Insights from genetic and ecological knowledge for conservation management of rhino rays from the Western Indian Ocean.

Groeneveld, M. J.*¹, Klein, J. D.¹, Bennett, R. H.², Bester-van der Merwe, A. E.¹

¹ Department of Genetics, Stellenbosch University
² Wildlife Conservation Society

Rhino rays are highly threatened by overfishing combined with climate change and low reproductive productivity. Catch and landing rates suggest drastic declines throughout most of their distributions. Yet, a lack of species-specific knowledge and taxonomic uncertainty persists, particularly for guitarfishes (Acroteriobatus spp.) and wedgefishes (Rhynchobatus spp.) in the Western Indian Ocean (WIO). Delineating populations and understanding the genetic connectivity of exploited species are important for their conservation management. When biological data from different species are pooled, species-specific fishery and demographic data can be overestimated or underestimated. This study investigated the population genetic structure of Rhynchobatus djiddensis and R. australiae from different locations across the WIO using a dual marker approach: (1) two mitochondrial gene regions (COI and the control region; n = 117), and (2) nine nuclear microsatellite markers (n = 146). The two species were delineated based on both marker types. For R. djiddensis, the sampling locations of South Africa and Mozambique were genetically homogeneous. For R. australiae, significant differentiation was found between sampling locations, with Madagascar and Tanzania being genetically the most similar. This information provides critical insights into the distribution range and stock structure of the whitespotted wedgefish species complex, highlighting priority populations and supporting the sustainable management of wedgefishes. However, detailed molecular attention is still necessary to resolve taxonomic issues and define appropriate spatial scales and conservation units for rhino ray management. As such, further research will focus on expanding species-specific information for guitarfishes and wedgefishes within the WIO region using molecular taxonomy, population and seascape genomics and community-based surveys. By combining scientific findings with local ecological knowledge from water users in coastal communities, a more realistic and equitable approach to conservation management of rhino rays can be taken.

Keywords: conservation genetics, elasmobranchs, rhino rays, seascape genomics, taxonomic uncertainty