Navy sonar might give whales the bends. Newfound tissue damage in beached whales and other cetaceans is suggestive of decompression sickness, which afflicts divers when they surface too quickly from a great depth. The work provides some of the first clues into how military sonar might cause whales to strand themselves and could eventually lead to regulations to protect the animals.
Whales seem to strand themselves when sick or dying. In the last decade, observers have noted strandings during or just after naval sonar exercises. Historical records of strandings and naval exercises have shored up the link, but exactly how the sonar would prompt whales to beach remains unclear (ScienceNOW, 10 February). One research group proposed that sonar might cause tiny bubbles in blood to quickly expand, damaging organs in something similar to decompression sickness. Many experts doubt that the animals--which are adapted to deep diving--could suffer from such a syndrome.
New evidence bolstering the idea comes from a Spanish research team headed by Antonio Fernandez, a veterinary pathologist at the University of Las Palmas de Gran Canaria. In September 2002, the group examined 10 of 14 beaked whales that stranded themselves in the Canary Islands just after the start of naval war games. In the 9 October issue of Nature, they report that all had hemorrhages and bubble-like lesions in several organs. Another article in the same issue describes similar tissue damage in eight of 1402 beached cetaceans examined over 11 years by a team coordinated by veterinary pathologist Paul Jepson of the Zoological Society of London. Together, the two studies suggest that cetaceans can suffer from decompression sickness and that naval sonar may somehow prompt it, Jepson says.
"It's important we have this information," says Ted Cranford, a marine mammalogist at San Diego State University. But Cranford and the researchers caution that the results, although consistent with the bends, are by no means proof. Scientists still need to figure out if sonar forces the whales to surface too quickly or whether it might damage tissue another way.