Relocating Australian tortoise sets controversial precedent

As long as it has been known to science, the diminutive western swamp tortoise has been in peril. By the time it was formally named in 1901—using a decades-old museum specimen—Pseudemydura umbrina was presumed extinct. And since it was rediscovered in the 1950s, biologists have struggled to protect it from the twin threats of habitat loss and introduced predators, which drove its numbers to bottom out at just 30 individuals in the 1980s. Now that climate change poses an even more urgent threat to the endangered tortoise, biologists have a controversial plan to safeguard its future—by moving it to new sites outside of its known historical range. The translocation, which took place today, makes the tortoise the first vertebrate to be deliberately relocated because of climate change.

The yearlong trial, several years in the planning, will track 12 captively bred juvenile tortoises released to each of two sites roughly 250 kilometers south of their native habitat on the outskirts of Perth, Australia. Although the sites aren’t ideal for the tortoises now, detailed modeling of rainfall, temperature, swamp hydrology, and tortoise biology predict they will be in half a century.

For the western swamp tortoise, whose numbers in the wild are now estimated at just 50 breeding adults, declining rainfall is the primary concern. The 15-centimeter-long tortoises feed when rains fill swampy habitats in winter, and then enter a state of dormancy known as estivation when the swamps dry out to clay pans in the late spring or early summer. The less rain in winter, the more likely the hatchlings and juveniles will starve before the next winter rains arrive. Swamps that were wet for 5 to 7 months of the year in the 1960s are now often dry for most of the year, and rainfall is set to decline further in the future. Hemmed in by urban sprawl and agricultural land, the tortoises can’t up and move, either. “It’s a double whammy,” says conservation physiologist Nicola Mitchell from the University of Western Australia in Perth, who is leading the trial.