Information

Shark

Shark

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

Sharks have become famous for shocking attacks on humans, although humans are not their food. Despite the fact that the skeleton of these fish is cartilaginous, some species accumulate so much calcium in it that it becomes hard like bone. However, sharks do not have real bones. The skeletal structure is common for all fish. Most sharks swim continuously. This is due to the fact that, firstly, they do not have a swim bladder, which helps to remain motionless in the water, and, secondly, most species do not have a mechanism for pumping water through the gills. That is, in order for oxygen to flow with water, the fish needs to move. Sharks are famous for their sharp sensory systems, feeling infinitely weak electric currents, low frequency sounds. It is a known fact that a shark's sense of smell allows it to feel a drop of blood dissolved in a million drops of water. However, vision in these fish is significantly inferior to sense of smell, which successfully compensates for this deficiency.

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 minor changes. Man knows little about these unique creatures, building his knowledge about sharks on the basis of films like "Jaws" in which terrible predators attack humans. Through the combined efforts of marine biologists and enthusiastic divers, some of the most common misconceptions about sharks have been debunked.

Most sharks eat humans. Most people get their knowledge of the underwater world only from the TV screen. This bloodthirsty fish, which has become a real symbol of horror and fear, appears as the main hunter for a person. A great many books and films are devoted to the collision of a man with sharks. It seems that these voracious and merciless creatures will destroy anyone who enters the water and ends up in their zone of perception. But is it really so? Scuba diving is gaining popularity, more and more people encounter sharks, are near them, observe and describe their behavior, while not getting any harm! It turns out that these predators are not so scary as the authors of films and novels try to present. Their purpose is clear - to evoke the maximum range of emotions in the viewer, without worrying about believability. Each shark attack on a person swells to incredible proportions, people think that this happens often. In history, there have indeed been cases of massive shark attacks on humans, especially during the world wars. This is due to the ingress of a large number of bloodied people into the water. Several centuries ago, when slaves were transported from Africa to America, the sick and the dead were simply thrown overboard to be eaten by sharks, which followed the ship in flocks in anticipation of easy prey. But if such a ship was wrecked, then no one survived. The next wave of tragedies was repeated during the Second World War, when a large number of ships sank, downed planes fell, which could not but attract sharks to floundering and panicking victims. These tragedies gave rise to a massive food fever among predators, creating the image of a monster devouring everything that moves. However, it is known that of the whole variety of species, only about 11 of them attacked humans. Most are just not enough to pose a threat. Large white sharks are absolutely unpalatable to humans, an attack is just a mistake, since predators confuse humans with sea lions or seals. In addition, such a shark lives at a depth, which significantly reduces the likelihood of meeting. Attacking a person, the shark pulls out a piece of meat, tasting it. Usually, realizing its mistake, the predator does not continue the attack. For a person, there is a great risk of dying from blood loss. Annually, according to statistics, only about 100 cases of an attack on a person are recorded. For comparison, elephants kill twice as many per year, and thousands of people die every year from dog bites. Even as a result of an allergic reaction to eating peanuts, approximately 90 people die each year. In recent years, the number of shark attacks has been steadily declining, partly explained by the decrease in the number of sharks.

Sharks are stupid animals with small, primitive brains. It turns out that sharks have a brain-to-body ratio comparable to that of birds and mammals. Scientists have conducted studies that have shown that conditioned reflexes are developed faster in a yellow shark and persist longer than in a cat or rabbit. This, of course, does not mean that intelligence is similar to that of animals, but nevertheless ... In recent decades, sharks have been intensively studied, the results have amazed the scientists themselves. In the conditions of the aquarium, three-meter lemon sharks, as well as their small counterparts (tiger and greenland sharks), were easily trained to push a target, ring a bell to get food as a reward. Sharks quickly learned to distinguish between correct and false targets, and the speed of learning was not inferior to laboratory rats.

Shark behavior is completely unpredictable. Jacques-Yves Cousteau in his book "The World of Silence" came to the following two conclusions: 1) the closer we "get acquainted" with sharks, the less we know about them; 2) you can never predict what a shark will do. And if one cannot disagree with the first conclusion, since the knowledge of any subject reveals more and more new facets of it, then it is necessary and possible to argue with the second statement. Research in recent decades has revealed a lot of interesting things in shark behavior, useful, in particular, for people who encounter them at sea. Suffice it to note that casual inexperienced bathers become victims of sharks, but professional scientists, videographers and photographers who encounter predators remain unharmed every day. They just know the behavior of sharks, predict their actions, and react accordingly. Consider how sharks find their prey and how they behave. Statistics on attacks on humans show that out of a group of people in the water, a predator chooses one and stubbornly pursues it until it gets it. The victim is determined based on the readings of the shark's sense organs, which picks up the slightest sound, electrical and mechanical impulses. Therefore, in order not to attract the attention of the shark, you should keep your activity to a minimum. A well-fed predator does not rush to prey immediately, from afar, but begins to circle around it, studying with the senses located on the sides. With a positive reaction to the signals of the victim, the shark begins to narrow circles - her appetite increases, she decided to taste the victim. The arch of the back indicates the extreme degree of arousal of the fish. By the way, the back arching pose is typical for many predators. The shark throw is lightning fast, the jaws are extended, and the terrible mouth is wide open. When the blood gets into the water, sharks go into a rage, begin to move chaotically, tearing apart and devouring everything that is nearby, including their own kind. This phenomenon is called "food fever". In this state, sharks become easy prey for fishermen, as they themselves grab shiny hooks even without bait. In this case, the behavior of sharks is really unpredictable. There were cases when sharks were able to scare off with a sharp exhalation of bubbles, flash, shouts and even blows to the face. Experts advise, in hopeless cases, to try all methods, even the most ridiculous ones. Most human attacks were carried out on solo bathers and surfers, due to their sudden movements on the surface, which attracted sharks. Submariners, on the other hand, are practically not attacked, since their movements are smooth, a person has much more opportunities to control the movements of predators, avoiding meeting. Swimming in a group also significantly reduces the risk of an accident. Thus, studying the psychology of these predators can help avoid accidents.

The shark, before attacking, must flip upside down. Sharks have movable jaws that move out like on hinges, therefore, in order to grab prey, no special maneuvers are required. Most sharks do not chew on their prey, but swallow it whole. The agitated shark pulls out a piece of meat and swims away to either continue to feed or, in case of a negative reaction, swim away. Flip on the back is sometimes characteristic of small species, which in this way try to bite large prey in half.

Sharks are constantly eating. Alfred Brehm wrote: "In general, gluttony should be considered one of the main properties of all fish, but among them sharks are undoubtedly the most voracious." They thought so before, they think so now. And they are wrong. In fact, sharks feed periodically. The frequency of her nutrition depends on metabolism, the availability of food, spent on capturing the strength. Shark nutrition is calculated using 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 a shark eats a mass in a year, only 8 times its body, whereas, for example, for a mouse-shrew, this coefficient is 600, and for an ordinary insectivorous bird - 300. In comparison, sharks generally sit on the strictest " diet ". For 10 years, ichthyologists have studied a three-meter sand shark, which ate from 70 to 100 kilograms of fish a year, which was 0.6 of its weight. That is, a large three-meter shark weighing more than half a ton eats only 250 grams per day. And this is enough for her!

Sharks eat everything. Some sharks are really omnivorous, eating whatever they come across. Hence the sailors' tales that bottles, coconuts, boxes and even dynamite were found in the stomachs of sharks. However, their main food is not all sorts of stuff, not even people, but plankton, squid, small and medium fish. Professional shark hunters have cut open 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 the bottom dwellers swim very slowly, no faster than 5 miles per hour. They can not swim at all, since they need oxygen, they can only stay afloat by moving non-stop. However, there are also very fast species. So, the lemon shark can reach speeds of up to 30 kilometers per hour. And the mako shark swims at a maximum speed of 35.2 kilometers per hour, even jumping out of the water. The blue shark is even faster at 36.4 kilometers per hour, or 10.1 meters per second. With the same speed, the record-holder overcomes the hundred-meter distance. Faster than sharks swim only flying fish before takeoff, swordfish and tuna. However, in general, for these predators, such speeds are an exception rather than a regularity.

Sharks cannot see in the dark. Sharks have different vision depending on their habitat and prey. It is known that some of them distinguish colors, and some species perceive light 10 times less intense than a person can see. For example, a blue shark, although it sees everything in black and white, but it orientates itself perfectly in the dark, it perfectly recognizes contrasts, for example, a light object against a dark background of water or vice versa. It is known about sharks that they are quite short-sighted, at long distances they rely little on the organs of vision. However, when approaching the target, the role of the eyes increases dramatically. The composition of shark eyes is such that they have few cones, which are responsible for visual acuity and color, but there are many rods that determine night vision, making the eye highly sensitive. Therefore, even dim lighting does not prevent the predator from identifying the object and its movements, especially if the background is contrasting. Shark vision adjusts to darkness, studies have shown that the sensitivity to light of the eye increases almost a million times after being in the dark for eight hours.

Shark is easy to kill. They say that, getting caught in a net or hooked, a shark quickly loses strength and does not resist. However, Dr. Nichols and Murphy talk about how they tried to destroy the shark in front of their eyes: "They hooked her, put a charge of lead from a magazine rifle in her head, threw a harpoon at her, then pulled out of the water onto the deck and released her intestines, but for a long time after that she seemed full of life - she beat her tail, opened and closed her eyes ... ". Believing this myth can be a fatal mistake. Even a gutted shark can easily pounce on an unwary fisherman. There is a known case when a caught predator was gutted by fishermen and thrown into the sea. Then the fishermen threw the hook again, using the shark's entrails as bait. Imagine their surprise when the fishermen caught the same shark with bait! It is hard to believe, but the fact is known that the mako shark tried to bite the person who wounded it, jumping to the shore after him. And there are a great many such stories, testifying to the insensitivity of sharks.

Shark is a useless fish. Sharks are at 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 ocean system. The shark is used by humans as a commercial fish. Employees at the University of Miami estimate that between 26 million and 73 million sharks are caught every year in the world. However, given that the fishermen "disguise" the shark as other commercial fish, these figures are clearly not final, but they already significantly exceed the estimates of the UN Food Program. It got to the point that the sharks themselves were on the verge of destruction. Nowadays 20% of shark species are listed in the International Red Book. Certain types of meat are excellent culinary dishes, and shark cartilage is used to make preparations to successfully fight cancer. More than three million tons of shark fins are sold to Hong Kong traders every year. They make the famous soup, which is said to relieve impotence and, moreover, reflects the financial situation of those who can afford to order a dish worth fifty dollars.

Sharks are found in Turkey. Turkey remains a favorite resort due to its availability and cheapness. Everyone knows that there are safe katran sharks in the Black Sea, therefore, like a bolt from the blue, the news sounded that in the waters of the Turkish resort of Bodrum and Marmaris, predatory sand sharks, dangerous to humans, appeared. However, the Turkish authorities have officially denied these rumors, no beaches have been closed due to the dangers. Officials believe that the mistake came from an incorrect translation, local media reported that the town of Bonjuk, closed, by the way, to tourists, is a shark breeding site. The journalists, greedy for sensations, fanned the sensation. It is possible that unscrupulous competitors, seeking to redirect the flow of tourists, had a hand in creating the myth. 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 shark species, there are those that debunk this myth. 26 shark species from coastal areas are able to enter estuaries and estuaries with brackish or fresh water. These are representatives of gray, prickly and mustelids, stingrays and sawn rays. A separate ecological group is made up of the mantura stingray - a large (up to 2 m) stingray, which constantly lives in the brackish water of the "border area", and does not go out into the sea. There is a group of euryhaline, which are capable of both living in the sea and settling and even breeding in rivers and freshwater lakes. There are 14 species of such sharks. These are representatives of the same families of gray sharks, sawn rays and stingrays. For example, the Atlantic sawdore and blunt shark are found 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 Lake Nicaragua has resulted in a form that never goes out to sea at all. Finally, there are forms that live in fresh waters all the time. There are 29 types of them. These include, for example, the river stingrays that live in the rivers of South and Central America, some representatives of the "ordinary" stingrayers and the Indian river shark. The latter constantly dwells in the Ganges, reaching its upper course. Mostly stingrays and sharks living in fresh water are found in tropical and warm rivers and lakes. Their greatest diversity is observed in the tropics. But from time to time they enter some rivers of North America and Southern Europe, the Mediterranean basin. Freshwater cartilaginous fish are found in large bodies of water; they are not found in small ponds and rivers. It is curious that all freshwater sharks are quite large, reaching sexual maturity with a length of about 2 m.The sizes of stingrays living in fresh waters vary from 20-30 cm to 2 m. As they have the greatest diversity of species living in freshwater shark water. In general, freshwater cartilaginous species are characterized by the same biological features as for their marine relatives. Even the structure of the gills has not changed and does not contribute to a better use of oxygen in warm water.

The shark in the sea is not afraid of anyone. Little known is the fact that sharks themselves serve as food for another strong sea hunter - the sperm whale, which feeds on no less than twenty species of sharks. At the same time, both small and gigantic sharks weighing up to half a tone become its prey. By actively hunting whales, humans have greatly reduced the population of sperm whales in the oceans. This allowed sharks to feel safe, especially since they are couch potatoes, and long migrations were peculiar to sperm whales. For some species of sharks, terrible enemies are their own brethren, stronger and larger. White, feline, tiger and blue sharks eat their relatives. A large, up to 4 meters long swordfish can also become a natural enemy. Small sharks are hunted by large rock perches, various rays, halibuts, big-eyed tuna. However, undoubtedly, the shark's biggest enemy is man. They fall into the nets set on tuna, they are caught for self-affirmation, in the end, they are used for real fishing. All this has led to a sharp decline in the shark population, to the fact that people have already begun to think about protecting these unique creatures. Even harmless giants (white, tiger shark, hammer fish) are ruthlessly destroyed by people. Today, fox and mako sharks, beloved by gourmets, have been practically destroyed off the coast of California. Lemon sharks are exterminated, going to bait for crabs. Hammerhead sharks, valuable for their fins, have been almost completely destroyed off the coast of Costa Rica. The jaws of white sharks are redeemed by collectors for 5 thousand dollars, the fishery attracted anglers so much that fishing for these fish within 200 miles of the coast of South Africa was declared a crime.

Watch the video: I Pet my Own Shark. My Animated Story (December 2020).