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Ocean warming, overfishing increase methylmercury toxin in fish: research by R. Prasad August 07,2019   |  Source: The Hindu

Despite a decrease in seawater concentration of methylmercury since the late 1990s, the amount of toxin that gets accumulated in certain fish which are higher in the food chain have been found to increase. The amount of methylmercury in fish higher in the food chain can change due to two reasons — ocean warming and dietary shifts due to overfishing by humans.

Based on 30 years (1970s and 2000s) of data and ecosystem modelling, researchers have found that there has been up to 23% increase in methylmercury concentration in Atlantic cod fish in the Gulf of Maine in the northwestern Atlantic Ocean.

The increase in the methylmercury concentration in cod fish has been due to changes in diet caused by overfishing. As a result of diet change, cod fish in the 2000s relied more on larger herring and lobster, which have higher concentrations of the toxin than other prey fish consumed in the 1970s.

In contrast, there has been 33-61% reduction in methylmercury concentration in spiny dogfish fish between 1970s and 2000s. This is because, in the 1970s, spiny dogfish fish consumed more of squid and other cephalopods, which have a higher toxin concentration.

“This work showed that as a result of a change in the diet due to overfishing, there was a increase in methylmercury


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