Japan was caught killing a whale deep inside Antarctic waters declared by Australia to be a protected whale sanctuary.
Sea Shepherd activists tracked the Japanese whaling fleet on Sunday, capturing the first images of Japan hunting whales in the Southern Ocean since Tokyo defied an international court ruling that declared the hunt to be illegal.
But the activists have since suffered a setback in their hope to disrupt the whale slaughter when heavy fog set in overnight and they lost track of the main abattoir ship, Nisshin Maru. The hunt was several hundred miles from Casey Station in Antarctica.
One of the Japanese harpoon ships sought to delay the Sea Shepherd vessel Steve Irwin, allowing the slower Nisshin Maru to escape radar range.
The activists had tracked the whaling fleet after a five-week search but will not disclose the location of its second and faster ship, the $12 million Ocean Warrior, for what it called tactical reasons.
Outrage erupted across the political spectrum on Monday after the activists made public the images of a harpooned minke whale about to be butchered.
The whale was apparently killed inside a marine sanctuary dating back to 1999, when it was first declared by the Howard government. The same waters are also subject to an international ban on commercial whaling.
But Japan has refused to recognise the sanctuary and claims the whaling is for scientific research - yet also allows the sale of the whale flesh in markets and restaurants. Tokyo has said it will kill 333 minke whales this year.
Labor described as "shocking" that the whale slaughter was getting underway as Japan's Prime Minister Shinzo Abe was meeting at the weekend with Malcolm Turnbull in Sydney.
Labor and the Greens are demanding the government take more direct action to stop the hunt.
Environment Minister Josh Frydenberg said in a statement the government is "deeply disappointed" by the resumption of whaling.
"Australia is opposed to all forms of commercial and so-called 'scientific' whaling. It is not necessary to kill whales in order to study them," Mr Frydenberg said.
Darren Kindleysides, from the Australian Marine Conservation Society, said Australia should not be "rolling out the red carpet" for Mr Abe but instead taking every legal and diplomatic avenue to stop whaling, including by the United Nations Convention on the Law of the Sea.
Japan was pursued in Federal Court over its whaling activities and fined $1 million but has refused to pay.
Australia also won a landmark 2014 decision against Japan in the International Court of Justice but Tokyo has since withdrawn from the court's jurisdiction on whaling cases.
A Japanese harpoon ship offloads a whale to the larger Nisshin Maru abattoir ship in 2013. Photo: Sea Shepherd
Greens senator Nick McKim has called on Australia's Border Force to send its vessels to the Southern Ocean to protect the Australian whale sanctuary and territorial waters.
Australia has dispatched patrol vessels to the waters to monitor the whaling in the past.
But only a handful of countries recognise Australia's territorial claims in Antarctica and officials are wary of any action that might disrupt the Antarctic treaty system, which puts all territorial claims on hold.
