Back in 2007, a landmark paper in Science changed how everyone thought about cownose rays. These smiley aquarium ambassadors suddenly became the most hated fish in the Atlantic. As the press release for that paper stated:
A team of Canadian and American ecologists, led by world-renowned fisheries biologist Ransom Myers at Dalhousie University, has found that overfishing the largest predatory sharks, such as the bull, great white, dusky, and hammerhead sharks, along the Atlantic Coast of the United States has led to an explosion of their ray, skate, and small shark prey species.
“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,” says co-author Julia Baum of Dalhousie.
The study, which described the evidence for a shark-ray-shellfish trophic cascade leading to a collapse of the Chesapeake Bay scallop fishery, became an instant classic. “This is the first published field experiment to demonstrate that the loss of sharks is cascading through ocean ecosystems and inflicting collateral damage on food fisheries such as scallops,” said Ellen Pikitch, then a professor at the University of Miami Rosenstiel School of Marine and Atmospheric Science and executive director of the Pew Institute for Ocean Science, in the original press release.
The study had all the ideal components of blockbuster research: it was led by one of the world’s most preeminent fisheries biologists. It played to both sides of an age-old rivalry; it had a strong shark conservation message, providing much needed data to support the claim that sharks are vital ecosystem components. Yet at the same time, the study hit home with locals and fishermen, explaining why a once lucrative fishery was reduced to a mere shell of its former glory. The phenomenon it described—a top-down trophic cascade, with sharks as the key species—had been hypothesized for years but never demonstrated. And, whether intended or not, the paper provided an easy and achievable solution for the area’s woes: fish the rays instead of the sharks, and everyone wins. Frankly, it just made sense.
“People thought ‘Finally! Some evidence for this top down control by sharks,’ and accepted it without critically reading and reviewing the paper,” said Dean Grubbs, an elasmobranch ecologist with Florida State University. Though Grubbs and others had issues with the paper’s methods and conclusions, especially regarding the reproductive biology of rays, their initial worries were drowned out by the loud trumpeting the paper received. “We were concerned that this could quickly get out of hand,” Grubbs said. And it did. The paper became one of the most well known studies ever conducted in marine ecology, garnering almost 900 citations in the last 9 years.
“It just seems like virtually everyone who wants to talk about shark conservation knows this story, and most of them believe it,” said Sonja Fordham, founder and president of the non-profit Shark Advocates International. But when she read the press release almost a decade ago, she remembers being “troubled” by the reference to “hordes” of cownose rays. Rays, after all, are just flattened sharks, and share many of the same life history characteristics that make sharks so vulnerable to overfishing in the first place. “The paper was very pro shark conservation, so I found it very surprising that it would not see the potential danger of suggesting that a different type of elasmobranch had run amok.”
Her worst fears were soon realized, as cownose rays became touted as sustainable seafood. The states where the rays are native, including Maryland and Virginia, pushed to put ray fillets on everyone’s plates. “As this fishery developed and this paper became more and more widely cited, we decided we had to put a rebuttal together,” said Grubbs. That rebuttal was published last week in Scientific Reports, and it tears the notion of a shark-ray-shellfish trophic cascade to shreds.
Sharks, Flat Sharks, and Shellfish
Grubbs was immediately skeptical of the the 2007 paper. One of the first red flags was that the species involved in the food web domino effect don’t interact that much in the oceans. Yes, they occur in the same areas, but if large sharks control cownose ray populations through predation pressure, then scientists should find lots of rays in the stomachs of those sharks all the time. Instead, all elasmobranchs combined (sharks and rays) are only a fraction of large sharks’ diets (less than 13%), and for most species, cownose rays are just a small portion of that. “Upon review of 39 published diet studies for the large coastal shark species considered, we determined that cownose rays have been identified only in the stomachs of blacktip and sandbar sharks in the northwest Atlantic, but at low frequencies of occurrence,” the authors explain. In blacktips, cownose rays were only 3% of the diet, while in sandbar sharks, they were a mere 0.3%. The lack of predation on cownose rays actually makes sense, given that a recent study off Australia found that reef sharks aren’t the top predators in their ecosystem, as previously believed; instead, sharks are akin to groupers or similar mid-size predatory fish. So right from the get-go, the idea that sharks control ray populations because they’re apex predators is tenuous at best.
The support for the cascade gets even shakier when the stomachs of the rays are factored in. Scientists have found that scallops and oysters aren’t among the main prey items of cownose rays. In Chesapeake Bay, for example, scientists identified oysters and hard clams in less than 3% of cownose ray stomachs, and only 5% of rays harvested from commercial oyster grounds actually contained oysters. In fact, cownose rays prefer clams over oysters to begin with, and softer shelled mollusks in general, as large oysters are too big and tough for the rays to eat.
So not only do the sharks rarely eat the rays, the rays rarely eat the shellfish that they are supposedly wiping out. Of course, that’s not nearly as compelling a story.
“I have heard tales of how a school of cownose rays can decimate the young shellfish in a clam or oyster bed,” wrote Mary Reid Barrow in 2010, opining on why it is so important to eat cownose rays. “Gangs of bad-boy rays are free to roam the bay wreaking havoc on clam and oyster beds for their favorite meals, with no sharks to police them.” Opinion pieces like Barrow’s began to appear in papers and magazines all along the east coast beginning in 2007. Even non-profit organizations were convinced by the compelling narrative, helping spread the notion that the rays were an environmental disaster. Though sharks barely eat rays, and rays barely eat scallops and oysters, the tale of a trophic cascade and the renegade rays sold hook, line, and sinker. Suddenly, it was open season on cownose rays, and people began killing as many as they could.
Cownose ray bow hunts, in particular, have become a popular sport. Photo by NatesPics
The market to support the culls, however, wasn’t as easy a sell. “I’m a great fan of Virginia’s sustainable seafood choices, like clams, oysters and striped bass,” Barrow wrote, “but ray meat is going to take some time.”
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Back in 2007, Fordham was in Brussels working European shark policy. “I remember a seafood company displaying at the Brussels seafood show with cownose ray, and they were advertising it as a sustainable seafood. I asked ‘on what basis do you call it sustainable?’ and she said ‘oh, it’s a nuisance.'”
“It’s got a meaty texture to it,” explained Mike Hutt, spokesman for the Virginia Marine Products Board in Newport News, VA, to The Washington Post‘s Eric Ruth in 2012. “We tell people it’s like veal, flank steak, pork.”
A lot of effort has been put into convincing customers to eat cownose rays, including an aggressive seafood marketing campaign bolstered by $75,000 in funding from the Virginia Marine Resources Commission. Since the name “cownose” wasn’t deemed appetizing enough, they were renamed “Chesapeake Rays.” Popular chefs were encouraged to create ray recipes. Local culinary schools were brought in for tasting events, and even the Virginia Aquarium pushed the animals as sustainable.
“The original marketing materials for the ‘Save the Bay, Eat a Ray’ campaign really made the most of this impression that the population was out of control,” explained Fordham.”It was the usual message of ‘Hey, try this great new seafood—veal of the Chesapeake! but also ‘It’s your responsibility to help the bay.'” But though the fish was featured by national outlets and on popular TV shows, the market never took off the way some had hoped.
That doesn’t mean the rays were left in peace, though. While the food market floundered, recreational ray fishing boomed. Thanks to locally organized bow fishing tournaments, an untold number of rays are killed annually in competitions for weight-based prizes.
Though these tournaments have been occurring for several years, recent footage of such “bloodbaths” like the videos above ignited a firestorm of criticism, putting animal rights activists at odds with environmentally-conscious ocean lovers. “I think it’s unfortunate that so many people believe that these animals are a scourge and out of control, and that bow hunting them would be a good sport,” said Fordham. She described some of the stomach-churning practices employed in the tournaments—practices which arose because the rays were so villainized. “Killing as many as you can and targeting pregnant females… it is all seen as good.”
The truth is, cownose rays were in the fishing industry’s crosshairs long before the 2007 paper. “Commercial fishers for bivalves have called for a fishery for cownose rays for many decades because they claimed that the rays were eating their product,” said Grubbs, even though the available data didn’t support their assertions. In addition to their bad reputation as shellfish thieves, cownose rays are considered a nuisance to fishermen because their large schooling aggregations can clog nets and trawls, damage expensive gear, and inhibit landings for more lucrative species. According to Grubbs, a fishery for cownose rays is proposed “every ten years or so,” but until the most recent push, the idea was always rejected. “Everyone recognized that starting a fishery for something with such low fecundity doesn’t make sense,” he said, “but then this Science paper in 2007 gave them scientific backing.”
Phantom Sharks and Terminator Rays
The essential argument of the 2007 paper was that of uncanny coincidence: sudden and substantial ray population increases coincided with sharp shark and scallop population declines, thus it seemed obvious that a lack of shark predation released the rays, allowing them to overpopulate and eat their way through the prized commercial shellfish fisheries.
However, for some unknown reason, Myers and his colleagues used only one shark survey with two stations to make their bold claims—”The eastern seaboard’s longest continuous shark-targeted survey (UNC), conducted annually since 1972 off North Carolina”—when other data sources were available. The Virginia Institute of Marine Science (VIMS) has conducted a similar survey with more stations for nearly as long (since 1973), for example, which Myers and his colleagues could have examined. Grubbs and his colleagues decided to compare the surveys considering they’re only about 200 kilometers apart, but when they used the VIMS shark count numbers instead of UNC’s, their results were shocking.
A fishery-independent shark survey from the Virginia Institute of Marine Science found shark populations increased alongside those of rays. Part 1 of Figure 2 from Grubbs et al. 2016
“Our data show that the increase in cownose rays in the 1990s and early 2000s coincided with an increase, not a decrease, in sandbar, dusky, and blacktip sharks,” said co-author Jack Musick, emeritus professor with William & Mary’s Virginia Institute of Marine Science who began the VIMS shark survey in the early 70’s. “That’s exactly opposite what you’d expect if a rise in ray numbers were caused by a drop in shark predation.”
That’s not to say that the VIMS numbers are right, either. According to the authors, the differences between the two surveys “illustrate the dangers of broadly interpreting results from a single index with limited scope and applying those results to an entire population.”
“We don’t posit that either the North Carolina or the Virginia surveys actually track the abundance,” said Grubbs. “We recommend that readers go to the stock assessments because those use all of the available data sets.” According to those assessments, large coastal sharks never declined to the levels suggested in the 2007 paper.
“There’s been this narrative of global declines in large fishes, particularly in large coastal sharks, and in many cases it’s true,” said Grubbs. The well known decline of shark species globally is part of what made the results of the North Carolina survey so easy to believe. But the United States was one of the first countries to regulate their shark fisheries, and since rules were imposed, the sharks have begun to rebound.”The fishery for large coastal sharks on the east coast of the US is one of the most aggressively managed fisheries in the world, and we’ve had some real positive outcomes,” said Grubbs.
The use of the single survey to track shark populations was much more than a small oversight, Grubbs asserted. “I won’t let them off the hook for just assuming that the one survey in North Carolina tracks the abundance of sharks,” he said, “because the stock assessments were available then. They’re free to the public; they’re open. So to not even cite those stock assessments and acknowledge that they’re there is inexcusable.”
It would still be possible, of course, for the second half of the cascade to be true—that increases in ray populations led to decreases in scallops and oysters—even if the sharks weren’t involved. But, as the new paper demonstrates, the timing of scallop and oyster declines doesn’t match up with the ray population increases. The shellfish fisheries were headed downhill for decades due to a myriad of factors, from overharvesting and habitat degradation to disease outbreaks and harmful algal blooms. “The stocks of those bivalves crashed way before the increase in cownose rays, so the rays couldn’t have been the culprit,” Grubbs explained, “unless, like The Terminator, cownose rays went back from the future to eat all the scallops and oysters.”
The shellfish fisheries were declining for decades before the rays took off. Figure 5 from Grubbs et al. 2016
Grubbs said that he’s “baffled” that the authors of the 2007 study overlooked the temporal mismatch. “I actually brought this up to one of the corresponding authors when he presented this paper before it was published,” Grubbs said. “That mismatch is just obvious.”
“I don’t know how they missed it, and I don’t know how the reviewers missed it.” Neither of the Science paper’s corresponding authors, Julie Baum and Charles Peterson, responded to requests for comment.
Lessons From The Ghost of Rays Past
Fishermen and locals often cite large herds of cownose rays as evidence that their populations are doing just fine. But, of course, that’s what the Brazilians thought when they started shipping their cownose rays to Korea in the 1980s.
Brazilian cownose rays were once plentiful, also appearing in schools that numbered in the thousands. From 1982-1985, these rays filled seine nets off Rio Grande do Sul, with hundreds to thousands caught in each haul. At first they were considered trash fish and tossed, but when the fishing community realized that the rays were considered a Korean delicacy, they began keeping their ray landings, and the Brazilian cownose ray market flourished. Then, the rays disappeared. By the early 2000s, just a couple decades after the fishery began, the animals could no longer be found in their native waters off Rio Grande do Sul. The Brazilian cownose ray is now listed as endangered, but the IUCN notes that the rays may actually be critically endangered—better surveys are needed to determine just how many are left.
Atlantic cownose rays are considered near threatened by the IUCN Red List, though that’s with no existing population size estimates. “If a fishery for cownose rays is ever established, it could be devastating to the population without proper monitoring,” the IUCN warns in its assessment. “There is an urgent need to determine the current population status and catch levels.” Yet such studies have not been conducted. “There’s no stock assessment, no fishery management plan for cownose rays,” Grubbs said. “So we really don’t know what their stock is doing.”
Without population numbers, the fisheries managers say they can’t set catch limits, but Fordham and others say that’s not true. “There’s a double standard here for sharks versus rays,” she said. “Along the Atlantic coast, there are about 20 species of sharks that are prohibited, and not all of them have population assessments.” She pointed out that basking sharks, white sharks, and whale sharks have never been properly assessed, but they’re not allowed to be fished. “It’s just the understanding and acceptance that these are vulnerable animals and having commercial fisheries for them is not a good idea.”
Like their shark relatives, cownose rays have an extremely conservative and vulnerable life history. They take six to eight years to mature, and females give birth to only one pup each year. “It has biology akin to a manta ray,” Fordham notes. “We don’t have a population assessment—we don’t have that kind of rigorous data—but we do have information about the biology that is sufficient to tell us that these animals cannot withstand heavy fishing pressure.” That biology also suggests that the rate of population increase claimed by Myers and his colleagues doesn’t hold up. According to Grubbs and his coauthors, cownose rays have one of the lowest lifetime fecundity estimates of any fish (even lower than most sharks!), and thus “such high population growth rates are inconsistent with the biology of the species.”
In July of 2010, the American Elasmobranch Society made an official resolution calling for immediate catch limits until a proper population assessment could be conducted:
“Therefore be it resolved that the American Elasmobranch Society urges Atlantic states where cownose rays are being landed, particularly Virginia and Maryland, to immediately impose precautionary cownose ray catch limits and initiate development of a population assessment and science-based interstate management plan, as a matter of priority.”
Those involved in the fishery have paid no heed to such concerns, claiming that four million pounds of ray could be caught without impacting the population (an oddly specific number given the lack of any kind of stock assessment). “If the market takes off, we’ll need to establish catch limits,” said John M.R. Bull, spokesman for the Virginia Marine Resources Commission, to Lorraine Eaton of The Virginian-Pilot.
Save the Bay, Eat Sustainable Seafood (NotCownose Rays)
For the past nine years, cownose rays have been demonized and punished for crimes they didn’t commit. But even with all the data presented in last week’s rebuttal, exonerating the rays may prove difficult. Restoring the rays reputation will require undoing years of targeted sales and marketing.
“There’s nothing to stop people from taking as many rays as they want right now,” said Fordham. She hopes that enough attention can be drawn to the new paper to convince managers to take the concerns about the rays’ sustainability seriously. “This is one of the most vulnerable even among the elasmobranchs,” she noted. “Trying to prevent disaster with some precautionary limits is an important first step.”
“I’m hoping that people get the message.”
Rays on the whole are more threatened and less protected than sharks, but Fordham is worried that people “just don’t care as much” about the flat sharks as they do about their relatives. “It’s a very compelling story to say that there are negative consequences for taking too many sharks,” said Fordham. “Now it’s time to expand our notion of what a shark is—the flat ones need attention, too.”
Protecting sharks and rays equally doesn’t mean that we have to stop fishing for these species altogether, say experts. In fact, a recent study found that elasmobranch scientists believe that sustainable shark fishing is doable. “When possible, shark researchers prefer policies that allow for sustainable fisheries exploitation over policies that ban all shark fishing,” said lead author on that paper and University of Miami shark scientist David Shiffman. But those fisheries depend upon reliable data on how many animals there are and detailed information about their biology and ecology. “The biology of the cownose ray does not support a full scale fishery,” said Shiffman. “I think we need strong, science-based management for the cownose rays—not ‘Eat a Ray, Save the Bay’ but ‘Save the Rays.'”
Scientists hope Grubbs et al.’s paper gives this guy something to smile about. Photo by aon168
It was a mistake to interpret the 2007 paper as an indictment of cownose rays. And when you think about it, the ‘kill the rays’ reaction to Myers paper makes no sense: the overwhelming response to a paper about how overfishing elasmobranchs can have negative consequences was to heavily fish an elasmobranch without any regard for the consequences.
“We’re most hopeful that this paper leads to more discussion and movement among the fisheries managers,” said Grubbs. “If they’re going to allow these bow fishing tournaments as well as other recreational fisheries and commercial fisheries to exist for cownose rays, then we hope that they try to assess what the stock status is and implement at least some precautionary catch limits.”
“These rays are very similar to (and perhaps even more vulnerable than) those large sharks that everyone is worried about,” he continued. “Allowing an unregulated fishery for them is as foolish as it was to let the fisheries for the large sharks to develop unregulated.”
Citation: Grubbs, R. Dean, et al. “Critical assessment and ramifications of a purported marine trophic cascade.” Scientific Reports 6 (2016): 20970. doi:10.1038/srep20970