Twenty-three fur seals, including eight pups, have been clubbed to death at a New Zealand breeding colony that was re-established two decades ago after the species was nearly wiped out by hunting. Some of the pups were just days old.

New Zealand's minister for conservation, Kate Wilkinson, appealed to the public to help track down the attackers. "To go around and club 23 seals to death over a number of days is very deliberate and you have to question the state of mind of someone who can carry out such a cruel and abhorrent attack," she said.

The Ohau Point seal colony on northern South Island is a popular tourist spot north of the town of Kaikoura, which is an international whale-watching centre. The department of conservation said the attacks took place over two weeks. The location may have delayed the discovery.

The colony stretches about 1.2 miles (2 km) along the coast and is at the bottom of a steep, 100ft (30m) cliff with no easy access, said department spokesman Rory Newsam.

Millions of fur seals were clubbed to death by hunters in the 1800s, but the hunts ended because of a drastic drop in numbers that raised fears the seals could be wiped out. The seals are not native to New Zealand.

The Ohau Point colony was reoccupied for breeding in 1990, and about 600 fur seal pups were born there in 2004, said Bruce Robertson, a seal specialist and senior lecturer in zoology at Otago University.

He said the long-term losses for the population could be dire. The attacks killed 13 breeding females, which meant 13 pups dependent on their milk would die and fewer pups would be born next year.

"Given this colony is increasing in size, this loss of life is a small setback," he said Monday. "However, large mammal populations cannot sustain the repeated loss of breeding females [and] any external influences can be detrimental."

Other live seals at the colony had been seen with injuries from the attacks, the area's conservation manager, Dave Hayes, said. The weapon used was a bat or club.

Under New Zealand law, killing or harming fur seals or other marine mammals incurs up to six months in prison or a fine of up to NZ$250,000 (£121,000).

A further fine of up to $7,600 for each marine mammal killed or harmed can also be imposed by the court.