Humans and Manta Rays: Declining Numbers, Threats and Chinese Medicine | Sea Life, Islands and Oceania

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THREATENED MANTA RAYS

Manta ray at Dharavandhoo, an island in the Maldives

Manta rays and devil rays are netted for their gill plates, which are in high demand for use in a Chinese tonic, and caught as bycatch by commercial fishers. As of 1994 only one species, giant devil ray, was listed as vulnerable to extinction. Now more species are. In general, sharks and rays are vulnerable to overfishing. They grow and mature slowly, and the size of the adult population closely determines the number of young produced, due to their “slow” reproductive strategy of investing a great deal of energy in relatively few young over a lifetime. [Source: Animal Diversity Web (ADW)]

The International Union for Conservation of Nature (IUCN) Red List lists manta rays as Vulnerable. The Convention on International Trade in Endangered Species (CITES) places them in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. In 2018, NOAA Fisheries listed the species as threatened under the Endangered Species Act.

Whether accidental or intentional, fishing has caused an estimated 30 percent decrease in populations of reef manta rays globally. There is also concern that climate change could affect plankton abundance and thereby reef manta ray populations. It takes manta rays eight to ten years to reach sexual maturity, and in their 30-year lifetime they can expect to produce a maximum of 16 “pups”. [Source: Animal Diversity Web]

Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems

Declining Manta Ray Populations

dead mantas

Decline of of manta rays and devil rays:
Giant manta ray numbers declined by 86 percent between 2005 and 2020 in some places.
Reef manta ray populations fell by 98 percent between 2005 and 2020 in some places.
Shortfin devil ray numbers dropped by 91 percent loss over 15 years between 2005 and 2020 in some places. [Source: Mónica Serrano and Sean McNaughton, National Geographic, July 15, 2021]

Information on the global distribution of giant manta rays and their population sizes is lacking. Regional population sizes are small, ranging from around 100 to 1,500 individuals, and in areas subject to fishing, have significantly declined. Ecuador is thought to be home to the largest population of giant manta ray, with large aggregation sites within the waters of the Machalilla National Park and the Galapagos Marine Reserve. Overall, given their life history traits, particularly their low reproductive output, giant manta ray populations are inherently vulnerable to depletions, with low likelihood of recovery. Additional research is needed to better understand the population structure and global distribution of the giant manta ray.[Source: NOAA]

Frank Pope wrote in The Times: In Mozambique, where some of the highest densities are to be found, populations have plummeted by 85 percent in a decade. Precipitous declines have also been recorded in India, Indonesia and Sri Lanka, and they have all but disappeared from the Sea of Cortez, Mexico, where they were once abundant. [Source: Frank Pope, The Times, January 14, 2012]

Threats to Manta Rays

The main threat to the giant manta ray is commercial fishing, with the species both targeted and caught as bycatch in a number of global fisheries throughout its range. Manta rays are particularly valued for their gill rakers, which are traded internationally and used in Chinese tonics. In Asia, manta rays are targeted by fisheries. The cephalic horns are sold for medicinal purposes or as delicacies. [Source: NOAA]

Other threats including entanglement in fishing nets, marine debris and pollution, recreational fishing interactions and vessel strikes. Giant manta rays are most susceptible to industrial purse-seine and artisanal gillnet fisheries.

Demand for the gills of manta and other mobula rays has risen dramatically in Asian markets. With this expansion of the international gill raker market and increasing demand for manta ray products, estimated harvest of giant manta rays, particularly in many portions of the Indo-Pacific, frequently exceeds numbers of identified individuals in those areas and are accompanied by observed declines in sightings and landings of the species of up to 95 percent.[Source: NOAA]

A shortage of shark fins has led suppliers to look for other sources to meet demand. Among the sources they are turning to are the wings of manta rays. They are targeted because the swim near the surface and are easy to catch and their wings are big. Most the fins end up in a poor man’s shark fin soup made ray cartilage and low grade shark fins.

Manta Ray Hunts and Pearl Divers

Moche manta ray, the Moche lived in Peru from about AD 100 to 700

Whalers from the village of Lamalera on Lembata, a harsh volcanic island near Flores in Indonesia hunt manta rays by jumping on their backs. Describing this Jeffrey Gettleman wrote in Los Angeles Times, "The fishermen stroked across the water, scanning for signs of life. After hours of searching, one sinewy fisherman, Francise Bole Beding, saw a black fin pop through the surface...Paddlers yanked in their oars. Mr. Beding, a harpooner, scampered to the bow, a crude spear in his hands. He coiled himself, preparing to leap down onto the prey and drive harpoon deep into its flesh.”

"The sight of a fin cutting through the water focused all minds on what swam below. Mr. Beding saw it was a manta ray, not a whale, and because the giant rays are swift swimmers, he had to attack quickly... Mr. Beding leaped. The rope tied to the end of his harpoon spooled out furiously. The boat careened to the side as the three-meter-wide manta tried to bolt, a harpoon driven deep into its back. Mr. Beding fought the fish in a cloud of red water until two men plunged overboard with heavy iron hooks to finish it off...The paddlers dragged the limp, 136-kilogram fish up on the deck. Mr Beding and the other men wriggled back into the boat."

Pearl diver Yashinori Maeda was almost killed by a manta ray that became entangled in his diving gear. He told National Geographic, "I was collecting oysters 70 feet down when a giant manta snagged my air hose and safety line. Then it must have panicked. It was so strong that it pulled my helmet off the breastplate, breaking the screw threads...Wearing lead shoes and a lead belt, I could not swim to the surface. I was drowning when my tender saw I was in trouble and pulled me up."

Manta Rays as Tourist Attractions

Manta ray in Yap
The presence of reef manta rays contributes to eco-tourism in areas such as Hawaii, East Africa, and Indonesia. In certain locations, tourists can be charged up to $3,000 to dive with mantas. Manta tourism in just seven sites was worth US$25 million a year in direct revenues in the early 2010s. It is estimated that worldwide tourism-related earnings are in the region of US$100 million a year, with a single manta being worth up to US$1 million over its lifetime. [Source: Frank Pope, The Times, January 14, 2012]

Because of their accommodating nature, mantas today have achieved the dubious status of dive-tourism attractions, luring humans to swim with them in closer-than-optimum quarters. For a species considered near threatened, however, this newfound popularity could literally be a lifesaver. Mantas, with their slow reproductive rate, are vulnerable to overfishing, so a robust tourist trade could give local communities an economic incentive to conserve the fish rather than kill them. It's a delicate balance, though — too many humans could drive mantas out of feeding grounds like Hanifaru Bay.

To avoid that, Stevens has proposed turning the bay into a marine sanctuary. A new Maldives president has vowed to strengthen the archipelago's marine protections, but his government has so far been slow to respond to Stevens's idea. "I'm not ruling out declaring Hanifaru a marine-life sanctuary. But we need to increase our ability to enforce existing environmental laws before creating new protected areas," says Environment Minister Mohamed Aslam.

In the Maldives, Stevens continues to catalog the local animals. (He's identified more than 1,500 individuals by their unique spot patterns.) His data also record the exact timing of the feedings, information that would be of great value to the local guide industry. Stevens hears the clock ticking, and he is scrambling to organize a self-policing regime among resorts and local guides before dive tourists overrun Hanifaru. "We don't want to ruin what we've got here," he says. If his plan works, Hanifaru Bay will remain a sanctuary for cyclone-feeding manta rays, with just enough room for whale sharks, and humans as well.

Chinese ‘Tonic’ Threat to Vulnerable Manta Rays

A little-known “coastal tonic” from Southern China has been resurrected by shark fin traders in the city of Guangzhou, according to a report published in in 2012. Among the ingredients of the tonic, which include endangered seahorses, pipefish and ginseng, is manta ray, driving a surge in demand for the vulnerable species.[Source: Frank Pope, The Times, January 14, 2012]

Frank Pope wrote in The Times: The most valuable part of the giant sea creatures is their gill rakers, which trap food before it passes over their gills. In Guangzhou, home to 99 percent of the trade, the average price for the intricately shaped cartilage is £160 a kilo, but it can fetch up to double that. Between 61 and 80 tonnes of gill rakers are sold in the town every year, with an estimated value of US$10 million. Traders in the city are already reporting a decline in the availability of large specimens.

Shawn Heinrichs, co-author of the report, which was funded by the charities WildAid and Shark Savers, said that traders were using existing shark trade networks to profit from the new demand for mantas. “Shark fin distribution networks are well established, and once you have a trading network you push new products through it,” he said.

Demand for the gills of manta and mobula rays rose dramatically in the 2000s for use in traditional Chinese medicine (TCM), even though they were not historically used for this purpose. "We first came across manta and mobula ray gills in Asian markets and followed the trail to the dried seafood markets of southern China," Manta Ray of Hope Project lead investigator Paul Hilton said.[Source: John R. Platt, Scientific American, January 17, 2012]

Scientific American reported: 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."

Protections for Manta Rays

Giant Manta rays 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 United States, Republic of Maldives, Philippines, and Western Australia have all established regulations or sanctuaries in an attempt to maintain healthy populations.

Conservationists are pushing to have international trade in the species banned through the UN wildlife trade convention. They recommend, according to The Times, “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. [Source: John R. Platt, Scientific American, January 17, 2012]

The Convention on Migratory Species’ 116 member parties baned fishing for giant manta rays and impose measures to safeguard their habitat after the group voted to protect the species. But efforts to address overutilization of the species through current regulatory measures are inadequate, as targeted fishing of the species still occurs despite prohibitions in a significant portion of the species’ range. Also, measures to address bycatch of the species in industrial fisheries are rare.[Source: NOAA]

Manta rays don’t “have any way of adapting to survive human pressures,” says Joanna Harris, a researcher at Manta Trust, a U.K.-based nonprofit. “The only way to halt the decline is to take action.” Harris, a doctoral candidate at the University of Plymouth, is working to understand environmental cues that prompt the fish to migrate, sometimes hundreds of miles, in search of food. How does it know where to go next, and when? A change in wind direction, which affects surface currents, appears to play a role. She says government officials, conservationists and scuba outfitters who lead reef manta ray-watching trips could all use such information to benefit the animals. [Source: Terence Monmaney, Smithsonian magazine, October 2022]

Protections seem to be effective in the Maldives, where catching reef manta rays is prohibited and rangers limit access to certain lagoons when the animals aggregate to feed. The island chain plays host to the world’s largest population of the majestic fish, with more than 5,000 individuals counted. The dark spot pattern on the underside of each one is unique and serves as an ID. The reef manta ray in this photograph, according to a Manta Trust database, is a juvenile male. His name is Naba.

Reef Manta Rays Thrive in Indonesia Thanks to Conservation Efforts

Raja Ampat archipelago in West Papua is home to Indonesia’s largest population of reef manta rays. Not so far away their populations have been depleted due to overfishing in East Nusa Tenggara and North Sulawesi in Indonesia, the Philippines and Papua New Guinea as well as in Mozambique in Africa. Edy Setyawan wrote in The Conversation: In Raja Ampat, there were anecdotal reports from the local community suggesting that reef manta rays were often caught unintentionally by non-local shark fishers. In the 1990s and early 2000s, sharks were heavily caught in Raja Ampat using large gillnets and longlines, not to mention other illegal and destructive fishing practices by outsiders. [Source: Edy Setyawan, Marine Ecologist, University of Auckland, The Conversation, November 24, 2022]

To protect marine biodiversity and ensure food security for local communities, the Raja Ampat government officially developed a marine protected area network in 2007. Since then, manta rays in the region have begun to enjoy some protection.Our new research, published in Frontiers in Marine Science, found reef manta ray populations in Raja Ampat have thrived over a decade of our study. This study suggests that the long-term implementation of conservation and management efforts implemented by Raja Ampat government has been fruitful.

Our research team managed to collect and curate manta ray images and sighting data from 2009 to 2019, thanks to citizen scientists and collaborators – especially divers and dive operators who contributed their manta ray photos. Unique markings on the underside of a reef manta ray that can be used to distinguish one from another through photographic identification. We used the sighting data to look into reef manta ray demographic trends in two marine protected areas with the most consistent data collection over a decade: Dampier Strait and South East Misool. In Dampier Strait, the estimated population increased from 226 to 317, with an annual compound growth rate of 3.9 percent. South East Misool’s population increased at a higher rate of 10.7 percent per year, from 210 to 511 individuals over a decade of study. The manta rays were estimated to have high survival rates. Each year, up to 93 percent of individuals in the populations survived. Furthermore, the populations typically saw a 20 percent boost from new individuals annually, which can be from newborns and/or larger rays from outside study areas. These resulted in the increase in manta ray populations in both marine protected areas.

The thriving populations of reef manta rays strongly suggest this species is well protected in Raja Ampat waters. Almost all known feeding and cleaning sites are located within the 2 million hectare marine protected area network. These sites, where manta rays frequently visit and gather for feeding and to be cleaned of parasites by cleaner fish, are important for their survival and health. We also found that El Niño events generated more intense upwellings (upward motion of seawater) – bringing cold and nutrient-rich water to the surface. These then increased opportunities for manta rays to feed in large feeding groups, enabling the manta rays to store much energy for reproduction and for mating.

During and shortly after the El Niño events, we observed high number of pregnant rays in the populations. Following this period, many of the expected baby manta rays likely live in sheltered nursery areas like Wayag lagoon or Fam Islands, both situated in Raja Ampat. They stay there for a few years – which could increase their chance of survival – before they are large enough to join adult populations, like those in the study areas. This research shows that it is not impossible to conserve large and highly migratory species such as reef manta rays. The series of conservation and management efforts implemented since 2007 by the Raja Ampat government has successfully minimised fisheries-related threats to manta ray populations. The creation of a network of nine marine protected areas actively patrolled by local communities and authorities have forced sharks fishers to relocate to areas outside Raja Ampat, or change their livelihood. The use of fishing gear like gillnets and longlines has been restricted throughout Raja Ampat waters. All of these have minimised shark fishing and the resulting potential of manta rays unintentionally being caught.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated April 2023