Shark

2023 Author: Molly Page | [email protected]. Last modified: 2023-08-25 12:41

Shark is a collective name. There are white, blue, tiger, feline, soup, herring, fox shark, nurse shark, hammerhead shark. Scientists count 350 species of these fish. And only 27 of them are accused of assaults on a person. And in a few, this is observed only once.

There are very small sharks no larger than a pencil and weighing about 200 grams, and there are huge ones - up to 20 meters in length. The weight of such giants reaches 20 tons.

The largest sharks - there are two types of them - the whale and the giant, never attack humans. They feed on plankton and small fish, filtering water through thousands of tiny teeth. White shark is considered aggressive and dangerous. It reaches 5-6 meters in length, occasionally up to 12. But the white shark is a rare fish.

Do sharks often attack humans? No, rarely. However, over the past 50 years, such cases have increased. This is due to the appearance in the sea of a large number of scuba divers who, not knowing the habits of sharks and not knowing how to handle them, by their behavior provoke their attack. In fact, sharks are scary cowards. They are afraid of people and try to stay away from them. This is the opinion of an expert in the biology and behavior of these fish, an American scientist, Professor Eugenia Clark, who has devoted her entire life to the study of sharks. Many times she put on scuba gear, went down to the sea and swam among the sharks. I watched them day and night also in the oceanarium.

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In order for a shark to attack a person, a whole range of conditions is necessary: first, it must be hungry - a well-fed one will never attack anyone; secondly, the temperature of the surrounding water should be at least 20 ° C, since at a temperature of 18-19 ° C sharks stop feeding. Such water is cold for them. In winter, sharks do not feed at all, except for those that live in the equatorial zone, where the temperature is constant throughout the year.

Sharks have a lifespan of about 30 years. This was established by tagging. In the same way, it has been proved that each shark has its own home, a permanent place where it lives and hunts. Small sharks were fixed on a special mark on the dorsal fin, the number, place and date of marking were recorded and released back into the sea. It happened that this fish again got into the nets after 3, 5, 10, 20 and even 30 years, in the same place where it was first caught and marked with a tag. Each time the shark was released back into the water. So it was proved that sharks are couch potatoes and do not make large migrations.

In several countries there is a permanent shark fishery. Delicious white shark meat is used as human food. It is considered a valuable and useful product. Soup shark fins are especially prized. Shark liver is widely used. It is rich in fat, which is high in vitamins. The leather is used for the manufacture of handbags, wallets, wallets and other leather goods. Felt cannot be made without shark skin, since soft fleece is made with special brushes made only from its skin. The caught shark is almost completely used. Even teeth are used to make souvenirs.

In a number of countries, over-fishing for sharks has led to the depletion of their stocks, and in some places a complete or partial ban on their fishing has already been introduced.

Can a shark drown? To this seemingly strange question, scientists answer in the affirmative. Can. The shark is always in motion with its mouth slightly open, continuously capturing fresh water, releasing it through the gill openings. The fact is that the jaw muscles found in teleost fish are poorly developed in the shark and do not contribute to the pumping and squeezing of water from the gill cavity. Therefore, it cannot pass through the gills the necessary volume of water for normal breathing - delivery of the required amount of oxygen dissolved in seawater. This circumstance makes the shark move continuously - day and night, due to which an intensive circulation of water is created, which washes the gills, ensuring breathing. A shark can rest for no more than an hour. Otherwise, she will die of suffocation.

True, in the World Ocean, Professor Eugenia Clarke discovered the only place where "resting" sharks were found. In the Caribbean Sea, at a depth accessible to a scuba diver off the coast of Mexico, extensive grottoes with several exits were discovered. There are springs of fresh water at the bottom. Sharks enter these grottoes and spend several days there. The current in the grotto is weakened. Sharks lay down on the bottom and go into a daze. All physiological functions of the body slow down dramatically. Only a few species of sharks enter these grottoes: bull shark, nurse shark, sand shark, Caribbean shark, once a blue has been registered.

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Some scientists explain the entry of sharks into the grotto by the fact that they come here to be treated for their wounds, diseases, or to get rid of external parasites that cannot live in desalinated water. Other scientists do not consider this assumption worthy of attention. The riddle does not yet have a generally accepted answer. It has yet to be solved.

In addition to all that has been said, it must be borne in mind that sharks do not have a swim bladder and, despite a large liver saturated with fat, sharks are deprived of the so-called neutral buoyancy. As soon as they stop moving, they slowly go to the bottom.

Sharks are fish whose secrets of life are still far from fully unraveled

Source: S. Klumov, candidate of biological sciences