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Giant mantas are deep-ocean predators

archive – Diving NewsGiant mantas are deep-ocean predators

A new scientific study into the food sources of giant mantas in the eastern Equatorial Pacific has revealed that the rays get most of their sustenance from the ocean depths rather than near the surface, as previously supposed.

The study by the Marine Megafauna Foundation (MMF), University of Queensland (UQ) and Proyecta Mantas Ecuador focused on the Isla de la Plata off Ecuador, which seasonally hosts the largest aggregation of giant mantas in the world.

As studying the contents of the rays’ stomachs is impractical, stable isotope analysis of manta muscle and zooplankton were used. This revealed that, while some 27% of the rays’ dietary intake came from surface feeding, the bulk derived from the mesopelagic zone – 200-1000m below the surface.

MMF researcher Katherine Burgess authored the project as part of a PhD at UQ. “Manta rays are one of the most iconic marine animals, yet we still know very little about their feeding habits,” she said. “The study reports much-needed information on the diet of this elusive species.”

The giant manta (Manta birostris) was first identified by the MMF’s Andrea Marshall. The species, like the reef manta ray (Manta alfredi), is on the IUCN Red List of Threatened Species.

It is formally protected in Ecuador along with other countries such as Indonesia, the Maldives, Mexico, New Zealand, the Philippines and parts of the USA, but understanding of its feeding habits is considered vital in helping to identify and conserve critical habitats and feeding sites.

“The deep ocean is the next frontier for open-ocean fisheries, and we are only just realising the potential reliance on this zone by threatened marine megafauna,” commented UQ Prof Anthony Richardson.

The study Manta birostris, Predator of the Deep?, published in Royal Society Open Science, can be read here

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