About 39% of 142 seafood samples from 81 stores and restaurants in New York City were shown by DNA tests to be mislabeled, including 94% of fish labeled as white tuna that turned out to be a type of mackerel that contains a toxin known to cause digestive problems, according to Oceana, an advocacy group. The U.S. imports more than 90% of its seafood, and 500 chefs and restaurant owners teamed up in October to sign an Oceana petition against seafood fraud.