埼玉県新河岸川における外来魚コクチバスの侵入状況と食性

抄録

 There have been rising concerns for invasions of alien smallmouth bass (Micropterus dolomieu) in lotic systems and its ecological impacts on native aquatic biodiversity in Japan. We surveyed the invasion of smallmouth bass and their food habits in an urban stream, Shingashi River in Kawagoe-city, Saitama, Japan. We observed that mature adult smallmouth bass seasonally migrate to an urban stream between the end of spring and summer for spawning. In addition, we observed that the hatched fry grew up to juvenile stage in the stream from summer to autumn and then emigrate during autumn-winter seasons. The sampled fishes predominantly preyed on non-indigenous large crustaceans; however, they demonstrated ontogeny dietary shifts, foraging on freshwater shrimp at juvenile stage to crayfish at adult stage. Our findings suggest that the mature adult fishes might prefer sites with depth and slow current velocity for spawning. Capturing the mature adults in those sites during their reproductive season might be an effective strategy for population control and eradication of the invasive species from the stream.