Abundance and Distribution of Walleye, Northern Squawfish, and Smallmouth Bass in John Day Reservoir, 1984-1985 Progress Report.

Abstract

Sampling was conducted in John Day Reservoir to collect walleye, northern squawfish and smallmouth bass. Changes in distributions during sampling were characterized from changes in catch per unit effort (CPUE) in sampling areas. Observed movements of marked and radiotagged fish were examined and used to define discrete populations. Abundances were estimated using a modified Schnabel multiple mark and recapture estimator. Abundance estimates were corrected for angler harvest, size specific vulnerability to gear, recruitment due to growth and tag loss during sampling. Age composition of catch was determined to characterize relative contributions of various year classes to the populations. Ages at which fish were fully recruited to gear were defined by catch curves. Survival of fully recruited year classes was calculated from differences in CPUE's between 1984 and 1985. Mean length at age was estimated and used to determine age specific incremental growth. Eighty-eight percent of walleye were caught in McNary tailrace or Irrigon-Paterson, whereas 95% of smallmouth bass were caught from Irrigon-Paterson to the John Day forebay. Abundances of walleye and northern squawfish with fork lengths greater than 250 mm and smallmouth bass with fork lengths greater than 200 mm were estimated to be 16,219, 95,407, and 11,259. Anglers harvestedmore » an estimated 235 walleye, 2004 northern squawfish and 4383 smallmouth bass during the sampling season. Six-year-old walleye, 4-year-old northern squawfish and 3-year-old smallmouth bass were most abundant in catches. Walleye and smallmouth bass were fully recruited to sampling gear by age 3. Age at which northern squawfish were fully recruited was uncertain. Mean survival was 46.1% for walleye and 46.5% for northern squawfish. Mean smallmouth bass survival was 46.5% in the lower and 43.7% in the upper reservoir.« less