View source for Atlantic cod

{{Short description|Species of fish}}
{{Speciesbox
| fossil_range = {{Fossil range|Pliocene|recent}}<ref>{{cite journal |last1=Fitch |first1=J.E |title=Teleost fish otoliths from Lee Creek Mine, Aurora, North Carolina (Yorktown Formation: Pliocene) |journal=Smithsonian Contributions to Paleobiology |date=1983 |volume=53 |pages=509–529 |doi=10.5479/si.00810266.53.509 |url=https://www.biodiversitylibrary.org/item/267478#page/519/mode/1up}}</ref>
| name = Atlantic cod
| status = VU
| status_system = IUCN2.3
| status_ref = <ref name="iucn status 1996">{{cite iucn |author=Sobel, J. |date=1996 |title=''Gadus morhua'' |volume=1996 |article-number=e.T8784A12931575 |doi=10.2305/IUCN.UK.1996.RLTS.T8784A12931575.en |access-date=19 November 2021}}</ref>
| image = Atlantic Cod, Atlantischer Kabeljau (Gadus morhua).jpg
| image2 = Atlantic cod.jpg
| image_upright = 1.1
| taxon = Gadus morhua
| authority = [[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]]
| range_map = Gadus morhua-Atlantic cod.png
| range_map_caption = Distribution of Atlantic cod
| synonyms = {{Specieslist
 |Asellus major|
 |Gadus callarias|Linnaeus, 1758
 |Gadus vertagus|[[Johann Julius Walbaum|Walbaum]], 1792
 |Gadus heteroglossus|Walbaum, 1792
 |Gadus ruber|[[Bernard Germain de Lacépède|Lacepède]], 1803
 |Gadus arenosus|[[Samuel L. Mitchill|Mitchill]], 1815
 |Gadus rupestris|Mitchill, 1815
 |Morhua vulgaris|[[John Fleming (naturalist)|Fleming]], 1828
 |Morhua punctatus|Fleming, 1828
 |Gadus nanus|Faber, 1829
 |Morrhua americana|[[David Humphreys Storer|Storer]], 1839
 }}
}}

The '''Atlantic cod''' ({{plural form}}: cod; ''Gadus morhua)'' is a [[fish]] of the family [[Gadidae]], widely [[seafood|consumed]] by humans. It is also [[Commercial fishing|commercially]] known as ''[[cod]]'' or ''codling''.<ref name=seaport>[http://www.seafood-portal.com/Fish_Products/Gadus_morhua:Atlantic_cod ''Atlantic Cod''] {{webarchive|url=https://web.archive.org/web/20091225151638/http://www.seafood-portal.com/Fish_Products/Gadus_morhua%3AAtlantic_cod |date=2009-12-25 }}. Seafood Portal.</ref>{{Refn|group=n|During the Middle Ages, [[Middle English]] used numerous forms such as ''mulvel'', ''milvel'', ''melvel'', and ''milwell'' to refer to fresh, large cod<ref name=milwell/> and ''morhwell'' to refer to smaller ones.<ref name=morwell>''Oxford English Dictionary'', 3rd&nbsp;ed. "morhwell, ''n.''" Oxford University Press (Oxford), 2002.</ref> Fresh cod was also known as the ''common cod'',<ref>{{Citation |last=Richardson |first=John |title=Fauna Boreali-Americana; or the Zoology of the Northern Parts of British America: Containing Descriptions of the Objects of Natural History Collected on the Late Northern Land Expeditions under Command of Captain Sir John Franklin, R.N. |volume= III: The Fish |contribution=93. Gadus Morrhua. (Auct.) ''Common Cod-fish'' |contribution-url=https://books.google.com/books?id=Rc5cAAAAcAAJ&pg=PA242 |pages=242–245 |location=London |publisher=Richard Bentley |date=1836 }}.</ref><ref>{{Citation |last=Grant |first=Francis William |title=The New Statistical Account of Scotland |volume=XI |contribution=Parish of Banff (Presbytery of Fordyce, Synod of Aberdeen.) |contribution-url=https://books.google.com/books?id=o5DVAAAAMAAJ&pg=PA12 |page=12 |date=1836 |location=Edinburgh |publisher=William Blackwood & Sons }}.</ref> the ''Scotch cod'',<ref>{{citation |editor-last=Riley |editor-first=Henry Thomas |title=Munimenta Gildallæ Londoniensis: Liber Albus, Liber Custumarum, et Liber Horn |volume= II, Part II., containing Liber Custumarum, with extracts from the Cottonian MS Claudius, D. II. |date=1860 |location=London |publisher=Eyre & Spottiswoode for Her Majesty's Stationery Office |contribution=Glossary of Mediæval Latin |contribution-url=https://books.google.com/books?id=XMMKAAAAYAAJ&pg=PA816 |page=816 }}.</ref> and as the ''green fish'' or ''greenfish''.<ref name=greenfish>''Oxford English Dictionary'', 3rd&nbsp;ed. "green fish, ''n.''" Oxford University Press (Oxford), 2011.</ref> "Greenfish", however, now more often refers to [[Greenfish (disambiguation)|other fish]]. Similarly, "codling" may refer to various [[morids]].}}

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]],<ref>C.Michael Hogan, (2011) [http://www.eoearth.org/article/Sea_of_Hebrides?topic=49523 ''Sea of the Hebrides''] {{webarchive |url=https://web.archive.org/web/20130524005430/http://www.eoearth.org/article/Sea_of_Hebrides?topic=49523 |date=May 24, 2013 }}. Eds. P. Saundry & C.J.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC.</ref> areas around [[Iceland]] and the [[Barents Sea]].

Atlantic cod can live for up to 25 years and typically grow up to {{cvt|100-140|cm|in|round=5}}, but individuals in excess of {{cvt|180|cm|in|-1}} and {{cvt|50|kg|lb|round=5}} have been caught.<ref>{{Cite news |date=2018-04-07 |title=Verdensrekordtorsken blir fransk middag |work=NRK |url=https://www.nrk.no/tromsogfinnmark/verdensrekordtorsken-blir-fransk-middag-1.13994150 |access-date=2022-04-04}}</ref><ref>{{Cite news |date=2022-03-29 |title=Bergey náði 50 kílóa þorski |work=MBL |url=https://www.mbl.is/200milur/frettir/2022/03/29/bergey_nadi_50_kiloa_thorski/ |access-date=2022-04-04}}</ref> They will attain sexual maturity between ages two and eight with this varying between populations and has varied over time.<ref name=":1">{{Cite journal |last=ICES |date=2021 |title=Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK) |url=https://ices-library.figshare.com/articles/_/18621326 |journal=ICES Scientific Reports |doi=10.17895/ICES.PUB.8211}}</ref><ref name=":2">{{Cite journal |last=ICES |date=2021 |title=. Northwestern Working Group (NWWG) |url=https://ices-library.figshare.com/articles/_/18621020 |journal=ICES Scientific Reports |doi=10.17895/ICES.PUB.8186}}</ref>

Colouring is brown or green, with spots on the [[Dorsum (biology)|dorsal]] side, shading to silver ventrally. A stripe along its [[lateral line]] (used to detect vibrations)<ref name="Bleckmann 13–25">{{Cite journal|last1=Bleckmann|first1=Horst|last2=Zelick|first2=Randy|date=2009-03-01|title=Lateral line system of fish|journal=Integrative Zoology|volume=4|issue=1|pages=13–25|doi=10.1111/j.1749-4877.2008.00131.x|issn=1749-4877|pmid=21392273|doi-access=free}}</ref> is clearly visible. Its [[habitat (ecology)|habitat]] ranges from the coastal shoreline down to {{convert|300|m|ft|-2|abbr=on}} 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 Canadian fishing economy until 1992, when the Canadian Government implemented [[Collapse of the Atlantic northwest cod fishery|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.<ref name="Frank" /> This absence of the [[apex predator]] has led to a [[trophic cascade]] in many areas.<ref name="Frank" /> 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.<ref name="iucn status 1996" /> A 2013 assessment covering only Europe shows the Atlantic cod has rebounded in Europe, and it has been relabelled least concern.<ref name=IUCN>{{cite iucn |author=Cook, R. |author2=Fernandes, P. |author3=Florin, A. |author4=Lorance, P. |author5=Nedreaas, K. |year=2015 |title=''Gadus morhua'' (Europe assessment) |volume=2015 |article-number=e.T8784A45097319 |doi= |access-date=10 July 2024}}</ref>

Dry cod may be prepared as unsalted [[stockfish]],<ref name="milwell">''Oxford English Dictionary'', 3rd&nbsp;ed. "milwell, ''n.''" Oxford University Press (Oxford), 2002.</ref><ref name="stockfish">''Oxford English Dictionary'', 1st&nbsp;ed. "stock-fish| 'stockfish, ''n.''" Oxford University Press (Oxford), 1917.</ref> and as [[curing (food preservation)|cured]] [[salt cod]] or [[clipfish]].{{Refn|group=n|Former names for salted cod include ''cured cod'',<ref name=greencod/> ''ling'',<ref name=greencod/><ref name=ling>''Oxford English Dictionary'', 1st&nbsp;ed. "ling, ''n.<sup>1</sup>''" Oxford University Press (Oxford), 1903.</ref><ref name=haberdine/> and ''haberdine''.<ref name=seaport/><ref name=haberdine>''Oxford English Dictionary'', 1st&nbsp;ed. "†&nbsp;haberdine, ''n.''" Oxford University Press (Oxford), 1898.</ref> Freshly-salted cod was known as ''green cod'', ''white cod'', ''corefish'',<ref name=greencod>''Oxford English Dictionary'', 3rd&nbsp;ed. "green cod, ''n.<sup>1</sup>''" Oxford University Press (Oxford), 2011.</ref> ''coursfish'',<ref name=stockfish/> and green fish or greenfish.<ref name=greenfish/> "Green cod" may also refer to the [[saithe]] (''Pollachius virens''), [[Pollachius pollachius|pollack]] (''P. pollachius''), or uncommonly to the [[lingcod]] (''O. elongatus'').<ref name=greenfish/> "Ling" now more often refers to [[Ling (disambiguation)|other fish]], particularly the [[common ling]] (''Molva molva'').<ref name=ling/>}}

==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==

[[Image:Atlantic cod under a shipwreck.jpg|thumb|left|Atlantic cod are [[demersal fish]]—they prefer sea bottoms with coarse sediments.<ref>[http://www.fishwatch.gov/seafood_profiles/species/cod/species_pages/atlantic_cod.htm Atlantic cod] ''NOAA FishWatch''. Retrieved 5 November 2012.</ref>]][[File:Jonge kabeljauwen oftewel gul rondom een wrak met andere vissen-4885742.webm|left|upright=1.35|thumb|Young Atlantic cod avoid larger cod and pouting (''[[Trisopterus luscus]]'') and crabs on a wreck in the southern [[North Sea]]]]

===Shoaling===
[[Image:Kabeljauwen houden zich op bij een wrak en bevrijden zichzelf-4885741.webm|upright=1.35|thumb|[[Shoaling and schooling|Shoaling]] Atlantic cod on a wreck in the [[North Sea]]]]

Atlantic cod are a [[Shoaling and schooling|shoaling]] species and move in large, size-structured aggregations. Larger fish act as scouts and lead the shoal's direction, particularly during post [[Spawn (biology)|spawning]] [[Fish migration|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.<ref name=Pitcher>{{cite book|last=Pitcher|first=TJ, Parrish JK|title=Functions of shoaling behaviour in teleosts|year=1993|publisher=Chapman and Hall|pages=363–427}}</ref>  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.<ref name=DeBlois>{{cite journal|last=DeBlois|first=Elisabeth M.|author2=Rose, George A.|title=Cross-shoal variability in the feeding habits of migrating Atlantic cod (Gadus morhua)|journal=Oecologia|date=1 January 1996|volume=108|issue=1|pages=192–196|doi=10.1007/BF00333231|pmid=28307750|bibcode=1996Oecol.108..192D|s2cid=1592090}}</ref>

===Predation===
Atlantic cod are apex predators in the Baltic and adults are generally free from the concerns of [[predation]].<ref name=":0">{{cite journal|last=Steneck|first=R. S.|title=Apex predators and trophic cascades in large marine ecosystems: Learning from serendipity|journal=Proceedings of the National Academy of Sciences|date=14 May 2012|volume=109|issue=21|pages=7953–7954|doi=10.1073/pnas.1205591109|pmid=22586126|pmc=3361373|bibcode=2012PNAS..109.7953S|doi-access=free}}</ref> Juvenile cod, however, may serve as prey for adult cod, which sometimes practice [[Cannibalism (zoology)|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.<ref name=Gotceitas>{{cite journal|last=Gotceitas|first=V|author2=S. Fraser |author3=J.A. Brown|title=Habitat use by juvenile Atlantic cod (Gadus morhua) in the presence of an actively foraging and non-foraging predator|journal=Marine Biology|year=1995|volume=123 | issue = 3|pages=421–430|doi=10.1007/bf00349220|bibcode=1995MarBi.123..421G|s2cid=84470358}}</ref>

Heavy fishing of cod in the 1990s and the collapse of American and [[Canadian cod]] stocks resulted in [[trophic cascade]]s. As cod are [[apex predator]]s, [[overfishing]] them removed a significant predatory pressure on other Atlantic fish and crustacean species. Population-limiting effects on several species including [[American lobster]]s, [[crab]]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.<ref name=":0" />

===Swimming===
Atlantic cod have been recorded to swim at speeds of a minimum of {{cvt|2|-|5|cm/s|kn}} and a maximum of {{cvt|21|-|54|cm/s|kn}} with a mean swimming speed of {{cvt|9|-|17|cm/s|kn}}. In one hour, cod have been recorded to cover a mean range of {{cvt|99|to|226|m}}. 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.<ref name=Lokkeborg>{{cite journal|last=LØKKEBORG|first=SVEIN|s2cid=25607249|title=Feeding behaviour of cod, Gadus morhua: activity rhythm and chemically mediated food search|journal=Animal Behaviour|date=1 August 1998|volume=56|issue=2|pages=371–378|doi=10.1006/anbe.1998.0772|pmid=9787028}}</ref>

===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 {{convert|2.5|C-change|0}} caused a highly costly increase in metabolic rate of 15–30%.<ref name=Claireaux>{{cite journal|last=Claireaux|first=G|title=Physiology and behaviour of free-swimming Atlantic cod (Gadus morhua) facing fluctuating temperature conditions|journal=Journal of Experimental Biology|year=1995|volume=198 | issue = 1|pages=49–60|doi=10.1242/jeb.198.1.49|pmid=9317317|url=http://jeb.biologists.org/content/198/1/49.short|access-date=27 October 2013|display-authors=etal|doi-access=free|bibcode=1995JExpB.198...49C}}</ref>

==Feeding and diet==
The diet of the Atlantic cod consists of fish such as [[Clupea|herring]], [[capelin]] (in the Eastern Atlantic Ocean), and [[sand eel]]s, as well as [[Mollusca|mollusks]], [[tunicate]]s, [[Ctenophora|comb jellies]], [[crustacean]]s, [[echinoderm]]s and [[Marine worm|sea worms]].<ref>{{cite web | url=https://animaldiversity.org/accounts/Gadus_morhua/ | title=Gadus morhua (Cod) | website=[[Animal Diversity Web]] }}</ref> Stomach sampling studies have discovered that small Atlantic cod feed primarily on crustaceans, while large Atlantic cod feed primarily on fish.<ref name=Daan>{{cite journal|last=Daan|first=N.|title=A quantitative analysis of the food intake of North Sea cod, Gadus Morhua|journal=Netherlands Journal of Sea Research|date=1 December 1973|volume=6|issue=4|pages=479–517|doi=10.1016/0077-7579(73)90002-1|bibcode=1973NJSR....6..479D}}</ref>  In certain regions, the main food source is [[decapods]] with fish as a complementary food item in the diet.<ref name=Klemetsen>{{cite journal|last=Klemetsen|first=A.|title=Food and feeding habits of cod from the Balsfjord, northern Norway during a one-year period|journal=ICES Journal of Marine Science|date=1 May 1982|volume=40|issue=2|pages=101–111|doi=10.1093/icesjms/40.2.101}}</ref> 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]], [[Merlangius|whiting]], [[Atlantic herring]], [[European plaice]], and [[common sole]], making fishery manipulation of cod significantly easier.<ref name=Daan /> 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.<ref name=Daan />

Atlantic cod practice some [[cannibalism (zoology)|cannibalism]]. In the southern North Sea, 1–2% (by weight) of stomach contents for cod larger than {{cvt|10|cm|in|0}} consisted of juvenile cod. In the northern North Sea, cannibalism was higher, at 10%.<ref name=Daan /> Other reports of cannibalism have estimated as high as 56% of the diet consists of juvenile cod.<ref name="Ponomarenko 1965 349–354">{{cite journal|last=Ponomarenko|first=I. Ja|title=Comparative characteristics of some biological indices of the bottom stages of 0-group cod belonging to the 1956, 1958, 1959, 1960 and 1961 year-classes|journal=Spec. Publ. Int. Comm. Northw. Atlant. Fish|year=1965|pages=349–354}}</ref>

When hatched, cod larvae are [[Precociality and altriciality|altricial]], entirely dependent on a yolk sac for sustenance until mouth opening at ~24 degree days.<ref name=":4">{{Cite journal |last1=Perez-Casanova |first1=J.C. |last2=Murray |first2=H.M. |last3=Gallant |first3=J.W. |last4=Ross |first4=N.W. |last5=Douglas |first5=S.E. |last6=Johnson |first6=S.C. |date=February 2006 |title=Development of the digestive capacity in larvae of haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) |url=https://linkinghub.elsevier.com/retrieve/pii/S0044848605003789 |journal=Aquaculture |language=en |volume=251 |issue=2–4 |pages=377–401 |doi=10.1016/j.aquaculture.2005.06.007|bibcode=2006Aquac.251..377P |url-access=subscription }}</ref> The stomach generally develops at around 240 degree days.<ref name=":4" /> Before this point the intestine is the main point of food digestion using pancreatic enzymes such as trypsin.<ref name=":4" />

==Reproduction==
[[Image:Gadus morhua (High Arctic, Canada).png|thumb|Atlantic cod in a High Arctic Lake in Canada. These cod resemble those of past Atlantic catches. Measuring {{cvt|47|-|53|in|cm|order=flip}} long and weighing between {{cvt|44|and|57|lb|kg|order=flip}}, it is easy to see that today's {{cvt|16|-|20|in|cm|order=flip}} commercially caught cod are less than half this size. A cod 2.7 times as long would weigh 20 times as much.]]
<gallery mode="packed">
Image:Gravid female cod.jpg|Spawning female in captivity
Image:Jonge kabeljauwen of gul nieuwsgierig bij een wrak-4885743.webm|Juveniles on a wreck in the [[North Sea]]
Image:Gadus morhua (head).jpg|Atlantic cod juvenile
Image:Gadus morhua Cod-2b-Atlanterhavsparken-Norway.JPG|Adult
</gallery>

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.<ref name=":1" /><ref name=":2" /> Their [[gonad]]s take several months to develop and most populations will spawn from January to May.<ref>{{Cite journal |last=ICES |date=2005 |title=Spawning and life history information for North Atlantic cod stocks |url=https://ices-library.figshare.com/articles/_/18624242 |doi=10.17895/ICES.PUB.5478}}</ref><ref>{{Cite journal |last1=Kjesbu |first1=Olav Sigurd |last2=Righton |first2=David |last3=Krüger-Johnsen |first3=Maria |last4=Thorsen |first4=Anders |last5=Michalsen |first5=Kathrine |last6=Fonn |first6=Merete |last7=Witthames |first7=Peter R. |date=April 2010 |editor-last=Marshall |editor-first=C. Tara |title=Thermal dynamics of ovarian maturation in Atlantic cod (Gadus morhua) |url=http://www.nrcresearchpress.com/doi/10.1139/F10-011 |journal=Canadian Journal of Fisheries and Aquatic Sciences |language=en |volume=67 |issue=4 |pages=605–625 |doi=10.1139/F10-011 |bibcode=2010CJFAS..67..605K |hdl=11250/108908 |issn=0706-652X|hdl-access=free }}</ref> For many populations, the spawning grounds are located in a different area from 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.<ref name="Ponomarenko 1965 349–354" /> 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.<ref name="Hutchings">{{cite journal |last=Hutchings |first=Jeffrey A |author2=Bishop, Todd D |author3=McGregor-Shaw, Carolyn R |date=1 January 1999 |title=Spawning behaviour of Atlantic cod: evidence of mate competition and mate choice in a broadcast spawner |journal=Canadian Journal of Fisheries and Aquatic Sciences |volume=56 |issue=1 |pages=97–104 |doi=10.1139/f98-216}}</ref>

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.<ref>{{Cite journal |last1=Kjesbu |first1=O S |last2=Solemdal |first2=P |last3=Bratland |first3=P |last4=Fonn |first4=M |date=1996-03-01 |title=Variation in annual egg production in individual captive Atlantic cod ( Gadus morhua ) |url=http://www.nrcresearchpress.com/doi/10.1139/f95-215 |journal=Canadian Journal of Fisheries and Aquatic Sciences |language=en |volume=53 |issue=3 |pages=610–620 |doi=10.1139/f95-215 |bibcode=1996CJFAS..53..610K |hdl=11250/109284 |issn=0706-652X|url-access=subscription }}</ref><ref>{{Cite journal |last=Kjesbu |first=O. S. |date=February 1989 |title=The spawning activity of cod, Gadus morhua L. |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1095-8649.1989.tb03302.x |journal=Journal of Fish Biology |language=en |volume=34 |issue=2 |pages=195–206 |doi=10.1111/j.1095-8649.1989.tb03302.x |bibcode=1989JFBio..34..195K |issn=0022-1112|url-access=subscription }}</ref> Each female will spawn between 2 hundred thousand and 15&nbsp;million eggs, with larger females spawning more eggs.<ref>{{Cite journal |last1=Skjæraasen |first1=Jon Egil |last2=Nilsen |first2=Trygve |last3=Kjesbu |first3=Olav S |date=2006-02-01 |title=Timing and determination of potential fecundity in Atlantic cod (''Gadus morhua'') |journal=Canadian Journal of Fisheries and Aquatic Sciences |volume=63 |issue=2 |pages=310–320 |doi=10.1139/f05-218 |bibcode=2006CJFAS..63..310S |issn=0706-652X}}</ref> Females release gametes in a ventral mount, and males then [[fertilization|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.<ref>{{Cite book|title=The DK Nature Encyclopedia|last=Burnie|first=David|publisher=DK Publishing, Inc|year=1998|isbn=0-7894-3411-3|location=New York|pages=[https://archive.org/details/dknatureencyclop0000unse/page/189 189]|url=https://archive.org/details/dknatureencyclop0000unse/page/189}}</ref>

== Parasites ==
{{See also|Diseases and parasites in cod}}

Atlantic cod act as intermediate, paratenic, or definitive hosts to a large number of parasite species: 107 taxa listed by Hemmingsen and MacKenzie (2001)<ref name="Perdiguero-Alonso 2008"/> and seven new records by Perdiguero-Alonso et al. (2008).<ref name="Perdiguero-Alonso 2008"/> The predominant groups of cod parasites in the northeast Atlantic were [[trematode]]s (19 species) and [[nematode]]s (13 species), including larval [[anisakid]]s, which comprised 58.2% of the total number of individuals.<ref name="Perdiguero-Alonso 2008"/> Parasites of Atlantic cod include [[copepod]]s, [[digenean]]s, [[monogenean]]s, [[acanthocephalan]]s, [[cestode]]s, [[nematode]]s, [[myxozoan]]s, and [[protozoan]]s.<ref name="Perdiguero-Alonso 2008"/>

== Fisheries ==
{{See also|Cod fisheries}}
[[Image:Atlantic cod, capture production, million tonnes, 1950-2022.svg|thumb|Global capture production of Atlantic cod (''Gadus morhua'') in million tonnes from 1950 to 2022, as reported by the [[Food and Agriculture Organization|FAO]]<ref>{{Cite web |title=Fisheries and Aquaculture - Global Production |url=https://www.fao.org/fishery/en/collection/global_production?lang=en |access-date=2024-05-06 |website=Food and Agriculture Organization of the United Nations (FAO)}}</ref>]]
Atlantic cod has been targeted by humans for food for thousands of years,<ref>{{Cite journal |last1=Ólafsdóttir |first1=Guðbjörg Ásta |last2=Pétursdóttir |first2=Gróa |last3=Bárðarson |first3=Hlynur |last4=Edvardsson |first4=Ragnar |date=2017-10-27 |editor-last=Corriero |editor-first=Aldo |title=A millennium of north-east Atlantic cod juvenile growth trajectories inferred from archaeological otoliths |journal=PLOS ONE |language=en |volume=12 |issue=10 |article-number=e0187134 |doi=10.1371/journal.pone.0187134 |issn=1932-6203 |pmc=5659679 |pmid=29077736|bibcode=2017PLoSO..1287134O |doi-access=free }}</ref> and with the advent of modern fishing technology in the 1950s there was a rapid rise in landings.<ref name=":3" /> Cod is caught using a variety of fishing gears including [[Bottom trawling|bottom trawls]], [[Longline fishing|demersal longlines]], [[Seine fishing|Danish seine]], [[jigging]] and [[Handline fishing|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.<ref name=":3">{{Cite journal |last1=Schijns |first1=Rebecca |last2=Froese |first2=Rainer |last3=Hutchings |first3=Jeffrey A |last4=Pauly |first4=Daniel |date=2021-10-27 |editor-last=Raicevich |editor-first=Sasa |title=Five centuries of cod catches in Eastern Canada |url=https://academic.oup.com/icesjms/article/78/8/2675/6359257 |journal=ICES Journal of Marine Science |language=en |volume=78 |issue=8 |pages=2675–2683 |doi=10.1093/icesjms/fsab153 |issn=1054-3139|doi-access=free |hdl=11250/2833698 |hdl-access=free }}</ref> [[International Council for the Exploration of the Sea|ICES]] and [[Northwest Atlantic Fisheries Organization|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 exceed 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 [[Collapse of the Atlantic northwest cod fishery|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===
{{main|Collapse of the Atlantic northwest cod fishery}}

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 {{cvt|300000|t|ST}} 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 {{cvt|800000|t|ST}} before a gradual decline set in. With the reopening of the limited cod fisheries in 2006, nearly {{cvt|2700|t|ST}} of cod were hauled in. In 2007, offshore cod stocks were estimated at 1% of what they were in 1977.<ref>{{cite news |url=https://www.cbc.ca/news/canada/newfoundland-labrador/n-l-funds-cod-fishery-research-on-15th-anniversary-of-moratorium-1.660303?ref=rss |archive-url=https://web.archive.org/web/20121104111114/http://www.cbc.ca/news/canada/newfoundland-labrador/story/2007/07/02/cod-moratorium.html?ref=rss |title=N.L. funds cod fishery research on 15th anniversary of moratorium |date=2 July 2007 |archive-date=4 November 2012 |url-status=live |publisher=[[CBC News]]}}</ref>[[Image:Atlantic cod landings western Atlantic.jpg|thumb|420x420px|Landings of Atlantic cod (''Gadus morhua'') in the western Atlantic from 1960 to 2019. Data source: NAFO.]]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&nbsp;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.{{citation needed|date=August 2022}}

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]].<ref name="Frank">{{cite journal|author=Kenneth T. Frank |author2=Brian Petrie |author3=Jae S. Choi |author4=William C. Leggett|s2cid=45088691 |year=2005|title=Trophic Cascades in a Formerly Cod-Dominated Ecosystem|journal=[[Science (journal)|Science]] |volume=308 |pages=1621–1623 |doi=10.1126/science.1113075|pmid=15947186|issue=5728 |bibcode=2005Sci...308.1621F }}</ref> 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&nbsp;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.<ref name="Press">{{cite news |author=The Associated Press |title=Cod Fishermen's Alarm Outlasts Reprieve on Catch Limits |work=The New York Times |date=12 February 2012 |url=https://www.nytimes.com/2012/02/12/us/cod-fishermens-alarm-outlasts-reprieve-on-catch-limits.html}}</ref>

===Northeast Atlantic cod===
[[Image:Atlantic cod landings eastern.jpg|thumb|418x418px|Reported landings of Atlantic cod (''Gadus morhua'') in the eastern Atlantic for each of the 16 populations/management units. Data source: ICES.]]
[[Image:NEAcodBiomass.png|thumb|Estimated biomass of the Northeast Arctic cod stock for the period 1946–2012, in million tons: Light blue bars represent the immature fraction of the stock, while the darker blue bars represent the spawning biomass.<ref>Arctic Fisheries Working Group of [[International Council for the Exploration of the Sea|ICES]], published in the ICES Report AFWG CM 2013, ACOM:05. The estimation method was standard [[virtual population analysis]].</ref>]]

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 [[International Council for the Exploration of the Sea|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 [[copepod]]s. 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 [[Atlantic herring|herring]]. The northeast Arctic cod also show [[Cannibalism (zoology)|cannibalistic]] behaviour. Estimated stock size was {{cvt|2260000|t|ST}} 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 {{cvt|200000|and|300000|t|ST}}. 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 <!-- (TAC) --> at {{cvt|27300|t|ST}}.<ref>{{cite web|url=http://portunusgroup.com/products/atlantic-cod/|archive-url=https://web.archive.org/web/20100509233101/http://portunusgroup.com/products/atlantic-cod/|url-status=usurped|archive-date=May 9, 2010|title=Our Products: Atlantic Cod|work=portunusgroup.com|access-date=22 November 2013}}</ref> [[Sustainable seafood advisory lists and certification#Guides and advisory lists|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|World War&nbsp;II]], but declined to a historic minimum of {{cvt|740000|t|ST}} in 1983. The catch reached a historic maximum of {{cvt|1343000|t|ST}} in 1956, and bottomed out at {{cvt|212000|t|ST}} in 1990. Since 2000, the spawning stock has increased quite quickly, helped by low fishing pressure. The total catch in 2012 was {{cvt|754131|t|ST}}, the major fishers being Norway and Russia.<ref>{{cite web|url=http://standardgraphs.ices.dk/download/HandlerDownload.ashx?year=2013&EcoRegion=137491&Species=44515|archive-url=https://web.archive.org/web/20140325115725/http://standardgraphs.ices.dk/download/HandlerDownload.ashx?year=2013&EcoRegion=137491&Species=44515|title=ICES Stock Database Disclaimer|access-date=25 March 2014|archive-date=25 March 2014}}</ref>

=== 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 [[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.<ref>{{Cite journal|last1=Berg|first1=Paul R.|last2=Jentoft|first2=Sissel|last3=Star|first3=Bastiaan|last4=Ring|first4=Kristoffer H.|last5=Knutsen|first5=Halvor|last6=Lien|first6=Sigbjørn|last7=Jakobsen|first7=Kjetill S.|last8=André|first8=Carl|date=2015-05-20|title=Adaptation to Low Salinity Promotes Genomic Divergence in Atlantic Cod (Gadus morhua L.)|journal=Genome Biology and Evolution|volume=7|issue=6|pages=1644–1663|doi=10.1093/gbe/evv093|issn=1759-6653|pmc=4494048|pmid=25994933}}</ref> 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.<ref>{{Cite journal|last1=MacKenzie|first1=BR|last2=Hinrichsen|first2=HH|last3=Plikshs|first3=M|last4=Wieland|first4=K|last5=Zezera|first5=AS|date=2000|title=Quantifying environmental heterogeneity:habitat size necessary for successful development of cod Gadus morhua eggs in the Baltic Sea|journal=Marine Ecology Progress Series|volume=193|pages=143–156|doi=10.3354/meps193143|bibcode=2000MEPS..193..143M |s2cid=3548719 |issn=0171-8630|doi-access=free}}</ref>

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.<ref>{{Cite journal|last1=Hemmer-Hansen|first1=Jakob|last2=Hüssy|first2=Karin|last3=Baktoft|first3=Henrik|last4=Huwer|first4=Bastian|last5=Bekkevold|first5=Dorte|last6=Haslob|first6=Holger|last7=Herrmann|first7=Jens-Peter|last8=Hinrichsen|first8=Hans-Harald|last9=Krumme|first9=Uwe|last10=Mosegaard|first10=Henrik|last11=Nielsen|first11=Einar Eg|date=2019|title=Genetic analyses reveal complex dynamics within a marine fish management area|journal=Evolutionary Applications|language=en|volume=12|issue=4|pages=830–844|doi=10.1111/eva.12760|issn=1752-4571|pmc=6439499|pmid=30976313|bibcode=2019EvApp..12..830H }}</ref> The immigration of eastern cod into the western Baltic management unit may mask a poor state of the populations in the western management unit.

==See also==
*[[Cod War]]
*''[[Sacred Cod]]''
*[[Cod as food]]
*[[Scrod]]

==Notes==
{{Reflist|group=n}}

==References==
This article incorporates CC BY-2.0 text from the reference.<ref name="Perdiguero-Alonso 2008">{{cite journal | last1 = Perdiguero-Alonso | first1 = D. | last2 = Montero | first2 = F. E. | last3 = Raga | first3 = J. A. | last4 = Kostadinova | first4 = A. | year = 2008 | title = Composition and structure of the parasite faunas of cod, ''Gadus morhua'' L. (Teleostei: Gadidae), in the North East Atlantic | journal = [[Parasites & Vectors]] | volume = 1 | issue = 1| page = 23 | doi = 10.1186/1756-3305-1-23 | pmid = 18638387 | pmc = 2503959 | doi-access = free }}</ref>
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{{Reflist}}

==External links==
* [https://fishbase.se/summary/Gadus-morhua.html FishBase]
* [http://www.ucd.ie/codtrace/codbio.htm Codtrace]
* [https://web.archive.org/web/20040405134957/http://www.cefas.co.uk/fishinfo/gadus_morhua.htm The Centre for Environment Fisheries and Aquaculture Science]
* [https://www.cdli.ca/cod/home1.htm The history of the northern cod fishery in Canada]
* [https://web.archive.org/web/20070620033246/http://www.ices.dk/committe/acfm/comwork/report/2006/oct/cod-347d.pdf ICES recommendation for the North Sea Cod stock (2007)]
* [https://web.archive.org/web/20070620033243/http://www.ices.dk/committe/acfm/comwork/report/2006/may/cod-arct.pdf ICES recommendation for the North East Arctic Cod stock (2007)]
* [https://web.archive.org/web/20090605190719/http://www.dfo-mpo.gc.ca/reports-rapports-eng.htm Reports on the status of Canadian fishing stocks, including cod]
* [https://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]
* [https://web.archive.org/web/20140714123943/http://www.fisherieswiki.org/species/show/1 Atlantic cod-Gadus morhua fishery profiles] Status of Atlantic cod fisheries, summarised in FisheriesWiki
* {{eol|206692}}
* View the [http://www.ensembl.org/Gadus_morhua/Info/Index/ Atlantic cod genome] in [[Ensembl]]
* [https://www.dfo-mpo.gc.ca/stats/commercial/sea-maritimes-eng.htm Government of Canada Seafisheries Landings]
* {{UCSC genomes|gadMor1}}
* {{sealifephotos|126436}}
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/.
{{commercial fish topics|state=expanded}}
{{cod topics}}

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[[Category:Fish described in 1758|Atlantic cod]]
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