Greenland shark

Greenland shark
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Squaliformes
Family: Somniosidae
Genus: Somniosus
Species: S. microcephalus
Binomial name
Somniosus microcephalus
Bloch & J. G. Schneider, 1801
Range of the Greenland shark
Synonyms
  • Squalus squatina (non Linnaeus, 1758)
  • Squalus carcharis (Gunnerus, 1776)
  • Somniosus brevipinna (Lesueur, 1818)
  • Squalus borealis (Scoresby, 1820)
  • Squalus norvegianus (Blainville, 1825)
  • Scymnus gunneri (Thienemann, 1828)
  • Scymnus glacialis (Faber, 1829)
  • Scymnus micropterus (Valenciennes, 1832)
  • Leiodon echinatum (Wood, 1846)

The Greenland shark (Somniosus microcephalus), also known as the gurry shark, or grey shark, or by the Inuit name eqalussuaq, is a large shark of the family Somniosidae ("sleeper sharks") native to the waters of the North Atlantic Ocean. These sharks live farther north than any other shark species. Many of the species' adaptations are due to it being one of the very few truly sub-Arctic species of shark. They are closely related to the Pacific and southern sleeper sharks.[2][3] The species has the most toxic meat of any shark.[4]

Description

This is one of the largest living species of shark, of dimensions comparable to those of the great white shark. Greenland sharks grow to 6.4 m (21 ft) and 1,000 kg (2,200 lb),[5] and possibly up to 7.3 m (24 ft) and more than 1,400 kg (3,100 lb).[6][7] Most Greenland sharks observed have been around 2.44–4.8 m (8.0–15.7 ft) long and weigh up to 400 kg (880 lb).[6][7] Males are typically smaller than females. It rivals the Pacific sleeper shark (possibly up to 7 m or 23 ft long) as the largest species in the family Somniosidae. The Greenland shark is a thickset species with a short, rounded snout, small eyes, and very small dorsal and pectoral fins. The gill openings are very small for the species' great size. 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.[6]

Dentition

The dentition of a Greenland shark.

When feeding on large carcasses, the shark employs a rolling motion of its jaw. The teeth of the upper jaw are very thin and pointed, lacking serrations. These upper jaw teeth, numbering from 48 to 52 teeth, act as anchor while the lower jaw does the cutting. The lower teeth are interlocking and are broad and square, 50 to 52 in count, containing short, smooth cusps that point outward.[6] Teeth in the two halves of the lower jaw are strongly pitched in opposite directions.[8]

Life history

The Greenland shark is an apex predator mostly eating fish. Recorded fish prey have included smaller sharks, skates, eels, herring, capelin, Arctic char, cod, redfish, sculpins, lumpfish, wolffish and flounders.[6] It may also prey on marine mammals such as seals. Bite marks on dead seals at Sable Island, Nova Scotia, and Hawarden suggest that this shark may be a major predator for them in the winter.[9] Rarely, these sharks have been found as far south as the Gulf of Mexico.[10]

Greenland sharks are some of the slowest-swimming sharks, which attain a maximum swimming speed about half the maximum swimming speed of a typical seal. Therefore, biologists have wondered how the sharks are able to prey on the seals. Greenland sharks apparently search out seals and ambush them while they sleep.[11] Greenland sharks have also been found with remains of polar bear, horses, moose,[12] and reindeer (in one case an entire reindeer body) in their stomachs.[6][13] The Greenland shark is also known to be a scavenger, but to what extent carrion (almost certainly the origin of the reindeer) figures into the slow-moving fish's stomach contents is unknown. It is known that the species is attracted by the smell of rotting meat in the water. They often congregate in large numbers around fishing operations.[6] The shark is often colonized by the parasitic copepod Ommatokoita elongata that eats the shark's corneal tissue, rendering them blind. This parasite is reportedly bioluminescent and gives the shark a greenish glow around the eye when seen in dark waters, but this has not been scientifically supported.[6][14] The shark occupies what tends to be a very deep environment seeking its preferable cold water (−0.6 to 10 °C or 30.9 to 50.0 °F) habitat. It has been observed at a depth of 2,200 m (7,200 ft) by a submersible investigating the wreck of the SS Central America. A specimen videotaped at 2,773 m (9,098 ft) off the coast of Brazil on 11 February 2012 may have been a Greenland shark, but cannot be distinguished in the video from a southern sleeper shark or Pacific sleeper shark.[15] A more typical depth for the species is above 1,200 m (3,900 ft). Frequently during the winter, when the sharks look for warmer waters to inhabit, they are often found at or near the surface of the water.[6]

As an ectotherm, the Greenland shark is slow, cruising at 0.76 mph (1.22 km/h) with a top speed of 1.6 mph (2.6 km/h).[16]

One Greenland shark was tagged off Greenland in 1936 and recaptured in 1952. Its measurements suggest that Greenland sharks grow at a rate of 0.5–1 cm (0.2–0.4 in) per year, thus the largest individuals may live about 200 years, making them among the longest-lived vertebrates on Earth.[17][18][19]

Reproduction

As recently as 1957, females were found to not deposit eggs in the bottom mud, but retain the developing embryos within their bodies so they are born alive after an undetermined gestation period. About 10 pups per litter are normal, each initially measuring some 90 cm (35 in) in length.[20]

Greenland sharks as food

The flesh of a Greenland shark is poisonous 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. Similar toxic effects occur with the related Pacific sleeper shark, but not in most other shark species, whose meat is often consumed fresh.[21]

It can be eaten if it is boiled in several changes of water or dried or fermented for some months to produce kæstur hákarl, often hákarl for short. Traditionally, this was done by burying the shark in boreal ground, exposing it to several cycles of freezing and thawing. It is considered a delicacy in Iceland.[22][23]

Inuit legends

The shark is not considered dangerous to humans, though Inuit legends of this species mention them attacking kayaks.[24] Although a very large shark likely could easily consume a human swimmer, the extremely cold waters it typically inhabits makes the likelihood of attacks on humans very low, and no cases of predation on people have been verified.[6]

The Greenland shark's poisonous flesh has a high urea content, which gave rise to the Inuit legend of Ekalugsuak, the first Greenland shark.[25] The legend says that an old woman washed her hair in urine and dried it with a cloth. The cloth blew into the ocean to become Ekalugsuak.[26]

The Greenland shark plays a role in cosmologies of the Inuit from the Canadian Eastern Arctic and Greenland. Igloolik Inuit believe that the shark lives within Sedna's urine pot, and consequently its flesh has an urine-like smell, and acts as a helping spirit to shamans.[27]

Research

The Greenland Shark and Elasmobranch Education and Research Group (GEERG) has 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.[26] 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; very little is known about this mysterious species.

An argument now suggests that the Greenland shark is responsible for "seal ripping" attacks on grey seals.[28] These attacks cause a corkscrew pattern of cuts and tears which spiral around a seal's body, following the grain of the collagen within the muscles and running at 45° to the seal's body. Seal deaths have been occurring over larger territories, including the north and east coasts of the UK, which suggests that the Greenland shark may be moving beyond its traditional habitat range. Recent research into the UK "corkscrew" seal deaths by the Sea Mammal Research Unit [29] concluded that the UK seal deaths were unlikely to have been caused by predation from the Greenland shark, rather being caused by blunt mechanical trauma "consistent with the seals being drawn through a ducted propeller" that are found on many ships. Additionally, the shark's slow speed (maximum speed of 1.6 mph or 2.6 km/h) limits its potential predation of seals to those that are asleep.[16] In August 2013, researchers from Florida State University caught the first documented Greenland shark in the Gulf of Mexico.[30]

See also

References

  1. ↑ Kyne, P. M., Sherrill-Mix, S. A. & Burgess, G. H. (2006). "Somniosus microcephalus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 5 February 2012.
  2. ↑ O'Donnell, Jacinth. Jurassic Shark documentary (2000); broadcast on Discovery Channel, 5 August 2006
  3. ↑ Yano, K.; Stevens, J. D.; Compagno, L. J. V. (December 2004). "A review of the systematics of the sleeper shark genus Somniosus with redescriptions of Somniosus (Somniosus) antarcticus and Somniosus (Rhinoscymnus) longus (Squaliformes: Somniosidae)". Ichthyological Research (Springer) 51 (4): 360–373. doi:10.1007/s10228-004-0244-4.
  4. ↑ Guinness World Records 2013, Page 048, Hardcover edition.
  5. ↑ Mills, Patrick (2006). Dewey, Tanya, ed. "Somniosus microcephalus". Animal Diversity Web. University of Michigan.
  6. 1 2 3 4 5 6 7 8 9 10 Eagle, Dane. "Greenland shark". Florida Museum of Natural History. Retrieved 26 June 2012.
  7. 1 2 Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. ISBN 978-0-85112-235-9.
  8. ↑ "Greenland Shark". Marinebiodiversity.ca. Retrieved 23 May 2011.
  9. ↑ Lucas, Zoe (March 2003). "Shark Predation on Sable Island Seals". Sable Island Green Horse Society. Retrieved 26 June 2012.
  10. ↑ "What Is a Greenland Shark Doing in the Gulf of Mexico?". Wired. 27 August 2013.
  11. ↑ Scales, Helen (June 2012). "Slow Sharks Sneak Up on Sleeping Seals (and Eat Them)?". National Geographic News. Retrieved 28 December 2012.
  12. ↑ "Moose-eating shark rescued in Newfoundland harbour". CBC News. 21 November 2013. Retrieved 21 November 2013.
  13. ↑ Howden, Daniel (12 August 2008). "Clash of the fiercest predators as shark eats polar bear". The Independent. Retrieved 26 June 2012.
  14. ↑ "Greenland Shark". Discovery. Retrieved 23 May 2011.
  15. ↑ "Video: Greenland shark at over 9100 feet deep (2770 m) off Brazil". The Dorsal Fin. Retrieved 21 February 2012.
  16. 1 2 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. doi:10.1016/j.jembe.2012.04.021.
  17. ↑ Caloyianis, Nick (September 1998). "Greenland Sharks". National Geographic 194 (3): 60–71.
  18. ↑ GEERG – Greenland Shark. Geerg.ca. Retrieved on 22 November 2013.
  19. ↑ The Greenland shark – world’s oldest? Dutch Shark Society. 7 November 2013.
  20. ↑ "Polar Seas: Greenland Shark". Elasmo-research.org. Retrieved 23 May 2011.
  21. ↑ Waldner, Ray (21 December 2004). "Shark Eating". Sport Fishing Magazine. Retrieved 26 June 2012.
  22. ↑ "My Encounter With Hákarl, The Worst Tasting Food On Earth". theexpeditioner.com.
  23. ↑ "Hákarl - Icelandic Fermented Shark". Islands.
  24. ↑ Stinson, Scott (24 October 2003). "Skipper Uses Knife To Kill 600-Kilo Shark". National Post. Archived from the original on 2 November 2003.
  25. ↑ O’Reilly, Lindsay. "The Greenland Shark", Canadian Geographic, March/April 2004. Retrieved 1 July 2007.
  26. 1 2 "Greenland Shark and Elasmobranch Education and Research Group". Geerg.ca. Retrieved 23 May 2011.
  27. ↑ Idrobo, Carlos Julián (2008) The Pangnirtung Inuit and the Greenland Shark. p. 66. MSc Thesis. Faculty of Environment, Earth and Resources, University of Manitoba
  28. ↑ Channel 5 documentary Retrieved 29 September 2010
  29. ↑ "Sea Mammal Research Unit" "Report on recent seal mortalities in UK waters caused by extensive lacerations", October 2010. Retrieved 5 January 2011
  30. ↑ Grubs, Dean (15 August 2013). "Deep-C Scientists Capture First Greenland Shark in the Gulf of Mexico"

Further reading

External links

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