For Earth Day's 40th anniversary, The Nature Conservancy is making an effort to address the problem of mercury in the seafood we consume. The only way to avoid mercury build-up in humans is to avoid eating those sea creatures with high-levels as a result of predation which acts to concentrate the toxin in organisms' flesh.
Of course, enjoy the sea's bounty, but be careful what you buy and what you order! Here are some links to help aid in the tricky seafood selection process:
FishPhone - a clever little text-message service to help you choose which fish...
Seafood WATCH - Monterrey Bay Aquarium's downloadable pocket guides for seafood shopping
The Nature Conservancy - go directly to the article by Kate Frazer, "From Sea to Plate"