for National Geographic Today
Researchers have developed a way to "fingerprint" cod.
The technique, essentially a genetic identification tag, enables researchers to determine a specific cod's place of origin, which could be particularly useful in enforcing international fishing quotas and catching poachers.
Until now there have been no means for determining where cod have been caught once they end up at the fish market.
A team led by Einar Nielsen of the Danish Institute for Fisheries Research identified genetic markersunique regions of DNAwhich the researchers are using to distinguish whether individual cod come from the northeastern Arctic Ocean, the North Sea, or the Baltic Sea. These three cod populations are thought to be at dangerously low levels, and fishing of them is tightly regulated.
The three populations are so different that as few as two or three fish "can provide an unambiguous conclusion about the origin of the sample," Nielsen and his colleagues wrote in a scientific report published in the September 20 issue of the journal Nature.
"I was impressed by how different these three populations were," said ecologist Jeffrey Hutchings of Dalhousie University in Halifax, Nova Scotia, who has studied cod populations extensively. "I would not have expected that," he added.
The "striking genetic differences" between the three populations could prove to be a valuable tool for management and conservation, particularly in a European context, said Hutchings. The North and Baltic Seas are fished by many nations, so testing cod from international trawlers could help determine which nations have been overfishing in certain regions.
The fingerprinting technique may not be as practical for distinguishing populations of cod in the northwest Atlantic. The reason: There are many fewer genetic differences between northwest Atlantic cod populations.
"You might need to look at tissue samples from 200 to 300 fish [rather than just a few] to distinguish cod from the Bay of Fundy versus the Scotian Shelf versus Georges Bank," said Hutchings. "We definitely need a technique that can be used locally, but fingerprinting may not be the best tool for local enforcement."
Cod in the northwest Atlantic have suffered the greatest decline of the species. According to a report by Hutchings published last year in Nature, overfishing off the coast of Newfoundland from the early 1960s to the early 1990s reduced the cod population by 99 percent.
It was widely believed that imposing moratoriums of two to five years was sufficient for these disappearing cod populations to rebound. But the Nature report by Hutchings revealed that fishes such as cod, Pacific sardine, haddock, halibut, and yellowtail flounder are not as resistant to large reductions in populations as previously thought.
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