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Characteristics, distribution and ecology
Taxonomische classification
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Author: (Bloch and Schneider, 1801)

Field Marks:
Short, rounded snout, heavy cylindrical body and small precaudal fins, two spineless, equal-sized dorsal fins, no anal fin, long ventral caudal lobe, first dorsal fin on back slightly closer to pelvics than pectoral fins, interdorsal space greater than distance from snout to second gill slits, no keels on base of caudal fin, upper teeth lanceolate, lower teeth with short, low, strongly oblique cusps and high, narrow roots.

Diagnostic Features:
Head moderately long, length from snout to pectoral fins 23% total length in specimen 299 cm total length; snout short and broadly rounded. Cusps of lower teeth short and low, strongly oblique, roots very high; total tooth rows 45 to 52/48 to 53. Insertion of first dorsal fin slightly closer to pelvic bases than pectoral bases; interdorsal space greater than distance from snout tip to second gill slits. No lateral keels present on base of caudal fin. Caudal peduncle short, distance from second dorsal insertion to upper caudal origin less than twice second dorsal base, distance from pelvic insertions to lower caudal origin less than dorsal caudal margin. Vertebral column without well-defined calcified centra, notochord secondarily expanded. Size large, exceeding 4 m.

Geographical Distribution:
North Atlantic and Arctic: From Cape Cod and the Gulf of Maine and Gulf of St. Lawrence to Ellesmere Island, Greenland, Iceland, Spitzbergen, the Arctic USSR (White Sea), and Norway to the North Sea and occasionally south to the Seine River mouth, France and possibly Portugal. South Atlantic and Antarctic: South Africa (Cape Columbine), Kerguelen Island, and possibly Macquarie Island.

Habitat and Biology:
An abundant littoral and epibenthic shark of the continental and insular shelves and upper slopes down to at least 1200 m. The Greenland shark is one of the larger sharks and by far the largest of Atlantic-Arctic and Antarctic fishes. In the Arctic and boreal Atlantic it occurs inshore in the intertidal and at the surface in shallow bays and river mouths during the colder months but tends to retreat into water 180 to 550 m deep when the temperature rises. At lower latitudes in the North Atlantic (Gulf of Maine and North Sea) it inhabits the continental shelves, and may move into shallower water in the springer and summer. In the southern hemisphere it is found in deepwater (677 m) off South Africa and in 145 to 370 m depth off Kerguelen Island. Water temperatures of places inhabited by these sharks range from 0.6 to 12 C.

This is a proverbially sluggish shark that gives almost no resistance to capture individuals up to 4.9 m long have been lured to the surface with baits and hauled out of the water with gaffs. It is easily fished through holes in the Arctic ice. In the Arctic summer Greenland sharks usually are close to the bottom but swim up towards the surface for prey.

Development is ovoviviparous; as most females taken are not gravid but have large numbers of large, yolky eggs, it was thought until relatively recently that the Greenland shark might be oviparous. One female 5 m long had 10 young about 37 cm long in 1 uterus; and these were presumably full term because their yolk-sacs were resorbed.

Although seemingly slow-moving, this shark is apparently able to capture large and active prey. Fishes are important food items and include herring, spiny eels, salmon and char, smelt, a variety of gadoids including cod, ling, pollock, and haddock, several flatfish including Atlantic and Greenland halibut, wolf-fish, redfish (Sebastes), sculpins, lumpfish, and skates and their egg-cases. The Greenland shark regularly devours marine mammals, including seals (a common prey item, possibly taken alive) and small cetaceans (possibly mostly as carrion); old stories of it attacking living great whales are apparently unfounded. Greenland sharks voraciously devour carrion and offal of all sorts from whaling, sealing, and fishing operations, and will gather to feast in great numbers around whaling stations, whale kills, fish processing operations, and ice flows with skinned seal carcasses. These sharks will glut themselves on such abundance, and seem insensate to blows from clubs or cutting instruments while gorging. Parts of drowned horses and an entire reindeer were found in large Greenland sharks. Other prey includes sea birds, squids, crabs, amphipods, marine snails, brittle stars, sea urchins, and jellyfish.

The Greenland shark has an unusual copepod parasite that attaches itself to the corneas of the eyes; usually only a single copepod is present on each eye. The copepods are highly conspicuous and may even be luminescent; and it has been speculated that their relationship to the shark is mutualistic and beneficial, with the copepods serving as lures to bring prey species in proximity to their hosts. Field observations are necessary, however, to determine if the parasites actually serve as lures.

Despite the great size of this shark and its apparent fondness for mammalian prey it has never been indicted in attacks on people. The Greenland shark is regarded as harmless by fishermen but is considered potentially dangerous by some writers. There are old, unsubstantiated and possibly mythical tales of Greenlanders in kayaks being attacked by these sharks.

Size:
Maximum total length at least 640 cm and possibly to 730 cm, but most adults between 244 to 427 cm; adult males reach at least 343 cm, adult females to at least 500 cm. Size at birth uncertain, but probably full-term fetuses were 37 cm long.

Interest to Fisheries:
The Greenland shark has long been fished in Greenland, Iceland and northern Norway for its liver oil, but its meat is also used fresh and dried for human and sled-dog food. The meat is toxic when fresh, unless carefully washed, but is harmless dried or semi-putrid. Eskimos have used the skin of the Greenland shark for making boots, and used the sharp lower dental bands as knives for cutting hair.

The Greenland shark is mostly fished with hook-and-line, longline gear or gaffs, but is often taken in seal and whale nets and cod traps.

Remarks:
Somniosus antarcticus was named by Whitley (1939) from a sketch and descriptive data from a Somniosus specimen found dead on a beach at Macquarie Island in the Antarctic. The specimen itself was not preserved, but tooth and skin samples were saved; however, it is uncertain whether these samples still exist. The descriptive data and sketch definitely indicate that the specimen represented a number of the subgenus Somniosus closest to S. microcephalus, but these are sufficiently generalized to prohibit the differentiation of S. antarcticus from S. microcephalus. As with certain other sharks, Whitley apparently named S. antarcticus primarily because of its southern hemisphere locality.

Bass, d'Aubrey and Kistnasamy (1976) reported a southern hemisphere Somniosus from South Africa as "S. microcephalus or a closely related species". Duhamel and Hureau (1982) reported several specimens from waters off Kerguelen Island as S. microcephalus. As southern hemisphere Somniosus have never been compared in detail with northern material, identification of these sharks as S. microcephalus must be considered tentative. However, available information does not justify the recognition of S. antarcticus on locality alone, and so this species is here placed as a tentative synonym of S. microcephalus.

Type material:
Holotype: Unknown. Type Locality: "Habitat in mari glaciali".

Greenland shark (Somniosus microcephalus)