The Yellow-eyed Penguin Trust, with support from Ngāi Tahu and the Department of Conservation (Doc), returned to Stewart Island for just the third comprehensive survey there since the turn of the century.
Preliminary results found 39 nests, or 20% of the 1999-00 numbers.
The results could indicate more than 200 yellow-eyed penguins, or hoiho, had disappeared from the area over the past two decades.
There were 153 nests in 2008-09 and 186 nests in 1999-00.
Trust general manager Sue Murray said while the decline mirrored what had been documented on the mainland over the same time period, it was a stark and confronting picture for the species.
The findings highlighted the importance of studying how the birds fared while foraging at sea, for which very little data was available around Stewart Island, she said.
Ngāi Tahu and Doc alongside the trust today released the season’s mainland hoiho numbers which estimated a minimum 178 breeding pairs on the coast between Oamaru and Curio Bay – 10 more nests than last season.
North Otago had a notable 15% increase in numbers, a statement from Doc said.
In 1999-00 on the mainland there were nearly 500 estimated nests.
After plummeting in 1990-91, yellow-eyed penguin numbers on the mainland peaked in the late 1990s with more than 600 nests on the mainland.
Some experts have predicted the birds would be locally extinct on the mainland by 2050.
The statement from the Department of Conservation today said the birds faced a range of threats both on land and at sea.
This year in particular, the birds had experienced ongoing issues with diseases such as diphtheria and an emerging unknown form of lung congestion affecting chick survival.
To reverse the population decline, Ngāi Tahu, the Yellow-eyed Penguin Trust, Doc, and the Ministry for Primary Industries released a recovery strategy and five-year action plan for the birds in August.
Priorities in the plan focus on managing human activities and disturbance and reducing impacts in marine and terrestrial habitats.
Breeding pair numbers:
- Banks Peninsula – 3
- North Otago – 47
- Otago Peninsula – 76
- Catlins – 55
- Rakiura – 39