Abstract
AbstractSkates are characterised by conservative body morphology which hampers identification and leads to frequent taxonomic confusion and market mislabelling. Accurate specimen classification is crucial for reliable stock assessments and effective conservation plans, otherwise the risk of extinction could be unnoticed. The misclassification issue is evident for the genus Dipturus, distributed worldwide, from the continental shelf and slope to the deep sea. In this study, barcode cytochrome oxidase I gene (COI) sequences were used along with species delimitation and specimen assignment methods to improve taxonomy and zoogeography of species of conservation interest inhabiting the Atlantic Ocean and Mediterranean Sea. In this study, we provided new evidence of the occurence of D. nidarosiensis in the Central‐Western Mediterranean Sea and the lack of Atlantic‐Mediterranean genetic divergence. The Atlantic endangered species D. laevis and D. batis clustered together under the same molecular operational taxonomic unit (MOTU) with any delimitation methods used, while the assignment approach correctly discriminated specimens into the two species. These results provided evidence that the presence of the barcode gap is not an essential predictor of identification success, but the use of different approaches is crucially needed for specimen classification, especially when threshold‐ or tree‐based methods result less powerful. The analyses also showed how different putative, vulnerable, species dwelling across South‐Western Atlantic and South‐Eastern Pacific are frequently misidentified in public sequence repositories. Our study emphasised the limits associated to public databases, highlighting the urgency to verify and implement the information deposited therein in order to guarantee accurate species identification and thus effective conservation measures for deep‐sea skates.
Highlights
Skates are cartilaginous fish of the family Rajidae which includes more than 150 described species, belonging to 17 genera (Last et al, 2016a)
Group I included exclusively specimens morphologically assigned to D. oxyrinchus, while Groups IV was formed by specimens morphologically identified as D. nidarosiensis, with the only exception of DIPH13 which corresponded to a sequence erroneously attributed to D. oxyrinchus (Vargas-Caro, 2018) and DIPH20 recorded in GenBank as D. springeri but reported in Barcode of Life Data Systems (BOLD) as D. nidarosiensis (Table S2)
DIPH32 was found in a single individual caught in the Indian Ocean (IND) and deposited in BOLD as D. intermedius
Summary
Skates are cartilaginous fish of the family Rajidae (order Rajiformes) which includes more than 150 described species, belonging to 17 genera (Last et al, 2016a). Most of them are benthic organisms with restricted geographical distributions, living between the shoreline and >4000 m depth (Orlov, Cotton and Byrkjedal, 2006; Ebert and Compagno, 2007) Despite their apparent restrictive habitat preferences (e.g., soft bottom substrates), skates exhibit a high degree of biodiversity and endemism (Ebert and Compagno, 2007). Due to their conserved dorsoventrally flattened body morphology, the identification of skates based solely on morphological characters can be problematic (Geraci et al, 2017). Skates are rarely targeted by fisheries, but their high susceptibility to by-
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