Stocking

Walleye stocking is big business across the Midwest, and anglers sometimes see this as a sure cure for slow fishing. Unfortunately, increasing walleye populations is not as easy as pouring more fish into a lake. As with recruitment in natural populations, many factors affect the survival, growth, and eventual contribution to the fishery of stocked fish.

Over the years, biologists have assessed differences in stocking fry—recent hatchlings less than an inch long—and larger fingerlings. Lately, studies also have compared the success of stocking small fingerlings (two inches or so) with larger fingerlings (up to four inches). Because walleye stocking is expensive in terms of manpower, equipment, and hatchery maintenance, agencies seek the most cost-effective stocking procedures that produce good fishing.

Recent breakthroughs in marking small fish have enabled many comparative studies, and biologists from five states reported these study findings at the walleye symposium. Biologists in South Dakota and Nebraska used oxytetracycline to mark young walleyes, immersing them in a bath of the antibiotic.

This treatment creates a fluorescent ring on otoliths and other bones. Dave Lucchesi of the South Dakota Game, Fish and Parks Department reported that in small South Dakota lakes, stocked fry strongly contributed to the population of young walleyes when sampled that fall. Fingerling stocking also increased walleye numbers, but not as dramatically as the stocking of tiny fry.

Daryl Bauer of the Nebraska Game and Parks Commission evaluated walleye stockings in 18 reservoirs throughout the state. In five of eighteen waters, stocking fingerlings maintained the fishery, with over 75 percent of year-class strength resulting from stocked fish. In five other reservoirs, however, where walleye populations were maintained by natural reproduction, stocking contributed far less to adult abundance. Also, Bauer noted that abundant larger gizzard shad tended to suppress walleye recruitment. Water releases from reservoirs also reduced recruitment, as stocked fish migrated through the dam to downstream impoundments.

At Rathbun Lake in Iowa, Larry Mitzner faced the daunting task of tripling the number of walleyes over 18 inches in the population. He evaluated stockings of fry and fingerlings raised both extensively (allowed to grow in ponds) and intensively (housed in hatchery raceways). Fry stocking at Rathbun seemed to be a boom or bust scenario, as some of the largest year classes (1985, 1986, 1993, 1995, 1997, and 1998) were based on fry stocking. Stocking fry at a rate or 2,000 to 3,000 per acre in spring yielded averages of 9 to 27 fingerling fish per acre in October.

Intensively raised fingerlings survived twice as well as those raised in ponds. Mitzner also compared results of stocking fingerlings in the fall and in the following spring, when they were almost a year old. In three of five years, fingerling walleyes stocked in spring survived better, but fall stocking was superior in the other two years. By 1992, the goal of tripling the population was met.

A cooperative study in five lakes in Illinois examined the survival and contribution to the fishery of three size classes of fish—fry, small fingerlings, and large fingerlings. In these waters, small fingerlings generally provided the best results, though some variation was seen among waters and various years. Fry and small fingerlings grew faster than large fingerlings in their first and second years. As a result, the researchers recommended that Illinois stocking protocols plant small fingerlings wherever they may be needed.

Dennis Schupp again took the stage to report his findings on stocking results in Minnesota. His results reflected those in Iowa, as fry stocking showed the ability to provide exceptional fishing, but was not consistently successful. Fingerling stocking tended to provide more stable fisheries. Stocking of any sort had a greater chance of success in lakes of fewer than 1,000 acres.

Schupp also noted that fry stocking tended to work best in lakes with higher total alkalinity, possibly because alkalinity tends to be higher in more fertile waters. Also, in moderately turbid waters, abundant black crappies spelled doom for stocked fry.