Black Bass and Bluegill as Invasive Alien Fish in Japan - Administrative Response and Technical Developments for Their Effective Control

In Japan, two North American centrarchid fishes, largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus established a nationwide distribution through the 1970s and 1980s in parallel with the growing popularity of "bass fishing". Their negative impacts were first experienced in Lake Biwa, Japan's largest (ca. 670 km² in surface area) and oldest (ca. 1 million years) lake, in the latter half of the 1980s, followed by many other tragedic cases all over Japan. After their introductions, more than a few indigenous species (fish and aquatic insects, etc.) became critically endangered, and some fisheries resources greatly declined. In response to this threat, intentional introductions of black bass (not only largemouth but also smallmouth bass M. dolomieu, which suddenly spread in the 1990s) and bluegill were prohibited in the fisheries regulations of all the prefectures of Japan by the end of the 1990s. In addition, the release of fish captured in recreational fishing was also forbidden in other regulations of some local governments, e.g., the Shiga Prefecture Ordinance for Regulation of Leisure Activities in Lake Biwa in 2003. After serious conflicts between interest groups concerning with nature conservation and recreational fishing, largemouth and smallmouth bass and bluegill as well as channel catfish Ictalurus punctatus and mosquito fish Gambusia affinis were finally designated as “Invasive Alien Species” by the “Invasive Alien Species Act” enacted in 2005. Not only intentional introductions but also importing, keeping, and transporting of live individuals of Invasive Alien Species are all prohibited in Japan by this act. The Ministry of the Environment started several model projects for effective control of black bass and bluegill in some water bodies selected for conservation reasons. The Fisheries Agency of the Ministry of Agriculture, Forestry, and Fisheries has also carried out a series of projects to suppress their populations, and this has resulted in a variety of technical developments. Here, I will briefly introduce the historical aspects of the nationwide establishment of black bass and bluegill populations, their ecological impacts on the indigenous biodiversity and fisheries, and social conflicts over their regulations. I will also describe the administrative response and technical developments for the effective control of these invasive alien fish in Japan.