Silver eel downstream migration in fragmented rivers: use of a Bayesian model to track movements triggering and duration

• Published in: Aquatic Living Resources
• Main Authors: Drouineau, Hilaire, Bau, Frédérique, Alric, Alain, Deligne, Nicolas, Gomes, Peggy, Sagnes, Pierre
• Other Authors: Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - INPT (FRANCE), Institut national de Recherche en Sciences et Technologies pour l'Environnement et l'Agriculture - IRSTEA (FRANCE), Université Toulouse III - Paul Sabatier - UPS (FRANCE), Institut de Mécanique des Fluides de Toulouse - IMFT (Toulouse, France)
• Format: Article in Journal/Newspaper
• Language: English
• Published: EDP Sciences 2017
• Subjects: Dynamique des Fluides; Biodiversité et Ecologie; Ingénierie de l'environnement; Anguilla anguilla; Silver eel; Migration delay; River fragmentation; Movement ecology; State-space model
• Online Access: http://oatao.univ-toulouse.fr/18391/; http://oatao.univ-toulouse.fr/18391/7/Drouineau_18391.pdf; https://doi.org/10.1051/alr/2017003

Obstacles in rivers are considered to be one of the main threats to diadromous fish. As a result of the recent collapse of the European eel, the European Commission introduced a Regulation, requiring to reduce all sources of anthropogenic mortality, including those caused by passing through hydropower turbines. Improving knowledge about migration triggers and processes is crucial to assess and mitigate the impact of obstacles. In our study, we tracked 97 tagged silver eels in a fragmented river situated in the Western France (the River Dronne). Using the movement ecology framework, and implementing a Bayesian state-space model, we confirmed the influence of river discharge on migration triggering and he distance travelled by fish. We also demonstrated that, in our studied area, there is a small window of opportunity for migration. Moreover, we found that obstacles have a significant impact on distance travelled. Combined with the small window, this suggests that assessment of obstacles impact on downstream migration should not be limited to quantifying mortality at hydroelectric facilities, but should also consider the delay induced by obstacles, and its effects on escapement. The study also suggests that temporary turbines shutdown may mitigate the impacts of hydropower facilities in rivers with migration process similar to those observed here.