A Bioenergetic Exploration of Piscivory and Planktivory During the early Life History of Two Species of Freshwater Fishes.

In order to explore the trophic relationships of two different feeding strategies during the nursery period a bioenergetic model is applied to the early life history stages of a piscivore, the muskellunge (Esox masquinongy, Esocidae: Salmoniformes) and a planktivore, the bluegill (Lepomis macrochirus, Centrarchidae:Perciformes). The model uses a balanced energy equation to predict consumption based on observed growth and calculated losses to metabolism, excretion and egestion. Estimates are temperature- and weight-dependent and are calculated on a daily basis over the duration of the nursery period. Ambient temperatures and the diet composition as determined from stomach content analysis were used in the model. Comparisons of consumption and metabolic rates between a piscivore and a planktivore suggest that the planktivore has a much higher metabolic rate resulting in greater weight-specific consumption and a larger maximum ration (g g-1 day-1 day-1) than the piscivore. The consumption of prey organisms in relation to prey standing crop by the planktivore ranged up to 2.5% of the standing crop per day, whereas in the piscivore population it approached 18% of standing crop per day; this suggests that consumption by the planktivore on the zooplankton population in eutrophic Crane Lake would likely have less of an effect on the prey population than that of the piscivore in bays of the St Lawrence River.