Evaluation of downstream migration mitigation actions for eel at an Archimedes screw pump pumping station

Eel, Anguilla anguilla (L.), mortality was studied in a Belgian lowland canal after downstream passage through a large and small de Wit-adapted Archimedes screw pump over a 12-month period. The hypothesis tested was the minimisation of fish injuries with the de Wit adaptation. Simultaneously, downstream migration through a Dutch pool and orifice fishway alongside the pumping station (PS) was monitored. Nets were mounted on the outflow of the pumps, and a cage was placed in the fishway. Based on the condition of the fish and injuries sustained, the assessed maximum mortality rates ranged from 19 +/- 4% for the large de Wit Archimedes screw pump to 14 +/- 8% for the small de Wit Archimedes screw pump. The screw adaptations did not substantially minimise grinding injuries and overall mortality, and the fishway did not mitigate downstream eel migration. To achieve escapement targets set in the eel management plans, fish-friendly pump designs and effective PS bypass solutions are needed.