Attorney-General Mark Dreyfus has angrily rejected Japanese claims that the Australian Government has "outsourced" its anti-whaling campaign to controversial activist group Sea Shepherd.

Mr Dreyfus was speaking as he wrapped up Australia's legal challenge to the whaling program at the International Court of Justice in The Hague.

Demanding Japan produce evidence to support its case for whaling, he said there was no evidence the whaling program was used for scientific purposes.

And he was highly critical of Japan's previous assertions to the court about Australia's relationship with anti-whaling activists, saying allegations Australia supported violent extremism were offensive and untrue.

"It is wholly untrue and ridiculous to suggest that Australia has outsourced Antarctic maritime enforcement to Sea Shepherd," he said.

Sorry, this video has expired Mark Dreyfus speaks with ABC News Breakfast

Japan has previously told the court Australia is engaged in an "alarmist crusade" against whaling.

Its lawyers argue the killing of whales in the Southern Ocean is part of a legitimate scientific program to establish whether commercial whaling is sustainable.

But Mr Dreyfus has told ABC News Breakfast that Japan's scientific justification for its whaling program is "not supported by any proper hypothesis".

"Japan called an expert who was unable to explain how they'd selected even the number of minke whales that has been the Japanese target for many years," he said.

"When you can't explain why you are killing that many whales, when you can't identify for the court what is the purpose of the activity in a scientific sense, it's not science at all."

Australia has one more day of closing submissions in the case, which is being presided over by 16 judges.

Japan will respond next week.

But Japan's delegation spokesman, Noriyuki Shikata, has already criticised Australia's case.

"Today we have not really heard effective legal rebuttal based on evidence and reasoning and we have an impression that many of the allegations are driven by emotions, not on science," he said.