Examining Interpopulation Variation in Bluegill Growth Rates and Size Structure: Effects of Harvest, Maturation, and Environmental Variables

Abstract

Understanding how life history variation and the environment affect growth and population size structure is an important theme of fisheries ecology. However, the interactions among important biotic and abiotic factors and their relative importance in the context of population-specific variation are seldom considered. We used an information theoretic approach to investigate how environmental variables interact with important life history parameters to influence population size structure of bluegills Lepomis macrochirus. We sampled bluegill populations in 23 Illinois reservoirs to examine the effects of temperature, water transparency, and prey availability and bluegill density, harvest, and size at maturation on bluegill growth and population size structure. Good growth and large body size were associated with warm, clear lakes containing abundant prey resources. An exception to this pattern was early growth (length at age 2): Larger body size at age 2 was associated with relatively low Secchi depth (i.e., turbid water). In addition, size at maturation was positively related to size of adult male bluegills. Interestingly, bluegill density and harvest mortality—factors that are often considered important within populations—did not contribute much explanatory power to our among-system models. Whereas harvest and density-dependent growth have been shown to influence individual bluegill populations, their effects across a range of populations appear to be mitigated by temperature, water transparency, and prey availability. Although growth of individuals can be influenced by a variety of factors, our investigation suggests that fairly straightforward mechanisms at broader spatial scales are responsible for explaining variation among populations.