Greenland Shark Facts (Somniosus microcephalus)

The blind shark that can live 500 years

Illustration of Greenland shark (Somniosus microcephalus)
Illustration of Greenland shark (Somniosus microcephalus).

Dorling Kindersley, Getty Images

The cold waters of the North Atlantic and Arctic Ocean are home to the world's longest-lived vertebrate: the Greenland shark (Somniosus microcephalus). The large shark goes by several other names, including gurry shark, grey shark, and eqalussuaq, its Kalaallisut name. The Greenland shark is best known for its impressive 300 to 500 year life span, as well as its use for its use in the Icelandic national dish: kæstur hákarl.

Fast Facts: Greenland Shark

  • Scientific Name: Somniosus microcephalus
  • Other Names: Gurry shark, grey shark, eqalussuaq
  • Distinguishing Features: Large gray or brown shark with small eyes, rounded snout, and small dorsal and pectoral fins
  • Average Size: 6.4 m (21 ft)
  • Diet: Carnivorous
  • Lifespan: 300 to 500 years
  • Habitat: North Atlantic and Arctic Ocean
  • Conservation Status: Near Threatened
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Chondrichthyes
  • Order: Squaliformes
  • Family: Somniosidae
  • Fun Fact: Chef Anthony Bourdain said kæstur hákarl was "the single worst, most disgusting and terrible tasting thing" he ever ate.

Description

Greenland sharks are large fish, comparable in size to great whites and in appearance to sleeper sharks. On average, adult Greenland sharks are 6.4 m (21 ft) long and weigh 1000 kg (2200 lb), but some specimens reach 7.3 m (24 ft) and 1400 kg (3100 lb). The fish are gray to brown in color, sometimes with dark streaks or white spots. Males are smaller than females.

The shark has a thick body, with a short, round snout, small gill openings and fins, and small eyes. Its upper teeth are thin and pointed, while its lower teeth are broad with cusps. The shark rolls its jaw to cut away pieces of its prey.

Greenland shark (Somniosus microcephalus)
Greenland shark (Somniosus microcephalus). NOAA Okeanos Explorer Program

Distribution and Habitat

The Greenland shark is usually found in the North Atlantic Ocean and Arctic Ocean between sea level and a depth of 1200 m (3900 ft). However, the fish migrate to deeper water further south during the summer. One specimen was observed off the coast of Cape Hatteras, North Carolina at 2200 m (7200 ft), while another was documented at 1749 m (5738 ft) in the Gulf of Mexico.

Greenland shark distribution
Greenland shark distribution. Chris_huh

Diet

The Greenland shark is an apex predator that feeds mainly on fish. However, it has never actually been observed hunting. Reports of scavenging are common. The shark supplements its diet with reindeer, moose, horse, polar bears, and seals.

Adaptations

While the shark feeds on seals, researchers are unclear how it hunts them. Because it lives in frigid water, a Greenland shark has an extremely low metabolic rate. In fact, its metabolic rate is so low that the species has the lowest swimming speed for its size of any fish, so it cannot swim fast enough to catch seals. Scientists hypothesize sharks may catch seals while they are sleeping.

The low metabolic rate also leads to the animal's slow growth rate and incredible longevity. Because sharks have cartilaginous skeletons rather than bones, dating their age requires a special technique. In a 2016 study, scientists performed radiocarbon dating on the crystals in the lenses of eyes of sharks caught as bycatch. The oldest animal in that study was estimated to be 392 years of age, plus or minus 120 years. From this data, it appears Greenland sharks live at least 300 to 500 years, making them the world's longest-lived vertebrate.

The biochemistry of the Greenland shark is adapted to allow the fish to survive extremely cold temperatures and high pressures. The shark's blood contains three types of hemoglobin, allowing the fish to obtain oxygen over a range of pressures. The shark is said to smell like urine, due to the high levels of urea and trimethylamine N-oxide (TMAO) in their tissue. These nitrogenous compounds are waste products, but the shark uses them to increase buoyancy and maintain homeostasis.

Most Greenland sharks are blind, but not because their eyes are small. Rather, the eyes are colonized by copepods, occluding the fish's vision. It's possible the shark and copepods may have a mutualistic relationship, with the crustaceans displaying bioluminescence that attracts prey for the shark to eat.

Reproduction

Very little is known about Greenland shark reproduction. The female is ovoviviparous, giving birth to about 10 pups per litter. The newborn pups measure 38 to 42 cm (15 to 17 in) in length. Based on the animal's slow growth rate, scientists estimate it takes about 150 years for a shark to reach sexual maturity.

Greenland Sharks and Humans

The high concentration of TMAO in Greenland shark flesh makes its meat toxic. The TMAO is metabolized into trimethylamine, causing potentially dangerous intoxication. However, the shark's meat is considered a delicacy in Iceland. The meat is detoxified by drying, repeated boiling, or fermenting.

Hákarl hanging to dry in Iceland.
Hákarl hanging to dry in Iceland. Chris 73

Although a Greenland shark could easily kill and eat a human, there are no verified cases of predation. Presumably, this is because the shark lives in extremely cold water, so the chance of interaction with humans is very low.

Conservation Status

The Greenland shark is listed as "near threatened" on the IUCN Red List. Its population trend and the number of surviving adults is unknown. Presently, the species is caught as bycatch and intentionally for Arctic specialty food. In the past, Greenland sharks were heavily fished for their liver oil and were killed because fisheries thought they posed a threat to other fish. Because the animals grow and reproduce so slowly, they have not had time to recover. The shark is also threatened by overfishing and climate change.

Sources

  • Anthoni, Uffe; Christophersen, Carsten; Gram, Lone; Nielsen, Niels H.; Nielsen, Per (1991). "Poisonings from flesh of the Greenland shark Somniosus microcephalus may be due to trimethylamine". Toxicon. 29 (10): 1205–12. doi:10.1016/0041-0101(91)90193-U
  • Durst, Sidra (2012). "Hákarl". In Deutsch, Jonathan; Murakhver, Natalya. They Eat That? A Cultural Encyclopedia of Weird and Exotic Food from around the World. pp. 91–2. ISBN 978-0-313-38059-4.
  • Kyne, P.M.; Sherrill-Mix, S.A. & Burgess, G.H. (2006). "Somniosus microcephalus". The IUCN Red List of Threatened Species. IUCN. 2006: e.T60213A12321694. doi:10.2305/IUCN.UK.2006.RLTS.T60213A12321694.en
  • MacNeil, M. A.; McMeans, B. C.; Hussey, N. E.; Vecsei, P.; Svavarsson, J.; Kovacs, K. M.; Lydersen, C.; Treble, M. A.; et al. (2012). "Biology of the Greenland shark Somniosus microcephalus". Journal of Fish Biology. 80 (5): 991–1018. doi:10.1111/j.1095-8649.2012.03257.x
  • Watanabe, Yuuki Y.; Lydersen, Christian; Fisk, Aaron T.; Kovacs, Kit M. (2012). "The slowest fish: Swim speed and tail-beat frequency of Greenland sharks". Journal of Experimental Marine Biology and Ecology. 426–427: 5–11. doi:10.1016/j.jembe.2012.04.021