Atlantic cod (Gadus morhua)
Also known as: cod, codling, haberdine
Morphology & Biology
The Atlantic cod (Gadus morhua) is a pelagic saltwater fish that lives in the open ocean. It is a member of the cod family (Gadidae). Historically, Atlantic cod up to 2m in length and weighing up to 96kg have been reported. Cod reach maturity when they are between 0.31–0.71m long, and can live up to a maximum of 25 years. Their colour depends on the habitat in which they live, ranging from reddish or greenish in waters populated with algae, to pale grey in deep water or near a sandy bottom. They have a clearly visible stripe running along both sides (known as the lateral line), through which they can sense vibrations.
Sexual maturity age depends on the territory. The more oceanic populations reach sexual maturity at around 6-9 years, whereas the more coastal cod may reach sexual maturity at around 2-4 years. Atlantic cod spawn once a year for a 2 to 3 month period in very large groups. Spawning mostly occurs in shallow warmer coastal waters in spring, between December and June. A large female can lay up to 5 million eggs. However, most of the eggs will be eaten by other species of fish and other sea creatures. After fertilisation the eggs will hatch after two to four weeks, depending on the temperature. Larvae are transparent and only 4mm long. Their size will increase by 40 times after just 10 weeks.
The larvae’s diet consists of plankton. As they grow, the young cod will enrich their diet with small crustaceans. Adults are carnivorous, eating sand eels, mackerels, haddocks, molluscs, squids and crabs. Adult cod are at the top of the food chain, being top predators for species such as haddock, and have almost no natural enemies. The biggest natural enemy for the adult cod is humans.
Distribution
The Atlantic cod is found on both sides of the Atlantic Ocean, from Cape Hatteras in North Carolina to around Greenland and Iceland. They are also found at the coasts of Europe, from the Bay of Biscay to the Barents Sea.
They are slow swimmers, travelling together in large schools. The larger fishes act as scouts, leading the school’s direction. Atlantic cod can perform very long migrations. They can migrate up to 5km per day.
Threats
The Atlantic cod has always been very heavily fished. Together with salmon and tuna, cod is one of the most consumed and commercially exploited fish in Europe. They are also known as “the beef of the sea”. Several wild cod populations collapsed in the 1990s, such as the Canadian population, with over 95% of individuals gone, which have never really recovered even when fishing limitations were implemented. The IUCN has declared the Atlantic cod to be vulnerable to extinction.
Fisheries & Aquaculture
The largest Atlantic cod fishery can be found in Norway and Iceland. Wild populations are targeted by the fishing industry, and the worldwide wild population is in a troubling state. They are predicted to become an endangered species in the very near future. This is concerning, as Atlantic cod are crucial for the balance of the ecosystem as a top predator species. It is crucial to remember that these figures do not show all the fish that had been captured. Many tonnes of fish are thought to go unreported, including bycatch of non-target species.
Due to technological advances, the artificial rearing of cod has drastically increased, meaning that the capture rate of farmed fish has grown significantly.
Fun fact
The Atlantic cod has a whisker-like protrusion on their lower jaw. This is called a ‘barbel’. The barbel is used to detect prey in low-light conditions or murky waters. Taste buds that can detect enzymes are found on these curious appendages that can aid the codfish in detecting potential food sources or danger.
