The Effects of Turbidity on Prey Selection by Piscivorous Largemouth Bass

Abstract

Turbidity in aquatic systems can change rapidly, affecting the visual ability of predators. Increased turbidity is known to reduce the reactive distance and foraging success of some planktivores and insectivores, leading to decreased growth rates. However, little is known about the effects of turbidity on prey selection by piscivores. We examined the interactions between largemouth bass Micropterus salmoides and their prey in 1.8-m-diameter tanks (58 cm deep) at four turbidity levels (0, 5, 10, and 40 nephelometric turbidity units [NTU]). Prey selectivity was significantly affected by turbidity. 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 northern crayfish Orconectes virilis. At 10 NTU, all three prey types had similar selectivity, presumably because the largemouth bass had more difficulty in capturing rapidly moving fish prey as their reactive distances decreased. At 40 NTU, the overall foraging rate was much lower and bluegills were selected significantly more often than the other prey types. Low light levels at the bottom of the tanks combined with reductions in visual clarity from clay sediments probably made it difficult for largemouth bass to feed effectively on virile crayfish at higher turbidities. Our results suggest that trophic interactions may be altered as turbidity levels change.