Distribution and habitat of the Ajime-loach, Niwaella delicata, in the Ai River, Osaka Prefecture

Abstract

Relationships between the distribution and habitat variables of the endangered Ajime-loach, Niwaella delicata, were investigated in the Ai River, part of the Yodo River system, Kinki District, Japan. The fish were distributed in reaches totalling 1.9km of the 13km surveyed, between 110m and 160m above sea level. Comparison and principal component analysis of sections where the Ajime-loach was present or absent demonstrated that major variables influencing distribution are low summer water temperatures, variable channel units, an abundance of loose stones and abundant groundwater discharge, all being necessary for future conservation of the species. And the consequences of the study suggest the importance of riparian forest, streambed disturbance by flooding and control of fine sediment input from the watershed to the habitat of the Ajime-loach.