The world's biggest scheme to certify that seafish come from sustainable sources has come under fire in a scientific journal, where researchers say the label is too generous and may "mislead" consumers.

Writing in the journal Biological Conservation, a team of scientists say that objections made to the Marine Stewardship Council (MSC) about its well-known labelling scheme fail to get properly vetted.

Out of 19 objections filed to the MSC, only one has been upheld that has led to a refusal to certify a fishery, the study said. It also said there had been cases of mislabelling.

Objections include lack of knowledge about the long-term impact of fishing; accidental catch of endangered sharks and turtles; and the impact of dredging or seafloor trawling on bottom-living species.

"The MSC's principles for sustainable fishing are too lenient and discretionary, and allow for overly generous interpretation by third-party certifiers and adjudicators, which means that the MSC label may be misleading both consumers and conservation funders," the paper, published on Friday, said.

The MSC was founded in 1997 as a joint project between the World Wildlife Fund (WWF) and Unilever, the food and household project giant, which wanted to buy all its fish from sustainable sources by 2005.

Its goal is to reassure consumers that the fish come from well-managed fisheries that encourage stocks to regenerate.

The MSC label, whose criteria were designed by environmental NGOs, academics and commercial interests, often carries a price premium at the shop counter.

Fisheries seeking certification pay a fee, ranging between $15,000 and $120,000 (11,538 and 92,300 euros), and must also stump up for an audit, which likewise is carried out by external assessors.

An individual or organisation that wants to raise an objection also has to pay a fee, capped at $7,500 (5,769 euros), but this can be waived in the event of financial hardship.

Responding to the criticism, the MSC said its procedure was "independent, fair and transparent."

It attacked the study on the grounds of methodology and said it also appeared to have a conflict of interest, as some of the researchers, or the NGOs that employed them, had filed about a third of the objections.

In nine cases where objections had been raised, fisheries were indeed given certification but had had to meet 13 additional conditions, the MSC said.

In addition, the MSC had refused certification to nine other applicants, even when no-one had lodged an objection, the group said.

In other cases, fisheries had been required to supply additional data about the impact of trawling on the ecosystem.

As of December last year, 183 marine fisheries had the MSC label and another 109 fisheries were seeking certification, which together would account for just over 10 percent of reported global catch.