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Review of three Southwestern Indian Ocean species of Rhinobatos Linck 1790 (Rhinopristiformes: Rhinobatidae)

Rachel M. Aitchison*, David A. Ebert, Bernard Séret, Simon Weigmann

*Corresponding author:

ABSTRACT: The shark-like rays (Rhinopristiformes) are among the most threatened species of cartilaginous fishes. The guitarfishes (Rhinobatidae) are one of five families in the order, with 62% of species assessed as Vulnerable or higher by the International Union for the Conservation of Nature (IUCN). Species-specific fisheries and conservation efforts have been limited, however, due to unresolved taxonomic issues and poor species descriptions. Presently, there are three described species of Rhinobatos from the Southwestern Indian Ocean (SWIO): Rhinobatos austini, R. holcorhynchus, and R. nudidorsalis. These three species have been mistaken for one another and are assessed as Data Deficient (DD) by the IUCN. Since the descriptions of R. austini and R. nudidorsalis, additional specimens have become available and a rediagnosis of these three species is required to clarify their taxonomic status. Morphometrics from four additional congener Indian Ocean species of Rhinobatos assessed by the IUCN were analyzed and serve as comparative material. In addition to a traditional morphological analysis, morphometrics from all seven species were analyzed using a Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). Results show distinct clusters for the SWIO Rhinobatos and indicate the nasal region is effective in differentiating species. Rhinobatos austini, R. holcorhynchus, and R. nudidorsalis are confirmed as distinct species and are rediagnosed based on new material. These rediagnoses provide taxonomic clarity for SWIO Rhinobatos and will aid in species-specific identification, leading to improvements in conservation and fisheries monitoring and management.