The Low-Frequency Active Sonar (LFA) Research Program
Over the past several years, the Navy has held public meetings and sponsored scientific workshops to discuss the reactions of marine animals to a new sonar system: the Surveillance Towed Array Sensor System Low Frequency Active (SURTASS LFA). These discussions led to the widespread consensus that controlled tests of how whales responded to SURTASS LFA signals were urgently needed. The Navy agreed to make available for this scientific research the SURTASS LFA system (the equipment, consisting of a vertical array of underwater sound projectors that produce signals in the 100-500 Hz region, and the vessel that operates the equipment).
Between September 1997 and March 1998, the Navy supported a three-part "Low-Frequency Sound Scientific Research Program" to determine possible effects of SURTASS LFA on whales at two sites off the California coast, and one site off of Hawaii. The research team included leading marine mammal scientists and underwater acoustics experts from several research institutions.
Organizations participating in research on possible effects of SURTASS LFA on large whales:
- Bioacoustics Research Program, Cornell Lab of Ornithology
- Hughes Aircraft Corporation
A three-phase approach
- Phase I of the research focused on possible responses of feeding fin and blue whales in the Southern California Bight in September and October 1997.
- Phase II of the research focused on possible effects of SURTASS LFA on gray whales migrating past the central California coast in January 1998.
- Phase III focused on responses of humpback whales wintering off the Kona Coast of the Big Island of Hawaii in February and March 1998.
In all three phases, the general approach of the experiments was to closely monitor the movements and behavior of whales before, during and after exposure to signals like those used by the operational SURTASS LFA system. The test signals, series of glissandos and hums similar to the sounds made by singing whales, were broadcast by the SURTASS LFA equipment. By a combination of extensive on-site measurements and sophisticated mathematical modelling of underwater sound propagation, the actual sound levels received by individual whales could be determined.
Monitoring whale responses to SURTASS LFA
For each of the three research projects, an extensive set of observation techniques was employed to document responses of whales to playback of LFA signals. The following list briefly summarizes the techniques that were used in the Low-Frequency Sound Scientific Research Program to monitor the distribution and behavior of whales in the research area, before, during, and after a period of LFA transmissions:
- Aerial surveys of whale distribution in the research area.
- Visual scans of whale distribution conducted on the playback vessel.
- Visual scans of whale distribution conducted on a separate observation vessel.
- Visual behavioral observations of individual whales conducted from a separate observation vessel.
- Acoustic recordings made to describe the underwater sound field (ambient and LFA generated) and the vocal behaviors of whales using:
- towed hydrophone arrays on the playback vessel
- towed hydrophone arrays on the observation vessel
- autonomous bottom-mounted recording units
- Sound Surveillance System (SOSUS) arrays
- Tagging and tracking of individual whales with radio transmitters and time-depth recorders to document diving histories and short-term movements.
- Surveys of prey fields to measure the occurrence and characteristics of the whales' food resources within the research area.
- Shore-based visual tracking of movements of whales.
Results of research thus far
Although the analysis of data from the three studies is not yet complete, preliminary results do not suggest any biologically significant impact of exposure to the LFA test signal in the types of conditions where SURTASS LFA would actually be employed. Whales that were exposed to sound levels between 120 and 150 dB showed short-term behavioral responses that do not seem to jeopardize the goals of their activity (feeding, breeding, migrating). Some of the singing whales that were exposed to SURTASS LFA sounds appeared to respond to the sounds, either by avoiding the playback vessel or by ceasing to sing. However, an equal number of whales exposed to the same sound levels continued to sing throughout the playback. Click here to see and hear an example of the latter.
Publications from the Low-Frequency Active Sonar (LFA) Research Program:
Croll, D. A., C. W. Clark, J. Calambokidis, W. T. Ellison, and B. R. Tershy. 2000.
Effect of anthropogenic low-frequency noise on the foraging ecology of Balaenoptera whales. Animal Conservation (in press).
Miller, P. J., Biassoni, N., Samuels, A., and Tyack, P. L. 2000.
Whale songs lengthen in response to sonar. Nature 405(6789): 903.