The economic importance of exports later declined with the drop in production of the American precious metal mines, such as Potos.[19] However, the growth in trade was strong in the early years. Numbering 17 ships in 1550, the fleets expanded to more than 50 much larger vessels by the end of the century. By the second half of the 17th century, that number had dwindled to less than half of its peak.[20] As economic conditions gradually recovered from the last decades of the 17th century, fleet operations slowly expanded again, once again becoming prominent during the reign of the Bourbons in the 18th century.[21]