Japan's own expert witness in the whaling case at the International Court of Justice has cast doubt on the number of whales it kills in its Antarctic program.

The expert, Norwegian Lars Walloe, also told the court that he did not like the inclusion of fin and humpback whales in the whaling program.

And he confirmed that a founding father of the global whaling treaty believed that if any whales were to be killed for scientific purposes, the number should be fewer than 10.

Australia is asking the ICJ to halt the Japanese program, known as JARPA II, which has a self-awarded quota of up to 935 minke whales, 50 fin whales, and 50 humpbacks.

Japanese whalers have taken more than 10,000 whales under the treaty's scientific permit clause, including 18 fin whales, but are yet to take any humpbacks.