Weak Effects of Density on Mean Length at Age and Condition of Largemouth Bass at Large Alabama Reservoirs

Abstract

We examined evidence for density‐dependent growth of Largemouth Bass Micropterus salmoides in the recruited life stage (age 2 and older) at eight large (>4,000 ha) Alabama reservoirs from standardized electrofishing survey data. Using mean length at age as a measure of cumulative growth and electrofishing catch rates as the basis for a cumulative index of density, we found weak support for the hypothesis that mean length at age was inversely related to Largemouth Bass density. The mean length at age of age‐5 Largemouth Bass was positively related to the cumulative density index, which is inconsistent with the prediction of an inverse association under compensatory density dependence. Moreover, the strength of the effect was weak, with a 9‐mm increase in mean length at age per 100% increase in the density index. No other age‐classes (ages 2 through 6 were examined) exhibited density‐dependent mean length at age. Similarly, relative weight was unrelated to the density index. Analyses of changes in mean length at age, relative weight, and the density index over time indicate that each of these variables have increased slightly since the mid‐1990s for some age‐classes. Our analysis of Largemouth Bass mean length at age at these reservoirs suggests that strong density‐dependent growth responses are unlikely in the recruited life stage at these large reservoir systems. If this is the case, implementing minimum length limits at these reservoirs is likely to avoid unintended negative consequences for Largemouth Bass growth and size structure.