For those who need a refresher course: mercury is released into the environment through a variety of causes (mostly human-induced) and ends up in the ocean. It is absorbed by plankton, who convert it to methylmercury. Plankton consists of many small animals. Animals who eat lots of plankton ingest methylmercury along with them. Animals who eat lots of animals who eat lots of plankton ingest lots of methylmercury.

Therefore, animals at the top of the food chain, ie big predatory fish like shark, tuna, king mackerel, tilefish, and swordfish have more mercury in their tissue than smaller fish. This, by the way, is the same reason why polar bear livers are toxic; eating seals, a fish-eating animal, result in them having excessively high concentrations of vitamin A in their livers. It's also why peregrine falcons, who never directly consumed DDT, ended up endangered due to DDT poisoning. The concept is called biomagnification.

Without knowing what type of fish the residents of the Seychelles eat, I would venture to guess they are probably eating fish common to the reefs around the area. These animals would tend to be smaller (as opposed to a 400-pound tuna) and therefore would not be top predators. Many of them might be algae-eaters, shellfish-eaters, or coral-eaters rather than filter feeders eating a lot of plankton, or carnivores eating a lot of fish. The percentage of mercury in their tissue would be less. Shellfish also have relatively low amounts of mercury, and any reef-dwelling community has plenty of shellfish to choose from.

For Americans, for whom "fish" means mainly large, deep-sea carnivorous fish such as tuna (the vast majority of the fish eaten in this country), the risks are much different. A diet consisting primarily of tuna is in no way comparable to a diet of multiple species of lower-risk fish and shellfish as eaten in other communities around the world. Mercury is concentrated and stored in these top predators. The effects of mercury have yet to be determined with precision, but the mercury is there. Any reasonable person would want to limit their intake of these species of fish, as there is no practical way to reduce the mercury concentration of these fish on the market.

popslashgirl - I think you might be overstating your case, here. While tuna is very popular in the USA ( about 2 1/2 lbs. per capita per annum ), shrimp is more popular - and the other popular fish don't seem to be in that "top-of-the-food-chain" "high-mercury" category.

Top 10 U.S. Consumption by Species Chart

Raw data from National Marine Fisheries Service. The Top Ten list was calculated by Howard Johnson, H.M. Johnson & Associates for NFI.

U.S. Per-Capita Consumption By Species in Pounds 2006 2005 2004 Shrimp:4.40 Shrimp:4.10 Shrimp:4.2 Canned Tuna:2.90 Canned Tuna:3.10 Canned Tuna:3.3 Salmon: 2.026 Salmon:2.43 Salmon:2.154 Pollock:1.639 Pollock:1.47 Pollock:1.277 Tilapia:0.996 Catfish:1.03 Catfish:1.091 Catfish:.969 Tilapia:.85 Tilapia:.696 Crab:.664 Crab:.64 Crab:.626 Cod:.505 Cod:.57 Cod:.603 Clams:.440 Clams:.44 Clams:.471 Scallops:.305 Flatfish:.37 Flatfish:.332

I appreciate the data. However, I'm not sure it changes my essential argument. The article says that the Times article is overstating the existance and impact of mercury in sushi tuna. They then rebut this using data from fish-eating residents of the Seychelles. The two are not comparable. It's deceptive to compare a diet of sushi tuna to a diet of unspecified "fish" eaten by communities that fish for their own consumption and therefore theoretically are eating local species of fish. (Not to mention, the data from the Seychelles is 10 years old, and mercury levels from 10 years ago may not be valid for comparisons with fish caught last month.)

Tuna is a big, deep-sea, carnivorous fish. We eat an awful lot of it--not as much as shrimp, but way more than anything else. According to your data, only salmon (relatively low-mercury) even comes close. The next closest, pollock, has consumption levels of roughly a third that of tuna. (Those numbers appear to be rising, possibly because of a tuna=mercury association.)

But the sheer amount of tuna being eaten, with tuna being a high-mercury fish, means that the mercury present in tuna is going to have more of an impact than the mercury present in, say, flatfish. If the average American eats .37 pounds of flatfish a year, mercury isn't such a big deal. It is a big deal if the average American is eating three pounds of tuna a year, especially since that means that half of Americans are eating MORE than three pounds--maybe much more. (I don't know how they calculated their averages, if it's a mean or median or something different.)

I don't disagree with this article's defense of eating fish. Fish are high in protein and packed with beneficial vitamins, minerals, and fatty acids. Eating fish is important, for a healthy body and mind. But mercury is important, too. There are hundreds of species of fish that are commercially available worldwide, and more than a dozen are seen commonly at a US grocery store's meat counter. Surely we can find a cut of fish for dinner that's less likely to contain a potentially toxic amount of mercury? And surely the author of this article can find a clearer and less flawed way of stating his position?

I think there is a real issue, though, with this statement :

"...For Americans, for whom "fish" means mainly large, deep-sea carnivorous fish such as tuna (the vast majority of the fish eaten in this country), the risks are much different..."

But the statistics show that tuna makes up only about 1/7 of the amount of fish Americans eat - so for the other 6/7ths, you don't seem to have a real mercury concern, relatively speaking.

So it seems to me that the Seychelles fish diet isn't all that different from the USA fish diet in the area of mercury.

That said, I do agree that restaurants seem to be serving too much tuna generally - and ought to diversify more. And people ought to be more conscious of the issue.

Hmmm.

Point: Popslashgirl

The article in the Times didn't reference average American fish consumption, it addressed the effects of eating an average dinner of sushi tuna once per week.

Having spent a year in a Pacific island country, I can testify that the primary catch of tuna is commercial. The residents prefer the richer-tasting reef fish to tuna and similar pelagic fishes.