Novel Predator-Prey Interactions Revealed in Turbid Environments Using Didson

Advancements in sonar technology have led to new possibilities for aquatic biologists. For example, dual-frequency identification sonar (DIDSON) can accurately observe and quantify behavioral interactions of organisms in the field, even under extremely turbid conditions. The goal of our study was to investigate behavioral responses of fish to changes in turbidity and predation risk using an unprecedented laboratory experiment. We used DIDSON to observe the swimming speed and schooling behavior of fathead minnows (Pimephales promelas). Trials were carried out in a 2,060 L tank at three different levels of turbidity (0, 50, and 100 nephelometric turbidity units [NTU]) and two levels of predation risk (presence or absence of a largemouth bass [Micropterus salmoides]). We found that, in the absence of the predator, minnows swam faster and less erratically as turbidity increased , whereas, in the presence of the predator, swimming speed was relatively unaffected by changes in turbidity. In addition, schooling behavior (i.e., synchrony of swimming and spatial proximity of individuals) was less apparent with increased turbidity and, contrary to expectations, in the presence of predation risk. These strong interactive effects of turbidity and risk indicate a complex and sometimes counterintuitive response of fish to changes in their environment.