Dynamics of the Unexploited Walleye Population of Pymatuning Sanctuary, Pennsylvania, 1997–1998

Abstract

Studies on the dynamics of unexploited fish populations are rare in the fisheries literature. The purpose of this research was to describe the dynamics of the unexploited population of walleyes Stizostedion vitreum of Pymatuning Sanctuary, a 530-ha eutrophic impoundment in northwestern Pennsylvania. We sampled walleyes with trap nets during the spring spawning runs in March and April 1997–1998. We estimated spawning adult abundance using the Schnabel multiple mark–recapture method and used walleye ages estimated from scales and otoliths for growth and mortality analyses. Population estimates of spawning adult walleyes were 29,693 and 23,298 fish in 1997 and 1998, respectively, or 56 and 44 fish/ha. The adult population was composed mostly of individuals greater than 500 mm total length. Compared with other populations, growth was excellent for juveniles but poor for adults. Average annual adult mortality was 32–41%, which is within the range of values reported for other exploited and unexploited populations but higher than we anticipated for an unexploited population. Recruitment of young walleyes to spawning age was low and dependent largely on first-winter mortality and possibly cannibalism. This population conforms to most predictions for unexploited populations: high density, high proportion of large individuals, slow growth, and relatively low mortality.