This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Demand for the gills of manta and mobula rays has risen dramatically in the past 10 years for use in traditional Chinese medicine (TCM), even though they were not historically used for this purpose, a team of researchers from the conservation organizations Shark Savers and WildAid has discovered.
"We first came across manta and mobula ray gills in Asian markets several years ago, and followed the trail to the dried seafood markets of southern China," Manta Ray of Hope Project lead investigator Paul Hilton said in a prepared statement (pdf) released on January 14. Specifically, the market was for gill rakers, the thin filaments that manta and mobula rays use to filter food from the water, which are being sold for up to $500 per kilogram. TCM practitioners are marketing the rakers—known locally as peng yu sai—as an ingredient for soup that they claim boosts the immune system by reducing toxins and enhancing blood circulation. Other supposed medical benefits include curing cancer, chickenpox, throat and skin ailments, male kidney issues and, as we often see with TCM, fertility issues.
None of these purported medical claims are supported by science nor are they supported by traditional Chinese medicine texts. According to the report, "One TCM practitioner interviewed reviewed all 6,400 remedies of the official TCM reference manual and found that peng yu sai was not listed. Practitioners interviewed admitted that gill rakers were not effective and many alternatives were available. In fact, many young TCM doctors are not even aware of this remedy, indicating that it is not included in current TCM curricula."
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Despite their non-traditional usage, the researchers estimate the market for gill rakers to be at least 61,000 kilograms a year, with an estimated value of $11.3 million. As much as 99 percent of the market for these rakers was in Guangzhou, the capital city of China's Guangdong Province. The researchers found that some of the gill raker trade is conducted by the same networks responsible for the devastating trade in shark fins, which have turned to rays for additional profits as worldwide shark populations decline.
Interestingly, the researchers found that the fishermen catching the animals dramatically undervalue their product. The greatest economic value from manta and mobula rays, according to the report, comes not from consumption but from tourism, because divers and other ocean tour visitors love to see them in the wild. The researchers found that direct tour operator revenue at just seven sites totals $27 million a year, and estimated the global tourism value of rays at more than $100 million yearly.
Population estimates for manta and mobula rays do not exist, but it is known that the number of these animals caught by fishermen in some areas has declined 50 percent since the 1960s. Beyond that, information on these creatures is hard to come by. Of the 11 manta or mobula ray species listed on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species, five are listed as "data deficient." Only one species—the giant devilray (Mobula mobular)—is listed as "endangered." Very little international protection exists for any of these species. Manta rays (Manta birostris, Red List status: "vulnerable") were added to the Convention on the Conservation of Migratory Species of Wild Animals in 2011, but this only protects them in international waters outside national borders.
The researchers recommend creating international trade moratoriums on the import and sale of gill rakers; educating consumers that TCM health claims are unverified and that the animals have more value in the water than out of it; establishing international protections under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES); and protecting critical manta ray habitat.
"If action is not taken quickly, manta and mobula rays will likely face regional extinctions because of unregulated fisheries," stated Michael Skoletsky, executive director of Shark Savers. "Anyone who has gone diving with mantas knows them to be intelligent, graceful and engaging animals. It would be a tragedy to lose them."
A 2009 IUCN study found that 32 percent of all pelagic (open-ocean) shark and ray species (collectively known as chondrichthyan fishes) are at risk of extinction.
Photos: Manta ray fishery, © Manta Ray of Hope Project. Manta ray swimming by Forrest Samuels via Flickr. Used under Creative Commons license