Install airlift fish passes

Supporting evidence from individual studies

1. A study in 2014 in an indoor channel in the USA (Haro et al. 2016; experimental set-up as Baker et al. 2019) found that an airlift fish pass at a simulated hydropower intake entrance was used by all American silver eels Anguilla rostrata to travel downstream at medium and high-water velocities, and most eels at low water velocities, and all eels that passed through it survived. All of 12–15 eels/trial (100%) passed through the airlift fish pass at water velocities of 1.2 and 1.5 m/s. Eleven of 15 eels (73%) passed through the fish pass at water velocities of 0.9 m/s. None of the eels that passed through died or had visible injuries. In October 2014, two screens were erected in a 6-m wide channel perpendicular to the water flow. A 'Conte airlift bypass' (constructed from steel and PVC pipe and fittings) was installed in one of the screens, with the entrance (31 cm diameter) located 11 cm above the channel floor. Air was injected into the pipe to create an upward flow (see paper for details). Wild-caught silver eels (597–940 mm long) were radio-tagged and released in the channel during one trial at each of three water velocities (velocity at pass entrance: 0.9, 1.2 or 1.5 m/s; 12–15 eels/trial). Eels were tracked with four antennas and an underwater video camera for 3 h from dusk. Eels were monitored for signs of injury for 48 h after each trial.  

   Study and other actions tested

   Referenced paper

   Haro A., Watten B. & Noreika J. (2016) Passage of downstream migrant American eels through an airlift-assisted deep bypass. Ecological Engineering, 91, 545-552.

2. A study in 2015 in an indoor channel in the USA (Baker et al. 2019; same experimental set-up as Haro et al. 2016) found that an airlift fish pass at a simulated hydropower forebay was used by two-thirds of American silver eels Anguilla rostrata, and all eels that passed through it survived. Overall, 55 of 84 eels (66%) passed through the airlift fish pass. None of the eels that passed through died or had visible injuries. In November 2015, two screens were erected perpendicular to the water flow in a 6-m wide channel. A 'Conte airlift bypass' (constructed from steel and PVC pipe and fittings) was installed in one of the screens, with the entrance (31 cm diameter) located 11 cm above the channel floor. Air was injected into the pipe to create an upward flow (see paper for details). During each of four trials, wild-caught silver eels (53–100 cm long) were radio-tagged and released in the channel (14–42 eels/trial). Eels were tracked with four antennas and an underwater video camera for 3 h from dusk. Eels were monitored for signs of injury for 48 h after each trial.  

   Study and other actions tested

   Referenced paper

   Baker N., Haro A., Watten B., Noreika J. & Bolland J.D. (2019) Comparison of attraction, entrance and passage of downstream migrant American eels (Anguilla rostrata) through airlift and siphon deep entrance bypass systems. Ecological Engineering, 126, 74-82.