Eels at the Edge: Science, Status, and Conservation Concerns

Managing Human Impact on Downstream Migrating European Eel in the River Meuse

Maarten C. M. Bruijs, R. H. Hadderingh, U. Schwevers, B. Adam, U. Dumont, and H. V. Winter


Abstract.—To evaluate mortality factors and potential mitigative measures during downstream passage of silver European eel Anguilla anguilla in the River Meuse, an integrated study was performed consisting of: 1) telemetric experiments where the descent of 150 transpondered eels was tracked at 14 detection stations; 2) monitoring daily commercial catches; 3) testing a system to predict migration events from activity of captive eels in riverside tanks (the Migromat system); and 4) measuring turbine mortality by netting eels at turbine outlets. Migromat systems installed at two hydropower stations predicted 41 migration events. Most warnings (58.5%) were false positives, but Migromat failed to predict only one migration event. Mortality of eels passing through a turbine at the Linne Hydropower station was 24%. However, part of the downstream migrating population bypassed the turbines by descending over adjacent weirs. Descending eels moved primarily in brief pulses that were associated with increasing discharge and especially during the first half of the night. Thirty-seven percent of transpondered eels released at Ohé en Laak reached the sea. Because both fisheries mortality (estimated at 22–26% by fishing recoveries) and hydropower mortality (estimated at 16–26%) were considerable, a reduction in fisheries harvest and implementation of turbine management by application of the Migromat warning system would substantially increase escapement of silver eels from the River Meuse.