How do Sharks, Whales and Dolphins Sleep?

| November 16, 2017

Learn all about how do sharks, whales and dolphins sleep? Sleep is a state in which the person or animal is less responsive to outward stimuli than in a usual waking state, but to a lesser extent than in the case of hibernation (in which an animal’s metabolic rate, temperature and breathing are all significantly reduced, and external stimuli may have little or no effect) or coma (in which unresponsiveness is complete and arousal may never occur) or the state induced during general anesthesia (in which a person cannot be awakened and fails to respond to even painful stimuli). An important aspect of sleep, therefore, in contradistinction to hibernation or coma for example, is that it must be easily and immediately reversible, and this should also be part of our definition.

Sharks are the terrors of the seas to some but the most graceful and amazing creatures to others. No matter what your personal opinion of sharks is you have to admit that sharks are interesting animals. They can range from 6 inches to 53 feet, live in freezing arctic waters or frequent the warm equatorial seas, viciously attack anything that moves or just open a gaping mouth for the smallest of creatures to enter. Sharks are amazing creatures and are studied constantly across the globe.

In general, dolphins and whales have two basic ways of sleeping, according to Scientific American. They either “rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal.”

Because whales are in a constant state of awareness scientists believe that whales are never able to fall completely asleep. Studies using electroencephalography on dolphins have shown that half of a dolphin brain does indeed shut down when resting, just as a human does when they fall asleep.

Humans, of course, can breathe while the conscious mind is asleep; our subconscious mechanisms have control of this involuntary system. But equipped with a voluntary respiratory system, whales and dolphins must keep part of the brain alert to trigger each breath.

How do sharks, Whales, and Dolphins Sleep

What is Sleeping?

Sleep is a large, important and familiar part of everyone’s life. Along with nutrition and exercise, it is one of the three pillars on which a healthy and happy life is based, and we spend about a third of our lives sleeping. But many aspects of it remain deeply mysterious and/or misunderstood. Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles.

How do sharks sleep?

Well, the question of how sharks sleep depends on how you define sleep. According to the Merriam-Webster online dictionary, sleep is “the natural periodic suspension of consciousness during which the powers of the body are restored.” We’re not sure sharks are able to suspend their consciousness, although it may be possible. Sharks such as Caribbean reef sharks, nurse sharks, and lemon sharks have been seen lying on the ocean bottom and in caves, but they seem to continue to watch what is going on around them during this time, so it’s not definite that they are sleeping. Sharks don’t have eyelids. “Their eyes are open, but I guess the images coming into their eyes are either ignored or simply sort of shunted to the background,” Burgess says. They “probably” don’t engage in REM or non-REM sleep. Sharks would find small gullies and sit stationary for long periods of time some for hours most probably sitting face first into current letting water still pass over their gills without having to move.

How do Whales sleep?

Whales do not sleep completely. In conclusion whales do rest, however they do not fall asleep the way humans and other animals do because they must remain conscious of their need for oxygen as they live in the ocean. When they rest they remain partially conscious so that they can react to danger and obtain more air when necessary and their body is designed to allow them to hold their breath for extended periods of time while minimizing the amount of energy they use when swimming. Their body also allows them to remain buoyant when at or near the surface of the water so that they can rest without using any energy to stay afloat.

How do Dolphins sleep?

Dolphins can sleep. Adult male dolphins, which generally travel in pairs, often swim slowly side by side as they sleep. Females and young travel in larger pods. They may rest in the same general area, or companionable animals may pair for sleeping while swimming. While sleeping, the bottlenose dolphin shuts down only half of its brain, along with the opposite eye. The other half of the brain stays awake at a low level of alertness. This attentive side is used to watch for predators, obstacles and other animals. It also signals when to rise to the surface for a fresh breath of air. After approximately two hours, the animal will reverse this process, resting the active side of the brain and awaking the rested half. This pattern is often called cat-napping.