自然河川におけるカワニナの流下と遡上

概要

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Drift and upstream movement of the freshwater snail Semisulcospira libertina were investigated at the Iwai River, Nara, Japan, from May 1999 to February 2000, in natural conditions. Water temperature, snail size and discharge were measured. Drift and upstream-movement were observed mainly from May to October, when water temperature was higher than 13.2℃. Most drifted snails were smaller than 6mm in shell width, whereas snails that moved upstream belonged to all size classes. The number of drifted snails per hour after rainfall (60≦discharge<130l/s) was smaller than during normal discharge (<60l/s), whereas the number of snails moving upstream per hour did not change between the normal discharge days and days after rainfall. From these results, it is concluded that small S. libertina disperse downstream by drift on days with normal discharge, and snails of all sizes move upstream irrespective of discharge rate.
2004-06-30