Integrating multi-temporal otolith elemental signatures reveals partial spatial structuring and connectivity in bluefish (Pomatomus saltatrix) along the Brazilian coast

Understanding population structure and connectivity in highly mobile marine fishes is fundamental for effective fisheries management. Bluefish (Pomatomus saltatrix) is an ecologically and commercially important coastal pelagic species, yet its population structure along the southeastern–southern Brazilian coast remains poorly understood. This study investigated spatial population structuring by integrating otolith elemental signatures representing different periods of the species' life history. Sagittal otoliths from 90 bluefish collected in Rio de Janeiro, São Paulo, and Santa Catarina were analysed. Whole-otolith elemental signatures were quantified using solution-based inductively coupled plasma mass spectrometry (SB-ICP-MS), whereas core and edge element:Ca ratios were determined using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). These complementary approaches provided integrated lifetime, early-life, and recent environmental records. Spatial variation was assessed using univariate and multivariate statistical analyses, including flexible discriminant analysis. Significant spatial variation was detected in whole-otolith, core, and edge elemental signatures, although each analysis revealed a distinct geographical pattern. Whole-otolith signatures primarily differentiated Rio de Janeiro from São Paulo and Santa Catarina, whereas core signatures distinguished São Paulo from the remaining regions and edge signatures separated only São Paulo and Santa Catarina. Flexible discriminant analysis showed moderate classification success (53–62%) and considerable overlap among sampling regions, indicating incomplete spatial differentiation. The contrasting elemental signatures recorded in different otolith regions demonstrate that each approach captured complementary environmental information reflecting different stages of the life history. Integrating whole-otolith, core, and edge elemental signatures provided a more comprehensive assessment of population structure than any individual approach alone. The results support partial spatial structuring and connectivity among P. saltatrix populations along the southeastern–southern Brazilian coast, highlighting the value of multi-temporal otolith chemistry for investigating population connectivity and providing information relevant for stock assessment and spatial fisheries management.