Do sharks sleep?

It is a common misconception that sharks as a species never sleep because they must constantly move to survive. Sharks do take periods of rest throughout the day, but this is very different from how other animals sleep.

Indeed, many types of sharks must constantly move to obtain life-sustaining oxygen from the water flowing over their gills. This type of shark is called an obligate ram ventilator because they take in water through their mouths and squeeze it out through their gills. Many sharks use a method called "buccal pumping," which involves sucking in water through their mouths and forcing it out through their gills using their cheek muscles. Other types of sharks are able to remain still because they have special structures called spiracles that force water through their gills. Some sharks use both blowholes and cheek pumps. If any of these species stop swimming because they become entangled in the net, they will eventually suffocate.

Regardless of their breathing method, sharks are capable of deep rest in a still state, but they do not enter sleep in the traditional sense. Their eyes are always open, their pupils still monitoring the movements of creatures swimming around them. Sharks capable of resting in a stationary state include whitetip reef sharks, Caribbean reef sharks, nurse sharks, whisker sharks, and lemon sharks.

Great white sharks have long been a topic of interest to marine biologists because so little is known about their life processes. Of course, the big question is "Do great white sharks sleep?" In 2016, researchers studying great white sharks on Guadalupe Island, off the coast of Mexico's Baja California peninsula, when they spotted a female great white shark that appeared to be sleeping. They found the answer. They tracked her with a robotic submersible and watched for several minutes as she drifted against strong currents in shallow water, looking almost catatonic as she opened her mouth and let water pass through her gills.

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