Migratory history of the Japanese eeI Anguilla japonica, as revealed by otolith microchemistry and stable isotope markers

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Environmental history of the Japanese eel Anguilla japonica collected from Omura Bay (54 Yellow eels, Kumamoto Pref.), Kuma River estuary (48 Yellow eels, Nagasaki Oref.), and East China Sea (7 Silver eels) were studied by examining strontium (Sr) and calcium (Ca) in their otoliths with wavelength dispersive X-ray spectrometry on an electron microprobe. The Sr/Ca ratios in the otoliths changes with both ontogenetic development and salinity of the habitat. The rarios significantly different between brackish and fresh water.The pattern change of the Sr/Ca ratios outside the freshwater mark indicated three types of migratory history : (A) river eels, (B) estuarines eels and (C) estuarine eeis with short period river life. According to the otolith Sr/Ca ratios, the occurrence of type A was 14% for Omura Bay, 15% for Kuma river estuary, and 14% for East China Sea and that of (B), 74% for Omura Bay, 62% for Kuma river estuary, 43% for East China Sea and that of (C), 12% for Omura Bay, 23% for Kuma river estuary, 43% for East China Sea. There was no difference in growth between each types.