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Researchers are running a kind of tag-and-release programme on rats in remote Fiordland to estimate their numbers and improve conservation efforts.
Just over 900 rats have been live-captured in the 14 months since the project began.
In that time some of the highest densities of rats on the New Zealand mainland have been recorded.
Dr Jo Carpenter is a postdoctoral researcher at Manaaki Whenua.
She speaks to Corin Dann.