CASE STUDY: Pest fish exclusion screens A case study of the effectiveness of exclusion screens in preventing the movement of pest fish through irrigation networks Introduction Regional Council, the Barron River Integrated The Mareeba-Dimbulah Water Supply Scheme Catchment Management Group, Mitchell River (MDWSS) is a network of piped siphons, Watershed Management Group, Tablelands balancing storages, weirs and concrete or Fish Stocking Society, Sunfish, Fisheries earth-lined channels located on the Atherton Queensland, the former Agency for Food and Tablelands in north Queensland. The network Fibre Sciences (now part of DAFF), Queensland was built during the 1950s to supply irrigation Conservation Council, Queensland Seafood water to the Barron, upper Mitchell and Industry Association, and SunWater. These Walsh river catchments. Water moves via this stakeholders also collaborated during the distribution network from Tinaroo Falls Dam screen design and construction phase. Screens on the Barron River in an easterly direction, were funded and installed by SunWater. while the Mitchell and Walsh river catchments Process flow in a westerly direction towards the Gulf A stakeholder committee with representatives of Carpentaria. from local and state government departments, Tinaroo Falls Dam is now home to a number of community and industry groups and water introduced fish species, including the invasive supply managers formed to work out the level Mozambique tilapia and the black mangrove of risk and potential management options for cichlid or spotted tilapia. Mozambique tilapia preventing the spread of tilapia from Tinaroo were first discovered in Tinaroo Falls Dam Falls Dam. The committee determined the during the late 1990s and black mangrove risk of tilapia being spread via the MDWSS cichlids were discovered a few years later. network to be very high and recommended Since their introduction, both species have a multi-faceted management approach. They rapidly colonised Tinaroo Falls Dam as well recommended increasing public awareness as most of the Barron River and its associated of the tilapia issue, further research into the tributaries. biology and ecology of both tilapia species, The presence of tilapia in Tinaroo Falls continued monitoring of westerly-flowing Dam has increased the risk of these species catchments for tilapia, and the installation of invading westerly-flowing Gulf of Carpentaria exclusion device(s) to stop the movement of catchments through the MDWSS network. Due tilapia through western parts of the irrigation to increased connectivity of Gulf systems network. during monsoonal flooding, tilapia have the A number of investigations and feasibility potential to rapidly colonise other parts of studies2 were done to determine the best the Gulf drainage, including environmentally exclusion device for the task. Physical and sensitive wetlands. Exclusion screens were electrical barriers were evaluated and possible trialled as a way to prevent the spread of installation sites were identified. The cost, tilapia species from Tinaroo Falls Dam into volume of water to be filtered, velocity of flow, western catchments via the MDWSS. physical size of the barrier, maintenance and Partners and management the size of the fish were important factors to A range of stakeholders contributed to a be considered. A decision was made to install tilapia risk assessment and management plan a static inclined screen, known as a Coandã- for the MDWSS in 20031 including several effect screen3, which was found to be the most local councils now operating as the Tablelands efficient and cost-effective screening device. CASE STUDY: Pest fish exclusion screens A case study of the effectiveness of exclusion screens in preventing the movement of pest fish through irrigation networks Features of the program • The self-cleaning function of the screen The main feature of this program was the use has helped keep ongoing maintenance of Coandã-effect self-cleaning screens. This costs to a minimum. was the first time that screens of this type had • The feeding of filtered material collected by been used in Australia for the exclusion of pest the screen into eastwards flowing sections fish. The screens are made up of horizontal, of the MDWSS has also worked to minimise stainless-steel wedge wires spaced at 0.5 mm the chance of tilapia spreading downstream intervals. Wires are tilted at an angle of 3–6 into western-flowing catchments. degrees toward the bottom of the screen panel • Extensive community consultation during to encourage the movement of debris down the screen design and construction the screen face. This configuration enables phase kept stakeholders informed of the self-cleaning function of the screen, and developments. This helped to increase reduces the need for mechanical cleaning. community confidence and support for the Coandã-effect screens are typically installed screening project. on the downstream face of an overflow weir, Other considerations so that water flows over and down the face of • Screens are relatively expensive to design, the screen panel. Filtered water falls through construct and install. the screen mesh and is collected in a channel • Material filtered by screens needs to be underneath the screen. Overflow water, debris disposed of at a sensible location to stop and fish are transported to a collection area possible downstream spread of fish. at the base of the panel and disposed of away from the original water source. • Screens need regular cleaning to prevent the build-up of calcifying algae that clog Results the screen and cause overflows. A 0.5 mm Hydro-Shear Coandã-effect self- • Ongoing surveillance programs are needed cleaning screen was installed on the West to ensure screens are working effectively. More info? Barron main channel in December 2004 at a cost of $1.3 million2. The 0.5 mm mesh was Conclusion selected to effectively exclude all tilapia In this case study, installation of a Hydro- Contact: life stages from the water, including eggs. Shear Coandã-effect screen successfully DAFF Queensland prevented the spread of tilapia through An interpretive sign was put up near the Primary Industries Bldg fish exclusion screen to give visitors a basic the Mareeba-Dimbulah Water distribution explanation of how the screen works and why network. This method may be applicable in 80 Ann St, Brisbane, it was installed. other circumstances where there is a need to Queensland, Australia So far, the exclusion screen has been control the movement of pest fish. GPO Box 46, Brisbane, successful in preventing the spread of tilapia References Qld through the MDWSS into western catchments. 1. Regional management plan for tilapia 13 25 23 (within Qld) or Recent fish surveys found black mangrove (Barron and Mitchell catchments). +61 7 3404 6999 cichlid juveniles immediately upstream of SunWater Annual Report the screens. However, no tilapia have been 2. SunWater (2005). Fax: +61 7 3404 6900 2004–2005 found in the channel system or the associated . [email protected] balancing storages below this point4. Ongoing 3. United States Department of the Interior annual fish surveys will continue to monitor (2003). Design Guidance for Coanda-Effect for tilapia both up and downstream of the Screens. exclusion screen. 4. Pearce MG, Shepherd L and Stewart R (2010). Pest Fish Exclusion Screens on What worked and why the Mareeba-Dimbulah Irrigation Scheme: • The mesh size and careful placement of the 2009-2010 Tilapia Surveys. Fisheries screen have been two important factors Queensland, Cairns. in the success of this program. Together, these worked to prevent the movement of Invasive Animals Ltd has taken care to validate the tilapia eggs and larvae, as well as juveniles accuracy of the information at the date of publication [April 2014]. This information has been prepared with and adults. care but it is provided “as is”, without warranty of any kind, to the extent permitted by law. pestsmart.org.au TILCS2.