DRERIP Ecosystem Conceptual Model: White sturgeon

The purpose of this report is to develop a conceptual life history model of white sturgeon (Acipenser transmontanus) and the factors that affect reproduction, growth, and survival in the Sacramento-San Joaquin Rivers and San Francisco bay-delta. This model can be used to organize, visualize, and evaluate how the complex life history of white sturgeon relates to the spatial and temporal variability of riverine and estuarine ecosystems and potential consequences of ecosystem restoration and water management alternatives. This model is compatible with the suite of environmental and species models developed by the Department of Fish and Game Ecosystem Restoration Program (ERP) to assess and prioritize proposed restoration actions for the delta. The model has a geographic emphasis on the Sacramento River and bay-delta regions, though the entire distribution of white sturgeon should be considered when population level responses are of concern, due to the migratory life history of this species.

The conceptual life history model incorporates information from numerous sources about white sturgeon, often relying upon life history information from populations outside California. While additional surrogate information from other North American sturgeons could have been used in the model, the distinctive diadromous and ecological characteristics of California white sturgeon limited the utility of these species’ information, thus information from other diadromous sturgeon species is only occasionally considered. Due to the limits of quantitative information about white sturgeon, this model is presented in a qualitative narrative, though numerical information is provided when available. While it will not provide quantitative limits on species take relative to maintaining a stable population size, it could be further developed into a population forecasting model since it divides the life history into life history stages, transition probabilities, and factors whose effects on reproduction and survival could be quantified.

Life history stage transitions are visualized in a series of life stage submodels highlighting the processes and relationships among ecological factors influencing the transition between stages (Figures 1 and 2). A complex set of conditions and processes are necessary to determine whether an individual white sturgeon completes the transition from one life stage to the next. Our knowledge of how biotic and abiotic factors are critical for maintaining healthy populations is fairly basic. Thus, the importance, predictability, and understanding of each of these linkages are identified in the model. Lastly, a similar characterization of independent stressors is undertaken to describe potential factors affecting survival during each life history stage in a known geographic region. This model is dynamic and not intended to be a final version. As new data become available, the model should be refined so managers and biologists have the most current information available.