Seasonality in the Trans-Atlantic Slave Trade

Trans-Atlantic pathways and harvest cycles

African and Atlantic coastal markets exhibited varying seasonal patterns in the numbers of slaves exported and imported. In the most seasonal slaving markets in the Atlantic world—Senegambia in Africa and the Chesapeake in the Americas—rainfall and temperature constraints reduced the number of “in crop months” and narrowed merchants’ trading windows. Comparatively few enslaved Africans shipped from northwest Africa between rainy July and November; Virginia and Maryland planters purchased most of their new agricultural workers between April and October. In Upper Guinea markets, most captains began sailing the Middle Passage in the North Atlantic spring, a time of the year that would place them in American markets in the North Atlantic summer. Strong links between Upper Guinea and the Carolinas-Chesapeake occurred because trans-Atlantic agricultural cycles meshed.

Captain Robert Doegood’s voyage on the Arthur in 1677-78 reached slaving markets in Africa and the Americas at the end of in-crop seasons, making this voyage atypical of those sailing from the Bight of Biafra to the West Indies. In the century prior to the American Revolution, British vessels departing Biafran ports in March or April often attempted to reach the in-season summer North American slaving markets rather than risk uncertain demand in out-of-crop Caribbean colonies. After May, with each passing month they decided increasingly to sell slaves in the British West Indies. Northern planters infrequently purchased enslaved Africans shipped from the Bight of Biafra’s fall provisioning-slaving season (Figure 3).

French and Portuguese slave traders also shifted agricultural workers between trans-Atlantic harvest cycles. Cap Français, the largest French West Indian port and the principal disembarkation center for French slaving vessels in northern St. Domingue, has the island’s rainiest October-February winter; the greatest number of enslaved Africans, correspondingly, arrived in the dry April-June quarter. In southern St. Domingue, the dry season occurs earlier, in December-February, the harvesting months and time of increased planter demand for labor. Whereas northern St. Domingue drew upon Senegal’s January-April provisioning-slaving season, French planters in the south purchased comparatively more Africans shipped overseas during the September-December provisioning-slaving seasons in the Bight of Biafra. In the late 1700s, the Portuguese resettled trading posts in coastal Guinea-Bissau, a staple rice region with a marked November-April provisioning-slaving season. Captains purchased enslaved Africans during these months to work in the May-July Maranhão rice season.