Hundreds of Baby Whales Have Died in Argentina This Year—and Scientists Are Scrambling to Understand Why
Their leading hypothesis is that the young cetaceans are dying from a bacterial infection, but experts are still trying to figure out why this year’s mortality rates are so high. Adults have also been washing up dead, possibly because of a toxic algal bloom
/https://tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/accounts/headshot/SarahKuta.png)
/https://tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/filer_public/09/57/09573b62-dd30-46ce-a950-0cd7cfd4803c/argentina-whales.jpg)
Hundreds of whale calves have washed up dead along Argentina’s coast in recent months, leaving scientists scrambling to determine what’s causing the deaths.
Every year, southern right whales migrate to the sheltered waters off Argentina’s Peninsula Valdes to give birth and rear their young. Between May and December, it’s not uncommon for dead whale calves to be found along the coast of Chubut province, in the center of the Patagonia region—some 20 to 30 percent of calves born in a given season may not survive, per Live Science’s María de los Ángeles Orfila. But this year, experts say the death toll appears to be much higher than usual.
They’re holding off on releasing the final tally until after the season ends. But preliminary figures suggest more than 300 southern right whale calves have died since June, roughly three times the previous record of 113 deaths set in 2012.
“The death rate [among young whales] is quite high this season in particular,” Mariano Coscarella, a biologist with Argentina’s Center for the Study of Marine Systems, tells the Agence France-Presse.
Because of the unusually high calf mortality, scientists sent tissue samples for analysis earlier than usual this year. Those samples tested positive for Erysipelothrix rhusiopathiae, a bacterium that can cause a skin infection called erysipelas.
Scientists suspect gulls are spreading the bacteria by pecking at southern right whale calves as they surface to breathe, creating wounds in their skin. The bacteria could already be present on the whales’ skin, or it might be transferred by a gull that previously pecked an infected whale.
E. rhusiopathiae was first detected in southern right whale calves in 2013. Scientists are still trying to understand what could have made it so deadly this year.
One possibility is that the bacteria itself has evolved, leading to more severe infections. Or perhaps, changes in food availability are affecting the mothers’ body condition and, as a result, the health and resilience of their newborn calves.
The deaths might also be connected to changes to marine conditions, such as water temperature, salinity or pH, possibly caused by climate change or El Niño. These shifts might be creating “this perfect storm where this bacteria is powerful enough to overcome the immunity of the babies and cause their deaths,” Marcela Uhart, a veterinarian at the University of California, Davis, who leads the Southern Right Whale Health Monitoring Program, tells the Associated Press.
Southern right whales were hunted to the brink of extinction during the 19th and 20th centuries. However, the population has rebounded since an international moratorium on commercial whaling was enacted in the 1980s. Today, an estimated 12,000 to 15,000 individuals live across the Southern Hemisphere.
Whalers are no longer killing southern right whales for their oil, meat and baleen. But these massive marine mammals—which can weigh up to 176,000 pounds and reach lengths of up to 56 feet—still face numerous threats. They’re vulnerable to chemical and noise pollution, entanglement in fishing gear, climate change, habitat degradation and vessel strikes.
For now, scientists say it’s too soon to tell whether and how this year’s calf die-off might affect the broader southern right whale population. But some are cautiously optimistic. Southern right whales have exceptionally long life spans, with some individuals possibly reaching 150 years old. Because of that, each cohort of calves has a smaller impact on the population as a whole.
“What would be concerning is if there were two, three or four episodes like this,” Coscarella tells Live Science.
Did you know? Southern right whales in Argentina
In early September, scientists counted 1,375 total southern right whales—including 409 calves—off the coast of Chubut province.
Meanwhile, juvenile and adult whales have also been found dead in Argentine Patagonia, which is unusual, reports Delfina Torres Cabreros for El País. Scientists think the more than dozen deaths might be related to harmful algal blooms, which occur when toxic algae grow rapidly due to climatic and environmental conditions. The blooms were also responsible for an unusual mortality event that primarily affected adult females in 2022.
Necropsies revealed that some of the juvenile and adult whales were in good physical condition and had large amounts of food in their stomachs when they died. Southern right whales are filter feeders that use their baleen—flexible plates that hang from their upper jaws—to skim tiny creatures called copepods and krill from the water.
The necropsy findings suggest they might have eaten prey that was contaminated by toxic algae, but researchers won’t know for sure until testing confirms whether biotoxins are present in the whale carcasses.
“This does not in itself prove poisoning, but it is a factor we are considering as part of the investigation,” Víctor Fratto, director of the Native Wildlife Rescue Program in Argentina who is helping to conduct the necropsies, tells the United Press International’s Banyeliz Muñoz.
/https://tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/accounts/headshot/SarahKuta.png)