Unique sleep solution - A Dreamy Dive to the Bottom

23 May, 2023

If you are surrounded by predators, it is dangerous to sleep, but the elephant seals have found their own fascinating solution.

They dive down towards safer depths, allow themselves to let go of control for a little while – and sing sleep in a dreamy spiral down towards the bottom.

Sleeping elephant seals on the beach at Año Nuevo in California. Photo: Jessica Kendall-Bar/University of California, Santa Cruz/TT

The sleep of elephant seals has long been a mystery to scientists. During the mating season, they can sleep more than ten hours a day on the beach – but what do they do when they are far out at sea to look for food, sometimes for up to eight months at a time?

Now new research shows that during these periods, the northern elephant seal can reduce its sleep to only about two hours per day. That’s as little as the land-based African elephant, which until now has been the mammal world record holder for scientifically documented little sleep needs.

But elephant seals can’t hold their breath for two hours straight, so instead they take repeated shorter naps during half-hour dives. When the oxygen starts to run out, they quickly speed up towards the sea surface again.

– Elephant seals are unusual in that they can shift between sleeping a lot when they’re on land, more than ten hours a day, and two hours or less when they’re out at sea,says researcher Jessica Kendall-Bar in a press release.

Northern elephant seals can spend seven to eight months foraging in the North Pacific, thousands of miles from land. Now scientists have found out how and where they sleep when they are on the open sea. Graphics: Anna-Lena Lindqvist/TT

“Dangerous to sleep”

Neither humans nor animals function without sleep, but it must take place under safe conditions. Each species has found its solution.
Bears retreat into the ice for months, hedgehogs go into near-death-like hibernation in leaf piles, and horses sleep standing up.

-If you lose control over your surroundings, it is dangerous to sleep in certain situations, such as for a person falling asleep at the wheel when driving a car, says Anders Hedenström, professor of theoretical ecology.

Whales and dolphins solve this problem by sleeping with one hemisphere of their brain at a time, which makes it possible to constantly keep one eye open and aware of their surroundings.

Some bird species take advantage of sleeping at high altitudes during gliding, while other bird species can force themselves to stay awake for several days at a time when they migrate – but then sleep all the more when they arrive. An example is the bar-tailed godwit that flies non-stop between Alaska and New Zealand, a journey that takes eight days.

-You can see that when migratory birds arrive after such a long flight, the first thing they do is lie down and sleep, rather than eat, says Anders Hedenström.
In the case of elephant seals, it is important not to lose control of their vision or other sense organs near the surface of the sea during their long journeys out at sea, because then they risk being attacked by great white sharks or killer whales.

A group of resting elephant seals and their cods on Drakes Beach in Point Reyes National Park in California, USA. Photo: Eric Risberg/AP/TT

Mapping the sleep landscape

Jessica Kendall-Bar and her colleagues at the University of California, San Diego, fitted 13 young female elephant seals with equipment similar to that used in sleep laboratories and other equipment to track their movement patterns as they swam across Monterey Bay.

During this relatively short trip, a total of 104 dives down to the bottom were recorded when the elephant seals were sleeping. The data could then be combined with previously collected data on the movement patterns of 334 adult elephant seals far out at sea, and the results were recently presented in the scientific journal Science.

Sov gott. Vilande sjöelefanter, fotograferade i nationalparken i Point Reys i kalifornien i USA. Foto: John Burgess/AP/TT

One of the points of mapping the sleep patterns of marine mammals is that it provides greater insight into how they can be protected. The researchers behind the study wanted to map what they call the elephant seal’s sleep landscape.

Usually you try to protect the areas where animals go to find food, but perhaps the places where they sleep are just as important, notes Jessica Kendall-Bar, who will now use the same methods to investigate more species.

Elephant seals are part of the earless seal genus and there are two species, the northern and the southern.
The northern elephant seal (Mirounga angustirostris) is found on the west coast of North America at California in the United States and Baja California in Mexico.

The southern elephant seal (Mirounga leonina) is found in the sub-Antarctic and Antarctic regions. The southern elephant seal is the largest seal species.

The elephant seal gets its name from the male’s proboscis-like, elongated snout.
They also have long canines, which are used in battles against rivals.

Females have one young per season. When the mating season is over, elephant seals embark on several months-long trips to the sea in search of food.
Sources: National Encyclopedia and National Geographic

Text: Cecilia Klintö/TT
Foto: John Burgess/AP/TT, Eric Risberg/AP/TT, Jessica Kendall-Bar/University of California, Santa Cruz/TT
Grafik: Anna-Lena Lindqvist/TT

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