Trace elements in the otoliths of the Japanese Spanish mackerel (Scomberomorus niphonius) in the southern Yellow Sea

Japanese Spanish mackerel (Scomberomorus niphonius) during spawning seasons were collected from Lüsi spawning ground in the southern Yellow Sea, then transverse sections of otoliths were analyzed from its core to the margin by using laser ablation ICPMS. Element∶calcium ratios were integrated with microstructural analysis to produce profiles of different life stages for measured elements. The results revealed that the detected Li, Na, Mg, Fe, Co, Sr and Ba were all heterogeneously distributed on the otolith. However, Ba∶Ca ratio fluctuated sharply with a range of 2.13–5.05 μmol/mol. The Ba concentration was normally high in the otolith cores (0–40 μm), declining rapidly in 40–320 μm areas and being low in the remaining areas (320–1 440 μm). Therefore, Ba∶Ca ratio showed significant difference between life stages: it was significantly higher in hatching stage than in wintering and spawning stages. It indicated that variation in Ba∶Ca ratio was most informative and S. niphonius seemed to prefer high Ba concentrations habitats at the stages of embryonic development and hatching before they soon swam away from this habitat at the stage of post-hatching development. Low Ba concentrations habitats seemed to be preferable for the stage of wintering and spawning. These results provided further evidence for the common migration trajectory.