The world's whaling watchdog moved Thursday to curtail Japan's annual whale hunt, conducted under scientific licence but blasted by critics as a commercial meat haul.

A resolution on "improving" the review of deadly research programmes, which Japan alone conducts, split the 70-year-old International Whaling Commission (IWC) into familiar camps -- pro- and anti-whaling.

Just two days earlier, the pro camp defeated a bid to create a whale sanctuary in the South Atlantic, which had required 75 percent of IWC member votes.

Thursday's resolution, however, needed a simple majority to pass. It garnered 34 "yes" votes to 17 cast by the camp that includes Japan and commercial whalers Norway and Iceland.

Championed by Australia and New Zealand, it will lead to the creation of a permanent "working group" to assist the IWC and its expert scientific committee to assess whaling programmes conducted in the name of science.

The outcome was hailed by conservation groups which accuse Japan of abusing an exemption for research hunts under a 30-year-old moratorium, which also allows controlled aboriginal subsistence whaling.

"Today's vote shrinks the... loophole that Japan has exploited ever since the global moratorium on commercial whaling came into effect," said Kitty Block of the Humane Society International.

"In defiance of the ban, Japan has issued itself a license to kill more than 15,000 whales under the guise of science" since 1986.

Resolutions are not legally binding on members of the commission, which has no policing function and cannot impose penalties.

"We will abide by the convention itself," Japan's commissioner to the IWC, Joji Morishita told AFP after the vote, referring to the International Convention for the Regulation of Whaling, the IWC's founding document.

Japan's whaling is a deeply divisive and recurring quarrel at the IWC's biennial meetings.

Under the scientific exception, national governments determine their own catch limits and issue whaling permits.

- 'Not justified' -

In 2014, the International Court of Justice (ICJ) found that permits issued by Japan were "not for purposes of scientific research" and instructed the country to halt its JARPA II programme.

Japan cancelled its 2014-15 hunt, only to resume it the following year under a new programme called NEWREP-A (New Scientific Whale Research Program in the Antarctic Ocean).

It killed 333 minke whales in the Southern Ocean that year -- many of them pregnant, according to observers.

The Southern Ocean hosts one of two whale sanctuaries in the world.

The meat from Japan's hunts ends up on supermarket shelves and in restaurants, in line with an IWC stipulation that whales taken for research must be eaten.

Morishita defended Japan's whaling, insisting it was to gather science data, and did not violate the ICJ judgment.

In its ruling, "it is clear that the ICJ assumes there can be future research activities," the commissioner told fellow delegates.

"The ICJ also said... that the use of lethal sampling per se is not unreasonable in relation to the research objectives."

But his New Zealand counterpart, Amy Laurenson, insisted that NEWREP-A was clearly "not in fact for purposes of scientific research.

"Japan has still not justified the use of lethal sampling," she said.

Under the new resolution, a working group will be appointed to consider the reports of the IWC's scientific committee on all new, ongoing and completed scientific whaling programmes.

It will report to the commission, which will express itself on the validity of every programme.

The International Fund for Animal Welfare welcomed the move as a further obstacle to Japan "unilaterally" issuing its own permits.

"We all know that scientific whaling is sham science, and simply commercial whaling by another name," said the organisation's Matt Collis.

IWC members put their differences aside just long enough on Thursday to pass a separate resolution on trying to save the critically endangered vaquita -- a small porpoise sometimes called Mexico's "panda of the sea".

There are fewer than 60 known individuals left in the Gulf of California, the vaquita's only home.

They perish in illegal nets used to catch totoaba, large fish whose swim bladders are believed in China to hold medicinal powers.

The vaquita decision urges IWC members to provide financial and technical assistance for Mexico to police a permanent gillnet ban, compensate affected fishers, and replace outdated fishing gear with safe alternatives.