Bay Journal

Plan to harvest cownose rays could be recipe for trouble

Fishery sought to reduce predation on oyster, grass beds; but rays' slow reproduction makes them particularly vulnerable

  • By Karl Blankenship on July 01, 2007
  • Comments are closed for this article.
A cownose ray produces only one pup per year. Rays, like sharks, are an elasmobranch, a type of fish whose skeleton is made of cartilage instead of bone. (R. Dean Grubbs) Cownose rays grow to about 3 feet in width. Adult males weigh about 26 pounds; females, 34. They are benthic feeders and flap their winglike fins against sediments to expose clams. (R. Dean Grubbs)

Last year, when scientists planted 750,000 oysters on a large reef in the Piankatank River, they thought it might prove to be a model for future large-scale restoration efforts.

Cownose rays, on the other hand, thought the exposed oysters lying on top of the reef were lunch. A herd of the winged fish descended on the reef, picking off the oysters. Within days, hardly any were left.

Tales of cownose rays ravaging oyster restoration sites, as well as some underwater grass revegetation projects, have become so common around the Bay that plans are in the works to turn the tables on them—by putting them on the table.

By creating a food market for rays—and therefore a fishery—some fishery managers hope to cull the ray population.

In Virginia, where the rays are most plentiful in the Bay, some consider them to be a more formidable obstacle to oyster restoration than the diseases that plague the shellfish. “In the next couple of years, it is our number one problem that we are trying to address for oyster restoration down here,” said Jim Wesson, who oversees oyster restoration efforts for the Virginia Marine Resources Commission.

Wesson said rays are not only an impediment to restoration, but also to aquaculture. New fast-growing strains of native oysters can be placed in the water and reach market size before succumbing to disease, but many oyster growers worry their investment will be wiped out by rays. “You could possibly have the private industry pour money into oyster restoration so it is not depending so much federal and state support,” he said.

But other scientists believe the solution being cooked up may be just as bad. If humans develop a taste for cownose rays, they say, it could result in taking too big of a bite out of the ray populations.

Dean Grubbs, program manager of the Shark Ecology Program at the Virginia Institute of Marine Science, called efforts to create a fishery “a really bad idea.”

Rays are slow-maturing fish: Females don’t reproduce until they are 7 or 8 years old, and males are typically 6 or 7. Further, females produce just one live pup per year. That, combined with the late maturity rate, is a recipe for overfishing, according to Grubbs and some of his colleagues.

A closely related species that lives off Brazil, Rhinoptera brasiliensis, which was targeted in the 1980s to supply a ray market in Korea was quickly overfished—and completely eliminated in some areas. The IUCN, an international scientific organization, recently warned the population may be “critically endangered.”

The IUCN has expressed similar concerns about the species found here. “If a fishery for the cownose rays is ever established, it could be devastating to the population without proper monitoring,” it said.

Cownose rays range from Brazil to New England, spending winters in warmer areas then migrating north in the summer. But no agency is responsible for managing the fish. As a result, no one knows the size of the population—or the number that enter the Chesapeake each year.

But concerns about cownose rays got a boost earlier this year when a study published in the journal Science blamed the overfishing of sharks along the East Coast for a booming ray population which, in turn, was causing declines in scallops, clams, oysters and other shellfish in the mid-Atlantic.

Cownose rays, the authors said, had increased by “an order-of-magnitude” since the 1970s, adding that the coastal population may number more than 40 million.

The paper said the “hyperabundant” cownose ray population consumes “a large quantity” of commercial and noncommercial bivalves. They estimated the cownose ray food demand in the Chesapeake alone was 840,000 metric tons of shellfish during their roughly 100-day occupancy—the 2003 Virginia oyster harvest was only 300 metric tons, the authors stated.

Others question whether the ray population has boomed. Grubbs and others are skeptical of the conclusion that cownose rays increased because sharks declined, saying the link between the species is not clear-cut. They say diet studies have not shown that rays are a significant portion of shark diets. And in the mid-Atlantic, most sharks don’t eat rays.

There are no surveys that effectively target cownose rays in the Bay or along the coast, they said, so evidence of a huge cownose ray increase is largely anecdotal. With its slow reproductive rate, they said a massive ray increase would have been difficult.

“The cownose ray situation is far from clear,” said John Musick, a professor of marine science at VIMS, and an expert on sharks. “I’ve been hearing anecdotal accounts that rays are up in the Bay since 1980. It depends on whose ox is gored.”

Grubbs and Musick said cownose rays could seem to be a bigger problem for oysters and grass beds simply because important foods such as razor clams, soft shell clams, oysters and other species are at, or near, record low abundances. So are underwater grass beds, which rays are blamed for destroying in their search for clams.

“If we hadn’t screwed up everything already, we wouldn’t be talking about this,” Grubbs said. “In a natural situation, they wouldn’t be a heavy enough predator to really worry about.”

Bob Fisher, a commercial fisheries specialist with the Virginia Sea Grant College Program at VIMS, said ray populations may be on the rise, but because of the decline of commercial fishermen—not necessarily sharks. Many fisheries which take rays in bycatch have been reduced over the years, both in the Bay and along the East Coast.

Complaints about rays have been rising not only in the Bay, but in other areas along the coast. “I’ve been hearing more and more from people in New Jersey and on the Eastern Shores of Virginia and Maryland of increasing problems with rays,” he said.

Tommy Leggett, an oyster fisheries scientist with the Chesapeake Bay Foundation, said the solution may not be a new fishery, but new restoration tactics. After losing so many oysters in the Piankatank project, the foundation and some others shifted gears to plant “spat on shell” oysters, where shells are placed in a tank so oyster larvae, or spat, settle on them.

When placed in the water, the shell provides a structure where the spat is protected from rays. A test last year involving the CBF; VIMS; and a commercial grower, the Bevins Oyster Company, planted 260 bushes of spat-on-shell, using native oysters bred to have some disease resistance and grow fast. It produced 775 bushels of market-size oysters.

“A cownose ray fishery may not be the best answer,” Leggett said. “Maybe the best answer is the restoration strategy using spat on shell. Rays have always been around, and they certainly didn’t devastate oyster reefs way back when—but then, our oysters grew in a reefy structure where rays couldn’t do harm to the oyster.”

Other solutions may be possible. Fisher has been working with techniques which, in effect, create a magnetic field that repels rays .

Nonetheless, Fisher supports having a cownose ray fishery—he’s researched potential markets since 1990. But he said the goal should not be to reduce predation on oysters because rays are highly opportunistic feeders, so that may never happen.

“A fishery should be developed for the cownose ray, but as a useable resource, something where management has to come in and impose strict requirements on its sustainability,” he said. A well- managed cownose ray fishery, he said, could provide a new income for watermen and a new product for the seafood industry.

Right now, Virginia’s cownose ray fishery is limited to the bycatch caught in other fishing gear. Instead of tossing them overboard, fishermen would have a market to sell rays. Also, the Virginia Marine Resources Commission for the first time is requiring fishermen to report their cownose ray catches to gather information.

With such a limited fishing effort, Wesson said it’s unlikely that rays will be overfished anytime soon. Spotter planes, used by the menhaden industry to find schools of fish, report seeing “millions and millions” of rays swimming into the Bay, he said. “It will take a number of years before we even approach getting cownose ray populations down to where there is a problem.”

The whole issue is moot, though, unless people are willing to eat rays. Unlike many other fish, cownose ray meat is dark. It has little fat but also little flavor—marketing efforts refer to it as “sauce friendly” because its taste largely depends on how it is prepared.

“People are very hesitant to try it,” Fisher said. “But once they try it, we’ve had 90 percent-plus liking it.”

The VMRC has supported marketing efforts aimed at enticing chefs to offer cownose rays on their menus. Some have begun offering the fish, usually as Chesapeake Ray—“cownose ray just doesn’t sound very enticing,” noted Shirley Estes, of the Virginia Marine Products Board. Over time, she said, “Chesapeake Ray” could find more acceptance at the dinner table. “Twenty years ago,” she pointed out, “no one was eating sushi.”

But scientists worry that more emphasis has been placed on developing a market than gathering information needed to manage a fishery.

That could change. The draft recommendations of the state’s Blue Ribbon Oyster Panel, which includes state officials, scientists, industry representatives and others, not only calls for building a market for rays, but also gathering more information to improve ray management.

“There was universal agreement that we’re not going to get very far with oyster restoration unless we figure out what to do with cownose rays,” said Jeff Corbin, assistant secretary for natural resources in Virginia.

But he agreed that even the most basic information about rays is lacking.

“It is kind of hard to set up a fishery on something when you don’t know how many fish you are going to be able to catch,” Corbin said. “Right now, they seem like a nuisance species, but when you are talking about something that only gives one birth a year, that is a situation where you can overfish that population pretty darn quick.”

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About Karl Blankenship

Karl Blankenship is editor of the Bay Journal and executive director of Chesapeake Media Service. He has served as editor of the Bay Journal since its inception in 1991. .(JavaScript must be enabled to view this email address).

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