The country's largest Maori-owned fisheries company regrets losing a large load of fish overboard that later washed up along kilometres of shoreline, it says.
A video posted on social media suggests dead snapper were left strewn along 6km of beach at Muriwai, west of Auckland.
Aotearoa Fisheries said a boat contracted to it was hit by three large waves in bad weather on Monday night near South Head in Kaipara Harbour.
Chief executive Carl Carrington said half a tonne of fish was lost in the 4m swells, and the vessel suffered considerable damage.
"It's certainly a loss of fish... we never like to see any sort of wastage, but in this particular situation we're very pleased we didn't lose any crew over the side, along with the fish.
"It was a very dangerous situation," he said.
Mr Carrington said there were no weather warnings on the night but conditions deteriorated quickly, with the three crew left "quite frightened" and describing it "like being in a washing machine".
He said waves came over the back of the William Rose and damaged its decking as a bag was being hauled on to the trawler.
"It's not uncommon for weather on the west coast to pick up and change quite quickly out there, that's the nature of fishing. We're talking an industry where they are out in the elements."
Mr Carrington said the 500kg of fish equated to about 500 fish lost overboard.
It was "certainly not a case of dumping", and the loss would be included in the company's quota, he said.
The Ministry for Primary Industries has been investigating the incident.
