Inter- and Intraspecific Variation in Dorsal Pigmentation Patterns of Skates (Rajidae) from the Cantabrian Sea: Evidence of High Variability in Raja clavata and Implications for Species Identification

Accurate species identification is essential to assess population trends and implement effective conservation measures. Many rajid species have life-history characteristics that increase their vulnerability to fishing mortality, while their conservation status differs among species. However, species identification within the family Rajidae is hampered by morphological conservatism and intraspecific phenotypic variation, which frequently lead to misidentification in fisheries surveys and seafood markets. Here, we combine COI DNA barcoding with a detailed photographic assessment of dorsal pigmentation patterns in 484 skate specimens collected from a fish wholesaler market in the Cantabrian Sea. Seven species were genetically identified as Raja clavata, Raja montagui, Raja microocellata, Raja undulata, Raja brachyura, Leucoraja naevus, and Leucoraja circularis. Substantial overlap in pigmentation patterns was detected among genetically distinct species, while R. clavata exhibited nine distinct morphotypes, five of which have not been previously described. We further investigated whether R. maderensis individuals display dorsal patterns distinct from those of R. clavata. Notably, a dark-crossbar pattern, previously unreported in R. montagui, was recorded in this species. Moreover, an unusually extreme case of hypomelanosis in R. microocellata is also discussed. Together, these findings demonstrate that dorsal pigmentation alone in processed individuals is insufficient for reliable species discrimination in skates and highlights the need to integrate molecular tools into fisheries monitoring and biodiversity assessments.