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

Abstract

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.

Keywords:

• Local extirpation
• aquaculture
• habitat
• exploitation
• predation
• Newfoundland

Acknowledgements

We would like to thank George Furey, Marc Bloom, Milton Shears and members of Miawpukek Mi’kamawey Mawi’omi, Conne River, in particular Ross Hinks, for their invaluable field assistance and support since 1986. In addition, we thank Chantelle Burke, Michelle Fitzsimmons, Amber Messmer, Rebecca Poole and Kristin Loughlin for their contributions to the scoring of potential threats. Bill Montevecchi, Garry Stenson, and Charmain Hamilton reviewed various sections of the manuscript with GS and CH kindly sharing preliminary results from seal surveys carried out in 2021. Thanks also to Keith Clarke, Rex Porter and Craig Purchase for providing comments on an earlier version of the manuscript. We also thank two anonymous reviewers, and also John Kocik and the Editor, Sandra Shumway for their help and assistance. Funding for the counting fence program was provided from Fisheries and Oceans Canada and the Miawpukek First Nation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The time series of smolt and adult salmon abundance information and climate data used in the Random Forest analysis are available on request. R scripts for running random forest analyses are available at: https://github.com/SarahLehnert/ConneDeclines/