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fishtrack story
29 Oct 2010
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Tributaries of the Clarence River in Northern New South Wales have long attracted the attention of those seeking to develop hydro-electricity, irrigation or domestic water supply schemes. Since 1924 flows from the Nymboida River have been diverted for the generation of hydro-electricity and together with the Orara River supply water for the Lower Clarence and Coffs Harbour communities. In an effort to ensure these water extractions do not impact upon river health a partnership project was initiated in late 2005. Acoustic tagging techniques have been employed to investigate the relationships between river flows and the movement of five key fish species, including the endangered Eastern Freshwater Cod and the iconic Australian Bass. Installation of 80 acoustic receiver stations extending over 600km of river length from the lower estuary into numerous upper freshwater tributaries, has enabled tracking of over 240 individual fish which have been surgically implanted with acoustic transmitters. Flows at particular times of the year can be important to different fish species. Three of the species tagged need to migrate to the estuary to breed making long journeys throughout the river system. One tagged Australian Bass travelled more than 1000km in 18 months making 2 migrations to the estuary and back to freshwater reaches. Relatively small rises in late autumn to early winter in 2008 and 2009 seemed to have triggered the downstream migration of Australian Bass to breed in the saline waters of the estuary. In 2010, there were no recordings of downstream migrations by Australian Bass, presumably because the rivers did not receive a fresh during this period and provide a trigger for movement. Fish movements were often impeded by instream barriers. Sometimes individuals stayed for extended periods below barriers, such as waterfalls or the Nymboida Weir until an increase in river flow provided an opportunity to move over or around the barrier. Ongoing summer and winter sampling of fish communities at 27 sites within the Clarence, Mann, Nymboida and Orara rivers has shown the Clarence gorge falls to have the most significant impact upon the species composition of the fish community. Located only 40km upstream from the Clarence river mouth, waterfalls within the Clarence gorge form a significant barrier to upstream migration of fish such as Bass and mullet. Scientists have modelled high resolution topographic and depth sounding data and predicted that the gorge falls have flooded out on average once every year and a half sufficiently enough to enable fish to move upstream. Comparisons of river flow data with the recorded movements of bass over or around the gorge, has confirmed these predictions and highlighted the importance of annual flood events in facilitating fish passage over the gorge. Fishtrack has demonstrated the importance of understanding the relationship between river flows and the life history of key fish species and together with its sister project in the Shoalhaven River holds much value in providing guidance in the management of water resources and maintaining river health in coastal NSW Rivers. Now and into the future.

Community fish research fish tracking river management
Comments (1)
alastair maple Tue, 2 Nov 2010 5:52pm