Scientists at the Smithsonian Environmental Research Center in Edgewater, Md., tracked a group of rays over two years. The rays, they found in research published last week in the journal Marine Ecology Progress Series, spend their winters around Cape Canaveral, Fla., then migrate north in the spring to the same rivers where researchers initially found them — perhaps the rivers and creeks where they were born.
The finding could be valuable as Maryland fishery regulators develop the state’s first plan to manage the cownose ray population, balancing the concerns of the seafood industry with the limited data available on the rays’ place in the Chesapeake ecosystem.
Cownose rays float over sandy stretches of the Chesapeake, flapping wings that can grow larger than a newspaper page to turn over the sediment and expose prey such as oysters and clams. Although the bivalves are an important part of the bay’s health, filtering out sediment and pollutants, that doesn’t make cownose rays villains, ecologists say.
They suspect the rays’ excavation of river and creek beds actually might help oysters and clams reproduce, though they said that has not been studied. And they know that cownose rays have been part of the bay ecosystem for eons, so they can’t be blamed for the dramatic loss of oysters over the past couple of centuries.
The new research indicates that the rays may be territorial — the ones spotted one summer in a waterway could be the same ones that appear there the next year, said Matthew Ogburn, a marine biologist at the Smithsonian center and lead author on the cownose ray study.
“That’s kind of a really exciting finding, to know they’re kind of your local rays, potentially, in that area,” Ogburn said.
But he said that also means harvesting too many rays in one area could affect a waterway for years to come. If no new rays are born, fewer might visit that area in later years.
“If you impact that one part of the population, it could take a long time for that one part of the population to recover,” he said.
Even though scientists still have questions about the role that rays play in the bay’s health, it could be devastating if they disappear, they said.
“They’re part of this whole ecosystem,” said Robert Fisher, a fisheries/seafood technology specialist at the Virginia Institute of Marine Science, who also worked on the ray-tracking research. “If you take one predator out of the system, it’s going to have an impact on whatever else is there.”
They also worry that cownose rays could be particularly vulnerable to being overfished because they don’t reach sexual maturity until ages 6 to 8; when they do, females can give birth only once a year, slowing the population’s overall rate of reproduction.
To track the rays, scientists worked with watermen, who often catch them in their nets by mistake. The researchers gathered a group of 42 rays from throughout the bay, tagged them with tiny transmitters and set them back into the water.
They found that all the rays spent their winters in the same Florida waters. But when they migrated north for the summer, the rays scattered across both Maryland and Virginia portions of the Chesapeake, as well as in Georgia, all of them to spots near where they were captured. Back in what appears to be their home waters, the females give birth and then mate again.
The researchers tracked the rays over two years, but were only able to get signals during both summer seasons for five rays. Four of them returned to the same waters where they had been initially caught, while the fifth one spent both summers in the Chesapeake, though one in Maryland waters and the other in Virginia.
Ogburn said that isn’t enough information to say for certain that the rays return to the same spots year after year. But he said he suspects that they are being drawn back to the same waters where they were born — a phenomenon found in other fish species such as salmon and sturgeon.
Previously, researchers knew little about cownose rays’ migration patterns. Past research hinted that the rays might return to the same areas, but the new study presents that case in finer and more thorough detail.
“The evidence seems to suggest they’re coming back to the same general area, at least,” Ogburn said.
The finding could factor into the plan Maryland is developing to regulate cownose ray fishing. The plan is required under a law the General Assembly passed last year — legislation that also banned ray-catching tournaments until July 1, 2019.
A work group that includes Ogburn and Fisher, as well as watermen, sportfishing enthusiasts and conservationists, is expected to begin reviewing a draft state plan soon, then offer it for public review. The plan is on track to be adopted by the end of the year, a deadline established in the law.
Any fishing regulations will also depend on the rays’ numbers.
John Van Alstine, a member of the group who is a waterman and oyster aquaculturist in Calvert County, said he notices cownose rays getting “more and more prevalent” feeding on his oyster beds. But until the state can gather more information like the Smithsonian study, it’s unclear how many of those rays he and other watermen can catch without harming the population, he said.
“We have oysters that get eaten up. They certainly are in my environment,” Van Alstine said. “We’re just trying to get as much information as we can so we can develop a good business practice.”