Effects of Water Velocity, Group Size, and Prey Availability on the Stream-Drift Capture Efficiency of Blacknose Dace, Rhinicthys atratulus

Abstract

In laboratory flow-tank experiments, I determined the effects of water velocity, group size, and prey arrival rate on the proportion of drifting prey a group of blacknose dace, Rhinicthys atratulus, captured. Water velocity, group size, and the interaction between the two accounted for significant proportions of the variance found in the stream-drift capture efficiency of the fish. Neither prey arrival rate nor any of the interactions which included prey arrival rate explained a significant proportion of the variance in the capture data. I present a regression relating water velocity and group size to the proportion of drift items fish capture that should be valuable for future studies offish habitat selection. Further analysis of the regression found an optimal water velocity for drift-feeding blacknose dace at between 24 and 27 cm∙s−1. Because of the significant interaction between water velocity and group size, the advantage of foraging in sites with optimal water velocity decreased as the number of intraspecific competitors increased.