Michigan Department of Natural Resources
Fisheries Research Report No.1835, 1976
Some Factors Influencing Size of the Year Class of Bluegills (Lepomis macrochirus) in Ponds
W. C. Latta and J. W. Merna
Abstract.-At the Saline Fisheries Research Station nine ponds) each about one-half acre in size, were planted in May 1966 and 1968 with matched adult bluegills 5.0-6.9 inches total length. The nine ponds were grouped into blocks of three, and on a random basis each pond of a block received 8, 16 or 32 bluegills. In late September or early October the ponds were drained to determine the number of bluegill fry produced. In both years spawning occurred in June and samples of fry were taken regularly thereafter to determine growth and food habits. Samples of zooplankton were taken each week in 1966 and biweekly in 1968. Benthos was sampled biweekly in 1966 and each month in 1968. A recruitment curve was drawn which shows the relationship between number of eggs and resulting bluegill fry. Survival and growth of fry in the ponds were density dependent. Production of bluegill fry, which is dependent upon growth and survival, reached a peak at about 12 g/m3 with a level of 120 eggs/m3. The ratio of production to standing crop of bluegill fry had a mean of 1.3. The fry ate zooplankton almost exclusively which resulted in a sharp decline in zooplankton abundance in mid-July in all ponds in both years. Benthic organisms were seldom eaten. The phytoplankton counts made in 1968 increased with the decrease in zooplankton abundance. Primary production measured during the summer by light-and-dark bottle oxygen determinations had a high correlation with phosphate concentrations and standing crop of phytoplankton. A stepwise multiple regression of the effects of number of eggs, primary production, and the square of each of these quantities, on number of bluegill fry indicated that number of eggs and number of eggs squared had the greatest correlation with number of fry (0.89) and accounted for 80% of the variation. However, the addition of primary production and primary production squared increased this correlation to 0.97 and the percentage of variation to 93%. MA