You can not tell but they are Sleeping

There seems to be a fascination that people have with sharks. There are horror stories, mysteries and things scientists are still learning about these fish. One of biggest quandaries that people speak about is how, if, or when sharks sleep?

When humans sleep they go into a deep REM sleep. This is when the real rest happens that rejuvenates the body. Sharks do not experience sleep in the same manner that humans do. In order to keep breathing sharks need a constant flow of water into their gills. There are two ways this can be accomplished.

Some sharks stay in some kind of constant motion to keep the water flowing through. It does not have to be swimming, per se, but enough movement to keep the water moving and bringing in oxygen over and through the gills.

Other sharks have spiracles. Spiracles are small openings that are right behind the eyes of a shark. The water is forced through those openings into the gills during restful periods. These are more common among the bottom dwelling sharks.

Another theory that has the backing of many scientists is that sharks “sleep” while they are sleep swimming. Part of the brain shuts down and rests while another part takes over the motion to keep the oxygen and breathing going.

One way of taking this down to a simple level is to think about how the human body works. You don’t have think about telling your heart to beat. Your brain takes care of that without you doing anything. Now if the part of your brain responsible for doing that is damaged, there are problems. Perhaps the part of the brain that keeps the sharks “swimming” does not ever shut off.

The circadian rhythm is often referred to as the internal body clock. There is much to learn about individual body clocks in both people and other living creatures. In the book Ecology of marine fishes: California and adjacent waters, Larry Glen Allen, describes the circadian rhythm in horn sharks and swell sharks. These particular sharks are much more active at night and tend to find rock crevices in the ocean floor and hole up during day time hours. That would indicate a circadian rhythm. It also points to some kind of rest or sleep.

Another interesting study was completed on Spiny Dogfish sharks. It was learned that these sharks coordinate the swimming movements through a central pattern generator located in the spine. R. Aidan Martin explains that this is probably how these sharks are able to continue to swim with unconscious or at least in some kind of resting state.

The answer to the question do sharks sleep is yes, but solid answers of how are not here yet.