Biting marine animals: sharks
Swimmers and divers are afraid of sharks, probably more than all other marine animals. Despite the huge number of novels, legends, and terrifying stories written in this topic, the evidence about the relationship between sharks and humans, little. Opinions about the aggressiveness of sharks are very different from “most dangerous sharks” to “none harm” to the person. Scientific data and records of military and civilian doctors make us think that the truth should be somewhere between these equally untenable extremes.
In areas where shark swimmer is faced with four problems: 1) what types of sharks most likely to attack, 2) how can they know, 3) what are their habits, and 4) what can be done to repel an attack, if it happens.
General information . There are about 350 species of sharks, but it is believed that the person attack 20. The size of sharks range from small cat sharks ( Scyliorhinidae ) and Requiem sharks ( Triakidae ), with a length of only 45 cm. becoming sexually Mature, to the giant whale shark, which can reach a length of over 15 m. Consolation that this huge monster only feeds on small marine organisms.
All sharks are carnivorous, but most species are too small, insufficiently armed or living at too great depths to be dangerous to humans.Natural food is big and well armed sharks, large fish, other sharks, seals and other marine animals. In General it should be assumed that any shark is potentially dangerous to humans, if it has a length of over 120 cm and well armed, especially when in the water is the blood and food.
A favorite subject of controversy among fishermen – how many rows of teeth do sharks used at the same time. Different species of sharks in different parts of the jaws of such series is four or five. In addition, each jaw has a few spare developing series, where the teeth are backward vertices. They are covered by a fold of mucous membrane and outside are not visible. If functioning teeth are lost, their replacement teeth from the next younger series. This process of tooth replacement continues throughout the life of the shark. Some species of sharks teeth can be replaced separately, and the other is a whole series! The row of teeth, forming like a continuous blade, it is usually replaced in its entirety. The replacement process takes a few days to a week or longer.
Physiologists have long been interested in how sharks find food in the water and injured animals. Although the mind of a shark, probably low order, and it is known that they do not have keen eyesight, their ability to find food is amazing. It is believed that they detect food using highly developed olfactory organs and lateral line system, which is extremely sensitive to vibrations of low frequency. Undoubtedly, the auditory nerves also help to detect sources of unusual underwater sounds. Sharks have an almost supernatural ability to detect at a great distance, helpless or wounded animal. Some researchers believe that to help them find food, and even special organs of taste.
The sharks ‘ behavior when foraging is different . When sharks hunt alone, their movement is rather slow. The shark immediately decided to attack the prey, but when attacking, can act suddenly and quickly. However, when the ship is sinking, falls into the sea the plane or an explosion occurs, ie when the water suddenly appears a lot of food and blood, the sharks will lash out and pounce on prey. So are some sharks Xarcharhinidae . In such cases, they pop up vertically from a depth directly to the surface, popping up out of the water and furiously grab all that you see. Then they are most dangerous; to scare them is almost impossible. Once, when a large flock of sharks devoured killed by the underwater explosion of groupers, among them cannibalism was observed. Until a big shark ate a redfish stuck between the corals, there was a second and in one fell swoop snatched the belly of the first shark. After a few seconds this helpless shark ate her relatives came to the rescue. Sharks often choose someone from the crowd of swimmers and only attack that person, ignoring all others, including those who are trying to save him. This phenomenon was observed more than once. On the other hand, the divers, often dealing with the sharks and claim that “their actions cannot be predicted”.
The danger of shark attacks is greatest in tropical and subtropical seas, between 30° North and 30° South latitude. It is believed that in the waters of the temperate zone sharks don’t attack, but that’s not entirely true, as clearly evidenced by reported cases of shark attacks in California and the East coast of the United States. Obviously, some species of man-eating sharks occasionally enter colder water in search of food, and then there are attacks. Particularly dangerous areas are Queensland, in Australia and South Africa. Despite the lack of published scientific data, it is also known that many of the attacks were on the Pacific side of Panama.
Most of the attacks occurred at water temperatures over 20° C, although there have been deaths at 15° C and lower. Most often the attacks happen in January, and the most dangerous time of day – from 15 to 16 hours. However, sharks feed throughout the day and especially at night.