The Greenland shark, Somniosus microcephalus, also known as the Sleeper shark, Gurry shark, Ground shark or Gray shark, is a large shark native to the waters of the North Atlantic Ocean around Greenland and Iceland. These sharks live further north than any other species. They are closely related to the Pacific sleeper shark. The size of the Greenland shark is impressive; it is so large, in fact, that its record is comparable to (and may exceed) that of the great white shark.
A 24 ft (7.3 m) specimen is frequently mentioned in the literature, and has come to be accepted as a general maximum length, despite the fact that the measurement is in dispute. As compared to the long-running discussion of the measurements of the great white shark, reported measurements of the Greenland shark face little scrutiny, as it is hardly as famous nor as ferocious as the other predatory sharks. Somewhat more credible is the reports of a 21.3 ft (6.4 m) specimen, caught off the Isle of May, Scotland, in January 1895. The weight was reported at 2,250 lbs (1,021 kg). References exist to a specimen with a weight of 3,000 lbs (1.4 tons), but in this case there is no note of the specimen’s length.
Habits and habitat
Greenland sharks are deep-water sharks, living at depths up to 1.24 mi (2,000 m). They feed mainly on fish and sometimes on mammals like seals. The stomachs of a few Greenland sharks have even been found to contain pieces from reindeer, horses, and even parts of a polar bear. An entire reindeer, minus its antlers, was found in the stomach contents of one Greenland shark.
This shark frequently has a relationship with a parasitic copepod, Ommatokoita elongata, that attaches itself to the cornea of the eye and feeds on the shark’s corneal tissue; the resulting scar tissue leads to partial blindness of the shark. This does not occur in all of the sharks though. The copepod is a whitish-yellow creature that is said to be bioluminescent and possibly serves the symbiotic function of attracting prey for the shark, like a fishing lure. This is suggested by the fact that these normally sluggish sharks have been found with much faster-moving animals (such as squid) in their stomachs.
The flesh of a Greenland shark is poisonous when fresh. This is due to the presence of the toxin trimethylamine oxide, which, upon digestion, breaks down into trimethylamine, producing effects similar to extreme drunkenness. However, it can be eaten if it is boiled in several changes of water or dried or rotted for some months (as by being buried 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 dangerous to humans, though there are Inuit legends of the fish attacking kayaks.
Canadian researcher William Sommers and the organization Greenland Shark and Elasmobranch Education and Research Group (GEERG) have 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 behavior of the Greenland shark by observing it underwater using scuba and video equipment and by placing acoustic and satellite tags (telemetry) on live specimens.