Sharks Can't Stop Swimming — So Do They Sleep?
It doesn't sound very relaxing.
The sleeping habits of sharks have always been a bit of a mystery. In order for most types of sharks to breathe, they have to be swimming, which means laying down to rest isn't possible for them. In order to sleep or take any type of rest, they would need to still be swimming while they do it.
So, how do sharks sleep or rest while still swimming?
As it turns out, sharks don't actually sleep. At least, not in the same way that humans do.
"Sleep is a concept that we think about from a human standpoint," George Burgess, director of the Florida Program for Shark Research, told The Dodo. "There's no particular indication that sharks sleep like humans do, that is, they don't find a place to lay down, close their eyes and check out for periods of time. They reduce their activity level, but it doesn't mean they stop doing their normal activities"
Instead of sleeping the way we do, many types of sharks do something called yoyo swimming, according to Burgess When a shark is yoyo swimming, he stops actually swimming and just starts gliding downwards. He does this until he hits the ocean floor, and then he swims back up to the surface and does it again. By gliding down instead of actually swimming, the shark is able to take a period of rest, which is his version of sleeping.
Sharks who typically live on the ocean floor take periods of rest as well, but their eyes stay open and they're still technically awake while they do so.
There was a case several years back where some scientists found a group of sharks of all different species sitting at the bottom of a cave in Mexico, and named them the sleeping sharks of Mexico. This sparked some rumors about the sleeping habits of sharks, but there ended up being a reason that the sharks chose that specific spot to gather.
"The cave was an underwater spring," Burgess said. "The freshwater inflow is like a narcotizing agent for these sharks. Kind of like the equivalent of an opiate house."
Sharks may not actually sleep, but they have their own way of taking periods of rest - which seems like a bummer, because honestly, sleep is pretty darn awesome.