Insights into Population Structure and Spatial Connectivity of the Bluefish Pomatomus saltatrix (Teleostei: Pomatomidae) Along the Southeastern–Southern Coast of Brazil Using Fourier- and Wavelet-Based Otolith Contour Descriptors

Otolith shape has been widely used as a tool to investigate the population structure of marine fish, as it reflects environmental, physiological, and genetic influences throughout the lives of individuals. The morphological variability of Pomatomus saltatrix sagittal otoliths along the southeastern–southern coast of Brazil was assessed using Elliptic Fourier Descriptors (EFDs) and Wavelet Transform Descriptors (WTDs). A total of 74 individuals from Rio de Janeiro (RJ, N = 25), São Paulo (SP, N = 24), and Santa Catarina (SC, N = 25) were analyzed. The coefficients obtained from both methodologies were subjected to multivariate analyses, including Permutational Multivariate Analysis of Variance (PERMANOVA) and Flexible Discriminant Analysis (FDA), combined with Jackknife Cross-Validation (JKC). The results showed high similarity in otolith shape among the sampled locations. Overall, PERMANOVA detected significant spatial differences for both EFD and WTD, although the proportion of variation explained by sampling location was low for both descriptors (<5%). After Bonferroni correction, no pairwise differences remained significant for EFD, whereas WTD indicated significant differences between SC and the other two sampling locations. Nevertheless, FDA indicated partial discrimination among sampling sites, with some overlap among groups for both descriptors. Despite this, JKC rates were high, reaching 92% for EFD and 87% for WTD. Overall, the results point to a pattern of weak spatial structuring in P. saltatrix along the southeastern–southern coast of Brazil. Although subtle morphological heterogeneity was detected among the analyzed locations, the evidence does not support the existence of completely isolated stocks. The observed patterns indicate weak spatial phenotypic differentiation and may be consistent with population connectivity; however, connectivity cannot be directly inferred from otolith shape alone and represents only one possible interpretation, as similar environmental conditions, shared growth histories, or limited discriminatory power of otolith morphology could also contribute to the observed scenario. Thus, the study reinforces the utility of otolith morphometry as a complementary tool for population studies and highlights the importance of integrating it with other phenotypic and genotypic approaches for a more comprehensive understanding of the structure of the species’ stocks.