Want your supermarket to sell more sustainable seafood? Get Greenpeace to mount a social media campaign against it — and nine to 10 months later, you’ll see endangered species like orange roughy and Chilean sea bass disappear from the seafood section.

At least that’s been Greenpeace’s success record so far when it comes to pressuring stores to serve up sustainable seafood. Back in July 2009, Greenpeace decried “Traitor Joe’s” fishy practices — to have the organic-friendly bargain grocery chain succumb to its sustainable seafood demands nine months later. Buoyed by that win, Greenpeace went after Costco’s “Wholesale Ocean Destruction” in June 2010 — and finally got Costco to revamp its seafood policies last week, 10 months later.

Now, Costo will eliminate red list species from its stores — at least until Marine Stewardship Certified options appear for those species — and shift to more sustainable tuna sources. The rest of Costco’s concessions are murkier: the discount chain will “pledge to play more of a leadership role within aquaculture,” “examine their remaining wild-caught species and determine how to best transition to the most sustainable alternative,” and “acknowledge the role that the canned tuna industry plays within the global sustainable seafood movement.”

Greenpeace points out that although Costco’s new practices won’t be perfect, they’re a step in the right direction. Thus, the nonprofit has declared victory.

Who’s next? My bet is on Publix, a supermarket chain that has debuted and marketed greener shopping options — but flunked Greenpeace’s latest Supermarket Seafood Sustainability Scorecard. Which lucky supermarket do you think Greenpeace will target next?

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