Cownose rays not to blame for shellfish declines, study says
Researchers led by Florida State scientist counter widely quoted 2007 study linking shark declines to an explosion in rays, which then devoured oysters, clams and scallops.
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Contrary to earlier research and popular belief, cownose rays are not to blame for declines in oyster and other shellfish stocks in the Chesapeake Bay, a new study asserts.
In a paper published today in the journal Scientific Reports, a team of scientists led by Florida State University’s Dean Grubbs counters a widely cited 2007 study that found that the overfishing of large sharks had led to an explosion in the population of rays, which in turn had devoured bivalves, clams and scallops along the East Coast.
The earlier study, published in Science, spurred campaigns in Maryland and Virginia to protect oysters and clams by targeting cownose rays, under the slogan “Save the Bay, Eat a Ray.”
Virginia’s Marine Products Board endorsed the creation of a ray fishery and promoted the majestic, hawk-like sea creature as the “veal of the Chesapeake.” In Maryland, local outdoorsmen organized bow fishing tournaments, where fishermen would shoot and kill hundreds of rays and win prizes for the animals based on weight. Neither state has a management plan for the species, though they and the Chesapeake Bay Program are working on one.
Grubbs and his co-authors concluded that the 2007 Science paper over-stated both the decline in big sharks and the ability of cownose rays to reproduce enough to devastate shellfish populations. Rays mature slowly and do not reproduce until age 6 or 7. Females produce only one pup a year, in a live birth. Furthermore, Grubbs said, oysters declined long before sharks, victims of disease, over-harvesting, over-sedimentation and habitat loss.
“Cownose rays have been used as a convenient scapegoat, and while they may negatively affect some efforts to restore harvestable shellfish stocks, they were not the cause of the collapse of shellfish fisheries, as the 2007 study claimed,” Grubbs said.
Grubbs said he hopes that the paper leads to precautionary regulations for the ray fishery before it’s too late; the Brazilian cownose ray, he said, is now critically endangered because of unregulated fisheries.
The Florida State-led work follows a study by Robert Fisher of the Virginia Institute of Marine Science, which examined the contents of rays’ stomachs and found that while they eat oysters, the shellfish are not their primary source of food. VIMS collaborated on the Florida State work, as did the U.S. Geological Survey and the National Oceanic and Atmospheric Administration. Fisher is continuing to work with Smithsonian Environmental Research Center’s Matt Ogburn to track rays’ migration along the coast and in the Chesapeake.
Grubbs’ co-leader, Charles Cotton, said he hopes that the new research will lead to a re-thinking of how to manage the ray species.
“One of our primary concerns that led to this study was the effect of a fishery with no harvest limits on a species with low reproductive rates, particularly as this was being incorrectly touted as an ‘environmentally responsible’ seafood choice,” he said. “Evidence-based management decisions are critical in preventing overfishing, as we’ve seen many times in the past with unregulated fisheries for other species of sharks and rays.”
The 2007 study built on a 2003 study by the same authors also published in Science, and it helped influence the open-season mentality on rays in Chesapeake Bay.
"With fewer sharks around, the species they prey upon -- like cownose rays -- have increased in numbers, and in turn, hordes of cownose rays dining on bay scallops, have wiped the scallops out," said co-author Julia Baum of Dalhousie University in Halifax, who was one of the authors of both the 2003 and 2007 studies.
The killing of the cownose rays had been an under-the-radar activity until spring of 2015, when animal rights groups filmed a bow fishing tournament on the Patuxent River. The video showed men shooting rays at close range, then beating them with baseball bats. The rays were not consumed, for the most part, as ray meat is hard to cook and has a strong urine taste. Some of the carcasses were used as fertilizer, but pictures of the dead rays piled high drew criticism that the tournament was nothing more than blood sport.
The video prompted both Virginia and Maryland, as well as the Chesapeake Bay Program, to review the way they manage the ray population in the Chesapeake, though no decisions have been made yet. Humane Society executives met with Virginia Marine Resources Commissioner John M.R. Bull after the video surfaced, who said the commission’s finfish advisory committee would look into the matter. VMRC spokeswoman Laurie Naismith said the commission wanted to fully study the issue instead of reacting to an upsetting video.
Robbie Bowe, the owner of an outdoors shop in Woodbridge, VA, who organized the tournaments in Southern Maryland for 18 years, told the Bay Journal last year that the men did nothing wrong.
“It was a profitable tournament and fun to be had by all. It was a great thing for the sportsmen,” he said.
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