Seasonal and daily rhythms of movements of fish fauna within the river Meuse equipped with modern migratory fish-passes

Four vertical slot fishways were installed within a 32-km stretch of the lower Belgian Meuse River basin. From 2010 to 2020, n=2526 individuals belonging to 16 fish species (potamodromous and diadromous) were continuously captured in the most downstream fishway, tagged with an RFID transponder and released upstream. These could be further detected in upstream river part within three fishways (two in the Meuse & one in an important tributary, the Ourthe) that were equipped with automatic RFID detection stations. We were able to highlight the seasonality and the daily rhythm of migration of all the marked species with a large variety of movement strategies. The choice of rheophilic species to migrate to a tributary of good ecological quality highlights a new accessibility to functional habitats. A fish passage efficiency was quantified with good values between 35.0% and 72.6% depending on the species. The installation of fish passes in a degraded river like the Meuse can be considered as a good example of effective restoration of ecological continuity.