Impacts of Thermal Discharges and Temperature Variability on Fish Habitat Suitability: A Bioenergetics-Based Approach

             Much effort has gone into monitoring how power plant thermal discharges influence fish movement and species distribution.  However, such studies are often unable to demonstrate how discharges influence fish habitat quality or how sub-lethal responses are affected.  Furthermore, few studies have evaluated the importance of sub-daily temperature variability typical of discharges.  In order to address these issues, we used a bioenergetics approach to quantify fish growth rate potential (GRP) to spatially and temporally compare fish habitat quality.  We investigated thermal gradients adjacent to two power plants on the Ohio River by placing stationary thermistors upstream and downstream from the discharges.  We divided the environments adjacent to both plants into spatially-explicit cells in which we calculated GRP for juvenile and adult smallmouth bass (Micropterus dolomieu) and walleye (Sander vitreus).  Fish GRP was calculated using different variations of bioenergetics models that incorporated sub-daily temperature variation.  These adjusted models allowed for a more realistic understanding of how discharges affect habitat quality compared to models that only incorporate mean daily temperatures.  The results of our bioenergetics approach are useful to plant operators, regulators, and fisheries managers in order to visualize and elucidate the potential benefits and drawbacks that thermal discharges have on fishes.