Document Details

DRERIP Ecosystem Conceptual Model: Green sturgeon

A. Peter Klimley, Joshua A. Israel | December 27th, 2008


The purpose of this report is to develop a conceptual life history model of North American green sturgeon (Acipenser medirostris) and the factors that affect reproduction, growth, and survival in the Sacramento and San Joaquin rivers and San Francisco Bay-Delta. This model can be used to organize, visualize, and evaluate how the complex life history of green 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 green sturgeon must be considered when population level responses are of concern, due to the unique, highly-migratory life history of this species.

The conceptual life history model incorporates information from numerous sources about green sturgeon, often relying upon life history information from populations outside the Southern Distinct Population Segment (DPS) and occasionally considering information from the sympatric white sturgeon (A. transmontanus). While surrogate information from other North American sturgeon could have been used in the model, the distinctive anadromous and ecological characteristics of green sturgeon limited the utility of these species’ information.

Due to the limits of quantitative information about green sturgeon, this model is presented in a qualitative narrative with numerical information 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 affects 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 fish completes the transition from one life stage to the next. Our knowledge of green sturgeon life history remains limited as to the relative importance of biotic and abiotic factors critical for maintaining self-sustaining populations of green sturgeon. 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 information becomes available, the model should be refined so managers and biologists have the most current information available.

Keywords

endangered species, fisheries, modeling, Sacramento–San Joaquin Delta