How Do Marine Animals Sleep?

Learn About Sleep in Marine Animals Such As Sharks, Whales and Walruses

Sleeping in the ocean is definitely different than sleeping on land. As we learn more about sleep in marine life, we're learning that marine animals don't have the same requirements for long periods of undisturbed sleep that we do. Here you can learn more about how different types of marine animals sleep.

Adult fin whale (Balaenoptera physalus)
Michael Nolan/Robert Harding World Imagery/Getty Images

Cetaceans (whales, dolphins and porpoises) are voluntary breathers, meaning they think about every breath they take. A whale breathes through the blowholes on top of its head, so it needs to come up to the water surface to breathe. But that means the whale needs to be awake to breathe. How's a whale going to get any rest? The answer may surprise you. Research on captive animals shows that cetaceans rest one half of their brain at a time, while the other half stays awake and makes sure the animal breathes.

Great Whtie Shark / Getty Images
Great White Shark (Carcharodon carcharias). Stephen Frink / Getty Images
Sharks need to keep water moving over their gills so that they receive oxygen. So that means they need to keep moving all the time... or do they? Some sharks do need to move all the time, and these sharks seem to be "sleep swimming," with some parts of their brain more active than others. Other sharks can rest, using spiracles to draw in oxygenated water.

If you thought you were sleep deprived, check out the sleep habits of a walrus. An interesting study reported that walruses are "the world's most unusual snoozers." The study of captive walruses showed that walruses sleep in water, sometimes "hanging out" by literally hanging from their tusks, which are planted on ice floes.