Humans have fished for Atlantic cod for hundreds of years, but over the last century demand has surpassed supply. As a result, cod stocks around the world are now tightly regulated, if not closed altogether. Enforcing these regulations, however, has proved difficult. Now researchers have developed molecular techniques, described today in the journal Nature, that should make enforcement more feasible.

Einar E. Nielsen of the Danish Institute for Fisheries Research in Silkeborg and colleagues studied the three principal cod populations that inhabit the northeastern Atlanticthose from the North Sea, Baltic Sea and Arctic Ocean. Analyzing tissue samples collected from the groups, the team identified so-called microsatellite genetic markers that correlate to the different populations. These markers, they found, can assign individual cod to their population of origin with better than 95 percent accuracy. In fact, the researchers report, "assignment is so reliable that testing as few as two or three individuals can provide an unambiguous conclusion about the origin of a sample that is claimed to originate from any one of the three samples populations, representing the majority of cod landings in the northeastern Atlantic."

Armed with techniques to identify the population of origin of individual cod in commercial landings and at fish markets, officials should have a much easier time of policing cod fishery regulations and identifying poachers. Furthermore, the researchers note that simply by adding more baseline samples, they could extend their identification repertoire to include other cod populations and populations of other species. "Similar analyses should prove valuable in ensuring that exploitation of fish stocks is sustainable," they write, "and that genetic resources are conserved in commercially important marine species."