Deep-diving whales may get bends

WASHINGTON — Sperm whales routinely dive more than two miles below the ocean surface to hunt for giant squid, but a study shows the huge mammals suffer a chronic loss of bone tissue from the bends, a painful condition well-known to human divers.

It long has been believed that sperm whales and other deep-diving mammals are immune from decompression illness, or the bends, which human divers encounter when they surface too rapidly and force nitrogen bubbles into their blood and tissues. Sperm whales have been known to dive as deep as 10,500 feet and stay down as long as an hour.

Michael Moore and Greg Early of the Woods Hole Oceanographic Institution found evidence of the bends in bones of modern sperm whales, but they also found the same damaged skeletons in whale bones up to 111 years old.

This suggests, Moore said, that sperm whales are neither anatomically nor physiologically immune from the effects of deep diving, even though they spend much of their 70-year lifetime at great ocean depths.

A report on the findings appears this week in the journal Science.

Moore said sperm whales apparently avoid decompression injury by controlling how rapidly they surface to breathe and how long they spend on the surface.

As a result, he said, any human activity that changes behavior could cause the whale to be injured further by the bends.

For instance, he said, if acoustic signals from submarines or other human activities caused a sperm whale to surface too rapidly or to remain on the surface too long, it could trigger the bends.

"If any acoustic stressors [such as submarine radio or sonar signals] were to override normal behavior, then they may run the risk of getting acute nitrogen problems which could cause pain and potentially strand them," Moore said. "This study opens the question that acoustic stressors may be impacting the normal physiology of these animals."

A study last year found that some beaked whales that beached themselves in the Canary Islands after a military sonar test bore evidence of suffering from decompression illness, suggesting they were driven to the surface rapidly by noxious underwater sounds.