Passage performance and behaviour of wild and stocked cyprinid fish at a sloping weir with a Low Cost Baffle fishway.

• The performance of Low Cost Baffles for upstream cyprinid passage was measured. • Fish passed the weir under a range of flow conditions post-LCB installation. • Larger fish were less likely to be successful than smaller fish. • No difference in the passage performance or behaviour between wild and stocked fish. • High potential for LCBs to be used as a retrofit fishway for steep sloping weirs. Weir construction has fragmented many rivers, resulting in the exclusion of some fish populations from suitable habitat. A cheap retrofit fishway for small, sloping weirs is the Low Cost Baffle (LCB) solution – A series of notched baffles perpendicular to flow on the downstream weir face, generating an angled passage route across the weir face. To test the degree to which LCBs can pass upstream-moving, lowland-river fish at steep weirs, LCBs were fitted onto a 1:3.3-sloping gauging-weir face, in an urban tributary of the River Thames, England. The study also compared the passage of wild and stocked fish (the latter are employed to facilitate population recovery in restored English rivers). Passive Integrated Transponder (PIT) antennas were positioned on the weir to record the upstream movement of PIT-tagged barbel (Barbus barbus ; n stock = 120), chub (Squalius cephalus ; n stock = 119; n wild = 194), dace (Leuciscus leuciscus ; n wild = 50), and roach (Rutilus rutilus ; n wild = 30). Over six months, more stocked fish attempted passage (58.9%) than wild (14.6%; χ 2 1 = 26.7, p < 0.001), but there was no difference in successful passage of those that attempted (stock = 34.0%; wild = 40.0%; χ 2 1 = 0.5, p = 0.49). Successful passage was achieved under a range of flow conditions. This study finds that LCBs have the potential to facilitate passage for cyprinid fishes at steep urban weirs that cannot readily be removed, but there is need for design improvements. This study also indicates that stocked and wild fish exhibited similar passage success, a finding with important management implications for achieving dispersal of stocked fish as a rehabilitation measure. [ABSTRACT FROM AUTHOR]