Elephant Seal Breeding Grounds in Argentina Struggle to Recover After Avian Flu Outbreak

In Argentina’s Península Valdés, elephant seals have returned to their breeding grounds, but their numbers are reduced. A massive outbreak of H5N1 avian influenza last year killed over 17,000 seals, wiping out nearly 97% of their pups. Now, only about a third of the usual population has come back. While the sound of barking seals once again echoes along the beaches, researchers find the scene bittersweet. “It’s beautiful to walk the beaches now and hear elephant seals again. At the same time, we’re walking among piles of carcasses and bones, and seeing very few elephant seal harems, so it’s still disturbing,” shared Marcela Uhart, director at UC Davis’s Wildlife Health Center.

The outbreak, which first struck in early 2023, revealed troubling new insights about the virus’s transmission. A study led by UC Davis and Argentina’s National Institute of Agricultural Technology (INTA) showed that H5N1 was spreading effectively among marine mammals, marking the virus’s first substantial leap across multiple countries in South America. Genetic analysis found that H5N1 had split into distinct clades, evolving separately in bird and mammal hosts. This adaptation is unprecedented and suggests the virus has an alarming capacity to mutate within new hosts. Virologist Agustina Rimondi explained, “This virus is capable of adapting to marine mammal species… our study also shows that H5 marine mammal viruses are able to jump back to birds, highlighting the need for increased surveillance and research cooperation in the region.”

This catastrophic outbreak has also undone decades of Conservation work, according to Valeria Falabella, head of coastal and marine Conservation at WCS Argentina. Falabella noted that the virus killed over half of the reproductive population, including many vital adult males and experienced females. Rebuilding the population could take decades.

Ongoing monitoring efforts are essential. WCS Argentina’s team, along with UC Davis researchers and INTA virologists, has been tracking each seal death at the breeding site. Although no new H5N1 cases have been found among seals this season, scientists are left with many questions. They are unsure how the virus was transmitted—whether by air, bodily fluids, or waste—and whether surviving seals might now carry protective antibodies.

As researchers search for answers, the virus’s impact on wildlife continues to ripple outward. Since entering Argentina, H5N1 has moved from wild birds to dairy cows, sea lions, and even swine, underscoring the virus’s potential to adapt and jump between species. Continued monitoring is critical to understanding these shifts, which may have serious implications for wildlife and human health.

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