Changes in Lake Trout Growth and Abundance after Introduction of Cisco into Lake Opeongo, Ontario

Abstract

We examined changes in annual age-specific growth rates of 0–8-year-old lake trout Salvelinus namaycush in Lake Opeongo, Ontario, after the introduction of cisco Coregonus artedii into the lake in 1948. Growth rates of piscivorous lake trout (ages 3–8) initially increased as the occurrence of ciscoes increased, and then decreased as the abundance of piscivorous lake trout increased and the size of ciscoes eaten decreased. Growth of non-piscivorous 1- and 2-year-old lake trout decreased as the occurrence of insects decreased and the abundance of 1- and 2-yearold fake trout increased. Prey abundance, prey size, and intraspecific competition appeared to be major factors influencing growth rates. As ciscoes came to dominate the diet of adult lake trout, cannibalism by adults on younger lake trout decreased, as did the mortality suffered by young lake trout. The cisco introduction improved the existing sport fishery for lake trout by raising annual maximum sustainable yield from about 0.18 kg/hectare to about 0.48 kg/hectare; however, this increase was accompanied by heightened sensitivity of the population to over exploitation.