Blood tissue samples were obtained from freshly caught tuna. Individuals' blood was sampled from the incision made by fishermen near the lateral line (close to the pectoral fin). Samples were frozen onboard (stored at -20°C), freeze-dried and finally ground to a fine and homogeneous powder prior to analyses. THg concentrations were measured on ~10 mg of powdered samples by thermal decomposition, gold amalgamation and atomic absorption detection (DMA-80, Milestone) at GET (Toulouse, France). The accuracy of measurements was checked against different biological standard reference materials (i.e., TORT-2: 0.270 ± 0.060 µg.g‑1, TORT-3: 0.292 ± 0.022 µg.g‑1, DOLT-4: 2.580 ± 0.220 µg.g‑1, and IAEA-436: 4.190 ± 0.360 µg.g‑1).
About ~1 mg of homogenized freeze-dried sample, packed in tin cups, were analyzed using a Costech elemental analyser coupled to an isotope ratio mass spectrometer (Thermo Scientific Delta Advantage with a Conflo IV interface) at Union College (New York, USA) to obtain the stable isotope values. Reference standards (EA Consumables sorghum flour (δ15N = 1.58 ± 0.15 ‰), in house acetanilide (δ15N = -0.96 ‰), IAEA-N-2 ammonium sulfate (δ15N = 20.3 ± 0.2 ‰), and IAEA-600 caffeine (δ15N = 1.0 ± 0.2 ‰) were used for isotopic corrections, and to assign the data to the appropriate isotopic scale with reproducibility better than 0.1 ‰.
The province of location is defined as the biogeochemical province modified by Houssard et al. (2017) (Houssard, P., Point, D., Tremblay-Boyer, L., Allain, V., Pethybridge, H., Masbou, J., Ferriss, B.E., Baya, P.A., Lagane, C., Menkes, C.E., Letourneur, Y., Lorrain, A., 2019. A Model of Mercury Distribution in Tuna from the Western and Central Pacific Ocean: Influence of Physiology, Ecology and Environmental Factors. Environmental Science & Technology 53, 1422–1431. https://doi.org/10.1021/acs.est.8b06058). The Archipelagic deep basins modified province (ARCHm), the Warm pool modified province (WARMm), the Pacific equatorial divergence province (PEQD), and the South Pacific Subtropical Gyre modified province (SPSGm).
Latitude and longitude information is presented on a 360 degrees scale.
