Diel Activity and Vertical Distribution of Yellow Perch (Perca flavescens) Under the Ice

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Abstract
Use of echo sounders showed that, under the ice in Lake Mendota, yellow perch (Perca flavescens Mitchill) have a bimodal diel pattern of activity. The first peak of activity, during midmorning, was much higher than the second, in midafternoon. Schools of fish in mid water made up the bulk of the fish traces per hour although individual fish were also commonly recorded. At night, when activity was much reduced, principally single fish were observed. The fish swam much more slowly at night than during the day.The activity pattern generally agreed with those reported by investigators for other lakes in that the perch were active during the day and relatively inactive at night.No well-defined change in depth distribution was noted. There was a tendency for the fish to move away from the bottom to a limited extent at night but no marked movement was recorded. The majority of fish were most often recorded at a depth of 30–60 ft (9–18 m), the main concentrations being in areas of the lake more than 50 ft (15 m) deep.