Effects of Geomorphological Structures on Genetic Differentiation among Brown Trout Populations in a Northern Boreal River Drainage

Abstract
The genetic structure of brown trout Salmo trutta was studied within the drainage of the River Ammerån, a tributary of the River Indalsälven in central Sweden. Samples from seven locations were analyzed with respect to five microsatellite loci. Allele frequencies in all samples were consistent with Hardy−Weinberg expectations. Allele frequencies at three resampled locations did not differ significantly between years. Allele frequencies were significantly different among locations, however, even over short waterway distances of less than 50 km. No pattern of isolation by distance was evident because genetic differences were correlated with subdivision by geomorphological structures (e.g., rapids and impassable waterfalls). We argue that each tributary of the River Ammerån should be regarded as an independent unit demanding an individual conservation and management plan.