fish and mercury, caused by coal powered plants etc

I find this chart super helpful when considering what type of fish to eat.  I know that when one is pregnant, they need to NOT eat tuna or any fish higher on the food chain.  But this goes for kids too, and since we eat quite a bit of sushi, this is an issue!
This article is helpful as far as where mercury comes from etc: http://www.sierraclub.org/sierra/201111/mercury.aspx
for taking action on some coal bills right now in October 2011:
PROTECT
Toxic Coal Ash
We need strong protections against toxic coal ash. Some in Congress would rather protect polluters. Tell your representative to support the EPA and oppose the Coal Residuals Reuse and Management Act (H.R. 2273).https://secure2.convio.net/sierra/site/Advocacy?cmd=display&page=UserAction&id=7161&autologin=true&s_src=111JZZNI02&s_subsrc=nonmember&JServSessionIdr004=eavk3yqdw2.app224a