Nation & World

BOSTON — An ocean experiment accidentally conducted amid the shipping silence after the Sept. 11 attacks has shown the first link between underwater noise and stress in whales, researchers reported Wednesday.

The analysis indicated a drop in a stress-related hormone found in right whales was tied to a dip in ocean noise that followed a near-standstill in ship traffic, due to security concerns after the attacks.

The work indicates whales and other sea life that use sound to communicate and travel can be harmed by the noise. That could prompt more research and eventually influence ocean traffic and development, said New England Aquarium scientist Rosalind Rolland, the report's lead author.

"This is definitely a very important piece in the puzzle that lends credence to the idea that, yes, we potentially have a problem out there and we need to learn a lot more about it," Rolland said.

The report combined data from two unrelated experiments in Canada's Bay of Fundy that happened to be occurring simultaneously. One involved acoustic recordings of right whales; the other the collection of whale feces samples, which contained stress-indicating hormones.

Rolland didn't realize until 2009 the information existed for the analysis, published Wednesday in the British journal Proceedings of The Royal Society B.

"Here is the first solid piece of evidence that says there's a link between noise level and stress," said Christopher Clark, director of the bioacoustics-research program at the Cornell Lab of Ornithology. Clark, who wasn't associated with the study, noted stress long has been tied to longevity, reproduction, disease and other key health indicators in whales.

There's no international standard for what ocean noise levels should be, and it's been tough to identify the problems caused, Rolland said.

The use of military sonar at sea has been one source of tension between governments and conservationists, who claim such sounds kill whales and other marine life.

Rolland said caveats come with any accidental study. A planned study would have had more acoustic and hormone data. This study obviously can't be repeated. And it's also unclear how much chronic stress from noise whales can take before the population is affected, largely because it's impossible to conduct controlled experiments on 50-ton animals.

But even with the caveats, Rolland said, "It's pretty good evidence. We have no other explanation for these findings."