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.

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.

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 (< 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.

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.

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.

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.

Five pop-up satellite archival (PSAT) tags (MiniPAT 348F-00; Wildlife Computers Inc., WA, USA) were deployed on oceanic manta rays (Mobula birostris) in May (n = 1) and July (n = 4) 2018 off the Tumbes region of the northern coast of Peru (Fig. 1). Mantas were visually located at the surface by boat-based searches carried out together with local fishermen, and externally tagged by free-divers. All tags were leadered according to Wilson et al. (2015). Briefly, leaders consisted of a ~15−17 cm length of 180 kg monofilament (Moimoi, X Hard) covered with one layer of Aramide and shrink wrap, and were attached to the manta via a custom-built titanium dart. Mantas were tagged by a swimmer with a pole in hand, and tags were placed into the dorsal musculature, off the midline of the posterior dorsal surface of each manta ray. PSATs were programmed to sample ambient light levels, ambient temperatures, and pressure at 3-5 second intervals and to detach after 90 (May) or 180 (July) days (Table 1). Depth and temperature time-series were transmitted at five-minute intervals, and recovery of two tags through collaboration with local community members allowed for the whole archival datasets to be downloaded.

MR1: 5218001

MR2: 5218005

MR3: 5218007

Tags from MR1 and MR3 were physically recovered, allowing download of the full data archives.

Data were extracted from the raw tag data using the Wildlife Computers Data Analysis Program 3.0 (available at https://wildlifecomputers.com/support/downloads/). Please refer to the PDF at https://static.wildlifecomputers.com/Spreadsheet-File-Descriptions-1.pdf for more detail on each file.