The BALANCE project combines a “mark-recapture” study approach and acoustic telemetry in order to get a robust quantification of the actual silver eel escapement from River Ems. The use of acoustic telemetry enables us to separate eels that start or continue their seaward migration after tagging from those that stay resident in the system before migrating at a later stage. The actual silver eel escapement is estimated from the proportion of migrating, individually marked fish in the total catch of a fishing gear. Acoustic receiver stations along the river provide insights into the migratory behaviour depending on the degree of maturation of the silver eels and allow the identification of local migration obstacles (e.g., through navigation locks). Moreover, the influence of environmental parameters (e.g., temperature, moon phase and river discharge) on the migratory behaviour will be analysed to enable predictions of the timing and magnitude of eel migration using environmental data.