Movements of juvenile Chinook salmon in the Sacramento Watershed, California

Juvenile Chinook salmon (Oncorhynchus tshawytscha) experience high rates of mortality as they out-migrate, frequently navigating through rivers heavily modified by human activities. Understanding patterns of movement and survival is key to informing management decisions in these human-dominated aquatic systems. Ultrasonic telemetry is a valuable tool allowing us to observe the movement patterns of aquatic animals. The first chapter of this dissertation examines the performance of an ultrasonic telemetry positioning system by comparing receiver arrays deployed in three diverse environments. It suggests that researchers utilizing a positioning system should focus on testing the geometry of receivers before the study begins, as well as minimizing receiver movements and maximizing the accuracy of speed-of-sound estimates. The second chapter uses an ultrasonic positioning system to observe the route selection of juvenile out-migrants at an artificial juncture in the tidal portion of the Sacramento River, California. The strongest predictor of ultimate migratory route was the relative water velocity at the river's junction with the water diversion channel. The third chapter describes patterns in survival through a segment of the lower Sacramento River. We applied a previously derived analytical model, the mean free-path length model, in a new way to determine whether predator densities or prey behaviors were more indicative of fine-scale mortality rates. The model indicated that the hatchery smolt were highly directional in their outmigration behavior, leading us to conclude that spatial patterns in survival of juvenile Chinook were driven by increasing density or efficiency of the predator community. Ultrasonic telemetry technologies can be valuable in habitats where direct observation of animals is difficult, including in large river systems such as the Sacramento River. Through the continuing advancement of these technologies, their careful application, and the appropriate union of empirical data and modeling approaches, we can provide valuable information about the movements and mortality patterns of species of conservation concern.