Reverse diel vertical movements of oceanic manta rays off the northern coast of Peru and implications for conservation
1. An understanding of the vertical movements of elasmobranchs across their range is crucial to defining critical habitat use, its overlap with anthropogenic activities and subsequently managing such interactions. 2. In this study, satellite telemetry was used to investigate the vertical habitat use of three oceanic manta rays (Mobula birostris) tagged on the northern coast of Peru. 3. All three oceanic mantas exhibited patterns of reverse diel vertical migration, where vertical movements were significantly deeper at night than the day, as well as an overall preference for surface habitats (less than 2 m). High-resolution archival data (3–5 s) from two recovered tags revealed fine-scale behaviours, where individuals predominately remained in coastal surface waters throughout the day, and oscillated up and down through a highly stratified water column at night. 4. Our results suggest that coastal vertical movements were motivated by a combined foraging and thermal recovery strategy, whereby oceanic mantas dived to forage on vertically migrating zooplankton at night and returned to surface waters to rewarm between dives, indicating that the coast of northern Peru may be a foraging habitat for these animals. 5. High use of surface waters here, however, may put oceanic mantas at high risk from several anthropogenic impacts such as entanglement with fishing gear and vessel strikes. 6. Increased sample size and the use of other techniques, such as animal-borne cameras and tri-axial sensors, are required to validate our foraging and thermal recovery hypothesis and confirm this region as a foraging habitat for oceanic mantas.