Almost 400 dolphins have been caught and killed by commercial fishing vessels in the last 20 years, according to new statistics.
Since 1996, 310 common dolphins, 21 dusky dolphins, 21 undefined dolphins, 16 pilot whales, 12 Hector's dolphins, nine bottlenose dolphins, five orcas and one Risso's dolphin have died after they were caught as bycatch.
The figures were released to the Herald by the Ministry of Primary Industries.
Trawling caught the most with over 80 per cent meeting their death this way.
Former skipper Gary Morris said 20 years ago it was easy to see thousands of common dolphins in the Bay of Islands. Now you're lucky if you see two dozen.
"You'd be travelling in one direction and they'd be coming past you in the other direction. They'd take half an hour to get past you there were that many of them.
"Those days have gone."
The worst year was 2014 where 54 dolphins were reportedly killed - that's more than one a week.
Morris said the amount of dolphin bycatch in the fishing industry kills is "staggering". The ex-skipper is involved in Fish Forever, a group campaigning for marine reserves in the Bay of Islands.
"There must be bloody more.
"Dolphins very conveniently don't float like fish, they sink straight to the bottom when you kill them."
Kiwi champion freediver William Trubridge penned a letter in January to the fishing industry calling for more protection for New Zealand's endangered dolphin species
Trubridge wrote that in the DoC Incident Database, between 2000-2006 less than one per cent of dolphin bycatch is reported by fishermen or independent observers.
"So the dolphins aren't fully protected, bycatch is definitely continuing, at a rate greater than what is reported, and fishing will eventually render the [Maui's] species extinct."
Trubridge urged fishermen and conservationists to unite. He suggested a move to sustainable fishing methods. If that resulted in less jobs, the Government should help fishermen into new roles and give them compensation as a solution, he said.
MPI spokesman Dave Turner said 8319sq km of sea is closed to trawl nets and more than 15,000sq km is closed to set netting to protect the Hector's and Maui's dolphins.
Turner said MPI is not aware of false reporting of dolphin captures.
"Fishing rules are in place to minimise the chance that fishers will capture dolphins. It is not an offence to accidentally capture a dolphin. It is however, an offence to fail to report any captures."
Last year it was revealed a fishing vessel hauled in two Hector's dolphins in 2012 but only reported one death, in breach of mandatory reporting requirements. No action was taken against the unnamed captain.
MPI said the two-year deadline for a prosecution over the unreported dolphin death had passed.
MPI is currently trialling a camera system that will allow it to directly monitor fishing activity on board all commercial fishing vessels. This will allow "verification and audit of fishers reporting of bycatch and discards," Turner said.
"It will ensure that being out of sight of land does not mean being out of sight of MPI."
A Seafood New Zealand spokesperson said no dolphin death is acceptable.
"The industry takes the death of any protected species seriously and is constantly working to find ways to further mitigate this. Examples include codes of practice around deploying and retrieving fishing nets and developing new trawl technology to reduce risk.
"In addition, many legislated closures exist to reduce the risk of capture.
"The industry also supports independent observers on board vessels to record any variance with good practice.
"When a dolphin is inadvertently caught by a commercial vessel the crew has a mandatory obligation to report that catch to authorities and return it to the sea."