通潤用水

We studied fish and aquatic insect faunas in Tsujun Yousui, an agricultural canal in Kumamoto Prefecture, which has been designated as an important cultural landscape by the Agency for Cultural Affairs of Japan. Between Decemnber 2007 and December 2008, we studied 18 sites within the canal and 2 sites within the neighboring rivers. We found 7 and 9 fish species in the canal and rivers, respectively. Tanakia limbata, which is listed as a threatened wildlife species in the Japanese Red List, was found only in the canal. In general, T. limbata appears on the plains; this is why it was very rare in this study area which had an altitude of over 400 meters. Among aquatic insects, several threatened species such as Lethocerus deyrollei, Agabus optatus Cybister brevis, and Appasus japonicus were found in the canal. Analysis with multiple regression models revealed positive correlations between the aquatic plant cover and the number of T. limbata individuals or insect species. Compared to the plant cover in the sites with concrete, the cover in the sites with concrete correlated with a lower number of T. limbata individuals and insect species. These results suggested that the revetments should be maintained without concrete for sustaining the biodiversity in this canal.