Iowa's muskellunge program was established in 1960 when 40 advanced fingerlings were stocked into West Okoboji Lake and a like number were stocked into Clear lake. The program was expanded in 1975 when 1,000 advanced fingerling muskies were stocked into Spirit Lake. Natural reproduction of muskellunge in these lakes is minimal; therefore, these fisheries are dependent upon stocking advanced fingerlings each fall. Despite these stockings, the density of muskellunge has steadily declined since 1984. In response to these declines, an investigation was initiated to determine the causes of the decline and develop management guidelines that will increase the densities of muskies in these lakes.

Beginning in 1991, all muskie fingerlings were marked with a freeze brand. In addition, all adult muskie caught each spring during the annual broodstock collection were individually marked with Visual Implant tags. The decrease in the muskellunge populations was attributed to a substantial decrease in recruitment. In fact, some years there was evidence that none of the stocked fingerlings survived. This decrease in recruitment was due to a shift from rearing muskies on a live diet (zooplankton-minnows), to a totally artificial dry diet. The poor survival of these fish was most likely due to a combination of poor health due to nutritional problems, poor color, and stocking much smaller fish than what were previously stocked. Fish reared on the pelleted diet were generally in poorer body condition, and were much smaller than those reared on natural prey items. Also, the camouflage barring on the pellet-reared fish was muted and virtually nonexistent. Fingerling muskies stocked in the spring produced the only significant recruitment observed in these lakes in the last 13 years. In fact, one stocking of only 572 muskies more than doubled the population of muskies in the Okoboji Lakes. Such success with stocking muskies in the spring could drastically change stocking stategies; fewer fish may need to be stocked, and management objectives could be met without annual stockings.

The benefits of these findings will be a decrease in the number of muskies produced and stocked each year, attainment of our management objectives, and a decrease in the stocking frequency. Muskies could be stocked every other year and, during the alternate years, hatchery space could be devoted to much needed walleye production.