Bluegill Recruitment, Growth, Population Size Structure, and Associated Factors in Minnesota Lakes

Abstract

To better understand the differences among populations of bluegill Lepomis macrochirus, we analyzed the relationships between bluegill recruitment, growth, population size structure, and associated factors from approximately 2,600 Minnesota lakes. Potential explanatory variables for our models included bluegill year-class strength, growth, population size structure, the relative abundance and mean weight of predator species, physical and chemical characteristics of lakes, summer air temperature, and season. Bluegill year-class strength, growth, and population size structure were more strongly related to each other than to predator and lake characteristics, temperature, or season. Growth of age-6 bluegills was positively associated with population size structure and inversely related to year-class strength, suggesting density-dependent growth effects for adult bluegills. Growth of age-3 bluegills was inversely related to Secchi depth, so early growth and productivity may be linked. Bluegill population size structure was positively associated with length at age 5, as expected from the analysis of growth, and was inversely associated with mean year-class strength. Bluegill year-class strength was negatively associated with population size structure, length at ages 4 and 5, and lake area. Although predator variables were not included in one- or two-variable regression models, bluegill growth was positively related to the relative abundance of yellow perch Perca flavescens, walleye Sander vitreus (formerly Stizostedion vitreum), black bullhead Ameiurus melas, and brown bullhead A. nebulosus and negatively related to that of largemouth bass Micropterus salmoides and yellow bullhead A. natalis. The results suggest that management strategies for improving bluegill growth and population size structure should focus on bluegill recruitment and growth rather than on external environmental factors.