Manta rays tagged to reveal secrets of a mysterious ocean giant


Conservationists from the Wildlife Conservation Society, the University of Exeter, and the Government of Mexico have used the latest satellite tracking technology to discover the feeding habitats and threats to the world's largest ray.

The research team used satellite telemetry to track open-ocean journeys of these remarkable animals, which have been known to grow to widths of 7.6 m/25', and the study has been published in the open access journal PLoS One.

"Almost nothing is known about the movements and ecological needs of the Manta ray, one of the ocean's largest and least-known species," said Dr. Rachel Graham, lead author on the study and director of WCS's Gulf and Caribbean Sharks and Rays Program. "Our real-time data illuminate the previously unseen world of this mythic fish and will help to shape management and conservation strategies for this species."

Tracking devices were attached to the backs of six rays during a 13-day research cruise in the southern Gulf of Mexico, and the tags provided data for a mean of 27 days.

"The satellite tag data revealed that some of the rays travelled more than 1,100 kilometres during the study period," said Dr. Matthew Witt of the University of Exeter's Environment and Sustainability Institute. "The rays spent most of their time traversing coastal areas plentiful in zooplankton and fish eggs from spawning events."

Manta rays are filter feeders that feed by swimming open-mouthed through clouds of plankton, capturing prey in their gill rakers, and despite their great size are harmless to humans and lack the stinger of the more well-known stingray.  They also possess the highest brain to body ratio of all sharks and rays and give birth to live young.  

Listed as "Vulnerable" by the International Union for Conservation of Nature (IUCN), their use for shark bait and the demand for gill rakers in traditional Chinese medicine, has seen an apparent decline of Manta rays in tropical regions.

The research also discovered that the tagged rays only spent a small percentage of time in marine protected areas, and the majority of their locations were within major shipping routes of the region — possibly opening them up to the danger of being struck by ships.

"Studies such as this one are critical in developing effective management of Manta rays, which appear to be declining worldwide," said Dr. Howard Rosenbaum, Director of WCS's Ocean Giant Program.

For further information see the paper: Graham RT, Witt MJ, Castellanos DW, Remolina F, Maxwell S, et al. (2012) Satellite Tracking of Manta Rays Highlights Challenges to Their Conservation. PLoS ONE 7(5): e36834. doi:10.1371/journal.pone.0036834

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