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 (Φ ST = 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.

DNA analysis of a large collection of shark fins from a US retail shop: species composition, global extent of trade and conservation - a Technical Report from the Monterey Bay Aquarium

“…For COI amplifications, we used modified Folmer COI primers [FishF1, FishF2, FishR1, FishR2 from (Ward, Zemlak, Innes, Last, & Hebert, 2005)], amplified with an extension temperature of 54°C, extension of 72°C, and denaturing of 94°C for 60 seconds each. For the putative control region, 374-521 bp was amplified using the primers GwF (5’-CTGCCCTTGGCTCCCAAAGC-3 ́) (Pardini et al, 2001) and 470r2 (5’- GCCATTAAAGGGAACTAGRGGA-3 ́), published in Giles et al (2016).…”

“…We were unable to find a COI sequence of the large tooth sawfish Pristis microdon , which appears in our Control Region data set (see below), although Pristis zijsron is available (accession EU398989.1). Likewise, two recently described mitochondrial lineages of the wedgefish genus Rhyncobatus (Giles et al, 2016) and the scoophead hammerhead Sphyra media are available from control region sequences but not COI. Our final reference COI collection consists of 177 sequences (sequences appended to Master COI data file, appendix 1).…”

“…From this set we chose one or two sequences from each species. Because these were of variable length, we trimmed each sequence to the length between our amplification primers (Giles et al, 2016). In addition, we collected representative control region sequences from one representative product sample of each of the species that we found in our Cytochrome oxidase survey.…”

“…Here we test 1,720 fins collected from a retail outlet on the west coast of the US that was shuttered after shark fin sales were banned. We use sequences of the mitochondrial control region (Giles, Riginos, Naylor, & Ovenden, 2016), compared to published data sources, to estimate the identity of fins on the basis of sequence similarity and phylogenetic placement. For a subset of 961 fins, we also sequenced a region of the COI gene, giving us a comparative data set to test the ability of these two gene regions to deliver accurate identifications.…”

Are guitarfishes the next sawfishes? Extinction risk and an urgent call for conservation action

“…Examples from developing world fisheries include the presence of cryptic, sympatric species (e.g. Henderson et al 2016) and considerable within-species variability in dorsal colouration and morphology (Giles et al 2016). Even apparently well-managed fisheries in the developed world may pose risks to sustainability due to the presence of undistinguishable sympatric taxa.…”