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

Abstract

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