ITHACA, N.Y. -- Humpback whales seem not to be bothered as they swim near a scaled-down version of the Acoustic Thermometry of Ocean Climate (ATOC) underwater speakers that produce a sound some critics fear would harm them, a Cornell University team of biologists has reported to the National Marine Fisheries Service.
When the independent biologists, who are hired to monitor marine mammal behavior before and during the ATOC experiment, previewed the low-frequency sound for the whales, nearby pods of humpbacks carried on as if it were just another noisy day in the ocean.
"In 84 trials beginning in February and continuing through March off the Kona-Kohala coast of Hawaii, we saw no overt response from the whales. For example, a cow-calf pod remained about 100 meters from our playback boat throughout an entire playback," said Adam S. Frankel Ph.D., the biologist from the Cornell Bioacoustics Research Program who directed the study. "We saw whales swim directly under the playback boat to join others in their pod, and in at least one case, a humpback continued singing very close to the speaker."
Previous observations of ATOC transmissions at Pioneer Seamount, the California coastal site for the other ATOC speaker, also found no sign of disturbance among marine mammals, including elephant seals and several whale species. Full operation of the controversial ATOC experiment is subject to approval of the National Marine Fisheries Service, which is reviewing reports from the Marine Mammal Research Program.
Start-up of ATOC was delayed in 1994 when some biologists and environmentalist groups expressed concern that ATOC sounds could harm -- or even deafen -- whales and other marine mammals with sensitive hearing. Run by Scripps Institution of Oceanography, ATOC seeks to measure global ocean temperature by transmitting sound signals along deep-ocean paths from California and Hawaiian speakers to 18 receivers cattered 150-10,000 kilometers away.
Because sound travels faster in warmer water, shorter travel times would indicate that the oceans are warming. The $5.7-million Marine Mammal Research Program is headed by Christopher W. Clark, director of the Cornell Bioacoustics Research Program.
The Hawaiian ATOC simulation used an underwater speaker about one-tenth the size and one-hundredth the power of the ATOC sound source to test effects of sound on nearby whales in relatively shallow water. Whereas the simulation sound source was located 1 kilometer offshore and 40 meters below the surface, the actual Kauai ATOC speaker will broadcast from 829 meters below the surface and 14 kilometers off shore. As will be the practice for ATOC, the Hawaii simulation speaker's decibel level was "ramped up" over five minutes to allow animals a chance to move away.
But if any Hawaiian whales responded to the sound, their reactions were not noted by shore-based observers in the field. The observers charted swimming courses of whale pods during sound transmission and during no-sound transmission periods. To ensure scientific objectivity, observers were not told when the sound (which is inaudible above water) was broadcast. The swimming courses during sound transmission and in no-sound periods were practically identical, Frankel's group reported.
The simulation experiments were conducted in mornings and afternoons. First, shore observers monitored normal whale behavior for at least 25 minutes. Then a 25-minute session of ATOC sound (or no-sound, for experimental "controls") commenced. Next, observers watched the whales' behavior for at least 25 minutes following the transmission session. The computer-generated ATOC tones were identical to what will occur throughout the Pacific, except that they were scaled down in volume to account for the closeness of the whales and the shallow depth of water.
Even during the ATOC non-transmission periods, the Pacific around the Hawaiian islands is hardly a quiet place, Frankel noted. Underwater microphones connected to one of the ATOC simulation boats recorded what whales and other marine mammals hear every day: the ocean's ambient sounds, such as wind and waves, seismic activity and animals, including the humpbacks themselves, vocalizing loudly. Offshore human activity -- from kayaks and larger recreational craft to fishing boats, tugs and barges, and U.S. Army landing ships -- produces loud sounds.
"We're getting very site-specific information on ambient noise and human-generated noise in the Hawaiian environment," Frankel said. Back in Ithaca, N.Y., scientists at the laboratories of the Cornell Bioacoustics Research Program are analyzing hundreds of hours of underwater sound recordings made during the ATOC session. They are listening for more subtle whale reactions to the simulated sound, such as changes in breathing rates and unusual vocalizations. One analysis tool is "Canary," a computer program originally developed at Cornell for examining bird sounds, and which is now adapted by researchers around the world -- not only to analyze vocalizations of animals of all kinds, but also seismic events, including underwater earthquakes as well as tornadoes and even heart EKGs.
"Whales are individuals, just like people, and some appear to be more sensitive than others," Frankel said. "Some react to a given vessel and some do not. Likewise, we may expect differences in how the whales respond to the ATOC project."
Monitoring of marine mammals' behavior must continue when the full-scale ATOC source is operating in Hawaii, Frankel said. One concern is for animals capable of diving through the so-called "deep sound channel," the 800- to 900-meter deep layer of water that catches and transmits sounds much farther than shallower parts of the ocean. Sperm whales are known to frequent the deep sound channel, but they are not believed capable of hearing low-frequency sounds of the type generated by ATOC.
"There's so much we need to learn about whales, especially about their sensitivity and response to sounds," Frankel commented. "Unfortunately, you can't just call a sperm whale into the lab, put on a set of earphones and give it a hearing test. So we're proceeding very cautiously."
ATOC-Marine Mammal Research Program scientists began gathering "baseline" data on whale behavior and distributions off the north shore of Kauai as early as 1993. One condition of federal permits to operate the ATOC sources is that if adverse effects are noted among marine mammals, the experiment will be modified or halted.
"ATOC is an important international study that can tell whether global climate conditions are changing, not only for those of us on the surface but for organisms in the oceans. Any noted changes in the ocean ecosystem could mean change on the surface ecosystem. It's definitely worth doing and I hope it can continue," Frankel said. "But we're here for the whales and the other marine mammals. It's their welfare we're primarily concerned about."