It's been an exceptional year for the whio, or blue duck, in Northern Fiordland, with 64 breeding pairs counted at an intensively managed 'security site' this year. 

Department of Conservation (DOC) Te Anau senior biodiversity ranger Andrew Smart said it was the first whio security site in the South Island to exceed its target of 50 breeding pairs. 

The 64 breeding pairs followed the record breeding season of 2017/18, which produced 107 whio ducklings.

"We went from 48 pairs at the end of last year to 64 when surveyed at the end of this year," Mr Smart said. 

"Whio have come a long way since 1999/2000, when only three pairs were found in the area."

The blue duck/whio is only found in New Zealand and is rarer than some species of kiwi. There are eight so-called whio security sites across New Zealand, which are intensively managed to protect their numbers. 

Mr Smart attributed the strong comeback of blue ducks in Northern Fiordland to extended trapping efforts and landscape-scale predator control in the security site, which covered the Worsley Stream, Castle River, the Clinton (West and North Branch and main Clinton), Neale Burn, Arthur River, Joes River, Sinbad, Tutoko River, Gulliver River, and the Cleddau River. 

This work was principally supported by Genesis Energy as well as Air New Zealand and other community partners.

The next closest security site in the South Island is on the Taipo River near Hokitika, which has a total of 36 breeding pairs.