Three‐dimensional migratory behaviour of European silver eels (Anguilla anguilla) approaching a hydropower plant

Published source details Kjærås H., Baktoft H. & Silva A.T. (2023) Three‐dimensional migratory behaviour of European silver eels (Anguilla anguilla) approaching a hydropower plant. Journal of Fish Biology, 102, 465-478.
Share Tweet Email

Actions

This study is summarised as evidence for the following.

	Action	Category
	Install nature-like fishways Action Link
	Install bypass systems alongside exclusion devices Action Link

Install nature-like fishways

A study in 2017 in a river in Falkenberg, Sweden (Kjærås et al. 2023; same study site as Calles et al. 2021) reported that a nature-like fishway at a hydropower station was used by more than half of tagged European silver eels Anguilla anguilla to migrate downstream. The nature-like fishway was used by 52 of 90 eels (58%) to travel downstream. Of those, 24 eels (27%) passed over weirs to access the fishway, and 28 (31%) through a hydraulic entrance. The remaining 38 eels (42%) used a bypass channel alongside a rack to pass the hydropower station. Passage time was significantly higher for eels using the fishway than the bypass (see paper for details). In 2013, a nature-like fishway was installed at one of two powerhouses at a hydropower station. Eels could enter the fishway over concrete weirs or through a hydraulic entrance. A bypass channel was installed next to a turbine intake with an angled bar rack at a second powerhouse. On 23–25 September 2017, downstream-migrating silver eels (98 eels, 64–100 cm long) caught in four traps, located 13–17 km upstream of the hydropower station, were tagged and released 20 km upstream. Eels were tracked passing the hydropower station using 33 hydrophones.

(Summarised by: Vanessa Cutts)
Install bypass systems alongside exclusion devices

A study in 2017 in a river in Falkenberg, Sweden (Kjærås et al. 2023) reported that a bypass system alongside a bar rack at a hydropower station was used by some silver European eels Anguilla anguilla to migrate downstream. Unless stated, statistical significance was not assessed. In total, 38 of 90 eels (42%) used a bypass system alongside a bar rack to migrate downstream. Of those, 22 eels (24%) used a bottom slot in the bypass system, while nine (10%) used a surface slot (slot use could not be determined for seven eels). The remaining 52 eels (58%) used a nature-like fishway to pass the hydropower station. In 2013, a ‘full-depth’ bypass was installed adjacent to a turbine intake with a 40-m angled bar rack (15 mm bar spacing, 30° angle) at one of two powerhouses at a hydropower station. A hydraulic gate at the bypass entrance had open slots at the top (30 cm wide x 65 cm high) and bottom (20 x 20 cm), and was fully opened periodically to clear debris. A nature-like fishway was installed at a second powerhouse in an adjacent channel. On 23–25 September 2017, downstream-migrating silver eels (98 eels, 64–100 cm long) caught in four traps, located 13–17 km upstream of the hydropower station, were tagged and released 20 km upstream. Eels were tracked passing the hydropower station using 33 hydrophones.

(Summarised by: Vanessa Cutts)