A few weeks ago, during the discussions around the industry-funded recommendations advising women to eat more fish, an important point was frequently raised (on this website and others): While we're all worrying about how much fish to eat, the world's fisheries are steadily being depleted.
This video from Greenpeace looks at that problem on a personal level in an interview with a Solomon Island fisherman. His catches can hardly sustain him because of the huge ships further off shore, catching enough tuna to satisfy "insatiable international markets." But the island nation has a plan to take back their fishing waters. (No embedded video this time -- click the image to go to the video.)
EWG's Safe Fish List tells you which fish are low in mercury, but if you want to consider the environmental impacts you can compare it with Seafood Watch's Seafood Guide.