Fish pass effectiveness for bullhead (Cottus gobio), perch (Perca fluviatilis) and roach (Rutilus rutilus) in a regulated lowland river

Abstract –  The effectiveness of a pool-and-weir fish pass in the regulated river Laarse Beek (Belgium) was assessed for bullhead ( Cottus gobio ), perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ) from August 2002 to April 2003. Fish were caught by electrofishing downstream, within and upstream of the fish pass. They were marked with visible implant elastomer tags and released downstream of the fish pass. Our results suggest that the fish pass is ineffective for the bullhead because none of the 1270 tagged bullheads were recaptured in the upstream study area. Passage failure most likely resulted from excessive water velocities in the fish pass. On the contrary, 8% of the tagged perch and 29% of the tagged roach were recaptured in the upstream study area. Several management strategies are proposed to allow free upstream passage of the endangered bullhead at the fish pass under study.