Swordfish from Canada are marked with a label from the Marine Stewardship Council at a Whole Foods in Washington, D.C. The MSC says its label means the fish were caught by a sustainable fishery, but critics says it's not always so clear. Margot Williams/NPR hide caption

itoggle caption Margot Williams/NPR

A sockeye salmon that was caught from the research vessel Miss Delta off the coast of Vancouver is examined. The MSC has certified the fish as "sustainable" even though there is concern from scientists and environmentalists. Brett Beadle for NPR hide caption

itoggle caption Brett Beadle for NPR

Dennis Roseman, left, and Jamie Manganello pull in a swordfish off the coast of Florida. The Day Boat Seafood company went through a complicated process to become certified as a sustainable fishery by the Marine Stewardship Council. Chip Litherland for NPR hide caption

itoggle caption Chip Litherland for NPR

Capt. Art Gaeten holds a blue shark that was caught during a research trip in Nova Scotia. Scientists are studying the impact of swordfish fishing methods on the shark population. Dean Casavechia for NPR hide caption

itoggle caption Dean Casavechia for NPR