Informing salmon conservation with population models that account for individual heterogeneity

Abstract

Managing threatened species requires information on their status and predictions of their response to management and environmental change. To develop this information, we often collect data and use them to parameterize population models capable of projecting populations into the future under different conditions. Within many populations, individuals vary in traits such as survival, age at maturity, and migration behavior that affect the variability in population abundance through time and how they respond to environmental conditions. In these cases, it may be necessary to develop more complex population models that account for this heterogeneity among individuals to inform conservation. Anadromous salmonids (Salmonidae spp.) face several threats that put populations at risk globally, and information is needed to make decisions about the allocation of resources for their conservation. They also commonly exhibit individual heterogeneity in life history traits like migratory behavior and habitat use within freshwater, which are known to affect population dynamics and can affect population responses to management.To inform salmon conservation, I developed and applied an integrated population model for Chinook salmon (Oncorhynchus tshawytscha) listed as Endangered under the Endangered Species Act, which spawn in the Wenatchee River Basin in Washington State. I first developed a model of the production of juveniles expressing different life history pathways (LHPs) of migration age from natal streams (Chapter 2) and used it to test hypotheses about drivers of the production of different LHPs. I developed a model of the survival and marine-return rates of fish between emigrating from their natal stream and returning to the Wenatchee River basin to spawn (Chapter 3) and examined how lifetime demographic rates varied among fish that had expressed different juvenile LHPs. Next, I combined the models of juvenile production and of subsequent survival and return rate, along with additional data, within a full integrated population model (Chapter 4) and projected the population into the future to assess its trajectory and examine how individual heterogeneity affects population stability. Finally, I worked with decision makers and scientific experts to develop management strategies for habitat restoration and hatcheries (Chapter 5), which I simulated the consequences of for the population.