Assessment of fish passage improvements in the Nepean River
Rourke, M. and Baumgartner, L., 2011. Assessment of fish passage improvements in the Nepean River. Presentation given at the 2011 Annual Australian Society for Fish Biology Conference and 5th Australian Technical Workshop on Fishways. 22 – 24 July 2011, Townsville, North Queensland, Australia.
The Hawkesbury-Nepean system is the second-largest river system in New South Wales. Dams in the upper reaches of the major tributaries supply 97% of Sydney’s drinking water. Downstream of the dams, 10 major weirs from Penrith to Maldon regulate the flow to supply water for irrigation. The fish community of the Nepean River includes many diadromous species whose migration and genetic exchange may be impaired by these weirs. Fish passage has recently been re-instated along the Nepean River from Penrith Weir to Douglas Park Weir by installing vertical slot fishways at all barriers. Monitoring of the fish community before and after fishway installation using electrofishing, PIT tagging, fishway trapping and genetic analysis is currently informing whether the fishways are operating to design specifications. Early results demonstrate that some species have increased their distribution, including diadromous species. Population genetic analysis of Australian smelt populations prior to the fishways has also identified significant genetic differences between populations above and below Wallacia Weir; indicating this weir is a major barrier to upstream movements of this species. Follow up sampling will now be undertaken to determine if these differences break down following fishway installation.