Elephant seals amaze scientists with their ability to sleep 1,200 feet deep under the ocean to avoid predators

April 23, 2023



When on months-long foraging expeditions, elephant seals fall downhill into the water in a "sleep spiral" to catch up on sleep, but they are trained not to drown, according to a new research.

To evade predators, seals dive to depths of up to 377 meters (1,235 feet), during which they slumber. According to recent research published in Science, they slide downward for around 10 minutes at a time during half-hour dives, and occasionally they even sleep on the ocean floor.

According to the University of California, Santa Cruz, this study is the first time that researchers have examined the brain activity and noted the sleeping patterns of a free-ranging, wild marine animal.

The study looked at how important sleep is for animals and noted that marine mammals "have particularly difficult conditions for sleep while they are at sea."

When do elephant seals sleep has been a major topic of discussion for many years, according to Daniel Costa, head of the UCSC Institute of Marine Sciences.

As elephant seals leave the Ao Nuevo Reserve for months at a time to travel to the Pacific Ocean, the lab employed tags to trace their movements.

Since they are always diving, according to the dive logs, Costa explained, "we assumed they must be sleeping during drift dives, when they stop swimming and slowly sink, but we truly didn't know.

It is "amazing," according to Professor Terrie Williams of UC Santa Cruz, who spoke to BBC News, that any creature would nod off while drifting hundreds of feet below the water's surface.

This isn't light slumber; this is the kind of paralytic, deep sleep that makes people snore. Surprisingly, the seal's brain consistently awakens them up before they run out of oxygen.

Williams added, "Consider waking up on the bottom of a pool; it sends a shudder down the spine.

With only two hours of sleep every day, African elephants presently hold the record for the least amount of sleep among mammals, but these latest findings indicate that elephant seals "challenge the record," according to UCSC.

Elephant seals spend very little time on the surface of the ocean and only briefly rise to breathe between dives because killer whales and sharks target them there, according to UCSC.

According to research leader Jessica Kendall-Bar, "They're able to hold their breath for a long time, so they can fall into a deep sleep on these dives down below the surface where it's safe."

Electroencephalogram (EEG) sensors were incorporated into neoprene headgear by the researchers in order to monitor the 13 juvenile female seals' brain activity.

According to Kendall-Bar, a postdoctoral associate at UC San Diego's Scripps Institute of Oceanography, "We utilized the same sensors you'd use for a human sleep study at a sleep clinic and a detachable, flexible adhesive to attach the headcap so that water couldn't get in and distort the signals."

The recordings revealed that the diving seals entered "slow-wave sleep" before moving on to REM sleep, which might result in a "sleep spiral" or sleep paralysis, according to researchers.

Elephant seals do sleep a lot when they are on land, roughly 10 hours, according to experts, who called this behavior "strange."
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