Estimated Life History of An Endangered Chinook Salmon Population and Its Implications for Population Viability

Survival and reproductive rates for endangered Sacramento River winter-run Chinook salmon in California were estimated as part of an evaluation of how incidental ocean fishery impacts affect population viability. We fit an age and sex structured population dynamics model to juvenile abundance and female spawner data for years 1996-2010. We then used the model to conduct stochastic simulations that evaluated the effects of incidental fishery exploitation and hatchery supplementation on population viability. Within the range of the data, we found the stock-recruitment relationship to be only weakly curvilinear. Estimated survival rates of fry to the end of age 2 were <0.5% except for one year when the estimate was >1%. Estimated survival rates of hatchery-origin juveniles were twice those of natural-origin juveniles on average, and the ratio of hatchery-origin to natural-origin juvenile survival rate was positively correlated with the proportion of female spawners that were of hatchery origin three years later (most females spawn at age 3). The simulation portion of this study indicated that the population would only be able to withstand relatively low exploitation rates, a direct result of the population’s relatively low estimated productivity.