Young Northern Elephant Seal (Mirounga angustirostris) in the Pacific Ocean
Nature Picture Library/Alamy
How can air-breathing animals sleep safely in the open ocean, where killer whales and great white sharks roam near the surface? It turned out to be a slow sinking to another 300 meters while taking.
This was discovered by Jessica Kendall Burr and her colleagues at the Scripps Institution of Oceanography in California, who developed a system to record the electrical activity, heart rate and movement of elephant seal brains. It consists of a head cap and several electrodes that can detect fin muscle contractions and a motion tracker.
After testing a few captive elephant seals, they attached the system to eight wild female seals with removable adhesive. The team did not do this because the men are larger in size and difficult to attach any kind of device to. Three of these wild seals spent time in the open sea while the device was installed, and two of his remained in shallow water or on the beach.
The device allowed the researchers to identify the movements of the seals when they were in slow-wave sleep (deep sleep) and rapid eye movement (REM) sleep (dreaming sleep). Using this, we were able to look back at previous time and depth records of over 300 wild females and identify when they were asleep and in which sleep stage they were.
According to the study, women in the open sea sleep less than 10 minutes at a time while diving and only about 2 hours total sleep per day, compared to about 10 hours on land. At a depth of about 100 meters, she enters slow-wave sleep and begins drifting downward. “I was really amazed at how well they could maintain their body position,” she says Kendall-Bar.
But when animals enter REM sleep, they lose control. Their bodies turn upside down and sink in a characteristic spiral. The seal then wakes up and swims back to the surface. At depths of less than 250 meters, seals sleep motionless on the seafloor like all other seals.
Other marine mammals have solved the problem of how to sleep in the ocean differently. Only half of the brains of whales and dolphins sleep at a time, while the other half is able to watch out for danger and keep breathing at the surface.
Fur seals use the same trick, reported Jerome Siegel of the University of California, Los Angeles in 2018. Unusually, however, fur seals can undergo both half-brain and whole-brain sleep. increase.
Siegel says he’s not surprised that elephant seals can survive on just two hours of sleep. “We previously reported that an African elephant in the wild sleeps an average of two hours for him,” he says. His team also found that dolphins and killer whales do not sleep at all during the first few months of life.
“Sleep hours don’t correlate with brain size or cognitive ability,” Siegel says.
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