Downstream dispersal of largemouth bass and bluegill from an irrigation pond

Abstract

Spread of the largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) has serious impacts on freshwater ecosystems in Japan. Irrigation ponds are known to serve as major habitats for largemouth bass and bluegill, which these alien fish are expected to disperse downstream via irrigation and drainage ditches. In this study, emigration of largemouth bass and bluegill from an irrigation pond was investigated during the irrigation period (from April to July in 2008) using traps set in irrigation and drainage ditches. In total, 12 and 37 individuals (body length > 3 cm) of largemouth bass and bluegill, respectively, were caught by the traps when water was discharged into the ditches. These fish that emigrated from the pond contributed 4. 0% (largemouth bass) and 7. 1% (bluegill) of the total number of each species (body length > 3 cm) that were captured in the pond by pond draining. These results indicate that dispersal of largemouth bass and bluegill from the irrigation pond is not uncommon. Eradication of such exotic fishes from irrigation ponds is important for conservation of aquatic communities around the ponds.