National Predator Control Programme operations lead Colin Bishop said the poisonous 6g cereal pellet bait was distributed at a rate of 2kg per hectare over a designated 40,000ha site.
It was carefully and skilfully distributed from helicopters along predetermined and monitored flight paths, he said.
The 80-tonne bait drop aimed to diminish the island’s rat and wild cat population that was preying on the island’s near-extinct southern New Zealand dotterel/pukunui.
With only 105 birds remaining, the success of the operation was critical as the breed was in "dire straits", he said.
Mr Bishop hoped other native birds would also benefit from bringing predators under control.
A Doc spokesperson said about 60 ground crew and seven helicopters began to set up on Wednesday. Bait application began early on Thursday and was completed by noon yesterday.
The Stewart Island predator control operation, in comparison with others completed nationally, was an average size.
"Operations more than twice this size are normal during beech mast events. It was designed to cover the home range of feral cats across pukunui breeding grounds to provide the maximum benefit to pukunui."
The Doc spokesperson said it had robust scientific evidence the poison broke down quickly and rapidly diluted to undetectable levels in water.
While there had been a small group of protesters on the island opposing the drop, overall the general sentiment from the island’s residents had been positive, Doc said in its statement.
"There has been a wide range of engagement with the community in the lead-up to the operation. We’ve been speaking with people on island and many are excited to be at the point to give pukunui a fighting chance."
Community members had been able to watch part of the operation and feedback had reflected that they appreciated the opportunity, the spokesperson said.
Doc budgeted $90 per hectare for this operation which takes into account the remote location.
Protect Raikura Trust chairwoman Furhama Ahmad said on Thursday the bait did not totally dilute in the water but Doc disputed that.
- By Toni McDonald
