After a long day, nothing feels better than a good night’s sleep. If you’re a shark lover, you’ve probably wondered if sharks ever enjoy the same luxury.
A Series of research proves that most sharks need to keep water moving through their gills to survive. Why? Because that’s how they get their oxygen.
It means they need to keep swimming to live. Or at least that’s a general belief. Which begs the question: Do sharks sleep? And do sharks sleep with their eyes open?
You are about to find out. Plus, you get to find out if sharks have to keep swimming– forever. Ouch, that must be a tough one.
Well, let’s get this show started already.
Can sharks stop swimming?
A core problem about sharks’ sleeping ability is their breathing.
You see, sharks can’t simply settle down to take a nap after a stressful swim. Their breathing is hinged on swimming.
Simply put, they can’t breathe if they stop swimming. So, they practically need to keep swimming to breathe.
Let’s take a wild guess; you also believe that’s a mean fate. Yea, that’s what we thought.
Obligate Ram Ventilators
What would you do if your oxygen depended on swimming? Never sleep, right? We wouldn’t say sharks never sleep, but sleeping means a completely different thing to them.
With over 500 shark species engulfed by the depths of oceans globally, the disparity in their nature isn’t surprising.
Not all sharks have to swim to breathe. But the ones that bear this burden are known as obligate ram ventilators. The name depicts how they swim with speed to force water through their gills.
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Sharks with spiracles are the exceptions to the “no swim; no oxygen” rule. What are spiracles? These are openings located behind the eyes.
Sharks use these openings to ingest water into the buccal space and pass it through the gills. With spiracles, sharks can breathe without swimming the length and breadth of the sea.
Unfortunately, not all sharks are privileged to own a spiracle. The bottom-dwelling sharks need it more. By nature, they lay still, ready to ambush their prey.
Most sharks have spiracles except species like the great white shark, hammerheads who swim nonstop.
Do sharks sleep?
Admittedly, sharks have been the subject of several kinds of research. It’s no wonder, though. Since movies and a couple of shark attacks portrayed them as the bad guys, people have developed an interest in their lifestyle.
Their sleeping habit has been a mystery long enough to be the subject of extensive studies. Sharks’ sleep doesn’t have a definite answer despite these studies. It’s nothing like having shades of black or white– In fact, it includes a few hues of gray.
But we’ll break it down.
What is “sleep” for a Shark?
For starters, the answer to this question is plagued with the difficulty of defining what ‘sleep’ means to sharks. As stated above, there are two categories of sharks.
Some have spiracles and are fortunate enough to breathe without swimming continuously. And the not-so-fortunate lot who have to keep swimming to keep the oxygen supply steady.
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It’s only reasonable for these two categories to have different sleeping postures.
As you’d expect, the sharks that swim continuously can’t afford to fall into a deep sleep (they certainly wouldn’t want an accident that could cost them their life!). Instead, they have inactive periods when they rest their brain.
During this period, they maintain a level of consciousness to keep swimming. That should count as sleeping, or it would have to suffice.
On the other side of the coin, you’d think sharks with spiracles would have a field day sleeping with ease since they can stop swimming. Right?
Not Enough Buoyancy
Err– it doesn’t work that way. It’s not so easy for them as well.
Sharks can’t call it a day when they wish and sleep. The thing is: sharks sink when they are not swimming; before you ask why it’s because they don’t have a swim bladder.
Agreed, their liver– which happens to be oil-filled– does offer some buoyancy. However, it’s not enough to keep sharks afloat. They can only float with the help of their pectoral and caudal fins.
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So, when they stop swimming, they have to sleep or rest at the rock bottom of the ocean. While swimming, these sharks breathe like obligate ram ventilator sharks. You could say they have two breathing patterns.
Even sharks that use spiracles only get deep rests instead of sleep.
Where do sharks sleep?
Shark’s rest hours often occurs in the depth of the ocean. Sometimes, the coral reefs or seabed are actual beds for them– for those that can remain stagnant.
However, other kinds of sharks can enter into their deep rest while swimming the lengths of the ocean– slightly conscious.
So, sharks sleep in the deep side of the ocean.
How do sharks sleep?
If you are the curious type, your curiosity probably goes beyond the question: do sharks sleep at night? You sure want a detailed description. And luckily, we are in the mood to give you some.
From the description above, you’d have a vivid image of how sharks breathe. Their sleeping is entirely dependent on that. Sharks that need to keep moving have a moment of rest.
Although they are conscious enough to keep swimming, their brain still experiences maximum rest.
Other sharks also sleep the same way. Except for this time, they stop moving and rest at the bottom of the ocean. So, they remain static throughout their rest period. However, studies have revealed that the deep rest period isn’t total.
Sharks can still monitor the happenings around them during these rests. For instance, they can sense and see potential threats long enough to prevent harm. There was a misconception that sharks engage in ‘sleep swimming’ and only rest half of their brain and swim with the other half.
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Studies have disregarded this notion. Research proves that there may be no link between swimming and the brain. It finds that the shark swims with the help of its spinal cord.
Do you know what this means?
These sharks may not be experiencing partial sleep Afterall. The wakeful and restful periods are quite different because they don’t use their brains while resting. The sharks indulge in absolutely restful sleep even though they keep swimming.
Resting for them requires submerging their heads into the current to force water into their mouth with ease.
Sharks also rest via a method called Yo-yo swimming. It involves swimming to the surface and gliding back into the ocean’s depth. There’s more to yo-yo swimming. You’ll find out soon enough.
How much do sharks sleep?
Sharks don’t particularly have a specific sleep time. So, they sleep as many times as their instincts allow. Most times, they have their restful moments several times in a day. Can’t say we blame them; they need the rest.
What happens when sharks don’t sleep?
Insomnia doesn’t cause any notable ailment in sharks. So, as you can guess, nothing happens when a shark doesn’t sleep. But they only have a few reasons why they may not sleep or rest. Some of them are migration, parental care, and spawning.
Sharks may also sacrifice their deep rest if there is more food when napping. The only thing that will cause death is if a shark sleeps in a way that cuts off access to oxygen-rich water.
Sharks have nothing to worry about so long as they get oxygenated water. Even lack of sleep doesn’t worry them!
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When Do Sharks Sleep
Taking a nap after an exacting task or at night is the norm with humans. But do sharks sleep at night? Or after an intense struggle with a prey? Or when exactly do sharks feel the need to knock it off– their way?
However, the Circadian Rhythm dictates when a shark sleeps. Not all sharks have a preferred sleeping time. I.e., they don’t sleep in the afternoon and stay active at night or vice versa. Since they don’t have a strict preference, how does a shark decide it’s time to sleep?
It’s instinctive for them. Sharks sleep whenever their instincts demand it. We’ve established that sharks only have deep rest. Hence, they have a series of it multiple times in a day. It’s hard to specify how many times a shark sleep.
Undoubtedly, they experience deep rest several times within 24 hours.
Do All Sharks sleep
All sharks have wakeful and restful periods. It means all sharks experience rest time, but it’s different for various species.
From the pre-established facts, sharks either breathe by ramming water into their mouths (obligate ram ventilating) and forcing it through their gills while swimming or via their spiracles.
The obligate ram ventilating sharks, also called buccal pumping sharks, may include:
- Mako shark
- Megamouth shark
- Whale shark
- Great white shark
- Hammerhead shark
- Thresher shark
Bottom-dwelling sharks, alternatively called sharks with spiracles, include:
- Whitetip reef shark
- Nurse shark
- Wobbegong shark
- Caribbean reef shark
- Lemon shark
Marine biologists believe that most sharks witness cycles of less consciousness and awareness.
How do sharks protect themselves while sleeping?
We bet one of the most impressive features of a shark’s partially active rest is the fact that its eyes are open. Imagine how vulnerable a shark could be while sleeping. They keep their eyes open because they have no eyelids.
Hence, sharks keep an eye on creatures around them even during their deep resting cycle. They can envisage and prevents any harm with ease. Instead of eyelids, they have a nictitating membrane covering their eyeball when they pounce on prey.
What do sharks do when they are not sleeping
The ocean is vast and maybe engaging for creatures like sharks. They either feast on their prey or swim around; although not all sharks are carnivores, most of them prey on other fishes.
Other popular species of sharks survive on plankton.
Sharks attack humans, but they scarcely do. That’s because they don’t see us as food– which is a good thing. Most shark attacks on humans were mistakes. And this happens to surfers often– they always seem like an attractive bag of food.
When sharks are not sleeping, they are either migrating or feeding. The truth is that the ocean is deep and wide– sleeping isn’t the only activity; sharks explore!
Any Pictorial Evidence?
Have sharks been filmed sleeping?
Luckily, there are videos to back up this claim. A video at Revillagegeido Mexico by divers revealed some white tip reef sharks lying stealthily on the ocean unbothered by human presence.
While sharks oscillate between activeness and deep rest, the little we can do is capture the moment. Right?
Another video also surfaced. This time, it portrays a Great White Shark zoning off to slumberland.
Sharks seem to get some rest from yo-yo swimming. What is yo-yo swimming? It’s when sharks swim up the surface and rest while descending into the deeper path of the ocean.
Well, that’s another form of resting for sharks. And we guess it works for them.
Will sharks die if they sleep?
Sharks don’t fall into deep slumber like other animals. The sharks that survive by buccal pumping only need to keep swimming– passively– to stay alive while resting. Shark species with spiracles can stop swimming long enough to have their rest.
Do sharks get tired of swimming?
Most shark species rely on swimming for their oxygen. In this case, we doubt they could ever get tired of swimming. Based on studies, these sharks swim nonstop even while resting.
So, to answer this question, no, sharks don’t get tired of swimming.
Do sharks suffocate if they stop swimming?
It depends. Sharks categorized as obligate ram ventilators require consistent movement to get oxygenated water. If they stop for any reason or get stuck in a net by error, they’d likely suffocate and die. Any obstruction of movement for these sharks truncates the flow of oxygen.
The other shark species that suck water through their spiracles can be static without tampering with their oxygen.
Sharks are unique animals with peculiarities. And one of them includes how they sleep. Other animals may enjoy the luxury of lying down to sleep without worries. But with sharks? It’s not that easy.
Sharks oscillate between the wakeful and restful periods. When confronted with the question, do sharks sleep? You now know that they certainly get their rest. But they aren’t deep sleepers– not like us.
We hope you learned something new!
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.