A BIOENERGETICS MODEL FOR ANALYSIS OF FOOD-CONSUMPTION PATTERNS OF BLOATER IN LAKE-MICHIGAN

We developed a bioenergetics model for bloater Coregonus hoyi based on a synthesis of studies on the energetics of bloater and other coregon ines. This model was applied to the Lake Michigan population with info rmation on water content, gonad weight, energy density, diet, and ther mal history. Water content (inversely correlated with energy density) of nonspawning Lake Michigan bloaters decreased linearly with increasi ng weight for fish smaller than 155 g. Model results indicated compara tively small seasonal changes in consumption, a result of high consump tion by bloaters at low temperatures and relatively small differences in the temperatures of occupied water between winter and summer. Growt h rates and food conversion efficiencies of bloater estimated from the model were higher by factors of 2-4 than comparable values for the al ewife Alosa pseudoharengus, indicating that Lake Michigan could suppor t a higher biomass of native coregonines than of the introduced alewif e. Bioenergetics estimates of annual consumption of Diporeia hoyi and Mysis relicta by both bloaters and alewives more than doubled between 1973-1975, when alewife dominated, and 1987, when bloater dominated. T his increase was most evident in the winter, when bloater feeding rate s were relatively high, and during summer, when alewives fed primarily on zooplankton.