"It is extraordinary that Japan, one of the most technologically advanced nations in the world, continues to kill an estimated 650 whales a year using 1940s science," said Susan Lieberman, director of the WWF's global species programme.

"We call on Japan to live up to its reputation as a technologically and scientifically advanced nation, and put an end to 'scientific whaling'," she said in a statement.

Whaling nations -- mainly Japan, Norway and Iceland -- are allowed to kill whales for scientific purposes under rules of the International Whaling Commission (IWC) even though the IWC imposed a moratorium on all commercial hunts in 1986.

Yet meat from whales caught for research often ends up in restaurants or shops after the scientists have done their work, leading many opponents to see the catches as a sham to circumvent the IWC moratorium.

Japan says it needs to slaughter whales to understand their life cycles. It says it needs to dissect their stomachs, for instance, to track diets, and needs to examine whale skeletons and blubber to see if they are exposed to pollutants.

Tokyo says the research will help determine whether stocks are robust enough to withstand commercial catches.

But the WWF said a biopsy dart could supply the evidence Japan needed. The long-term diet of a whale could be seen from a genetic sample of its skin, for instance.

"Japan's whaling programme is about business and politics, but not sound science," Lieberman said.

Japan has threatened to quit the IWC if the organisation fails at its next meeting in South Korea on June 20 to approve a set of rules that would allow limited commercial whaling.

Whaling nations in turn accuse the IWC of extending the moratorium on commercial hunts year after year despite scientific evidence that some whale stocks have recovered.