1Toyota Yahagi River Institute, Toyota, Aichi 471-0025, 2The United Graduate School of Agricultural Science, Ehime University, Kita, Kagawa 761-0795, 3Department of Life Science, Kagawa University, Kita, Kagawa 761-0795, 4School of Human Sciences, Sugiyama Jogakuen University, Nisshin, Aichi 470-0131, 5Yahagi River Natural Ayu Research Association, Toyota, Aichi 471-0025, Japan
The horizontal distribution of larval and juvenile ayu Plecoglossus altivelis altivelis, and its relation to the amounts of organic matter in sediments, were investigated in the sea around the Yahagi Estuary within 4 km from the rivermouth in their two reproductive seasons (1st: November 2002-February 2003, 2nd: November 2003-March 2004). Ayu were collected with aqua lamps within 1 km area from the coast, and also east of the rivermouth in both years except late February to early March when ayu annually start to ascend the river. Significant negative correlations were found between the distribution of ayu and the amounts of organic matter in the sediments; the larvae and juveniles being collected above the bottoms with less than 1% ignition losses and less than 6 mg g-1 total organic carbon content.