Assessment of Walleye Fry and Fingerling Stocking in the Okoboji Lakes, Iowa

Abstract

During 1984–1989, the stocking program for fry and fingerlings ofwalleye Stizostedion vitreum in interconnected East and West Okoboji lakes was evaluated to determine the contribution of each stocking to year-class abundance, Sac fry were stocked in East Okoboji Lake at rates of 8,154–11,119/hectare between 1984 and 1989. Stocked fry contributed significantly to the autumn young-of-the-year (age-0) population each year; resulting densities ranged from 4.5 to 56.1 fingerlings/hectare. Each year, mortality of stocked fry was over 99% during the first 6 months after stocking. Large fingerling walleyes (total length, 100–150 mm) were stocked in West Okoboji Lake at rates of 30.2–68.2/hectarebetween 1984 and 1988. Initial contribution ofthese stocked fingerlings to autumn young-of-the-year abundance ranged from 70 to 99%. However, first-year mortality of stocked fingerlings was 2–16 times greater than that of naturally produced fish or fingerlings originating from sac fry introductions. Also, initial mortality of stocked walleye fingerlings raised in the Spirit Lake Hatchery was 4–6 times greater than initial mortality of fingerlings raised in nursery lakes. Therefore, contributions of stocked walleye fingerlings should be assessed the year after stocking rather than during the same year. During June and July of 1989, small fingerlings (total length, 50 mm) were stocked at a density of 69.7/hectare in West Okoboji Lake, The autumn population survey indicated a young-of-the-year population density of 10.1/hectare; 49% of this population was attributable to the stocked 50-mm fingerlings.