Mercury levels in adult bluefish off the North Carolina coast have dropped 43% since 1972, according to a new study in Environmental Science & Technology. This is, as Scientific American notes, not just good news for the bluefish, but “for the entire predator fish population in the Mid-Atlantic.” (Other predatory fish in the region include favorites like tuna and swordfish.)
And of course, it’s great news for seafood lovers, too.
The scientists’ hypothesis for the drop in mercury in the fish is simple: Measures taken to reduce the use of coal—a primary contributor to mercury in the environment—have worked, resulting in less mercury ending up in the ocean. Coal consumption in the US dropped 23% between 2008 and 2012 alone, and 34% in Canada in the same period, the researchers note. These kinds of reductions, they say, could lead to lower mercury levels in other fish as well, “unless such reductions are overwhelmed by a continued increase in mercury emissions from Asia.”
In 2011, researchers caught and immediately iced a total of 40 bluefish off the North Carolina coast to measure their mercury levels. As a point of comparison, they used mercury levels in bluefish measured in the early 1970s from the region known as the Mid-Atlantic Bight, which includes waters from Cape Cod down to the coast of North Carolina. (Because bluefish is a predator, it would have relatively higher levels of mercury than smaller fish lower on the food chain.)
They found “a clear distinction in mercury concentrations across most fish weights, with the 1972 study showing higher concentrations of mercury for any given weight.” Ultimately, they calculated a 43% decline, or about 10% per decade. They describe their findings as “quite unexpected” because the 1972 levels had, at the time, been attributed to “natural background levels,” not human activity. The theory changed in the 1990s, and this research further establishes that it was humans, after all, that put all that extra mercury in the water.