North Carolina Crayfishes 113 



THE HYDROLOGIC UNITS AND THEIR CRAYFISH FAUNAS 



Seventeen major river basins generally are recognized within 

 North Carolina (Heath et al. 1975:152). All of them include smaller 

 hydrologic units, some of which are autonomous drainage systems 

 within the State. All but five of the major river basins lie within the 

 huge drainage of the Atlantic Ocean, and flow generally east and 

 south to empty into broad, saline estuaries and sounds of the ocean. 

 The exceptions are (1) the Hiwassee, Little Tennessee, French Broad, 

 and Watauga rivers, which drain north and west into the Tennessee 

 River, and (2) the New River, which drains north and west via the 

 Kanawha River into the Ohio River. These western North Carolina 

 waters ultimately flow into the Mississippi River drainage of the Gulf 

 of Mexico. In North Carolina, the west-flowing and east-flowing 

 montane headwaters of river systems are separated by the Appalach- 

 ian (Eastern Continental) Drainage Divide, represented in the State 

 by the Blue Ridge physiographic province. 



The Waccamaw River and its tributaries, along with Lake 

 Waccamaw, are recognized as a hydrologically and faunistically 

 distinctive drainage unit by some biologists (see Bailey 1977: 

 269, 273; Shute et al. 1981:18-22), and are so treated here. Another 

 hydrologic unit, the Northeast Cape Fear River, probably also should 

 be considered an autonomous drainage system, because it does not 

 join the Cape Fear River until it reaches the estuary at Wilmington. 

 In addition, the Northeast Cape Fear is faunistically distinct, apparently 

 lacking over a dozen species of lowland freshwater fishes found 

 in the Coastal Plain portions of the Cape Fear itself (Rohde et 

 al. 1979:114-115: Menhinick 1991). The Northeast Cape Fear also 

 lacks two crayfish species found in the lower Cape Fear, but has one 

 species that is absent from the Cape Fear (see below). Historically as 

 well as faunistically, the Northeast Cape Fear appears to have more 

 in common with the New (White Oak) drainage system than with the 

 Cape Fear. During the Pleistocene, when sea level attained its 

 highest stand (as indicated by the Surry Scarp, which marks the marine 

 terrace formed by the Wicomico Sea), much of the southeastern 

 Coastal Plain of North Carolina was covered by the ocean (Rohde 

 et al. 1979:113, 116). This inundated area included today's New 

 (White Oak) River drainage, most of the Northeast Cape Fear, and 

 part of the lower Cape Fear. The early coastal Cape Fear and North- 

 east Cape Fear basins were at that time broadly separated, and they 

 are still separate systems today. 



