Faculty of Bioresources, Mie University, Tsu, Mie 514-8507, Japan
Based on long-term observation data (from April 1993 to December 2002) on megabenthos in Ise Bay, central Japan, seasonal and interannual variations in abundance, biomass and spatio-temporal distributions were examined for the dragonet Repomucenus valenciennei dominating in the bay. Then, to examine when and where their recruits are located within the bay, recruits were collected using small-size trawl nets from May 2000 to December 2002. The abundance and biomass of the dragonet decreased in summer when oxygen-poor water developed in the bay, and increased from autumn to next spring when the oxygen-poor water disappeared. Recruits were mainly located in the innermost part of the bay in spring to winter, particularly in winter. According to the cohort separation based on body length histograms, the decrease of the dragonet abundance in summer was induced by avoiding the oxygen-poor water or by high mortality due to the oxygen-poor water. On the other hand, the increase of the dragonet abundance from autumn to next spring was due to recruitment.