Question: How do whales breath when they sleep if they have to come up to breath every so often?

Laurence Perreault Levasseur answered on 16 Jun 2014:

This is a very cool question! I remember wondering the same thing many years ago! Where I grew up there is a HUGE river, and there are loads of whales and dolphins in it. Once I went in a sea kayak on that river, and a whale started following us!! We also actually saw sleeping whales, and the guide (you should always be with a guide to do something like that!!!) explained the answer:

In order not to drown, whales must remain partly conscious in order to know when their breathing hole is at the surface and they can breath, and when it’s under the water and they shouldn’t. So that means that while their brain rests, there is a part of their brain that is still active.

It happens like this: while they sleep, whales and dolphins always keep half of their brain awake, at a low level of alertness. They also keep one eye open (the opposite side of the awake half of the brain). This way, they can watch for predators, obstacles and other animals, and they know when they need to go back up to the surface to breath! During that time, the other half of the brain is sleeping and resting, and have the other eye closed. Every about 2 hours, they switch which side of the brain is sleeping and which is awake, and the invert the open and the closed eye!