Influence of Angling on Age Structure and Growth of Bluegills in Northern Wisconsin Lakes

Abstract

Abstract: Bluegill sunfish (Lepomis macrochirus) have long been heavily targeted by anglers in a consumption oriented fishery. Anglers catch bluegill over a wide size range but only harvest those large enough to have food value. Analysis by WDNR of the size structure and harvest from Wisconsin lakes indicates that the abundance of desirable­ sized bluegill in both populations and creel have dropped considerably. This research will analyze patterns of growth of bluegill from northern Wisconsin lakes and develop growth comparisons between stunted and non-stunted bluegills. Objectives are to: 1. Describe and compare patterns of growth in bluegill populations that vary in harvest pressure and quality status; 2. Determine the growth potential of a stunted bluegill population. Methods consisted of age and growth analysis from heavily fished versus lightly fished lakes in the same watershed. Scales from these populations came from samples taken and archived by the WDNR and supplemented as necessary by field sampling bluegill populations. Growth of immature bluegills from one stunted and one non-stunted population was compared in a controlled laboratory setting. The fish were fed live mealworms at a ration of 4% for 26 days and 6% for another 30 days. Length and weight measurements were determined at periodic intervals. Results indicate both Crystal and Deep Lake grew at different rates when ration sizes were increased in a control environment suggesting genetics maybe a factor in their life history. Back calculation comparison of Crystal and Deep Lake showed similar growth rates for ages 1-4, but superior growth seen by Crystal Lake for age 4-8 with a decrease in growth by Deep Lake.