Evaluation of supplemental walleye stocking in northern Wisconsin lakes

Supplemental stocking of walleye Sander vitreus is an important component of fishery management programs in North America. We conducted an experimental study in 23 northern Wisconsin lakes over a 4-year period to assess differences in year-class strength with and without supplemental stocking. These study lakes all hosted walleye fisheries targeting mixed-recruitment populations (i.e., ones with both natural reproduction and supplemental stocking). We tested for differences in catch per effort (CPE) between stocked and nonstocked years using a general linear mixed model. Catch per effort of age-0 walleyes was 2.3 greater per shoreline mile when lakes were stocked, suggesting that stocking increases year-class strength by about 0.13 age-0 walleyes/acre. Catch per effort values approximated a Poisson distribution, most lakes showing low CPE of age-0 walleyes whether or not they were stocked. Stocked fingerlings were marked with oxytetracycline as fry to determine the percent contribution of stocked fish to the year-class and to estimate 3-month survival. The mean survival of stocked fingerlings until autumn was 3.4%. Results for individual lakes varied, and these differences may be useful for managers in prioritizing waters for stocking. One lake showed strong survival of stocked fish and increases over nonstocked year-classes during both stocking events; this is consistent with literature reports documenting successful supplemental stocking in 5% of case histories.