Sydney - The scientists who each year accompany Japanese whaling boats to the Southern Ocean say minke whales are getting lighter because competition for krill is getting more intense.

Their study, published in the journal Polar Biology, relied on the examination of 6,779 specimens of the smallest whales. It stated that over the past 18 years minkes have lost 9 per cent of their blubber because of more intense competition among whales and the effect on krill numbers of climate change.

The quality of the research was criticised by Australian Antarctic scientist Nick Gales.

"If there's a real decline in blubber then the reasons for that are much more varied and it could be a whole range of things that have nothing to do with the amount of krill and whales," he said.

Japan has continued whaling under the guise of scientific research since a moratorium on commercial hunting was accepted by most nations in 1986.

Gales conceded that the study of dead whales could come up with findings that would not be possible when research was restricted to live whales.

"There are some things on animals that we can't measure without killing them," he said, "(but) the more important question is really whether or not you need to measure those things in the first place and whether the science that can come out of that is important enough." (dpa)