Commercial fishers operating off Auckland's coast around vulnerable seabirds are twice as likely to report accidentally capturing them when cameras are on board.

That's according to a trial where bottom-longline fishers voluntarily carried cameras on their boats to see how practices affected the nationally vulnerable black petrel - the species most at risk from commercial fisheries in New Zealand.

A Fisheries NZ report on the trial, over 2016/2017, found seabird captures on the pilot fleet, operating in the Hauraki Gulf and Bay of Plenty, was around twice as high when the vessels had cameras on board than when they were without cameras.

The findings come as Fisheries Minister Stuart Nash this month announced a further rollout of cameras aboard New Zealand's inshore fishing fleet to around 345 inshore vessels by 2024 in two tranches.

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The cameras are designed to monitor illegal by-catch - fish for which they do not hold quota, along with accidental deaths of marine mammals and/or seabirds.

It is not an offence to kill seabirds while fishing but it is an offence to fail to report catching them.

While Nash made it clear the cameras would be focused on all vessels operating in high risk areas, coalition partner New Zealand First expressed concern at the proposal, particularly the costs and privacy concerns for smaller vessels.

Forest & Bird chief executive Kevin Hague said the latest camera trial showed why cameras on boats were needed across the whole fishing fleet, including smaller inshore boats.

"This Hauraki trial shows why it's important that smaller inshore fishing boats must have cameras too.

"They are too small to take government observers, yet they are a big risk to coastal species like albatrosses, shearwaters, petrels, penguins, and dolphins."

The vessels that took part were also volunteers, and could be considered among "New Zealand's most responsible fishers", Hague said.

"Yet even then, the presence of cameras on board is enough to encourage them to report much more diligently, compared to when there is no camera."

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Studies in Australia had shown huge increases in reporting of captures when cameras were introduced.

When cameras were trialled on deep-water boats in Australia's tuna fishery, in which the boats were selected rather than volunteering, they were nine times more likely to report catching seabirds.

A Fisheries NZ report from January also found having observers onboard vessels targeting migratory species saw a ninefold increase in reporting of non-fish bycatch.

Nash made it clear in his camera announcement that through the rollout he expected improved verification of catch reports, including in black petrel habitats.

Hague said they supported the "risk-based" distinction of which vessels to target with cameras, but were concerned with comments from New Zealand First around exemptions for smaller boats.

New Zealand First's fishing spokesman Shane Jones told the Herald installation of cameras on fishing boats needed to be driven by a "robust business case".

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He had concerns about both costs, particularly for smaller vessels, and "mass surveillance of an industry".

"A business case needs to be brought back from the Ministry of Fisheries reflecting engagement with the industry, which is likely to have to bear the costs.

"In the post-Covid environment too, with a fishing industry with an aging workforce and vessels moving into a heavily regulated sphere, I doubt many in the industry will survive, certainly the inshore fishery on the West Coast."

The first tranche of cameras are planned to be installed on around 165 fishing vessels in high risk areas, including the habitats of Hector's dolphins, Antipodean and Gibson's Albatross, black petrels, and hoiho penguins.

The second proposed roll-out would involve another 160 fishing vessels, which operated in lower-risk areas but where protected species, such as fur seals, the common dolphin, flesh-footed shearwater, and Salvin's albatross, were still significant.

Vessels covered by both tranches primarily used trawl, longline, set net, purse seine or Danish seine fishing methods.

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The cameras would cover all inshore areas where fishing posed significant risks to protected species, and record activity on vessels responsible for about 84 per cent of the inshore catch, by weight.

While the capital and operating costs were difficult to assess, they were estimated to be around $40m to $60m over four years.

That would include research into new camera technology and digital monitoring developments.