Earlier in the day, Japanese Chief Cabinet Secretary Yoshihide Suga said that Tokyo had made a decision to pull out from the IWC starting in 2019 to resume commercial whaling in July after a 30-year pause.
Suga said that "although scientific evidence has confirmed that certain whale species/stocks of whales are abundant", anti-whaling countries remain focused "exclusively on the protection of whales".
Since 2002, Sea Shepherd has opposed Japanese whaling operations in the Southern Ocean Whale Sanctuary with expeditions to Antarctic waters first in 2002 followed by continuous campaigns from 2005 until 2017.
Faced with collapsing whale stocks, the IWC agreed to a moratorium on commercial whaling from 1986, a move credited with saving several species from imminent extinction.
Tony Burke, the Australian environment minister who took Japan to the International Court of Justice in 2014 and secured the halt on whaling in the southern oceans, says he has mixed feelings about the announcement, which heralds the reemergence of whaling for money.
Former Defence Minister Itsunori Onodera, who now serves as adviser to the ruling Liberal Democratic Party's fisheries committee, said he supported a decision to withdraw from the IWC, in an interview with Japan's NHK television.
The decision will spell the end of Japan's whaling in the Southern Ocean that has seen its boats in clashes with anti-whaling group Sea Shepherd. Critics considered the research a sham, little more than a cover for commercial whaling.
Much of the meat ends up in shops, even though most Japanese no longer eat it. Whale consumption accounted for 0.1 percent of all Japanese meat consumption, according to the Asahi newspaper. Humane Society International said it fears that such action will open the door for "a new chapter of widespread renegade slaughter of whales for profit".More news: Winter Storm to Arrive Late Tonight
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In a notable shift, Japan also said it will no longer conduct controversial hunts in the Antarctic Ocean - where its fleet of whaling ships have killed 333 whales in each of the past two years, under the justification of performing whale research.
"By leaving the IWC, Japan is rejecting multilateralism and setting a very bad precedent for conservation, which will likely have very serious negative consequences for the world's whales", she said.
Leaving the IWC means Japanese whalers will be able to resume hunting in Japanese coastal waters of minke and other whales now protected by the IWC.
"It's clear that the government is trying to sneak in this announcement at the end of year away from the spotlight of global media, but the world sees this for what it is", Sam Annesley, executive director of Greenpeace Japan, said in a statement.
The ever-dwindling demand means an uncertain outlook for Japan's whaling.
Japan's request for a resumption of commercial whaling was most recently denied at the IWC meeting in September. Little oversight of Japan's whaling practices, Fuchs added, could "spell doom for some populations".
The country's commercial whaling will be limited to "species whose abundance has been scientifically verified, such as the minke, sei and Bryde's", a fishery ministry official said.
Yoshie Nakatani, an official at the foreign ministry's fisheries division, said Japan would still attend IWC meetings. Japanese people ate more than 233,000 tons of whale meat per year in 1962, but just 3,000 tons in 2016, according to government data.