Bird flu hits sea lion population at Kangaroo Island breeding ground

South Australia's sea lion population is increasingly being affected by H5 bird flu, with four of the mammals — including one pup — testing positive for the virus.

The sea lions were among 12 found dead on the North Page and South Page islands, a key breeding location for the animals between the South Australian mainland and Kangaroo Island.

SA Environment Minister Emily Bourke said there has also been a mass mortality event involving crested terns on the Pages, with about 900 of the birds found dead.

"This isn't new in the sense of a new species, but it is an event of significance to be highlighting today," she said.

Ms Bourke said out of 10 deceased sea lions available for testing, three adults and one pup returned positive results.

The results bring the total number of South Australian sea lions with bird flu up to five, following a positive case at Kangaroo Island's Seal Bay last week.

There have been significant fears from environmentalists that the virus could devastate the sea lion population, which is recorded as endangered on international threatened species lists.

Macquarie University marine science professor Robert Harcourt said the Pages Islands had one of Australia's largest sea lion colonies and that there were "real concerns there could be a large mortality event".

"Our best hope is that we have a number of deaths but that we don't have thousands of them going," he said.

"They stay in the same region for their lives and they don't hop over to another state and come back, like other seals might do, which makes them really, really vulnerable."

Dr Harcourt said sea lions were evenly spread across Australia's 73 islands, meaning mortalities were unlikely to match those observed at Heard Island.

"Some of the islands won't get affected at all, and if that happens, then we have a small group from which to regrow the population over time," he said.

A bird flu outbreak on Heard Island, an Australian territory in the Indian Ocean, has killed more than 13,000 baby seals since last year.

Ms Bourke said the latest cases in the state were "concerning" in light of those Southern Ocean events, but discussions are underway with the federal government to gain approval for a vaccine trial targeting mammals.

"We are pulling every lever possible to show we are willing, able and capable of participating in a national vaccine program," she said.

Separately, magpies have also tested positive at Hindmarsh Island, which Ms Bourke said was an indication the virus would eventually travel further inland.

"We've seen it in Monarto, we've seen it in metropolitan areas, within inland areas in South Australia," she said.

"This isn't a coastal issue … it is a national issue, and it is being addressed that way."

The government said two dead sea lions on Liguanea Island, off the southern point of Eyre Peninsula, were also tested but returned negative results for bird flu.

Vaccine trial

Ms Bourke said a separate vaccine trial aimed specifically at birds has been underway at Cleland Wildlife Park, with more than 150 vaccines administered since last month.