SynopsisStocking of fish from other populations has been commonly employed for enhancement of wild brown trout, Salmo trutta, populations in north Spain. Young hatchery reared brown trout of central European origin were introduced into some Asturian rivers every year since 1984. Based on variation at the isozyme locus LDH-C1* and at the microsatellite locus BFRO 002, two genetic markers race-specific in Salmo trutta, we detected introgression of foreign genomes into native gene pools in some Spanish trout populations where only pure native individuals were present 10 years ago. We strongly suggest development of alternative management policies for conservation of Spanish natural brown trout populations without endangering the traditional recreational fisheries.
Found on the southernmost edge of the species' natural distribution, North Iberian Atlantic salmon populations are extremely vulnerable to environmental change. In the last few decades, associated with global indicators of climate change, these populations have been experiencing a sharp decline. Efforts have been made to address their decline, principally through stocking, supportive breeding and habitat restoration (enabling accessibility to upstream spawning sites). The efficiency of each of these measures has been different. In this study, focused on the river Sella containing one of the largest Spanish populations as a case study, we demonstrate that accessibility and habitat improvement have been the most efficient measures for increasing population size. Supportive breeding accounts for some level of population increase, but generally lower than 10%. Finally, our review suggests that stocking should be discarded as a restoration method because it encompasses threats to natural variation of Atlantic salmon and also the sympatric brown trout. RÉSUMÉRestauration et amélioration des populations de saumon Atlantique : ce que nous avons appris de rivières nord-ibériques Situées en bordure méridionale de la distribution naturelle de l'espèce, les populations nord-ibériques de saumon Atlantique sont extrêmement vulnérables aux changements environnementaux. Dans les dernières décennies, en relation avec les indicateurs globaux du changement climatique, ces populations ont connu une forte baisse. Des efforts ont été faits pour enrayer le déclin, principalement à travers l'alevinage, l'élevage de géniteurs et la restauration de l'habitat (permettant l'accessibilité aux frayères en amont). L'efficacité de chacune de ces mesures a été différente. Dans cette étude, axée sur la rivière Sella contenant l'une des plus grandes populations espagnoles comme étude de cas, nous démontrons que l'accessibilité et l'amélioration de l'habitat ont été les mesures les plus efficaces pour augmenter la taille de la population. L'élevage de soutien de géniteurs représente un certain niveau d'augmentation de la population, mais généralement inférieur à 10 %. Enfin, notre étude suggère que l'alevinage doit être abandonné comme mé-thode de restauration, car elle comporte des menaces à la variabilité naturelle du saumon Atlantique et aussi de la truite fario sympatrique.
Atlantic salmon stocks in northern Spain are at the southern range of the species distribution. As such they are likely more vulnerable to environmental change and human disturbance. The Nalon-Narcea River salmon is one such population in Asturias, Spain. The river is dammed throughout the watershed with few fish passage facilities. However, angling data show that salmon returns are consistent although the population is relatively small. We have employed one tributary as a model, the River Trubia. Although some problems of agriculture and industrial pollution have been detected downstream, an upstream habitat evaluation suggests that adequate spawning and juvenile habitat exists. The regional Government has proposed to construct fishways for allowing upstream passage of salmon. This would potentially increase salmon production, but there are also some concerns like increased hybridization of salmon and trout which is already evident downriver and which previous work suggests will increase as salmon colonize new habitat, and potential changes in fishing regulations as salmon distributions shift upriver and away from traditional angling areas. Here, we present an overview of ecological and social aspects of salmon habitat restoration in the River Nalon-Narcea that we hope will provide solutions that balance costs and benefits and may be applicable to other anadromous populations. RÉSUMÉLa restauration du saumon de l'Atlantique natif fonctionne dans le nord de l'Espagne : les coûts dépassent-ils les avantages ?Les stocks de saumon atlantique dans le nord de l'Espagne sont à la limite sud de la distribution de l'espèce. Comme tels, ils sont probablement plus vulnérables aux changements environnementaux et aux perturbations humaines. Le saumon de la rivière Nalon-Narcea est une de ces populations dans les Asturies, en Espagne. La rivière est endiguée, avec quelques passes à poissons. Toutefois, les données de pêche montrent que les retours de saumon sont bons bien que la population soit relativement faible. Nous avons employé un affluent comme modèle, la rivière Trubia. Bien que certains problèmes de pollution agricole et
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