MONITORING/RESEARCH TO INCREASE UNDERSTANDING OF THE POTENTIAL EFFECTS OF SURTASS LFA SONAR TRANSMISSIONS ON BEAKED WHALES AND/OR HARBOR PORPOISES
A monitoring and research provision was included in the 2012 MMPA Final Rule and subsequent annual LOAs for SURTASS LFA sonar that required the Navy to consider research or monitoring strategies that would increase the understanding of the potential effects of SURTASS LFA sonar transmissions on beaked whales and/or harbor porpoises. The Navy’s first step in this effort was to convene a group of recognized scientific subject matter experts in the fields of marine bio-acoustics, marine mammal biology and hearing, and marine behavioral sciences to evaluate and recommend possible research or monitoring efforts. The goal of this Scientific Advisory Group (SAG) was to specifically evaluate and recommend a practical strategy for the Navy on the possible monitoring and research efforts it could undertake to provide information on how exposure to SURTASS LFA sonar might affect the behavior of beaked whales and/or harbor porpoises.
The Navy organized a group of renowned marine scientists and bio-acousticians to form the SAG, which included:
- Dr. Christopher W. Clark
- Dr. Daniel P. Costa
- Dr. William T. Ellison
- Dr. Jason Gedamke
- Dr. Ronald A. Kastelein
- Dr. Brandon L. Southall (chair)
The SAG convened twice during 2012 to 2013 and developed a strategic, iterative, parallel research approach for beaked whales (primarily involving field work with existing methods) and harbor porpoises (primarily involving laboratory studies with existing methods) that could be implemented to address specific information gaps, if deemed necessary. The LFA SAG Report of their recommended research approach was submitted to the National Marine Fisheries Service in August 2013.
In their report, the SAG concluded that the available data suggest that the potential for adverse effects to beaked whales and harbor porpoises from exposure to SURTASS LFA sonar appears limited. They also concluded that the potential effects of SURTASS LFA sonar on marine mammal species within these two odontocete taxa would depend largely on the frequencies of the transmissions relative to the species’ hearing sensitivity, the species’ responsiveness to underwater sounds, and the spatial overlap between SURTASS LFA sonar mission areas and the species’ distributions. However, the SAG concluded that a number of research questions should be addressed to verify this conclusion and provided several specific recommendations to address the research questions.
LOW FREQUENCY SOUND SCIENTIFIC RESEARCH PROGRAM (LFS SRP)
When the use of SURTASS LFA sonar was first proposed in the mid 1990’s, very little data existed upon which an assessment of the potential effects could be based. Therefore, the Navy convened the Low Frequency Sound Scientific Research Program (LFS SRP) to investigate the reaction of species engaged in critical, biologically-important behaviors to the low-frequency transmissions produced by the LFA system. Species were selected that were believed to be sensitive to low-frequency sound. If the prevailing hypothesis was confirmed that received sound levels of approximately 140 dB would cause avoidance behaviors by marine mammals, then LFA probably would not have been deployed or its use would have been severely restricted.
The LFS SRP was conducted in three phases. The chart shows the location of each phase.
- Phase I (Sept-Oct 97) – Species: Blue and Fin Whales
- Phase II (Jan 98) – Species: Gray Whales
- Phase III (Feb-Mar 98) – Species: Humpback Whales
LFS SRP Phase I
The primary objective of Phase I was to determine whether exposure to low-frequency sounds elicited disturbance reactions from feeding blue or fin whales. The goal was to characterize how whale reactions vary to the sounds depending on: (1) the received level of the sound, (2) changes in the received level, and (3) whether the system was operating at a relatively constant distance or approaching a whale.
Phase I Research Approach
Bottom Bounce Acoustic Field
- Sound is refracted (bent) downward and reflects upward off the seafloor
- Simulated the type of sound field that whales could experience from a distant source
Direct Path Acoustic Field
- Omni-directional sound field (sound levels are same throughout the water column)
- Simulated the type of sound field that whales could experience from an approaching source
Phase I Research Assets
Research Vessel Cory Chouest
- Source Ship (played LFA acoustic transmissions)
- Collected acoustic recordings with SURTASS towed array, especially of whale vocalizations
Research Vessel Dariabar
- Independent observation vessel
- Marine mammal experts observed fin and blue whale behavior
- Collected acoustic recordings, especially of whale vocalizations
Research Vessel John Martin
- Surveyed prey fields (whale food)
- Tagged blue and fin whales with time/depth recorders to assess dive behavior
- Documented the distribution and density of marine mammals
- Autonomous seafloor acoustic recording units
- Acoustic recordings from Navy seafloor passive hydrophone arrays
Phase I Results
- Full and reduced LFA source power transmissions were used.
- Highest received levels at animals estimated to be 148-155 dB rms.
- In 19 focal animal observations (4 blue whales and 15 fin whales), no overt behavioral responses were observed. Note: A “focal animal” is an individual animal selected for intensive observation during an experiment.
- No changes in whale distribution could be related to LFA operations; whale distributions closely tracked the distribution of food.
- One preliminary analysis of whale sound detections indicated a slight decrease in whale calling activity during LFA operations, but this was not confirmed by a second analysis.
SRP Phase II
- Quantify responses of migrating gray whales to low-frequency sound signals.
- Compare whale responses to different received levels (RL).
- Determine whether whales respond more strongly to RL, sound gradient, or range to the source.
- Compare whale avoidance responses to the low-frequency source when located in the center of the migration corridor versus in the offshore portion of the migration corridor.
Phase II Research Assets
For this phase of the Scientific Research Program, a sound source was moored offshore of the central California coast, near Point Buchon. Shore-based observers tracked whales using methods that provided highly sensitive measures of avoidance responses. Observers on the playback vessel (100 ft work boat) also carefully monitored marine mammals to stop broadcasting in case of worrisome behavioral reactions or if any marine mammals were sighted at close enough range that the sound level to which they were exposed might exceed the maximum planned exposure level (155 dB).
- A single source was used to broadcast LFA sounds at source levels up to 200 dB re 1 uPa at 1 m.
- When the source was moored 1 mile offshore, in the middle of the migration path, whales showed avoidance responses similar to those reported by Malme et al. (1983, 1984).
- Whales returned to their migration path within a few kilometers.
- When the source was moored 2 miles offshore, responses where much less, even when the source level was increased to achieve the same received level for most whales in the middle of the migration corridor.
- Offshore whales did not appear to avoid the louder offshore source.
SRP Phase III
Acoustic Playback Vessel
Assess potential effects of LFA signals on behavior, vocalization and movement of humpback whales off the Kona coast.
Phase III Research Approach
- Shipboard visual and acoustic observation
- Shore-based visual observation
- Controlled exposure of whales to LFA transmissions from SURTASS LFA source
- SURTASS ship (passive only) available for better localization and additional observations
- Additional R/V collected visual, acoustic and sound field data
- Applicable mitigation measures employed during all operations
Phase III Research Assets
For this phase of the SRP, the Research Vessel Cory Chouest operated off the west coast of the big island of Hawaii. A passive SURTASS ship also participated to listen for whale songs. Shore-based observers tracked whales. Calibrated hydrophones were deployed from a small vessel to measure received levels (RL), verify the transmission loss (TL) models, and improve determination of the sound field to which the whales were exposed. This vessel also followed individual humpback whales and described in detail their surface behaviors before, during, and after LFA transmissions. Visual and acoustic observers on the playback vessel (R/V Cory Chouest) carefully monitored marine mammals in order to stop broadcasting in case of worrisome behavioral reactions or if any marine mammals were sighted at close enough range that the sound level to which they were exposed might exceed the maximum planned exposure level.
Phase III Summary
- 33 LFA playback (acoustic transmission) experiments
- More than 950 humpback sightings
- 500 hours of passive acoustic data collected
- Whale exposure levels of 115 dB to 152 dB
- Variety of responses to playbacks, including temporary cessation of song and apparent temporary avoidance response
- Many whales continued to sing and interact with other whales during playbacks
- Three aerial surveys conducted as part of separate research project but included Phase III study area during playbacks
- Whale distributions and abundances compared with similar survey data from 1993 and 1995
Phase III Results
- Maximum exposure levels were as high as 152 dB.
- Roughly half of the whales that were visually observed ceased their song during transmissions, but many of these did so while joining a group of whales (when singers usually stop their songs).
- All singers who interrupted their songs were observed to resume singing within tens of minutes.
- Analysis of one data set showed that whales increased their song lengths during LFA transmissions, but a second analysis indicated that song length changes were more complicated, and depended on the portion of the song that was overlapped by LFA transmissions.
- A delayed response to LFA transmissions was observed, in the form of an increase in song length that occurred 1-2 hours after the last transmission.
- Overall patterns of singer and cow-calf abundance were the same throughout the experiment as they were during several years of prior study.