Hundreds of whale calves have mysteriously died in Patagonia — and scientists are racing to find out why

Since June, more than 300 southern right whale calves have died in Argentine Patagonia, marking an unprecedented die-off, according to scientists. This number surpasses the previous annual record set in 2012 when 113 calves died. Laboratory tests have confirmed the presence of the pathogenic bacterium Erysipelothrix rhusiopathiae in the deceased calves.

This bacterium, previously identified in southern right whale calves in 2013, has scientists puzzled about the factors that could have led to such a significant infection-driven die-off. The researchers are eager to understand the changing threat to the species, the broader ecosystem, and human health implications, along with potential management strategies.

The first dead calves were found on the beaches of Península Valdés in June at the beginning of the breeding season. In a typical year, calf mortality in this species ranges from 20% to 30%, but this year's losses have far exceeded these numbers. The final mortality figure will be released in December by the Southern Right Whale Health Monitoring Program.

Scientists have expedited routine research to identify any differences this year compared to previous years. The bacterium E. rhusiopathiae, which can cause erysipelas, a skin infection that can spread through the bloodstream and damage vital organs, is not exclusive to whales. It can be found in marine environments and various animals, including fish, crustaceans, birds, and pigs.

Although the presence of the bacterium does not necessarily indicate illness, many questions remain about its presence in whales and how it could have led to this massive die-off.