SharkoFiles: Greenland Shark

The Greenland sharks are known for their long life span. In fact, there is no known vertebrate that has a longer life span. The carbon dating of the nuclei in the Greenland shark eye lens indicates that the oldest Greenland shark may be over 500 years of age. Generally, Greenland sharks are slow swimmer with swimming rate of about 1.9 miles per hour. In terms of length, the Greenland shark is a shark that rivals the great white shark which is capable of reaching 23 feet. However, most are between the range of 6.5 feet and 13 feet.

The Greenland sharks are known to be harmless to human despite their sizes probably because humans rarely visit the habitat of the sharks which prefer cold region of water. They are generally found in the cold water environment of the Arctic and North Atlantic Oceans. Despite being one of the largest predatory sharks on earth, yet the Greenland shark life history is equally one of the most elusive. The Greenland shark is quite talented at swimming unseen, in fact, it was not until 1995 that this species of shark was captured on film as it has been elusive to detection for many years. It took an additional 18 years before it is possible for anyone to capture a video depicting Greenland Sharks in their natural habitat.

According to the IUCN conservation status, the Greenland sharks are considered to be a near threatened species probably because of their liver oil which is commercially valued.

Taxonomy

The Greenland Shark specie name is Somniosus microcephalus. It belongs to the family of the sleeper shark Somniosidae of the order Squaliformes.

Morphology

The Greenland shark is one of the biggest species of sharks that prowl the ocean. It has a not so large, narrow, pointed, smooth edged teeth along its upper jaw, while on its lower jaw, the teeth are larger and broader with powerfully oblique cusps. The shark has a varying coloration with adult adorning a brown, black, purplish gray or slate coloration. The Greenland shark has a small eye having a spiracle above and behind the eye. Most of these sharks are blind as a result of association with worm like parasites known as copepods that hang from their eyes. It has small dorsal fins of identical sizes and the caudal fin is asymmetrical. The Greenland shark lacks anal fin. The shark is known to grow as long as about 23 feet.

Adaptation

The Greenland sharks have an impeccable sense of smell, hence it is not difficult for them to find food. They mostly hunt beneath the ice of the cold, freezing water of the arctic. Since they are blind, the dark environment makes no significant difference in their chances of catching preys. The Greenland shark has a toxic skin that is poisonous if consumed directly. This factor serves as a form of defense mechanism to ward off predators. It is also assumed that the copepod dangling from the cornea of the shark helps in luring prey close to the vicinity that can be easily caught and consumed by the Greenland shark.

Feeding

The Greenland sharks are known to be ocean scavenger similar to the vultures because they can eat almost anything from living animals to dead carcass. Even though the Greenland shark is big enough to hurt or even kill a human, however, record shows that they are particularly non-confrontational. The Greenland sharks feed on fishes such as capelin, char, halibut, lumpfish and salmon. In addition to fishes, the sharks likewise feed on marine mammals, including sea lions, cetaceans and seals. At times they also feed on the dead carcass of dead mammals such as reindeer that got drowned in the icy water.

Habitat

The Greenland sharks inhabit the arctic and subarctic waters having temperature as low as 2 to 7^oC. They are the only shark species that tends to tolerate Arctic conditions throughout the year. The shark prefers to dwell very deep in the ocean. During the summer period, Greenland shark can dwell up to about 600 to 2400 feet below the water level. They are however known to swim close to the surface and near the edge of ice flows during winter. The geographical location where these sharks can be found include the North Atlantic Ocean from Baffin Island to the Gulf of St. Lawrence. They are likewise found as far south as the Gulf of Maine and occasionally Gulf of Mexico.

Reproduction

Greenland sharks have viviparous mode of reproduction. The mother shark can give birth to about 10 pups in a litter. In general, the reproductive process of the Greenland shark is not well known due to the difficulty in observing the species in its environment.

Life span

The Greenland shark is reputed to be the longest living vertebrate on earth. It has been discovered by scientists that the shark may possibly live up to 400 or more in age. This longevity is assumed to be due to their slow metabolism since they reside in cold condition. The analysis of Greenland shark tissue suggested that the lifespan of the shark is between the range of 252 and 512 years with the possible average being 390 years.

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