Better the devil you know: towards sustainable management of devil rays in the Indian Ocean

"Devil rays (Mobula sp.) are large, planktivorous and highly mobile species, with a circumglobal distribution in tropical and warm temperate waters.
Six out of the eight described species are found within the Indian Ocean classified as endangered (M. mobular), data deficient (M. kuhlii), vulnerable (M. alfredi, M. birostris, and M. tarapacana) and near threatened (M. thurstoni) by the IUCN redlist. The growing wildlife trade for their gill plates, used for food and traditional medicine in East Asia, is driving the expansion of targeted devil ray fisheries (O'Malley et al., 2017) but it is unknown if populations can sustain growing exploitation levels. The limited information on the life history of devil rays suggests they display extreme k-selected traits, including extremely low fecundity, producing a single pup annually or biannually. This makes it unlikely that current exploitation is sustainable. Devil rays are common in small-scale fisheries (SSF), which provide an important source of protein and income for coastal communities worldwide (Béné et al., 2007). SSF fisheries are prevalent but poorly documented and largely unregulated in the Indian Ocean (e.g. Temple et al., 2018). Ensuring SSF sustainability is vital in protecting the livelihoods of these coastal communities, with declines in high value species, such as devil rays, likely having negative implications on these peoples. Evidence-based assessment of devil rays is inhibited by the lack of available data, with knowledge gaps across all species for abundance and population trends; distribution and migratory patterns; life history; spatial and temporal ecology; and fisheries catch rates, composition and trade. Given the global threat, the IUCN Species Survival Commission and Shark Specialist Group have produced a Global Devil and Manta Ray Conservation Strategy, where the Indo-Pacific is listed as a priority region (Lawson et al., 2017). This project aims to address current data gaps to work towards regional assessment of devil ray species in the Indian Ocean, in line with this strategy. The genetic population structure of devil rays in the Indian Ocean will be investigated, defining management units and informing trans-national management actions where shared stocks of devil ray species exist. Age and growth will be determined for each species sampled to inform future fisheries management. Further life history data (e.g. maturity and fecundity) will be collected to determine parameters (e.g. age-at-maturity and rebound potentials) vital for future stock assessment. The methods and outputs of this work will be applicable to other devil ray species and regions globally."