Experimental analysis of a reduced daily bluegill limit in Minnesota

The effect of a reduced daily limit (from 30 to 10 fish/d) on the size structure of bluegills Lepomis macrochirus in eight Minnesota lakes was measured with a controlled and replicated experiment. Bluegiils from four treatment lakes (daily limit of 10 fish) and four control lakes (daily limit of 30 fish) were sampled in 2 years prior to regulation implementation and in the fourth and fifth years after regulation implementation. Repeated-measures analysis of variance was used to test for changes in two measures of size structure: mean length and 90th percentile length. The mean length of bluegills sampled in trap nets was significantly greater in treatment lakes than in control lakes at the end of the experiment. Bluegill 90th percentile lengths were higher during the postregulation period than the preregulation period, but not significantly so (although the P-value approached significance). Postregulation increases in length at maturity and growth rate were observed in the treatment lakes that exhibited the strongest responses in size structure. Results of the experiment suggest that regulations designed to significantly reduce angling harvest have potential for improving bluegill size structure.