The Effects of Turbidity On the Feeding Ecology of Adult Largemouth Bass

Turbidity in aquatic systems can change rapidly, affecting the visual ability of predators.  The effects of turbidity on planktivorous and insectivorous fish are well studied, but little is known about the effects of turbidity on piscivorous fish.  We examined interactions of piscivorous largemouth bass Micropterus salmoides with prey at different turbidity levels (ranging from to 0 – 57 NTU; drinking-water clarity to 7-cm Secchi depth) in 2-m diameter tanks and using diet data from field-collected fish.  At lower turbidity levels (0 and 5 NTU) largemouth bass consumed mostly gizzard shad Dorosoma cepedianum and bluegills Lepomis macrochirus and had negative selectivity for crayfish Orconectes virilis.  At 10 NTU, all three prey types had similar selectivity, presumably caused by increased difficulty in capturing rapidly moving fish prey as reactive distances decreased.  At 40 NTU bluegills were selected significantly more than the other prey types.  Foraging return was greatly reduced by increases in turbidity, but the rate of decline was greater with gizzard shad prey than with bluegill prey.  Field data were highly variable among lakes, but showed similar patterns to lab experiments when significant differences were found.  Our results suggest that trophic interactions may be altered as turbidity levels change.