Their main threat is from fishing activity, and this would be reduced with widespread training to mitigate seabird bycatch, along with improved monitoring that would include the use of cameras.
"The black petrel is special to the Hauraki Gulf and we want to make sure that seabird smart practices are the norm for anyone fishing on the gulf, whether commercial or recreational fishers," said Janice Molloy, convenor of the Southern Seabird Solutions Trust.
Ms Molloy, who was among 50 people at a formal signing of the pledge at Leigh, north of Auckland, said there was "a lot of work ahead" to increase the numbers of black petrel, and a collaborative approach was the "best way forward".
Forest and Bird seabird conservation advocate Karen Baird saw the new collaboration as "crucial to making long-lasting and effective change in the fishing industry".
Ms Baird said conservation and industry groups had been taking "swipes at each other for years.... but we are now sitting around the table and all agreeing".
She hoped the model could be copied in other fisheries in New Zealand and overseas as a way to protect seabirds like the black petrel.
Seafood New Zealand chief executive Tim Pankhurst said the industry saw value in collaborating to find long-term solutions for protecting marine wildlife.
The working group's efforts, Mr Pankhurst said, were "a tangible demonstration of how organisations, often with differing interests, can work together in a positive and proactive way".
The pledge comes ahead of Forest and Bird's upcoming Bird of the Year campaign, which this year focuses on seabirds.
The campaign, which opens on Monday, encourages Kiwis to pick a seabird to promote by way of posters or videos, with voting to close on November 24.
The campaign has so far drawn the support of New Zealand First leader Winston Peters, who has chosen the Buller's shearwater, and United Future leader, who is backing the Northern royal albatross, or toroa.
Participants will be able to select their birds from next week at the website www.seabirdoftheyear.org.nz