Japan, under fire overseas for whaling it justifies as research, has released its findings -- whales are losing blubber because ocean resources are growing scarce.
But critics said the recent study, which involved the slaughter of thousands of whales, is little more than window-dressing for Japan's pursuit of commercial whaling.
Japan is frequently criticised by the West for conducting annual whaling missions under the pretext of "lethal research" when most of the meat ends up in supermarkets, restaurants or school lunches.
Japan says that whaling is part of its culture but contends that it does not violate a 1986 international moratorium on hunting as it is conducting research. Only Norway and Iceland defy the moratorium outright.
The study used research on 6,779 whales, of which more than 4,500 were killed including some which were pregnant.
It found that the oceans are facing a shortfall of krill, a vital component of the food chain, due to climate change and the recovery of species such as humpback whales.
According to the study, Antarctic minke whales shed nine percent of the blubber over 18 years, corresponding to an annual weight loss of 17 kilograms (38 pounds).
Blubber is vital for whales because it helps to retain heat in cold waters and store energy and nutrition. Minke whales swim to the Antarctic every summer to feed and to warm waters during the winter to breed.
The study, led by Kenji Konishi of Japan's government-backed Institute of Cetacean Research, called for further study on krill, saying that the very future of the eco-system was at stake.
Investigating "the dynamics of the widely distributed krill population is quite difficult, so that monitoring energy storage by a krill consumer, such as the minke whale, can be most useful," it said.
The study was published in Polar Biology, a journal with editorial offices in Germany and Alaska, after several other journals rejected it, a researcher said.
Conservationists dismissed the study and said that researchers could also use non-lethal methods such as sonar to gauge krill populations or ultrasound to monitor whales.
"There is no need to kill whales to study them. 'Research' whaling is just commercial whaling under another name," said John Hocevar, oceans specialist at environmental group Greenpeace.
In any case, blubber thickness is "not a very good indicator" of health in whales, he said, recommending instead measuring the ratio of girth or length compared with the ocean giants' weight.
Conservationists also worried about the study's suggestion that the lower availability of krill was due to recovering populations of humpbacks and other big whales.
Last year, Japan planned to kill humpback whales for the first time in decades. It dropped the idea due to international pressure, including protests in Australia, where humpback watching is a popular pastime.
Greenpeace blamed global warming and the subsequent melting of sea ice for the shortage of krill as ice provides sanctuary for the tiny animals.
"If we want to solve this problem, humans need to deal with global warming," said another Greenpeace marine specialist, Wakao Hanaoka.
Hocevar said: "While some species have started to recover, no whale population has reached the level it had before industrial whaling began."