RELATIONSHP BETWEEN FISH COMMUNITY STRUCTURE AND ENVIRONMENTAL FACTORS OF URBAN STREAMS IN THE TSURUMI RIVER SYSTEM

Abstract

 Urbanization causes river environmental degradation and reduction of biodiversity. The purpose of this study is to reveal the relationship between environmental factors and fish community structure of highly urbanized small and medium sized river. The 71 sites surveyed were classified into three groups based on similarity of fish fauna: tidal, non-tidal, and low species diversity. In the non-tidal area, domestic alien species were selected as indicator species, and in the low species diversity area, many non-native loach species (Misgurnus sp (clade B2)) were observed, which may have an impact on native fish species. On the other hand, the number of carnivorous non-native fish species was extremely low, and the degradation of the physical environment of the stream channel due to urbanization is considered to be the most significant factor in the decline in species diversity. The low species diversity was also associated with low velocity and depth diversity, indicating that the urbanization rate and the degree of concrete coverage of the streambed are the main causes of the environmental degradation.