Efficacy of a side-mounted vertically oriented bristle pass for improving upstream passage of European eel (Anguilla anguilla) and river lamprey (Lampetra fluviatilis) at an experimental Crump weir

摘要

Globally, populations of diadromous anguilliform morphotype fish, such as eel and lamprey, have experienced substantial declines, partly as a result of habitat fragmentation caused by river infrastructure. In the UK, a new configuration of hydraulically unobtrusive bristle pass (side-mounted and vertically oriented) has been developed to help upstream moving European eel (Anguilla anguilla) negotiate gauging weirs. The efficacy of vertically oriented bristle passes remains untested, despite their potential as a low-cost low-maintenance solution to improve habitat connectivity at low-head structural barriers worldwide. This study assessed the ability of small (82–320 mm) and large (322–660 mm) European eel and adult (291–401 mm) river lamprey (Lampetra fluviatilis) to pass upstream over an experimental Crump weir installed in a large open-channel flume with (treatment) and without (control) side-mounted vertically oriented bristle passes under three different hydraulic regimes. Both species were highly motivated to explore their surroundings and move upstream during the trials. Under flooded control conditions, passage efficiency (the total number of times fish passed the structure as a percentage of total attempts) and passage success (the number of fish that passed the structure as a percentage of those that attempted) were high, delay was short, and number of failed attempts before passage was low for both species. When difference in head was at its greatest (230 mm) and velocity and its variation downstream were high (maximum u and ?: 2.43 ms?1 and 0.66 ms?1, respectively), the upstream movement of small eel and lamprey was blocked, and passage efficiency and success for large eel low (4.6% and 17.2%, respectively). For large eel that successfully passed, delay was long, and number of failed attempts before upstream passage was high. When bristle passes were installed, passage efficiency for small (91.5%) and large eel (56.7%), and passage success for large eel (76.5%) and lamprey (36.7%) was higher, while delay and the number of attempts before passage was lower for both species. Bristle passes helped European eel and river lamprey pass a small experimental Crump weir, although interspecific variation in efficacy was evident.