Lifetime success and interactions of farm salmon invading a native population

Farm Atlantic salmon escape and invade rivers throughout the North Atlantic annually which has generated growing concern about their. impacts on nativ e salmon populations. A large-scale experiment was therefore undertaken in order to quantify the lifetime success and interactions of farm salmon inva ding a Norwegian river. Sexually mature farm and native salmon were genetic ally screened, radio tagged and released into the River Imsa where no other . salmon had been allowed to ascend. The farm fishes were competitively and reproductively inferior, achieving less than one-third the breeding succes s of the native fishes. Moreover, this inferiority was scs biased, being mo re pronounced in farm males than females, resulting in tho principal route of gene flow involving native males mating with Farm females. There were al so indications of selection against farm genotypes during early survival bu t not thereafter. However, evidence of resource competition and competitive displacement existed as the productivity of the native population was depr essed by more than 30%. Ultimately the lifetime reproductive success (adult to adult of the farm fishes was 16% that of the native salmon. Our results indicate that such annual invasions have the potential for impacting on po pulation productivity, disrupting local adaptations and reducing the geneti c diversity of wild salmon populations.