Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

De-congesting London: Improving River Connectivity for Lowland River Fishes in Urban Streams (#33)

Angus J Lothian 1 , Chris J Gardner 2 , Toby Hull 2 , Daniel Griffiths 3 , Eleanor R Dickinson 1 , Martyn C Lucas 1
  1. Durham University, Durham, DURHAM, United Kingdom
  2. South East Rivers Trust, Carshalton, Surrey, United Kingdom
  3. Environment Agency, Addington, Kent, United Kingdom

Weir construction has fragmented many lowland rivers, resulting in the exclusion of some fish populations from suitable habitat.  A cheap retrofit fishway for sloping weirs with a gradient of ~1:5 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 fish at steeper weirs, LCBs were fitted onto a 1:3.3-sloping 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; nstock =120), chub (Squalius cephalus; nstock =119; nwild =194), dace (Leuciscus leuciscus; nwild =50), and roach (Rutilus rutilus; nwild =30). Over six months, more stocked fish attempted passage (58.9%) than wild (14.6%; χ21 =26.7, p <0.001), but there was no difference in successful passage (stock =34.0%; wild = 40.0%; χ21 =0.5, p =0.49). Stocked fish took longer to complete passage (mean =9.3 hrs) than wild (mean =3.3 hrs; t47.3 =2.1, p =0.04).  This study finds that LCBs can facilitate passage for lowland-river fishes at steep urban weirs that cannot readily be removed. Although some fish failed to pass the weir, others succeeded on several occasions. This could be a result of inter-individual variation in motivation rather than LCB inadequacy. This study also indicates that stocked and wild fish exhibit similar passage success, a finding with important management implications.