The Atlantic cod (: cod; ''Gadus morhua'') is a

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

of the family Gadidae, widely consumed by humans. It is also commercially known as '' cod'' or ''codling''.''Atlantic Cod''
. Seafood Portal. In the western Atlantic Ocean, cod has a distribution north of Cape Hatteras,

North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...

, and around both coasts of

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

and the

Labrador Sea The Labrador Sea (; ) is an arm of the North Atlantic Ocean between the Labrador Peninsula and Greenland. The sea is flanked by continental shelf, continental shelves to the southwest, northwest, and northeast. It connects to the north with Baffi ...

; in the eastern Atlantic, it is found from the Bay of Biscay north to the

Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five oceanic divisions. It spans an area of approximately and is the coldest of the world's oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...

, including the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

, the

North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...

, Sea of the Hebrides, areas around

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

and the Barents Sea. Atlantic cod can live for up to 25 years and typically grow up to , but individuals in excess of and have been caught. They will attain sexual maturity between ages two and eight with this varying between populations and has varied over time. Colouring is brown or green, with spots on the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

side, shading to silver ventrally. A stripe along its lateral line (used to detect vibrations) is clearly visible. Its

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

ranges from the coastal shoreline down to 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 Canada 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 Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

) 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 The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological spe ...

, 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,''Oxford English Dictionary'', 3rd ed. "milwell, ''n.''" Oxford University Press (Oxford), 2002.''Oxford English Dictionary'', 1st ed. "stock-fish, 'stockfish, ''n.''" Oxford University Press (Oxford), 1917. and as cured salt cod or clipfish.

Taxonomy

The Atlantic cod is one of three cod species in the genus '' Gadus ''along with Pacific cod and Greenland cod. A variety of fish species are colloquially known as cod, but they are not all classified within the ''Gadus'', though some are in the Atlantic cod family, Gadidae.

Behaviour

Shoaling

Atlantic cod are a shoaling species and move in large, size-structured aggregations. Larger fish act as scouts and lead the shoal's direction, particularly during post spawning migrations inshore for feeding. Cod actively feed during migration and changes in shoal structure occur when food is encountered. Shoals are generally thought to be relatively leaderless, with all fish having equal status and an equal distribution of resources and benefits. However, some studies suggest that leading fish gain certain feeding benefits. One study of a migrating Atlantic cod shoal showed significant variability in feeding habits based on size and position in the shoal. Larger scouts consumed a more variable, higher quantity of food, while trailing fish had less variable diets and consumed less food. Fish distribution throughout the shoal seems to be dictated by fish size, and ultimately, the smaller lagging fish likely benefit from shoaling because they are more successful in feeding in the shoal than they would be if migrating individually, due to social facilitation.

Predation

Atlantic cod are apex predators in the Baltic and adults are generally free from the concerns of predation. Juvenile cod, however, may serve as prey for adult cod, which sometimes practice cannibalism. Juvenile cod make substrate decisions based on risk of predation. Substrates refer to different feeding and swimming environments. Without apparent risk of predation, juvenile cod demonstrated a preference for finer-grained substrates such as sand and gravel-pebble. However, in the presence of a predator, they preferred to seek safety in the space available between stones of a cobble substrate. Selection of cobble significantly reduces the risk of predation. Without access to cobble, the juvenile cod simply tries to escape a predator by fleeing. Additionally, juvenile Atlantic cod vary their behaviour according to the foraging behaviour of predators. In the vicinity of a passive predator, cod behaviour changes very little. The juveniles prefer finer-grained substrates and otherwise avoid the safer kelp, steering clear of the predator. In contrast, in the presence of an actively foraging predator, juveniles are highly avoidant and hide in cobble or in kelp if cobble is unavailable. Heavy fishing of cod in the 1990s and the collapse of American and Canadian cod stocks resulted in trophic cascades. As cod are apex predators,

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

them removed a significant predatory pressure on other Atlantic fish and crustacean species. Population-limiting effects on several species including American lobsters,

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

s, and shrimp from cod predation have decreased significantly, and the abundance of these species and their increasing range serve as evidence of the Atlantic cod's role as a major predator rather than prey.

Swimming

Atlantic cod have been recorded to swim at speeds of a minimum of and a maximum of with a mean swimming speed of . In one hour, cod have been recorded to cover a mean range of . Swimming speed was higher during the day than at night. This is reflected in the fact that cod more actively search for food during the day. Cod likely modify their activity pattern according to the length of daylight, thus activity varies with time of year.

Response to changing temperatures

Swimming and physiological behaviours change in response to fluctuations in water temperature. Respirometry experiments show that heart rates of Atlantic cod change drastically with changes in temperature of only a few degrees. A rise in water temperature causes marked increases in cod swimming activity. Cod typically avoid new temperature conditions, and the temperatures can dictate where they are distributed in water. They prefer to be deeper, in colder water layers during the day, and in shallower, warmer water layers at night. These fine-tuned behavioural changes to water temperature are driven by an effort to maintain homeostasis to preserve energy. This is demonstrated by the fact that a decrease of only caused a highly costly increase in metabolic rate of 15–30%.

Feeding and diet

The diet of the Atlantic cod consists of fish such as herring, capelin (in the Eastern Atlantic Ocean), and sand eels, as well as mollusks, tunicates, comb jellies, crustaceans,

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

s and sea worms. Stomach sampling studies have discovered that small Atlantic cod feed primarily on crustaceans, while large Atlantic cod feed primarily on fish. In certain regions, the main food source is decapods with fish as a complementary food item in the diet. Wild Atlantic cod throughout the

depend, to a large extent, on commercial fish species also used in fisheries, such as Atlantic mackerel, haddock, whiting, Atlantic herring, European plaice, and common sole, making fishery manipulation of cod significantly easier. Ultimately, food selection by cod is affected by the food item size relative to their own size. However, providing for size, cod do exhibit food preference and are not simply driven by availability. Atlantic cod practice some cannibalism. In the southern North Sea, 1–2% (by weight) of stomach contents for cod larger than consisted of juvenile cod. In the northern North Sea, cannibalism was higher, at 10%. Other reports of cannibalism have estimated as high as 56% of the diet consists of juvenile cod. When hatched, cod larvae are altricial, entirely dependent on a yolk sac for sustenance until mouth opening at ~24 degree days. The stomach generally develops at around 240 degree days. Before this point the intestine is the main point of food digestion using pancreatic enzymes such as trypsin.

Reproduction

File:Gravid female cod.jpg, Spawning female in captivity File:Jonge kabeljauwen of gul nieuwsgierig bij een wrak-4885743.webm, Juveniles on a wreck in the

File:Gadus morhua (head).jpg, Atlantic cod juvenile File:Gadus morhua Cod-2b-Atlanterhavsparken-Norway.JPG, Adult Atlantic cod will attain sexual maturity between ages two and eight with this varying between different populations and has also varied over time with a population. Their

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

s take several months to develop and most populations will spawn from January to May. For many populations, the spawning grounds are located in a different area than the feeding grounds so require the fish to migrate in order to spawn. On the spawning area, males and females will form large schools. Based on behavioral observations of cod, the cod mating system has been likened to a lekking system, which is characterized by males aggregating and establishing dominance hierarchies, at which point females may visit and choose a spawning partner based on status and sexual characteristics. Evidence suggests male sound production and other sexually selected characteristics allow female cod to actively choose a spawning partner. Males also exhibit aggressive interactions for access to females. Atlantic cod are batch spawners, in which females will spawn approximately 5–20 batches of eggs over a period of time with 2–4 days between the release of each batch. Each female will spawn between 2 hundred thousand and 15 million eggs, with larger females spawning more eggs. Females release gametes in a ventral mount, and males then fertilize the released eggs. The eggs and newly hatched larvae float freely in the water and will drift with the current, with some populations relying upon the current to transport the larvae to nursery areas.

Parasites

Atlantic cod act as intermediate, paratenic, or definitive hosts to a large number of parasite species: 107 taxa listed by Hemmingsen and MacKenzie (2001) and seven new records by Perdiguero-Alonso et al. (2008). The predominant groups of cod parasites in the northeast Atlantic were

trematode Trematoda is a Class (biology), class of flatworms known as trematodes, and commonly as flukes. They are obligate parasite, obligate Endoparasites, internal parasites with a complex biological life cycle, life cycle requiring at least two Host ( ...

s (19 species) and

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

s (13 species), including larval anisakids, which comprised 58.2% of the total number of individuals. Parasites of Atlantic cod include copepods,

digenean Digenea (Gr. ''Dis'' – double, ''Genos'' – race) is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as ''flukes'') with a syncytial tegument and, usually, two suckers, one ventral and one ...

s, monogeneans, acanthocephalans, cestodes,

s, myxozoans, and protozoans.

Fisheries

Atlantic cod has been targeted by humans for food for thousands of years, and with the advent of modern fishing technology in the 1950s there was a rapid rise in landings. Cod is caught using a variety of fishing gears including bottom trawls, demersal longlines, Danish seine, jigging and hand lines. The quantity of cod landed from fisheries has been recorded by many countries from around the 1950s and attempts have been made to reconstruct historical catches going back hundreds of years. ICES and NAFO collects landings data, alongside other data, which is used to assess the status of the population against management objectives. The landings in the eastern Atlantic frequently exceeds 1 million tonnes annually from across 16 populations/management units with landings from the Northeast Atlantic cod population and Iceland accounting for the majority of the landings, Since 1992, when the cod moratorium took effect in Canada, landings in the western Atlantic have been considerably lower than in the eastern Atlantic, generally being less than 50,000 tonnes annually.

Northwest Atlantic cod

The Northwest Atlantic cod has been regarded as heavily overfished throughout its range, resulting in a crash in the fishery in the United States and Canada during the early 1990s. Newfoundland's northern cod fishery can be traced back to the 16th century. On average, about of cod were landed annually until the 1960s, when advances in technology enabled factory trawlers to take larger catches. By 1968, landings for the fish peaked at before a gradual decline set in. With the reopening of the limited cod fisheries in 2006, nearly of cod were hauled in. In 2007, offshore cod stocks were estimated at 1% of what they were in 1977. Atlantic cod landings western Atlantic

Technologies that contributed to the collapse of Atlantic cod include engine-powered vessels and frozen food compartments aboard ships. Engine-powered vessels had larger nets, greater range, and better navigation. The capacity to catch fish became limitless. In addition, sonar technology gave an edge to detecting and catching fish. Sonar was originally developed during World War II to locate enemy submarines, but was later applied to locating schools of fish. These new technologies, as well as bottom trawlers that destroyed entire ecosystems, contributed to the collapse of Atlantic cod. They were vastly different from old techniques used, such as hand lines and long lines. The fishery has only recently begun to recover, and may never fully recover 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 have had population explosions and have become the top predators, affecting the survival rates of cod eggs and fry. In the winter of 2011–2012, the cod fishery succeeded in convincing NOAA to postpone for one year the planned 82% reduction in catch limits. Instead, the limit was reduced by 22%. The fishery brought in $15.8 million in 2010, coming second behind Georges Bank haddock among the region's 20 regulated bottom-dwelling groundfish. Data released in 2011 indicated that even closing the fishery would not allow populations to rebound by 2014 to levels required under US federal law. Restrictions on cod effectively limit fishing on other groundfish species with which the cod swim, such as flounder and haddock.

Northeast Atlantic cod

The Northeast Atlantic has the world's largest population of cod. By far, the largest part of this population is the Northeast 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 Northeast 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 An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands. An archipelago may be in an ocean, a sea, or a smaller body of water. Example archipelagos include the Aegean Islands (the o ...

. 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 lives, 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 show cannibalistic behaviour. Estimated stock size was in 2008. The North Sea cod stock is primarily fished by

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...

member states, the United Kingdom 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 . Due to concerns about

, catch quotas were repeatedly reduced in the 1980s and 1990s. In 2003, ICES stated a high risk existed of stock collapse if then current exploitation levels continued, 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 The Council of the European Union, often referred to in the treaties and other official documents simply as the Council, and less formally known as the Council of Ministers, is the third of the seven institutions of the European Union (EU) a ...

endorsed the EU/Norway Agreement and set the total allowable catch at . Seafood sustainability guides, such as the Monterey Bay Aquarium's Seafood Watch, often recommend environmentally conscious customers not purchase Atlantic cod. The stock of Northeast Arctic cod was more than four million tons following World War II, but declined to a historic minimum of in 1983. The catch reached a historic maximum of in 1956, and bottomed out at in 1990. Since 2000, the spawning stock has increased quite quickly, helped by low fishing pressure. The total catch in 2012 was , the major fishers being Norway and Russia.

Baltic cod

Decades of overfishing in combination with environmental problems, namely little water exchange, low salinity and oxygen-depletion at the sea bottom, caused major threats to the Baltic cod stocks. There are at least two populations of cod in the

: One large population that spawns east of Bornholm and one population spawning west of Bornholm. Eastern Baltic cod is genetically distinct and adapted to the brackish environment. Adaptations include differences in hemoglobin type, osmoregulatory capacity, egg buoyancy, sperm swimming characteristics and spawning season. The adaptive responses to the environmental conditions in the Baltic Sea may contribute to an effective reproductive barrier, and thus, eastern Baltic cod can be viewed as an example of ongoing speciation. Due to drastically low cod population sizes, commercial fishing of eastern Baltic cod is prohibited since 2019. However, unfavourable environmental conditions in the eastern Baltic Sea, i.e., low salinity and increasing oxygen-depletion at the sea bottom, led to presently only the Bornholm Basin (Southern Baltic Sea) having sufficient conditions for successful reproduction of eastern Baltic cod. The western Baltic cod consists of one or several small subpopulations that are genetically more similar to the North Sea cod. In the Arkona basin (located off Cape Arkona, Rügen), spawning and migrating cod from both the eastern and western stocks intermingle in proportions that vary seasonally. The immigration of eastern cod into the western Baltic management unit may mask a poor state of the populations in the western management unit.

Notes

References

This article incorporates CC BY-2.0 text from the reference.

External links

FishBase

ICES recommendation for the North Sea Cod stock (2007)

ICES recommendation for the North East Arctic Cod stock (2007)

* ttps://web.archive.org/web/20070305182003/http://www.fisheries.no/marine_stocks/fish_stocks/cod/north_east_arctic_cod.htm Governmental Norwegian fact sheet on North-East Arctic Cod
Atlantic cod-Gadus morhua fishery profiles
Status of Atlantic cod fisheries, summarised in FisheriesWiki * * View th
Atlantic cod genome
in Ensembl
Government of Canada Seafisheries Landings
* * Pauly, Daniel, and Ashley McCrea Stru. "Atlantic Cod: Past and Present." Sea Around Us, 21 May 2015, www.seaaroundus.org/atlantic-cod-past-and-present/. {{Authority control Atlantic cod Commercial fish Fish of the Arctic Ocean Marine fish of Europe Fish of Europe Fish of the North Sea Fish of the Baltic Sea Fish of Greenland Fauna of Atlantic Canada Fauna of the Northeastern United States Game fish Atlantic cod Atlantic cod Canadian cuisine New England cuisine