To answer whether or not whales sleep (which is often asked because whales live in water), we first need to explain what affects a whale’s ability to sleep compared to land animals such as humans.
Whales, like humans, are mammals and share many of the same physiological traits, including the need to breathe air.
However, one significant difference between humans and whales involves what affects a human or land animal’s ability to breathe.
A whale’s ability to breathe compared to humans is significantly altered because humans live on land and whales live in the ocean.
This difference significantly impacts the sleeping and breathing habits of whales and humans.
Because we live on land, most of the time, humans do not have to be conscious or completely control their breathing.
Breathing comes naturally to us whether or not we are aware that we are always breathing.
Unlike whales, we do not have to consistently fear drowning or worry about coming up for air when we go to sleep, and we usually only become aware of our breathing when we swim or run to exhaustion.
Whales do not have this luxury, and unlike fish, whales do not have gills that fish use to extract oxygen from the water, so they must come to the surface to get their oxygen.
This constant need to be aware of their oxygen requirements causes whales to be conscious of their breathing because if they could ignore their need to return to the surface, they would drown.
To help whales survive in the ocean, these mammals have specialized lungs that allow them to extract more oxygen from the air than humans and other land animals. This helps them transfer blood to vital organs and hold their breath significantly longer than most animals.
Some researchers believe that whales can use up to 90% of the air they inhale, while humans only use around 15%.
In addition, whales can consistently monitor their oxygen level and shut down nonvital components to maximize their blood flow and are highly efficient swimmers.
As a result, they minimize the energy they use to stay submerged underwater for extended periods.
Depending on the species, whales can hold their breath anywhere from 5 minutes to over an hour but are limited in how long they can stay submerged before they run out of oxygen or drown; therefore, whales are considered conscious breathers.
That means that whales are always aware of their breathing and oxygen needs.
How Does This Affect Sleep?
Because whales are constantly aware, scientists believe that whales can never fall completely asleep.
Studies using electroencephalography on dolphins have shown that half of a dolphin’s brain does indeed shut down when resting, just as humans do when they fall asleep.
The other half of the brain, however, remains active, allowing the dolphin to stay semi-conscious of its breathing so that it does not drown.
This process of semi-resting periods is also believed to be a part of all cetaceans.
It includes all species of whale, dolphin, and porpoise.
While it may be possible for whales to rest almost anywhere, they will likely be found at or near the surface of the water, either still or barely moving during this semi-resting state so that they may quickly replenish their oxygen when necessary.
You can imagine how a whale would be affected if it fell asleep as a human does.
If a human were to fall asleep in the water, they would likely sink and drown because the body is not adapted to this type of lifestyle and would have trouble responding to this type of emergency on a regular daily basis.
At the very least, we would wake up in a panic, flailing to swim in the right direction and startled by any predator that tried to attack us.
Eventually, we would end up tiring ourselves out from constantly swimming and panicking, which would cause us to use up our oxygen much faster, plus our thin layer of fat, compared to the thick layer of blubber whales possess, would do very little to protect us from the cold/freezing waters that surround us.
This is why it is so vital that whales always remain conscious and alert, as their need for oxygen dramatically affects their ability to sleep.
Aside from having this level of control over their breathing, whales are also relatively buoyant, making it easy for them to stay upright and near the surface when at rest so that it is easy to replenish their oxygen supply.
This ability to remain buoyant and float also makes it easier for whales to rest in the water than humans, polar bears, and other animals that consistently use their energy to surf and surface above the water.
All of these factors work together to provide whales with an easy and seamless way to stay alert, react to predators and threats and remain prepared, even when resting.
Conclusion
In conclusion, whales do rest.
However, they do not fall asleep like humans and other animals because they must remain conscious of their need for oxygen as they live in the ocean.
When they rest, they remain partially conscious to react to danger and obtain more air when necessary.
Their body is designed to allow them to hold their breath for extended periods while minimizing the amount of energy they use when swimming.
Their body also allows them to remain buoyant at or near the water’s surface.
As a result, they can rest at the surface without using any energy to stay afloat.