Life History Variability in a Population of California Coastal Coho Salmon

Coho salmon have relatively simple life histories compared to some other salmon species. In California, most coho salmon have a three-year life cycle split evenly between fresh and salt water. Even within this basic framework, there are often numerous life-history pathways, involving different juvenile rearing habitats occupied at different times, which individuals in a given population can adopt and still succeed. Maintaining this life history diversity can stabilize populations, because the population as a whole is less vulnerable to localized events that only affect a subset of life histories. However, managing for life history diversity presents a number of challenges. We illustrate some of these challenges for an intensively monitored coho salmon population in Northern California. There are at least four common juvenile life history patterns in this population, two of which are not susceptible to the standard sampling approach for estimating juvenile production (spring smolt trapping). Different assumptions about the fate of these life history types lead to very different recommendations for habitat protection and restoration. Monitoring efforts can help resolve these issues by continuing to develop techniques to provide information on the life history composition of populations and the relative survival and fecundity of different life history pathways.