| The aim of this study is to estimate the effect of conservation plan of the rare freshwater sculpin, Cottus pollux (middle-egg type) in the Honmyo River dam project by population viability analysis (PVA). The Honmyo River is approximately 21 kilometers in length of the main stream with a steep gradient from Gokaharadake (1,057 m altitude) to the Ariake Sea. The catchments area is 87 square kilometers (km2). The annual mean flow-rate is 0.4 cubic meters per second (m3/s), the daily maximum flow-rate is 24 m3/s, and the daily minimum flow-rate is 0.1 m3/s. The habitat condition of Cottus pollux in the Honmyo river system has been surveyed under the environmental impact mitigation project of the Honmyo River dam since the year of 2000, and transportation of the fish from areas that will be inundated by dam construction to two habitat patches in the upstream area and another habitat patch in the watershed were conducted from 2001 to 2004. The fish population monitoring survey from 2002 to 2005 showed that the fish were reproducible at the transported habitat patches. However, two points need to be clarified for the successful conservation of the fish. The first is whether sustainable life cycles can be established at transported habitat patches. The second is a quantitative evaluation of conservation strategies in terms of viability of the fish population. For both purposes, we developed a simulation model of population viability of the fish. The model was calibrated using data from 2004 to 2005, and was used to compare five scenarios (A-E) that assume the existence of the dam and various combinations of mitigation strategies. We have shown that scenario E, in which Cottus pollux ME is transported to three patches, is the best among four mitigation scenarios. |
