I found this video a few days ago from the Surfrider Foundation on marine plastic pollution. It's 12 minutes long, but if you have the time, it's worth the watch.

A new report from the World Wildlife Federation (WWF) claims that breeding populations of Atlantic Bluefin Tuna in the Mediterranean will collapse by 2012 if fishing continues at its current rate. Demand for the fish is driven primarily by sushi restaurants in Japan and elsewhere.

Source

The WWF has information about how to avoid irresponsibly harvested tuna, as does Seafood Watch.