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

Automated summary

The study found that European eels choose to pass through pumping stations, gravity sluices, or retreat upstream during downstream migration. It is recommended to make operational changes to increase the attractiveness of gravity sluices to reduce passage through hazardous pumping stations.