Researchers are worried "skinny" blue whales spotted off Australia's coast are not finding enough to eat due to warming oceans killing their food.
The life cycle of blue whales found in Australian waters takes them to the southern coast, searching for krill to eat, before they migrate north to warmer waters around Indonesia to breed.
Each year, the Blue Whale Study undertakes an aerial survey of the animals feasting off the coast between Robe in South Australia and Portland in Victoria.
Chief executive and senior research scientist Dr Peter Gill said his team had spotted more whales than in previous years but the size of some animals observed in recent surveys was concerning.
"We've seen a number of skinny blue whales, researchers on the west coast have seen skinny blue whales, and that's a bad sign," he said.
"That means probably they're not getting enough food at some stage in their life cycle."
Dr Gill says that while blue whales are "massive animals, they have a thin blubber layer and need to be in feeding areas year-round".
"Their breeding areas up in Indonesia are rich and productive waters, but there's been signs those waters are warming quite quickly in the past few years, and that's bad news for krill, which likes cold water," he said.
"There's concerns at the moment about the effects of climate change on the wellbeing of this population of blue whales, which are still an endangered species."
Whales indicative of ocean health
Blue whales can grow up to 33 metres long and can weigh up to 200 tonnes.
Wildlife scientist Dr Vanessa Pirotta said whale size and mass was a key indicator of their health for researchers.
"We'd expect an animal that's spent the entire summer predominantly feeding to be in relatively good condition," she said.
"But when observations are made and they're looking quite thin, maybe this is a suggestion that there could be something else environmentally going on
"This might be indicative for blue whales that the environmental conditions [are] not being so favourable to provide them with those feeding conditions to migrate north."
Dr Pirotta added that the health of whales was an indicator for the health of the world's oceans, given their habits and large migration patterns.
"We can use these animals potentially as a canary in the coal mine to learn about changes in the ocean that we're not yet aware of," she said.
"Just looking at the animal can't give us the entire picture of what's going on internally, but what it can do is provide scientists with that snapshot to see they're not in good nick.
"Body condition, photographs and surveys that go on across years are really important in helping us to build pictures and an understanding of the changes these animals might be facing."
