A review of the possum population showed nu' />

The country's possum population has more than halved in the last 20 years, according to new research.

A review of the possum population showed numbers were down from 60 to 70 million in the 1980s to about 30 million.

Landcare Research reviewed the figures on behalf of Northland Regional Council and the Animal Health Board and delivered the results to the National Possum Control Agencies conference today.

The revised figures showed control measures were having a significant impact on possum numbers, Landcare Research spokesman Bruce Warburton said.

Possum control is carried out on about 13.3 million hectares nationwide - about half of all vegetated land -- for conservation purposes or to stop the spread of bovine tuberculosis.

Possum numbers have reduced by more than 50 per cent in Hawke's Bay, Manawatu, Wanganui and West Coast but Wellington had the greatest reduction of 87 per cent.

Mr Warburton said New Zealand could support about 48 million possums without control measures.

He also said possum control was not done for the sole purpose of reducing numbers and the figures were only estimates.

"So although the number of possums might be of general interest, it is critical that the focus of possum control remains on achieving the desired outcomes and that numbers killed or overall percentage reduction is not used to measure control success," he said.