How Australian scientists brought Norfolk Island’s thumbnail-sized snails back from the brink of extinction

13 July 2024

First there’s a bulge on the right-hand side of the snail’s neck and then slowly – because everything in the snail world happens slowly – a fully formed baby snail emerges, shell and all.

In a quarantined captive breeding facility at Sydney’s Taronga Zoo, adult Campbell’s keeled glass-snails popped out more than 20 babies last week.

After initially struggling to reproduce in captivity, Advena campbellii are now breeding like rabbits – or maybe like snails – and scientists are now planning to release some back into their only known home, a small valley on the tiny Norfolk Island in the middle of the Pacific.

The thumbnail-sized snail was officially extinct when, in March 2020, pictures taken by local citizen scientist Mark Scott found their way to the inbox of Dr Isabel Hyman, a malacologist (snail scientist to you and me) at the Australian Museum in Sydney.

“Mark had seen these snails – quite big – that he didn’t recognise. I’d been there years before. I thought they were gone,” Hyman, who jumps with excitement at remembering seeing the pictures for the first time, says.

The images showed a distinctive angular shape and a bicolour shell. Hyman was almost certain it was the “extinct” species. She went with colleagues to the island and Scott led her to the spot, where she overturned a decayed palm frond to find a line-up of the snails.

Dr Isabel Hyman, a research scientist at the Australian Museum, inside a room full of breeding tanks of Campbell’s keeled glass-snail. Photograph: Mike Bowers/The Guardian

“My heart was beating so fast. I was super excited. But then immediately there was another thought: ‘We have to make sure we do everything we can to protect it’,” she says.

From two trips to the area inside the island’s national park, 40 of the snails were flown to a dedicated and quarantined captive breeding facility at Taronga Zoo in Sydney.

But the fight to save the snail and to get the conditions just right for lots of baby-making was only just beginning.

Within six months all the original snails were dead, and for the first two years the number of births was barely enough to keep up with the deaths of the snails, which are only thought to live for about 10 months.

Hyman says: “We’d told the community we were going to return them but it was painful to think that if they all died, was that all we’d done? Weaken the population even further? We were worried we might not have done any good at all.”

Mark Scott, Isabel Hyman and Frank Koehler on Norfolk Island, the day the snails were rediscovered. Photograph: Adnan Moussalli/Museums Victoria

‘They’re getting up to lots’

After finding the snails, the team secured grants from the Australian Museum Foundation, the National Geographic Foundation, the Mohamed bin Zayed Species Conservation Fund and the Australian Research Council.

Zookeepers and the science team pored over their regime for the snails, taking tips from other captive breeding programs around the world, in particular Hawaii where several land snails are facing extinction. They made one small change at a time and then waited for the results.

They tweaked the temperature, humidity, the diet (a paste of calcium carbonate, oatmeal, nettle leaf, fish food and vitamins), how they were fed and the vegetation in the tanks.

In late 2023, there were still only eight adults among the 70 snails. Now, there are 300 snails.

Tarryn Williams Clow is a zookeeper and leads the captive breeding program for the snails at Taronga Zoo.

Most of her captive breeding experience has been with exotic mammals including black rhinos, cheetahs, otters and tigers. The risk of being mauled is, presumably, greatly reduced with snails.