Mercury bioaccumulation patterns in deep-sea fishes as indicators of pollution scenarios in the northern Pacific of Mexico

Mercury (Hg) bioaccumulation in deep-sea fauna (> 200 m depth) of the northern Mexican Pacific is unknown. We measured the total Hg concentration (THg µg/g wet weight) in 18 fish species, caught between 90 and 1100 m depth, in two ecoregions of the Mexican Pacific: The Gulf of California (GC) and the western coast of Baja California (BC), in the Southern Californian Pacific. We assessed spatial (ecoregion and depth) and biological (species, tissues, trophic position, sex and size) patterns of bioaccumulation. The highest THg concentrations were observed in liver (geometric mean: 1.28 ± 2.31 µg/g, range: < Method Detection Limit (MDL)–16.17 µg/g), followed by muscle (geometric mean: 0.34 ± 0.53 µg/g, range: < MDL–6.12 µg/g) and gonad (geometric mean: 0.29 ± 0.49 µg/g, range: < MDL–2.18 µg/g). The maximum limit established for human consumption (1 µg/g wet weight) was exceeded by 7.8% of the muscle samples and 31% exceeded the protection threshold for possible harmful effects in fish (0.2 µg/g wet weight). We observed that THg concentrations tended to increase at higher trophic levels, total lengths and condition factors. Our results indicate a clear differentiation of the mercury bioaccumulation patterns between GC and BC, where GC species (200–500 m) had consistently higher liver/muscle concentration ratios than those from BC (600–1100 m). Altogether, the findings presented in this study are possible evidence of differential scenarios of environmental contamination.