As Australia’s largest water manager considering the migration of native fish is an important part of running our sustainable business.
Without dams, fish that need to migrate between freshwater and salt water to complete part of their lifecycle can do so freely. Short finned eels migrate from the sea into freshwater as juveniles (elvers) where they grow and mature and lampreys migrate from the sea into freshwater streams as adults where they spawn. Dams can be a significant obstacle to these annual migrations, so we are assisting migration at Trevallyn Dam on the South Esk River, and at Meadowbank Dam on the Derwent River.
- Trevallyn elver ladder
Eels are ecologically important in Tasmanian inland waters as they are the only large, native, predatory fin fish. Eels breed in the sea and juvenile eels (elvers) return to freshwater streams, migrating upstream in large numbers every year in late spring and summer.
The Trevallyn elver ladder provides safe passage for elvers over Trevallyn Dam. The elvers climb up the ladder and are automatically transferred into waters to continue their journey throughout the South Esk catchment where they can mature.'
Hydro Tasmania has been tackling the elver migration issue at Lake Trevallyn since 1996. Every location is unique, and it has taken a while to get the design right. The current elver ladder and automated trap, completed in 2009, has proven to be highly successful. It was built at the eastern abutment of the dam to utilise the internal drainage channels and runs up the side of the stairwell rising 30 metres through the dam wall, making it the highest operational ladder in the southern hemisphere. The ladder is very efficient at facilitating the migration of elvers past Trevallyn Dam and is effective throughout the season, handling periods of low and high migrations without mortalities. The estimated yield for the 2010-11 migration season was 100,000 elvers, the ladder handling in excess of 5000 elvers per week during peak season.
‘Helping eels climb dam walls: the elvers' story’, provides an insight into eel migration and how the Trevallyn elver ladder works, download the pdf >
- Meadowbank fish trap
At Meadowbank Dam, a short fish ladder leads to a large fish trap. This trap, operated by the Inland Fisheries Service (IFS), collects elvers during their annual migration (from late spring to early autumn), which are then relocated into Lake Meadowbank and other Hydro lakes as part of a re-stocking program.The Meadowbank trap is also used for adult lampreys which migrate upstream in early spring. Lampreys are primitive jawless eel like fish that spend most of their life in the sea but migrate into freshwater streams to spawn. Although they are very efficient climbers, using their sucker like mouth (called an oral disk) to cling onto surfaces, they cannot climb over the dam wall – it’s just too high. Lampreys caught in the trap are relocated into Lake Meadowbank where they can continue their journey upstream and complete their lifecycle.