Study challenges blaming rays for Chesapeake oyster collapse

Research aims to absolve ancient stingrays of Chesapeake oyster collapse.

The cownose ray is experiencing a rebranding. Once maligned as a scourge of Chesapeake Bay oysters — "Save the Bay, Eat a Ray" urged a failed campaign to promote ray meat — the native species is being defended by researchers challenging theories blaming them for decimating oyster populations.

"We just want to dispel this myth that somehow the cownose rays are responsible for the collapse of shellfish," said Dean Grubbs, the associate director of research at Florida State University's Coastal and Marine Laboratory.

Grubbs recently published a study in the journal Scientific Reports that challenges past research suggesting that the dwindling population of sharks, which eat rays, resulted in more rays eating more shellfish.

"Cownose rays are natural predators ... and may inhibit some efforts to mitigate shellfish stock declines that resulted from overfishing, disease and habitat loss," Grubbs said in the study. "There is no evidence the cownose rays were the cause of the declines, but rather have been portrayed as scapegoats."

The rays, which can grow to the size of a doormat and forage by flapping their winglike fins and stirring up sediment to expose prey, drew wider public attention after ray fishing tournaments last summer.

Wildlife advocates filmed one tournament in St. Mary's County in June. The video showed edited scenes of fishermen using bows and arrows to shoot rays swimming at the surface. The rays were hauled in, flapping wildly, and then clubbed. One ray was visibly pregnant; some dead rays were dumped overboard. The video went viral, outraging viewers and transforming the rays' status from pariahs of the bay to abused animals.

A teenager started an online petition calling for the tournaments to be banned, and more than 94,000 people signed it. Tournament organizers said the clubbings were necessary to protect fishermen from venomous barbs on the spines of the rays. The cownose ray is a type of stingray but the venom is not usually deadly and has been compared to a bee sting.

State Department of Natural Resources officials have been working with biologists to gather research on the rays. The data "may be used to determine if the species is in need of management," said Karis King, a department spokeswoman.

In October, state officials and marine biologists along the Atlantic Coast, including Grubbs, convened in Baltimore for a workshop to share research and plan for the future of cownose rays.

Migrating rays arrive in the Chesapeake in May and remain until early fall. Schools of as many as 200 rays swim north, hunting for food. No one knows how many rays arrive each year, or precisely where they travel after leaving the bay. The rays are often seen flapping their fins at the surface. Sometimes they're mistaken for sharks.

The cownose ray is perhaps most famous for stinging Capt. John Smith, the English explorer famous for helping found Jamestown and the Virginia Colony. The sting was so severe that his crew thought he was going to die. Smith was stung at the mouth of the Rappahannock River, at a place now called Stingray Point. Legend has it that he was saved by Native Americans.

The ray remained in relative obscurity after that until it emerged as a scapegoat for the bay's plummeting oyster population, which is languishing at about 1 percent of its historic level. (Oyster beds once rose so high they scraped the ships of European explorers.)

While the decline in oysters has long been blamed on disease, habitat loss and overfishing, a March 2007 study in the journal Science suggested that the overfishing of sharks, which prey on rays, had led to more cownose rays eating the shellfish.

The Chesapeake Bay Program, the state and federal partnership charged with restoring the bay and its tributaries, issued a report in 2010 titled "On the Brink: Chesapeake's Native Oysters," which said fishing for the cownose ray should be encouraged.

Then the bow-fishing tournaments focused a different kind of attention on the rays.

"Conservation groups that were concerned about the bow-fishing tournaments seemed to start to bring the animal into the public eye," said Matthew Ogburn, a marine ecologist who is studying the rays at the Smithsonian Environmental Research Center in Edgewater.

After the October workshop, participants released a report in January that acknowledged claims by waterman that rays were devouring oyster beds but added that researchers had determined that oysters are not a dominant part of a ray's diet.

Then Grubbs' study, published Feb. 15, challenged the findings of the 2007 shark study and questioned whether ray populations had actually jumped. What's more, he said, even though a ray's jaws and teeth are designed to crush shellfish, their small mouths prevent them from munching large oysters.

"The oysters were gone long before," Grubbs said. "I understand the concerns of the watermen, but the solution is to protect the product: cages or whatever it may be. Not to try and control the predators. You'll never be able to."

Grubbs also cited research showing cownose rays birth a single pup, which would limit a sudden spike in population.

"It's a reasonable argument the Grubbs paper makes," said Ogburn, who was not involved with Grubbs' study. "There have been declines in shellfish fisheries in the Northeast in places the cownose rays don't go."

At the Smithsonian research center, Ogburn is tagging rays with transmitters to study their migration patterns.

"Hopefully, we'll get to a more balanced view of the cownose ray," he said. "It's a really interesting natural inhabitant of the Chesapeake Bay that we don't know much about."

tprudente@baltsun.com

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