There is a significant body of evidence that global stocks of freshwater eel (family Anguillidae) are in decline, and it is likely that the vulnerability of anguillid eels to anthropogenic disturbances is compounded by their often arduous migration requirements.
While short finned eels (Anguilla australis) are adept at negotiating a wide range of natural instream barriers, large dams and weirs impact upon both upstream and downstream migration. Trevallyn dam is located in the downstream reaches of Tasmania’s largest water catchment, and blocks the migratory path of eels between the Tamar estuary and the South Esk River. Upstream migration of juvenile eels past the dam is facilitated via an elver ladder and a trap and transfer program, however the dam spills infrequently and downstream migrating eels have little option but to pass through Trevallyn power station to reach the estuary.
Hydro Tasmania conducted a range of studies to understand the migration behaviour of eels around the power station intake. The results of these studies informed the design of a downstream eel bypass for Trevallyn dam. Construction of the bypass commenced in February 2020 and wet commissioning was conducted in June 2020.
A monitoring program to assess the performance of the bypass will be conducted during the 2020-2021 migration season. A range of approaches will be used, including downstream netting, the deployment of Sensorfish to quantify passage hydrological characteristics, and the use of Adaptive Resolution Imaging Sonar and underwater video to observe eel behaviour in and around the bypass entry.