Bacterial Infection Suspected in Surge of Southern Right Whale Calf Deaths Off Patagonia

Hundreds of southern right whale calves have perished in recent months off the coast of Argentine Patagonia, triggering alarm among scientists and authorities. Preliminary investigations suggest a bacterial infection may be driving the unusually high mortality rate observed this season.

Dozens of carcasses have washed ashore in Chubut Province this week alone. Fatalities have been documented since June, striking one of the species’ primary breeding grounds in the South Atlantic.

“The mortality rate among calves is quite high, especially this season,” said Mariano Coscarella, a researcher at the Marine Mammals Laboratory of the National Scientific and Technical Research Council (CONICET).

Bacteria Among Leading Hypotheses

Veterinarians are examining whether erysipelas—an infectious disease caused by bacteria commonly found on the skin of these mammals—is responsible for the die-off.

Chubut authorities report that initial analyses point to a common marine bacterium, though the investigation remains open to definitively determine the cause.

Coscarella stated that current evidence suggests a natural cause, though he cautioned that a potential link to human activity cannot be entirely excluded. The provincial government is coordinating with the scientific community to identify the origin of the event.

Critical Calving Habitat

Puerto Madryn and the adjacent Valdés Peninsula constitute one of the world’s most important breeding refuges for the southern right whale. Annually, large numbers congregate in these waters to mate and rear their young. Adults can reach 17 meters in length and weigh approximately 40 tonnes.

In 2025, a record 2,110 whales were counted in the area, roughly 800 of them juveniles. This year’s census stands at 1,375 animals, including nearly 400 calves, according to Coscarella’s data.

Despite the elevated mortality this season, the researcher noted that the event does not currently pose a medium-term threat to the regional population. The species’ longevity—estimated at roughly 60 years—is a key factor supporting that assessment.

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