Application of shape analysis for the identification of pelagic fish stocks

Abstract This study explores local variations in body and otolith shape of Trachurus trachurus from the Ibero-Mauritanian coastal stock in the South European Atlantic Shelf ecoregion, essential for effective stock management. We used geometric morphometrics and wavelet functions to analyze samples from Galicia, Peniche, and the Gulf of Cádiz. Comparing fresh and frozen specimens revealed significant shape changes due to freezing. Our results confirm that unique environmental conditions in the South European Atlantic Shelf ecoregion contribute to distinct local populations. The northern population had a more elongated body and lanceolate otoliths, while the southern population displayed a wider body and oval otoliths. Central region specimens exhibited intermediate characteristics. Four distinct morphotypes were identified, with region-specific distributions. These findings suggest local adaptations within the Ibero-Mauritanian stock, emphasizing the need to account for these differences in management strategies to ensure sustainability. Future studies should include larger, more diverse samples, especially from the Mediterranean, to further understand stock structure.