New Zealand-Rabbit problems for farmers.

NEW ZEALAND-RABBITS ARE BACK.

Authorities confirm a definite resurgence in rabbit numbers in parts of the South Island high country, with populations at their highest levels since Rabbit Haemorrhage Disease (RHD) was illegally introduced in Central Otago in the spring of 1997.

Pest control agencies in Canterbury, Otago and Marlborough all report a steady increase in the number of rabbits tested showing immunity to the fatal RHD virus, with average immunity levels of around 60 per cent and peaks as high as 79 per cent.

"Environment Canterbury has been monitoring rabbit numbers since the 1990s and there’s definitely been a resurgence," said the council’s biosecurity team leader Brent Glentworth. As the population increases, the proportion of rabbits immune to the RHD virus also increases, he said.

Rabbit populations in parts of Canterbury are approaching pre-1997 levels, before the introduction of RHD, despite the application of 800 tonnes of carrots and an unknown quantity of pindone pellets to control them, Mr Glentworth said.

Surveys in spring 2008 showed rabbit numbers increased in nine out of 11 pest control districts in Canterbury. In the MacKenzie Basin, rabbit numbers have increased for the sixth consecutive year.

Historically the semi-arid regions of the MacKenzie Basin, Omarama, Kurow and parts of the Waikari, Amuri and Kaikoura districts are most at risk because of their rabbit-prone soils.

The only two pest districts in Canterbury that showed a drop in rabbit numbers were Waikari and Amuri, a direct result of targeted pest control operations there, Mr Glentworth said.

Without major input to control rabbit numbers this season, Mr Glentworth said the problem would be much worse after the next couple of breeding seasons.

Farmers were in a tricky situation because pest control costs had escalated and were often the first expense to be cut from their budgets during tight economic conditions.

"I would hate to see farmers cut corners on rabbit control, which could compromise the effectiveness of poisoning operations," Mr Glentworth said. "We can’t afford to let standards slip."

A lot of the skills and technical standards of control operations had slipped in the last 12 years, he said.

Environment Canterbury does have an enforcement role and can act on default on rabbit control operations if it is in the public interest to do so. But Mr Glentworth said the council preferred to support farmers in "the war on a common enemy".

With increasing levels of immunity, many rabbits had not been exposed to poisons so a co-ordinated approach was required for effective control.

"The last thing we want is neophobic or poison shy rabbits," he said. "This is a great opportunity to get good kills of naïve rabbits if the work is co-ordinated."

Further south, a recent report to the Otago Regional Council confirms an increase in rabbit numbers to the highest levels since RHD was first recorded in Central Otago in spring 1997.

RHD was still the major cause of death in Otago rabbit populations but its impact was decreasing as immunity levels had levelled off at an average of 61 per cent in 2007, the report said.

Rabbit numbers exceeded maintenance levels set by the council on 10,600ha of the province, most of that in Central Otago apart from 300ha in East Otago and 40ha in North Otago.

The main problem area was in traditionally rabbit-prone areas around Tarras, Luggate and Lowburn, on the Kyeburn River and east of Waipiata near Ranfurly.

Rabbit mortality was much higher on the coast and in wetter parts of South and West Otago, where rabbit numbers were lower than threshold levels set by the council.

The ORC is currently considering a new regional pest management strategy that will require landowners to maintain rabbit numbers at level three or lower on the modified McLean Scale by October 2012.

The new policy is expected to have a major impact on properties in North Otago, Tarras, Cromwell and Alexandra with an estimated 25,000ha of land likely to be affected.

In Marlborough, current RHD immunity levels range between 30 and 70 per cent with the average of around 60 per cent consistent with those in Otago and Canterbury.

The focus there was on developing conventional control programmes in consultation with landowners, said Alan Johnson, environmental science and monitoring manager for the Marlborough District Council. No enforcement or default notices had been issued to landowners in Marlborough, Mr Johnson said.

Landowners were responsible for delivering six control programmes covering 7041ha in 2007/08 in the upper Awatere Valley and Clarence catchments where rabbit numbers exceeded its high country threshold (level four on the modified McLean Scale).

Mr Johnson said rabbits were a serious problem in parts of the upper Awatere Valley and Molesworth Station, but the RHD virus was still working in parts of Marlborough.