Spatial variation in otolith elemental composition of the Pacific herring Clupea pallasii in northern Japan

In order to examine whether otolith elemental composition of Pacific herring Clupea pallasii reflected spatially specific differences in capture location, we analyzed the elemental compositions in the edge portion of each otolith, which corresponded to the period immediately prior to the capture, as an indicator of the geographic areas in which the outer otolith was deposited. We collected 7 fish groups from 5 coastal sites: Tomamae offshore, Ishikari Bay, Akkeshi Bay, Lake Furen and Miyako Bay along the Japanese coast. Six elemental ratios, Na/Ca, Mg/Ca, K/Ca, Cu/Ca, Sr/Ca and Ba/Ca, were measured in the edge areas of each otolith by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Significant differences were shown in all mean elemental ratios of otoliths among 4 sampling groups in the 2005 year class and among 3 sampling groups in the 2006 year class. The classification accuracy with the jackknife cross-validation using quadratic discriminant function analysis ranged from 80 to 98% and 78 to 100% in the 2005 and 2006 year classes, respectively. Our findings are comparable to those in previous studies and are further evidence that otolith chemistry is a potential tool for identifying the Pacific herring groups with different habitat-use histories and migration patterns.