Startling new film, shot in the Arctic, exposes the cruelty of whaling as nations gather for the most crucial meeting in deciding the fate of the leviathans in a quarter of a century.
The footage - filmed by investigators from the World Society for the Protection of Animals (WSPA) and the Environmental Investigation Agency - is of the slaughtering of a minke whale by a Norwegian vessel, in defiance of an international agreement.
Although it was hit by an explosive-tipped grenade in good hunting conditions, the whale took more than two and a half minutes to die. Campaigners say this proves that whaling can never be carried out humanely. In less good conditions, where it is harder to aim harpoons accurately, many whales take 10 minutes or more to perish.
Leah Garcés, WSPA's director of campaigns, says: "Despite this hunt taking place in optimum weather conditions, the kill is not instantaneous. This would not be an acceptable 'time of death' for a farm animal, so why should it be permitted for whales?"
Today nations will examine the issue at a special workshop on whale-killing methods being held, at the initiative of British ministers, on the West Indian island of St Kitts, before the annual meeting of the International Whaling Commission - which regulates world whaling - opens there on Friday.
But the commission's meeting is expected to rule out all consideration of attempts at humane killing, and weaken the protection of whales anywhere, in the biggest setback for the giant creatures in decades.
This is because Japan and other whaling nations are likely to achieve a majority on the 66-member commission for the first time since - in one of the greatest-ever international wildlife conservation victories - it declared an official moratorium on commercial whaling in 1982.
Japan and Iceland have got round the ban by exploiting a loophole that allows them to kill whales for "scientific" purposes, while Norway defies it altogether. Japan has spent the last decades giving aid to small, often landlocked, countries to try to persuade them to join the commission and vote on its side. Last year it announced: "The reversal of history, the turning point, is soon to come."
Japan will not have enough votes to overturn the ban - under the rules, it needs three-quarters of the vote for that. But a simple majority will enable it to undercut any other measures that protect whales - such as sanctuaries in the Indian and Southern oceans, attempts to turn the commission into a conservation body, and any bid to develop more humane killing methods.