Influence of Changing Seasons on Schooling Behavior of Yellow Perch

Abstract

Analysis of echo-sounder and sonar records made on Lake Mendota during summer and winter indicated that the schooling behavior of yellow perch, Perca flavescens (Mitchill), changed markedly between the two seasons. The distance separating individuals in schools during summer was less than 1.5–2.0 ft, consequently producing dense traces on the recorder charts which showed no definition of individuals. During winter, however, the fish-to-fish distances often were greater than 1.5–2.0 ft, producing many traces showing the individual fishes in a school. The mean distance between the top and bottom fish in a school during winter was 22.1 ft (6.7 m); in summer only 8.5 ft (2.5 m). High correlations existed between light transmission of the water and school size (r =.77) and between temperature and school size (r = −.89). The possible adaptive significance of this seasonal change in behavior is discussed.