Not all fish are contaminated equally

Jack Shafer over at Slate likes to snark at the New York Times, but this time he’s out of his league. Shafer claims that the NYT story on mercury levels in sushi was “scaremongering,” and that studies on seafood consumption in Chile, the Seychelles, and Samoa proved that there is no such thing as mercury poisoning.

Pity Shafer’s Biology 101 teacher, since he clearly missed the bit about the food chain. All fish are not created equal. Methylmercury (the toxic form of mercury) reaches the ocean from the atmosphere, usually via coal fumes, and is incorporated into phytoplankton. Each step up the food chain indirectly incorporates more phytoplankton, and thus more mercury. So zooplankton-eating fish (like sardines) have far less mercury than fish-eating fish (like tuna or swordfish).

The NYT article dealt specifically with bluefin tuna, a top predator in the relatively polluted Mediterranean and North Atlantic. People in Chile, the Seychelles, and Samoa aren’t gorging themselves on bluefin tuna, not when a single fish sells for $45,000. They probably aren’t eating many other top predators on a daily basis, not when Chile’s anchovy fishery is the most productive in the world, and the Seychelles & Samoan islands teem with coastal reef fish.

However, there are people who eat a lot of top marine predators – the Inuit and other Arctic native peoples. Their diet of seals and whales is trophically comparable to tuna, and they are suffering severe health effects from mercury and PCBs. I’m all for Shafer keeping a sharp eye on the NYT, but ignorant criticism without even a perfunctory grasp of the biology (he doesn’t even mention that bluefin tuna are critically overfished!) does not help either people or tuna.

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