Do sharks sleep

Do sharks sleep? Sharks do not sleep like humans. Some of the shark species need to swim all time, but this fact is not true for all sharks. It is a wrong conception that all sharks do not sleep because they have to keep moving to stay active and alive. Some species of shark, such as nurse sharks, contain spiracles. These spiracles push water along their gills that allow them for stationary rest. Sharks have restful and active periods. Sharks also have to do a period of rest in the whole day. But this sleep is very different from the sleep of other animals.

:black_large_square: Obligate ram ventilators

:star: It is also true that different types of sharks must have to keep moving. They must keep moving to get their life oxygen from the water. This oxygen has to pass through gills. These kinds of sharks are called obligate ram ventilators. This is because these sharks get water in their body with the help of the mouth and they excrete and force this water out from the gills.

:black_large_square: Buccal bumping

:star: There is a method called buccal pumping. Many sharks use this method. From this method, water is passed through the mouth and then pulled out of gills with the help of cheek muscles. Many other species of sharks have the ability to remain at rest. This is because they have special structures called spiracles. These spiracles help the body move the water out from the body through gills. Many sharks use both buccal pumping and spiracles. They use both of these when they have to stop swimming. This is the condition when they are gripped in a net and feel suffocation.

:star: Many methods they can use to persuade the process of breathing. Sharks have the capacity to be related to deep rest while not sleeping traditionally. They do not contain eyelids. Their eyes always seem to be open. Their pupils have the capability to see the motion of substances that are moving around them. While being stationary, sharks are capable of doing rest. This includes the whitetip reef shark, nurse shark lemon shark, and the wobbegong.

:black_large_square: Great white sharks

:star: Among marine biologists, the great white shark is a subject of interest for a very long time. This is because there is not sufficient information about this shark. These biologists were also searching about the question of their sleep. In 2016, biologists were studying great white sharks, and they learned that when this species of shark came in contact with females that looked to be in a state of slumber. They follow her with a robotic submersible.

:star: They watched her for a few minutes when she drifted in deep water with a strong current. At this time, she opens her mouth so that water can pass through the gills. This happens to appear in an almost catatonic state.

:black_large_square: What is a shark?

:beginner: Sharks are included in a group called elasmobranch fish. Sharks are characterized with the help of a cartilaginous skeleton. A shark contains 5 to 7-gill slits on the side of the head. Sharks also include pectoral fins, which are not fused to the head. Modern sharks are classified as clade Selachimorpha. Sharks are also the sister group to the rays. Shark term has also been used for extinct members of subclass Elasmobranchii, outside the Selachimorpha, i.e., Xenacanthus, Chondrichthyes, i.e., holocephalid eugenedontodans, and Cladoselache.

Scientific classification
Kingdom Animalia
Phylum Chordate
Class Chondrichthyes
Subclass Elasmobranchii
Infraclass Euselachi
Superorder Selachimphora

:black_large_square: Orders


  • Carcharhiniformes
  • Heterodontiformes
  • Hexanchiformes
  • Lamniformes
  • Orectolobiformes
  • Pristiophoriformes
  • Squaliformes
  • Squatiniformes
  • +Cladoselachiformes
  • +Hybodontiformes
  • +Xenacanthida
  • Elegestolepis
  • += extinct

More than 420 million years ago, the species of shark had been found. Sharks differ from elasmobranchs, and their shape resembled simple fishes. This is because of their fusiform shape of the body and gill clefts on every side of the head. Although there are exceptions that sharks commonly have rough skin. The color of the skin is dull grey. Tooth-like scales roughen the body of the shark. The tail of the shark is upturned, asymmetrical, and muscular. Sharks have a pointed snout that goes forward and over the mouth set that has sharp triangular teeth.

:black_large_square: Facts about sharks

There is no swim bladder in sharks. But they swim eventually to keep them from sinking towards the bottom. There are almost more than 400 living species of sharks. These species of sharks are grouped in 14-30 families taxonomically. This grouping is done with the help of different authorities. Many large species of sharks can be dangerous for humans. Commercially, many sharks are fished. But in the late 20th and early 21 centuries, overfishing results in a decreased population of some species of sharks.

:black_large_square: Habits

Some species of shark are non-descriptive in color. Their color varies from grey to cream, yellow-brown, slate, or blue and sometimes patterned with bands, spots, marblings, or protuberances. The sharks’ which are the oddest looking, are hammerheads, i.e., Sphyrna. Hammerheads are those sharks whose head looks like hammers which are double-headed. These sharks have an eye on each stalk. The wobbegong sharks are those whose skin flaps, and protective coloration is also present. This coloration resembles the color of the seafloor. The vernacular shark, i.e., Prionace glauca, has a blue color, the name indicates the color of sharks.

  • White color sharks are called great white sharks. The scientific name of the great white shark is Carcharodon carcharias.
  • The lemon shark also indicates the color of the shark. The scientific name of lemon shark is Negaprion brevirostris.
  • The whale shark and basking shark may weigh several tons. Both these sharks are harmless but large in weight. These sharks subsist on plankton that is strained from the sea with the help of modified gill rakers.
  • The growth of whale sharks may be up to 18 meters, i.e., 59 feet in length.
  • Basking shark may reach at the length of 14 meters as fully grown.
  • All other sharks feed on smaller sharks such as squid, fish, octopuses, and other invertebrate and shellfish.
  • The largest fish in predatory species is the white shark. This shark is voracious 6 meters, i.e., 20 feet. White sharks attack dolphins, sea turtles, seals, large fish, and maybe humans.
  • Greenland shark is more sluggish in cold deep waters. These sharks feed on large fish, seals, and even swimming reindeer. These sharks can also scavenge Whale carcasses.
  • Normally, sharks, attack fish as predators. There are open ocean species such as mackerel, mako, and thresher sharks. These sharks eventually feed near the surface, and they are very sought after with reel and rod for sport.
  • Some sharks are powerful and beautiful streamlined swimmers. These are open oceans sharks, and they feed on marlin and fast tuna.
  • There are also species of sharks which are bottom-feeding species. These species are the blunt-headed and stout form that helps have more sluggish habits.
  • There are also shellfish eater sharks. These sharks have crushing, pavement like and coarse teeth.

:black_large_square: Fertilization of shark

The fertilization in sharks is internal. The male shark is dominant as the male shark induces the sperm in the female, with the help of special copulatory organs. These special organs are called claspers that are derived from pelvic fins. The young offspring in many species of sharks hatch from the eggs. These offspring are born alive. Many other species of shark lay eggs and then nourish them in the uterus. There is a placental attachment to the mother in the uterus through which nutrients are provided to offspring. Many species of sharks can consume their siblings before their birth.

:black_large_square: Origin of sharks

:star: The origin of sharks is obscure. But according to the geologic record, the origin goes back at least to the Devonian period. The origin of sharks in the Devonian period is almost 358.9 million years ago. In the middle of the Devonian Epoch, the fossil shark-like fish appeared. These shark-like fish become the dominant vertebrates of the Carboniferous Period, which is 358.9 million to 298.9 million years ago.

:black_large_square: Modern sharks

:star: Modern sharks were discovered in the early Jurassic Epoch, which is 201.3 million to 174.1 million years ago. At the end of the Cretaceous period, the species of sharks were expanded into the present-day families. The Cretaceous period was almost 145 million to 66 million years ago. Overall the morphology of sharks has been modified over the years. They also have improved their swimming and feeding mechanisms. Both fossil and modern sharks have highly diagnostic teeth.

:black_large_square: Extensive movements

:star: The geographic ranges of sharks are not well known. The extensive movements of sharks are closely related to feeding, reproductive activities, and seasonal environmental changes, from large sharks, tagging returns on the east coast of the US. This tells about the regular movement between Florida and New Jersey. After crossing the southern Atlantic ocean, blue sharks have been recovered. A species of shark was recovered whose name was tagged spiny dogfish. The scientific name of spiny dogfish was Squalus acanthias.

:star: This species was recovered after traveling about 1600 k, i.e., 1000 miles in 129 days. The improvement in tracking technologies contains the use of satellite tags. These tags continuously signal to orbit satellites when there is the revelation of shark surface and that manner, roaming and migratory patterns, and transoceanic movements. These movements are beginning to understand different species of sharks.

:star: Some species of sharks, such as bull sharks, enters the freshwater. Riverine sharks are small to medium-sized sharks, and this species of shark is exceptionally bold and voracious.

:black_large_square: Fascinating

:star: Sharks were stars in many blockbuster movies, such as blood-seeking villains. But in reality, sharks are more fascinating and complicated than it is seen in pop culture. The top predators of the ocean, i.e., sharks, have evolved into almost 500 species. These species come in all different sizes and colors that have different behavior and diets.

:black_large_square: Anatomy

:star: Like skates and rays, sharks are related to a subclass of fish which is called Elasmobranchii. In this subclass, species of sharks have a skeleton made up of cartilage, not bone. They have gill slits that help filter oxygen from the water. Sharks are the largest species on this planet earth. Sharks can grow up to 55 feet. There is a shark called dwarf lantern sharks that can grow up to eight inches. The mouth of a shark is lined with the help of many teeth that help them attack the prey. These teeth can fall out and then regrow. Their teeth are present in different shapes and sizes. The shapes are serrated like a razor to triangular in shape like a spear.

:memo: Summary

In the past, there was a false belief that sharks cannot sleep because breathing will stop when they sleep. But this is not true. The color of sharks is different for various species. They evolve their color according to the ocean’s surface so that they can hide from predators and prey. Sharks also have eyes that have similarities with the human eye. Fertilization in sharks takes place internally. The mouth of a shark contains many teeth as teeth are essential to capture the prey.

:black_large_square: Most sharks have good eyesight

:pencil2: The eyes of sharks are similar to the eyes of humans but with some exceptions. In response to different light situations, sharks have the ability to open and close the pupil. This fact is similar to humans, but many species do not have this capability. The eyes of sharks also have cornea, retina, lens, and iris. In a shark’s retina, rods and cones are present. This allows the shark to see in different conditions of light and to see detail and color. In the backside of the eye, sharks have a mirror-like layer which is similar to cats. This layer is called tapetum lucidum. This layer also increases the light’s intensity.

:pencil2: Once, it was considered that sharks have low vision, but now we know that it was false and sharks have sharp vision. Researchers have said that sharks’ eyes are 10x more sensitive to light compared to humans**.**

:black_large_square: Special electroreceptor organs

:pencil2: There are small black spots in the body of sharks. These spots are present on the mouth, eyes, and nose. These are also called ampullae of Lorenzini. These special electroreceptor organs help the shark sense electromagnetic fields and temperature shifts in the ocean.

:black_large_square: Sharks can go into a trance

:star: When a person flips from upside down, the shark then got into a state called a trance. This condition of sharks is called tonic immobility. Only because of this reason, the scientist studies them in this condition whenever you see them.

:black_large_square: Behavior

Sharks are present in shallow and deep waters in all the oceans of the world. Sharks are also present at some migrating large distances to feed and breed. Some species of sharks are solitary, but other species are found in groups at various degrees. For example, lemon sharks have been present in the form of groups to socialize. Researchers are still trying to get a perfect figure for the life of sharks, but they have only studied the ages of a fraction of sharks.
Greenland sharks are the earth’s longest-lived vertebrates. This shark lived for almost 272 years. Many species of shark eat invertebrates and smaller fish. But some larger species of shark feed on sea lions, seals, and other mammals that live in the marine environment.

:black_large_square: Attack

:purple_heart: Sharks don’t attack humans. Even the attacks of sharks have been increased since 1900. This is done because of better recording of attacks and an increase in the human population. They are increasingly rare. A beachgoer has one chance of being attacked in 11.5 million chances.

:black_large_square: Threats

May be shark is not an essential threat to us, but we are a threat for sharks. Humans have a connection to a drastic decrease in the population of sharks. Overfishing is the largest threat to sharks. Every year, almost 100 million sharks are killed. There is a Chinese dish which is called shark fin soup. Because of making this dish, sharks are being killed. Some fisheries allow the catching of all sharks and fishes, but some have banned shark fishing.
Some fishermen just take the fins from live sharks and drop the animals back in the ocean. In the ocean, sharks will be drawn and then bleed out. The practice of doing this is called shark finning. This is done to save the space in boats and not to surpass fishing quotas. A decrease in the number of sharks is not good news for the health of the ocean. To balance the food web, sharks are critical predators.

:black_large_square: Sharks do not have bones

:pushpin: Sharks do not have bones as they use gills to filter the oxygen from water. There is a special fish called elasmobranchs. This fish is only made of cartilaginous tissues. These tissues are like clear stuff by which the human nose and ears are made of. In this category, there are sawfish; skates rays are included. The body, which is made up of a cartilaginous skeleton, is much lighter than simple bone. The livers of sharks are fully covered with the help of low-density oil. Both these facts help the sharks to be buoyant.

:pushpin: As we know that sharks do not have bone, but they can be fossilized. When sharks age increases, they form calcium salts in their skeletal cartilage to get strengthened. The jaws of sharks which are dried, appear and feel solid and heavy like simple bones. These minerals allow the sharks to fossilize perfectly. The teeth of sharks contain enamel, so the teeth also play an important role in the fossil record.

:black_large_square: Frequently asked questions

:one: How many species of sharks are there?

There are almost 520 species of sharks. These species are counted at this present time, but new species are described at all times. If we calculate the total amount of fishes, then there are 1200 species of cartilaginous fishes. These fishes include skates, sharks, chimeras, and rays.

:two: How long have sharks existed?

Sharks exist from almost 400 million years ago. There is a record by fossils that indicate that there are ancestors of modern sharks that swam in the sea from 400 million years ago. Shark is a very old species that has been discovered. 400 million years is the time that makes sharks older than dinosaurs. With time, sharks are also changed very little.

:three: What is an elasmobranch?

Elasmobranch includes skates, rays, and sharks. Elasmobranch is a very close group of fishes. This group has five or more gill slits on each side of the head and cartilaginous skeletons. If we compare these with bony fishes, then bony fishes have a single gill cover and bony skeleton.

:four: Do sharks have bones?

No, there are no bones in a shark. All other fishes and sharks that belong to class Chondrichthyes do not have a true bone. But they contain cartilaginous skeleton. Cartilage is so strong as it can give support to the body of sharks. It is the type of connective tissue that is soft than true bone. In humans, cartilage is found in the nose and ear. It is very difficult to find out the fossil remains of sharks as cartilage is very soft than a bone.

:five: How long do sharks live?

The life of a shark depends on the species of shark. There is no maximum data about sharks, but many ages of sharks vary according to species. Some species of shark, such as dogfish (Mustelus canis), live for almost 16 years. But the other species, such as the porbeagle shark, live for almost 46 years. If we compare, then a shark called a Whale shark is the largest shark in the world. This shark can live up to 100 years. Greenland sharks also live more than 400 years.

:six: What does shark skin feel like?

The skin of the shark feels exactly like sandpaper. The skin of a shark is made up of small structures that look like teeth. These structures are called placoid scales. It is called dermal denticles. These structures are present towards the tail, and it helps to decrease the friction in the water when sharks have to swim. Because of the presence of this, if someone touches the skin from head to tail, it feels very smooth. But if you touch in the opposite direction from tail to head, it feels like rough and sandpaper. When the shark grows, the size of the placoid scale does not increase. A shark species called the silky shark; the ski of this shark feels very silky and smooth.

:seven: Do sharks sleep?

Yes, some species of sharks sleep. Once, it was believed that sharks do not sleep as they had to swim constantly to get their breathing process perfectly. There was a belief that sharks cannot sleep more than several minutes. The water, rich in oxygen, flows through the gills when sharks move in the water. This water allows the sharks to breathe perfectly. But this is also a fact that some species of sharks do not swim at all time, so this belief is wrong that sharks cannot sleep. Some species of sharks, such as the nurse shark, contain spiracles that hit water along their gills that give this shark a stationary rest. Sharks do not sleep like humans, but they have restful and active periods.

:eight: Can sharks hear?

Yes, sharks can hear. Sharks contain a great sense of hearing. Their ears are present inside their heads on both sides. The ears are not present on the external side like humans. At a frequency that is lower than 1000 Hz, sharks can listen best. This is the range of almost all natural aquatic sounds. Because of their sense of hearing, sharks can easily find their prey by splashing and swimming in water. To pick up sounds and vibrations, sharks also use their lateral line system.

:nine: Why do sharks have so many teeth?

In the whole life of sharks, they shed teeth. Sharks contain a lot of teeth that are arranged in the form of layers. If any of them break, there is a sharp production of teeth that takes their place. Sharks can shed their teeth in their whole; thus, sharks are found on the beaches. As the whole shark decomposes, it cannot be fossilized, but sharks’ teeth can be easily fossilized.

:keycap_ten: What are sawfishes?

Sawfishes are related to sharks very closely. They have tooth-studded snouts, flat and long saws in their body. These fishes are found off the coast of the United States. The types of these fishes that are found are called smalltooth sawfish and largetooth sawfish. These species of sawfish are now considered endangered species by the World Conservation Union (IUCN) and the U.S Marine Fisheries Service.

11. What do sawfish use their saws for?

Sawfishes use their saws for hunting. The researchers saw salty or muddy bottoms of shores and rivers that have saws of marine invertebrates. These are like cucumber, scallops, crayfish, worms, shrimp, and crab. Sawfish can get their prey from the sand and mud by using their saw. They can also use saw to injure and capture prey such as small fishes.

12. What is the fastest shark?

Fastest shark is shortfin mako . The scientific name of this shark is Isurus oxyrinchus. This shark has made a record as it can swim at the speed of up to 43 mph, i.e., 70 km/ h. this speed can also chase some of the fastest fishes such as swordfish and tuna.

13. Is shark meat found in supermarkets is safe for humans?

In most cases, yes, shark meat is safe. Although we know that the flesh of shark contains a large amount of methylamine, urea, and any toxin which is not washed away. But when shark meat is cleaned and then cooked, it will completely disappear. Although sharks also contain a high level of heavy metals, in older and larger individuals. There is low fat in shark meat, and it gives a good source of proteins.

14. Why most sharks have a lighter color underneath?

The coloring of sharks helps them to hide from prey and predators. There is a color pattern in sharks that swim in open water. This coloring of sharks is called countershading. The upper part of the shark is dark in color. This dark color makes it difficult to see the shark from the upper side of the ocean. The shark’s underside is light in color so, this color blends really well with the water when it has to be seen from the lower side of the ocean. So, countershading makes it difficult for prey and predators to see the shark.

15. Do sharks have good eyesight?

The eyes of sharks are similar to the eyes of humans but with some exceptions. In response to different light situations, sharks have the ability to open and close the pupil. This fact is similar to humans, but many species do not have this capability. The eyes of sharks also have cornea, retina, lens, and iris. In a shark’s retina, rods and cones are present. This allows the shark to see in different light conditions and see detail and color. In the backside of the eye, sharks have a mirror-like layer which is similar to cats. This layer is called tapetum lucidum. This layer also increases the light’s intensity. Once, it was considered that sharks have low vision, but now we know that it was false and sharks have sharp vision. Researchers have said that sharks’ eyes are 10x more sensitive to light compared to humans.

:memo: Conclusion

Sharks have unusual biological characteristics; delayed maturation, slow growth, the reproductive cycle is very long, and a low life span. Fertilization occurs in sharks. This is done internally. Female sharks produce small numbers of young offspring that is born as fully developed small shark. These newly born sharks are large at the time of birth. Some species of sharks do sleep, but some of them require swimming all the time, so these species cannot sleep. The sleep of sharks is different from other animals. There are five to seven-gill slits that help sharks to filter oxygen from water. Sharks have sharp vision. Sharks do not contain bones. The stable body of the shark is due to the cartilage skeleton.

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