Deep-Diving Manta Rays May Use the Ocean’s Midnight Zone Like a Natural GPS

Scientists found manta rays dive nearly a mile deep to navigate the open ocean.

In the darkness nearly a mile beneath the ocean’s surface, where the pressure would crush a human and temperatures hover just above freezing, a creature with wings wider than a car glides through the abyss. It’s not searching for food or fleeing danger, but most likely finding direction.

That’s the conclusion of a study that’s the first of its kind to examine in detail the extreme deep-diving behavior of oceanic manta rays (Mobula birostris). The findings, published in the journal Frontiers in Marine Science, reveal that the rays can dive to depths of 1,250 meters (4,100 feet, or about three-quarters of a mile), part of the water column known as the midnight zone, which researchers say may help them navigate across thousands of miles of open water.

“No one ever dreamed mantas would go this deep,” Mark Erdmann, shark conservation director at the NGO Re:wild and a co-author of the study, told Mongabay. “The likely reason the mantas braved the cold, dark, deep waters was not in search of food, nor to avoid predators, but likely for navigational purposes.”

An international team of researchers tracked 24 manta rays between 2012 and 2022. They attached special tags to the animals in waters near Peru, Indonesia and Aotearoa New Zealand, recording more than 46,000 dives.

The rays appear to gather navigational information from the stable conditions of the deep ocean, where temperature, oxygen levels and possibly even Earth’s magnetic field provide more reliable signals than at the constantly changing surface waters.

“By diving down and ‘sampling’ these signals, they could build a mental map that helps them navigate across vast, featureless stretches of open ocean,” Calvin Beale, who led the research while completing his Ph.D. at Murdoch University in Australia, said

“What surprised me most was just how deep these animals can go and how often they do it,” Beale told Mongabay. “It shows that manta rays use far more of the ocean than we ever realized, including deep offshore waters that are rarely protected.”

The rays didn’t simply plummet straight down. Instead, they descended in a step-like pattern, pausing briefly at different depths. They spent almost no time at the bottom before beginning their gradual, stepped ascent back to the surface. Researchers found no evidence of the back-and-forth movements that indicate hunting.

Scientists say these pauses likely allow the rays to sample environmental conditions at various depths. “By diving down and ‘sampling’ these signals, they could build a mental map that helps them navigate across vast, featureless stretches of open ocean,” Beale said.

The extreme dives were rare. Only 79 reached depths greater than 500 m (1,640 ft) during the entire study. Yet their timing revealed their importance: Rays typically made their first deep plunge within 24 hours of leaving the continental shelf for the open ocean.

After these extreme dives, the rays often covered distances of more than 200 kilometers (120 mi) in the following days, swimming with clear direction.

The study also revealed regional differences. In Indonesia’s mostly shallow seas, only five extreme dives occurred. Peru recorded just three, as most rays there stayed in coastal waters.

New Zealand’s waters, where the ocean floor drops sharply from the coast, saw 71 of the 79 extreme dives. The rays there were often heading toward the tropical waters near Fiji and Tonga, especially as the Southern Hemisphere winter approached.

The New Zealand rays appear to use the dives to “take a better bearing” before their northward migration, Erdmann told science outlet New Atlas. At depth, he said, the rays are likely reading natural signals from the ocean bottom like magnetic field lines.

RelatedPosts

Underwater maintenance robot-snakes look scary but are actually quite cool
Climate change is destabilizing marine food webs
The oxygen in the oceans has decreased by 2% in the past 50 years
The devastating state of ocean pollution in one depressing photo

The rays spent extended periods at the surface both before and after the extreme dives, likely warming their bodies in preparation for the frigid deep waters and recovering afterward.

These findings carry important implications for protecting oceanic manta rays, which are classified as endangered on the IUCN Red List. The research shows that these animals depend on both coastal feeding areas and deep-ocean regions for navigation.

“Understanding that they depend on both surface and deep habitats means conservation can’t focus only on coastal feeding areas; it also needs to include the broader oceanic environments they travel through,” Beale said.

“The most obvious connection with conservation is how these long-distance migrations put mantas at risk of negative fisheries interactions,” Erdmann said.

For the New Zealand mantas, which seem to all migrate north toward Fiji, Tonga and Tuvalu, and occasionally as far east as the Cook Islands — a distance of about 3,000 km (1,900 mi) — there’s a high risk their journeys will run through fishing grounds.

“We now have pretty strong evidence of four of our tagged mantas being killed in blue water fisheries southwest of Tonga,” Erdmann said. “This of course is a serious concern for this endangered species.”

He and colleagues have raised this issue with the New Zealand Department of Conservation.

“We’d love to see some eventual restrictions on fishing in the middle of the ocean mantas’ migration routes — which may eventually require presentations to regional fisheries management organizations,” he said.

“It also reminds us,” Beale said, “that the deep ocean — which regulates Earth’s climate and underpins global fisheries — remains poorly understood but vitally important.”

Citation: Beale, C. S., Runtuboy, F., Sianipar, A. B., Beer, A. J. E., Kadarusman, Erdmann, M. V., … Gleiss, A. C. (2025). Deep diving behaviour in oceanic manta rays and its potential function. Frontiers in Marine Science, 12, 1630451. doi:10.3389/fmars.2025.1630451

This article originally appeared on Mongabay.