Effects of walleye stocking on population abundance and fish size

Data from Minnesota Department of Natural Resources lake surveys and stocking records were used to examine the effects of stocking programs involving walleye Stizostedion vitreum on the abundance and size of fish in walleye populations and to determine to what extent and under what conditions these effects occurred. We used data from 4,470 surveys in 1,924 lakes and from 20,634 walleye stocking records in 1,716 lakes. The analyses were conducted for various sizes of stocked fish and stocking frequencies and for lake groups with different walleye reproductive status. We reached the following conclusions. (1) Stocking in lakes without natural walleye reproduction increased walleye population abundance, but stocking in lakes where reproduction occurred had no effect on population abundance. (2) In lakes without walleye reproduction, walleye mean weight was reduced by stocking. In lakes with walleye reproduction, fry stocking decreased the mean weight of fish, but fingerling stocking had no effect on weight. The decrease in weight resulting from stocking was greater in lakes without natural walleye reproduction than in lakes with natural reproduction. (3) In situations where stocking affected population abundance or fish size, an increase in stocking frequency had diminishing effects. In general, where total population abundance increased as a result of stocking, the walleye mean weight decreased.