Shark



Shark

are large marine fish that have a cartilaginous skeleton. On the sides of the head they have a number of gill slits, their main weapon is sharp teeth. The body of the sharks is elongated, and the tail is unequal. There are about 370 species of sharks. The smallest, carnivorous dwarf shark, has a length of only 15 centimeters, and a whale shark, feeding on plankton, reaches a length of 13 meters. They are widespread – they live in the coastal waters and in the open sea, and there are species that live even in rivers. Most species are viviparous, but some lay eggs. The vast majority of sharks are predators, the main food for them are fish, mollusks, echinoderms, benthic invertebrates and worms.

Sharks are famous for their shocking attacks on humans, although people are not their food. Despite the fact that the skeleton of these fish is cartilaginous, some species accumulate in it so much calcium that it becomes rigid, like a bone. However, there are no real bones for sharks. The structure of the skeleton is common for all fish. Most sharks swim continuously. This is due to the fact that, firstly, they do not have a swimming bladder that helps to remain immobile in water, and, secondly, most species do not have a mechanism for pumping water through the gills. That is, to get oxygen from the water, the fish must move. Sharks are famous for their acute sensory systems, feeling infinitely weak electric currents, low frequency sounds. It is known that the smell of a shark allows her to feel a drop of blood dissolved in a million drops of water. However, the sight of these fish is much inferior to the sense of smell, which successfully compensates for this shortcoming.


Sharks are the most mysterious creatures in the ocean. Their age is tens of millions of years, only in the last ten million years the species has undergone insignificant changes. People know little about these unique creatures, building their knowledge about sharks on the basis of films like “Jaws” in which terrible predators attack a person. Thanks to the joint efforts of marine biologists and enthusiast divers, it was possible to debunk some of the most common misconceptions about sharks.

Most sharks eat people.

Most people derive their knowledge of the underwater world only from the TV screen. The main hunter for man appears this bloodthirsty fish, which has become a real symbol of horror and fear. A great number of books and films are dedicated to the clash between a man and sharks. It seems that these gluttonous and ruthless creatures will destroy anyone who goes into the water and finds themselves in the zone of their perception. But is it really so? Diving is gaining popularity, more and more people are facing sharks, are next to them, observe and describe their behavior, and do not get any harm! It turns out that these predators are not so terrible, as the authors of films and novels try to present. Their goal is clear – to cause the viewer to have a maximum range of emotions, not caring about plausibility. Each attack of sharks on a man swells to an incredible size, people think that this happens often. In history, there have actually been instances of a massive attack of sharks on humans, especially during world wars. This is due to the ingress of a large number of bloodied people into the water. Several centuries ago, when transporting slaves from Africa to America, the sick and the dead were simply thrown overboard, to be eaten by sharks who flocked to the ship in anticipation of easy prey. But if such a ship was wrecked, then no one remained alive. The next wave of tragedies was repeated during the Second World War, when a large number of ships sank, dropped down aircraft, which could not help attracting sharks to floundering and panicking victims. These tragedies engendered a massive food fever in predators, creating the image of a monster devouring everything that moves. However, it is known that of all the diversity of species, only about 11 of them attacked humans.The greater part is simply not enough to constitute a threat. To large white sharks people are absolutely unattractive, an attack is just a mistake, since predators confuse a person with sea lions or seals. In addition, such a shark lives at depth, which significantly reduces the likelihood of a meeting. Attacking a person, a shark pulls out a piece of meat, trying it. Usually, having understood their mistake, the predator does not continue the attack. For a person, the risk of dying from loss of blood is great. Annually, according to statistics, only about 100 cases of attacks on people are recorded. For comparison, elephants are killed twice a year, and thousands of people die from dog bites every year. Even as a result of an allergic reaction to the use of peanuts, approximately 90 people die each year. In recent years, the number of attacks of sharks has been steadily declining, in part this is explained by the decrease in the number of sharks.

Sharks are stupid animals with a small, primitive brain.

It turns out that in sharks the ratio of brain size to body size is comparable to birds and mammals. Scientists conducted studies that demonstrated that the yellow shark conditioned reflexes are produced more quickly, and last longer than in a cat or a rabbit. This, of course, does not mean animal-like intelligence, but still … The last decades of sharks have been intensively studied, the results astonished the scientists themselves. In aquarium conditions, three-meter lemon sharks, as well as their small counterparts (tiger and Greenland sharks), were easily trained to push the target, ring the bell to get food as a reward. Sharks quickly learned to distinguish between correct and false targets, and the rate of training was not inferior to laboratory rats.

The behavior of sharks is absolutely unpredictable.

Jacques-Yves Cousteau in his book “The World of Silence” came to the following two conclusions: 1) the closer we “get to know” with sharks, the less we know about them; 2) you can never predict what a shark will do. And if the first conclusion can not be disagreed, since the knowledge of any subject reveals more and more of its facets, then with the second statement it is necessary and possible to argue. Studies of recent decades have revealed many interesting things in the behavior of sharks, useful, in particular for people who face them in the sea. Suffice it to say that accidental inexperienced bathers become victims of sharks, but professional scientists, videographers and photographers who face predators daily remain unscathed. They simply know the behavior of sharks, foresee their actions, respectively, and reacting. Consider how sharks find prey and how they behave in doing so. Statistics of attacks on a person shows that from a group of people in the water, a predator chooses one and perseveres it until he gets it. The victim is determined on the basis of the testimony of the sense organs of the shark, which catches the slightest sound, electrical and mechanical impulses. Therefore, in order not to attract the attention of a shark, one should reduce its activity to a minimum. A well-fed predator does not rush to prey immediately, from afar, but begins to circle beside her, studying the senses located on the sides. With a positive reaction to the victim’s signals, the shark begins to narrow the circles – its appetite increases, it decided to try the victim. Bending of the back indicates an extreme degree of excitation of fish. By the way, the posture with arched back is characteristic for many predators. The shark’s throw is lightning fast, the jaws are pushed, and the terrible mouth is wide open. When the blood gets into the water, the sharks get furious, start chaotically moving, tearing apart and devouring everything that has been around, including their own kind. This phenomenon was called “food fever”. In this condition, sharks become easy prey for fishermen, as they themselves grab the shiny hooks even without bait. In this case, the behavior of sharks is really unpredictable. There have been cases when sharks managed to scare off with a sharp exhalation of bubbles, flash, cries and even punches in the face.Experts advise in desperate cases to try all methods, even the most ridiculous ones. Most of the attacks on humans were committed to single bathers and surfers, because of their sudden movements on the surface, which attracted sharks. Submariners are practically not attacked, because their movements are smooth, the person has much more control over the movement of predators, avoiding meeting. Swimming people in the group also significantly reduces the risk of an accident. Thus, studying the psychology of these predators can help to avoid accidents.

Shark, before attack, must turn upside down belly.

Sharks have movable jaws that extend like hinges, so that in order to grab prey no special maneuvers are required. Most sharks do not chew prey, but swallow whole. An excited shark pulls out a piece of meat and sails to either continue eating or, in case of a negative reaction, swim away. A turn on the back is sometimes peculiar to small species, which in this way try to bite in half a large prey.

Sharks eat constantly.

Alfred Breh wrote: “In general, gluttony should be considered one of the main properties of all fish, but among them sharks are undoubtedly the most voracious”. So they thought before, they think even now. And they are mistaken. In fact, sharks eat periodically. The frequency of her nutrition depends on the metabolism, the availability of food, spent on the capture of forces. The food of sharks is calculated on the example of individuals staying in aquariums. The characteristic is the ratio of the weight of the feed per year to the weight of the animal. It is estimated that the shark eats for a year a mass that is only 8 times its body, whereas, for example, for a mouse-shrew, this factor is 600, and for an ordinary insectivorous bird – 300. In comparison, sharks generally sit on the strictest ” diet “. Ichthyologists for 10 years studied a three-meter sand shark, which annually consumed 70 to 100 kilograms of fish, which was 0.6 of its weight. That is, a large three-meter shark weighing more than half a ton eats up to 250 grams a day. And it is enough of this!

Sharks eat everything.

Some sharks are really omnivorous, eating everything they get. Hence the sailors’ tales that bottles, coconuts, caskets and even dynamite were found in the stomachs of sharks. However, their main food is not at all a different thing, not even people, but plankton, squid, small and medium fish. Professional shark hunters have uncovered the stomachs of more than three hundred of these fish to check the contents. Alas – nothing interesting, no human remains, no jewelry.

All sharks swim very fast.

Quite the opposite, most of them, living on the bottom, swim very slowly, no faster than 5 miles per hour. They can not swim at all, because they need oxygen, they can stay afloat without stopping moving. However, there are very fast species. So, the lemon shark can develop speed up to 30 kilometers per hour. A shark-mako swims with a maximum speed of 35.2 kilometers per hour, jumping even out of the water. The blue shark is even faster – 36.4 kilometers per hour, or 10.1 meters per second. With the same speed, the runner-recorder overcomes the hundred-meter mark. Faster than sharks are floating only flying fish before take-off, swordfish and tuna. However, in general, for these predators, such speeds are more likely an exception than regularity.

Sharks do not see in the dark.

Depending on the habitat and extraction, sharks have different eyesight. It is known that some of them distinguish colors, and some species perceive light at 10 times less intensity than a person can see. For example, a blue shark, although it sees everything in black and white, but navigates perfectly in the dark, recognizes contrasts, for example, a light object against a dark background of water or vice versa. About sharks it is known that they are rather short-sighted, at great distances they rely little on the organs of sight.However, approaching the goal, the role of the eyes increases dramatically. The composition of the eyes of sharks is such that they have few cones responsible for visual acuity and color, but many sticks that determine night vision, making the eye highly sensitive. Therefore, even dim lighting does not prevent the predator from determining the object and its movements, especially if the background is contrast. Vision of the shark adapts to the darkness, studies have shown that sensitivity to light of the eye after an eight-hour stay in the darkness increases almost a million times.

Shark is easy to kill.

It is said that when you get on the net or on a hook, the shark quickly loses its strength and does not resist. However, Dr. Nicols and Marfi talk about how they tried to destroy the shark before their eyes: “She was hooked, put a lead in her rifle in her head, threw a harpoon into her head, then dragged her out of the water onto the deck and released her guts, but for a long time after that she seemed full of life – she beat her tail, opened and closed her eyes … “. Belief in this myth can turn into an irreparable mistake. Even a gutted shark can easily attack an incautious fisherman. A case is known when a captured predator was gutted by fishermen and thrown into the sea. Then the fishermen again threw the hook, using as a bait the insides of the shark. Imagine their surprise when the fishermen caught the same shark on the bait! It’s hard to believe, but the fact is that the Mako shark tried to bite the injured person, jumping after him to the shore. And such stories, indicating the insensitivity of sharks, a great many.

Shark is a useless fish.

Sharks are the top of the food chain and play an important role in regulating the dynamics of populations of marine organisms. The existence of these fish is very important for the health of the entire oceanic system. The shark is used by man as a commercial fish. Employees of the University of Miami calculated that every year in the world is caught from 26 million to 73 million sharks. However, given the fact that the fishermen “mask” the shark under other commercial fishes, these figures are clearly not final, but they are already significantly higher than those estimated by the UN Food Program. It came to the point that the sharks themselves were on the verge of destruction. Now 20% of the species of sharks are listed in the International Red Book. Meat of some species is an excellent culinary dish, and shark cartilages are used to prepare preparations for the successful fight against cancer. From year to year, more than three million tons of shark fins are sold to Hong Kong merchants. Of these, a famous soup is prepared, which, they say, relieves impotence and, moreover, reflects the financial situation of those who can afford to order a dish worth fifty dollars.

There are sharks in Turkey.

Turkey remains a favorite resort, due to its availability and cheapness. Everyone knows that there are safe shark-katrans in the Black Sea, so the news was sounded like a bolt from the blue, and that predatory sand sharks, dangerous to humans, appeared in the Turkish waters of Bodrum and Marmaris. However, the Turkish authorities officially denied these rumors, there were no beaches because of the dangers. Officials believe that the error went from the wrong translation, local media reported that the place Bondjuk, closed, by the way, for tourists, is the breeding ground for sharks. Greedy sensational journalists spread a sensation. Perhaps, the creation of the myth was also supported by unfair competitors, who are trying to redirect the flow of tourists. Naturally, such a rumor can scare people away from Turkish resorts. By the way, sand sharks are considered one of the most dangerous in the water area of ‚Äč‚ÄčAfrica, some individuals are able to bite a person in half.

Sharks live only in the sea.

Among all the variety of species of sharks, there are those that debunk this myth. 26 species of sharks from coastal areas are able to enter estuaries and mouths of rivers with brackish or fresh water.They are representatives of gray, prickly and kuni sharks, stingray rays and sawtooth rays. In a separate ecological group, the tail-mantle is isolated – a large (up to 2 m) stingray, which lives permanently in the brackish water of the “borderland”, and does not leave the sea at all. There is a group of euryhalines that are able to live in the sea, and settle and even multiply in rivers and fresh lakes. There are 14 such sharks. These are representatives of all the same families of gray sharks, sawfish and stingray. For example, the Atlantic sawfish and the tufted shark occur in the Amazon up to its upper reaches, as well as in the Ganges and Zambezi rivers, several thousand kilometers from the mouth. The evolution of the shark in the lake of Nicaragua led to the formation of a form that never leaves the sea at all. Finally, there are forms that live in fresh waters constantly. There are 29 species. These include, for example, river tailings that live in the rivers of South and Central America, some representatives of “ordinary” tailings and the Indian river shark. The latter always dwells in the Ganges, reaching its upper course. Basically, rays and sharks that live in fresh water are found in tropical and warm rivers and lakes. The greatest diversity exists in the tropics. But occasionally they go to some rivers of North America and Southern Europe, the Mediterranean basin. Freshwater cartilaginous fish are found in large water bodies, they are not found in small ponds and rivers. It is curious that all freshwater sharks are fairly large, reaching puberty at a length of about 2 m. The dimensions of the stingrays that live in fresh waters range from 20-30 cm to 2 m. As they have the greatest diversity of species living in freshwater water sharks. In general for fresh-water cartilaginous are the same biological features, as for their marine relatives. Even the structure of the gills has not changed and does not contribute to the better use of oxygen in warm water.

The shark in the sea is not afraid of anyone.

Little is known about the fact that sharks themselves serve as food for another strong sea hunter – a sperm whale, which feeds no fewer than twenty species of sharks. At the same time, its prey becomes both small and giant, weighing up to half a shark. Actively hunting for whales, a man cut the population of sperm whales in the World Ocean. This allowed sharks to feel safe, especially since they are homebodies, and sperm whales were characterized by long migrations. For some species of sharks, terrible enemies are their own brothers, stronger and larger. White, cat, tiger and blue sharks eat white. A large enemy, up to 4 meters long, swordfish can become a natural enemy. On small sharks large stone perch, different stingrays, halibut, large-eyed tuna are hunted. However, undoubtedly, the greatest enemy of a shark is a man. They get into the networks, put on the tuna, they catch them for self-assertion, after all, they are carrying out the most real fishing. All this led to a sharp reduction in the population of sharks, to the fact that people have already begun to think about protecting these unique creatures. Even harmless giants (white, tiger shark, hammer-fish) are mercilessly destroyed by people. Today near the shores of California, the gourmet sharks and makos, loved by gourmets, are practically destroyed. Destroyed lemon sharks, going to the bait for crabs. Shark hammers, valuable by their fins, are almost completely destroyed off the coast of Costa Rica. The jaws of white sharks are redeemed by collectors for $ 5,000, fishing so attracted anglers that catching these fish within 200 miles of the coast of South Africa was declared a crime.



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