CONSEQUENCES OF PREY FISH COMMUNITY DYNAMICS ON LAKE TROUT (SALVELINUS-NAMAYCUSH) FORAGING EFFICIENCY IN LAKE-SUPERIOR

We used a size-structured model, indexed by age, that combines bioener getics and foraging theory to evaluate the effects of prey fish commun ity structure (species dominance, size structure, and density) on the diet and net foraging efficiency of lake trout (Salvelinus namaycush) in Lake Superior. Prey size structure was important for young lake tro ut but decreased in importance for older lake trout, especially with i ncreasing prey density. The model predicted that rainbow smelt (Osmeru s mordax) should dominate the diet of young lake trout due to the size -dependent capture limitations of larger prey. In contrast, lake herri ng (Coregonus artedi) should dominate the diet of oldest lake trout ow ing to a higher net energy return than rainbow smelt. Model results ar e consistent with age-specific diet and size-at-age of lake trout duri ng the last 40 years. Diets of intermediate-sized lake trout do not re flect the recent resurgence of lake herring populations. Absence of a dietary switch is probably due to higher capture probability for rainb ow smelt. Lake trout growth and production will likely be highest with a mixed prey species assemblage of young rainbow smelt and older lake herring.