River connectivity restoration for upstream-migrating European river lamprey: The efficacy of two horizontally-mounted studded tile designs

摘要

Many rivers are heavily fragmented, resulting from anthropogenic cross-channel structures. Cost-effective solutions are needed to restore habitat connectivity for migratory fishes, including those of conservation concern, such as the European river lamprey (Lampetra fluviatilis). Studded material is becoming increasingly used as a low-cost retrofit solution for lamprey passage at sloping weirs, although little is known about the efficacy of the material or what stud arrangements may be most effective. This study tested whether expanding a single-density studded tile (SDT) lane from 1 to 2-m width increased passage success (n(released)= 133), and also compared the passage performance between a SDT lane and a dual-density studded tile (DDT) lane (n(released)= 115) at a sloping weir, using PIT telemetry. No passage was recorded (n(attempted)= 89) at the 2-m wide SDT lane, but 61.6% (n(passed/attempted)= 53/86) passed using DDT/SDT lane combination. However, increased passage efficiency was likely a result of high river flow (Q2.0-Q30.6) during DDT/SDT comparison versus low (Q8.3-Q88.5) while the 2-m wide SDT lane was employed. There was no evidence that passage occurred using solely one stud configuration. It is, therefore, hypothesised that passage of river lamprey at weirs is more dependent on flow regime than the provision of either stud configuration. However, with 46.1% (n(passed/released)= 53/115) of those released during DDT/SDT comparison passing on the instrumented section (10.5% of weir face), the provision of studded tiles may aid in lamprey passage at high flows, presumably as the tiles generate a low-velocity boundary layer that can be utilised as lamprey swim above the studs.