From The Penguin History Of Latin America, by Edwin Williamson (Penguin, 2003), Kindle pp. 172-173:
In practice, the royal legislation concerning the enslavement of Indians was ignored virtually in its entirety by the Portuguese in Brazil. The hunting of Indian slaves was to continue throughout the colonial period. However, the nature of slave-holding in Brazil underwent a slow but eventually decisive change after about the middle of the sixteenth century. Indians along the coast were becoming scarce: as hostilities between settlers and natives grew fiercer, tribes withdrew into the hinterland; at the same time diseases started to thin their ranks. The available labour force was drastically depleted, intensifying the competition between missionaries and planters for Indian manpower.
An obvious solution lay in the importation of African slaves to work on the Brazilian plantations. The Portuguese had been operating a slave-trade along the African coast for nearly a century, and they were splendid mariners, so there was therefore no impediment to extending the trade to the New World. Even though African slaves were more expensive than Indian, there were two distinct advantages to the owners: the Africans had the same immunities to viral infections as the Europeans, and they were reputed to be better suited to the kind of hard labour required on the plantations. The demand for labour in the burgeoning sugar industry of Brazil was to lead to an enormous expansion of the African slave-trade (and demand would grow a few decades later in the 1580s when planters in the islands and coastal areas of the Spanish Indies began to seek a replacement for vanishing Indian manpower).
How many slaves were imported into Brazil is not reliably known, and what figures there are remain in dispute, but it is clear that the numbers were very high. By the end of the sixteenth century there may well have been between 13,000 and 15,000 black slaves in Brazil, constituting some 70 per cent of the labour force on the plantations. The white population of Brazil in around 1585 has been estimated at 29,000. During the first half of the seventeenth century about 4,000 slaves a year were imported into Brazil; from about 1650 to 1680 this figure rose to about 8,000, after which it began to tail off. In the eighteenth century the volume of imports began to increase once more when the gold-mining industry pushed up overall demand – Bahia alone received some 5,000 to 8,000 slaves a year. In the north-east as a whole slaves made up about half the population – over two-thirds in the sugar-growing areas. So many were imported partly because the mortality rate of the black slave population was so high and because its rate of procreation fell consistently below the level of replacement – an index of the tremendous demoralization and physical strain that afflicted the slaves. Philip Curtin estimates that in the course of the seventeenth century Brazil took a 41.8 per cent share of the total number of slaves transported to America.
The arrival of Africans in such huge numbers was to add a new demographic dimension to the Portuguese colonies in the New World. Since such a great part of the population was non-white, race mixture soon produced, as in the Spanish Indies, very many people of intermediate ethnicity – mulattos or pardos (white-black), mamelucos or caboclos (white-Indian) and cafusos (Indian-black). Brazil would become an extremely colour-conscious society, and racial features were an important element in social ranking and cultural identification. The inescapable reality was that the sugar economy, as created in the middle of the sixteenth century, made slavery a founding fact of Brazilian society.