Abundance and Distribution of Walleye, Northern Squawfish and Smallmouth Bass in John Day Reservoir and Tailrace, 1984 Annual Report.

Abstract

Walleye, northern squawfish and smallmouth bass abundances were estimated in John Day Reservoir using a modified Schnabel multiple mark and recapture estimator. Sampling was conducted from March 25 to August 31 using gill nets, trap nets, boat electrofishing, angling and an angler survey. A total of 858 walleye, 4552 northern squawfish, and 1599 smallmouth bass were collected. Discrete populations were defined according to observed movements of recaptured and radiotagged fish. Abundance estimates were corrected for angler harvest, size selectivity of gear, tag loss and recruitment due to growth during sampling. In addition, the likelihood of biases resulting from differential mortality of marked fish was examined. Abundances in John Day pool of walleye and northern squawfish with fork lengths greater than 250 mm were estimated at 15,832 and 80,486. Abundances of smallmouth bass with fork lengths greater than 200 mm were estimated to be 2596 in lower John Day pool and 1791 in upper John Day pool. Walleye and northern squawfish moved throughout the pool, whereas movements by smallmouth bass were more localized. Angler harvests of walleye and smallmouth bass in upper John Day pool from April through August were estimated at 309 and 584 fish. Angler harvest of northern squawfish was negligible. Most walleye collected were age 5. The most abundant age groups of northern squawfish and smallmouth bass were 10 and 2. 10 refs., 28 figs., 12 tabs.