California Chinook salmon are in a state of crisis. Several runs in the Central Valley and Central Coast are in danger or threatened by extinction, and the remnant commercial Chinook fishery is maintained only through the rearing and release of huge numbers of Central Valley fall-run juveniles. All hopes of recovering wild stocks in the Sacramento River system are challenged by various forms of habitat degradation and mortality, direct and indirect, caused by water diversions. In this project, the fellow will implant miniaturized acoustic transmitters into sub-yearling winter-run Sacramento River Chinook. The smolts will be tracked on their outmigration to sea, using an existing array of monitors, updated with receivers capable of detecting the signals from the new miniaturized tags. The survivorship data gathered during this project will be combined and compared with a parallel tracking study of fall- and springrun Chinook. Findings will allow managers to better evaluate the effects of different flow conditions and water management practices on salmon survival. Of particular interest will be to compare salmon survivorship when the Delta Cross Channel gates are open and closed.