How Do Whales Sleep?

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

Whales need to be conscious when they sleep in order to swim and breathe, which is why USWS works for them. Unlike humans, whales are conscious breathers, which means they have to continuously think about and control their breathing. To avoid drowning, whales can’t enter deep sleep, so USWS is the perfect solution for them.

How Long Do Whales Sleep?

Whales have been observed to sleep an average of 7.1% of the day or approximately 25 minutes, the least any mammal sleeps. However, this record has been observed only when whales sleep vertically, their sleep can be longer when they are sleeping horizontally. This can be true since whales can utilize USWS when they are doing low-level activities.

Why Do Whales Sleep Vertically?

There is no conclusive observation as to why whales sleep vertically. However, some experts speculate that it may be due to the fact that this allows them to remain conscious and aware of their environment. Another is to help them stay close to the surface for breathing, or it may be just preference.


Whales sleep in a vertical position to conserve energy and remain aware of their surroundings. They enter into unihemispheric slow-wave sleep (USWS), which allows one half of their brain to stay awake while the other half sleeps. This process helps them avoid drowning and conserve energy. Whales have been observed sleeping an average of 25 minutes per day, which is the lowest amount of sleep for any mammal.