MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14325

ABSTRACT: Yellowfin tuna Thunnus albacares is a commercially important fish species widely distributed between 40°S and 40°N. This study investigates mixing rates between the tropical and temperate areas of the western Pacific Ocean was investigated using stable carbon (δ¹³C_otolith) and oxygen isotopes (δ¹⁸O_otolith) in whole otoliths for small juveniles (mean: 5.8 cm standard length (SL)) and otolith cores for large juveniles (32.4 cm SL). The density distribution of δ18O_otolith values for small juveniles showed a significant difference between the areas, whereas patterns for large juveniles were almost identical between areas. In addition, modal values for large juveniles spanned several small juvenile modes. The density distribution of δ¹³C_otolith values for small juveniles had a single significantly different mode for each area, whereas the distribution of δ¹³C_otolith values for large juveniles in these areas was bimodal, particularly in the temperate area; these modes corresponded to those for small juveniles in each area. These modal patterns indicate that the majority of large juveniles captured in the temperate area have tropical origins, and mixing from tropical to temperate areas occurs between the areas before recruitment to fisheries in each area. These connectivity patterns during the early life history can contribute to refinement of stock assessments of this commercially valuable species.