Sharks and rays are some of the most enigmatic creatures in our oceans, yet there are few that are more fascinating and mysterious than manta and mobula rays. Known collectively as the mobulids, these inquisitive creatures range throughout the tropical and subtropical oceans of our world in search of the patches of zooplankton on which they feed. Mobulid rays are distinguished from other rays by their highly specialised filter-feeding behaviour: using their enlarged mouths and modified gill plates, they strain zooplankton, fish spawn and small fishes from the water around them.
These large-bodied and slow-growing animals have one of the lowest fecundity rates of all elasmobranchs. Their populations are small, highly fragmented and sparsely distributed around the world, and in fact no-one knows with any certainty just how large – or small – the global mobulid population really is. Collectively, their low fecundity, the small size of their local populations and their migratory and aggregating behaviour make mobulids extremely vulnerable to overexploitation and their populations slow to recover from any losses.
The greatest threat to mobulid rays is excessive take – both targeted and incidental – by fisheries, a take that increasingly is being driven by the international trade in gill plates for use in an Asian health tonic purported to treat a wide variety of ailments. As a result, some mobulid populations in South-East Asia, the Indian Ocean and Africa are showing declines of more than 80%. Of particular concern is the exploitation of these species in their critical habitats, where numerous individuals can be targeted with relatively high catch-per-unit effort. For such intrinsically vulnerable species, even small negative pressures on a population are likely to have severe consequences for its survival.
In view of their vulnerable life history traits and in response to the growing threat from the gill plate trade, several significant steps have been taken in recent years to improve the conservation status of mobulids. In 2011, the oceanic manta ray Manta birostris was listed on the Convention for the Conservation of Migratory Species (CMS). At the same time, both it and the reef manta ray M. alfredi were reclassified on the IUCN Red List of Threatened Species as Vulnerable. In 2013 collaborative efforts between researchers and NGOs saw the genus Manta listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) and the following year the reef manta ray and all mobula ray species were listed on CMS. More recently, in 2016 the genus Mobula joined manta rays on CITES Appendix II, driven by an impressive number of proposing governments, supporters and NGOs. Yet these growing protective measures notwithstanding, manta and mobula rays remain extremely vulnerable to exploitation.
Having started out in the Maldives, the Manta Trust is now active in about 16 countries worldwide promoting the conservation of manta and devil rays and their habitat through research, awareness and education. Three of its current major operations are the Global Mobulid ID Project, which aims to provide a taxonomic, morphological and genetic identification guide to manta and devil rays; the collection of data about ray landings in India, which will inform conservation management in that country; and the Indonesian Manta Project, which works to promote an appreciation of manta and devil rays among local people.