Atlantic cod

The Atlantic cod (pl.: cod; Gadus morhua) is a fish of the family Gadidae, widely consumed by humans. It is also commercially known as cod or codling.

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.

Atlantic cod can live for up to 25 years and typically grow up to 100–140 cm (40–55 in), but individuals in excess of 180 cm (70 in) and 50 kg (110 lb) have been caught. 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 coastal shoreline down to 300 m (1,000 ft) along the continental shelf.

Atlantic cod is one of the most heavily fished species. Atlantic cod was fished for a thousand years by north European fishers who followed it across the North Atlantic Ocean to North America. It supported the US and Canadian fishing economy until 1992, when the Canadian Government implemented a ban on fishing cod. Several cod stocks collapsed in the 1990s (decline of more than 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, per a 1996 assessment that the IUCN notes needs updating. A 2013 assessment covering only Europe shows the Atlantic cod has rebounded in Europe, and it has been relabelled least concern.

Dry cod may be prepared as unsalted stockfish, and as cured salt cod or clipfish.

Taxonomy

The Atlantic cod is one of three types of cod in the group called Gadus, along with Pacific cod and Greenland cod. Many fish are called "cod" by people, but not all of them belong to the Gadus group, though some are part of the Atlantic cod family, Gadidae.

Behaviour

Atlantic cod are known to swim together in large groups called shoals. Bigger fish often lead the way, especially when moving to find food after laying eggs. All fish in the group usually have equal chances to eat, but larger fish may eat more varied and larger amounts of food.

Young Atlantic cod need to be careful of larger predators, including other cod. They choose where to swim based on how safe they feel. When they sense danger, they hide among rocks or seaweed to stay safe.

Atlantic cod can swim at speeds from very slow to quite fast, and they usually swim more during the day when they are looking for food. They also change their swimming and other behaviors depending on the water temperature, preferring colder water during the day and warmer water at night to save energy.

Feeding and diet

Atlantic cod eat a variety of foods such as fish like herring and capelin, as well as squid, mussels, clams, and small animals like crustaceans. Small cod mainly eat crustaceans, while larger cod prefer to eat fish. In some places, their main food is small sea creatures called decapods, with fish as extra food.

Atlantic cod sometimes eat other younger cod, a behavior called cannibalism. In some areas, up to 10% of what they eat is other young cod. When cod are very small, they depend on a yolk sac for food until they can start eating on their own.

Reproduction

Atlantic cod start to mature between ages two and eight, depending on the group. Their special organs for having babies take several months to grow, and most groups lay eggs from January to May. During this time, males and females come together in large groups. Scientists think this is similar to how some birds choose mates, where males show off and females pick a partner.

These fish lay many batches of eggs over a few weeks, with a few days between each batch. A female can lay from two hundred thousand to fifteen million eggs, and bigger females lay more. The eggs and tiny baby fish float in the water and move with the currents, sometimes ending up in special areas where they can grow safely.

Parasites

See also: Diseases and parasites in cod

Atlantic cod can host many different parasites. Scientists have found that these fish can carry 107 different kinds of parasites. In the northeast Atlantic, the most common parasites are certain worms and tiny creatures. These parasites include small animals called copepods, as well as other types like digeneans, monogeneans, acanthocephalans, cestodes, nematodes, myxozoans, and protozoans.

Fisheries

See also: Cod fisheries

Atlantic cod has been caught by people for food for thousands of years. In the 1950s, with new fishing technology, the amount caught rose quickly. Cod is caught using many kinds of fishing tools, such as bottom trawls, demersal longlines, Danish seine, jigging, and hand lines. Countries have kept records of how much cod is caught since the 1950s. ICES and NAFO collect these records to help manage the fish population. In the eastern Atlantic, more than 1 million tonnes of cod are caught each year, with the Northeast Atlantic and Iceland catching the most. Since 1992, when fishing was limited in Canada, catches in the western Atlantic have been much smaller, usually less than 50,000 tonnes a year.

Northwest Atlantic cod

Main article: Collapse of the Atlantic northwest cod fishery

The Northwest Atlantic cod has been overfished for a long time, leading to a big drop in the fishery in the United States and Canada in the early 1990s.

Newfoundland's northern cod fishery dates back to the 1500s. Until the 1960s, about 300,000 tonnes of cod were caught each year. Better technology allowed bigger catches, and by 1968, the yearly catch reached 800,000 tonnes. After that, the numbers started to fall. When limited fishing started again in 2006, only about 2,700 tonnes were caught. By 2007, the fish population was just 1% of what it was in 1977.

New technologies helped cause the drop in Atlantic cod. Engine-powered boats could travel farther and carry bigger nets. Sonar, developed during World War II to find enemy submarines, was used to locate fish. These changes, along with bottom trawling that damaged ocean ecosystems, helped cause the cod population to crash. These new methods were very different from older ways, like using hand lines and long lines.

The fishery is only now starting to recover and may not fully return because of changes in the ocean food chain. Atlantic cod used to be a top predator, eating smaller fish and animals. With fewer big fish, their prey increased and now affect cod eggs and young fish.

Northeast Atlantic cod

The Northeast Atlantic has the largest cod population in the world. Most of this group is called the Northeast Arctic cod, or skrei, found in the Barents Sea. These fish spawn along the Norwegian coast in March and April. The young drift north to the Barents Sea, where they live until they return to spawn. As they grow, they eat krill and small fish, and adult cod mainly eat capelin and herring. In 2008, the estimated population was about 2,260,000 tonnes.

The North Sea cod is mainly caught by European Union countries, the United Kingdom, and Norway. In the 1970s, catches were between 200,000 and 300,000 tonnes a year. Because of worries about overfishing, the amount allowed to be caught was reduced in the 1980s and 1990s. In 2003, experts said the fish could crash if fishing continued at that rate and suggested stopping all fishing in 2004. However, the amount allowed to be caught was set at 27,300 tonnes. Some guides advise people to avoid buying Atlantic cod to help protect the fish.

The Northeast Arctic cod population was over four million tonnes after World War II but dropped to a low of 740,000 tonnes in 1983. The catch was highest in 1956 at 1,343,000 tonnes and lowest in 1990 at 212,000 tonnes. Since 2000, the population has grown because there has been less fishing. In 2012, the total catch was 754,131 tonnes, mostly by Norway and Russia.

Baltic cod

Decades of overfishing and problems in the environment have threatened Baltic cod. There are two groups of cod in the Baltic Sea. One group spawns east of Bornholm and is adapted to the salty water there. Because of very few cod left, fishing this group has been banned since 2019. However, the water conditions in the eastern Baltic are still not good for the fish to survive. Only the Bornholm Basin currently has the right conditions for them to reproduce.

The other group of cod in the western Baltic is more like the North Sea cod. In the Arkona basin, near Cape Arkona and Rügen, fish from both groups mix, making it hard to know how well the western group is doing.