Annual Recurrence of the Critically Endangered Bowmouth Guitarfish (Rhina ancylostomus) in Djibouti Waters

SIMPLE SUMMARY: One of the least understood and most threatened groups of elasmobranchs is the Rhinopristiformes, the guitarfishes, wedgefishes, and sawfishes. Numbering more than 60 species, this order includes a high percentage of Critically Endangered and Endangered species, as designated by the International Union for the Conservation of Nature. There is a dearth of data on these species due to sightings being infrequent and unpredictable. Globally, Rhinopristiformes are both directly targeted for their meat and large fins and are caught as bycatch in their near-shore habitats. We report here a consistent and predictable long-term presence of the Critically Endangered bowmouth guitarfish (Rhina ancylostomus) in the Gulf of Tadjoura, Djibouti. This species has been reliably encountered during diving and whale shark research activities (November–February) over seven seasons, indicating long-term site fidelity of R. ancylostomus within the area. Currently receiving minimal legal protection and facing unknown fishing pressures and ecological risks, these animals and their habitat should be prioritized for research and conservation. ABSTRACT: The bowmouth guitarfish (Rhina ancylostomus) is among the most endangered of marine vertebrates, and evidence of severe declines and localized extinctions has been reported. Yet its life history and ecology suffer from a lack of scientific attention due to the scarcity and unpredictable movements of the species. By collecting opportunistic records from 2015 to 2023 during diving activities, this study describes for the first time the occurrence of a predictable aggregation of R. ancylostomus in the Gulf of Tadjoura (Djibouti). These data provide a key record of this species in the area, whose presence is strongly associated with sandy seabeds and corals at approximately 35 m depth. Based on the opportunistic sightings of R. ancylostomus during diving activity, Ras Eiro and Ras Korali appear to be the currently known core habitats for this species and may serve as breeding or feeding grounds. Overall, our data show that the Gulf of Tadjoura is a globally important conservation hotspot, and therefore its protection should be prioritized.