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Trace elements (Ba, Sr) and stable isotopes (δ13C and δ18O) of otoliths from young-of-year (YOY) skipjack tuna were examined to determine whether there is sufficient distinction of chemical signatures among three main nursery areas of the equatorial Indian Ocean (West, Central and East) to retrospectively determine individual´s natal origin. Higher δ18O values in the otolith material deposited during the first fourth months of life were observed in YOY skipjack tuna captured in the western Indian Ocean nursery, but, in general, the chemical signatures of the three nursery areas largely overlapped. Random forest cross-validated classification success of fish to their nursery area was low (46%). This may suggest (1) that early life history stage skipjack tunas from the three different nursery areas lived in a chemically homogenous environment or (2) that fish moved between nursery areas in the first months of life. Our results suggest the use of these otolith signatures alone are not sufficient to understand skipjack stock structure in the Indian Ocean. Future research should explore larvae or younger skipjack tuna, ideally sampling at finer scale temporal stratification (i.e. by monsoon and year) to resolve questions regarding skipjack stock structure in the Indian Ocean.
