Investigators probe deaths of hundreds of whales in Patagonia

A bacterial infection is suspected of killing hundreds of baby whales in Patagonia, a marine mammal researcher said Thursday, as scientists continue to investigate an unusually high mortality rate among southern right whale calves.

This week, dozens of dead calves washed up on beaches in southern Chubut Province, continuing a disturbing trend that began in June.

"The death rate [among young whales] is quite high this season in particular," said Mariano Coscarella, a researcher at the Marine Mammals Laboratory of the CONICET national scientific research council in Puerto Madryn.

Although infant mortality is common among southern right whales, Coscarella said the number of deaths recorded this season was unusually high.

Veterinarians investigating the cases suspect an outbreak of erysipelas, a serious disease caused by bacteria commonly found on the whales' skin. The hypothesis has yet to be confirmed.

"It seems to be a natural cause, however we cannot completely rule out the influence of human activity," Coscarella said.

The Chubut provincial government said Wednesday that it was working jointly with scientists and specialised research teams to examine the dead whales and analyse samples.

"According to the information available until now, it would seem to be a bacteria common in the sea which can cause systemic infection in baby whales," the government said in a statement published September 23, adding that there was no evidence so far to attribute the deaths to human activity.

Puerto Madryn and nearby Peninsula Valdés are internationally recognised as one of the most important breeding grounds for southern right whales in the Southwest Atlantic. The animals can grow up to 17 metres (55 feet) in length and weigh an average of 40 tons, roughly the equivalent of four elephants.

A record 2,110 whales were counted in the area in 2025, including more than 800 calves. This year's survey counted 1,375 specimens, among them nearly 400 young whales, Coscarella said.

When the latest census was released, researchers noted that the difference from the previous year's figures was within the natural fluctuations expected in the population.

Coscarella said the recent deaths did not constitute a medium-term threat to the population because acute mortality of this kind generally affects only a fraction of newborn whales, while southern right whales have a long life expectancy.

Local authorities put their average lifespan at around 60 years.