A worker cuts a steak from a piece of tuna at a fish market. Seafood counters used to be simpler places, where a fish was labeled with its name and price. Nowadays, it carries more information than a used-car listing. Where did it swim? Was it farm-raised? Was it ever frozen? How much harm was done to the ocean by fishing it? (Scott Eells/Bloomberg)

Seafood counters used to be simpler places, where a fish was labeled with its name and price. Nowadays, it carries more information than a used-car listing. Where did it swim? Was it farm-raised? Was it ever frozen? How much harm was done to the ocean by fishing it?

Many retailers tout the environmental credentials of their seafood, but a growing number of scientists have begun to question whether these certification systems deliver on their promises. The labels give customers a false impression that purchasing certain products helps the ocean more than it really does, some researchers say.

Backers respond that they are helping transform many of the globe’s wild-caught fisheries, giving them a financial incentive to include environmental safeguards, while giving consumers a sense of what they can eat with a clear conscience.

To add to the confusion, there are a variety of certification labels and guides, prompting retailers to adopt a hybrid approach, relying on multiple seafood rating systems or establishing their own criteria and screening products that way.

As of Sunday, for example, Whole Foods stopped selling seafood listed as “red” by the Monterey Bay Aquarium and Blue Ocean Institute — including octopus, gray sole and Atlantic halibut — because these species are overfished or caught in a way that harms ocean habitat or other species. The move has sparked criticism from New England fishermen, who are now barred from selling to the upscale chain. Whole Foods also sells only pole- or line-caught canned tuna, which harms fewer species than conventional tuna-fishing methods.

Target no longer sells farmed salmon — which has come under fire for consuming a disproportionate amount of forage fish and creating several other problems — and has pledged that by 2015 it will sell only fresh and frozen fish that are “sustainable and traceable.” Wegmans said it will not obtain seafood from the Ross Sea in the Antarctic, which many environmentalists say should be off-limits to fishing, and this fall it will start selling oysters from plots it has leased in the Chesapeake Bay as part of a fishery restoration project. Beginning in June, Wal-Mart, the nation’s largest seafood retailer, will require all of its fresh and frozen wild-caught and farmed seafood to be certified by a third party as sustainable or have a plan in place for suppliers to be certified. At this point, 76 percent of its suppliers are certified.

Blue Ocean Institute President Carl Safina, a scientist who published the first sustainability rankings for commonly eaten fish in 1998, said that a decade ago, eating a piece of fish was akin to eating a piece of bread.

“You just picked it up and ate it. It wasn’t subject to any discussion or inquiry,” he said. “Now it’s a broad discussion about where it came from, about whether it’s sustainable. This is enormous progress compared to the change we’ve made to any other form of food production in the same amount of time.”

The most stringent and commonly used certification is that of the Marine Stewardship Council, which has certified 148 wild-caught fisheries, or between 6 and 7 percent of the global supply. It uses independent reviewers to determine whether a fishery earns an MSC-certified label and can be classified as sustainable — meaning that the fish is relatively abundant, the fishery is well managed, and catching it does not harm other species or ocean habitats.

It is a measure of the attention focused on the world’s fish stocks that the council’s work has come under scrutiny.

A study published online last week in the journal Marine Policy showed that, for fish stocks where there was sufficient information, 31 percent of MSC-certified stocks were overfished and subject to continuing overfishing.

“Certifiers must sharpen their criteria and close any loopholes,” said Rainer Froese, a senior scientist at the Helmholtz Centre for Ocean Research and lead author of the study, who said consumers should still buy certified seafood. “Given that there are thousands of [fish] stocks, there needs to be some guidance on which ones you can eat and have a good conscience.”

MSC officials have questioned the Marine Policy analysis, saying it exaggerated the rate of overexploitation by not adequately accounting for year-to-year fluctuations in fish stocks. “The MSC standard is consistent with best practice and specifically excludes fisheries that are overfished,” David Agnew, the council’s director of standards, said in a statement.

“They don’t certify perfect fisheries. They certify well-managed fisheries,” said Michael Sutton, the Monterey Bay Aquarium vice president, who helped set up the certification system while working at the environmental group WWF International.

The debate over the effectiveness of seafood certification systems has sparked several competing academic papers in the past few years, although the Marine Policy analysis was the most comprehensive overview so far. An upcoming publication in the Reviews in Fisheries Science suggests fisheries improved their environmental performance throughout the certification process; other papers in journals such as Nature, Fauna & Flora International and Conservation Biology have argued these requirements need to be strengthened.

For operators such as Scott Taylor, co-founder of Day Boat Seafood in Lake Park, Fla., spending more than three years and over $100,000 to be certified by the MSC in December was a worthwhile business proposition. Taylor sells swordfish caught with long lines and buoy gear in his Atlantic Ocean fishery, and he has pledged to have observers on all of his boats within five years to ensure that they minimize the number of turtles and sharks caught accidentally.

“There has to be a way to differentiate the product” as environmentally friendly, Taylor said of the benefit to fishermen of an MSC certification. “Does that mean there’s a financial incentive for them? In short, yes, there has to be.”

But several researchers and environmentalists question whether every MSC-certified fishery meets those high standards, and they say that a few questionable ones undermine the better-managed fisheries. On Thursday, the council approved the eastern Canada swordfish long-line fishery, which kills roughly 35,000 sharks and a few hundred endangered sea turtles each year.

“The bar has been lowered gradually, and now they certify everything that moves,” said Daniel Pauly, a marine biologist at the University of British Columbia Fisheries Center who once supported MSC certification.

Kerry Coughlin, the MSC’s regional director for the Americas, said in a statement that the Canadian swordfish fishery “has committed to efforts to further protect turtles, ensure the sustainability of the swordfish stock, and monitor and research shark bycatch. Working together, all parties involved have advanced efforts to ensure a sustainable harvest that does not harm other marine populations.”

Meanwhile, some fisheries, including Iceland’s and several in Alaska, are opting for the Irish-based Global Trust Certification, which evaluates their performance on the basis of U.N. guidelines that several scientists said are less stringent. Global Trust spokesman Michael Carroll said his group holds fisheries to a high, internationally recognized standard.

For some American consumers, the credibility of these standards is critical. Snejana Andjelkovic, shopping at the Whole Foods store on P Street NW in the District, said she scrutinizes labels “because I care about the environment and what I eat, what I put in my stomach.”

Pointing to the Chilean sea bass sitting on ice — from a small fishery off the Falklands that was certified by the MSC — Andjelkovic said she wouldn’t buy it, because the vast majority of Chilean sea bass is caught illegally and unsustainably. “They say it’s okay,” she said. “That’s not true.”

Others at the same counter, such as Jessica Max, an information technology recruiter, were more confused by the labels.

“I care about things like frozen and fresh,” she said, buying shrimp and MSC-certified Chilean sea bass. “I would appreciate if they were more meaningful and consistent.”