How Do Dolphins Breathe While Sleeping?

Dolphins Rest Only Half Their Brains at Time

Dolphins spend their entire lives in the ocean, yet need to breathe air from the surface to survive. They must visit the surface to breathe regularly, 24 hours a day - so how do they ever manage to get any rest? A closer look reveals that dolphins and whales have evolved sleep habits which enable them to do it all at once.

How Often Do Dolphins Need to Breathe?

To insure that they only breathe when above water, dolphins have conscious breathing functions, unlike land mammals. This prevents them from drowning, but it means that a dolphin must constantly be in a conscious state to breathe, which presents an interesting challenge when it comes to their sleep behaviour.

Although dolphins are capable of staying underwater 7 minutes on average, they more typically surface to breathe around 1.5 to 4 times per minute. However, when they sleep, their body functions slow down and they tend to breathe less frequently.

Dolphin Brain Function

As mammals, dolphins must sleep in order for their brains to rest and to be able to function properly. However, in a marine environment, it is unsafe for them to enter a state of complete unconsciousness. This is primarily because they must be conscious in order to breathe.

Scientific American cites studies that have shown that dolphins actually shut down one half of their brain at a time in order to give their brains necessary rest. While one hemisphere of the brain rests, the other is active.

Although this half does not function at full alertness, it monitors surroundings for potential hazards and controls breathing. The dolphin will alternate brain consciousness every few hours in order to allow both sides of the brain to rest.

Where Do Dolphins Sleep?

Dolphins sleep in a variety of locations and postures. The 3 most common dolphin sleep zones are:

• near the surface with their blowhole exposed so they can breathe
• near the floor of their environment
• swimming in a slow circular pattern

The second and third of these behaviours require the animals to move to the surface periodically to breathe. However, their ability to shut down only one hemisphere of their brain at a time allows the alert half of the brain to monitor these movements, and to get the rest their brains need. This capability is crucial in environments where it would not be safe for them to sleep at the surface.

These behaviours emphasize the complex evolution these and other marine mammals have undergone to be able to survive the underwater environment.