The U.S. and 18 other nations attending a meeting this week on migratory fish approved a plan on Tuesday to create a commission to regulate tuna catches in the Pacific Ocean, but Japan is threatening to ignore any new regulations. Pacific tuna populations are not yet endangered, but backers of the plan say new rules are necessary to ensure a sustainable harvest in the future. Japan, however, is complaining that the boundaries of the zone to be regulated by the commission would place unfair restrictions on the nation.