Mercury levels in the seafood supply are on the rise, and climate change and overfishing are partially to blame, according to a new study. Scientists said mercury levels in the oceans have fallen since the late 1990s, but levels in popular fish such as tuna, salmon and swordfish are on the rise. 

According to a new study by Harvard University researchers in the journal Nature, some fish are adapting to overfishing of small herring and sardines by changing their diets to consume species with higher mercury levels. 

Based on 30 years of data, methylmercury concentrations in Atlantic cod increased by up to 23% between the 1970s and the 2000s. It links the increase to a diet change necessitated by overfishing

But overfishing isn't the only contributor to higher mercury levels in fish. Climate change — and the rising ocean temperatures that come with it — means fish are more active and need more food to survive. Consuming more prey means consuming more mercury. 

The study also found that mercury levels in Atlantic bluefin tuna have increased by an estimated 56% due to seawater temperature rise since 1969. 

Climate change "is not just about what the weather is like in 10 years," said lead researcher Amina Schartup. "It's also about what's on your plate in the next five."

Scientists said human exposure to methylmercury — the compound created when mercury enters the ocean — is especially risky for pregnant women, as it has been linked to long-term neurological disorders when fetuses are exposed in the womb. It is considered a major public health concern by the World Health Organization

"It's not that everyone should be terrified after reading our paper and stop eating seafood, which is a very healthy, nutritious food," senior author Elsie Sunderland told Reuters. "We wanted to show people that climate change can have a direct impact on what you're eating today, that these things can affect your health ... not just things like severe weather and flooding and sea level rise."

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