Cooperative Fish and Wildlife Research Units Program: Wisconsin Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Recruitment failure has been observed in some northern Wisconsin walleye Sander vitreus populations that formerly supported moderate to high levels of recruitment. Recruitment is measured using catch-per-effort of age-0 walleyes in fall electrofishing surveys, so recruitment bottlenecks are occurring in the first year of life. Recruitment failure could be linked to a variety of factors, including changes in habitat availability and fish communities within these lakes. Initially, predation by largemouth bass (a species that has experienced widespread increases in abundance) was thought to be a potential factor regulating walleye recruitment. Previous work conducted by the Wisconsin Cooperative Fishery Research Unit and others has demonstrated that largemouth bass predation is probably not a limiting factor in the walleye recruitment process. However, other species may have also experienced increases in abundance (e.g., black crappies, bluegills) and modeling conducted by Center for Limnology at UW-Madison suggests that the time at which walleyes enter the littoral zone after a pelagic larval stage could determine the degree to which predation affects recruitment. Furthermore, recent work from Ontario and Wisconsin has indicated that loss of suitable optical and thermal habitat may be affecting survival and recruitment of young walleyes. In collaboration with the Wisconsin Department of Natural Resources, we are initiating an intensive study of walleye early life history. This work will encompass a range of walleye populations, including those that have exhibited recent recruitment failure and populations that exhibit high levels of recruitment on a relatively consistent basis. Our primary objectives are to determine if: 1) larval and juvenile walleye abundance, survival, foraging success, diet composition, and growth vary among populations; 2) predation by northern pike, black crappies, bluegill, and yellow perch could affect walleye recruitment; 3) availability of suitable optical and thermal habitat varies among lakes in relation to walleye recruitment patterns and 4) zooplankton abundance, community composition, and size structure varies in relation to larval growth and survival and subsequent recruitment. Additionally, we will identify when age-0 walleyes enter the littoral zone to improve model projections regarding the effects of predation on walleye year class strength.