University of Western Australia: Bold plan to find ‘Goldilocks’ wetlands for Western Swamp Tortoise

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On National Threatened Species Day, one of the world’s rarest reptiles is taking the spotlight as researchers from The University of Western Australia and the Department of Biodiversity, Conservation and Attractions work to bring it back from the brink.

“Our goal is to find the ‘Goldilocks’ just-right wetland that will reliably retain water and allow a population to establish successfully and without impacting other threatened species.”

Associate Professor Nicki Mitchell, UWA School of Biological Sciences
With support from the World Wide Fund for Nature-Australia, a team recently ‘translocated’ 44 critically endangered Western Swamp Tortoises bred at Perth Zoo to a new habitat in the South West region of Western Australia as efforts continue to try and protect the species from climate change.

Also known as the Western Swamp Turtle and Short-necked Tortoise, it has the smallest surviving population of any Australian reptile. Struggling from twin threats of habitat loss and introduced predators, it was believed to be extinct until two were rediscovered in 1953.

Since 1989, Perth Zoo has bred more than 1200 of the tortoises, with more than 1,000 released in the wild at Moore River and, in more recent times, into wetlands at Scott National Park in the State’s South West.

Associate Professor Nicki Mitchell from UWA’s School of Biological Sciences, said the initiative was one of a handful of global examples of ‘assisted colonisation’, with the tortoise believed to be the first threatened vertebrate to be deliberately introduced into new habitats because of climate change.

“It was likely always a rare species, but climate change is presenting a major new challenge because the swamps that tortoises occupy used to hold water for up to seven months of the year but in recent years of low winter rainfall may only hold water for half this time,” Associate Professor Mitchell said.

“Female tortoises need a relatively high winter rainfall year to produce eggs in late spring and young hatchlings need another high rainfall year to have enough time to grow to a size so they can survive their first summer. This is getting harder to achieve as Perth’s climate shifts to a lower average winter rainfall.

“For the past 15 years we’ve been trying to learn if we could establish new wild populations of the tortoise to aid its long-term survival because they can’t relocate themselves.”

A physiological ecologist focussed on anticipating and mitigating the effects of climate change on threatened species, Associate Professor Mitchell and her team carried out detailed modelling of how tortoises are expected to grow and reproduce in wetlands selected in the South West as potential release sites.

“While it may be a bit cold in the south at present, we’re anticipating that environments in southern wetlands could offer ideal conditions in the longer-term,” Associate Professor Mitchell said.

“Because the Western Swamp Tortoise has longevity similar to humans, they will experience a systematic change in the climate across their lifetime. Our goal is to find the ‘Goldilocks’ just-right wetland that will reliably retain water and allow a population to establish successfully and without impacting other threatened species.”

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