Interactions between Stocked Walleyes and Native Yellow Perch in Lake Thirteen, Minnesota: A Case History of Percid Community Dynamics

Abstract

Studies of interactions among percids are important for understanding the fish community consequences of using stocking as a management tool and for understanding the ecological role of percids in lakes where they are native species. Percid community responses to discontinuing, then resuming, the stocking of walleye Sander vitreus were monitored in Lake Thirteen, Minnesota, a north temperate lake with a long-term history of walleye fry stocking. Fish population assessments during 1986–2002 tracked changes in relative abundance, size structure, and growth rates of yellow perch Perca flavescens and walleyes in response to discontinued walleye stocking during 1989–1996. Large changes occurred in the size structure and relative abundance of walleyes. The effect of discontinued stocking was to decrease the abundance of younger age-classes of walleyes in the lake. Reduced predation on small yellow perch allowed their numbers to increase and led to reduced growth rates while stocking was discontinued. When stocking was resumed, predation by stocked walleyes reversed the trend, reducing yellow perch numbers and improving their growth rates. Density-dependent growth was evident for both walleyes and yellow perch. Bioenergetics modeling confirmed walleye predation as a plausible explanation for most changes in the yellow perch population. Manipulation of stocking, and the resulting shifts in predator sizes, caused structural changes in the percid populations that altered levels of intraspecific competition for both the predators and prey.