PARENT SESSION
Oral Session 62: Fish Ecology II: Salmon.
Presiding: J Power
Wednesday, August 4, 8:00 AM to 11:30 AM, Meeting Room B 117.

Population viability analysis of chinook salmon: What do we learn by including climate variability and density dependence?

Zabel, Richard^*,1, Scheuerell, Mark¹, McClure, Michelle¹, Williams, John¹, ¹ Northwest Fisheries Science Center, Seattle, WA, USA

ABSTRACT- Population Viability Analysis is a common tool for conservation biologists, but the choice of viability metric is often limited by data availability. Long-term population counts provide information on trends and extinction risks, while short-term demographic data can help assess sensitive life stages. Snake River spring/summer chinook salmon, a federally-listed species, is a rare example where data are available on long-term trends in abundance and on temporal variability in key demographic rates. This allowed us to build a stochastic life-cycle model that incorporated both environmental variability and density dependent effects. Based on 40 years of data, we related adult survival to ocean-climate indices, and we related juvenile survival to the density of spawners. By characterizing the interaction between climate cycles and density dependence, we assessed the strengths and weaknesses of a variety of viability metrics. For example, modeled extinctions were not randomly distributed through time, as is often assumed, but were driven by ocean conditions. Also, the sensitivity of annual population growth rate to changes in vital rates varied through time, with some stages more important when the population was increasing and others more important when the population was declining. We conclude that many commonly-used viability metrics are relevant on a short time scale, but long term management of at-risk species is greatly enhanced by understanding the factors that contribute to population cycles.

Key words: chinook salmon, density dependence, population viability, climate factors