EXTRACTION OF TEMPORAL AND SPATIAL PROPERTIES ON HABITAT OF RIVER SNAIL BY MEANS OF STATISTICAL APPROACH

Abstract

National Monitoring of Biological Indices in Rivers has been conducted in Japan. The data of biology and other indices have been accumulated in qualitative form. In recent years, since river engineering works in consideration of the biological environment are required, utilization of the survey data is expected. In this study, river snail (Semisulcospira libertina) was focused as a biological index. Civil parameters such as river width, depth, and flow velocity, temperature, turbidity, and bed material are mainly used for analysis on rivers selected from all of Mie Prefecture. Area properties and temporal properties on snails were obtained by analyzing data set using both quantification theory and Borda count. Properties of habitat were investigated on Oomatagawa River in the south of Mie Pref. by using self-organizing map (SOM). The relationship between habitat of snail and civil parameters was investigated by the means of statistical methods. River width, bed material, and turbidity made a large contribution to the habitat of time series properties. These three parameters were also important for the habitat of local area properties. Because there is a less organic matter of river water as feed-in Higashi-Kisyu, periphyton on gravel surface could largely contribute to the habitat of snails. The possibility of habitat for river snail was showed on a SOM. It was possible to distinguish between easy habitat and a difficult one to live.