Fisheries experts say China is vastly under-reporting the catches its fishing boats are taking from distant waters. A study released in March says Chinese boats are taking as much as 12 times official figures, particularly off the coast of West Africa. The United Nations food agency, however, says the study is overstating the problem.
China's growing economy, and appetite for seafood, has created the largest distant water fishing fleet in the world.
Official figures from 2011, the latest year available, show China had more than 1,600 fishing boats in waters outside what it defines as its exclusive economic zone.
From 2000 to 2011 Beijing reported those boats were responsible for an average annual overseas catch of 368,000 tons.
But research by the University of British Columbia and The Pew Charitable Trusts estimates the actual catch was far larger - about 4.6 million tons per year.
Daniel Pauly is a fisheries scientist at the University of British Columbia and author of the study (who spoke to VOA via Skype). "The Chinese fisheries, the distant water fisheries, do not publish data on what they catch. Chinese fishery statistics are very problematic," he said.
The study, titled China's Distant-Water Fisheries in the 21st Century
, was released in March and funded by the European Parliament.
Researchers estimated the actual catch by examining media and online reports to determine what boats were fishing where and for how long. Then they estimated how much each boat could expect to catch, given its size.
The study found most of China's under-reported catch, about 3.1 million tons, was taking place in rich fishing waters off the coast of West Africa.
The United Nations Food and Agriculture Organization publishes China's official fishing data.
Richard Grainger is chief of statistics and information at the FAO's Fisheries and Aquaculture Service. He acknowledges "major failings" in China's distant water fisheries data but nonetheless says the study's estimates are too high.
"The estimate is about three million tons and that would be nearly as much as the 3.8 million tons produced by 22 west African coastal states and 38 distant water fishing nations combined," Grainger explained.
Researchers acknowledge that the study's estimates have a relatively high margin of error because of the difficulty of gauging catches using their methodology.
Despite disagreement over how much the official figures undercount, Grainger acknowledges the tallies are too low partly because some Chinese catches are sold directly to African nations and are not counted among the distant water catches.
Fisheries scientist Pauly says some Chinese boats also operate under foreign flags to obscure their origin.
He says European boats are also guilty of under-reporting but the numbers are on a much smaller scale than China.
"The [European] fleet, altogether, was at most half of the fleet from China. And, now it is largely substituted…like a zero sum game. And, in some countries, the Chinese vessels have replaced European vessels," noted Pauly.
And, unlike European countries, China does not make public the fishing access agreements signed with other countries.
The secret deals and underreported catches threaten efforts to keep ocean fish stocks at sustainable levels, says scientist Pauly.
"The point is that you cannot assess what [is] the state of a stock if you don't know at all what is taken from it," stated Pauly. "And, we know from independent sources that the stocks are not doing well in West Africa. That we know."
Despite the shortcomings in the data, the FAO says China has improved the accuracy of its fishing statistics over the years, particularly in reporting its domestic catches. China was for years inflating its domestic catch as Chinese officials sought to portray themselves as more productive.