It confirmed its support for a report on the issue prepared by Oamaru Blue Penguin Colony science and environmental manager Dr Philippa Agnew, which recommended a prohibition on fireworks within a 3km radius of the harbour.
And the department asked that it be consulted by the council or event organisers for any similar future events in the area.
"The evidence shows that this type of display causes an unacceptable level of disturbance to wildlife in the harbour area and that future events of this nature should be prohibited or face prosecution under the Wildlife Act 1953," a December 10 letter to council recreation manager Erik van der Spek from DoC Geraldine district operations manager Duncan Toogood said.
"There's an increasing issue with what's meant with the Wildlife Act,'' Kircher said last week. ''And the response has been that it's not quite as strict as some people have been interpreting it. In this case we had decided already 'Let's look at alternatives [to fireworks this year]'."
"We do need to look at how we deal with things in the future, because we don't want to have to stop everything people might enjoy around town. We need to understand the effects and actually what the legislation says."
He said the last time Oamaru hosted New Year's Eve celebrations at Oamaru Harbour, in 2017, the fireworks display had been smaller and less "percussive" than the Oamaru on Fire's event.
Dr Agnew was approached by both Oamaru on Fire organiser Anton Roswell and the council before Oamaru on Fire and while Dr Agnew said there was anecdotal evidence of the effects of fireworks at the harbour on seabirds, from a Te Papa seabird specialist visiting Oamaru during 2017's Chinese New Year celebrations, she had no reason to deny the permission the event organiser and the council sought.
But she informed both the council and the event organiser she would look into the effects on the birds during the event.
The video, she said, provided clear evidence of disturbance of the protected species.
"If the birds just ran around on the wharf and then settled ... we may have been able to live with that," Dr Agnew said. "But the fact that every single individual shag abandoned the wharf and entered the water, I was really surprised. I didn't expect it. It was awful to watch."
DoC informed the council it would not pursue the matter with the Oamaru on Fire organiser, but that a breach of the Wildlife Act of this nature could incur a prison term of up to two years, a fine of up to $100,000, or both.