He and his colleagues said there was no evidence of bacterial disease in the whales. Autopsies showed that their blood vessels, livers, hearts, kidneys and fatty tissues were filled with large and rapidly expanding gas-filled cavities caused by the sonar pulses, the scientists said.

The bubble damage, they said, was the same as the damage caused by nitrogen bubbles that divers experience in their tissues when they suffer decompression sickness, or the "bends."

Although the British and Spanish scientists proposed that the whales might have actually developed decompression sickness — possibly by diving and surfacing in panic as sonar impulses reached them — Costa maintained that deep-diving marine mammals cannot get the bends because their lungs collapse when they dive and expel the gases they have breathed at the surface.

The most likely explanation for the bubbles found in the beached whales, said the British and Spanish scientists, is that the sonar impulses created the bubbles directly in nitrogen molecules that were already suffusing their tissues.