Turbidity Affects Foraging Success of

Abstract.—The effects of suspended sediment on nongame fishes are not well understood. We examined the effects of suspended sediment (i.e., turbidity) on reactive distance and prey capture success at spring– autumn (128C) and summer (188C) temperatures for rosyside dace Clinostomus funduloides in an artificial stream. Experimental turbidities ranged from 0 to 56 nephelometric turbidity units (NTUs) at the two temperatures, and sample sizes for each turbidity–temperature combination ranged from 5 to 10 fish. All fish were tested at a single, randomly selected turbidity. Nonlinear regression (dosage–response curves) detected a negative relationship between turbidity and reactive distance at both spring–autumn (R2 0.96) and summer (R20.90) temperatures. Turbidity also had a strong negative effect on capture success at both spring–autumn (R2 0.88) and summer (R2 0.70) temperatures. Two-way analysis of variance showed that turbidity and temperature were significant in all models (P, 0.0001) and that there were no significant interactions. The median effective concentrations (EC50s, i.e., the concentrations required to elicit a response equal to 50 % of the maximum response observed) for reactive distance regressions were 9.9 NTUs in spring and autumn and 9.2 NTUs in summer. Data from moderately impacted streams in the region indicate that these streams possess turbidities that exceed the EC50s approximately 50 % of the time. These results suggest that turbidity negatively affects the foraging behavior of rosyside dace at even low to intermediate levels (.9 NTUs) and that these effects may vary seasonally. Increased suspended sediment loads in North American streams pose an important management concern for fisheries biologists (Barrett et al. 1992