Restoration of native Atlantic salmon runs in northern Spain: do costs outweigh benefits?

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.Original Abstract: Les stocks de saumon atlantique dans le nord de l'Espagne sont a la limite sud de la distribution de l'espece. Comme tels, ils sont probablement plus vulnerables aux changements environnementaux et aux perturbations humaines. Le saumon de la riviere Nalon-Narcea est une de ces populations dans les Asturies, en Espagne. La riviere est endiguee, avec quelques passes a poissons. Toutefois, les donnees de peche montrent que les retours de saumon sont bons bien que la population soit relativement faible. Nous avons employe un affluent comme modele, la riviere Trubia. Bien que certains problemes de pollution agricole et industrielle soient detectes en aval, une evaluation de l'habitat de frai et juvenile amont suggere que l'habitat adequat existe. Le gouvernement regional a propose de construire des passes a poissons pour permettre le passage amont du saumon. Ce serait potentiellement augmenter la production de saumon, mais il y a aussi certaines preoccupations, comme l'hybridation accrue du saumon et de la truite qui est deja evidente en aval. Des travaux anterieurs sug