Cooperative Fish and Wildlife Research Units Program: Washington
Education, Research and Technical Assistance for Managing Our Natural Resources

Re-introduction of anadromous salmonids above previously impassable dams is becoming an increasingly common mitigation strategy in the Pacific Northwest. The reservoirs impounded by these dams create novel habitats that juvenile salmonids can use for rearing and migration corridors. Therefore, understanding how environmental conditions, seasonal food supply, competition, and predation influence potential growth and survival of juvenile salmonids will be important when evaluating the feasibility of proposed re-introductions above historically impassable dams. 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, but the quantity, quality, and spatial distribution of available food resources can significantly alter these thermal responses. By combining data or projections of thermal stratification regimes with the vertical distribution of prey and bioenergetic capabilities of species and life stages of fish, we can formulate predictions about spatial-temporal overlap among prey, competitors and predators. When overlaid on life history requirements, we can identify potential bottlenecks to growth or survival and evaluate responses to climatic variability, water management, or new species.