This project aims to improve knowledge of the demography and migratory movements of two Camargue eel sub-populations located upstream of the Vaccarès lagoon: in the Fumemorte basin and in the Grandes Cabanes basin. The aim of this study is to assess the success of the restored continuity between the Petit Rhône, the Grandes Cabanes and the Etang du Vaccarès. The aim of this project is to identify the periods and environmental factors involved in the downstream migration process, which will make it possible to recommend management measures to optimise the return of eels to the sea. To have the same type of monitoring between two river basins located to the east (Fumemorte) and west (Grandes Cabanes) of the Vaccarès lagoon is a unique opportunity to study the connectivity within a lagoon system between canals, marshes and ponds.