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IIT-H, Harvard University study mercury accumulation in fish

Published - August 09, 2019 10:59 pm IST - SANGAREDDY

Though there is decrease in mercury pollution, the amount of mercury found in fish are different among different species

Variation in the accumulation of mercury in fish is the result of changes in sea temperature and dietary pattern of fish due to overfishing.

A joint research by the Indian Institute of Technology, Hyderabad (IIT-H), Harvard University, and Fisheries and Oceans Canada, a Canadian government agency, has found that though there has been a decrease in the levels of mercury pollution, the amount of mercury found in fish have been different in different species – some types of fish have less mercury than before, and some, alarmingly more.

The research, published this month in the international peer-review journal Nature , broadly studied how climate change impacts mercury accumulation in fish.

The variations in the accumulation of mercury in fish is the result of changes in sea temperature in the recent years and changes in the dietary pattern of fish due to overfishing.

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The research was led from India by Asif Qureshi, associate professor, Department of Civil Engineering, IIT-H, and co-authored by Amina Schartup, Colin Thackray, Clifton Dassuncao, Kyle Gillespie, Alex Hanke and Elsie Sunderland.

There have been global efforts to reduce the amount of mercury entering the ocean to reduce the amount of mercury found in fish and other marine animals. Working in this direction, the researchers focused on whether these and other environmental measures alleviated or exacerbated the problem of increased mercury levels in fish. For the study, they chose the Gulf of Maine, a well-studied but also exploited marginal sea in the Atlantic Ocean, to understand the trends in mercury accumulation in fish. The researchers used three decades of data on ecosystem and mercury concentrations and developed a model for mercury bio-accumulation.

Fish metabolism

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“There are three factors that result in mercury accumulation in fish – overfishing, which leads to dietary changes among marine animals, variations in the temperature of the sea water, which leads to changes in fish metabolism that gears towards survival rather than growth, and changes in the amounts of mercury found in sea water as a result of pollution,” said Dr. Qureshi, who wrote the first version of the model code.

The researchers included all three factors in their modelling studies.

“Our results help to explain why the variations in mercury concentrations have been mixed across different types of fish, despite overall reductions in mercury release into the sea since the 1970s,” Dr. Qureshi said.

Using this understanding, the researchers also modelled the mercury levels found in the Atlantic BlueFin Tuna (ABFT). There was a decrease in tissue mercury levels in the ABFT between 1990 and 2012, and this was driven by a fall in sea temperature during that period. However, continued warming in the Gulf of Maine would cause a reversal and the amount of mercury in ABFT could increase to almost 30% by 2030. This highlights the importance of sea temperature on mercury accumulation in the marine food chain.

Although this study was carried out in the Atlantic Ocean, mercury levels in fish in other seas and oceans are likely to have a similar relationship with sea temperature, fishing practices and mercury pollution levels.

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