With mortality rates high and birth rates low among Jamaican slaves, white plantations depended on the continued importation of slaves from Africa; one-third of all slaves brought to the New World on British ships went to Jamaica. The death rate was so high that 500,000 slaves had to be imported to increase the island's slave population by just 250,000. The mortality rate for white Jamaicans was nearly as great, and more than a third died from tropical diseases within three years of their arrival. While the black slaves and white planters died in large numbers from diseases and illnesses, the free towns of the Jamaican Maroons experienced large increases in population.