Marine Stewardship Council
The Marine Stewardship Council seems to be making some real progress... lodging in the mind of the consumer and raising awareness of the importance of sustaining the world's fish stocks.
As awareness of the issues grow the main challenge would seem to be "can I trust the blue label, is it really proof of sustainable practices?" In fisheries, more than in many other industries, this seems to be the big difficulty. They need to be more explicit in their communications about how this is achieved.
Despite this, I hope you'll be looking for the blue label yourself!