The country's biggest and most important fishery is in serious trouble.

Skippers fishing in the West Coast hoki ground are struggling to catch the fish, and say they're no longer there in large numbers.

As a result, the industry has decided to voluntarily give up millions of dollars' worth of quota.

Hoki earned New Zealand $61 million in exports this year. It's what you've probably been served at your local chip shop, and it's used in McDonald's Fillet-O-Fish burger.

But there's a problem in the biggest hoki ground on the West Coast, says Te Ohu Kaimoana (Māori Fisheries Trust) chief executive Dion Tuuta.

"What industry skippers are noticing is that in one area in the West Coast, the fish are not turning up in the numbers expected."

There are five hoki grounds in New Zealand. Four are still fishing well, according to the industry - but the massive West Coast fishery is not, prompting all the big players to cut the quota there by 22 percent.

"This is a significant undertaking by the industry," says Mr Tuuta. "It's going to cost them millions."

There's another undertaking - fishing during spawning periods, or in areas where juveniles are, will stop.

Newshub understands the NIWA vessel Tangaroa recently surveyed hoki grounds and also found problems.

Greenpeace executive director Russel Norman says the fishing industry only has itself to blame.

"I reckon they've just collapsed the fishery, and now they've got to respond to the fact that they've caused such immense destruction to the fishery that the amount of fish they're catching is going down."

Te Ohu Kaimoana, which represents iwi fishing interests, thinks it could be due to climate change.

"We have noticed some warmer water temperatures this season, but we are waiting for the science to catch up and tell us what is going on out there," says Mr Tuuta.

Forest and Bird's Kevin Hackwell says the fishing industry must take climate change seriously.

"All the signs are that we will carry on having even higher and higher temperatures with climate change, which means that over time, the hoki fishery may actually disappear.

"It's a real worry, so it's good the fishermen are responding now."