Atlantic cod - Gadus morhua                           

Diagnostic features
Head relatively narrow, interorbital space 15 to 22% of head length. Predorsal distance less than about 33% of length.  Colour: variable, brownish to greenish or grey dorsally and on upper side, pale ventrally.

Geographical distribution
Cape Hatteras to Ungava Bay along the North American coast; east and west coasts of Greenland extending for variable distances to the north, depending upon climate trends; around Iceland; coasts of Europe from the Bay of Biscay to the Barents Sea, including the region around Bear Island.

Atlantic cod - Geographical distribution

Habitat and biology
The Atlantic cod is generally considered a demersal fish, although its habitat may become pelagic under certain hydrography conditions, when feeding or spawning. The presence of cod usually depends on prey distribution rather than on temperature.  However, whatever the reason, larger fish are found in colder waters in most areas (0-5°C). It lives in almost every salinity from nearly fresh to full oceanic water, and in a wide range of temperatures from nearly freezing to 20C°.

This species is widely distributed in a variety of habitats from the shoreline to well down the continental shelf, to depths over 600 m, but is mostly found within the continental shelf areas from 150-200 m.    Tagged cod at Jan Mayen, which have been recaptured on the spawning grounds around Iceland, indicate that these fish must have crossed in water over 1000 m deep. It is unlikely that cod swim as deep as this; although, they have been trawled in depths up to 460 m.  While Atlantic cod is essentially a fish of the open sea, it appears regularly in various river mouths in Maine and Massachusetts during late autumn and winter. Cod are gregarious during the day; forming compact schools that swim between 30 and 80 m above the bottom, and scatter at night. To the south of its range, cod is found in shallow water only during the winter and there, as elsewhere, it is the younger smaller fish that live close inshore.

Although the spawning period varies among the North Atlantic subpopulations, most cod in the eastern and western parts of this ocean spawn from December to June.  Usually the cod spawn at or near the bottom. There is some evidence that cod leave the bottom and school pelagically to spawn in preferred temperatures when bottom temperatures are unsuitable.

The maximum range of temperature for spawning is from below 0°C to about 1 2°C, with most spawning taking place over the lower half of this range. The Gulf of Maine stock spawns in colder waters than the other stocks. The distribution of spawning stocks widely depends on the oxygen content of the bottom water but on the whole, cod are rather local in their choice of spawning grounds in the Gulf of Maine as well as in Norwegian waters.

The major spawning area in the eastern Atlantic is the North Sea, generally at depths of less than 50 m and never beyond 200 m, especially in the Bornholm basin (Denmark) where the egg density appears to be rather high (late April, end of May). The Atlantic cod spawns once a year.

The Atlantic cod is a voracious and omnivorous species. Larvae and postlarvae feed on plankton, juveniles mainly on invertebrates, and older fish on invertebrates and fish, including young cod. Small crustaceans are of oustanding importance (90%) in the food of juveniles (up to 25 cm length). They are progressively replaced by decapods of medium and large size. Fish become more important than crustaceans in the diet of older individuals. Other systematic groups play a smaller role as forage organisms: polychaetes (less than 10%); echinoderms and other benthic organisms (minor quantities); and occasionally seaweeds (Irish moss - Chondrus crispus) and others. While the proportion of benthic organisms shows hardly any change throughout the year, fish consumption varies seasonally. Deep-water cod show preference for herring throughout the summer and autumn (peak June-July), but in winter and during the spawning period, they sustain themselves on mixed food in coastal areas. Feeding occurs at dawn and dusk, but small fish (of less than 20 cm) feed continuously. 

Size
The various races reach different sizes, the oceanic cod often reaches 1 m and is known to attain a length of 2 m. Local races have smaller fish.

Fisheries
Among the most important of all commercial fishes, cod has been called "beef of the sea". The Atlantic cod has been exploited ever since man began to fish in the seas of Europe. Its value as a prime food-fish is enormous, and when salted and dried, it keeps for winter-time use or export.

The Atlantic cod is caught mainly with bottom otter trawls and pelagic trawls. Devices such as handlines and cod traps are being recently replaced by gillnets (especially in Newfoundland). Other types of gear used are longlines, Danish seines, purse seines, twin beam trawls, light trawls, shrimp trawls and pound nets. The major fishing grounds are boreo-arctic, mostly around Iceland, in the Barents Sea, off Newfoundland and West Greenland, in the Norwegian Sea, off Spitzbergen, and around Bear Island.

It is marketed fresh, chilled or frozen as fillets or whole, salted or sugar-salted, dried and salted, dried and unsalted, in brine, or smoked. Other products obtained from cod are salted cheeks, liver oil and eggs (smoked or as frozen roes).

Source: FAO