72 Fred C. Rohde and Rudolf G. Arndt 



Pen, Green Briar, and Butler Mill branches, and several unnamed tribu- 

 taries. Its maximum length is 10.5 km (9.0 km straight-line) and its area 

 23.8 km 2 . The creeks are bordered by mature lowland forest of red 

 maple, Acer rubrum; American holly, Ilex opaca; green ash, Fraxinus 

 pennsylvanica; tulip tree, Liriodendron tulipifera; sweetgum, Liquidamber 

 styraciflua; black tupelo, Nyssa sylvatica; and sweetbay, Magnolia virgin- 

 iana; some upper parts, however, pass through agricultural fields. 



In the upper system the dominant creek substrate is mud and mud- 

 sand, and typical stream width and depth in spring are 1 m or less, and 

 some 20 cm, respectively. Gravel patches appear downstream and 

 become more common lower in the system. Greatest stream width is 7 m, 

 at a point below an impoundment (Craigs Pond) on lower Butler Mill 

 Branch. The uppermost waterways sometimes dry completely, and areas 

 just downstream of these form pools. Current and flow in the lower 

 system are strong all year. Storms often cause local creekside flooding. 

 Aquatic vegetation, consisting of several vascular species and filamentous 

 green algae, is local and often luxuriant. Rocks, usually prominent in C. 

 bairdi habitat, are absent. 



Coitus bairdi is found only in areas of permanent and pronounced 

 flow (Fig. 1). In its upstream distribution, C. bairdi is found only over 

 gravel patches, where concomitantly there is a stronger current. Creek 

 width here is often only 1 m, with depths to 5 cm. Patches are typically 

 about 1 m long and 0.3 m wide, comprised of fine gravel and sand, and 

 located several dozen meters apart. Cottus bairdi occurs but sparingly on 

 these patches. Gravel patches and C. bairdi are both progressively more 

 common farther downstream in Horse Pen, Green Briar, and Butler Mill 

 branches. Cottus bairdi is not found below or just above Craigs Pond, 

 although prior to impoundment it likely did occur in both areas. 



All preserved specimens and related data, unless otherwise specified, 

 were collected in a sampling area located in the downstream part of the 

 study area (Fig. 1), over and near two large and easily accessible gravel 

 riffles (of 4.6 m X 6.5 m and 4.6 m X 28.0 m). The strongly meandering 

 stream here is 4 to 5 m wide, with a substrate of alternating gravel riffles, 

 mud-bottom pools, and sand. The riffles are several cm deep, the pools to 

 1.2 m, and sand occurs at intermediate depths. The banks are steep and 

 frequently undercut, with masses of exposed fine tree roots. The south 

 bank abuts lawns behind homes, and the north side is mostly forested. 

 Concrete block riprap has been placed along the developed shore to 

 prevent erosion. Dominant aquatic vegetation is pondweed, Potamo- 

 geton sp.; water starwort, Callitriche palustris; water purslane, Ludwigia 

 palustris\ bur reed, Sparganium sp.; and unidentified filamentous green 

 algae. Vegetation occurs primarily in cleared, sunlit areas near the homes 

 and highway. Cottus bairdi is abundant throughout. The water, usually 



