The Greenland polar shark is the largest representative of the cathodiformes, belonging to the genus Somniosidae. Refers to cartilaginous fish, which are not yet widely studied.
Habitat
This is the most cold-loving shark of all members of the family, preferring a water temperature in the range from 1 to 12 ° C. The range of Selahia covers the North Atlantic Ocean, the Arctic Ocean and includes the Scandinavian countries, the USA, Canada, Russia, Iceland and Germany. The Greenland polar shark (somniosus microcephalus) lives in a wide vertical range - from the continental and island shelf to 2000 m or more. In summer, it most often occurs at a depth of 200-500 m, and in winter - closer to the surface. It makes daily and seasonal migrations, determined by the movement of plankton and small animals that make up its diet.
Appearance
The Greenland polar shark is in sixth place in size after white, reaching 8 meters in length and weighs up to two tons. But the average size of individuals is 4 m, and weight - 800 kg.
Her body has a streamlined torpedo shape. The head is small in size relative to the entire carcass. The mouth of the predator is on the bottom. The jaws are wide and slow. The lower one is dotted with blunt square teeth, and the upper one is rare sharp. The height of those and others does not exceed 7 mm. The caudal fin is heterocercal, the dorsal fin is rounded and small in size.
The body of Selahia is brown to almost black, sometimes with a greenish tint. Dark purple spots are located throughout the body. The eyes of a shark are small, green, without a protective membrane. They are able to glow in the dark, which is explained by the accumulation of bioluminescent copepods parasitizing in the area around the eyes of this giant.
Structural features
The Greenland polar shark has a large fatty liver, which exceeds 20% of the total body weight. This body performs the function of an additional float.
Shark tissues are highly saturated with ammonia and trimethylamine oxide. Such compounds prevent the freezing of blood, support the performance of proteins and the normal course of biological processes in the north. Both substances are toxins, so shark meat not only has a disgusting taste, but also can lead to poisoning - under the influence of gastric juice, trimethylamine oxide is converted into trimethylamine, which causes an alcoholic effect. The shark has no bladder, therefore waste products are excreted through the skin.
These animals are notable for their impressive size and slowness. Its speed of movement is surprisingly small - no more than one kilometer per hour. This is due to the fact that, living in cold waters, the majority of the energy the selachia is forced to spend on heating its own body. The Greenland polar shark is a long-liver among the representatives of the animal world. As established, its life expectancy is up to 500 years.
Nutrition
The large size, low speed of movement and the small mouth of Selahiy significantly affect what the Greenland polar shark eats. She is too slow, cautious and even to some extent cowardly, therefore, she most often watches for sleeping, sick or weak seals and, thus, preys on them. The main diet includes organic garbage, carrion and small animals such as cod, flounder, sea bass, octopus, crab, squid, and stingray. In the stomachs of these predators were found jellyfish, algae, the remains of reindeer and polar bears. The smell of rotting meat attracts Greenland sharks, so they can often be found near fishing boats.
Breeding
This period falls at the end of spring. Selahia refers to ovoviviparous animals - it carries an 8 cm devoid of cornea eggs inside itself. For one litter, up to ten cubs with a size of at least 90 cm are born in a Greenland shark. Females acquire reproductive ability when they reach the age of 150 years, their length at this point is 4.5 m, in males it is less than about 3 m.
Human interaction
The polar (or bowhead) shark belongs to overpredators. Nobody hunts her, the only enemy is man. These sharks are the target of fishing because of the liver, which people use to produce technical fat rich in vitamins. The Greenland Polar Shark has been given the status of “Close to Vulnerability”. This species is closely monitored by conservation organizations, as the shark population is decreasing every year, in part due to slow reproduction.
As mentioned above, raw selahia meat is very toxic, due to its high content of urea and TMAO. But the natives of the north learned to process it for eating and feeding domestic animals - soaking and repeated boiling allows you to neutralize toxins. Icelanders, descendants of the glorious Vikings, prepare from it a traditional dish of hakarl. Today, sharks are also engaged in fishing in some other countries. She is quite phlegmatic and completely non-aggressive. Surprisingly, such a giant, caught in the net, behaves very quietly. Some fishermen consider these marine inhabitants to be pests - for damage to gear and the extermination of fish.
Cases of attack by polar sharks on humans are extremely rare, because in the cold places where they live, the probability of meeting is very small. However, there is a known case when the cause of the fact that a group of divers had to climb the surface of the water was the Greenland polar shark.
Interesting Facts
Today, according to the results of numerous studies, it is known that the Greenland polar shark is the oldest vertebrate in the world. However, to establish this fact, scientists had to make a lot of effort. The fact is that most of the methods used to determine the age of the animal are not applicable to the polar shark. She does not form layers of calcium carbonate in the ears, which determine the age of most fish; Selahia vertebrae are soft, like paraffin, which does not allow to establish life expectancy by the growth of vertebral rings.
The age of the polar sharks was determined by the proteins in the center of the lens of the eye. It grows throughout life, and its proteins are formed at the stage of embryonic development. Radiocarbon analysis made it possible to determine their lifetime by the content of the carbon-14 isotope, which burst after atomic bomb testing. One of the sharks studied by specialists was 392 years old. Taking into account the error of the radiocarbon research method, it was found that polar sharks can live up to 500 years. Such a longevity is explained by the fact that all life processes in cold water are slower than that of heat-loving representatives of this family.