"Distribution of Plecoptera (Insecta) in the Yahagi River system, central Honshu, Japan, with special reference to the river environments"

"Stonefly nymphs (Insecta, Plecoptera) were collected in 2000-2014 at 61 sites in the Yahagi River system, central Honshu, Japan. At least 45 taxa of Plecoptera were identified. Out of these 24 were identified to the species level. Each taxon (species) of Plecoptera tended to occur in a characteristic scale of river basins (area of catchment basin) and in a characteristic zone of altitude. This occurrence pattern of each taxon (species) in the Yahagi River is similar to that observed in the Tama River system, central Honshu, Japan. Along the mainstream of the Yahagi River, downstream continuous occurrences of Oyamia, Xanthoneuria (Perlidae) and Isoperla (Perlodidae) were partly interrupted by the lacks of occurrences below the Yahagi Dam, the largest dam in the river system. This result suggests that the dam could affect these genera. A few nymphs of Perlodes frisonanus (Perlodidae), a near-threatened species in the Japanese Red List, were collected in 2000-2004 at two sites in the lower mainstream, but they were never found thereafter. Distribution of this species and Tadamus sp. before human impact are presumed to have been wider than in the present, based on the comparison with the other habitat of the two species in the Takatoki River, Shiga Prefecture, Honshu, Japan.