Deep diving behaviour in oceanic manta rays and its potential function

Calvin S Beale^1,2,3*Ferawati Runtuboy^3,4Abraham Sianipar^1,2,5Angela J E Beer²Mark Erdmann⁶Edy Setyawan^5,6Lydia Green⁷Clinton A J Duffy⁸Samantha Andrzejaczek⁹Barbara Ann Block⁹Kerstin Forsberg¹⁰Mark Meekan¹¹Adrian C Gleiss¹

• ¹Murdoch University, Perth, Australia
• ²Raja Ampat Manta Project, Denpasar, Indonesia
• ³State University of Papua, Manokwari, Special Region of West Papua, Indonesia
• ⁴Graduate School, Bogor Agricultural University, Bogor, West Java, Indonesia
• ⁵Elasmobranch Institute Indonesia, Denpasar, Indonesia
• ⁶University of Auckland, Auckland, New Zealand
• ⁷Manta Watch Charitable Trust, Auckland, New Zealand
• ⁸Auckland Museum, Auckland, New Zealand
• ⁹Stanford University, California, United States
• ¹⁰Planeta Oceano, Migramar, Mexico City, Mexico
• ¹¹University of Western Australia, Perth, Australia

Deep dives are performed by a range of marine megafauna, yet their function remains poorly understood. Proposed functions include foraging, predator avoidance, and navigation, but limited fine-scale data have hindered rigorous testing of these hypotheses. Here, depth time-series data from eight recovered and 16 non-recovered satellite tags deployed on oceanic manta rays (Mobula birostris) in Indonesia, Peru, and New Zealand were examined to characterise extreme dives and identify their potential function. From a total of 46,945 dives, 79 extreme dives (>500 m) were recorded, 11 of which were documented from recovered tags and associated high sampling frequency. Extreme dives were distinguished by rapid descents (up to 2.9 m s⁻¹), brief horizontal “steps” at depth, gradually slowing ascents, and extended periods spent near the surface both before and after diving. Unlike typical foraging dives, no substantial bottom phase was observed, and vertical oscillations—expected if feeding at depth—were absent. Extreme dives also occurred more frequently with increasing distance from the continental shelf edge as well as preceding periods of high 72-h distance travelled, indicating they may inform subsequent movements. We propose that extreme dives enable oceanic manta rays to survey the properties of the water column, likely gathering environmental cues—such as temperature, dissolved oxygen, or geomagnetic gradients—to guide navigation and or the decision to leave or remain in a general area. In open-ocean environments where external reference points are absent, such costly but infrequent dives may provide critical information for long-distance movements. Our results offer new insights into the role of extreme diving behaviour in oceanic manta rays and highlight the importance of fine-scale data for understanding deep-diving behaviours in marine megafauna.