Effects of geomorphological structures on genetic differentiation among brown trout populations in a Northern Boreal river drainage

The genetic structure of brown trout Salmo trutta was studied within the dr ainage of the River Ammeran, a tributary of the River Indalsalven in centra l Sweden. Samples from seven locations were analyzed with respect to five m icrosatellite loci. Allele frequencies in all samples were consistent with Hardy - Weinberg expectations. Allele frequencies at three resampled locati ons did not differ significantly between years. Allele frequencies were sig nificantly different among locations, however, even over short waterway dis tances of less than 50 km. No pattern of isolation by distance was evident because genetic differences were correlated with subdivision by geomorpholo gical structures (e.g., rapids and impassable waterfalls). We argue that ea ch tributary of the River Ammeran should be regarded as an independent unit demanding an individual conservation and management plan.