H5N1 killed 17,000+ seal pups Argentina

H5N1 bird flu killed more than 17,000 southern elephant seals in Argentina in 2023, according to researchers cited by The Conversation on August 6. The same strain was also linked to an estimated 13,359 dead southern elephant seal pups on Australia’s Heard Island in 2025, extending a pattern of mass mortality in marine mammals that scientists say has followed the virus across continents. Since 2021, this H5N1 lineage has spread globally and infected poultry, dairy cattle and wildlife, according to Phys.org and other reports. ### How large was the Argentina die-off? Península Valdés in Argentina recorded an “unprecedented mass mortality” of about 17,000 southern elephant seals during the 2023 outbreak, according to a Nature Communications paper on the event. The paper said pups were hit hardest, and a separate summary cited by The Conversation said more than 17,000 southern elephant seal pups were killed during that breeding season. (indailyqld.com.au) UC Davis said in a November 2024 update that the outbreak killed more than 17,000 elephant seals, including about 97% of pups, at Península Valdés. The university said researchers returning a year later found the colony quieter and smaller after the H5N1 event. ### What happened on Heard Island? Heard Island, an Australian sub-Antarctic territory, saw another major elephant seal die-off in 2025. (nature.com) The Conversation and related republications said an estimated 13,359 pups died there, while a June 2026 preprint describing drone and ground surveys reported 17,364 total pups and 13,359 estimated deaths, equal to about 76% mortality. (ucdavis.edu) The Australian Antarctic Program said on June 18, 2026 that scientists had finalized findings from voyages to Heard Island and McDonald Islands after H5 avian influenza was detected there in October 2025. Its statement said the work documented mass mortalities in southern elephant seal pups and contributed to understanding how the virus reached the islands. (indailyqld.com.au) ### How did scientists tie the deaths to H5N1? Nature Communications reported that researchers detected clade 2.3.4.4b H5N1 viruses in elephant seals associated with the Argentina mass mortality event. The paper said the viruses belonged to a clade seen primarily in marine mammals in the region, supporting the link between H5N1 infection and the seal deaths. (antarctica.gov.au) The Heard Island preprint said drone surveys from October 2025 and January 2026, combined with viral genome analysis, confirmed Influenza A H5N1 clade 2.3.4.4b on the island. The authors reported mortality rising rapidly in some harems, with the highest observed harem mortality reaching 97%. ### How broad is this outbreak beyond seals? Phys.org reported on August 5 that this H5N1 strain has spread to every continent since 2021. (nature.com) The report said the virus has infected poultry, dairy cattle and wildlife, and has threatened aquatic mammals including southern otters, dolphins and porpoises in addition to pinnipeds such as sea lions, fur seals and elephant seals. (biorxiv.org) A March 2026 Phys.org report on separate research said H5N1 in marine mammals had killed more than 50,000 seals and sea lions along South America’s coast. That tally placed the Argentina elephant seal losses within a broader regional wave of marine-mammal mortality. ### What are researchers proposing next? Australia has already confirmed H5N1 in 102 wild seabirds across five states, The Conversation said on August 6, and researchers including Jane Younger argued the country should identify high-risk wildlife populations for possible vaccination. (phys.org) The article said the United States vaccinated California condors after H5N1 killed 21 of the critically endangered birds, and France has run a vaccine trial in wild king penguin chicks on Crozet Island. (phys.org) The next concrete steps are in those published recommendations and field findings: Australian Antarctic Program data from Heard Island are already public, and researchers are pointing to targeted vaccination planning for closely managed wildlife populations most at risk from H5N1. (antarctica.gov.au) (indailyqld.com.au)