Determination of trace elements in otoliths of chum salmon Oncorhynchus keta by laser ablation-ICP-mass spectrometry

Trace element levels in the otoliths of chum salmon Oncorhynchus keta were examined by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). A close linear relationship in the Sr/Ca ratios between X-ray analysis with an electron microprobe (EPMA) and LA-ICPMS analysis was found, suggesting that the latter technique could be used to distinguish the marine and freshwater life phases. Mg, Zn, Ba and Sr concentrations of the otoliths differed between the freshwater and seawater growth zones. Mg and Zn concentrations in the freshwater growth zone were significantly higher than those in the seawater growth zone, while Sr and Ba concentrations in the former were significantly lower than in the latter. The relationship between Sr concentration and Mg, Zn, and Ba concentrations at each ablation showed significant correlations. These results suggest that trace element compositions may reflect differences between freshwater and seawater environmental conditions.