Norway pollock

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Norway pollock
Theragra finnmarchica.jpg
Scientific classification (disputed)
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gadiformes
Family: Gadidae
Genus: Theragra
Species: T. finnmarchica
Binomial name
Theragra finnmarchica
Einar Koefoed, 1956[1]

Theragra finnmarchica or Norway pollock is a rare fish of family Gadidae (codfish) only known from the Barents Sea. Until recently, its known range would have made it an endemic species to Norway, but one specimen was captured from Russian waters in 2004.[2] Moreover, current evidence suggests that T. finnmarchica is the same species as Alaska pollock (Theragra chalcogramma or Gadus chalcogrammus). The range of T. finnmarchica is fully separate from Alaska pollock, and the history of T. finnmarchica in the Barents Sea remains a mystery.[3]

Description[edit]

Theragra finnmarchica was described as a new species to science by Norwegian zoologist Einar Koefoed in 1956,[1] based on two specimens landed in Berlevåg, northern Norway, in 1932 (hence the Norwegian name, "Berlevågfisk"). Based on morphological differences, Koefoed considered T. finnmarchica a new species related to but separate from T. chalcogramma.

Current status[edit]

Until recently, Theragra finnmarchica was known only from very few specimens. Between 1957 and early 2002, seven specimens were caught.[4] However, in 2003–2004, 31 new specimens were caught. All specimens were large (465–687mm in total length) and caught in the coastal waters between Vesterålen in the west and Varangerfjord in the east. By 2006, 54 individuals had been recorded.[5]

Sequencing of mitochondrial DNA of two specimens of T. finnmarchica and 10 T. chalcogramma revealed no significant genetic differences, leading Ursvik et al.[6] to suggest that T. finnmarchica and T. chalcogramma are the same species. An analysis of a much larger material (44 T. finnmarchica and 20 T. chalcogramma) using both genetic and morphological methods led to similar conclusions.[5] While the putative species could not be separated genetically, they showed some consistent differences in morphological characters. Nevertheless, only one character showed no overlap. Byrkjedal et al.[5] conclude that T. finnmarchica should be considered a junior synonym of T. chalcogramma. These analyses also suggest that T. finnmarchica is a near relative of the Atlantic cod, and that both Alaska and Norway pollock should be moved to genus Gadus.[5]

T. finnmarchica is listed as Near Threatened in the 2010 Norwegian Red List for Species[7] based on criteria D1: "Very small or geographically very restricted population: Number of mature individuals". It is currently not listed in the IUCN Red List.

References[edit]

  1. ^ a b Koefoed, Einar (1956). "Theragra finnmarchica n. sp. A fish caught off Berlevåg allied to the Alaskan pollack, Theragra chalcogramma Pallas from the Bering Sea". Fiskeridirektoratets Skrifter, Serie Havundersøkelser. 11 (5): 3–11. 
  2. ^ Privalikhin, A. M.; Norvillo, G. V. (2010). "On the finding of a rare species—Norwegian pollock Theragra finnmarchica Koefoed, 1956 (Gadidae)—in the Barents Sea". Journal of Ichthyology. 50 (2): 143–147. doi:10.1134/S0032945210020013. 
  3. ^ Christiansen, Jørgen S.; Svein-Erik Fevolden; Ingvar Byrkjedal (2009). "Berlevågfisken - en nordnorsk torskefisk med aner i Stillehavet (The Gadoid Fish Berlevågfisk)". In Ann-Lisbeth Agnalt et al. (eds.). Kyst og havbruk 2009 (PDF). Fisken og havet. Bergen, Norway: Institute of Marine Research. pp. 54–55. 
  4. ^ Christiansen, Jørgen S.; Svein-Erik Fevolden; Ingvar Byrkjedal (2005-04-01). "The occurrence of Theragra finnmarchica Koefoed, 1956 (Teleostei, Gadidae), 1932–2004". Journal of Fish Biology. 66 (4): 1193–1197. doi:10.1111/j.0022-1112.2005.00682.x. ISSN 1095-8649. 
  5. ^ a b c d Byrkjedal, I.; D. J. Rees; Jørgen S. Christiansen; Svein-Erik Fevolden (2008-10-01). "The taxonomic status of Theragra finnmarchica Koefoed, 1956 (Teleostei: Gadidae): perspectives from morphological and molecular data". Journal of Fish Biology. 73 (5): 1183–1200. doi:10.1111/j.1095-8649.2008.01958.x. ISSN 1095-8649. 
  6. ^ Ursvik, Anita; Ragna Breines; Jørgen S. Christiansen; Svein-Erik Fevolden; Dag H. Coucheron; Steinar D. Johansen (2007-06-07). "A mitogenomic approach to the taxonomy of pollocks: Theragra chalcogramma and T. finnmarchica represent one single species". BMC Evolutionary Biology. 7 (1): 86. doi:10.1186/1471-2148-7-86. ISSN 1471-2148. PMC 1894972Freely accessible. PMID 17555567. 
  7. ^ "Theragra finnmarchica". Artsdatabanken.no. Retrieved 23 March 2012.