Downstream passage of silver European eel (Anguilla anguilla) at a pumping station with a gravity sluice

The European eel (Anguilla anguilla (L.)) is critically endangered after a multi-decadal decline. Anthropogenic disruption to downstream migration, including at water control structures such as pumping stations, thought be one of the contributing factors. Some stations only operate during floods and river drains through sluice gates under influence gravity (‘gravity sluice’ hereafter) all other times. Gravity sluices are considered safe passage route for migrating silver eels, but it not known if eels approach or pass them. This novel study aimed understand timing, routes fine-scale behaviour (n = 7) immediately upstream station with using acoustic telemetry. During study, three passed pumps (42.9%) despite operating 8% time that was open, two (28.6%) remaining retreated (28.6%). Long delays (up 21 days) were observed detected retreating back 10 times) prior passing downstream. It recommended operational changes implemented make more attractive thus reduce hazardous pumps.