What is killing whale calves in Patagonia? bacteria under suspicion

Hundreds of southern right whale calves have died in recent months in Argentine Patagonia, in an episode that has put scientists and authorities on alert. Initial investigations point to a bacterial infection as a possible cause of an exceptionally high mortality rate this season.

Just this week, dozens of dead whale calves have appeared on beaches in the province of Chubut, in southern Argentina. Cases have been recorded since June, affecting one of this species' main breeding grounds in the South Atlantic.

"The mortality rate among calves is quite high, especially this season," explained Mariano Coscarella, a researcher at the Marine Mammals Laboratory of the National Scientific and Technical Research Council (Conicet), speaking to AFP.

Bacteria among the main hypotheses

Veterinarians are now investigating whether erysipelas, an infectious disease caused by bacteria that are often present on the skin of these mammals, could be behind the deaths.

Authorities in Chubut have indicated that initial analyses point specifically to a common marine bacterium, although the investigation remains open to establish with certainty what is causing the fatalities.

Coscarella believes that for the moment the evidence points to a natural cause, but warns that a possible influence of human activity still cannot be completely ruled out.

The provincial government says it is working together with the scientific community to determine the origin of the episode.

One of the southern right whale's main calving grounds

Puerto Madryn and the nearby Valdés Peninsula form one of the major breeding refuges for the southern right whale. Every year, large numbers of whales arrive in these waters to mate and raise their young. These cetaceans can reach around 17 metres in length and weigh about 40 tonnes as adults.

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

Despite the high number of deaths recorded this season, the researcher notes that the episode does not, for now, pose a medium-term threat to the region's whale population.

The species' longevity is one of the factors behind that assessment. Local authorities estimate that a southern right whale can live for around 60 years.