Arctic cod
From Wikipedia, the free encyclopedia
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 Arctic cod, Arctogadus glacialis
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| Arctogadus glacialis Peters, 1872 |
The Arctic cod (Arctogadus glacialis) is a deepwater fish closely related to the true cod (genus Gadus). It has several common names, including "Polar cod" and "Greenland cod". Note, however, that another species, Boreogadus saida, also shares the common names "Arctic cod" and "Polar cod", while the name "Greenland cod" refers additionally to the species Gadus ogac. One predator is the narwhal.
It is widely distributed in the western part of the Arctic basin, also the northwest and northeast coasts of Greenland. Its range is between 85° and 72° north latitude. Arctic cod can be found at depths of up to 1000 m, and frequently under ice.
The arctic cod favours temperatures below 4°C and it is one of the few fish that thrives in temperatures below 0°C. Antifreeze proteins in its blood are one adaptation responsible for this ability.
With its widespread distribution and abundance, this fish is a key component of Arctic food webs and is a primary food source for narwhals, belugas, ringed seals, and seabirds. It is also preyed upon by other fishes such as arctic charr, Greenland halibut, and Atlantic salmon. Arctic cod are the main consumers of plankton in the upper water column (unlike their relative, the Atlantic cod, which feeds on the bottom). As they grow, they graduate from a diet of copepods to a diet of marine worms, adult copepods, shrimp and may even become cannibalistic. With a usual lifespan of no more than six years, they are relatively short-lived. The age of an arctic cod can be determined by counting annual rings of growth in its otoliths, the tiny bones in their inner ear, much like counting the rings of a tree.
It is silvery in appearance and can grow up to 30 cm in length. It lacks the chin barbels of other cod species.
The weight of these fish can be correlated with their length. One measuring 10 cm would weigh about 10 g, one measuring 20 cm, about 70 g, and one measuring 28 cm, about 180 g.
Age can also be correlated with length, although it has been noted that Arctic cod in the Arctic Ocean usually grow more slowly than those off the Labrador coast. In general, at the age of one year, these fish are about 9 cm long. By the end of the second year they measure about 15 cm, and by the age of three, about 20 cm. Their growth rate appears to decrease slightly after the third year, four-year-olds averaging only about 22 cm and five-year-olds, 25 cm. For example, off the coast of northern Labrador, the arctic cod is typically 25 to 30 cm, while individuals off eastern Newfoundland rarely exceed 18 cm in length.
Although this species has a similar appearance to other codfishes, it is easily recognized by its slender body, deeply forked tail, projecting mouth, and small chin barbels. It is plainly coloured, brownish, spotted above, and silvery on the belly. Its typical, cod-like fins are almost black, with a pale streak at the base.
Arctic cod feed on invertebrates, such as crabs and molluscs, as well as on smaller fish. They are eaten by narwhals, seals and by other fish and they form an important part of the Arctic food chain. The species is of minor commercial value.
On the basis of current knowledge, it is not possible to estimate the abundance of Arctic cod in the Canadian Arctic. Based on data obtained from exploratory fishing off northern Labrador in September, 1978, it is supposed that there were several hundred thousand tonnes of the fish there at that time.
Estimates of Arctic cod from echo sounder surveys of an area of about 18,000 square miles off southern Labrador and northern Newfoundland during 1978 suggest that there were then about 100,000 tonnes of the fish in the area, mainly the young-of-the-year.
That increase in the population of Arctic cod in the NewfoundlandLabrador area may have been the result of environmental conditions in the Arctic and may have been short lived. Abundance indices since 1979 indicate that the numbers of Arctic cod there have since decreased.
In the polar waters of northern Canada, arctic cod spawn each year in the late fall and early winter. Amazingly, up to 10% of a male's body weight consists of gonads! At spawning time, females produce from 9000 to 21,000 eggs that are 1.5 mm in diameter. However, little is known about its mating behaviour.
[edit] References
- Arctogadus glacialis (TSN 164704). Integrated Taxonomic Information System. Retrieved on 30 January 2006.
- "Arctogadus glacialis". FishBase. Ed. Ranier Froese and Daniel Pauly. 10 2005 version. N.p.: FishBase, 2005.
- Template:Www.arcticcod.com.au
- http://www.dfo-mpo.gc.ca/zone/underwater_sous-marin/ArcticCod/artcod-saida_e.htm
- http://www.arctic.uoguelph.ca/cpl/organisms/fish/marine/gadidae/arctic.htm
Arctic Cod are generally known as Arcies
