Portoroz - Pro- and anti-whaling nations dug in their heels at a key meeting on Monday where Japan sought to lift a 30-year-old moratorium on commercial hunts while others pushed for a sanctuary in the Atlantic.
Meeting host Slovenia urged compromise for the majestic marine mammals' sake, but member states of the International Whaling Commission (IWC) cleaved almost immediately into historic factions.
"The moratorium on commercial whaling should and could be lifted on a stock-by-stock basis based on sound scientific evidence," Japan insisted in a written submission.
The commission's own advisory scientific committee "has confirmed that certain stocks of whale species are recovered", which implies the moratorium is outdated, it argued.
Japan's yearly whale hunt, which it says is carried out in the name of science, is a recurring and deeply divisive issue at the 88-member IWC's biennial gatherings.
The organisation's 66th meeting, scheduled to run until Friday, opened in the Adriatic resort of Portoroz on Monday.
Scientific hunts are exempt under the IWC's 1986 moratorium, but critics insist Japan abuses the provision for commercial catches.
The meat ends up on supermarket shelves and in restaurants, in line with an IWC stipulation that whales taken for science must be eaten.
"It is a loophole that the IWC never anticipated being routinely exploited by a country in order to kill whales for profit, but that is precisely what Japan has been doing since 1987 to kill more than 15 000 whales," said Kitty Block of conservation group Humane Society International.
The International Court of Justice ruled in 2014 that Japan was abusing the scientific exemption.
Tokyo cancelled its 2014/15 hunt, only to resume it the following year, killing an estimated 300-plus animals.
New Zealand and Australia are asking the IWC to introduce stringent reviews for scientific whaling projects.
"It is clear that Japan's stated research objectives can be met using non-lethal means and we urge Japan to cease its lethal practices," reads a document submitted by New Zealand.
The Netherlands, on behalf of the European Union, "strongly support maintaining the moratorium on commercial whaling and invite countries that continue commercial or other whaling activities to consider ceasing them."
Besides Japan and communities which received aboriginal whaling licences from the IWC, Norway and Iceland conduct commercial hunts, having submitted objections to the moratorium.
Japan, for its part, opposes the creation of a South Atlantic whale sanctuary, a proposal of Argentina, Brazil, Gabon, South Africa and Uruguay which carries the backing of the European Union and others.
Tokyo's commissioner to the IWC, Joji Morishita, highlighted the intractability of the divide.
"One side... is supporting the total protection of whales under any circumstances, no kill, no one whale should be killed," he told journalists at the meeting.
The other, "like Japan, is supporting sustainable utilisation of marine living resources including whales," he said.
"These positions are so... fundamentally different and that is causing the difficulties or stalemate or deadlock of this organisation. Unless we address this issue in some manner we will just be repeating the same thing, meeting after meeting."
Japan, Norway and Iceland are traditionally in their own corner at the biennial IWC meetings, which seek to balance issues of national sovereignty, subsistence rights and culture, with conservation of Earth's natural bounty.
This year's meeting marks the 70th anniversary of the commission's founding, and the 30th birthday of the moratorium estimated to have prevented the killing of tens - even hundreds - of thousands of whales.
Conservationists say whales still face a multitude of perils, from hunters and ship strikes to getting snared in fishing gear and pollution.
"(...) It is in the interests of all of us to give back to the cetaceans their living environment," Slovene Environment Minister Irena Majcen urged delegates.
"This is something that should unite us."