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 blueg ills Lepomis macrachirus and largemouth bass Micropterus salmoides in a macrophyte bed in Lake Onalaska, a backwater lake in the upper Missi ssippi River. The diets of adult and age-0 bluegills were similar and changed seasonally probably in response to changes in life stages of m acroinvertebrates (i.e. emergence of winged adults). Diets and diel pa tterns of abundance of bluegill suggest that age-0 and adults were fee ding in the vegetated, littoral zone. Predation by age-0 largemouth ba ss appears to influence use of vegetated habitat by age-0 bluegills. I n summer, when most age-0 bluegills were vulnerable to predation by ag e-0 largemouth bass, bluegill abundance was strongly correlated with v egetation biomass. In October and November, piscivory by age-0 largemo uth bass was limited by gape. Consequently, the relationship between t he abundance of age-0 bluegills and vegetation biomass was weakened be cause predation risk by age-0 largemouth bass was reduced.