Do Sharks Sleep?
You remember the tune that Dory from Finding Nemo would always sing? “Just keep swimming, just keep swimming, just keep swimming, swimming, swimming…” Yeah, I hear Ellen DeGeneres’ voice in my head singing it too. It’s catchy! But when it comes to the sleeping patterns of sharks it’s also what everybody thinks to be true.
But wait, isn’t it true that they are just always swimming around? If they stop swimming, don’t they lose oxygen in their gills? Well, yes sometimes. But not all of them! Some of them have openings behind their eyes called spiracles (see below) which allow them to take in oxygen when they are not moving.
However, it is true that most sharks need to "just keep swimming…”
But wait, how do sharks sleep then? Well, to be honest, we don’t exactly know. Infact, we are not even sure that they do sleep? Oceanic scientists have recently watched a shark that certainly seemed to be sleeping, but it is difficult to know exactly.
What’s so hard about finding a napping shark? Well, for starters, most species do not have eyelids -- so it’s not like they close their eyes to rest. And, as Dory reminded us, many are always moving around.
Some sharks seem to do what is called "yo-yo swimming." This is when the shark swims to the surface of the water and then rest as they float back to the ocean floor and then “yo-yo” back to the surface again. Can you imagine needing to workout between nap sessions?
It is also difficult to know when a shark is sleeping because we usually understand sleep as a significant change in brain waves. This gives two challenges: for one thing, we can’t easily scan the brains of sharks in the water, but for another, we couldn’t even know when to try to scan them.
The portion of the nervous-system which guides sharks swimming isn’t actually located in the brain, it’s located in their spinal cord. So, from a distance, you might see a shark with its eyes open and swimming as normal, but it could actually be asleep. This is why it’s so tricky to understand them!
Next time you’re out in the water and you find yourself worried about any nearby sharks, just remember that there is nothing to fear. They might not even be awake! But, for peace of mind, it's a good idea to get your Shark OFF shark repellent jewelry before your next adventure. We want to help you "Lose the Fear and Love the Ocean".