Evaluation from otolith Sr stable isotope ratios of possible juvenile growth areas of Japanese eels collected from the West Mariana Ridge spawning area

The widely distributed East Asian Japanese eel Anguilla japonica constitutes a single genetically homogeneous population with a single spawning area near the West Mariana Ridge. Otolith ⁸⁷ Sr/ ⁸⁶ Sr ratios of adults (categorized as “river“, “estuarine” or “sea” eels, according to their habitat use history determined from otolith Sr:Ca ratio analysis) collected from the spawning area in 2008 and 2009 were examined in an attempt to determine their juvenile growth areas. In addition, ⁸⁷ Sr/ ⁸⁶ Sr ratios of water samples from rivers in China, Taiwan, Korea, and Japan were determined. Otolith ⁸⁷ Sr/ ⁸⁶ Sr ratios of the “river”, “estuarine” and “sea” eels were 0.707793, 0.708580-0.709944 and 0.709068, respectively, and water sample ratios from China, Korea, Taiwan, and Japan were 0.7104320-0.7141010, 0.7190826-0.7227976, 0.7115523-0.7146914 and 0.706191-0.712484, respectively. “River” and “estuarine” eels, which had otolith ⁸⁷ Sr/ ⁸⁶ Sr ratios less than 0.7092 (seawater ratio), appeared to have inhabited Japanese rivers and/or estuaries because similarly low isotope ratios were recorded only from Japan. However, the juvenile growth areas of other eels were unknown, as their origins could not be determined from otolith ⁸⁷ Sr/ ⁸⁶ Sr ratios alone, and required further information regarding otolith elemental and isotope compositions.