Do Sharks Sleep?

Sharks are enigmatic creatures, but if there's one emotion we've felt comfortable assigning to them over the centuries, it's severe crankiness. But what if it's not in their nature to be underwater rage machines? What if they're just really tired? Do sharks need a nap? While we're at it, could they nap if they wanted to?

The short answer is "not really," but the caveats seem to be almost as varied as the ocean's many Jaws variants themselves. See, there are over 400 species of sharks out there, and those are just the ones we know and make movies about. Their physiologies are myriad and, due to their habit of living underwater, largely undocumented. Universal facts about the creatures are few and far between, with even the old "sharks have to keep moving or they'll die" truism only holding up some of the time. Asking if sharks sleep is sort of like asking if birds fly. It depends on which one you're talking about and how you define the action in question.

Tiger sharks, for example, exhibit a behavior called "yo-yo swimming" where they'll ascend to the surface, then semi motionlessly sink down to the ocean floor. Some scientists believe that this is when their brain switches off and rests for a time, while a recent study written about in The Atlantic says that it's actually a strategy used to help forage for food.

Other species seem to be deep into what club enthusiasts call "the ol' cuddle puddle." In a video captured by National Geographic, a group of about twenty whitetip reef sharks all cozy up together in what has to be the most potentially deadly bundle of adorableness ever caught on camera. They fidget, and are aware of their surroundings, but the display doesn't seem to serve any purpose besides kicking back and enjoying some down time.

Long story short: as far as we've been able to tell, sharks aren't likely to ever wreck your morning by telling you about the weird dream they had last night. But some of them love snuggling. Just don't act on that information the next time you go for a snorkel.