How Do Whales and Dolphins Sleep?

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Whales and dolphins are some of the most majestic marine mammals in the ocean. Mammals both on sea and land share similar characteristics including the need to breathe and sleep, but the way land mammals and marine mammals breathe and sleep are distinctive differences between the two types of mammals. Because whales and dolphins spend their entire lives at sea, you may be wondering, how exactly do whales and dolphins sleep? And, how is it different from land mammals?

These may seem like obvious questions, but the answers may surprise you! Keep reading to find out how whales, dolphins, and porpoises sleep underwater.

Do Whales and Dolphins Sleep? A Look at Brain Function

The very short answer to this question is YES, whales and dolphins do sleep but it is more similar to resting because their brains don’t completely shut off, which is very different from how humans and other land mammals sleep. When humans sleep, their brains go into a state of partial or total unconsciousness, allowing them to shut off senses such as smell and sight.

This is not the case for marine mammals. When whales and dolphins sleep, their brains go into what is referred to as unihemispheric sleep, also referred to as slow-wave sleep. This type of sleep involves turning off only one hemisphere of the brain, while the other hemisphere of the brain monitors breathing function and what is going on in the environment around them. Studies have shown that within 24 hours, each hemisphere of a marine mammal’s brain can get 4 hours of sleep for a total of 8 hours altogether.

Reasons for Unihemispheric Sleep

One reason why marine mammals must keep half of their brains alert while they sleep is because their breathing must always be consciously controlled while underwater, unlike humans whose breathing is involuntary. If their brain completely shut down at any point during sleep, then they will likely drown because their breathing would not function.

Another reason why their brain remains partially awake is because it keeps vital physiological body functions active. One important physiological process, for example, is the muscle movement needed to control body temperature in cold underwater climates. Unihemispheric sleep also allows dolphins and whales to monitor their environment while they sleep to look out for predators or other threats. During unihemispheric sleep, if a whale’s left hemisphere is asleep, it will close its opposite eye and vice versa. So, if the left hemisphere is asleep, the right eye will be shut, and the left eye will remain open to monitor surroundings.

How Do Whales and Dolphins Sleep?

Scientists have observed whales, dolphins, and porpoises sleep in two ways. Sometimes, they will hang vertically suspended underwater near the surface of the ocean, which allows them to easily breach the surface and take in air when needed.

Another method whales and dolphins engage in is swimming slowly at the surface of the ocean, propelling themselves along. This method is particularly important for mother dolphins and whales with new calves. When baby whales and dolphins are born, they have to sleep next to their mother in what is referred to as echelon swimming, where they are suspended to the mother while she tows them along. The reason for this is because they are not born with enough blubber to keep them afloat in the water. So, when mother whales and dolphins give birth, they will have to sleep on the move for the first few weeks of their offspring’s life to keep them afloat.  

The Harbor Breeze Whale Watching Experience

For an up close and personal experience with whales and dolphins in their natural habitat, we invite you to a Long Beach whale watching and Los Angeles whale watching cruise with Harbor Breeze – an unforgettable trip the entire family will love. We have experienced and enthusiastic naturalists aboard each and every trip that will narrate and educate you on the characteristics and lifestyles of these majestic sea mammals. Contact us today for ticket information!

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