Changes in fish assemblages after the first flow releases to the Snowy River downstream of Jindabyne Dam.
Since construction of the Snowy Mountains Hyrdo-electric scheme in 1968, flows in the Snowy River downstream of Jindabyne Dam had been reduced to only 1% of natural flows. This has had substantial impacts on riverine habitats and the abundance and distribution of fish throughout the catchment. In order to rehabilitate the Snowy River, the NSW government initiated an environmental flows program, where flows in the lower Snowy will be increased over a number of years, until 28% of natural flows are provided for the environment. This is predicted to result in significant improvements in fish communities in the Snowy catchment.
As part of the environmental flows program, the NSW government initiated a long-term, before-after sampling program to gauge the response of fish populations to the provision of environmental flows. This report presents the results from fish sampling done over the 6-year period 2000-2005. In the first three years (2000-2002) the sampling described the fish communities present in the catchment before any environmental flows were released. In the subsequent three years (2003-2005) we documented the response of fish assemblages to the first incremental increase in environmental flows (an amount of water equivalent to 6% of natural flows). The abundance, diversity and size-structure of native fish species, the abundance of trout, the abundance of introduced pest species, and the quality of fish habitat were compared before and after implementation of the new flow regime. To date, no significant response has been detected for any of these variables. This was not unexpected given the very modest increase in flow rates. Most of the measured variables should, however, respond to environmental flows once at least 20% of natural flows have been provided over the next few years.