Scientists monitor tuna by measuring toxins

Toxins tell tuna's tale:  The Atlantic bluefin tuna (Thunnus thynnus) population is split into two groups, with the 45 degree meridian acting as a rough dividing line. Some fish swim across the line to feed or spawn, and scientists and fishery managers would like to know how many fish make the ocean crossing. Naomi Lubick reports on a new research paper that uses two potent classes of pollutants — polychlorinated biphenyls (PCBs) and chlordanes — as a geographical tracers. By looking at the ratio of the various chemicals, the scientists can tell where the fish have been. Chlordanes are especially good because they are banned in the European Union, so if chlordane residue appears in a tuna caught in the Mediterranean, the fish must have spent time in the western Atlantic. The initial data show that more eastern Atlantic fish visit the western Atlantic than was previously assumed.  (Environmental Science and Technology)

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