ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.

Likely effects on growth and mortality of brown trout (Salmo trutta L.) in the Goulburn River after Mitigation of Coldwater Discharge from Lake Eildon, Australia

Paul Brown

Marine and Freshwater Resources Institute, Department of Primary Industry. Private Bag 20, Alexandra, VIC 3714, Australia.
Email: paul.brown@nre.vic.gov.au

Published empirical models for growth and natural mortality were examined to investigate some of the potential effects on brown trout populations of flows managed to increase river temperatures downstream of a large reservoir. Models were fitted to length-at-age and size-at-maturity observations for brown trout and to three years of river temperature data, to predict growth rates. Best fits of the models suggested that both food availability and temperature regime currently limit growth. Flow management scenarios for the Goulburn River downstream of Eildon Reservoir that increase the average daily river temperature by 2 and 4 șC, substantially reduce the potential for brown trout growth. An average daily 2 ^oC increase reduced the potential maximum size of brown trout by 4–38% and increased the time taken to reach 300 g by up to 31%. An average 4 ^oC rise reduced the potential maximum size of brown trout by 30–43% and increased the time taken to reach 300g by 66–144%.

Existing models of the effects of environmental temperature on rates of natural mortality also suggest that raised water temperature will result in increased brown trout mortality rates although uncertainty associated with empirical temperature-mortality models is high.

Currently the Goulburn River downstream of Eildon supports a socially and economically valuable recreational trout fishery. The present study shows that the quality and quantity of brown trout that would be available under strategies proposed to mitigate coldwater flows are unlikely to continue to sustain a viable, high quality trout fishery.

Room 1 Thursday 11.30 am