Efficiency of a dual density studded fish pass designed to mitigate for impeded upstream passage of juvenile European eels (Anguilla anguilla) at a model Crump weir

This study demonstrated that juvenile (glass) eels utilised a specific substrate (eel tiles) to circumvent a model Crump weir under an experimental setting. Upstream passage efficiency was 0% and 67% for the unmodified (no studded eel tiles on the downstream face; control) and modified (with studded eel tiles on the downstream face; treatment) setups, respectively, and greater for a small (59%) compared to large (41%) stud configuration. Eels were active and motivated to ascend the weir during both control and treatment setups. Approach and attempt rates were elevated during the first few minutes of the treatment compared to control trials. Eels were edge oriented under both setups, and ascended the weir through the tiles during single burst swimming events (reaching estimated speeds of 68.5 cm s-1). Eel tiles may provide a cost effective solution for mitigating impacts of anthropogenic barriers to juvenile eel migration. Further research is required to determine passage efficiencies under higher flows, for a greater size range of eel, and for other migratory anguilliform fish (e.g. lamprey, Lampretra spp. and Petromyzon marinus L.). The performance of eel tiles should be validated through robust field studies