Effects of Fry and Fingerling Introductions on Walleye (Stizostedion vitreum vitreum) Production in West Blue Lake, Manitoba

Walleye (Stizostedion vitreum vitreum) were introduced into West Blue Lake, Manitoba, as fry in 1971 and as fry and fingerlings in 1972. Introduced fish were selected to possess malate dehydrogenase (MDH) isozyme phenotypes different from native walleye. The fingerlings were also fin clipped. During the summer months of 1973, 1974, and 1975 fish were recaptured by gill net. Muscle from recaptured fish was used for the determination of MDH isozyme phenotype whereby the contribution of the introduced fish to year-class abundance, biomass, and production was calculated.The 1971 introduction augmented the year-class by 38% but this brood provided only 1.3% of the total catch during the September 1974 to August 1975 period. In contrast, the 1972 introductions formed 99% of the year-class and contributed 37.8% of the total catch in the same 1974–75 period. The fingerling introduction formed only 7.0% of the 1972 year-class abundance in 1975.Introduced fish provided 54% of the total walleye production of 260 kg (wet weight) during the period September 15, 1974 to August 8, 1975. Production by introduced fish was apportioned as follows: 1972 fry 91%; 1972 fingerlings 7.4%; 1971 fry 1.7%. This investigation demonstrates the important contribution that introduced walleye fry may make to production and the utility of isozyme "tagging" in the evaluation offish introductions. Key words: walleye, Stizostedion, production, fry introductions, malate dehydrogenase, MDH, isozymes, fish, introduction evaluation