From Tuesday, a new class of fishing boats must have cameras fitted to film their catch and release methods.
All commercial surface longline boats will require cameras as part of a $68 million government programme to improve bycatch reporting over four years.
Otago University zoology professor Bruce Robertson said government data showed consistent underreporting of fishing bycatch for New Zealand sea lions, fur seals and common dolphins.
"Cameras are a good tool to ensure bycatch is properly reported, which is a requirement under New Zealand fisheries law. It is not illegal to incidentally kill a marine mammal while commercial fishing in NZ waters so long as it is reported," he said.
"We can only have so many government observers on vessels, and they can't be awake 24/7 - some of these boats are operating around the clock."
Marine wildlife conservation organisation, Sea Shepherd NZ, filed legal proceedings in the United States in 2022 to "try [to] protect the Māui dolphin" from certain fishing methods.
It saw a preliminary injunction on the export of nine species of fish to the US caught using inshore trawling and set net methods on the west coast of the North Island.
The fishing industry has been consulted on the staged camera rollout, which began last August and will cover an estimated 85 percent of commercial inshore catches once it is completed in February 2025.
But Robertson said the government had missed a big opportunity by not covering deepwater fishing practices.
"With these fishing vessels, in the past, there has been issues with compliance with laws, for example, we have seen vessels disregard labour laws. Given the labour laws were ignored, it is reasonable to ask whether the reporting requirements for fishing bycatch are being followed," he said.
"Without cameras on vessels to record marine mammals' bycatch and consistent underreporting, we do not have a good understanding of the risk [commercial fishing poses] to marine mammals.
"New Zealand prides itself on being a leader in sustainable fishing practices and our seafood is marketed as sustainable to international markets...cameras are an important way to demonstrate this," Robertson said.