FREE BLACK SLAVE CATCHERS?

I was shocked to read of “free black slave catchers” in Louisiana along the [Mississippi River’s] “east bank above New Orleans, on the “German Coast”, where there were “dozens of slave labor camps [that] stretched back from the river into French-surveyed ‘long lots’, narrow strips of land that ran a mile or two across cleared ground to a dense belt of forested swamps....The swamps themselves were almost impenetrable , full of alligators, snakes, panthers , and bears . Runaways sought refuge in the swamps, hiding from overseers and free black slave-catchers .” P. 56-57, “Heads,” THE HALF HAS NEVER BEEN TOLD (2016) by Edward E. Baptist. I do not recall ever reading of “free black slave-catchers” in America, only in Africa. But I will read on!