Do Sharks Sleep? If Yes, When, Where and How?

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If you are here, you probably wondering, do sharks sleep? Or where sharks sleep? And do sharks die if they stop moving?

Do sharks just keep moving for eternity, or do they take some rest and actually feel the need to sleep before continuing through the endless stretch of water before them? And if they do ever sleep when, where, and how do they do it?

Hold on! We will answer each of those questions we just successfully planted in your mind. Here you go…

The biggest and the loudest question is, do sharks sleep? To be conclusive and succinct, I’d say yes, they do. Sharks sleep, but it doesn’t go like the mama-shark tucks the baby shark in, and they fall in deep slumber. No, sharks do not curl up like humans and sleep the ‘human way’. The shark definition of sleep is different, and below is more and all about it.

Where do sharks sleep?

Sharks mostly roam the deep waters no matter what they show in the movies (get the joke?), and that is where they sleep. Sharks sleep in the deeper parts of the ocean in contrast to most marine creatures preferring coral reefs or sandy sea beds.

Ever seen how (in a sleepover) one of your friends likes to take up the edge of the bed, another willing to sit right next to the food, and one occupying the other edge of the bed? It’s more or less with sharks only here they are divided based on their species.

Some shark species such as the Caribbean and nurse sharks usually rest or lie in a less-conscious state in the ocean bottom and caves. Some like to swim to the top and then slowly sink downwards (called yo-yo swimming).

Note: We aren’t completely sure whether sharks lying in the ocean bottle with negligible movements are sleeping or not.

How do sharks sleep?

Sharks don’t just cuddle up and sleep; in fact, they do not even close their eyes while they are asleep or immobile (the primary reason being the absence of eyelids). There are two main methods sharks use to rest or, as we might call it, ‘sleep’. These are:

Buccal Pumping
Immobile Sleeping while breathing through spiracles.

However, let us clear the one myth that people often tend to get caught up around considering sharks and sleep.

Myth: Sharks die if they stop moving.
This is both true and false about shark sleep. However, focusing on the myth, multiple shark species are capable of staying completely immobile in order to rest. Usually, the bottom-dwelling sharks and a few other marine creatures such as rays and skates clear the mist of doubt, therefore, proving that not all sharks die if they stop moving.

Now, this is where the post picks up the thrust. How exactly do sharks sleep?
Let’s discuss the two steps aforementioned below:

Buccal Pumping:

Ram ventilators and buccal pumping sharks can increase their oxygen levels and energy by swimming faster with their mouths open wide.

In layman’s terms, the general consensus of shark-observers believes that most sharks use ‘buccal pumping’ or ‘obligate ram ventilation” to remain at the ‘resting’ status or, let’s say, suspending consciousness (as per the definition of sleep).

Buccal pumping basically means ‘breathing through the cheeks where the sharks suck in water through their mouth and then forcefully expel it out of the gills. Sharks successfully expel water through their gills using their cheek muscles or buccinator or cheek muscles. Sharks move the floor of the mouth rhythmically, which is apparent from the external structure, which strongly gives us to believe that most sharks use buccal pumping for resting.

Buccal pumping is usually applied for what we can call ‘sleep swimming’, and the method is used by sharks that can not afford to stay immobile in order to rest. Sharks achieve this ‘sleep swimming state without any hindrance because it has been evident in research that sharks use their spinal cord and not their brain for coordinating their moving and swimming in the water.

This, therefore, makes it quite possible to put the brain at rest while the spinal cord coordinates the swimming movements, thus allowing the shark to ‘sleep’. Obligate ram ventilation sharks can also show a significant increment in the oxygen levels in their body by swimming faster and opening their mouth, which doesn’t cause any oxygen deficiency, which otherwise could lead to drowning.

Buccal pumping sharks are called ram ventilators or buccal pumpers.

Thresher sharks, blue sharks, megamouth sharks, whale sharks, great white sharks, mako sharks, and hammerhead sharks are the sharks that are believed to use buccal pumping for resting or experiencing rest periods while their brain is less conscious.

Immobile Sleeping:

The oceanic breeds of sharks, generally the bottom-dwelling ones, have the ability to stay immobile in order to sleep while still allowing the oxygen to circulate through their body. When active and in motion, the sharks living in the bottom breathe and ventilate in the same process as the pelagic sharks, and it is only during the resting phase when the breathing method changes. Bottom-dwelling sharks, in order to sleep, sink to the bottom of the ocean floor and use their spiracles to circulate water through their gills and the system associated.

What are Spiracles?

Spiracles are the special apparatuses or holes behind a shark’s eyes that allow them to force oxygen-rich water through their gills, thus maintaining the oxygen levels in the body. In many other marine animals, spiracles act like snorkels that stick out of the ocean bottom or the sand nearby, incurring and expelling water out of the gill slits. A number of marine animals have been filmed with their spiracles closing and opening behind their eyes.

How did Spiracles evolve?

Although biologists aren’t sure, spiracles most possibly evolved from gill slits or openings. In fishes such as sturgeon, paddlefish, bichirs, and other primitive fishes lacking a jaw, spiracles were simply referred to as the gill slits behind the mouth of these jawless fishes. In most cartilaginous fishes, spiracles before evolution as breath-supporting mechanisms were hole-like openings that were small in size.

Some scientists are also of the opinion that spiracles are associated with amphibians, and especially the hearing organs of toads and frogs.

Examples of other marine animals using spiracles

Benthic Chondrichthyes, such as a horn shark, round ray, or shovelnose guitarfish, live on the seafloor, with mouths located on the bottom of their heads to get food from the sand below them. Stingrays, the shovelnose guitarfish, or other benthic Chondrichthyes, such as horn sharks and angel-sharks, use spiracles for breathing.

Angel sharks, to stay immobile, dwell at the bottom of the ocean, dig into the sand and protrude their spiracles out to let water pass through it. Spiracles allow these creatures to camouflage at places (where oxygen can not penetrate) to prevent or prepare for the attack while still allowing them to breathe.

Sharks that stay immobile to sleep are Horn Shark, Angel Shark, Nurse Shark, Lemon Shark, White Tip Reef Shark, Wobbegong Shark, and Caribbean Reef Shark.

Yo-Yo Swimming

Very often, sharks such as mako and blue sharks sleep through yo-yo diving or yo-yo swimming, wherein the sharks swim to the surface of the ocean and then slowly glide downwards towards the ocean floor. This ‘shark version’ of sleep is one way for sharks to allow their brain to be less active while still keeping up with the movement to breathe.

When do sharks sleep?

If we are to guesstimate, sharks do not have a specific time to rest their brain or sleep. They never stay completely unconscious. They keep oscillating between an active state when they are predating or moving and doing other activities to restful periods of ‘sleep’ when their brain is less active.

However, sharks are mostly nocturnal predators, therefore indicating the possibility that they sleep during the day and perform active movements during the night. Although, to the contrary, most sharks associated with yo-yo diving are said to be sleeping during the night when they are not preying or eating.

What happens if sharks don’t sleep?

If we go by the dictionary to define sleep, sharks do not sleep. However, a suspending consciousness is also considered sleep, which implies that sharks do sleep or rest in general terms. If sharks go without resting, there is probably not much that shall happen; however, sharks usually do not opt for complete sleep deprivation (for no reason at all).

Sometimes, sharks may go without sleep for prolonged periods when they migrate or have been looking after the offspring (parental care) or spawning. One of the most resorted reasons when sharks go without sleep is when there is abundant food material available at periods they should be sleeping.

Is there any video of Sharks sleeping?

Yes, sharks have often been filmed using robot cameras that delve into the ocean for research or other purposes. There have also been multiple instances when mariners and divers have seen sharks sleeping right next to them.

Sources:

  1. Spiracles and How They Aid in Breathing on Fish, Whales, and Insects, ThoughtCo.

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