In the depths of the ocean, where sunlight does not penetrate, giant devil rays perform maneuvers that long remained a puzzle even for biologists.
These impressive creatures, the size of a small automobile, descend into zones of cold and high pressure, not lingering there for long. A new study has, for the first time, clarified why mantas execute such risky dives. Naked-Science reports on this.
What is known about giant devil rays
Mantas, or Mobula birostris, are considered the largest rays on the planet: their body width reaches seven meters, and their mass exceeds two tons. Despite their substantial size, they remain among the most enigmatic oceanic species.
These animals inhabit tropical and subtropical waters and can undertake lengthy migrations, traversing vast expanses lacking visible landmarks.
It was previously assumed that mantas preferred to stay in warm surface layers rich in plankton and rarely descended to great depths. However, observations from satellite tags affixed to the animals revealed an entirely different picture and forced a reevaluation of established ideas about the behavior of these rays.
How the research was conducted
An international team of biologists led by Calvin Stephen Dewar from Murdoch University in Australia fitted 24 mantas with satellite transmitters.
The study was conducted in three remote areas: off the coast of Peru, in the Indonesian archipelago of Raja Ampat, and near New Zealand.
The devices gathered data on the location and depth of dives; some units surfaced to transmit the collected information. Over ten years of observation, researchers amassed over 2,700 days of data—one of the largest datasets on manta behavior.
The analysis showed that the rays are capable of descending to depths exceeding 1,200 meters, significantly surpassing earlier estimates. A total of 79 “extreme” descents deeper than 500 meters were registered, with the record reaching 1,250 meters.
Most of these dives were recorded off the coast of New Zealand, where the rays frequently leave the continental shelf, venturing into the open sea.
Why mantas make deep dives
The most surprising finding was that these descents were not related to foraging. Mantas hardly paused at great depths, which rules out searching for food. The descents did not appear to be a reaction to a threat: the speed and trajectory of movement remained stable.
Observations of behavior preceding and following the dives played a special role. It turned out that a deep descent was followed by a prolonged recovery period near the surface, and then several days of active travel, during which the mantas covered over 200 kilometers. This pattern indicates a navigational purpose for these maneuvers.
The scientists hypothesized that mantas utilize the depths to “read” environmental parameters. At greater depths, the characteristics of the Earth’s magnetic field, water, and illumination change.
This gathered information may serve as a sort of map, helping them navigate in the open ocean where familiar reference points are absent.
Why behavior differs among populations
Deep dives occur considerably less often in Peruvian and Indonesian mantas, the reason being the specifics of the local ecosystems. In Raja Ampat, mantas reside in rich coral reefs and stay in shallow waters that ensure stable access to sustenance. Relatively shallow zones also prevail in Peru.
The situation near New Zealand is quite different. Here, the seabed drops away quickly, forming deep trenches. Mantas must traverse such regions during their movements, making deep dives an obligatory component of their navigational behavior. This is not an exception but a vital element of their survival strategy.
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