Australia is to present what it says is proof that Japan's scientific whaling programme is cruel, to the meeting of the International Whaling Commission.
Environmentalists who filmed Japanese boats whaling in the Antarctic say that some animals took 30 minutes to die. Japan says these cases are exceptions.
Caribbean nations have criticised the West for a "colonial" attitude.
Australian Environment Minister Ian Campbell is due to present the report during Sunday's deliberations.
Early sessions on Sunday saw a fourth straight defeat for Japan, this time on a motion calling for the abolition of the Southern Ocean whale sanctuary.
Japan currently conducts "scientific" whaling there as it is permitted to do under IWC rules, but commercial hunting in the Antarctic would not be possible while the sanctuary exists.
Time to death
During the last Antarctic whaling season, which saw a doubling of Japan's annual "scientific" catch to just over 1,000, Greenpeace filmed a number of kills at close range.
It's simply impossible for the harpooner to hit the whale close enough to the brain to ensure a reliable clean kill in all cases
Vassili Papastavrou, Ifaw
The footage has now been analysed by scientists working with another conservation group, the International Fund for Animal Welfare (Ifaw).
"We found that for one whale the time to death was over half an hour; we found that the average time to death was 10 minutes," said Ifaw's Vassili Papastavrou, "and in two out of the 16 occasions, asphyxiation was the likely form of death."
The whales were asphyxiated, he said, because harpoons entered their bodies near the tail and the animals were held upside down in the water.
Link to rest:
http://news.bbc.co.uk/2/hi/science/nature/5091674.stm