The introduced yellowfin goby (YFG) is now common throughout the tidal portion of the Sacramento-San Joaquin River system. We investigated its habitat use, size and diet in the Mokelumne River, an eastern tributary to the system. Catch per unit effort (CPUE) by boat electrofishing was significantly higher in the fall than all other seasons sampled over four years. Habitat type, turbidity and dissolved oxygen were not significantly related to CPUE between years and seasons. Temperatures were negatively related to CPUE in fall sampling only. Delta outflow and CPUE showed a significant negative relationship. Fish captured ranged from 27 mm SL (standard length) (33 mm TL (total length)) to 155 mm SL (196 mm TL) (mean 113 mm SL (138 mm TL)), with largest fish captured during the fall. Seasonal and annual analysis showed a diet composed of a variety of macroinvertebrates, including chironomids, gammarids, aquatic isopods and ephemeropterans with no difference in composition among seasons or years. The YFG’s generalist diet gives it an advantage as a successful invader, but salinity requirements appear to limit its expansion potential.

A primary goal of the Central Valley Project Improvement Act is to at least double natural production of Chinook salmon (Oncorhynchus tshawytscha), in California Central Valley (CV) streams on a sustainable basis. Achievement relies on restoration actions that involve both discharge (e.g., dam releases) and non-discharge (e.g., gravel augmentation, screening) components. Annual adult and juvenile abundance estimates for individual watersheds must be tracked to assess effectiveness of individual actions. However, to date, no substantial efforts have been taken to demonstrate success or deficiencies of their implementations. A major challenge in interpreting time series of counts at any one life stage is that they reflect the cumulative effects of both freshwater and marine factors over the full life cycle. To address this issue, we developed a conceptual framework based on ratios of the abundance of consecutive CV fall-run Chinook salmon life stages and how variation in these ratios tracks key independent variables during the freshwater portion of the life cycle. Model validation with several case studies shows that estimates of previous stage class production correlate well with estimated individuals produced in the next class, indicating that transition rates tend to vary within a constrained range, and that monitoring programs generate abundance estimates whose errors are small enough not to swamp out the underlying signal. When selected environmental parameters were added to demonstration models, abundance estimates were more closely modeled and several tested relationships between environmental drivers and life-stage transition rates proved consistent across watersheds where data were available. Results from this generalized life-stage conceptual model suggest a potential framework for tracking the success of actions meant to improve survival for a given life stage within an individual stream and for determining how successive stages respond to these changes. Though examples are provided for CV Chinook salmon, these concepts can be applied wherever migratory salmonid populations and associated environmental data are being adequately monitored.