Sharks, shark species
The shark is a collective name. There is a white shark, blue, tiger, cat, soup, mackerel, shark-Fox, nurse shark, hammerhead shark. Scientists consider 350 species of these fish. And only 27 of them are accused of attacks on humans. And a few that occur only once.
There are very small sharks the size of a pencil and weighing about 200 grams, and there are huge – up to 20 metres in length. The weight of these giants reaches 20 tons.
The biggest sharks – two species of whale and a giant, never attacking the person. They feed on plankton and small fish, straining out the water through thousands of tiny teeth. Aggressive and dangerous is the white shark. It reaches 5 – 6 metres long, rarely up to 12. But the white shark is a rare fish.
How often do sharks attack people. No, rarely. However, over the last 50 years such cases have become frequent. This is due to the emergence of a large number of sea divers, who, not knowing the habits of sharks and not knowing how to handle them, by their conduct provoke their attack. Actually sharks are scary little shits. People they fear and try to stay away from them. So says the expert on the biology and behavior of these fish American scientist, Professor Eugene Clark, who throughout his life devoted himself to the study of sharks. Many times she put on scuba gear, descended into the sea and swam with the sharks. Watched them day and night and also in the Oceanarium.
So as the shark attacked the man, requires a whole series of conditions: first, it must be hungry – well-fed will not attack anyone; secondly, the temperature of the water should not be below 20 degrees, because at a temperature of 18 – 19 degrees sharks stop eating. This water is cold for them. In winter, sharks do not eat at all, except those who live in the Equatorial zone, where the temperature is constant the year round.
The lifespan of sharks for about 30 years. This was determined by tagging. In the same way it is proved that each shark has his house, a permanent place where she lives and hunts. Little aculeatum strengthened on the dorsal fin marks, recording the number, location and date of tagging and were released back into the sea. It happened that this fish fell again in the network after 3, 5, 10, 20 and even 30 years, in the same place where she was first caught and marked. Every time the shark was released into the water again. So it has been proven that sharks are homebodies and do not make large migrations.
In some countries there is a constant fishing for sharks. Delicious white shark meat goes for human consumption. He is considered to be a valuable and useful product. Especially prized fins of soupfin sharks. Widely used the liver of sharks. It is rich in fat, high in vitamins. Leather is used to make handbags, purses, wallets and other leather haberdashery. Without the skin of sharks can not be made of felt, as soft fleece make special brushes made up only out of her skin. Caught shark is almost fully used. Even the teeth are used for making Souvenirs.
In some countries, over-hunting of sharks has led to their depletion, and in some places already introduced full or partial ban on fishing them.
Can a shark drown? This seemingly strange question scholars answer in the affirmative. Can. The shark is always in motion with mouth ajar, constantly capturing fresh water, releasing it through the Gill openings. The fact that jaw muscles are present in bony fishes, sharks are poorly developed and does not contribute to the pumping and squeezing of water from the Gill cavity. So she can’t pass through the gills of the necessary volume of water for normal respiration – delivery of the desired amount of dissolved seawater oxygen. This fact makes the shark continuously – day and night to move, thereby creating intense circulation of water which bathes the gills ensuring breath. Shark may entertain no more than an hour. Otherwise it will die from suffocation.
However, in the oceans, by Professor Eugenia Clark was revealed to the only place where found “resting” sharks. In the Caribbean, is available for diver depth off the coast of Mexico discovered extensive caves with multiple exits. At the bottom there are springs of fresh water. Here in these grottoes the shark come and spend a few days. Over in the grotto weakened. Sharks fall to the bottom and fall into a stupor. All physiological functions of the body are slowed down dramatically. In these caves comes only a few shark species: bull, amalananda, sand, Caribbean, was once registered blue.
Some scientists explain the approach of sharks in the grotto by the fact that they come here to heal from wounds, disease, or free of external parasites, which cannot live in fresh water. Other scientists do not believe the assumption is noteworthy. The mystery still has no accepted answer. Its yet to be solved.
Furthermore, we must bear in mind that sharks have no swim bladder and, despite the large liver is saturated with fat, sharks are deprived of the so-called neutral buoyancy. Once they stopped moving, slowly go down.