Spatio-Temporal Patterns of Foraging Success for Fishes in an Illinois Stream

Abstract

Stomach contents of 10 fish species were examined to evaluate several scales of spatio-temporal variation in foraging success within an Illinois stream. Most species fed primarily on aquatic or terrestrial invertebrates, but one species (Pimephales notatus) specialized on fine detritus. Fish ate a wide variety of invertebrate taxa, and diet overlap based on prey taxa was extensive among fish species and age classes. Foraging success, measured by number and size of prey eaten, varied among seasons, years, substrate composition and amounts of woody debris. However, no factor influenced foraging success of all species, and no two species responded identically to all factors. Fish generally fed most successfully in June, and least successfully in October. Some fish ate more or larger prey in a study area with gravel-cobble substrates than in a silt-sand area, and many ate more or larger prey in sites with woody debris than in sites from which debris was removed. In addition, aquatic invertebrates increased in abundance in silt-sand substrates when fish were excluded, but did not increase in gravel-cobble substrates, suggesting a greater potential for resource depression in the silt-sand area. Stream fishes apparently face continuous variation in food availability at several temporal and spatial scales. Because changes in availability are often unpredictable and influence each species differently, the competitive environment of stream fishes may be in a state of constant flux. Anthropogenic modifications of streams may create conditions that favor fishes such as certain cyprinids which have highly opportunistic feeding habits.