Water pollution, habitat degradation and river fragmentation are primarily responsible for biodiversity losses observed in freshwater ecosystems globally, greatly impacting anadromous fish species including twaite shads (Alosa fallax) throughout their range. In the Scheldt Estuary and River (Belgium and The Netherlands), twaite shads were considered extinct after disappearing during the 20th century due to poor water quality resulting from inadequate water management and habitat destruction. The species however reappeared and started reproducing in 2014.
This study used acoustic telemetry and tagged individuals internally, aiming to inform water management plans and contribute to the sustainable return of the species in the Scheldt. While focusing on the spawning migration of 20 fish the year following their tagging, the study identified the different phases of their migration before investigating their timing, duration and speeds. It also explored environmental variables linked to the timing of the spawning migration phases and demonstrated that the species uses Selective Tidal Stream Transport (STST) during its upstream and downstream migration. The project provides strong fundamental knowledge for the first time on the migration and lifecycle of the species in the Scheldt. This enables the identification of specific research targets for future phases of the project.
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