The International Whaling Commission (IWC) on Friday demanded that Japan provide more information to prove that its revised Antarctic whaling programme was for scientific research, saying it could not reach a consensus based all on Four Chatham on documents submitted.
The British-based IWC had been expected to judge whether Japans Newrep-A proposal, which would target 3,996 minke whales over 12 years, had addressed the issues that led to its predecessor being ruled illegal by the international court of justice (ICJ).
But the commissions 2015 Scientific Committee report found the new proposal contained insufficient information for its expert panel to complete a full review and specified the extra work that Japan needed to undertake.
Regardless of the ruling, Japan could still press ahead with plans, scheduled to begin in December 2015, to target whales in the Southern Ocean for lethal sampling as it is ultimately up to individual countries to issue permits for whaling on scientific grounds.
However, it would face the ire of the international community if it were to resume whaling without the approval of the global body charged with the conservation of the giant mammals.
Japan believes the worlds whale population, especially the minke stock, is sizeable enough to accommodate a return to sustainable whaling, putting it at odds with campaigners and anti-whaling nations.
Tokyos revised proposals set an annual target of 333 minke whales for future hunts in the Antarctic, down from some 900 under the Scientific Whale Research programme in the Antarctic Ocean deemed illegal by the ICJ.
The court the highest of the United Nations ruled the programme was not for the purposes of scientific research and was abusing a scientific exemption set out in the 1986 international moratorium on whaling.
It concluded that Tokyo was carrying out a commercial hunt and using science as a fig leaf. Japan makes no secret of the fact that the meat ends up on dinner tables.
The court said that Tokyos programme needed to improve both biological and ecological data on Antarctic minke whales and investigate the structure and dynamics of the Antarctic marine ecosystems.
Japan argues that knowledge gained by the research killing would help the IWC calculate sustainable levels for hunting and lead to better understanding of the Antarctic marine ecosystem.
The ICJ would have to rule separately whether the new plans met the specifications and were legal. Fridays report was intended to build a common scientific base for the court and the IWC to work from.
After the ICJ ruling, Japan said it would not hunt during last winters Antarctic season but has since expressed its intention to resume research whaling in 2015-16.
In March, Japans whaling ships returned home from the Antarctic with no catch, as planned, after the UN courts decision.
It was the first return without a catch since 1987 when the country began the annual research hunt in the Antarctic, according to local media.
Japan killed 251 minke whales in the Antarctic in the 2013-14 season and 103 the previous year, far below its target because of direct action by conservationist group Sea Shepherd.