How can whales and dolphins sleep without drowning?

2000/05/31 Elhuyar Zientzia

• Zoologia

Although dolphins and whales live in the sea, they are mammals and have to sleep like mammals.

Humans normally breathe unconsciously, that is, breathing is not a conscious action. For whales and dolphins, breathing is a conscious act, and every time they have to breathe, the brain sends them the command to breathe and go up to the surface of the water to breathe.

Thus, sleeping is not easy for these marine animals. And being asleep they cannot receive messages that they have to breathe and if they do not breathe they would drown. But whales and dolphins have a special system and do not sleep like us.

The dream of these animals is not a deep sleep. When dolphins and whales are asleep, a brain hemisphere and the opposite eye sleep. Thus, half of the awake brain controls breathing and the open eye sees dangers. This situation changes every two hours. That is, for two hours the left hemisphere and the right eye of the brain will sleep, and during the next two hours the right hemisphere and the left eye of the brain.

When whales and dolphins sleep, oxygen is only used to supply vital organs: the heart, brain, and muscles needed to swim. The body of these animals is able to withstand large amounts of carbon dioxide and can significantly reduce the breathing rate during sleep.

Thanks to these features, dolphins and whales can sleep without choking risk.