Relationship between mercury, organochlorine compounds and stable isotope ratios of carbon and nitrogen in yellowfin tuna (Thunnus albacares) taken from different regions of the Pacific and Indian Oceans

The aim of this study was to compare the δ15N, δ13C, Hg and organochlorines (PCBs, p,p′-DDE and trans-nonachlor) in the yellowfin tuna taken from several regions of the Pacific and Indian Oceans. The highest values of δ15N and δ13C were observed in the tuna taken from Sri Lanka and Maldives (Indian Ocean), while the lowest values were observed in the tuna taken from Hawaii. In contrast, the highest Hg concentration was observed in the tuna taken from Hawaii, while the lowest concentration was observed in the tuna taken from Sri Lanka and Maldives. These orders of δ15N, δ13C and Hg may reflect the geographical characteristics of those among nine regions. On the other hand, the highest concentration of each organochlorine was found in the tuna taken from New Zealand, while the lowest was found in the tuna sample from Hawaii, probably reflecting the anthropogenic contamination among eight regions. The inter-regional variations in organochlorines were markedly larger than those in Hg concentration. The Hg uniformly distributed in the area under the normal curve of Hg concentration against δ13C or δ15N value, while the organochlorines did not. This difference may be ascribed to the fact that Hg is of natural and anthropogenic origins, while the organochlorines are of anthropogenic origin. A principal compartment analysis of δ13C, δ15N, Hg and organochlorines apparently clarified the tuna taken from eight regions into 5 groups of Sri Lanka and Maldives, New Zealand, Australia, Hawaii and Japan.