A U.S.-backed proposal to ban the export of Atlantic bluefin tuna prized in sushi was rejected Thursday by a U.N. wildlife meeting, with scores of developing nations joining Japan in opposing a measure they feared would devastate fishing economies.

It was a stunning setback for conservationists who had hoped the 175-nation Convention on International Trade in Endangered Species, or CITES, would give the iconic fish a lifeline. They joined the proposal’s sponsor Monaco in arguing that extreme measures were necessary because the stocks have fallen by 75 percent due to widespread overfishing.

“Let’s take science and throw it out the door,” said Susan Lieberman, director of international policy with the Pew Environment Group in Washington. “It’s pretty irresponsible of the governments to hear the science and ignore the science. Clearly, there was pressure from the fishing interests. The fish is too valuable for its own good.”