Elephant Seals Take Power Naps During Deep Ocean Dives

It lengthy appeared as if African elephants have been the champions of the all-nighter. They can get by on about two hours of sleep. Other mammals want far more, like koalas (20 hours) otherwise you (no less than seven plus no less than one robust cup of espresso).

But the biggest dwelling mammals on land have some competitors at sea. Northern elephant seals are additionally in a position to maintain themselves on about two hours’ sleep, in response to a research printed Thursday within the journal Science. The research discovered that Northern elephant seals sleep far much less at sea than they do on land, and the z’s they do catch at sea are caught lots of of ft under the ocean’s floor. The research’s authors consider that sleeping within the deep permits the seals to power-nap with out being eaten by prowling predators.

Northern elephant seals, that are discovered alongside the West Coast, are champion divers that may descend to depths of two,500 ft and keep below for about two hours. They aren’t as massive as elephants, however males can weigh as a lot as a automotive and stretch 13 ft lengthy. To preserve their blubbery bulk, Northern elephant seals should spend round seven months at sea annually, gorging on fish and squid.

During these epic voyages, the seals are weak to predation by nice white sharks and killer whales. Some marine mammals, comparable to dolphins and fur seals, can relaxation half of their mind at a time. This kind of slumber, often known as unihemispheric sleep, permits some mammals at sea to snooze with one eye open, actually, which prevents predators from catching them off guard. However, elephant seals sleep like us, shutting down their brains utterly.

Jessica Kendall-Bar, now a postdoctoral fellow on the Scripps Institution of Oceanography in San Diego, questioned how Northern elephant seals managed to sleep, given how a lot time they should spend consuming and avoiding being eaten whereas at sea.

To learn how elephant seals keep away from waking up within the maw of an orca or a shark, Dr. Kendall-Bar labored with colleagues on the University of California, Santa Cruz, to design a tool that would monitor the seals’ mind waves, coronary heart charges, dive depths and motion. The gadget is noninvasive and suits atop the seal’s head like a swim cap. The staff connected the units to the heads of a number of seals and monitored their sleeping habits for 5 days. The knowledge collected by the units revealed a bedtime routine in contrast to some other.

“They dive down, cease swimming and start to glide,” Dr. Kendall-Barr mentioned.

As they go deeper, their mind exercise begins to decelerate.

“Then they transition to REM sleep, the place they flip the wrong way up and spin in a circle, falling like a leaf,” she mentioned.

While in fast eye motion, or REM, sleep, which is the deepest stage of sleep, the seals stayed the wrong way up, oblivious to their sluggish descent.

After sleeping for round 10 minutes, the seals would all of the sudden get up and make their means again to the floor. During these sleep dives, some seals sank over 1,000 ft, typically discovering themselves on the seafloor.

The seals Dr. Kendall-Bar and her monitored colleagues took a number of sleep dives every day, offering them with round two hours of sleep in complete. When Northern elephant seals haul out on land to breed and molt, they sleep for over 10 hours a day. During that point, the seals aren’t consuming, which can clarify their want for additional sleep.

“Sleep is an adaptive trait,” mentioned Jerome Siegel, a professor of psychiatry on the University of California, Los Angeles, who research the evolution and performance of sleep. “Animals have advanced to sleep in sure conditions and never in others.” It makes excellent sense, Dr. Siegel mentioned that elephant seals would restrict the period of time they spend sleeping whereas at sea to take advantage of their meals consumption and scale back the period of time they’re weak to predators.

That would not make seal sleep habits any much less spectacular.

“Northern elephant seals exhibit unparalleled flexibility of their sleep length,” Dr. Kendall-Barr mentioned. “No different mammal goes from sleeping about two hours a day for over 200 days to sleeping 10.8 hours a day.”

Dr. Kendall-Bar hopes her staff’s findings will help within the safety of marine mammals.

“Learning extra about the place, when and the way marine mammals sleep at sea might help scientists enhance the administration of their essential resting habitats,” she mentioned.

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