Ultrasonic telemetry was used to determine habitat use and activity patterns of nine adult muskellunge in a 1540 hectare natural lake from spring 1978 to fall 1979. M About 80% of summer and early fall contacts (N=1292) occurred in three large, relatively shallow, vegetated bays. Study fish exhibited significant summertime changes in depth of water occupied, association with vete5tation and general activity. Fish activity was negatively associated with surface water temperatures; activity was greatest over the 11-17°C range. There was a positive association of fish activity with water transparency (Secchi disk depth). Significant diel behavioural variations occurred during June when there were crepuscular peaks in fish movement rates, activity and water depth use. There were no identifiable sex- or size- dependent differences in any of the studied behaviours.
The study fish appeared to adjust their basic foraging patterns to maintain an optimal feeding strategy in response to seasonally changing environmental factors. After the spawning period and through midsummer, the fish behaved as searching predators as evidenced by relatively high levels of activity, extensive movements, use of a variety of water depths and habitat types and pronounced crepuscular activity. By late summer, the fish exhibited behavioural characteristics of a sedentary ambush predator (e.g., reduced activity), strong allegiance to activity centers associated with vegetation and little diel variation in activity. These seasonal changes in muskellunge habitat use and behavior may contribute to the distinct seasonality of the fishery for this species in West Okoboji Lake, maximum catch rates occurring in late summer and early fall.