An analysis of smolt survival with implications to flow management

Smolt survival through the Columbia/Snake river hydrosystem and tributaries of the Snake River are evaluated with the XT-model, which describes predator-prey interactions in terms of migration distance and time, temperature, turbidity, and a random encounter velocity between predators and prey. In this formulation, smolt survival depends on both distance traveled and exposure time, and the importance of each depends on the amount and character of predator and prey motions. The model is used to analyze factors that determine survival characterized in a PIT tag database of over five thousand individual survival estimates derived from PIT tagged fish between 1995 and 2002. The analysis indicates chinook and steelhead survival through the hydrosystem depends on migration distance, temperature, and the amount of spill at dams. In the tributaries above Lower Granite Dam, spring chinook survival depends on distance traveled from the release sites above the dam. Steelhead survival depends on migration distance and migration time but is independent of temperature, flow and turbidity. Fall chinook survival above Lower Granite Dam depends on travel distance and time, temperature, and turbidity. Evaluating the impact of flow augmentation and water withdrawals on smolt survival requires considering, first, how these flow management actions affect water velocity, turbidity and temperature, and second, how these properties affect smolt survival. The analysis suggests that flow management actions affect only fall chinook in the tributaries and that the impacts may be positive or negative. Furthermore, the analysis indicates that empirical regression techniques, without ecological foundations, are inadequate to understand and characterize the effects of water management actions of smolt survival.