Characterizing changes in maturity of lakes resulting from supplementation of walleye populations

We constructed mass-balance models in two lakes to measure changes in community maturity associated with walleye stocking. Community maturity is related to stability. Stability, in terms of a particular community structure and total biomass, is a desirable characteristic. It is important to understand how management actions, such as fish stocking and fishery regulations, affect the stability of aquatic communities in order to effectively manage them. Walleye are stocked throughout North America and have the potential to dramatically affect aquatic ecosystems. We examined simulated changes in maturity, as measured by Finn's cycling index and relative overhead, associated with walleye stocking. We simulated three scenarios for each lake: (1) changes in angler effort associated with walleye stocking, (2) changes associated with the physical addition of juvenile walleyes, and (3) changes associated with both the physical addition of juvenile walleyes and changes in angler effort. For each scenario we also examined the role of prey vulnerability by varying the vulnerability parameter for each scenario. We found that expected increases in angler effort associated with walleye stocking generally acted to decrease community maturity and more than offset small increases associated with the physical addition of juvenile walleyes. Changes in maturity metrics were more dramatic when prey vulnerability was high (i.e. “top–down” control) than when then they were low (i.e. “bottom–up” control). Walleye stocking may cause aquatic systems to be less stable due to expected increases in the amount of angler effort, particularly in systems controlled primarily through top–down mechanisms.