矢作川水系におけるカワゲラ類の分布に与える人為的影響

Abstract

Stonefly nymphs (Insecta, Plecoptera) were collected at 78 sites in the Yahagi River system, central Honshu, Japan in 2015-2016. In addition to the data from literature on the nymphs, at least 45 taxa of Plecoptera were identified, and 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, not only in the zone under the altitude ca. 1000 m, but also in the zone over ca. 1000 m. For instance, Scopura montana (Scopuridae) and Isoperla towadensis (Perlodidae) nymphs were abundant at small-scale mountain streams (catchment basin : smaller than 0.1 km2) and at the altitudes higher than ca. 1000 m. This indicates that the suitable habitat of each taxon (species) about area of catchment basin and about the altitude is similar to that observed in the Tama River system, central Honshu, also in the streams at the altitudes over ca. 1000 m. Oyamia lugubris (Perlidae) nymphs were not collected at all between the four dams along the Tomoe River, the largest tributary of the Yahagi River. These sites are included in the suitable habitat for Oyamia lugubris about the area of catchment basin and about the altitude, but O. lugubris did not occur. It is not clear whether artificial impacts affect the occurrence, or not. Xanthoneuria (Perlidae) nymphs were collected continuously above the Yahagi Dam, but they were not collected at all below the dam, where six other dams are located. Isoperla nymphs were also abundant above the Yahagi Dam, and they were collected below the dam too, but they were rare in the drought stretches below the diversions. Xanthoneuria and Isoperla nymphs may be affected by artificial alteration of river environment by the dams.