Northern elephant seals are the second-largest kind of seal. The males have huge noses that can look like an elephant’s trunk! Sometimes, these seals are out on sand. They may be fighting each other or raising their babies. The animals also snooze for about 10 hours each day on the beach.
However, northern elephant seals spend most of their lives in the water. The animals go into the ocean for about eight months of the year. They catch fish and squid to eat. Scientists wondered: When do the seals catch Z’s?
Jessica Kendall-Bar led a study to find out. She and her team worked with seals in California’s Año Nuevo State Park. The experts used tags to track the seals’ movements and how deep they go in the water.
Kendall-Bar also found a way to record a seal’s brain waves. That information tells scientists when the seal is asleep. “We used the same sensors you’d use for a human sleep study,” Kendall-Bar said. But these sensors needed to stand up to a seal’s diving, so the team attached a head cap to keep water away.
The study showed how seals sleep at sea. In shallower waters, the animals sometimes rest on the seafloor. But in the ocean deeps, they take short naps while diving! The data showed the seals diving down and entering a deep sleep. Next, they moved into rapid-eye-movement (REM) sleep. In that state, the seals turned upside-down. They continued sinking in a spiral pattern, like a falling leaf.
These diving naps don’t last long. The seals sleep in short bursts of about 10 minutes. And altogether, the animals get by on about two hours of sleep each day! That’s a lot less than most . The seals are up against African elephants for who can sleep the least. Elephants also get about 2 hours of snoozing.
Unlike elephants, northern elephant seals hold their breath while sleeping. After all, they are snoozing under water! The researchers have an idea about why the seals nap so deep. The surface of the ocean is more dangerous. Sharks or killer whales could eat the seals. Luckily, the seals are “able to hold their breath for a long time,” Kendall-Bar said. “So they can go into a deep on these dives, where it’s safe.”
Kendall-Bar plans to use her system to study other animals. What more can she learn about snores?
Updated April 26, 2023, 5:02 P.M. (ET)
By Ashley Morgan