Do Sharks Sleep and Other Fun Facts

One common myth about these giant fish is that because they are always on the move, sleeping would be impossible. There are many species of shark who don't swim round continuously and some will actually lie still and rest at the very bottom of the sea bed. Enjoy this educational resource page for home schooling, learning fun and more.

Sharks do not appear to have a sleep function in the way that human beings do. However, it hasn't yet been proven scientifically as to whether these fish have their own unique mode or style of sleeping. So it is possible that they do go to sleep - just not in the sense or meaning of the word that we are used to.

Sharks have gills or respiratory organs which are slits on the sides of their heads. Water must move or flow over the gills to enable these fish to obtain their necessary oxygen supply and be able to breathe. So many species do have to swim or move continually in order to obtain the oxygen that they need to live.

If this is the case, why can some species lie still or rest on the bottom of the sea bed? Some of these magnificent creatures have the addition of small openings located behind their eyes. These are called spiracles and they help to move water across the gills while still or at rest. This means that they do not have to move or swim constantly in order to breathe.

In the human meaning of what it is to be asleep, unless we're doing some nocturnal sleep-walking, we tend to simply lie still and this uses up a lot less energy than when we're awake and up on the move.

Sharks that are still and at rest, however, have to work harder and process energy in order to get oxygen moving over their respiratory gills so they can breathe. It's debatable, therefore, whether these fish are really and truly at rest just because they happen to be lying still because, for some species, this process actually requires using up more energy. And just because this creature looks to be still doesn't mean they are actually asleep - as divers and other marine life are well aware!

Even for those species who need to swim constantly in order to breathe, it is thought that they can have both active and restful periods. Parts of this animal's brain may be at rest or less active even whilst they swim - a bit like sleep swimming.

Despite having eyelids, these creatures do not actually close their eyes - not even whilst they lie still (if they are a species that is able to be motionless) nor while having a rest period in terms of limited brain or cerebral activity.

The upper and lower eyelids on these fish do not close all the way across the eyes. So they are unable to blink as humans can. Our blink functionality is there so that our eyes are kept clean and moist. With sharks, their eyes are kept clean due to the fact that they are swimming through water.

Some species have a 3rd eyelid, for want of a better term, which covers over each eye. This is called a nictitating membrane.

The membrane seems to function as protection for the eyes when hunting or during an attack where the eyes may get scratched. So the membranes act as protective shields in these instances.

Other species, such as the Great White and Whale Shark, have no membrane but are able to roll their eyes back into the protection of the eye socket instead. This makes them look even more fierce because you can no longer see their pupil or iris, just the white of their eye. Eyelids vary from species to species. The one thing that is clear is that if sharks do actually go to sleep, they don't close their eyes to do so.

Scientists don't really know for sure whether sharks actually do sleep although it may well be that these fish employ periods of rest and activity. Our natural and internal clock means that humans normally and naturally sleep at night time - although it happens that some of us have been able to adapt to sleep during the day. A circadian rhythm is something that we naturally adhere to and this is a 24 hour cycle where we need to have rest and then be awake.

Some sharks also adhere to this circadian rhythm. There are species which are more active during our daytime hours and some are more active at night.To increase their chances during hunting for prey, many species will hunt during dawn and dusk when the light visibility is dimmer and therefore what they are hunting is at a real disadvantage because of it. If they do have an actual mode ofsleep, it's not likely to be employed while they're actively searching for something to eat.

Luckily for sharks, they don't actually need to employ their brains in order to swim. Swimming movements or reflexes come from the spinal cord and are dictated by what is known as a Central Pattern Generator. So they could swim around even while they are unconscious or asleep.

It may be that some of the cerebral activity in this animal shuts down while it is in a period of rest. As the shark doesn't require its brain to swim it can simply carry on moving. It is very like sleep swimming instead of sleep walking that occurs in some humans. I hope you've enjoyed reading my wizzles page today, thanks for your visit. Now what else can you learn about this wonderful creature of the deep.