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Size, species, capture location: What makes tuna get high on mercury?

Tuna, in both cooked and raw forms, is found on restaurant menus, in sandwiches, and on the family table. While tuna flesh is widely appreciated, it does contain a natural toxin known as methylmercury, which is generating a considerable number of questions and concerns. A multidisciplinary study (Houssard et al. 2019) has accurately mapped the methylmercury content of a number of tuna species of the central and southwest Pacific for the first time. This is the zone in which more than half of the world’s tuna is caught and subsequently exported, ending up on the plates of consumers. This study reveals that the methylmercury content of tunas depends not only on the size and species of the fish, but also on where they were caught. These results enable us to inform and advise tuna lovers.

To address the potential health risks associated with the naturally occurring methylmercury, the French Institute of Research for Development (IRD), the Pacific Community (SPC) and the University of New Caledonia (UNC) undertook research on the mercury content of a number of tuna species in the western and central Pacific Ocean. Using specimens collected since 2001 by Pacific national observer programmes and stored in the tuna tissue bank managed by SPC (Sanchez et al. 2014), IRD has in recent years performed more than 1000 muscle tissue mercury content assessments on yellowfin, bigeye and albacore tunas.

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