Passage efficiency of offset and straight orifices for upstream movements of Iberian barbel in a pool‐type fishway

Although coarse fish species are frequently the predominant taxa found in rivers, they are often neglected in fish passage studies. Detailed knowledge on the impact of hydraulics on the movements and swimming performance of these species is very limited. In this study, offset and straight orifices in a pool‐type fishway prototype were tested in terms of their suitability for Iberian barbel's (Luciobarbus bocagei) upstream movements. The effects of water velocity and turbulence descriptors on fish swimming performance were herein also analysed. Overall, the offset configuration was found to have a significantly higher rate of fish passage success (68%) than the straight arrangement (28%). The time taken to successfully negotiate the fishway was also significantly lower when it featured an offset configuration, particularly for small adults. Of all analysed hydraulic parameters, Reynolds shear stress (RSS) seemed to be the one that most strongly influenced the movements of Iberian barbel within the fishway. The findings provide evidence that the barbel's swimming performance and capacity to successfully migrate upstream through a fishway strongly depend on the arrangement of orifices and turbulence, in particular RSS, within a fish pass. More detailed research focusing on other ‘weak’ swimmers is recommended to improve future designs of pool‐type fishways suitable for other coarse species. Copyright © 2010 John Wiley & Sons, Ltd.