Effects of Stem Density of Artificial Vegetation on Abundance and Growth of Age‐0 Bluegills and Predation by Largemouth Bass

We evaluated the effects of stem density on the attraction of bluegills Lepomis macrochirus and largemouth bass Micropterus salmoides to mats of artificial vegetation in a 5‐ha impoundment in southwestern Ohio. We also used field enclosures to examine the effects of artificial vegetation density on growth of age‐0 bluegills and on predation risk of age‐0 bluegills (< 50 mm total length, TL) from largemouth bass. The densities used were 0 (zero), 400 (low), 961 (medium), and 3,844 (high) stems/m2. Underwater surveys of mats indicated significant differences in numbers of age‐0 bluegills among vegetation densities; high‐density mats always attracted significantly more age‐0 bluegills than other densities. Numbers of larger bluegills (>50 mm TL) were similar among vegetation densities, whereas largemouth bass were more abundant near high‐density mats. Lengths of age‐0 bluegills did not differ significantly among stem densities, suggesting that selection of cover density did not depend on fish size. In addition, growth of age‐0 bluegills over 117 d in enclosures did not differ significantly with respect to stem density. In field enclosures, high‐density mats significantly reduced predation risk for age‐0 bluegills relative to low‐ and zero‐density mats; predation risk did not differ significantly between high‐ and medium‐density mats. Laboratory experiments indicated no differences in predation rate between zero‐ and low‐density treatments, but predation rates were significantly lower in medium and high stem densities than in low and zero densities, and high‐density mats offered significantly greater protection than medium‐density mats. This study, together with information from other studies, provides evidence that age‐0 bluegills need not sacrifice growth for safety when they select high vegetation density under natural conditions.