Changes in stock composition of annual Atlantic salmon catches in the Baltic Sea on basis of DNA-microsatellite data and Bayesian estimation

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DNA level information, an 8-loci microsatellite baseline database of 26 Atlantic salmon (Salmo salar L.) stocks, has been analysed using a Bayesian estimation method to estimate stock and stock group proportions of Finnish catches in the Baltic Sea area. The proportions of five stock groups important in terms of fisheries management were assessed in catch samples taken in three years (2000, 2002 and 2003). The catch samples were representative of Finnish fishery in the Gulf of Bothnia and Gulf of Finland. In the Gulf of Bothnia area, catches are composed of three major units: wild fish, Finnish hatchery fish and Swedish hatchery fish. Owing to decreasing amounts of hatchery fish, the proportion of wild fish shows a rising trend in catches from the Åland Sea, increasing from 43% to 76% in 2000-2003. In the eastern Gulf of Finland, the largest contribution was made by local hatchery fish, the Neva salmon, which is released by Finland, Russia and Estonia. Both wild and hatchery fish occurred in the northern Gulf of Bothnia in 2003, but not in 2002. In the western part of the Gulf of Finland, fish originating from the Main Basin made a substantial contribution. The threatened, eastern, Estonian wild stocks were recorded only in the western part of the Gulf, with a 4% proportion.