Credit: Dick Walker/Gilbert's Potoroo Action Group
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What is assisted migration?
Assisted migration, in relation to climate change, will involve taking threatened species and moving them from one site to another in order to escape changes in temperature and rainfall, or extreme weather events, that could make their original location unsuitable in the future. Assisted migration can also be called translocation, managed relocation or assisted colonisation, and can involve both plants and animals.
Why might it be necessary?
While some species have already shifted their range in response to climate change, not all can move so easily. Many will not be able to move fast enough to keep pace with climatic changes, while urban areas and habitat loss could hinder movement in others. For animals and plants already restricted to mountaintops, there could be nowhere left to go.
Also, events triggered by climate change, like wildfire, flood or drought, could devastate the entire habitat used by a species, such as the critically endangered Western swamp tortoise, whose estimated range is only five square kilometers in Western Australia.
Proponents of assisted migration argue that there may be no option but to ship species like these somewhere new.
Can it work?
Assisted migrations in Australia have, to date, been undertaken to protect animals from introduced predators, not in response to climate change. For example, the Gilbert's potoroo, Australia's most endangered mammal, is threatened by cats and foxes. Potoroos have been translocated to a predator-free island where they are now breeding successfully.
In the first test of assisted migration in response to climate change, British researchers moved a population of butterflies 65 km north of their current range to a site predicted to be climatically suitable. The butterflies persisted at the new site and have expanded their range, leading the scientists to conclude that assisted migration could save some species from climate change.
What are the problems?
Opponents argue that the risk of a relocated species becoming a pest in its new home outweighs any potential benefit. As Australia spends millions battling cane toads, rabbits and foxes, we should understand the risks of moving species beyond their native range.
It will be hard to predict a suitable new site and even harder to prove climate change is the main threat and not habitat loss or another factor. A failed relocation could cause further declines in already imperiled species.
However, advocates counter that such risks can be minimised and that the alternative - to do nothing and watch species become extinct - is not an option.
Assisted migration will most likely occur when extinction is imminent and risk of the species becoming a pest at the new site is low. Many animals and plants once had larger geographic ranges across Australia, so moving them to sites within their historic range could prove the least risky option.
Despite the controversy, assisted migration is supported by the Ecological Society of Australia and a number of prominent scientists.
Which species could be candidates?
As yet, no species have been flagged as candidates for assisted migration in response to climate change in particular in Australia, and the strategy is likely to be used only as a last resort.
However, a new study aims to identify sites for the potential relocation of the Western swamp tortoise. The tortoise is highly vulnerable to drought and high temperatures, and translocations have already been carried out within its historic range, suggesting that Australia's most endangered reptile could be the first aboard the new Noah's Ark.