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Boreogadus

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(Redirected from Boreogadus saida)
"Polar cod" redirects here. For the related species which shares its common names, see Arctogadus glacialis.
Boreogadus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gadiformes
Family: Gadidae
Genus: Boreogadus
Günther, 1862
Species:
B. saida
Binomial name
Boreogadus saida
(Lepechin, 1774)
Synonyms
  • Gadus saida Lepechin, 1774
  • Merlangus polaris Sabine, 1824
  • Boreogadus polaris (Sabine, 1824)
  • Pollachius polaris (Sabine, 1824)
  • Gadus fabricii Richardson, 1836
  • Gadus agilis Reinhardt, 1837

Boreogadus saida, known as the polar cod[1][2][3] or as the Arctic cod,[1][4][5] is a fish of the cod family Gadidae, related to the true cod (genus Gadus). Another fish species for which both the common names Arctic cod and polar cod are used is Arctogadus glacialis.

Species Description

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B. saida has a slender body, a deeply forked tail, a projecting mouth, and a small chin barbel. It has three dorsal fins and two anal fins, which are all separate from each other. The caudal fin is concave, the pectoral fins reach beyond the end of the first dorsal fin, and the pelvic fins are elongated rays. The lateral line is interrupted along the entire length of the fish.[2] It is plainly coloured with brownish spots and a silvery body. Greenlandic Inuit fishers have described two morphotypes of Arctic cod, a lighter-colored variety and a darker-colored variety.[6] Arctic cod are frequently misidentified as polar cod (Arctogadus glacialis) during their larval and early juvenile stages. The species can be differentiated through the analysis of otoliths or molecular data.[7]

Arctic cod grow to an average length of 25 cm (9.8 in), and a maximum length of 40 cm (16 in)[2].

Geographical Distribution

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This species is found further north than any other fish[8] (beyond 84°N) with a circumpolar distribution spanning the entire North Polar Basin above Russia, Alaska, Canada, and Greenland.[9] More specifically, in the Arctic Ocean, Bering Sea, Chukchi Sea, Beaufort Sea, Hudson Bay, Baffin Bay, Greenland Sea, Barents Sea, Kara Sea, Laptev Sea and the Eastern Siberian Sea.[6] Arctic cod occur in almost all Arctic and Subarctic marine habitats, ranging from coastal waters, the mesopelagic zone, the deeper central Arctic Ocean, and under ice. Arctic cod are the most abundant demersal Arctic species in the Beaufort Sea.[6]

Arctic cod exhibit diel vertical migration patterns during winter and spring, but migration is not observed during summer.[6]

Habitat

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Early life stages of Arctic cod are found near the surface in both ice-covered and open water, however, adults are found deeper in the water column.[10] In the Canadian Arctic, Arctic cod will separate vertically in the water column by size, with younger fish in the upper 100 meters of the water column, and juvenile and immature fish below 200 meters.[11]

The image shows a close-up view of five Boreogadus saida lying horizontally in a pile within a plastic basket with orange slats. Each fish has a number label placed above it, ranging from 1 to 5, helping distinguish them from one another. These fish appear similar in shape and color, with silvery bodies, large eyes, and prominent mouths. However, the top three fish, labelled 1 to 3, are slightly darker in color. The bottom two fish, labelled 4 to 5, are slightly lighter in color and smaller.
Dark (1,2,3) and Light (4,5) morphotypes described by Inuit fishers[6].

Arctic cod can also be found in dense schools near glacial fronts and polynyas.[6] Subsurface plumes of freshwater discharged from glaciers create foraging hotspots, aggregating zooplankton where they are stunned or killed by osmotic shock, making them easy prey for Arctic cod.[6] Greenlandic Inuit fishers have reported the presence of Arctic cod near the Sermilik and Sermeq Avannarleq glaciers, located off the southwestern coast of Greenland.[6]

Reproduction and Life Stages

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Arctic cod have multiple reproductive cycles throughout their lives.[10] Arctic cod are an r-selected species, meaning they reach maturity early and produce high numbers of offspring. On average, a female will lay between 9,000 to 21,000 eggs.[2] Spawning occurs between September and April, and peaks between January and February.[10] Spawning locations are not fully known, but spawning is suggested to occur in the Barens Sea to the southwest of the Svalbard Island chain, and the Kara and Pechora seas.[10] In the Canadian Arctic, spawning is suggested to occur near the Franklin and Darney bays. In the Pacific Arctic, spawning is suggested to occur in the northern Bering Sea, Chukchi Sea, and Kotzebue Sound. Greenlandic Inuit fishers have noted a spawning area near Saattut Island.[6]

The development and viability of Arctic cod eggs depend heavily on temperature. Eggs develop normally between -1.5ºC and 3ºC; however, hatching success severely declines above 2ºC.[10] Incubation time decreases as temperatures increase: at 1.5ºC, it will take 79 days for larvae to hatch, but at 3.8ºC, incubation time decreases to 29 days.[10] In the Canadian Arctic, Arctic cod hatch under the ice from January to July and remain under the ice until Fall.[11]

Arctic cod larvae can be between 3.5mm and 7mm after hatching; however, in experimental settings, length after hatching decreases when temperatures increase. The larvae have a higher temperature tolerance range than the eggs. Larvae are euryhaline, meaning that they can withstand different salinity concentrations.[10] Therefore, they can be found in areas with glacial meltwater, in river mouths, or in ice-covered areas. The larger the larvae is, the higher the chance of survival it has, especially during the transition between yolk feeding to exogenous feeding.[10]

Juvenile Arctic cod have a much larger temperature tolerance range than larvae and eggs, tolerating temperatures from 0ºC to 12ºC.[10] Arctic cod exhibit isometric growth, but allometric fat storage.[10] Juvenile Arctic cod are found in the pelagic zone of the water column and descend deeper after their first summer. Some juveniles are found within cavities in sea ice.[10] It is hypothesized that juveniles that have hatched late remain sympagic to avoid predation from adult Arctic cod and competition from other juvenile Arctic cod. Arctic cod reach sexual maturity at around age 2 to 3.[10]

Adult Arctic cod can tolerate temperatures up to 13.5ºC and function best between 3ºC and 10ºC.[10] Adults are found deeper than 100 meters in the water column and are not associated with sea ice.[10]

Adaptations to Arctic Waters

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Arctic cod have several adaptations that allow them to function in freezing polar waters where most other species could not. These waters, though incredibly cold, have a lower freezing point due to their high salt content. While Arctic cod do have higher salt concentrations in their bodies compared to fish in warmer waters, this only accounts for half of the decrease in the cod’s freezing point.

It is a hardy fish that survives best at temperatures of 0–4 °C (32–39 °F), but may tolerate colder temperatures owing to the presence of antifreeze protein compounds in its blood. They group in large schools in ice-free waters.

B. saida feeds on plankton and krill. It is in turn the primary food source for narwhals, belugas, ringed seals, and seabirds. They are fished commercially in Russia.

Although very populous throughout the Arctic Ocean, it still can be a victim to population threats through human actions. Global warming has increased steadily over the past years, and it has caused an increase in ocean temperatures of the Arctic Ocean. Boreogadus saida live in extremely cold water temperatures, and therefore they have adapted to the cold. Their larvae must be in 3 °C to hatch normally, and a rise in ocean temperatures can easily lead to phenotypic changes of this cod species. Possible alterations of the species due to increasing ocean temperatures include, smaller size, reduced fecundity, earlier maturation, and increased investment in reproduction at an early age for some.

References

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  1. ^ a b Froese, Rainer; Pauly, Daniel (eds.). "Boreogadus saida". FishBase. April 2012 version.
  2. ^ a b c d Daniel M. Cohen; Tadashi Inada; Tomio Iwamoto & Nadia Scialabba, eds. (1990). FAO species catalogue. Vol. 10. Gadiform fishes of the world (Order Gadiformes). An Annotated and Illustrated Catalogue of Cods, Hakes, Grenadiers and other Gadiform Fishes Known to Date. Food and Agriculture Organization of the United Nations. pp. 27–29. ISBN 978-92-5-102890-2.
  3. ^ Polar cod Institute of Marine Research, Norway
  4. ^ Arctic Cod: Boreogadus saida Arctic Ocean Diversity. Census of Marine Life.
  5. ^ Arctic Cod Archived November 22, 2011, at the Wayback Machine Aquatic species. Fisheries and Oceans Canada.
  6. ^ a b c d e f g h i Bouchard, Caroline; Farnole, Patrick; Lynge-Pedersen, Kristine; Dahl, Parnuna Egede; Christiansen, Henrik (2023-06-22). "Arctic cod ( Boreogadus saida ) in fjord and glacial habitats: a collaborative study with Uummannap Kangerlua fishers". Arctic Science. doi:10.1139/as-2023-0014. ISSN 2368-7460.
  7. ^ Bouchard, Caroline; Mollard, Salomé; Suzuki, Keita; Robert, Dominique; Fortier, Louis (2016-06-01). "Contrasting the early life histories of sympatric Arctic gadids Boreogadus saida and Arctogadus glacialis in the Canadian Beaufort Sea". Polar Biology. 39 (6): 1005–1022. doi:10.1007/s00300-014-1617-4. ISSN 1432-2056.
  8. ^ Christiansen JS (2012): TUNU Programme: Euro-Arctic marine fishes - Adaptation and evolution. pp 35-50. In: Adaptation and Evolution in Marine Environments, Vol. 1: The Impacts of Global Change on Biodiversity. Springer-Verlag, Berlin Heidelberg.
  9. ^ Edwards, A.J. (June 1992). "FAO Species Catalogue. Vol. 10. Gadiform fishes of the world (Order Gadiformes). An annotated and illustrated catalogue of cods, hakes, grenadiers and other gadiform fishes known to date". Marine Pollution Bulletin. 24 (6): 442. Bibcode:1992MarPB..24..326E. doi:10.1016/0025-326X(92)90599-2. Retrieved 22 November 2023.
  10. ^ a b c d e f g h i j k l m n Geoffroy, Maxime; Bouchard, Caroline; Flores, Hauke; Robert, Dominique; Gjøsæter, Harald; Hoover, Carie; Hop, Haakon; Hussey, Nigel E.; Nahrgang, Jasmine; Steiner, Nadja; Bender, Morgan; Berge, Jørgen; Castellani, Giulia; Chernova, Natalia; Copeman, Louise (2023-08-08). "The circumpolar impacts of climate change and anthropogenic stressors on Arctic cod ( Boreogadus saida ) and its ecosystem". Elem Sci Anth. 11 (1). doi:10.1525/elementa.2022.00097. ISSN 2325-1026.
  11. ^ a b Herbig, Jennifer; Fisher, Jonathan; Bouchard, Caroline; Niemi, Andrea; LeBlanc, Mathieu; Majewski, Andrew; Gauthier, Stéphane; Geoffroy, Maxime (2023-09-22). "Climate and juvenile recruitment as drivers of Arctic cod ( Boreogadus saida ) dynamics in two Canadian Arctic seas". Elem Sci Anth. 11 (1). doi:10.1525/elementa.2023.00033. ISSN 2325-1026.

Pepijn De Vries, Jacqueline Tamis, Jasmine Nahrgang, Marianne Frantzen, Robbert Jak, Martine Van Den Heuvel-Greve, Chris Klok, Lia Hemerik (2021). Quantifying the consequence of applying conservative assumptions in the assessment of oil spill effects on polar cod (Boreogadus saida) populations.

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