Southern right whales now wait five years between births – warming seas are to blame

A half‑century of aerial surveys over the Great Australian Bight shows the whales' calving cycle has stretched from three years to five years, a change first noted in this year's census.

In 2024 researchers counted 520 whales, including 235 cow‑calf pairs; 61 of those pairs (more than 30% of the total) were mother‑calf groups. This is down from 646 whales and 304 calves the year before and represents a 20% drop compared with numbers from ten years ago.

Dr. Claire Charlton explained that rising water temperatures reduce sea‑lice populations, which in turn leads to fewer krill – the main food for southern right whales. With less krill, the whales struggle to build enough body condition for successful breeding, so they postpone calving.

Dr. Joshua Smith added that the long‑term data now show many more solitary whales and a population that is no longer growing. He described the overall trend as stagnating, with fewer breeding pairs each season.

The shift to a five‑year breeding interval highlights how climate‑driven changes in the ocean food web can directly affect the reproductive timing of an endangered species, underscoring the need for continued monitoring and protection.

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