Abundance and Distribution of Northern Squawfish, Walleyes, and Smallmouth Bass in John Day Reservoir, Columbia River

Abstract

Abstract We used mark-recapture and catch-per-unit effort data to estimate abundances and distributions of three potential predators on juvenile salmonids migrating through John Day Reservoir in 1984–1986. The northern squawfish Ptychocheilus oregonensis was the most abundant predator (estimated population: 85,316), followed by smallmouth bass Micropterus dolomieu (34,954) and walleye Stizostedion vitreum (15,168). Because of uncertainty in sampling and assumptions of the mark-recapture estimator, the combined abundance of these three predators could lie between 50,000 and 500,000. We believe, however, that bias is probably negative, and that any errors should result in conservative estimates. Northern squawfish were common reservoir-wide, but large concentrations occurred immediately below McNary Dam near the head of John Day Reservoir. Walleyes were largely restricted to the upper third of the reservoir, whereas the number of smallmouth bass increased progressively downriver. As judged by abundance and ...