Police say they have identified four teenagers they allege were responsible for fatally shooting a leopard seal at a Northland beach.

Acting Sergeant Willie Paniora from Dargaville Police said on Wednesday the teens, two aged 16 and two aged 15, had been referred to Youth Aid in relation to the incident.

"This matter was very upsetting for the community and we hope that this update will provide the public with some degree of reassurance."

The seal was shot in the face near Glinks Gully, Northland on July 24 with what Department of Conservation operations manager for the Kauri Coast, Stephen Soole believed was a rifle.

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The dead seal was found by local Shane Searle, who took a video.

"I just couldn't believe someone would do this, especially when I saw it the day before and the leopard seal was majestic sunbathing and doing no harm."

Paniora thanked the Dargaville community for the help they provided during the search for those involved.

"We hope this serves as a notice that we will not tolerate this type of cruel and reckless behaviour."

How the teens got hold of the firearms used to shoot the seal was not yet known but police said "they were looking into it".

While leopard seals mainly live in Antarctica, the animals often spend up to a year or more in New Zealand waters.

The seals are protected under the Wildlife Act and the Marine Mammals Act, and those harming them face up to two years' imprisonment and fines of up to $250,000.