Invasive pests cost Aotearoa $12b, study shows

Weeds, rodents, stoats, possums, fire ants and other invasive species cost Aotearoa New Zealand about $170 million per year.

That’s according to new research by Waipapa Taumata Rau, University of Auckland and the University of Aberdeen in collaboration with CNRS (the French National Centre for Scientific Research).

From 1968 to 2020, the cost was about $12.4 billion, report the researchers, who used a database called Invacost, which was launched in France to boost understanding of the worldwide economic toll of invasive species.

The amounts include damage to agricultural crops, timber products, and human health and the money spent on preventing and managing pest invasions.

Aotearoa is a world leader in eliminating invasive species, with initiatives including Predator Free 2050, a campaign to remove predators such as rats, stoats, ferrets, weasels and possums.

These efforts are needed because New Zealand has the world’s highest proportion of threatened native species.

“Increasing efforts to tackle invasive species, including but not exclusively through Predator Free 2050, will be of immense benefit, says Dr Zach Carter, a researcher in the School of Biological Sciences at Waipapa Taumata Rau, University of Auckland. “We can do more in prevention, by doubling down on biosecurity and rapid eradication.”

The estimates may only hint at the true economic cost, because of an absence of complete data and difficulties in quantifying all economic impacts.  

“New Zealand has a proud pioneering role in invasive species management and is at the forefront in this area globally,” says Dr Thomas Bodey, a research fellow in the School of Biological Sciences. Despite this, invasive species still pose a huge burden to the country’s economy, which can be mitigated with enhanced management, he says.

Native animals which evolved in the absence of predators such as rats are highly vulnerable. Feral cats have contributed to at least 20 extinctions of bird species in New Zealand, while three species of rats (Rattus rattus, R. exulans and R. norvegicus) have contributed to at least 40; and stoats have contributed to at least 10.

The common brushtail possum, introduced to New Zealand from Australia, is described by the Department of Conservation as one of the greatest threats to our natural environment.

Climate change can fuel the spread of invasive species since changes in air and water temperature may prompt them to move to new locations.

The study suggested that Aotearoa is spending far more than most other countries on prevention and management relative to the nation’s gross domestic product.

The research was published in PeerJ.