Atlantic cod - Gadus morhua 




Summary of issues specific to the Baltic region

There is one large Baltic cod population that spawn at a single site east of Bornholm. Baltic cod is genetically distinct and adapted to the brackish environment.

Current management regulations

Baltic cod is one of the major cod stocks globally. Presently ICES identify two popluations of cod in the Baltic: one large population that spawn east of Bornholm and one population spawning west of Bornholm.

Gaps between management and scientific evidence

It is unclear if there are several spawning populations within the western population. Moreover the extent of spillover from the eastern cod stock to areas west of Bornholm is uncertain.



Species Number of  genetic studies Baltic population structure Baltic population diversity Baltic effective population size Temporal data Genetic risks Management recommendations
> 10 One eastern population and one to several western populations Low One estimate of >500 Some Eastern cod population may not be replenished if depleted
Two stocks


Summary of key published genetic information

The Baltic harbours one large population that spawn east of Bornholm and one to several population spawning west of Bornholm. Historically spawning occured also in the Gdansk deep and off Gotland but these populations seems to have gone extinct. There are spawning aggregations in Öresund and Kattegat which are genetically distinct from both the eastern Baltic cod and North Sea cod. These findings are supported in several studies using different types of neutral and coding genetic markers. These studies indicate that the eastern cod population has been isolated for a long time, possibly already from the time of colonisation 6-8 000 BP. Adaptations to the Baltic Sea environment include a different hemoglobin type, egg bouyancy, sperm swimming characteristics and spawning period.

Key publications

Sick K 1965. Haemoglobin polymorphism of cod in the Baltic and the Danish Belt Sea. Hereditas 54: 19-48. Abstract

Nissling A, Westin L 1997. Salinity requirements for successful spawning of Baltic and Belt Sea cod and the potential for cod stock interactions in the Baltic Sea. Mar Ecol Progr Ser 152: 261-271. Abstract

Nielsen EE et al 2003. Evidence of a hybrid-zone in Atlantic cod (Gadus morhua) in the Baltic and the Danish Belt Sea revealed by individual admixture analysis. Mol Ecol 12: 1497-1508 PubMed

Andersen Ø, Wetten OF, De Rosa MC, André C et al 2009. Haemoglobin polymorphisms affect the oxygen binding properties in Atlantic cod populations. Proc Royal Soc B 276: 833–841. PubMed

Larsen PF, Nielsen EE, Meier K, Olsvik PA, Hansen MM, Loeschcke V 2011. Differences in salinity tolerance and gene expression between two populations of Atlantic Cod (Gadus morhua) in response to salinity stress. Biochem Genet DOI 10.1007/s10528-011-9490-0. PubMed

More information about cod at IUCN - International Union for Conservation of Natural Resources  

CONTRIBUTOR (January 2012)
Carl André, University of Gothenburg, Sweden

Responsible editor: Carl André, University of Gothenburg, Sweden 
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