Advanced methods for assessing temperature effects on fish

At many hydropower and water projects in the west and south, instream flow releases are augmented to provide summer water temperatures cool enough for fish. Temperature effects are typically assessed only by predicting whether or not a simple criterion will be exceeded. Two models that overcome the limitations of this approach have been evaluated. Bioenergetics models predict how temperature affects fish growth. This approach is established in the literature and is relatively simple and inexpensive. A more complete alternative is the CompMech models developed by the Electric Power Research Institute, which incorporate many complex effects of temperature on the fish populations. These models have been calibrated to several study sites and used to evaluate effects of climate change. The main advantage of these advanced methods is that they provide an 'incremental' approach that allows comparison of alternative temperature regimes and design of cost-effective mitigation. Drawbacks include the models' sensitivity to uncertain variables like food availability, and that predicted changes in growth may actually be manifested as changes in fish abundance, making calibration and verification difficult.