Combining Bioenergetic Responses of Fish to Thermal Regimes and Productivity in Reservoirs: Implications for Conservation and Re-Introduction of Anadromous Salmonids

Temperature, food availability, and predation risk form vertical gradients determining growth and survival for fish in lakes and reservoirs. These gradients change on inter-annual, seasonal, and diel temporal scales and are strongly influenced by climatic variability, conflicting water demands and management. Temperatures associated with optimal growth and energy loss vary both among life stages and species of fish, but the quantity and quality of available food resources can significantly alter these thermal responses. Greater understanding of how water management affects the timing, magnitude, and duration of thermal stratification, and how key species and their supporting aquatic resources respond can improve strategies for development and operation of water storage facilities within the context of localized environmental and ecological constraints.

An emerging trend for coldwater reservoirs in the Pacific Northwest has been to re-introduce anadromous salmon above historically impassable dams. Thermal regimes and the existing ecological communities in the reservoirs and tributary habitats above these dams will determine the seasonal importance of lotic and lentic habitats for rearing or migration corridors. The feasibility of reservoir rearing and migration can be evaluated by combining mass- and species-specific thermal growth response curves with temporal dynamics in the vertical and longitudinal thermal structure of reservoirs and associated distribution of food resources (primarily zooplankton). The value of reservoirs as rearing habitats or migration corridors could be compared with coincident tributary conditions to predict the likely temporal-spatial distribution of optimal conditions for growth and survival of different species or life stages of salmonids within the watershed and how these conditions might change under different climatic or water management scenarios.