2023-04-23 06:00:14
MBut why are they called elephant seals? Because the scientific name of Mirounga didn’t please Darwin? Because, with a weight of some 2 tons, the male crushes, by far, all the other pinnipeds? Because “dominants” develop a trunk-shaped nose? Since Friday April 21 and an article published in the journal Sciencea new answer enriches the catalog: because, with two hours of sleep per night, during the seven months that it spends at sea, the northern elephant seal (Mirounga angustirostris) joins the African elephant in first place on the list of the smallest sleepers.
This result, the team from the University of California at Santa Cruz (UCSC) owes it to the development of a revolutionary sensor. Invented by Alexei Vyssotski, from the University of Zurich (Switzerland), to record the brain waves of birds, it was adapted to the marine world by Jessica Kendall-Bar. Thanks to a Neoprene cap and gold detectors, the UCSC researcher managed to monitor the sleep of thirteen individuals, five in the laboratory and eight in the natural environment, in the Año Nuevo reserve in California.
The results amazed her: while during the five months of the breeding period that it spends on land, the animal sleeps ten hours a day, its daily sleep duration plunges to two hours the rest of the year. , in water. And even : “He reaches them with short naps of about ten minutes, during his half-hour dives at the bottom of the ocean”, says Jessica Kendall-Bar. Because it is in the deep sea, up to 2,000 meters deep, that the animal finds food and security. Conversely, the two minutes he spends on the surface between two dives put him at the mercy of killer whales and white sharks.
Napoleonic naps
By analyzing the recordings, the researchers observed both the slow waves of deep sleep and the faster ones of REM sleep. Just like us. But they noted in animals a particularly long duration of the second (up to 25% of the total, against less than 10% in most species). Above all, thanks to the concomitant measurement of the animal’s movements, also carried out by the sensors, they were able to follow the physical behavior of the animals in these two states. In deep sleep, the pinniped stops swimming and evolves in a normal position, belly down, following a more or less straight downward oblique trajectory. But when he switches to REM sleep, he loses control of his body, rolls over, belly up, and spirals down to the bottom.
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