Pollutants in your sushi provide clues to fish's origin.

Dickhut, RM, AD Deshpande, A Cincinelli, MA Cochran, S Corsolini, RW Brill, DH Secor and JE Graves. 2009. Atlantic bluefin tuna (Thunnus thynnus) population dynamics delineated by organochlorine tracers. Environmental Science and Technology doi:10.1021/es901810e.

The meat from bluefin tuna is prized throughout the world.  This long-lived, highly mobile species can migrate extraordinary distances, adding to the difficulty of managing and conserving their populations. 

Experts are uncertain about the extent and rate of their travels and how much their two main populations – one in the Mediterranean Sea and the other in the Gulf of Mexico – mix. Both populations can travel great distances and mingle in the North Atlantic.

A recent study published in the journal Environmental Science and Technology uses an unconventional method to shed light on these fish's elusive lives. By measuring pollutants in the fish's tissues, the U.S. and Italian research team was able to delineate where in the world individual fish are from and glean more information about the life histories of the two fish stocks. For example, about 10 percent of the Mediterranean population migrate. The fish move to the western Atlantic as youngsters (1-year-olds) and return as early as 5-year-olds, presumably to breed.

Pollution signatures – the blend of chemicals in the environment – are unique to different geographical areas of the world. The researchers targeted the pollution signatures of persistent contaminants – such as organochlorine pesticides and polychlorinated biphenlys (PCBs) – because they remain stable in tissues for a long time and tend to be passed from small fish to large up the food web. As top tier predators, bluefin tuna accumulate these contaminants to a high degree.

It is unfortunate, but now a reality,  that pollutants are such an entrenched part of our world they can be useful to study the habits of some of the most compelling and valued species.