Restoration and enhancement of Atlantic salmon populations: what we have learned from North Iberian rivers

Abstract

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.

Keywords

• stocking
• restoration
• connectivity
• re-colonization
• Salmo salar