The relationships between brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), non-game fish populations and selected physical and chemical parameters were investigated in four streams draining the Blue Ridge Mountains in north-central Virginia during low flow conditions in August, 1981 and 1982. Multiple regression and discriminant function analysis identified average stream width and maximum stream temperature as the main environmental factors related to brook and brown trout abundance and distribution. Furthermore, consistent fish species assemblages relative to brown trout distribution were observed in the study streams.

The movements of tagged brown trout in two streams were assessed for the period from June 1981 to July 1982. Most brown trout remained within 200 m of original tagging sections, 98.7% in the Conway River (78 out of 79) and 71.4% in the North Fork Thornton River (7 out of 9). The 1979, 1978 and 1977 year class fish (ages 2+, 3+ and 4+) exhibited extremely restricted movements and were invariably recaptured at original capture locations while the 1980 year class (age 1+) displayed small net upstream movements (<80 m) throughout the period. Two 1980 year class individuals displayed extensive movements (17.0 km downstream and 1.2 km upstream). These movements were characteristic of other stream resident brown trout populations.

Results of this study suggest that brown trout may expand their range upstream into currently allopatric brook trout zones. It would likely be a slow but steady process which could be accelerated by infrequent long-range movements. The potential for establishment of reproducing brown trout populations and impacts of brown trout on native brook trout populations can be assessed utilizing fish species assemblages, average stream width and maximum stream temperature prior to further brown trout introductions in this region of Virginia.