- A new 33-year study finds that southern right whales off Australia are having calves less often, with the average time between births rising from 3.4 to 4.1 years since 2015, a trend researchers link to climate-driven changes in the Southern Ocean.
- Shrinking Antarctic sea ice and warming waters are reducing the availability of krill and copepods, the whales’ main food sources, leaving females struggling to rebuild their energy after nursing and delaying their next pregnancy.
- The reproductive slowdown is not unique to Australia, with similar declines documented in southern right whale populations off South Africa and Argentina, raising concerns for a species still recovering from near-extinction due to commercial whaling.
- Researchers are calling for expanded marine protected areas, stricter management of Antarctic krill fisheries, and urgent action on climate change to protect the species.
Southern right whales (Eubalaena australis) off Australia’s southern coast are having calves less often than they used to. A new study links this slowdown to warming water and shrinking sea ice in the Southern Ocean.
The study, conducted by researchers at Australian, South African and U.S. institutions and published this month in Scientific Reports, tracked more than 1,100 calving events from 696 individual female whales at a major breeding ground in an area called the Great Australian Bight within the Yalata Indigenous Protected Area.
Since around 2015, the average time between births rose from 3.4 years to 4.1 years. For a species that reproduces slowly, that shift adds up.
“These extended calving intervals mean fewer calves are being born overall, and this reduces population growth over time,” lead author and marine biologist Claire Charlton from Flinders University writes in The Conversation. “Southern right whales have been celebrated as one of conservation’s success stories … But our new research shows this success story is changing.”
Between 1991 and 2024, scientists used photo-identification data to tell the whales apart. Each whale has a unique pattern of callosities, or patches of thickened skin, on its head that distinguishes one from another.
Using this long-term whale dataset, along with environmental records, researchers found that half of the variation in birthing intervals can be explained by environmental conditions in the whales’ feeding grounds.
“Over the past decade, the ocean has warmed, the ice is melting and there have been dramatic shifts in food availability weather patterns,” writes Charlton. “Our analysis shows longer calving intervals coincide with these environmental changes, suggesting the impacts of climate change on conditions in the Southern Ocean are linked to whales having fewer calves.”
The whales in the study spend their summers feeding in Antarctic waters, then migrate north each winter to Australia’s southern coast to breed and give birth to their young.
Antarctic sea ice provides critical habitat for krill, the tiny crustaceans that southern right whales rely on for food at high latitudes. As ice has declined due to climate change, krill habitat has shrunk.
At the same time, mid-latitude waters where the whales also feed have been warming and becoming less productive. Warmer waters favor salps, jellyfish-like creatures that thrive when conditions are poor for krill and copepods. Salps are far less nutritious than whales’ preferred prey.
For whales (and all mammals), pregnancy and nursing are physically demanding. Nursing can drain roughly a third of a female’s body weight, and she needs to fully replenish her energy stores before she can breed again. When food is scarce, that recovery takes longer, and the gap between calves grows.
“As mammals, the choice to have a baby is demanding,” Peter Corkeron, a marine ecologist at Griffith University who was not involved in the research, told The Guardian. “When conditions are getting worse, you pull back on having as many babies.”
Charlton calls southern right whales a “sentinel species: animals whose health reflects broader changes in their environment.” He said problems with whales signal broader problems in the ecosystem.
“[Right whales] play a really important role in marine ecosystems,” Kelly Keen, a Ph.D. student at the University of California, Santa Cruz, who studied whale ecology, told Mongabay. “They do a lot of ocean mixing, vertically and horizontally. They deliver and recycle these nutrients, essentially by fertilizing the ocean waters with their feces.”
Southern right whales were hunted to near-extinction in the 18th and 19th centuries through commercial whaling operations. But through the efforts of scientists as well as international protection and the creation of marine sanctuaries, the species slowly made a comeback in the 20th century.
According to an International Whaling Commission assessment, there were roughly 13,600 individuals globally in 2009. Australia’s population, now estimated between roughly 2,300 and 4,000 individuals, is still only a fraction of pre-whaling numbers.
The new study finds that the reproductive slowdown has been reducing population growth since 2016 or 2017. And Australia is not alone; another Scientific Reports study, this one published in 2023, found reproductive rates have been slowing down in southern right whale populations off South Africa and Argentina as well.
To protect these whales, Charlton calls for limiting threats such as “whales being struck by ships, getting entangled in ropes and being exposed to noise pollution.” The study authors call for stronger protections, including “expanded marine protected areas, tighter management of Antarctic krill fisheries, and continued long-term monitoring.”
“The future of southern right whales is likely to be closely tied to the management of krill harvesting and addressing climate change,” Charlton writes.
Industrial fishing vessels harvest krill primarily for fish feed and dietary supplements. A 2025 study found that krill catches reached a historic high of 0.5 million tons in 2024, and warned that current catch limits do not account for climate variability or krill population dynamics.
As whale populations recover and krill habitat shrinks due to climate change, scientists warn that competition between industrial fishing and wildlife is likely to worsen.
“We need to listen,” writes Charlton, “and act — while there is still time.”
Banner image of Southern right whales in Hermanus, South Africa. Photo by Rhett Butler.
Abandoning Antarctic krill management measure threatens conservation progress (commentary)
Citations
Charlton, C., Germishuizen, M., O’Shannessy, B., McCauley, R., Vermeulen, E., Seyboth, E., … & Burnell, S. (2026). Climate-driven reproductive decline in Southern right whales. Scientific Reports, 16(1), 5352. doi:10.1038/s41598-026-36897-1
Meyer, B., Arata, J. A., Atkinson, A., Bahlburg, D., Bernard, K., Cárdenas, C. A., … & Ziegler, P. (2025). Adjusting the management of the Antarctic krill fishery to meet the challenges of the 21st century. Proceedings of the National Academy of Sciences,122(37). doi:10.1073/pnas.2412624122
Vermeulen, E., Thavar, T., Glarou, M., Ganswindt, A., & Christiansen, F. (2023). Decadal decline in maternal body condition of a Southern Ocean capital breeder. Scientific Reports, 13, Article 3228. doi:10.1038/s41598-023-30238-2
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