There are all sorts reasons why fish stocks are rapidly dwindling around the world. But one underrated problem is illegal fishing. One recent study found, for instance, that as many as one-third of the fish haul in areas like the Southwest Atlantic Ocean were caught illicitly.

Zoom. Enhance. (Chris Ratcliffe/BLOOMBERG)

In the past, tests to verify the source of different fish haven’t been very accurate. “[I]t’s really hard to determine what sorts of fish you’re receiving at the dock,” explains Kimberly Warner, a scientist at the D.C.-based advocacy group Oceana. “You can’t always tell with traditional DNA testing.”

That’s why so many marine conservationists — and others worried about overfishing and the “end of fish” — are so excited about a seemingly obscure new study in Nature Communications that outlines a novel method for figuring out where those fish that appear on the dock are actually coming from.

The study comes out of a E.U.-funded project called FishPopTrace that launched in 2008. The authors, led by Bangor University’s Gary Carvalho, say they’ve figured out a way to differentiate fish populations of the same species — to distinguish between, say, legal cod from the Eastern Baltic and illegal cod from the North Sea. By examining “single nucleotide polymorphisms,” tiny genetic variants, the researchers could determine the origins of Atlantic cod, Atlantic herring, sole, and European hake to within 93 to 100 percent accuracy.

That could prove incredibly useful. The E.U. already requires countries to label the origins of various fish products. Next year, member nations will have to launch pilot projects to trace populations. But, until now, there hasn’t been a good way to verify that these methods are actually accurate. “You’re never going to be able to track every single fish,” says Warner. “But these tests will go a long way in verifying the traceability standards.”

Of course, expanding this database to include other types of fish won’t be cheap or easy. The FishPopTrace project, after all, cost €4 million and has taken about four years just to build a forensics database for four fish species. And, in an interview with Science magazine, Carvalho explains that even if a global database is built, actually checking fish hauls could take 24 hours and cost $25 per fish. It’s a potential deterrent against illegal fishing, but not a free one.

Then again, rampant illegal fishing isn’t cheap, either: One 2009 study estimated that illicit fishing was costing the global industry about $10 billion to $23.5 billion per year. And, of course, if unchecked illegal catches are making conservation impossible — and fish populations everywhere start collapsing — that could cost a fair bit, too.

Related: The end of fish, in one chart.