The study of fish dispersal in the central Appalachians is a perplexing problem to ichthyologists who often must rely on geological literature to determine past drainage relationships. Many classical geomorphological treatments of drainage history and evolution are often dated (1884–1934), and controversial as well. Biogeographers sometimes make conjectures about past drainage relationships on the basis of present species distributional patterns even though complementary geological data are lacking. In view of that, it has been stressed that Zoogeographic conclusions regarding past drainage patterns are best based on facts supported by a combination of geological and biological evidence (Hack, 1969; Ross, 1969).
Stream piracy (or capture) is a mode, of drainage rearrangement and divide migration that may be initiated from various geological processes—for example, uplift, faulting, glaciation, folding, volcanic activity, and the like. In a capture, an entire section of stream may be diverted from one drainage to another. Physical features that frequently contribute to this phenomenon are a combination of steeper gradient, softer substrate, higher discharge, and lower elevation of the pirate stream (Bonnett, 1977). Geological criteria for establishing a stream piracy include elbows of capture, barbed tributaries, abandoned channels, wind gaps, and large valleys occupied by small streams. With a piracy, intradrainage or interdrainage transfer of biota is facilitated. However, it is expected that the pirate stream receives more species from the captor than it delivers (Jenkins and others, 1972), unless the fauna of the captured stream is depauperate. Efficiency of faunal dispersal may be related to the physical conditions associated with stream captures and the amount of time the pirate and captive streams are in contact.