SURFACE SCHOOLING AND FEEDING BEHAVIOR IN THE WHITE BASS, <i>ROCCUS CHRYSOPS</i> (RAFINESQUE), IN LAKE MENDOTA1

Abstract

Zooplankters of the genus Daphnia comprise the bulk of the food of the white bass, Roccus chrysops , in Lake Mendota, Wisconsin. Compact schools of white bass are conspicuous at the surface from May through October. Planktonic Daphnia are highly aggregated, on a relatively small scale in foamlines or roll vortices, and on a larger scale by horizontal convergence on the leeward side of important shoal areas. The white bass are able to locate regions of high concentrations of air‐locked and/or free‐swimming Daphnia, as shown by highly significant differences between the mean numbers of organisms found within and outside of feeding areas. Suggestions are made as to the mechanisms involved. The relatively limited but significant vertical migration of Daphnia in Lake Mendota consists of typical morning and evening maxima at the surface. The pattern of feeding activity of the white bass is shown to correspond with the morning and evening concentrations of Daphnia in the surface waters. Some effects of the feeding behavior upon the efficiency of food‐intake are discussed.