Thousands of baby seals died on two remote sub-Antarctic islands. Scientists now think they know why

Thousands of baby seals perished on two remote sub-Antarctic islands, prompting new scientific inquiry

Australian researchers uncover possible cause behind mass seal pup deaths

Thousands of baby seals died on two - A severe outbreak of bird flu has led to the loss of approximately 13,000 seal pups on Heard and McDonald Islands, located in the distant Southern Ocean. The Australian Antarctic Program’s drone surveys in October and January uncovered grim evidence of the devastation, with seal pup carcasses strewn across the islands’ volcanic terrain. These findings have raised urgent questions about the virus’s spread and its impact on the region’s wildlife.

Heard and McDonald Islands, situated roughly 2,485 miles (4,000 kilometers) southwest of Australia, have historically served as a refuge for marine mammals and seabirds. The current crisis has targeted southern elephant seals particularly, with 76% of the 17,000 pups born on the islands succumbing to the disease. In one area, the mortality rate among pups reached 97%, according to the program’s analysis.

“The one uncertainty remaining from current surveys is the effect on the adult breeding population,” said Jarrod Hodgson, a senior research scientist. While the focus has been on seal pups, data from January also indicated hundreds of adult king penguins had died, marking an unusual spike in their mortality rate. The virus’s presence in the region highlights its growing reach, as noted by wildlife biologist Julie McInnes.

“These observations of H5 bird flu at Heard Island and McDonald Island are the first detection in an Australian external territory and show the continued eastward movement of the virus around the sub-Antarctic,” McInnes explained. She added, “Our results show a similar pattern to other sub-Antarctic islands, such as South Georgia, where elephant seals have been hardest hit.”

Genetic analysis suggests the H5N1 strain was likely introduced from the French Crozet Islands, 1,800 km to the north, during the late summer of 2025. Despite the outbreak, the Australian mainland and New Zealand remain free of the virus as of February. The study, published in the preprint journal BioRxiv, has yet to undergo peer review but underscores the growing threat to Antarctic ecosystems.