New Zealand Journal of Marine and Freshwater Research abstracts
Predicting growth and mortality of brown trout (Salmo trutta)in
the Goulburn River after mitigation of cold-water discharge from Lake Eildon,
Australia
Paul Brown
Primary Industries Research Victoria
Department of Primary Industry
Private Bag 20
Alexandra, VIC 3714
Australia
email: paul.brown@dpi.vic.gov.au
Abstract 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 (Salmo trutta) and to 3 years of river
temperature data, to predict growth and mortality. Best fits of the models
suggested that both energy intake and temperature regime currently limit
growth. Flow management scenarios for the Goulburn River downstream of Eildon
Reservoir, Australia, that increase the average daily river temperature by
2 and 4°C, substantially reduce the potential for brown trout growth.
An average daily 2°C 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°C rise reduced the potential maximum size of brown trout
by 30-43% and increased the time taken to reach 300 g 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 brown and rainbow trout
fishery. The present study shows that the quality and quantity of brown trout
that would be available under strategies proposed to mitigate cold-water
flows are unlikely to continue to sustain a viable, high quality trout fishery.
Keywords brown trout; Salmo trutta; growth; natural
mortality; energetics model; river temperature; cold-water pollution; Goulburn
River; tailrace
M03095; Received 15 December 2003; accepted 5 March 2004; Online publication
date 8 June 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38:
279-287
0028-8330/04/3802-0279 © The Royal Society of New Zealand 2004
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