Entrance geometries of closed-conduit fishways to attract juvenile fishes

Abstract

Fishway effectiveness relies on successful fish attraction and entry, yet limited research has explored the impact of entrance design on fish attraction. This study addresses this knowledge gap by evaluating different entrance geometries, water velocity, and related characteristics of flow for attracting Australian native fishes into closed conduit fishways. Novel laboratory experiments combined detailed hydrodynamic measurements of the velocity fields with live fish experiments, using silver perch (Bidyanus bidyanus) and Australian bass (Percalates novemaculeata). Four entry geometries comprising a circular entrance (FO), a slotted entrance (slot), a semi-circular entrance (SC), and a submerged quarter circle (QC) were tested. Three attraction velocity configurations of (i) V_a = 0 m/s, (ii) constant velocity (V_a = 0.15 m/s at the entrance for each of the entrance geometries); and (iii) constant momentum flux (0.12 N for each entrance geometry) was examined at a water depth of d = 0.18 m. There were distinct differences in the attraction flow patterns between entrance geometries. The strongest turbulent kinetic energy (TKE) values were found near the channel bed at Z = 0.1 d, with TKE significantly reduced by up to 60 % in the upper layer (Z = 0.7 d). The swimming trajectories for silver perch and Australian bass varied with different entrance geometries. While in the SC entrance, most silver perch used the jet sidewall, for the QC entrance, silver perch displayed a preference for swimming along the middle of the channel and along the non-jet sidewall, suggesting that the flow submergence for the QC entrance may have affected fish response. The presence of silver perch and Australian bass in the entrance tube clearly suggests that they can be attracted to diverse geometries without exhibiting a distinct preference for particular combinations of entrance geometries and velocities. TKE values <160 cm²/s² were recommended for attracting juvenile silver perch and Australian bass with longer residence time in the entrance tube.