Survey of Molesworth Station deer numbers

Date 27 March 2019

Deer numbers on Molesworth Station are beginning to recover after being reduced by a pest control operation in 2017, according to a milestone report by Manaaki Whenua Landcare Research.

The annual survey work was undertaken in February and March 2019 to assess the change in the abundance of red deer in parts of Molesworth Station treated by a TBfree aerial 1080 operation in October 2017, and in adjacent untreated areas.

OSPRI Chief Operating Officer Matthew Hall said: “The use of 1080 for large scale pest control operations is currently the most effective tool we have to achieve our TB eradication goals. Our work also has biodiversity benefits by reducing possum, rat and stoat numbers.

Mr Hall says. “Recognising that there can sometimes be a significant deer by-kill from pest control operations, OSPRI is working with industry partners to develop improved deer repellent baits.”

“We are trialling two new repellents in the hope that they’ll be more effective and available for operations to treat the remaining TB risk areas of Molesworth Station. It is important to note that the by-kill was higher in the open terrain of Molesworth than in a heavily forested region like the West Coast.”

To track the changes in the Molesworth deer population, OSPRI commissioned independent organisation Manaaki Whenua Landcare Research to assess deer recovery by researching comparative numbers in treated and untreated areas.  

The aerial operation in October 2017 to reduce possum numbers over 62,000 hectares of the station killed about 90 percent of deer in the block. Deer numbers in the adjacent unpoisoned block have remained stable. The survey has shown a slight recovery in the poisoned block.


OSPRI, manager of the TBfree eradication programme, conducted the possum control operation to interrupt the TB infection cycle on Molesworth. Despite the success of the TBfree programme in the wider region, TB-infected wildlife remains present on Molesworth and adjoining properties and represent an infection risk for the cattle farmed there.

The station has the longest continuous TB-infected cattle herd in the country. The nine-year project to clear infection on the station is pivotal to eradicating bovine TB and reducing the impact of the disease on New Zealand’s meat and dairy exports. TB eradication in Molesworth is expected in 2026.

Reports and links