Initial effects of the exploitation of walleye, Stizostedion vitreum vitreum (Mitchill) on the boreal percid community of Henderson Lake, Northwestern Ontario

Abstract

The effect of large scale exploitation of walleye Stizostedion vitreum vitreum on the boreal percid community of Henderson Lake, northwestern Ontario, was studied from 1979 to 1981. Investigations centered on the two major predators in the community, the walleye and the northern pike Esox lucius. Population estimates were done in 1979, 1980 and 1981, and the accuracy of Schnabel, Schumacher Eschmeyer and Peterson estimates were compared. Previous to exploitation (1979-1980) both walleye and northern pike exhibited the lowest production and P/—B ratios yet recorded for either species (walleye 4-14 yrs, P=1.01 kgha[superscript -1] yr[superscript -1], P/B =0.137; northern pike 7-14 yrs, P=0.716 kgha[superscript -1] yr[superscript -1] , P/—B =0.086). Low production in both species was partially attributed to competition for major prey species, and the small size of available prey items. Sticklebacks Pungitius pungltius, yellow perch Perca flavescens and mayfly subimagoes Ephemoptera sp. were the most important prey items in the lake. Long-term patterns of prey utilization by both predators showed considerable annual variation. Abundant white sucker and cyprinid species were not important in the diet of either walleye or northern pike, and may represent a net energy loss to the production of these two species.