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Endangered Species Research

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ESR 41:303-317 (2020)  -  DOI:

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

Ana Almodóvar1,*, Sheila Leal1, Graciela G. Nicola2, José Luis Hórreo3, Eva García-Vázquez4, Benigno Elvira1

1Department of Biodiversity, Ecology and Evolution, Complutense University of Madrid (UCM), Madrid 28040, Spain
2Department of Environmental Sciences, University of Castilla-La Mancha (UCLM), Toledo 45071, Spain
3Department of Biodiversity and Evolutionary Biology, National Museum of Natural Sciences (MNCN), Spanish National Research Council (CSIC), Madrid 28006, Spain
4Department of Functional Biology, University of Oviedo, Oviedo 33003, Spain
*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, 2 alleles exclusive to the River Sella were absent in the contemporary sample, and 14 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 with non-native Scottish broodstocks between 1970 and 1990 caused the introgression found in the contemporary sample when compared with the pristine population. An abrupt decrease was evident when the estimates of effective number of breeders were adjusted to take into account overlapping generations (NbAdj), effective population size (NeAdj) estimated from NbAdj, and number of breeders estimated using the sibship assignment method (NbSIB). 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.

KEY WORDS: Conservation genetics · Effective population size · Foreign stocking · Genetic variability · Introgression · Population genetics · Salmonidae

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Cite this article as: Almodóvar A, Leal S, Nicola GG, Hórreo JL, García-Vázquez E, Elvira B (2020) Long-term stocking practices threaten the original genetic diversity of the southernmost European populations of Atlantic salmon Salmo salar. Endang Species Res 41:303-317.

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