Do sharks sleep? Sharks never sleep is a common misconception. It was believed because some species of sharks must keep swimming constantly to stay alive. Sharks do engage in short spans of rest throughout the day, but it is quite different from the kind of sleep that other animals engage in. Sharks that are able to sleep while stationary include the whitetip reef shark, the nurse shark, the Caribbean reef shark, the wobbegong, and the lemon shark.
Sharks are a group of elasmobranch fish which has a cartilaginous skeleton, 5 to 7 gill slits on the sides of the head, and pectoral fins that are not fused to the head.
Elasmobranchs include sharks, rays, and skates.
Elasmobranchs are a closely related group of fishes, differing from bony fishes by having cartilaginous skeletons and 5 or more gill slits on each side of the head. In contrast, bony fishes have bony skeletons and a single gill cover.
There are approx. more than 470 species of sharks split across twelve orders, including 4 orders of sharks that have gone extinct:
Carcharhiniformes: Widely known as ground sharks, the order includes the grey reef, blue, tiger, bull, blacktip reef, Caribbean reef, blacktail reef, whitetip reef, and oceanic whitetip sharks (collectively called the requiem sharks) along with the catsharks, houndsharks, and hammerhead sharks. They are distinguished by an elongated snout and a nictitating membrane which shields the eyes during an attack.
Heterodontiformes: They are mostly referred to as the bullhead or horn sharks.
Hexanchiformes: Examples from this group include the cow sharks and frilled sharks which moderatedly resembles a marine snake.
Lamniformes: They are widely called as the mackerel sharks. They include the basking shark, goblin shark, megamouth shark, the thresher sharks, shortfin & longfin mako sharks, and great white shark. They are differentiated by their large jaws and ovoviviparous reproduction. The Lamniformes also include the extinct megalodon, Carcharodon megalodon.
Orectolobiformes: They are commonly named as the carpet sharks, including wobbegongs, zebra sharks, nurse sharks, and the whale shark.
Pristiophoriformes: These are the sawsharks, with an elongated, toothed snout that they use for slashing their prey.
Squaliformes: This group has the dogfish sharks and rough sharks.
Squatiniformes: Also known as angel sharks, they are flattened sharks with a strong resemblance to stingrays and skates.
|† Xenacanthida (Xenacantiformes)|
It is hence true that many types of sharks must keep moving in order to receive life-giving oxygen from the water passing through their gills. These kinds of sharks are called as obligate ram ventilators because they draw water in through their mouths and force it out through their gills.
Many sharks use a method known as buccal pumping in which water is pulled in through the mouth and forced out through the gills by the cheek muscles.
While nurse sharks are able to stay stationary because they possess special structures called spiracles, which force water through their gills. Some sharks use both spiracles and buccal pumping. If any of these species were to stop swimming because, for example, they were trapped in a net, they would eventually suffocate and die.
Whatever method they use to breathe, sharks are able to engage in spans of deep rest while still but do not fall asleep in the traditional sense. Lacking eyelids, their eyes remain perpetually open and their pupils still monitor the motion of creatures swimming around them.
In 2016, researchers studying great white sharks there on Guadalupe Island, near the coast of Mexico’s Baja California Peninsula discovered the answer when they came across a female that appeared to be in a state of sleep swimming. Following her with a robotic submersible they watched for few minutes as she drifted in shallow water against a strong current, her mouth was open so the water passed through her gills in which appeared to be an almost catatonic state.
Recent studies show that it is the spinal cord, not the brain that causes sharks to swim. For this reason, it is now considered that some always-moving sharks may experience rest periods wherein their brains are less active.
Evidence shows that sharks, like dolphins (which are mammals, not fish) may “turn off” one side of their brain when they go into a deep resting or sleeping cycle. Forget about sleeping with one eye open. When a shark is in a deep rest period half of its brain is active, and both of its eyes are always widely opened.
Sharks never close their eyes because they have no eyelids. Instead, they have a translucent “nictating membrane” that shields the eyeball right before the shark bites its prey.
Most sharks spend their time cruising and eating calmly. Almost all sharks are carnivores and most of them feed on fish. It is worth noting that the biggest shark of all, the massive forty-foot long Whale shark, feeds on plankton, which are some of the smallest creatures in the ocean.
Sharks very rarely attack humans. When a shark attack does occur, it is mostly a case of mistaken identity. Surfers suffer more shark bites than anyone, usually because they looked like a savory seal or tasty sea turtle to a nearby shark.
Sharks are remarkable creatures, perfectly suited to survival. Carbon dating of excavated shark teeth proves that sharks, in forms very similar to 21st century sharks, swam the seas of Earth long before the appearance of dinosaurs. Just imagine that. Sharks have been able to survive mass extinctions of the most powerful creatures on Earth, and yet they have still survived. Interestingly enough, from what we understand, the biggest threat to sharks since the beginning of their existence is HUMANS!
Despite their deceitful dodgy reputation as savage man-eating killers most of the sharks cause no harm to humans. In fact, people are far more threatening to shark populations than any ocean dwelling shark species is to people. Sharks may kill around a dozen people yearly, but humans kill tens of millions of sharks every year on the low end, and hundreds of millions on the high end.
If all the sharks around the globe vanished tomorrow, the oceans would not survive for long. Sharks are a crucial part of the food chain and work hard to protect healthy ocean ecology. The more you understand about these amazing sea creatures, the less you are likely to fear them, and the more likely you are to appreciate the massively important role they play in our own survival.
WHAT DO SHARKS HAVE INSTEAD OF BONES?
Even more, the flexibility of cartilage gives sharks the capability to bend more elastically than boned fishes.
Both are elasmobranchs, a subclass of fishes with cartilaginous skeletons, and five to seven gill slits. Beyond these similarities, both classes of fish inspire a certain sense of awe - that often has more to do with myth than fact.
Here are six common myths about sharks and rays.
Myth 1: Sharks Must Swim Constantly, or They Die
Myth 2: Sharks are the Number One Cause of Animal-Related Deaths
Sharks are generally perceived as vicious predators. Well known movies such as Jaws have popularized this perception, making sharks some of the most feared creatures in the animal kingdom. However, this perception is based largely on myth. The reality is that only a handful of the more than 350 species of shark in the world’s oceans are considered dangerous to humans.
Myth 3: All Rays Have Poisonous Stingers
Myth 4: Sharks Can Detect a Single Drop of Blood in the Ocean
Sharks are often portrayed as having an almost supernatural sense of smell. However, reports that sharks can smell a single drop of blood in a vast ocean are greatly exaggerated. While some sharks can detect blood at one part per million, that hardly qualifies as the entire ocean. Sharks do, however, have an acute sense of smell and a sensitive olfactory system–much more so than humans.
Myth 5: Sharks Don’t Get Cancer
The idea that sharks don’t get cancer seems to stem from scant clinical evidence that cartilage has antiangiogenic properties–i.e., it inhibits the development of blood vessels, which are crucial to the growth of cancerous tumors–and since shark skeletons are made of cartilage, it follows (albeit somewhat loosely) that they can’t get cancer. Recent studies and literature reviews have found that while the incidence of cancer in sharks and related fishes such as rays does seem to be low, cancerous tumors, including chondromas (cancers of the cartilage), have in fact been found in sharks.
Sharks can gestate for up to two years. The Indian elephant has a gestation period of 22 months; humans, nine months; and mice, a mere three weeks.
Sharks have been around since well before the Age of Dinosaurs. Their evolutionary record extends back 450 million years.
Sharks and rays are cosmopolitan in distribution. They are found in waters all over the planet, from shallow coastal waters to the dark depths of the open ocean, from tropical seas to the Arctic and Antarctic regions, and even in salt water and fresh water.
Shark skin, or shagreen, feels rough if you stroke it in one direction (back to front), but smooth if you stroke it in the other (front to back). Shark skin is covered with modified scales, known as dermal denticles, which contribute to their superb hydrodynamics. Fabric for high-tech racing swimsuits, seen in recent Olympic competition, has been modeled after it as this design reduces drag and turbulence.
Sharks have a tongue referred to as a basihyal. The basihyal is a small, thick piece of cartilage located on the floor of the mouth of sharks and other fishes.
It appears to be useless for most sharks with the exception of the cookiecutter shark. The cookiecutter shark uses the basihyal to rip chunks of flesh out of their prey.
Taste is sensed by taste buds located on the papillae lining the mouth and throat of the shark. The taste receptors help the shark decide if the prey item is suitable or not prior to ingesting the item.
All sharks are carnivores, meaning that they only feed on other animals, not plants. This has major implications in terms of the strength and structure required from their jaws. The jaw needs to be powerful and flexible. It needs to grab and hold prey, and then rip and tear at it. Further, it needs to push moving prey into the mouth to be swallowed.
Sharks do not chew their food, but gulp it down in huge chunks. Because the shark’s skeleton contains no bone, but only cartilage, areas requiring extra strength and support, like the jaw, need special adaptations.
In the end, we found out that sharks are vertebrates under the class of fish known as cartilaginous fish. And, for emphasis, sharks are not invertebrates! They do not have bones, yes, but their cartilage forms a vertebral column which qualifies sharks as vertebrates!
They have a backbone (vertebrae), a spinal cord, and a notochord. This is what makes them vertebrates, just like us humans.
But don’t let the word “bone” confuse you. The difference is that the backbone of a shark is made of cartilage. While our human backbones are made up of a column of bones.
Do Sharks Have Lips?
Yes. Sharks have lips and their teeth are embedded in them. Amazingly, many people think the teeth are embedded in the jaw. However, this is not the case. Incredibly, the jaw is used to provide force while biting their prey. Without a doubt, this force allows them to be efficient hunters.
Do Sharks Have Ears?
Sharks do not have ears. Instead, they have a small opening on the side of their head. Amazingly, this leads to the inner ear. Incredibly, sharks might be able to hear prey up to a few miles away.
The inner ear includes a lateral line. Interestingly, this lets the shark detect pressure and changes in speed in the water. Without a doubt, it makes them a more efficient hunter. Impressively, sharks can sense frequencies that range from 25 Hertz to 50 Hertz. Lastly, this is thanks to their inner ear.
Do Sharks Have Taste Buds?
A shark takes a bit of the prey before they commit to eating it. This helps them determine if it is good to eat. Sharks need a high-fat diet. If the prey does not taste fatty the shark won’t eat it.
Do Sharks Have Hair?
No. Sharks do not have hair. Only mammals have hair. Mammals have fur and hair on the surface of their skin. Sharks have scales instead. Scales help them to swim.
Dolphins have hair. Dolphins are similar to sharks. However, dolphins are mammals. Sharks are not mammals. Sharks are actually fish.
Do Sharks Have Eyelashes?
Firstly, if sharks need to protect their eyes they will close or roll them. Secondly, some species such as the Great White shark will roll their eyes to protect them.
As mentioned above, the general consensus is that sharks evolved to have cartilage rather than bones. But why would this group of marine animals need to evolve in such a way:
Well, there are advantages to having a cartilaginous skeleton.
It’s lighter than a bone skeleton – sharks avoid being weighed down by heavier bone density thanks to the lightness of cartilage.
It provides better buoyancy – this helps sharks float in water, allowing them to use the least amount of energy to stay afloat in their natural habitats.
It creates a thick skin – since cartilage is not as hard and protective as bone, all sharks have thick skin which helps protect them from injury.
It is much more flexible – being all cartilage means sharks can bend, twist, and turn in record-breaking speeds. This makes them the respectable predators that they are.
It allows for faster swimming – the combination of a lighter weight, flexibility, and buoyancy allows the shark to swim faster while still conserving energy.
It makes jaws more extendable – even though a shark’s jaw contains calcified cartilage, it’s still much more flexible than bone. This gives them the ability to open wide.
It allows for a stronger bite force – one of the scariest things about sharks is their massive, powerful bite. This is all made possible by the flexibility in the cartilage.
It enables faster healing – a broken bone can take ages to heal. Luckily for sharks, having cartilage means that they heal much faster. It can also mean that it’s easier for them to be injured, though.
There’s no size limit – unlike bone, cartilage leaves unlimited room for growth. Which allows sharks and other cartilaginous fish to grow to exceptional sizes.
Essentially, sharks are faster, stealthier, and better at hunting their prey thanks to their evolved cartilaginous skeletons. They’re able to conserve energy while moving through the water and have fewer limits in size, speed, and even depths.
The largest shark, and also the largest fish in the ocean is the whale shark (Rhincodon typus). This massive plankton-feeder reaches lengths of over 20 metres (60 feet).
The smallest shark is a deepwater dogfish shark known as the dwarf lanternshark (Etmopterus perryi). This species which is found in the Caribbean Sea is mature at under 20 centimetres (~8 inches).
The fastest shark is the shortfin mako (Isurus oxyrinchus).
The shortfin mako has been recorded to reach burst swimming speeds of up to 43 mph (70 km/h). It can chase down some of the fastest fishes such as tuna and swordfish.
Is a shark a mammal, a reptile, or a fish?
These are common misunderstandings about sharks. No, a shark is not a mammal like whales, nor is it a reptile like alligators**. A shark is actually a fish!**
How many bones does a shark’s skeleton have?
That’s a trick question – the answer is none ! Sharks are cartilaginous fish, meaning that their skeletons are made entirely of cartilage (the same squishy material that is found in our human nose and ears).
Can sharks smell?
Yes, amazingly well. Their sense of smell is so powerful that sharks can detect a blood drop in an Olympic-sized pool.
Which shark has the biggest teeth?
The prehistoric Megalodon was the largest shark to have ever lived, and its teeth could grow up to seven inches long . Relative to body size, the Cookiecutter Shark has the largest teeth. This species is rather small, but it uses the large teeth in its round mouth to take cookie-sized bites from the flesh of larger marine creatures, like dolphins.
How strong is a shark’s bite?
Unbelievably, a shark bite can generate up to 40,000 pounds of pressure per square inch.
Will sharks drown if they stop swimming?
Yes, some sharks need to swim continuously to stay alive. Sharks obtain oxygen for breathing from the water that flows over their gills. If they stop swimming, no more water flow means no more oxygen, so breathing stops. However some bottom-dwelling sharks have adaptations for breathing even while they are still on the sea floor. For example, carpet sharks and some other species have spiracles behind their eyes that aid with breathing.
How strong is a shark’s bite?
Unbelievably, a shark bite can generate up to 40,000 pounds of pressure per square inch.
How much do sharks eat in a day?
Some sharks seem to eat all the time. For example, the Great White Shark is always on the hunt: in a year it eats 11 tons of food! (An average person eats more like half a ton of food per year). The Blue Shark is a glutton: it will eat until it regurgitates, and then go right back to eating. Most sharks eat a meal every couple of days. If necessary, though, they can go for a few weeks without eating. Like people and most other animals, sharks can store extra energy as fat, for use later when food is limited.
Sharks shed teeth their whole lives.
Sharks have many teeth arranged in layers so if any break off, new sharp teeth can immediately take their place. Sharks can shed thousands of teeth during their life, this is why sharks teeth can be found washed onto beaches.
Shark teeth also fossilize easily while the rest of the shark decomposes.
Sharks have an excellent sense of hearing with ears located inside their heads on both sides rather than external ears like humans. Sharks can hear best at frequencies below 1,000 Hertz which is the range of most natural aquatic sounds. This sense of hearing helps shark locate potential prey swimming and splashing in the water. Sharks also use their lateral line system to pick up vibrations and sounds.
Sharks have eyes that are similar to the human eye with some exceptions.
Sharks have the ability to open and close the pupil in response to differing light situations similar to humans while most fish do not possess this ability. A shark’s eye also includes a cornea, iris, lens, and retina. Rods and cones are located in the shark’s retina, allowing the shark to see in differing light situations as well as to see color and detail. Although it was once thought that sharks had very poor vision, we now know that sharks have sharp vision. Research has shown that sharks may be more than 10x as sensitive to light as humans. Scientists also believe that sharks may be far-sighted, able to see better at distance rather than close-up, due to the structure of the eye. Vision varies among species of sharks due to differences in the size, focusing ability, and strength of the eyes.
Shark skin feels exactly like sandpaper.
It is made up of tiny teeth-like structures called placoid scales, also known as dermal denticles. These scales point towards the tail and helps to reduce friction from surrounding water when the shark swims.
Whatever method they use to breathe, sharks can engage in periods of deep rest while still but do not fall asleep in the regular sense. Lacking eyelids, their eyes remain perpetually open, and their pupils still monitor the motion of creatures swimming around them.
Most species of shark need to remain in constant swimming motion to keep water flowing over their gills, or else they will suffocate. But like all animals, sharks still need to sleep. Surprisingly, very few shark species have ever been witnessed sleeping, and many scientific mysteries still exist around shark shuteye.
The faster they swim, the more amount of water is pushed through their gills. If some species of shark, stop swimming they stop receiving enough oxygen. They move or die. Other shark species, such as the reef shark, breathe using a combination of buccal pumping and obligate ram ventilation.
Sharks have a tongue referred to as a basihyal. The basihyal is a tiny, thick piece of cartilage located on the floor of the mouth of sharks and other fishes. It appears to be useless for most sharks with the exception of the cookiecutter shark.
The 7 animals that need barely any sleep to survive
Just like we check under our beds for monsters, sharks check for dolphins before nodding off. That’s right, the toughest kids on the undersea block swim in fear of dolphins. Flexibility Gives Dolphins the Upper Fin.
While great white sharks are unlikely to attack whales on a regular basis – as a fully-grown whale can inflict serious damage just by hitting a shark with its tail – apex predators are responsible for keeping ecosystems in balance.
All sharks has their oxygen intake from water so they can breathe. But sharks like these ones can’t pump water over their gills. So to be alive, the sharks have to constantly swim forward. This keeps water filtering through their gills, so they’re always taking in oxygen to breathe.
Try to maintain eye contact with the shark. Stay calm. Keep your eyes on it. Show them you’re a predator, as well." If a shark approaches, you can push them away. You don’t want to start a fight you are likely to lose, but you may avoid one by letting the shark know you’re not docile.
Great white sharks are mostly thought of as the most fearsome predators in the ocean. But even these sharks are afraid of something. A new study found that when great whites have encountered killer whales, or orcas, near their hunting grounds, they’ve fled and stayed away.
In the past, there was a false belief that sharks cannot sleep because breathing will stop when they sleep. But this is not true. Some sharks need to swim continuously to stay alive. Sharks obtain oxygen for breathing from the water that flows over their gills. Sharks do engage in short spans of rest throughout the day, but it is quite different from the kind of sleep that other animals engage in.