The impact of wallabies in the South Island could come with a price tag of up to $67 million by 2027, a new report reveals.
The cost of the pests, including the impact on the environment and lost agriculture revenue, has already reached $23.7m a year.
Concerns following increased sightings of the pest, which is concentrated in South Canterbury, and growing concern about costs prompted the Ministry for Primary Industries to contract researchers to review the current situation.
“Because of an increasing number of sightings outside these species’ containment areas (as designated by regional councils), there is growing concern over the increasing cost of their impacts and the increasing challenge of containing them,” the review said.
However Environment Canterbury says $67,000,000 a year in ten years is a conservative estimate.
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The containment zone included Two Thumb Range, the Albury Range, the Kirkliston Range, Grampian Mountains, Hunter Hills, and Kakahu Bush.
At present the Bennett’s wallaby, which is found primarily in the Hunter Hills in Waimate, occupied an estimated 5,322 square kilometres in the South Island.
“However, the large number of confirmed sightings and animals shot outside of this area suggest that they may occupy as much as 14,135 square kilometres.
“Based on current estimated rates of spread, the distribution of Bennett’s wallaby in 50 year’s time is likely to be between 9,621 and 20,631 square kilometres, but possibly as large as 44,226 square kilometres,” the review said.
It assumed rates of spread would stay constant.
The current total annual cost of the impacts of the Bennett’s wallaby in the South Island was estimated to be $23,700,000.
That included $22,200,000 in revenue lost to agriculture and $1,500,000 to ecosystem services and biodiversity values.
If Bennett’s wallabies were allowed to spread without any active management, it was estimated the total cost of their impact in 10 years would increase to $67,000,000 annually.
Dave and Cecilia Latham and Bruce Warburton were contracted to conduct the review.
Lead researcher Warburton said the figures were not surprising because the population had been expanding for some time.
“The challenge is trying to find where they are occurring in low density areas, they are difficult to detect, there is a lot of uncertainty where that outer boundary is.
“There is research going into better detection methods to find these outlying individuals, some of the outlying population has not been natural it has been from illegal release, clearly the ones up at Christchurch, it’s not through natural causes.”
Pest population was best managed at an early stage before they expanded, he said.
”They (ECan) have some challenges, they are dealing with the expanding population and even if you have detected them you have to remove them all so how can you be confident?”
Environment Canterbury regional leader of biosecurity Graham Sullivan said the researchers were well known to ECan, and Bruce Warburton was a New Zealand scientific expert on wallabies.
The cost estimates for the impact of the wallaby for now and in 10 years time were conservative, he said.
The report aligned with ECan views, he said.
When asked if the review would influence ECan to change its approach for its pest management strategy Sullivan said “Environment Canterbury has proposed a change to managing wallabies in its Regional Pest Management Plan, which is currently under review”.
ECan spent $80,000 annually controlling wallabies out side of the containment zone. Control inside the containment zone was the responsibility of landowners.
In October a draft annual report from ECan revealed the council had failed to hit its biodiversity target for pest control in the past financial year, and wallaby numbers in South Canterbury were increasing.
Sullivan said at the time no-one knew how many wallabies there were and it was impossible to even estimate.
Warburton said the public played its own role in preventing the spread and suggested education would be helpful.
“If we can get the wider population to be aware of wallabies, we need to encourage people not to release them and let the councils know. It’s about educating. The Waimate council uses them on their emblem but they are an invasive species.
“The more they spread the harder it gets to control them.”
Six species of wallabies were introduced into New Zealand during the late 1800s, either for recreational hunting or as part of the then desire to acclimatise exotic species. Four of these species are found on Kawau Island, with dama wallaby also found around Rotorua, and Bennett’s wallabies found in South Canterbury and North Otago.
Populations of both these species continue to spread on the mainland and have negative impacts on primary production and indigenous biodiversity.