Using Telemetry and a Fish Behavioral Model to Assess Fish Habitat Changes Caused by Alteration of River Morphology

In this study, we aimed to evaluate and compare the influence of the physical environmental characteristics of the Chikuma River on the biological community between 1893 and the present. The study was conducted on a floodplain in the middle reaches of the Chikuma River in Nagano Prefecture, central Japan. We reconstructed the past morphology of the Chikuma River from topographic survey results and hypsographic maps of the region around the river from 1893. Velocity distributions in 1893 were estimated from these recorded hydrologic parameters. Then, the behavioral patterns of virtual fish were simulated by the IBM on the basis of the reconstructed past velocity distribution. The flooded area differed between past and present regardless of the actual river discharge. In 1893, water overflowed the banks of the main channel during floods, creating a large flooded area. The simulated fish behaviors in 1893 differed from the fish behaviors recorded in 2003. The results for 1893 indicated that the fish occupied a large area where they can cruise. The fish sought refuge in low current velocity areas next to the river bank during floods. Once the fish found a low current velocity area, they did not move to another area until after the flood subsided. These results indicate that floodplain had important ecological function which supply refuges are for fish community and conservation and restoration flood plain in effective for river restoration.