2022 Volume 16 Pages 79-95
In June 2019, the establishment of smallmouth bass was confirmed in Kotogawa Dam Reservoir in Yamanashi Prefecture, Japan. The elevation of the reservoir is 1,453.5 m, which is the highest elevation of a water body where smallmouth bass have been established in Japan. In 2020, we evaluated the status of the population of smallmouth bass and captured the bass using gillnet, spear gun, and angling. A total of 640 smallmouth bass were caught, and the highest catch per unit of effort of fish caught was by gill netting. The growth rate of the bass was slow, and the females spawn over 20 cm in total length. Based on the results of the capture, it is considered effective to use gill nets to target mature bass over 20 cm in total length from mid-May, when the surface water temperature exceeds 12°C, to mid-July, and to target immature bass after mid-July to reduce spawning by bass in the following year. Additionally, spawning beds of the bass were very difficult to find by divers in the reservoir, because most of the bottom of the shore of the dam was covered by gravel formed by water level fluctuation. Therefore, it is important to develop other effective methods of finding spawning beds and removing larvae.
