The secret life of manta rays

The long-held belief by scientists that manta rays gracefully roam vast stretches of the open ocean may not be true.

“Our research shows that manta rays stay in comparatively small areas,” said Joshua Stewart, a doctoral student in marine biology at UC San Diego’s Scripps Institution of Oceanography.

Stewart and his collaborators placed satellite tags on manta rays off Mexico and in the Indo-Pacific. Monitoring revealed that the rays — which can live more than 40 years — remained close to where they were tagged.

The researchers also took tissue samples of the manta rays to make sure they were studying the same populations of creatures.

Their findings were published Monday in the journal Biological Conservation.

Scientists are concerned about the welfare of manta rays. The animals are increasingly being targeted by fishermen, who want the animal’s gill plates. They’re widely used in traditional Chinese medicine.

Manta rays are gregarious, gentle creatures that often interact with divers and snorkelers in places like Hawaii. But fairly little is known about them because manta rays mostly live in remote areas of the open ocean near sea mounts and offshore islands.

Stewart spent a lot of time tagging and studying the animals in the Revillagigedo islands, about 240 miles southwest of Cabo San Lucas.

“They are capable of swimming long distances, but they didn’t,” said Stewart, who was sometimes overshadowed by manta rays, whose wingspan can be up to 23 feet wide.

gary.robbins@sduniontribune.com

Robbins writes for the San Diego Union-Tribune