An investigation of exotic rusty crayfish (Orconectes rusticus) and rainbow smelt (Osmerus mordax) interactions in lake food webs: The Sparkling Lake biomanipulation (Wisconsin)

The increasing introduction rate of nonnative species into new ecosystems is one of the most pressing ecological issues. Although prevention of new introductions is preferable, proactive management of the food web may be one way to allow native species to reestablish in the ecosystem. As part of a team effort, I participated in a biomanipulation experiment in Sparkling Lake, Wisconsin to eradicate the exotic rusty crayfish (Orconectes rusticus ) and rainbow smelt (Osmerus mordax) through heavy exploitation and predator augmentation. I addressed several questions related to potential outcomes of the biomanipulation and effects of rusty crayfish and rainbow smelt in aquatic food webs: (1) What is the trophic role of rusty crayfish in lake littoral zones? (2) Do rusty crayfish exist at low abundance? and (3) What food web interactions lead to smelt dominance, and what management actions can lead to smelt decline? Lastly, I provided an up-to-date summary of results from the biomanipulation.; Modeling simulations substantiated by stable isotopes from northern Wisconsin lakes revealed that rusty crayfish are primarily predators. Through time, abundant rusty crayfish exhaust invertebrate prey and destroy macrophytes that provide habitat for juvenile Lepomis (bluegill, L. macrochirus and pumpkinseed, L. gibbosus). Macrophytes and Lepomis both decline after rusty crayfish become abundant. Lakes with abundant macrophytes sustained dense Lepomis populations that, through predation, maintained low populations of rusty crayfish. Thus, an endogenous feedback may either lead to a lake dominated by abundant rusty crayfish or by predatory Lepomis.; Modeling simulations indicated that effects of rainbow smelt invasions may be fostered by harvest of adult walleye by anglers. In the model, harvest allowed smelt to establish a large population that led to declines of walleye (Sander vitreum) and cisco (Coregonus artedii). Smelt did not establish without walleye harvest. Other simulations indicated that current management in the Sparkling Lake biomanipulation may successfully reduce the smelt population. The rusty crayfish and rainbow smelt populations in Sparkling Lake appear to be decreasing as a result of the biomanipulation. In conclusion, I suggested continuing the biomanipulation for five more years to allow slow-changing biotic pools time to respond to the current management.