The carcasses began appearing in June, and this week they arrived in numbers. On the beaches of Chubut province, in Argentine Patagonia, dozens of dead southern right whale calves have been found in the space of a few days, according to Euronews — part of a die-off that has run into the hundreds over recent months and has put scientists and provincial authorities on alert. The stretch of coast involved is not just any shoreline; it is one of the species’ principal breeding grounds in the South Atlantic, the place the whales come to reproduce.
“The mortality rate among calves is quite high, especially this season,” Mariano Coscarella, a researcher at the Marine Mammals Laboratory of Conicet, Argentina’s National Scientific and Technical Research Council, told AFP. “Especially this season” is doing considerable work in that sentence — calf deaths are a feature of any calving ground; a die-off of this scale is not.
An ordinary bacterium, an open question
The leading hypothesis is infection. Veterinarians are investigating whether erysipelas — an infectious disease produced by bacteria frequently present on the skin of these mammals — is responsible for the deaths. Authorities in Chubut say initial analysis points specifically to a common marine bacterium, while stressing that the investigation remains open and no cause has been established with certainty. Coscarella, for the moment, reads the evidence as pointing toward a natural origin, though he cautions that a possible influence of human activity cannot yet be ruled out entirely. The provincial government says it is working alongside the scientific community to determine where the episode came from.
The calving ground
Puerto Madryn and the nearby Valdés Peninsula form one of the major refuges of the southern right whale. Every year the animals gather in these sheltered waters to mate and raise their young. An adult can reach around 17 metres in length and weigh about 40 tonnes. The census numbers trace the population year by year with a surveyor’s patience: in 2025 a record 2,110 whales were counted in the area, roughly 800 of them juveniles; this year the tally stands at 1,375 animals, including nearly 400 calves, according to data Coscarella provided.
Against that arithmetic, the researchers’ assessment of the die-off is measured. Despite the unusually high number of deaths, Coscarella says the episode does not, for now, pose a medium-term threat to the region’s whale population. Longevity underwrites that judgment: local authorities estimate a southern right whale lives about 60 years, long enough for a population to absorb a terrible season and still be counted in the censuses of decades to come. A whale can live sixty years. The calves found on the beaches of Chubut this week had weeks.