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By Rachel Nuwer, ScienceNOW
It’s no wonder that fish stocks around the world are plummeting. Up to 25 percent of the global catch comes from illegal, unreported, and unregulated fishing. Now, science has stepped in to offer a new method to identify contraband fish. A €4 million pan-European project, launched in 2008 and called FishPopTrace, has devised a much-anticipated way to differentiate marine populations of the same species with up to 100 percent accuracy.
Regulatory agencies like those in the European Union are trying to crack down on the illegal fish trade, but the task is not easy. How does a manager tell the difference between, for example, an illegally harvested Northeast Arctic cod and a perfectly legal Eastern Baltic cod? They belong to the same species but come from very different populations.
The new approach relies on genetic variants called single-nucleotide polymorphisms. SNPs occur when tiny segments of DNA differ between populations. For example, the Northeast Arctic cod may have a C nucleotide in the middle of a gene, whereas the Eastern Baltic cod may instead have a T in the same position.
The researchers decided to focus their method on four of the most over-exploited fish species in Europe: cod, hake, herring, and sole. They wanted to figure out the smallest number of SNPs needed to accurately identify a population. To do that, they first flagged hundreds or thousands of SNPs in each species. Then they used simulations to identify the most reliable pattern of SNPs for identifying populations of each species. For example, with just 14 SNPs, the researchers were able to pinpoint the source of 98 percent of 766 samples of hake.
All in all, the new method’s accuracy varied from 93 percent to 100 percent. The researchers think most of the scant outliers that slipped through the SNP test were likely migrant fish that had sneaked into other populations. In the real world, sampling several fish from each catch should take care of this problem. Gary Carvalho, a molecular ecologist at Bangor University in the United Kingdom and coordinator of FishPopTrace, and colleagues published their results today online in Nature Communications.
“This is a tremendous breakthrough,” says Kimberly Warner, a senior scientist at the international advocacy group Oceana located in Washington, D.C., who was not involved in the study. “These are critical tools in our fight against illegal fishing and mislabeling and enable us to put some teeth into our fisheries laws and eco-certifications.”
This technique arrives just in time. The European Union requires all E.U. member states to undertake pilot studies of fish population tracing tools by 2013. Already, the European Union demands species and origin labels on all fish products. Existing DNA tests can easily determine species, and SNPs will potentially reveal the origin, at least for the four species studied in FishPopTrace. The United Kingdom will likely be the first to vet the authenticity of fish origin labels on supermarket shelves in an upcoming pilot project.
The researchers hope the tool can be used far beyond European ports. Indeed, the United Nations Food and Agriculture Organization recently established its own fisheries forensics expert group and is keen to adopt the new technique, Carvalho says. The researchers think that the threat of forensic testing will be a significant deterrent against illegal harvesting. For this goal to be realized, though, all countries need to be on board. If not, criminals will unload at ports with lenient inspectors rather than those that use forensic validation. “Fish don’t respect national boundaries,” Carvalho says. “There’s no point in the U.K. doing this if neighboring nations don’t also adopt it.”
Identifying SNPs for all commercial species will be expensive, but once an open-access database is in place, the researchers say that the tests could be widely used. “We anticipate a global database where these data on genetic signatures -- the SNP signatures -- can be openly downloaded,” Carvalho says. So long as labs are properly equipped, samples can usually be analyzed in less than 24 hours -- still a long time in the fish business -- and cost less than $25 per fish.
This story provided by ScienceNOW, the daily online news service of the journal Science.
*Image: NEFSC/NOAA
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