Global fish catches are significantly higher than official reports, and declines in fish stocks are greater than have been previously estimated, according to a new study.

Writing in the journal Nature Communications, Daniel Pauly and Dirk Zeller of the Sea Around Us project at the University of British Columbia conclude that the annual global fish catch is roughly 109 million metric tons, about 30 percent higher than the 77 million officially reported in 2010 by more than 200 countries and territories. This means that 32 million metric tons of fish goes unreported every year, “more than the weight of the entire population of the United States.”

These new figures show that overfishing worldwide is greater than had previously been thought, the authors say. According to the Food and Agriculture Organization of the United Nations, the global marine fish catch peaked in 1996 at 86 million metric tons, before declining slightly to its present level; the new study argues that the peak catch, in 1996, was in fact 130 million metric tons and has been declining, on average, by 1.2 million metric tons per year.

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“The world is withdrawing from a joint bank account of fish without knowing what has been withdrawn or the remaining balance,” Pauly said.

One of the reasons for the discrepancy in the catch figures, Pauly and Zeller say, is that official totals greatly underestimate the size of artisanal and subsistence fisheries worldwide. To their surprise, they found that these accounted for 25 percent of total catches; they slightly increased over the study period as more people participated. The bulk of the decline over the last 20 years, however, was due to decreases in industrial fisheries.

“Our results indicate that the declining is very strong and the declining is not due to countries fishing less,” Pauly said during a teleconference to announce the study. “It is due to the countries fishing too much and having exhausted one fish after the other.”

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The study arose from skepticism over the completeness of FAO figures, largely due to the fact that they rely on national governments reporting their own tallies, which for political or other reasons they might not always be disposed to do accurately.

Furthermore, when nations reported “no data,” that would “later be turned into a zero, which is a bad estimate  of the catch of an existing fishery.” Over the course of a decade, Pauly, Zeller and their team scoured existing records dating back to 1950, delved into colonial archives, consulted with 400 researchers around the globe and even pored through receipts and invoices.

FAO has pushed back against the findings; in an email to Christopher Pala at Science Magazine, Marc Taconet, chief of FAO’s Fishery Statistics and Information Branch in Rome stated that, “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.”

He did, however, “concur with the paper’s call upon countries’ responsibilities for improving reporting and for mobilizing funding resources.”

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Some of the solutions Pauly and Zeller propose for improving the quality of records include better funding to enable FAO to support its member countries, and asking those countries to file separate figures for industrial and artisanal fisheries and to provide both documented and, when data are poor, estimated catches.

However, they note that while such moves would improve records, catches will continue to decline unless there are more widespread efforts to impose fishing caps and rebuild stocks.