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In brown trout (Salmo trutta L.), spatial patterns of population structure have been extensively studied. However, less attention has been paid to the short-term temporal stability of genetic diversity and factors modeling its distribution. Brown trout populations from three tributaries of the Esva River were genetically monitored in 2010 and 2011 by microsatellite loci. Boom-and-bust population dynamics associated with fluctuations of water flows explained large variations in population size, but they did not cause significant changes in genetic diversity. The pattern of population structure differed between the two sampling years because of a group of hatchery individuals identified in 2011. The native genetic diversity distribution was stable and supported the occurrence of two major genetically homogeneous populations, where populations from the Chaballos stream were different from the Viella-Choudral group. This pattern slightly fits a geographical model of structure, but the high isolation of the Chaballos populations is a consequence of artificial barriers that have restricted migration. Altitude and distance to the river outlet also affected the connectivity between populations. The understanding of factors modelling population structure will be of assistance in designing strategies to restore gene flow, critical to maintaining genetic diversity in freshwater fish species inhabiting unstable hydrologic environments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Populations living on the periphery of a species range are subjected to intense habitat pressures that stress their vulnerability to threats. South Iberian brown trout (Salmo trutta) populations are located on the southwestern boundary of the species range in Europe. This region has been described as a contact zone between Atlantic and Mediterranean populations in other fish species, and allozyme data detected natural hybridization between native Atlantic and Mediterranean brown trout in this area. Nevertheless, native pattern of populations relationships are threatened by hybridization with exogenous hatchery fish. Allozyme data and complete mtDNA control region sequences were used to analyse the ongoing processes of human mediated hybridization between native and hatchery brown trout in this region. Estimates of the persistence of hatchery genes detected a high level of introgression in some of the sampled locations (hatchery ancestry more than 25% in GF-1, GF-2 and GF-3), but results differed from both kinds of markers. The low intrapopulation diversity (H s =0.051) indicated that genetic drift could explain discrepancies between markers. At individual level, the complementary use of both markers detected more hatchery origin fish than those detected by the use of a single technique. Based on these results, the importance of considering a large number of genetic markers to evaluate introgression accurately is emphasized. The ability of the current management policies to the protection and conservation of marginal populations that retain complex and special evolutionary histories such as those studied is also questioned. [Copyright &y& Elsevier]

Genetic changes in the population structure of brown troutSalmo truttain the eastern Pyrenees were monitored during the 1990s. Stocking with cultivated exogenous fish has resulted in introgressed populations where those with higher introgression coefficients also have the highest values of heterozygosity. Nevertheless, this increase of local diversity reflects a decrease of genetic differentiation between populations and loss of native alleles. These changes obscure native gene pools and modify evolutionary distinctions among native brown trout populations. [ABSTRACT FROM AUTHOR]

1. The brown trout (Salmo trutta) represents one of the main freshwater resources in Spain, but habitat alterations and overharvesting have contributed to the decline or disappearance of numerous natural populations. In addition, reinforcement programs of wild populations based on releases of hatchery reared fish of exogenous origin compromise the conservation of remnant native trout resources. 2. We present allozymic data from Central Spain trout populations including stocked and unstocked populations. Although the levels of genetic variation observed were low and affected by hatchery releases (p = 18.23%, Ho= 3.39%), they were within the range observed in other European areas. 3. The effective introduction of hatchery reared fish is genetically homogenising the populations in the studied area and disturbing the ancestral pattern of genetic variation that distinguishes the Tajo and Duero basins. Within the eight natural populations analysed, seven had alleles assigned to the foreign trout. The introgression in these populations, following the LDH-5*90 allele frequency, ranged between 2% and 29.4%, but those values are not in concordance with the respective stocking effort undertaken in each population. Moreover, the release of hatchery-reared fish does not solve the problems related to the reduced size of wild populations and their recruitment instability. [ABSTRACT FROM AUTHOR]

Evidence of different degrees of genetic interactions of exogenous hatchery fish with native populations was electrophoretically obtained from collections of brown trout from four heavily fished areas and eight adjacent protected and unfished areas in northeastern Spain. Although some degree of hybridization or introgression was detected in each collection based on fixed differences between hatchery and native fish at the LDH-C * locus and less distinct differences were found at three other loci (sMDH-A2*, IDHP-2*, IDHP-3*), fished populations had significantly lower levels of hatchery genes than protected ones. The greater persistence of native fish in areas that were fished and stocked appeared to reflect a greater susceptibility of hatchery-reared fish to angling. Although it remains uncertain whether this difference is innate or a reflection of hatchery rearing, stocking was ineffective in enhancing the recipient population in the exploited river. These data suggest that different strategies may be needed for protection of native populations in fished and protected areas and that more intense measures may be required in the latter instance. [ABSTRACT FROM AUTHOR]