# Southern right whale mortality in Chubut, Argentina > Live situation record from CLSTR: https://clstr.news/situations/southern-right-whale-mortality-in-chubut-argentina > Updated: 2026-10-21T22:12:22.000Z. Sources: 85. Developments: 9. In early September 2026, the first aerial census of the season along the Península Valdés coastline in Chubut, Argentina, recorded 1,375 Southern right whales, including 409 calves. This was a notable decrease from the 2,110 whales recorded in 2025, though researchers from the Marine Mammal Laboratory (LAMAMA) noted such fluctuations are natural and remain within expected values. By late September, investigations intensified into an unusually high mortality rate among Southern Right Whale calves in the region, specifically near Puerto Madryn and Península Valdés. Since June, dozens of carcasses have been discovered, leading experts to fear that the current season could surpass the record of 113 deaths documented in 2012. By mid-October, the investigation shifted focus as the mortality pattern became more atypical. While previous calf deaths were linked to the bacterium ‘Erysipelothrix rhusiopathiae’, which is associated with septicemia and multi-organ failure, recent carcasses of juveniles and large adults do not show the skin lesions typically associated with this pathogen. Following the discovery of seven whales dead within a single week in mid-October, researchers have proposed two distinct causes for the mortality. While calves are linked to the aforementioned bacterium, the deaths of adults and juveniles—who appeared to be in good nutritional condition—are being investigated under the hypothesis of red tide poisoning from natural biotoxins. By late October, reports indicated a record loss of more than 340 calves in the Nuevo and San José gulfs, representing over 70 percent of the calves counted this season. Greenpeace Argentina has expressed concern regarding human and industrial pressures, highlighting threats such as seismic exploration for hydrocarbons, increased maritime traffic, and the risk of offshore oil spills. ## Claims - There has been a significant increase in the number of dead Southern Right whales found on the Patagonian coast. (corroborated by 3 sources) - Calves are being particularly affected by the deaths. (corroborated by 3 sources) - Bacteria have been detected in tissue samples from the deceased whales. (corroborated by 3 sources) - Kelp gulls may cause injuries to the whales' skin and fat layers, creating entry points for pathogens. (corroborated by 3 sources) - Marcela Uhart of the University of California, Davis, is leading a research team investigating the deaths. (corroborated by 3 sources) ## Timeline ### 2026-10-21: Whale deaths reported in Argentine Patagonia Southern right whales are dying at high rates in Argentine Patagonia. Scientists are investigating bacterial infections and red tides as potential causes amid concerns over industrial activity. 2 sources. https://clstr.news/cluster/whale-deaths-reported-in-argentine-patagonia ### 2026-10-19: Whale deaths reported in Península Valdés and Puerto Madryn Multiple southern right whales have died near Península Valdés and Puerto Madryn, Argentina. Scientists suspect bacterial infections in calves and red tide biotoxins in adults. 2 sources. https://clstr.news/cluster/whale-deaths-reported-in-pennsula-valds-and-puerto-madryn ### 2026-10-15: Whale deaths in Chubut prompt environmental investigation Researchers in Chubut, Argentina, are investigating the recent deaths of five whales, including adults and juveniles, potentially linked to red tide algae ingestion. 3 sources. https://clstr.news/cluster/whale-deaths-in-chubut-prompt-environmental-investigation ### 2026-10-13: Southern Right Whales found dead in Chubut, Argentina Scientists in Chubut, Argentina, are investigating a surge in Southern Right Whale deaths near Puerto Madryn, exploring bacterial infections and environmental toxins as potential causes. 13 sources. https://clstr.news/cluster/puerto-madryn-reports-unusual-number-of-dead-whales ### 2026-10-06: Southern Right whales face rising mortality in Patagonia Scientists are investigating a sudden rise in Southern Right whale deaths, particularly among calves, on Argentina's Patagonian coast, citing potential bacterial infections and injuries from kelp gulls. 5 sources. https://clstr.news/cluster/southern-right-whales-face-rising-mortality-in-patagonia ### 2026-10-02: Argentina investigates unusual deaths of southern right whale calves Scientists are investigating an unusual mass mortality of southern right whale calves along Argentina's Patagonian coast, with marine bacteria and kelp gull attacks cited as potential causes. 7 sources. https://clstr.news/cluster/southern-right-whale-calves-washing-up-dead-in-argentina ### 2026-09-28: Southern Right Whale calf deaths rise in Argentina Scientists in Argentina are investigating a record-breaking rise in Southern Right Whale calf deaths near Península Valdés, with bacterial infection suspected as the primary cause. 11 sources. https://clstr.news/cluster/southern-right-whales-face-high-mortality-in-argentina ### 2026-09-24: Patagonia whale calves mortality investigation underway in Argentina Scientists are investigating the deaths of hundreds of Southern Right Whale calves in Patagonia, Argentina, with a bacterial infection suspected as the primary cause. 43 sources. https://clstr.news/cluster/southern-right-whale-calf-deaths-reported-in-pennsula-valds ### 2026-09-08: Chubut aerial whale census records 1,375 Southern right whales The first 2026 aerial census in Chubut, Argentina, counted 1,375 Southern right whales, including 409 calves, a figure scientists describe as within normal natural fluctuation levels. 7 sources. https://clstr.news/cluster/chubut-aerial-whale-census-records-1375-southern-right-whales --- Cite as: Southern right whale mortality in Chubut, Argentina. CLSTR, https://clstr.news/situations/southern-right-whale-mortality-in-chubut-argentina