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

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

Une analyse prospective en halieutique : le cas de la recherche sur les poissons migrateurs amphihalins

International audienceInsights provided by futures analyses are becoming increasingly important for planning research activities in ecology in order to provide innovative solutions to society in the face of unprecedented environmental changes (Cook, Inayatullah, Burgman, Sutherland, & Wintle, 2014). Few applications exist in fisheries science. A rigorous methodology was applied to draw potential areas for future research on diadromous fishes circa 2030 that could be useful to a broader audience of European fisheries scientists. Diadromous fishes are species that migrate between fresh waters and the sea to complete their life cycle. First, twenty drivers were identified and fell within the scope of (i) diadromous fish conservation, (ii) their place and roles in modern societies, (iii) the main features of the world of science and research, and (iv) the main characteristics of research activities on this biological group. Past and future driver developments (i.e. retrospective analysis and hypotheses respectively) were examined. Then, the combination of drivers' hypotheses within each of the four components listed above led to micro-scenarios describing how the components could plausibly change in the next fifteen years. Finally, global scenarios were obtained by juxtaposing four micro-scenarios, one for each of the components. Challenges that were identified from these global scenarios were mostly structural, intellectual with frequent revisions of theoretical and unchallenged concepts and ethical, and can be useful to better inform future changes in priorities and focus areas, technical investments, and funding opportunities operated by laboratories or individual researchers working on diadromous fishes. Also, this case study exploring the role of foresight in guiding research, particularly the part on the methodological description, could be of relevance for researchers in general