Yes, dolphins sleep when they are tired or need to rest, but not in the same way humans or other land mammals sleep.
Unfortunately, dolphins do not have the same luxury as other animals regarding getting a good night’s rest.
To answer whether or not dolphins sleep and how they rest, we first need to examine the factors that affect their ability to sleep.
Dolphins are marine mammals and share many of the same characteristics as land animals (such as humans), including the need to breathe air.
Because humans and other mammalian species live on land, it is much easier for us to breathe.
We do not have to be consistently conscious of our environment or oxygen needs.
We also don’t have to worry about drowning when we go to sleep since no water around us can prohibit our breathing.
In addition, most humans are relatively safe from being attacked by other animals when they rest, so it’s much easier to get a good night’s rest when needed.
Dolphins, on the other hand, spend their entire lives in the ocean, and while both the dolphin species and fish live in the water, fish are born with gills that allow them to pull oxygen directly from the water.
Dolphins do not have this luxury because they are born with gills instead of lungs.
As a result, they must always be aware of their surroundings and need oxygen, which can only be found above the water’s surface.
If their oxygen level becomes too low, the dolphin must reach the water’s surface to get more oxygen.
Otherwise, it risks the possibility of drowning.
And even though dolphins can hold their breath for extended periods, compared to most land animals, they are still very limited in their ability to stay submerged without oxygen.
Studies using electroencephalography have been performed on dolphins better understand what happens when a dolphin sleeps.
They have shown that when a dolphin rests, half of its brain shuts down, similar to a human’s brain when we sleep.
The other half of the brain, however, remains active, allowing the dolphin to stay semi-conscious of their environment to prevent the dolphin from drowning and will enable it to monitor its oxygen supply.
While dolphins can rest in most environments (including below the surface of the water), most dolphins will be found resting near the surface to give them the best opportunity to acquire oxygen if needed.
Aside from consistently being aware of their oxygen level, dolphins must also remain mindful of potential predators in the area, which limits their sleep and requires them to stay at least partially aware of their surroundings.
Both factors (oxygen and threats) play a significant role in why dolphins rest differently than humans and land animals.
Because dolphins are constantly aware of their need for oxygen, marine biologists refer to dolphins as conscious breathers.