Turbidity enhances feeding abilities of larval Pacific herring, Clupea harengus pallasi

Abstract

Fishes inhabiting estuaries, rivers, and embayments are subject to turbid conditions. Larvae of many fishes utilize estuaries as nursery areas. For visual plankton feeders such as larval fishes, turbidity may reduce search and reaction distances, resulting in lowered feeding abilities. In this study feeding Pacific herring larvae, Clupea harengus pallasi, were exposed to suspensions of estuarine sediment and Mount Saint Helens volcanic ash at concentrations ranging from 0 mg · l−1 to 8 000 mg · l−1. In all experiments, maximum feeding incidence and intensity occurred at levels of suspension of either 500 mg · l−1 or 1000 mg · l−1 with values significantly greater than controls (0 mg · l−1). Feeding decreased at greater concentrations. The suspensions may enhance feeding by providing visual contrast of prey items on the small perceptive scale used by the larvae. Larval residence in turbid environments such as estuaries may serve to reduce predation from larger, visual planktivores, while searching ability in the small larval perceptive field is not decreased.