The Central Valley Spring-Run Chinook Life Cycle Model and Its Pre-Spawning Mortality Component: Evaluation of Water Management Impact on the Population Dynamics

Central Valley spring-run Chinook salmon populations are listed as threatened under the Federal Endangered Species Act (ESA) since 1999. They exhibit unique features throughout their life cycle and our goal is to show how water management could strongly influence their dynamics at the life stage as well as at the population level. One of the characteristic of adults spring-run Chinook salmon is that they leave the ocean as immature and hold in high elevation pools throughout the summer before spawning. As a result significant mortality events during the summer holding period have been reported in Butte Creek population, one of the Central Valley streams that continue to harbor a sustaining population. Based on data from pre-spawning mark-recapture carcass surveys conducted each year in Butte Creek, a generalized linear mixed model (GLMM) has been developed to clearly identify the different factors (i.e. flow, water temperature, fish density…) influencing the survival of adult spring-run during the summer months. The results obtained will then be incorporated in the Central Valley spring-run Chinook salmon life cycle model and will help assess the influence of water management in the spawning habitat on the evolution of spring-run population abundance.