By: Brady Cheng
Northern elephant seals swim for a long time, but only sleep for two hours a day in total.
It’s amazing how they can go on long journeys without sleeping that much. They are also hunted by sharks and killer whales, but they can survive on only fish and squid. They dive all the time, but rarely sleep.
They sleep very peculiarly, though. “The data revealed that when a northern elephant seal wants to sleep at sea, it first dives 60 to 100 meters (200 to 360 feet) below the surface. Then, it relaxes into a glide. As the seal nods off, it keeps holding itself upright for several minutes. But then, the seal slips into a stage of rest known as REM sleep. During this sleep stage, the animal’s body becomes paralyzed. A slumbering seal now flips upside-down and drifts in a gentle spiral toward the seafloor.”(Maria Temming). This shows that first, they first dive underneath, and they slip into REM sleep and their body gets paralyzed. Next, the seal gently floats down to the seafloor. This takes about 20 minutes every time they rest after a sea journey, and then they wake up. It’s very fascinating, and they sleep very differently from humans. They also don’t get grouchy when they don’t get enough sleep like humans do(sometimes).
Another fascinating part about their sleep routine is that they sleep with half their brain on at a time. “Curiously, the sleep habits of northern elephant seals seem quite different from those of other marine mammals. When studied in the lab, many marine mammals sleep with just half their brain at a time. That half-awake state allows dolphins, fur seals and sea lions to constantly watch for predators. They literally sleep with one eye open.”(Maria Temming). This would be really helpful because if they don’t have one half of the brain on, then a predator could easily eat them when they are snoozing. Having half the brain on, it would be useful to look out for predators. Also seals are usually tasty snacks for other predators so they can’t be dozing completely and just get eaten and get surprised. That is why they sleep with half their brain on.
These seals are very smart and they have very different sleep routines. You should learn more about them, because they are very fascinating creatures! If you don’t like to sleep, or can’t sleep, maybe you’re part-seal!