Quantifying smolt survival from source to sea: informing management strategies to optimise returns

SMOLTrack III started on January 2020 and ended in December 2022.

Despite conservation efforts, wild Atlantic salmon stocks have experienced declines throughout the global range of distribution. Maximising the number of wild smolts in good condition that leave the river to the ocean can help minimise the impacts of changing ecosystems and low marine survival. Based on the platform developed in SMOLTrack I and II, this project (SMOLTrack III) investigated several key factors potentially contributing to smolt mortality during their transition from freshwater to the marine environment.

The project achieved three objectives:

  1. evaluation of wild smolt survival during migration
  2. quantifying the influence of climate change on salmon production
  3. evaluate telemetry-based assessments to provide accurate information on smolt migration and survival.

The findings from SMOLTrack III have advanced our understanding of how bottlenecks can influence the size of smolt runs and highlight the benefits of moving smolts past identified bottlenecks. These results are highly relevant for policy makers and managers seeking to reduce smolt mortalities during their riverine migration. The recent increase in awareness about negative effects of barriers and other bottlenecks is in part an outcome of the studies performed in SMOLTrack I – III. Identifying and removing/mitigating bottlenecks may represent one of the fastest and potentially easiest ways of increasing adult return of salmon populations. SMOLTrack III also provided the foundation for a temperature logger infrastructure with an extensive latitudinal distribution, which will be used to track the ongoing effects of climate change on wild salmon stocks. Finally, the findings from objective 3 indicate that trapping smolts during their seaward migration does not influence their survival, further validating the standard operating procedure (SOP) and the method of using trapped smolts for investigating behaviour and survival. These findings are highly relevant to improve methods used by the academic community and fisheries managers monitoring smolt runs, using fish traps.