Change of fish fauna in ponds after eradication of invasive piscivorous largemouth bass, Micropterus salmoides, in north-eastern Japan.
The change in fish fauna was monitored in ponds within irrigation systems in Iwate prefecture, north-eastern Japan to evaluate the effectiveness of eradicating the invasive piscivorous largemouth bass, Micropterus salmoides. Eleven study ponds were categorized into three pond groups: bass-dwelling (n=3), bass-eradicated (n=3) and non-invaded ponds (n=5). Species richness and diversity, which temporally decreased in bass-dwelling ponds, increased in basseradicated ponds. Furthermore, in bass-eradicated ponds, the mean numbers of topmouth minnow and freshwater goby were gradually restored, but in bass-dwelling ponds the numbers decreased and both species eventually disappeared. Although the eradication of piscivorous invaders is helpful for restoring fish species diversity in ponds, its effectiveness varies among species, and other alien fish such as the rose bitterling (Rhodeus ocellatus ocellatus) often invade and proliferate in the bass-eradicated ponds. To ensure successful restoration of native biota and avoid undesirable results, it is necessary to plan and implement continuous monitoring and adaptive management after eradication of alien predators.