Modeling the effect of habitat availability and quality on endangered winter-run Chinook salmon (Oncorhynchus tshawytscha) production in the Sacramento Valley

Link To Share This Poster: https://cdmcd.co/abyvJr
Live Discussion Link: https://cdmcd.co/PJ9xzb

Francisco J. Bellido-Leiva and Jay R. Lund, Department of Civil and Environmental Engineering, University of California, Davis, Davis, CA, Francisco J. Bellido-Leiva, Robert A. Lusardi and Jay R. Lund, Center for Watershed Sciences, University of California, Davis, Davis, CA, Robert A. Lusardi, Wildlife, Fish and Conservation Biology, University of California, Davis, Davis, CA

Background/Question/Methods
Reconciliation between water uses and sustaining aquatic species populations requires an effort to identify and quantify essential habitat characteristics for ecosystem health and valuation methods to predict ecosystem response to restoration actions. This process is particularly challenging for anadromous fish species such as California’s Sacramento River Chinook salmon runs, due to their limited geographic range and diverse life history habitat requirements. Tools, such as life-cycle models, are needed to manage population dynamics and quantify the composite effects of processes across space and time. This work focuses on the federally endangered and endemic Sacramento River winter-run Chinook (Oncorhynchus tshawytscha) by developing the Winter-Run Habitat-based Population Model (WRHAP). WRHAP is a conceptual, freshwater rearing stage model based on previously published studies, empirical field data, laboratory studies, and expert knowledge. It includes alternative rearing habitats reported in the literature (i.e., floodplains, off-channel, and tributaries), defines rules of habitat use based on instream conditions, and incorporates a juvenile growth module that combines bioenergetics modeling with empirical growth rates. As such, model structure allows to analyze relationships between juvenile fitness, function of rearing path taken by individuals, and their success to reaching their saltwater stage.
Results/Conclusions
Model outputs reasonably follow observed out-migration patterns, with simulated juvenile abundancies at recording locations (Red Bluff, Knights Landing and Chipps Island) generally lying within observations’ confidence intervals (r2 = 0.94, 0.58, 0.44; respectively). Outputs also provide a realistic smolt size distribution arriving at the San Francisco Bay. This effort demonstrates the importance of currently “non-critical” habitats (as defined by the Endangered Species Act) for juvenile development. For instance, floodplain habitat contributed to a quarter of the total simulated out-migrating biomass despite being used by < 18% of total number of outmigrants for <10% of total rearing days. Similarly, off-channel growth presented one of the highest sensitivities, explaining ~13% of average juvenile weight variance. Furthermore, this habitat greatly enhances juvenile migration survival, especially for brood years with short residence times along the upper Sacramento River, with a three-fold increase in survival compared to individuals that reared exclusively at the mainstem. The model shows the utility of a simple population model to explore relationships between habitat quality/quantity and juvenile development, and to assist water/environmental management and decision-making processes focused on species recovery.