It was unclear for a long time whether the still mysterious shark needs sleep. But now it turns out that wide-eyed sharks are taking a nap.

It’s a question scientists have been pondering for some time: do sharks actually sleep? The answer has long been shrouded in mystery. It was thought that sharks, which constantly have to swim to breathe, may not doze at all. But a new study now proves that these cold-blooded and fearsome animals may be more like us than you might think.

Interesting question

Researchers are very interested in whether or not sharks sleep. “Sharks are the earliest living vertebrates with jaws,” the researchers write in their study. “Therefore, they may play an important role in understanding the evolutionary history of sleep among vertebrates. Yet very little is known about whether or how these ancient predators sleep.”

Did you know…
…oceans are rapidly losing their sharks and rays? The number of sharks and rays has plummeted by more than 70 percent in the past 50 years. Researchers fear for the survival of quite a few species. And that would mean that we can no longer study important and interesting issues, such as the subject in the current study. Read more here quickly.

To get to the bottom of it, the team decided on the so-called checkerboard swell shark (Cephaloscyllium isabellum) – a nocturnal animal – to be subjected to a closer inspection. They then looked for behaviors characteristic of sleep. Think of closing the eyes, a lower metabolism and a slower reaction time.

nap

The study leads to an interesting discovery. Because it seems that the checkerboard swell shark takes a nap every now and then. “We have found the first physiological evidence of sleep among sharks,” the researchers say. What does that show? “Sleeping sharks not only have a reduced responsiveness, they also have a lower metabolism,” the researchers write. In addition, the checkerboard swell shark also has a somewhat peculiar posture when it sleeps. Similarly, a flat body position seems to indicate that the shark has dozed off.

wide eyes

It means that sharks also need sleep and therefore look more like us than we think. There is, however, an interesting difference. When we go to sleep, we close our eyes. The checkerboard shark does not always do that. At night, the shark often sleeps with both eyes wide open – a somewhat creepy sight. He does close his eyes during the day, although the researchers don’t think this has anything to do with his sleeping state. “External factors, such as incoming light, may explain it,” they suggest.

All in all, the researchers show that even the shark, a primitive vertebrate, needs sleep and is likely to become more energetic thanks to a good night’s sleep. An important step that somewhat expands our knowledge of these mysterious animals, although much is still unknown about sleeping sharks. “Sleep is still largely unstudied in this diverse group of cartilaginous fish,” the researchers write. “Future studies should therefore focus on other physiological cues, such as changes in brain activity. That will give an even more complete picture of how these vertebrates sleep.”