Abstract
While the stocking of captive-bred fish has been occurring for decades and has had substantial immediate genetic and evolutionary impacts on wild populations, its long-term consequences have only been weakly investigated. Here, we conducted a spatiotemporal analysis of 1428 Atlantic salmon sampled from 1965 to 2006 in 25 populations throughout France to investigate the influence of stocking on the neutral genetic structure in wild Atlantic salmon (Salmo salar) populations. On the basis of the analysis of 11 microsatellite loci, we found that the overall genetic structure among populations dramatically decreased over the period studied. Admixture rates among populations were highly variable, ranging from a nearly undetectable contribution from donor stocks to total replacement of the native gene pool, suggesting extremely variable impacts of stocking. Depending on population, admixture rates either increased, remained stable, or decreased in samples collected between 1998 and 2006 compared to samples from 1965 to 1987, suggesting either rising, long-lasting or short-term impacts of stocking. We discuss the potential mechanisms contributing to this variability, including the reduced fitness of stocked fish and persistence of wild locally adapted individuals.
Highlights
Anthropogenic pressures on natural populations have the potential to alter the distribution of genetic diversity within and among wild populations
Ecology and Evolution published by John Wiley & Sons Ltd
In line with Perrier et al (2011b, 2013) this study confirms that stocking may have a relatively high impact on the distribution of genetic diversity within and among populations
Summary
Anthropogenic pressures on natural populations have the potential to alter the distribution of genetic diversity within and among wild populations. Genetic information from archived fish scales can allow for inferences to be made about the recent evolution of genetic structure among wild fish populations (Nielsen et al 1999; Nielsen and Hansen 2008). The neutral genetic structure among numerous Salmonid populations is thought to have been recently affected by various increasing anthropogenic pressures such as rapid contemporary climate change, habitat degradation and disconnection, fish farm escapees, and stocking. Farmed escapees are responsible for low to modest modifications of population genetic diversity in relation to the density of native populations (Glover et al 2012).
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