Unveiling regional population structure in blackbelly rosefish Helicolenus dactylopterus through otolith shape analysis

In the face of escalating fishing pressures and environmental change, deciphering the population structure of marine species is crucial for effective management and conservation. The blackbelly rosefish Helicolenus dactylopterus , which inhabits the northeastern Atlantic and the Mediterranean Sea, serves as a model species, yet its population structure remains poorly understood despite its vulnerability to overfishing. We investigated morphotypic differentiation in otolith contour shape, examining otolith variability across sampled regions, including mainland Portugal, the Canary Islands, Mauritania, Atlantic Morocco, and Catalonia in the northwestern Mediterranean Sea, using wavelet functions. Our results reveal clear regional variation, with classification rates exceeding 94%. Two clusters were identified, separating African from European populations, with otolith shape variability linked to the anterior region, height, and postero-ventral margin. European populations exhibited thinner, more elongated otoliths, while African populations showed wider, more elliptical shapes. Juvenile otoliths closely resembled adult shapes. By incorporating juvenile fish, this study provides a more comprehensive understanding of regional population boundaries based on otolith morphotypes. It investigates the spatial variability of otolith shapes and explores their potential relationship with environmental conditions at depth, particularly temperature and salinity, offering new insights into blackbelly rosefish population structure. These findings contribute to improving population identification techniques and have important implications for sustainable fisheries management.