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sound is the potential consequences of the size of their body and anatomical features with respect to the wavelength of mid- frequency sonar transmissions. MacLeod and D’Amico (2006) compared body lengths of Cuvier’s beaked whales from the mass strandings in Greece 1996 and Canaries 2002 with those of all types of Cuvier’s beaked whale strandings from around the world, and found that the beaked whales which stranded coincident with sonar transmissions had body lengths less than 5.5 meters. Underwater the wavelength of sound at 3 kHz, the dominant frequency of tactical sonar transmissions, is approximately 0.5 m. Thus the characteristic dimensions of their overall size and prominent anatomical features are between about 0.1 and 10 times the wavelength of incident sound (0.05 – 5 meters). In this regime sound is partially reflected, scattered, and diffracted and these secondary waves constructively and destructively interfere with the incident sound and each other to produce regions of high and low sound intensity levels throughout the whale’s body. Therefore because of their anatomy, a simple model will not accurately predict the interaction between mid-frequency sonar and Cuvier’s beaked whale. To address this issue, the National Oceanographic Partnership Program funded a 3-year project last year to develop a sophisticated computational model of a “virtual beaked whale” that will accurately model this complex acoustic interaction. Results of this effort will also be forth- coming within the next 2-3 years.
Progress on recommendations for noise exposure criteria
In the absence of data, scientists and government regula- tors have always been precautionary in recommending noise exposure criteria for marine animals. The observations of bowhead and gray whales exposed to drilling and dredging sounds in the early 1980’s indicated that a received broadband SPL of 120 dB re 1 μPa was the threshold for behavioral dis- turbance of baleen whales; however, strict worldwide adher- ence to this criterion would have effectively shut down all sci- entific research in the ocean—even the research needed to learn more about the effects of sound on other marine species.
In 1995, based on observations of whales exposed to seismic air gun pulses and ATOC signals, NOAA Fisheries set a sound pressure limit of 180 dB re 1 μPa that could not be exceeded for mysticetes and sperm whales, and 190 dB re 1 μPa for most odontocetes and pinnipeds. However in the late 1990’s, the 180 dB limit began to be applied to all species and all sounds (including SURTASS LFA) after an expert panel convened by the High Energy Seismic Survey (HESS) team decided that the best available data in 1997 indicated that received sound pressure levels exceeding 180 ±10 dB, averaged over the pulse duration, could potentially have adverse effects with the ±10 dB variability depending on species (HESS 1999). Given the new hearing data for dol- phins and white whales since that time, the 195 dB re 1 μPa2-s SEL level for onset of TTS has recently been applied to many odontocete species.
A panel of scientific experts that was originally convened and supported by NOAA Fisheries, has met for several years and just recently completed the most comprehensive set of
recommendations for marine mammal noise exposure crite- ria. The results of their efforts were published in a special issue of the journal, Aquatic Mammals (Southall et al., 2007). These recommendations, which account for different types of sounds and different effects for multiple species, are yet to be vetted in the scientific and environmental communities.
Recommendations for noise exposure criteria for fish have followed a similar path, but with more emphasis on hearing and direct injury instead of behavior. Because of the relatively small size of most fish with respect to underwater acoustic wavelengths, their whole body will oscillate back and forth when exposed to most anthropogenic sound sources, making non-auditory tissue damage more likely than in marine mammals. Because smaller fish have less iner- tial resistance to motion, they are more at risk. The first rec- ommendation for a noise exposure limit for fish was made in 1990 for a U.S. Navy intermediate scale submarine test facili- ty being built on Lake Pend Oreille in Bayview, Idaho (Hastings, 1990). Very little data were available at that time so the recommendation for “no harm” was 150 dB re 1 μPa based on earlier data showing that goldfish had TTS after being exposed to pure tones near this level for 4 hours (Popper and Clarke, 1976). After the PIDP in 2000, Caltrans actively supported an assessment of all available data to establish recommendations for noise exposure criteria appli- cable to pulsed sound from impact pile driving. The latest rec- ommendations (Carlson et al., 2007) for direct injury exposure criteria are an SEL ranging from 183 to 213 dB re 1 μPa2-s, depending on mass of the fish. These end points are based on data from a blast experimental study on juvenile fish (Govoni et al., 2003) and the SURTASS LFA CEE on larger fish (Popper et al., 2007), respectively. In addition dual criteria consisting of a peak SPL and cumulative SEL were recom- mended for TTS based on the results of the riverine air gun study by Popper et al. (2005). These data indicate that salmonids will experience a TTS of 20-25 dB after a cumula- tive SEL of only 185 dB re 1 μPa2-s.
As reported in the January issue of Acoustics Today, in October 2007 the Accredited Standards Committee S3, Bioacoustics, approved the formation of a new subcommittee, S3/SC 1 Animal Bioacoustics (Delaney and Blaeser, 2008). Three previously existing working groups (WG) were moved into this Subcommittee, including S3/SC 1/WG 2 Effects of Sound on Fish and Turtles. This WG has been meeting since September 2004 to formulate standards for noise exposure cri- teria for fish and turtles. A similar working group for marine mammals would greatly facilitate establishment of standards for noise exposure criteria for these animals.
Where do we go from here?
Because beaked whales are the only group of marine mammals known to have died from exposure to anthro- pogenic sound, determining the causal mechanisms of those stranding events remains a top research priority in the near future. But another very critical issue is the lack of hearing data for mysticetes. There are no behavioral or electrophysiological hearing data for any species of these large baleen whales. Effects of sound on their hearing and subsequent behavior are
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