Stream drift feeding and microhabitat competition of invasive smallmouth bass Micropterus dolomieu, native Japanese dace Tribolodon hakonensis and pale chub Opsariichthys platypus in the Nogu River, Japan

Foraging behavior and microhabitat use of native Japanese dace, pale chub, and invasive smallmouth bass were studied in the Nogu River, Nagano, Japan. Chub, dace and smallmouth bass all used drift feeding as their dominant foraging behavior. Chub drift fed most frequently, followed by dace, and smallmouth bass drift fed significantly less frequently than both native species. Chub and dace utilized microhabitat that had significantly higher flow velocity than smallmouth bass. However, smaller chub and dace were found in areas with lower flow velocity compared to larger individuals. Prey resource competition between smallmouth bass and native cyprinids, especially smaller individuals, is suspected due to similar feeding methods and microhabitat use.