"Catastrophic" Mortality Rates In 2022-23 In Argentine Elephant Seal Populations From Avian Flu - 97% Among Pups

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Dead elephant seals on a beach in Argentina. (Photo by Maxi Jonas/WCS)

An epidemic of avian flu in Patagonia appears to be on the decline after decimating southern elephant seal populations for the last year and half, with researchers finding no new cases in recent surveys of the coast. But the recovery process for many colonies, which were nearly wiped out in some areas, could be just beginning. The H5N1 influenza hit populations of southern elephant seals (Mirounga leonina) and other marine mammals and birds in August 2023, spreading across multiple provinces of Argentinian Patagonia and sending researchers scrambling to study the outbreak. With cases now on the decline, researchers are turning their attention to studying the worst-hit colonies as they recover their previous population numbers, a process that could take decades.

“There were no mortality events from avian flu” observed during the recent surveys in the province of Chubut, said Valeria Falabella, the director of coastal-marine conservation at the NGO Wildlife Conservation Society (WCS) Argentina. “The not-so-good news is that the number of individuals, most notably reproductive females, was way below what was expected.” The 300-kilometer (186-mile) coastline of the Valdés Peninsula, a popular breeding area for southern elephant seals, saw 17,400 of the 18,000 pups die at the end of last year, according to a December 2023 study in Marine Mammal Science. Usually only approximately 180 die. The study described the spiking mortality rate as “catastrophic.”

The flu likely jumped to marine mammals in the area from South American terns (Sterna hirundinacea), mostly affecting elephant seals but also spreading to sea lions (Otaria flavescens) and fur seals (Arctocephalus australis), researchers said. They worried the flu would jump to other species, such as orcas (Orcinus orca), which feed on seals, but that threat never appeared to materialize. H5N1 influenza is present in bird species across the globe and has caused outbreaks in poultry and dairy cows in the U.S., while also spreading to other marine mammal species in South America. In isolated cases, it has also spread to humans, often because they have regular contact with infected animals.

The rapid elephant seal die-off altered social structures in many colonies, according to a study in Nature Communications, with less-dominant adult males replacing dead alpha males. There was also a “patchy distribution” of females with pups, which are usually more densely packed together, as well as abandoned sick pups, the study said.

EDIT

https://news.mongabay.com/2024/11/elephant-seal-colonies-in-argentina-face-long-recovery-after-catastrophic-avian-flu/