Eradication of smallmouth bass Micropterus dolomieu illegally released into Lake Motosu

We captured smallmouth bass Micropterus dolomieu from Lake Motosu by gillnets and spearfishing. From 1997 to 2004, 68 smallmouth bass were caught by gillnets and 18 by spearfishing. Catch per unit effort (CPUE) of smallmouth bass by gillnets gradually decreased from 0.36 in 1997 to 0 in 2002. The CPUE by gillnets and under-water observation rate were high in the southeast zone before 1998 and significantly higher in the northwest zone after 1999. The annual estimated capture rate of smallmouth bass by gillnets was consistently more than 50%. Smallmouth bass were illegally released into Lake Motosu for fishing; however, they were unable to establish in the water body. Smallmouth bass might have been eradicated since they did not reproduce, their extermination began quickly, habitat information was fed back to gillnet operation, and the capture rate using gillnets was high.