H5 Avian Flu Causes Mass Elephant Seal Die-Off in Australian Territories

A pathogenic strain of H5 avian flu killed 13,300 southern elephant seal pups on the Heard and McDonald Islands, according to Australian scientists. Genetic analyses confirmed the virus reached the subantarctic territory likely via wild animals from the French Crozet Islands in August 2025, marking the first detection of the virus in an Australian external territory.

How did the H5 avian flu impact the seal population?

Australian researchers discovered thousands of carcasses during a research mission. Ground and aerial surveys conducted between October 2025 and January 2026 counted 13,300 dead southern elephant seal pups in the territory.

Scientists from the Australian Antarctic Program reported that the pups were the most severely affected. In some seal “harems,” mortality rates reached as high as 97%.

Did You Know? The Heard and McDonald Islands are uninhabited by humans, and access to the archipelago requires official agreement from the Australian government.

Where did the virus originate and how did it spread?

Researchers estimate the virus was introduced in August 2025. They believe infected wild animals traveled from the Crozet Islands, a French subantarctic archipelago located approximately 1,500 kilometers to the northwest.

The affected islands sit 4,000 kilometers southwest of mainland Australia in the south Indian Ocean. Biologist Julie McInnes stated that this detection shows the “progression continue du virus vers l’est,” or the continuous progression of the virus toward the east.

Expert Insight: Samantha Carter notes that the movement of H5 avian flu from the Crozet Islands to an Australian external territory underscores the high risk posed by migratory wild animals. The extreme mortality rate in seal pups suggests that subantarctic breeding colonies could be particularly vulnerable as the virus continues its eastward expansion.

What could happen next in the region?

The virus may continue to spread further east across the south Indian Ocean. Other breeding colonies in the region could be at risk if infected animals continue to migrate.

Avian Flu in Antarctica

Continued genetic monitoring is likely to be a priority for researchers to track the movement of the pathogenic strain. Future surveys may be necessary to determine if the population can recover from the 97% loss seen in specific harems.

Frequently Asked Questions

How many southern elephant seal pups died?
Surveys conducted between October 2025 and January 2026 counted 13,300 dead pups.

What caused the mass mortality event?
Genetic analyses confirmed the cause was a pathogenic strain of H5 avian flu.

Where did the virus likely come from?
Researchers believe it was introduced in August 2025 by infected wild animals from the French Crozet Islands.

How do you think the loss of such a high percentage of seal pups will affect the local ecosystem?