Chinook Salmon in the California Central Valley: An Assessment

Abstract

This paper summarizes information on recent historical distribution and abundance of chinook salmon in the California Central Valley drainage, focusing on the period from the 1950s to today. Most of the principal Central Valley streams that historically supported salmon runs still do so, but nearly half of them have lost at least one seasonal salmon run and several major streams have had all their salmon runs extirpated. Overall abundance of chinook salmon in the Central Valley system has decreased to less than 75% of their number in the 1950s. Fall-run chinook salmon in the Sacramento River basin compose by far the most abundant Central Valley stocks, but they substantially declined between 1953–1966 and 1967–1991. Fall-run chinook salmon stocks in the San Joaquin River basin and Sacramento-San Joaquin Delta tributaries showed various changes between 1953–1966 and 1967–1991 but altogether constitute only a minor portion (now 4%) of the total Central Valley spawning escapements. Three other chinook salmon runs (winter, spring, late-fall) have shown much more pronounced reductions in recent decades. Central Valley salmon have been heavily supported by hatchery production, but the effects of hatcheries on natural stocks remain poorly understood. Major efforts are underway to restore regional chinook salmon and steelhead stocks, several of which are listed under both California and U.S. endangered species statutes.