The Greenland shark, Somniosus microcephalus, also known as the sleeper shark, gurry shark, ground shark, grey shark, or by the Inuit Eqalussuaq, 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 shark species. They are closely related to the Pacific sleeper shark. The size of the Greenland shark is impressive: its largest recorded specimens are comparable in size to the great white shark.
Habits and habitat
Greenland sharks are deep-water sharks, living at depths up to 2,000 m (6,600 ft). Though famously sluggish when hunted (they can be dragged out of the water with one's bare hands), they feed on agile prey such as fish, and on mammals like seals
. The stomachs of a few Greenland sharks have even been found to contain pieces from reindeer
, and even parts of a polar bear
. An entire reindeer, minus its antlers, was found in the stomach contents of one Greenland shark. Greenland sharks are even cannibalistic, eating each other, because they are immune to each other's toxic flesh.
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. Also, studies show the Greenland shark could probably detect light from darkness. The copepod is a whitish-yellow creature that was said to be bioluminescent, but this was proven false by American shark parasitologist George Benz. Some theorize that the function of the copepod is to attract 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. However, the theory of copepods acting as fishing lures is weakened by reports by Canadian wildlife biologists in Arctic Canada, where Greenland sharks have been sighted snatching caribou from the water's edge. Biologists know little of the shark's reproduction and life cycle, aside from ovoviviparity; its lifespan may be as long as 200 years.
Recently, the Greenland shark has been regularly observed in the St. Lawrence Estuary, where it swims in deep and shallow water. The Greenland shark in the St. Lawrence is not completely devoid of the parasitic copepod, Ommatokoita elongata, and a number of specimens without the parasite do show signs of scarring on the cornea. In fact, the population in the St. Lawrence appears to be very visual.
Greenland sharks as food
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. Occasionally, sled dogs that end up eating the flesh are unable to stand up due to the neurotoxins
. 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.
Similar toxic effects occur in the related Pacific sleeper shark, but not in most other shark species, whose meat is often consumed fresh .
- In an Inuit legend, an old woman washed her hair with urine, and then dried her hair with a gray cloth. The cloth blew away and became the first Greenland shark.
- The shark is not dangerous to humans, though there are Inuit legends of the fish attacking kayaks.
- Inuit consider Greenland sharks a scavenging nuisance.
The Greenland Shark and Elasmobranch Education and Research Group (GEERG) has been studying the Greenland shark in the Saguenay Fjord
and St. Lawrence Estuary
. 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 behaviour of the Greenland shark by observing it underwater using scuba and video equipment and by placing acoustic and satellite tags (telemetry) on live specimens.