Frontiers in Marine Science (Nov 2015)
Genetic integrity of European grayling (Thymallus thymallus L. 1758) within the Vienne River drainage basin after five decades of stockings
Abstract
European grayling of the upper Vienne River drainage basin represent the westernmost populations inside the natural distribution of the species. Since the 19th century, their extension across this sub-basin has been dramatically reduced by the harnessing of the river network for dams, initially serving mills but then hydroelectric power generation. Since the 1960s, local fishing authorities have attempted to compensate for these declines with stocking programs, but the efficiency of these efforts have never been accurately monitored. We aim to evaluate the genetic imprints of these stocking programs and thus provide an indirect measure of the long-term survival of stocked fish. Three target populations were analyzed at both mtDNA (Control Region) and nDNA levels (12 µSats), and compared to populations representative of surrounding drainage basins or fish farm facilities. Among 37 "wild" fish sequenced, only three control region haplotypes were identified, all belonging to the highly divergent Loire basin lineage. Two were specific to the Upper Vienne area, and one was observed in some individuals of the most downstream location, but previously described from the upper Allier sub-drainage. Microsatellite analysis of 87 "wild" fish also demonstrated a rather low diversity within each population (but typical for the Loire drainage) with all Upper Vienne individuals belonging to a single diagnosable unit. This genetic cluster was clearly distinct from all other samples including hatchery strains, which strongly supports its native origin. The only piece of evidence of a possible stocking contribution was the occurrence of the Allier haplotype, but it cannot be excluded that this haplotype was also native to this reach of river. The total lack of genetic impact of five decades of stocking deeply questions the efficacy of this management approach, at least in a regional context.
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