Modeling Infection and Mortality of Juvenile Chinook Salmon due to Disease caused by Ceratonova Shasta in the Klamath River

Disease can often shape population dynamics but complex host-parasite interactions can be difficult to incorporate into life cycle models. Juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Klamath River become infected with the myxozoan parasite Ceratonova shasta when the polychaete worm Manayunkia speciosa releases actinospores into the water column. In the Klamath River, disease prevalence and actinospore concentrations have been routinely monitored since 2005, providing information about population-level disease prevalence. Concurrently, sentinel experiments with fish held in-river for a known duration have revealed that mortality increases with spore concentration and temperature. We developed statistical models to relate rates of infection and mortality to spore concentrations and temperature. We then incorporated these models into a dynamic life-cycle simulation model to understand how migration and exposure of juvenile Chinook salmon influences the magnitude and location of their mortality in the Klamath River. This model provides an estimate of disease-related mortality at the population-level, which can then be incorporated as a life-stage transition probability in a broader life-cycle model.