Assessing introgression of foreign strains in wild Atlantic salmon populations: variation in microsatellites assessed in historic scale collections

1. Genetic variation at five microsatellite loci was analysed in a collection of scales (1970–97) sampled from Atlantic salmon adults returning to the Nivelle River (South France).
2. Native and foreign fish (from an allochthonous Scottish stock introduced into the river to increase population size) were clearly identified as all foreign individuals released in the river were physically marked.
3. Introgression of foreign genes into the native gene pool has occurred, although the reproductive success of foreign Atlantic salmon in the wild was lower than that of native individuals.
4. The utility of old scale samples for investigating the impact of foreign stocking on wild fish populations is demonstrated in this work.