Otolith shape reveals regional phenotypic differentiation in Dentex macrophthalmus across the Atlantic and Mediterranean

Resolving population structure is essential for sustainable fisheries management, yet regional phenotypic differentiation remains poorly understood in many broadly distributed demersal species. This study used otolith contour shape to examine phenotypic variation in the large-eye dentex, Dentex macrophthalmus , across four regions spanning the eastern Atlantic and Mediterranean Sea: Cape Verde, Mauritania, Guinea-Bissau, and Greece. A total of 662 sagittal otolith pairs from juveniles and adults were analysed using wavelet-based shape descriptors, multivariate ordination, and artificial neural network classification. Otolith shape differed significantly among regions in both life stages, indicating that differentiation was detected independently in juveniles and adults. In juveniles, shape variation was driven primarily by differences in r ostrum and antirostrum development, notch depth, and dorso-ventral expansion. In adults, differences among regional samples were expressed more strongly through rostrum morphology and variation in the dorsal and postero-ventral margins. Overall classification accuracy reached 75.2% in juveniles and 73.4% in adults. The clearest broad-scale pattern involved a contrast between the Mediterranean and Atlantic samples, although substantial heterogeneity was retained among Atlantic localities. Because sampling years differed among regions, the observed patterns may reflect both spatial and temporal variation. Environmental factors, including temperature, may also have contributed, but were not directly tested. Together, the results show that otolith contour shape is a useful phenotypic marker for distinguishing regional samples of D. macrophthalmus and provide a foundation for integrative studies of stock identity and connectivity.