Document: BET-3-81-13

Population viability of Puget Sound chinook salmon: The importance of knowing population structure.

SANDERSON, B.*, M.RUCKELSHAUS and P.MCELHANY

National Marine Fisheries Service, Seattle, WA 98112 USA ¹

Abstract:
An important charge for conservation ecologists is to quantify the probability that endangered species will survive in the future. Although assessments of extinction risk are a standard step in evaluating population viability, such analyses are often needed before data describing population structure and abundance are fully available. In this study, we evaluated how estimates of population viability differ in relation to how populations are spatially defined and how much information is available. We addressed these questions using abundance time series for endangered Puget Sound chinook salmon. We compared extinction risks for small, individual populations to those for larger aggregations of these individual populations. The small and large units for analyses were purposefully chosen because they are spatial scales currently used by managers to make management decisions regarding chinook salmon, although these management units may not represent true biological populations. Overall, extinction risks were much greater for individual populations compared to aggregations of individual populations (9/13 cases, data were standardized to eliminate population size biases). This suggests that if these small, individual populations were closer to the true biological populations, management actions that occur at larger, aggregated scales may result in the loss of individual populations. We also evaluated how the estimated extinction risk varied with the amount of data available in space and time. Overall, extinction risks were lower for areas with more geographic coverage and with longer time-series, although the results were dependent on the particular sequence of years used in the analysis. These results demonstrate how different characterizations of population structure and data coverage affect estimates of population viability. Furthermore, these results highlight the importance of conducting viability analyses on biologically defined populations.

Keywords: extinction risk, salmon, population structure

This abstract is being presented at: 9:15 AM in session:
Oral Session #57: Ocean-Going Fish and Mammals.