Sharks, description and lifestyle
Currently, more than 450 types of sharks are known: from deep-water shallow Etmopterus Perryi, only 17 cm long, to the whale shark, the length of which reaches 12 meters.
Sharks are widespread in all seas and oceans, from the surface to a depth of more than 2000 meters. Basically live in seawater, but some species are capable of living also in fresh.
Most sharks refer to the so-called real predators, but separate species, in particular the whale, giant and bigger shark, – Filtrates, they feed on plankton, squid and small fish.
Skeleton, leather, teeth and jaws
Skeleton sharks noticeably different from the skeleton of bony fish – There are no bones in it, and it is fully formed from cartilage tissues.
Shark covered with placoid scales whose scales are rhombic plates ending with a spike protruding out of the skin. On the structure and strength of scales is close to the bones, which gives reason to call it with skin cloths. These teeth have a wide base, a surrendent shape and very reliefly defined crown. In most, the crowns are very sharp and firmly adjacent to each other, so the skin may seem relatively smooth, if you spend your hand from the head to the tail, and vice versa – coarse like sandpaper – if they lead in the opposite direction.
Most sharks teeth have the shape of sharp dentin cones and sit on the cartilage of the upper and lower jaws. The teeth are regularly replaced as the conveyor principal or exaggeration − Their replacement is constantly growing up from the inside. In terms of its structure and origin, these are modified placoid scales.
Depending on the diet and lifestyle, the teeth and jaws are very different from different types of sharks. Don sharks whose food is usually protected by a solid shell, have hundreds of small smooth teeth. Pelagic species are characterized by very sharp teeth fitted for easy penetration. In such a shark, like a tiger, teeth of the knife shape, intended to break the meat of a major victim. Food Rudimentary Small Teeth Sharkton.
Buoyancy
Unlike bony fish, the shark has no swimming bubble. Instead, a huge liver, cartilage skeleton and fins helps to compensate for the negative buoyancy.
Most sharks must be constantly moving in order to keep breathing, so can not sleep long. However, some species, such as the tasty shark-nyanka, are able to pump water through the gills, which allows them to relax at the bottom.
Digestive system
After the random shark meals are able to starve for a long time, slowly and economically spending accumulated resources, and in general their need for food is relatively small. For example, contained in captivity three-meter Australian sand shark weighing 150 kg per year eaten only 80-90 kg of fish.
Sharks periodically produce the eversion of the stomach – turn it through the mouth outside into the aquatic environment for the purpose of purification. It is curious that at the same time never damage the stomach with their numerous teeth.
Selication, vision and hearing
Smearing at sharks ? One of the main sensory systems. Experiments showed high sensitivity sharks to smells. The sense of smell is presented by nostrils ? Small bags on the face that transmits water to olfactory receptors. The smell is involved in the search for mining and partners for breeding.
White shark for smell is used 14% of the brain. Especially well developed smelling at the hammerhead sharks ? Speakers on a decent distance from each other on the head of a peculiar form of nostrils allow you to clearly determine the direction of the source of the smell. Studies have shown that sharks react to smells of wounded or alarmed mining.
Sharks are able to catch the smell of blood, divorced in proportion 1: 1 000 000, which can be compared with one teaspoon on the swimming pool of medium sizes.
The structure of the shark eye is mostly the same as all vertebrates, but with some features. Shark eye has a special reflective layer ? Tipetum ? Located behind the retina. Tapetum sends the last light back through the retina so that he once again influenced receptors, thus enhancing the sensitivity of the eye. This significantly increases visual acuity, especially in conditions of insufficient illumination.
Another feature in some species is the presence of a blinking age, which closes the eye directly during the attack on the sacrifice, protecting it from damage. Sharks who do not have a blinking century, when attacking the victim, roll eyes.
Earlier it was believed that the eye of the shark contains too few colums and is not able to distinguish colors and small details. However, modern technologies allowed to prove the opposite. The acuity of visual visibility of some kind of sharks of the human is up to 10 times.
Aclave hearing body ? This is an inner ear enclosed in a cartilage capsule. Sharks perceive predominantly low sounds 100–2500 Hz. Most sharks are able to distinguish between infrasound with a frequency below 20 Hz. The inner ear is also an equilibrium authority.
Electric and magnetically desigration
Electrodeceptor ACC device is represented by Lorentzini ampuls ? It is immersed in the skin small connective tissue capsules from them from them tubes that open on the skin surface.
Sharks react to electrical fields with tension of only 0.01 μV / cm. Therefore, they are able to detect victim over electric fields created by the operation of respiratory muscles and hearts.
Life expectancy and reproduction
Each view has a certain life expectancy, and it is not easy to appreciate it for all sharks. In general, sharks grow relatively slowly, and in general, we can say that most of the species lives 20-30 years.
However, spotted barbed shark, living more than 100 years different. Kita sharks are known at similar age.
At the shark characteristic of cartilaginous fish inner fertilization, primitive uterus and a fairly perfect placental connection. The fruit is developing in the uterus and appears to light well adapted to independent life. The newborn sharks are well developed by the musculoskeletal system, the digestive system and the senses, which allows themselves to eat and quickly increase the mass.
Sharks produce a different number of cubs ? Some types of up to 100, other two—three. White shark gives birth about 3?14 shark at once.
Unlike most bony fish producing millions of eggs, the principle of continuing a kind of sharks aims rather on quality than by number.
Caring for some types of offspring (aculenok is for some time under the guardianship of the mother) allows you to provide sharks a high survival rate, which means lower fertility.
Lifestyle and food
In the traditional view of the shark, it looks like a lonely hunter, furrowing ocean expanses in search of production. However, such a description is applicable only to several types. Very many sharks lead a somewhat inactive life.
Contrary to popular belief that shark is only «Machine for hunting», Learn only by instincts, recent studies have shown the ability of some species to solve problems, social behavior and curiosity. In 1987, in the area of South Africa, a group of seven white sharks by joint efforts he painted half-thrown to the shore of the Dead China in a deeper place for meals.
The ratio of mass brain and body at sharks is about equivalent to the same indicator in birds and mammals.
Mostly sharks move with cruising speed of about 8 km / h, but when hunting or attacking the average shark is accelerated to 19 km / h. Shark-Mako is able to accelerate to a speed of 50 km / h. White shark is also capable of such fuvers. Such exceptions are possible due to the warmth of these species.
Preferences in food at sharks are very diverse, and they depend on the characteristics of each species, as well as from habitats. The main food for sharks are fish, mammals, plankton and crustaceans.
For example, Lamina, Mako and blue sharks feed mainly by sea fish pelagic species, and the shape of their subtle sharp teeth is adapted to grant production in motion.
White shark prefers seals and sea lions, but if possible, hunting on whale mammals, since the features of her teeth allow you to grab big pieces of flesh.
In the diet of the bottom species, the sharks are mostly crabs and other crustaceans, and their teeth have a short length and are adapted to the flushing of the shell.
Giant, bigger and whale sharks feed on plankton and small marine organisms. Most species are carnivorous.
Some species, such as a tiger shark, are almost omnivores and swallow almost everything that comes across to them.
Contents in captivity
Currently, a relatively small number of species is contained in captivity. And there is no reason. One of the mains is that the most famous (consequently, the most interesting public) species are quite difficult to catch and transport, without causing harm to fish.
After all, mostly, this is large and aggressive fish, which during fishing on the bait are in a state of hunting for prey ? that is, in high excitation.
In addition, when extracting from water, some species may simply crush their internal organs by their own weight, and this must be taken into account during the movement of the shark from the ocean into an artificial tank.
The next difficulties arise and upon arrival of the shark into an aquarium, which should have the necessary capacity for the normal life of these fish, as well as take into account their increased sensitivity to electromagnetic waves.
Field and hunting
Along with other shark fish, many years have been the object of fishery (more than 100 species).
The fishing industry in sharks is interesting:
- The meat used by many cultures in food (despite the fact that the observations showed the predisposition of the body shark to the accumulation of mercury, the content of which in the meat was significantly increased due to environmental pollution).
- Feds that are in Asia by the main ingredient for a delicacious soup, as well as using applications in Eastern Medicine.
- Cartilage, around which are still disputing about his therapeutic properties against cancer tumors.
- Liver containing fat rich in vitamin A and group B vitamins, and used as raw materials for making medicines.
- Leather used in haberdashery and as abrasive material.
The main fishery is conducted in the Atlantic Ocean, where industrial are 26 species, about a third of the shark is mined in the Indian Ocean, and one and a half times less sharks are caught in a quiet. Approximately 100 million sharks around the world.
Sharp sharks can be divided into three directions:
