In the western Atlantic Ocean cod has a distribution north of Cape Hatteras, North Carolina, and round both coasts of Greenland; in the eastern Atlantic it is found from the Bay of Biscay north to the Arctic Ocean, including the North Sea, areas around Iceland and the Barents Sea.
Several cod stocks collapsed in the 1990s (declined by >95% of maximum historical biomass) and have failed to 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 Northeast Atlantic is the world's largest population of cod. By far the largest part of this population is the North-East Arctic Cod, as it is labelled by the ICES, or the Arcto-Norwegian cod stock, also referred to as skrei, a Norwegian name meaning something like "the wanderer", distinguishing it from coastal cod. The North-East Arctic Cod is found in the Barents Sea area. This stock spawns in March and April along the Norwegian coast, about 40% around the Lofoten archipelago. Newly hatched larvae drift northwards with the coastal current while feeding on larval copepods. By summer the young cod reach the Barents Sea where they stay for the rest of their life, until their spawning migration. As the cod grow, they feed on krill and other small crustaceans and fish. Adult cod primarily feed on fish such as capelin and herring. The northeast Arctic cod also shows cannibalistic behaviour. Estimated stock size was in 2004 1.6 million tonnes.
The North Sea cod stock is primarily fished by European Union member states and Norway. In 1999 the catch was divided among Denmark (31%), Scotland (25%), the rest of the United Kingdom (12%), the Netherlands (10%), Belgium, Germany and Norway (17%). In the 1970s, the annual catch rose to between 200,000 - 300,000 tons. Due to concerns about overfishing, catch quotas were repeatedly reduced in the 1980s and 1990s. In 2003, ICES stated that there is a high risk of stock collapse if current exploitation levels continue, and recommended a moratorium on catching Atlantic cod in the North Sea during 2004. However, agriculture and fisheries ministers from the Council of the European Union endorsed the EU/Norway Agreement and set the total allowable catch (TAC) 27,300 tons.
The spawning stock of North-East Arctic cod was more than a million tons following World War II, but declined to a historic minimum of 118,000 tons in 1987. The North-East Arctic cod catch reached a historic maximum of 1,343,000 tons in 1956, and bottomed out at 212,000 tons in 1990. Since 2000, the spawning stock has increased quite quickly, helped by low fishing pressure. However, there are worries about a decreased age at first spawning (often an early sign of stock collapse), combined with the level of discards and unreported catches. The total catch in 2003 was 521,949 tons, the major fishers being Norway (191,976 tons) and Russia (182,160 tons).
Newfoundland's northern cod fishery can be traced back to the 16th century. "On average, about 300,000 tonnes of cod was landed annually until the 1960s, when advances in technology enabled factory trawlers, many of them foreign, to take larger catches. By 1968, landings for the fish peaked at 800,000 tonnes before a gradual decline set in. With the reopening of the limited cod fisheries last year, nearly 2,700 tonnes of cod were hauled in. Today, it's estimated that offshore cod stocks are at one per cent of what they were in 1977"
The fishery has yet to recover, and may not recover at all because of a possibly stable change in the food chain. Atlantic cod was a top-tier predator, along with haddock, flounder and hake, feeding upon smaller prey such as herring, capelin, shrimp and snow crab. With the large predatory fish removed, their prey has had a population explosion and have become the top predators.
Debbie MacKenzie has presented an alternative explanation of the collapse of the cod stocks of the Grand Banks and beyond According to MacKenzie, sustained massive overfishing by drag-trawlers has depleted the nutrient cycle of a closed ecosystem (surface plankton, schools of fish, bottom-feeders and dwellers). The depletion of biomass leaves the ocean starving, and lack of growth leaves unfixed carbon dioxide in the atmosphere. The ocean of evidence is in surface plankton depletion at the base of the food chain, a dearth of filter-feeders in favour of seaweed fed on nitrogen-loaded water, to the loss of bottom-feeders, cod and pelagic fish which were at the top of the food chain. The solution is: i) to stop strip-mining the ocean floor with destructive dragnets, ii) to feed the remaining fish with food, not the suffocating waste from sewage and chemical fertilizer polluted estuaries that causes pseudo-eutrophication, and most importantly iii) to enforce the regulation of commercial fishing very effectively.
Cod populations or stocks can differ significantly both in appearance and biology. For instance, the cod stocks of the Baltic Sea are adapted to low-salinity water. Organisations such as the Northwest Atlantic Fishery Organization (NAFO) and ICES divide the cod into management units or stocks; however these units are not always biologically distinguishable stocks. Some major stocks/management units on the Canadian/US shelf are (see map of NAFO areas) are the Southern Labrador-Eastern Newfoundland stock (NAFO divisions 2J3KL), the Northern Gulf of St. Lawrence stock (NAFO divisions 3Pn4RS), the Northern Scotian Shelf stock (NAFO divisions 4VsW), which all lie in Canadian waters, and the Georges Bank and Gulf of Maine stocks in United States waters. In the European Atlantic, there are numerous separate stocks: on the shelves of Iceland, the coast of Norway, the Barents Sea, the Faroe Islands, off western Scotland, the North Sea, the Irish Sea, the Celtic Sea and in the Baltic Sea.