Final answer:
The leading cause of death at sea was illness, specifically infectious diseases. Slave ship captains were constantly fearful of illness as every person who died reduced their profit.
Step-by-step explanation:
The leading cause of death at sea was illness, specifically infectious diseases. The close quarters of slave ships allowed for the rapid spread of diseases such as trachoma, which left victims blind. Slave ship captains were constantly fearful of illness as every person who died reduced their profit.