Can Diving Mammals Avoid the Bends?

Thanks to technology like Crittercam, we know more than ever about animals’ lives underwater. But scientists know less about how whales, seals, and other marine mammals can handle the pressure of life in the deep.

(Explore a Crittercam deep-sea interactive.)

In human divers, decompression sickness—or the bends—is a relatively well-known phenomenon that causes gas bubbles to form in the body as they rise back to the surface. The condition can be mild, causing joint pain, or deadly.

For a while, scientists had thought animals were somehow immune to the bends.

Biologists use an ultrasound device on a live dolphin. (Photo by Tom Kleindinst, WHOI)

“Until recently, the dogma was that marine mammals have anatomical and physiological and behavioral adaptations to make the bends not a problem,” Michael Moore, director of the Woods Hole Oceanographic Institution (WHOI)’s Marine Mammal Center, said in a statement.

But now, recent studies suggest the animals are susceptible to the condition, yet are able to actively avoid getting it, said Moore, who was part of an April 2010 workshop on marine-mammal diving at WHOI.

For instance, scientists conducted necropsies on beaked whales that had stranded on the Canary Islands in 2002 following exposure to sonar from naval exercises. The results revealed their bones and other tissues had been damaged by nitrogen gas bubbles, which can obstruct blood flow.

Gas-induced lesions on a rib of a dead sperm whale. (Photo by Tom Kleindinst, WHOI)

That research suggests that diving marine mammals manage—rather than minimize—the nitrogen in their bodies depending on the situation, according to a new paper on the subject, published December 21 in the Proceedings of the Royal Society B.

Because it’s hard to research diving mammals, scientists have come up with some creative work-arounds. At WHOI, for instance, Moore and colleagues have CT scanned marine-mammal lungs to figure out how gases behave in the body. The team has also looked for gases in live, stranded dolphins via a portable veterinary ultrasound unit (see picture above).

Scientists have also identified physical adaptations in deep-diving birds and reptiles.

For instance, emperor penguins may have a supercharged form of a blood protein that allows them to dive underwater for more than 20 minutes on a single breath, National Geographic News reported in 2007.

The research showed that penguins in Antarctica return from long fishing excursions under the sea ice with the lowest blood oxygen levels ever recorded in wild animals. With such depleted reserves, experts say, other creatures would black out and suffer tissue damage.

And in 2010, scientists found that leatherback turtle buoyancy is likely determined by the amount of air they inhale above the surface before they dive. Many animals exhale before they dive, but the leatherback descends with a lungful of air.

(Watch a video of leatherbacks diving.)

For marine mammals, WHOI’s Moore noted that stressors—such as human-made noises—could be a concern if the animals are forced to rise too quickly.

Human divers, for instance, have other options—they can grab another tank or go into a decompression chamber.

But “what does a dolphin do normally when it’s surfaced?” he asked. “The next thing to do is to dive, and the one place you can’t do that is in shallow water, or most particularly if you are beached.”

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Meet the Author
Christine Dell'Amore, environment writer/editor for National Geographic News, has reported from six continents, including Antarctica. She has also written for Smithsonian magazine and the Washington Post. Christine holds a masters degree in journalism with a specialty in environmental reporting from the University of Colorado at Boulder. Her book, South Pole, was published in 2012.