Answer:
Many ships of these trades had other hidden agendas, like blackbirding and slave trading.
One example of this is captain Thomas James McGrath of the Tasmanian whaler Grecian, In June 1863 he reached 'Ata and invited people on board for trading, when at least half of the population, at least 144 people, was onboard he locked the compartments and the ship departed from the atoll. These people never returned to their homes.