Canada's major supermarket chains won unusual praise from Greenpeace on Wednesday for starting to rid their shelves of 'destructively fished or farmed' seafood. In a report, Greenpeace ranked eight major grocery chains on their efforts to help improve the sustainability of the seafood they buy and sell. It said that 'following pressure by environmental organizations and the public,' retailers have started adopting sustainability policies for their seafood supply chains, and stopped selling up to 15 'destructively fished or farmed' species. These species include dredged Atlantic sea scallops and salmon from farms said to contaminate the marine environment. But more can be done to protect the oceans, Greenpeace said. 'Supermarkets have stopped selling imperiled species such as shark, skates and bluefin tuna, which are not big sellers,' said Beth Hunter, Greenpeace oceans campaign coordinator. 'Now retailers need to focus on no longer selling fish that may be consumer favorites, but are still destructively fished or farmed.' Overwaitea, Loblaw, Safeway, Walmart, Metro, Sobeys, Federated Co-operatives and Costco -- in this order -- were ranked from best to worst for their efforts. Costco received the lowest ranking because it has not indicated any plans to discontinue to the sale of unsustainable fish or develop a seafood policy. Overwaitea received the highest overall score because it stopped selling species at risk, started implementing a seafood policy and is actively promoting sustainable seafood initiatives to customers and suppliers. 