By: Yimo Liu

Northern elephant seals are experts on napping. They swim at sea for many months but barely sleep at all. During journeys across the sea, they snooze for less than 20 minutes at a time. In total, these seals sleep for only 2 hours a day. Their sleep schedule is similar to that of African elephants. Researchers shared their discovery about the sleep habits of northern elephant seals in the April 21 Science. “It’s important to map these extremes of [sleep behavior] across the animal kingdom,” says Jessica Kendall-Bar. She studies sea mammals at the University of California, San Diego. Learning how much or how little sleep different animals receive could help show why animals, including people, sleep at all.

Northern elephant seals spend most of their time in the Pacific Ocean. At sea, they hunt for fish. Then, they go to sleep. Scientists gave special caps to two of the seals that would track their emotions and brain waves. It showed that the seals dove deep down in the sea in a relaxed manner. Then they would drift off to sleep while they glided down to the bottom of the sea far below the level of water where sharks and killer whales prowl.

Scientists decided to try the caps on the two seals from Año Nuevo State Park somewhere else. They released the seals at another beach, about 60 km south of the park. To swim home, they had to cross the deep Monterey Canyon. After the seals fell asleep, they swam through the canyon.

The funny part is that when the seals reach land, they can sleep safely without worrying about getting eaten. They sleep for about 11 hours on land.

It seems that the seals really need rest after a long sea voyage. They get rest in the ocean, but it’s not enough with thoughts about getting eaten while you’re sleeping.