Abundance and habitat use of juvenile sunfish among different macrophyte stands

Juvenile Lepomis sunfish (<75 mm total length, TL) density, plant stem density and invertebrate density were compared in the 3 most common habitats in the littoral zone of Cedar Lake, a Midwestern North American reservoir: nonvegetated areas, stands of the exotic macrophyte Eurasian watermilfoil (Myriophyllum spicatum) and stands of American pondweed (Potomogeton nodosus). Eurasian watermilfoil stands consistently had significantly higher stem density and invertebrate density than American pondweed stands. Juvenile sunfish densities were significantly higher in vegetated habitats than nonvegetated areas, but no significant differences were observed between the 2 vegetated habitats. Juvenile sunfish densities were initially higher in American pondweed stands than Eurasian watermilfoil stands, but fish density in American pondweed stands declined dramatically as water levels fell in autumn. Juvenile sunfish size structure was related to habitat type, with the smallest fish associated with Eurasian watermilfoil (38.2 mm TL), intermediate fish associated with American pondweed (43.1 mm TL), and the largest fish associated with nonvegetated habitats (51.2 mm TL). We suggest resource agencies should focus vegetation management efforts on eradicating Eurasian watermilfoil stands to provide foraging access for large mouth bass to improve their growth rate and reduce stunting of sunfish. However, management agencies must recognize that a healthy plant community below the depth of water level fluctuation may be the only source of cover for juvenile centrarchids during late summer in reservoirs prone to fluctuating water levels.