Brian M. Roth

Reciprocal Relationships Between Exotic Rusty Crayfish, Macrophytes, and Lepomis Species in Northern Wisconsin Lakes

A bstractThe non-native rusty crayfish (Orconectes rusticus) has invaded many lakes of northern Wisconsin, profoundly changing littoral zones in the process. There are other lakes that have been invaded, but do not exhibit these changes. We hypothesized that endogenous feedbacks could form involving rusty crayfish, the macrophytes they destroy, and Lepomis species whose abundance is positively related to macrophyte abundance and also consume juvenile crayfish. We assessed this proposal with long-term data from one lake, a regional comparative study, and a case study of Lepomis predation on crayfish. Through time and across lakes, abundances of rusty crayfish, littoral macrophytes and species of the genus Lepomis were related in a fashion that indicated a set of feedbacks that regulate the abundance of all three. Intense predation on juvenile crayfish by abundant Lepomis is capable of maintaining some crayfish populations at low abundance. Thus, some lakes display profound ecological changes where crayfish achieve high abundance, and others sustain crayfish at low abundance. Consequently, lakes invaded by rusty crayfish may take on the appearance of alternative ecological regimes. Direct experimentation is necessary to determine if, and under what conditions, a lake can exist in either regime.

Impact of rainbow smelt (Osmerus mordax) invasion on walleye (Sander vitreus) recruitment in Wisconsin lakes

Rainbow smelt (Osmerus mordax) are invaders of inland lakes in the Laurentian Great Lakes region of North America and have negatively affected native fish populations. Walleye (Sander vitreus) comprise an important fishery throughout the Great Lakes region and could be affected by rainbow smelt invasions. We test for declines of young-of-the-year walleye (YOY-W) density in 12 of the 26 known rainbow smelt invaded lakes in Wisconsin. Invaded lakes showed significantly lower YOY-W densities than uninvaded lakes during the period 1985–2004. In 94% (17/18) of years, YOY-W densities from invaded lakes were lower than those from uninvaded lakes. Declines (~70%) in YOY-W densities were observed in three lakes with data from before and after rainbow smelt invasion. For 10 invaded lakes with more than two YOY-W density estimates between 1985 and 2004, YOY-W densities averaged 13% below expected densities. Our results demonstrate the potential impacts of rainbow smelt invasion on walleye tribal, commercial, and rec...