By: Katelyn Wei

The northern elephant seals swim in the ocean for several months and take short naps on shore. When on their journey, they only sleep around 20 minutes at times. They only get around two hours of sleep a day.

“It’s important to map these extremes of across the animal kingdom,” says Jessica Kendall-Bar, who studies marine mammals at the University of California, San Diego. Analyzing how long each animals sleep can help answer the question why animals and people sleep.

Knowing how seals slip can motivate people to find methods of protecting the places where they sleep. Normally, the northern elephant seals stay in the Pacific Ocean for most of the year. Those animals hunt for fish, squid, and more. They are normally hunted by sharks and orcas. The seals are vulnerable the most to predators at the sea surface, so they only come out to the air for a couple of minutes.

Kendall-Bar’s team wanted to find out if northern elephant seals do sleep while diving. To find out, they put a cap on two seals. These caps can record the animal’s brain waves, to show when they were asleep.

Looking at the brainwaves, researchers can see how seals move when sleeping. The team released the seals on the Coast of California. Then they match the brain wave readings to their diving motions to show how the seals get sleep on long journeys.

The data showed the northern elephant seal wants to sleep at sea. It first dives and then relaxes into a glide. It can descent hundreds of meters in their naps. However, that is where sharks and orcas normally settle. When the seal wakes up, it swims back to the surface.

Compared with other sea mammals, the northern elephant seals have quite different sleep habits. Most marine mammals sleep with half of their brains asleep, and the other half awake. They sleep with one eye open.

“It’s pretty cool” that elephant seals get by without one-sided sleep, Kendall-Bar says. “They’re shutting off both halves of their brain completely and leaving themselves vulnerable.” Diving far below the predators is how seals rest easily.