Origins and genetic diversity among Atlantic salmon recolonizing upstream areas of a large South European river following restoration of connectivity and stocking

Abstract

The restoration and maintenance of habitat connectivity are major challenges in conservation biology. These aims are especially critical for migratory species using corridors that can be obstructed by anthropogenic barriers. Here, we explored the origins and genetic diversity of Atlantic salmon (Salmo salar) recolonizing upstream areas of the largest South European Atlantic salmon population (Adour drainage, France) following restoration of connectivity and stocking. We genotyped 1,009 juvenile individuals, sampled either in continuously inhabited downstream sites or in recently reconnected and recolonized upstream locations, at 12 microsatellite loci. We found significant fine scale genetic structure, with three main genetic clusters corresponding to the Nive, Nivelle and Gaves rivers. Within each of these clusters, samples collected in continuously inhabited and recently recolonized sites had comparable allelic richness and effective population sizes and were only weakly differentiated. Genetic structure among basins was also similar among continuously inhabited and recently recolonized sites. The majority of the individuals sampled from recently recolonized sites were assigned to neighboring continuously inhabited downstream sites, but noticeable proportions of fish were assigned to samples collected in more distant sites or identified as putative hybrids. Overall, this study suggests that the restoration of accessibility to upstream areas can allow for the recolonization and effective reproduction of Atlantic salmon from proximate downstream refugia, which does not decrease local diversity or disrupt existing genetic structure. (Résumé d'auteur

Ice sheets and genetics: Insights into the phylogeography of Scottish Atlantic salmon, Salmo salar L.

“…While time required for LLD to establish the first populations is unclear, based on contemporary observations on salmon colonization (Nielsen, ; Perrier et al. , 2011, Perrier et al., ), subsequent LRE into newly available adjacent rivers and tributaries within regions probably took just decades, once rivers or tributaries became habitable, and probably involved relatively greater numbers of founders. Yet, the observed population differentiation is greater within regions.…”

“…When rivers or tributaries are newly habitable, colonization by local range expansion (LRE) occurs (e.g. Nielsen, ; Perrier, Guyomard, Bagliniere, & Evanno, ; Perrier, Le Gentil, Ravigne, Gaudin, & Salvado, ) where local populations exist but it can colonize by long‐distance dispersal (LDD) over 1,000s of kilometres (King et al., ; Nielsen, ).…”

Disentangling individual movement between populations from effective dispersal in the facultative anadromous Salmo trutta L.

“…Since the 1980s, however, habitat connectivity has been continuously improved. Accessibility of upstream spawning sites to salmonid fishes, albeit incomplete, is now operational in all four salmonid migratory corridors as detailed in Perrier, Le Gentil, Ravigne, Gaudin, and Salvado (). However, despite ongoing efforts, spawning of anadromous salmonids remains rare in the upper part of Gave de Pau.…”

“…Accessibility of upstream spawning sites to salmonid fishes, albeit incomplete, is now operational in all four salmonid migratory corridors as detailed in Perrier, Le Gentil, Ravigne, Gaudin, and Salvado (2014).…”

Restored river habitat provides a natural spawning area for a critically endangered landlocked Atlantic salmon population

“…There is a growing number of encouraging examples, where anadromous Atlantic salmon have started to return to the restored rivers, where they have been previously extirpated (e.g. [30,[46][47][48][49]). The common denominator in all the successful cases of re-establishment of anadromous salmon is the restoration of the formerly uninhabitable habitats.…”