When you buy what looks to be a nice piece of certified sustainable fish at the supermarket, you'd like to think that's exactly what you're getting. Unfortunately, things aren't always what they seem, according to researchers who have analyzed DNA isolated from store-bought, eco-labeled Chilean sea bass and report their findings in the August 23 issue of Current Biology.
"We found that, for fish purchased in US groceries, not all those labeled as MSC-certified Chilean sea bass are actually MSC-certified Chilean sea bass," said Peter Marko of Clemson University. MSC stands for the Marine Stewardship Council, an international organization dedicated to recognizing and rewarding sustainable fishing.
In the case of Chilean sea bass, MSC certification labels should indicate that a fish was harvested from the only recognized sustainable Chilean sea bass fishery, a population living in waters surrounding the sub-Antarctic island of South Georgia and a nearby plateau called Shag Rocks, Marko explained.
In fact, some of the fish that his team purchased turned out to be other species entirely. Of those that were Chilean sea bass, some 15 percent were genetically distinct from fish collected previously from the certified fishery. One sample carried a haplotype (defined as a combination of genetic variants in cellular components known as mitochondria) that has only been found on the other side of the globe, in the southern Indian Ocean. Other haplotypes that the researchers uncovered amongst fish marked with an MSC-certified label commonly trace to South American waters, and still others had never been recorded before in previous genetic surveys.
"The simplest explanation for this result is that other species plus Chilean sea bass from other, uncertified fisheries are being added to the supply chain for MSC-certified Chilean sea bass," Marko said. Although unexpected, "the results are not exactly shocking," given widespread mislabeling in the seafood industry and potential profits to be made.
It isn't clear who is responsible for the misleading labels, given that fish pass through many hands from the time they are caught to the time they are purchased.
"There is no question that organizations like the Marine Stewardship Council are trying their best to guide consumers to sustainably harvested seafood, but it is currently difficult to guarantee the geographic origins of fish," Marko said. He added that the MSC has been working on ways to confirm fishes' origins, and the new study may serve as a model for how to go about that.
The only thing it seems that concerned consumers can really do for now is keep Chilean sea bass off their dinner menus. "At a grocery or on a plate in a restaurant, Chilean sea bass from South Georgia looks the same as Chilean sea bass from other parts of the world," Marko said.
Explore further: Full-annual-cycle models track migratory bird populations throughout the year