Application of otolith microchemistry to reconstruct for migration historyof amago salmon Oncorhynchus mason ishikawai, captured at the Ohta River

To reconstruct migratory history of amago salmon Oncorhynchus mason ishikaw ai, captured in the Ohta River, the otolith Sr/Ca concentration ratios as l ife history transect in accordance with the migration pattern between sea a nd freshwater were analyzed by wave-length dispersive X-ray electron microp robe. Based on otolith Sr/Ca concentration ratios, 26 out of 27 individuals were categorized as belonging to an anadromous population. Of these anadro mous individuals, two fish migrated between estuarine water and freshwater. Tracing the migratory history, a typical anadromous population migrated in to the estuary in mid-January, then into the coastal water in mid-February and, subsequently, returned to the river in mid-June.