An environmental advocacy group says the Government needs to do more to hold the fishing industry accountable after an error highlighted significant bycatch issues.

The Ministry for Primary Industries confirmed that 39 dolphin captures reported in December last year were actually a coding error. Two months later, it admitted the slip-up and the species caught was actually petrels.

Forest and Bird spokesman Geoff Keey said it was "hugely concerning" no one at the ministry or the fishing company involved seemed to notice or react at the time of the incident.

"Swapping dead dolphins for dead seabirds is no great relief for Forest and Bird," Keey said.

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"Those three incidents in 2017 were equivalent to a 20-fold increase on the previous annual average of dolphin captures, yet neither MPI or the fishing company noticed anything was out of the ordinary," Keey said.

He questioned why the ministry did not investigate immediately.

"If a camera had been on this boat, MPI could have reviewed the footage, and the mistake would have likely been caught much earlier. This is yet another reason for the Government to commit to cameras on commercial fishing boats."

A ministry spokeswoman said the dataset the information came from was based on reporting provided by commercial fishers and was used to inform fisheries management decisions.

"MPI acknowledges that this incident should have been investigated, even though in retrospect the data was found to be wrong.

"We are ensuring that processes are in place so that incidents like this are investigated promptly. In the longer-term integrated electronic reporting will provide more up-to-date information that can be acted on more quickly.

"Forest and Bird was informed of the coding error by the business involved in December (almost immediately after the data was provided to Forest and Bird by MPI) who acknowledged having provided the inaccurate data in the first place."