Pro-whaling nations looking to take a majority in the International Whaling Commission (IWC) for the first time lost a key early vote.
Members voted 30 to 27 to defeat a proposal offered by Japan to change voting procedures at the IWC to a secret ballot.
Conservationists said it was too early to claim victory because three states - Gambia, Togo and Nauru - that recently joined the IWC and appear to side with pro-whaling members did not vote because they did not pay their dues or have yet to arrive in Ulsan.
African and Caribbean nations largely supported Japan's measure, saying they wanted secret ballots to avoid pressure from conservation groups and anti-whaling states.
The annual meeting ends on Friday in Ulsan, a former whaling port in South Korea.