Study on Trace Element Characteristics in Otoliths of Pacific Saury (Cololabis saira) in Northwest Pacific Ocean

The Pacific saury (Cololabis saira), widely distributed in the North Pacific Ocean, is a significant pelagic fishery species in China and has been designated as a priority management species by the North Pacific Fisheries Commission (NPFC). This study examined the trace element characteristics of Pacific saury otoliths and the migration patterns of this species. Based on samples collected from the high seas of the Northwest Pacific Ocean, we estimated their daily age, measured the trace element contents of the otoliths at various life history stages, and analyzed the Sr/Ca, Ba/Ca, Mg/Ca, and Na/Ca values in the otoliths and their relationship with sea surface temperature (SST) changes. The main findings were as follows: (1) Cluster analysis showed significant differences (p < 0.05) in the Sr/Ca, Ba/Ca, Mg/Ca, and Na/Ca values in the core regions of otoliths among the clusters. (2) An analysis of the elemental characteristics across life history stages showed significant differences (p < 0.05) in the Sr/Ca values prior to the juvenile stage (31~90 d) and following the young stage (91~180 d). Significant variations (p < 0.05) in the Ba/Ca values during the juvenile and immature stages imply vertical migration behavior. Additionally, the Mg/Ca and Na/Ca values in adult stages showed significant differences (p < 0.05) to those in early life history stages. (3) GAM fitting and cross-correlation function tests demonstrated a statistically significant (p < 0.05) nonlinear lagged relationship between the otolith Sr/Ca values and SST.