It seems Whole Foods Markets is having to fend off many successful competitors in Natural Foods retailing. In Arizona alone, the Sprouts and Sunflower Markets chains are hammering away at Whole Foods. While Whole Foods appears to be growing well, so are their competitors.
What's most useful about the story is it describes how competitors like Trader Joe's and Sprouts claim lower prices. They give an excellent example comparing Whole Foods' wild caught salmon prices with the farmed varieties available at their competitors for 1/5th the price.
The whole story is at the Arizona Star.