Greenland shark (Somniosus microcephalus)
| Also known as: | gurry shark, large sleeper shark, sleeper, sleeper shark |
|---|---|
| French: | Laimargue Du Groenland |
| Spanish: | Tiburón Boreal, Tollo De Groenlandia |
| Kingdom | Animalia |
|---|---|
| Phylum | Chordata |
| Class | Chondrichthyes |
| Order | Squaliformes |
| Family | Somniosidae |
| Genus | Somniosus (1) |
| Size | Max length: approximately 7 metres (2) |
Classified as Near Threatened (NT) on the IUCN Red List (1).
Amongst the world’s largest sharks, the Greenland shark is an elusive species of dogfish that inhabits the icy waters of the Arctic and the northern Atlantic (1) (2) (3). Also known as the large sleeper shark for its sluggish movements, the body is heavy-set, the spineless dorsal fins are greatly reduced, and the snout is short and rounded (2) (4). For a shark of its size, the gill slits are also notably small, and located low on the side of the head (3) (4). Although this shark’s colouration ranges from brown to black to grey, the skin is often marked with dark lines or white spots, whilst the entire body is covered in closely packed, teeth-like denticles (4).
The Greenland shark occurs in the northern Atlantic and Arctic oceans (1).
During the cold winter months the Greenland shark moves inshore in search of warmer waters, and is often seen near the surface in shallow bays and river mouths. In the summer, it generally returns to deeper water between 180 and 550 metres, but has been recorded down to 2,200 metres (1) (4).
Despite being a characteristically sluggish species, the Greenland shark is known to feed on an incredibly wide variety of prey, including relatively large and active species of fish, seals and even cetaceans (2) (4). Other food items include seabirds, squid, crustaceans and molluscs, as well as all sorts of carrion and offal, making it a regular visitor to the waters around whaling stations and fishing operations (2). Somewhat bizarrely, even parts of horses and entire reindeer have been found in the stomachs of some large Greenland sharks (2) (4).
Almost all Greenland sharks are parasitized by a strange copepod that attaches itself to the shark’s corneas, over time severely damaging its eyesight. However, given that this shark spends much of its time at depths where light does not penetrate, it probably has little use for its small eyes. In the past, it has been speculated that the copepod may act as a fishing lure to attract the shark’s prey, but there is currently no scientific evidence for this theory (2) (3) (4).
The Greenland shark appears to be a long-lived, late maturing and slow growing species (1) (4). It reproduces ovoviviparously, with the female carrying a large number of soft-shelled eggs before giving birth to live young (2) (4).
Historically, the Greenland shark was significantly targeted by shark liver fisheries in the waters of Greenland, Norway and Iceland. Although commercial fishing for Greenland shark liver oil ceased in the 1960s, this species is still frequently taken as bycatch in other fisheries, and also caught for human and sled dog consumption. The meat is toxic when fresh, inducing a drunk like state in both humans and dogs, but becomes edible once it has been dried. Unfortunately, the extent to which fishing is affecting the Greenland shark population is unknown, but there is speculation that its population could be declining, particularly given the shark’s slow growth rate (1) (2) (4).
The current priority is to accurately assess historical catch data for the Greenland shark in order to determine whether its population is actually declining, and to monitor bycatch rates within the various fisheries that overlap its range (1).
To find out more about the conservation of rays and sharks, see:
- Save Our Seas Foundation:
www.saveourseas.com - IUCN Shark Specialist Group:
www.iucnssg.org - Shark Research Institute:
www.sharks.org - Shark Trust:
www.sharktrust.org
This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk
- Bycatch: In the fishing industry, the part of the catch made up of non-target species.
- Cetaceans: A group comprising all whale species; therefore including dolphins and porpoises.
- Copepod: Large and diverse group of minute marine and freshwater crustaceans belonging to the subclass Copepoda. They usually have an elongated body and a forked tail.
- Crustaceans: Diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
- Denticles: In some fish, modified scales that resemble teeth.
- Dorsal fins: In fish, the unpaired fin(s) found on the back of the body.
- Molluscs: A diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
- Ovoviviparously: Ovovivipary is a method of reproduction whereby the egg shell is weakly formed and young hatch inside the female; they are nourished by their yolk sac and then ‘born' live.
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IUCN Red List (June, 2009)
http://www.iucnredlist.org - Compagno, L.J.V. (1984) 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. Food and Agriculture Organization of the United Nations, Rome.
- Caloyianis, N. (1998) Greenland sharks. National Geographic, 194(3): 60 - 71.
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Florida Museum of Natural History (July, 2009)
http://www.flmnh.ufl.edu/fish/Gallery/Descript/GreenlandShark/GreenlandShark.html