Maintenance of a Walleye, Stizostedion vitreum vitreum, Fishery in a Eutrophic Reservoir

Hoover Reservoir, a very eutrophic environment, produces a successful fishery for walleye. However the population can only be sustained by stocking due to the absence of high quality summer habitat, intensive exploitation, poor recruitment of most natural year-classes, and poor growth of adult walleye. The oxygen temperature regime brought about by eutrophication forces the adult walleye to live at an above optimum temperature regime for maximum growth during the summer months. Because of the climate and geographical location, the preferred temperatures of the desired prey, young gizzard shad, are far above that of the adult walleye. This makes the shad less accessable to predation for a large portion of the day further reducing the growth of older walleye. Poor recruitment of large natural year-classes results from the absence of gizzard shad fry which spawn much later than walleye, at the time larval walleye convert from a planktonic to a piscivorous feeding habit. Large year-classes of walleye are produced in years when fry were stocked. Stocked fry were produced in hatcheries from spawn obtained at the reservoir. Fry were stocked in the reservoir just at or in advance of shad spawning, whereas in most years naturally produced fry appeared well in advance of shad spawning. This delayed appearance of stocked walleye fry probably accounts for their successful year-class production. This walleye spawning stock had an estimated mean biomass of 13.6 kg/ha and a mean annual production of 2.2 kg/ha between 1967 and 1973. Key words: Hoover Reservoir — Ohio, Percidae, Stizostedion, management, fry stocking