Manta Rays' Deep Dives Redefine Marine Navigation Strategies

Oceanic manta rays (Mobula birostris) are plunging over 1,200 meters into the abyss to gather critical environmental data, challenging long-held assumptions about their behavior, a new study reveals. By sampling temperature, dissolved oxygen, and potential geomagnetic gradients during these extreme dives, the rays may be using the ocean depths as a "vertical survey" to navigate and decide whether to migrate to new feeding grounds, researchers say. The findings, based on satellite tagging of 24 manta rays across Indonesia, Peru, and New Zealand, highlight an unexpected sophistication in how these creatures interact with their environment. The study recorded nearly 47,000 dives, with 79 classified as "extreme" (exceeding 500 meters). The rays descended at speeds up to 2.9 meters per second-far faster than a human swimmer-then lingered briefly before ascending. Notably, these dives lacked prolonged bottom phases or oscillations typically seen in prey hunting. Instead, the data suggests the dives are information-gathering missions. After such dives, manta rays often traveled hundreds of kilometers in a purposeful, exploratory pattern, indicating the data collected influenced their movement decisions. The physiological toll of these dives is significant. At depths where temperatures plummet and oxygen levels are low, manta rays-ectothermic animals-face rapid cooling. Researchers speculate the rays minimize exposure by descending quickly and using anaerobic metabolism or temporary gill restriction, akin to "breath-holding" seen in some sharks. Prolonged surface intervals before and after dives likely serve as recovery periods to warm and reset their bodies for the next extreme excursion. Geographic patterns further underscore the strategic nature of these dives. Most extreme dives occurred in New Zealand, where manta rays venture beyond the continental shelf into deeper waters. In contrast, rays in Indonesia and Peru remained in shallower coastal areas, with extreme dives coinciding with shelf departures. Statistical models confirmed that distance from the shelf edge strongly predicts the likelihood of such dives, suggesting they are timed to broader movement decisions rather than constrained by bathymetry alone. While the study does not definitively link the dives to geomagnetic navigation, evidence from other marine species like sea turtles and sharks supports the hypothesis. The researchers also note unanswered questions: How much energy do these dives cost? Do they coincide with oceanographic features like thermoclines or seamounts? Could they indirectly communicate with other rays or test habitat quality? "These dives open a window into a hidden layer of life," said the study's authors. "What we observe at the surface is only a fraction of their story." The findings not only redefine manta ray behavior but also underscore the complexity of marine megafauna strategies, challenging assumptions that deep dives are solely for feeding or predator avoidance.