Australia has confirmed its first case of the H5N1 bird flu virus on Macquarie Island, a sub-Antarctic territory known for its vulnerable elephant seal population. The highly pathogenic virus was detected in samples taken from an elephant seal and a kelp gull on the island, according to Chief Veterinary Officer Beth Cookson.

Macquarie Island, situated in the Southern Ocean roughly midway between Tasmania and Antarctica, is recognized as a UNESCO World Heritage site. It serves as a crucial breeding ground for southern elephant seals, a species particularly susceptible to the H5N1 virus. These seals can weigh up to 3,600 kilograms (7,936 pounds), and previous outbreaks have resulted in pup mortality rates exceeding 90%.

Australia had previously confirmed the presence of H5N1 earlier this year, becoming the last continent to report the virus. It was first detected in late 2025 on Heard Island, another Australian sub-Antarctic territory. There, the virus reportedly killed more than 13,000 seal pups, underscoring the substantial threat avian influenza poses to these remote ecosystems.

In response to the outbreak threat, the Australian Department of Environment announced in August that it would withdraw personnel from a research station on Macquarie Island. The decision was based on concerns regarding the psychological well-being of expeditioners amid a potential H5N1 outbreak.

Authorities have warned that the virus is likely to cause notable mortality among elephant seals during the upcoming breeding season. The outbreak on Macquarie Island represents a significant development given the isolated nature of these populations and the potential ecological impacts of the disease. Monitoring and management efforts are expected to continue as experts assess the ongoing situation.