Major change off Aussie coast linked to 'worrying' event thousands of kilometres away
While smaller fluctuations in their departure are normal, researchers from the University of Queensland have observed a 'clear and sustained change' since 2021 and published their findings in the journal Scientific Reports. Lead author, Associate Professor Rebecca Dunlop, believes there is likely a connection to warming waters around Antarctica, as it causes:
A depletion of sea ice
Which leads to a reduction in algae
And this means less food for krill
As a result, krill numbers drop, and there's less food for humpbacks
'Post 2020, there has been a significant decline in sea ice, and it's during that period that they changed their migration,' Dunlop told Yahoo News Australia.
"It seems they're returning to those feeding grounds earlier.'
Why whales must accumulate huge amounts of blubber
To carry out their 10,000km migration, humpbacks need to build up an enormous amount of blubber.
Females face an even bigger challenge because they're normally pregnant as they travel to their winter breeding grounds, and then have to give birth and produce milk to sustain the calf.
During their time in the tropical north, they generally don't eat except for during the odd temporary stopover, adding pressure on them to return home to Antarctica as their energy runs out.
'If they've got less energy... then obviously that's going to change how they behave and how they migrate,' Dunlop said.
If the oceans keep warming and the sea ice keeps declining, then that has massive impacts, not just for whales, but for everything else that lives down there.Associate Professor Rebecca Dunlop
Two separate events could increase pressure on food resources
East Antarctic whale numbers plummeted to around 300 individuals in the 1960s, primarily due to hunting by the Soviets. After whaling was banned a decade later, numbers rebounded and in 2025 they're estimated to be close to 40,000.
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Today, the population is thought to exceed pre-hunting numbers, which were thought to be roughly 30,000. There are concerns that vanishing krill combined with increasing humpback numbers could create a 'perfect storm' of pressure on their food resources.
'You've got this train crash happening where you've got more whales trying to feed on less krill,' Dunlop said.
'We have no idea what the carrying capacity is in the Antarctic, because we don't know what the krill density is. We don't know if the numbers have overshot, or what's going to happen in the future. Numbers might start to decline, or they might absolutely crash.'
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