A life history model for assessing alternative management policies for depressed chinook salmon

Population and fishery dynamics are modelled to assess performance of alter native harvest policies for chinook that spawn in western North America. Th e sensitivity of model performance to variations in stock productivity and patterns of environment variation are explored to evaluate the trade-off be tween risk of extinction and benefits from harvest. Results indicate maximu m economic benefit and low risk of extinction is not likely under the prese nt harvest policy. Even with a conservative harvest-threshold policy, where in harvest rates are reduced at low stock size and are zero if the stock si ze declines below an abundance threshold, the risk of extinction is signifi cantly reduced compared to fixed harvest rate policies. Simulated abundance forecast errors within the historical range degraded model performance onl y slightly. With the constraint that risk of extinction be held below an ac ceptable level, socio-economic indicators reveal an optimal han;est-thresho ld policy at a fractional harvest of surplus abundance of about 0.45 and a threshold near 100 female spawners per stock. Based on coded-wire tag resul ts for a major hatchery population, the mean historical harvest rate (1983- 1991) was 0.6. (C) 1999 nternational Council for the Exploration of the Sea .