January 17, 1996 Contact: Robert Irion (408) 459-2495; irion@ua.ucsc.edu

FIVE TRANSMISSION CYCLES AND MARINE-MAMMAL SURVEYS COMPLETED IN CALIFORNIA PORTION OF ATOC PROJECT

FOR IMMEDIATE RELEASE

SANTA CRUZ, CA--Marine biologists report progress in their research to measure the effects of low-frequency sounds on marine mammals. During the first five transmission cycles from the California sound source in the Acoustic Thermometry of Ocean Climate (ATOC) project, the researchers observed no dramatic changes in marine-mammal behavior that would have required them to stop the broadcasts.

Scientists have spotted large numbers of whales, dolphins, and other animals near the sound source during aerial and boat-based surveys, both when the source has been on and when it has been silent. Although the scientists have detected no apparent changes in behavior, any conclusions must await the collection of additional data plus detailed analysis, which is now under way.

"Even though we got a late start, the research program is going extremely well," says marine biologist Dan Costa of the University of California, Santa Cruz, who leads ATOC's Marine Mammal Research Program for California. "The exciting thing is that we have seen lots of animals in the study area even during the winter months, when we weren't sure what to expect."

The ATOC sound source is located on the Pioneer Seamount, about 50 miles offshore from Half Moon Bay and 3,200 feet under the ocean surface. A concern about this location was that scientists might not see enough animals in the area to gauge whether the sounds affected marine mammals in any way. However, ATOC surveyors have seen numerous whales in the area, as well as hundreds and sometimes thousands of Pacific whitesided dolphins. The whales include dozens of sperm whales, a species of particular interest because they dive to depths of thousands of feet, which could take them near the sound source.

"If we continue to see large numbers of animals near the Pioneer Seamount, we'll be in a better position to draw some conclusions about their behaviors," Costa says.

Other species sighted to date include humpback whales (which migrated out of the area after December), blue whales, fin whales, gray whales, Baird's beaked whales, Cuvier's beaked whales, killer whales (orcas), and pilot whales; Risso's dolphins, northern right whale dolphins, and Dall's porpoises; northern elephant seals, California sea lions, Steller sea lions, and northern fur seals; and leatherback sea turtles.

The source has broadcast for two cycles at low power (185 decibels at a distance of three feet from the source) and for three cycles at full power (195 decibels, ten times louder at the same distance). The intensity of the sounds, which are akin to low-pitched rumbles, diminishes rapidly through the water with distance. Transmission cycles at 185 dB took place on December 2-3 and December 21-23; 195 dB transmission cycles occurred on December 28-January 1, January 4-6, and January 10-12.

During each cycle, the source turned on for twenty minutes every four hours. It ramped up to full volume for five minutes at the start of each twenty-minute broadcast. Each cycle lasted from one to four days, depending on weather conditions.

The overall goal of the surveys was to ascertain the distributions and abundances of animals near the sound source both before and during the transmission cycles. The research team surveyed the ocean mainly via airplane, which offered faster and more complete coverage than a boat. The aerial surveyors are trained marine-mammal observers from the Cascadia Research Collective, under the direction of chief scientist John Calambokidis. The team surveyed the area before each transmission cycle, then did another flight 24 hours after the cycle began. Each survey covered a square of ocean surface about 50 miles on a side, centered over the sound source.

Both of the 185 dB broadcasts and the first two 195 dB broadcasts included aerial observations at the moment the source turned on. This let the team watch for any immediate changes in animal behavior. Costa also led two boat-based observations, for the first 185 dB cycle and the first 195 dB cycle.

Costa expects to use boat surveys in the future when especially large groups of animals are sighted, and for planned studies on elephant seals that will form a key component of the Marine Mammal Research Program. This spring, the team will transport several elephant seals near the sound source and monitor their returns to shore at Ano Nuevo. Time-depth recorders attached to the elephant seals will show whether the deep-diving animals steer away from Pioneer Seamount or change the depth or duration of their dives during their trips home.

Initial data from fourteen naturally migrating elephant seals, each carrying a satellite tag that tracks position in the ocean, have shown no dramatic changes in their routes to Ano Nuevo from the Gulf of Alaska. Most of the animals passed directly over Pioneer Seamount, even when the source was on.

Tentative plans for the next several months call for at least one more transmission cycle at 195 dB in January, two in February, and then at least two per month in March and April. ATOC's Marine Mammal Research Program is scheduled to run at least through September 1996.

Editor's note: For comment on ATOC's Marine Mammal Research Program, contact Dan Costa at costa@biology.ucsc.edu or (408) 459-2786. For overall comment on ATOC, call program manager Peter Worcester at the ATOC Office, Scripps Institution of Oceanography, (619) 534-1294.

Press Releases Home | Search Press Releases | Press Release Archive | Services for Journalists

Maintained by:pioweb@cats.ucsc.edu