The first time you see an oceanic manta ray (Mobula birostris) glide near the surface of our sun-dappled ocean waters, it’s easy to think that this is all there is to their world. But researchers who tag these gentle giants have discovered a hidden side of their lives — a side that unfolds far below the sparkling surface, in the silent, cold depths of the ocean. Occasionally, a manta ray will vanish from sight, plunging hundreds of meters down into darkness, descending faster than a human can even comprehend.
Why? Well, a team of scientists have set out to find out.
In a recent study spanning Indonesia, Peru, and New Zealand, scientists recorded nearly 47,000 dives from 24 tagged manta rays. Among them, 79 stood out as “extreme dives” or dives that are deeper than 500 meters (1,640 ft), with some plunging over 1,200 meters (4,000 ft). The rays would linger near the surface for long periods before diving, then drop at speeds up to 2.9 meters per second (9.5 ft/s), faster than a human swimmer could sustain for even a few strokes. At depth, they moved in brief horizontal steps before ascending slowly, again lingering at the surface after resurfacing. And what is striking is what they didn’t do: there was no prolonged bottom phase, no oscillations hunting for prey. What makes these dives even more intriguing is what happens afterward. The rays often travel hundreds of kilometers (over 120 miles) in the three days following an extreme dive. But this wasn’t random wandering. No, the tags showed it was purposeful, exploratory movement and a pattern soon emerged. The extreme dives are not about immediate energy gain or thermoregulation… instead, they may serve as information-gathering missions. By plunging into the depths, manta rays likely sample environmental cues (i.e., temperature, dissolved oxygen, and potentially geomagnetic gradients) to guide navigation or decide whether to remain in an area or move on. These cues could be their sort of compass, a way to decide whether to linger in one area or move on to a new feeding ground.
Diving over 1,000 meters (3,280 ft) isn’t easy. At these depths, temperatures drop drastically and oxygen levels can be low. Large-bodied ectothermic animals like manta rays experience rapid cooling, yet the rays seem to minimize their time in the cold by descending at high speed, possibly using anaerobic metabolism or temporarily restricting gill ventilation, similar to “breath-holding” behaviours observed in some shark species. The long pre- and post-dive surface intervals observed may serve as warming and recovery periods, essentially priming and resetting their bodies for these demanding excursions. These constraints may explain why such dives are infrequent compared to related species like the Chilean devil ray (Mobula tarapacana), which routinely performs deep dives.
Where these dives happen also tells a story. Most extreme dives occurred in New Zealand, where manta rays leave the continental shelf for deeper waters, while in Indonesia and Peru, rays largely remained in shallower coastal areas, with occasional extreme dives coinciding with when they were leaving the shelf. Statistical models run by the scientists support this, showing that distance from the shelf edge strongly predicts the likelihood of an extreme dive. So it seems that these dives are not constrained by bathymetry alone; rather, they appear to be strategically timed events linked to broader movement decisions.
The characteristics surrounding these taxing excursions to the deep certainly seem to suggest they function as a vertical survey of the ocean. While geomagnetic navigation remains a hypothesis, there is evidence from other elasmobranchs and even sea turtles that magnetic cues can inform large-scale orientation. Whether manta rays use deep dives to sense geomagnetic gradients or rely primarily on other environmental signals remains an open question. We also don’t yet know how much energy a single extreme dive costs or whether the information gained offsets this investment, how horizontal steps during descent and ascent relate to oxygen, thermal limits, or sensory sampling, and whether these dives are timed to coincide with specific oceanographic features such as thermoclines or seamounts. Could extreme dives be a way to explore new areas, test habitat quality, or even communicate indirectly with other rays? The truth is, each plunge raises as many questions as it answers, revealing just how little we know about the hidden strategies of these oceanic giants. What we do know is that these latest findings not only challenge the assumption that deep dives are always linked to feeding or predator avoidance, but underscores a broader truth about marine megafauna: the behaviours we observe at the surface are only a fraction of the story. Fine-scale, high-resolution data from recovered satellite tags are opening a window into a hidden layer of life, revealing strategies and adaptations that allow animals to navigate, survive, and thrive in the most challenging of environments.
What other secrets lie hidden beneath the waves that we have yet to detect? Could other seemingly simple surface behaviors — such as gentle glides, sudden turns or synchronized group movements — also encode strategies for survival in ways we can’t yet perceive? Each minute movement may be a chapter in a story we are only beginning to read. As technology advances and our window into the deep improves, one has to wonder: how much more intelligence, adaptability, and subtlety exists in the lives of oceanic giants than we have ever imagined?
