Specialists with firearms and night vision will hunt foxes on Granite Island over the coming fortnight in an effort to save what is left of a once burgeoning little penguin population south of Adelaide.

A fox attack that killed up to nine penguins earlier this month has reduced the population to as few as 12 birds, with fears another attack could wipe out the population altogether.

A bait laid by the Department of Environment and Water (DEW) has since been taken by a predator, but sightings of a fox crossing the causeway has prompted further action including the island's closure at night on Monday to Thursdays.

"We'll have people over there with firearms looking for the foxes, so it's just a temporary closure while we make sure there are no foxes over there," DEW Conservation and Wildlife director Lisien Loan told ABC Radio Adelaide.

"Since the bait was taken we've seen no evidence of a fox but after this more recent sighting we are getting some of our specialist pest controllers down there who can use night vision and thermal imagery to double check there's none on the island.

"We've also installed an ultra-sonic fox deterrent on the causeway [to Victor Harbor], so that emits a high frequency that dogs and foxes do not like."

She said it had been 14 years since foxes were last on the island.

Ms Loan said the last official count of penguins in 2012 recorded 30 on the island, although it was reported last year that the population had increased to 44.

It is a dramatic reduction from more than 1,000 at the start of the century, a decline that has been attributed to a variety of causes, from seal and fox predation, to climate change, fishing and human interference.

Victor Harbor City Council Mayor Moira Jenkins said, between the department and volunteers counting the penguins, it was estimated there were between seven and 12 penguins left.

"We really want to be able to protect them," she said.

"It's just so sad."

She said several members of the public had reported seeing foxes on the causeway and the council was keen to work with the Government to erect a fox-proof gate.

Ms Loan said DEW was in talks with the Department of Infrastructure about installing a fox-proof fence with a "spring-loaded gate" on the causeway.

The State Government also has plans to demolish the heritage causeway altogether and replace it with a concrete and steel structure a proposal that has prompted a protest petition that has been signed by nearly 9,000 people.

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Granite Island penguin population in peril prompting specialists to hunt foxes at night - ABC News