Field research of environmental properties of drainage canal and fish distribution in yatsu paddy field, Chiba prefecture [Japan]
2005
Koizumi, N.(National Inst. for Rural Engineering, Tsukuba, Ibaraki (Japan)) | Takemura, T. | Okushima, S. | Yamamoto, S. | Aiga, H.
Since the 1960's, numerous land consolidation projects have been performed in rural areas in Japan, and many functions for fish habitat have been degraded in the drainage canals. To clarify environment factors required for restoration of fish habitat, we investigated that relationship between morphological and physical environmental factors and fish distribution in 29 drainage canals in Yatsu paddy field of the Shitada-gawa River basin. Chiba Prefecture Field data were sampled from July 2002 to June 2004 at monthly intervals and analyzed statistically, yielding the following results. First, one to ten fish species including threatened species in the Red List and Red Data Book of Japan and Chiba Prefecture occurred in the aggregate of 13 main drainage canals during the investigation. Loach Misgurnus anguillcaudatus was found in all drainage canals, and appeared to be the dominant species in this basin. Species richness in the drainage canals appeared to be limited by structural barriers which were 20 cm above the height of drops at the drainage canal junctions with the main stream. Second, comparison of population density of loach in the improved and non-improved drainage canals indicated that drainage canal improvement with land consolidation and inflow of domestic waste water to the drainage canals degraded habitat for loach. Loach population in the improved drainage canals with both walls made of concrete decreased largely during non- and the beginning irrigation periods. To restore the population in the drainage canal, it is important that a substrate armored with gravel be improved to a substrate that can support vegetation.
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