The influence of attraction flow on upstream passage of European eel (Anguilla anguilla) at intertidal barriers

River structures can delay or prevent upstream migration of the critically endangered European eel Anguilla anguilla (L.). Eel ladders are frequently installed to mitigate for the impacts of barriers. There has been little quantitative testing to optimise attraction to pass facilities. The effect of plunging and streaming flow on pass efficiency was tested within field trials using four eel ladders at an intertidal weir with little seaward freshwater discharge. Eel passage was 2 fold higher in the presence of plunging flow. Water temperature and height of tide were also significant factors influencing daily catch. A strong 'edge effect' influenced route choice, with greatest catches in traps positioned at the channel sides. Route choice was related to body size with largest size classes (> 121 mm) mostly passing towards the centre of the channel. The findings show that simple manipulation of hydrodynamic conditions at the entrance to upstream eel passes can improve passage efficiency for both juvenile and adult life-stages. (C) 2012 Elsevier B.V. All rights reserved.