Japan's decision to pull out of the International Whaling Commission (IWC) could lead to an increase in commercial hunting, according to New Zealand's former whaling commissioner, Sir Geoffrey Palmer.
The Japanese government on Wednesday confirmed it will restart commercial whaling in July.
It will stop its so-called scientific whaling in the Antarctic Ocean, and only fish in seas near Japan and the country's exclusive economic zone.
Sir Geoffrey, a past Prime Minister, and New Zealand's representative on the commission for eight years until 2010, said Japan may go ahead with its often repeated threat to set up a separate organisation of countries that support commercial whaling.
"Japan is advocating for 'sustainable whaling', the idea that if you don't kill too many, you could keep whaling."
If Japan succeeded in persuading "like-minded" nations to join it, this could lead to an increase in whaling, he said.
"It is really a very unfortunate thing for the International Whaling Commission to lose Japan.
"And although the commission has been full of absolutely tremendous disagreement for 30 years, nevertheless it has prevented the unbridled slaughter of whales."
The decision - an unusual step for Japan, which stresses multilateralism in its diplomacy - sparked swift criticism.
"The declaration... is out of step with the international community, let alone the protection needed to safeguard the future of our oceans and these majestic creatures," international conservationist group Greenpeace said.
"As the chair of the G20 (Group of 20) in 2019, the Japanese government needs to recommit to the IWC and prioritize new measures for marine conservation."
Australia urged Japan to return to the IWC "as a matter of priority", its environment minister, Melissa Price, said in a statement.
"The Australian Government is extremely disappointed," Ms Price said. "Australia remains resolutely opposed to all forms of commercial and so-called 'scientific' whaling."
Japan has long defied such protests to conduct what it calls scientific research whaling, having repeatedly said its ultimate goal was to whale commercially again.
In 2014, the International Court of Justice ruled that Japan should halt its Antarctic whaling.
Japan suspended its hunt for one season to re-tool its whaling program with measures such as cutting the number of whales and species targeted, but resumed hunting in the 2015-2016 season, capping its Antarctic catch with a quota of 333 whales annually.
Japan has long maintained that most whale species are not endangered and that eating whale is part of its culture.
It began scientific whaling in 1987, a year after an international whaling moratorium began.
Much of the meat ends up on store shelves, 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.
Influential lawmakers in Prime Minister Shinzo Abe's Liberal Democratic Party whose constituencies include whaling communities have long lobbied for a resumption of commercial whaling. Mr Abe's own electoral district includes Shimonoseki, a whaling port in western Japan.
rnz.co.nz / Reuters