Do you ever feel like those emails you send to behemoth companies—you know, the ones expressing your desire for more eco- and health-minded choices—fall on deaf ears? Start your keyboards: Such communication works.

After eight months of pressure from consumers, headed by eco-watchdog Greenpeace, retail giant Costco has announced that it will stop selling unsustainable seafood choices -- a huge win for our overfished, beleaguered oceans. Specifically, Costco will eliminate 12 "red list" species: Atlantic cod, Atlantic halibut, Chilean sea bass, Greenland halibut, grouper, monkfish, orange roughy, redfish, shark, skates and rays, swordfish, and bluefin tuna.

Not only that: Costco also pledges to be a leader in aquaculture developments and issues around canned tuna, and to partner with the World Wildlife Fund in continuing sustainability issues. This follows Greenpeace's victory with Trader Joe's, which agreed in March 2010 to establish similar sustainable-seafood policies. Greenpeace reps say the policies aren't yet perfect, but they're a great start; and, given the immense purchasing power these stores represent, it's thrilling to see collective consumer voices and eco-organizations making a real difference.