Photo: George Schmahl (Flower Garden Bank National Marine Sanctuary)

Manta rays are among the most charismatic undersea megafauna, but there’s still a lot we don’t know these flat, ginormous sea-dogs. Now, in trying to understand how their populations are connected in the Gulf of Mexico, scientists have made a wild discovery.

In Flower Garden Banks National Marine Sanctuary, which sits about 110 miles southeast of Galveston, researchers found the first deep sea manta ray nursery. They chronicled the find in a newly released study in Marine Biology.

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“The first few dives I had with mantas were truly unforgettable,” Joshua Stewart, a PhD student at Scripps Institute of Oceanography, told Earther. “As I became more interested in them, it became clear that there are so many huge knowledge gaps in our basic understanding of manta biology and ecology.”

That’s why Stewart was diving with staff at the marine sanctuary a few years ago, trying to understand ray population connectivity in the Gulf of Mexico and Caribbean. On one dive, he wanted to collect a tissue sample for genetic analysis from a smaller ray he saw. As he was swimming under the ray trying to get a picture of its spot pattern—a pattern that is unique on each ray—he noticed its small, undeveloped claspers, organs that are part of its reproductive system. That meant the ray was a juvenile, something Stewart had only encountered a few times on dives.

When we got back to the boat, he mentioned this to the sanctuary scientists who told him they frequently saw juvenile males on their dives. That set the new discovery in motion. Because the sanctuary had been keeping detailed records of manta ray sightings and their size as well as photographs, Stewart was able to reconstruct a history of the rays of Flower Garden Banks going back to 1982.

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That predates the sanctuary by a decade, but Stewart said “a big part of the reason we were able to classify this as a nursery habitat is thanks to the ongoing research and monitoring activities by the sanctuary research team.”

In all, the researchers compiled 104 observations of rays included their size while another 95 photos provided more data points. The data revealed a high number of juvenile rays, including a number that hung around for longer periods of time. Young rays were also present every year save 1996.

In the ecology world, nurseries are often classified based on three criteria: there are more juveniles there than in other locations, species hang around, and the area is used on the regular. Clearly Flower Garden Banks fit the bill, making it the first deep sea ray nursery ever discovered.

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“The fact that the Flower Garden Banks has been shown to be a nursery area for juvenile manta rays emphasizes the importance of National Marine Sanctuaries (and other marine protected areas) to provide protection for America’s special marine areas,” George Schmahl, the sanctuary’s superintendent, told Earther. “The Flower Garden Banks provide critical habitat not only [for] iconic species like manta rays, but for a variety of other fish species of commercial and recreational importance, contributing to the economic health of the Gulf of Mexico.”

Indeed, the discovery of this nursery in a protected area only underscores the value of conservation and long-term research. Stewart said the finding gives researchers new clues as to where to look for other nurseries around the world. And keeping nurseries stay safe from the ravages of commercial fishing and fossil fuel exploration could help ensure that ray numbers don’t continue their decline, something that’s being driven by bycatch and traditional medicine demands in China.

“Protecting the juvenile stage will be an important task for managers—we’re lucky that this manta nursery seems to be largely within a sanctuary already!” Stewart said.

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