Greenland shark

TheGreenland shark(Somniosus microcephalus), also known as thegurry sharkorgrey shark, is a largesharkof the familySomniosidae("sleeper sharks"), closely related to thePacificandsouthern sleeper sharks.Inhabiting the North Atlantic and Arctic Oceans, they are notable for their exceptional longevity, although they are poorly studied due to the depth and remoteness of their natural habitat.
Greenland sharks have the longest lifespan of any knownvertebrate, estimated to be between 250 and 500 years.They are among the largest extant species of shark, reaching a maximum confirmed length of 6.4 m (21 ft) long and weighing over 1,000 kg (2,200 lb). They reach sexual maturity at about 150 years of age, and their pups are born alive after an estimatedgestationperiod of 8 to 18 years.The shark is ageneralistfeeder, consuming a variety of available foods, including carrion.
Greenland shark meat is toxic to mammals due to its high levels oftrimethylamineN-oxide,although a treated form of it is eaten inIcelandas a delicacy known askæstur hákarl.Because they live deep in remote parts of the northern oceans, Greenland sharks are not considered a threat to humans. A possible attack occurred in August 1936 on two British fisherman, but the species was never identified.
The Greenland shark is one of the largest known extant species of shark, with adults growing to around 400 to 500 cm.The largest confirmed specimen measured up to 6.4 metres (21 ft) long and weighed around 1,023 kilograms (2,255 lb).The all-tackleInternational Game Fish Association(IGFA) record for this species is 775 kg (1,709 lb).It rivals thePacific sleeper shark(possibly up to 7 m or 23 ft long) for the largest species in the familySomniosidae.
The Greenland shark is a thickset species, with a short, rounded snout, small eyes, and small dorsal and pectoral fins.The gill openings are very small for the species' great size. Female Greenland sharks are typically larger than males.
Coloration can range from pale creamy-gray to blackish-brown and the body is typically uniform in color, though whitish spots or faint dark streaks are occasionally seen on the back.
The shark is often infested by thecopepodOmmatokoita elongata, a crustacean which attaches itself to the shark's eyes.It was speculated that the copepod may displaybioluminescenceand thus attract prey for the shark in a mutualistic relationship, but this hypothesis has not been verified.These parasites also damage the eyeball in several ways, leading to almost complete blindness. This does not seem to reduce the life expectancy or predatory ability of Greenland sharks, due to their strong reliance on smell and hearing.
The genome of the Greenland shark was published in 2024. It is 6.45 Gb (billionbase pairs) in length.
When feeding on large carcasses, the shark employs a rolling motion of its jaw. The 48 to 52 teeth of the upper jaw are very thin and pointed, lacking serrations. These upper jaw teeth act as an anchor while the lower jaw proceeds to cut massive chunks out of the prey.
The 48 to 52 lower teeth are interlocking, broad and square in shape, containing short, smooth cusps that point outward.Teeth in the two halves of the lower jaw are strongly pitched in opposite directions.
As both scavengers and active predators, Greenland sharks have established themselves as apex predators in Arctic ecosystems.They primarily eat fish (cod,wolffish,haddock, andskates)and seal.Some Greenland sharks have been found to also eatminke whale.Small Greenland sharks eat predominantlysquid, as well assea birds,crabs,amphipods,marine snails,brittle stars,sea urchins, andjellyfish, while the larger sharks that are greater than 200 cm (79 in) were discovered eating prey such as epibenthic and benthic fishes, as well as seals and smallcetaceanssuch asoceanic dolphinsandporpoises.The largest of these sharks were found having eatenredfish, as well as other highertrophic levelprey.
It is proposed that, because of their slow speeds andlow twitch speed muscle fiber, Greenland sharks hunt marine mammals, such as seals and smaller cetaceans, that are asleep, injured, or sick, as well as scavenging. Regarding most other benthic species, they utilize their cryptic coloration, and approach prey undetected before closing the remaining distance, expanding their buccal cavity to create suction, drawing in prey. This is the likely explanation for why the gut contents of Greenland sharks are often whole prey specimens.
Greenland sharks have also been found with remains ofmoose,polar bear,horse, andreindeer(in one case an entire reindeer body) in their stomachs.The Greenland shark is known to be ascavengerand is attracted by the smell of rotting meat in the water. The sharks have frequently been observed gathering around fishing boats.They also scavenge on seals.
Although such a large shark could easily consume a human swimmer, the frigid waters it typically inhabits make the likelihood of attacks on people very low. No cases of predation on humans have been verified.
The Greenland shark prefers cold water temperatures (-1.1 to 7.4 °C) and deep water (100 to 1,200 m).As anectothermliving in a just-above-freezing environment, this species is sluggish and slow-moving, with the lowest swim speed and tail-beat frequency for its size across all fish species, which most likely correlates with its very slow metabolism and extreme longevity.It swims at an average of 0.34 m·s, with its fastest cruising speed only reaching 0.74 m·s.Because this top speed is a fraction of that of a typical seal in their diet, biologists are uncertain how the sharks are able to prey on the seals. It is hypothesized that they may ambush them while they sleep.
Greenland sharks migrate annually based on depth and temperature rather than distance, although some do travel. During the winter, the sharks congregate in the shallows (up to80° north) for warmth but migrate separately in summer to the deeps or even farther south. The species has been observed at a depth of 2,200 metres (7,200 ft) by a submersible investigating the wreck of theSSCentral Americathat lies about 160nautical miles(180 mi; 300 km) east of Cape Hatteras,North Carolina.Daily vertical migration between shallower and deeper waters has also been recorded.
In August 2013, researchers fromFlorida State Universitycaught a Greenland shark in theGulf of Mexicoat a depth of 1,749 m (5,738 ft), where the water temperature was 4.1 °C (39.4 °F).Four previous records of Greenland shark were reported from Cuba and the northern Gulf of Mexico.A more typical depth range is 0–1,500 m (0–4,900 ft), with the species often occurring in relatively shallow waters in the far north and deeper in the southern part of its range.
In April 2022, a largeSomniosusshark was caught and subsequently released onGlover's Reefoff the coast ofBelize. This shark was identified as being either a Greenland shark or a Greenland/Pacific sleeper sharkhybrid. This observation is notable for being the first possible record of a Greenland shark from theWestern Caribbean, and being caught on a nearshorecoral reef(the only other record of this species from the Caribbean was made from a deep-water habitat off the Caribbean coast ofColombia). The discovery indicates that Greenland sharks may have a wider distribution in the tropics, primarily at greater depths, than previously believed.
The Greenland shark has thelongest known lifespanof all vertebrate species.It is estimated that the species has a lifespan of at least 272 years, with the oldest individual estimated to be 392 ± 120 years of age. Estimates of age were made usingradiocarbon datingof crystals within the lenses of their eyes.Greenland sharks are estimated to reach sexual maturity at around 150 years of age at which point females measure around 4.19 ± 0.04 meters and males measure around 2.84 ± 0.06 meters.One Greenland shark was tagged off the coast of Greenland in 1936 and recaptured in 1952. Its measurements suggest that Greenland sharks grow at a rate of0.5–1 cm (1⁄4–1⁄2in) per year.Efforts toconserveGreenland sharks are particularly important due to their extreme longevity, long maturation periods, and the heightened sensitivity of large shark populations.
Greenland sharks are born alive (a process known asovoviviparity) after an estimated gestation period of 8–18 years.Estimates of litter size have varied across studies. Some studies suggest that this species produce up to 10 pups per litter, each initially measuring some 38–42 cm in length.Based on these estimates, It is thought that, due to their extreme longevity, Greenland sharks can have between 200 and 700 pups during their lifetime.Within a Greenland shark's uterus, villi serve a key function in supplying oxygen to embryos. It is speculated that oxygen supply is a major limiting factor in the size of litters.Other studies, however, have estimated that Greenland sharks may produce from 200 to 324 pups per litter, measuring between 35–45 cm in length.
Like otherelasmobranchii, Greenland sharks have high concentrations of the two nitrogenous compoundsureaandtrimethylamineN-oxide(TMAO) in their tissues, which increase theirbuoyancyand function asosmoprotectants. TMAO also counteracts theprotein-destabilizingtendencies of ureaand deep-water pressure.Its presence in the tissues of both elasmobranch andteleostfish has been found to increase with depth.
The blood of Greenland sharks contains three major types ofhemoglobin, made up of two copies ofαglobin combined with two copies of three very similarβsubunits. These three types show very similar oxygenation and carbonylation properties, which are unaffected by urea, an important compound in marineelasmobranchiiphysiology. They display identical electronic absorption and resonance inRaman spectroscopy, indicating that theirheme-pocket structures are identical or highly similar. The hemoglobins also have a lower affinity for oxygen compared to temperate sharks. These characteristics are interpreted as adaptations to living at great water depths.
The shark has historically been hunted for itsliver oilup until the development ofsynthetic oilsand cessation of export of liver oil and skin from Greenland in the 1960s.In the 1970s, the species was seen as a problem for other fisheries in western Norway and the government subsidized a fishery to reduce the stock of the species.Today, the Greenland shark is primarily caught as bycatch in industrial fisheries. While about 25 Greenland sharks are caught per year by artisanal fisheries targeting the species in Iceland, 3,500 are caught annually as bycatch in the Arctic and Atlantic Oceans.
The shark is likely affected by quantity, dynamics, and distribution of Arctic sea ice.The rate of projected loss of sea ice will continue to negatively influence the abundance, distribution and availability of prey, while, at the same time, providing greater access for fishing fleets.There is greater potential for new fisheries to develop as more productive and abundant southerly species invade the warming Arctic waters.
Greenland sharks are recognized as the longest-lived vertebrates on earth. They have a slow growth rate, late maturity period, and lowfecundity, making the management and conservation of this species very important. As a result of their low productivity and extreme longevity, this species is particularly susceptible tooverfishingand bycatch. Therefore, Greenland sharks' longevity and conservative life history traits, in tandem with their vulnerability to accidental catching and commercial fishing, promotes a growing concern for the sustainability of this species.
The flesh of the Greenland shark is toxic because of the presence of high concentrations of urea andtrimethylamine oxide(TMAO). If the meat is eaten without pretreatment, the ingested TMAO is metabolized intotrimethylamine, which may be auremic toxin. Occasionally,sled dogsthat eat the flesh are unable to stand up because of this effect. Similar toxic effects occur with the relatedPacific sleeper shark, but not in most other shark species.
Greenland shark meat is produced and eaten in Iceland where, today, it is known as a delicacy calledhákarl. To make the shark safe for human consumption, it is first fermented and then dried in a process that can take multiple months. The shark was traditionally fermented by burying the meat in gravel pits near the ocean for at least several weeks. In the present day, shark cuts are typically fermented in containers that are perforated to allow liquid to drain. The fermentation process converts urea into ammonia and TMAO into TMA, which then drains as liquid from the meat. The meat is then excavated and hung in strips to dry for several more months.
The Greenland shark's poisonous flesh has a highureacontent, which gave rise to theInuitlegend ofSkalugsuak, the first Greenland shark.The legend says that an old woman washed her hair in urine (a common practice to killhead lice) and dried it with a cloth. The cloth blew into the ocean to become Skalugsuak.Another legend tells ofSedna, whose father cut off her fingers while drowning her, with each finger turning into a sea creature, including Skalugsuak.
The Greenland shark plays a role incosmologiesof the Inuit from the Canadian Eastern Arctic and Greenland.IgloolikInuit believe that the shark lives within the urine pot ofSedna, goddess of the sea, and consequently, its flesh has a urine-like smell and acts as a helping spirit to shamans.