Modify operation of underwater turbines

Supporting evidence from individual studies

1. A replicated, controlled study in 2007–2010 at five hydropower stations along a river in Virginia and West Virginia, USA (Eyler et al. 2016) reported that shutting down turbines at night led to reduced mortality rates of migrating American eels Anguilla rostrata. Overall mortality rates of American eels migrating downstream past dams at five power stations were lower during periods when turbines were shutdown (0–7%) than during normal turbine operations (6–38%), although Results are not based on tests of statistical significance. Similar numbers of eels passed dams while turbines were shutdown (17–35 eels/dam) and during normal operations (16–52 eels/dam). From 15 September to 15 December 2007–2010, turbines at five hydropower stations (3–4 turbines/station) were shut down from 18:00 to 06:00 h and all water diverted to the dam spillway. Normal operations were resumed at all other times. In September–December 2007–2009, a total of 145 eels (average length 85 cm) were captured by electrofishing in the Shenandoah River upstream of each hydropower station. Captured eels were fitted with radio tags and released. Tagged eels were tracked passing each dam from September 2007 to August 2010.  

   Study and other actions tested

   Referenced paper

   Eyler S.M., Welsh S.A., Smith D.R. & Rockey M.M. (2016) Downstream passage and impact of turbine shutdowns on survival of silver American eels at five hydroelectric dams on the Shenandoah River. Transactions of the American Fisheries Society, 145, 964-976.

2. A study in 2015–2016 in a river in southern Germany (Økland et al. 2017) found that lifting a turbine at a power station allowed more than half of migrating European silver eels Anguilla anguilla to pass safely, although a third of eels still passed through the turbine when it was lowered. Thirty-four of 66 tagged eels (52%) passed through the section containing the turbine while the turbine was lifted. Twenty-four eels (36%) passed through the turbine when it was lowered. Data on turbine operation was not available when the remaining eight eels (12%) passed the turbine. A further 36 tagged eels passed the power station via other routes (24 eels over the dam or via flood gates, nine eels via a side stream, three eels via a fishway). In 2015, a total of 136 silver eels (65–101 cm length) were captured in the river Kinzig, fitted with radio tags, and released 10 km upstream of the power station. Stationary receivers were placed upstream and downstream of a movable ‘Kaplan’ bulb turbineat the power station. Tagged eels were recorded passing the power station from October 2015 to May 2016 when the turbine was lifted (on 12 occasions for an average of 2.3 days, total 35 days) and lowered (the remainder of the time). 

   Study and other actions tested

   Referenced paper

   Økland F., Teichert M.A.K., Havn T.B., Thorstad E.B., Heermann L., Sæther S.A., Tambets M. & Borcherding J. (2017) Downstream migration of European eel at three German hydropower stations. Norwegian Institute for Nature Research (NINA) report, 1355.