Anecdotal evidence suggests mantas are under threat, and China may be a major reason for it.
Manta rays are vulnerable on two fronts: as bycatch — getting caught in industrial fishing nets targeting different types of tuna — and, increasingly, because of traditional Chinese medicine, or TCM.
Manta rays are harvested for their gill rakers, which allow the fish to filter food from water. Some Chinese believe they have healing properties or are good at cleaning out toxins. One Chinese-language website claims gill rakers enhance the immune system, promote blood circulation and aid in the treatment of cancer, skin disease and infertility.
“It’s just cartilage,” said Dewar, echoing skepticism expressed by many scientists.
The article makes two more interesting points. One, that the number of mantas living and the number caught are unknown. But their reproduction is slow so that bodes ill for their recovery from heavy capture which is suspected. Second, the use of gill rakers is apparently NOT traditional. There is no history of it as medicine. It’s just a fad.