Nereus research fellow Colin Thackray (Harvard University) and Principal Investigator Elsie Sunderland (Harvard University) are co-authors with others on a new publication in the journal Nature. For their study, they investigate how climate change and overfishing are contributing to the bioaccumulation of neurotoxin methylmercury (MeHg) in the tissues of top ocean predators. This MeHg build up in the environment and subsequent marine food webs has ramifications for a large segment of the world’s population that relies on seafood for their nutritional needs, due to the potential long-term neurocognitive impacts on those who consume contaminated fish. The authors looked at Atlantic cod (Gadus morhua) and Atlantic bluefin tuna (Thunnus thynnus), how overfishing and rising ocean temperatures have influenced their mercury (MeHg) concentrations over the past three-four decades, and how warming seawaters and fisheries management will help determine future mercury levels. You can read the full abstract below:

Abstract: More than three billion people rely on seafood for nutrition. However, fish are the predominant source of human exposure to methylmercury (MeHg), a potent neurotoxic substance. In the United States, 82% of population-wide exposure to MeHg is from the consumption of marine seafood and almost 40% is from fresh and canned tuna alone1. Around 80% of the inorganic mercury (Hg) that is emitted to the atmosphere from natural and human sources is deposited in the ocean2, where some is converted by microorganisms to MeHg. In predatory fish, environmental MeHg concentrations are amplified by a million times or more. Human exposure to MeHg has been associated with long-term neurocognitive deficits in children that persist into adulthood, with global costs to society that exceed US$20 billion3. The first global treaty on reductions in anthropogenic Hg emissions (the Minamata Convention on Mercury) entered into force in 2017. However, effects of ongoing changes in marine ecosystems on bioaccumulation of MeHg in marine predators that are frequently consumed by humans (for example, tuna, cod and swordfish) have not been considered when setting global policy targets. Here we use more than 30 years of data and ecosystem modelling to show that MeHg concentrations in Atlantic cod (Gadus morhua) increased by up to 23% between the 1970s and 2000s as a result of dietary shifts initiated by overfishing. Our model also predicts an estimated 56% increase in tissue MeHg concentrations in Atlantic bluefin tuna (Thunnus thynnus) due to increases in seawater temperature between a low point in 1969 and recent peak levels—which is consistent with 2017 observations. This estimated increase in tissue MeHg exceeds the modelled 22% reduction that was achieved in the late 1990s and 2000s as a result of decreased seawater MeHg concentrations. The recently reported plateau in global anthropogenic Hg emissions4 suggests that ocean warming and fisheries management programmes will be major drivers of future MeHg concentrations in marine predators.


Schartup, A.T., Thackray, C.P., Qureshi, A., Dassuncao, C., Gillespie, K., Hanke, A. & Sunderland, E.M. (2019). Climate change and overfishing increase neurotoxicant in marine predators. Nature, 2019. DOI: 10.1038/s41586-019-1468-9 link

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