Testing of dead rats that washed up on North Beach near Westport confirms they were not killed by 1080 toxin, the Department of Conservation said today.
Eight rats were tested and one weka. None of the animals tested positive for 1080.
Maanaki Whenua Landcare Research tested the rats.
Two other rats were too decomposed to be able to test them, DOC reported.
The agency's West Coast operations director, Mark Davies, in a statement said it’s unlikely that the animals came from an area where 1080 had been used.
“We don’t know the source of the dead rats but it’s possible they came from beech forest areas closer to Westport in the Buller Gorge, affected by flood conditions,” said Mr Davies.
Five of the rats were sent to Massey University School of Veterinary Science, where post-mortem examinations were completed. Researchers there were unable to determine the causes of death.
About 680 dead rats were washed onto North Beach on November 9 and 10.
All the rats were buried following advice from West Coast Regional Council.
A Department of Conservation spokesperson said the bodies were tested for 1080, but not other substances.
"We had hoped that the pathology result would provide some more information about how the rats died," they said in a statement.
"The possibility of 1080 as a cause of death of the rats was raised, and as operations had occurred in catchments that have had 1080 treatment that could have possibly led to the rats on the beach, and because of the public interest in this matter, this was the toxin that was tested for.
"The cause of death is unknown – but the deaths are not a result of 1080 poisoning."
Other animals were also washed up with the rats, including an octopus, starfish, a calf and a large amount of fish.