At the start of last season, there were 227 nests counted on mainland New Zealand, which includes Stewart Island and Whenua Hou/Codfish Island.
That was down from 261 two years earlier.
Conservation Minister Eugenie Sage at the weekend released a draft recovery strategy for the species along with a five-year action plan, created with Ngāi Tahu, the Yellow-eyed Penguin Trust and Fisheries New Zealand.
It promised an extra $220,000 over three years towards the animal's conservation.
Mattern hoped in the future more focus would be placed on marine threats to the birds, which had been neglected in the past.
This involved rising sea temperatures, food shortages and set netting.
The strategy promised to "turn around the fortunes" of the endangered animal, but Mattern said he "had his doubts" about this on the mainland.
The next hope were populations on the subantarctic islands, the numbers of which were largely unknown, which did not have mainland threats such as dogs and set nets.
Penguin Place manager Lisa King said Mattern's numbers were "probably quite right".
The centre had 304 individual birds through its rehab centre last season, out of a total estimated mainland population of 700. Its recent average was 100 annually.
"The population is in big trouble. It is depressing, but there's only so much you can do."
The strategy was left "far too late", she said.
"We'll need a lot of luck."
Penguin Place rehab manager Megan Abbott said while there were a range of reasons for the penguins coming to the facility, the most common was starvation.
Yellow-eyed Penguin Trust executive officer Sue Murray said the trust was putting more resources into the Catlins, Stewart Island and its own reserves for early disease management to help the penguins.