Relationship between River Landscape and Fish Habitat in Yamaguchi Prefecture

摘要

Rivers are an important habitat for aquatic organisms, and different river landscapes affect the distribution of these organisms. Oishi (2014) found that a river landscape can be categorized into four types (Ⅰ: sandbar, Ⅱ: step-pool, Ⅲ: bedrock, and Ⅳ: flat riverbed) using two parameters: the Froude number and the width/depth ratio. He further predicted that types I and II would be good fish habitats, whereas types III and IV would require some additional measures to be taken to become good habitats. In this study, we examine Oishi's prediction based on field observations in 30 sections of 8 rivers by counting the number of fish species caught by electro-fishing in each section and by calculating the Froude number and width/depth ratio based on information obtained from field surveys. A fish habitat is classified as good when the width depth ratio is higher than 6. In addition, we visually estimated the landscape type of the sections. Visual estimations showed higher relationship with the number of fish species than Width/Depth ratio. Landscape evaluations based on visual observations might also be meaningful for habitat evaluation.