Evaluation of Stocking Walleye Fry to Enhance a Commercial Fishery in a Large, Canadian Prairie Lake

Abstract

More than 100 million fry of walleye Stizostedion vitreum are stocked annually into lakes of the prairie provinces of Canada to enhance sport and commercial fisheries. However, the success of this practice has not been evaluated. We introduced 7.1 million genetically marked walleye fry into Dauphin Lake, a 50,000-hectare lake in Manitoba, in 1985 to evaluate fry stocking as a tool for fishery enhancement. The 1985 walleye cohort was fully recruited into the commercial fishery at age 3 (in 1988). We sampled commercial catches in the winters of 1988 and 1989 to determine the phenotypes for supernatant malate dehydrogenase in 727 3-year-old walleyes and 657 4-year-old walleyes of the 1985 (enhanced) year-class. The introduced fish contributed about 2.9% to the 1985 year-class of walleyes. The survival of walleye fry from the time of stocking to age 3 (in the fall) was estimated at 0.04%. At current walleye harvest rates in Dauphin Lake (about 13,000 kg/year), the stocked fish were expected to contribute 114 fish or 80 kg to the commercial catch in 1988, and about 420 kg to the commercial fishery over the 10 years that they would remain vulnerable to the fishery. The cost of producing fry for stocking was Can$0.46/1,000 fry. For the commercial fishery, the cost: benefit ratio of the 1985 stocking program was estimated at about 2.6:1. The number of fry produced by natural spawning in Dauphin Lake in 1985 was estimated at 230–249 million, and the number of eggs laid was estimated at 2,817 million. Therefore, the survival of naturally produced eggs to hatching was estimated at 8–9%.