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Greenland Shark: Somniosus microcephalus

Family: Somniosidae
Common names

Greenland Shark, Sleeper Shark.

Binomial

Somniosus microcephalus.

Synonyms

Laemargus microcephalus, Leiodon echinatum, Scymnus glacialis, Scymnus gunneri, Scymnus micropterus, Somniosus brevipinna, Squalus borealis, Squalus microcephalus, Squalus norvegianus.

Identification

A very large, heavy-bodied shark with relatively small fins. Snout length roughly equal to mouth width. Small, spiracle behind eye. Eyes often have a parasitic copepod attached. Dorsal fins long and low. First dorsal fin origin midway between pectoral fin free rear tip and pelvic fin origin. Second dorsal origin over pelvic fin insertion. Pectoral fins small with rounded free rear tips. Caudal fin has a weak pre-caudal notch.
Dorsal coloration either mottled or plain grey to brown. Ventrum slightly paler than dorsum.

Size

Maximum length possibly 640cm (Jenkins 1925) but there is a report of a 7.3m specimen. The Greenland shark may be the world’s largest predatory shark, but historical reports may be ‘estimates’. In a study by Hansen in 1963, out of 411 Greenland sharks measured, none exceeded 4m total length. Records of a 5.49m animal by Bigelow and Schroeder seem credible. Size at birth 40-50cm.

Greenland Shark, Somniosus microcephalus, A member of the sleeper shark family. Baie Comeeau, Quebec, Canada, Saint Lawrence River, Atlantic Ocean.

Conservation Status

VULNERABLE

The Greenland Shark has an estimated generation length  of 150 years; incredibly long compared to other elasmobranchs and all other animals on earth. Because of its extremely slow rate of growth and and late age of maturity, it is extremely vulnerable to population depletion.

There has been a targeted fishery for greenland sharks (for its for liver oil) since the 13th century. This increased in the 17th Century until the mid 1900s when synthetic oils replaced shark liver oil. To Currently, the greenland shark is a bycatch species in trawl, longline, and gillnet fisheries with approximately 3,500 individuals caught each year. It is usually discarded, with an unknown rate of post release mortality.

Greenland Shark, Somniosus microcephalus, A member of the sleeper shark family. Baie Comeeau, Quebec, Canada, Saint Lawrence River, Atlantic Ocean.
Habitat

A boreal / cold-temperate species usually found in deep water of the continental shelf and slope but occasionally enters shallow bays. From the surface to 2647m.

Distribution

North Atlantic Ocean. Found across the high arctic to the southern USA and possibly the Gulf of Mexico, and to northern Portugal. Some evidence suggests that the Greenland shark may also occur around the coast of Antarctica but sightings are likely misidentifications of other sleeper sharks.

Reproduction

An aplacental viviparous species (without a yolk-sac placenta).  Litter size 7-10. Reproduction cycle probably biennial.

Diet

Feeds on an extremely wide variety of pelagic and benthic fishes (herring, Atlantic salmon, Arctic char, capelin, redfish, sculpins, lumpfish, cod, haddock, Atlantic halibut, Greenland halibut, sharks and skates) as well as marine mammals such as seals and small cetaceans, and sea birds, squids, crabs, amphipods, marine snails, brittle stars, sea urchins, and jellyfish. One animal had the remains of a caribou in its stomach; likely an animal that drowned while swimming between islands rather than direct predation.
Some researchers have theorized that the Greenland shark uses the parasites covering its eyes to lure prey but this seems unlikely as they do not have bioluminescent properties.

Behavior

A very slow swimmer that is probably capable of short bursts of speed when hunting fast moving prey such as pinnipeds and squid.

Reaction to divers

Greenland sharks are easily approached. They usually either tollerate or completely ignore divers but if disturbed, the generally speed up and quickly outpace divers. Sometimes quite curious, making multiple passes before moving on.

Diving logistics

From around 2005 until 2010(?), Greenland sharks started showing up each summer in a shallow bay a few kms east of Baie Comeau, on the north bank of the St Lawrence Estuary in Quebec, Canada. No one was able to ascertain why the sharks visited the area. Jose Castro has suggested that they swim into the brackish bay to kill and shed the parasites that cover their eyes. Although few of the sharks that were seen there had parasites, they were mostly juveniles which could also explain their lack of parasites. I suspect there may have been a whale carcass or other attractant on the seabed nearby that eventually stopped sending out a scent. Whatever the reason, they have not returned.

There are no other spots where divers encounter Greenland sharks but they are known to congregate around Sable Island off the coast of Nova Scotia when the seals are there. This is not an area many divers are able to visit but it might be a good place to try if you have access to a boat.

Some divers at Baie Comeau felt that making noise (e.g. banging their tanks with a metal bar) resulted in Greenland sharks coming in to investigate the noise. I didn’t find this helped very much at B.C. but it is worth a try. Chumming may also be effective but it did not work in Baie Comeau.

Similar species

Pacific Sleeper Shark In the arctic ocean there may be some overlap in the range of these two enormous sleeper sharks. They cannot be easily distinguished from each other in the field.

Little Sleeper Shark Distinguished by size and more slender appearance. As well as more southerly range.

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