Since it started actively eradicating possums in 2011, the group has removed 20,000 from the peninsula.
Trust chairman Hoani Langsbury said based on the group’s estimates, there were only about 600 possums left in the area.
As their numbers diminished, it had become increasingly difficult to find and eradicate the remaining possums, Mr Langsbury said.
As part of its proof of eradication, new AT220 traps would be left around the peninsula, about one per 20ha.
The network of traps would be monitored electronically for the re-invasion of possums.
The benefits of the eradication programme were huge, especially for native birds.
The natural re-establishment of tui was one example.
Kereru, which had not been seen on the peninsula for at least 80 years, had also been spotted in Otakou and around the marae.
"And that’s without actively doing re-introductions, so they’re naturally re-occurring," Mr Langsbury said.
There had also been an increase in the number of kahu.
"And we’ve had at least one sighting of a New Zealand falcon."
The biodiversity group was started in 2008 and aimed to make the peninsula predator-free by 2050.
Over the years, various tactics had been used against the possums, including poisoning, trapping and shooting.
Poisoning was the most common, Mr Langsbury said.
The group also used new tools, such as monitored leg hole traps and live catch traps, which allowed accidentally trapped domestic pets to be released.
The programme had been a community effort, involving contractors, volunteers, landowners and residents.
