2004 – Modelling the Response of Native Fish to Altered Habitat, Flow and Temperature Downstream of Large Dams

Simon A. Treadwell, Michael Shirley, Rory Nathan, Kylie Swingler

The Murray Darling Basin Commission through its native fish strategy has embarked on a comprehensive program for improving fish health in the basin. The strategy is aimed at managing and mitigating a range of threats including loss of habitat, altered flow regimes and thermal pollution downstream of large dams.

To help identify the relative benefits of different management options SKM developed a numerical ecological model. The model produces an index score that provides a measure of condition for native fish under various habitat, flow and temperature scenarios. The model uses a series of preference curves that define habitat requirements, critical spawning periods, spawning temperature thresholds and upper and lower temperature limits for egg, larval and adult survival. An index score of 1 is applied if conditions are ideal and an index score of 0 is applied if conditions are intolerable. Different temperature time series and habitat extent can be modelled to generate condition scores related to each fish life-history stage. Comparisons between the natural condition and those related to various reservoir release regimes can be made, for example to examine the likely effects of cold water releases or the benefits that could be achieved through the use of multi-level outlets. This can be compared with the relative benefits of restoring habitat or changing flow regime.

The results from a case study examining the relative benefits to native fish from managing flow, temperature and habitat downstream of Dartmouth Dam will be presented.

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