The Department of Conservation (DOC) says it is appalled that a second sealion, the mother of the juvenile sea lion found shot at the end of last month, has also been found shot dead in Catlins.

At the end of September, DOC said a baby sea lion had been shot and left to die a slow death in the Catlins Estuary.

The pup's mother, named Jade, was found dead on Tuesday night about 100 metres from where the pup had been found.

She had begun to decompose, and it is believed she washed up there during the recent flooding.

DOC Southern South Island operations director Aaron Fleming said shooting a sea lion was an appalling thing to do and completely unacceptable.

He said sea lions were a protected species and it was a serious offence to intentionally injure or kill one.

"It goes without saying these kinds of incidents must stop," Fleming said.

"Most people will be deeply disgusted by this sort of behaviour against a protected species and the DOC team is genuinely shocked.

"It is a tragedy both mother and pup have been shot. DOC staff are determined to find the person responsible and urging the public to contribute any information which may help the investigation."

DOC said it was a major setback for the species' Southland population, where only seven pups were born this year. Sea lions began breeding in the Catlins again in 2006 and today there are just 12 breeding age females in the local area.

Fleming said they did not know when, where or why the sea lions were shot, and any information could help.

The NZ Sea Lion Trust is offering a $6000 reward for information leading to a successful prosecution.

NZ Sea Lion Trust co-chairperson Shaun McConkey said it was important to remember that the sea lions were taking fish to feed themselves and their young, not just for recreation or enjoyment.

"Sea lions were wiped out on the mainland by human hunting, 250 years on and we're still doing the same thing. The killing of a breeding female is a devastating loss to a small population that has only recently returned to the area."

Fleming said a local vet performed an x-ray and examination and found about 50 shotgun pellets. Some of these will be forensically tested to see if they match the pellets found in her pup.

"She was lying down and facing away from the shooter, with most pellets entering her chest and spine."

Jade was born under a crib at Kākā Point in 2016, and was named after the late son of the bach owners.

Under the Wildlife Act, it is illegal to injure or kill protected native wildlife like sea lions and anyone who does so can face punishments of up to two years imprisonment and/or a fine of up to $250,000.

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