Atlantic cod populations respond differently to predators depending on what region of the Atlantic Ocean they occupy. Atlantic cod are susceptible to being consumed by large marine mammals (harp and harbor seals) and sharks. In the northwest Atlantic Ocean most of the large predatory fish have been removed and cod (and similar species) act as dominant predators in this region. In other parts of the Atlantic Ocean with large harp seal populations the number of Atlantic cod has been greatly reduced due to consumption by seals. Cod larvae are vulnerable to smaller predators such as zooplankton. Juveniles are preyed on by species such as dogfish, squid, and halibut. Cannibalistic behavior becomes apparent as adult Atlantic cod readily consume juveniles. Although adult Atlantic cod have relatively few predators compared to their young, they still must be on the lookout for large marine animals. The greatest predatory threats to cod are those that lurk above the surface. Humans are responsible for drastically lowering Atlantic cod populations through well-developed fisheries. The economy of several regions is dependent upon these fisheries and the great demand for large numbers of Atlantic cod has resulted in overfishing and reduced cod stocks.
Known Predators:
Atlantic cod reach a maximum length of 150 to 200 cm. On average, cod weigh 40 kg and the greatest recorded weight is 96 kg. The color of Atlantic cod varies with respect to the enviroment in which the fish lives. Water with large volumes of algae will yield a red to greenish skin color. A pale grey color is more prevalent for fish found on the ocean floor or on sandy bottoms. The Atlantic cod has 1 chin barbel, 3 dorsal fins, and 2 anal fins. It also has a pronounced lateral line from the gills to the tail (Wildscreen and U.K. Charity 2004). The coloring of cod is often shaded from top to bottom. The dorsal area of the fish may be a rich brown to green and fade to silver towards the ventral side. Some cod may have brown/red spots on the sides and back.
Range mass: 96 (high) kg.
Average mass: 40 kg.
Range length: 200 (high) cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
Atlantic cod can reach a maximum lifespan in excess of 20 years, with a minimum lifespan of a few hours/days (shortly after the eggs are released). Within the last 100 years typical lifespans have changed drastically as a result of commercial cod fisheries. Most recently, fisheries have begun harvesting younger fish.
Range lifespan
Status: wild: 0 to 20 years.
Average lifespan
Status: wild: 16.0 years.
Atlantic cod are marine benthopelagic fish, living near the bottom and in the open ocean (Riede 2004). Cod also inhabit brackish waters. Cod can be found in a wide range of habitats within the ocean, from the shoreline down to the continental shelf. They can be found at depths of 500 to 600 meters in coastal waters and are also numerous in open ocean waters. These fish are located in a temperate climate with a range in temperature from 0 to 20 degrees Celsius. Geographically the majority of the population lies within a latitude of 80 to 35 degrees north (Frimodt 1995).
Range depth: 600 (high) m.
Habitat Regions: temperate ; saltwater or marine
Aquatic Biomes: pelagic ; benthic ; brackish water
Gadus morhua is commonly known as Atlantic cod and can be found along the eastern and northern coasts of North America, along the coasts of Greenland, and from the Bay of Biscay north to the Arctic Ocean, including the Atlantic waters around Iceland, the North Sea, and the Barents Sea.
Biogeographic Regions: atlantic ocean (Native )
The diet of Atlantic cod is best described as opportunistic because they feed on anything they are capable of capturing. At all life stages, however, they eat primarily other animals. During the larval stage they feed on smaller organisms such as zooplankton. Juveniles feed on shrimp and other small crustaceans. Adult Atlantic cod consume squid, mussels, clams, tunicates, comb jellies, brittle stars, sand dollars, sea cucumbers, and polychaetes, and are also cannibalistic. The choice of prey included in the diet seems to play a role in determining the skin color of cod. Those that feed on crustaceans tend to appear more brownish in color whereas a blue-green pigment may be the result of a diet consisting primarily of fish.
Animal Foods: fish; mollusks; aquatic or marine worms; aquatic crustaceans; echinoderms; other marine invertebrates; zooplankton
Plant Foods: phytoplankton
Primary Diet: carnivore (Piscivore , Eats non-insect arthropods)
The main role that Atlantic cod have in the ecosystem is their involvement in the food chain. Atlantic cod feed upon a variety of organisms such as invertebrates, crustaceans, and zooplankton. Larger marine organisms (i.e. sharks, seals) prey upon and consume Atlantic cod. The interplay between predators and prey is the key way in which cod influence their ecosystem. No information concerning specific relationships (mutualism, parasitism, etc.) was available.
There is limited information available on the communication among cod. Atlantic cod are hypothesized to communicate through the production of sound via drumming muscles. Sound production is correlated with mate selection during spawning season. It is hypothesized that the degree to which males are able to produce acoustic sound is positively associated with the overall fitness of the males, with those having larger drumming muscles producing greater sound waves and out-competing others.
Communication Channels: acoustic
Perception Channels: tactile ; acoustic ; chemical
Atlantic cod was listed as a vulnerable species in 1996. In the early 1990’s many cod populations collapsed in areas where commercial fishing was intense. The collapse is attributed to overfishing, and specifically to the commercial fishing of older/larger cod which resulted in a smaller population of fertile females and the harvesting of young fish before they have had a chance to mature and reproduce. The prosperity that fishermen enjoyed prior to the collapse lured many into the commercial fisheries and as a result the cod population was negatively affected.
Some efforts have been made to help certain cod populations rebound. Moratoriums and fishing regulations were placed in regions of Canada but were unsuccessful in maintaining or increasing population size. The main deterrent in properly managing cod stocks relates to the geographic range which the cod occupy. Cod are found throughout the waters of the Atlantic, and since these are international waters it makes it difficult for any one region to impose certain regulations. Research shows that populations can easily fall below the “Safe Biological Limits,” which represent the number of fish needed to maintain a proper population. Biologists argue that regulation alone will not be enough to keep the cod population at a sustainable level, but it is a start. Suggestions such as no-catch zones in areas of spawning and along migration routes may be helpful if enacted. As cod stocks move towards critically low levels, it is apparent that serious conservation efforts must be put into place to prevent the devastation of this important fish species.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: vulnerable
Atlantic cod pass through a series of four life history stages as they develop. Initially they begin as pelagic eggs which are located in harbors, bays, and offshore banks. The eggs are associated with an incubation temperature around 2 to 8.5 degrees Celsius. The eggs are buoyant and remain close to the surface waters. Studies have shown that egg mortality is independent of temperature but increases at lower salinities. Next, the larval stage takes place. Larvae are located in pelagic waters and their growth is correlated with the volume of zooplankton which can feed upon the sac larvae at this stage. During the third stage, juveniles occur in coastal and offshore waters in the summer and deeper waters in the winter. They are tolerant of temperature changes from 6 to 20 degrees Celsius and they often use vegetation as a predator avoidance strategy. The final stage is adulthood. They live at temperatures less than 10 degrees Celsius and primarily inhabit the ocean floor.
Although Atlantic cod have been an economic asset to humans, they can also create problems for economies based solely on cod fisheries. Those who depend upon the success of cod fisheries as a source of income can be hurt financially if fisheries fail. The collapse of the cod fisheries in the 1990’s took a toll on the economies of New England and Canada. In this case, the stocks were not managed properly and resulted in a 96% decrease in population size since 1850. Fishermen who rely on the cod population to make a living are left with financial burdens when the stock collapses.
Atlantic cod provide an extremely important fishery in many regions especially in the northwest Atlantic. The success of this commercial fishery has been the main source of economic wealth for areas such as New England and Canada, with Atlantic cod even being labeled “Newfoundland currency”. Up until the 1990’s, Atlantic cod was not only an economic mainstay for many people but also a dominant member of the food chain within the waters of the Atlantic. Atlantic cod is marketed widely, primarily for human consumption. The flesh is mild and Atlantic cod are a popular table fish. The liver of Atlantic cod is also processed to produce cod liver oil which is used as a vitamin supplement.
Positive Impacts: food
There is a limited amount of information on Atlantic cod spawning behavior which may suggest complex mating systems. Researchers are aware that mating behavior in Atlantic cod can include reproductive strategies such as sound production by males and mate selection by females. Although these behaviors have been observed, the causes and consequences of such behavior, and their specific interplay within the mating systems continue to be studied. Atlantic cod are considered "batch-spawners", as females only release 5 to 25% of their total egg complement at any time.
One study on the acoustic sound production of Atlantic cod provides some insight into possible mating behaviors. Drumming muscles are present in both males and females, yet males tend to have more pronounced muscles. The mass of the drumming muscles increases in males prior to spawning and larger males have larger muscles. This suggests that the amplitude of sound production might be a determinant in the success of spawning and selection by females. Observations of Atlantic cod behavior support the hypothesis that females are responsible for mate selection. The biology of the drumming muscles in males, as well as the circling behavior of numerous males around prospective females supports the female selection hypothesis. It is worth noting that dominance hierarchies can also be established. Males with greater body sizes and those who were successful in spawning sometimes appear to dominate the population and act aggressively towards “lesser” males.
Recent research suggests that anthropogenic noise pollution in the water (via oil/gas exploration and drilling) could pose a threat to the success of sound production and the role it plays in the reproduction process.
Mating System: polygynandrous (promiscuous)
Many stocks of cod exhibit migratory behavior 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. Although spawning can occur year round, peak spawning levels occur in the winter and spring. As the population moves inshore it may disperse temporarily to feed if large amounts of prey are present. Cod spawn annually, and spawning takes place within a three month period. Cod employ a ventral mount position in which a male uses his pelvic fins to clasp onto a female and then position himself properly beneath her. Cod spawn in dense concentrations of more than 1 fish per cubic meter and multiple pairs of fish can be observed spawning in the same water column. Spawning occurs near the ocean bottom in temperatures between 5 to 7 degrees Celsius. The eggs that are produced are pelagic, and drift (often towards the surface) for approximately 2 to 3 weeks before hatching and reaching the larval stage. There is some debate as to the age of sexual maturity for cod. Age and size at maturity often vary amongst different populations with northeastern populations maturing around 5 to 7 years and southern populations maturing between 2 to 3 years. A recent finding suggests that cod are moving towards a reduction in age and size for sexually mature fish. In 1959 the median age of maturity was 6.3 years for females and 5.4 years for males. In 1979 the age of maturity was listed as 2.8 years for both sexes. Now, the median age of sexual maturity is between 1.7 to 2.3 years and corresponds to a length of 32 to 41 cm.
Breeding interval: Spawning takes place once a year for a duration of 3 weeks to 3 months.
Breeding season: Breeding csn occur year round; peak spawning recorded in winter/spring months.
Range number of offspring: 9 million (high) .
Average gestation period: 2 to 3 weeks.
Range age at sexual or reproductive maturity (female): 1.7 to 5.4 years.
Range age at sexual or reproductive maturity (male): 1.7 to 7 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
There is no indication that any parental involvement exists on the behalf of either females or males after the eggs are released. The high mortality rate of the offspring (eggs) is attributed, in part, to the lack of parental care. The reproductive strategy of high fecundity levels may be a response to the absence of protection the eggs receive once released into the water. Although the survival rate is low, the sheer number of eggs produced is huge.
Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female)
The Atlantic cod (PL: cod) (Gadus morhua) is a benthopelagic fish of the family Gadidae, widely consumed by humans. It is also commercially known as cod or codling.[3][n 1] Dry cod may be prepared as unsalted stockfish,[4][10][n 2] and as cured salt cod or clipfish.[n 3]
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,[14] areas around Iceland and the Barents Sea.
Atlantic cod can live for up to 25 years and typically grow up to 100–140 cm (39.4-55.1 in), but individuals in excess of 180 cm (70.9 in) and 50 kg (110.2 lbs) have been caught.[15][16] They will attain sexual maturity between ages two and eight with this varying between populations and has varied over time.[17][18]
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)[19] 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 Canada fishing economy until 1992, when there was 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.[20] This absence of the apex predator has led to a trophic cascade in many areas.[20] 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.[2] A 2013 assessment covering only Europe shows the Atlantic cod has rebounded in Europe, and it has been relabelled least concern.[21]
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.
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.[23] 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.[24]
Atlantic cod are apex predators in the Baltic and adults are generally free from the concerns of predation.[25] 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.[26]
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 them removed a significant predatory pressure on other Atlantic fish and crustacean species. Population-limiting effects on several species including American lobsters, crabs, 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.[25]
Atlantic cod have been recorded to swim at speeds of a minimum of 2–5 cm/s (0.039–0.097 kn) and a maximum of 21–54 cm/s (0.41–1.05 kn) with a mean swimming speed of 9–17 cm/s (0.17–0.33 kn). In one hour, cod have been recorded to cover a mean range of 99 to 226 m (325 to 741 ft). 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.[27]
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 2.5 °C (5 °F) caused a highly costly increase in metabolic rate of 15 to 30%.[28]
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, crustaceans and sea worms. Stomach sampling studies have discovered that small Atlantic cod feed primarily on crustaceans, while large Atlantic cod feed primarily on fish.[29] In certain regions, the main food source is decapods with fish as a complementary food item in the diet.[30] Wild Atlantic cod throughout the North Sea 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.[29] 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.[29]
Atlantic cod practice some cannibalism. In the southern North Sea, 1–2% (by weight) of stomach contents for cod larger than 10 cm (4 in) consisted of juvenile cod. In the northern North Sea, cannibalism was higher, at 10%.[29] Other reports of cannibalism have estimated as high as 56% of the diet consists of juvenile cod.[31]
When hatched, cod larvae are altricial, entirely dependent on a yolk sac for sustenance until mouth opening at ~24 degree days.[32] The stomach generally develops at around 240 degree days.[32] Before this point the intestine is the main point of food digestion using pancreatic enzymes such as trypsin.[32]
.png)
Spawning female in captivity
Juveniles on a wreck in the North Sea
.jpg)
Atlantic cod juvenile
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.[17][18] Their gonads take several months to develop and most populations will spawn from January to May.[33][34] 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.[31] 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.[35]
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.[36][37] Each female will spawn between 2 hundred thousand and 15 million eggs, with larger females spawning more eggs.[38] 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.[39]
Atlantic cod act as intermediate, paratenic, or definitive hosts to a large number of parasite species: 107 taxa listed by Hemmingsen and MacKenzie (2001)[40] and seven new records by Perdiguero-Alonso et al. (2008).[40] The predominant groups of cod parasites in the northeast Atlantic were trematodes (19 species) and nematodes (13 species), including larval anisakids, which comprised 58.2% of the total number of individuals.[40] Parasites of Atlantic cod include copepods, digeneans, monogeneans, acanthocephalans, cestodes, nematodes, myxozoans, and protozoans.[40]
Atlantic cod has been targeted by humans for food for thousands of years,[41] and with the advent of modern fishing technology in the 1950s there was a rapid rise in landings.[42] 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.[42] 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.
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 300,000 t (330,000 short tons) 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 800,000 t (880,000 short tons) before a gradual decline set in. With the reopening of the limited cod fisheries in 2006, nearly 2,700 t (3,000 short tons) of cod were hauled in. In 2007, offshore cod stocks were estimated at 1% of what they were in 1977.[43]
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.[20] 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 federal law. Restrictions on cod effectively limit fishing on other groundfish species with which the cod swim, such as flounder and haddock.[44]
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. 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 2,260,000 t (2,490,000 short tons) in 2008.
The North Sea cod stock is primarily fished by European Union 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 200,000 and 300,000 t (220,000 and 330,000 short tons). Due to concerns about overfishing, 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 endorsed the EU/Norway Agreement and set the total allowable catch at 27,300 t (30,100 short tons).[46] 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 740,000 t (820,000 short tons) in 1983. The catch reached a historic maximum of 1,343,000 t (1,480,000 short tons) in 1956, and bottomed out at 212,000 t (234,000 short tons) in 1990. Since 2000, the spawning stock has increased quite quickly, helped by low fishing pressure. The total catch in 2012 was 754,131 t (831,287 short tons), the major fishers being Norway and Russia.[47]
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 Baltic Sea: 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.[48] 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.[49]
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.[50] The immigration of eastern cod into the western Baltic management unit may mask a poor state of the populations in the western management unit.
This article incorporates CC BY-2.0 text from the reference.[40]
{{cite journal}}: Cite journal requires |journal= (help) The Atlantic cod (PL: cod) (Gadus morhua) is a benthopelagic fish of the family Gadidae, widely consumed by humans. It is also commercially known as cod or codling. Dry cod may be prepared as unsalted stockfish, and as cured salt cod or clipfish.
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 (39.4-55.1 in), but individuals in excess of 180 cm (70.9 in) and 50 kg (110.2 lbs) 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 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 Canada fishing economy until 1992, when there was 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.
