Combined COI barcode‐based methods to avoid mislabelling of threatened species of deep‐sea skates

Abstract

Skates 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.

First Integrative Morphological and Genetic Characterization of Tremoctopus violaceussensu stricto in the Mediterranean Sea

“…For both genetic markers, COI and 16S, sequences deposited under the name T. violaceus proved to be T. gracilis . This study once again confirms that errors/misidentifications are common in public repositories [ 7 , 53 ], probably because there are not many and easily applicable taxonomic characters used in the field to distinguish them, especially separating T. violaceus and T. gracilis . These discrepancies between the morphological and molecular identification, suggest adopting a more precautionary approach when reassigning old records to a different species based solely on the colour patterns deducted from drawings/photos [ 8 , 9 , 10 ] or extending the geographical range of species (e.g., T. gracilis within the Mediterranean Sea), based solely on sporadic observations, described in conference papers almost impossible to find for consultation [ 19 ].…”

Morphological Traits and Capture Depth of the Norwegian Skate (Dipturus nidarosiensis (Storm, 1881)) from Two Mediterranean Populations

“…The geographical distribution here reported confirms the presence of the Norway skate in Sardinian waters in the southernmost part of the Island. Nonetheless, on the other one hand, the catch of a specimens in northeast and of another on the western coasts of Sardinia, reported here for the first time, returns a more precise picture of the real distribution of this species around the island, in this regards, future samplings could confirm a much wider distribution than what is known so far [5][6][7][8][9][10][11]38]. Indeed, the scarcity of catches in the western part of Sardinia could be due to a lower pressure of deep fishing targeting red shrimps (A. foliacea and A. antennatus) [52] in the area, resulting in fewer opportunities to catch a species with such a deep distribution as that of D. nidarosiensis.…”

“…Considering also that most of the catches in GSA 11 came from an experimental deep-sea trawl fishing campaign (800-1700 m) organized by the University of Cagliari, other hypotheses in terms of habitat differences than the mere possibility of capture should also be investigated. In this regard, a continuous monitoring of the catch of both fishery depending (landing and discard) and independent (scientific trawl survey) should be endorsed in order to fill the gaps in distribution knowledge on this species and other deep-sea elasmobranchs [38].…”

“…Moreover, in the sites where Norwegian skate specimens were found in Mediterranean, the sea bottom is mainly characterized by canyons, steep ground and slopes of high depths which are unfavorable to the trawling activity [59]. Therefore, it is foreseeable that in the near future there may be new reports of this species in other areas than those already reported in recent [13,15,38].…”

“…Moreover, morphometric analysis is considered one powerful, cost-effective tools to identify and characterize fish stocks [31][32][33], to determinate the structure of fish assemblages [34] and to distinguish between fish populations [34][35][36]. The identification of the populations within the same species through multifactorial discriminant analysis can lead to a better knowledge of a species in term of evolution, ecology and behavioral characteristic [31,36], contributing to its management within a conservation strategy perspective [37,38]. Indeed, fish stocks are considered as the key units in marine management research [39] and reference within.…”