Climate crisis linked to fall in southern right whale birth rates as researchers raise ‘warning signal’ | Whales

After decades of recovery, southern right whales are showing signs of a climate-driven decline in reproductive rates, which scientists say is a “warning signal” about changes in the Southern Ocean.

After being hunted to extinction by commercial whaling in the 19th and 20th centuries, southern right whales remained endangered in Australia.

But long-term monitoring has revealed a worrying slowdown in reproductive rates since 2017. Instead of giving birth to a calf every three years, southern right whales have shifted to four- or five-year cycles, says Dr. Claire Charlton, a marine biologist and director of Current Environmental.

For more than three decades, scientists have used photo identification data collected from Australia’s Great Bight to study the species, identifying individuals by unique patterns of a type of callus, called calluses, and tracking their migrations and breeding behavior over time.

Charlton, who runs the Great Australian Bight right whale program, says southern right whales are “magnificent animals” – “just their size and the fact that they live 150 years”.

“They feed in Antarctic and sub-Antarctic waters during the summer, then migrate to our shores during the winter,” she explained. “The whales come every year to breed, mate, rest and socialize.”

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The research, published in Scientific Reports, linked changing breeding cycles to climate-induced changes in their feeding grounds in Antarctica and sub-Antarctica.

“We know that as the ocean warms, sea ice melts, which causes other environmental changes,” said Charlton, the study’s lead author.

The paper analyzes birthing intervals over 35 years, revealing a correlation between reproductive rates and sea ice extent, prevalence of marine heatwaves, prey availability and other climate-related changes.

The researchers said similar trends had been observed in southern right whale populations in South America and South Africa, with other krill-dependent predators also facing pressure from marine heatwaves and declining sea ice.

It’s a “warning signal” about how climate change is affecting marine life, Charlton said, highlighting the urgent need for coordinated conservation efforts.

Whale scientist Vanessa Pirotta, who was not involved in the study, said long-term data was key to understanding these long-lived animals and how they might adapt to a changing environment.

“We must continue to learn more about [southern right whales] given that we are responsible for much of their loss and the current situation of their populations,” Pirotta said.

Commercial whaling ceased in Australia in 1979 and was banned by the International Whaling Commission in the late 1980s. Reduced to fewer than 300 animals, Australian populations now range between 2,346 and 3,940 individuals, approximately 16 to 26% of pre-whaling levels.

Southern rights are like “ocean tractors”, said Dr Peter Corkeron, a marine ecologist and deputy principal investigator at Griffith University, who was not involved in the study. To feed, the whales sought out areas dense with zooplankton and “came back and forth as if they were mowing the lawn.”

The change in birthing intervals is a sign that conditions in Antarctica and sub-Antarctica were no longer as good as they once were, he said.

“As mammals, the choice to have a baby is demanding,” he said. “If a woman wants to maximize her reproductive output over her lifetime, she needs to find a balance between having babies and living a long time. When conditions get worse, you stop having as many babies.”

“Anthropogenic climate change affects everything,” Corkeron said. “It’s just another message, if people choose to pay attention to it, that we need to do something about this.”