Install deterrents at water intake and discharge points (e.g. acoustic devices, electric or bubble screens, lights)

Supporting evidence from individual studies

1. A study in 1987 in a river in Burgum, the Netherlands (Hadderingh et al. 1992) found that installing lights at the entrance of a water intake channel at a power station led to fewer yellow and silver European eels Anguilla anguilla passing through compared to a water intake channel with no light, and lights placed above and below the water deterred more eels than just lights above the water. Over 10 nights, fewer eels passed through an intake channel illuminated from above and below (53–550 yellow eels/night and 3–77 silver eels/night) than an intake channel with no light (132–985 yellow eels/night and 6–87 silver eels/night). In addition, when intake channels were lit from above but not below, 0% of yellow eels and 6% of silver eels were deterred (numbers not reported). In October 1987, a water intake channel was illuminated using high-pressure mercury lamps placed 1 m above the water surface and an incandescent underwater lamp placed below the water at the bottom of the intake. Eels were monitored entering two channels next to each other, one illuminated and one dark, over 12 nights. In a second experiment, lights were placed above both channels (but not below) and switched on and off on alternate nights. 

   Study and other actions tested

   Referenced paper

   Hadderingh R.H., van der Stoep J.R. & Habraken J.M.P.M. (1992) Deflecting eels from water inlets of power stations with light. Irish Fisheries Investigations Series A (Freshwater), 36, 78-87.

2. A study in 1988 in a river in the Netherlands (Hadderingh et al. 1992) found that fewer European eels Anguilla anguilla passed through a water intake channel at a hydroelectric power station with a light barrier than without. An average of 23 eels/night passed through an intake channel on nights when the light barrier was switched on compared to an average of 68 eels/night when it was switched off. In September–October 1988, a light barrier (4.5 m width) was placed 4 m in front of a water intake channel to deflect eels away from a power station. The barrier consisted of two high pressure 2,000 W mercury lamps placed 1.5 m above the water and nine 200 W incandescent lamps placed 2.6 m below the water. Over 12 nights, the lights were switched on every other night. Eels were caught in nets at the outlet after passing through the intake channel. 

   Study and other actions tested

   Referenced paper

   Hadderingh R.H., van der Stoep J.R. & Habraken J.M.P.M. (1992) Deflecting eels from water inlets of power stations with light. Irish Fisheries Investigations Series A (Freshwater), 36, 78-87.

3. A controlled study in 2013 in a river in Dorset, UK (Piper et al. 2019) found that an acoustic deterrent device did not reduce the number of migrating European eels Anguilla anguilla that passed through a hydropower intake, and eels had longer more erratic movements when the device was turned on. Similar numbers of eels passed through a water intake when the acoustic device was turned on (total 14 eels) and off (total 18 eels). With the device turned on, eels had more erratic movements and longer tracks (average 85 m) than when the device was off (average 38 m). In November 2013, an infrasound (12 Hz) 'Profish' device was suspended in the water column in the centre of an intake channel of a redundant hydropower facility. The device was switched on (emitting continuously) or off during alternating nightly trials over 10 consecutive nights. Fifty migrating silver eels (56–78 cm long) captured downstream were tagged and released immediately upstream of the intake channel during each trial. Eels were tracked by an array of eight hydrophones. 

   Study and other actions tested

   Referenced paper

   Piper A.T., White P.R., Wright R.M., Leighton T.G. & Kemp P.S. (2019) Response of seaward-migrating European eel (Anguilla anguilla) to an infrasound deterrent. Ecological Engineering, 127, 480-486.