Dynamics of piscivory by lake trout following a smallmouth bass invasion: A historical reconstruction

Our objective was to assess the dynamics of piscivory by lake trout Salvelinus namaycush in Lake Opeongo, Ontario, following the introduction of smallmouth bass Micropterus dolomieu early in the 1900s. The effects of this introduction on lake trout were thought to be of slight significance at the time, but they may have been obscured by the introduction of cisco Coregonus artedi in 1948. Our analyses of take trout stomach contents and stable isotopes of archived scales indicated that several dietary changes occurred in advance of the cisco introduction. These changes included the consumption of fewer yellow perch Perca flavescens, fewer but larger lake whitefish C. clupeaformis, and larger lake whitefish for a given lake trout size. Stable isotope analyses were consistent with a decline in the importance of littoral prey for young lake trout before the introduction of cisco. We hypothesize that the indirect effects of smallmouth bass on the pelagic fish community explain these patterns.