Sharks are creatures that don’t sleep. They change their activity level throughout the day, cycling between an active state and a restful state. In the restful state, they slow down or halt their swimming to conserve energy, but they do not close their eyes and slip into a sleep-like state.
Some shark species have a sleep-like inactivity called “bottoming” or “sitting on the bottom.” During this period, sharks often rest with their eyes open, staying alert to potential threats or food sources. A 2022 study in the journal Biology Letters offered the first physical proof that at least one shark, the draughtsboard shark (Cephaloscyllium isabellum), genuinely sleeps: resting animals dropped their oxygen use and lay flat against the seabed, with eye closure turning out to be a far less reliable cue than body posture.
Why Can’t Sharks Sleep?
Sharks can’t close their eyes since they lack eyelids. Because of this, scientists think sharks don’t sleep like humans and other animals.
How Do Sharks Rest?
Sharks rest in various ways based on their species.
They rest either by stationary swimming or lying on the ocean floor.
Learn more about how sharks rest.
Some sharks gather oxygen through ram ventilation. They need oxygen-rich water to flow against their gills by swimming; otherwise, they’ll drown. This is why they appear to be swimming idly even when resting.
Sharks on the ocean floor breathe through buccal pumping. They use their cheeks to pump water towards their gills, letting them rest without drowning.
