Ocean noise

Fish and whales have their own language of drumming sounds and clicks as they search for food and socialize deep in the ocean. Scientists are trying to understand how man-made noise in the ocean produced by ships, exploration for oil and gas and military sonar affects marine mammals' ability to communicate.

The questions are particularly pressing because the Navy is proposing a 660-square-mile sonar range off the coast of North Carolina to train sailors and pilots to detect submarines. They would use pulses of sound bounced off submerged objects to pinpoint and track submarines.

The Navy's draft environmental study has said sonar exercises would disturb some whales but rejected the possibility of deaths. But the National Oceanic and Atmospheric Administration has questioned the Navy's assumptions about the range and urged the Navy to study the potential for deaths, particularly of beaked whales.

"It's a contentious issue," Brandon Southall, director of NOAA's ocean acoustics program in Maryland, said during a scientific panel discussion at Duke University on Monday. "There is a considerable amount of uncertainty."

Scientists have linked several fatal whale beachings to the use of midfrequency sonar, but they don't understand how the pulses of sound harm the animals.

Peter Tyack, a senior scientist at Woods Hole Oceanographic Institution in Massachusetts, said there had been about a dozen incidents in which mass strandings occurred in the vicinity of Naval sonar exercises. "We still face the puzzle of why they strand," Tyack said.

Scientists do not have an effective way to monitor beaked whales' whereabouts, but research in the past two years offers hope, Tyack said. Beaked whales live deep in the ocean and have shown sensitivity to sonar. Tyack and other scientists attached listening devices, called acoustic tags, to about 15 beaked whales two years ago and monitored them as they dived to forage for food. They heard the whales make clicking sounds at regular intervals after they reached a certain depth. The clicks intensified to a buzz as the whales zeroed in on prey.

Researchers working with the Navy were able to pick up the sounds of beaked whales through underwater microphones at a Navy training center in the Andros Islands in the Bahamas, Tyack said. He said it may be more effective to listen for whales than to try to spot them when they surface for air. "Things look promising to determine a way of telling where they are and aren't," Tyack said.

Andrew Read, a professor at Duke University's Marine Lab in Beaufort, said the Navy is developing monitoring programs that would add to the body of information about marine mammals. "I'm sure we are going to find there are a lot more beaked whales off the coast of North Carolina that we thought there were," Read said.

While the Navy has used sonar for decades, the proposed range marks the first time the Navy has sought approval under federal laws protecting marine mammals to conduct sonar exercises. "The battlefield with regard to military sonar is right here," Southall said. "We are going through the painful first steps with regard to regulation."

Source: The News & Observer Publishing Company