By Richard Black
Environment correspondent, BBC News website, Anchorage, Alaska
Japan will consider walking away from the International Whaling Commission and setting up a rival organisation.
A Japanese decision to leave the IWC would be a major blow
It was especially irked by the refusal of anti-whaling countries to discuss a small amount of commercial whaling by four Japanese coastal communities.
Japan has made similar statements in previous years.
Environmental groups say the meeting paid too little attention to important issues such as the number of cetaceans hit by ships, and climate change.
After securing a narrow majority of members for last year's meeting - the first majority in 20 years - pro-whaling countries again found themselves in the minority here, and lost a number of key votes.
A recruitment campaign by European and South American countries over the last year brought more members into the IWC to vote for the anti-whaling bloc.
After initial signals that both sides were looking for dialogue and co-operation, the commission closed its four-day annual meeting with familiar acrimony in its later stages.
Japan's priority for this 59th IWC meeting was to secure a small commercial catch of minke whales for four of its coastal communities with a history and culture of whaling.
Japan says its whale hunt is for scientific, not commercial, reasons
Anti-whaling countries regarded this as a breach of the 21-year moratorium on commercial hunting.
The Japanese delegation said the reluctance of anti-whaling nations to discuss a way forward was a disappointment.
"We were not expecting only polite language and dialogue, but the first steps to a mutually acceptable compromise, which we did not see," said a strained-looking Joji Morishita, Japan's alternate (deputy) whaling commissioner.
Japan had offered in return to consider reviewing its plan to include humpback whales, a priority issue for New Zealand and Australia, in its Antarctic hunting programme which it conducts in the name of scientific research.
Mr Morishita suggested that after Australia's and New Zealand's refusal to talk about a compromise, the humpback hunt would go ahead, though possibly with some unspecified revisions.
A Japanese decision to leave the IWC would be a major blow to the organisation's relevance, as it is now the world's major whaling nation.
Some conservation groups see the threat as a bargaining tool.
Another of Japan's alternate commissioners, Akira Nakamae, declared that establishing a rival organisation was a possibility.
"We're greatly interested in the idea of holding a preparatory meeting setting up a conservation and management organisation for cetaceans which... could be a replacement for IWC," he said.
However, with the IWC enshrined as the world's sovereign body on whaling, it is not clear what the status of such a new body might be.
Conservation groups were generally pleased with the passing of a resolution re-affirming the commercial whaling moratorium, and with its condemnation of scientific hunting.
But some said issues crucial to whale welfare had been allocated far too little time.
"No time was spent discussing the 3,288 cetaceans that have died worldwide during the course of the meeting in Anchorage because of human impacts such as ship strikes, pollution, bycatch and climate change," said Junichi Sato of Greenpeace.
Some of the most threatened cetaceans such as the baiji or Yangtze River dolphin, which scientists have declared "effectively extinct", do not come under the IWC's mandate.
Of the species that do, the most endangered are the north Pacific and north Atlantic right whales, which now number a few hundred each. Populations were brought low through hunting, but the main threat now comes from being hit by ships.
Many delegates and observers of various viewpoints believe the IWC needs urgent reform.
The IWC is enshrined as the world's sovereign body on whaling
Members agreed to hold a special meeting in about six months' time to examine how to take things forward.
The Netherlands has been a prime mover behind reform attempts, and its commissioner Giuseppe Raaphorst saw reasons for optimism.
"We still have to do some work to get closer to each other," he told BBC News.
"And I hope that we don't just talk about our principles, but make practical arrangements to get control over whaling."
Mr Morishita said Japan had few hopes for the special meeting, but would contribute if it could.
Another issue resolved on the final day was Denmark's controversial application for an expansion of subsistence hunting by Inuit communities in its territory of Greenland.
By a narrow majority the meeting approved a small increase in the minke catch, and, with restrictions, the inclusion of bowhead whales for the first time.
A final sign of Japan's disappointment was the withdrawal of its bid to host the 2009 IWC meeting in Yokohama. It said it had looked forward to hosting a meeting of an organisation which worked normally.