Rabbits still cost ag $206m a year but that's down nearly 90pc on $2b

After they were introduced in the 1850s, rabbit numbers exploded in Australia. By the 1940s, there were 600 million across the country, outnumbering humans 80 to one.

A new report released by Centre for Invasive Species Solutions chief executive Andreas Glanznig shows controlling rabbit numbers had huge benefits for primary producers and threatened species.

"The value of new rabbit haemorrhagic disease virus variants naturalised since 2014 to Australian agriculture is expected to save $4b over the next 30 years," he said.

"This builds on the benefits already achieved over a 60-year period of $81.8b, following the release of the myxoma virus in 1950 and the first rabbit haemorrhagic disease virus in 1995."

The report, Benefits of Rabbit Biocontrol in Australia: An Update, also reveals that the removal of rabbits just as good for the environment, allowing native vegetation to thrive, causing feral cat and fox numbers to plummet, and native mammals to bounce back.

Mr Glanznig warned against complacency.

"You only have to watch some of the old black and white footage from the 1950s to see how destructive rabbits can be in large numbers," he said.

"They are absolute eating machines, consuming around 15 per cent of their body weight a day, and cost Australian agriculture around $206 million every year."

Rabbits can begin breeding at four months old and, if conditions are right, produce about five litters a year, creating a new 5060-strong family.

The financial impact of rabbits on agriculture was $2b a year until a breakthrough was made with the myxoma virus release in 1950, which killed 99.8 per cent of infected rabbits.

The Australian rabbit population had rebounded to about 300 million by 1995, when the first rabbit haemorrhagic disease virus (RHDV1) was released, killing 98 per cent of rabbits in arid areas.

In 2009, a benign endemic rabbit calicivirus gave rabbits some protection from the lethal RHDV1 infection, reducing its the effectiveness.

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Five years later, the unplanned arrival of a second rabbit haemorrhagic disease virus (RHDV2) cut rabbit populations by an average 60 per cent and up to 80 per cent in some populations, including some rabbits with immunity to RHDV.

In 2017, the coordinated release of a new RHDV1 strain, RHDV1-K5, knocked down an average of 34pc of rabbits nationally but was outcompeted by RHDV2 at a landscape scale.

Mr Glanznig said it was essential to stay ahead of the rabbit's ability to develop genetic resistance because even small numbers had really negative impacts on native vegetation and animals.

"We know that Mulga, for instance, are impacted by rabbits with densities as low as one rabbit per 100 hectares, that's the equivalent of one rabbit per 90 rugby league playing fields," he said.

Long-term scientific monitoring showed the release of rabbit haemorrhagic disease viruses was the single most important and cost-effective conversation action for small, threatened mammals in the southern arid zone, and a range of taxa and ecosystems in recent decades.

Scientists found, for example, that the abundance of small mammals like the Dusky Hopping-Mouse, the Spinifex Hopping Mouse and the Plains Mouse in Australia's arid zone grew 365 per cent with the arrival of the first rabbit haemorrhagic disease virus.

"This shows that rabbit biocontrol is fundamental to protecting Australia's globally important wildlife and threatened species, as well as generating benefits to agriculture worth several hundred million dollars every year," Mr Glanznig said.

"It is a technology that keeps on giving for our environment and primary industries."

The Centre for Invasive Species Solutions is working on the fourth phase of a long-term rabbit biocontrol pipeline strategy to develop genetic biocontrol technologies, more efficient ways to monitor rabbit abundance impacts through new satellite imaging methodologies, and the use of artificial intelligence.

"A long-term strategic approach to rabbit biocontrol R&D will ensure that Australia is not pushed onto the back foot in managing one of our most costly vertebrate pests," Mr Glanznig said.