Reef manta ray habitat use and residency at a remote marine protected area

Reef manta rays Mobula alfredi are large, filter-feeding elasmobranchs known to aggregate in coastal areas and island archipelagos. Effective spatial conservation strategies, such as marine protected areas (MPAs), for this mobile marine species rely on a comprehensive understanding of movement behavior. To better understand movement patterns, we externally deployed 58 acoustic tags on reef mantas at the Palmyra Atoll National Wildlife Refuge and monitored the presence of mantas on an extensive array of acoustic receivers (n = 85) for close to a decade. We documented an average maximum residency rate of 88% as well as consistent use of all 4 primary habitat types at Palmyra—the lagoon system, reef terrace, forereef, and channel. Notably, the highest rates of detection were recorded in the nutrient rich lagoon habitats (69% of detections). Manta movements displayed a diel structure, with a preference for the forereef, reef terrace, and channel during daylight hours, and the lagoon at night. We also found bimodal peaks of activity during new and full moons. In addition, detections around the atoll increased during the cooler periods of fall and winter. Our findings demonstrate that the no-fishing regulations at Palmyra Atoll are an effective spatial management strategy for this resident population of reef mantas and indicate that reef ecosystems in remote locations may be well-suited for designation as MPAs, offering protection for threatened elasmobranch species.