Patterns of foraging and distribution of bluegill sunfish in a Mississippi River backwater: influence of macrophytes and predation

We studied the trophic interactions and spatial distributions of bluegills Lepomis macrochirus and largemouth bass Micropterus salmoides in a macrophyte bed in Lake Onalaska, a backwater lake in the upper Mississippi River. The diets of adult and age‐0 bluegills were similar and changed seasonally probably in response to changes in life stages of macroinvertebrates (i. e. emergence of winged adults). Diets and diel patterns of abundance of bluegill suggest that age‐O and adults were feeding in the vegetated, littoral zone. Predation by age‐O largemouth bass appears to influence use of vegetated habitat by age‐0 bluegills. In summer, when most age‐O bluegills were vulnerable to predation by age‐O largemouth bass, bluegill abundance was strongly correlated with vegetation biomass. In October and November, piscivory by age‐O largemouth bass was limited by gape. Consequently, the relationship between the abundance of age‐O bluegills and vegetation biomass was weakened because predation risk by age‐O largemouth bass was reduced.