Scientists have long suspected a link between mass whale strandings and the Navy's use of powerful sonar systems, but the evidence - dying whales washing ashore when sonar exercises occur - has been mostly anecdotal.
Now, international researchers have identified a disorder similar to decompression sickness, or the bends, as the cause of at least some whale beachings, and they say military sonar is most likely to blame.
The new findings, being reported today in Nature, are based primarily on necropsies of 10 whales that stranded themselves in the Canary Islands during an international naval exercise last year that included a U.S. ship.
The incident drew worldwide attention, and environmentalists in California sued this year to stop the Navy from developing a farther-reaching system.
All of the Canary whales examined had widespread bubble formation in tissue and blood vessels, the study says. The same thing occurs in scuba divers who surface too quickly after a deep dive.
"The bubbles forming in these animals may not be immediately fatal," said Paul Jepson, a lead author of the study and a researcher at the Zoological Society of London. "But it does make them distressed or causes impairment, and it's quite logical to conclude that this is what leads them to strand."
The study challenges the conventional notion that marine mammals cannot suffer from decompression sickness.
But more important, said Jean-Michel Cousteau, director of the Ocean Futures Society in California, it demonstrates the toll that underwater noise pollution can have on marine life.
The Navy, stressing that it uses highly trained lookouts and other methods to protect whales, is reluctant to accept the study's conclusions.
"Previous studies have not, to date, revealed evidence of decompression sickness as suggested by the article," Lt. Cmdr. Cappy Surette, a Navy spokesman, said in an e-mail message. "The National Oceanic and Atmospheric Administration and the U.S. Navy were not invited to participate in the studies conducted of these beaked whales and, as a result, we are unable to determine the actual cause of the strandings."