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During the many months they spend at sea gorging on fish and squid, the massive mammals sleep only about two hours a day.
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A sleeping 2-month-old northern elephant seal at Año Nuevo State Park, Calif.Credit...Rachel Holser
By Annie Roth
April 20, 2023
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It long seemed as though African elephants were the champions of the all-nighter. They can get by on about two hours of sleep. Other mammals need much more, like koalas (20 hours) or you (at least seven plus at least one strong cup of coffee).
But the largest living mammals on land have some competition at sea. Northern elephant seals are also able to sustain themselves on about two hours’ sleep, according to a study published Thursday in the journal Science. The study found that Northern elephant seals sleep far less at sea than they do on land, and the z’s they do catch at sea are caught hundreds of feet below the ocean’s surface. The study’s authors believe that sleeping in the deep allows the seals to power-nap without being eaten by prowling predators.
Northern elephant seals, which are found along the West Coast, are champion divers that can descend to depths of 2,500 feet and stay under for about two hours. They are not as big as elephants, but males can weigh as much as a car and stretch 13 feet long. To maintain their blubbery bulk, Northern elephant seals must spend around seven months at sea each year, gorging on fish and squid.
During these epic voyages, the seals are vulnerable to predation by great white sharks and killer whales. Some marine mammals, such as dolphins and fur seals, can rest half of their brain at a time. This type of slumber, known as unihemispheric sleep, enables some mammals at sea to snooze with one eye open, literally, which prevents predators from catching them off guard. However, elephant seals sleep like us, shutting down their brains completely.
