This reminds me of a German man I used to know, he would only eat imported foods claiming that everyone in the US looks like aliens due to their constant diet of genetically modified foods. He actually meant it...
I can't take these studies seriously, because the ocean is just too big to pollute in any meaningful way by humans (save massive oil spills). I would be more worried about a study done on a small stream, river, or pond, which could contain very high levels of bad stuff because it's much smaller and easier for humans to pollute. I have never heard of any group of people dying off or living shorter lives because they ate a lot of fish in their diets, however I hear about the ones who credit fish for longer lifespans all the time. The mercury scare is new, personally I am all for it, means lower prices on the fish I love and or less over fishing. My diet is probably about 1/3 fish, none are on this list though.