Effect of Dams on Fish Assemblages of the Tachia River, Taiwan

Abstract

A total of 37 species was caught in the Tachia River from the Kukuan Dam to the river mouth between 1989 and 1992. Species richness increased from seven species upstream to 32 species downstream in the river. Shannon-Wiener’s species diversity also increased from 1.24 in the upstream to 2.52 in the downstream section. The fish fauna of the Tachia River could be divided into three fish zones acccording to the fish fauna study of Tsao (1994), this study, and the positions of dams in the river. Varicorhinus barbatulus and Crossostoma lacustre were the dominant species in the upper segment between the Kukuan and Tienluen Dams. Zacco spp., Acrossochelius paradoxus, and Hemimyzon formosanum were the most abundant species in midstream between the Tienluen and Shikuan Dams. Zacco spp. Tilapia sp., and Mugil cephalus were the dominant species in the downstream segment below Shikuan Dam. Both fish richness and diversity indices were higher in the down-stream than upstream sections. Among six widely distrubuted speices, Zacco spp. were not found upstream of Tienluen Dam, although it was dominant below Tienluen Dam. Except for the section below Shikuan Dam, the fish species richness and relative abundance showed no seasonal change. In the section below Shikuan Dam, more species and individ-uals were sampled in summer and autumn than in spring or winter. In flooding periods (e.g., summer and autumn), some species which predominated in upstream sections, including V. barbatulus, Leiocassis adiposalis, H. formosanum, and C. lacustre, could be col-lected frequently below Shikuan Dam. Species occurring near the river mouth could move further upstream during the flooding period. Native Anguilla japonicus and Sicyopterus japonica were caught near Shikuan Dam during the flooding period. The dams play a role in regulating downstream flow which may disrupt the river gradient and block upstream fish migration, and thus subsequently affect zonation of fish fauna in this river system.