We used microsatellite markers to investigate levels and structuring of genetic diversity in trout (Salmo trutta L.) sampled from 16 rivers along the south coast of Cornwall in southwest England. This region is characterised by many small coastal streams with a few larger catchments. At a regional level, genetic structuring of contemporary populations has been influenced by a combination of events, including the last Ice Age and also more recent human activities over the last millennium. All populations are shown to have gone through strong genetic bottlenecks, coinciding with increased exploitation of mineral resources within catchments, beginning during the Medieval period. At more local levels, contemporary human-induced habitat fragmentation, such as weir and culvert construction, has disproportionally affected trout populations in the smaller catchments within the study area. However, where small catchments are relatively unaffected by such activities, they can host trout populations with diversity levels comparable to those found in larger rivers in the region. We also predict significant future loses of diversity and heterozygosity in the trout populations inhabiting small, isolated catchments. Our study highlights how multiple factors, especially the activity of humans, have and continue to affect the levels and structuring of genetic diversity in trout over long timescales.

1174 fish from 26 southern Cornish (UK) streams and rivers were screened for variation using 18 sets of microsatellite primers resulting in the amplification of 19 loci. Primers for locus One102 amplify two loci with non-overlapping size ranges and therefore could be scored independently. Foward primers were labelled with flourescent tags and PCR products were separated on a Beckman-Coulter CEQ8000 automatic DNA sequencer and scored using it's associated fragment analysis software.

Data file is in GenAlEx input format. Alleles are scored as fragment lengths and missing data is scored as zero.