Standing knee-deep in a swamp, the researchers plucked three dozen tortoises one by one from cardboard boxes, lowering them into the water. Then they watched as some of Australia’s most critically endangered reptiles took off into the wetlands, bound for an audacious experiment in climate adaptation.
The project, set in a national park in Western Australia, is the latest flash point in a knotty scientific debate. The western swamp tortoise’s natural habitat in Australia is becoming increasingly unsuitable as temperatures rise and rainfall decreases. So conservationists are moving some of the animals 200 miles south, to a cooler place where they have never lived before. Experts say it could be the only way to ensure the tortoises’ survival in the wild.
It is believed to be the first time researchers have tried to relocate a vertebrate species to a new habitat because of climate change. Doing so is a huge gamble, though, and not just for the tortoises. Introducing species into a new landscape can have unpredictable and sometimes catastrophic consequences, and ecosystems are so complicated that no amount of research can predict the full effects. A seemingly innocuous species can become an invasive one in a new environment — something that few countries know better than Australia, where the introduction of European species, including rabbits, cats and foxes, decimated native wildlife.
The Australian experiment is an example of the difficult choices the world will face with increasing frequency if it does not curb global warming. As the rise in temperatures outpaces species’ ability to adapt, a growing number are being pushed closer to extinction. Moving them to more hospitable terrain — known as assisted colonization or assisted migration — is one of a suite of new techniques, some on the outer edge of science, that could help save select endangered species. But the efforts have also fueled a debate about how, or even whether, humans should manipulate nature in a quest to protect it.
To Nicola Mitchell, an associate professor of conservation physiology at the University of Western Australia and the project’s lead scientist, the central question is: Do we let nature run its course and “let our species die because of climate change? Is that a natural ending? Or do we have an ethical responsibility to save these species?”
Long believed extinct before a chance rediscovery in the 1950s, western swamp tortoises now number about 800 in the wild. (The relocated tortoises were all bred in captivity.)
Only one self-sustaining population exists in the wild, containing about 70 adult turtles. That population, on the outskirts of Perth, faces the dual threat of habitat loss from the city’s growth and of climate change, which has shrunk the cool, wet periods the tortoises need to feed and breed, before they hibernate through the hot summer months.
Surrounded by the city, the tortoise cannot move to a new habitat on its own. It lives for 100 years, so its life cycle is too long to be able to naturally evolve to adapt to the changing environment.
Professor Mitchell began to look at assisted colonization to protect the species around 2008, she said, when debate about the approach took off in earnest as the effects of a warming climate became increasingly clear. Today, the scientific community seems little closer to reaching a consensus, though she hopes the tortoise trial will nudge the discussion.
The wetlands in Scott National Park, where the captive tortoises were released, are currently colder than the animals’ natural habitat, but Professor Mitchell’s modeling predicts that the climate there should be ideal in about 50 years, as temperatures continue to climb. That could make it a good long-term habitat for the tortoises, given their life spans.
In the meantime, trackers that the scientists spent hours painstakingly gluing to the tortoises’ shells will be used to monitor their body temperature and movement. If the trial runs into any problems, “we can potentially undo our mistakes by recapturing them,” Professor Mitchell said.
The tortoises were the third batch released in the area. Previously, a second location in a different part of Western Australia was tested and deemed unsuccessful — although the climate conditions were suitable, the food sources were not.
The most recent release, in August, was particularly nerve-racking for the scientists, because it was the first involving baby tortoises. The researchers methodically hunted for the perfect patch of reeds and then released the tortoises, which fit in their palms.
“Off he goes,” Nick Rodriguez, a masters student at the University of Western Australia, said as one tortoise started to swim. But after seeing that the fingernail-size tracker on its back was causing the animal to tilt sideways, the scientists spent the evening gathering all the babies back up and returning them to a zoo.
While it is impossible to completely predict the tortoises’ impact on the new environment, the team expects the effects to be limited. The tortoise has a very constricted diet of invertebrates and tadpoles and breeds slowly, meaning its population is unlikely to explode.
Still, some biologists who study invasive species have likened assisted colonization to playing “ecological roulette.”
Because of the difficulty of forecasting introduced species’ effects, ecologists are unable to ensure that they will “avoid serious, irreversible consequences,” said Anthony Ricciardi, an invasive-species biologist and a vocal critic of assisted colonization.
“Even if such consequences are uncommon, their risk of occurrence increases with each species introduction,” he said via email.
Other scientists worry that the approach will distract from addressing the root cause of the threat: global warming. It is also unlikely to be a scalable solution, and it would require scientists to make fraught decisions about which species are worth saving.
“To move enough species to resolve this threat basically seems untenable,” said Mark Schwartz, a conservation scientist at the University of California, Davis.
The scientists involved in the experiment acknowledged that the strategy, to some extent, picks winners and losers. They also acknowledged that some may not see it as the best use of limited resources. The money might have been put more efficiently toward, say, trying to eradicate invasive species.
Gerald Kuchling, a herpetologist who is involved in the trial, said he was uneasy about the possibility that it would pull focus away from what he saw as the bigger priority: protecting the tortoises’ one remaining wild habitat.
“In the end, I think it is a question of your personal ethics and morals,” he said.
While Professor Schwartz, the University of California scientist, had some reservations about assisted colonization, he noted that it was the least invasive of a host of new technologies that are becoming available, including gene editing, to make animals more climate-proof.
Projects like the tortoise relocation could help inform more difficult conversations in the future about how far society is willing to go to save species, he said.
In the case of the Australian tortoises, it took nearly a decade to start the experiment after Professor Mitchell wrote the first grant application. Ultimately, she said, the experiment could provide a road map for future efforts.
“I think you need to try, and learn, and share what you’re learning,” she said, adding: “It will become a catalyst for change, I think, if it’s successful.”