Article ID: 24-00017
Smallmouth bass (Micropterus dolomieu) is an invasive fish native to North America, and in recent year its distribution in Japan has been expanding rapidly, causing concern about its negative impact on the ecosystems of rivers where it has introduced its species. Therefore, management of the invasive species has been carried out in several rivers but there have been no successful eradication attempts. Since smallmouth bass tends to inhabit large rivers, it is necessary to determine the extent of their distribution and the reaches where population densities are high to promote more efficient management. In this study, environmental DNA (eDNA) was used to determine the distribution of smallmouth bass in the Kushida River, Mie Prefecture and the condition of their invasion into the tributaries. The eDNA surveys were conducted a total of four times in the summer (August 30-31, 2021 and September 12-13, 2022) and winter (January 27-28, 2021 and February 8-9, 2022). The eDNA of smallmouth bass was detected in the Kushida River mainstream, approximately 1 - 40 km from the mouth and eDNA detection site at the most upstream was consistent across all surveys. Spatial distribution seems to be limited by artificial barriers located upstream of the uppermost detection sites. The eDNA was detected in a relatively large tributary river, suggesting a potential risk of colonization in tributaries. Even in the small tributaries, the eDNA was detected in summer, indicating that they were invading, albeit temporarily. These findings suggested that when smallmouth bass invade a river, they disperse and colonize a broad area, including tributaries. Widespread management is costly and difficult to eradicate. Therefore, it is most important in the management of invasive alien species in rivers to not introduce in the water system and to exterminate them when their populations are low.
