SAN DIEGO – The University of California, San Diego, has discovered the world’s first known nursery for manta rays, an idyllic spot in the Gulf of Mexico where the “gentle giants” approach divers along colorful reefs.
An exploration team led by Josh Stewart, who is finishing up his doctorate in marine biology at the university’s Scripps Institution of Oceanography, made the discovery and confirmed its importance over the past few years.
He was aided by colleagues from NOAA who manage the site, which is part of the Flower Garden Banks National Marine Sanctuaries, about 70 miles south of Galveston, Texas.
Finding adult manta rays is easy. But in a mystery that has long confused scientists, juveniles rarely swim openly in defined places during the four to five years that it takes them to become adults.
Stewart has been trying to solve the mystery for years, and had some initial success in 2016 when he saw a juvenile oceanic manta ray (Mobula birostris). He later saw more juvenile mantas and, with help from the NOAA researchers, determined that he’d happened upon a nursery. The discovery was published in the journal Marine Biology.
The juveniles were largely found in an area when the sea floor slopes into deeper water. “We think they may be feeding on specific types of zooplankton there, then migrating up toward the surface, where we saw them,” Stewart said. “They might be hanging around the banks because it could be a little safer than open water. We’ve seen them so rarely (in the past) that we know very little about these juveniles.”
But Stewart can say with certainty that simply hanging in the water, waiting for manta rays to arrive, is a remarkable thing to experience. He said the adults “are gigantic. They can have a 21-foot wingspan. And they’re super-friendly. … Mantas are curious. They’re interested in why divers are blowing bubbles. They’ll hang out. I can’t think of another large animal that will do that with you.”