Predation by native sunfishes (Centrarchidae) on the invasive crayfish Orconectes rusticus in four northern Wisconsin lakes

Introduced rusty crayfish (Orconectes rusticus) often establish abundant populations in lakes where they negatively impact native food webs. However, rusty crayfish do not become abundant in all lakes. Fish predation has been posed as one potential mechanism limiting rusty crayfish density, but there is limited empirical evidence to support this hypothesis. Using a case study approach, we quantified the extent and timing of predation on nonnative rusty crayfish by three native centrarchids in four northern Wisconsin lakes with contrasting crayfish densities. We estimated population-level predation effects on rusty crayfish using bioenergetics models in combination with fish and crayfish abundance estimates. Bluegill (Lepomis machrochirus) and pumpkinseed (Lepomis gibbosus) consumed young-of-year crayfish exclusively whereas rock bass (Ambloplites ruspestris) consumed a wide size range of crayfish. Rusty crayfish were found in Lepomis diets primarily in late June and early July while rock bass consumed crayfish throughout the summer. Per individual, rock bass consumed more crayfish biomass than Lepomis, but at the population-level, higher Lepomis densities resulted in greater numbers of crayfish and more crayfish biomass consumed by Lepomis than rock bass. Lepomis populations consumed 8 x , 14 x , 22 x and 120 x more individual crayfish than rock bass populations in the four study lakes. Bioenergetics simulations revealed that dense populations of Lepomis were capable of consuming a large percentage of the juvenile crayfish population in two of our study lakes. In systems with high Lepomis densities, Lepomis consumption of juvenile rusty crayfish may play a significant role in the invasion and establishment dynamics of rusty crayfish.