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Greenland sharks are also known as sleeper sharks, ground sharks, gray sharks, and gurry sharks. They are known as ekalugssuak in Greenland, hakarl in Iceland, and hakjerring in Norway.

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Behavior

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Like all sharks, Somniosus microcephalus has a lateral line which aids in the detection of movement in the surrounding waters. Sharks also have especially keen chemical perception. No communication has been observed within the species.

Perception Channels: tactile ; vibrations ; chemical ; electric

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Tanya Dewey, Animal Diversity Web
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Conservation Status

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The status of Greenland shark populations are not well known. They support a fishery for liver oil in Greenland, Norway, and Iceland, but some researcher suspect that populations have diminished. They have an estimated population doubling time of 14 years.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: near threatened

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Life Cycle

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Development in Somniosus microcephalus is ovoviviparous; litters of up to ten pups have been observed. Size of fully grown young at birth has not been confirmed but is thought to be around forty centimeters. Most adults grow to between two and four meters in length.

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Benefits

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Unless properly washed or dried, Greenland shark meat is toxic to humans. Like most sharks, Greenland sharks rarely attack unless harassed.

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Benefits

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Somniosus microcephalus is commonly fished by people in the Arctic regions (Norway, Iceland, and Greenland) for its liver oil and meat. People of the Inuit tribes have also been known to use its skin to make boots and its teeth as knives.

Positive Impacts: food ; body parts are source of valuable material

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Associations

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Many of these sharks have copepod parasites, Ommatokoita elongata, attached to the corneas of their eyes. A single, female copepod will attach itself to one of the corneas, resulting in corneal damage and blindness in one eye. This does not seem to negatively effect the shark, as they do not rely on their vision. It has been suggested that the bioluminescence of these parasites helps lure prey, thus resulting in a mutualistic relationship, but there is no evidence to support this.

Mutualist Species:

  • Ommatokoita elongata
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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Trophic Strategy

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Fish, marine mammals, and carrion are three staples in the diet of Somniosus microcephalus. Fish include herring (Clupeinae), salmon (Salmonidae), smelt (Osmeridae), cod (Gadidae), pollock (Theragra), haddock (Melanogrammus), halibut (Hippoglossus), redfish (Hoplostethus), sculpins (Cottoidei), lumpfish (Cyclopterus), and skates (Rajiformes). Seals (Phocidae) and small whales (Delphinidae) are also common food items. Drowned horses and reindeer have also been found in the stomachs of captured specimens. Somniosus microcephalus has been observed feeding in great numbers on carrion produced by commercial whaling and fishing operations.

Animal Foods: mammals; fish; carrion ; mollusks; aquatic crustaceans; echinoderms; cnidarians

Primary Diet: carnivore (Piscivore )

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Distribution

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Somniosus microcephalus is found in the north Atlantic, from the coast of New England and Canada to Scandinavian waters. They occasionally venture as far south as the mouth of the Seine River in France.

Biogeographic Regions: atlantic ocean (Native )

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Habitat

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Somniosus microcephalus live mainly on continental and insular shelves. They occupy intertidal regions in addition to some river mouths and shallow bay areas during the winter months and often move to depths from 180 to 550 meters during warmer months. They have been observed as low as 1200 meters, with one observation at 2200 meters off the coast of Georgia - extending its range both geographically and in terms of depth. In northern parts of their range, Greenland sharks are found from 0 to 1200 meters in waters from 1 to 12 degrees Celsius. In southern parts of their range, these sharks may occur at greater depths.

Range depth: 145 to 1200 m.

Average depth: 180-550 m.

Habitat Regions: temperate ; polar ; saltwater or marine

Aquatic Biomes: pelagic ; coastal

Other Habitat Features: estuarine ; intertidal or littoral

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Life Expectancy

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No specific information about the longevity of Somniosus microcephalus exists. Some scientists speculate that these sharks may live in excess of 100 years.

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Morphology

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Somniosus microcephalus is a large, sluggish shark that averages between 2 and 4 meters in length. Most of the body is a medium grey or brown in color and sometimes exhibits dark transverse bands or small spots or blotches that are lighter or darker than the base color. The snout is short and rounded, and the body is heavy and cylindrical in shape with small precaudal fins. No spines are present in the two equally-sized dorsal fins, and the ventral lobe of the caudal fin is slightly elongated. No anal fin is present. The skin is quite rough, exhibiting denticles with curved pointed cusps. Teeth in the upper and lower jaws differ in shape; upper teeth are spear-shaped while the lower teeth are shaped with high roots and low bent cusps for slicing.

Range mass: 700 to 1000 kg.

Range length: 40 to 640 cm.

Average length: 244 to 427 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger; sexes shaped differently

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Associations

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There are no known predators of adult Greenland sharks because of their very large size.

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Kevin Wehrly, University of Michigan-Ann Arbor
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Reproduction

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Mating by this species has never been observed, but females have been found with mating scars on their caudal fins. Therefore, it is inferred that, as is the case with most sharks, males bite females until they submit. Fertilization occurs internally.

Mating System: polygynandrous (promiscuous)

Mating has never been observed in this species and little information is available concerning reproduction in Greenland sharks or related species.

Average number of offspring: 10.

Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); ovoviviparous

There is no specific information on parental investment in Greenland sharks. However, most sharks are independent immediately after birth. Females provide developing embryos with rich food sources to support their development.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female)

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Mills, P. 2006. "Somniosus microcephalus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Somniosus_microcephalus.html
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Patrick Mills, University of Michigan-Ann Arbor
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Brief Summary

provided by Ecomare
The Greenland shark is an inhabitant of the deep North Pole seas. However every once in a while, it is seen in Dutch waters. Greenland shark meat is toxic and can only be consumed when prepared in a special way. The skin of this shark is used to bind books. Greenland sharks are omnivores. Scientists have found the strangest food items it their stomachs, such as reindeer, dogs, cats and even a polar beer. These animals were probably already dead when the shark consumed them.
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Diagnostic Description

provided by FAO species catalogs
fieldmarks: 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. Head moderately long, length from snout to pectoral fins 23% total length in specimen 299 cm total length.

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.

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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Size

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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 at least 500 cm. Size at birth uncertain, but probably full-term fetuses were 37 cm long.
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Brief Summary

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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 spring and summer. In the southern hemisphere it is found in deep water (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, presumably 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, squid, 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 necessarily, however, to determine if the parasites actually serve as lures.

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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Benefits

provided by FAO species catalogs
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.Catches for this species were reported to FAO only for the years 1957,1963-66 and 1971, then since 1973 the total catch has been ranging from 19 to 157 t. The total catch reported for this species to FAO for 1999 was 51 t. The countries with the largest catches were Iceland (51 t). The Greenland shark is mostly fished with hooks and lines, longline gear or gaffs, but is often taken in seal and whale nets and end traps . According to Bonfil (1994), during the first half of this century Norway had a fishery for Greenland sharks. Myklevoll (1989c) reports that this fishery for the liver oil, operated both as a specialised activity and in combination with sealing. Myklevoll provides data that show this fishery peaked in 1934, when 17,201 hectolitres of liver oil were landed. According to Myklevoll (1989c) this fishery ceased in 1960 because of falling market prices for the oil rather than because of scarcity of fish. Castro et al. (in press) citing Jensen (1914) mention that a fishery for this species started in Greenland in the early 19th century, that by 1857 the catch was estimated at only 2,000-3,000 sharks per annum and in the 1910s it had grown to 32,000 sharks per year. Conservation Status : Given our poor knowledge about the Greenland shark, it has not yet been possible to assess this species for the IUCN Red List. Because of its size and habitat, it is expected to be a very slow growing shark that probably deserves a more careful approach for exploitation. Additional information from IUCN database Additional information from CITESdatabase
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FAO species catalogue Vol.4. Sharks of the world. An Annotated and Illustrated Catalogue of Shark Species Known to Date Part 1 - Hexanchiformes to Lamniformes. Compagno, L.J.V. 1984. FAO Fish. Synop., (125) Vol.4, Part 1
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Diagnostic Description

provided by Fishbase
A gigantic, heavily-bodied dogfish shark with a moderately long, rounded snout and small, low dorsal fins; lower caudal lobe long; upper jaw with small single-cusped teeth and lower jaw with moderate-sized, bent-cusped, slicing teeth (Ref. 5578). Medium grey or brown in color, sometimes with transverse dark bands or small light spots (Ref. 5578).
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Recorder
Cristina V. Garilao
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Life Cycle

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Ovoviviparous (Ref. 247). Distinct pairing with embrace (Ref. 205).
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Cristina V. Garilao
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Migration

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Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.
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Kent E. Carpenter
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Morphology

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Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0; Vertebrae: 41 - 44
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Trophic Strategy

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Reported abundant on continental and insular shelves and upper slopes down to at least 1,200 m (Ref. 247) and recorded to as deep as 2,200 m (Ref. 55584) on theh Mid-Atlantic Ridge (Ref. 119696). Epibenthic-pelagic (Ref. 58426). In the Arctic and boreal Atlantic, it occurs inshore in the intertidal and at the surface in shallow bays and river mouths during colder months, retreating to depths of 180-550 m when the temperature rises (Ref. 247). Feeds on pelagic and bottom fishes (herring, spiny eels, Atlantic salmon, Arctic char, smelt, gadoids including cod, ling, pollock and haddock, capelin, redfish, sculpins, lumpfish, Atlantic halibut, Greenland halibut, wolf-fish, redfish (Sebastes) and skates and their egg cases (Ref. 247, 5951), marine mammals, seals (common prey and possibly taken alive) and small cetaceans (most probably mostly as carrion), sea birds, squids, crabs, amphipods, marine snails, brittle stars, sea urchins, and jellyfish. Known to voraciously devour carrion and offal from whaling, sealing and fishing operations (Ref. 247, 58240).
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Recorder
Pascualita Sa-a
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Biology

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Found on continental and insular shelves and upper slopes down to at least 1,200 m (Ref. 247) and to as deep as 2,200 m (Ref. 55584). Epibenthic-pelagic (Ref. 58426). In the Arctic and boreal Atlantic, it occurs inshore in the intertidal and at the surface in shallow bays and river mouths during colder months, retreating to depths of 180-550 m when the temperature rises (Ref. 247). Reported to be found in temperatures from -1.8° to 17.2°C but commonly below 5°C at with salinity range of 29.4-35.5. It is capable of undertaking long migrations (Ref. 119696). Feeds on pelagic and bottom fishes (herring, Atlantic salmon, Arctic char, capelin, redfish, sculpins, lumpfish, cod, haddock, Atlantic halibut, Greenland halibut and skates (Ref. 5951)), sharks and skates (Ref. 5578), seals and small cetaceans, sea birds, squids, crabs, amphipods, marine snails, brittle stars, sea urchins, and jellyfish (Ref. 247, 58240). Radiocarbon dating of eye lens nuclei from 28 caught female Greenland sharks (81-502 cm TL) revealed a life span of at least 272 years, the oldest being nearly 400 years; age of sexual maturity is about 150 years. This large species is slow-growing (Ref. 110949). Petromyzon marinus was reported to have been attached to S. microcephalus (Ref. 58185). Ovoviviparous (Ref. 205). Utilized fresh and dried for human and sled-dog food (flesh is said to be toxic when fresh); Eskimos also used the skin to make boots, and the sharp lower dental bands as knives for cutting hair (Ref. 247). A very sluggish shark (Ref. 28609). Reports in literature of lengths exceeding 640 cm TL (e.g. up to 730 cm TL in Ref. 247) remain unverified. Common length 244-427 cm TL (Ref. 119696).
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Importance

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fisheries: minor commercial; gamefish: yes; price category: low; price reliability: reliable: based on ex-vessel price for this species
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Greenland shark

provided by wikipedia EN

The Greenland shark (Somniosus microcephalus), also known as the gurry shark, grey shark, or by the Kalaallisut name eqalussuaq, is a large shark of the family Somniosidae ("sleeper sharks"), closely related to the Pacific and southern sleeper sharks.[2] The distribution of this species is mostly restricted to the waters of the North Atlantic Ocean and Arctic Ocean.

The Greenland shark has the longest known lifespan of all vertebrate species (estimated to be between 250 and 500 years),[3] and is among the largest extant species of shark. It is a generalist feeder, consuming a variety of available foods.[4] As an adaptation to living at depth,[5] it has a high concentration of trimethylamine N-oxide in its tissues, which causes the meat to be toxic.[6] Greenland shark flesh, treated to reduce toxin levels, is eaten in Iceland as a delicacy known as kæstur hákarl.[7]

Description

The Greenland shark is one of the largest living species of shark. It usually grows 6.4 m (21 ft) long and weighs 1,000 kg (2,200 lb),[8][9] but has been recorded at up to 7.3 m (24 ft) and more than 1,400 kg (3,100 lb).[10][11] Most Greenland sharks observed have been around 2.4–4.8 m (8–16 ft) long and weigh up to 400 kg (880 lb).[10][11]

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.[10]

Dentition

 src=
The dentition of a Greenland shark

When feeding on large carcasses, the shark employs a rolling motion of its jaw. The 48–52 teeth of the upper jaw are very thin and pointed, lacking serrations. These upper jaw teeth act as an anchor while the lower jaw proceeds to cut massive chunks out of the prey for a quick and easy meal.

The 48–52 lower teeth are interlocking and are broad and square, containing short, smooth cusps that point outward.[10] Teeth in the two halves of the lower jaw are strongly pitched in opposite directions.[12]

Behavior

Diet

The Greenland shark is an apex predator and mostly eats fish, and has been observed actively hunting seals in Canada.[4] The prey found in the stomachs of Greenland sharks is an indicator of the active hunting patterns of these predators.[13] Recorded fish prey have included smaller sharks, skates, eels, herring, capelin, Arctic char, cod, rosefish, sculpins, lumpfish, wolffish, and flounder.[10] Small Greenland sharks eat predominantly squid, while the larger sharks that are greater than 200 cm (79 in) were discovered eating prey such as epibenthic and benthic fishes as well as seals. The largest of these sharks were found having eaten redfish, as well as other higher trophic level prey.[14]

Greenland sharks, because of their slow speeds, often hunt prey that are asleep. Using their cryptic coloration, they can approach prey undetected before closing the remaining distance by opening their large buccal cavity in order to create a suction that draws in the prey. This is the likely explanation as to why the gut contents discovered in Greenland sharks is often whole prey specimens.[13]

Greenland sharks have also been found with remains of seals, polar bears, moose,[15] and reindeer (in one case an entire reindeer body) in their stomachs.[10][16] The Greenland shark is known to be a scavenger, and is attracted by the smell of rotting meat in the water. The sharks have frequently been observed gathering around fishing boats.[10] It also scavenges on seals.[17]

Although such a large shark could easily consume a human swimmer, the frigid waters it typically inhabits make the likelihood of attacks on humans very low, and no cases of predation on people have been verified.[10]

Movement

As an ectotherm living in a just-above-freezing environment, the Greenland shark has the lowest swim speed and tail-beat frequency for its size across all fish species, which most likely correlates with its very slow metabolism and extreme longevity.[18] It swims at 1.22 km/h (0.76 mph), with its fastest cruising speed only reaching 2.6 km/h (1.6 mph).[19] Because this top speed is only half that of a typical seal in their diet, biologists are uncertain how the sharks are able to prey on the faster seals. It is hypothesized that they may ambush them while they sleep.[20]

Greenland sharks migrate annually based on depth and temperature rather than distance, although some do travel. During the winter, the sharks congregate in the shallows (up to 80° north) for warmth but migrate separately in summer to the deeps or even farther south. The species has been observed at a depth of 2,200 metres (7,200 ft) by a submersible investigating the wreck of the SS Central America that lies about 160 miles (260 km) east of Cape Hatteras, North Carolina.[21] Daily vertical migration between shallower and deeper waters has also been recorded.[22]

In August 2013, researchers from Florida State University caught a Greenland shark in the Gulf of Mexico at a depth of 1,749 m (5,738 ft), where the water temperature was 4.1 °C (39.4 °F).[23] Four previous records of Greenland shark were reported from Cuba and the northern Gulf of Mexico.[24] A more typical depth range is 0–1,500 m (0–4,900 ft), with the species often occurring in relatively shallow waters in the far north and deeper in the southern part of its range.[25][26]

Other behaviors

The shark is often colonized by the copepod Ommatokoita elongata, a crustacean which attaches itself to the shark's eyes.[27] It was speculated that the copepod may display bioluminescence and thus attract prey for the shark in a mutualistic relationship, but this hypothesis has not been verified.[28] These parasites also damage the eyeball in a number of ways, leading to almost complete blindness. This does not seem to reduce the life expectancy or predatory ability of Greenland sharks due to their strong reliance on smell and hearing.[27][29] The shark occupies what tends to be a very deep environment seeking its preferable cold water (−0.6 to 12 °C or 31 to 54 °F) habitat.[1]

When hoisted upon deck, it beats so violently with its tail, that it is dangerous to be near it, and the seamen generally dispatch it, without much loss of time. The pieces that are cut off exhibit a contraction of their muscular fibres for some time after life is extinct. It is, therefore, extremely difficult to kill, and unsafe to trust the hand within its mouth, even when the head is cut off. And, if we are to believe Crantz, this motion is to be observed three days after, if the part is trod on or struck.

— Henry William Dewhurst, The Natural History of the Order Cetacea (1834)[30]

Longevity

The Greenland shark has the longest known lifespan of all vertebrate species.[31] One Greenland shark was tagged off the coast of Greenland in 1936 and recaptured in 1952. Its measurements suggest that Greenland sharks grow at a rate of 0.5–1 cm (0.2–0.4 in) per year.[32] In 2016, a study based on 28 specimens that ranged from 81 to 502 cm (2.7–16.5 ft) in length used radiocarbon dating of crystals within the lenses of their eyes to determine their approximate ages. The oldest of the animals sampled, which also was the largest, had lived for 392 ± 120 years and was consequently born between 1504 and 1744.n1 The authors further concluded that the species reaches sexual maturity at about 150 years of age.[31][33][34] Efforts to conserve Greenland sharks are particularly important due to their extreme longevity, long maturation periods, and the heightened sensitivity of large shark populations.[35]

Reproduction

As recently as 1957, females were found not to deposit eggs in the bottom mud, but retain the developing embryos within their bodies so they are born alive (a process known as ovoviviparity) after an estimated gestation period of 8–18 years.[18] About ten pups per litter is normal, each initially measuring some 38–42 cm (15–17 in) in length.[33][36] Within a Greenland shark's uterus, villi serve a key function in supplying oxygen to embryos. It is speculated that due to embryonic metabolism dealing with reproduction, this only allows for a limited litter size of around 10 pups.[37] It has been estimated that due to their extreme longevity, Greenland sharks can have 200 to 700 pups during their lifetime.[18]

Physiological adaptations

 src=
Greenland shark at Admiralty Inlet, Nunavut, with an Ommatokoita

Like other elasmobranchii, Greenland sharks have high concentrations of the nitrogenous waste products urea and trimethylamine N-oxide (TMAO) in their tissues, which increases their buoyancy[38] and function as osmoprotectants. TMAO also counteracts the protein-destabilizing tendencies of urea[39][40] and of deep-water pressure.[5][40] Its presence in the tissues of both elasmobranch and teleost fish has been found to increase with depth.[5][41]

The blood of Greenland sharks contains three major types of hemoglobin, made up of two copies of α globin combined with two copies of three very similar β subunits. These three types show very similar oxygenation and carbonylation properties, which are unaffected by urea, an important compound in marine elasmobranch physiology. They display identical electronic absorption and resonance Raman spectra, indicating that their heme-pocket structures are identical or highly similar. The hemoglobins also have a lower affinity for O2 compared to temperate sharks. These characteristics are interpreted as adaptations to living at great water depths.[42]

As food

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Greenland shark meat or kæstur hákarl in Iceland

The flesh of the Greenland shark is toxic because of the presence of high concentrations of trimethylamine oxide (TMAO). If the meat is eaten without pretreatment, the ingested TMAO is metabolized into trimethylamine, which can produce effects similar to extreme drunkenness. Occasionally, sled dogs that eat the flesh are unable to stand up because of this effect. Similar toxic effects occur with the related Pacific sleeper shark, but not in most other shark species.[43][44]

The meat can be treated for safe consumption by boiling in several changes of water, drying, or fermenting for several months to produce kæstur hákarl. Traditionally, this is done by burying the meat in boreal ground for 6–8 weeks, which presses the TMAO out of the meat and also results in partial fermentation. The meat is then dug up and hung up in strips to dry for several more months.[45] It is considered a delicacy in Iceland.[46][47][48]

Inuit legends

The Greenland shark's poisonous flesh has a high urea content, which gave rise to the Inuit legend of Skalugsuak, the first Greenland shark.[49] The legend says that an old woman washed her hair in urine (a common practice to kill head lice) and dried it with a cloth. The cloth blew into the ocean to become Skalugsuak.[50] Another legend tells of Sedna whose father cut off her fingers while drowning her, with each finger turning into a sea creature, including Skalugsuak.[51]

The Greenland shark plays a role in cosmologies of the Inuit from the Canadian Eastern Arctic and Greenland. Igloolik Inuit believe that the shark lives within the urine pot of Sedna, goddess of the sea, and consequently its flesh has a urine-like smell, and acts as a helping spirit to shamans.[52]

Ecological importance

Role in Arctic ecosystems

As both scavengers and active predators, Greenland sharks have established themselves as apex predators in Arctic ecosystems. They eat a wide variety of fish, seals, and other prey within these ecosystems and have an important role in the intricate food web.[13][14]

Conservation and management

Greenland sharks are recognized as the longest-lived vertebrates on earth. They have a slow growth rate, late maturity period, and low fecundity, making the management and conservation of this species very important. As a result of their low productivity and extreme longevity, this species is particularly susceptible to overfishing. Therefore, Greenland sharks' longevity and conservative life history traits, in tandem with their vulnerability to accidental catching and commercial fishing, promotes a growing concern for the sustainability of this species.[53]

Threats

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Overfishing and climate change are the main driving factors of Greenland shark diminishing numbers

The shark has historically been targeted for its liver oil up until the development of synthetic oils and cessation of export of liver oil and skin from Greenland in the 1960s.[54] In the 1970s, the species was perceived as a problem for other fisheries in western Norway and the government subsidized a fishery in order to reduce the stock of the species.[55] Approximately 3,500 individuals are taken as bycatch each year in the Atlantic and Arctic Ocean and Barents Sea.[56] More than 1,000 individuals are caught annually from Arctic waters south to USA waters.[57] Annual catch of Greenland shark from the Barents Sea was estimated to be around 1,200 individuals per year.[56][1]

The shark is also likely affected by anthropogenic climate change, which is affecting the quantity, dynamics, and distribution of Arctic sea ice.[58] The rate of projected loss of sea ice will continue to negatively influence the abundance, distribution and availability of prey, while, at the same time, providing greater access for fishing fleets.[58] Further, there is greater potential for new fisheries to develop as more productive and abundant southerly species invade the warming Arctic waters.[59][1]

See also

References

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Greenland shark: Brief Summary

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The Greenland shark (Somniosus microcephalus), also known as the gurry shark, grey shark, or by the Kalaallisut name eqalussuaq, is a large shark of the family Somniosidae ("sleeper sharks"), closely related to the Pacific and southern sleeper sharks. The distribution of this species is mostly restricted to the waters of the North Atlantic Ocean and Arctic Ocean.

The Greenland shark has the longest known lifespan of all vertebrate species (estimated to be between 250 and 500 years), and is among the largest extant species of shark. It is a generalist feeder, consuming a variety of available foods. As an adaptation to living at depth, it has a high concentration of trimethylamine N-oxide in its tissues, which causes the meat to be toxic. Greenland shark flesh, treated to reduce toxin levels, is eaten in Iceland as a delicacy known as kæstur hákarl.

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Diet

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Feed on fishes, including herring, Atlantic salmon, Arctic char, capelin, redfish, sculpins, lumpfish, cod, haddock, Atlantic halibut, Greenland halibut and skates, as well as cephalopods, gastropods, crustaceans, sea birds and marine mammals.
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North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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Distribution

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Greenland, Davis Strait to Eastport, Maine
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North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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Habitat

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Cool northern seas; found near the surface of estuaries, shallow bays and coastal waters during winter and cooler waters to 600m in summer.
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North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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Habitat

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North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS) North-West Atlantic Ocean species (NWARMS)
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