DIEL PERIODICITY OF ACTIVITY AND VERTICAL DISTRIBUTION OF PERCH (PERCA FLAVESCENS MITCHILL) UNDER THE ICE.

An echo sounder was utilized from early January to midMarch to collect information on the daily activity patterns and depth distributions of yellow perch in Lake Mendota, Wisconsin, a highly productive eutrophic lake with winter characteristics very similar to other eutrophic lakes of temperate regions. The ice reaches a thickness of at least 20 inch 50 cm and the lake usually remains icecovered for an average of 114 days. Recordings of 24 hours duration were made throughout the winter at selected sites. It was learned from these observations that the yellow perch are active primarily during daylight hours with peak periods occurring in mid-morning and early afternoon. Usually the afternoon peak is of smaller magnitude than the morning peak. The peaks are in large part owing to perch schools which are active at those times. There was a marked difference in the number of perch recorded at shallow stations as compared to deep stations. The number of fish recorded was always much larger at the deep over 50 feet stations. Perch appear to remain concentrated in the deeper portions of the lake throughout the duration of ice cover. Author