Assessing Indonesian manta and devil ray populations through historical landings and fishing community interviews

Abstract

International concern is growing with regard to the sustainability of manta and devil ray (collectively mobulids) fisheries as demand for mobulid products has increased in international markets over the last decade. While Indonesia has been reported to be one of the worlds’ top three catchers of mobulid rays, detailed information on these fisheries and the status of Indonesian mobulid populations are lacking. Through collection of historical and recent mobuild fisheries data from published and unpublished sources, this study aimed to identify trends in abundance of Indonesian manta and devil rays and explore socio-economic factors and incentives associated with mobulid fisheries. Comparison of catches from 2001-5 to the most recent data from 2013-14 revealed dramatic declines in mobulid landings over the study period of 64% at Cilacap, 75% at Lamakera, and 94% at Tanjung Luar. The largest declines were observed for Manta spp. and the two large devil rays, Mobula tarapacana and Mobula japanica. Anecdotal reports indicated that catches had declined substantially at three additional sites and local extirpations are strongly suspected to have occurred at three locations. A lack of data on the population ecology of Indonesia’s mobulids makes it difficult to determine whether natural fluctuations may be playing a part in the declining catch rates. However, mobulid life history traits, including low reproductive rates and late age of sexual maturation, indicate that fishing pressure is likely the primary driver in these declines. Interviews in Lamakera, a community which depends on income from its targeted mobulid fishery, suggest that programs focused on education, training and infrastructure development to enable shifts to sustainable livelihood alternatives are likely to offer the most successful path to long-term conservation and management of manta and devil rays, while simultaneously yielding economic and social benefits to fishing communities.