Seasonal distribution of Ryukyu-ayu Plecoglossusaltivelis ryukyuensis in the Katoku River, Amami-oshima Island, southern Japan

Abstract

The longitudinal distribution of Ryukyu-ayu Plecoglossus altivelis ryukyuensis in the Katoku River, a small stream on Amami-oshima Island, southern Japan, was observed from December 2003 to November 2004. The number of Ryukyu-ayu in pools was greater than in glides or riffles in each life history season [spawning (Nov. to Feb.), up stream migration (Mar. to May) and growth (Jun. to Oct.) seasons], an analysis by Spearman’s correlation coefficient by rank test indicating that such abundance in pools tended to be consistently greater in lower reaches. This suggests that large pools in lower reaches are an important habitat for Ryukyu-ayu in the Katoku River. Accordingly, for the future conservation of the lower reaches and creation of large pools may be a positive step of this endangered fish.