While many of the cases of mercury poisoning seem to occur in people who ate tuna every day or nearly everyday (aside from the sheer monotony, I think that it is basically a terrible idea to eat the same protein everyday, no matter what it is) I think it is best to err on the side of caution with this one.
While the FDA has a guideline for acceptable levels of mercury (which is rather high by other countries standards), even this rather lax level is likely exceeded depending on what tuna you buy. Studies conducted in 2006 estimated that some canned tuna exceeds the federal limit by 30-50%.
After some research, here is my preliminary approach:
-Completely give up buying canned albacore. Albacores are big, long-lived fish and therefore have more mercury stored up in their tissues. This is the easy part. While I used to enjoy the snowy whiteness of Albacore, I now think canned Albacore has less flavor than other "tuna" anyhow.
Personally, I think (at a minimum) that Albacore should be labeled with a warning label for small children!
-Stay away from Bluefin and imported Yellowfin (except Atlantic Yellowfin). This is a good idea for environmental as well as mercury reasons. Bluefin Tuna are being depleted due to overfishing. Imported Yellowfin/Bigeye Tuna are caught with long lines that threaten other sealife including cute sea turtles.
-Buy only chunk light tuna, and eat it no more than once per week. Chunk light tuna is usually skipjack, a much smaller (and therefore lower mercury) fish. Also, skipjack reproduce quickly and are fished using reasonably eco-neutral methods. Ideally, it would be great to find pole-fished skipjack. Glenryck products look good, but I am not sure they are available here. Bumble Bee tuna had relatively low mercury levels compared to other brands of canned tuna in some studies.
I am going to stick with chunk light tuna. But if you *really* want albacore, go with something like American Tuna, which is pole-caught pacific albacore, which they report is between 2-5 years old (the elderly tuna, which can get up to around 40 years old, have a lot more mercury.)
-Treat high-grade, fresh tuna like a treat, not a staple. When possible, stick to troll/pole fished US-fished Albacore (moderate mercury, safely fished) or Atlantic Yellowfin for both grilling and sushi. Stay away from tuna from other places! Luckily this will become easier to do as COOL (Country of Origin Labeling) becomes more widespread (see below).
-Eat more small fish! On the upside, a lot of folks are saying the thing to do is to eat smaller fish, maybe even the smallest fish. Anchovies and sardines fulfill for me many of the same cravings that tuna does. Small, short-lived fish don't have the buildup of mercury or other contaminants present in their larger neighbors, and many of these small fish are fished in an eco-friendly or eco-neutral manner.
-Check what you are buying. When in doubt, remember to consult the Environmental Defense Fund's "Seafood Selector" or the Monterey Bay Aquariums Seafood Watch. Greenpeace UK has also issued a canned tuna guide for UK brands of canned tuna. I would love to see one of these for the US. In the meantime, the other thing you can do is...
-Advocate for better labeling. From Food and Water Watch:
"Country of Origin Labeling, or COOL, is a program of the U.S. Department of Agriculture that requires that all seafood products bear a label stating where the fish was harvested and whether it was wild-caught or farm-raised.
This is a good step, however, the program exempts all processed seafood from these labeling requirements. Consequently, only about half of the seafood sold in stores has a COOL label."
Wouldn't it be great to have some Country of Origin labeling on our canned tuna?
For more on the politics behind tuna, see this good but depressing Mother Jones article. The article glazes over the difference between the different types of canned/foil-bagged tuna, but has some good background on the FDA decisions and some of the major lawsuits.