ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Physical and Biological Impacts of Cold Water Dam Releases

Jarod Lyon, Ruth Lennie, Tom Ryan and Charles Todd

Arthur Rylah Institute For Environmental Research, HEIDELBERG, AUSTRALIA

THEME: ASFB

Irrigation releases from large dams are often made from outlets well below the dam stratification layer. As a result the thermal regimes of rivers downstream are greatly altered. Changes include reduced seasonal temperature range, rapid changes in temperature reduced the diurnal temperature variation, as well as delaying peak seasonal temperatures. As part of an Agriculture, Forestry and Fisheries Australia (AFFA) funded project, this project has collected evidence on the physical and biological impacts of cold water releases, particularly on native freshwater fish species found in the southern Murray-Darling Basin. Continuous temperature loggers installed in regulated streams including the Goulburn, Mitta Mitta, and Murray Rivers demonstrated changes in thermal regimes below these large dams compared to that in the relatively unregulated rivers such as the Ovens River. Egg survival of five native freshwater species (Murray Cod, Golden Perch, Silver perch, Freshwater Catfish, Trout Cod) demonstrated an intolerance for temperatures below 15°C. Two species of freshwater fish (Murray Cod and Freshwater Catfish) grown in five different temperatures (from 12.5 to 24.5°C) demonstrated the physiological impaction of cold temperatures, with fingerlings grown in temperatures at 15.5°C and less having signs in reduced growth rates and possible long-term side effects including stunting. Burst swimming performance of fish was measured on Golden Perch fingerlings acclimated to different water temperatures (12.5 to 24.5°C) and found a significantly reduced burst-swimming capability at temperatures below 15.5°C. In comparison trout species have a greater burst swimming capability than Golden Perch, which could lead to a significant competitive advantage where the two species co-exist. Temperature preference of Murray Cod, Golden Perch and Rainbow Trout acclimated to five different temperatures demonstrated that most native species preferred a warmer temperature of 26°C to 30°C, compared to the cooler temperatures favoured by trout species Simple populations dynamic models (e.g. Murray Cod) were deployed using the physical or biological information obtained from the other components of this project. They demonstrate the impacts of altered thermal regimes on the survivorship and sustainability of fish populations attempting to exist downstream. Native fish populations have obviously been significantly impacted by the altered thermal regimes. However, with targeted physical and biological monitoring, they can provide an inexpensive assessment of the benefits of specific management options prior to undertaking expensive amelioration works.