A Review of Factors Potentially Contributing to the Long-Term Decline of Atlantic Salmon in the Conne River, Newfoundland, Canada

Species extinction and population extirpation are now widespread across aquatic ecosystems with many diadromous species, including Atlantic salmon (Salmo salar), in decline throughout much of the North Atlantic. Declines can occur simultaneously at both large and small regional scales rendering factors driving the decreases more elusive. On the south coast of Newfoundland abundance of Atlantic salmon at Conne River fell by 92% over a period of almost four decades in contrast with most other populations in the region suggesting local factors may be contributing to the decline. Here factors potentially contributing to the long-term decline of salmon are reviewed by (1) examining long-term trends in abundance and survival at different life stages, (2) presenting a synopsis on the presence and absence of factors impacting survival and productivity of this population, (3) using a semi-quantitative two dimensional classification system, based on expert opinion, to rank factors potentially contributing to the decline, and (4) utilizing a quantitative Random Forest analysis to complement the expert opinion approach in identifying factors possibly affecting salmon abundance in this south coast Newfoundland population. Results from both qualitative and quantitative analyses identified factors associated with salmon aquaculture as a possible driver of the decline. Additional factors include the influence of both climate change and predation in freshwater and marine habitats. As various Atlantic salmon populations across the native range approach extirpation, the results further highlight the necessity of river-specific analyses in addition to long-term monitoring and fine-scale demographic and threat information in the prioritization of research necessary for conserving or restoring endangered populations.