Evaluating the Contribution of Stocked Walleye Fry and Fingerlings to South Dakota Walleye Populations through Mass Marking with Oxytetracycline

Abstract

The contributions of stocked fry and 20–40-mm fingerlings of walleye Stizostedion vitreum to fish populations had not been thoroughly evaluated in eastern South Dakota lakes because of the difficulty in differentiating between stocked and naturally produced fish. This study evaluated methods of mass-marking juvenile walleyes by immersion in an oxytetracycline (OTC) solution and assessed their subsequent contribution to natural populations in South Dakota lakes. The efficacy of marking walleye fry was evaluated at OTC concentrations of 500 and 700 mg/L; fry marked at 700 mg/L had brighter, more easily distinguished marks than did those marked at 500 mg/L. Test-pond fingerlings marked as fry at 700 mg/L all exhibited marks. Hatchery-pond returns of walleye fingerlings 35–45 d after marking suggested no significant differences in the survival of unmarked fry and those marked at 500 or 700 mg/L. The annual (1996–1998) contribution to electrofishing catch per unit effort (CPUE; defined as catch per hour) of fall age-0 walleyes in four lakes averaged 93% (range, 81–100%) for stocked fry and 87% (32–100%) for stocked fingerlings. Moderately strong to strong year-classes of fall age-0 walleyes were observed for 11 of 12 year-classes in lakes stocked with fry and 8 of 16 year-classes in lakes stocked with fingerlings. Gill-net CPUE (number/set) of age-1 and older walleyes in summer 1999 and 2000 sampling exceeded the South Dakota Game, Fish, and Parks objective of 15 fish/h in two of four fry-stocked lakes but was less than 8 fish/h in all fingerling-stocked lakes.