En_Fish in hand

Helping fish migrate

Tasmania has 25 species of native freshwater fish. Some of these are diadromous, that is, they migrate between fresh and marine waters to complete their life cycle.  Short finned eels occur throughout many of the state’s river catchments, and are the state’s largest, native, predatory freshwater fish.

Their migratory behaviour requires them to travel to the Coral Sea to spawn. Juvenile eels then eventually return to rivers to mature. It’s an arduous journey that we work hard to make as safe possible with regards to our dams. We work collaboratively with the Inland Fisheries Service to assist their passage past barriers that may block their migration. We have particular strategies at Trevallyn Dam in northern Tasmania, and Meadowbank Dam in the south.

 

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Trevallyn elver ladder

At Trevallyn Dam, elvers (young eels) use a ladder to ‘climb’ the dam wall and reach the South Esk River and beyond. We also work with the IFS to capture elvers from the Tamar Estuary and transport them upstream past the dam.  

We’ve been supporting elver migration at Trevallyn for more than 20 years, and the ladder has been in place since 2009.

It’s arguably the busiest elver ladder in the southern hemisphere, passing 10’s of thousands of elvers each week in peak season. The system uses the dam’s internal drainage channels. It runs up the side of the dam’s internal access stairwell, rising about 30 metres through the dam wall.

 

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Meadowbank fish trap

At Meadowbank, just north of New Norfolk, we use a short ladder and large fish trap to collect elvers and move them safely upstream into Lake Meadowbank.

The system also supports adult lampreys (primitive jawless eel-like fish) which migrate upstream in early spring.



Downstream eel migration

We’re also turning our attention to helping adult eels at Trevallyn migrate downstream to the Tamar Estuary and out to sea.

To help those eels pass Trevallyn Dam, and avoid the turbines and hydraulic stresses of Trevallyn Power Station, we studied downstream migration for several seasons.

We mounted an Adaptive Resolution Imaging Sonar (ARIS) on the power station intake for two migration seasons, to closely observe eel behaviour around the clock, and implanted 105 eels with acoustic tags to track their movement. The results provided valuable insights into their behaviour around the dam and intake, and highlighted an opportunity to develop a downstream eel bypass at the site, which we’re currently designing.

© Hydro-Electric Corporation 2018