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DNA detective work reveals where in the ocean shark fins came from

  • A team of international researchers developed a method of using DNA analysis to trace the origins of shark fins, and to determine if vulnerable and endangered species were being trafficked.
  • Sharks are highly valued for their fins, which are used in a luxury food item, shark fin soup, commonly sold in Hong Kong and China. The global trade of shark fins is responsible for killing more than 73 million sharks each year.
  • Using DNA analysis, the researchers identified that scalloped hammerheads, a critically endangered species, were being fished out of the eastern Pacific Ocean between Baja California and northern Peru.
  • The researchers are currently working with government agencies and NGOs to help inspectors conduct rapid in-port DNA testing on shark fins to identify species and location of origin.

In 2013, Demian Chapman ambled down the streets in the Sheung Wan district in Hong Kong, where thousands of yellowed shark fins were drying on the sidewalk, or packed in clear plastic bags, ready for a quick sale.

“I saw more sharks in the form of fins on the street in one afternoon than I had in an entire career working in the ocean,” Chapman, a scientist at Florida International University, told Mongabay. “I asked myself, ‘What can I do as a geneticist to unlock this trade?’”

Shark fins being dried on the street in Hong Kong. Image by Ocean Asia.

As many as 73 million sharks end up in the global shark fin trade each year, with the fish being killed 30 times faster than they can reproduce, according to a report by the Washington, D.C.-based NGO Oceana. Fishermen mainly target sharks for their fins, which are used to make shark fin soup, a luxury food item that can fetch exorbitant prices. The fins are so valuable, it’s become a common practice for fishermen to cut off the fins from a living shark, then throw the animal back into the water, where the sharks, unable to swim, will slowly drown.

More than 70% of the fins that end up in Hong Kong come from vulnerable or endangered species, including scalloped hammerheads (Sphyrna lewini), great hammerheads (Sphyrna mokarran), and oceanic whitetips (Carcharhinus longimanus), despite the fact that they’re protected by CITES, an international treaty used to prevent endangered animals and plants from being illegally traded. When shipments of shark fins arrive in Hong Kong, it is sometimes possible for inspectors to visually identify the species, but once the fins have been skinned and bleached in preparation for sale, they tend to look alike, Chapman said.

These concerns led Chapman and a team of researchers to embark on an ambitious project: they developed a way to analyze the DNA from shark fins to determine if vulnerable and endangered species were being caught up in the trade, and to identify the origins of trafficked species. Their findings were recently published in Animal Conservation.

Shark fins for sale in the Sheung Wan district in Hong Kong. Image by Stan Shea.

In Hong Kong, a team of local collaborators purchased shark fin “trimmings” consisting of cartilage, muscle and skin cut off from the main part of the fin, and sold to customers who want to make an inexpensive version of shark fin soup, according to Chapman. However, the DNA in these trimmings is “pretty degraded,” Chapman said, so he and his colleagues needed to amplify what was in there.

“We use a polymerase chain reaction (PCR) to make millions and millions of copies of this tiny little fragment of the part of the genome that they inherit from the mother,” Chapman said. “It’s like a barcode that we can put it into a database, and it tells us what species we’re looking at.”

The team focused their DNA analysis on the scalloped hammerhead, a critically endangered species that’s commonly traded in Hong Kong. This shark was a natural choice because of the existing library of DNA data on the species, as well as its tendency to return to the same place in the ocean for breeding, which makes its genetic makeup easy to identify.

“They have these nine distinct populations … because the females are homing back to a certain region to give birth,” Chapman said. “Because they’re doing this generation after generation, you get these distinct signatures in the DNA zip code that are associated with regions, and we can read those, so we can trace them back.”

A scalloped hammerhead, a critically endangered species. Image by Deron Verbeck.

The study found that most scalloped hammerheads traded in Hong Kong were coming from the eastern Pacific Ocean between Baja California and northern Peru, where the species is undergoing a sharp decline. Chapman and his team are currently working to use DNA analysis to identify other shark species being traded in Hong Kong, and they hope their detective work can help protect vulnerable species and immobilize illegal activity.

However, monitoring the shark fin trade in Hong Kong isn’t easy. “So many shipments are coming into Hong Kong, but not very many get inspected,” Chapman said.

Gary Stokes of Oceans Asia, who has spent the past 20 years investigating the shark fin trade in Hong Kong, corroborates this claim.

“Only 1% of all containers are inspected,” Stokes told Mongabay. “Shark fin traders nowadays often mislabel shipments as many shipping lines refuse to carry shark fins. So in almost all cases, the shipments will never even be inspected. For those that do get inspected, often by untrained officers, one shark fin looks like another. Traders will also bury endangered shark fins in the middle of legal shark fins. This makes it almost impossible to detect.”

Shark fin trimmings drying on the street in Hong Kong. Image by Stan Shea.

It can also be difficult to tell where sharks were fished, even if officials trace a shipment of fins back to its source, Stokes said.

“We have on some shipments been able to trace back to the country that the fins were exported from, however a shipment [of sharks] from, say Nicaragua, may not have been caught there, just landed by vessels fishing on the high seas,” Stokes said.

Since the onset of the COVID-19 pandemic, many restaurants and shops in Hong Kong have been closed, and large events like weddings, where shark fin soup is a commonly served delicacy, have been temporarily banned. Yet Stokes says the trade hasn’t stopped, and that shark fin stocks are “backing up.”

In fact, on May 6, Hong Kong customs officials intercepted an enormous 26-ton shipment of shark fins from Ecuador, the largest of its kind ever to be discovered in a Hong Kong port. It’s estimated that the fins come from about 38,500 vulnerable and endangered sharks, including common thresher sharks (Alopias vulpinus) and silky sharks (Carcharhinus falciformis).

One of the shipping containers holding 26 tons of shark fins that was intercepted in May 2020. Image by HK Customs.

Despite these setbacks, Chapman says he is hopeful that DNA analysis will help disable the trade. He and his team are currently working with the Agriculture Fisheries and Conservation Department in Hong Kong, as well as Oceana in Peru, to help inspectors conduct rapid in-port DNA testing to identify fins that can’t be visually identified.

DNA analysis of shark fins can also encourage local conservation efforts, Chapman said.

“If we know that the Pacific is supplying most scalloped hammerhead fins, then we know we need to make big investments in that region for conservation,” Chapman said. “So eventually, it should have an effect, or hopefully would have an effect, on people doing any sort of illegal activity in that region.”

Citation:

Fields, A. T., Fischer, G. A., Shea, S. K., Zhang, H., Feldheim, K. A., & Chapman, D. D. (2020). DNA Zip-coding: Identifying the source populations supplying the international trade of a critically endangered coastal shark. Animal Conservation. doi:10.1111/acv.12585

Banner image credit: Shark fins set out to dry on a sidewalk in the Sheung Wan district of Hong Kong in 2011. Photo by Nicholas Wang via Wikimedia Commons (CC BY-SA 2.0).