Abstract
Trapping by snap-traps (8.5cm wide, 14cm long) with raw fish meats was carried out at 191 sites along 63 river systems ranging from Honshu, Kyushu, Shikoku, to Oki, Japan. One hundred and thirty-nine specimens of the Japanese water shrew, Chimarrogale platycephala, were obtained from 86 sites in 177 sites in Honshu and Kyushu. No specimens were found in Shikoku and Oki Islands. The relationships between the number of traps set at each trapline and the number of water shrewes caught revealed that the water shrew was a territorial creature. The lower limits in the altitudinal distribution of habitat were lower in northern districts compared with southern habitats. The upper limits appeared to be depending on the altitude of the uppermost stream of each river. Field observations suggested that the water shrew had plural activity cycles in a day. Preferable habitats for the water shrew were swift streams or rivers with abundant shelters on the river bed; the shelters usually consist of boulders, large rocks or fallen logs with underside cavities or slits and/or of water-eroded cavities made along river bank. There were many instances in which no water shrews were trapped, although the habitats retained a full composition of the above elements. In many of these cases, engineering works such as construction of roads, dams, pastures, ski grounds, etc. were observed on the upper streams or on the catchment of the river. These construction works produced muddy water flow which affected the aquatic insects that the water shrew fed on. These observations suggested that the water shrew was very sensitive to the artificial change in the river environments.
