Effects of Prey and Predator Abundances on Prey Consumption and Growth of Walleyes in Western Lake Erie

Abstract

Declining growth and delayed age at maturity of walleye Stizostedion vitreum from 1965 to 1984 indicated that the speciesˈ large Lake Erie population was taxing the capacity of the prey fish community to support it. We examined the effects of prey and predator abundances on walleye diets and estimated the total predatory demand of age-0 through age-6 walleyes in western Lake Erie during 1986–1988. Walleye diets reflected prey fish abundances. Gizzard shad Dorosoma cepedianum and shiners (emerald shiner Notropis atherinoides and spottail shiner N. hudsonius) were the major prey in years when they were abundant. In years when these prey species – especially gizzard shad – were not abundant, walleyes consumed more white perch Morone americana and (to a lesser degree) yellow perch Perca flavescens. Total consumption by the walleye population was relatively constant, ranging from 83,700 tonnes in 1987 to 94,300 tonnes in 1986. Bioenergetics modeling showed that greater fishing mortality imposed on strong walleye year-classes could reduce competition among older cohorts; however, because diets of age-0 and age-1 walleyes differ from diets of older fish, few prey made available by greater harvests would be used by small walleyes to increase their growth. Walleye density and gizzard shad availability interact to influence prey consumption and walleye growth in western Lake Erie, High predatory demand and reduced growth of walleyes occur when large walleye year-classes predominate.