A Study of the Warmwater Fisheries in Four Lakes in Southeast Wisconsin
Michaelis, Keith R.
University of Wisconsin-Stevens Point, College of Natural Resources
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Vital statistics were described for populations of largemouth bass (Micropterus salmoides) and panfish, mainly bluegill (Lepomis macrochirus), in Lakes Beulah (338 ha), Rockland (16 ha), Pretty (26 ha), and Browns (160 ha) in southeastern Wisconsin. Proportional stock density values for largemouth bass were below recommended management objectives (40-60%) in Beulah (13%), Rockland (13%), and Pretty (14%) Lakes, and within the objective range in Browns Lake (58%). Relative weight (a condition index) values for largemouth bass were satisfactory in all lakes except Browns Lake in fall. Largemouth bass growth in Rockland, Pretty, and Browns Lakes was similar to each other and the state average up to age 5. Growth of largemouth bass in Beulah Lake was similar to that in the other lakes and to the state average up to age 3, and significantly slower thereafter. Estimated total annual mortality rate of large mouth bass ranged from 52-79%. The exploitation rate (87%) of largemouth bass in Rockland Lake in 1980 was probably an overestimate. Population estimates of largemouth bass in Rockland Lake were 77 (for fish 130 mm long) and 37 ( 160 mm long) fish per hectare in spring and fall of 1980, and 46 (160 mm long) and 44 (160 mm long) fish per hectare in spring and fall of 1981. The estimated standing stock of largemouth bass in Rockland Lake was 13 and 10 kg/ha in spring and fall of 1981. Proportional stock density of bluegills was below recommended management objectives (20-40%) in Rockland (17%), Pretty (5%), and Browns (1%) Lakes, and within the objective range in Beulah Lake (40%). Condition of bluegills was satisfactory in Beulah and Rockland Lakes, and poor in Pretty and Browns Lakes. Bluegill growth in all lakes was significantly slower than the state average, and bluegills in Pretty and Browns Lakes grew significantly slower than those in Beulah and Rockland Lakes. Estimated total annual mortality rates of bluegills ranged from 39-77%. Estimated fishing pressure in 1980 ranged from 107-348 hrs/ha. Catch of largemouth bass, bluegills, and all species combined ranged from 12-73, 132-459, 199-687 fish/ha, respectively. Corresponding harvest values ranged from 4-20, 37-210, and 79-301 fish/ha. An index of abundance (number caught/hour of electro fishing and fyke netting combined) of bluegills 80-140 mm long was inversely correlated with proportional stock density, relative weight, and growth rate, and positively correlated with total annual mortality rate. Community structure, measured by proportional stock density, did not meet the recommended management objective in any lake. Proportional stock density for largemouth bass and bluegills was positively correlated with various angling quality statistics. Length limits established for largemouth bass in 1982 as a result of this investigation were a slot-length limit of 305-406 mm in Beulah and Rockland Lakes, and a minimum length limit of 406 mm in Pretty and Browns Lakes.