Elephant seals can sleep while diving

November 11th, 2009 - 1:38 pm ICT by ANI  

Washington, November 11 (ANI): In a new study, scientists have determined that during some of their dives, migrating northern elephant seals slowly roll on their backs and allow themselves to sink downward, catching some sleep as well, to rest in the ocean depths.

Moving from their breeding colonies in California to their wintering areas in the mid-Pacific and around Alaska, the seals spend two to eight months at sea without a single pit stop.

There’s no land to climb on along the roughly 2,000- to 3,000-mile (3,200- to 4,800-kilometer) voyage, and the seabed is often miles below the surface.

It’s long been known that, during the seals’ epic migrations, the animals engage in repetitive dives down to depths of 984 feet (300 meters) or more.

Now, according to a report in National geographic News, a study of young elephant seals has revealed that during some of these dives, elephant seals roll on their backs and allow themselves to sink.

The seals wobble as they drift down, and most of the time their bodies follow circular paths toward the bottom of the sea, according to study co-author Russel Andrews, of the University of Alaska, Fairbanks.

“They resemble a leaf that has dropped from a tree branch and is falling toward the ground, fluttering from side to side,” he said.

These slow periods of aimless drifting suggest to the researchers that the seals are resting-and maybe even catching some sleep.

Elephant seals rarely spend more than a few minutes on the surface during their migrations, and seals have never shown the same one-sided brain activity that dolphins and whales do during lab studies.

“Elephant seals apparently can’t rest and remain vigilant at the same time, so we figured they were using an alternative solution,” Andrews said.

To investigate, a team led by Yuko Mitani, of the National Institute of Polar Research in Tokyo, fitted six juvenile elephant seals from California’s Ano Nuevo State Reserve with data loggers.

The seals were then released about 21 to 43 miles (35 to 70 kilometers) away and tracked as they made their way back to the Ano Nuevo reserve, a trip that took the seals one to five days to complete.

“Fortunately for us, as the seals swam back to the rookery, they performed the same kind of repetitive, deep-diving behavior that they do on their migrations across the Pacific,” Andrews said.

During some of those dives, the tags revealed, the seals fluttered like leaves toward the ocean floor.

Mitani’s team thinks this method of sinking allows the seals to rest without falling too far too fast. (ANI)

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