How Do Marine Animals Sleep?

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

By
Jennifer Kennedy
Jennifer Kennedy
Marine Science Expert
  • M.S., Resource Administration and Management, University of New Hampshire
  • B.S., Natural Resources, Cornell University
Jennifer Kennedy, M.S., is an environmental educator specializing in marine life. She serves as the executive director of the Blue Ocean Society for Marine Conservation.
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Updated on February 07, 2019

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.

How Whales 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.

Walruses - Unusual Sleepers

Pacific walrus (O. r. divergens) in Chukotka, Russia

 Mike Korostelev www.mkorostelev.com / Getty Images

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.

How Sharks Sleep

Sharks use their spiracles to draw in oxygenated water.

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Kennedy, Jennifer. "How Do Marine Animals Sleep?" ThoughtCo, Feb. 16, 2021, thoughtco.com/how-do-marine-animals-sleep-2291914. Kennedy, Jennifer. (2021, February 16). How Do Marine Animals Sleep? Retrieved from https://www.thoughtco.com/how-do-marine-animals-sleep-2291914 Kennedy, Jennifer. "How Do Marine Animals Sleep?" ThoughtCo. https://www.thoughtco.com/how-do-marine-animals-sleep-2291914 (accessed April 2, 2025).