Hydro Tasmania has successfully enabled upstream and downstream migration of short-finned eels through Trevallyn dam. Hydro Tasmania has installed an upstream juvenile eel ladder and downstream eel pass to enable these diadromous species to complete their life cycle.
The lifecycle of short-finned eels (Anguilla australis) commences in the Coral Sea, migrating to Tasmania’s inland waters where they can reside for decades until their final migration back to the Coral Sea for spawning. While short-finned eels they are highly capable of 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. The 27m high concrete gravity dam blocks the migratory path of eels between the kanamaluka / Tamar estuary and the South Esk river.
Upstream migration of juvenile eels is facilitated via an elver ladder commissioned in 2006 and a trap and transfer program, while downstream migration is facilitated by an eel bypass which was commissioned in 2020.
Performance of the bypass was assessed using hydro acoustics (Adaptive Resolution Imaging Sonar) in conjunction with traditional netting methods to provide annual passage estimates, and the results indicate that the bypass is performing beyond its design expectations.