"We can gather a large amount of information from each of these records," Patrick Miller, of the University of St. Andrews in Scotland, said at a May meeting of the American Geophysical Union in Baltimore, Maryland.
Miller's team found that despite the fact that airguns are designed to beam energy downward, the whales encountered substantial decibel levels at distances as far as 7.4 miles (12 kilometers) away.
The animals didn't attempt to flee from the noise, and they didn't display any dramatic alterations in their diving behavior.
"They didn't suddenly change direction," Miller said. "All eight whales did behaviors that were normal for sperm whales."
But Miller says that the fact that the whales continued to dive doesn't mean that they weren't disturbed by the sound.
From the animals' perspective, he says, it may be better to endure the noise and stay where they know there is food rather than move to a quiet location where they don't know if there's anything to eat.
The survey did reveal that while the sound was on, diving whales seemed more lackadaisical, making fewer strokes with their flukes.
The marine mammals also tended to emit fewer buzzing noisessounds that sperm whales make when closing in on the squid that are their prey.
Fewer buzzes, Miller said, means fewer prey capture attempts, indicating that the noise might be interfering with the whales' hunting ability.
Not surprisingly, however, there is a lot of variation in the frequency with which whales find prey, even under the best of circumstances.
"We need more data," Miller said. "It would have been really nice to have gotten even three or four more tests."
Miller's team also noted that the whale that was closest to the airguns during the experiment spent the entire time resting on the surface. As soon as the airguns were turned off, the animal began to dive.
"That suggests that the whale delayed diving until the end," he said. "Maybe it was just sleeping really well, and when the airgun stopped it said, Gee, I'm hungry.
"But it was a really long resting bout, so that's an indication that the whale avoided deep diving while the [airgun] was on."
Roberto Racca, president and CEO of JASCO Research, Ltd., a Canadian research and development firm, also spoke at the meeting.
"We need a way to monitor stress," Racca said. "If an animal is staying there and suffering, that's important. You can't tell if an animal is just grinning and bearing it or if it's comfortable."
Once scientists know what levels of sound are harmful, it's possible to use their increased knowledge of underwater sound dispersal to determine how close a whale can be before oil exploration operations should be shut down.
That type of analysis should be an important step in planning offshore surveys, Racca says.
"It affects the selection of routes and equipment."
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES