Greenland shark

Greenland shark. Also known as the gurry shark or grey shark, it is a large species of sleeper shark native to the cold waters of the North Atlantic Ocean and the Arctic Ocean. It is one of the largest extant species of shark, rivaling the great white shark in size, and is renowned for its extreme longevity, with some individuals estimated to live for several centuries. This slow-moving, apex predator is a crucial component of the Arctic ecosystem and has a unique biological relationship with the parasitic copepod Ommatokoita elongata.

Description and characteristics

The Greenland shark possesses a heavy, cylindrical body with a rounded snout and small eyes. Its coloration ranges from slate-gray to brownish-black, sometimes with dark bands or white spots. The skin is notably rough, covered in dermal denticles that resemble small, sharp teeth. Unlike many active predatory sharks, its fins are relatively small and paddle-like, an adaptation to its slow, energy-conserving lifestyle in frigid waters. A distinctive feature is the frequent presence of the bioluminescent copepod Ommatokoita elongata attached to its corneas, which may act as a lure for prey. The species has very low concentrations of urea and trimethylamine N-oxide in its tissues, compounds which in other sharks help with osmoregulation, but in the Greenland shark are present at levels that would make its flesh toxic to humans if untreated.

Distribution and habitat

This shark has a circumpolar distribution in the North Atlantic, with records from the Barents Sea and Svalbard to the waters off Newfoundland and Labrador, Greenland, and Iceland. It is primarily a deep-water species, commonly found at depths between 200 and 1,200 meters along continental shelves and slopes. However, it ventures into shallower, inshore waters, particularly in the high Arctic during colder months, and has been observed under the ice of the Arctic Ocean. Its range extends as far south as the Gulf of Maine and the North Sea, though sightings in these regions are less frequent. The shark tolerates a wide range of temperatures, from just below freezing to about 10°C, but shows a strong preference for waters between -1 and 4°C.

Life history and longevity

The Greenland shark is the longest-lived vertebrate known to science. Using radiocarbon dating of eye lens nuclei, scientists from the University of Copenhagen have estimated the age of large individuals to be between 272 and 512 years old. This exceptional longevity is attributed to its extremely slow metabolism and growth rate, estimated at less than one centimeter per year. It is an ovoviviparous species, with females giving birth to relatively large litters of live young after a gestation period believed to be several years long. Sexual maturity is not reached until an estimated age of 150 years, a life history strategy that makes the species particularly vulnerable to population declines from overfishing or bycatch.

Diet and feeding behavior

As an apex scavenger and opportunistic predator, its diet is remarkably diverse. Stomach content analyses have revealed remains of teleost fish like halibut and herring, other sharks, skates, eels, and invertebrates such as cephalopods and crustaceans. It is also known to consume carrion, including the flesh of reindeer, horses, polar bears, and moose, likely scavenged. Its slow swimming speed belies an active hunting capability; it is believed to ambush sleeping prey or use a powerful suction force generated by its large gill slits and pharynx. The parasitic copepod on its eyes may produce a faint light, potentially attracting curious prey within striking range in the dark depths.

Relationship with humans

Historically, the flesh of the Greenland shark is toxic when fresh due to high levels of trimethylamine N-oxide, but it can be rendered edible through a fermentation process known as hákarl in Iceland. It has been caught for centuries, primarily for its liver oil used in lamps and as a lubricant. In modern times, it is taken as bycatch in bottom trawling and longline fishing operations for Greenland halibut and shrimp, leading to conservation concerns. The International Union for Conservation of Nature lists it as Vulnerable. Research expeditions, such as those led by the Greenland Shark and Elasmobranch Education and Research Group, use tagging studies to learn more about its migration and ecology. It features in the folklore of the Inuit, who knew it as an important, if sometimes dangerous, creature of the deep.

Category:Sharks of the Atlantic Ocean Category:Fauna of Greenland Category:Arctic fauna