Atlantic cod

The Atlantic cod (Gadus morhua) is a benthopelagic fish of the family Gadidae, widely consumed by humans. It is also commercially known as cod or codling. Dry cod may be prepared as unsalted stockfish, as cured salt cod or clipfish. In the western Atlantic Ocean, cod has a distribution north of Cape Hatteras, North Carolina, and around both coasts of Greenland and the Labrador Sea; in the eastern Atlantic, it is found from the Bay of Biscay north to the Arctic Ocean, including the Baltic Sea, the North Sea, Sea of the Hebrides, areas around Iceland and the Barents Sea. The largest individual on record was 1.8 m (6 ft) long and weighed 96 kg (211 lb), but usually the cod is between 61 cm (24 in) and 1.2 m (4 ft) long and weighs up to 40 kg (88 lb). Males and females are similar in size and weight. Atlantic cod can live for 25 years, and usually attain sexual maturity between ages two and four, although cod in the northeast Arctic can take as long as eight years to mature fully. Colouring is brown or green, with spots on the dorsal side, shading to silver ventrally. A stripe along its lateral line (used to detect vibrations) is clearly visible. Its habitat ranges from the shoreline down to the continental shelf. Several cod stocks collapsed in the 1990s (declined by >95% of maximum historical biomass) and have failed to fully recover even with the cessation of fishing. This absence of the apex predator has led to a trophic cascade in many areas. Many other cod stocks remain at risk. The Atlantic cod is labelled vulnerable on the IUCN Red List of Threatened Species. Adult cod form spawning aggregations from late winter to spring. Females release their eggs in batches, and males compete to fertilize them. Fertilized eggs drift with ocean currents and develop into larvae ('fry'). Age of maturation varies between cod stocks, from ages two to four in the west Atlantic, but as late as eight years in the northeast Arctic. Cod can live for 13 years or more. The Atlantic cod is one of three cod species in the genus Gadus along with Pacific cod and Greenland cod. A variety of fish species are colloquially known as cod, but they are not all classified within the Gadus, though some are in the Atlantic cod family, Gadidae. Atlantic cod are a shoaling species and move in large, size-structured aggregations. Larger fish act as scouts and lead the shoal's direction, particularly during post spawning migrations inshore for feeding. Cod actively feed during migration and changes in shoal structure occur when food is encountered. Shoals are generally thought to be relatively leaderless, with all fish having equal status and an equal distribution of resources and benefits. However, some studies suggest that leading fish gain certain feeding benefits. One study of a migrating Atlantic cod shoal showed significant variability in feeding habits based on size and position in the shoal. Larger scouts consumed a more variable, higher quantity of food, while trailing fish had less variable diets and consumed less food. Fish distribution throughout the shoal seems to be dictated by fish size, and ultimately, the smaller lagging fish likely benefit from shoaling because they are more successful in feeding in the shoal than they would be if migrating individually, due to social facilitation.