Otolith shape and chemistry as tools for investigating the population connectivity of the white mullet (Mugil curema) on the of Atlantic north-eastern Brazilian coast

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Mugil curema is a euryhaline fish highly abundant in the estuarine and coastal waters of Brazil, representing an important halieutic resource. The species plays a key ecological role by transferring matter and energy between habitats via migratory patterns. However, its population dynamics, habitat connectivity and movement patterns remain poorly understood. This study aimed to examine population structure through sagittal otolith shape and chemistry. In May 2023, ninety sub-adult individuals were collected from coastal zones near three estuarine systems - Camaratuba, Gramame, and Paraíba - in Paraíba state, northeastern Brazil. Otolith contour was assessed using elliptical Fourier descriptors (EFD), while the elemental chemical signatures (ECS) were analyzed using solution-based inductively coupled plasma mass spectrometry. Both univariate and multivariate statistics were applied to evaluate population differences among sites. EFD results showed significant shape variation, with a 57 % overall reclassification rate; D2 and D3 were most discriminative according to univariate tests. ECS analysis provided stronger site differentiation, with significant differences in elemental ratios, namely Na:Ca, Mg:Ca, Mn:Ca, Ba:Ca, Fe:Ca, Co:Ca, Li:Ca, Ni:Ca and Rb:Ca. The ECS method alone achieved an 82 % overall reclassification rate. When combining EFD and ECS, overall reclassification accuracy rose to 84 % and cluster analysis showed clearer sample separation among sites. These findings indicate that environmental heterogeneity in Paraíba’s coastal zone - linked to proximity to estuarine systems - promotes population differentiation. The results underscore spatial structuring and limited connectivity between populations, offering valuable insights into movement ecology. These patterns suggest that site fidelity or restricted dispersal plays a role in shaping population structure. Such knowledge can support targeted conservation and management strategies for coastal-estuarine ecosystems, particularly in maintaining adult fish stocks.