This study is the first assessment of the species composition of the largest shark fin market in Mainland China. The species identification methodology applied in this study to both Guangzhou and Hong Kong is a conservative approach that allows for the identification of nearly all elasmobranchs to the species level, with a few exceptions where species complexes are present14. The number of species found during our sampling of Guangzhou was 43 species or species complexes, excluding samples identified only to the genus level. This was very similar to the number found in Hong Kong with equivalent sampling effort (44). The total number of species found in Hong Kong (n = 81 species/species complexes) reported by Cardeñosa et al.7 over a longer sampling period (4 years) is similar to the prediction of the maximum confidence intervals from the species richness estimates and the abundance rarefaction curve from the smaller sampling effort in Guangzhou. Given this accuracy for Hong Kong, we suggest that a larger sampling effort in Guangzhou would yield a similar number of species overall.

While we present a robust comparative survey of species richness in these two markets our approach is conservative and therefore underestimates the total species richness. The statistical models we used to estimate total species richness from these data (i.e., Chao1, Chao1-bc, iChao1, ACE, and ACE1) use the frequencies of rare species in the sample to infer the number of undetected species and assume that species are not missed in the sample15,16. There are, however, a number of ways for us to miss species in our conservative species identification approach: the presence of species complexes that cannot be resolved with the genetic marker used (e.g., the blacktips), when the taxonomy of species in unresolved (e.g., within the ray family Rhinobatidae [wedgefish], where there are misidentified and misclassified sequences in GenBank and BOLD; and on occasions when our mini-barcodes are too short or contain nucleotide ambiguities that preclude identification lower than genus . Future work could sequence a longer portion of the COI or other loci for fin trimmings that could only be identified to genus or complex in the present study and use species delimitation approaches and/or comparisons to sequences from vouchered specimens to fully resolve the species richness of these markets.

The proportion of species or species groups in IUCN threatened categories was similar for the parallel sampling efforts: 37.9% (Hong Kong) and 41.8% (Guangzhou). The present study thus extends the previous work in Hong Kong7,9 by revealing that Guangzhou is trading fins from a similar diversity of sharks, rays, and chimaeras, and more than a third of the traded species exhibit high extinction risk. We also found that CITES-listed species were prevalent in Guangzhou, although potential latency of products imported prior to implementation in late 2014 (hammerheads, oceanic whitetips) or 2016 (silky, threshers) makes it difficult to pinpoint how much of this represents illicit trade (i.e., specimens imported into China without appropriate CITES documentation). It is also unclear how much of this originates from whole fins initially imported (and perhaps reported to CITES) into Hong Kong and then reexported and processed near Guangzhou.

Guangzhou exhibits a strong skew in species composition, being dominated by a small subset of the total species diversity (e.g., only 13 species represented by > 20 fin trimmings). Most of these were oceanic sharks that represented the largest proportions overall (71.6%)7,9. Skewed species composition was also characteristic of Hong Kong, with skews to many of the same species that dominated Guangzhou7,9. The only substantial difference in composition between the two sampling locations was that the shortfin mako was almost twice as common in the Guangzhou than in Hong Kong trimmings (i.e., 4.16% vs. 2.37%) and had a higher incidence (i.e., higher proportion of bags with identified shortfin mako shark trimmings). As a result, it modeled as the fifth most common species in Guangzhou where it was ninth behind several coastal species (e.g., spinner [C. brevipinna], bull [C. leucas], Java [C. amboinensis]) that were more common in Hong Kong7. This could potentially mean there are different and direct supply chains for this species into Mainland China, possibly their own high seas longline fleet, which may increase its presence in trimmings in Guangzhou relative to Hong Kong. This potential input into China is an important issue since the shortfin mako was recently listed on CITES Appendix II. The distant water fleet is now required to report landings of this species to CITES under “Introduction from the Sea” rules8.

The similarity between the species composition of fin trimmings in the shark fin markets of Hong Kong and Guangzhou extends previous studies that suggest these two markets are connected10 and is not surprising considering the proximity (129 km) and overland connections (road, rail) between these cities. Hong Kong has historically been the trading port of entry to mainland China, where fins arrive and are sent to the Guangdong Province for processing and processed fins are sent back to Hong Kong and other major cities in mainland China for consumption10. We suggest that some of the similarity we observed is driven by a similar supply chain for the trimmings: fins from Mainland China and Hong Kong are largely processed in Guangdong and resulting trimmings are then returned to these hubs for sale in their local retail markets. Although the border separating Hong Kong and Guangzhou is not international, CITES permits for listed species are required for transit (Hong Kong Agriculture Fisheries and Conservation Department [AFCD], pers comm). Given the prevalence of CITES listed species in both markets during our survey we suggest some surveillance investments for CITES listed shark products at the Hong Kong-China border is likely warranted20,21.

Despite the contemporary similarity found between the species composition of a fin market proxy in Hong Kong and Guangzhou, we suggest that capacity building and systematic studies of other fin trade hubs within Mainland China, Viet Nam, Singapore, Japan, Thailand, Taiwan, and Malaysia, are needed. Shark fin imports have declined sharply in both Hong Kong and especially China since 20112 for a variety of potential reasons (e.g., changes in reporting and sourcing, new policies prohibiting extravagant spending by the governmental sector, reduced public demand), while imports have increased in some of these other hubs2. Since these hubs are less culturally and geographically connected to Hong Kong and Guangzhou, they are likely to have different inputs and preferences that could affect species composition. Indeed, some appear to focus on small, low value fins as opposed to the large valuable ones mainly traded in Hong Kong and China2. We therefore recommend investments in approaches to monitor the species composition of these hubs as well, in order to gain a clearer understanding of the species-specific dynamics of the international shark fin trade. Nonetheless, continued monitoring of the Hong Kong-Guangzhou hubs is necessary given the relatively high proportion of species threatened with extinction and/or listed under Appendix II of CITES in our surveys.

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