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Official statistics tend to understate catches by local fishers, a new study finds. Here, a  Somali man carries a sailfish to Mogadishu's fish market in 2013.

Official statistics tend to understate catches by local fishers, a new study finds. Here, a Somali man carries a sailfish to Mogadishu's fish market in 2013.

AMISON Public Information/Flickr (CC0 1.0)

Official statistics understate global fish catch, new estimate concludes

Commonly cited statistics have understated the size of the global seafood catch by about 30%, a new tally finds. The estimate, drawn in part from a painstaking effort to gather statistics on poorly documented subsistence, recreational, and illegal fisheries, suggests that the world catch has also declined more steeply since the 1990s than official figures indicate.

Overall, fishers caught an estimated 109 million metric tons (mt) of fish in 2010, researchers report today in Nature Communications. That’s well above the 77 million mt that nations reported to the Food and Agriculture Organization (FAO) of the United Nations, which keeps global catch statistics.

The reconstructed 2010 catch was 15% below peak landings of 130 million mt in 1996, estimate the researchers, who are based at the University of British Columbia (UBC), Vancouver in Canada. In contrast, FAO figures for the same 14-year period showed an 11% decline, from 86 million mt to 77 million mt.

The researchers also suggest that incomplete statistics have led FAO to make questionable pronouncements: Not long ago, they note, one of the agency’s reports described global catch levels as “practically stable.” The new figures challenge that idea, the researchers say.

FAO officials, however, are pushing back against the validity of the new numbers. “Comparing reconstructed catches with FAO statistics would be like comparing apples and oranges,” wrote Marc Taconet, chief of FAO’s Fishery Statistics and Information Branch in Rome, in an email. He added that based on “several sources of biases in the [study’s] method and the wide uncertainty ranges, we express reservations that the paper’s conclusions of declining catch trends can be strongly opposed to FAO’s reports of stable capture production trends in recent years.”

Many fisheries scientists have long been skeptical of the completeness of FAO’s statistics. The agency relies on national governments to estimate all of their catch except discards, and many nations don’t have the interest or capacity to tally landings from artisanal, subsistence, and recreational fisheries. And some nations have over- or underreported catches for political reasons, or ignored illegal landings, further complicating efforts to understand how fish stocks—a key source of protein—are faring.

To try to fill those gaps, researchers with the Sea Around Us project at UBC tapped into a worldwide network of colleagues. Over more than a decade, they attempted to reconstruct historic catches by scouring a range of sources, including academic papers, government websites, and reports gathering dust in local libraries and government archives.

The biggest surprise, says lead author Daniel Pauly of UBC, was the size of the artisanal and subsistence catches, primarily in the developing world: They amounted to 25% of the total. Overall, these catches slightly increased during the study period as more people participated, the researchers found.

These fisheries are also putting worrying pressure on many fish stocks, the study concluded. In small island countries sprinkled across the Pacific and the Caribbean, for instance, Pauly says, “the situation is much worse than anyone knew: the catches of local reef fish were crashing all over the place and the government officials didn’t know or care.” Pauly hopes the study “will get governments to focus more on their local fisheries.”

Shrinking industrial landings, however, were responsible for most of the recent global catch decline, the researchers concluded. Industrial landings, which make up about 75% of the global total, dropped by about 2% a year between the 1990s and 2010, they estimate.

Some eye-popping findings emerged from the examination of the industrial catch, the researchers say. West African nations, for instance, historically appear to have reported to FAO just 40% of the catches made by local vessels in near-shore waters, found UBC’s Dyhia Belhabib. And foreign vessels that lacked licenses to fish in those waters accounted for just over one-half of the offshore catch, she found.

Such findings highlight the need for nations, and FAO, to improve record keeping, the authors say. Better numbers, they add, will be essential to developing policies to protect a key food source. “Fish stocks are like bank accounts,” says co-author Dirk Zeller, senior scientist and executive director of Sea Around Us. “You need to know how much there is, and at what interest rate your money’s growing, so you can decide how much you want to take out.”

One step FAO could take, the authors say, is asking nations to report both documented and estimated catches. “Most countries use extensive estimation, approximation and raising procedures, especially in developing countries,” Zeller says. “Hence essentially all countries could estimate uncertainties around their reported data if they chose.”

“We concur with the paper’s call upon countries’ responsibilities for improving reporting and for mobilizing funding resources,” FAO’s Taconet said, adding that the agency “always welcomes research efforts. … This type of research is crucial for stimulating international discussion on unreported catches.”

What the reconstruction team has done “is monumental!” wrote Trevor Branch, a fisheries scientist at the University of Washington, Seattle, in an email. Although he doubts all of the numbers are accurate, he expects the data will improve over time as more specialists contribute to the database.