Sea migration patterns in the Atlantic salmon: a comparative study of two stocks and their hybrids

The sea migration patterns of the Atlantic salmon in the Baltic Sea was examined in a crossing and transplantation experiments. Two genetically different salmon stocks originating from rivers Neva and Iijoki and their hybrids were released as smolts (6 561, 485 and 993 smolts, respectively) into the estuary of the Kymijoki, in the Gulf of Finland. The spatial and temporal marine distributions of the experimental groups were analysed from tag recovery data received during 31/2 years (42 months) after release. The recovery rate was 6.5%–17.5%. Multi-way contingency analysis showed that the spatial distributions of the stocks differed in the sea. The feeding migration distance of the hybrids was longer than that of the parental Neva stock, and the male line affected the spatial marine distribution of the hybrids more than did the female line. Genetically different parental stocks showed no significant difference in migratory behaviour in this experiment. No differences were recorded in the temporal distributions of the stocks in the sea. The observed differences confirm that the sea migration pattern is a stock-specific, inherited trait. The longer migration pattern of hybrid stocks than that of parental stocks may be due to coadaptive gene combinations that break down in crossing or to a high phenotypic variation in parents within the stocks.