Melbourne, Australia: Highly pathogenic H5N1 avian influenza has killed an estimated 13,000 southern elephant seal pups on Australia's remote Heard Island, scientists said, marking the first detection of the virus in an Australian external territory.
Researchers from the Australian Antarctic Program (AAP) found mortality rates averaging 76 percent among seal pups, with some colonies losing up to 97 percent, based on drone surveys conducted in October 2025 and January 2026, an AAP statement said on Thursday.
Total southern elephant seal pup production was estimated at about 17,000, it said, adding the drone surveys also revealed elevated mortality in penguins, though impacts were most severe in seals.
The virus, part of the globally circulating H5N1 clade 2.3.4.4b, was detected in six species, including elephant seals, king and gentoo penguins, Antarctic fur seals and seabirds, according to the findings submitted to a scientific journal and released as a preprint.
By January 2026, widespread seal pup deaths were recorded across breeding sites, with drone evidence also indicating mortality on nearby McDonald Island without ground confirmation, researchers said, noting a similar pattern to other sub-Antarctic islands such as South Georgia, where elephant seals have been hardest hit.
"These observations of H5 bird flu at Heard Island and McDonald Island are the first detection in an Australian external territory," said the study's lead author, wildlife biologist Julie McInnes.
Genetic analysis suggests the virus likely arrived around August 2025 via wildlife movements from the French sub-Antarctic Crozet Islands, about 1,800 km away, indicating continued eastward spread of the virus across the sub-Antarctic.
AAP Scientists conducted 120 drone flights covering more than 1,600 km to assess mortality across the islands, enabling surveys of inaccessible breeding sites with minimal disturbance.
