Humpback whales now migrate weeks early, signaling big ocean changes

Humpback whales travel thousands of kilometers each year, migrating between Antarctic feeding grounds and tropical breeding areas. This journey demands energy, timing, and favorable environmental conditions.

New research from the University of Queensland has revealed that these whales now head south significantly earlier than before, by about three weeks.

This shift in humpback whale migration is not just a quirk of nature. It may be a response to deeper changes in the Southern Ocean.

Whales are now migrating earlier

Between 2003 and 2024, the southern migration peak shifted from early October to mid-September.

“Acoustic and visual surveys show the peak of the southern migration in 2003 was in early October but by 2024, we observed it was in the middle of September,” noted Professor Rebecca Dunlop, lead author of the study.

This change was found across different whale groups: adult males, mothers with calves, and mixed adult groups.

Singing males, tracked through acoustic surveys, also showed a 22-day shift. These consistent patterns point to a population-wide response, not just isolated variation.

Less ice and krill

Whales feed mostly on Antarctic krill, which depend on sea ice for food and shelter. Since 2016, sea ice in regions like the Ross Sea has declined sharply. By 2024, ice levels had dropped by over six million square kilometers.

Whales do not eat much during their migration. They rely on the fat reserves built up during the summer.

“Fewer available krill prior to the migration could be forcing the whales back to the feeding grounds earlier,” said Dunlop.

Environmental records confirm the link. An earlier return south was strongly correlated with low sea ice and specific chlorophyll-a levels (a marker of ocean productivity) during summer feeding periods.

Whales migrate with growing pressure

The eastern Australian humpback whale population has rebounded from near extinction. It grew from just 300 individuals in the 1960s to around 40,000 today.

But this success comes with consequences. More whales mean more competition for krill. At the same time, krill fishing for fishmeal and supplements has intensified.

Earlier shifts in whale migration were not seen during past periods of population growth. But now, under growing environmental pressure, the timing has started to change. This suggests that climate impacts, not crowding, may drive the shift.

Whales show similar trends globally

This pattern is not isolated to Australia. Populations along the western coast of Australia, California, and even South America have also shown changes in timing. Some arrive earlier at breeding grounds, others leave feeding grounds sooner.

“The later years of this study coincide with a pronounced decline in sea ice coverage beyond usual annual fluctuations,” said Dunlop.

These declines were especially sharp after 2021. That is exactly when the migration pattern began to shift.

A greater energy cost

Humpback whales are resilient. They have bounced back before. But the current situation is different. Environmental changes are now faster and broader. While whales still migrate and reproduce, the energy cost may be increasing.

“I am concerned at some point we may see a decline in birth rates because females won’t have the energy to support migrating north, giving birth and getting their calf back to the feeding grounds,” warned Dunlop.

Researchers are now investigating if whales also leave the feeding grounds earlier. If both legs of the journey shift, it may point to long-term changes in life cycle and reproductive success.

Whale migration and ocean changes

Whales respond to changes in food, ice, and temperature. Their migration is tied to the pulse of the ocean. Shifts in their patterns signal broader disruptions in marine ecosystems, affecting balance and biodiversity.

Monitoring whale timing can help track how quickly the Southern Ocean changes. The data may also provide insight into the health of connected species. But more studies on whale health and krill populations are needed to understand the full impact.

For now, whales continue their incredible journey. But their timing tells a different story – one that’s shaped by a changing planet.

The study is published in the journal Scientific Reports.

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