The findings, published in Frontiers in Marine Science, stem from a decade-long tagging program in Peru, Indonesia, and New Zealand. Lead author Dr Calvin Beale, who completed his PhD at Murdoch University, explained that the deep dives, followed by long-distance travel, likely help mantas collect environmental information rather than search for food.
"We show that, far offshore, oceanic manta rays are capable of diving to depths greater than 1,200 meters, far deeper than previously thought," Beale said. "These dives, which are linked with increased horizontal travel afterwards, may play an important role in helping mantas gather information about their environment and navigate across the open ocean."
Researchers tagged 24 manta rays between 2012 and 2022 at three sites: Raja Ampat in eastern Indonesia, off the coast of Tumbes in northern Peru, and near Whangoroa, New Zealand. Eight of the tags were recovered after months adrift, while 16 transmitted data via satellite. In total, the devices recorded 2,705 tag-days of data and captured 79 deep dives, including one to 1,250 meters.
Most extreme dives occurred off New Zealand and began soon after the mantas moved from continental shelves into deep ocean waters. The dives showed a stepped descent pattern with little time spent at the deepest point, indicating they were not linked to hunting or predator avoidance. Instead, the rays may have been detecting magnetic, chemical, or temperature cues to construct mental maps for navigation.
Beale said the stability of deep-ocean conditions might make them ideal for such sampling. The dives often ended with slow resurfacing and surface recovery periods, followed by extensive travel of more than 200 kilometers in the following days.
In Peru and Indonesia, extreme dives were rare, likely due to the shallow nature of local seas. By contrast, the steep drop-offs around New Zealand offered mantas greater opportunities to dive deep for navigational cues.
"Understanding the nature and function of deep dives helps explain how animals cross vast, seemingly featureless oceans and connect ecosystems thousands of kilometers apart," Beale noted. He emphasized that the study relied on limited tagging data and that future research should use larger samples to confirm the rays' navigation strategies.
"Our study highlights how dependent migratory species are on both coastal and offshore habitats, stressing the need for international cooperation in their conservation," he added. "It also reminds us that the deep ocean - which regulates Earth's climate and underpins global fisheries - remains poorly understood but vitally important."
Research Report:Deep diving behaviour in oceanic manta rays and its potential function
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