Abstract
Conventional paddy farmland consolidation in Japan has been said to have negative impacts on biodiversity in rural areas. Especially, transforming earthen irrigation and drainage canals into concrete canals has caused catastrophic damage to aquatic animals. The canal structure and flowing water for the non-irrigation season in the farm drain of a paddy field is very significant for aquatic animals utilizing a paddy field as a spawning ground. The purpose of this study was to clarify the influence of canal structure, that is, the canal bed and side materials, on aquatic animals based on a field survey of the distribution of fishes and aquatic insects at two sites in the same farm drain of a paddy field in Shimodate City, Ibaraki Prefecture, Japan. The sampling interval was one month during the period from April 2002 to March 2003. The results indicated the followings: (1) Overall, the biomass of aquatic animals at an earth canal in the farm drain was larger than that at a concrete canal. (2) Misgurnus anguillicaudatus (Dojou) was the most frequently captured fishes. Orthetrum albistyrum speciosum (Shiokaratombo) was the most continually captured aquatic insects. (3) Misgurnus anguillicaudatus appeared to be affected by the canal bed material composed of mud but relatively unaffected by the side material. (4) Orthetrum albistyrum speciosum appeared to be affected by the particle size composition of the canal bed material and preferred argilliferous soil to sandy soil. (5) To enrich the biodiversity in the farm drain of a paddy field for the future, our results suggested that maintaining an earth canal is highly priority.
