A conservation heavyweight says it's time New Zealanders talked about controversial new technology likely needed to help win our war on pests.
A new scientific review has found current approaches wouldn't be enough to reach the country's goal of clearing all rats, stoats and possums from the mainland by 2050.
To save our under-pressure native biodiversity, big challenges lay ahead: notably rolling out operations over wider areas, getting public backing, and finding scientific solutions to turn the tide.
That included contentious genetic technology that could knock down populations by boosting the chance of certain genes being inherited, or by "silencing" gene sequences unique to particular pest species.
Before these could be put into practice, the review found, there were big technical challenges to overcome – along with "significant social, ethical and regulatory hurdles".
Predator Free 2050 chairman Sir Rob Fenwick felt it was important that the public nonetheless talked about them.
"The sooner we have the public conversation about the risks and rewards of using or investigating these tools, the sooner we'll know whether they are a useful tool or not," he said.
"At the moment, we simply don't know, because we've had this 15-year absence of research on it since Corngate – so we've been left behind in the world and we've got to catch up, if we are going to use it."
Strict regulations under the HSNO Act have tightly controlled the use of GMOs in New Zealand since 2003.
While the review singled out some genetic techniques, its lead author, Associate Professor Elaine Murphy, said what appeared the most promising ones today might not be so a decade or two from now.
Murphy, a predator ecologist with the Department of Conservation and Lincoln University, added scientists also still had much to learn about the genetic make-up of the pests being targeted.
"There are things that we can be doing now that can help us, but I don't think we should be going boots and all into gene drives now."
The review found the ability to effectively reverse some of the new technologies could be critical to gaining public acceptance - not to mention stopping them from wiping out species in other countries where they weren't considered pests.
Another of the review's authors, Associate Professor James Russell, felt New Zealand shouldn't just pursue breakthrough technologies, but also improve and expand current measures.
The University of Auckland conservation biologist emphasised that if wider issues like regulatory barriers and social acceptance couldn't be addressed, New Zealand wouldn't be able to meaningfully progress toward its 2050 goal.
"The regulatory environment is particularly important as it is often overlooked and sometimes out of date," he said.
"Our Wildilfe Act desperately requires updating to be fit for purpose in the 21st century, while rules around the use of pest control tools must strike the right balance between efficiency, welfare and safety."
The review comes after National criticised Conservation Minister Eugenie Sage for sending Predator Free 2050 a letter in which she ruled out investing in research into genetically modified organisms and technologies.
She told the Herald she wanted the government-created company to focus on existing measures like traps, toxins, lures and landscape-scale approach, adding there was no "silver bullet" genetic approach ready to be used.
"In the context of gene drives and other gene editing technologies, I am aware that researchers believe they could potentially be useful for the eradication of pests in New Zealand, but a great deal of research and understanding, as well as public acceptance, is required before such technologies could be implemented."
Any future research on genetic technologies would require full regulatory approval, she said.
Royal Society Te Apārangi has begun to explore some of the social, cultural, legal and economic implications of gene editing in New Zealand, through panel discussions and discussion documents.
"This kind of engagement is useful to begin to understand some of the issues involved," Sage said.
While National has proposed updating restrictions if elected to government, Environment Minister David Parker's office has confirmed there are no plans for a reform.
NZ's rat invasions revealed
Meanwhile, another new study, led by Russell, has revealed for the first time the invasive history of New Zealand's two most common species of rat.
The University of Auckland researchers drew on population genetics methods to find out how the ship rat and Norway rat had invaded the country.
The findings revealed this hadn't just happened through population booms since their introduction aboard settlers' ships, but also through arrivals that continued well into the 20th century.
The researchers found widespread genetic diversity among the most common species, the ship rat, with at least four different invasions in the North and South Island and on offshore islands like Great Barrier Island and Stewart Island.
Each new invasion was trackable through new genes being introduced into the gene pool.
The Norway rat was found to have a more limited diversity, with two main invasions across New Zealand – one on the North Island and offshore islands, and the other on the South Island, potentially with both English and Chinese origins.
"The genetics show how quickly rats would have overrun New Zealand when they arrived, and eaten their way through our bird and reptile populations," Russell said.
"Using these results, today we can trace new arrivals of rats across New Zealand which will be critical if we are serious about reaching our goal of being predator free by 2050."
As both common rat species quickly established and rapidly spread by the 19th century, they displaced the kiore or Pacific rat introduced by Polynesian settlers in the late 13th century.
Eventually, the kiore rat became restricted to remote parts of both main islands and a few offshore islands.