Fishways are installed worldwide to facilitate accessibility to functional habitats and to increase the ecological continuity of rivers. Their evaluations are increasing, but complete studies in the field with wild individuals are still scarce. In the lower Bocq River (Belgium), a pool type fishway was installed in 2011. A combined passive-integrated-transponder-tag and radio-telemetry system was designed and installed downstream of the dam and in the fishway to analyse fine-scale individual fish behaviour. Three fish species (brown trout, European grayling, and barbel) were captured in the river; n = 125 fish were tagged and released downstream of the fishway. Behavioural metrics were proposed and used in order to attain a comprehensive view on the efficiency of the fishway, including attraction and entrance efficiency, searching and passage delays, and overall and adjusted passage efficiency. The results indicate a major problem in terms of attraction efficiency (48.9% for the trout, 20.5% for the grayling, and 41.2% for the barbel) and time to find the entrance of the fishway (mean 65.1 hr for the trout and 538.9 hr for the grayling).For fish that succeed to approach the entrance of the fishway, the passage efficiency was 86.9% for the trout, 55.5% for the grayling, and 7.1% for the barbel. The time taken to cross the structure was reasonable for the salmonids (mean < 1.5 hr for trout and grayling) but very long (21 hr) for the barbel. Our results underline the necessity of a holistic approach to evaluate fishway efficiency using precise comprehensive metrics and hydraulic characterization.

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Résumé -Le projet Life Environnement WALPHY, co-financé par l'Union Européenne, a eu pour objectif de réaliser des travaux de restauration de la qualité hydromorphologique du Bocq, affluent de la Meuse. La continuité longitudinale, qui concerne la libre circulation des poissons et le transport naturel des sédiments, a été fortement perturbée par un grand Mots-clés -restauration hydromorphologique, travaux de réhabilitation, suivis écologiques et hydromorphologiques, DCE Abstract -The Life Environment project WALPHY, co-funded by the European Union, aimed to improve hydromorphology of the Bocq catchment, a tributary of the Meuse. Longitudinal continuity, which concerns the free movement of fish and sediments, was strongly affected Hydroécol. Appl.

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