New Zealand’s role in the Pacific slave trade is "a dark piece of our history" that is often overlooked, Pacific researcher Scott Hamilton says.

Dr Hamilton says the idea that New Zealand was involved in the slave trade conflicts with our image of ourselves.

He told Sunday Morning that in the 1870s, Pacific Island slaves worked in New Zealand flax mills and on the estates of some our wealthiest citizens.

“We think of ourselves as the good guys and it’s the Australians and the Americans that had slavery, ‘we didn’t do any of that’.

“But as I’ve discovered, we did. And it’s a dark piece of our history but I think it is worth remembering.”

In his book The Stolen Island: Searching for ‘Ata, he tells the story of a slave raid by New Zealand and Tasmanian sailors on the isolated Tongan island of 'Ata in 1863 where nearly 150 people were stolen for sale in the slave market in Peru.

‘Ata is a tiny island – roughly 1.5 square kilometres - about 150km south of Tongatapu, the main island of Tonga, he says.

Settled by Tongans in the 1600s, it is surrounded by high cliffs, battered by wild seas and has almost no reef.

Photo: Supplied

“And despite all of [those] odds in this incredible tough environment they created a thriving society, Dr Hamilton says.

“[But] this was all destroyed in the first week of June 1863 when a man named Thomas McGrath brought a ship up from New Zealand with a mixed Tasmanian/New Zealand crew.”

McGrath had had some previous successes as a whaler, although he had wrecked several boats, and had decided that taking slaves would be more profitable than whaling – which was in decline because of over-exploitation.

About 150 ‘Atan men, women and children had swum out to greet the ship, and they had been invited below deck to either view merchandise for trading, or to share a meal – the accounts vary.

“And they don’t get back on the deck. He battens down the hatches and the ship sails away,” Dr Hamilton says.

“He [then] sailed to the north of Tonga to the island of Niuafo’ou where he took 30 men, and then he sold the lot of them to a slaver who took them to Peru.”

Peru was the notorious centre of the Pacific slave trade at the time. But just as the ‘Atans arrived, pushback from the clergy, revolts on the islands, and internationally pressure had led to the Peruvian government rescinding the law legalising slavery.

Instead of being sold on, the ‘Atans were kept in a dank warehouse at the port with other Islanders awaiting repatriation. Then smallpox arrived, spreading quickly through the warehouse, killing many.

Dr Hamilton says McGrath was never tried for the slave raid, but he did face justice for thwarting customs after he returned to Stuart Island with illicit, undeclared, cargo.

During this trial he denied taking part in the slave trade saying he was just ferrying islanders around, which elicited laughter in the court, which did not believe him

‘He never faced justice for what he did really,” Dr Hamilton says.