ゼニタナゴAcheilognathus typus再導入個体群の急激な減少：愛好家等の採集圧による可能性

抄録

Although overfishing has been recognized as a major factor threatening the existence of rare freshwater fishes, no case studies exist on the impact of collection pressure by fish enthusiasts and traders. In 2021, a habitat of reintroduced Acheilognathus typus, a species rarely seen the previous year, was visited every day by such enthusiasts. A monitoring survey indicated subsequently that the mean number of captured A. typus had decreased from 25.0 individuals/day in July 2021 to 1.6 individuals/day in October, the October 2021 figure being about one-tenth of that for September-October 2020. In addition, the standard length of A. typus in 2021 (56.8–59.5 mm) was greater than in 2020 (47.2 mm), possibly due to a thinning effect caused by the reduced fish numbers. During the period surveyed, some 50 to 100 fish enthusiasts and traders visited the habitat, apparently collecting thousands of A. typus by fishing or in bait traps. Such collecting pressure has clearly driven the reintroduced population of these rare fish to significantly low levels within a short period.