The Sea to Hume Fishway Program was the largest fish passage rehabilitation project ever undertaken in Australia. It involved constructing 16 world-class fishways, restoring migration options to over 2500 kilometres of the Murray River. Lee Baumgartner explains why this achievement is so significant and how this program will contribute to the recovery of native fishes.
The concept of facilitating fish passage at potential barriers in the Murray-Darling Basin (MDB) has been discussed since the early 1900s, coinciding initially with a Murray cod summit in 1903, and continuing following the construction of weirs along the River Murray in the 1920s. The weirs fragmented the Murray main channel, preventing fish from completing important spawning, feeding and recolonisation movements.
The first fishway built in the MDB was at Lock 6 in 1930, with another at Lock 15 in 1936. At that time, fishway designs that were doing a great job passing salmon in the northern hemisphere, were used in Australia. It was almost 50 years late that we would realise that salmon fishway designs are inadequate for Australian native fish. This led to work identifying designs tailored to the swimming abilities and behaviour of Australian fish.
The River Murray Commission’s Working Group on Native Fish was convened in 1983, and during the next three years made recommendations on the construction of fishways. Research was commissioned, which culminated in the first ever design specifications for Australian native fish. These specification were used to construct a vertical slot fishway on the Murray River at Torrumbarry Weir which was a phenomenal success, allowing year-round passage upstream for the first time in over 50 years.
Still, another 20 years passed before the implementation of the Native Fish Strategy, which, combined with a need to meet legislative requirements as part of a lock and weir upgrade, presented a once-in-a-generation opportunity to facilitate fish passage along the entire length of the Murray River. This was the genesis of the Sea to Hume Fishway Program.
In 2001, there were 20 main barriers to fish migration along the length of the River Murray, with fish passage only possible at Torrumbarry Weir, or during high-flow events when weirs were removed or drowned out. Recognising the immense scale of the job, a fish passage task force comprising engineers, fish biologists and river operators was established. These experts standardised the initial design criteria and the construction process began. It took just 12 years, and a cost of around $78 million, to construct 16 world-class fishways suitable for Australia’s native fish. Fish from as small as 40 millimetres, and as large as 1 metre, can now move from the Coorong in South Australian, to the Hume Dam near Albury, a distance of some 2500 kilometres.
It was important that fishway designs were based on native fish ecology, and this proved to be an excellent opportunity to use an adaptive management approach – to build a fishway, learn about its performance, and apply successful design techniques at the next barrier.
The performance of fishways was assessed by a unique tri-state research collaboration between New South Wales, Victoria and South Australia. While the monitoring program has now concluded, the collaboration of these researchers continues, and is another legacy of this innovative program.
The first vertical slot fishway design aimed to pass all fish species, something that no other fishway project had aspired to. Building such a fishway was costly, requiring a lot of sheet piling, excavation and concrete. The tri-state team were asked to identify an alternative more cost-effective solution. Following a series of experiments it was decided that it was more cost-efficient, and biologically effective, to build a pair of fishways targeting small-bodied and large-bodied species separately. The large species fishway could have faster water and a steeper slope, while the small fish could pass via a lock, producing hydraulic conditions far better for their passage.
The tri-state team also developed and implemented Australia’s biggest ever fish movement monitoring system. Using microchip technology, similar to those used in pet animals, listening stations were installed in every fishway constructed as part of the Sea to Hume Fishway program. The microchips, otherwise known as PIT tags (passive integrated transponder), track individual fish through the fishways. The PIT system network established by the tri-state team has since expanded to include other, non-murray fishways,s such as those on The Living Murray environmental works at Chowilla and Koondrook-Perricoota, the Stevens weir and the Edward River offtake, and a number of fishways throughout the New South Wales and Victorian areas of the MDB.
The tri-state team has implanted PIT tags in over 24,000 fish, with many more fish being tagged by other monitoring programs throughout the MDB. The PIT detection system has the ability to monitor the movement of Murray cod, Golden perch Silver perch, Bony hearing, lamprey and Freshwater catfish. A significant number of carp have also been tagged, which will inform future control efforts.
The PIT tag system has erected some long-range migrations of individual fish. Silver and Golden perch migrations have been recorded over distances of more than 1000 kilometres. Some species have also exhibited coordinated movement behaviour, with several individuals detected at fishways within hours of each other, and then detected again at the next fishway upstream. More remarkably, the system is able to be linked with flow data, enabling mangers and researchers to report on the success of environmental water delivery, thus helping report on Basin Plan objectives. The legacy of the PIT reader system will be a much better understanding of the ecology of native fish, and an improved ability to measure the success of the mitigation of barriers to fish passage.
Completing the Sea to Hume Fishway Program was a significant achievement, but now is the most exciting time for fish ecologists and river mangers. With over 2500 river kilometres available for fish passage, and an Australian-first PIT monitoring system in place, the activities and outcomes of the Sea to Hume Fishway Program and tri-state team, will become more and more apparent into the future.
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