The scnDNA locus Pan I reveals concurrent presence of different populations of Atlantic cod (Gadusmorhua L.) within a single fjord

The genetic population structure of Atlantic cod in Ullsfjord, north Norway, was studied by analysing allele frequencies at the scnDNA locus pantophysin (Pan I) in 2597 fish. The Pan I frequencies displayed distinct horizontal stratification within the fjord, which persisted over seasons and years. In the spring spawning season, mature cod predominated by the Pan IA allele typical for Norwegian coastal cod, inhabited the inner, more isolated part of the fjord, whereas immature cod predominated by the north-east Arctic cod typical Pan IB allele were found in the outer part open to Barents Sea water. Young of the year caught in the autumn displayed a predominance of the Pan IA allele throughout the fjord. The present study provides evidence for the existence of a local stock of breeding coastal cod in the inner part of Ullsfjord, whereas the outer part is likely to represent feeding grounds for young year classes of north-east Arctic cod. Comparisons with previous studies indicate, however, that there is temporal variation in the relative abundance of north-east Arctic cod and Norwegian coastal cod in the outer part of the fjord.