The world's oceans have been overfished far more than reported, according to a new study.
The report, published in the journal Nature Communications, reanalyzed worldwide catch data and compared it to information that the Food and Agriculture Organization of the United Nations uses. Researchers found that from 1950 to 2010, up to 30 percent more fish -- about 32 billion kilograms a year -- were caught than reported to the agency.
Much of this unreported seafood stems from small-scale fisherman, illegal operations and millions of tons of bycatch, or fish accidentally caught and then discarded.
In the same time period, global catch rates have fallen nearly three times faster than estimated as the industry struggles to find healthy populations to fish.
"You have a situation where we have long ceased to live off the interest," said Daniel Pauly, a professor at the University of British Columbia. "We now live off the capital."
Pauly and the study's co-author, Dirk Zeller, said a long history of commercial enterprises jumping from fishery to fishery has decimated global populations. While some countries like the United States, Australia and parts of Europe have quota systems in place when numbers grow dire, many other nations offer no such protection.
"Throughout most of the world there is effectively no management," Pauly said. "This sounds weird when you're in the [U.S.] and you know that there's a Coast Guard protecting the waters. But fisheries in the majority of the world have no management -- there are nominal rules that are simply not respected, or there are no rules."
He said aside from fisheries in Antarctica, which remains one of the last bastions of ocean, most have been grossly mismanaged. Around 9 percent of all fish caught -- equating to billions of tons -- are thrown out, the unintended victims of bycatch from mass fishing enterprises like shrimp trawlers.
Last year, a World Wildlife Fund study found many of the planet's fish populations were on the "brink of collapse," pointing to stocks of tuna and other fish that have declined by more than half since just 1970.
Pauly said consumers only need to look at the relatively common meal of fish and chips, which used to heavily feature cod. Now, as stocks of the fish have fallen to the point that officials have instituted months-long bans on catch, cheaper alternatives have mostly replaced the cod.
"It's very difficult to find the fish you expect," he said. "Cod is now a delicacy, and this process of luxurization is already underway."
Correction: A previous version of this article misstated the amount of fish that went unreported annually, giving the amount in tons rather than kilograms.
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