Nature is always surprising and raises questions that science strives to answer. Thanks to new technologies, we can observe animals in their natural habitats and thus study and understand many peculiarities that until recently were a mystery. For example, how can it be possible that marine mammals – like whales and dolphins, which need air to breathe as we do – can live their entire existence in the water? And, if they need air to breathe, how do whales sleep without drowning? If you want to learn more about this issue, don’t miss this article from Thefishinfo, because we tell you how whales and dolphins sleep and why they don’t drown. 
Read Also: How sharks sleep?
How Whales Sleep
Unlike humans, we don’t need to think to breathe, whales breathe voluntarily. Our breathing is reflex during sleep and we even continue to breathe even though we are unconscious; for this reason, our brain manages to completely disconnect while we sleep and we can reach phases of deep sleep. Not so for whales, which even while sleeping need to be aware of their breathing. So don’t whales sleep? Does your brain not need to rest? The answer to both questions is yes: the whale’s sleep and their brains also need rest.
The big difference between marine mammals (whales) and land mammals (us) is that seafarers have a brain that is capable of connecting and disconnecting their hemispheres independently. Our brain, by contrast, is unable to function using only one of its hemispheres. This peculiarity of marine mammals, like cetaceans, allows them to sleep by resting only half their brain. In this way, a part of the brain remains alert, ensures that the animal breathes, that no danger lurks, and even allows it to move while sleeping.
Read Also: 10 Largest Fish Species Today
What is this way sleeping called?
This way of sleeping is called slow-wave uni-hemispheric sleep. It allows marine mammals to sleep in cycles, alternating the resting cerebral hemisphere and the one that remains waking. Thanks to him, these animals can survive during sleep. This original way of sleeping has the disadvantage that it hardly allows them to reach the REM phase of deep sleep and, when they do, it lasts only a few minutes.
This way of sleeping prevents the whales from separating from the herd during sleep, as they can stay in motion next to each other. This activity during sleep is vital for cetaceans since it minimizes the loss of body temperature due to the cold water, something that could lead to death if they remained still. Also, this contributes to the survival of the calves, which grow in movement together with the mother while they are babies. Thanks to a technique called step swimming, the calf is placed in a position where the mother’s turbulence of movement propels it and keeps it next to it. During the first weeks of life, the mother cannot stop at any time, otherwise, the calf would drown, as it cannot yet float on its own.
How dolphins sleep
The system used by dolphins to sleep is the same as the one we have explained with the whales. Their ability to function alternately with a single hemisphere of the brain means that dolphins can enjoy several complete cycles of sleep per day (approximately two hours each).
Although sleep habits vary by species, dolphins — unlike whales, which often sleep in deep water and rise to the surface to breathe — prefer to sleep in surface water, and some even float during sleep. A curious detail is that some dolphins rest horizontally, but others do so vertically.
However, dolphins have more peculiarities, since their sleep is deeper than that of whales and they can reach the REM sleep phase more easily, although it does not last more than a few minutes. Furthermore, they sleep with one eye open and one closed; the open is the opposite of the area of the brain that remains in operation. The part of the brain that remains awake is not one hundred percent, but it can detect movement and determine when it is necessary to go up to breathe.
In the sea, standing still can mean death, which is why most dolphins also move during sleep. Adult males do this in pairs and swim very slowly. Females and young swim in large herds, use the step swimming system and also take turns watching out for natural hazards and obstacles.
Why whales and dolphins don’t drown when they sleep
To know how whales sleep without drowning, we have to know how they breathe. Their respiratory system has lungs just like ours, and they are proportional to their size, that is, much larger than ours.
The equivalent of our nose is a hole that they have on their head and that is covered with a skin membrane called a blowhole. According to the experts, the movement of this “cover” is completely voluntary, which means that the animal has to be conscious to be able to open the blowhole, breathe and then close it when submerging so that no water enters its lungs.
That is why whales and dolphins do not drown when they sleep; your respiratory system remains closed and water cannot penetrate your lungs. It is almost impossible for a marine mammal to drown while sleeping, although it can suffocate due to lack of oxygen if it does not breathe in time.
The morphology of marine mammals has also developed other skills as part of their adaptation to the marine environment:
Their large lungs allow them to take huge puffs of air.
Your body tolerates higher levels of CO² than terrestrial animals, so it takes much longer for your brain to start the respiratory process.
They can maintain their blood supply with “minimal services”, because when they sleep their blood only flows to the vital organs and processes. While they sleep, their digestion, for example, stops. Published By Thefishinfo.com