Status and Issues in Ecological Engineering Techniques for Conserving Fish in the Paddy Field Areas of Japan

Abstract

Though land consolidation for paddy field areas has contributed to an increase in food supplies and an improvement in convenience, it has changed the physical structures and deteriorated paddy field ecosystems throughout Japan. Eco-friendly land consolidation in paddy field areas has been conducted based on the implication of ecosystem deterioration. Ecological engineering techniques, such as the placement of fish ladders between paddy fields and irrigation canals, were developed and applied to actual paddy fields to conserve fish. However, the techniques were not evaluated sufficiently. Therefore, I reviewed status and issues of ecological engineering techniques for conserving fish, which are often reported in Japan. This review showed the installation of fish ladders between paddy fields and drainage canals, as well as the construction of artificial ponds and wetlands, have contributed to providing fish with spawning and nursery areas in the paddy fields areas of Japan. On the other hand, the effects of ecological engineering techniques in canals, such as the construction of concrete block habitats, are not clear, although the techniques have already been applied to actual paddy field areas. Studies evaluating the effects of these techniques, which were applied for canals especially, should be conducted, and researchers and engineers should elucidate the most suitable structures, locations, scales and maintenance techniques for these constructions to best conserve fish in paddy field areas.