Manta and mobula rays span the tropics of the world and are among the most captivating and charismatic of marine species. However, their survival is severely threatened by growing fisheries pressure driven by demand for the gill rakers that the animals use to filter feed. This project is the first global assessment of what is currently known about manta and mobula biology, the threats they face, the fisheries and trade that target them, non-consumptive and sustainable uses for communities to profit from them, current conservation measures and urgent steps recommended to prevent regional extinctions.
Global manta and mobula ray populations are currently unknown. Even the leading scientists interviewed for this project were not prepared to offer estimates on global populations for any species. Likewise, many questions remain unanswered regarding their biology and behavior. What is known, however, is that these species are slow to mature (8-10 years+), are long-lived (40 years+), and reproduce very slowly. A manta ray will give birth to as few as a single pup every two to five years. By comparison, the Great White Shark, a highly vulnerable species protected under Appendix II of CITES, may produce more young in one litter than a manta ray will in her entire lifetime. Further underscoring the vulnerability of manta rays, scientists believe that specific regional populations may be genetically different from other populations.
These characteristics make manta and mobula rays extremely vulnerable to overfishing, regional depletion and local extirpation. While they are also taken as bycatch in certain fisheries, these rays are subject to significant directed fishing pressure throughout their range. Indonesia, Sri Lanka and India have the largest documented fisheries, with targeted fisheries also reported in Peru, Mexico, Thailand, China, Mozambique, Ghana, and other locations. Total annual documented global landings are ~ 3,400 mantas (M. birostris only) and ~94,000 mobulas (all species). Unreported and subsistence fisheries will mean true landings are likely much higher.
While local subsistence fisheries for meat have been carried out for centuries, in the past decade the growing markets for gill rakers have significantly increased fishing effort. A mature Manta birostris (oceanic manta ray) can yield up to 7 kilos of dried gills that retail for as much as US$500 per kilo in a market in China. Established shark fin trade networks have exploited the opportunity to profit from gill rakers, especially as shark populations have declined.
Historically both fisheries and markets have been largely undocumented and completely unregulated. Consequently many of these fisheries are in rapid decline. The past decade has seen significant declines in both number and size of manta rays landed in primary fishery sites in Indonesia, Mozambique, India and Thailand. M. birostris has all but disappeared from the Sea of Cortez. Fishermen in the Philippines reported a 50% decline in manta ray landings from the 1960s to 1990s, and in Sri Lanka, fishermen also reported declines in catches.
Manta and mobula gill rakers are promoted as a cure for a wide array of ailments from chickenpox to cancer in some Chinese communities. Gill rakers are sold primarily in Chinese markets and directly marketed by importers from the hub of the trade in Guangzhou, Southern China. Guangzhou trade is as much as 99% of the global market. Market analysis suggests total annual gill raker trade volume in excess of 61,000 kg (and perhaps as high as 80,000 kg) with an estimated value of US$11.3 million per year.
Despite the marketing, a number of Traditional Chinese Medicine (TCM) practitioners stated that gill rakers are not a legitimate acknowledged component of mainstream TCM. No interviewees were able to locate any references in TCM texts, and one practitioner confirmed that gill rakers are not included in the official TCM manual. Several interviewees admitted belief that gill rakers were not effective and suggested that many alternatives were available. No vendors offered any evidence of efficacy in the product.