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A large bank-protection works project undertaken during winter (from late October 2001, to late March 2002) in the middle reaches of the River Shinano, Japan's longest river, drastically altered the riverbed structure. To assess the effect of the project on the river's crane flies, we collected larvae and pupae with a Surber sampler in the construction area and in a control area from April to June, 2002. We also collected crane fly adults with light traps around the construction area from April to July of 2000, 2001 and 2002, as background information for the effects portion of this study. As a result, we described a total of 31 newly recorded crane fly species in the middle reaches of the River Shinano. In all three years of study, the sex ratio for all taxa combined was 74.8 to 75.5 percent males. Antocha was the dominant taxon, Antocha (Antocha) bifida was the dominant species, and its abundance did not differ significantly among years. The age structure of the Antocha bifida larval population changed in the construction area following construction, but not in the control area. Our data suggest that the bank-protection project significantly affected the Antocha bifida larval population in the study area.
Acknowledgements
We wish to thank, Dr. T. Okino, Waseda University, for his valuable advice on the fieldwork and Dr. T. Torii, Keio High School, for his valuable advice on the taxonomy of Antocha (Antocha) bifida. We would also like to thank Dr. N. Nakamoto and Mr. M. Takeda, and colleagues at the Department of Applied Biology, Shinshu University, for their generous support and assistance during the research program. Three anonymous referees read an earlier version of this paper and made many valuable comments that resulted in its improvement. Part of the present study was supported by the River Ecology Research Group of Japan (Chikuma River Group), the River Environment Fund in charge of the Foundation of River Watershed Environment Management, Japan and Grant-in-Aid for 21st Century COE Program by the Ministry of education, Culture, Sports, Science, and Technology.