A 14.0-inch minimum length limit on largemouth bass (Micropterus salmoides) was assessed from 1972-1976 at Big Creek Lake, Iowa, a new 850-acre lake impounded in autumn 1971. The objective of the length limit was to prevent overharvest of bass and maintain quality fishing in terms of catch per effort (C/E) and mean size. The bass were sampled each spring to determine population characteristics while a sport-fishery survey was conducted to document C/E, harvest, and exploitation. The largemouth bass population was dominated by fish stocked in 1972 and 1973. Growth rates were best during the first 2 years of impoundment; proportional stock densities were 0 in 1973, 57% in 1974, 56% in 1975, and 8% in 1976. Numerical density of the largemouth bass gradually declined from 50 per/acre in 1974 to 16 per/acre in 1976 while standing stock increased from 18 lbs/acre in 1973 to 29 lbs/acre in 1975, then fell to 6 lbs/acre by 1976. Anglers creeled 26; 1,738; 1,903; and 375 largemouth bass in 1973-1976, respectively. Sublegal largemouth bass comprised 28-39% of the total harvest each year. Catch success was related to population density and followed the same trend, decreasing from 0.85 largemouth bass/hour in 1974 to 0.16 per/hour in 1976. These catch rates of largemouth bass exceeded the state-wide average (0.07 per/hour), as did mean weight in the creel—2.1 lbs compared to 0.9 lb. The exploitation rate of the 1972 year class was 0.1% in 1973, 13% in 1974, 37% in 1975, and 71% in 1976. The 14.0-inch minimum length limit prevented overharvest because the estimated angler catches and releases equalled or exceeded the population size each year. In effect, the length limit prolonged the harvest of the 1972 year class. However, the most critical problem at Big Creek Lake was poor year-class success. Fishing quality declined after 1974 because the 1974 and 1975 year classes were poorly represented and a slower-growing 1973 cohort did not enter the fishery as dramatically as did the 1972 year class. After this investigation ended, the minimum length limit was reduced to 12.0 in.
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