Oceanic manta rays aggregating near a major population center have far higher injury rates than at an offshore protected area

October 2024

P. Santiago Dominguez-Sanchez, Aldo Zavala-Jimenez, Iliana Fonseca-Ponce, Katherine R. Kumli, Robert D. Rubin, Joshua D. Stewart

Keywords: Mobula birostris • Conservation • Revillagigedo • Bahía de Banderas • Population threats • Bootstrapping

Summary: The oceanic manta ray (Mobula birostris), an endangered species, faces significant threats such as bycatch and vessel strikes, despite full protection in Mexico. This study compared injury rates between manta rays in the remote Revillagigedo Archipelago and the heavily trafficked Bahía de Banderas. From 2014-2022 in Bahía de Banderas and 1978-2020 in Revillagigedo, injury rates were much higher in Bahía de Banderas (31.7%) compared to Revillagigedo (5.2%), with many injuries linked to vessel collisions and fishing gear. The findings underscore the urgent need for enhanced conservation efforts, particularly in coastal regions with high levels of human activity.

Abstract

“The oceanic manta ray Mobula birostris is an Endangered species facing numerous anthropogenic threats that have led to population declines worldwide. Although oceanic manta rays are fully protected in Mexico, this species is still threatened by bycatch and vessel collisions, which jeopardize the population’s stability and recovery. This study compares the prevalence and types of injuries observed in oceanic manta rays between the remote Revillagigedo Archipelago National Park and Bahía de Banderas, an area of high vessel traffic and small-scale fisheries in Mexico. Using visual censuses and photo-identification techniques conducted from 2014 to 2022 for Bahía de Banderas and from 1978 to 2020 for the Revillagigedo Archipelago, we found significant disparities in injury rates between the 2 regions. The overall injury rate was substantially higher in Bahía de Banderas (31.7%) than in the Revillagigedo Archipelago (5.2%), with a notable proportion of injuries attributed to anthropogenic causes, particularly vessel collisions and fishing gear entanglement. Moreover, the severity and types of injuries varied significantly, with a higher incidence of major injuries in Bahía de Banderas. These findings highlight the importance of marine protected areas for oceanic manta rays and emphasize the critical importance of implementing targeted conservation measures, especially in coastal regions with high maritime activity, to safeguard oceanic manta ray populations from further decline. We encourage the community and stakeholders to implement conservation actions urgently to preserve the vulnerable oceanic manta ray population in Bahía de Banderas and other coastal areas inhabited by this species.”

Author Affiliations

  • Ocean Ecology Lab, Marine Mammal Institute, Oregon State University

  • Proyecto Manta Pacific México

  • The Manta Trust

  • Coastal Science & Policy Program, University of California, Santa Cruz

  • Tecnológico Nacional de México/IT Bahía de Banderas

  • Pacific Manta Research Group, University of California

  • MigraMar

Funding

  • Disney Conservation Fund

  • Connell & Associates

  • The National Geographic Society

  • Save Our Seas Foundation

  • The Punta de Mita Foundation

  • Walter and Mary Munk