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.
See on www.mantatrust.org