What Is in Your Shark Fin Soup? Probably an Endangered Shark Species and a Bit of Mercury

Abstract

Shark fin soup, consumed by Asian communities throughout the world, is one of the principal drivers of the demand of shark fins. This near USD 1 billion global industry has contributed to a shark population declines of up to 70%. In an effort to arrest these declines, the trade in several species of sharks is regulated under the auspices of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Despite this legal framework, the dried fins of trade-regulated sharks are frequently sold in markets and consumed in shark fin soup. Shark fins found in soups break down into a fibrous mass of ceratotrichia, meaning that identifying the species of sharks in the soup becomes impossible by visual methods. In this paper, we use DNA barcoding to identify the species of sharks found in bowls of shark fin soup collected in Singapore. The most common species identified in our samples was the blue shark (Prionace glauca), a species listed as Near Threatened on the International Union for Conservation of Nature (IUCN) Red List with a decreasing population, on which scientific data suggests catch limits should be imposed. We identified four other shark species that are listed on CITES Appendix II, and in total ten species that are assessed as Critically Endangered, Endangered or Vulnerable under the IUCN Red List of Threatened Species. Globally, the blue shark has been shown to contain levels of mercury that frequently exceed safe dose limits. Given the prevalence of this species in the examined soups and the global nature of the fin trade, it is extremely likely that consumers of shark fin soup will be exposed to unsafe levels of this neurotoxin.

Blood in the water: DNA barcoding of traded shark fins in Singapore

“…Sphyrna lewini, the scalloped hammerhead, is the third most commonly encountered shark in this work. This high prevalence is consistent with a range of other work performed in Southeast Asia (Sembiring et al, 2015;Wainwright et al, 2018;Liu et al, 2021;Choy and Wainwright, 2022;Seah et al, 2022), and this species is recognised as one of the top four most traded in international shark fin markets (Cardeñosa et al, 2018;Fields et al, 2018). As previously suggested (Liu et al, 2021), the schooling behaviour that S. lewini engages in could mean it is easier to catch and therefore preferentially targeted.…”

“…Sequences were then referenced against The Barcode of Life Data System (BOLD) and GenBank. We deemed a species identification positive and unambiguous if BOLD returned a 100% match and indicated no matches with other closely related congeneric species, and if the same species was the top match in GenBank (Choy and Wainwright, 2022)…”

“…Fins are considered a delicacy, a status symbol and are frequently served in soup at celebratory events. Additionally, fins are highly prized in Traditional Chinese Medicine (TCM) practices where they are reputed to have a host of beneficial effects, from improving general wellbeing, to claims promoting anti-cancer properties (Clarke et al, 2007;Dent and Clarke, 2015;Teo, 2015;Choy and Wainwright, 2022).…”

Advancing DNA Barcoding to Elucidate Elasmobranch Biodiversity in Malaysian Waters

“…The Cytochrome c oxidase subunit 1 mitochondrial gene (CO1) is suggested as a highly suitable marker for DNA barcoding, as it can discriminate between closely related species across diverse animal phyla [ 36 ], including sharks and rays [ 39 , 40 ]. To date, DNA barcoding has been successful in identifying elasmobranch species from dried fins, tissues, and carcasses [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. This is highly beneficial for non-taxonomists to identify species with reasonable confidence even in the absence of whole specimens.…”

“…DNA barcoding—more specifically, CO1 analysis—has been used widely to aid in the species identification of elasmobranchs from various regions, such as Australia [ 36 , 42 , 43 ], China [ 44 ], the Philippines [ 50 ], Indonesia [ 51 ], Singapore [ 45 , 47 ], India [ 19 , 52 , 53 ], Bangladesh [ 54 ], Southern Africa [ 46 , 55 ], the United Kingdom [ 56 ], the Mediterranean Sea [ 57 ], the North Atlantic Ocean [ 58 ], the United States [ 49 ], and Brazil [ 59 , 60 , 61 ]. To date, limited published DNA barcoding studies in Malaysia have focused on rays but not on sharks [ 9 , 34 ].…”