Effects of Vegetation Density on the Ontogeny to Piscivory of Juvenile Largemouth Bass

Abstract

AbstractFirst‐year overwinter survival is a frequent bottleneck to the recruitment of Largemouth Bass Micropterus salmoides. Early ontogeny to piscivory provides increased overwinter survival through increased growth and the accumulation of lipids. This ontogeny is thought to be slowed by dense and complex vegetative habitats, but this hypothesis has not been directly tested. To address this question, we conducted enclosure experiments for 5 weeks during the typical time that juvenile Largemouth Bass would transition to piscivory (i.e., midsummer). Thirty‐two enclosures were constructed across two 0.10‐ha ponds and given one of four stem densities of simulated vegetation (0, 50, 250, and 500 stems/m2). Three juvenile Largemouth Bass and 30 juvenile Bluegills Lepomis macrochirus were added to each enclosure. All fish were sampled twice per week. Largemouth Bass growth was measured on all sample dates, and stomach samples were collected to determine diets on one date each week. Bluegill sizes and densities were manipulated to maintain the number of fish at 30 fish that were 25–35% of Largemouth Bass TL after each sampling event. Largemouth Bass stomach contents (percent by weight) were initially dominated by insects, and the bass transitioned to mostly fish prey by the end of the experiment. The use of fish prey, as measured by the presence of surviving Bluegills in the enclosures, significantly increased at the beginning of the second week at all stem densities, but fewer fish prey were eaten by bass in the 250‐stems/m2 treatment than in all other treatments throughout the experiment. Largemouth Bass also grew less in the 250‐stems/m2 treatment. We concluded that vegetation density does affect the foraging rate of piscivorous juvenile Largemouth Bass, but not necessarily the timing of the ontogeny to piscivory. However, differing results between this experiment and other previously published studies suggests vegetation may have an interactive effect with available prey types.