Population characteristics of yellow perch, Perca flauescens (Mitchill), in Indiana waters of Lake Michigan in 1975, with discussion of sample variability and gear selectivity
Yellow perch, Perca flavescens, were collected by night trawling and gill netting at 5 m in a study area near Kintzele Ditch in Indiana waters of Lake Michigan during the months of June through September, 1975. Additional collections made by the Indiana Department of Natural Resources and the U.S. Fish and Wildlife Service using gill nets were included in some aspects of the study.Population characteristics were analyzed and compared to other studies. The rate of growth was significantly greater than in past Great Lakes' populations. The calculated length-weight relationships and growth rates were comparable to those reported by recent studies for southern Lake Michigan. Growth differed between males and females of the same age, and different ages were often represented in the same length interval. Nearly all male yellow perch were mature by age I and 130 mm. About half of the age II females and most at the 200 mm length interval were mature. Sex ratios were variable.Higher catch-per-unit-effort (cpe) was related to warmer water temperatures to the thermocline level. When water temperatures were mixed resulting in low inshore temperatures, cpe values were lower.There existed a great deal of sample variability within and between gear types as a result of seasonal population availability, gear characteristics, and non-random distribution of the population.Trawling, although more efficient than gill netting at sampling total numbers and widest range of lengths, was selective for smaller fish, and gill netting was selective for larger fish. Depth (from 5 m to 18.3 m) and particular gill net methods employed had little effect upon the sizes and length-percent frequency distribution sampled.Great differences between percentage age compositions compiled from trawl and gill net catches reflected the size selectivity of the gears. These results raised questions concerning the validity of management techniques involving percentage age composition and cpe index values to determine relative year class strength.The age groups I and II were represented by the proportion 8:2 (1:11) in the trawl catch which adequately sampled the sizes including the age I and II fish. Further study would be needed to determine the validity and usefulness to management considerations of this method of relative year class strength determinations. Recommendations for additional study were made.