Low-frequency sonar may be killing dolphins and whales by making them surface too quickly, causing what divers call "the bends."

A team of British and Spanish researchers has found gas bubbles in the internal organs of 14 whales that were found on a beach in the Canary Islands.

The bubbles are a classic symptom of decompression sickness suffered by human divers who surface too quickly. The illness can be fatal in people.

The whales in the Canary Islands became stranded four hours after the use of military sonar during an international naval exercise.

Scientists have known that some deaths of whales and dolphins were connected to the use of naval sonar, but they were unable to determine why the cetaceans were affected.

The team, directed by veterinarian Paul Jepson of the Zoological Society of London, says their findings indicate the sonar caused the formation of nitrogen bubbles in the whales' vital organs.

Post-mortem examination revealed bubbles in blood vessels in their brains and livers, as well as clots of fat in blood in their brains, livers, lungs, kidneys and other tissues. Some of the blood vessels had exploded.

The sonar may be confusing the whales, and causing them to change their diving patterns, or surface too quickly. Another possibility is that loud noises might cause gas bubbles to form in deep-diving marine mammals.

Jepson says the findings should be considered in regulating the use of naval sonar.

The study appears in Thursday's issue of the journal Nature.