Abstract
Aquatic animals were monitored at two different artificially constructed streams near a dam lake (Higashi-Arakawa dam lake, Shioya-Cho, Tochigi prefecture) in central Japan. One (stream A) was an U-shaped, shallow stream in a park situated near the dam lake and was constructed in an openspace without any structural consideration as habitat for aquatic animals. The other (stream B) was also an U-shaped stream but large stones were placed inside for the purpose of providing space between stones as habitat for animals, and the stream inself was surrounded by trees and grassland.
In both streams, we set up two 4m-long experimental blocks and placed floating stones inside them. We monitored the number of each aquatic animal species by collecting them before and after the placement of floating stones. We also censused frogs in both streams.
The number of aquatic animal species and their numbers both increaced in the experimental blocks in the stream B but not in the stream A. Frogs, especially a stream-living species Buergeria buergeri, were found to breed in the stream B but again not in the stream A. The difference between the results from two streams seemed to be related to the difference in the surrounding environment and the original structure with or without considerations as habitat for animals.
We proposed some ideas on stream construction that would be suitable for animals to use as their habitat and yet not harmfull for the primary function of the stream in time of heavy rain.
