Giant Manta Rays Behaviors Revealed by GPS Tracking

22 May 2012

Historically, not much has been known about the ecological requirements of giant manta rays — fish that grow up to 25 feet wide and glide through our ocean waters with breathtaking beauty — until now.


In the first ever study using satellite GPS tracking on six giant rays — four females, one male and one undetermined sex (juvenile) — scientists have learned a few of the Manta’s secrets, including that these alluring creatures with triangular-like wings favor to travel vast distances filter-feeding in their search for food.

Since manta rays (Manta birostris) are currently designated as “vulnerable“, or threatened for extinction, by the International Union for the Conservation of Nature, learning more about their habits and risks for injury or death are critical to improving their long-term survival. Manta rays are being chopped up as churn by fisherman using it for shark bait, hit by shipping boats, and caught by fishermen to be used for traditional Chinese medicine. What’s more, the species only gives birth to one or two offspring every one to two years, leaving them extra vulnerable to risks of overexploitation.

“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 Rachel Graham, lead author on the study and director of WCS’s Gulf and Caribbean Sharks and Rays Program, in a statement. “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.”

Scientists from the Wildlife Conservation Society, the Government of Mexico, the University of Exeter, have published their study in the journal PLoS ONE, which details their findings of 64 days of satellite tracking of the manta rays — until the GPS trackers fell off.

The study revealed that the giant manta rays traveled nearly 700 miles during the two month period around the Yucatan peninsula. “The satellite tag data revealed that some of the rays traveled more than 1,100 kilometers 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.”

Through analyzing GPS tracking data, the researches noted that the manta rays predominantly remained in waters less than 50 meters deep, and preferred warmer waters 78.8°F to 86°F (26-30°C).

But perhaps what was even more revealing — and concerning — is that that rays spent close to 90 percent of their time not within Marine Protected Areas, which are areas where human contact is minimized. In other words, the manta rays spent the majority of their time swimming in major shipping routes, leaving them vulnerable to strikes by ships. Only 11.5 percent of the time were they tracked residing in the Marine Protected Areas.

Having the highest brain-to-body ratio of all rays and sharks, manta rays are considered harmless to humans in that they lack the dangerous stinger, which the better-known stingray have.

“While the broader migratory movements of manta rays are still not known, it is clear that satellite tracking technology has the potential to offer great inroads into understanding movements and contextualising spatially explicit threats to this species,” the researchers said in the online journal.


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