Seasonal Changes in Swimming Rates of Yellow Perch in Lake Mendota as Measured by Sonar

Abstract

Sonar equipment was used during 1966 to study the relation between seasonally changing temperatures and swimming speeds of yellow perch, Perca flavescens (Mitchill), in Lake Mendota and the movements of the fish with respect to water currents in the lake. From its lowest point during winter (0–5 C) the rate of movement increased with increasing water temperatures until the maximum rate was reached during mid-summer when water temperatures were 20–25 C. As the lake cooled in autumn, the swimming speeds declined. The range of speeds in the frequency distribution during winter was less than that during summer when the distribution was spread out and encompassed a wide range of speeds. The swimming rate increased linearly with increasing temperature. The swimming speeds of individual perch were commonly only one-half those of schools at a given temperature interval suggesting that a “group effect” was correlated with the behavior of the perch schools. No consistent orientation of fishes to the currents in the lake was observed. The swimming direction of perch could not be correlated with the direction of the currents.