Study

Efficient and timely downstream passage solutions for European silver eels at hydropower dams

  • Published source details Calles O., Elghagen J., Nyqvist D., Harbicht A. & Nilsson P.A. (2021) Efficient and timely downstream passage solutions for European silver eels at hydropower dams. Ecological Engineering, 170, 106350.

Actions

This study is summarised as evidence for the following.

Action Category

Install nature-like fishways

Action Link
Eel Conservation in Inland Habitats

Install bypass systems alongside exclusion devices

Action Link
Eel Conservation in Inland Habitats
  1. Install nature-like fishways

    A study in 2014–2015 in a river in Falkenberg Sweden (Calles et al. 2021; same study site as Kjærås et al. 2023) found that a nature-like fishway at a hydropower station was used by almost half of tagged European silver eels Anguilla anguilla to pass a hydropower station during downstream migration. Over two years, 26 of 59 tagged eels (49%) used a nature-like fishway to pass a hydropower station. The other tagged eels used a bypass channel next to a turbine intake with a bar rack (27 eels, 46%) or failed to pass the hydropower station and remained in the reservoir (3 eels, 5%). A 'large' nature-like fishway was created in 2013 by modifying the main river channel at one of two powerhouses at a hydropower station. A bypass channel was installed next to a turbine intake with an angled bar rack at a second powerhouse. In each of two years, 30 migrating silver eels captured 13–70 km upstream of the hydropower station were tagged and released at dusk either immediately upstream (during four nights in September 2014) or 24 km upstream (during three nights in September–October 2015). Eels were tracked passing the hydropower station using an array of eight antennas. One eel was not detected due to tag failure. 

    (Summarised by: Anna Berthinussen)

  2. Install bypass systems alongside exclusion devices

    A study in 2014–2015 in a river in Falkenberg, Sweden (Calles et al. 2021) found that a bypass system alongside a bar rack at a hydropower station was used by almost half of tagged silver European eels Anguilla anguilla migrating downstream and no tagged eels entered a turbine intake. Over two years, 27 of 59 tagged eels (46%) used a bypass system to pass a hydropower station. The other tagged eels used a nature-like fishway (29 eels, 49%) or failed to pass the hydropower station and remained in the reservoir (3 eels, 5%). None of 39 tagged silver eels that entered the turbine intake channel passed through the bar rack and into the turbines. In 2013, a full-depth bypass system was installed adjacent to a turbine intake with a 40-m angled bar rack (15 mm bar spacing, 30° angle relative to the intake banks) 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. In each of two years, 30 migrating silver eels captured 13–70 km upstream of the hydropower station were tagged and released at dusk either immediately upstream (during four nights in September 2014) or 24 km upstream (during three nights in September–October 2015). Eels were tracked passing the hydropower station using an array of eight antennas. One eel was not detected due to tag failure. 

    (Summarised by: Anna Berthinussen)

Output references
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