Minke whales shedding blubber: study
Japanese scientists have released a study that suggests whales are losing blubber because ocean resources are growing scarce, a claim discounted by others as flawed.
The study, which was published in Polar Biology, after several other journals rejected it, was based on the research of 6779 whales, of which more than 4500 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 have shed on average 9% of their blubber during the past 18 years, corresponding to an annual weight loss of 17 kilograms.
Minke whales swim to the Antarctic every summer to feed, and to warm waters during the winter to breed.
Blubber is vital for whales because it helps to retain heat in cold waters and store energy and nutrition.
The study, led by Professor Kenji Konishi of Japan's government-backed Institute of Cetacean Research, called for further study on krill, saying that the very future of the ecosystem 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," say the authors.
Japan has been frequently criticised for conducting annual whaling missions, which it says does not violate a 1986 international moratorium on hunting as it is conducting research.
Conservationists dismiss the study and says 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," says John Hocevar, oceans specialist for environmental group Greenpeace.
He says blubber thickness is "not a very good indicator" of health in whales, recommending instead measuring the ratio of girth or length compared with the ocean giants' weight.
Conservationists are also worried about the study's suggestion that the lower availability of krill was due to recovering populations of humpbacks and other big whales.
Dr Nick Gales from the Australian Antarctic Division says the study failed to address criticisms of its methodology when it was first presented at a conference in Japan two years ago.
"The science behind showing those correlations and trends is very weak at best, and the explanation they put forward is extremely simplistic," Gales told ABC radio.
"If there is a real decline in blubber then the reasons for that are much more varied. It could be a whole range of things that have nothing to do with amount of krill and whales."
According to Gales, some of the data from the study contradicts its main finding that minke whales are suffering.
"What they're showing, claiming to show, from their lethal sampling is that these whales are doing incredibly well," he says. "It's difficult to know which is right."