Predictive Models of Benthic Macroinvertebrate Density for Use in Instream Flow Studies and Regulated Flow Management

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Abstract
As an adjunct to the U.S. Fish and Wildlife Service incremental method for determining habitat suitability for sport fish species at various discharge levels, we propose a similar method for determining optimum conditions for stream macroinvertebrates that stresses predictions of density maxima and flow predictions for maintenance of suitable lotic habitat.The curve fitting equations of the computer simulation showed high reliability in predicting physical habitat tolerances of selected aquatic insects. An example using Nectopsyche lahontonensis is presented.The new predictive model, by exponential polynomial analysis, answers criticisms of earlier models which do not include the dependence of velocity and depth in stream channel hydraulics. The added cross-product term in the model altered the predicted peak responses (density) with random changes in depth and velocity. Although the new model improves the predictions, its effectiveness in stream management has yet to be tested.Key words: habitat suitability, macroinvertebrates, exponential polynomial analysis, flow management, Nectopsyche lahontonensis