Seafood offerings at Sweetbay Supermarket, Wal-Mart, Target and Whole Foods got improved ratings in Greenpeace's latest "Seafood Sustainability Scoreboard." But other Florida supermarkets — Publix, Winn-Dixie, Aldi, Save-A-Lot and Costco — flunked for the second year. The scorecard is an attempt to rate each chain's policies on not selling severely overfished species, picking vendors that use sustainable capture methods and issuing labels and materials that teach shoppers how to choose seafood without depleting the supply. Even with the improved grades, however, no chain that sells in Florida rated higher than a "D." "It's frustrating in Florida, where the five lowest-rated chains would not even cooperate by sharing their practices and policies," said Casson Trenor, a senior markets campaigner for Greenpeace. "So we relied on third parties who audited several of their stores."