Dolphins sleep underwater. However, they can’t breathe underwater, so they need to come up for air every once in a while. This kind of sleeping is called unihemispheric slow-wave sleep (USWS), which means that half the brain stays awake whilst a dolphin sleeps to come up for air when needed.
Do the dolphins keep their eyes closed while sleeping?
Dolphins use a sleeping method called unihemispheric, which means half of their brain is always awake when they sleep. On the brain side, that is, awake, the eye will remain open, and on the other side, the eye will be closed. You will never see a dolphin sleeping underwater with both eyes closed unless there is a severe problem.
Dolphins can even determine which half of the brain requires rest. The awake side will always have the eye open.
Can a dolphin drown whilst sleeping?
Dolphins can control their breathing by using the unihemispheric sleeping method to avoid drowning. But if they are caught in a net or trying to escape from a predator, they might go too deep in the water and not get enough oxygen. A newborn dolphin might suffocate because it has not learned how to get back to the surface of the water for air. These are some of the reasons that a dolphin might sadly die.
Unihemispheric
This unique method of sleeping helps the dolphins remain alert to reach the water surface to fill their lungs with oxygen when required. It also helps a dolphin stay alert even while sleeping, enabling them to protect themselves and their young against predators.
Even though sharks do not generally attack dolphin pods, the dolphin calves are vulnerable to large marine predators. The unique sleeping pattern of dolphins helps them protect their young. Along with that, the unique sleeping pattern of the dolphins allows the mother dolphin to nurse their babies whenever necessary.
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Why do the dolphins need to come to the surface while sleeping?
Dolphins can only hold their breath underwater. They cannot breathe underwater, so they need oxygen like any other mammal. They come to the surface while sleeping to take a breath.
When they are asleep, the dolphins need to remain conscious to breathe. The reason for this unique behaviour is that they can live.
Dolphins need a unihemispheric method of sleeping to make sure they do not drown. They will always consciously know when they need to take a breath.
What will happen if a dolphin goes into a deep sleep?
If a dolphin goes into a deep unconscious sleep, like humans underwater, it would lose control of its breathing pattern and either drown or suffocate to death. The only time dolphins can achieve deep sleep is if the dolphin is logging. Logging is when they float on the surface when asleep. However, they are at much greater risk from predators when using the logging sleep technique.
Other Sleeping Methods
Dolphins generally use different sleeping methods to ensure that they do not drown. So, while sleeping, dolphins either rest quietly in the water floating horizontally or vertically or keep on swimming slowly next to each other.
Individual dolphins sometimes enter a deep form of sleep during the night. This type of sleep is known as logging. In this condition, a sleeping dolphin looks just like a log floating on the surface of the water.
While sleeping and swimming simultaneously, dolphins remain in a state pretty similar to napping.
The young dolphins rest, eat and sleep while at the same time their mothers tow along in the slipstream. This condition is known as echelon swimming.
Echelon swimming
As the baby dolphins are not born with enough body fat, also known as blubber, it is challenging to stay afloat naturally. Mother dolphins can’t stop swimming for the first few weeks after birth. They can only apply the echelon swimming. If the mother stops swimming for even a little time, the baby dolphin will start to sink.
When do dolphins generally sleep?
Just like us humans, dolphins generally sleep at night. But unlike us, they cannot sleep for long periods at any one stretch. Dolphins sleep for a couple of hours at a time.
They almost always remain active late at night to hunt for squid or fish.
How long do dolphins sleep per day?
On average, dolphins generally spend about 8 hours on and off sleeping per day. However, this is not all in one go. It’s a few hours of sleep at any one time throughout the day.
How long can a dolphin hold its breath?
A dolphin can hold its breath between eight to ten minutes. After this time, a dolphin will need to head to the surface for some oxygen. They can even do this automatically whilst sleeping underwater using a method called unihemispheric.
Dolphins are marine mammals, and just like all other mammals, they need oxygen to survive. Unlike the fishes that breathe through their gills, dolphins need to hold their breath while they dive deep underwater.
The light bone structure helps the dolphins float below the water’s surface without spending much energy. This allows the dolphins to pop up on the water’s surface with the help of their tails.
The dolphins also have a higher tolerance for carbon dioxide. That means their brain does not get triggered by a breathing response until the carbon dioxide level reaches a much higher than humans.
While resting, the breathing rate of a dolphin can drop to 3 to 7 times per minute. That is a unique adaptation seen in almost every marine mammal.
