Atlantic cod

The Atlantic cod (pl.: cod; Gadus morhua) is a fish of the family Gadidae. Many people eat it. It is also called cod or codling.

In the western Atlantic Ocean, cod lives north of Cape Hatteras, North Carolina, and around 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 grow up to 100–140 cm (40–55 in) long. Some very big ones, over 180 cm (70 in) and 50 kg (110 lb), have been caught. It is usually brown or green with spots on its back, and it has a silver belly. A stripe runs along its side. It lives near shorelines and also deeper down to 300 m (1,000 ft).

Atlantic cod is one of the most fished species in the world. People have fished it for a long time. It was very important for fishing in the US and Canada until 1992, when Canada stopped people from fishing cod. Many groups of cod fish got very small in the 1990s and have not fully grown back yet, even though fishing stopped. This has changed some areas where the fish live. Many other groups of cod fish are still at risk. The Atlantic cod is labelled vulnerable on the IUCN Red List of Threatened Species.

People can prepare dry cod in different ways, such as stockfish, cured salt cod or clipfish.

Taxonomy

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

Behaviour

Atlantic cod swim together in large groups called shoals. Bigger fish often lead the way, especially when looking for food. All fish in the group usually have equal chances to eat.

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 based on the water temperature, preferring colder water during the day and warmer water at night to save energy.

Feeding and diet

Atlantic cod eat many kinds of food such as fish like herring and capelin, as well as squid, mussels, clams, and small animals like crustaceans. Small cod mainly eat crustaceans, while bigger 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. 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 grow up between ages two and eight, depending on the group. Their special parts 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 have many different parasites. Scientists have found these fish can carry many kinds of parasites. In the northeast Atlantic, the most common parasites are 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 for food for thousands of years. In the 1950s, new fishing tools let people catch more. Cod is caught in many ways, such as bottom trawls, demersal longlines, Danish seine, jigging, and hand lines. Groups like ICES and NAFO keep track of how much cod is caught to help protect the fish. In the eastern Atlantic, more than 1 million tonnes of cod are caught each year. Since 1992, catches in the western Atlantic have been 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 caught too much, which caused a big drop in numbers in the United States and Canada in the early 1990s.

Newfoundland's northern cod fishery began in the 1500s. Until the 1960s, about 300,000 tonnes of cod were caught each year. With better technology, catches grew to 800,000 tonnes by 1968. After that, numbers fell. When fishing was limited 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 go farther and carry bigger nets. Sonar was used to find fish. These changes, along with bottom trawling, helped cause the cod population to fall. The fishery is only now starting to recover and may not fully return because of changes in the ocean food chain.

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 lay eggs along the Norwegian coast in March and April. The young drift north to the Barents Sea, where they live until they return to lay eggs. 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.

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 catching too much fish and environmental problems have threatened Baltic cod. There are two groups of cod in the Baltic Sea. One group spawns east of Bornholm. Because there are very few of these cod left, fishing this group has been banned since 2019. 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.