Using Otolith Microstructure to Determine How Freshwater Conditions Influence Salmon Production

Previous studies have shown correlations between food abundance in freshwater habitats and salmonid growth and survival, suggesting that food resources could influence juvenile salmon production. To determine if freshwater conditions influenced growth of juvenile winter run salmon in California’s Sacramento River we used a mixed effect model to analyze otolith microstructure data from 196 individuals collected between 1998 and 2007. Fixed effects included in the model were year, water temperature, flow velocity, turbidity, salmon density, and initial feeding date. Daily water temperatures and flow velocities were estimated with a hydrodynamics model developed for the Sacramento River, turbidity was from gauge data, and salmon density was estimated from screw trap data. Initial feeding date was calculated from the number of increments between the otolith feeding check and the capture date.  Results indicate that growth was dependent on year, water temperature, velocity, and initial feeding date whereas turbidity and salmon density were not included in the top models. These results suggest that juvenile winter run salmon were not food limited while rearing in the Sacramento River.