Influence of Winter Drought by Slope Failure on Mortality of Unionid Mussels in a Valley Ditch

Abstract

A ditch was dammed by a slope failure of a shoulder in the Kitsuregawa Hills located in eastern Tochigi Prefecture resulting in flooding of a paddy plot and the drought of the former ditch. In order to investigate the consequences on Inversiunio jokohamensis habitation, capture and environmental conditions were examined on 19 February, 2012. Furthermore a hearing investigation was also performed on 18 February and 9 December, 2012. The following information was acquired from these results. 1) Death rate for 10 days drying-up was estimated at 0.29. 2) A significant positive correlation was observed between survival rate and average substratum depth, with the highest survival rate for the deepest substratum depth. 3) The death rate in surface substratum was highest and the dead individuals were probably due to being frozen. This study suggested that mussel habitat and ditch ecosystem may degrade in ditches without maintenance in the future.