This project will be conducted by the US Geological Survey (USGS), US Fish and Wildlife Service (USFWS), and Pacific Northwest National Laboratory (PNNL).  The goal of this project is to provide empirical data and analyses on the dam passage timing, travel rate, survival, and life history variation of fall Chinook salmon juveniles in the Clearwater River that subsequently pass downstream in the four lower Snake River reservoirs from spring to winter.  The lack of this information has made it difficult to plan and evaluate aspects of hydrosystem operation including transportation and the timing and location of summer spill.  We propose to use radio telemetry, PIT tags, a gene expression study, and bioenergetics to study migratory behavior, survival, and life history.  Subyearling fall Chinook salmon will be collected and tagged weekly September through November at Lower Granite Dam to estimate fall and winter bypass probability and survival at the dam.  The effects of of cool water released from Dworshak Reservoir will be further investigated by examining whether cool water interrupts physiological development such that it could explain fish choosing a yearling life history strategy.  This will be accomplished by studying gene expression and physiological development during rearing and migration in the Snake and Clearwater rivers.  This work will be further validated by using bioenergetics modeling to examine how growth opportunity is affected by factors such as changes in fish physiology, temperature during summer flow augmentation, and food resources during rearing and migration periods.  Each component of this study will provide additional understanding of the factors that contribute to some fish adopting a subyearling life history while others hold over and adopt a yearling life history.