(CN) – The National Marine Fisheries Service proposed threatened status for the giant manta ray, under the Endangered Species Act, but determined the reef manta is not currently imperiled. The action is in response to a November 2015 petition filed by the Defenders of Wildlife conservation organization.
The agency’s 12-month review acknowledged that increased demand for manta ray gill rakers for supposed health benefits in the Asian market, combined with other threats, has depleted some populations of the giant manta ray up to 95 percent. Gill rakers are cartilaginous projections involved with filtering tiny prey, such as plankton, that is suspended in the water that passes through the gills. The rakers are not involved in the gas exchange of the breathing process.
“We’re pleased to see that the National Marine Fisheries Service is taking the plight of the giant manta seriously. We are disappointed that the agency did not propose to list the reef manta ray,” Defender’s senior staff attorney Jane Davenport said. “Both species face serious threats. Climate change is changing the distribution of their planktonic prey and damaging the health of their coral reef habitats. Microplastic pollution is a growing threat to these filter feeders. Manta rays are also victims of an all-too-familiar exploitation, where a big animal is killed for a small, but very lucrative, part of its body. The trade in manta ray gill plates has exploded in recent years, and low reproductive rates means that these slow-growing populations simply cannot keep up with the insatiable demand. When you add the thousands of manta rays that are killed as bycatch in nets meant for other fish, you get two species on the brink of crisis.”
Giant manta rays have been measured up to 23 feet wide and can weigh as much as a ton, the agency said. Each giant manta can yield up to 15 pounds of dried gill rakers, or plates, going for more than $300 a pound, according to the Defenders. Up to 99 percent of the market for gill plates goes through China, with an estimated $5 million in annual trade, representing more than 4,500 mantas killed per year, according to the group’s petition.
Although they are also caught for their meat, cartilage and skin, the interest in manta ray gill rakers for their healing properties has significantly increased demand, “incentivizing fishermen who once avoided capture of manta rays to directly target these species,” the agency noted.
“Manta rays are valued for their gill rakers, which are traded internationally, and the best information available indicates that the giant manta ray has experienced potentially significant population declines in the Indo-Pacific and eastern Pacific portions of its range from fisheries-related mortality,” agency spokesperson Kate Brogan said. Mantas are found in all the ocean basins of the world, according to the proposal.
According to the listing action, the “the use of gill rakers as a remedy, which was widespread in Southern China many years ago, has recently gained renewed popularity over the past decade as traders have increased efforts to market its healing and immune boosting properties directly to consumers,” such as “curing diseases from chicken pox to cancer, boosting the immune system, purifying the body, enhancing blood circulation, remedying throat and skin ailments, curing male kidney issues, and helping with fertility problems.”
However, the Defenders maintain that the increased market for manta gill rakers over the past decade is due to spurious claims for supposed medicinal purposes that are not part of traditional Asian medicine practices.
“The gill rakers are marketed as being anti-inflammatory, clearing away heat and toxic material, and eliminating stasis to activate blood circulation. There is absolutely no scientific proof to back up these claims, and there are not even any records in the traditional Chinese medicinal texts which list manta or mobula rays gills as being used in this way. So it appears as though this is a fairly new product, clever marketing of a readily available and cheap bycatch source from the fisheries. Marketed as a ‘medicine’ on the basis that because mobulid rays are capable of filtering the water to catch their food, their gill rakers when consumed can also filter and remove toxins from our human bodies,” researcher Guy Stephens was quoted as saying in the Defender’s petition.
The manta rays are also threatened by climate change, which affects their planktonic prey, from tiny plastic beads, used mainly in cosmetics, that clog their gills, and from entanglements in fishing gear and boat strikes, particularly from tourist boats that take groups out to known sites to view the huge graceful creatures as they congregate to feed, or to be cleaned of parasites by smaller fish.
As with many long-lived species, their own low population growth rate also adds to the combined effects of these threats. Giant mantas are slow to reach reproductive maturity, and a female may give birth to only 5 to 15 pups in her lifetime. Their population growth rate is one of the lowest among shark and ray species, the agency said.
Comments are due March 13 and public hearing requests are due by Feb. 27.