Date

Summer 2022

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

The shark-like rays (Order Rhinopristiformes) are found worldwide and are among the most threatened species of cartilaginous fishes. The guitarfishes (Family Rhinobatidae) are one of five families in this order, with many species being assessed as vulnerable, endangered, or critically endangered by the International Union for Conservation of Nature (IUCN). Current fisheries and conservation efforts are limited, however, due to unresolved taxonomic issues and poor species descriptions. Presently, there are three described species of Rhinobatos from the Southwestern Indian Ocean: Rhinobatos austini, R. holcorhynchus, and R. nudidorsalis. These three species of Rhinobatos are often mistaken for one another and are assessed as Data Deficient (DD) by the IUCN. Until its description in 2017, R. austini was misidentified with the poorly defined, offshore of eastern Africa species R. holcorhynchus. Rhinobatos nudidorsalis was described from a single specimen caught far offshore from Madagascar near the Mascarene Ridge in 2004, but prior to its description it may also have been previously misidentified as R. holcorhynchus. The issue of misidentification is often amplified by a lack of consistency in terminology and measurements used by taxonomists for the Rhinopristiformes. Since the descriptions of R. austini and R. nudidorsalis, additional specimens have become available. Thus, a redescription of these three species is needed to clarify their taxonomic status. In addition, a guide to guitarfish morphology is needed to standardize measurements for this group by clarifying techniques and minimizing error across research groups.

Several Rhinobatos species descriptions and FAO (Food and Agricultural Organization of the United Nations) catalogs for cartilaginous fishes were reviewed to describe and define guitarfish measurements. Morphometrics from four congener species of Rhinobatos from the Indian Ocean that have been assessed by the IUCN were analyzed and served as comparative material for the three DD species. In addition to the traditional morphological analyses used to distinguish guitarfish species, morphometrics from all seven species were analyzed using three multivariate statistics: a Non-Metric Multidimensional Scaling (nMDS), a Principal Component Analysis (PCA), and a Linear Discriminant Analysis (LDA). Results from the LDA show distinct clusters for species of Indian Ocean Rhinobatos and indicate that the nasal region is effective in differentiating Southwestern Indian Ocean species. In addition, R. austini, R. holcorhynchus, and R. nudidorsalis are confirmed as distinct species and redescribed based on new material. These redescriptions provide taxonomic clarity for Southwestern Indian Ocean guitarfishes and will aid in species-specific identification, leading to improvements in conservation and fisheries monitoring and management.

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