Mercury stable isotopes reveal sources of methylmercury and prey in giant Pacific bluefin tuna from the western North Pacific Ocean

Sources of methylmercury (MeHg) in adult Pacific bluefin tuna (Thunnus orientalis, PBT) from the western North Ocean (WPO) were examined using mercury stable isotopes. Significant increases δ202Hg and Δ199Hg values with PBT size age, along those potential prey, indicate a shift source MeHg accumulated by as they age. Among adults WPO, this likely involves greater accumulation epipelagic prey Kuroshio extension large vs. small medium-sized PBT. For all adults, little is spawning grounds near Taiwan. Significantly lower Δ199Hg/Δ201Hg ratios their WPO than central eastern different sources or transformations prior to food web further east. Our results show that oceanic webs vary across regionally within WPO.