Genetic refuges for a self-sustained fishery: experience in wild brown trout populations in the eastern Pyrenees

Management policies balancing harvest and conservation of natural populations of fish are difficult to establish, both scientifically and politically. This issue is particularly difficult when those populations represent native genetic resources. Since 1997, several brown trout populations in the eastern Pyrenees Mountains (Spain) were designated as 'genetic refuges' under varying fishing regulations, where releases of hatchery-origin fish are not permitted. We analysed genetic variation in samples of brown trout from six of those refuge populations and four non-refuge populations within the same region. Each population was sampled in four separate years: 1993, 1999, 2004 and 2006. Our analyses were based on a diagnostic allele (LDH-C*90) that distinguishes native and exogenous hatchery populations. Comparisons were based on stocking histories before and after refuge designations and on three management strategies: fished, unfished and catch-and-release. Overall, we detected significant genetic introgression resulting from past stocking practices despite the current restriction of hatchery releases imposed by the recent genetic refuge policy. However, this new policy has prevented detectable introgression from increasing throughout the region and together with additional measures on length and number of captured fish is contributing to self-sustained fisheries that are achieving conservation goals. Quick acceptance of 'genetic refuges' by anglers in one particular river, the Ter River basin, has been a key factor in protecting native gene pools compared with the Segre River basins where refuges were not readily accepted.