The greatest success in Canterbury has been in the Mackenzie area, with initial figures on rabbit reductions in some areas as high as 89 per cent. High country farmers, regional council personnel, and scientists applauded the effectiveness of the virus at the annual South Island high country committee conference in Christchurch on Monday.

Canterbury Regional Council biosecurity team leader Graham Sullivan said there were two factors that may have caused the irregular results in North Canterbury.

First, there may have been differences in the way the virus was released in North Canterbury. Second, the results may have been skewed by the area's geography, which consisted of dry inland areas broken with irrigated ones.

The findings replicated patchy results from similar areas in Australia, he said.

Farmers in North Canterbury were still needing to use conventional controls to suppress numbers.

However, the virus had still had some success in North Canterbury. With the recent drought, rabbit numbers would have been "through the roof", he said.

The greatest success in Canterbury had been in the Mackenzie area, with initial figures on rabbit reductions in some areas as high as 89 per cent.

Since the introduction of the virus the pattern had been one of increasing rabbit numbers during breeding, followed by a crash as RHD became resurgent.

The cost savings in rabbit control to the regional council and farmers were also good news, Mr Sullivan said. RHD had saved farmers $300,000 in control costs, and a average saving of about $5 to $7 a stock unit. Normally 1000 tonnes of poisoned carrots were dropped annually. No poisoned carrots had been dropped since the illegal introduction of the virus in 1997, highlighting its effectiveness. Annual night count figures were up to several hundred rabbits a kilometre in some areas, but the average for October-November was 1.4 a kilometre

In Otago, results had also been dramatic. The virus there had delivered a significant blow to the rabbit population.

Otago Regional Council chief executive Graeme Martin said the release of RHD in Otago had been nothing short of a success story. Monitoring sites covering a wide area showed night counts as high as 17 rabbits a kilometre in August to February but as low as four a kilometre. This had not been seen in Otago before, he said. Pre - virus numbers had been as high 100 a kilometre