Oceanic Manta Rays: Navigating the Depths for Environmental Cues

Recent research has revealed that oceanic manta rays (Mobula birostris), the largest ray species, can dive to depths exceeding 1,200 meters (approximately 4,000 feet), a behavior previously underestimated. An international team of researchers, led by Dr. Calvin Beale from Murdoch University, tagged 24 manta rays across three locations: Raja Ampat in Indonesia, Tumbes in Peru, and Whangaroa in New Zealand. The study, published in *Frontiers in Marine Science*, recorded a total of 2,705 tag-days, during which the rays exhibited extreme diving behavior on 79 occasions, predominantly off the coast of New Zealand.

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The study suggests that these deep dives are not primarily for feeding or evading predators. Instead, the manta rays appear to utilize these excursions to gather environmental information, such as changes in temperature, oxygen levels, and the Earth's magnetic field. Dr. Beale noted, “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.” The rays typically initiate these dives shortly after moving away from the continental shelf, indicating a potential navigational purpose.

Giant Rays Dive Deep to Map the Ocean FloorWhen researchers tracked 24 giant manta rays into the deep, they discovered an amazing new behaviourFrontiers in AntibioticsNew AtlasIFL Science

The data indicated that the mantas dive in a stepped pattern, spending minimal time at maximum depths. This behavior suggests they are sampling environmental cues rather than hunting. Following these dives, the rays often traveled significant distances, sometimes covering up to 200 kilometers (124 miles) in a few days. The research highlights that the underwater topography off New Zealand, where the seafloor drops steeply, facilitates these extreme dives, unlike the shallower coastal habitats in Peru and Indonesia.

Giant Rays Dive Deep to Map the Ocean FloorFrontiers in Medical TechnologyWhen researchers tracked 24 giant manta rays into the deep, they discovered an amazing new behaviourNew AtlasIFL Science

While the findings are groundbreaking, some experts emphasize the need for caution in interpreting the data. The study's sample size of 24 individuals and reliance on intermittent data collection may limit the conclusions drawn about the broader population of oceanic manta rays. Future research is necessary to confirm these behaviors across larger groups and different environments.

Frontiers in Medical Technology

Dr. Mark Erdmann, Shark Conservation Director at Re:wild, remarked on the significance of the study, stating, “Understanding the nature and function of deep dives helps explain how animals cross vast, seemingly featureless oceans and connect ecosystems thousands of kilometers apart.” The researchers stress the importance of international cooperation in conservation efforts, given the migratory nature of these species and their reliance on both coastal and offshore habitats.

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• “Far offshore, oceanic manta rays are capable of diving to depths greater than 1,200 meters, far deeper than previously thought,” — Dr. Calvin Beale, Murdoch University

Giant Rays Dive Deep to Map the Ocean Floor

• “By diving down and 'sampling’ these signals, they could build a mental map that helps them navigate across vast, featureless stretches of open ocean.” — Dr. Calvin Beale, Murdoch University

When researchers tracked 24 giant manta rays into the deep, they discovered an amazing new behaviour

• “As Beale noted, “Our study highlights how dependent migratory species are on both coastal and offshore habitats, stressing the need for international cooperation in their conservation.” — Dr. Calvin Beale, Murdoch University

Giant Rays Dive Deep to Map the Ocean Floor

The research team plans to continue tagging oceanic manta rays in New Zealand during the summer months, aiming to gather more data on their movements and behaviors. This ongoing research is expected to provide further insights into the ecological roles of these majestic creatures and the importance of protecting their migratory routes.

Cosmos Magazine