One of oldest species animals, mysterious and poorly studied - are sharks, or, as they are also called, selahs. Many myths and legends surround this representative of the marine fauna and form a prejudice against amazing fish. Selachians began to systematically study during the Second World War, during battles in the basins of the quiet and Indian oceans. The task was to find a means of protecting people from attacking them marine predators.
Shark is a fish or a mammal
The list of these marine predators includes more than 400 species, which are polarly different: from the smallest deep-water, barely growing to 17-20 cm, to the giant - the whale shark, a huge 20-meter high-tonnage specimen.
The name "mammal" speaks for itself. Those animals that feed their babies milk are called "mammals."
The shark does not nourish its cubs with milk, besides, the shark breathes with the help of such a device - “gills”. Shark is a fish.
In size, of course, these predators are comparable to dolphins or some species of whales. But in the sea kingdom there are many of the same size, but different in content.
In the modern classification of the animal kingdom, sharks and skates constitute the subclass of Sharks, which enters the class of cartilage fish. Cartilaginous fish, mammals, as well as humans, form a single type for a number of similar signs - Vertebrates.
The skeleton of bony fish consists entirely of bones, in sharks there are only cartilage. A large amount of calcium makes cartilage hard and durable. Curved, impressive size mouth is placed on the bottom of the head.
The large and soft caudal fin is asymmetrical - the upper lobe is much larger than the lower one. Bony fish move freely with their lateral fins, unlike selachians.
Bony fish and shark, what are the similarities and differences
Mammals and sharks, what are the differences
One of the unique properties is electroreception, the ability to sense electrical and magnetic signals the environment. Used to detect prey, orientation in space, to maintain communication with their relatives.
Electroreceptor sensory organs are found in selachians and skates, as well as in some species of bone fish. Among mammals, the presence of electroreceptors can boast the Australian platypus and, presumably, echidna. The ampoules of Lorenzini - the so-called electroreceptor apparatus predator, which she successfully uses at the time of the attack.
In the process of evolution, the relief of the Earth changed - on the land there were oceans or, on the contrary, the continents went under the waters. Some forms of life disappeared, others appeared. Only Selachs continued to exist for almost 500 million years. Some representatives of this unique and unexplored species almost did not change.
The largest copy is fossil carhadon, the ancestor of the great white shark. Its size was restored by found fossilized teeth, the size of which is 10–15 cm. It is supposed that seven people could fit in its mouth. The smallest, now living representative of the species - dwarf glowing shark only 7 cm long
Sharks are predatory fish, dangerous and aggressive inhabitants of the ocean, the oldest known animals. So it is considered, and millions of people believe in this, drawing knowledge of these unique creatures from Hollywood horror thrillers. Let us see what we know about these amazing creatures that appeared much earlier than all civilizations of the world and perfectly adapted to modern life. What is a shark? Is it a fish or a mammal?
Amazing fish
All scientific and encyclopedic publications claim that sharks are cartilaginous fish, that is, they have absolutely no bones in their bodies, which makes them stand out from their modern habitats. Together with the absence of gill covers and the characteristics of the structure of scales, the cartilage ostyak indicates the primitiveness of the organization of the species, and more precisely its ancient origin: it is known that 400 million years ago these fish were already swimming in the world's oceans. Despite this, sharks are one of the most advanced species of carnivorous ocean fish. For a long time, adapting to the ever-changing environment, they perfectly adapted and now get along perfectly with modern bony fishes and marine mammals, not yielding to them either in speed, or in agility, or in hunting skills. The list of sharks includes more than 400 species that are polarly different: from the smallest deep-water, barely growing to 17-20 cm, to the giant - the whale shark, a huge 20-meter high-tonnage individual.
An important difference from bony fish are the methods of reproduction. Some species of sharks are viviparous, i.e. give birth to live young. Some lay eggs protected by a dense cornea. Far from all the secrets of their life are revealed: there are species whose secrets of reproduction of their offspring are still behind seven seals. Therefore, the question often arises: "Is a shark a fish or a mammal?"
Features of the form
The cartilaginous skeleton and the absence of bones are the main signs of the attitude of these fish to a primitive organization. But, as mentioned above, this does not prevent the shark from dwelling in almost all the oceans of the planet, having long won fame as the most dangerous and aggressive predator. In addition, nature has taken care of the protection of this amazing animal. It is difficult to find something that is more protective than the scales that a shark has. Located from the head to the tail, it feels like a satin finish to the touch, but you should not hold your hand in the opposite direction - from tail to head: sharp teeth pierce the skin. Coarse sandpaper compared to this perfect protection is a weak resemblance.
Consider the device scales. Each scale of cartilaginous fishes is supplied with a small thorn with a pointed back. From above the spike is covered with a layer of the strongest enamel, and its expanding base is spliced with the skin of fish. In the cavity of this process are the blood vessels and nerve branches. The size of the scales on the body of the fish is different: the largest fish is located on the head, the thorns in the mouth of the shark, having somewhat transformed, ceased to be the protection of the skin and turned into a sharp and extremely dangerous weapon of attack - magnificent teeth.
Main weapon
Being modified scales, shark's teeth are arranged in strict chess order, in several rows. During the life of the predator, the teeth grow constantly, and when one row is abraded, new ones located in the depths of the mouth germinate. Shark teeth do not serve to chew food. She does not know how to do this. Their main purpose is to hold the prey, tear it apart to swallow it without interference. Have different types sharks have a different shape of teeth, which is dictated by the peculiarities of lifestyle. Bottom, feeding on crustaceans in hard shell have teeth with flat, ribbed surface that can crush lime defenses. Predator fish have long, sharp teeth to grab moving prey, or wide, with a serrated edge, designed to rip the meat of a large prey. Plankton sharks have practically no need for teeth, they are small in these species, barely reaching 3-5 mm.
Another feature of cartilaginous fish is the absence of gill covers. Their role is performed by 5-7 gill slits located behind the head, the number of which is determined by the type of sharks, and the presence is distinctive feature. However, like all fish, these predators, getting oxygen from water, pass it through the gills. The presence of the respiratory system, characteristic for waterfowl, gives an exhaustive answer to the question: "Is a shark a fish or a mammal?"
Amazing abilities: sense of smell, electroreceptor apparatus and lateral line system
It is impossible to overestimate the possibility of smelling in sharks. This is one of the most advanced basic sensory systems. Experiments have shown not only the high sensitivity of fish to odors, but truly amazing. The shark can catch the smell of blood diluted in water at a ratio of 1: 1,000,000, and constantly use the smell when looking for prey or partners for breeding in the mating season. In determining the location of the object, probably, in addition to a highly developed sense of smell, other organs and systems are also involved: hearing, as well as the lateral line located on the surface of the fish body, capable of feeling both negligibly weak mechanical movements and the smallest in the water, and playing an important role when hunting, communicating with fellows and orienteering.
There are unproven scientific assumptions about the ability of these predators to catch odors spread through the air, which led the researchers to the strange behavior of the white shark. She often raises her face above the surface of the water surface, as if sniffing.
The unique ability of sharks to detect a victim by the movements of the respiratory and cardiac muscles, electric fields with insignificant voltage, has been scientifically proven. Long-term observation of the migration of some species over fairly long distances in a straight line made it possible to reveal the possibility of their orientation in the Earth’s magnetic field.
Vision
The uniqueness of this representative of the fauna once again underlines the special structure of the eye, which provides both protection against external stimuli and excellent visual acuity. Features of the device of the organ of vision of the shark are in the presence of a blinking century, closing the eye at the time of the attack on the victim, thereby protecting it from damage. In fairness, it should be noted that not all species have eyelids. These individuals roll their eyes when attacking the victim.
Moreover, the shark's eye has a special reflective layer located behind the retina, which enhances the sensitivity of this organ and significantly increases visual acuity even in low light. Today, it does not require proof of the fact that the vision of some species of these fish is many times greater than that of humans.
Shark breeding
Unlike most teleost fishes, which produce millions of eggs, reproduction of their own kind in sharks is aimed more at quality than at quantity. Characteristic features of cartilaginous fish — internal fertilization, widespread egg production, and live birth, significantly reduce the mortality of offspring, allowing for a high survival rate and lower fecundity.
Depending on the species, sharks can be egg-laying, viviparous and oviparous. Oviparous is almost a third of all species. After internal fertilization, the female lays eggs covered with a gelatinous protein layer, protected on top of it with a hard shell that protects the contents from dehydration and external damage. The supply of nutrients in the egg is enormous, it does not dry out during the full development of the embryo, which, it should be noted, is quite long. As a rule, a small number of eggs are laid at the same time: from 1 to 12. The only exception is laying up to 500 eggs up to 8 cm. Slow embryo development pays off a lot - the small shark hatched is perfectly adapted to life and differs from an adult only in size.
A distinctive feature of egg-breeding is that, having hatched from fertilized eggs, the young remain in the mother's oviduct for some time, being born developed and perfectly adapted to independent living. Information on the timing of gestation of offspring in the egg-breeding species requires clarification. According to some data, this period ranges from several months to two years, like that of a barbed shark, which is a record among all vertebrates.
In the womb of viviparous individuals up to 30-80 embryos can develop simultaneously. Regardless of the type of shark and mode of reproduction, all are distinguished by the reproduction of small but capable of independent offspring.
Plankton sharks
Most of these fish are common in the oceans and seas, inhabiting the water column from the surface to a two-kilometer depth, and are classified as true predators. But there are exceptions in this family: the bigmouth, giant, whale and some other shark species are filter feeders, feeding on plankton, small fish and squid.
The largest are whale and giant sharkreaching a length of 20 and 15 meters respectively. Being planktonic fishes, they slowly move, having opened a mouth, in the center of clusters of plankton, driving water through the gill openings with special outgrowths-plates, filtering out a huge amount of water and extracting all living organisms larger than 2 mm from it. 
There is very little information about the reproduction of plankton species. Thus, the life of a giant shark is completely unknown. Whale - egg-laying. The eggs laid by her reach quite impressive sizes: the length can be 0.7 m, width - 0.4 m. Despite the enormous size, the planktonic shark fish, the photo of which is presented in this article, is completely non-aggressive and very slow.
The world of sharks is amazing and diverse. Some of them are bottom-dwelling and feed on crustaceans and invertebrates, such as small cats, no larger than 1 meter in length. The object of the trade is the prickly quark shark, a photo of which is also presented in the article.
Fishing katran
Katran, having a wide distribution, is the only species inhabiting the Black Sea. This sea shark extremely cold-loving and does not like warm water. Perhaps this explains the fact that the Black Sea quatane rarely reaches 1 meter in length, although in the North Sea the size of this fish is 1.5-2 m. Thorny sharks practically do not rise to the surface of the water and do not approach the shore. They live at a sufficient depth, falling into large shoals. Catrans feed on bottom invertebrates and bottom fish - flounder, whiting, successfully hunt shoals of Hamsa.
It is striking that the Katran is an egg-bearing fish, the pregnancy of which lasts an incredibly long time - up to 2 years. Sharklets are born absolutely ready for the predator's adult life. Inaccessible to humans, protected and cautious, they grow to adulthood without any problems. These sharks in the sea are safe for humans. They never swim close to the swimmers. The incredible system of highly developed sense of smell and the feeling of the slightest frequency oscillations helps the katran to avoid encounters with people. 
Flocks of this fish approach the coast in late autumn. Then begins the fishing season. The second name of sharks - prickly - given to katranam for a reason. This fish is able to deliver a lot of trouble when it gets out of the trawl. It possesses not only strong scales, but also sharp spines before dorsal fins, at the base of which are poison glands. In contact with them you can get a portion of the poison, though not fatal, but bringing certain inconveniences. The Atlantic Ocean is the most generous catches on the Atlantic: sometimes it is possible to catch up to 20 thousand fish in one notice.
The prickly shark is not just a tasty fish, it is very gentle and, of course, healthy. In the skillful hands of a good cook, the meat of the katran turns into magnificent delicacies, wholesome and delicious dishes. Immutable rule in the preparation of shark meat is a mandatory discharge of blood immediately after the fish are caught. It has a high concentration of ammonia. If you do not get rid of the blood, the product will be hopelessly spoiled. The advantage of such dishes is the fact that there are no bones in their meat, because this fish is cartilaginous.
Valued and skin Katranov. The abrasive properties of the cuticles are always used by craftsmen in many industries: from carpenters, cabinetmakers and carpenters to furriers.
Tiger shark
Fully justifying the reputation of the storm of the tropical seas, tiger shark, yielding to white in the number of recorded attacks on a person, significantly exceeds it in the percentage of deaths after encounters with it. The name of the shark is determined by its external features. The tiger shark (or sea tiger) is so named because of the dark transverse stripes on the gray, brown-gray or greenish background of the body, which eventually turn pale. Preferring shallow waters, these sharks rarely fall below 300 meters, the cold waters do not attract them at all. The outstanding size of the fish - 7-8 meters in length and weight about a ton - put it in the row most large species. The streamlined body shape with a large head, blunt snout and 5th gill slits, as well as a large maw with jaws, equipped with 280-300 flat, scraper-shaped teeth with a notch, and a well-developed upper lobe caudal fin - this is an incomplete portrait of this dangerous fish. 
Sea tigers are tied to the chosen places, they do not like to leave the limits of their own residence. Being solitary predators, tiger sharks sometimes come together in groups if there is enough food. But more often they patrol their area one by one.
The diet of these predators is made by pinnipeds mammals, dolphins, fish, and even small representatives of their own species. They are so omnivorous that the contents of their stomachs, presenting a set of objects that are far from organic food, surprises researchers. For their exorbitant omnivorous tiger sharks received the mark of "sea scavengers". But more than relevant for them is the ability to turn the stomach through the mouth for rinsing in water, allowing you to get rid of completely indigestible objects such as banks, bags, various debris.
This dangerous shark refers to the egg-breeding, bearing their offspring 14-16 months and giving birth in the litter to 80 sharks, up to half a meter in size each.
Great white shark
Exceptionally large aggressive predator - white shark or karharodon, long and firmly holding the sad primacy of the number of attacks on people, is found in the surface waters of all the oceans of the Earth except the Arctic, preferring a temperate and warm climate. It does not occur in cold waters, and also does not live in light-salted or desalinated seas. For example, in the Black Sea karkharodon does not appear. Most likely to meet with great white sharks on the coast of California, near the Mexican island of Guadeloupe, in the Mediterranean and Adriatic seas, off the coast of New Zealand, where they can swim in small flocks. The waters of the seas, where the fur seals abound in abundance, are especially loved by these predators. For a long time, there was an opinion about the constant coastal existence of white sharks, however, it was proved that the fish migrate from the coast of California to African latitudes, swimming more than 20 thousand km in a year. 
Being the largest modern predator (some specimens reach a length of more than 10 meters with a body weight of up to 3.5 tons), the white shark does not give the victim any chance of escape. This species owes its name to the color of the abdominal part - light or dirty-white. Its dorsal part is of darker tones: gray, greenish. Like all shark species, the white one has no air bubble, which explains the constant movement of the fish.
She treats food more biasedly than her tiger sister. The little shark eats medium-sized fish, mammals. Grown-up carcharodons hunt seals, dolphins, and smaller representatives of the species. Adults do not avoid young or sick whales, often performing outstanding tactical moves when attacking, which only confirms their intellectual abilities. This dangerous shark has long proved that any prey is in the teeth.
Little information is available on the reproduction of offspring. As well as many species, they are ovovivivip with gestation period of 11 months, at the end of which 1-2 pups adapted for independent life appear. Today, the population of white sharks is rapidly decreasing, there are no more than 3,500 of them all over the world. View listed in the Red Book.
Sharks in the ocean - a fascinating and scaring sight at the same time. It can both delight and plunge into shock. Who saw not only the photo big sharks, but the pack of white hunters with their own eyes will never forget this. After all, even pictures with images of predatory fish excite the imagination. The world of sharks is amazing, fantastic and dangerous. The most ancient creature and modern cruel predator get along in a unique animal, attracting attention, again and again raising the question: "Is a shark a fish or a mammal?"
Currently, more than 450 species of sharks are known: from deep-sea shallow Etmopterus perryi, only 17 cm long, to the whale shark, whose length reaches 12 meters.
Sharks are widespread in all seas and oceans, from the surface to a depth of more than 2000 meters. Mostly live in sea water, but some species can also live in fresh water.
Most sharks belong to the so-called real predators, but some species, in particular, whale, giant and big-mouthed sharks, are filter feeders, they feed on plankton, squid and small fish.
Skeleton
The skeleton of a shark is noticeably different from the skeleton of a bony fish - it has no bones, and it is completely formed from cartilage tissue. Leather
The shark is covered with placoid scales, scales of which are rhombic plates ending in a thorn protruding from the skin to the outside. The structure and strength of the scales is close to the bones, which makes it possible to call it skin teeth. These teeth have a wide base, a flattened shape and a very prominently outlined crown. For the most part, the crowns are very sharp and fit snugly together, so the skin may appear relatively smooth if you run your hand from head to tail, and vice versa - coarse, like sandpaper - if you move in the opposite direction. Teeth and Jaws
The teeth of most sharks have the shape of sharp dentine cones and sit on the cartilages of the upper and lower jaws. The teeth regularly change as they fall out or wear out according to the conveyor principle - their replacement constantly grows from the inside. According to its structure and origin, these are modified placoid scales. Depending on the diet and lifestyle, the teeth and jaws are very different in different types of sharks. Bottom sharks, whose food is usually protected by a hard shell, have hundreds of small, smooth teeth. Pelagic species are characterized by the presence of very sharp teeth, adapted for easy penetration into the flesh of prey. In sharks such as tiger teeth, a knife-shaped teeth designed to tear the meat of a large prey. Plankfish-eating sharks have rudimentary small teeth.
Buoyancy
Unlike bony fish, sharks do not have a swim bladder. Instead, a huge liver, a cartilaginous skeleton and fins help to compensate for the negative buoyancy. Most shark species need to constantly move in order to maintain their breathing, so they cannot sleep for long. However, some species, such as a whiskered nurse nanny, are able to pump water through the gills, which allows them to rest at the bottom.
Digestive system
After a hearty meal, sharks are capable of starving for a long time, slowly and economically using accumulated resources, and in general their need for food is relatively small. For example, a three-meter-high Australian captive sand shark weighing 150 kg per year eaten only 80-90 kg of fish. Sharks periodically produce eversion of the stomach - turn it through the mouth out into the aquatic environment for the purpose of purification. It is curious that this will never damage the stomach with its many teeth.
Sense of smell
Smell of sharks? one of the main sensory systems. Experiments have shown sharks' high sensitivity to odors. Are the olfactory organs represented by the nostrils? small bags on the face, passing the water to the olfactory receptors. Smell involved in the search for prey and partners for reproduction. The white shark uses 14% of the brain for smelling. Smelling is especially well developed in hammerhead sharks? The nostrils of a peculiar shape, spaced a decent distance from each other on the head, make it possible to more clearly determine the direction of the source of the smell. Studies have shown that sharks respond better to smells of wounded or disturbed prey.
Sharks are able to catch the smell of blood, diluted in a ratio of 1: 1 000 000, which roughly can be compared with one teaspoon per swimming pool of medium size.
Vision
The structure of the shark eye is for the most part the same as that of all vertebrates, but with some peculiarities. Does the shark's eye have a special reflective layer? tapetum? located behind the retina. Tapetum directs the light that has passed through the retina so that it again acts on the receptors, thus enhancing the sensitivity of the eye. This significantly increases visual acuity, especially in low light conditions. Another feature in some species is the presence of the blinking century, which closes the eye directly during the attack on the victim, protecting it from damage. Sharks that do not have a blinking century, while attacking the victim roll their eyes.
It was previously believed that the shark's eye contains too few cones and is unable to distinguish colors and small details. However, modern technology has allowed to prove the opposite. Visual acuity of some species of sharks is sharper than a human up to 10 times.
Hearing
Shark organ? it is the inner ear enclosed in a cartilage capsule. Sharks perceive mostly low sounds of 100–2500 Hz. Most sharks are able to distinguish infrasound with a frequency below 20 Hz. The inner ear is also an organ of balance. Electro and Magnetoreception
Is the electroreceptor apparatus of sharks represented by the ampoules of Lorenzini? these are small connective tissue capsules immersed in the skin with tubes emanating from them that open to the surface of the skin. Sharks react to electric fields of only 0.01 µV / cm. Therefore, they are able to detect the victim by the electric fields created by the work of the respiratory muscles and the heart.
Lifespan
Each species has its own specific lifespan, and it is not easy to evaluate it for all sharks. In general, sharks grow relatively slowly, and in general it can be said that most species live for 20–30 years. However, the record life expectancy is different spotted prickly shark, living more than 100 years. Known and whale sharks with a similar age.
Breeding
In sharks, intrinsic fertilization, a primitive queen, and a fairly perfect placental bond, characteristic of cartilaginous fish. The fetus develops in the uterus and is born well adapted to independent living. In newborn sharks, the musculoskeletal system, the digestive system and the senses are well developed, which allows you to feed on your own and quickly build up weight. Do sharks produce different numbers of cubs? some species up to 100, others only two — three. The great white shark gives birth to about 3–14 sharks at a time.
Unlike most teleost fishes, which produce millions of eggs, the principle of procreation in sharks focuses more on quality than on quantity.
The care of some species for the offspring (the little chick has been under the care of the mother for some time) allows the sharks to have a high survival rate, and hence lower fertility.
Lifestyle
In the traditional view, the shark looks like a lonely hunter, plowing the ocean in search of prey. However, this description applies only to a few species. Very many sharks lead a sedentary inactive life. Contrary to popular belief that the shark is just a “hunting machine”, driven by instinct alone, recent studies have shown the ability of some species to solve problems, social behavior and curiosity. In 1987, in the South African region, a group of seven white sharks jointly dragged a dead whale half-beached into a deeper place for a meal.
The ratio of the mass of brain and body in sharks is approximately equivalent to the same indicator in birds and mammals.
Mostly sharks move at a cruising speed of about 8 km / h, but when hunting or attacking, the average shark accelerates to 19 km / h. The mako shark can accelerate to a speed of 50 km / h. The white shark is also capable of such jerks. Such exceptions are possible due to the warm-bloodedness of these species.
Nutrition
The preferences in food of sharks are very diverse, and they depend on the characteristics of each species, as well as on their habitats. The main food for sharks are fish, mammals, plankton and crustaceans. For example, lamina, mako and blue shark eat mainly sea fish pelagic species, and the shape of their thin sharp teeth is adapted to catch prey in motion.
The white shark prefers seals and sea lions, but when possible, it also hunts whale mammals, since the peculiarities of its teeth make it possible to snatch off large pieces of flesh.
Crabs and other crustaceans are the main part of the diet of bottom sharks, and their teeth are short in length and adapted for breaking shell.
Giant, big-eel and whale sharks feed on plankton and small marine organisms. Most species are carnivorous.
Some species, such as the tiger shark, are almost omnivorous and swallow almost everything that comes their way.
After all, for the most part these are big and aggressive fishes, which while hunting for bait are in a state of hunting for prey? that is, in arousal.
In addition, when extracting from water, some species may simply crush their internal organs with their own weight, and this must be taken into account when the shark moves from the ocean to an artificial reservoir.
Regular difficulties arise on the arrival of sharks in the aquarium, which must have the necessary capacity for the normal functioning of these fish, as well as take into account their increased sensitivity to electromagnetic waves.
Fishing and hunting
Along with other fish, sharks have been fished for over many years (more than 100 species). The fishing industry in sharks is interesting:
The meat used by many cultures for food (despite the fact that observations have shown the susceptibility of the organism of sharks to the accumulation of mercury, the content of which in meat has increased significantly due to environmental pollution).
Fins, which in Asia are the main ingredient for gourmet soup, as well as those used in oriental medicine.
Cartilage, around which there are still disputes about his medicinal properties against cancer tumors.
Liver containing fat rich in vitamin A and B vitamins, and used as a raw material for the manufacture of medicines.
Leather, which is used in haberdashery and as an abrasive material.
The main trade is conducted in the Atlantic Ocean, where 26 species are industrial, about a third of sharks are harvested in the Indian Ocean, and another half as many sharks are caught in the Pacific. Approximately 100 million sharks are harvested annually around the world.
The catch of sharks can be divided into three areas:
Fishing for the purpose of applying their meat, liver, cartilage, skin and fins? that is, the full use of fish.
The so-called bycatch? when the shark is an occasional catch when catching other fish.
Fishing for the purpose of mining only fins. This is the most irrational (the weight of the fins is up to 4% of the whole body) and the inhuman way of shark mining, which received the name finning in English? when fins are the only target, and the rest of the carcass is thrown away to rot on the shore or back into the sea.
In addition to fishing for industrial purposes in the world, there are also such reasons for hunting sharks as ensuring the safety of beaches, reducing the natural threat of industrial fish and just extreme hunting and fishing.
Common Shark Misconceptions
The shark must constantly swim to stay alive. In fact, many species are able to rest, lying on the bottom and pumping water through the gills. Most sharks attack humans and kill them. Only a few species of sharks regularly make unprovoked attacks on humans, and this is mainly due to an error in the identification of prey.
Sharks swim at high speed. In fact, the sharks cruising speed is quite small, as they need to save energy. However, this does not prevent them from developing a high, so-called “throwing” speed just before the victim’s attack.
Sharks adore human blood. Sharks do not favor any blood. On the contrary, having cut off a piece of flesh from a person, they usually spit it back, because this meat is not the high-fat food that they need to replenish their energy reserves.
Sharks are omnivores. Most species prefer to wait for the opportunity to get their usual food instead of eating everything.
Sharks are not subject to cancer. This belief, which existed for a long time, caused the death of a huge number of sharks, caught by man for the sake of "anti-cancer" cartilage. However, the observation of sharks in captivity, as well as in natural environment habitat, showed the presence of individuals with organs affected by cancer. The number of cases of cancer was greater where water is more polluted (including from human activity).
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Of all the inhabitants of the ocean sharksseem to enjoy the greatest fame and the worst notoriety. Most of them are large creatures with a long body, having the most streamlined shape, which allows them to develop impressive speed and make long journeys.
Sharks - predators and therefore, as a rule, are armed with teeth, sharp as a razor. Teeth grow in the mouth in 5-15 rows. The power of the jaws is monstrous. They act like nippers, and a large predator costs nothing in half to eat a small dolphin. From such a load, the teeth in the front working rank quickly wear out and fall out, but they do not have to take care of the false teeth. Shark teeth are crawling.
The whole shark life of the teeth line is slowly but steadily moving towards the end of the muzzle, and the next rank is always in place of the failed one. Sometimes all the teeth from the first rank do not have time to fall out, their remnants crawl out of the mouth to the outside. This is not surprising. After all, the whole body of a shark is covered with large scales, nothing but the size and shape, not significantly different from the teeth.
Possessing an excellent weapon and bloodthirsty disposition, sharks fearlessly attacking all living things. Shark hearing, like most fish, is also not up to par, but the smell is beautiful. In addition, sharks are equipped with sideline organs, which allow perturbing the water caused by the movement of a large creature for 200-300 meters.
Sharks - ancient creatures. Their skeleton does not consist of bones, but of cartilage. They do not have a swim bladder, and, in order not to sink, they constantly have to work with their tail and fins and swim, swim, swim. And the shark breathing apparatus is primitive. They cannot, like teleost fishes, take water into their mouths and release it through their gills. For the water to circulate in the gills, the shark must move, swim with its mouth open. If her movement slows down, she begins to experience a lack of oxygen. Relax, lying on the bottom, can only small coastal sharks, which at this time reduce the level of metabolism.
When it comes to sharks, coral islands, the hot southern sun, wide sandy beaches and slender silhouettes involuntarily appear. Few people know that our northern seas are teeming with sharks. Ordinary spiny sharkbetter known as katranIt is widely distributed in the Black, White, Barents, Okhotsk, Bering and Japan Seas. It is small, usually not more than 1 m. For a person, it is not dangerous, and you can swim near Odessa and Ochakov, where the quatra are especially numerous, without fear. True, you can’t attribute this shark to the number of our friends, as it destroys a lot of useful fish.
Katran refers to the number of edible sharks: it is smoked, and, we must pay tribute, the balyk of it is slightly inferior to the sturgeon. Special fat is melted from the katran. Katranium Fat - Squalene (from the Latin name of the shark - Squalius) is the lightest of all animal fats.
Polar shark - absolutely amazing creature. It is found only in the Arctic Ocean, in the adjacent seas and in the northernmost part of the Atlantic Ocean. And although it is a fairly close relative of the katran, it looks quite impressive: up to 6.3 meters in length and up to a ton in weight.
Polar shark - predator. It feeds on fish, corpses of whales and seals, and maybe it attacks on live pinnipeds. Although this giant fish is a rather phlegmatic creature and, caught on a hook, it allows you to pull yourself aboard the ship like a sack of potatoes without offering any resistance to a successful angler, it could be a serious danger in water, but the cases of attacking a person are unknown. In summer, sharks stay at a depth of 150-500 meters, and although in winter they rise closer to the surface, it is simply not necessary to encounter a person in the water in a predator.
Polar shark edible. Even in the last century, its fishery in the Barents Sea were fishermen from Greenland, Norway, Iceland and our Russian coast-dwellers. At the beginning of our century, fishing for sharks has almost ceased. And this is hardly useful for fishing, because the shark is gluttonous, it eats a lot of commercial fish. But the polar predator somehow imperceptibly fell out of our sight, even zoologists do not know how much it is in our northern seas.
Recently Arkhangelsk fishermen recalled the polar shark. In the White Sea, they conducted trial fishing for hook tackle, such as the usual shale. The results exceeded all expectations: every tenth hook returned with a shark. It turns out that there are a lot of sharks and it is not difficult to get them, and, perhaps, soon fish farms from shark meat and highly vitamins fish oil will be supplied to the poultry farm.
Due to incorrect information, sharks have a bad reputation. Nevertheless, you will appreciate these fish when you learn the basic facts from the life of sharks.
Approximately 465 known shark species live in the oceans today.
It is difficult to estimate the population of each species of shark separately, since the range of each species covers a very large geographic area. But the total number of sharks in wild nature constantly going down.
While many of us are afraid of sharks, we need to know that Man is the Largest predator on the planet. People worse than sharks. In fact, people kill over 73 million sharks annually.
On average, between 30 and 50 shark attacks are reported annually, only between 5 and 10 of these attacks prove fatal to humans. The chances of dying from a shark attack are much lower than the chances of dying from a hornet, wasp, bee or dog attack. You can think of sharks as horrible man-eating predators, but in reality, only 3% of sharks — a small minority — are dangerous to humans.
Shark dinosaur precursors. They are older than dinosaurs by 200 million years. With that, for 450 million years (the geological age of sharks), these ancient fauna representatives have not changed a bit.
Sharks are the top of the food chain - the top of the predators of the marine expanses, they regulate populations of all species.
Recent studies have shown - there is a massive depletion of sharks. This has cascading implications for changes in the entire ocean ecosystem.
Sharks are fish
Sharks belong to the family of cartilaginous fishes. The difference between the cartilaginous and bony fishes is that the skeleton of cartilage is lighter and more flexible.
Sharks breathe through a series of gill slits, 5-7 gill slits are located on both sides of their bodies.
All sharks have several rows of teeth. They lose their teeth on a regular basis, but new teeth continue to grow and replace lost ones.
When the shark dies, the salt of the sea water completely dissolves its skeleton, leaving only the teeth.
Shark skin "consists of a series of scales that act as an external frame for easy movement in the water. The upper side of the shark is usually dark to mix with water, it is not visible from above. And their lower part is white, in harmony with the lighter surface of the sea below. It helps sharks disguise.
Sharks have a very keen sense of smell, capable of detecting blood in water at a distance of several miles.
The eyes of sharks have a surprisingly wide overview, cover almost 360 degrees. Their panoramic view of the underwater world inhibits only two blind spots, one in front of the muzzle, and the other directly behind the head.
Sharks are adapted to life in a wide range of different temperatures of the aquatic environment.
Some species live in shallow, coastal areas, other species live in deep waters, on the ocean floor, and others - on the surface in the open ocean.
The brown shark lives along the outer continental shelves and submarine ridges. Their homes are too deep for people, so we know almost nothing about them.
Some species, such as the bull shark, are able to live in both salt and fresh water.
Most sharks are active in the evening and at night - this is the time of their hunting.
Sharks are able to migrate over long distances - on the scale they can cover entire ocean basins.
There are single shark species, and there are social ones that prefer to live in groups.
How do sharks eat and what do they eat?
- Some shark species, such as the white shark, attack from below. As a rule, their prey are seals and sea lions.
- Shark species on the ocean floor have developed the ability to collect bottom food.
- There are species of sharks that attack schooling fish.
- Large and giant sharks feed like whales, filtering ocean water through a wide-open mouth. During filtration, large amounts of plankton and krill are swallowed.
Shark Facts You Should Know
Sharks mature slowly and reach reproductive age at 12-15 years. A whale shark can reproduce its first offspring only at the age of 30 years. This, combined with the fact that many species give birth to only one or two cubs, means that sharks have great difficulty recovering. That is why their population has declined so much.
The gestation period of a shark lasts from 5 months to 2 years, depending on the type of shark. Some female sharks use semen from several males to create a single litter.
Shortly after birth, the shark, while still a puppy, swims away from the mother. They are able to stand up for themselves from birth. Sharks are born with a full set of teeth and are able to eat and live independently.
All sharks are peculiar to cannibalism. At the same time, cannibals are not only adults, prenatal cannibalism is manifested by sharks, feeding on the eggs of fellows, which the female produces during pregnancy. That's because from the litter in 80 eggs, only 1-2 sharks are born.
Sharks, which eat the eggs of their brothers and sisters in the womb, are not vicious. They are simply looking for nutrients to support themselves as they grow.
Shark - is a miniature copy of the parents. In the photo are tiger sharks.
The largest known extinct species of sharks, Megalodon, reached a maximum length of 20 meters (67 feet).
Of the living, the largest is the giant whale shark. She can reach a body length of 15 meters.
TOP of the smallest sharks:
- Dwarf prickly shark (Squaliolus laticaudus) - the usual length of the body is 15-20 cm, and the maximum - 24 cm.
- Dwarf Glowing Shark (Euprotomicrus bispinatus) - fish length 20-25 cm.
- Long-tailed shark (Heteroscymnoides marleyi) is a small fish, 12.5-30 cm long.
- Light-tailed shark (Euprotomicroides zantedexchia) - maximum length 20 cm.
- Cuban shark Cunha (Triakidae barbouri) - maximum 35-40 cm.
Glowing shark - record holder minimalism
Some of the famous shark species drown if they stop moving. They do not have a swim bladder, so they have to swim all the time - they spend a lot of energy in motion. Compare. The great white shark needs 11 tons of food every year! A human being eats half a ton of food a year.
The Great White Shark (Karharodon, Carcharodon carcharias), the Mako (black-tailed, mackerel, blue-gray) shark and the Salmon shark (Lamna ditropis) of the herring family have no muscles, they pump water through their mouths and gills. During the entire voyage, they keep their mouths open, this keeps them alive.
Sharks have a big liver. Liver sharks contain a lot of oil. This makes the liver a relatively floating organ - it helps sharks keep their balance in the water.
Poking a shark in the nose or eyes to fend off their attack does not help. It is better to beat them in the gills (these are large cracks along the muzzle) - this tactic works much more effectively against sharks. Most sharks swim away when their target is difficult to reach for their food. More chances to die from drowning than from shark attacks. It's true.
Tiger sharks, great white sharks and bull sharks (stupid bull sharks) in most cases attack people from behind. Their prey is that which is of human size. They are strong enough to attack and inflict a deadly bite.
In extremely rare cases when a shark bites you, it is most likely that it will not take a second bite. In attacks on humans, sharks usually hold them for a few seconds, and then let go, as soon as they realize that they have tried not a sea creature.
20-30 percent of sharks are on the verge of extinction. The main culprit is industrial fishing: they accidentally catch sharks on hooks and nets. And due to the over-popularity of shark fins (commercial demand), the populations of some shark species have declined by about 90%.
The blue shark (Prionace glauca) is considered the rarest type of shark.
Another rare species is the Corrugated (fringed) shark, Chlamydoselachus anguineus. They are often called living fossil sharks. They live at a great oceanic depth of 1000-1500 meters.
Eggs of sharks are very different in appearance from those eggs that are laid by birds, lizards or crocodiles. They are often protected by capsules or leathery pouches. In the case of the horny shark, they are called "mermaid wallets."
Contrary to popular belief, sharks are not color blind, they distinguish colors well. Divers claim that sharks attract certain colors - the “yummy” for them is the yellow color, the color of some wetsuits. While the color preferences of sharks have not been proven, scientists know that sharks living in a well-lit room of an aquarium, distinguish colors - people use this as signals.
Angel sharks, also known as sand devils (Squatina), burrow into the piles of sand. From there, they lie in wait, expecting unsuspecting fish.
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