Southern right whales signal climate stress

Southern right whales were once regarded as evidence that conservation efforts could succeed. Intensive hunting had driven these giants close to extinction, but legal protections allowed their population to begin recovering slowly.

For many, the species became a conservation success story. However, fresh research has revealed a troubling shift. Scientists believe these whales could be providing an early warning of climate change affecting the oceans.

The new study was led by researchers from Flinders University and Curtin University, working with international partners in the United States and South Africa.

Decline in southern right whales

The findings reveal that southern right whales are producing fewer calves than they did previously. This reduction raises major concerns for both ocean health and the species’ future.

Southern right whales, scientifically named Eubalaena australis, inhabit the Southern Ocean. Specialists describe them as a “sentinel species.”

In other words, changes to their condition may expose changes occurring across the broader ecosystem. When whale populations alter, it is likely that the ocean environment is changing as well.

30 years of tracking whales

Researchers examined more than 30 years of records gathered from 1991 to 2024.

The research was conducted at the Head of the Great Australian Bight, within the Yalata Indigenous Protected Area in South Australia. Across several decades, specialists photographed individual whales to monitor births and reproductive patterns.

The data indicate that females are now taking more time between calves. This extended interval results in fewer offspring over time. Reproductive rates have declined during the past decade.

The researchers associate this fall with substantial environmental shifts. Antarctic sea ice has declined, ocean conditions have changed, and the Antarctic Oscillation, a climate pattern, has stayed in a positive phase for longer stretches. Each of these developments influences food availability.

As sea ice contracts, krill populations may decrease. Krill are tiny shrimp-like animals that sit at the bottom of the food chain. Southern right whales rely heavily on krill in Antarctic waters. Reduced food supplies leave less energy available for pregnancy and nursing.

Whales signal climate stress

Dr Claire Charlton, an academic, director of Current Environmental Pty Ltd and long-term leader of the Australian Right Whale Program in the Great Australian Bight, outlines the gravity of this trend. She is also an adjunct academic at Flinders University and a researcher at Curtin University.

“This reproductive decline represents a threshold warning for the species and highlights the urgent need for coordinated conservation efforts in the Southern Ocean in the face of anthropogenic climate change,” said Dr. Charlton.

“These findings add to global evidence showing the sensitivity of southern right whales to climate variability in their offshore foraging grounds, reinforcing their role as effective ecological indicators of environmental change.”

Comparable trends have been observed by research teams in South America and South Africa. Seabirds and other whale species that depend on krill are also experiencing pressure. Marine heatwaves and declining sea ice create further strain.

Climate impacts are spreading

Although climate change in Antarctica may appear remote, its consequences extend to Australia’s coastline. Southern right whales cover vast distances, with females calving in more sheltered coastal waters, including locations in South Australia.

Dr Charlton highlights long-term observation in the Great Australian Bight as evidence of why thorough research is important. Such shifts become apparent only through data collected over many years.

“Long-term monitoring in the Great Australian Bight shows how climate impacts are influencing animals that seek sanctuary in our coastal waters, emphasizing the value of annual research spanning four decades for detecting changes to population trends,” noted Dr. Charlton.

History demonstrates how delicate recovery can be. Commercial whaling in the 1800s and early 1900s almost eliminated this species worldwide.

International safeguards enabled numbers to increase gradually. Nevertheless, the population remains well below its original level.

A population that’s still vulnerable

Aerial surveys conducted between 1976 and 2024 place Australia’s southern right whale population at between 2,346 and 3,940 individuals.

This represents just 16 percent to 26 percent of the population before large-scale whaling. Calf numbers have fallen too: they reached a high of 222 calves in 2016, while researchers recorded 200 calves in 2024.

Limited food is not the sole threat. Human activities create additional hazards. Ship strikes can injure or kill whales, underwater noise disrupts communication, fishing equipment may entangle animals, and coastal development harms breeding habitat.

“Ongoing annual research across biologically important areas in Australia is essential to inform population assessments, guide coordinated conservation action to support adaptive strategies to safeguard threatened species into the future,” said Dr. Charlton.

Some whales have started adapting their feeding behaviour. Rather than remaining in high-latitude Antarctic waters, some groups are now looking for food in sub-Antarctic regions.

Their diet has also moved away from being mainly krill towards more copepods, another small marine animal. Although this shift demonstrates adaptability, it may not completely address the challenge.

Recovery at risk

After global hunting had almost wiped them out, southern right whales became a symbol of hope. Now, the species functions as a living warning signal.

Declining calf numbers point to stress within the ocean. Higher temperatures, diminishing ice and human activity are combining to create a new reality.

Ocean wellbeing is closely tied to climate stability. When a large marine mammal has difficulty reproducing, it delivers a clear message.

Safeguarding the Southern Ocean and limiting climate impacts could help provide a safer future for this whale and the many other species that share its environment.