Environmental water monitoring in unregulated rivers – Fish assemblages of Coopers Creek and the Wilsons River, with special reference to the Eastern Freshwater Cod
Butler, G., Mackay, B., and Hutchison, J., 2009. Environmental water monitoring in unregulated rivers – Fish assemblages of Coopers Creek and the Wilsons River, with special reference to the Eastern Freshwater Cod. A report prepared by the NSW Department of Primary Industries on behalf of the NSW Office of Water. NSW Office of Water, Sydney, Australia. 21pp. Available on-line at www.water.nsw.gov.au
Maccullochella ikei is endemic to the Clarence and Richmond River systems of northern New South Wales. A combination of factors including over-fishing, unsustainable land clearing practices, sedimentation, river regulation, introduced species and water pollution, resulted in the species becoming locally extinct throughout the Richmond Basin by the mid 1970s. Restocking programs between 1988 and 2002 saw over 65,000 M. ikei fingerlings stocked throughout the Richmond River catchment, including 13,000 in the Wilsons River System. On 1st July 2004, 31 Water Sharing Plans (Plans) came into effect throughout New South Wales, including the Coopers Creek Water Sharing Plan. The purpose of the Plans is to provide water to sustain aquatic environments, whilst defining an allowable level of extraction for agriculture, mining and urban use. Specific water requirements for key species, especially listed threatened species, are incorporated into the Plans. The eastern freshwater cod, Maccullochella ikei, was selected as one of the key species for the north-eastern region of NSW, and special flow provisions were included in the Coopers Creek Plan to meet its water requirements. Previous fish sampling in the Wilsons River system, including Coopers Creek, has been sporadic and has returned only limited catches of M. ikei. Doubts remain over the survival and breeding status of M. ikei in both systems. The aim of this study was to undertake a comprehensive survey of the fish assemblages in the Wilsons River and Coopers Creek, and to determine the abundance, distribution, and where possible, the age structure of the M. ikei population in these two sub-catchments.
Twenty-seven sites were sampled in the Wilsons River (14) and Coopers Creek (13) in May-August 2008, using electrofishing, bait-trapping and angling. A combined total of 3461 fish representing 22 species were captured or observed in both systems. The most abundant species were Reteropinna semoni, Melanotaenia duboulayi and Gobiomorphus australis. Anguilla reinhardtii was the most abundant of the large-bodied species. Tandanus tandanus, Macquaria novemaculata and two mullet species were also recorded throughout Coopers Creek and the Wilsons River. No M. ikei were captured at any site, but one individual was observed in the middle reaches of Coopers Creek. There was no significant difference in the fish assemblages between the two systems, but there were significant differences in the fish assemblages with altitude in both Coopers Creek and the Wilsons River. The low number of M. ikei observed in this study is similar to that reported in previous studies and indicates that while stocked cod have survived in Coopers Creek and the Wilsons River, the numbers are most likely very low.