02/15/2013

The Silence of the Clams

Walleye painting by Timothy Knepp

I have just spent over a month in Michigan. Ann Arbor is a great town and has a dazzling array of restaurants, but I found myself avoiding seafood. How fresh can a clam be in Michigan? OK, I’m spoiled. I can go down to the shore here at SeaCat’sRest and dig clams so fresh they don’t have time to scream before I drop them into boiling water. I had to work in the scream thing because I came up with this great title, but in reality I’m just fishing for a reason to use it.

Michigan has great freshwater fish: whitefish, smoked chub, lake trout and my favorite, walleye. But there’s the mercury¬† problem. Michigan’s fish advisory tells us:

from: www.michigan.gov/documents/FishAdvisory03_67354_7.pdf

Wow! Scary! The mercury is atmospheric, emitted mostly by coal burning power plants and concentrated in the fat of fish over time. Asia is the biggest polluter by far. Every step in the food chain concentrates the mercury approximately ten times. This is called biomagnification. Therefore a plant eating fish (or mammal) has much less mercury because it doesn’t eat the fat of other animals in which the mercury is concentrated. Mercury is one toxin among many, but it is the most important. Others include PCBs and Dioxins.

Human health risks from methylmercury exposure have been widely documented, and include neurological effects, impaired fetal and infant growth, and possible contributions to cardiovascular disease.

www.dartmouth.edu/~toxmetal/…/pdf/sources_to_seafood_report.pdf

So what about fish from salt water? Doesn’t marine fish from Maine’s coastal waters also have unhealthy levels of mercury? Yes and no. True, older, bigger fish like bluefish, swordfish or shark, or fish which spend part of their lives in fresh water like striped bass should not be eaten by pregnant or nursing mothers. Also, the toxin-concentrating part of the Maine Lobster, the tomalley or liver ( the part Julia Child loved to make a sauce out of) should be avoided. But the State of Maine also says, “All other ocean fish and shellfish, including canned fish and shellfish: Pregnant and nursing women, women who may get pregnant and children under 8 years of age can eat no more than 2 meals per week.” That’s pretty liberal compared to the Michigan guidelines. The diluting effect of the vast ocean and the active tidal currents help to spread the toxins out so that Maine coastal seafood is not faced with the toxin uncertainty of freshwater ecosystems. The thing about saltwater fish is that the mercury levels are pretty unvarying. For example, the mercury level of .3 parts per billion is an average for a given species throughout the world’s oceans. If a given species had that level in Lake Michigan it might have twice that in one of Michigan’s interior lakes or rivers. This is because the local environment’s acid levels could be higher, putting more atmospheric mercury into solution.¬† So the warnings for Michigan’s fish must reflect this by assuming the worst case. Even more restrictive are the government warnings about Maine’s freshwater fish. No fish should be eaten by pregnant women or children under 8 except landlocked salmon or brook trout, one meal per month.

The take away from this brief review of the mercury problem in fish is to 1) observe the consumption guidelines for the fish in question, 2) Make sure the fish comes from a larger body of water and 3) eat young or small fish, and remove the fatty parts. Maine has a low level of mercury inputs, but most mercury comes from the atmosphere anyway. With our strong tidal currents, Maine’s coastal waters have no “hot spots” like an acidic Adirondack lake or industrial harbor. There’s still too much mercury for a perfect world, but as we move away from coal and other fossil fuels, the future looks brighter. As for clams, mercury is not the problem, pollution or red tide (paralytic shellfish poison) is what you call the hotline for: 1-800-232-4733 or 207-624-7727.

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Comments on The Silence of the Clams »

02/16/2013

Pat @ 5:25 pm

Great title! You didn’t really have to write anything else. But very informative.

02/17/2013

Barb @ 8:17 pm

As a Michigander I have to say, “It’s not our fault!!” Most of our pollutants come from the Chicago area, and fall on our otherwise pristine waters. You can’t change weather patterns.

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