Natural and reduced anthropogenic injuries rates in reef manta rays (Mobula alfredi) from the Chagos Archipelago, central Indian Ocean

Abandoned, lost, or otherwise discarded fishing gear (ALDFG) accounts for nearly two-thirds of plastic debris in the open ocean and can entangle marine megafauna. Reef manta rays (Mobula alfredi) are susceptible to entanglement in ALDFG, with consequences ranging from sublethal injuries to mortality. Mobula alfredi are listed as Vulnerable to extinction on the IUCN Red List of Threatened Species, in part, due to their slow reproduction rate and susceptibility to unsustainable fishing pressures. Their exposure to ALDFG could further hinder their survival; therefore, it is essential to quantify the impacts of ALDFG. This study assesses a photographic identification database for evidence of entanglement and other injuries in the reef manta ray population of the Chagos Archipelago, a large, remote, no-take marine protected area (MPA) in the Indian Ocean where illegal fishing persists. Only one individual (0.3% of the photographed population, n = 325) showed evidence of entanglement injury, which is substantially lower than rates reported in other populations globally (mean = 7.1%). Additionally, 18.2% of the population showed evidence of predatory bites, which is comparable to the percentage of individuals with predation injuries in other populations (mean = 21.5%). The results of this study suggest that the remoteness, protected status, and large size of the MPA may contribute to reducing entanglement of reef manta rays. Continued enforcement of the MPA is essential to reduce illegal fishing activities and other anthropogenic impacts on the species it protects.