Cod is a marine cold-water fish. It has three dorsal and two anal fins and a pronounced lateral line from the gills to the tail. The most characteristic feature is a barbule, a whisker-like projection on the chin. Colouring varies from rich brown to green to silver and it may display brown/red speckles on the sides and back.

Behaviour

Cod is a marine bentho-pelagic fish, meaning that it can be found resting on the sea floor or just above it at depths of 500 to 600 metres, in coastal waters and in open oceans. Like many species, cod form into large, loose shoals when small, but become solitary once they are larger. Many stocks of cod exhibit migratory behaviour during their reproduction season due to seasonal variations in water temperature. Typically, a cod population moves into warmer waters during winter and early spring to begin spawning.

Cod are indiscriminate eaters with a varied diet consisting of fish and invertebrates, including marine worms, prawns, shellfish, crabs, lobsters and octopus.

Cod are sexually mature at around four years old and an adult female will produce around five million eggs in a season.  Atlantic cod pass through a series of four life history stages as they develop. Beginning as pelagic eggs located close to shore, they hatch (after 10-30 days, depending on water temperature) into larvae which still live in pelagic waters. During the third stage, juveniles occupy coastal and offshore waters where they can tolerate temperature changes from 6 to 20 degrees. The final stage is adulthood when they primarily inhabit the ocean floor.

Size

• Average length: 100cm (maximum 150-200 cm)
• Average weight:  30-40 Kg
• Average lifespan: 12-15 years; can live up to 20 years

Status

Atlantic cod is listed as vulnerable on the IUCN Red List, due to intensive commercial pressure. In the North Sea, stocks were at their lowest level on record in the early 2000s. A Cod Recovery Plan was put in place by the EU and Norway. By 2017, cod stocks had reached their highest levels in thirty-five years. This recovery was short-lived. By summer 2019, the International Council for Exploration of the Sea (the organisation which provides advice on fish stocks and quotas), stated that North Sea cod was back at “critically low levels”. North Sea cod were placed back onto the list of commercial fish to be avoided.

Distribution

The majority of the Atlantic cod population lies within latitudes of 80 to 40 degrees north. Commonly found throughout UK waters, cod are semi-migrational, with some moving to colder Scandinavian waters in the summer, and others staying around the UK all year round.

When to see

In autumn, adult cod migrate down from colder Scandinavian waters to join the smaller immature cod, thus swelling the population. The winter is generally synonymous with cod fishing in many parts of the UK, when numbers of fish are at their highest.

Facts

• Cod found around the UK are primarily a species called Atlantic cod (Gadus morhua), even if they are found in the North Sea, English Channel and other areas. There are two other species of true cod: Pacific cod (Gadus macrocephalus) which is not found in British waters and Greenland cod (Gadus ogac) which may occur in the far north of UK waters.
• Cod’s liver is a rich source of oil which contains vitamins E, A and D and omega-3 fatty acids.
• Cod have been commercially important for many centuries with evidence existing that the Vikings used to catch and salt cod as far back as the year 800AD.
• Cod are able to withstand water temperatures as cold as -1.5 degrees Celsius by producing plasma anti-freeze proteins which prevents their blood from forming ice crystals.
• Cod plays a ­keystone role in the North Sea ­ecosystem as both predator and prey. Continued decline will risk other ­species loss and a loss in biodiversity.