Effects of prohibited harvest of largemouth bass on the largemouth bass and bluegill fisheries in two Minnesota lakes

Abstract.--Effects of an experimental regulation prohibiting harvest of largemouth bass were evaluated for two lakes in the Minneapolis- St. Paul metro-politan area over a 10-year period. The objective of the regulation was to improve the size structure of bluegill populations by limiting recruitment, via increasing abundance of predatory largemouth bass. The evaluation utilized a before-after/control-impact (BACI) experimental design with two experimental regulation lakes and two control lakes. Statistical power of the analyses was low because of the small sample of lakes and high variability of the data, limiting the conclusiveness of the study. There were statistically significant positive effects of the regulation on largemouth bass density in both experimental lakes, and some indication of an im-provement in largemouth bass quality. However, there was only a weak negative correlation between largemouth bass density and bluegill recruitment, and as a result the regulation was ineffective at improving the quality of the bluegill fisheries. In addition, growth curves suggested the lack of bluegill ≥ 200 mm may have been the result of selective harvest of large bluegill rather than stunted growth due to exces-sive bluegill recruitment