The majestic humpback whales along Australia’s east coast are now returning south weeks earlier than they did just two decades ago. According to groundbreaking research conducted by the University of Queensland (UQ), this shift in migration timing is likely linked to rising ocean temperatures and declining sea ice in the Southern Ocean.
📊 What the Study Reveals
Dr. Rebecca Dunlop, Associate Professor at UQ’s School of the Environment, led the long-term study using acoustic and visual surveys. The findings are striking: the peak of the southern migration in 2003 occurred in early October, whereas by 2024, it shifted to mid-September—a change of approximately three weeks earlier.
“Although yearly migration timing can vary by about two weeks, since 2021 we’ve observed a clear and consistent trend toward earlier movement,” explained Dr. Dunlop.
🌊 Why Is This Happening?
The research points to environmental cues that whales likely rely on, such as food availability and climate conditions in the Southern Ocean, where these whales spend their feeding season.
- Sea ice and krill connection: Krill, the main food source for humpbacks, feed on algae that grow under sea ice.
- Decline in sea ice: Recent years have seen significant reductions in Antarctic sea ice, reducing krill populations.
- Feeding pressure: With fewer krill available, whales may be cutting their feeding season short, prompting earlier migration south to conserve energy.
🐋 Migration and Reproduction Under Threat
Humpback whales do not feed during their winter migration to tropical breeding grounds, such as the Great Barrier Reef. They rely heavily on fat reserves built during the summer feeding season.
“If whales don’t have enough time to build up energy reserves, it could impact their ability to reproduce and support their calves during the journey back,” Dr. Dunlop warned.
Although the eastern Australian humpback whale population has rebounded from about 300 in the 1960s to nearly 40,000 today, rising climate stressors could once again place this species at risk.
🔍 Other Potential Factors Considered
Researchers explored whether increased population density or human activity on the breeding grounds might explain the earlier migration. However, these factors were ruled out, as the timing shift only became evident after 2021, aligning with record-breaking ocean temperatures and climate-driven changes in sea ice.
🌍 A Global Trend?
Similar early migration patterns are now being reported in other humpback whale populations—along Western Australia and even South America. This suggests a broader ecological shift affecting the species globally.
“If females can’t accumulate enough energy for the long migration and calving, we may eventually see a decline in birth rates,” Dr. Dunlop cautioned.
🔬 What’s Next?
Further research is underway to assess whether northbound migration—from Antarctic feeding grounds to northern breeding areas—is also occurring earlier due to the same environmental pressures.
📖 Reference:
Dunlop, R. et al. (2025). Southern Ocean humpback whales are shifting to an earlier return migration. Scientific Reports. DOI: 10.1038/s41598-025-07010-9
Source: University of Queensland