“We believe the bear is under great pressure,” he said from Washington. “It should not be traded internationally.”

Image Bluefin tuna unloaded in Japan in September. A trade ban on the species has been rejected. Credit... Ko Sasaki for The New York Times

Canada, Greenland and several indigenous communities, which led the effort to defeat the proposal to protect the polar bear, contended that the bear population was healthy and that it could sustain limited hunting and trade in pelts and body parts.

While there is near-universal agreement that the bluefin stocks are in danger, Japan’s argument resonated with other fishing nations, which were uneasy about what would have been the first intrusion of the endangered species convention into a major commercial fishery.

But Iccat’s own record on managing the fish is widely seen as unsuccessful: the bluefin population has declined by roughly 80 percent since 1970. And while the organization, which has no effective enforcement mechanism, can set quotas, it has set the catch above the level that its own scientists say is safe to ensure the health of the species.

A senior Japanese official said that his country shared the international concern about bluefin stocks, but that the Atlantic fisheries agency was the proper body to regulate its trade, not the United Nations convention.

Masanori Miyahara, chief counselor of the Fisheries Agency of Japan, said after the vote that Japan would now be under pressure to abide by Iccat’s new, lower quotas for bluefin harvesting, according to The Associated Press. Iccat moved in November to reduce the bluefin quota to 13,500 tons from 22,000 tons for this year, and said that if stocks were not rebuilt by 2022 it would consider closing some areas.

“I feel more responsibility to work for the recovery of the species,” Mr. Miyahara said, The A.P. reported. “So it’s kind of a heavy decision for Japan, too.”