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Watching fish on the Murray River has led to innovative fishways that are helping restore environmental flows of rivers in Australia.
Efforts to restore river health are just as much about restoring the river ecosystem as about restoring environmental flows. Much effort is being made in Australia to restore the river ecosystems of “icon” rivers. This is driving clever innovation in many areas, including how to assist the recovery of endangered native freshwater fish, which play a crucial role in the ecosystem of rivers. Native freshwater fish have struggled for many reasons, including the imposition of numerous barriers to their movement plus the introduction of non native species like the European carp that cause significant environmental damage, such as degradation of water quality. They also compete for food with native species. To address the barriers to fish movement, fishways are now being placed in many of Australia’s rivers to help fish pass through, around or over these barriers. Catching carp
Alan Williams, whilst employed by Goulburn Murray Water, invented a design for a fishway that catches up to 90% of the European carp that pass through it without harming native fish.
It is a viable and practical, low cost method of separating invasive carp from native fish. Williams’ insight came in late 1998 at his weir at Torrumbarry (Victoria) while he was watching the Murray River. He noticed that carp jump and native fish don’t. And that simple observation has led to the successful mechanism and design of this fishway.Williams stated that the current working model was notinvented overnight. “I started experimenting withfishway designs slowly back in 1999 without success. Forinstance, it took some experimentation to realise that the barrier had to be at least 150 mm high or else the native fish would also be able to jump enough to get through. Then I met Ivor Stuart from the Victorian Department of Sustainability and Environment and his colleagues at Arthur Rylah Institute, who agreed to help me develop the final effective design for this new fishway device. They helped to get funding from The Murray-Darling Basin Commission in Canberra to develop the cage and associated research.”
How does it work?
“As the fish swim upstream they are caught in the first cage of the trap,” says Williams. “The carp jump into a second cage, leaving the native fish free to be released to continue their journey upstream. Whilst the carp jump into the second cage the native fish wait for the floor of the first cage to automatically open. Getting the automated technology and timing right was the most challenging part of the final design. The floor of the first cage could not open too early as the carp may jump back into the river, but it could not wait too long because some of the adult native fish were moving upstream to spawn. ”To address this design challenge they developed a fully automated tipping system to ensure that native fish do not have to wait long for the floor of the first cage to open. “A simple timer switches on a pump to deliver water to an overhead drum, used as a counterweight to lift the first cage,” says Stuart. “Luckily, carp move and jump during the daytime, while many natives are nocturnal, so setting the timer for 10pm maximises the catch of carp but delays native fish the least. In future, a fish counting system will replace the timer to better detect when enough fish are still in the first cage and send a signal to start moving the counterweight to open the floor of the first cage. “The Murray-Darling Basin Commission is installing these carp cages (or Williams cages) in a series of new fishways along 1,500km from the mouth of the Murray River all the way up to Torrumbarry Weir. The lower Murray is where carp are most common.” Open source technologyOne of the reasons for the rapid uptake of this technology is that Williams, Stuart and their team decided not to patent the invention and make the intellectual property open source for the public good. Hence the relevant government and water authorities who are making use of this innovation can either manufacture it in-house, using their own teams of mechanics, or they can hire local mechanics to make this novel pest control technology. “Once we had invented this and it clearly worked, we asked ourselves ‘what is our goal?’” says Stuart. “Our goal is to ensure, that within the next 10 years, the levels of carp in rivers in Australia and around the world are dramatically reduced. Making this invention’s intellectual property freely available will help ensure the rapid uptake of this technology and make it possible to achieve this goal. Already there is interest in this innovation from New Zealand and the USA. These are very simple and cheap devices to build.” The cage is not just a good idea, but an example of fast co-operative development to the stage where new cages on the Murray River are already having an impact on carp populations. http://www.g-mwater.com.au/
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