry required). The shipboard end of the tow cable is attached to a junction box or onboard cable. Output data are recorded on a computer with an RS-232 serial port.
Both the gravimeter and magnetometers are “passive” instruments and do not emit sounds, impulses, or signals, and are not expected to affect marine mammals.
Nearshore and Onshore Survey Operations
To collect deep seismic data in water depths that are not accessible by the Langseth (less than 25 m [82 ft]), seafloor geophones and both offshore and onshore seismic sources will be used. The currently proposed locations for the seafloor geophone lines between Point Buchon and Point San Luis are shown in Figure 7 of the IHA application.
Twelve Fairfield Z700 marine nodes would be placed on the seafloor along two nearshore survey routes as a pilot test prior to the full deployment of 600 nodes scheduled for 2013. The northern route (Crowbar Beach) traverses the Point Buchon MPA north of Diablo Canyon Power Plant. The southern route (either Green Peak or Deer Canyon) is located south of the Diablo Canyon Power Plant. The approximate locations of the proposed nodal routes are depicted in Figure 7 of the IHA application. Six nodes would be placed at 500 m (1,640.4 ft) intervals along each route for a total length of 3 km (1.9 mi). Maximum water depth ranges from 70 m (229.7 ft) (Crowbar) to 30 m (98.4 ft) (Deer Canyon). Marine nodes would be deployed using a vessel and (in some locations) divers and will be equipped with ultra-short baseline acoustic tracking system to position and facilitate recovery of each node. The tracking equipment will be used to provide underwater positioning of a remotely operated vehicle during deployment and recovery of the nodes.
The seafloor equipment will be in place for the duration of the data collection for the offshore 3D high energy seismic surveys plus deployment and recovery time. Node deployment will be closely coordinated with both offshore and onshore survey operations to ensure survey activities are completed before the projected batter life of 45 days is exceeded. PG&E anticipates using a locally-available vessel to deploy and retrieve the geophones. The vessel would be a maximum of 50 m in length. The Michael Uhl, which is locally available, its sister vessel, or a vessel of similar size and engine specification, is proposed for this purpose.
Onshore, a linear array of ZL and nodals will be deployed along a single route on the Morro Strand to record onshore sound transmitted from the offshore airgun surveys. Route location is shown in Figure 9 of the IHA application. Ninety nodes would be placed at 100 m (328 ft) intervals along the strand for a total route length of approximately 9 km (5.6 mi). The autonomous, nodal, cable-less recording devices (see Figure 9 of the IHA application) would be deployed by foot into the soil adjacent to existing roads, trails, and beaches. The nodal systems are carried in backpacks and pressed into the ground at each receiver point. Each nodal would be removed following completion of the data collection. PG&E estimates that the onshore receiver activities would be conducted over a 2 to 3 day period, concurrent with the offshore surveys. The onshore receivers would record the offshore sound sources during the seismic operations. Figure 10 of the IHA application depicts the area where the onshore receivers are proposed to be placed along the Morro Strand. PG&E and NMFS have determined that onshore activities are unlikely to impact marine mammals, including pinnipeds at haul-outs and rookeries, in the proposed action area.
More information on the vessels, equipment, and personnel requirements proposed for use in the offshore survey can be found in sections 1.4 and 1.5 of the IHA application.
Dates, Duration, and Specified Geographic Region
The proposed project located offshore of central California would have a total duration of approximately 49.25 operational days occurring during the November through December, 2012 timeframe, which will include approximately 24 days of active seismic airgun operations. Mobilization will initiate on October 15, 2012, with active airgun surveys taking place from November 1 through December 31, 2012. Below is an estimated schedule for the proposed project based on the use of the Langseth as the primary survey vessel (the total number of days is based on adding the non-concurrent tasks):
- Mobilization to project site—6 days;
- Initial equipment deployment—3 days (includes offshore geophone deployment);
- Pre-activity marine mammal surveys—5 days (concurrent with offshore deployment activities);
- Onshore geophone deployment—2 to 3 days (concurrent with offshore deployment activities);
- Equipment calibration and sound check (i.e., sound source verification)—5 days;
- Seismic survey—23.25 days (Survey Box 4 will be surveyed first followed by Survey Box 2, 24/7 operations in all areas);
- Survey Box 4 (survey area within Estero Bay)—9.25 days;
- Survey Box 2 (survey area from Estero Bay to offshore to the mouth of the Santa Maria River)—14 days;
- Streamer and airgun preventative maintenance—2 days;
- Additional shut-downs (marine mammal presence, crew changes, and unanticipated weather delays)—4 days;
- Demobilization—6 days.
Placement of the onshore receiver lines would be completed prior to the start of offshore survey activities and would remain in place until the offshore survey can be completed. Some minor deviation from this schedule is possible, depending on logistics and weather (i.e., the cruise may depart earlier or be extended due to poor weather; there could be additional days of seismic operations if collected data are deemed to be of substandard quality).
The latitude and longitude for the bounds of the two survey boxes are:
Survey Box 4:
35° 25′ 21.7128″ North, 120° 57′ 44.7001″ West
35° 20′ 16.0648″ North, 121° 9′ 24.1914″ West
35° 18′ 38.3096″ North, 120° 53′ 29.9525″ West
35° 14′ 42.003″ North, 121° 3′ 36.9513″ West
Survey Box 2:
34° 57′ 43.3388″ North, 120° 45′ 12.8318″ West
34° 55′ 40.383″ North, 120° 48′ 59.3101″ West
35° 25′ 40.62″ North, 121° 00′ 27.12″ West
35° 23′ 57.26″ North, 121° 04′ 37.28″ West
Description of the Marine Mammals in the Area of the Proposed Specified Activity Back to Top
Thirty-six marine mammal species (29 cetaceans [whales, dolphins, and porpoises], 6 pinnipeds [seals and sea lions], and 1 fissiped) are known to or could occur off the central coast of California study area. Several of these species are listed as endangered under the U.S. Endangered Species Act of 1973 (ESA; 16 U.S.C. 1531 et seq.), including the North Pacific right (Eubalaena japonica), humpback (Megaptera novaeangliae), sei (Balaenoptera borealis), fin (Balaenoptera physalus), blue (Balaenoptera musculus), and sperm (Physeter macrocephalus) whales. The Guadalupe fur seal (Arctocephalus townsendi) and Eastern stock of Steller sea lion (Eumetopias jubatus), and southern sea otter (Enhydra lutris nereis) are listed as threatened under the ESA. The southern sea otter is the one marine mammal species mentioned in this document that is managed by the U.S. Fish and Wildlife Service (USFWS) and is not considered further in this analysis; all others are managed by NMFS. While in their range, North Pacific right, sei, and sperm whale sightings are uncommon in the proposed project area, and have a low likelihood of occurrence during the proposed seismic survey. Similarly, the proposed project area is generally north of the range of the Guadalupe fur seal. Table 2 (below) presents information on the abundance, distribution, population status, conservation status, and population trend of the species of marine mammals that may occur in the proposed study area during November to December, 2012.
Table 2. The habitat, regional abundance, and conservation status of marine mammals that may occur in or near the proposed seismic survey area off the central coast of California. (See text and Table 4 in L-DEO and PG&E's application for further details.)
|Species||Habitat||Population estimate3(minimum)||ESA1||MMPA2||Population trend3|
|NA = Not available or not assessed.|
|1U.S. Endangered Species Act: EN = Endangered, T = Threatened, DL = Delisted, NL = Not listed.|
|2U.S. Marine Mammal Protection Act: D = Depleted, NC = Not Classified.|
|3NMFS Stock Assessment Reports.|
|North Pacific right whale (Eubalaena japonica)||Pelagic and coastal||NA (18 to 21)—Eastern North Pacific stock||EN||D||No information available|
|Gray whale (Eschrichtius robustus)||Coastal, shallow shelf||19,126 (18,017)—Eastern North Pacific stock||DL—Eastern North Pacific stock EN—Western North Pacific stock||NC—Eastern North Pacific stock D—Western North Pacific stock||Increasing over past several decades|
|Humpback whale (Megaptera novaeangliae)||Mainly nearshore, banks||2,043 (1,878)—California/Oregon/Washington stock||EN||D||Increasing|
|Minke whale (Balaenoptera acutorostrata)||Pelagic and coastal||478 (202)—California/Oregon/Washington stock||NL||NC||No information available|
|Sei whale (Balaenoptera borealis)||Primarily offshore, pelagic||126 (83)—Eastern North Pacific stock||EN||D||No information available|
|Fin whale (Balaenoptera physalus)||Continental slope, pelagic||3,044 (2,624)—California/Oregon/Washington stock||EN||D||Unable to determine|
|Blue whale (Balaenoptera musculus)||Pelagic, shelf, coastal||2,497 (2,046)—Eastern North Pacific stock||EN||D||Unable to determine|
|Sperm whale (Physeter macrocephalus)||Pelagic, deep sea||971 (751)—California/Oregon/Washington stock||EN||D||Variable|
|Pygmy sperm whale (Kogia breviceps)||Deep waters off the shelf||579 (271)—California/Oregon/Washington stock||NL||NC||No information available|
|Dwarf sperm whale (Kogia sima)||Deep waters off the shelf||NA—California/Oregon/Washington stock||NL||NC||No information available|
|Cuvier's beaked whale (Ziphius cavirostris)||Pelagic||2,143 (1,298)—California/Oregon/Washington stock||NL||NC||No information available|
|Baird's beaked whale (Berardius bairdii)||Pelagic||907 (615)—California/Oregon/Washington stock||NL||NC||No information available|
|Mesoplodon beaked whale (includes Blainville's beaked whale [M. densirostris], Perrin's beaked whale [M. perrini], Lesser beaked whale [M. peruvianis], Stejneger's beaked whale [M. stejnegeri], Gingko-toothed beaked whale [M. gingkodens], Hubbs' beaked whale [M. carlhubbsi])||Pelagic||1,204 (576)—California/Oregon/Washington stock||NL||NC||No information available|
|Bottlenose dolphin (Tursiops truncatus)||Coastal, oceanic, shelf break||1,006 (684)—California/Oregon/Washington stock 323 (290)—California Coastal stock||NL||NC D—Western North Atlantic coastal||No information available Stable|
|Striped dolphin (Stenella coeruleoalba)||Off continental shelf||10,908 (8,231)—California/Oregon/Washington stock||NL||NC||Unable to determine|
|Short-beaked common dolphin (Delphinus delphis)||Shelf, pelagic, seamounts||411,211 (343,990)—California/Oregon/Washington stock||NL||NC||Variable with oceanographic conditions|
|Long-beaked common dolphin (Delphinus capensis)||Coastal, on continental shelf||27,046 (17,127)—California stock||NL||NC||No information available, variable with oceanographic conditions|
|Pacific white-sided dolphin (Lagenorhynchus obliquidens)||Offshore, slope||26,930 (21,406)—California/Oregon/Washington stock||NL||NC||No information available|
|Northern right whale dolphin (Lissodelphis borealis)||Slope, offshore waters||8,334 (6,019)—California/Oregon/Washington stock||NL||NC||Unable to determine|
|Risso's dolphin (Grampus griseus)||Deep water, seamounts||6,272 (4,913)—California/Oregon/Washington stock||NL||NC||Unable to determine|
|Killer whale (Orcinus orca)||Pelagic, shelf, coastal||240 (162)—Eastern North Pacific Offshore stock 346 (346)—Eastern North Pacific Transient stock 354 (354)—West Coast Transient stock||NL EN—Southern resident||NC D—Southern resident, AT1 transient||No information available, No information available, Declining, Increased and slowing|
|Short-finned pilot whale (Globicephala macrorhynchus)||Pelagic, shelf coastal||760 (465)—California/Oregon/Washington stock||NL||NC||Unable to determine|
|Harbor porpoise (Phocoena phocoena)||Coastal and inland waters||2,044 (1,478)—Morro Bay stock||NL||NC||Increasing|
|Dall's porpoise (Phocoenoides dalli)||Shelf, slope, offshore||42,000 (32,106)—California/Oregon/Washington stock||NL||NC||No information available|
|California sea lion (Zalophus californianus)||Coastal, shelf||296,750 (153,337)—U.S. stock||NL||NC||Increasing|
|Steller sea lion (Eumetopias jubatus)||Coastal, shelf||49,685 (42,366)—Western stock 58,334 to 72,223 (52,847)—Eastern stock||T||D||Decreasing in California|
|Guadalupe fur seal (Arctocephalus townsendi)||Coastal, shelf||7,408 (3,028)—Mexico stock||T||D||Increasing|
|Northern fur seal (Callorhinus ursinus)||Pelagic, offshore||9,968 (5,395)—San Miguel Island stock||NL||D||Increasing|
|Northern elephant seal (Mirounga angustirostris)||Coastal, pelagic in migration||124,000 (74,913)—California Breeding stock||NL||NC||Increasing|
|Pacific harbor seal (Phoca vitulina richardsi)||Coastal||30,196 (26,667)—California stock||NL||NC||Increasing|
|Southern sea otter (Enhydra lutris nereis)||Coastal||2,711—California stock||T||D||Increasing|
In the Pacific Ocean, harbor porpoises are found in coastal and inland waters from California to Alaska and across to Kamchatka and Japan (Gakin, 1984). Harbor porpoises appear to have more restricted movements along the western coast of the continental United States, than along the eastern coast, with some regional differences within California. Based on genetic differences that showed small-scale subdivision within the U.S. portion of its range, California coast stocks were re-evaluated and the stock boundaries were revised. The boundaries (i.e., range) for the Morro Bay stock of harbor porpoises are from Point Sur to Point Conception, California. The vast majority of harbor porpoise in California are within the 0 to 92 m (0 to 301.8 ft) depth, however, a smaller percentage can be found between the 100 to 200 m (328 to 656.2 ft) isobaths. A systematic ship survey of depth strata out to 90 m (295.3 ft) in northern California showed that harbor porpoise abundance declined significantly in waters deep than 60 m (196.9 ft) (Caretta et al., 2001b). Additionally, individuals of the Morro Bay stock appear to be concentrated at significantly higher densities in one specific area of their overall range, which NMFS is referring to as their “core range,” and density is much lower to both the North and South of this area. This core range has the larger number of harbor porpoise sightings and the largest number of harbor porpoise individuals observed during line-transect surveys and is defined for the purposes of this analysis from 34.755° through 35.425° North latitude (see transects 3 to 6 in Table 1 of Appendix B of the IHA application). For the Morro Bay stock, the best estimate of abundance is 2,044 animals and the minimum population estimate is 1,478 animals. There has been an increasing trend in harbor porpoise abundance in Morro Bay since 1988. The observed increase in abundance estimates for this stock since 1988 implies an annual growth rate of approximately 13%. Appendix B of the IHA application includes more detailed information on the density figures and calculations for the Morro Bay stock of harbor porpoise. Figure 1 of Appendix B shows the fine-scale density (including core habitat of higher density) as well as the proposed tracklines of Survey Box 4 and Survey Box 2.
Refer to sections 3 and 4 of L-DEO and PG&E's application for detailed information regarding the abundance and distribution, population status, and life history and behavior of these other marine mammal species and their occurrence in the proposed project area. The application also presents how L-DEO and PG&E calculated the estimated densities for the marine mammals in the proposed survey area. NMFS has reviewed these data and determined them to be the best available scientific information for the purposes of the proposed IHA.
Potential Effects on Marine Mammals Back to Top
Acoustic stimuli generated by the operation of the airguns, which introduce sound into the marine environment, may have the potential to cause Level B harassment of marine mammals in the proposed survey area. The effects of sounds from airgun operations might include one or more of the following: tolerance, masking of natural sounds, behavioral disturbance, temporary or permanent hearing impairment, or non-auditory physical or physiological effects (Richardson et al., 1995; Gordon et al., 2004; Nowacek et al., 2007; Southall et al., 2007). Permanent hearing impairment, in the unlikely event that it occurred, would constitute injury, but temporary threshold shift (TTS) is not an injury (Southall et al., 2007). Although the possibility cannot be entirely excluded, it is unlikely that the proposed project would result in any cases of temporary or permanent hearing impairment, or any significant non-auditory physical or physiological effects. Based on the available data and studies described here, some behavioral disturbance is expected, especially for the Morro Bay harbor porpoise stock, which could potentially be displaced from their core habitat during all or part of the seismic survey or longer. A more comprehensive review of these issues can be found in the “Programmatic Environmental Impact Statement/Overseas Environmental Impact Statement prepared for Marine Seismic Research that is funded by the National Science Foundation and conducted by the U.S. Geological Survey” (NSF/USGS, 2011).
Richardson et al. (1995) defines tolerance as the occurrence of marine mammals in areas where they are exposed to human activities or man-made noise. In many cases, tolerance develops by the animal habituating to the stimulus (i.e., the gradual waning of responses to a repeated or ongoing stimulus) (Richardson, et al., 1995; Thorpe, 1963), but because of ecological or physiological requirements, many marine animals may need to remain in areas where they are exposed to chronic stimuli (Richardson, et al., 1995).
Numerous studies have shown that pulsed sounds from airguns are often readily detectable in the water at distances of many kilometers. Several studies have shown that marine mammals at distances more than a few kilometers from operating seismic vessels often show no apparent response. That is often true even in cases when the pulsed sounds must be readily audible to the animals based on measured received levels and the hearing sensitivity of the marine mammal group. Although various baleen whales and toothed whales, and (less frequently) pinnipeds have been shown to react behaviorally to airgun pulses under some conditions, at other times marine mammals of all three types have shown no overt reactions. The relative responsiveness of baleen and toothed whales are quite variable.
The term masking refers to the inability of a subject to recognize the occurrence of an acoustic stimulus as a result of the interference of another acoustic stimulus (Clark et al., 2009). Introduced underwater sound may, through masking, reduce the effective communication distance of a marine mammal species if the frequency of the source is close to that used as a signal by the marine mammal, and if the anthropogenic sound is present for a significant fraction of the time (Richardson et al., 1995).
Masking effects of pulsed sounds (even from large arrays of airguns) on marine mammal calls and other natural sounds are expected to be limited. Because of the intermittent nature and low duty cycle of seismic airgun pulses, animals can emit and receive sounds in the relatively quiet intervals between pulses. However, in some situations, reverberation occurs for much or the entire interval between pulses (e.g., Simard et al., 2005; Clark and Gagnon, 2006) which could mask calls. Some baleen and toothed whales are known to continue calling in the presence of seismic pulses, and their calls can usually be heard between the seismic pulses (e.g., Richardson et al., 1986; McDonald et al., 1995; Greene et al., 1999; Nieukirk et al., 2004; Smultea et al., 2004; Holst et al., 2005a,b, 2006; and Dunn and Hernandez, 2009). However, Clark and Gagnon (2006) reported that fin whales in the North Atlantic Ocean went silent for an extended period starting soon after the onset of a seismic survey in the area. Similarly, there has been one report that sperm whales ceased calling when exposed to pulses from a very distant seismic ship (Bowles et al., 1994). However, more recent studies found that they continued calling in the presence of seismic pulses (Madsen et al., 2002; Tyack et al., 2003; Smultea et al., 2004; Holst et al., 2006; and Jochens et al., 2008). Dilorio and Clark (2009) found evidence of increased calling by blue whales during operations by a lower-energy seismic source (i.e., sparker). Dolphins and porpoises commonly are heard calling while airguns are operating (e.g., Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a, b; and Potter et al., 2007). The sounds important to small odontocetes are predominantly at much higher frequencies than are the dominant components of airgun sounds, thus limiting the potential for masking.
Pinnipeds have the most sensitive hearing and/or produce most of their sounds at frequencies higher than the dominant components of airgun sound, but there is some overlap in the frequencies of the airgun pulses and the calls. However, the intermittent nature of airgun pulses presumably reduces the potential for masking
Marine mammals are thought to be able to compensate for masking by adjusting their acoustic behavior through shifting call frequencies, increasing call volume, and increasing vocalization rates. For example, blue whales are found to increase call rates when exposed to noise from seismic surveys in the St. Lawrence Estuary (Dilorio and Clark, 2009). The North Atlantic right whales (Eubalaena glacialis) exposed to high shipping noise increased call frequency (Parks et al., 2007), while some humpback whales respond to low-frequency active sonar playbacks by increasing song length (Miller et al., 2000). In general, NMFS expects the masking effects of seismic pulses to be minor, given the normally intermittent nature of seismic pulses.
Marine mammals may behaviorally react to sound when exposed to anthropogenic noise. Disturbance includes a variety of effects, including subtle to conspicuous changes in behavior, movement, and displacement. Reactions to sound, if any, depend on species, state of maturity, experience, current activity, reproductive state, time of day, and many other factors (Richardson et al., 1995; Wartzok et al., 2004; Southall et al., 2007; Weilgart, 2007). These behavioral reactions are often shown as: Changing durations of surfacing and dives, number of blows per surfacing, or moving direction and/or speed; reduced/increased vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); visible startle response or aggressive behavior (such as tail/fluke slapping or jaw clapping); avoidance of areas where noise sources are located; and/or flight responses (e.g., pinnipeds flushing into the water from haul-outs or rookeries). If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007).
The biological significance of many of these behavioral disturbances is difficult to predict, especially if the detected disturbances appear minor. However, the consequences of behavioral modification could be expected to be biologically significant if the change affects growth, survival, and/or reproduction. Some of these significant behavioral modifications include:
- Change in diving/surfacing patterns (such as those thought to be causing beaked whale stranding due to exposure to military mid-frequency tactical sonar);
- Habitat abandonment due to loss of desirable acoustic environment; and
- Cessation of feeding or social interaction.
The onset of behavioral disturbance from anthropogenic noise depends on both external factors (characteristics of noise sources and their paths) and the receiving animals (hearing, motivation, experience, demography) and is also difficult to predict (Richardson et al., 1995; Southall et al., 2007). Given the many uncertainties in predicting the quantity and types of impacts of noise on marine mammals, it is common practice to estimate how many mammals would be present within a particular distance of industrial activities and/or exposed to a particular level of sound. In most cases, this approach likely overestimates the numbers of marine mammals that would be affected in some biologically-important manner.
Baleen Whales—Baleen whales generally tend to avoid operating airguns, but avoidance radii are quite variable (reviewed in Richardson et al., 1995; Gordon et al., 2004). Whales are often reported to show no overt reactions to pulses from large arrays of airguns at distances beyond a few kilometers, even though the airgun pulses remain well above ambient noise levels out to much longer distances. However, baleen whales exposed to strong noise pulses from airguns often react by deviating from their normal migration route and/or interrupting their feeding and moving away. In the cases of migrating gray and bowhead whales, the observed changes in behavior appeared to be of little or no biological consequence to the animals (Richardson, et al., 1995). They simply avoided the sound source by displacing their migration route to varying degrees, but within the natural boundaries of the migration corridors.
Studies of gray, bowhead, and humpback whales have shown that seismic pulses with received levels of 160 to 170 dB re 1 μPa (rms) seem to cause obvious avoidance behavior in a substantial fraction of the animals exposed (Malme et al., 1986, 1988; Richardson et al., 1995). In many areas, seismic pulses from large arrays of airguns diminish to those levels at distances ranging from 4 to 15 km (2.2 to 8.1 nmi) from the source. A substantial proportion of the baleen whales within those distances may show avoidance or other strong behavioral reactions to the airgun array. Subtle behavioral changes sometimes become evident at somewhat lower received levels, and studies have shown that some species of baleen whales, notably bowhead, gray, and humpback whales, at times, show strong avoidance at received levels lower than 160 to 170 dB re 1 μPa (rms).
Researchers have studied the responses of humpback whales to seismic surveys during migration, feeding during the summer months, breeding while offshore from Angola, and wintering offshore from Brazil. McCauley et al. (1998, 2000a) studied the responses of humpback whales off western Australia to a full-scale seismic survey with a 16 airgun array (2,678 in  ) and to a single airgun (20 in  ) with source level of 227 dB re 1 µPa (p-p). In the 1998 study, they documented that avoidance reactions began at 5 to 8 km (2.7 to 4.3 nmi) from the array, and that those reactions kept most pods approximately 3 to 4 km (1.6 to 2.2 nmi) from the operating seismic boat. In the 2000 study, they noted localized displacement during migration of 4 to 5 km (2.2 to 2.7 nmi) by traveling pods and 7 to 12 km (3.8 to 6.5 nmi) by more sensitive resting pods of cow-calf pairs. Avoidance distances with respect to the single airgun were smaller but consistent with the results from the full array in terms of the received sound levels. The mean received level for initial avoidance of an approaching airgun was 140 dB re 1 μPa (rms) for humpback pods containing females, and at the mean closest point of approach distance the received level was 143 dB re 1 μPa (rms). The initial avoidance response generally occurred at distances of 5 to 8 km (2.7 to 4.3 nmi) from the airgun array and 2 km (1.1 nmi) from the single airgun. However, some individual humpback whales, especially males, approached within distances of 100 to 400 m (328 to 1,312 ft), where the maximum received level was 179 dB re 1 μPa (rms).
Data collected by observers during several seismic surveys in the Northwest Atlantic showed that sighting rates of humpback whales were significantly greater during non-seismic periods compared with periods when a full array was operating (Moulton and Holst, 2010). In addition, humpback whales were more likely to swim away and less likely to swim towards a vessel during seismic vs. non-seismic periods (Moulton and Holst, 2010).
Humpback whales on their summer feeding grounds in southeast Alaska did not exhibit persistent avoidance when exposed to seismic pulses from a 1.64-L (100 in  ) airgun (Malme et al., 1985). Some humpbacks seemed “startled” at received levels of 150 to 169 dB re 1 μPa. Malme et al. (1985) concluded that there was no clear evidence of avoidance, despite the possibility of subtle effects, at received levels up to 172 dB re 1 μPa (rms). However, Moulton and Holst (2010) reported that humpback whales monitored during seismic surveys in the Northwest Atlantic had lower sighting rates and were most often seen swimming away from the vessel during seismic periods compared with periods when airguns were silent.
Studies have suggested that South Atlantic humpback whales wintering off Brazil may be displaced or even strand upon exposure to seismic surveys (Engel et al., 2004). The evidence for this was circumstantial and subject to alternative explanations (IAGC, 2004). Also, the evidence was not consistent with subsequent results from the same area of Brazil (Parente et al., 2006), or with direct studies of humpbacks exposed to seismic surveys in other areas and seasons. After allowance for data from subsequent years, there was “no observable direct correlation” between strandings and seismic surveys (IWC, 2007: 236).
Reactions of migrating and feeding (but not wintering) gray whales to seismic surveys have been studied. Malme et al. (1986, 1988) studied the responses of feeding eastern Pacific gray whales to pulses from a single 100 in  airgun off St. Lawrence Island in the northern Bering Sea. They estimated, based on small sample sizes, that 50 percent of feeding gray whales stopped feeding at an average received pressure level of 173 dB re 1 μPa on an (approximate) rms basis, and that 10 percent of feeding whales interrupted feeding at received levels of 163 dB re 1 µPa (rms). Those findings were generally consistent with the results of experiments conducted on larger numbers of gray whales that were migrating along the California coast (Malme et al., 1984; Malme and Miles, 1985), and western Pacific gray whales feeding off Sakhalin Island, Russia (Wursig et al., 1999; Gailey et al., 2007; Johnson et al., 2007; Yazvenko et al., 2007a, b), along with data on gray whales off British Columbia (Bain and Williams, 2006).
Various species of Balaenoptera (blue, sei, fin, and minke whales) have occasionally been seen in areas ensonified by airgun pulses (Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006), and calls from blue and fin whales have been localized in areas with airgun operations (e.g., McDonald et al., 1995; Dunn and Hernandez, 2009; Castellote et al., 2010). Sightings by observers on seismic vessels off the United Kingdom from 1997 to 2000 suggest that, during times of good sightability, sighting rates for mysticetes (mainly fin and sei whales) were similar when large arrays of airguns were shooting vs. silent (Stone, 2003; Stone and Tasker, 2006). However, these whales tended to exhibit localized avoidance, remaining significantly further (on average) from the airgun array during seismic operations compared with non-seismic periods (Stone and Tasker, 2006). Castellote et al. (2010) reported that singing fin whales in the Mediterranean moved away from an operating airgun array.
Ship-based monitoring studies of baleen whales (including blue, fin, sei, minke, and humpback whales) in the Northwest Atlantic found that overall, this group had lower sighting rates during seismic vs. non-seismic periods (Moulton and Holst, 2010). Baleen whales as a group were also seen significantly farther from the vessel during seismic compared with non-seismic periods, and they were more often seen to be swimming away from the operating seismic vessel (Moulton and Holst, 2010). Blue and minke whales were initially sighted significantly farther from the vessel during seismic operations compared to non-seismic periods; the same trend was observed for fin whales (Moulton and Holst, 2010). Minke whales were most often observed to be swimming away from the vessel when seismic operations were underway (Moulton and Holst, 2010).
Data on short-term reactions by cetaceans to impulsive noises are not necessarily indicative of long-term or biologically significant effects. It is not known whether impulsive sounds affect reproductive rate or distribution and habitat use in subsequent days or years. However, gray whales have continued to migrate annually along the west coast of North America with substantial increases in the population over recent years, despite intermittent seismic exploration (and much ship traffic) in that area for decades (Appendix A in Malme et al., 1984; Richardson et al., 1995; Allen and Angliss, 2010). The western Pacific gray whale population did not seem affected by a seismic survey in its feeding ground during a previous year (Johnson et al., 2007). Similarly, bowhead whales have continued to travel to the eastern Beaufort Sea each summer, and their numbers have increased notably, despite seismic exploration in their summer and autumn range for many years (Richardson et al., 1987; Allen and Angliss, 2010). The history of coexistence between seismic surveys and baleen whales suggests that brief exposures to sound pulses from any single seismic survey are unlikely to result in prolonged effects.
Toothed Whales—Little systematic information is available about reactions of toothed whales to noise pulses. Few studies similar to the more extensive baleen whale/seismic pulse work summarized above have been reported for toothed whales. However, there are recent systematic studies on sperm whales (e.g., Gordon et al., 2006; Madsen et al., 2006; Winsor and Mate, 2006; Jochens et al., 2008; Miller et al., 2009). There is an increasing amount of information about responses of various odontocetes to seismic surveys based on monitoring studies (e.g., Stone, 2003; Smultea et al., 2004; Moulton and Miller, 2005; Bain and Williams, 2006; Holst et al., 2006; Stone and Tasker, 2006; Potter et al., 2007; Hauser et al., 2008; Holst and Smultea, 2008; Weir, 2008; Barkaszi et al., 2009; Richardson et al., 2009; Moulton and Holst, 2010).
Seismic operators and PSOs on seismic vessels regularly see dolphins and other small toothed whales near operating airgun arrays, but in general there is a tendency for most delphinids to show some avoidance of operating seismic vessels (e.g., Goold, 1996 a,b,c; Calambokidis and Osmek, 1998; Stone, 2003; Moulton and Miller, 2005; Holst et al., 2006; Stone and Tasker, 2006; Weir, 2008; Richardson et al., 2009; Barkaszi et al., 2009; Moulton and Holst, 2010). Some dolphins seem to be attracted to the seismic vessel and floats, and some ride the bow wave of the seismic vessel even when large arrays of airguns are firing (e.g., Moulton and Miller, 2005). Nonetheless, small toothed whales more often tend to head away, or to maintain a somewhat greater distance from the vessel, when a large array of airguns is operating than when it is silent (e.g., Stone and Tasker, 2006; Weir, 2008; Barry et al., 2010; Moulton and Holst, 2010). In most cases, the avoidance radii for delphinids appear to be small, on the order of one km or less, and some individuals show no apparent avoidance.
Captive bottlenose dolphins (Tursiops truncatus) and beluga whales exhibited changes in behavior when exposed to strong pulsed sounds similar in duration to those typically used in seismic surveys (Finneran et al., 2000, 2002, 2005). However, the animals tolerated high received levels of sound before exhibiting aversive behaviors.
Results for porpoises depend on species. The limited available data suggest that harbor porpoises show stronger avoidance of seismic operations than do Dall's porpoises (Stone, 2003; MacLean and Koski, 2005; Bain and Williams, 2006; Stone and Tasker, 2006). Dall's porpoises seem relatively tolerant of airgun operations (MacLean and Koski, 2005; Bain and Williams, 2006), although they too have been observed to avoid large arrays of operating airguns (Calambokidis and Osmek, 1998; Bain and Williams, 2006). This apparent difference in responsiveness of these two porpoise species is consistent with their relative responsiveness to boat traffic and some other acoustic sources (Richardson et al., 1995; Southall et al., 2007).
Most studies of sperm whales exposed to airgun sounds indicate that the sperm whale shows considerable tolerance of airgun pulses (e.g., Stone, 2003; Moulton et al., 2005, 2006a; Stone and Tasker, 2006; Weir, 2008). In most cases the whales do not show strong avoidance, and they continue to call. However, controlled exposure experiments in the Gulf of Mexico indicate that foraging behavior was altered upon exposure to airgun sound (Jochens et al., 2008; Miller et al., 2009; Tyack, 2009).
There are almost no specific data on the behavioral reactions of beaked whales to seismic surveys. However, some northern bottlenose whales (Hyperoodon ampullatus) remained in the general area and continued to produce high-frequency clicks when exposed to sound pulses from distant seismic surveys (Gosselin and Lawson, 2004; Laurinolli and Cochrane, 2005; Simard et al., 2005). Most beaked whales tend to avoid approaching vessels of other types (e.g., Wursig et al., 1998). They may also dive for an extended period when approached by a vessel (e.g., Kasuya, 1986), although it is uncertain how much longer such dives may be as compared to dives by undisturbed beaked whales, which also are often quite long (Baird et al., 2006; Tyack et al., 2006). Based on a single observation, Aguilar-Soto et al. (2006) suggested that foraging efficiency of Cuvier's beaked whales may be reduced by close approach of vessels. In any event, it is likely that most beaked whales would also show strong avoidance of an approaching seismic vessel, although this has not been documented explicitly. In fact, Moulton and Holst (2010) reported 15 sightings of beaked whales during seismic studies in the Northwest Atlantic; seven of those sightings were made at times when at least one airgun was operating. There was little evidence to indicate that beaked whale behavior was affected by airgun operations; sighting rates and distances were similar during seismic and non-seismic periods (Moulton and Holst, 2010).
There are increasing indications that some beaked whales tend to strand when naval exercises involving mid-frequency sonar operation are ongoing nearby (e.g., Simmonds and Lopez-Jurado, 1991; Frantzis, 1998; NOAA and USN, 2001; Jepson et al., 2003; Hildebrand, 2005; Barlow and Gisiner, 2006; see also the “Stranding and Mortality” section in this notice). These strandings are apparently a disturbance response, although auditory or other injuries or other physiological effects may also be involved. Whether beaked whales would ever react similarly to seismic surveys is unknown. Seismic survey sounds are quite different from those of the sonar in operation during the above-cited incidents.
Odontocete reactions to large arrays of airguns are variable and, at least for delphinids and Dall's porpoises, seem to be confined to a smaller radius than has been observed for the more responsive of some mysticetes. However, other data suggest that some odontocete species, including harbor porpoises, may be more responsive than might be expected given their poor low-frequency hearing. Reactions at longer distances may be particularly likely when sound propagation conditions are conducive to transmission of the higher frequency components of airgun sound to the animals' location (DeRuiter et al., 2006; Goold and Coates, 2006; Tyack et al., 2006; Potter et al., 2007).
Pinnipeds—Pinnipeds are not likely to show a strong avoidance reaction to the airgun array. Visual monitoring from seismic vessels has shown only slight (if any) avoidance of airguns by pinnipeds, and only slight (if any) changes in behavior. In the Beaufort Sea, some ringed seals avoided an area of 100 m to (at most) a few hundred meters around seismic vessels, but many seals remained within 100 to 200 m (328 to 656 ft) of the trackline as the operating airgun array passed by (e.g., Harris et al., 2001; Moulton and Lawson, 2002; Miller et al., 2005). Ringed seal sightings averaged somewhat farther away from the seismic vessel when the airguns were operating than when they were not, but the difference was small (Moulton and Lawson, 2002). Similarly, in Puget Sound, sighting distances for harbor seals and California sea lions tended to be larger when airguns were operating (Calambokidis and Osmek, 1998). Previous telemetry work suggests that avoidance and other behavioral reactions may be stronger than evident to date from visual studies (Thompson et al., 1998).
During seismic exploration off Nova Scotia, gray seals (Halichoerus grypus) exposed to noise from airguns and linear explosive charges did not react strongly (J. Parsons in Greene et al., 1985). Pinnipeds, in both water and air, sometimes tolerate strong noise pulses from non-explosive and explosive scaring devices, especially if attracted to the area for feeding and reproduction (Mate and Harvey, 1987; Reeves et al., 1996). Thus, pinnipeds are expected to be rather tolerant of, or habituate to, repeated underwater sounds from distant seismic sources, at least when the animals are strongly attracted to the area.
Hearing Impairment and Other Physical Effects
Exposure to high intensity sound for a sufficient duration may result in auditory effects such as a noise-induced threshold shift—an increase in the auditory threshold after exposure to noise (Finneran, Carder, Schlundt, and Ridgway, 2005). Factors that influence the amount of threshold shift include the amplitude, duration, frequency content, temporal pattern, and energy distribution of noise exposure. The magnitude of hearing threshold shift normally decreases over time following cessation of the noise exposure. The amount of threshold shift just after exposure is called the initial threshold shift. If the threshold shift eventually returns to zero (i.e., the threshold returns to the pre-exposure value), it is called temporary threshold shift (TTS) (Southall et al., 2007).
Researchers have studied TTS in certain captive odontocetes and pinnipeds exposed to strong sounds (reviewed in Southall et al., 2007). However, there has been no specific documentation of TTS let alone permanent hearing damage, i.e., permanent threshold shift (PTS), in free-ranging marine mammals exposed to sequences of airgun pulses during realistic field conditions.
Temporary Threshold Shift—TTS is the mildest form of hearing impairment that can occur during exposure to a strong sound (Kryter, 1985). While experiencing TTS, the hearing threshold rises and a sound must be stronger in order to be heard. At least in terrestrial mammals, TTS can last from minutes or hours to (in cases of strong TTS) days. For sound exposures at or somewhat above the TTS threshold, hearing sensitivity in both terrestrial and marine mammals recovers rapidly after exposure to the noise ends. Few data on sound levels and durations necessary to elicit mild TTS have been obtained for marine mammals, and none of the published data concern TTS elicited by exposure to multiple pulses of sound. Available data on TTS in marine mammals are summarized in Southall et al. (2007). Table 1 (above) presents the estimated distances from the Langseth' s airguns at which the received energy level (per pulse, flat-weighted) would be expected to be greater than or equal to 180 or 190 dB re 1 µPa (rms).
To avoid the potential for injury, NMFS (1995, 2000) concluded that cetaceans and pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding 180 and 190 dB re 1 μPa (rms), respectively. NMFS believes that to avoid the potential for Level A harassment, cetaceans and pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding 180 and 190 dB re 1 μPa (rms), respectively. The established 180 and 190 dB (rms) criteria are not considered to be the levels above which TTS might occur. Rather, they are the received levels above which, in the view of a panel of bioacoustics specialists convened by NMFS before TTS measurements for marine mammals started to become available, one could not be certain that there would be no injurious effects, auditory or otherwise, to marine mammals. NMFS also assumes that cetaceans and pinnipeds exposed to levels exceeding 160 dB re 1 μPa (rms) may experience Level B harassment.
For toothed whales, researchers have derived TTS information for odontocetes from studies on the bottlenose dolphin and beluga. The experiments show that exposure to a single impulse at a received level of 207 kPa (or 30 psi, p-p), which is equivalent to 228 dB re 1 Pa (p-p), resulted in a 7 and 6 dB TTS in the beluga whale at 0.4 and 30 kHz, respectively. Thresholds returned to within 2 dB of the pre-exposure level within 4 minutes of the exposure (Finneran et al., 2002). For the one harbor porpoise tested, the received level of airgun sound that elicited onset of TTS was lower (Lucke et al., 2009). If these results from a single animal are representative, it is inappropriate to assume that onset of TTS occurs at similar received levels in all odontocetes (cf. Southall et al., 2007). Some cetaceans apparently can incur TTS at considerably lower sound exposures than are necessary to elicit TTS in the beluga or bottlenose dolphin.
For baleen whales, there are no data, direct or indirect, on levels or properties of sound that are required to induce TTS. The frequencies to which baleen whales are most sensitive are assumed to be lower than those to which odontocetes are most sensitive, and natural background noise levels at those low frequencies tend to be higher. As a result, auditory thresholds of baleen whales within their frequency band of best hearing are believed to be higher (less sensitive) than are those of odontocetes at their best frequencies (Clark and Ellison, 2004). From this, it is suspected that received levels causing TTS onset may also be higher in baleen whales than those of odontocetes (Southall et al., 2007).
In pinnipeds, researchers have not measured TTS thresholds associated with exposure to brief pulses (single or multiple) of underwater sound. Initial evidence from more prolonged (non-pulse) exposures suggested that some pinnipeds (harbor seals in particular) incur TTS at somewhat lower received levels than do small odontocetes exposed for similar durations (Kastak et al., 1999, 2005; Ketten et al., 2001). The TTS threshold for pulsed sounds has been indirectly estimated as being an SEL of approximately 171 dB re 1 µPa  ·s (Southall et al., 2007) which would be equivalent to a single pulse with a received level of approximately 181 to 186 dB re 1 µPa (rms), or a series of pulses for which the highest rms values are a few dB lower. Corresponding values for California sea lions and northern elephant seals are likely to be higher (Kastak et al., 2005).
Permanent Threshold Shift—When PTS occurs, there is physical damage to the sound receptors in the ear. In severe cases, there can be total or partial deafness, whereas in other cases, the animal has an impaired ability to hear sounds in specific frequency ranges (Kryter, 1985). There is no specific evidence that exposure to pulses of airgun sound can cause PTS in any marine mammal, even with large arrays of airguns. However, given the possibility that mammals close to an airgun array might incur at least mild TTS, there has been further speculation about the possibility that some individuals occurring very close to airguns might incur PTS (e.g., Richardson et al., 1995, p. 372 ff; Gedamke et al., 2008). Single or occasional occurrences of mild TTS are not indicative of permanent auditory damage, but repeated or (in some cases) single exposures to a level well above that causing TTS onset might elicit PTS.
Relationships between TTS and PTS thresholds have not been studied in marine mammals, but are assumed to be similar to those in humans and other terrestrial mammals (Southall et al., 2007). PTS might occur at a received sound level at least several dBs above that inducing mild TTS if the animal were exposed to strong sound pulses with rapid rise times. Based on data from terrestrial mammals, a precautionary assumption is that the PTS threshold for impulse sounds (such as airgun pulses as received close to the source) is at least 6 dB higher than the TTS threshold on a peak-pressure basis, and probably greater than 6 dB (Southall et al., 2007).
Given the higher level of sound necessary to cause PTS as compared with TTS, it is considerably less likely that PTS would occur. Baleen whales generally avoid the immediate area around operating seismic vessels, as do some other marine mammals. Some pinnipeds show avoidance reactions to airguns, but their avoidance reactions are generally not as strong or consistent as those of cetaceans, and occasionally they seem to be attracted to operating seismic vessels (NMFS, 2010).
Stranding and Mortality—When a living or dead marine mammal swims or floats onto shore and becomes “beached” or incapable of returning to sea, the event is termed a “stranding” (Geraci et al., 1999; Perrin and Geraci, 2002; Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a stranding under the MMPA is that “(A) a marine mammal is dead and is (i) on a beach or shore of the United States; or (ii) in waters under the jurisdiction of the United States (including any navigable waters); or (B) a marine mammal is alive and is (i) on a beach or shore of the United States and is unable to return to the water; (ii) on a beach or shore of the United States and, although able to return to the water is in need of apparent medical attention; or (iii) in the waters under the jurisdiction of the United States (including any navigable waters), but is unable to return to its natural habitat under its own power or without assistance.”
Marine mammals are known to strand for a variety of reasons, such as infectious agents, biotoxicosis, starvation, fishery interaction, ship strike, unusual oceanographic or weather events, sound exposure, or combinations of these stressors sustained concurrently or in series. However, the cause or causes of most strandings are unknown (Geraci et al., 1976; Eaton, 1979; Odell et al., 1980; Best, 1982). Numerous studies suggest that the physiology, behavior, habitat relationships, age, or condition of cetaceans may cause them to strand or might pre-dispose them to strand when exposed to another phenomenon. These suggestions are consistent with the conclusions of numerous other studies that have demonstrated that combinations of dissimilar stressors commonly combine to kill an animal or dramatically reduce its fitness, even though one exposure without the other does not produce the same result (Chroussos, 2000; Creel, 2005; DeVries et al., 2003; Fair and Becker, 2000; Foley et al., 2001; Moberg, 2000; Relyea, 2005a, 2005b; Romero, 2004; Sih et al., 2004).
Strandings Associated with Military Active Sonar—Several sources have published lists of mass stranding events of cetaceans in an attempt to identify relationships between those stranding events and military active sonar (Hildebrand, 2004; IWC, 2005; Taylor et al., 2004). For example, based on a review of stranding records between 1960 and 1995, the International Whaling Commission (2005) identified ten mass stranding events and concluded that, out of eight stranding events reported from the mid-1980s to the summer of 2003, seven had been coincident with the use of mid-frequency active sonar and most involved beaked whales.
Over the past 12 years, there have been five stranding events coincident with military mid-frequency active sonar use in which exposure to sonar is believed to have been a contributing factor to strandings: Greece (1996); the Bahamas (2000); Madeir (2000); Canary Islands (2002); and Spain (2006). Refer to Cox et al. (2006) for a summary of common features shared by the strandings events in Greece (1996), Bahamas (2000), Madeira (2000), and Canary Islands (2002); and Fernandez et al., (2005) for an additional summary of the Canary Islands 2002 stranding event.
Potential for Stranding from Seismic Surveys—Marine mammals close to underwater detonations of high explosives can be killed or severely injured, and the auditory organs are especially susceptible to injury (Ketten et al., 1993; Ketten, 1995). However, explosives are no longer used in marine waters for commercial seismic surveys or (with rare exceptions) for seismic research. These methods have been replaced entirely by airguns or related non-explosive pulse generators. Airgun pulses are less energetic and have slower rise times, and there is no specific evidence that they can cause serious injury, death, or stranding even in the case of large airgun arrays. However, the association of strandings of beaked whales with naval exercises involving mid-frequency active sonar (non-pulse sound) and, in one case, the co-occurrence of an L-DEO seismic survey (Malakoff, 2002; Cox et al., 2006), has raised the possibility that beaked whales exposed to strong “pulsed” sounds could also be susceptible to injury and/or behavioral reactions that can lead to stranding (e.g., Hildebrand, 2005; Southall et al., 2007).
Specific sound-related processes that lead to strandings and mortality are not well documented, but may include:
(1) Swimming in avoidance of a sound into shallow water;
(2) A change in behavior (such as a change in diving behavior) that might contribute to tissue damage, gas bubble formation, hypoxia, cardiac arrhythmia, hypertensive hemorrhage or other forms of trauma;
(3) A physiological change such as a vestibular response leading to a behavioral change or stress-induced hemorrhagic diathesis, leading in turn to tissue damage; and
(4) Tissue damage directly from sound exposure, such as through acoustically-mediated bubble formation and growth or acoustic resonance of tissues.
Some of these mechanisms are unlikely to apply in the case of impulse sounds. However, there are indications that gas-bubble disease (analogous to “the bends”), induced in supersaturated tissue by a behavioral response to acoustic exposure, could be a pathologic mechanism for the strandings and mortality of some deep-diving cetaceans exposed to sonar. The evidence for this remains circumstantial and associated with exposure to naval mid-frequency sonar, not seismic surveys (Cox et al., 2006; Southall et al., 2007).
Seismic pulses and mid-frequency sonar signals are quite different, and some mechanisms by which sonar sounds have been hypothesized to affect beaked whales are unlikely to apply to airgun pulses. Sounds produced by airgun arrays are broadband impulses with most of the energy below one kHz. Typical military mid-frequency sonar emits non-impulse sounds at frequencies of 2 to 10 kHz, generally with a relatively narrow bandwidth at any one time. A further difference between seismic surveys and naval exercises is that naval exercises can involve sound sources on more than one vessel. Thus, it is not appropriate to expect that the same to marine mammals will result from military sonar and seismic surveys. However, evidence that sonar signals can, in special circumstances, lead (at least indirectly) to physical damage and mortality (e.g., Balcomb and Claridge, 2001; NOAA and USN, 2001; Jepson et al., 2003; Fernández et al., 2004, 2005; Hildebrand 2005; Cox et al., 2006) suggests that caution is warranted when dealing with exposure of marine mammals to any high-intensity sound.
There is no conclusive evidence of cetacean strandings or deaths at sea as a result of exposure to seismic surveys, but a few cases of strandings in the general area where a seismic survey was ongoing have led to speculation concerning a possible link between seismic surveys and strandings. Suggestions that there was a link between seismic surveys and strandings of humpback whales in Brazil (Engel et al., 2004) were not well founded (IAGC, 2004; IWC, 2007). In September, 2002, there was a stranding of two Cuvier's beaked whales in the Gulf of California, Mexico, when the L-DEO vessel R/V Maurice Ewing was operating a 20 airgun (8,490 in  ) array in the general area. The link between the stranding and the seismic surveys was inconclusive and not based on any physical evidence (Hogarth, 2002; Yoder, 2002). Nonetheless, the Gulf of California incident plus the beaked whale strandings near naval exercises involving use of mid-frequency sonar suggests a need for caution in conducting seismic surveys in areas occupied by beaked whales until more is known about effects of seismic surveys on those species (Hildebrand, 2005). No injuries of beaked whales are anticipated during the proposed study because of:
(1) The high likelihood that any beaked whales nearby would avoid the approaching vessel before being exposed to high sound levels, and
(2) Differences between the sound sources operated by L-DEO and those involved in the naval exercises associated with strandings.
Non-auditory Physiological Effects—Non-auditory physiological effects or injuries that theoretically might occur in marine mammals exposed to strong underwater sound include stress, neurological effects, bubble formation, resonance, and other types of organ or tissue damage (Cox et al., 2006; Southall et al., 2007). Studies examining such effects are limited. However, resonance effects (Gentry, 2002) and direct noise-induced bubble formations (Crum et al., 2005) are implausible in the case of exposure to an impulsive broadband source like an airgun array. If seismic surveys disrupt diving patterns of deep-diving species, this might perhaps result in bubble formation and a form of the bends, as speculated to occur in beaked whales exposed to sonar. However, there is no specific evidence of this upon exposure to airgun pulses.
In general, very little is known about the potential for seismic survey sounds (or other types of strong underwater sounds) to cause non-auditory physical effects in marine mammals. Such effects, if they occur at all, would presumably be limited to short distances and to activities that extend over a prolonged period. The available data do not allow identification of a specific exposure level above which non-auditory effects can be expected (Southall et al., 2007), or any meaningful quantitative predictions of the numbers (if any) of marine mammals that might be affected in those ways. Marine mammals that show behavioral avoidance of seismic vessels, including most baleen whales, some odontocetes, and some pinnipeds, are especially unlikely to incur non-auditory physical effects.
Potential Effects of Other Acoustic Devices
L-DEO and PG&E will operate the Kongsberg EM 122 multibeam echosounder from the source vessel during the planned study. Sounds from the multibeam echosounder are very short pulses, occurring for 2 to 15 ms once every 5 to 20 s, depending on water depth. Most of the energy in the sound pulses emitted by this multibeam echosounder is at frequencies near 12 kHz, and the maximum source level is 242 dB re 1 μPa (rms). The beam is narrow (1 to 2°) in fore-aft extent and wide (150°) in the cross-track extent. Each ping consists of eight (in water greater than 1,000 m deep) or four (in water less than 1,000 m deep) successive fan-shaped transmissions (segments) at different cross-track angles. Any given mammal at depth near the trackline would be in the main beam for only one or two of the nine segments. Also, marine mammals that encounter the Kongsberg EM 122 are unlikely to be subjected to repeated pulses because of the narrow fore-aft width of the beam and will receive only limited amounts of pulse energy because of the short pulses. Animals close to the ship (where the beam is narrowest) are especially unlikely to be ensonified for more than one 2 to 15 ms pulse (or two pulses if in the overlap area). Similarly, Kremser et al. (2005) noted that the probability of a cetacean swimming through the area of exposure when a multibeam echosounder emits a pulse is small. The animal would have to pass the transducer at close range and be swimming at speeds similar to the vessel in order to receive the multiple pulses that might result in sufficient exposure to cause TTS.
Navy sonars that have been linked to avoidance reactions and stranding of cetaceans: (1) Generally have longer pulse duration than the Kongsberg EM 122; and (2) are often directed close to horizontally versus more downward for the multibeam echosounder. The area of possible influence of the multibeam echosounder is much smaller—a narrow band below the source vessel. Also, the duration of exposure for a given marine mammal can be much longer for naval sonar. During L-DEO and PG&E's operations, the individual pulses will be very short, and a given mammal would not receive many of the downward-directed pulses as the vessel passes by. Possible effects of a multibeam echosounder on marine mammals are described below.
Masking—Marine mammal communications will not be masked appreciably by the multibeam echosounder signals given the low duty cycle of the echosounder and the brief period when an individual mammal is likely to be within its beam. Furthermore, in the case of baleen whales, the multibeam echosounder signals (12 kHz) do not overlap with the predominant frequencies in the calls, which would avoid any significant masking.
Behavioral Responses—Behavioral reactions of free-ranging marine mammals to sonars, echosounders, and other sound sources appear to vary by species and circumstance. Observed reactions have included silencing and dispersal by sperm whales (Watkins et al., 1985), increased vocalizations and no dispersal by pilot whales (Rendell and Gordon, 1999), and the previously-mentioned beachings by beaked whales. During exposure to a 21 to 25 kHz “whale-finding” sonar with a source level of 215 dB re 1 µPa, gray whales reacted by orienting slightly away from the source and being deflected from their course by approximately 200 m (656.2 ft) (Frankel, 2005). When a 38 kHz echosounder and a 150 kHz acoustic Doppler current profiler were transmitting during studies in the Eastern Tropical Pacific, baleen whales showed no significant responses, while spotted and spinner dolphins were detected slightly more often and beaked whales less often during visual surveys (Gerrodette and Pettis, 2005).
Captive bottlenose dolphins and a beluga whale exhibited changes in behavior when exposed to 1 s tonal signals at frequencies similar to those that will be emitted by the multibeam echosounder used by L-DEO and PG&E, and to shorter broadband pulsed signals. Behavioral changes typically involved what appeared to be deliberate attempts to avoid the sound exposure (Schlundt et al., 2000; Finneran et al., 2002; Finneran and Schlundt, 2004). The relevance of those data to free-ranging odontocetes is uncertain, and in any case, the test sounds were quite different in duration as compared with those from a multibeam echosounder.
Very few data are available on the reactions of pinnipeds to echosounder sounds at frequencies similar to those used during seismic operations. Hastie and Janik (2007) conducted a series of behavioral response tests on two captive gray seals to determine their reactions to underwater operation of a 375 kHz multibeam imaging echosounder that included significant signal components down to 6 kHz. Results indicated that the two seals reacted to the signal by sign