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People May Interfere With Whales' Songs

Science: Researchers find that the animals may become confused by sound pollution.

June 20, 2002|EMILY SINGER | TIMES STAFF WRITER

Researchers have identified the source of a deep rumbling in the ocean as the song of the male fin whale, raising concerns that its mating calls are being disrupted by sound pollution from sonar and commercial shipping.

The whales sing in a very low frequency that can travel long distances across the ocean. Because man-made sounds, like sonar, occur in a similar range, scientists speculate that the whales' "love songs" are being drowned out, according to a new study of fin whales published today in the journal Nature.

Christopher Clark, director of the bioacoustics research program at Cornell University and co-author of the study, said whales once could talk to neighbors 100 miles away, but now might only find friends and mates within five to 10 miles. For a fin whale in a noisy part of the ocean, its "world would suddenly get smaller," Clark said, adding that the animals' shrinking sphere of communications could limit their breeding encounters.

Designated an endangered species by the U.S. Fish and Wildlife Service, fin whales are dispersed over the world's oceans. Their present population is estimated to be about 40,000 in the Northern Hemisphere and up to 15,000 to 20,000 in the Southern Hemisphere.

Because the whales are so spread out, scientists were unable to pinpoint them as the source of the booming ocean songs. Using a technique that is similar to one the U.S. Navy uses to track submarines, researchers were able to attribute the song, one of the loudest in the sea.

Scientists used an array of 16 underwater microphones to pinpoint the source of the sounds, which they matched to locations of the whales. The acoustic tracking technique "is like being in a crowded room with your eyes closed," Clark said.

Scientists also had to get close enough to the whales to collect a sample of skin cells, which they then tested to determine the sex of the animal.

Unlike the sometimes high-pitched songs of the humpback whale, fin whale songs are in a low frequency range that is undetectable to the human ear.

Clark said whales from the same area sing the same song, which lasts 10 to 15 minutes and has a very stylized structure. More distant whales have a different "dialect," he said.

The direct impact of the man-made noise pollution on whale breeding is still uncertain. There is evidence that some sonar sounds can deafen or daze whales.

"One hundred years ago, the ocean was 100 times quieter," Clark said. "Some of these animals can live that long and remember when the ocean was a much quieter place."

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