UC Davis

Considerable resources have been invested in freshwater restoration worldwide to improve degraded ecosystems, achieving variable degrees of success. To maximize potential ecological benefits with restoration, a prioritization process to select promising conservation plans should occur before investments. Optimization frameworks facilitate this process, allowing the structured coordination of complex watershed-scale efforts. Such frameworks require valuation methods to identify and quantify essential habitat characteristics for ecosystem health and tools to predict ecosystem response to proposed restoration efforts. This is especially important and challenging for species with complex life cycles and a broad geographic range over heterogeneous habitat, such as Pacific Chinook salmon. This research builds an optimization framework to maximize returning adult abundance for the federally endangered and endemic Sacramento River winter-run Chinook (Oncorhynchus tshawytscha) in California. We first developed a conceptual freshwater rearing stage model, denoted as Winter-run Habitat-based Population Model (WRHAP), based on published studies, empirical field data, laboratory studies and expert knowledge. It includes off-mainstem rearing habitats, defines rules of habitat use, and incorporates a juvenile growth module. The model was then expanded (e.g., hatchery operations, ocean-stage mortality; WRHAP-SEA), and embedded into the optimization framework to evaluate the population-level response to a set of potential restoration/recovery actions. Optimized portfolios of actions were further analyzed to estimate their effect on winter-run Chinook viability. A case study characterizing spatiotemporal off-channel dynamics, one of the most promising restoration actions identified, shows the potential of remote sensing imagery to inform environmental managers on areas and habitat features (e.g., residence time, inundation flows) for proposed restoration efforts. The results of this research show the crucial importance of 'non-critical' habitats (as defined by the Endangered Species Act) on winter-run Chinook salmon persistence, and the promising recoveries in abundance, spatial structure, diversity, and growth rate from defined optimal portfolios, which could place winter-run Chinook salmon at a low-risk of extinction. As such, this dissertation introduced a method to build robust valuation and decision-making tools to assist environmental management processes focused on species recovery.