Author(s): Emilie Zimmer; Sylvie Tomanova; Laurence Tissot; Dominique Courret; Romain Roy; Thierry Lagarrigue; Aurelien Frey; Jeremy Beguin; Marc Lerquet; Dylan Colson; Damien Sonny; Michael Ovidio

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Keywords: Intake channel; Weir; Fish passage; Hydraulic and physical variables

Abstract: Downstream migrating juveniles (smolts) of Atlantic salmon (Salmo salar L.) are confronted to many migration barriers before reaching the sea, such as hydropower facilities (HF including a weir and an intake channel associated to a hydropower plant HPP). Passing through these barriers can cause varying degrees of smolt damage, depending on the route taken (intake channel or weir). The knowledge of the factors involved in the route selection of smolts at a site is crucial to evaluate the HF impact on fish downstream migration and to propose appropriate mitigation solutions. In this study we aimed to investigate how the HF hydraulic environment and physical configuration can influence the migration route selection of smolts. For this, we compiled migration routes of individually tagged salmon smolts (N= 727) from previous telemetry studies conducted at eight different HFs on five different rivers located in France and in Belgium, during seven different years. We defined multiple hydraulic and physical descriptors on each studied site. Using a selection procedure of candidate variables and a binomial generalized linear model, we identified descriptors that best explained the smolt migration route selection . Our study shows that metrics, easily obtained from aerial views, in addition to hydraulic characteristics, can be useful to estimate the smolt route selection when crossing a HF. This is an essential information for stakeholders allowing them to assess the HF impact on smolt downstream migration and to better target mitigation measures.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.219

Year: 2026