Q:

Do sharks sleep?

A:

Quick Answer

Sharks do not sleep in the way that land animals such as humans do, but sharks do experience quiet periods and undergo what is called sleep-swimming. It was once believed that all sharks had to stay awake constantly in order to move water over their gills to breathe.

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Full Answer

Many species of shark need to swim in order to breathe, but sharks have developed adaptations that allow them to undergo states of lowered consciousness so that their bodies can rest. The sharks that experience something closest to human sleep are species such as the nurse shark, which have spiracles that squirt water across the gills while the shark is at rest. Sharks in this state still have open eyes, and their pupils track the motion of animals in front of them, so it is not a true sleep state.

Sleep-swimmers such as the spiny dogfish continue to move while unconscious. In spiny dogfish, swimming is not a higher brain function, so they can continue to swim regardless of whether they are mentally alert.

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