Effect of body length on swimming capability and vertical slot fishway design

Abstract

A dam will be built in the upper Han River, China, disrupting fish migration and gene exchange, and a vertical slot fishway will be constructed to mitigate the impacts. Of the forty-two local species identified, eight were selected as target species, based on migration, habitat suitability, protection class, economic value and historical status. Fish swimming capability and the effect of body length on swimming ability were assessed by measuring induced flow velocity (Uind), critical swimming speed (Ucrit), and burst speed (Uburst) by stepped velocity tests in a modified Brett-type swimming respirometer. The research led to two primary findings: (1) The absolute values (m/s) of Uind, Ucrit and Uburst tended to increase with body length, while relative values (bl/s) tended to decrease. (2) The effective flow velocity for 90% of the tested fish (EF90) was used to set engineering design criteria for flow velocity; Uind-EF90 = 0.17 m/s, Ucrit-EF90 = 0.59 m/s, and Uburst-EF90 = 0.94 m/s. According the three EF90 values, literature references, fishway guidelines and design codes in China, the recommended velocity criteria for the vertical slot fishway are as follows: entrance velocity, 0.35–0.47 m/s (0.6–0.8 Ucrit-EF90); pool velocity, 0.17–0.59 m/s (from Uind-EF90 to Ucrit-EF90); vertical slot velocity, 0.86–0.94 m/s (from lowest Uburst to Uburst-EF90); exit velocity, > 0.17 m/s (Uind-EF90). The results of this study add to existing knowledge on the effect of body length on swimming ability and improve vertical slot fishway design.