Author: Natasha Hynes
Sharks face a number of threats with one of those being shark finning. Shark fins are highly valuable and used in products such as shark fin soup. This practice has contributed to overfishing and a major decrease in shark populations. Many different species are finned for these products, including endangered and vulnerable ones. The Convention on International Trade in Endangered Species is an international treaty that helps protect endangered animals and plants. Species listed under Appendix 1 are highly threatened species and their trade is usually prohibited. Species listed under Appendix 2 are less threatened than those under Appendix 1, but their trade is still highly monitored to ensure they are not over-exploited. Many sharks and other elasmobranchs are listed under this these categories. Nonetheless, these CITES-listed species can be found available for purchase.
Identifying species from fins only is already a challenge. When fins from sharks are then dried and process, the chances of identifying the species are virtually zero. Fortunately, researchers have developed methods to determine species from these highly processed bits of fin: DNA barcoding. Using methods to extract DNA from fins, researchers can compare DNA from fins available at market with DNA that was extracted from known species. Researchers in Malaysia used DNA barcoding to determine the species composition of shark products available for local sale.
The researchers in this study extracted DNA from over 140 shark fins obtained at markets on the east coast of Malaysia. They found 23 taxa from their extractions. Of these taxa, 11 are CITES Appendix 2 taxa, and one Appendix 1 genus was found – the critically endangered sawfish. Here is the full list of species found in the study:
Bull shark
Spot-tail shark
Great hammerhead shark
Silky shark
Scalloped hammerhead shark
Bowmouth guitarfish
Blue shark
Bottlenose wedgefish
Silvertip shark
Tiger shark
Shortfin mako shark
Spinner shark
Pelagic thresher
Giant shovelnose ray
Snaggletooth shark
Pigeye shark
Dusky shark
Common sawshark
Common guitarfish
Smooth hammerhead shark
Requiem shark (to genus only)
Wedgefish (to genus only)
Sawfish (to genus only)
Bull Shark Image Credit: Jillian Morris
Spot Tail Shark Image Credit: Fishbase- Tassapon Krajangdara
Most of the fins in the study belonged to bull sharks and spot-tail sharks. While these species have been discovered in other Southeast Asian markets, they usually make up only a small percentage of the species found. The high number of bull shark and spot-tail shark fins available at market might mean there is a targeted fishery for these species in the area. However, neither of these species is protected by CITES, despite being classified as Near-Threatened by the International Union for Conservation of Nature (IUCN).
Shark fins dried and drying Credit: Jillian Morris, Gary Stokes
A huge piece of the conservation puzzle is knowing which species are at risk. When fins available at market have almost no identifiable features, it is difficult to determine if protected species are still being targeted in fisheries. Using DNA barcoding, the researchers in this study were able to get a better picture of the species composition available in markets in Malaysia. This information can be used to create policies and inform law enforcement. The researchers suggested continued monitoring of species available for sale to aid conservation and management.
References:
Seah, Y.G., Kibat, C., Hew, S. et al. DNA barcoding of traded shark fins in Peninsular Malaysia. Rev Fish Biol Fisheries (2022). https://doi.org/10.1007/s11160-022-09713-y