Manta and mobula rays are large filter feeding animals, whose flesh is considered to be of relatively poor quality by humans all around the world. As a result these animals have not been widely targeted for human consumption through commercial fisheries in the past. However, in recent years this has changed. Manta rays and their close relatives are now rapidly becoming a more desirable product, making them a target for fishermen all over the tropical and temperate oceans of the world.
So what has happened? Why the sudden change of fortunes for these unfortunate rays? The underlying answer to these questions is not a new story, in fact it’s a tale of depressing repetition played out in our oceans and throughout our planet on a regular basis. The difference this time is that the latest targets are the mantas, which are paying the price of becoming the latest commodity in the often senseless and environmentally destructive Chinese Medicinal Trade. The ray’s feathery gill plates, which they use to filter the plankton from the water, have become a product and as a result these harmless animals are paying the price of humanity’s selfish ignorance…
What are Gill Plates?
The gill plates, or branchial filaments, are thin cartilage filaments that enable the manta and mobula rays to filter plankton out of the water column. Every manta or mobula has five pairs of gills, each protected inside a gill slit.
Inside each of the ten gill slits there is one complete feathery gill plate which forms a circle around the periphery of the slit, trapping their planktonic food as it is funnelled through the mobula or manta ray’s mouth and out through these gill plates.
These plates, once dried, are the most valuable parts of the mobulid rays and drive the commercial fishery of these rays around the world, with particularly large fisheries present in India, Sri Lanka and Indonesia. Although the plates comprise just a tiny percentage of a manta or mobula’s mass, they sell for significantly more than the rest of the body parts put together.
While plates are used from both mobula and manta rays, the gill plates from mantas (usually oceanic manta rays; M. birostris) fetch the highest prices, followed by the larger species of mobulas (generally M. tarapacana and then M. japanica), with the price reducing as the size of the plates decreases.
The demand for gill plates is so high that in certain countries, such as Sri Lanka, fisherman who used to avoid catching mobulid rays, due to their propensity to destroy and entangle fishing nets, are now driven to fill their boat’s holds with mobulid rays when returning to harbour.
This demand, coupled with the dwindling supplies of more desirable fish catches (such as sharks, tunas and billfishes) now gives the fishermen even greater incentives to actively target mobulid rays in order to maintain their livelihood.
The international trade in mobulid gill plates which is being driven by the current demand in the Chinese Medicine trade appears to be a relatively new phenomenon, with demand significantly increasing in the last couple of decades. Those selling or promoting the use of this product claim the plates can treat health issues ranging from asthma, to skin rashes, to chicken pox and even cancer. Some of the practitioners also maintain that gill plates reduce toxins, boost the immune system and aid in the detoxification of the bloodstream.
However, reviews of available literature, along with interviews of well respected practitioners have revealed that there is no evidence to support any of these claims, with some practitioners even admitting that gill plates are not effective and that many other alternatives are available. Gill plates are often consumed in a soup (locally called “Peng Yu Sai”) which is made from a few main ingredients (gill plates, ginseng and dried pipefish) and are not considered “prestigious”, like shark fins, but are solely regarded as an ingredient in a medicinal product.
It appears that the increasing demand which has arisen in the last few decades is due to product marketing by Chinese retailers who have seen an opportunity, created by a relatively available commodity, to market a new product into the traditional medicine industry, falsely “reviving” this remedy which in reality does not even exist in the traditional literature. It appears as though one of the marketing strategies plays on consumers fears over the increasing prevalence of modern disease outbreaks such as Bird Flu, Swine Flu and SARS.
The sales pitch suggests that as these fishes are able to filter particles from the water with their gill plates, if consumed, these plates will therefore aid in the detoxification and purification of the consumer’s body by filtering these diseases or toxins from the human body. Most consumers are unaware that the product comes from manta and mobula rays, indeed most consumers are not even aware of what a manta or mobula ray is and therefore they have no idea of the impact their choices are having on these increasingly vulnerable species.
In order to maintain this supply of gill plates, large numbers of manta and mobula rays are being landed at fish markets around the world. This is having dire effects on the populations of mobulid rays and reports have already been published on decreases, or complete crashes, of ray populations around the world. It also appears that the giant oceanic manta ray (M. birostris) is likely to be the most heavily affected by this unsustainable and senseless fishery.
Identifying Mobulid Parts
One of the key factors to legally ending this trade is being able to accurately identify the gill plates of mantas and mobulas. In support of the successful 2013 CITES application for the genus Manta to be added to Appendix II of CITES The Manta Trust team and our close colleagues, with support from the Pew Environment Group and the Save Our Seas Foundation, put together a Field Identification Guide of the Gill Plates of Mobulid Rays which can be downloaded by following the link.