Review of three southwestern Indian Ocean species of Rhinobatos (Rhinopristiformes: Rhinobatidae)

Abstract

The shark-like rays (Rhinopristiformes) are among the most threatened species of cartilaginous fishes. The guitarfishes (Rhinobatidae) are one of 5 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 3 described species of Rhinobatos from the southwestern Indian Ocean (SWIO): R. austini, R. holcorhynchus, and R. nudidorsalis. These 3 species have been mistaken for one another and are assessed as Data Deficient by the IUCN. Since the descriptions of R. austini and R. nudidorsalis, additional specimens have become available and a rediagnosis of these 3 species is required to clarify their taxonomic status. In the present study, morphometrics from 4 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 7 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. R. 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.