Spatio‐temporal genetic variability in sea trout (<i>Salmo trutta</i>) populations from north‐western Spain

Summary 1. Genetic variation at five microsatellite loci was investigated in six sea trout ( Salmo trutta ) populations to describe their spatio‐temporal genetic variation in north‐western Spain. We observed significant genetic variation between river basins, and isolation by distance with restricted gene flow between neighbouring rivers, which suggests an important homing behaviour. 2. Despite these populations suffering a serious demographic decline during 1998, we did not detect any reduction in their genetic variation, suggesting a reasonably high effective population size and temporal stability. 3. Genetic differences among rivers should be taken into account in future management activities. Given the high genetic variability and the temporal stability observed, we believe that no supportive breeding programmes are presently needed in these populations.