Investigations into the accidental fatal poisoning of stock and family pets after separate ground-based 1080 pest control operations in Northland have recommended system changes be made to avoid similar future problems.
Three dogs and two heifers died after the ground-based Northland pest control operations.
The first deaths occurred in the Tanekaha Community Pest Control Area (CPCA) in late September when the heifers found their way through 'deteriorated' fencing into an area where possums and rodents were being targeted as part of a kiwi recovery programme and ate leftover material in bait stations.
Then in mid-October, three dogs died after two - a Labrador and a German shepherd - apparently scavenged the carcass of a possum in a paddock that had been killed in a similar operation in the Hukerenui CPCA.
The third dog is thought to have died after consuming material vomited by the first two.
Both control operations involved 1080 and were jointly managed by local communities and the Northland Regional Council.
The council has now released the outcomes of its separate investigations into the two incidents.
The Council's deputy CEO, Bruce Howse, who is also the Council's group manager for environmental services, described the cases - one of which involved family pets and the other farm stock - as "unfortunate and highly regrettable".
He said the Council was sorry for the associated distress the animals' owners had experienced and had given them an assurance the incidents were being treated very seriously.
"Both incidents have been very carefully investigated and the lessons learned will be incorporated into any future operations using 1080, which remains an essential tool of our pest control toolbox," he said.
The investigations found the heifer deaths, in particular, were an unfortunate series of events, risks and factors - any of which in isolation would have been unlikely to have resulted in any harm.
These included deteriorating fences, "miscommunication" over toxin removal and the lack of an identified project leader with overall responsibility for the operation.
Howse said in the case of the Tanekaha group, it had carried out three previous similar operations since its formation in 2012, none of which had experienced any issues.
"However, while there were already a number of existing checks and balances, we accept that improvements to current procedures are needed in both cases and the reviews have recommended a number of changes that will be implemented as a result."
Recommendations included that all council-supported pests control operations using any toxins had a detailed project plan, communications plan and risk assessment to ensure critical details and issues were not missed.
It also said those should also be peer-reviewed before an operation began.
While landowner consent and communication plans had been done previously, these would be even more robust in the wake of the deaths.
Howse says in the case of the dog deaths, an initial "knockdown" of the significantly-high possum populations in the area before the 1080 operation may also have reduced the resulting number of possum carcasses and associated risk to dogs.
He said both the Tanekaha and Hukerenui CPCA groups enjoyed good support from their local communities, which the Council appreciated greatly and was keen to see continue.