Whales sleep for only a short time, while also in a vertical position with one of their brains shut off. This means that one half of their brain is awake while the other half is asleep. This process is called unihemispheric slow-wave sleep (USWS).
USWS in Whales
Unlike humans, whales are conscious breathers, so they have to stay aware enough while resting to keep swimming and breathing. Because they always have to manage each breath themselves, fully shutting down for deep sleep would be risky. USWS solves that problem and lets them rest without drowning.
How Long Do Whales Sleep?
Whales sleep an average of 7.1% of the day, about 25 minutes, the least of any mammal. When they sleep vertically, this record holds. However, their sleep can last longer if they sleep horizontally. This happens as whales use USWS during low-level activities.
Why Do Whales Sleep Vertically?
Scientists still aren’t certain why whales adopt an upright posture to rest. One idea is that it helps them stay partly alert to what’s happening around them. Staying vertical may also keep them near the surface so breathing is easier, though it could simply be a habit.
