Genetic and phenotypic diversity in the wedgefish Rhynchobatus australiae, a threatened ray of high value in the shark fin trade

Abstract

Rhynchobatus spp. (wedgefishes) are large benthopelagic shark-like rays with fins that are highly prized in the international shark fin trade. They are among the most threatened groups of sharks and rays globally. While Rhynchobatus spp. are known to be under considerable fishing pressure as a group, taxonomic confusion among species within the genus has compromised species-specific fishery and demographic data that are urgently needed for developing effective management strategies. Rhynchobatus australiae (Whitley, 1939) is a large Indo-West Pacific species reaching 2 to 3 m that is classified as Vulnerable on the IUCN Red List. This study combines new empirical data from field surveys with data obtained from verified reference specimens to investigate genetic and phenotypic variation in R. australiae and its relative incidence in fisheries. R. australiae dominated Rhynchobatus catch in fisheries surveys across Southeast Asia, and was the most commonly recorded species of the genus in Australia (94% and 58% of captures respectively, n = 207). Study specimens were consistent with a single species with moderate spatial mtDNA variation (ΦST = 0.198, p < 0.0001). We show that R. australiae can be reliably differentiated from other Indo-Pacific species with nadh2 (1044bp), and a section of the control region (456bp) short enough to amplify DNA from processed fins in international trade. We document aspects of morphological variability to assist in the description of external characters that differentiate this species. This is the first range-wide intraspecific study on any wedgefish species, and provides the most complete synthesis of mtDNA data to date for identifying Rhynchobatus fins in the global shark fin trade.