Inferring leader-follower behavior from presence data in the marine environment: A case study on Reef Manta Rays

October 2025

Juan Fernández-Gracia, Jorge P. Rodríguez, Lauren R. Peel, Konstantin Klemm, Mark G. Meekan & Víctor M. Eguíluz

Summary: In Muncar, East Java, Indonesia, five mobulid ray species are caught primarily as bycatch in drift gillnets, with juveniles dominating landings. Pelagic longlines and purse seines also contribute to captures. Spinetail devil ray (Mobula mobular) catch rates have declined sharply over 2015–2024, and fishers perceive a general decrease in mobulid availability. Rays are used locally for smoked meat and, occasionally, gill plates enter international trade. The Bali Strait appears to serve as a key juvenile habitat. The study highlights urgent conservation needs, advocating expanded legal protection, bycatch mitigation, and socio-economic strategies for sustainable fisheries management.

Abstract

“Mobulid rays (genus Mobula) comprise ten species of highly threatened filter-feeding rays, seven of which occur in Indonesia and five of which are caught in small-scale fisheries off Muncar, East Java. We conducted a study in Muncar from 2015 to 2024 to assess mobulid ray catch composition, trends in mobulid ray catch rate, demography, and the socio-economic context of their fisheries through fish market surveys (n = 1467) and interviews with fishers (n = 30), fish collectors (n = 4), and processors (n = 15). The study shows that mobulid rays are at high risk from target and bycatch in Muncar and are mainly caught in drift gillnets. A declining trend in the catch rate of M. mobular, compounded by mobulid ray declines reported by fishers, and a majority of immature specimens across Muncar’s fisheries indicate that mobulid rays are likely overfished in East Java. Illegal landings of M. birostris and M. alfredi, and evidence of mobulid gill plate trade intended for international exportation highlight an urgent need for better enforcement of existing national protections and international conservation provisions. This study highlights a critical need for improved conservation of all mobulid ray species in Indonesia given their high extinction risk and the unsustainable fishing pressure they face. This will require swift enforcement of CITES through better trade control, improved protective legislation, and fisheries management for all mobulid ray species, with measures targeted toward local fisheries characteristics and socio-economic context.”

Full publication

Author Affiliations

  • Instituto de Física Interdisciplinar y Sistemas Complejos IFISC (CSIC-UIB)

  • Australian Institute of Marine Science, Indian Ocean Marine Research Centre (IOMRC), University of Western Australia

  • Save Our Seas Foundation

  • The Manta Trust

  • Oceans Institute, University of Western Australia

  • Ocean Sciences and Solutions Applied Research Institute

Funding

  • MISLAND

  • CSxAI

    Govern de les Illes Balears

  • Save Our Seas Foundation

  • The Manta Trust and SOSF