There is a significant body of evidence that global stocks of freshwater eel (family Anguillidae) are in decline. Of the 19 known species or subspecies of freshwater eel, four are listed as threatened on the IUCN Redlist. It is likely that the often arduous catadromous migration requirement of anguillid eels contributes to the vulnerability of this family to anthropogenic disturbances.
Short finned eels (Anguilla australis) are an important component of south eastern Australia’s native freshwater fish fauna. While they 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 short finned 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 deployed an adaptive resolution imaging sonar (ARIS) on the intake of Trevallyn power station and implanted downstream migrating eels with Juvenile Salmon Acoustic Telemetry system (JSATS) tags to obtain information on migrating eel behaviour around the dam, power station intake, and tailrace.
The study showed that there is significant potential to explore the development of downstream passage facilitation at Trevallyn, as eels showed aversion to entering the power station intake, and did not necessarily enter it upon their initial encounter. Hydro Tasmania is currently designing a downstream bypass system that aims to safely pass eels downstream by capitalising on the results of the migration behaviour study.