Within this market, the demand for prime-aged slaves, given by the ages 15–30, accounted for 70 percent of the slave population relocated to the Deep South. However, due to the fact that the ages of slaves were often unknown by the traders themselves, physical attributes such as height often dictated demand in order to minimize asymmetric information. With slaves moving further south through the slave trade, conditions and treatment of slaves were understood to decline as they moved further south. In comparison to working in relatively small groups and perhaps alongside some farming families in the Upper South, they were forced to do field work in large gangs under close white supervision, and had less control over their time. The dense trees and underbrush of many riverfront areas in Louisiana and Mississippi were being cleared for the first time to develop plantations, adding to their struggles.