Japanese whalers have shipped home 333 dead whales - including about 200 pregnant cows - prompting Australia to declare anew it is considering legal action over the slaughter.
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The whalers, who claim their annual whale hunt is for "scientific research", admitted some of the harpooned minke whales had been expecting twins.
Japan's Institute for Cetacean Research said the prevalence of pregnant whales indicated the health of the population.
Japan defied a ruling by the international court to stop whaling, resuming its hunt over the summer months in the face of international condemnation.
The court had ruled Japan's whale hunt illegal in a case brought by Australia, but Tokyo announced new guidelines in November to justify killing more than 4000 whales in the next 12 years, and has since withdrawn from the court's jurisdiction.
Foreign Minister Julie Bishop said Australia would continue to push for Japan to comply with its international obligations and the principles set out in the International Court of Justice's judgment.
Asked about the prospect of Australia taking further legal action, Ms Bishop said the government was "considering all avenues to achieve compliance with the court's decision".
Japan's insistence on the right to kill whales coincides with the country's drive for closer ties to Australia.
Tokyo is bidding for the multibillion-dollar contract to build Australia's fleet of 12 submarines to enhance what Japan's Prime Minister Shinzo Abe has called a "special relationship".
Anti-whaling activists Sea Shepherd had attempted to disrupt Japan's 115-day whale hunt over the summer, but said in February the group's vessel Steve Irwin had been unable to locate the four-ship fleet.
Japan has nominated a vast area of the Southern ocean as hunting grounds and Sea Shepherd said some of the whales had been killed inside the area declared by Australia as a sanctuary.
Sea Shepherd said Australia had made an "empty response" to the resumption of whaling, refusing to disclose the fleet's location or send a vessel to prevent the slaughter.
Commercial whaling was banned in 1982 after years of rampant harvesting, with a loophole provided for "scientific research".
Australia successfully challenged Japan's whaling in the international court, arguing it had simply hunted under the guise of research.
The Turnbull government flagged the prospect of legal action in December, but Japan's decision to withdraw from the court's jurisdiction has complicated any response, with arbitration under the law of the sea understood to also be considered.
Don Rothwell, an international law specialist from the Australian National University, said the next confrontation with Japan was likely to be at the International Whaling Commission in October.
"The Commission meeting this year could prove to be quite pivotal for not only legal but diplomatic responses," Professor Rothwell said.
Ms Bishop said Australia would continue efforts in the International Whaling Commission to "strongly oppose commercial whaling and so-called 'scientific' whaling, uphold the moratorium on commercial whaling, and to promote whale conservation".
Comment was sought from the Japanese embassy in Canberra.
