The Greenland shark, Somniosus microcephalus, also known as the sleeper shark, gurry shark, ground shark, grey shark, or by the Inuit name Eqalussuaq, is a large shark native to the waters of the North Atlantic Ocean around Greenland and Iceland. These sharks live farther north than any other shark species. Many of the species' adaptations are due to it being the only truly sub-Arctic species of shark. They are closely related to the Pacific sleeper shark.
This is one of the largest living species of shark, of dimensions comparable to those of the great white shark. Greenland sharks grow to 6.4 m (21 ft) and 1,000 kg (2,200 lb), and possibly up to 7.3 m (24 ft) and more than 1,400 kg (3,100 lb). However, most Greenland sharks observed have been around 2.44–4.8 m (8.0–16 ft) long and weigh up to 400 kg (880 lb). Males are typically smaller than females. It rivals the Pacific sleeper shark (possibly up to 7 m or 23 ft long) as the largest species in the family Somniosidae. The Greenland Shark is a thickset species with a short, rounded snout, small eyes, and very small dorsal and pectoral fins. The gill openings are very small for the species' great size. Coloration can range from pale creamy-gray to blackish-brown and the body is typically uniform in color, though whitish spots or faint dark streaks are occasionally seen on the back. Due to their cold environments, Greenland Sharks are thought to grow at a very slow rate. There are no reliable data on their life span, but fully grown Greenland sharks have been recaptured 16 years after being tagged.
When feeding on large carcasses, the shark employs a rolling motion of its jaw. The teeth of the upper jaw are very thin and pointed, lacking serrations. These upper jaw teeth, numbering from 48 to 52 teeth, act as anchor while the lower jaw does the cutting. The lower teeth are interlocking and are broad and square, 50 to 52 in count, containing short, smooth cusps that point outward. Teeth in the two halves of the lower jaw are strongly pitched in opposite directions.
The Greenland shark is an apex predator mostly eating fish. Recorded fish prey have included smaller sharks, skates, eels, herring, capelin, char, cod, redfish, sculpins, lumpfish, wolffish and flounders. However, it may also prey on marine mammals such as seals. Bite marks on dead seals at Sable Island, Nova Scotia and Hawarden suggest that this shark may be a major predator for them in the winter months. Since Greenland sharks are perhaps one of the slowest-swimming shark and attain a maximum swimming speed that is about half the maximum swimming speed of a typical seal, biologists have wondered how the sharks are able to predate the seals. Some evidence has been found that Greenland sharks search out seals and ambush them while they sleep. Greenland sharks have also been found with remains of polar bear, horses and reindeer (in one case an entire reindeer body was found in the shark's stomach) in their stomachs. The Greenland shark is also known to be a scavenger but to what extent carrion (almost certainly the origin of the reindeer) figures into the slow-moving fish's stomach contents is unknown. It is known, however, that the species is attracted by the smell of rotting meat in the water. They often congregate in large numbers around fishing operations. The shark is colonized by the parasitic copepod Ommatokoita elongata that eats the shark's corneal tissue. It has been reported that this parasite is bioluminescent and gives the shark a greenish glow around the eye when seen in dark waters but this has not been scientifically supported. The shark occupies what tends to be a very deep environment seeking its preferable cold water (-0.6 to 10 °C (31 to 50 °F)) habitat. It has been observed at a depth of 2,200 m (7,200 ft) by a submersible investigating the wreck of the SS Central America. A specimen video-taped at 2,773 m (9,098 ft) off the coast of Brazil on February 11, 2012 may have been a Greenland shark, but cannot be distinguished in the video from a southern sleeper shark or Pacific sleeper shark. However, a more typical depth for the species is above 1,200 m (3,900 ft). Frequently during the winter, when the sharks look for warmer waters to inhabit, they are often found at or near the surface of the water.
As recently as 1957 it was found that the females do not deposit eggs in the bottom ooze, but retain the developing embryos within their bodies so that they are born alive after an undetermined gestation period. 10 pups per litter is normal, each initially measuring some 90 cm (35 in) in length.
Greenland sharks as food
The flesh of a Greenland shark is poisonous. This is due to the presence of the toxin trimethylamine oxide, which, upon digestion, breaks down into trimethylamine, producing effects similar to extreme drunkenness. Occasionally, sled dogs that end up eating the flesh are unable to stand up due to the neurotoxins. Similar toxic effects occur with the related Pacific sleeper shark, but not in most other shark species, whose meat is often consumed fresh.
However, it can be eaten if it is boiled in several changes of water or dried or fermented for some months to produce Kæstur Hákarl, often Hákarl for short. Traditionally this was done by burying the shark in boreal ground, exposing it to several cycles of freezing and thawing. It is considered a delicacy in Iceland and Greenland.
The shark is not considered dangerous to humans, though there are Inuit legends of this species attacking kayaks. Although it is likely the very large shark could easily consume a human swimmer, the extremely cold waters it typically inhabits makes the likelihood of attacks on humans very low, and there are no verified cases of predation on people.
The Greenland shark's poisonous flesh has a high urea content, which gave rise to the Inuit legend of Skalugsuak, the first Greenland shark. The legend says that an old woman washed her hair in urine and dried it with a cloth. The cloth blew into the ocean to become Skalugsuak.
The Greenland shark occupies a minor role within Inuit cosmologies in the Canadian Eastern Arctic and Greenland. For the Igloolik Inuit, this fish lives within Sedna's urine pot (hence the urine-like smell of its flesh) and is conceived as a shaman’s helping spirit.
The Greenland Shark and Elasmobranch Education and Research Group (GEERG) has been studying the Greenland shark in the Saguenay Fjord and St. Lawrence Estuary since 2001. The Greenland shark has repeatedly been documented (captured or washed ashore) in the Saguenay since at least 1888. Accidental captures and strandings have also been recorded in the St. Lawrence Estuary for over a century.
Current research conducted by GEERG involves the study of the behaviour of the Greenland shark by observing it underwater using scuba and video equipment and by placing acoustic and satellite tags (telemetry) on live specimens; however, overall very little is known about this mysterious species.
There is now an argument suggesting that the Greenland shark is responsible for 'Seal Ripping' attacks on grey seals. These attacks cause a corkscrew pattern of cuts and tears which spiral around a seal's body, following the grain of the collagen within the muscles and running at 45 degrees to the seal's body. Seal deaths have been occurring over larger territories, including the north and east coasts of the UK, which suggests that the Greenland shark may be moving beyond its traditional habitat range. However, recent research into the UK "corkscrew" seal deaths by the Sea Mammal Research Unit  concluded that the UK seal deaths were unlikely to have been caused by predation from the Greenland shark, rather being caused by blunt mechanical trauma "consistent with the seals being drawn through a ducted propeller" that are found on many ships.
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