Grad Student Discovers World's First Known Manta Ray Nursery

Oceanic mantas typically set up spawning sites far from coastal areas, making their populations, particularly juveniles, hard to access and study. G.P. Schmahl/FGBNMS

Things often hide in plain sight, like the keys you misplaced or the file you need for work tomorrow.

Or a manta ray habitat off the coast of Texas.

In what is considered a first, researchers have found a manta ray nursery in the Gulf of Mexico off the coast of Texas in the National Oceanic and Atmospheric Administration's (NOAA) Flower Garden Banks National Marine Sanctuary.

The discovery could give us new insights into the behavior of these gentle giants of the sea, especially the young ones.

Where juvenile manta rays hang out

Joshua Stewart, a marine biology Ph.D. candidate at Scripps Institution of Oceanography at the University of California San Diego, has studied manta rays for seven years, so he's seen plenty of adults in the wild. In 2016, however, while conducting research about the manta ray population at Flower Garden Banks, he spotted a juvenile, a rare sight.

"The juvenile life stage for oceanic mantas has been a bit of a black box for us, since we're so rarely able to observe them," Stewart said in a Scripps-issued statement.

The reason for this is that mantas set up spawning sites in the middle of the ocean, far from coasts. So while we're able to observe adults when they're out in the wild, there are huge swathes of their lives and biology we know little about.

When Stewart reported his sighting to others at the sanctuary, they reported that they were seeing young mantas all the time.

"And that's when I knew that this was a really special, unique place," Stewart told NPR.

Stewart and his team combed through 25 years worth of dive logs and photo identification data collected over the years by the sanctuary and determined that about 95 percent of the mantas visiting Flower Garden Banks were juveniles, measuring an average of 7.38 feet (2.25 meters) in wingspan. Adults can reach up to 23 feet (7 meters) in wingspan.

Rays were identified by the spot pattern on their undersides. Each pattern is unique to that manta, similar to fingerprints for humans.

Stewart and his team published their findings in the journal Marine Biology.

There are a few potential reasons why the manta rays set up this location as a spawning site. First, the sanctuary, which lies about 100 miles south of Texas, contains coral reef systems that have remained healthier than others in the region, making the zone hospitable to all kinds of marine life. Second, certain types of zooplankton, the favored prey of mantas, are in abundance in the deeper, colder waters of the sanctuary.

So the area is ideal for the developing mantas. There's plenty of food to eat for the young mantas, but the presence of the shallower, warmer warmers near the reef allow them to dive into the ocean, eat and then return to recover their body temperature. Researchers will begin to tag juveniles to study their comings and goings.

The importance of ocean sanctuaries

Juvenile manta ray with diver at Flower Garden Banks National Marine Sanctuary
A diver follows a juvenile manta ray in the waters of the Flower Garden Banks National Marine Sanctuary. G.P. Schmahl/FGBNMS

The discovery of the nursery highlights the value of marine protected areas, particularly for threatened and endangered species. Giant manta rays were listed as threatened under the U.S. Endangered Species Act in January 2018.

"Nowhere else in the world has a manta ray nursery area been recognized — which heightens the importance of the sanctuary for these pelagic species," George Schmahl, superintendent of Flower Garden Banks National Marine Sanctuary, said in the statement. "The discovery of the sanctuary as a nursery area for the species raises many more questions, some of which we can hopefully start studying with Josh Stewart and other partners."

Flower Garden Banks is pursuing plans that will expand the protected area with additional reefs in a northwestern portion of the Gulf of Mexico.

These protected areas also afford researchers the opportunity to learn more about marine life and that, in turn, can help us better protect them.

"There's so much we don't know about mantas and that's exciting from a science perspective because it means there are so many questions still waiting to be answered," Stewart explained in the statement. "From a conservation perspective, it means that a lot of the questions that you get to answer will actually be meaningful and have an impact on management."