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

A general view of Heard Island and McDonald Islands is pictured. A deadly strain of bird flu sweeping through remote islands near Antarctica has devastated the native wildlife population, killing an estimated 13,000 seal pups, as well as penguins and seabirds, researchers say. (Courtesy Australian Antarctic Division/Doug Thost via CNN Newsource)

A deadly strain of bird flu sweeping through remote islands near Antarctica has devastated the native wildlife population, killing an estimated 13,000 seal pups, as well as penguins and seabirds, researchers say.

Drone surveys conducted by the Australian Antarctic Program in October and January revealed “sobering” images of seal pup carcasses littering the grayish volcanic shores of Heard and McDonald Islands, Jarrod Hodgson, a senior research scientist at the organization said.

The islands, which sit about 2,485 miles (4,000 kilometres) southwest of mainland Australia have long been an isolated sanctuary for breeding birds and marine mammals.

The southern elephant seal pup mortality was estimated to be 76 per cent across a population of 17,000 seal pups born on the islands, the program said. One area had a concentrated death rate of 97 per cent.

“The thing we don’t know from our surveys so far is what the impact was on the breeding adult population of southern elephant seals,” Hodgson said.

Data collected in January also revealed several hundred adult king penguins across Heard Island have died, with scientists noting mortality was above normal levels.

“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,” wildlife biologist Julie McInnes said.

“Our results show a similar pattern to other sub-Antarctic islands, such as South Georgia, where elephant seals have been hardest hit,” added McInnes, who is also lead author of the group’s study.

As of February, the Australian mainland and New Zealand didn’t have any cases of the H5N1 strain, which has spread among birds worldwide and affected some mammals.

Analysis of genetic data suggested the H5 bird flu was likely introduced to the islands through wildlife from the French sub-Antarctic Crozet Islands, 1,800 km away, likely arriving around August 2025.

The findings have been published in the scientific journal BioRxiv but have not yet been peer reviewed.

By Kathleen Magramo, CNN