Spot the Difference: Morphometrics Reveals Key Traits for Distinguishing Two Cryptic Juvenile Skate

Accurate species identification is essential for effective management of threatened species, especially those with overlapping distributions and similar morphologies. Skate (Order Rajiformes) exhibit a highly conserved superficial morphology, which has resulted in a long history of taxonomic confusion and misidentification within this group. The flapper skate (Dipturus intermedius) and common blue skate (D. batis) are prime examples of this challenge; both species inhabit the Northeast Atlantic and share a complicated, intertwined taxonomic history. Given their overlapping distributions, precise species identification is necessary to ensure targeted management actions. Despite the availability of reliable morphological keys for larger specimens, identification of juveniles remains challenging because many diagnostic features are underdeveloped or obscured by damage. This study aimed to identify additional traits for differentiating juvenile (< 100 cm) flapper and common blue skate by employing morphological approaches validated through molecular techniques. The analysis focused on identifying distinct features that remain detectable in damaged specimens, ensuring the method's practical applicability in field conditions. We identified four robust features that can be used to differentiate juveniles of the two species: ventral coloration, disc shape, anterior disc margin shape and rostrum shape. The findings presented here enhance data accuracy for juvenile flapper and common blue skates, support targeted conservation actions, and contribute to the effective management and long-term recovery of these threatened species.