SHARK . superorder of cartilaginous fish. Includes 8 units and approx. 350 species distributed in all oceans. The most diverse and numerous sharks in the tropics, but occur also in temperate and even in cold waters. Live in the water column and near the bottom, at great depths and in the coastal shallows. Ascend rivers for hundreds of kilometers (eg. the Amazon) that inhabit lake Nicaragua and some others. In Russian waters approx. 10 species, including katrenova shark (spiny dogfish), polar shark, mackerel sharks and hammerhead sharks .
The body of sharks is well adapted to fast and maneuverable swimming. It has an elongated, torpedo-like shape and ends in a large tail fin. DL. body from 15-20 cm (some kind of old-fashioned recourses and weasel sharks) to 20 m (with a weight of 12-14 tons) of whale shark . Since the density of the body of sharks is greater than the density of water, they must constantly move, not to go to the bottom. Best swimmers – Mako speeds up to 60 km/h; when the throw to the prey speed increases. Jaws are armed with a large number of sharp teeth, easily cut through any sacrifice.
Sexual maturity is reached quite late, eg. the porbeagle in 10-12 years, the old-fashioned recourses in 14-19. The lifespan in some species up to 30 years, but in most species it is unknown. The sharks dvoistvennosti, eiaiioeoa and a live birth . Fertility varies from 2 to several dozens of embryos. There are species that have formed but not yet born embryos devour their fellows. This so-called embryonic cainism – named after the biblical character Cain who killed his brother Abel.
Sharks are active predators, evolved among aquatic and terrestrial predators inordinate voracity. Their food consists of fish, including their relatives, benthic animals, marine mammals (dolphins, seals, sea otters). Indiscriminately sharks grab everything that comes, is stranded on the water for recreation birds, poisonous stingrays, sea turtles, garbage from ships and even mine (there was such case).
Often the victim of a shark becomes a man. There are many credible stories of the terrible loss of life from these bloodthirsty animals. Sharks grab not only trapped in the water people, but tails and teeth break up the boats, pull people from life rafts. The signal for shark attack may even serve a small concentration of the blood, whose presence in the water sharks due to the good feel of smell at a great distance. It is considered that dangerous for a man 40-50 species, among which the most terrifying white shark . or man-eater, Mako, hammerhead shark, tiger shark. Plankton is the biggest shark is the whale and the giant is absolutely not dangerous to humans. Although sharks have been studied for almost centuries, many features of their biology and lifestyles are poorly known.
Sharks have long served as a target species. The meat of most species are edible, from the liver vytaplivaete rich in vitamins fat. Shark fin soup – a popular dish in Chinese cuisine. Appreciated also the skin of sharks. Often destroy sharks because they harm fisheries by eating the breaking catches and fishing gear. Many species of sharks – the object of sport fishing.