Upstream dataset, only 13 populations upstream of the Kanayama dam; 15-km dataset, only between population pairs with a waterway distance of <15 km. The confidence interval (95% CI) in the entire dataset and upstream dataset was obtained by bootstrapping testing in Mantel tests, while the 95% CI for the 15-km dataset, which is not matrix style, was obtained by simple bootstrapping. In the comparison of the same region, the results calculated using eDNA datasets obtained after the three types of treatment are also displayed: Treatment 1, removal of low read frequencies; Treatment 2, bold removal of low read frequencies; Treatment 3, conversion to semi-quantitative rankings. See Table S4 for the full combinations.