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Mercury Levels In Pacific Tuna Likely To Rise

Researchers have learned that up to 80 percent of the toxic form of mercury, called methylmercury and found in North Pacific Ocean fish, is produced deep in the ocean. Yellowfin tuna, skipjack tuna, bigeye tuna and mahi-mahi tuna were four of the nine species used to conduct the study.

University of Michigan and University of Hawaii researchers believe that their study solves the longstanding question surrounding how mercury gets into open-ocean fish. Results found that it is most likely that bacteria cling to sinking bits of organic matter.
Joel Blum, the lead author of the Geoscience paper said that the mercury identified in Pacific fish close to Hawaii likely travelled through the air for thousands of kilometers before being deposited on the ocean surface as rainfall.

He added that North Pacific fisheries are downwind from quickly industrializing countries such as India and China that have a growing reliance on coal-burning power plants. These factories contribute massively to mercury pollution.

It is also believed that levels of the toxin in Pacific Ocean fish are likely to rise in coming decades. The investigation used isotopic measurement techniques developed at the University of Michigan to come to its conclusion.

Blum explained “The implications are that if we are going to effectively reduce the mercury concentration in open-ocean fish, we’re going to have to reduce global emissions of mercury, including emissions from places like China and India.”



While mercury is present in tuna, many studies focus on the implications of this, while commonly ignoring the fact that selenium, another element found in tuna, works as a natural defense against mercury and contributes to healthy brain development.

In the study, nine species of fish had tissue samples taken that were analyzed. The nine fish types all swim at different depths in the ocean in a region near Hawaii. Results concluded that the level of mercury in predatory fish increased with depth.

The findings hold importance because scientists expect mercury levels at intermediate depths in the North Pacific to rise over future decades.

The work by the researchers suggests that if this trend continues there will be increased threat to North Pacific fisheries, regarded as one of the world’s most important sources of seafood.