No models exist for quantitatively estimating the impact of chronic or episodic increases in turbidity on juvenile salmon growth rates. To provide a credible basis for quantifying the impacts of increased turbidity, and to provide a tool for developing monitoring and assessment guidelines for forestry impacts on stream turbidity, we have developed a basic drift-foraging bioenergetics model to predict the impact of turbidity on juvenile salmon growth rates. The model involves developing a function reducing the reactive distance of fish to drifting invertebrates as a function of increased turbidity, and inserting this function into a bioenergetics model that predicts growth of fish based on invertebrate drift-feeding. Over the 4-month course of this project, model development involved 1) a review of the primary literature to identify studies that have documented turbidity-reactive distance relationships for salmonids 2) Statistical analysis and data-fitting for these studies to derive an average function describing decrease in reactive distance with increasing turbidity 3) Insertion of this function into a bioenergetics drift-feeding model 4) Testing of the bioenergetics model to see whether it could predict observed decreases in growth rates of fish experimentally documented in the published literature. The model appears to be very successful in terms of predicting observed changes in growth rates based on the only published study with sufficient data to test it. The model has enormous potential as a management tool to predict sub-lethal effects of impaired water quality by providing a credible basis for evaluating how changes in turbidity and channel structure affect fish growth. In it?s final form, this model will provide an accessible tool for developing monitoring and assessment guidelines for forestry impacts on stream habitat and water quality, pending sufficient funding for its development. Jordan Rosenfeld, Josh Taylor.
Rosenfeld, Jordan, Taylor, Josh; British Columbia Ministry of Water, Land and Air Protection. 2003. Modelling the effects of changes in turbidity and channel structure on growth of juvenile salmonids. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2003MR359