Loss of regional population structure in Atlantic salmon, Salmo salar L., following stocking

Many wild Atlantic salmon populations have been stocked with cultured fish during the past century. To evaluate the degree and the direction of the resulting genetic changes in wild southern European populations of Atlantic salmon, the variation at microsatellite loci was examined in historical and modern scale samples from five Spanish and two French rivers. Significant genetic differentiation between neighbouring rivers, which is typical of Atlantic salmon and which existed before stocking, appears to have been lost after only a decade of stocking with fish of foreign origin. Apparent introgression of foreign-origin genes into local gene pools was detected in the populations studied. These results indicate that stocking risks the loss of genetic diversity in wild salmon populations.