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ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01029

Long-term stocking practices threaten the original genetic diversity of the southernmost European populations of Atlantic salmon Salmo salar

Ana Almodóvar*, Sheila Leal, Graciela G. Nicola, José Luis Hórreo, Eva García-Vázquez, Benigno Elvira

*Corresponding author:

ABSTRACT: Many Atlantic salmon Salmo salar populations in Europe are threatened by previous stocking with foreign hatchery strains. Temporal patterns of genetic characteristics of salmon from northern Spain, the southernmost European populations, were compared before and after species decline and heavy stocking with specimens from northern Europe. Eleven microsatellite loci were analysed in archival (scales from 1958–1960) and contemporary (2007–2008) samples from the River Sella. Temporal analyses revealed a similar heterozygosity between archival and contemporary samples, despite a drastic decrease in population abundance, while the contemporary sample showed a higher allelic richness due to the occurrence of foreign alleles. Considering only the alleles with at least 4% frequency in the archival sample, two alleles exclusive of the River Sella were absent in the contemporary sample and fourteen alleles showed a decrease of at least 4% frequency. Four alleles common in Scotland showed a high occurrence in the contemporary sample, so they are good candidates as markers of introgression of foreign genes. The heavy stocking made with non-native Scottish broodstocks between 1970–1990 caused the introgression found in the contemporary sample compared with the pristine population. Adjusting estimates of effective number of breeders considering overlapping generations (NbLD(adj)), effective population size (Ne(adj)) estimated from Nb(adj) and estimated number of breeders with the Sibship assignment method (NbSIB) showed an abrupt decrease. The very low effective size values found in the contemporary sample, together with the detrimental synergy between genetic drift and high rates of introgression, represent a severe risk for the conservation of native salmon.