Construction of a firefly stream by using a physical habitat evaluation method

Abstract

Firefly (Luciola cruciata) is a popular and historically important insect in Yamaguchi prefecture. In the midstream of Fushino river, we could see a lot of fireflies four or five decades ago but now we cannot see not only the fireflies but also marsh snails (Semisulcospira libertina), the only feed for the firefly. Although the local government is planning to restore the firefly habitat in Fushino River, there are a lot of difficulties to accomplish the plan because they need to consider various firefly habitat requirements which spread from stream, ground and even to the sky together with snail habitat requirements which have not known well enough. To boost the efficiency of the restoration work, we build habitat suitability criteria (HSC) of surrounding environments (distance to paddy field, woods, slopes and city zones) and instream environments (velocity, depth and channel index) for the firefly and the snail. A physical habitat model with the HSC reveals that the midstream of Fushino River is not a good habitat for the firefly in current situation. Based on this information, an artificial stream for firefly is designed along the river and the instream habitat condition of the stream is evaluated using PHABSIM (Physical Habitat Simulation) software. Based on the calculated result, minor stream improvement works and effective flow management procedure are proposed. Post construction monitoring shows the firefly larva landing points show good accordance with the good habitat zones predicted by PHABSIM.