Effects of Angling on a Previously Fished and an Unfished Warmwater Fish Community in Two Wisconsin Lakes

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Abstract
Population structure and other vital statistics were determined for warmwater fish populations in 2 adjacent lakes for 2 successive 3-yr periods. Allen Lake (7.8 ha), containing bluegills Lepomis macrochirus, pumpkinseeds L. gibbosus, yellow perch Perca flavescens, large-mouth bass Micropterus salmoides and northern pike Esox lucius, was open to angling during and for about 10 yr before the investigation. Mid Lake (4.7 ha), with the same species, was closed to angling until fishing was permitted throughout the 2nd 3-yr period. Before angling began in Mid Lake, large proportions of the population were of large, old fish, and total annual mortality rates (which were natural mortality rates) were low. The fished populations in Allen Lake comprised mainly small or intermediate size fish throughout the study. After angling in Mid Lake the fish populations and their vital statistics became like those in Allen Lake: length- and age-frequency distributions shifted toward smaller sizes and younger ages, mean age and life spans decreased, mortality rates increased and proportional stock density declined from values above to values below recommended ranges. The changes in population structure were most pronounced for yellow perch, followed in order by pumpkinseeds, bluegills, largemouth bass and northern pike. Estimated fishing effort was 231 h in May 1976, the 1st month that Mid Lake was opened to angling, and declined to 62 h/ha in May 1979; harvest and catch rate also declined. Estimated exploitation rates (%) in May 1976 for fish of sizes acceptable to anglers were 86 for yellow perch, 74 for pumpkinseed, 35 for bluegill, 53 for largemouth bass and 46 for northern pike; most fish were taken in the first 2 days. Growth rates in Mid Lakes did not change within the period of the study but bluegills and pumpkinseeds in Allen Lake were growing more slowly than those in Mid Lake before the advent of angling.

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