Watching the migration of whales up Australia’s east coast, researchers have documented something “worrying”. Humpbacks are leaving their northern breeding grounds for Antarctica three weeks early.

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:

  1. A depletion of sea ice

  2. Which leads to a reduction in algae

  3. And this means less food for krill

  4. 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.”

Two humpbacks breaching during the early morning.

Humpbacks travel up to 10,000km during their migration. Source: Bronwyn Keller

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.

The entrance to Woodside Petroleum's Pluto development (C) is shown on the Burrup Peninsula in the north of Western Australia on June 17, 2008. Piles of red rock which typify the Burrup area are the site for perhaps one million pieces of Aboriginal rock engravings several thousands of years old and considered by some to be the greatest concentration of such ancient art in the world. The peninsula in the resource-rich Pilbara region is also home to increasing amounts of industrial activity, including a gas processing plant, a fertiliser plant and iron ore facilities which are threatening the rock images of long-extinct animals and what are believed to be mythological creatures.

After the United States and Russia, Australia is considered the world’s third-largest exporter of fossil fuels, the main drivers of climate change. Source: GREG WOOD/AFP via Getty Images

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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