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

Abstract

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 I A 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 I B 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 I A 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.