The Animal Health Board says there's a direct link between the drop in possum numbers and outbreaks of tuberculosis in cattle.
The estimated number of possums in New Zealand has fallen to about 30 million, down from highs of 70 million in the 1980s, according to Landcare Research.
Animal Health Board technical manager Paul Livingstone says, as an example, the Wellington region has had an 89% drop in possum numbers and also the largest drop in the number of infected herds.
He says more than 300 herds were infected in the 1980s, compared with five in June this year.
