Diel rhythm in activity of walleye, Stizostedion vitreum vitreum

Abstract

Walleye, Stizostedion vitreum vitreum, generally moved along shore, mostly within 100 m, and were relatively inactive during the day. Activity, probably in relation to feeding, increased coincident with changing light intensity during the onset of darkness and daylight. Data were corroborative from ultrasonic tracking, gill net catches and echograms. Ultrasonic telemetry indicated that the majority of swimming speeds, 86%, were below 1 B.L. s−1 and maximum swimming speeds, up to 3.7 B.L. s−1, coincided with periods of maximum catches by gill net shortly after dusk. Walleye were consistently in the essentially homo‐thermous epilimnion and did not experience wide variations in ambient temperature. However, since light strongly influences activity, it is likely that light level rather than temperature limits the depth distribution of walleye.