Impact of Predation by Smallmouth Bass on Sockeye Salmon in Lake Washington, Washington

Abstract

Abstract In the Lake Washington basin, run sizes of sockeye salmon Oncorhynchus nerka and other anadromous salmon species declined during the 1980s. Reduced survival of juvenile sockeye salmon in the lake suggested that increased predation may have contributed to the decreased run size. Introduced smallmouth bass Micropterus dolomieu were considered to be a potential cause of increased predation on juvenile salmonid populations. Ultrasonic tracking showed limited spatial and temporal overlap between smallmouth bass and juvenile sockeye salmon. Substantial overlap occurred only in the littoral zone during the migration of the sockeye salmon fry from the Cedar River into the lake and during the out-migration of smolts from the lake through the Lake Washington Ship Canal into Puget Sound. Salmonids occurred in smallmouth bass stomachs only during the out-migration of smolts from Lake Washington to Puget Sound. For smallmouth bass larger than 150 mm total length, juvenile salmonids constituted 28% of the diet...