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Thursday, 6 April, 2000, 17:49 GMT 18:49 UK
Mammal cam reveals diving secrets
Dolphin (Kevin McDonnell)
A dolphin carries the camera pack (Kevin McDonnell)
How do seals, whales and other marine mammals dive so deep on just one gulp of air? Where do they get the energy to do it?

Basically, they're turning the motor on and off in the course of a dive

Terrie Williams
Scientists attached video cameras and other sophisticated instruments to these creatures to find some answers.

And it appears the animals start their dives with a few powerful strokes and then spend much of the rest of the descent in an easy glide to conserve oxygen.

The team looked at Weddell seals hunting beneath the ice in the Antarctic, a northern elephant seal diving in Monterey Bay, a bottlenose dolphin swimming off the coast of San Diego and a 100-tonne blue whale diving in waters close to northern California.

The camera was linked to other equipment
Video cameras were coupled with data from time-depth recorders, speed meters and other instruments. These revealed that all the marine mammals used the same laid-back, energy-saving approach to diving.

Most began with 30 to 200 seconds of swimming followed by a relaxed glide for the remainder of the journey downwards.

"Basically, they're turning the motor on and off in the course of a dive, and that enables them to reduce oxygen consumption by 10 to 15% compared with what they would need if they swam all the way down," said team member Professor Terrie Williams from the University of California, Santa Cruz.

A Weddell seal performed the most remarkable feat, gliding for 6.2 minutes while descending to 540 metres.

What surprised the researchers was how the animals all used common tactics to go deep, even though they are very far apart on the evolutionary tree. The animals' lungs collapse progressively with increased pressure.

Resting allows the animals to extend their dives
"The mass of the animal remains the same while its volume decreases, so it starts to sink," Professor Williams explained.

"The progressive collapse of the lungs in marine mammals preadapts them for taking advantage of the buoyancy change. By resting on the way down, the animals are able to extend their dives.

"They're pacing themselves, saving energy and conserving oxygen until they need to expend it for hunting or avoiding predators."

The research, which is published in the journal Science, was funded by the US Office of Naval Research, the National Science Foundation, and the National Geographic Society.

Whale John Calambokidis
A blue whale heads for the deep (John Calambokidis)

Watch a sealcam
A seal's view under the Antarctic ice
See also:

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